Thursday, November 6, 2014

Cool weather expected to turn much colder next week

If you don't like cool weather, I recommend you stop reading now. OK maybe not, but this post is going to be all about below normal temperatures, so put on your gloves and earmuffs and continue on, intrepid readers!

What's average?

We'll start with where we're supposed to be, because sometimes that gets lost in the day-to-day forecasts. We get used to a certain pattern and don't realize that it's really supposed to be cooler/warmer than what we've experienced. The shock comes when it warms up/cools down to near normal and we instinctively think it's "abnormal." So, our average high on November 6 is 66 and average low is 47, resulting in a daily average of 57. Record highs are averaging the lower 80s right now and record lows are in the mid 20s.  Baseline established...

So what about this cold weather I am hearing about?

You may have already seen plenty of talk floating around on social media about typhoons resulting in Arctic outbreaks, polar vortices, and maybe even a "crap app" that had snow on its forecast for Memphis on November 15. I'm here to set the record straight.

It's all true. Kind of. (Yes, the app had it. No, it's not in my forecast!)

Former Super Typhoon Nuri in the northern Pacific is indeed making waves (massive ones in the Bering Strait, and even contributing to some in the upper atmosphere) that will result in an intrusion of cold air into the U.S., mainly east of the Rockies by next week. Before then, last night's cold front and another Saturday (which should pass through dry) will bring below average temperatures through Sunday, including upper 30s for morning lows.

By Tuesday, a much stronger push of cold air invades the central portion of the U.S., with a cold front forced southeast. We'll warm up nicely on Monday ahead of the front (upper 60s), then as the front passes through, rain chances go up Tuesday and temperatures will probably start to fall by late in the day. The airmass behind the front will have originated as Arctic air and, though modified, will likely bring our coolest weather so far this fall for the latter half of next week and into the mid-month weekend.

There is talk that this pattern of below normal temps could continue right through the end of the month... I'm not ready to go there yet, but we'll see.  Let's take a look at some graphics that will paint a picture of just how cold we're talking. (Click any image for a larger version. All graphics except the last courtesy WeatherBell Analytics.)  For our detailed MWN Forecast for the next 7 days, click here.

GEFS ensemble model forecast of departure from normal surface temps for the period Nov 7-12 (in Celsius). The Mid-South is depicted as 3-4C below normal, which would equate to about 50F vs our expected average of 55F.  Cool, but not too bad.
GEFS ensemble model forecast of departure from normal surface temps for the period Nov 12-17 (in Celsius). The Mid-South is depicted as about 7-8C below normal, which would equate to about 40F vs our expected average of 54F.  Now that's cold!

GEFS ensemble model forecast of departure from normal surface temps for  just one day, Nov 13 (in Celsius). The Mid-South is depicted as 9C below normal, which would equate to about 37F vs our expected average of 54F.  That's a daily average, meaning the low is colder than that and the high is warmer than that, but they average to 37. Whoa.

The GFS model surface forecast for next Thursday morning shows massive high pressure extending from central Canada to the Mid-South. The freezing line is the dark blue line that extends from the east coast through the Deep South into the Rockies. A HUGE portion of the U.S. would drop below freezing given this scenario with single digits (or lower) over the Northern Plains.
The GEFS ensemble model forecast highs and lows for the next 10 days shows the sharp dropoff in temps the middle of next week with a moderating trend starting the following week. These are NOT our forecast temps but provide an idea of the magnitude of cold air this model is forecasting. (BTW, our other long-range models agree fairly well.)

The official temperature outlook from NOAA for Nov. 12-16 indicates a 90% chance of below normal temperatures over a large portion of the Mississippi Valley and Upper Midwest. It's extremely rare to see 90% on these daily graphics, which speaks to the near certainty of this cold air outbreak, but not necessarily to its magnitude. Graphic courtesy NOAA.
So is this just a taste of things to come this winter or a one-shot deal? My 2014-'15 MWN Winter Outlook might provide some helpful information in that regard! I presented it to attendees of the NSA/Mid-South Winter Weather Workshop in Millington this morning and will be releasing a video blog containing the information to our MWN Insiders on Friday. The rest of you will get to view it a few days later, probably on Monday. If you want to see it early, we recommend you join our Insiders newsletter here!

Are you hoping for a cold and snowy winter or just hoping it goes by quickly and spring comes early?

Erik Proseus
MWN Meteorologist

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