The overnight update to the official severe weather outlook from the Storm Prediction Center nudged the Level 3 risk back a little to the south and west in our viewing area. The Level 3 of 5 risk now runs from about Savannah, TN to near Russellville and Phil Campbell in Alabama and then to the west. The "standard" Level 2 of 5 risk remains in place across the remainder of the viewing area over southern middle Tennessee and north Alabama. Off to the west, the Level 4 of 5 risk is still in place across Mississippi, but it was shifted southward to be centered over central areas of Mississippi. The main overall timeframe we will be watching runs from about 6:00 PM this evening through around 3:00 AM during the early morning hours. IF we are able to get severe storms in our local area this evening and overnight, all threat types will be possible, including a potential tornado risk. However, there are multiple limiting factors in play with this setup that may work to lessen the risk to our local area, if not keep the severe weather off to our south completely.
We will start with the in-house "Futurecast" model from Baron. It starts us off with mostly sunny skies at daybreak with temperatures in the low to mid 40s. Clouds increase through the morning, but with some sun breaks, and we may even see a few light showers through the mid morning as moisture begins to move into the area. Temperatures are into the upper 50s and lower 60s on Futurecast here by 9am and then into the mid to upper 60s by midday as showers and thunderstorms become more widespread back over north Mississippi and west Tennessee. These look to be elevated, with the better juice and surface-based instability still off to the south into central Mississippi.
By the afternoon, the Futurecast model starts shifting these storms over into southern middle Tennessee and parts of northwest Alabama. These storms still look "elevated" in nature, but they may produce isolated instances of pea to dime size hail and 30-40 mph wind gusts. As we get into the early evening, this run of the Futurecast model brings the warm front and surface-based instability up into northeast Mississippi and near northwest Alabama. As it does this, it has a robust supercell thunderstorm race northeastward near the warm front out of northeast Mississippi into northwest Alabama. IF such a thing were to happen, a storm like that near the warm front would have a chance of being severe, including the risk of producing tornadoes. Futurecast is keying in on that potential in the 6PM to 9PM timeframe for northwest Alabama.
As that storm moves north of the warm front near the Tennessee River and weakens, the Futurecast model develops more widespread rain and thunderstorms over portions of central Alabama to our south by 8-9PM. These continue to grow in coverage and act to disrupt the unstable air from continuing to move north into our area. From here on out, Futurecast continues to bring waves of showers and thunderstorms into southern middle Tennessee and north Alabama through about 1-3AM, but they aren't able to grow severe because of storms to the south blocking the unstable air to move in. By 3-6 AM, the cold front itself is sweeping through the area and ending the thunderstorms across our area as colder and drier air rushes in.
The HRRR model has a similar idea, but it is more widespread with the afternoon and evening storms across middle Tennessee and north Alabama, and this acts to reinforce the cooler and stable air in place across our region and keep the main severe weather risk to the south. During the 6PM-9PM frame, the HRRR also has some kind of rotating storm trying to interact with a boundary over portions of northwest Alabama south of the Tennessee River, similar to the Baron Futurecast. IF this were to occur, there may be a severe/tornado threat with such a storm. However, the HRRR model has the air near the ground more stable during this time, and that may help to keep such a storm cluster more "elevated" and reduce the tornado risk. By mid to late evening into the overnight, the HRRR does the same as the Baron Futurecast, with clustering storms to our south and blocking the unstable air from ever moving into our area, keeping the main severe storm risk well off to our south.
Here is a look at the rotation tracks from both the Baron Futurecast and the HRRR models. Both of them key in on the idea that the best conditional threat for rotating storms in our area will be in northwest Alabama near and south of the Tennessee River and then back into northeast Mississippi. The Baron Futurecast is stronger with these rotation tracks because it allows more unstable air to move northward into those regions. The HRRR, in comparison, still has a rotation track there, but it's very possible that storm may be in a more elevated environment, reducing the chances of that storm rotation making it into the lower levels. Both models are in good agreement that the better chances of rotating storms would likely be south of Tennessee, even though the threat isn't completely zero.
As outlined, there are multiple limiting factors that could act to either reduce the threat to our viewing area, limit it to just northwest Alabama, or possibly keep the severe storms completely to our south. After looking at all the data and how everything evolves, the main above is MY idea of how this may play out...
The areas in green, north of the Tennessee River in north Alabama on up through Tennessee: I don't want you to turn your back on this threat. The threat IS still there, and there could be changes on the smaller scale that allow unstable air to move northward. However, the latest data has been consistently leaning away from that potential, and it is more likely that the better severe weather threat (especially in terms of a tornado threat) stays off to your south. It's very possible that severe storms in these areas may not materialize at all, but we can't rule out the potential. But even if they don't, a few storms may produce pea to dime size hail or wind gusts of 30-40 mph.
Areas in yellow, near and south of the Tennessee River over north Alabama: IF we are going to have severe storms (especially in terms of a tornado risk) in our viewing area counties, this is where it would be most possible, but there's still a very real chance that the severe/tornadic storms don't materialize even here either! However, there is at least some threat for cellular type storms to interact with a warm front boundary in these areas, and there may be just enough low-level instability to allow for rotating storms. Having said that, if storms in north Alabama during the afternoon are widespread, that may keep the instability off to the south, and would shunt any severe weather risk even south of these areas.
Areas in red back over central Mississippi, well southwest of our viewing area, are locations that have the highest severe storm and tornado threat, including the potential for long-tracked strong to violent (EF2 and greater intensity) tornadoes. That type of risk remains well to our southwest.
Even aside from the severe storm risk, heavy rain will be likely with the storms, and a widespread 1 to 2 inches of rain looks likely for most areas. Locations that see repeated rounds of storms over the same area may see as much as 3+ inches of rain in isolated spots. This would act to increase the potential for localized flooding and flash flooding.
Again, we don't want you to turn your back on this severe weather threat. While there are multiple limiting factors that may cause severe storms to not materialize in our viewing area, the threat IS there, and you have to be ready to receive warnings if they are issued and seek shelter accordingly! The Tennessee Valley Weather Center will be staffed, and we will be ready to provide LIVE updates should any severe storms threaten our viewing area.