Friday, November 30, 2012

December 2012 Discussion - Analysis and Forecast


The fact of the matter is, the month of December will probably end up warmer than normal as a whole. Don't believe the CFS weeklies, they're bringing this cool-down too quickly.

As i've consistently been saying since October, Siberian snow cover anomalies for that same month can and will impact cold weather in the following winter months. Because of a deep below normal snow anomaly in the first half of October, I'm not surprised one bit by the warmth that has been experienced across the nation, and am not surprised by the incoming warmth that will push temperatures well past average values for this time of the year.

One thing I find encouraging is the Bering Sea ridge will be shifting north into the Arctic Circle. Good, that means the Polar Vortex will be faced with another challenge of holding itself together while the Bering Sea ridge has now moved into its territory. However (and this is the disgusting part), the ridge will set up in a manner that forces a persistent trough to set up near Greenland, which would mean the dreaded positive NAO.

As if matters couldn't get any worse. This is like trying to solve a puzzle, but you keep receiving some pieces at some times and losing other pieces at other times.

Don't think for a moment that this winter will be anything like last. Last winter, Siberia nailed the forecast with snowfall in October 2011 dry as a bone. Lo and behold, the winter of 2011-2012 ended up as one of the warmest in history.

Before we can even think about getting cold and snow to the States, we have to beat the 'obstacle course'. One of these obstacles is the Bering Sea Ridge / negative PNA issue. We should have the former cleared up in due time. However, the negative PNA obstacle could pose problems later on.

If we have the ridge moving north into the Arctic Circle, we're going to see an opposite reaction according to physics. East Asia will be observing this principle, with a deep troughing pattern setting up in response to this strong ridge now leaving the Bering Sea. However, the polar vortex has to go somewhere- it doesn't just leave because a big high pressure system is getting in the way. What we are likely to see is a shifting of the polar vortex east, either into Canada or Greenland. This track of the polar vortex will depend on the strength and placement of the ridge of high pressure. I find it very plausible for the polar vortex to want to move east into one or both of these areas in response to the high pressure development over north Asia.

THERE IS GOOD NEWS, HOWEVER: The ensembles are toying with the idea of this ridge vaulting  into North Europe, which could then combine with a Greenland ridge and possibly strike up a negative NAO. Could this happen? I would like to see some more ensemble runs before I say yes, but if such a solution happens, cold could become more prevalent than I am thinking. Not a freeze-out, but on a general cooler tone.

We are indeed seeing a sudden stratospheric warming, but keep in mind this warming is coming from record low levels at the 70mb level of the stratosphere. This SSW puts the 70mb temperatures still well below normal, so don't expect the stratosphere to save the day and banish cold weather to the south for at least a couple weeks.

The Madden-Julian oscillation is waking up from its deep sleep in the circle of death (COD), and is now in the weakest possible state in Phase 2. Slight strengthening of this phase is expected before moving back into Phase 3 and eventually - you guessed it - into the Circle of Death. But there may be hope. The NCEP forecast above depicts the MJO surging into Phase 1, which would support a wet and stormy weather pattern prevailing across the Eastern US. Height anomalies during Phase 1 support a deep Bering Sea trough, a positive PNA pattern and nice negative NAO pattern, essentially your typical college care package, but with gold and silver inside rather than small toiletries. The Phase 1 even gives some love to the idea of high pressure (HP) anomalies in north Asia, not unlike the extreme high pressure forecasted in the top image.

But before you sprint to the streets, proclaiming that the winter is coming on, full steam ahead, I must caution you to remain weary of the polar vortex. I do not trust the idea that the HP in North Asia will combine with a negative NAO to cut the polar vortex in half, as the MJO showed. No- I expect the HP anomalies in North Asia to overwhelm the Arctic. In response to the strong HP, a very strong LP (low pressure) anomaly will develop both in South Asia and potentially the Arctic Circle. If the latter idea occurs, Greenland would more than likely be affected. Hesitant ensemble forecasts of the NAO confirm my skepticism on the idea of the weather pattern suddenly favoring cold and snow in the East.

Want to know why I disprove the CFS v2 temperature anomaly for the Week 4 forecast today? This- the long range CFS v2 Arctic Oscillation (AO) forecast I managed to dig out of the bowels of the Climate Prediction Center. The black line enhances the neutral 0 line between above and below normal anomalies. The CFS v2 projects the AO to remain nearly always above normal through December and into early January, but don't believe that January stuff. Focus on the mid to late December timeframe. If you had been focusing on Siberia (like I have been), you would know that such an Arctic Oscillation forecast IS plausible, and that means a stronger polar vortex, and the HP in North Asia could push that east into Greenland to fight a negative NAO, or the North Asia ridge could move east to combine with Greenland and form a negative NAO.

In summary, I'm not too optimistic for December. The storm pattern will get more active as the Bering Sea ridge moves north into North Asia, but this movement will provoke a stronger polar vortex (unless the ridge moves into Greenland), and thus better possibilities for warm weather. However, if all turns out alright, January and February will still be cold. Fingers crossed, folks.


Significant Stratospheric Warming Event Ongoing

A significant stratospheric warming event, or SSW event, is currently ongoing across the lower stratosphere.

The above image shows 70mb values from 2011 and 2012. The green dashed line displays average stratospheric values for that time of year. If we look at the most recently observed line in the stratosphere, we see that significant warming has occurred, with a sharp spike in temperatures now being observed.

