COLD UPDATE WITH A CURVEBALL LATE...

December 1, 2017

After another 50 degree day it's time to put a wrap on November. It was certainly a tail of two months, the first half chilly, the second half mild. Here in Cedar Rapids (like many other Midwest cities) the first half of the month averaged 7 degrees below normal and the second half 7 above. In the end it comes out a wash. As the old saying goes, averages are comprised of extremes and that was certainly the case with November's temperatures.

 

Moving on let's get you updated on the change to colder weather. The first order or business was the morning run of the EURO. It was pretty funky and radically different than previous runs with significantly less cold long range. I'm not sure what to make of this trend. Maybe it was just a bad run, maybe it's the right idea. It really becomes apparent at the end of the 15 day cycle. The EPS control ensemble has this for a 500mb pattern. Zonal flow and relatively mild nationwide December 15th.

Compare that with the GEFS ensemble for the same time frame. A broad deep cold trough covering much of the nation. You can't draw up  more of a contrast than that!

The GEFS is more consistent and I like that but the EURO has better physics and its skill scores are better at that range. I'm a little mystified. We'll worry about that later.

 

Before we get to that point the GFS and EURO operational are still pretty consistent with a powerful front that brings some rain Monday and a significant cool-down next week. Of the two major models, the GFS is colder as you would expect with its bitterly cold pattern at day 16.

 

Here's the comparison of the two models and the big chill in the 10 day forecasts. The GFS meteogram followed by the EURO.

The GFS 10 day high/lows compared to the EURO. A little easier to see the slightly colder trend of the GFS vs EURO.

All things considered, there's pretty good consistency in the timing of the cool off and the individual temperatures. High confidence here.

 

The precipitation part of the forecast is not so great in the Monday/Tuesday time frame, especially in my local area. The GFS is noticeably wetter compared to the drier EURO. Here's the GFS.

Now the EURO. The answer is probably drier considering the dryness if the past month. Still a bit early to refine the numbers but there is clearly a major difference in my southern counties.

Here's a larger perspective of the two forecasts over the Midwest. The GFS.

Now the EURO. Wisconsin gets the lions share of the much needed precip.

Once this system goes by the northwest flow should really cut-off the feed of moisture to the Midwest. December 16th almost the entire country has PWATS (precipitable water vapor) values under 0.20". In the upper Midwest .04" or less. Bone dry!

Needless to say when there's no moisture its tough to get storms. What action there is would be tied to fast moving clippers that could scare up some light snow or flurries in spots. Here's the 16 day precipitation departures. Ugh!

 

I'm really concerned this dry pattern could be with us for awhile so hopefully we can catch some rain on Monday's front because after that it looks cold and ridge dead from a storm standpoint. Hope that changes soon. Happy Friday and roll weather...TS

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© 2019 Terry Swails