Pattern Change Ahead?

If you're ready for some real Wisconsin winter, Mother Nature seems to have heard your prayers.

November has been unusually mild.  Every day of the month has been above normal -- until yesterday, when our 35-degree high broke that momentum.  By the time today and tomorrow are in the books, we'll have had 3 straight days of below normal highs.

The mild weather has been courtesy of a strong Pacific jet that is effectively blocking any Canadian cold from settling in for the long haul.  Also preventing the Canadian cold is the lack of Canadian cold.  Our neighbors to the north have also been above normal all month.

But weather models are starting to agree on a change over the next 7-10 days.  Here are 4 different model looks at the end of next weekend (11/27-11/28).

  

These "500 mb geopotential height" maps are showing the mid level of the atmosphere.  Click on one of the maps and note the numbers in the 500s.  These represent the height of a pressure surface above sea level.  The lower the number, the colder the air mass.  That's because cold air is denser than warm air.  The color blue indicates colder than normal; red indicates warmer than normal.

So, these 4 models are agreeing on a colder air mass by the time Thanksgiving weekend is done.  That means at least a temporary breakdown of the strong Pacific jet that's been keeping us mild.  The average high at the end of November is 38, so colder than normal temperatures mean precipitation will fall as snow.

The lines on those maps are also wavier than they've been in the last few weeks, and that means a stormier pattern.  So it's no surprise that models are also starting to suggest more precipitation events and stronger systems.  In fact, GFS is already showing two storm systems in our area the first week of December -- right after that cold air settles in.

Incidentally, our first shot at measurable snow could be this Friday -- the day after Thanksgiving.  Remember 4 weeks ago, when I predicted our first measurable snow would be this Saturday night?  FOUR WEEKS AGO?  Right now, this looks like 1-2".  But I'm keeping an eye on it.

Stay up to date here and on Facebook, and as always, let me know if you have any questions!