While the stratosphere is so high up in the atmosphere, it does have significant implications on our weather now. What the warming stratosphere does is it weakens the polar vortex, which, when the vortex is strong, can restrict cold air from the US. Now that a SSW is occurring, the polar vortex is weakening, and a stronger push of cold air south should begin. However, the presence of the ongoing ridge over the Bering Sea (and the ECMWF's idea of said polar vortex restrengthening over Canada) tells me to be cautious of any incoming cold weather calls.


Thursday, November 29, 2012

Christmas 2012 May Be Cold, Snowy For Some

Image from WeatherBell Models.
The long range CFS model is forecasting a potentially cold and snowy Christmas week, as we enter the final days of November and launch into December. The above image shows the CFS model forecast for the December 21- December 26 timeframe, which does include Christmas. The CFS is projecting that a very strong cold blast will break into the nation, bringing below-average temperature anomalies to near double-digits, especially near the Ohio Valley. The warm temperature anomaly in the West is supportive of a positive PNA pattern, so such a solution as pictured above does not seem that far-fetched by looking solely at this image.

Image from WeatherBell Models.
This is the forecast snow depth for the same time period. The image shows 4 ensemble members forecasting the maximum snow depth by the December 21 - December 26 period. I might as well give a synopsis of my own on this forecast before you get too excited. First off, I highly doubt that San Antonio Texas will be under 4-6 inches of snow on Christmas, so I prefer to discount the upper-right corner image. Also, the idea of 1 foot of solid snow from the Plains, Midwest, Southeast, Northeast and Great Lakes is not that realistic. The most realistic forecast I see on here is on the top-left, where over a foot of snow is coating the Mid-Atlantic, with more in the Northeast.

So, the CFS v2 is projecting a cold and snowy Christmas. However, I don't trust the CFS model, as it does not have the best track record, but it certainly is interesting to see!


Wednesday, November 28, 2012

December 1-2 Winter Weather Event - Northeast

Property of WeatherBell Models.
This is the snow depth forecast for the upcoming winter weather event for the Northeast. The above image is the total accumulated snowfall until December 2nd, and, as you can see, the Northeast gathers some accumulation, with totals ranging from under an inch right along the coast to as much as 6-7 inches in northeast New York. Vermont and New Hampshire also look to get a few inches of accumulation, with the most snow being right near the border.

The system doesn't look to be too strong, so the event will not last that long. The snow will likely begin around the early morning hours of the 1st, so no significant travel impacts are expected. However, it appears possible that airports in the region may have some slight delays. The early rush hour may start off slow, but generally no troubles.


November 29-30 Winter Weather Event - North Plains

A snow event looks to take place over the Northern Plains on November 30th. The above image, courtesy WeatherBell Models, shows radar reflectivity forecasts from the NAM model. However, this is a reflectivity 4-hour streak, meaning it combines a 4 hour span of radar return forecasts into one image. This image shows where the heaviest snow will strike, which appears to be North Dakota.

Some snow may also fall in Minnesota and Wisconsin , but the main event will definitely be in North Dakota. I anticipate snow amounts to add up to 2-5 inches, centered in northeast North Dakota. The central part of the state will receive a messy slush, as a rain-to-snow event occurs with this system. Devils Lake and Grand Forks are most likely to see the best accumulation (the former location over the latter), while Jamestown and areas in the northern part of James River will see a more rain-sided event with snowflakes mixed in the further east you go.

This event is likely to start in the middle of rush hour as rain and transition to snow by the end of the rush hour period, approximately 6-7 PM central time. Snow will fall into the very early hours of the morning, and end by the 10 AM central hour on November 30th.


December 10-12 Long Range Potential Winter Storm

I am officially opening up the discussion on a potential December 10-12 storm system that has been in many of the last couple days of the GFS model forecast.

Top left: 500mb heights. Reds are low pressures, purples are high pressures.
Top right: Pressure values. High/Low pressure systems are outlined.
Bottom left: 700mb relative humidity. Higher humidity values are in darker greens.
Bottom right: Precipitation. Any values above the red line are snow, any values below the line indicate rain.
For quite some time now, the GFS model, as pictured above, has been projecting a strong storm system to develop in the Plains and move northeast and strengthen, in a path all too familiar to those that went through the 2011 Groundhog Day Blizzard. This particular image above is of the 12z GFS for December 11th, depicting a strong storm system in the top right image. Precipitation in the bottom left image is widespread, with much of the Midwest getting snow while the Southeast is hammered with rain and storms. But first, let's determine the likelihood of such an event even happening.

It should be noted that 9 of the last 11 GFS model forecasts have had this storm system- a good sign as far as reliability goes.

This is something called the Pacific-North American Index, or PNA. In positive phases, storms are directed at the Midwest, like the above example shows, and negative phases generally induce warmer spells over the East US and storms diverted to the Plains or Deep South. These two images are separate forecasts of the PNA, with the left image being from the ESRL/PSD agency and the right image from the NCEP, essentially the GFS Ensembles. Because the NCEP is just composed of the GFS Ensembles, I favor the ESRL/PSD ensemble forecasts. That agency has the PNA just as negative as the NCEP, but has the index spike around December 8-12 to only weak negative values, which would help out this storm system into taking the track the forecast at the top of this post is showing.

However, when I take a look at the individual 12z GFS Ensembles for this same timeframe, it occurs to me that sometimes, you can't trust forecasts like these. The ensembles have a strong ridge over the northeast Pacific and West Coast, typical of a positive PNA. While it is not necessarily a positive PNA, it is apparent to me that such a set-up could indeed support a storm of this magnitude and track.

