Friday, December 27, 2013

January 17-21 Potential Colorado Low / Panhandle Hook Winter Storm

This is an updated look at the January 17-21 potential winter storm, which had previously been titled the January 18-20 winter storm. The timeframe was extended to provide a 'cushion', as a look at some new indices favor a wider timeframe.

This is a long range post, and many found the notion of me publishing such a far out storm possibility appalling. However, the evidence is building for a potential storm system in this timeframe, and if you'll just give this post a good read, you can see why I'm posting about it this early.

This image above from the Weather Prediction Center (WPC) shows the mid-level pattern over Alaska on January 1st. There are two systems marked on here; one storm system is over Alaska, as the dip in the height contours shows, and another storm is marked by the red 'L' just offshore of far eastern Russia. We're going to be watching the red 'L' for this storm system. Model guidance sees this storm cutting north over the western Bering Sea, and this is where we employ Joe Renken's Bering Sea Rule. The Bering Sea Rule states that when a storm moves through the Bering Sea, a storm system then moves through a portion of the United States 17 to 21 days later. If we see this system cutting north in the western Bering Sea around the December 31 - January 1 timeframe, we can then predict a storm system to cut north in the US as well 17-21 days later, which brings us to the January 16-22 time period. Because the storm is projected to cut north in the western Bering Sea, Joe Renken does believe that this signals a Great Lakes Cutter system around the 20th of January. Other subjects I will discuss below lend additional credibility to this timeframe laid out, as well as the predicted track of the storm.

The following MJO OLR portion is copied from my previous December 23 post on this storm, because the information remains valid.

The Bering Sea Rule isn't the only long range piece of guidance we can use to detect a potential storm. Here, in a CFS four-member ensemble forecasts developed by Kyle MacRitchie, we see the long range projection of the Madden-Julian Oscillation, in its eight-phase phase space diagram. Using this graph, we see that the MJO is projected to enter Phase 5 around December 27th, which all ensemble members agree on. Now, we'll take a look at the Outgoing Longwave Radiation (OLR) composites in the mid-latitudes for a Phase 5 MJO.
This MJO composite, developed by Nicholas Schiraldi, shows OLR anomalies in the 30 day period before and the 30 day period after the MJO hits Phase 5. In this case, negative lag days on the left side of the image show the number of days before the MJO gets to Phase 5 territory, while positive lag days on the left legend depict the number of days after the MJO hits Phase 5. We can substitute the lag day of 0 for December 27th, as that is when the CFS forecast above predicts we will get into that Phase 5 MJO. Looking ahead, we will ignore the red circled portion (that is for an upcoming post) and will instead take a look at the black circled part of the graph, where you can see blues shaded in. A look at the longitudes at the bottom of the image tells us the strongest negative OLR anomalies will be centered between the 85 West and 100 West longitude lines. If we put that together with the indication that this OLR anomaly chart is valid for latitudes between 55N and 40N, we find that the latitude lines cover the entire United States from Canada to Mexico, while the 85W and 100W longitude lines cover the US from roughly the Central Plains to the Great Lakes. If we clarify that negative OLR anomalies mean stormy weather, and observe that the circled blues are moving north and east, we can deduce that a Phase 5 MJO results in a storm system crossing the US across the Plains, Midwest and Great Lakes in roughly a northeast (or even east-northeast) direction. If we glance at the lag days on the left for when this storm would occur, we find that the circled blues encompass lag days of +17 to +25, meaning the storm would hit anywhere in a 17 to 25 day timeframe after the MJO hits Phase 5. 17 to 25 days after the projected December 27th arrival of the MJO at Phase 5 puts this potential storm system in the January 15-23 period. Now, in order to cut down on the large timeframe, I decided to shorten the positive lag days to cover the strongest negative anomalies only, which gave me a projected storm timeframe of January 18-21.

So we now have two timeframes for a potential storm system. The Bering Sea Rule gives us a timeframe of January 16-20, while the MJO OLR Composites give us a broad timeframe of January 15-23, which I shortened to January 18-21. If we put those two dates together, we end up with a broad-brush timeframe of January 15-21, which covers all dates outlined by either one or both indices. If we shorten that January 15-21 period to only include dates that both indices highlight, we end up with a January 18-20 timeframe for this potential Plains/Midwest/Great Lakes storm system.

How do we know the track of this storm?

Well, we've already deduced from the OLR charts that the longitude and latitude markings would strongly suggest a Plains/Midwest/Great Lakes storm system, moving northeast as it crosses those regions. With that in mind, I took a look at a device created by Larry Cosgrove and found two plausible storm tracks.

Image created by Larry Cosgrove.
The first track possible is a Panhandle Hook (A) system. We can see that this system fits the bill that was outlined by the OLR charts. It originates in the Plains and move northeast through the Midwest and Great Lakes. These systems tend to bring heavy wintry precipitation to the Midwest, Great Lakes and upper Plains, and, if all goes right, these systems can attain massive amounts of moisture from the Gulf of Mexico to enhance these wintry precipitation prospects.
Image created by Larry Cosgrove.
The second track that also fits the bill is a Colorado Low (A). The system originates in the Plains and then moves northeast across the Midwest and Great Lakes before progressing into Canada. The MJO OLR charts confirm that this storm is also a possibility, and the last time I used the MJO OLR charts to make a long term prediction, the results were spectacular. Because this potential event is still about a month away, we don't know how the teleconnections will react to possibly force this storm in a different direction than what the MJO OLR composites predict will happen. (End copied portion from Dec 23 post)

The next item to discuss also comes from Joe Renken, and it is one that has been discussed on this blog frequently. This is the East Asian correlation, which states a storm system in East Asia is reciprocated in the United States 6-10 days later.

