December 18-21 Potential Significant Winter Storm (Updated 12/11)

The potential is rising for a major winter storm to affect the Central and East US. Let's see how this could all unfold.

This is the Hour 168 forecast from today's 12z (6:00 AM) run of the National Weather Service's GFS model. This is the sea level pressure (white lines) and 500 millibar level (colors) forecast for the morning of December 18th. In this forecast, we see a large blue circle in the southern Plains, as well as a low pressure system near the Gulf Coast. The aligning of white lines (isobars) in a circular formation around the 'L' near the Gulf Coast, as well as the blue area in the South Plains suggests the presence of a storm system. This does look to be the storm system we are watching for this time period.

Going ahead a bit to the morning of December 19th, we now see that our storm system is predicted to move due east and become a strong coastal storm in an event that would be all too familiar to Superstorm Sandy, which I will discuss further later on. In a few words, I don't believe this forecast. The atmospheric pattern is much more conductive for a storm track either through the Plains or into the Ohio Valley/Midwest, the latter of which I think is more likely.

We now move on to the European weather service's ECMWF model, known as the most reliable forecasting model man has made to date, although recently this model has been slipping. The same rules apply for colors and white lines. This is the forecast from the ECMWF, valid on the morning of the 18th. Here, we see our low pressure system in the South Plains just like the GFS. Pay attention to what happens in this next forecast frame for the morning of the 24th.

The ECMWF takes this storm into the Southeast and off the coast! The reason I am so shocked is because this is a huge change from what the ECMWF was previously showing. Before, we had multiple forecasts of this system going into the Ohio Valley and Midwest, bringing rain and possibly good snows to those areas. When I come to situations like these, where the models suddenly change their forecast, I say 'Look at the trends'. So, I don't think I'll take this forecast too seriously unless tonight's new ECMWF forecast shows a similar idea. I will describe more why I don't think this forecast is correct further down.

Now here's where things get serious. This is the forecast from the 12z ECMWF ensemble prediction system (also known as the ECMWF EPS). To think of this the right way, imagine that forecast of the ECMWF above, but now there are 51 of those forecasts, combined into one, and that's the ECMWF EPS. Given, each different forecast has at least some change in their parameters so there is a difference from the actual ECMWF model, but when it comes to the ECMWF EPS, there's no model that can match that skill, so take that into account when seeing this forecast.
The ECMWF EPS starts out the morning of December 18th with our storm system in the southern Midwest, rather than the South Plains. Additionally, the system is not as strong as the ECMWF/GFS are showing. Why is this significant? Because if the ECMWF EPS goes up against the ECMWF/GFS, who do you think will win: 2 models with very high skill, or 51 models with the same high skill?

We now move ahead to the morning of December 19th. We now see the ECMWF EPS has taken this system into the waters just offshore the New England/Mid Atlantic area. It is stronger than the past forecast image. To me, this seems like the more obvious solution, because this is essentially what the ECMWF model itself was showing for quite a while before today's sudden change.

Now, let's discuss just why I'm so confident in the ECMWF EPS, and am disregarding the ECMWF and GFS.

(Originally posted Dec. 9, NEW INFORMATION ADDED on 12/11) The Lezak Recurring Cycle, or LRC is involved in this situation. Using the 53 day LRC timetable, I traced back December 18th to October 28th, and here is the 500mb pattern observed that day.

Look at that! We see a strong system in the Ohio Valley on this day, as well as a weak high pressure system in the Southwest indicating a possible positive PNA. There is a negative NAO in place, though we can't tell whether it is west or east based. This is our storm system that we could see hit on Dec. 18-21, and is the same system that the ECMWF was doing so well with before it got lost.

There is a method to the ECMWF and GFS' madness, and it is shown below.

Our storm system has now moved to the east, wobbling a bit as it did so, and combined with Sandy. Notice we still had our positive PNA showing itself with high pressure in the West US. If we were to follow this system and discount Sandy, I still believe an eastward movement would have prevailed, likely not as fast if Sandy were not present. The lack of Sandy in this potential storm system, combined with a positive PNA and east-based negative NAO leads me to believe that this forecast system should go a little more to the north and east than it did in October. 
The ECMWF and GFS are pulling the idea of a Sandy repeat, not in strength but in track. Personally, we all know Sandy isn't going to happen every 53 days, so we won't see this system ride the South US and shoot up the coast. If it DOES end up happening, it won't be a HUGE surprise, but it will be something I was not initially predicting.