Also enhancing my investigation into this particular storm is the West Pacific Oscillation (WPO) and East Pacific Oscillation (EPO). These two indices affect the Bering Sea, which is currently experiencing an Omega Block. An Omega block involves a high pressure forming in any given area. In response to the sudden increase in height anomalies (a.k.a. the formation of a high pressure system), a stormy pattern develops in the immediate vicinity of the high pressure system, forcing height anomalies down on either side of the high pressure system. This creates the Greek symbol Omega (if you were to look at the 500mb height chart), hence the name 'Omega Block'. The WPO/EPO, both of which affect this block which just happened to form in the Bering Sea, are looking to be on the move near this storm's potential occurrence.

The EPO looks to be more or less positive during the storm's potential arrival. Such a solution would mean that a disturbance would try to form over the Bering Sea, thus hurting the high pressure system stationed over that body of water. If we want cold weather to enter the nation, it is an absolute must that we get that Omega block out of the Bering Sea, and this positive EPO could be helped by the WPO. The WPO index is looking to be trending to weak negative territory by the middle of the second week of December, which is when we could expect this strong storm system to hit. This more positive trend to the WPO also enhances the atmosphere to attempt and create a stormy pattern in the place where this Bering Sea Omega Block is.

The 12z GFS Ensembles have the Omega block retrograding north into the Arctic Circle, which would weaken the polar vortex and help cold air flow south. If such a solution were to happen, I see little reason to why we should give up the second half of December.

All in all, keep your eyes peeled. I'm seeing changes in the teleconnections, and when you get changes in the teleconnections, it's not all that difficult to see a brief stormy pattern as the pattern shifts from one phase to another. If the WPO/EPO/PNA forecasts verify on their forecasts as shown above, there could indeed be potential for a storm like this to blow through. Encouraging signs are also emerging from ensemble and model forecasts, as shown above by the GFS/GFS Ensembles.


Oct-Nov Temperature Correlation to Dec-Jan-Feb Found

An article connecting temperatures in October and November to the following 3 winter months (December, January and February) seems to have proved the long-held theory that fall trends can influence the upcoming winter.

The correlation is cited in the summary of this article:

In summary, temperature at the Blue Hill Observatory during October-November
correlates to some degree to the following winter temperature more than half the time, with an
overall correlation of 0.45
and with much higher and much lower correlation over some ten-year
periods during the 20th century. Both precipitation and snowfall, which are much more highly
variable than temperature, are in general essentially uncorrelated between ON and the following
winter, though some correlation is occasionally apparent over some years due to random
variations. As a result, ON precipitation and snowfall provide little predictive capability of the
subsequent winter precipitation and snowfall. Although ON temperature appears to provide some
prognostic information about the following winter temperature, the extent to which the
correlation is effective very likely depends on the specific atmospheric dynamical processes than
dominate the weather conditions during particular fall and winter seasons.

 0.45 may not seem like much, but that's saying that, out of 100 winters, 45% of those winters had temperature connections to the previous fall's temperatures. That's a pretty significant correlation. Let's take a look back at our October 2012 temperatures to see what we could see this winter.

This map showing October 2012 temperatures displays a very below-normal October was observed, especially across the Ohio Valley, Mississippi Valley, South Plains, Central Plains and Northern Plains. It does appear that the Northern Plains achieved the lowest temperature for the month of October- a good sign for the coming winter if you like cold weather.

Of course, this article mentions October AND November, so I would like to see November temperatures before I make a conclusion on what fall temperatures could mean for this winter.


Long Range NAO Forecast Supports Cold Northeast Winter

This is a long range NAO forecast from the Univ. of Albany. The top image shows the observed NAO values in red, and the forecasted NAO index in gray. The colored lines are separate ensemble members. The bottom line shows the variance, or difference between the ensemble members at any given time in their forecasts. Any spike of gray above that dashed red line indicates that the ensemble members are too far apart to be useful in a forecast.

Looking ahead into mid and late December, it seems that all but 1 ensemble member are forecasting a strong negative NAO. Considering it's only one ensemble member against 3, I support the idea of a deep negative NAO through December. Into January, we see the ensemble members regulate themselves, which seems a little too conservative to me. If Siberia's snow cover in October comes true, the AO will be negative, and the close relationship between the AO/NAO tells me that the NAO is more likely to be negative like the AO will probably be in mid-late January.

February brings the ensemble members going every which way, so I don't feel like it's a good idea to decipher that month until the ensemble forecast members have settled down. Despite this February uncertainty, the other two winter months certainly are looking supportive of a cool and stormy Northeast and general East US.


Tuesday, November 27, 2012

Solar Cycle 24 Well Below Normal

An analysis of Solar Cycle 24 in comparison to cycles 21, 22 and 23 reveals that Cycle 24 is running well below normal in comparison to the others.

The Sun runs on 'cycles' that last a few years for each one. Each cycle has a direct affect on Earth's temperature. For example, if a solar cycle were well above normal, temperatures on Earth would end up slightly warmer than normal. If a solar cycle were well below normal, slightly cooler temperatures would be observed on Earth. The latter example is the scenario we are currently seeing.

If we use previous cycles to compare to this one, we see that, by this time, Cycles 21 and 22 had already reached their maximum sunspot number for that cycle. Seeing as Cycle 24 is not even close to 100 sunspots at this time, it looks like Cycle 24 will begin to drop back down in the next 6 to 8 months as other cycles have done in the following 12 months from where Cycle 24 is now.

This will have more significant impacts later on, and they will be addressed when the time comes.


Splitsville for Polar Vortex

The ECMWF is holding firm with its idea to split the polar vortex in the next 10 days.

This is the 100mb forecast for 240 hours away, or 10 days out. I encircled the newly-split polar vortex in black (they are now called vortices), and highlighted the factor that is making this happen. There is a strong ridge that will be in place over the Bering Sea (which does not bode well for the East US' winter, but is Cloud 9 for skiers in the West) that will break up the polar vortex. It appears that one piece of this vortex will spin south into Canada and the Northern Plains, and the other piece will slide into Russia and eastern Asia.

