January 2-6 Potentially Significant Winter Storm

I'm still keeping an eye on the January 2-6 time frame for a potentially significant winter storm.

In a similar set-up to this past weekend's winter and severe storm event, we see a strong storm system passing over East Asia on December 27th. Using the correlation that states weather in East Asia is reciprocated over the United States 6-10 days later, it is logical to believe that the January 2-6 period may see a winter storm. The reason I say it is potentially significant is because this same instance happened 6-10 days before this past weekend's storm, where a strong system hit Japan. Then, this past weekend, we saw the severe weather and significant snow/ice that qualified the event as a significant storm system. The strength of that Japanese trough only tells me that we are in for another potentially big storm system come January 2-6.

The atmospheric set up for this potential storm is looking pretty interesting. The North Atlantic Oscillation (NAO), whose forecast is shown above by the ECMWF model, is projected to continue a recent weakening trend to negative territory by the time New Year's Day comes around. This means that the high pressure that has been dominating the Southeast will finally be gone. This also means that the door for East Coast storm systems will be open for once in the last while. And despite the NAO then projected to rise again (which is very possible (even likely)), the risk of East Coast storms will remain in place, albeit diminished.

The reason the door for East Coast storms will remain open is because the Pacific North American (PNA) index is projected to be positive in the long term, especially during this timeframe. The GFS Ensembles predict that the PNA will remain positive through January 2-6, meaning the Southeast ridge should be suppressed. Thus, storms will be able to cross through the Southeast, and possibly even make their way up the coast. Because of this +PNA forecast, the track for this potentially significant storm is still up in the air. Right now, I would outline the Ohio Valley and East Coast for potential areas in line for this storm. I say the Ohio Valley because that possibly-positive NAO may not allow for an East Coast storm, and I say the East Coast because the PNA will be positive, which will allow for suppression of the dreaded Southeast ridge that has fended off East Coast snowstorm chances for a while now.

Still a lot of items to be figured out, but I feel comfortable saying that there is potential for a significant winter storm around the January 2-6 timeframe, and that this storm may affect the Ohio Valley or East Coast (with other locations also still in the mix).

This will most likely be my last post for the day, so a Merry Christmas & Happy Holidays to everyone!

Andrew

ECMWF Weeklies Send Polar Vortex Crashing into United States

The new run of the ECMWF Weeklies sends the polar vortex crashing down into the United States -- twice.


The forecast from the European weeklies above shows a lobe of the polar vortex plummeting from the upper latitudes to the Eastern US, bringing extreme cold weather along with it. The 850mb temperature anomaly forecast above shows anomalies as low as 26.3 degrees Celsius below normal. Converting Celsius to Fahrenheit tells us that 26.3 degrees below normal is the equivalent of 47.34 degrees Fahrenheit below normal! Considering average highs across Georgia range from the 50s to the 60s, we would be talking about highs in the single digits in southeast Georgia if this forecast verifies.


The scene is repeated again nearly a week later, as the ECMWF Weeklies take another polar vortex lobe and drop it down into the Northeast, bringing another bout of frigid temperatures along. Temperature anomalies are not as intense, but the message of anomalously cold weather hitting the East still gets through loud and clear.

So, could this happen?

Yes, but it probably won't. The polar vortex is projected to be split up into two vortices (one in southern Canada, one towards Eurasia) as ridging takes over across the Arctic Circle. And while anomalously cold weather is possible as the vortex stationed in Canada is moved closer to the United States, I can't foresee a massive breakdown in temperatures involving a polar vortex lobe collapsing into the United States. It's a possibility, yes, but a very small one.

Andrew

January 18-20 Potential Colorado Low / Panhandle Hook Winter Storm

This post will discuss the potential for a winter storm around the January 18-20 period. While this post may seem pretty far-fetched, I assure you that there is potential for a storm in this timeframe, and if you read on, you'll see why as well.

The latest 5 day 500mb height forecast from the Weather Prediction Center over Alaska shows a storm system entering the Bering Sea on December 30th, as the 'L' on the bottom center panel shows. Here is where we employ the Bering Sea Rule, a rule created by Joe Renken after his observation of storm patterns in the Bering Sea and the United States. It is stated that a storm system in the Bering Sea then results in a storm system for the United States approximately 2.5 to 3 weeks later, or 17-21 days later. If we see a storm system entering the Bering Sea on December 30th, we extrapolate that date to the Bering Sea Rule guideline of 17-21 days and end up with a storm timeframe of roughly January 16-20.

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. However, by using all of the indices at my disposal above, I feel pretty confident that there is at least a decent potential of a storm system in the US for this timeframe. The strength of said system is to be determined, but there is definitely potential here.

