Sunday, April 28, 2013

Late Season Snowstorm Targets Midwest

The GFS model is predicting a late season snowstorm will hit the Midwest and western Great Lakes regions over the next 5-10 days.

Shown above is the accumulated snowfall forecast from now until May 6th. We see a swath of accumulating snowfall stretching from the eastern half of Iowa into Wisconsin and the Upper Peninsula of Michigan. The amounts in this swath of snow are anywhere from 2 inches to nearly one foot, with the latter end of the spectrum centered over Iowa and the U.P. of Michigan. Accumulating snow even goes as far south as Missouri, with that state and Illinois getting in on amounts as high as 2 to as much as 4 inches in isolated spots.

I am incredibly skeptical of this forecast. The GFS model is known to have a cold bias when it comes to winter weather, and the impending pattern change does nothing to help forecast accuracy. In my opinion, if this scenario even works out, we would see a chilly night in IL/MO without any snow, and maybe some plowable snow into Iowa- certainly not at the level being predicted. I find it hard to believe that the GFS model has a viable case at this point in time.


Nasty Squall Line Hits Texas on Wednesday

The Storm Prediction Center has outlined a small area of severe weather potential for Wednesday, May 1st. This outline encompasses south central Oklahoma into north central Texas.

The NAM model shows a rather small region of high instability over central Texas, extending into central Oklahoma. This image is valid for the afternoon of Wednesday. This stretch of high instability is slightly different from the SPC outlook in that the most able regions for thunderstorm development are just a hair east of the outlook proposed by the SPC, especially in Oklahoma. Thunderstorm development is expected to commence in the late afternoon hours after the layer of stability erodes. This image shows surface-based instability, which is essential for thunderstorms to get going. However, in order for thunderstorms to start forming, the layer of stability must be eroded. The stability is seen in the shaded regions. When you have high instability with no blue shading, thunderstorms are most readily able to form.

Projected radar reflectivity for Wednesday evening shows the development of a nasty squall line stretching from Oklahoma into Texas. The greatest threat of severe weather then appears to be damaging winds and large hail. The lack of strong helicity in the vicinity of the highest instability tells me that the tornado risk will be rather minimized. Regardless of the biggest threat, it's certainly looking like a severe weather event will unfold on Wednesday.


Summerlike Warmth Just Days Away

The first blast of summerlike warmth appears to be just a couple days away, as Old Man Winter is beat back for the first time in this unusually cold spring.

Maximum Tuesday Temperatures
The short range NAM model is projecting temperatures to soar past the 80 degree mark as far north as Chicago, IL and the Quad Cities in Iowa. This model forecast has been rather consistent with extremely warm temperatures stretching as far north as those two cities, although in this forecast the warmth appears to have been slightly dialed back. Temperatures in western Texas could flirt with the 100 degree mark, and the thermometer will situate itself well into the 80s and 90s across multiple Plains states on Tuesday. Unusually warm temperatures will continue out to the east into the Ohio Valley and even poking into Canada.

Maximum Wednesday Temperatures
The cold front will show its full force on Wednesday afternoon, but the warmth ahead of this frontal boundary will continue to show its might. We see a large swath of 80s from Texas as far north as Michigan. The warm sector shoots well into eastern Canada, where 60s and 70s prevail. It looks like almost every state in the central and eastern US will be able to achieve temperatures as high as the 60s on the low end and 80s on the high end. Once again, western Texas will see temperatures close to 100, but not at the three-digit benchmark.


Saturday, April 27, 2013

Severe Weather Targets Plains This Evening

A slight risk of severe weather has been issued by the Storm Prediction Center for today, April 27th. This risk covers the states of Texas, Louisiana, Arkansas, Mississippi, Alabama and Tennessee.

Current frontal analysis shows the storm system of interest currently crossing over into western Arkansas. Warm front extends through the middle of Arkansas and cuts through central Mississippi, while a trailing cold front is draped across Texas. High precipitable water values shown in green indicate the warm front is doing its job in transporting energy and warmth up from the Gulf of Mexico, adding fuel to the fire that will start this evening in the states mentioned above. The storm system appears to be pushing northeast, and this should allow the warm front to pull the warmth and moisture north to encompass the rest of the states expected to be under a threat for severe weather tonight.

Short range NAM model predicts surface-based instability to be in excess of 3000 j/kg in some spots, with little to no capping inversion in the slight risk area. Thunderstorm formation is anticipated to be consistent with a damaging wind/hail risk. Elevated helicity values combined with this excessive instability should allow for an isolated tornado threat, especially in eastern Texas into southeast Arkansas. Relatively lower instability values will be present towards the easternmost portion of the slight risk area in Tennessee. I believe that we will see thunderstorms fire in that area, although the comparison of Tennessee's instability and the 3000 j/kg in Louisiana tells me the storms in TN will not be as significant as those in the Gulf Coast states.

