December 2012 Long-range Forecast

And here begins the December long-range forecast released by Northwest Ohio Storm Prediction Center!

I'm not going to go into detail about the long-range factors going into this forecast, as I well know that only true "weather geeks" really care about them. So for this, I will only make mention of the truly important factors.

Currently, the Equatorial Pacific is in the neutral ENSO phase, which us "weather geeks" like to sometimes call, "La Nada", which just references the fact that Neutral winters tend to have less affect on North American weather than do other variables. SST anomalies have been fluctuating, but have generally averaged just slightly above normal in the Equatorial Pacific. Current MJO forecasts (Madden Julian Oscillation, a weather pattern or frequency that occurs in the tropics, but can affect weather across the Pacific, as far away as the United States) suggest that in the next few weeks it will be going through phases 8,1, and 2. Phase 8 generally favors the strengthening of an El Nino, while phases 1 and 2 favor "La Nada's" and La Nina's. Another variable that I look at is the NAO, as well as the AO. The NAO stands for North Atlantic Oscillation, which is related to atmospheric pressure across the North Atlantic, and the AO stands for the Arctic Oscillation which is related to pressure anomalies across the Arctic (and including the stratospheric circulations). Both of these have been in the negative phase for nearly the ENTIRE fall. Last year, it was hard to keep the two negative. A negative AO/NAO couplet suggests a greater potential for cold weather to invade the Northern and Eastern United States, including the Midwest. Using a forecast of persistence, I can see the NAO staying near neutral or negative for the month of December (including the AO as well). Other variables related to my forecast include snow cover across Canada, the PDO index, the PNA index, solar cycle variation, etc. I will not go into detail on these.

As for the forecast, I'll start with the lower Great Lakes forecast. For the last few days of November and very beginning of December, long-range forecast models indicate that the pattern will become very "changeable", and is likely to go through a "pattern change" around the same time. In fact, it is all-together likely that this pattern change is marked by a major Arctic blast into the Great Lakes, which would usher in the first major lake effect snow event of the season. In the same time frame, both the NAO and AO are expected to go at least slightly negative, which supports the development of blocking across the North Atlantic, and thus a "stopped" and unchanging pattern. This could in fact allow arctic air intrusions to become more likely in December. At this point I do NOT believe that the December 2012 trough/ridge pattern will be very "blocked". This means that I do expect the pattern to still be rather "changing", but more likely to yield arctic air intrusions. In all, for the lower Great Lakes, expect slightly below normal temperatures, due to the Arctic air masses, but averaging in any "sustained" warm ups as well. As for precipitation, I expect near normal precipitation, as the storm track will favor Alberta Clippers into the region, but most "wet" storms will likely head south of the area. Areas downwind of the Great Lakes will likely see above normal precipitation and snowfall. For the rest of the Great Lakes and Ohio Valley, I think it will be definitely possible to see one decent snowstorm, but in light of recent events, most storm systems will likely feature a mix of ice/snow or heavy rainfall.

For the rest of the United States, expect below normal temperatures from the Northern Plains to the East Coast, with the core of the Arctic air still existing across Western Canada. An active southeastward storm track from the Northern Plains into the Ohio Valley and along the East Coast, will favor above normal precipitation in coastal cities, with near to below normal precipitation across the Southern Plains and Southwest United States. In the Great Lakes, precipitation will be near normal except for the Lake effect "belts". The Northern Plains will likely see near to above normal precipitation due to the storm track. This pattern I can see happening about two or three times during the month of December, each lasting about three or four days before a more transient trough/ridge pattern sets in, between these periods of Arctic cold. These will be the times when Midwestern storms make their way in, and a Great Lakes Cutter results, a storm that travels from the Central Plains into the Great Lakes region, bringing warmer conditions and heavy rains to the Ohio Valley and much of the East.

I will not yet release a Christmas Day forecast until December begins.

One point I would like to make and that is this: Once again, because of the fragile state of the ENSO phase especially, and the way the PDO has been trending, I can see that it is possible, that we see a storm track through the Ohio Valley, with near to above normal temperatures, but well above normal precipitation and potentially snowfall. This could in fact happen if a Western trough develops, which will eject disturbances into the Midwest region. I will keep an eye on this.

Here's the official forecast map:

 

Temperature Anomaly Forecast Map.

And here is the snow cover maps.. Comparing this year to last year:

Snow cover for November 2011

Snow cover November 2012, well above what last year saw.

European Ensemble Forecasts Support Pattern Change

Last Wednesday, Northwest Ohio Storm Prediction Center released a long range forecast, explaining that the ensembles were predicting a more transient and "potentially" stormier long range pattern. As you can see, this past week, we saw a major West Coast storm move into the Midwest, and slam the Upper Midwest with as much as four feet of snow, high winds throughout the Central Plains, and heavy rains to a widespread area. Not only that, but it brought along with it the first true Arctic blast of the season, with the lake effect snow affecting a large area of Michigan.