The polar vortex coming into your backyard is nothing to mess with. It has the name polar vortex for a reason. When the polar vortex comes around, you best prepare for temperatures colder than you've seen this entire season. This vortex is carrying air gathered from Greenland, Siberia and far northern Canada, which means that the air that comes around will have traits of those regions. In summary, it's cold.

This polar vortex split (and subsequent warming) will lead to the Arctic Oscillation dropping negative, which would bring cold air south into the US. However, that cannot fully happen until that Omega block high pressure system in the Bering Sea gets out of there.


Late November 2012-2013 Winter Thoughts

This is a post concerning my winter thoughts as of Late November. We'll get things going right away.

ENSO Region SST Anomalies

Latest Weekly SST Anomaly Over the ENSO Regions
The El Nino-Southern Oscillation, or ENSO phenomenon involves the warm or cool anomaly of sea surface temperatures (SST's) over the Equatorial Pacific waters. The top image shows the ENSO anomalies per region, with Nino 1+2 being the furthest east near the coast of South America, and Nino 4 being west of the 180th Meridian. As you can see, Nino regions 4 and 3.4 are pretty warm, actually achieving El Nino state. An El Nino is when these waters are at or above 0.5 degrees above normal. A La Nina has water temperatures at or below -0.5 degrees below normal. Both temperatures are in Celsius. If you now look at the bottom pair of images, you will see the observed SST's and SST anomalies. The warmest waters are centered from 140W to 160E, which does include the Nino 3.4 and Nino 4 regions.

Despite this warming and hinting of an El Nino, I support a Neutral ENSO winter, which is neither an El Nino or La Nina. The neutral ENSO phase can be thought of as if you're taking a shower and the water is room temperature- neither hot nor cold.

This image above is an observed image of the Quasi-Biennial Oscillation, or QBO. The QBO involves wind directions in the upper levels of the troposphere and stratosphere. When the QBO is negative, winds are westerly, or eastward. A positive QBO involves easterly, or westward winds. The Lower 48 is most commonly given colder weather in a negative QBO, as a negative phase of the QBO is able to influence the North Atlantic Oscillation (NAO) into going negative, which only continues to enhance cold potential, especially for the East US.

In the image above, negative anomalies (Negative QBO) is shown in white, while positive QBO values are shown in grays. As you can see, there has been a positive QBO movement from the upper stratosphere recently. When the positive QBO movement progresses down into the troposphere, this occurs at a rate of about 0.6 miles per month. However, the movement has been slowed recently at the 20mb mark. If we look on the right, it shows kilometers. If the QBO descends at 1 km per month, it would take the entire winter to get down towards the 30mb mark.

AMO Values for 2012. These are organized in months, with
January the first value after '2012', to October, the most recently calculated month.
The line of values above is of the Atlantic Multi-Decadal Oscillation, or AMO. In a positive phase of the AMO, the water temperatures in the far north Atlantic are above normal. This, in turn, enhances the potential for ridges of high pressures to form and sustain themselves over Greenland. This phenomenon is commonly called the negative NAO. In a negative AMO, cold water temperatures are observed, leading to a stormier trend over Greenland, bringing about an increased likelihood for a positive NAO.

This is a comparison of October 17th water anomalies and November 14th water anomalies. You can see a diminishing of warm waters over northern Canadian waters and west Greenland waters, signifying a dying positive AMO. However, the New England waters are well above normal, supporting at least part of the positive AMO. The positive AMO has been dying off slowly as shown in the values listed above, and this has been happening by about 0.100 per month. If we apply that to this situation, we could see the positive AMO gone by January or February. However, the strong warming trend over east Canada tells me that the positive AMO should stick around through the winter months.

This is a graph showing Northern Hemisphere snow anomalies from October through November of this year. Typically, when October snowfall is above normal, the Arctic Oscillation goes negative the following winter. Likewise, when the snowfall anomalies are below normal, the AO tends to stay above normal in the following winter, meaning warmer than normal temperatures. An analysis of this past October shows a negative anomaly for the first half of October, which means December could be lost to warmth. Considering we already have the Bering Sea under a massive Omega block, such a solution is not out of the question. I expect January into February to favor cold temperatures, with the latter month bringing down the hammer as far as cold weather goes.

All in all, I'm expecting a gradual turn-around from these warm temperatures to cold weather, especially in the latter half of the season. A negative NAO / Negative AO combination will support cold weather and storm action for the Northeast, some of which will be diverted west thanks to an intermittent positive PNA. Winter will hit the best in the Northeast, with the runner-up being the Midwest, Plains and Ohio Valley.


Monday, November 26, 2012

GFS Hinting At Long Range Storm System

The past 4 model runs of the GFS had some form of storm system and subsequent cold weather outbreak hit the Eastern US in the long range. This event usually happened between the December 10 - December 12 timeframe, with only the 12z GFS disagreeing from a unanimous December 10th storm date.

The 0z GFS had a monster storm system form along the East Coast in an event that would have decimated the region with more than 2 feet of snow and a monster cold outbreak just behind the system that would have brought freezing temperatures down to the Gulf Coast.

The 6z GFS had a similar set-up, but took the storm into Canada while leaving the cold outbreak to sink south just like the 0z GFS. Not as far south, but still down into Georgia and Alabama, among others.

The 12z GFS is the anomaly to these 4 model runs, as it took the storm to New England and pulled the cold air with it (out to sea) in unusual fashion. Additionally, unlike the 0z and 6z model runs, this forecast had the event happen 2 days later, on December 12th.