At the present time... latest upper air soundings reveal a fairly substantial capping inversion stretching from the Gulf Coast into Louisiana and Mississippi. Not concerned with this development, as lower level stability is normal in the mornings. The sounds analyzed with that lower level layer of stability were mainly outside of the 3000 j/kg belt shown above, and the one sounding within that belt had a rather weak stability layer. Upper and mid level wind fields have a streak of slightly enhanced winds on the south flank of the storm system, and these winds should fall along the slight risk area later on this evening.

Storm Action Day status: A Storm Action Day will NOT be declared today.


Friday, April 26, 2013

2013-2014 Winter Preliminary Model Forecast Overview

This is an overview of what forecast models are currently suggesting may be happening in the time leading into the winter of 2013-2014. This is not my Preliminary Winter Forecast- that comes out in June.

We'll start with the probabilities of different states of the El Nino-Southern Oscillation (ENSO) phenomenon. The red bars on the bar graph suggest the probability of an El Nino, defined by above-normal sea surface temperatures in the eastern Equatorial Pacific. The blue bars represent the potential for a La Nina, which is indicated by below-normal sea surface temperatures in the eastern Equatorial Pacific. As the third name suggests, the green bars predict neutral ENSO conditions, which means there is no presence of above or below normal temperatures in the region. Moving through the year of 2013 to the last set of bars, defined as NDJ 2013 (November-December-January 2013), we see pretty equal chances of each type of ENSO condition, but if you want to be picky we can differentiate between which one is so prevalent. The neutral-ENSO condition has the highest probability (just below 40%), with La Nina in close pursuit (roughly 35%). The chances of an El Nino rise throughout the forecast period, but end up immediately below 30% to round out the predicted El Nino conditions. While the probabilities may seem unusually low right now, you have to remember that we are looking at the end of the forecast period, hence the confidence of the forecast is unusually low. Also of significance is that the winter's ENSO period typically develops during the summer months- this idea is true for nearly every year.

Looking at the OND 2013 (October-November-December 2013) temperature forecast from the long range American CFS V2 model, we see widespread probabilities of below normal temperatures across Canada and creeping into the North Plains and Upper Midwest. We can also see above normal temperatures near Greenland- these warm temperatures could mean high pressure in that region, and this could mean a higher probability of below normal temperatures in the Eastern US. We also see spots of above normal temperatures in the Southern Plains and shying into the Southwest. This may or may not mean a little high pressure tendency in those regions, and this could also try to push below normal temperatures into the East US. Don't get excited yet, however- we're 8 months away from the first month of winter. I can't even describe how low confidence is on this forecast.

As for the precipitation forecast, we see a large swath of above normal precipitation extending from the Midwest and across the Great Lakes. There is an enhanced swath of above normal precipitation probabilities in the Ohio Valley and southern Midwest. This set-up of precipitation is more typical of a La Nina pattern. Below normal precipitation in the Southern Plains adds to my suspicion of that high pressure tendency in the region, and this tendency could extend into the Southwest as the pocket of below normal precipitation in northern California shows. Again, confidence is extremely low.


Incredible Closed Low Engulfs US in May

A very unusual weather pattern will be setting up at the start of May, and this unusual weather pattern is one I haven't seen in at least several years.

The image above shows projected vorticity values on May 5th. Vorticity is the spinning of air, and appears in the presence of storm systems. We see high vorticity values centered in the Midwest, curling into a circular formation across the north-central states. This circular motion in the vorticity areas, combined with multiple full-circle contour lines across the Midwest and the general north-central United States region indicates we are dealing with a massive closed low. The closed low is formed when a storm system is cut off from the jet stream and meanders along with little to no influence from the jet stream. Usually, closed lows are relatively small and are more of a nuisance event. This closed low, however, will be of pattern-changing status. This closed low is just like the others, except it will be so large that the weather pattern across North America will be altered as a result.

What can we expect from this event?

The answer is just what you hope it isn't: we are expecting snowfall across portions of the Midwest, Plains and Ohio Valley. At the moment, accumulation appears possible in areas of higher elevation and areas in the western Ohio Valley. The closed low will bring down a massive bubble of cold air from Canada and spread it around the central and east US to provoke multiple chances of (possibly accumulating) snowfall.


