Saturday, December 19, 2015

More detail on a warm and wet holiday week

A brief Saturday afternoon blog post as eyes start turning towards Christmas week and, as most of you know by now, weather that looks nothing like the first days of winter (which begins Monday at 10:48pm). We described it like this on social media this morning:

And I know what you're thinking...

What's up is a large subtropical high pressure ridge over the southeastern U.S., an Arctic jet stream that is well north of its usual winter solstice position, and the peak of El Nino conditions in the Pacific Ocean. Putting all that together results in temperature anomalies (departure from average) for the period December 21-26 that look like what is shown below, according to the American model ensemble. Yes, that is at least 10°F above average for much of the eastern U.S. and Canada! (Normal highs this week are near 50 with lows in the mid 30s. I expect we'll see several lows that are well above our average high temperatures this week.)

Temperature anomalies from Dec 21-26 from the GEFS model ensemble indicating well above normal temperatures for the eastern U.S./Canada during Christmas week. Graphic courtesy WxBell.
 That's why we won't be seeing anything close to a white Christmas. But it doesn't mean we'll be dry. In fact, the American GFS model predicts precipitation for the next 10 days looks like the next figure - 4-5" of rain through the morning of December 29th. Honestly, for some areas of the Mid-South that could be a little low looking at other long-range model solutions.

Total precipitation forecast by the GFS model through Tuesday morning, December 29. Graphic courtesy WxBell.
With excessive warm air and lots of moisture in place, as well as passing low pressure systems, we will also be in for some thunderstorms. The chance for severe weather is still questionable, but we'll be keeping an eye on it. Possibly the best chance is Wednesday as low pressure and a cold front affect the region and temperatures reach near 70° but it is too soon to tell. It does appear that we may get a relative "break" from the rain behind that Wednesday system which could mean a drier Christmas eve.

However, by Christmas Day, it looks like we're back into the southerly flow, which would mean a return of rain chances. Both the American GFS and European models project a potent low pressure system and cold front move around the 27th-28th. That could be our best chance of severe storms, but it's way too soon to know how that will pan out.  Here's our best shot at the next 6 days:

Instead of hot chocolate, we could be saying "pass the sweet tea" on Christmas morning. Stay tuned for additional detail the next few days.

Erik Proseus
MWN Meteorologist

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