Luckily, the 18z GFS erased any hopes of a 12z GFS occurrence, but changed the storm track as it brought a strong system into the Midwest and Great Lakes, with snow hitting those same areas. Cold air did not have time to flow south, as another storm system was right on its heels.

Now, the GFS model alone in the long range is equivalent to playing with fire- you must be VERY careful with it, or you will get burned (i.e. disappointments after a storm does not happen). However, considering this has now been at least 4 model runs in a row that have showed some form of storm system and subsequent cold outbreak in the Lower 48, this does catch my eye. The GFS has been known to catch trends when certain events come back in forecasts over and over again, like the 4 examples shown above.

I will watch this system and provide updates as necessary, but this is a wait-and-see moment for now.


Omega Block in Bering Sea Likely To End Soon

The Omega Block currently ongoing over the Bering Sea, as shown above, looks to be coming to an end in the next few weeks. As the name implies, an Omega Block is characterized by a blocking high pressure system in the atmosphere. In response to such high pressures, persistent troughing (stormy) patterns form to the left and right of this high pressure system, resulting in the Greek Omega shape, and thus the Omega Block.

The top image shows the GFS Ensembles' 500mb height anomaly forecast for Hour 384. Those of you affluent in the weather model forecasting business know that Hour 384 is the end of the GFS run and generally considered worth nothing that far out. However, when you get ensembles that come along, the idea changes, and suddenly you have 20 different forecasts coming together. The GFS Ensembles believe that the Omega block over the Bering Sea will dissipate by Hour 384, thus ending the NE Pacific trough and moderating the continuous warm shots that the nation has seen and will continue to see for another week or two. The bottom image is the GFS model itself, and the model shows this Omega block being pushed to the west- not the best situation, but good enough so that the persistent trough over the West Coast can leave the area and provoke a positive PNA pattern to set up behind the persistent trough, which has now moved west with the Omega Block. What the GFS ensembles actually try to do is push this Omega Block north into the Arctic Circle area to weaken the Polar Vortex and break the floodgates of cold air in Canada, which could then flow south, possibly into the US.

But it's not all about the models- it's also about the teleconnections. This is an image depicting two agencies' forecasts for two teleconnections (atmospheric functions). The top two images are of the EPO (which we don't care about at the moment) and the two bottom images portray the forecast for the WPO, or West Pacific Oscillation. The WPO is in a deep negative phase thanks to this Omega Block. In the positive phase, you typically see a strong low pressure sitting over the Bering Sea.
Anyhow, the two bottom images represent two forecasts. The one on the right is of the NCEP (essentially the GFS Ensembles), and the one on the left is from the ESRL/PSD (they have their own ensembles and thus, in my opinion, are more trustworthy). The ESRL believes the WPO will go down even deeper into negative territory as we approach December, but gradually go back positive as we pass through the first week or two of December. On the other hand the NCEP believes that the WPO will succeed in trying to stay as negative as possible well into December. However, note how the NCEP begins to rise near the end of the forecast. This, combined with the trending-positive ESRL forecast, tells me that there is a consensus for the WPO (thus the Omega Block) to be weaker in a week or two than it is now.

All in all, I feel like I can say that the first two weeks of December will be lost to this Omega Block. However, supportive signs are showing up that tell me the last half of December will be open for more winter-like conditions. Fingers crossed!!


CFS Model Grossly Over-Exaggerates December Forecast

The Climate Prediction center's Coupled Forecast System model, or the CFS model (version 2) has put out a new December forecast that crosses the line between unrealistic and just plain absurd.

The top image is the anomaly forecast for the month of December, and the bottom image is the skill forecast (areas where the model is very confident in its forecast). As you can see, the CFS has temperature anomalies well over 1.5 degrees above normal spreading from the West Coast, through the Rockies and well into the Plains. Temperature anomalies exceeding 1 degree above normal exist in just about every state in the Lower 48, with the possible exception of eastern Florida. The skill map is confident in the East US' warmth and the Plains, but not so much for the Rockies.

This forecast is just plain ridiculous. The model is going off the idea that the persistent Omega Block will continue through the rest of the month, which, as shown in the GFS forecasts below, is likely not going to happen.

The top image shows the GFS Ensembles' 500mb height anomaly forecast for Hour 384. Those of you affluent in the weather model forecasting business know that Hour 384 is the end of the GFS run and generally considered worth nothing that far out. However, when you get ensembles that come along, the idea changes, and suddenly you have 20 different forecasts coming together. The GFS Ensembles believe that the Omega block over the Bering Sea will dissipate by Hour 384, thus ending the NE Pacific trough and moderating the continuous warm shots that the nation has seen and will continue to see for another week or two. The bottom image is the GFS model itself, and the model shows this Omega block being pushed to the west- not the best situation, but good enough so that the persistent trough over the West Coast can leave the area and provoke a positive PNA pattern to set up behind the persistent trough, which has now moved west with the Omega Block.

Now, there is definitely potential for this blocking to stick around in the Bering Sea and make December warm. However, there is one more reason why you should not take the CFS for what it's saying.

This is the CFSv2 model's RMS Error for 2m temperatures in forecasts made in November. What this shows is the gap between forecasted situations by the CFSv2 and observed conditions for that same forecasted timeframe. Basically, this is the difference of those two factors. The DJF period (December, January, February) is shown above, and it appears that forecasts made in November typically verify extremely warm in the DJF period. This not only includes this December forecast, but the other two winter months that we don't particularly care for at the moment.
The CFS' track record is definitely a warm-biased one, meaning it has a tendency to forecast conditions too warm according to this map.