Andrew

January 2-6 Potentially Significant Winter Storm

I'm looking at the January 2-6 period for a potentially significant winter storm.

ECMWF Ensemble 500mb height anomaly forecast for December 28

GFS Ensemble 500mb height anomaly forecast for December 27

Global ensemble guidance is in good agreement that an anomalously strong storm will push through Japan in the two or three days after Christmas. The GFS Ensembles push the energy out of Japan 12 hours quicker than the European ensembles, but the main point right now is that there very well could be another significant storm system pushing through East Asia. Using the 6-10 day correlation between East Asian weather and United States weather, I am monitoring the nation for another potentially significant winter storm. I say it could be significant, because the East Asian system looks to be strong. Thus, the system in the US has a good chance of being strong around the January 2-6 period.

The jet stream pattern from the ECMWF ensemble set leading up to the storm looks very interesting. We see the two branches of the jet stream separating over the northeast Pacific, leading to ridging in those waters and in the West Coast. We then see the two branches merge again over the East US, which tells me this might be an East Coast storm.

Teleconnections don't look to be too favorable for an East Coast snowstorm, with ridging continuing across the Southeast thanks to the positive phase of the North Atlantic Oscillation (NAO). This Southeast ridging pattern is confirmed with the projected negative Pacific North American (PNA) index. Both of these lead me to believe that while an East Coast storm would appear possible based on the jet stream pattern above, I would expect the pattern to be relatively similar to the one currently in place across the nation. That would mean this potentially significant storm may affect the Plains, Midwest and Great Lakes again, in relatively similar fashion to the December 20-23 winter storm.

The West Pacific Oscillation (WPO) and East Pacific Oscillation (EPO) are projected to be negative during this timeframe, meaning cold air could be more prevalent than what we are seeing right now. While cold air availability is a case-by-case basis for winter storms, this upcoming potentially significant winter storm should have at least some base of cold air to work with, especially if the -WPO and -EPO cooperate as they should.

Andrew

Stratospheric Polar Vortex to Come Under Attack

The stratospheric polar vortex looks to be coming under attack in the next week or two.

The ECMWF forecast for Wave 2 activity shows highly anomalous values arising in the far upper stratosphere, mainly extending from the top of the stratosphere (1mb) to the middle-ish part of the stratosphere, ending up at the 20 or 30 millibar area. It is easy to see the attack that the stratosphere is undergoing, with the highly active Wave 2 values defining the polar vortex being strained in an attempt to be split into two vortices. There are two major types of wave activity- Wave 1 and Wave 2. In Wave 1 activity scenarios, the stratosphere undergoes distress as a major ridge attempts to displace the polar vortex from the Arctic, while keeping it fully intact. With Wave 2 activity, the polar vortex is experiencing ridging across the upper latitudes, making the vortex want to split into two vortices. These vortices can then shift to lower latitudes and bring extreme cold weather to the regions affected. In this specific case, it isn't looking like this projected polar vortex intrusion will do the job of splitting up the vortex.

This image, showing multiple wind speed and flux forecasts from the ECMWF, sums up the idea that while this will be a rather intense attempt by the stratosphere to break up the polar vortex, it won't actually finish the job. On the top panel, we have the projected wind speed of the top of the stratosphere, at the 1 millibar level (where this big stratospheric intrusion will be centered). The wind speed is projected to actually increase over the next 10 days, meaning the polar vortex will strengthen. We would want to see a steep drop-off in wind speeds in order to identify that this stratospheric event would actually be breaking up the vortex. The second panel shows wind speeds at the 10 millibar level (blue) and 30 millibar level (red). Again, we would want to see dropping wind speeds to indicate a weakening vortex, but as that indication has not been given, I do not anticipate a splitting vortex. The third panel shows the sharp spike in Wave 2 geopotential activity, which tells us about that incoming stratospheric intrusion, and this is confirmed with the increasingly-elongated EPV flux arrows on the bottom panel. If we see the arrows get larger, the attack on the polar vortex would intensify. But because the ECMWF can't show forecasts beyond 10 days, we don't know how intense the event actually gets.

In the long range, the GFS model sees things getting a little more interesting. This model allows a large strip of warm temperatures to surge into the Arctic via Eurasia, which does appear to be going up against the polar vortex (shown in the blues and purples). Now, the accuracy of the GFS in the long range is pretty low, so this forecast is pretty dicey to begin with. However, going off of the ECMWF beginning a pretty solid stratospheric attack on the polar vortex, the idea of this attack continuing and even intensifying isn't that far fetched as the Wave 2 geopotential height anomalies increase per the ECMWF. So, while this forecast above may not verify as it is shown above, something similar in terms of a continued attack on the polar vortex is possible.

Andrew