Global models are now expecting that this pattern be disrupted until Thanksgiving Week (next week). The disruption will occur as a major Gulf of Alaskan low becomes prevalent. It will cause the jet stream to "split", indicating that the pattern will be rather dry and inactive, with no major storms expected to hit any part of the United States until late next week. NOW, Global models as well as the ensembles are forecasting a potential pattern change at the end of Thanksgiving week (that could potentially screw up my entire winter forecast). In fact, the ensembles are forecasting that the Aleutian/Gulf of Alaskan low will begin to "dig" into the West Coast. In response, a strong elongated jet streak will begin to form across the Northern Plains, which will allow the PV (Polar Vortex) to begin shifting southward again. At the same time, ridging (North Atlantic blocking) will build into Greenland, forcing a trough to form in the East, with a flat ridge developing over the West. In fact, this could be the beginning of more widespread arctic air into the United States.

The storm that could bring these changes could either be a Midwest storm system, a Northeast coastal low, or both. In fact, both of these possibilities have been suggested by the global models. In my opinion, here is what will happen. A large storm will drop southeastward in the Midwest, drawing an Arctic air mass into the East. On the edge of the cold front, a secondary low could develop and move along the East Coast. Currently, there are too many differences to in fact make an accurate forecast of what will happen. In any case, this change will occur on Thanksgiving Day or the few days afterward.

More Details of the Winter Outlook

A preview of the winter forecast that is to be released later this week. It could get quite interesting this winter.
 

One thing I would like to mention is this: There are two VERY different scenarios (in my mind) that could play out. In one scenario, it becomes very similar to a hybrid El Nino winter, one in which a western ridge prevails over the Rocky Mountains and Western states, with a mean trough over the Central and Eastern United States. This would create a storm track across the Deep South and into the Western Atlantic, at which point some storms will travel up the coast and some will move out to sea. IF this scenario were true, then this would be the most common path of storm systems. This is already supported by what has happened this fall. What this would mean for the Midwest and Ohio Valley is a very cold and DRY winter, with a few periods of warmth as the Western ridge ejects eastward.  Areas along the Great Lakes would see above normal lake effect snowfall. Anywhere else in the Ohio Valley and Midwest would likely see a lack of precipitation and thus snowfall.

In Scenario TWO, this winter turns out similar to a La Nina winter hybrid. A strong Pacific jet stream sets up across the United States, with the development of a strong South-eastern ridge, while a cold Arctic air mass exists across the West and Western Canada. This would indicate a winter with near normal temperatures for the area (lower Great Lakes region), but above normal precipitation and near normal snowfall. Let me state this though: In this scenario, the first part of December will likely feature a split flow regime, indicating that the Lower Great Lakes and Midwest will probably be devoid of storm systems, but due to shallow arctic air masses, temperatures will likely be kept near to below normal. By very late December, the pattern transitions to a very strong Pacific jet, with a weak mean trough in the West, with a ridge of high pressure over the Northern Gulf of Mexico. This would put the storm track across the Midwest and through the North-eastern states. I believe that this has a likelihood of occurring due to the rapidly expanding snowpack across Western Canada and the Northern Plains. In that case, well below normal temperatures will prevail across the Northern Plains and the West, with near normal temperatures across our area, but with above normal precipitation. The East would feature near to above normal temperatures, but generally wetter conditions. I believe, if this scenario occurred, that this will last through mid-January or so, before transitioning to deeper Arctic pattern, in which the NAO/AO go strongly negative, and a backloaded winter would be the case for a good chunk of the East. February, in this scenario would be the best case for Nor'easters and monster snowstorms.

At this point, I really do not have much confidence in either of these. Either one may occur.

IN any case, I do believe this winter will likely be worse towards the end of the winter. At this point, its likely that once the winter turns for the worse over the area (cold arctic air), it will stay cold and dry. If Scenario two plays out (this is based off of the forecast that a Neutral ENSO will persist and could possibly become a weak La Nina by the end of the winter), then expect a warm, but possibly wet December through January, before colder weather builds into the region.

This is the less likely scenario in which a strong Pacific Jet stream works its way across North America.

The scenario in which the NAO/AO goes strongly negative during the months of January and February, leading to a back loaded winter.

Final Winter Outlook Being Released.

Either tonight or tomorrow I will be releasing Northwest Ohio Storm Prediction Center's official and FINAL winter outlook for the winter of 2012-2013. Even though this forecast center mainly focuses on weather across the region, this forecast will deal with EACH region of the United States.

This forecast will be primarily based off of long term climate signals, including the ENSO (El Nino/La Nina Southern Oscillation) phase, atmospheric blocking across the North Atlantic, SST anomaly patterns across the North Pacific and North Atlantic, the current storm track and jet stream pattern, and the solar cycle. Many other factors MUST be taken into consideration. A few of these variables are very hard to forecast more than two weeks out, mainly including the atmospheric blocking signals, which will be determined in the next few weeks.

I will also include in part of my forecast about what the climate models are forecasting for the upcoming winter as well. Some of these models differ considerably from my forecast, and several of them coincide rather well.

This forecast should be done sometime this week.

As for a sneak peek into the forecast here's a few things of what I expect:

• Quite possibly a slow start to winter
  (December could end up being very warm across a good majority of the United States, except for the Northern Plains and Pacific Northwest).
• NO past years match up quite well with this year
• Data points to a back-loaded winter regardless of winter's start (This means that a harsh January and February is likely).
• Periods of record warmth, are just as likely this winter as brutal cold, making it a very VERY changeable winter.