Not only that, but this chart of multiple models' forecasts for the month of December show that the CFSv2 is the ONLY MODEL to show a torch for the first month of winter. The only reason the NMME and IMME models are showing warmth is because of the CFSv2 is averaged into their forecasts.

So please, winter weather lovers, do not get so fired up about the CFS' forecast. In my eyes, it's the least desirable model (next to the Japanese and Canadian models) to use for a forecast. Do you REALLY think that December will bring extreme warmth to the nation??

Sunday, November 25, 2012

What Does The Drought Mean For This Winter?

This past summer, there was a massive drought spread across much of the Plains, Midwest and Rockies, at times putting much more than half the country under drought conditions. So, as we approach winter and we see the drought still ongoing in the central and North Plains, the question becomes, what could the drought do for winter?

Less Precipitation
When you have a drought, it means the soil is very dry. When a storm system comes through, it will drop precipitation and moisten up the soil again. However, for drought-stricken areas, this precipitation must fall in a multi-day event for the soil to actually moisten up for good. Because of the dryness of the soil, when storm systems come through, the system will have no moisture to pick up from the soil, meaning that the system can dry up and weaken. It's a very vicious cycle, but unfortunately it does happen. Drought-stricken areas are naturally given a disadvantage right out of the gate when the winter starts.

Warmer Temperatures
Let's go back to the soil moisture issue, but let's say this is a sunny day. High pressure is over the area, but weak enough so clouds can form if provoked. On this day, we'll say that a weak cold front is moving into a drought area. Because clouds form by warm air (and moisture) being lifted off from the near-surface air, soil moisture does become an issue here. In a lack of soil moisture, less clouds form, and thus the sun stays out longer, slightly enhancing temperatures in the day. The lack of clouds at night enables the day's heat to be released back out into space, meaning that temperatures are slightly lower at night.

Those of you in this drought can expect a very slight lowering in precipitation and a very slight raising of temperatures this winter due to the factors I described above. These changes will not nearly be significant, but if you were to break it down into the decimals, you could see a small change.


What Can Folklore Tell Us About This Winter?

Many of you may remember when I asked two Facebook questions, one asking the anomaly of acorns you had seen in your town, and the other asking if the amount of roadkill you had seen was above or below normal. Why did I ask those questions?


Something that Brett Anthony of KSHB uses is called the 'Acorn Theory'. As this post of his illustrates, the amount of acorns on the ground can help determine the snow amount for the upcoming winter. So, for those of you wondering why there are so many acorns, it could be Mother Nature's way of telling you that a harsh winter is incoming. If there is a below normal amount of acorns, a less cool and snowy winter may be on the way.


As nasty a subject it is, this is actually a legitimate predictor of winter. Let's say you told me that you have been seeing a ton of roadkill. What this means is that the animals are extremely active. Why are they so active? They are preparing for winter. The animals are scurrying around, gathering equipment for winter. Because they're so active, more roadkill is observed. If you are seeing a strikingly low amount of roadkill, the animals aren't too concerned about this winter, and you shouldn't be either- it could very well be warm.

So whether it's acorns or roadkill, there are some tools out there that can help us predict this winter. All you have to do is look.


Wild, Wild December Ahead For East Coast

A wild month of December could be ahead for the East Coast, including the Northeast, Mid-Atlantic and New England, thanks to several factors, but could also be hampered by one big player. Let's jump right in.

This is the forecast for the North Atlantic Oscillation (NAO) in the next several days from the Climate Prediction Center. The NAO involves the presence or lack of a semi-permanent storm system or ridge over Greenland. If that ridge of high pressure is in place over Greenland, this is a negative NAO, which then creates a favorable pattern for cold and storms in the Northeast. The ensemble forecasts from the CPC call for a big dip in the NAO by the start of December. From then onward the NAO becomes a bit more difficult to forecast, as the ensemble members begin to spread out. However, the general idea is for a negative NAO to continue.

This is the forecast for the Arctic Oscillation (AO) in the next couple of weeks from the same ensemble forecasts from the Climate Prediction Center (CPC). The AO's forecast has more of a consensus than the NAO's forecast, which means higher confidence. The ensemble members predict a plummeting AO through the end of November, but also keeps the AO negative through the rest of the forecast period. When you have the AO in the negative phase, the cold air in the Arctic is released south, and temperatures trend on the chillier side for much of the Lower 48.

This is the Pacific North American index (PNA) forecast from the same CPC ensemble members, for the same time period. Note how the PNA has been negative for the last few weeks, and this is thanks to a persistent stormy pattern over the Northeast Pacific, and I will explain more about this next. The PNA forecast ensemble members have the PNA staying negative, but trending more positive in the future. A negative PNA has a warmer pattern over the East, while a positive PNA displays cold and stormy conditions in the East US.

Here is the problem we need to watch. There is something ongoing in the Bering Sea called an 'Omega Block' pattern, where a ridge of high pressure forms in the Bering Sea, with storms on either side. This creates the Greek Omega sign, as I outlined in the image above (and which was the first to note). Now, this Omega block has encouraged a persistent stormy pattern to develop to the east of the high pressure, which is the base of the negative PNA. So this is a pretty darn stubborn pattern, which has been holding for quite a bit. If we don't see this Omega block get going soon, December could be in trouble.

Let's divert our attention away from the Bering Sea for the moment and look in the upper left hand corner of this image. That area is East Asia, and this forecast for 3 days away shows a strong storm hitting the region. The GFS Ensemble averages (as seen above) have a stormy pattern persisting in the East Asia region for at least a week. Those of you who have followed me for a while know that there is a correlation between East Asia storms and East Coast storms, with a gap between the two of 6-10 days. So, if we see that strong storm in East Asia valid for November 28th, we could see another stormy pattern in the East US from December 4th- December 8th, and possibly beyond if a stormy pattern persists in the East Asian region for a longer time.