Shown above is the 360 hour 500mb height anomaly forecast across the Northern Hemisphere. While this is definitely in the long range, I feel it is worth mentioning here, as it does help to prove storm prospects for this January 17-21 time period. Looking towards Japan at Hour 360 (January 11), we see stormy weather, as indicated by the deep blues over the region. If we are to say that this East Asia correlation comes into play here, extrapolating January 11th 6-10 days out brings us to a potential storm timeframe of January 17-21, which fits perfectly into the allotted timeframe.

After examining these three items, we have come up with three timeframes, with one set forward by each item we examined.

•Bering Sea Rule:                                     January 16-22
•MJO OLR Composite:                            January 15-23 (tighter timeframe of January 18-21)
•East Asian Correlation (Typhoon Rule): January 17-21

The general consensus of a storm system in mid/late January is pretty clear; the trick is nailing down a more pinpointed timeframe, rather than a generalized time period.

We still aren't done- there is one more item rooting for this Colorado Low/Panhandle Hook storm: the ECMWF Weeklies.

This is an image from the ECMWF Weeklies Control forecast, showing us mean sea level pressure anomalies and contours. This image is valid for January 19th into the 20th, and the storm system in question is clearly defined by the deep negative MSLP anomalies over eastern Oklahoma. The yellow arrow I drew connects the deepest point of the storm in this image with the center of the storm approximately 24 hours later. You can see how that arrow takes the storm through the Southern Midwest into west central Ohio. Because this storm fits the bill for crossing the Midwest/Ohio Valley in the MJO OLR Composite timeframe, and because it happens over the period allotted by the Bering Sea and Typhoon Rules, I have decent confidence that while this storm may not show up in future ECMWF Weekly forecasts, we could see this sort of scenario play out with this very possible winter storm.


January 2-6 Potentially Significant Winter Storm

There is the chance for a potential winter storm around the January 2-6 timeframe.

Model guidance has been firm on the idea of a strong storm system passing through Japan tomorrow morning, on December 27th. This is shown well by the ECMWF 500mb height anomaly projection for that timeframe above. If we utilize the correlation that states a storm in East Asia then results in a United States storm 6-10 days later, we find a potential winter storm hitting the nation around the January 2-6 timeframe.

Here is the 12z ECMWF 500mb vorticity forecast for January 4th, where we see two pieces of energy impacting different portions of the nation. There is energy coming down from Southwestern Canada, as well as a storm system over southern Texas and into northern Mexico. It seems to be that these two pieces of energy would be involved in this potential winter storm. If you have been watching the models, you will recall that the ECMWF showed a triple phase (three pieces of energy phasing/merging) that then created a monster storm system. While that storm was forecasted to occur in the outlined January 2-6 period, and it was deemed possible at the time, the ECMWF no longer shows such a solution, and the likelihood of such an event happening is low.

This is the ECMWF Pacific North American (PNA) index forecast. We can see that the PNA is projected to be negative for when the possible storm timeframe comes about.

During a negative PNA, we tend to see big high pressure form across the Gulf of Alaska. Because we have a big rise in height anomalies over that body of water, there is a response of a dropping in height anomalies over the West Coast, meaning stormy weather forms in that region, as the graphic above from NCSU illustrates. Thanks to that stormy weather in the West, high pressure likes to form in the Southeast, and the two arrows (which illustrate the wind pattern in the area) combine over the Plains to show the storm track of systems during a negative PNA. Now usually, negative PNA storms like to go up into the Plains because the Southeast ridge is usually very strong. In this case, however, the positive NAO helps to keep the overall atmospheric pattern very progressive, meaning we don't see any persistent high or low pressure systems in any given area. There is some conflict over the predicted phase of the PNA, with the NCEP Relative Measure of Predictability charts supporting a positive PNA, and the ECMWF forecast here going with a negative PNA. The vorticity chart further up on this post more resembles a positive PNA, but I guess this sort of variability is to be expected with the event still nearly 10 days away.

Forecasts for the North Atlantic Oscillation (NAO) are also a bit messy, most likely due to the impending weather pattern shift. The GFS Ensemble set shows the NAO descending from its moderate positive state to a more neutral position by the time January 2nd rolls around. From there, the ensemble mean takes the NAO back into weak positive territory, and I actually think we see an intensification of the positive NAO more than what is forecasted for the 2nd and 3rd. A piece of the polar vortex will be rather close to Greenland, and it's possible that the ensembles are underestimating the +NAO that will arise as a result.

Regardless of how these teleconnections end up, let's go ahead on the basis that the ECMWF will be correct in its 500mb vorticity forecast above. The model doesn't really phase the two systems together in the vorticity forecast above (though on the most recent run, it nearly does-- remember I made this post last night to be released today), and I don't think that lack of phasing is correct. Based on the seemingly-positive PNA, I would expect the Canadian energy to dive further south and at least come close to interacting with the southern energy. As far as the iffy NAO, the chart immediately above suggests a weak positive NAO or neutral NAO, but some 500mb charts I looked over hinted at more of a negative NAO, further adding to the confusion. I'm not ready to say if this storm will definitely cut north to ride the East Coast, but I do feel comfortable saying that there does look to be a chance for a potentially significant winter storm during this timeframe. Until we know more details on teleconnections, we won't know much more on track.