THE GOOD OLD DAYS...
As expected the weather around the central Midwest improved significantly just in time for Thanksgiving. Most areas south of HWY 20 enjoyed some sunshine and highs areawide were seasonal, generally in the mid 40s. All things considered, Turkey Day 2020 was a keeper, especially compared to some of the cold and snow we've dealt with around Thanksgiving in years past.
Speaking of that, one of the worst storms surrounding Thanksgiving pounded the "southeast half" of my area the weekend of November 25-26th, 2018. Blizzard warnings were issued and record breaking snow of 14" inches fell in the Quad Cities. Along with the snow 50 mph winds created white out conditions. Here's a trip down memory lane. This shot was taken in the Quad Cities as the storm was in the process of producing snowfall rates of 1-2" per hour.
There was a very sharp edge to the northern edge of the snow with amounts in some counties ranging from a trace in the north to 8 inches in the south (a distance of 30 miles) The worst of the snow fell southeast of a line from near Des Moines to south of Cedar Rapids and Dubuque on to Freeport and Rockford in Illinois.
Here's a tighter view of snow totals around my area. Not a flake where I was in Cedar Rapids. I cried...
I also remember another post Thanksgiving weekend ripper in 1985 when I was living in Dubuque. We had about 16 inches Nov 30th-Dec 1 and much of the eastern half of the state was pretty much buried. I recall watching the Packers play Tampa Bay in the game they called the snow bowl. The same storm dumped more than a foot there as well. That was fun to watch.
To tell you the truth there's not much going in the rest of the holiday weekend so if you are a Black Friday shopper, picking out the Christmas tree, putting up some holiday lights, or traveling on the roads the weather will be cooperative with more dry weather and temperatures that are typical for the season.
That leads us into December and this is the part of the forecast which is most challenging to me. What I will be watching is the evolution of a pattern change that should at the very least bring us a more wintry type pattern for at least the first 2-3 weeks of the month. Models are still struggling to define the overall solution which becomes essential in determining the amount of cold and snow (if any) that ends up falling.
Well over a week ago I mentioned in a post the thing to watch for in early December was rising heights in NE Canada which indicates blocking associated with the negative phase of the NAO (North Atlantic Oscillation). This is the EURO 500mb jet stream pattern December 2nd. Note the area in red where pressures are higher relative to average.
That constitutes a block which forces colder air out of Canada and allows the storm track to undercut the block.
You can see below how the EURO ensembles are depicting a strongly negative NAO in early and mid December. That certainly implies periods of colder weather. Depending on the precise position of the storm track it could be snowier but precipitation is harder to foresee than temperatures, especially in the Midwest on the western edge of the trough.
Another signal for colder conditions is the PNA (Pacific North America Oscillation) The positive phase is one which allows cooler air to push.
The positive PNA upper level structure.
The EPO (Eastern Pacific Oscillation) is essentially in a neutral phase. If we could get this to go negative the door would really be wide open for some Arctic air but so far this teleconnection has been resistant to moving towards the negative phase.
One very critical player is the MJO (Madden Julien Oscillation) The extended projections of the EURO show a general trend for the MJO to stay in the null phases with little amplitude. If, the MJO decides to shift into the cold winter phases of 8, 1, and 2 it can overpower the other teleconnections I outlined and win the day. However, if like last winter it swings towards the warm phases of 4, 5, and 6 it would increase the chances of a mild December, much like last year. I will be paying close attention to where this trend goes since it is such a big driver. However, as it stands now if it holds near the null phases for the next 2-3 weeks there is strong evidence that the -NAO and +PNA will lead the eastern half of the nation (including my area) into a cooler than average period. That would also increase the chances of snow, although I currently don't see much on the modeling that looks impressive for the next week or so.
Bottom line is there's plenty of potential for some wintry weather heading into December. Unfortunately, we're are early in the game and confidence in how the pattern eventually evolves is still lower than I would like. I'm still waiting to see all the players that will ultimately be on the field. Roll weather...TS
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