© 2019 Terry Swails

CHALLENGES LEADING INTO CHRISTMAS....

December 14, 2017

The biggest thing on the charts today is the cold air the U.S. model (GFS) is shown delivering just before Christmas. If it comes full bore as advertised, old St. Nick will feel right at home as this is a true North Pole air mass.

 

Right up front I will tell you the models have been a nightmare to deal with the past couple of weeks. They seem to be having a real problem resolving the pattern much beyond 5 or 6 days with any degree of consistency. Ironically the GFS has been doing better than the EURO so we'll see if it ends up scoring a coup. It certainly fits what the MJO (Madden Julian Oscillation) is showing which is a tour through the cold phases of 7, 8 the last 10 days of December. Follow the dotted green lines.

The operation run of the GFS Wednesday afternoon came in really bullish on the cold. This is what its 500mb jet stream pattern looks like December 23rd.

It's even more amplified the 27th with cold air all the way to south Texas and the Gulf.

The 5 day average temperature departure for December 22nd-December 27th. That is flat out widespread cold centered on the Midwest. We don't want that.

To give you an idea of the potential of this air mass here's what the model has for lows the 23rd.

The wind chills in NW Minnesota are pushing 50 below! Some places north of Lake Superior at -54.

Now if this ends up happening it could be a problem if you want a White Christmas. There would be a point when the cold is so dominate it overwhelms the pattern. The baroclinic boundary will be so far south by Christmas that only the deep south and eastern seaboard is in the game for meaningful snow. There would be just one window in the Midwest when the cold arrives that some sort of storm could spin up. That looks to be around December 20-21st.

 

Around this time frame the models have been on again off again with a hybrid type clipper that crosses the Midwest. Here's the GFS surface depiction the morning of the 22nd.

The track across southern Iowa keeps the snow band in northern Iowa, southern Wisconsin, and extreme northeast Illinois.

The GEFS ensemble mean (comprised of 51 members) has some tracks that are further south and the model average of all solutions looks like this. That's better for my area.

The new operational GFS just came in and while cold, its not nearly as amplified and bitter in my area. It also has more of a southwest flow than northwest component so the snow it develops is oriented in a different direction SW to NE. It's also a bit later arriving the 23rd-24th.

After Christmas it gets even snowier but latching on to a consistent solution is once again a problem. About all I can say is there's a ton going on and lots of weather challenges on the table leading up to and after Christmas. No doubt there will be some modifications going forward but at least for now, the GFS is going down a cold road as Christmas comes into sight. It will take a few more days to get a handle on any snow. Roll weather...TS. 

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