Upper Stratosphere Becoming Agitated

Latest indications from the Climate Prediction Center are that the upper stratosphere is becoming agitated as we enter the heart of spring.

The animation shown above details the last 30 days of temperature anomalies at the 10 millibar level of the world, known as the upper stratosphere. The last month of temperature observations has revealed two bodies of above-normal temperature anomalies. The first body of warmth made an initial push to the Arctic in the Bering Sea, but after the attempt was foiled, the warmth appears to have shifted into Siberia and may be making a second attempt. The second swath of warmth also shifted east from the northern Atlantic into much of Canada. This area of warmth has been more oppressed as far as being able to push north, and it seems to be weakening in the last couple frames of the animation. Nonetheless, the uneasiness in the northern hemisphere tells me that the atmosphere is determined to shift into its summer stages, where bodies of warmth like the ones shown above are not present. Time will tell when this happens, but until it does, I suppose you can't blame the atmosphere for staying in a wintry pattern over the last several weeks.


2013 Official Atlantic Hurricane Outlook

Hello everyone, and welcome to The Weather Centre's Official 2013 Atlantic Hurricane Outlook. We begin with my analog package.

We start now with the analog package. I utilized the Pacific-Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) for this outlook's analog years. The PDO involves a positive and negative phase, where each phase depends on the prominent water temperature anomaly in the Northeast Pacific. A glance at the sea surface temperature chart for the northeast Pacific reveals a swath of above normal water temperatures in the offshore regions of the Gulf of Alaska, with below normal temperatures immediately offshore of North America and Alaska. This is the typical signature of the negative PDO. As for the Atlantic Multidecadal Oscillation, we also see a positive and negative phase with this index. The positive AMO signifies warmer than normal water temperatures across the waters off Greenland and in the far north Atlantic Ocean. In the same sense, the negative AMO allows below normal water temperatures to encompass the North Atlantic waters.

After choosing specific years from these two indices, I combined my chosen years and used the ones that had both the PDO and AMO in phases similar to what we are currently anticipating. As a result, I came up with the years 1951, 1952, 1955, 1956, 1999, 2000, 2008, and 2011. All of these years had a clear negative Pacific-Decadal Oscillation and positive Atlantic Multidecadal Oscillation, which is what we are experiencing now and what we should experience moving forward into the spring and summer months.

Let's take a look at an archive of hurricane tracks during the aforementioned years to see if we can see a trend in my analog years that could assist in helping us find a common track for the upcoming season.

In 1951, we saw a storm season that had many storms going out to sea rather than towards the US Mainland. At least 3 of those storms didn't even have a chance of making it to the United States. However, there were a few storms that did have a close brush with the Carolinas, as well as one landfall in Florida. A couple storms did make a threatening track towards the Gulf, but for one reason or another they did not hit the US. One storm (Hurricane Charlie) did hit Mexico, the Yucatan Peninsula, and Jamacia. All in all, the trend for this year was a slight Gulf threat with multiple close calls on the East Coast.

1952 was not unlike 1951 in terms of where tropical systems went. While the Gulf of Mexico was considerably quieter with no systems actually in the heart of the Gulf, there was one landfallig system in the Southeast US, another landfall in Florida, and at least 3 storms that ended up recurving out to sea. The system that struck Florida, which formed on Groundhog Day (yes, in February), was never named. Hurricane Able was the system that hit the Southeast. The trend in this season was a threat to the East Coast and a rather quiet Gulf of Mexico.

1955's Atlantic Hurricane season involved a pretty darn active season in terms of landfalling tropical systems. We saw multiple impacts on the Gulf Coast, especially in Louisiana and Mississippi. We also saw possibly more than 2 separate landfalls on the East Coast, all of which struck the Mid-Atlantic (one also sideswiped the Northeast). Tropical Storm Brenda was one of the systems that hit the Gulf Coast, and it was Hurricane Connie that slammed into the East Coast. Tropical Storm Five followed Brenda into the Gulf, while Hurricane Diane took a hint from Connie and sped towards the East Coast to make landfall. The clear trend here is an active landfalling season in the Gulf and East Coast.

1956 continued the idea of storms running dangerously close to the US Mainland, even making landfall a couple points along the way. We saw a rather unusual season in that the majority of the storms took almost a due-north path out to sea. Usually, storms will form off the coast of Africa and curve west before doing a 180 and going out to sea. In this season, the storms just formed and made their intentions clear as day. Tropical Storm One, the first named system of the season, impacted the Gulf with a landfall. Both Hurricane Anna and Tropical Storm Dora hit Mexico, while Hurricane Flossy did a double-take by hitting the Yucatan Peninsula and the Gulf Coast. An unnamed subtropical cyclone hit Florida and skirted into the Mid-Atlantic. The trend in this season is clear: Tropical cyclone threats were highest in the East Coast and Gulf Coast.

