Sunday, February 21, 2016

Warmth departs, low pressure brings a weather variety mid-week

A warm few days comes to an end tonight as a cold front moves through the metro this evening. Showers and a few thunderstorms will depart to our south by late evening. No more 60s and 70s in the forecast for the foreseeable future!

Monday will be a "tweener" day as the front sinks further south in to Mississippi and weak high pressure builds in on the back side of the front. Temperatures will be in the mid to upper 50s in the afternoon, which is very near normal, with mainly overcast conditions.

By Tuesday, the front will pull back to the north as low pressure develops in east Texas and moves northeast across AR. This will spread rain back into the region by the afternoon hours as temperatures climb to similar levels as Monday. Tuesday night will see widespread rainfall and increasing wind as the low tracks somewhere very close to the metro. Computer models still have some variation with respect to the ultimate track, and strength, of the low, but it will be close enough to bring gusty wind and periods of heavy rain as temperatures remain in the 40s. The NAM model shown below indicates the low nearly over Memphis at midnight Tuesday night.

The NAM model depicting low pressure nearly over Memphis at midnight Tuesday night. Snow is wrapping in on the northwest side of the system from MO into western AR while strong storms are possible southeast of the metro. (WxBell)
The track of the low pressure system is important for a couple of reasons. Due to its strength, it will draw unstable, warm air north from the Gulf ahead of the track. Strong wind aloft will aid in the potential for severe storms in the southeast quadrant of the storm system. Given the current storm track, that potential will be south of the metro as shown by the current severe weather outlook from the Storm Prediction Center below. A shift in that track to the north would bring the warm sector further north, as well as the threat for severe storms.

The best chance of severe weather will be to our south on Tuesday as the most unstable air is pulled north by the developing low pressure. (SPC)
In addition, the strength of the low will mean it will draw cold air around the backside of the system. The "wrap-around" precipitation in the northwest quadrant will move across Arkansas and the metro Wednesday as that cold air wraps in. Rain is expected to change to snow in northern AR and possibly the Missouri Bootheel as the system pulls out to the northeast. The NAM model depicts temperatures falling into the 30s as far south as northwest Mississippi Wednesday (see image below). This aspect of the forecast will need to be closely monitored as well. A deeper system that tracks further south could pull enough cold air in to cause a changeover in precip further south.

The NAM model predicts temperatures falling into the 30s Wednesday morning. (WxBell)
Given the current forecast model scenario, the probabilities of accumulating snow are highest in a swath northwest of the metro as shown by the Weather Prediction Center in the graphic below. For now, I expect temperatures will stay warm enough for all rain Wednesday as precip ends from west to east during the day, but don't be surprised if temperatures fall into the upper half of the 30s Wednesday afternoon.

Snowfall probabilities are minimal in the metro, but much higher not far to our northwest. (WPC)
Once the mid-week system moves out, a dry, mainly sunny, and seasonal few days are expected, which could take us right through the end of the month. A couple of long-range solutions are hinting at some shenanigans again next weekend, but are inconsistent and misleading at best and foolish at worst (for now).

Erik Proseus
MWN Meteorologist

Follow MWN on Facebook, Twitter, and Google+
Visit on the web or on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!

No comments: