UPDATE: (Kara James, wrote an excellent blog earlier today. It follows verbatim, after this update.) Latest models are showing that we will see the potential for some strong thunderstorms (possibly briefly severe) on our Friday night and into early Saturday morning. This could develop well after sunset on our Friday night. The main severe weather threat with these storms will be in the form of strong winds, lightning and heavy rain. Most of these storms will move into Western Tennessee by later on Saturday morning (close to sunrise). This will not be the main strong/severe thunderstorm event that we are expecting. The main event is still scheduled to be on Saturday evening and into the wee hours on Sunday.
Here is Kara's update from earlier today: Good morning! We're going to have another warm day (63F), but a cloudier one than the past few days. High clouds are streaming in from the west in advance of our next storm system, which will be impacting us tomorrow through early Sunday morning. While strong and a few severe storms are expected, the good news is that for Christmas we'll be sunny and quiet.
A stalled cold front and incoming upper low are what's going to cause heavy rain and thunderstorms this weekend. Ahead of that system for today and tomorrow rich Gulf moisture will be pushing north, energizing the atmosphere. Adding to that very warm temps for this time of year (upper 60's/low 70's) means there will be plenty of available energy in the atmosphere for storms. The lifting mechanism is the cold front, which is expected to stall just north of us tomorrow. We'll be in the "warm sector", the best place for thunderstorm development.
Isolated to scattered showers and thunderstorms will begin tomorrow, but the very heavy rain and stronger storms will not happen for us until later on Saturday. That's when the upper low will swing through and kick the cold front through the WTVA viewing area. Most storms will be happening in the evening and overnight hours for us, but a few cold pop up west of us in the afternoon. The main threats from any storms that form will be gusty straight line winds (60+ mph), but a few spin up tornadoes on the edges of squall lines are possible too. If any storms form ahead of the main line they will be able to rotate as well. Regardless of storm strength, we'll all get heavy rain too. 2"+ is possible from now through early Sunday.
There are a few limiting factors for this setup, including timing. An evening system means no energy from the sun is helping fuel the atmosphere, but low level dynamics may overtakes the lack of energy from the sun. Another factor is synchronization between upper level dynamics and surface features. The best upper lift stays north/west of us when the cold front is approaching, which may help keep the strongest storms from forming in our area. In any case it's good to be prepared in case something does happen in your town. Stay with WTVA for the best coverage!