Monday, December 15, 2014

A warm start to a chilly week with periods of wet weather

Yesterday was a great December day with temps in the mid 60s and lots of sunshine. Despite off and on rain, it's also a mild day today as the rain out-raced the cold front, so warm Gulf air continues to flow into the region as the cold front lingers to our west. The front will move through late this afternoon however, bringing an end to the 60s for the foreseeable future. This was just the first in a series of weather systems to affect the region this week.

Tuesday and Wednesday will be "tweener" days as high pressure briefly takes over following today's front and our next weather system affects the region Wednesday night. Colder air will filter in behind tonight's front bringing highs Tuesday back down to near normal in the 50s. Lows will drop to near freezing Wednesday morning and clouds will increase during the day, holding temperatures down in the 40s for the daytime hours.

Forecast mid-level pressure (500mb or ~18,000') Wednesday morning indicating a flat ridge over the southern U.S. Graphic courtesy WeatherBell Analytics.

The pattern shift that persists through the end of the week begins Wednesday night as moisture rides up into the area on west-southwesterly wind flow, bringing a period of light precipitation - the second weather system of the week. Right now, it appears temperatures will remain above freezing all night with lows in the mid 30s. This scenario bears watching though in case surface temps trend any colder. The most likely precipitation type if NOT rain will be light freezing rain. Again, ice is not currently in the forecast.

GFS forecast precipitation amounts from midnight through 6am Thursday as moisture and precip arrive from the west. Amounts range from 0.25-0.50". Graphic courtesy WeatherBell Analytics.

GFS forecast temps at 6am Thursday, indicating mid 30s across the metro. Graphic courtesy WeatherBell Analytics.

Very light precipitation is possible again on Thursday and Thursday night with cloudy skies and cool temperatures. The last weather system of the week arrives early Friday as low pressure develops over Texas and moves east. Odds are that this low will bring a fair amount of rain Friday into early Saturday as it travels by to our south. Amounts of 1-2" are possible. There are signs from one medium-range computer model (the European) that there could be enough cold air filtering in on the backside of the low Friday night to POSSIBLY change rain over to light snow. However, none of the other models depict this same scenario as of now. In fact, the European model became much less bullish with snow in this morning's data, so confidence increases in a relatively warmer solution (but still cold for those who will be out in the elements!).

As always, there are many factors that will affect the eventual outcome, including strength and track of the low and resultant amount of cold air that moves in and how quickly it does so. We are carrying RAIN in the forecast but continue to monitor. We're hopeful for a mainly dry, but chilly, weekend as the season officially changes from autumn to winter Sunday evening. Also, looking ahead, it currently looks dry and cool for the Autozone Liberty Bowl next Monday (40s).

Farther out (too far if it were any day but Christmas), long-range models are pointing to one more southern stream system around Tuesday/Wednesday similar to this Friday's, then a chilly Christmas Day that looks dry. We'll update again in a few days with the latest thinking and be sure to follow us on social media for any updates. Also, be looking for a blog later tonight on the history of Christmas Day weather in Memphis! Hint: it doesn't bode well climatologically for a white holiday.

Erik Proseus
MWN Meteorologist

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