On December 8th, 1941, United States President Franklin D. Roosevelt delivered the time honored "a date which will live in infamy" speech to a Joint Session of the US Congress. It was delivered one day after the Empire of Japan's attack on the US naval base at Pearl Harbor and the Japanese declaration of war on the United States. It marked the beginning of a 4 year conflict that ended with the detonation of nuclear bombs. December 7th is still one of of the darkest moments in U.S. history and nearly 76 years later it indeed lives on as a day of reflection and remembrance.

Earlier today as I was looking at data with nothing but weather on my mind. My analysis led me to the conclusion December 7th was about the day we undergo a significant pattern change that will lead us into a wintry world. I was going to tell you all to write December 7th on your calendars as a day of change, then it occurred to me it was the anniversary of Pearl Harbor (the reason for the first paragraph above). In respect to that date strike the calendar idea.

However, It does not change the fact that our run of nice weather which started November 20th will come to an abrupt end in about a week. Here's the EURO operational meteogram for Cedar Rapids showing the transition to cold December 4th to the 8th when the high goes from 55 to 15 degrees. It also shows and inch of snow...progress!

The GEFS had this for 16 day temperatures

I definitely have high confidence in the cool-down as all the major models show it kicking into high gear within the period December 10-15th. Here's the 850 departures on the GEFS. The 0 line at 850 is the threshold for snow to develop if precipitation were to fall. Notice that has plunged to Alabama.

The GEM (Canadian) departures for the same period.

The EPS (EURO) 850 departure. Very bullish!

If you are wondering what the pattern looks like at 500mb (jet stream level) here you go. The source region for our air is right off the polar regions of North America. The map below is a forecast for December 13th. That is a very cold look indeed.

While the pattern is cold, It's also on the dry side. I've seen minimal signs of amplification with any waves or clippers just yet. However, no matter how light it is, chances are that any precipitation that falls after December 4th will be in the form of snow. Still waiting for some positive news there. I'm optimistic something will come down the pike soon. Roll weather...TS

© 2020 Terry Swails