Another factor supporting an intense December is the Madden-Julian Oscillation (MJO). The MJO involves where a stormy pattern is in certain parts of the Bay of Bengal, Pacific Ocean and Atlantic Ocean. These different areas where the stormy pattern could be make up the 8 phases of the MJO. This forecast for the MJO has Phases 8-1 coming on, possibly into Phase 2 if this forecast verifies. The average conditions for temperatures (bottom right images) and precipitation anomalies (top right images) for Phases 1 and 2 are shown, and these two phases generally bring cooler than normal and wetter than normal conditions to the East US. Not so much Phase 2 as Phases 8-1.

So we have a favorable NAO, AO and MJO coming in for the next week or two. I would really like to see that Omega block get out of the Bering Sea as soon as possible. If that block holds steady for the next few weeks, precipitation could be affected, especially for the Ohio Valley, Plains and other similar regions. However, I feel that the negative NAO/AO will be able to squeeze in good shots of cold air in between ridges set up by the Omega Block.

Something interesting that has been found is a negative correlation (Factor 'A' goes positive, so Factor 'B' goes negative) between the 30 day sunspot cycle and the PNA index. So, we are seeing the 30 day sunspot cycle begin to go back down to its negative (as shown in the image above), so it is plausible that we could see this Omega Block start to back off, leading to a slightly better pattern for a positive PNA to develop.


Saturday, November 24, 2012

Climate Model Overview For Winter 2012-2013

Many of you have seen my 'What Are The Models Saying This Winter?' segments, where I would highlight a few models and show you what they would be saying this winter. Well, I have gathered 4 of the long range models I feel give you the widest spread of what is being forecast for this winter.

If you want to see the previous 'What Are The Models Saying This Winter?' posts, the links are below.

Part 1: Click Here
Part 2: Click Here
Part 3: Click Here
Part 4: Click Here

This is the Beijing Climate Center (BCC)'s 500mb height anomaly forecast for the winter months of December-February. North America is actually above that deep red blob on the picture. The continent is shown as upside down, so it is a little hard to see. However, if we look closely, we see a blue swath extending through the South US and up the East Coast. This below normal height anomaly refers to the presence of a stormy pattern over that area. Such a forecast is not impossible- the North Atlantic Oscillation (NAO) is expected to be very negative throughout the winter, so a storm track through those areas is quite a realistic scenario.

This is the Climate Prediction Center's Climate Forecast System (CFS) model, valid for the 3 winter months. On the left is temperature anomalies for winter, and on the right is precipitation anomalies. The CFS has a very warm winter for much of the West US, but also predicts warmth on the East Coast, as well as in the northern Arctic. The precipitation forecast calls for a dry Plains, a dry West Coast and Alaskan coast, as well as a wet New England.
Already I am seeing problems with this forecast. A warmer than normal north Arctic and northeast Canada tells me that there will be a ridge in place over that area, effectively a negative NAO. This would bring cold and stormy weather to the Northeast, not warm weather. Also, a warm anomaly in the West US implies a pattern similar to that of a positive PNA, where a ridge sets up in the West US and brings cold to the East US, again defying the warmth forecast. I do believe the precipitation forecast, however.

This is NASA's forecast for this winter. The NASA forecast has not been known to be too reliable, but I'll show it anyhow. The temperature forecast from NASA supports a warm Plains, Rockies and Southeast, with cooler than normal temperatures in the Northwest and far into New England. As for precipitation, a very wet Southeast and southern Ohio Valley is expected, but a very dry West Coast is expected.
The northern Arctic is neutral in temperature, telling me that NASA does not believe in a persistent negative NAO pattern. I believe that the 3 year gap between observed NAO values and winter conditions in North America will bring the NAO to a good negative stance this winter. Additionally, a very snowy October Siberia tells me that the nation will be cooler than normal in the end, especially thanks to February. I don't support the NASA forecast at the moment.

This is the ECCA ensemble forecast for the winter. Temperature forecasts are on the left, and Precipitation forecasts are on the right. The darker shaded areas on the left show skill areas on the model, meaning that the forecast has higher confidence than other areas. The ECCA is predicting a warm nation, especially in the South Plains and Southeast. However, cold temperatures are predicted in the central Plains.
I would expect these cold temperatures to be extended further north, and feel that the ensembles are just unsure of the whole situation. It doesn't take into account October conditions in Siberia or the 3 year NAO-North American Winter lag, so such a forecast can be forgiven. The precipitation forecast does not seem all that crazy, but I would extend wet conditions into the Southeast and dry up some of the Central Plains if I had my way.

These are a few models of many, and I picked out the ones that don't necessarily have the best track records, but express forecasts from as many different agencies as possible.


November 27-29 Potential Winter Storm (Updated 11/24)

This is the snow depth forecast from this morning's 0z GFS model for just after 6 days out. As you can see, the GFS takes the system down through the south and begins to turn it up the East Coast in typical Nor'easter fashion. When the storm system gets near the New England coastline, the system's pressure plummets, indicating a rapid strengthening of the storm system. It gets even stronger as it nears Maine, leading to accumulating snowfall over much of the Northeast US.

Frankly, this isn't such a bad scenario. It has become evident that the system will take the path through the southern US and out into the Southeast Coast. Because there will be a negative North Atlantic Oscillation (NAO) in place, the storm track will favor a path for this system up the East Coast, as this GFS forecast is indicating.

I'm still sticking with my forecast that I put out yesterday, which calls for rain near the coastline in the Northeast and snow inland. I should note that, thanks to the GFS, my snowfall expectations for the Northeast inland regions have been enhanced. I will play with the idea of putting out a snowfall forecast today or tomorrow, but at the moment, the ECMWF and GFS remain at odds with each other over this system.


Sea Surface Temperatures Supporting Positive PNA

This is the change of sea surface temperatures from September 2012 to October 2012, focused in on the north and central portions of the Pacific Ocean. What I am showing above appears to bode well for a positive PNA developing.

The PNA, the acronym for the Pacific North American index, is based in the northeast Pacific Ocean and has tremendous effects on the weather observed in North America. The PNA has two phases: positive and negative. In the positive phase, cold air tends to flow south and the storm track is shifted so it favors the Midwest/Great Lakes for precipitation. In a negative PNA, warmer weather is favored in the nation, while the storm track tends to miss much of the Eastern US. For example, in the Chicago Blizzard of 2011, there was a positive PNA happening that enabled the blizzard to go where it went.

The PNA is enhanced by sea surface temperatures. In above normal SST anomalies, the Pacific North American index tends to favor a positive phase over negative. In negative SST anomalies, the negative phase of the PNA is supported.

In the above one month change of SST's, we can see that warming has taken place across the northeast Pacific. Cooling has also taken place across the north central and northwest Pacific, but that is another post in itself.

The fact that we are starting to see warming in the Northeast Pacific is exciting. If such a warming trend continues through the month of November, the chances of a positive PNA will only continue to increase. This would, in turn, lead to more precipitation in states like Colorado and the east central Rockies, as well as the Midwest and Ohio Valley. A sturdy negative NAO would only help the Northeast as well.


Friday, November 23, 2012

Geomagnetic Storm Begins

The image below is the Planetary K index, which can show of geomagnetic storms that are ongoing here on Earth. As you can see, the anticipated CME (Coronal Mass Ejection) has hit the earth, and will continue through the night.

If we use the value of 4 on this K index, we can figure out how far south the aurora Borealis can be seen. The value of 4 equates to the aurora Borealis being seen way up north in Canada and maybe in the Upper Midwest.


November 27-29 Potential Winter Storm Discussion (Updated 11/23)

This is the 12z GFS model forecast for 90 hours away, which is in the early morning of November 27th. We can see our low pressure system currently in southeast Arkansas. Considering the incoming pressure of a massive ridge in the Plains, the GFS has this system move off to the east and eventually up the coast. I will discuss more on why and how those two things happen later on. The 850mb temperatures, which are shown as the colors on this image, are pretty warm across the board and would likely only support snowfall in New England if this situation verified.

This is the Canadian's GEM model forecast for 90 hours out, meaning that the GFS and GEM models are forecasting at the same timeframe of November 27th in the early morning. The GEM has this system slightly stronger and faster than the GFS, and also settles the incoming high pressure system further south, hence the quicker pace. However, 850mb temperatures are slightly cooler in the GEM forecast than the GFS. The GEM had been predicting this storm shooting into the Midwest, but this forecast does not allow such a scenario to happen, as the ridge originally predicted to be in the Southeast is now well offshore.

This is the United Kingdom's UKMET model forecast for 96 hours out, meaning that this is the forecast for the morning of November 27th, 6 hours later than the GFS/GEM. The UKMET prefers the placement of the high pressure system in the Plains to be further north than the GEM and more in line with the GFS, however, the GEM's 850mb temperatures appear to be reciprocated in this forecast. The UKMET does not have this system go directly up the coast, which is plausible as I will explain just below.

This is the chart of the NAO from the Climate Prediction Center (CPC) showing the past NAO observations from late summer to now in black, as well as the ensemble forecasts of the North Atlantic Oscillation in red. The CPC's ensembles are predicting the NAO to plummet just around the time that this storm system comes around, but it will be somewhat neutral/slightly negative before the storm system arrives. Considering there is a 4 day lag between when the NAO changes phases and when the effects of the new NAO phase arrive, it is possible that the effects of a neutral/slightly negative NAO could be present as the storm rolls around rather than a strong negative NAO.

In a negative NAO, cold and snow is encouraged to hit the East US, but the placement of where the negative NAO is key. There is an east-based and west-based phase of the NAO. In a west based NAO, the most prevalent sign of a certain NAO phase is to the west of Greenland. For example, if there were a west-based negative NAO, the ridge that produces the negative NAO would be to the west of Greenland. In an east-based NAO, the ridge would then be to the east of Greenland. The NAO will likely be in the east-based phase when this storm rolls around, meaning that the Midwest would be favored for cold and snow rather than the Northeast, hence why I was promoting a north track more than this new south track consensus.

There is also something worth looking at called the Pacific-North American index, or PNA. In a positive PNA, you see storms hitting the Midwest and Ohio Valley and most of the East US, whereas a negative PNA favors the storm track further into the west, near the North Plains. The ensemble forecasts for the PNA have the index to be negative through the time that the storm rolls around, which would not favor a Midwest track. This is why there is that wiggle room for that north track to go bad, and it looks like this, combined with a negative NAO has persuaded the models to have the storm start inland (east-based negative NAO sign) but eventually move offshore and give precipitation to New England (general negative NAO sign).

Based on recent model trends and teleconnection forecasts, I expect rain all along the Gulf Coast, Southeast and southern Ohio Valley before the system goes out into the Atlantic Ocean. Snow will likely fall in the southern Midwest, Ohio Valley and Northeast, with heavy snow hitting West Virginia. Rain will fall across the immediate coastline in New England, with possibly heavy snow inland.