1999 was no different than previous years. We saw multiple tropical cyclones skirt immediately offshore of the Eastern Seaboard, and the Gulf of Mexico came under fire. We saw extreme southern Texas take a landfall from Hurricane Bret, while Florida was surrounded by several near-misses and at least two landfalling systems. It was Hurricane Dennis that took one of the most awkward tracks I have ever seen a tropical cyclone take. It began to curve out to sea after narrowly missing eastern Florida, but suddenly make a hard turn south, then a hard turn west before making landfall in the Mid-Atlantic as a weak tropical cyclone. The trend continues; East Coast and Gulf Coast were threatened in this season.

The year 2000 was a bit different in that the number of threats to the East Coast was reduced. We saw more of a tendency for storms to curve out to sea earlier than storms in, say, 1999. The state of Florida did bear the brunt of at least one landfall (courtesy of Hurricane Gordon), while Alabama and Georgia were affected by a tropical cyclone known as Tropical Storm Helene. A tropical depression also made landfall in the western Gulf Coast, although it is not shown in the map above. The Gulf Coast definitely made headlines as the most affected area this season, with the East Coast in a not-so-close second.

2008 brought an absolutely chaotic Atlantic hurricane season. We saw over half a dozen tropical cyclones hit the Gulf Coast, with one cyclone hitting the East Coast. Tropical Storm Cristobal affected the East Coast, while Hurricane Dolly and Tropical Storm Edouard hit the Gulf Coast. Tropical Storm Fay zig-zagged through Florida, while Hurricane Gustav ravaged the Gulf. Hurricane Hanna hit the Eastern Seaboard, and it was Hurricane Ike that dominated the Texas coast. The trend is probably the clearest we have seen in all of the analog years: The Gulf experienced the largest threat, with the East Coast also getting in the action.

My last analog year, 2011, echoed previous analog years, but also raised the recurring theme of storms curving out to sea. We saw the heavy majority of tropical cyclones curving out to sea in 2011, with little to no damage coming between them. However, there were two Gulf Coast landfalls that were weak, as well as one Mid-Atlantic landfall. The final analog year continued the idea that the US mainland was threatened.

The next piece of evidence I want to show you is a chart of the latest observed sea surface temperature anomalies over the Atlantic Ocean. I outlined three regions of anomalies- an above-normal sea surface temperature (SST) area in and just south of Greenland, a below normal SST area to the east-northeast of the Mid-Atlantic coastline, and a large swath of above normal SST values from the coast of Africa and west into the Caribbean. This type of arrangement of SST anomalies is called an Atlantic Tripole. Years that had an Atlantic Tripole in place had a positive correlation with the monthly hurricane total from June to July and Accumulated Cyclone Energy (ACE) values. This positive correlation means that, since the Atlantic Tripole is in its positive phase right now, we could reasonably expect more tropical cyclones than normal to form this season, and those cyclones could have more energy than normal, which would then raise the ACE index.

I am monitoring the El Nino-Southern Oscillation at this time, and current sea surface temperatures suggest we are wavering between an El Nino and neutral-ENSO conditions. The CFS long range model forecast shown above projects any hint of an El Nino dying off going through the summer months and rest of spring months. A variety of ensemble members from the CFS forecast system average out to produce a neutral-ENSO situation through the hurricane season. The lack of a solid El Nino or La Nina means more weight is placed on smaller-scale factors that we will look at later on in this article.

Based on all the factors listed above, and after observing tropical outlooks from other sources, I have composed a map detailing the areas where I believe a tropical cyclone of any strength (tropical storm or stronger) could strike. Areas outlined in green show the probability of a landfall as 'Low'. This means that climatology and projected atmospheric factors don't especially portray the outlined area as prone to a tropical cyclone landfall. Areas in yellow are denoted as having a 'Moderate' risk of a landfalling cyclone. The 'Moderate' risk means that climatology and multiple atmospheric values tell me the risk of a landfall is above the historical norm, but not by much. Another way to look at it is just over 50-50, favoring a landfall (55-45, if you like). Finally, the red areas depict a 'Fairly High' chance of a landfalling tropical cyclone. I would put 'High', but you can't really put that out unless the outlook is made days before the season starts and your confidence is over 100%. To play it on the safe side, I define the 'Fairly High' category as regions where climatology and multiple atmospheric factors are contributing to what could be the hotbed of activity for tropical cyclone threats to land. It should be noted that this 'Fairly High' region could be extended further west and maybe a tad north if my analysis continues to be favorable for landfalling cyclones. That subject will be addressed further in coming updates as we inch closer to the hurricane season.


