Thursday, December 24, 2015

After yesterday, severe weather is now in the rear-view mirror... right?

Wow, what a day. An outbreak of severe thunderstorms swept through areas from the Midwest and Ohio Valley into the Mid-South on Wednesday afternoon and evening, bringing high wind, large hail, and at least one long track tornado. The north Mississippi supercell that dropped a tornado near Clarksdale, MS continued east-northeast at near highway speeds as it tore through places like Como, Holly Springs, and Ashland. Preliminarily, the NWS in Memphis has assigned an EF-3 rating to the twister that at times was up to 3/4 mile wide, though a full assessment of the nearly 150 mile path will take days.

The forecast from the Storm Prediction Center and local NWS offices, and relayed through media partners and private enterprises like MWN, was overall very good. See the mid-day SPC risk area below with preliminary storm reports below. The Enhanced Risk area in particular matched up well with where severe weather actually occurred, while the Moderate Risk and "Particularly Dangerous Situation" Tornado Watch correctly captured the north Mississippi beast.

The warnings issued by the local NWS office also were spot on and correctly highlighted the threats that were imminent or ongoing, including the use of the rare "Tornado Emergency" Warning for Holly Springs, well before the tornado devastated southern portions of the town. The cumulative warning map below shows just how widespread the threat was. Fortunately, most of the metro outside of Holly Springs, was spared nature's wrath, despite some reports of up to quarter size hail in Bartlett and strong wind gusts as the storms moved through. We were fortunate indeed!

NWS Severe Thunderstorm (yellow) and Tornado (red) warnings issued on December 23, 2015.
So now we get a break for a while right? Well... from high threat severe weather, yes, but from lower-end strong storms and rainfall, no.  As you have noticed, it doesn't feel like Christmas Eve outside, despite a cold front moving through yesterday. The overall upper air pattern has changed very little and near-record warmth continues.

Despite a very pleasant spring (err, winter) day today, clouds and rain move back in tonight as yesterday's front turns back north as a warm front and puts us right back in the warm sector for the weekend. As it slowly meanders through the area tonight and tomorrow, rain chances return and thunderstorm chances also appear high, starting after midnight tonight and continuing off and on through Christmas Day. Unless Santa arrives before midnight tonight, he's going to need rain gear and a lightning rod on his sleigh! Rudolph's nose might come in handy tonight.

The chance of severe weather with tonight's storms is low, but not zero. SPC has a Marginal Risk (category 1 of 5) over the metro, mainly for a few strong wind gusts or some hail. However, along the front, there is a fair amount of "atmospheric spin," which COULD result in a weak tornado. However, this threat is nowhere close to yesterday's. We think you should go to sleep tonight dreaming of a White Christmas and just have the weather radio or StormWatch+ in your app on, just in case. We don't think you'll need it.

The SPC severe weather outlook for tonight shows a low-end risk of severe weather, mainly after midnight.
On Christmas Day, storms will remain possible along the corridor marked by the frontal boundary. Once again, a Marginal Risk of severe weather is indicated by SPC, as shown below. The main threats remain a stray damaging wind or hail report, with a very small risk of a weak tornado during the morning or afternoon. Again, remain aware but don't change any plans, other than making sure your plans are all indoors, despite the warm weather! Rainfall on Christmas Day could reach an inch, especially in north MS.

The SPC severe weather outlook for Christmas Day also shows a low-end risk of severe weather, mainly morning and afternoon
As we become firmly entrenched in tropical Gulf of Mexico air Saturday, record highs in the mid 70s will be threatened and the rain threat shifts north of the metro, outside of a stray shower or three. It'll feel like April. On Sunday, the front moves back into the area as low pressure forms over the Southern Plains. This will mean increased rain and thunderstorm chances. Then as the low, or its attendant cold front, move through the region sometime between Sunday night and Monday night, we continue with high rain chances, but with temperatures falling a bit (but still above normal). Severe weather during this period is still a question mark. The more definite scenario is a LOT of rain. The NWS says as much as 4-5" is possible in some areas between now and Tuesday morning with much of it falling Sunday and Monday. Flash Flood Watches appear likely for that period.

Total precipitation forecast by the NWS through Tuesday morning. The Mid-South is in an area that could receive up to 5" of rain while even higher totals are expected to our north and west, where flooding is nearly certain.
 Behind that system, it appears we finally get to experience more seasonal temperatures as the pattern flips heading into the New Year. For trend purposes only, check out the GFS forecast temperatures for the next two weeks. It looks more like January as January arrives!

GFS model forecast temps for the next two weeks. Use for trend purposes only (numbers are not exactly right). Winter is coming!
To all of our friends and followers, we wish you a blessed Christmas! We'll be watching the weather so feel free to check in and we'll be sure to keep you abreast on Facebook and Twitter. (And if you're still looking for a last minute Christmas gift, get yourself the MWN mobile app and go ahead and pay the $8 for StormWatch+. Or give someone else $8 and tell them to get it! After yesterday, I'm not sure why you wouldn't.)

Merry Christmas!

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: