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Last night I kicked around the possibility of a pattern change towards mid-January that could create some helter skelter. By that, I mean the cold and snow that often comes with the heart of winter. As you all are aware, we are just now coming out of the shortest days of the year. The low sun angle and limited amount of sunshine have been building cold for months at northern latitudes. If it's going to make a move on the Midwest in a big way, climatology says the next three weeks are time of year to look for it. On average, the coldest low of the winter is usually in the period January 16-21

Now I want you to take a look at a few things that are catching my attention, some for several days, other's have come to light within the past 24 hours.

The first thing I want to start with is the EPO (eastern Pacific oscillation). It is my experience that if the EPO is positive, it means there's minimal ridging over western Canada and the United States. Without that in place, the source region for air masses is the Pacific where the air is far warmer than what's in Canada and the Polar regions. Just look at temperature departures the first 5 days of January with a positive EPO in place.

Here's the 500mb flow showing the lack of ridging over the west. That deep trough over the Gulf of Alaska is forcing mild air into southern Canada.

Now lets go out to January 17th on the GFS and note all the red showing up from Alaska to California. That's a ridge going up that seeds the source region for our air masses with Arctic air. The jet stream would then be in a position to deliver it.

What would cause that? The EPO flipping to negative. The GFS ensemble is showing that trend in its EPO teleconnection going from strongly positive to negative.

The Canadian EPO ensemble is really gung ho! Sharply negative by January 15th.

Look what that does to temperature departures around North America. Compare the negatives of 30-40 below normal to the positives I showed above.

The GFS is indicating a full fledged Arctic outbreak. That's the first time I've seen such severe cold so I'm reluctant to fully get on that wagon until I see more evidence. However, the Canadian and EURO are also leaning towards colder solutions so the I think the general trend to cold has merit.

Another factor which will likely contribute to the depth of the cold and its overall potential is the stratospheric warming that is taking place at the pole. Here, at the highest level of the atmosphere heights are warming. In essence what that does is increase pressure forcing the cold air that usually resides there further south and into the lower levels where it can be felt in places like the Midwest. One of the ways this manifests itself is in a negative AO (Arctic oscillation). The negative AO (as a teleconnection) is cold signal, especially in conjunction with the negative EPO.

Now if this happens, it is unlikely to impact the central Midwest until about day 10. It's also early in the game and I am not fully confident we will see the depth of the cold that the GFS and Canadian are indicating. However, the evidence is mounting that the potential is there and I'm quite interested to see where the trends take us in coming days.

Meantime, the next week looks quiet and seasonal. Areas of fog will again be possible from time to time, especially at night and in the morning due to the stagnant nature of the extensive high that will remain locked in place.

So basically, chances for rain or snow look small the next 8-10 days. However, with the addition of the colder pattern the potential for snow systems is expected to increase beyond that for much of the northern half of the nation. The ensembles, which basically go out 15 days are showing that trend. Here's those snowfall forecasts.



The Canadian GEM

While there's not much to focus on in the short term, there's plenty to keep me entertained in the long range. Isn't weather fun! All right, that's all for now. Roll weather...TS

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