Preferred Forecast: ECMWF EPS
Confidence: 45%

Andrew

Bering Sea Signaling at New Year's Day Big Storm Potential

I got a lot of criticism for releasing my original post on the potential for a New Year's Day storm, but such criticism doesn't deter me. I do these posts in the interests of YOU, so you won't be stranded on a big day like New Year's after a surprise storm comes through.

Above, we see the 24 hour forecast from the Ocean Prediction Center (OPC), the oceanic branch of the National Oceanic and Atmospheric Administration (NOAA). This chart depicts 500 millibar forecasts, with depressions and 'L' signs in the image characterizing low pressure areas, and arcs and/or the letter 'H' signifying high pressure areas. In this forecast, we see not one, not two but THREE separate storm systems in the western Bering Sea. (If you want to get technical about it, there is only one, but eventually the other two will find their way in there.)

Those of you who have followed me for a while know that I look to the Bering Sea for estimates on long range storms. This is no exception. The folks over at the AccuWeather Forums have found a correlation between a strong storm in the Bering Sea, and a strong storm in the US 2.5 to 3 weeks later (18-21 days later).

This forecast map is valid December 11. If we take that date out 18-21 days, we end up with a timeframe of December 29-January 1: Right in the middle of holiday traffic, potentially right on New Year's Day. If this rule (called the Bering Sea Rule) is put into effect here, and these three storms follow said rule, we could see quite a stormy period in the days leading up to New Year's Day.

Before you ask questions, no, I do not know the track, and no, I do not know what regions or cities could even possibly be affected by this. What I typed above is all I know.

Andrew

December 18-21 Potential Major Winter Storm

There is growing potential for a winter storm during the timeframe of December 18-21. Let's see what the models are saying.

This is the European's ECMWF model, and here we see a storm system coming out of the South Plains with a central minimum pressure of 996 millibars. Looking at the atmospheric set-up surrounding this system, we see a strong high pressure system in south central Canada, so that makes my enthusiasm for an Ohio Valley hit go down slightly. However, watch that extended dark orange color, as we could see a high pressure try to form in that region, which could provoke this storm slightly to the north.

Advancing 24 hours to the morning of December 19, we see that this system has moved north and actually into the Ohio Valley, thanks in part to a developing high pressure system in the Gulf Coast and what appears to be another high pressure system to the east of this system. The storm system in question is now predicted by the ECMWF to be 991 millibars, a pretty strong storm. Notice how it is more elongated than compressed, with those 991mb values trying to push east into the Mid Atlantic. This could be a sign that the system wants to split, but that's too far out for me to be confident in deciphering.

I can't say I'm sure what the GFS forecast for the afternoon of December 18th is showing. It does have a low pressure system in the picture, but the GFS has the system just offshore Florida in a bizarre set-up that could turn into a nasty Nor'easter. I have no idea what the GFS is doing, but to entertain those in a snow drought, let's move on.

Wow. The GFS bombs out a storm just off the Mid-Atlantic coast on the afternoon of December 19th. Again, this is pretty bizarre. I'm just not even sure what to say about this forecast other than... wow.


(Originally posted Dec. 9, edited slightly) The Lezak Recurring Cycle, or LRC is involved in this situation. Using the 53 day LRC timetable, I traced back December 18th to October 28th, and here is the 500mb pattern observed that day.

Look at that! We see a strong system in the Ohio Valley on this day, as well as a weak high pressure system in the Southwest indicating a possible positive PNA. There is a negative NAO in place, though we can't tell whether it is west or east based. Does this look familiar to the first image shown? You bet. It looks like our 53 day cycle is working.


The models are having some trouble, so let's go a day ahead to October 29th and see what happened.

Our storm system has now moved to the east, wobbling a bit as it did so, and combined with Sandy. Notice we still had our positive PNA showing itself with high pressure in the West US. If we were to follow this system and discount Sandy, I still believe an eastward movement would have prevailed, likely not as fast if Sandy were not present. The lack of Sandy in this potential storm system, combined with a positive PNA and east-based negative NAO leads me to believe that this forecast system should go a little more to the north and east than it did in October.

Looking at this 53 day timetable, I think I know why the GFS is acting so weird. It is trying to imitate Sandy in its forecast, with a strong storm system sliding up the coast. However, I highly doubt such an event will happen- the GFS is likely playing its games.

Preferred Forecast: ECMWF
Confidence: 35%

Andrew

December 14-17 Potential Winter Storm

The models are converging on the potential for a winter storm during the December 14-17 timeframe.

We'll start off with the American's GFS model. This is the sea level pressure (SLP) anomaly forecast for hour 120, or 5 days' time. We can see this potential winter storm emerging from the Plains as a 1005 millibar storm system, cloaked in dark blue, signaling below normal height anomalies for the region (a.k.a. a low pressure system). A few things to note here, we can see two high pressure systems on either side of this system. We have a 1022 millibar high pressure system in the Southeast, as well as a high pressure system in Canada. The latter is shown in orange colors. These two high pressure systems could create a straining of the jet stream, which means the storm could squeeze through the Ohio Valley, in between the two areas of high pressure.

24 hours later, on the morning of December 16th, we see that our system has taken the path it should with two high pressure systems on either side. The storm system has moved into Ohio, with the central minimum pressure now at 1003 millibars, still fairly high for a storm system, indicating it is weak. At this point, it could go one of two ways- out to sea in a due-east path, or shoot north into Canada. It will come down to the placement of this 1027mb high pressure system in Canada. Personally, the more climatologically-favored path would be east and possibly up the New England coast, but we'll have to wait to see what future forecasts say.

Unlike the GFS model, the European's ECMWF model shows plain values of SLP, rather than anomalies. The ECMWF ejects this system from the West as a pretty strong 997 millibar system. It is also a bit further north than the GFS' 120 hour forecast (this ECMWF forecast is also for 5 days out), but the main issue is strength difference. We see two areas of high pressure to the east, one in the Mid Atlantic and one in Canada. The system has to go somewhere, and that 'somewhere' will be towards the weaker high pressure system.

The Hour 144 forecast from the ECMWF model has the system diverted to the northeast, because a storm system won't just hightail it right at the weaker high pressure system- it will still be diverted. This storm is now in southeast Wisconsin, with a minimum central pressure of 997 millibars, unchanged from the previous forecast. Obviously the ECMWF is further north than the GFS, but I don't want to mess with that right now.

Preferred Forecast: ECMWF
Confidence: 45%

Andrew

December 17-20 Potential Major Winter Storm

There is now increasing potential for a major winter storm to occur over the East US. Let's jump right in.

Many of you know how I follow the Lezak Recurring Cycle (LRC), and track it every year to nail down who could get the best out of this winter. Well, thanks to the research of some fine folks at the AccuWeather Forums, it appears that this year's cycle will be 53 days. I tried to apply that timeframe to this potential storm system, and here's what I found.

This is the 500mb geopotential height anomaly for December 18th over North America. As the legend indicates, cool colors depict below normal heights, while warmer colors describe above normal heights. The forecast shows a deep low pressure system in the South Plains and near the Gulf Coast. In response to this deep disturbance, a positive PNA is trying to form. As we know, a positive PNA favors a storm track through the Ohio Valley/Midwest. Notice the presence of an east-based negative NAO as well. While a negative NAO is favorable for cold and snow in the Northeast, an east-based negative NAO (the ridge is east of Greenland) can favor the Plains and Midwest for cold and storms.

Using the 53 day LRC timetable, I traced back December 18th to October 28th, and here is the 500mb pattern observed that day.

Look at that! We see a strong system in the Ohio Valley on this day, as well as a weak high pressure system in the Southwest indicating a possible positive PNA. There is a negative NAO in place, though we can't tell whether it is west or east based. Does this look familiar to the first image shown? You bet. It looks like our 53 day cycle is working. **For future reference, ignore Hurricane Sandy in these observation images.**

This is the sea level pressure (SLP) forecast for December 18th, and we can see a strong storm system emerging from the Plains at this time. This system is likely to move northeast in response to the previously-mentioned negative NAO, but not towards the coast, as a positive PNA interjects and may try to send this system into the Ohio Valley.

The models are having some trouble, so let's go a day ahead to October 29th and see what happened.

(Again, IGNORE SANDY.) Our storm system has now moved to the east, wobbling a bit as it did so, and combined with Sandy. Notice we still had our positive PNA showing itself with high pressure in the West US. If we were to follow this system and discount Sandy, I still believe an eastward movement would have prevailed, likely not as fast if Sandy were not present. The lack of Sandy in this potential storm system, combined with a positive PNA and east-based negative NAO leads me to believe that this forecast system should go a little more to the north and east than it did in October.

Now, we are on December 19th with the ECMWF forecast, and we see our storm system has indeed moved to the northeast in response to the PNA and NAO, and the LRC. The system's strength is now holding at a very nice 987 millibars, with tight isobars indicating strong winds are ongoing across New England and parts of the Ohio Valley and Midwest. Despite this, 850mb temperatures tell me rain would be the big story, but with a positive PNA, negative NAO and possible negative AO, that could very well change.

It does look like the ECMWF has a pretty darn good handle on this system, especially with such a good match-up with the LRC. I believe that this storm system will happen, the question is, who will get hit the worst?

Andrew