Friday, December 7, 2012

Another warm December weekend ends in thunderstorms

This time last week, we were talking about an unusually warm December weekend and the potential for thunderstorms early in the work week.  It's deja vu all over again!  While one very warm weekend in December is not unusual, two in a row is somewhat rare.  However, the way this weekend is ending we'll not see the 70s again for some time. A blast of winter is moving in!

Before we get to winter, let's talk about the lead-up to the main event, which is the chance of thunderstorms over the next couple of days. A cold front will move into the Mid-South on Saturday, setting up very close to I-40 from Little Rock to Memphis to Nashville by Saturday afternoon. Though we'll stay on the "warm side" of the front, any minor disturbances that move along it will combine with temperatures near 70 and plenty of moisture from the Gulf to set off scattered showers and thundershowers.

While there will be a slight chance of showers again Saturday morning (as we had the past couple of mornings), it appears that the chance goes up a little in the afternoon (to about 40%) and a few showers could generate some lightning and rumbles of thunder, though no severe weather is expected.  Overall, any thunder should be widely scattered and, unfortunately, not something we can pinpoint 24 hours out. Outdoor events, such as local Christmas parades planned for the afternoon, will need to be monitored closely.  Rain chances appear to increase further after dark Saturday with a good chance of showers and a few thunderstorms near and ahead of the front.

A cold front will reside just to our north Saturday evening, bringing a chance of rain and  a few t'storms.
Late Saturday night, the front will begin to retreat back to the north as low pressure forms along it to our southwest. Rain chances decrease substantially by Sunday morning as the Mid-South will once again be firmly in the warm sector of the next weather system.  The focus then shifts to the low pressure system to our west and the re-emergence of Saturday's front, as it gets a significant "shove" from a Canadian cold front that will be escorting MUCH colder air into the region.

As the low travels along the approaching front, it will bring increasing atmospheric dynamics, particularly wind aloft, and will be pushed along by a strong jet stream.  As the low and cold front approach the region late Sunday, we expect more thunderstorms to break out from east Texas into the Mid-South.  Due to the amount of wind energy associated with this system and the large temperature contrast along the front, there is a small chance that a few thunderstorms could be strong to borderline severe Sunday evening into the early overnight hours just ahead of and along the front.  The timing is still somewhat uncertain, but it appears the best chance for any strong storms will be from around dusk (5pm) until midnight.  Damaging straight-line wind would seem to the be the biggest threat, besides lightning.  The Storm Prediction Center has placed our area under a small probability of severe weather Sunday (see graphic below).

Area with an elevated risk of seeing severe weather Sunday. The risk is not high at this time and damaging wind will be the main threat.
In addition, rain could be heavy at times with this system, and it will continue behind the front into the morning on Monday as more waves form along the front while it slowly sinks south.  Plan on a wet start to your work week and likely rain-induced delays in your commute. The heaviest and steadiest rain will fall overnight Sunday night into early Monday. The graphic below shows the potential for up to 2" of rain in the metro this weekend into Monday.

Expected precipitation amounts approach 2" in the metro with the next weather system.
The other big story with this front will be the return of WINTER. Temperatures will fall quickly from the 60s Sunday evening into the 40s by Monday morning. Very little if any recovery in the temperatures is expected Monday, depending on how long the rain sticks around. With showers and clouds over the area and a brisk north wind, temps will hold in the 40s all day Monday and wind chills will likely be in the 30s. Quite a difference from a projected high in the lower 70s Sunday!

The map below shows the sharp temperature contrast behind the front.  Note that very cold air originates in Canada and extends across most of the western U.S. behind the front. This will mean a prolonged period of much cooler weather as we go through next week.

Canadian high pressure behind the front will mean a significant drop in temperatures as we start next week. will keep you updated throughout the weekend on expected and current weather conditions. Follow us on Facebook and Twitter (links below) for the latest information and download our mobile app on Android or iPhone for the most recent forecast and detailed radar information from StormView Radar.

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