Wednesday, April 24, 2013

Next Winter Could Be Unusually Frigid

New and bold data has been uncovered, suggesting that the winter of 2013-2014 may be unusually frigid ('frigid' being defined as temperatures ending up below normal for the winter timeframe).

The data I uncovered was the result of digging through records of the Arctic Oscillation. I put together the proposition of using early spring Arctic Oscillation values to predict the next winter's temperatures and atmospheric flow throughout the Northern Hemisphere. For this case, I used years where Arctic Oscillation values in February were negative, but the year after that, the AO values were even deeper into negative territory. For example, if February 1978 had an Arctic Oscillation value of -0.75, and February 1979 had a value of -2.08, I would use February 1978 to compare to the current year and see if the patterns match up. If the patterns do match up, it would be plausible to expect a negative Arctic Oscillation in the forthcoming winter, thus a higher potential for cold. The image above shows 500 millibar height anomalies for five different years- February 2009, 1984, 1977, 1968 and 1962. You may immediately notice years like 2009 for its Northeast impacts, as well as 1984, the year before the epic polar vortex collapse. All of these years have had a negative Arctic Oscillation value in February of that year, to be followed one year later by an even more negative AO value. A quick glance over the image reveals low pressure in the East US, general high pressure across Canada and towards Greenland, as well as to the north of Europe. Low pressure tendencies are found in Western Europe, the Bering Sea and East Asia. I'm going to show observed height anomalies for this past February next; bear in mind the placement of the high and low pressure tendencies in the image above when looking at February 2013 below.

Let's run over the checklist of high and low pressure tendencies we looked at above and compare them to what February 2013 held in store. We see low pressure in the East US, as well as high pressure anomalies in Canada and into Greenland. We also observe deep low pressure in western Europe, in addition to East Asia and the Bering Sea. High pressure prevails to the north of Eurasia. Taking a look at the images together should set off multiple alarms- all the items I listed in the last couple of sentences appeared not only in February 2013, but also in the averaged-out 5 years image at the top of this post. Now, there are a few differences, like extreme high pressure in the northeast Pacific in 2013, as well as more extended low pressure in the multiple year image that we don't see in 2013. However, you get the general idea- there are several similarities between these images.

So, what does this all mean? Well, we've managed to figure out that the atmospheric flow in February 2013 is at least reasonably similar to that of the five years listed above. This means that, going forward, it is plausible to be on the lookout for a pattern similar to 2009, 1984, 1977, 1968 and 1962 going forward. What this also means is that the winter of 2013-2014 could see some similar features as far as the winters of 2009-2010, 1984-1985, 1977-1978, 1968-1969, and 1962-1963 go.

The image above shows average surface temperature anomalies for the aforementioned winters. We see a wide swath of below normal temperatures stretching from the northern Plains into the Midwest and engulfing the Central and East US regions. This widespread cold shouldn't be surprising- January 1985 was the month where the polar vortex truly collapsed, while the winter of 2009-2010 was the snowiest of record for many. All in all, the analog years spell a chilly winter ahead.

I understand if you don't really get how I chose the analog years, my explanation at the top may not have been as sufficient as I would have liked. If you have any questions, comment them below and I'll try to answer them as soon as possible.

**Don't forget, the Anniversary Festivities begin April 26th with two MAJOR posts!!**


Tuesday, April 23, 2013

Spring Makes a Big Comeback

It looks like spring is going to make a huge comeback in the next week, as model guidance is building consistency with very warm temperatures encompassing everyone in the Plains and east.

Model forecasts of medium-range mid-level height anomalies show a massive ridge building over North America in the next 6-10 days. The European model (left) has this ridge centered in southeast Canada, bringing unusually warm temperatures to those in the East and Central US. The American GFS model on the left portrays this ridge of high pressure splitting into two areas of interest- the West US and Canadian Maritimes. The two model solutions are extremely different with the atmospheric set-up, but predicted temperature spreads are really pretty similar between the two forecast systems.

This nine-panel image of predicted maximum temperatures over the dates listed below each image show how this massive warm-up is projected to evolve. The warmest temperatures seem to want to go over the entire nation, save the Rocky Mountains. The strength of the ridge shown above would certainly support such an idea of widespread warmth, so my position on the idea of this extreme spread of warmth is not one of rejection.


Monday, April 22, 2013


I figured this should probably be addressed before anyone begins to wonder and rumors swirl.

Posting has been much more limited as of late due to a multitude of factors, the most prevalent being the lack of topics to post about. Also factoring into the quiet trend here is how the last few weeks have become unusually busy, restricting my access to the computer. Until we get back into a severe weather event and those dreadful summer heat waves, posting may very well remain below normal. I have no timetable for when this busy period will end, unfortunately.


Saturday, April 20, 2013

Spring Pulls A Vanishing Act; Returns for May

Spring continues to do its magic and will be pulling a vanishing act until the beginning of May.

Pictured above is the 500 millibar height anomalies from forecast Day 6 to Day 10. Cold colors show low pressure anomalies, while warm colors portray high pressure. In the forecast image above, we see strong low pressure building over the Arctic to allow for a strengthening polar vortex. As a result of this  strengthening, warm weather is typically favored. However, high pressure building south of Greenland and in the Northeast Pacific will coerce the low pressure further south and allow cold air to make itself available in all the areas shown in blue. Again, usually, warm air would be favored as the cold air would be kept up north in the presence of such strong low pressure over the Arctic. However, the angling of those two previously mentioned high pressure systems will let the polar vortex squeeze some of that unseasonably colder air further south.

The long range American ensembles show 500 millibar height anomalies over the next sixteen days from left to right, top to bottom. We can see the polar vortex pushing south towards the US/Canada border, but by the time May rolls around in the bottom row of forecast images, we see abundant high pressure across the nation. This abundant high pressure formation is what is supposed to happen with strong low pressure in the Arctic. It looks like the nation-wide high pressure formation in early May would be tempered in the East US just because of persistent high pressure stirring around Greenland, but cold air should not prevail like it will in the next couple of days.


Snow Rounds Out Atypical April

It looks like snow will be rounding out the last days of April.

The NAM model forecast has two swaths of accumulating snow in the Midwest and Plains. The stripe of snow in the Midwest looks to put down upwards of 6 inches in many spots, especially across Wisconsin and southeast Minnesota. Lighter totals will be observed into northern Nebraska and southern South Dakota. The second body of snow will be more significant, but will cover less ground. Kansas will get hammered with totals flirting with (and in some cases, exceeding) one foot of snow. The heaviest amounts appear to be centered in the northern part of the state, with central Kansas being the cutoff for the heaviest snow. Normally, I would address this as Old Man Winter's last hurrah, but with the way this April has been going, I wouldn't be surprised to see sporadic, light snowfall chances into May.


Friday, April 19, 2013

**BREAKING NEWS: Boston Bombing suspect in custody**


The Boston police department has tweeted, indicating the suspect in the Boston Marathon bombings is IN CUSTODY. This is a CONFIRMED REPORT.

Wednesday, April 17, 2013

Long Range Pattern Preventing Sustained Warmth

The long range weather pattern is not looking friendly in terms of sustained warm weather.

Shown above is a composite chart of 16 days worth of forecasted 500mb height anomalies from the American GFS Ensembles. The days increase from left to right, top to bottom. The current situation we are in (top left image) includes low pressure in the West and high pressure in the East. This set up allows for warm weather and thus potential for severe weather like we are seeing today and tomorrow. However, over the next week or two, low pressure looks to swing south and east from Canada and the Rocky Mountains to land in the East US. From there, high pressure appears to set up in the West US, and this provides us with the signal that colder temperatures are on the way for many in the central and east US. In the very long range, on the bottom row of images, forecasts show high pressure engulfing the nation from coast to coast. This would support a warmer scenario, but unless we see sustained low pressure in the West US, i'm not willing to buy into a scenario that gives actual springtime temperatures for the East US.


Significant Severe Weather Episode Tomorrow, April 18th

There appears to be growing evidence that tomorrow will hold what is being called a 'Significant severe weather episode' by the Storm Prediction Center, as shown in their most recent discussion:



Model guidance suggests squall line formation will commence around noon to 2 PM central time tomorrow afternoon. The squall line is expected to begin in Oklahoma/Kansas/Texas and quickly shift eastward. Further development is expected, first along the southern fringes to cover the Gulf Coast, and then building towards the Great Lakes. This would fall right in line with the Storm Prediction Center's outlook, with a severe squall line building north as the afternoon progresses into evening. Basically anyone in the moderate risk area should expect to bear the brunt of this potentially hazardous squall line. The above image valid for 10 PM central time, shows the squall line still racing east, spanning from one border to another. It's not that often you'll see a squall line with that far a reach.

Tomorrow may be a Critical Storm Action Day. It will certainly be a Storm Action Day.


Monday, April 15, 2013

Severe Weather Outbreak Likely in Next Four Days

**This post is dedicated to all those affected by the tragic bombings at the Boston Marathon and the newly-reported JFK Library bombing this afternoon. Our thoughts and prayers go out to the victims.**

The next four days are filled with severe weather potential. Let's break down each day and the cities affected.

Today- April 15th

Storm system is present in Texas this afternoon with associated dry line forming in the western portion of the state. Slight risk of severe weather extends from Texas through Oklahoma and into Missouri. Surface analysis shows a warm front draped along this slight risk area, and it is expected that both this frontal boundary and the incoming storm system will be factors in this evening's severe weather risk. Overall parameters for severe weather support tornado potential in eastern Oklahoma and southern Missouri, with an enhanced damaging wind threat in the same areas.

Tomorrow - April 16th

Model guidance indicates the storm system will continue to churn in the Southern Plains, with the previously mentioned warm front now becoming stationary and draping itself over much of the slight risk area. Expected thunderstorm development will be along this frontal boundary and associated slight risk area. Closer analysis of the slight risk area reveals the risk to be on the low end, meaning this will not be a widespread severe weather event in terms of severity.

Wednesday - April 17th

This is the outbreak day. The Storm Prediction Center has issued a rare moderate risk area for Oklahoma and southeast Kansas. It's not solely the presence of the moderate risk that makes this rare, it's the fact that this moderate risk area was put out two days in advance. The last time we saw a moderate risk area two days out from a severe weather event was last year. I can't put my finger on it, but I believe that the event ended up being a High Risk severe weather event. Predicted analysis for Oklahoma overnight Wednesday shows high tornado parameters and widespread instability across the region. I will be watching model forecasts in coming hours and days, but this event is looking more potent than the last event that never really materialized.

Thursday - April 18th

The long range outlook from the Storm Prediction Center has a wide portion of the southern Midwest and Gulf Coast states in a risk area. The SPC doesn't issue specific risk areas for more than two days in advance, they only put out outlines. The associated SPC discussion indicates that this risk will be for a squall line event following Wednesday's event. I will be looking at that event in the future, but my primary focus is on Wednesday's event.


Saturday, April 13, 2013

Severe Weather Outbreak Possible Next Week

A severe weather outbreak looks possible on Tuesday and Wednesday across a wide portion of the Southern Plains.

A storm system looks to drop across the Rocky Mountains and sweep eastwards, forming a low pressure system in the southern Plains. This low pressure system will form a dry line in western Texas. As the storm system lifts northeast, the dry line will expand north and east in accordance with the motion of the storm. This will place Tuesday's severe weather risk in the vicinity of the center of the storm system. Storm initiation on Tuesday should occur overnight, as lower level winds ramp up and the jet stream inches further east as the storm system drags northeast. Storm formation should begin as individual cells that begin to cluster into multiple-cell storms. Tornadoes do not appear to be favorable- despite sufficient instability, lower level capping issues may hinder extreme supercell growth. Additionally, cloud bases are not as low as they could be to foster tornado development. Best chance for tornadoes is likely to be in central Oklahoma and into eastern Oklahoma in coordination with overnight strengthening of lower level wind speeds.


Friday, April 12, 2013

April 16-19 Potential Winter Storm and Severe Weather

There is potential for a wintry side and a severe side to the next storm system in the US. We will start with the severe side.

The Storm Prediction Center has outlined two areas of interest in the Southern Plains- one on April 16th (purple) and another on April 17th (green). These outlines serve as long range indications that the SPC is monitoring the potential for a severe weather event on April 16th and 17th.

Model forecasts have been consistent with having a storm system sweeping through the Rocky Mountains before shifting east and provoking active weather in the outlined areas. The American GFS and European ECMWF models are in good agreement on this type of scenario happening. However, what happens when the system gets into the Plains is a different story. Precipitation forecasts from the European model show a very active event over the purple outlined area for April 16th, but sounding forecasts from the GFS are much less enthusiastic. Primary concern with the sounding data is what appears to be a strong capping inversion (thunderstorm suppressor) from the surface to about 4000 meters off the ground. This capping inversion is predicted to be stronger than the event we saw, making the event difficult to get going. Past the layer of stability, the instability higher off the ground is weaker than what we saw with the previous event. These two factors make for a hard time in getting thunderstorms to form. When moving forward in time, sounding forecasts become slightly better for thunderstorm development, with instability rapidly increasing throughout the day in eastern Oklahoma. Despite this, concern remains with the lack of instability from the surface to roughly 3200 meters above ground level.

Now, as for the wintry side, there is already a model battle setting up. The European model (top image) wants to take the storm on a track going through Chicago and the Lower Great Lakes to drop snow in the Upper Midwest. A severe weather event would then persist in the Ohio Valley and Southeast. The American model (bottom image) prefers to take the southern and faster route when compared to the European model. The American GFS model ends up dumping a significant amount of snow in the Midwest rather than the Upper Midwest, as the European model appears to show. The snowfall forecast from the European model below illustrates this potential:

A quick glance at other models and ensembles reveals that the American GFS model is on the losing side, with the Canadian and US Navy models agreeing with the European northward solution. The United Kingdom's forecast model agrees with the American solution, but the UK's model usually is not the best with forecasting storm systems. The American ensemble members agree with its parent GFS model, but that's to be expected. All in all, we are still a while away before we reach a solution on this event.


Thursday, April 11, 2013

Medium-Range Pattern: Cold West, Warm East

The overall pattern over the next 6 to 10 days is looking more and more like Old Man Winter isn't ready to let go, even though we're quickly pushing into mid-spring.

Shown above is the medium range height forecast across North America. In areas of cooler colors, low pressure is favored. In the same sense, warm colors indicate high pressure tendencies. Looking at the European model's forecast above, we see persistent low pressure pushing south from Canada into the Western US and Plains. In response to the low pressure in the West, high pressure is inclined to form in the Eastern US, and this trait is reflected nicely on the European model's above forecast. If the jet stream follows the low and high pressure waves, I would expect the jet stream to keep a relatively strong stance over the southern Rockies and southern Plains in response to the persistent low pressure anomalies in the area. When the jet stream approaches the high pressure area in the East US, it is expected the stream should make a quick move northeast through the Midwest and Great Lakes. This would put the last two regions in the temperature battle zones, and possibly in whatever severe weather risk may come along while this pattern is in place.

Lower level temperature anomalies for the same timeframe emphasize the cold weather deeply entrenched in the Rockies and Plains as a result of the low pressure pushing south from Canada. In the same sense, the high pressure anomalies in the East US result in above-average temperatures in the next 6-10 days. I expect the East US, mainly the Northeast and New England regions to get in on springlike temperatures, maybe even summerlike temperatures if the warm-up is strong enough. As for the Central Plains, that deep cold pocket from eastern Montana into the Dakotas, Nebraska and Kansas will return the Plains region into early springtime temperatures, possibly as chilly as late winter temperatures. The severity of both temperature anomalies is to be determined, but this pattern is certainly going to provide a chilly period for many people west of the Mississippi River.


Wednesday, April 10, 2013

April 11th Severe Weather Event

I expect a severe weather event to unfold tomorrow, April 11th.

Short range model guidance suggests the cold front currently working its way east across the nation will fire off another day's worth of severe weather. Highest risk appears to be placed across Alabama and Georgia in the area of the highest instability. Overall instability is moderate at best, with highest values in the aforementioned areas. Helicity in the atmosphere will be decently high across all areas, but the lack of high instability makes for a rather low-moderate tornado risk. I can see a situation in which weak tornadoes evolve from this set-up, but I do not expect several big tornadoes across the Medium Risk area. High Wind index looks to be high for this event, as the typical cold front merging of severe thunderstorms occurs to form a squall line. New model forecasts indicate instability will be higher than previously thought, and that storm cells may be stronger than previously thought. I'm going to stay with my current thinking on the graphic above; I feel that the graphic best interprets my thinking right now.

Main concern for any tornadoes rests in the areas you see above with isolated storm cells. This image is valid for 8 PM Central Time, 9 PM Eastern Time on April 11th. Any tornadic activity is most likely to originate from isolated thunderstorms popping in Georgia, the Carolinas and Tennessee. These isolated storms would feed off of the instability and decent helicity to possibly provide a base for tornadic activity. The extent of this potential tornado activity is to be determined, and that determination should be made tomorrow morning.


Massive Snowstorm Headed for Minnesota

A recent forecast image from the American GFS model shows portions of Wisconsin, South Dakota and Minnesota receiving snow totals above 2 feet in some spots, with Minnesota possibly getting in on 30 inches of pure snow!

Bear in mind this forecast is unlikely to verify exactly, as it is very rare to see extreme snow totals like this at any time in the year, much less in mid-spring. A more recent forecast has the same states getting anywhere from 10-16 inches of snow, and this range still seems pretty high. While it does seem pretty high, it technically is realistic- it isn't spring without a major storm system bringing a big winter storm and big severe weather event. While the most recent forecast shows only 10-16 inches, previous forecasts today have shown amounts still flirting with 2 feet of solid snow in many places.