Weather is warm, muggy, but quiet across the Tennessee Valley early on this Sunday morning. We’ve had a few spotty thundershowers developing as close to us as western Tennessee within the past hour or so, but these are lifting more sharply northeastward than yesterday morning’s storms, and these shut miss our local area off to the west. Temperatures in our area early this morning range from the mid to upper 60s in Giles and Marshall Counties of TN to as warm as the mid 70s over toward Savannah TN, with lower 70s elsewhere across southern TN, northwest AL, and northeast MS. Dewpoints are running high, ranging from the mid/upper 60s to the lower 70s. Meanwhile, the main upper-level disturbance that will trigger tonight’s storm threat for us is ejecting out across the Southern Plains. This has been driving ugly storms overnight from Kansas, Oklahoma, and Texas, over into Arkansas and Missouri. As of the time of this blog being typed, there was still an ongoing tornadic supercell with a long history of major damage across northern Arkansas. Fortunately, this particular round of storm activity will stay well off to the north of our area this morning, but it has prompted a Tornado Watch to be extended as far east as northwestern portions of Tennessee early this morning.
The NWS Storm Prediction Center maintains a Level 2 of 5 risk of severe weather across all of our viewing area that goes through the overnight hours tonight and the predawn hours of Monday morning. The NWS has also expanded their Level 2 of 4 risk of excessive rainfall (what we call a flooding risk of “possible” to make it easier for you to understand what it means) southward through all of southern middle TN and far north Alabama and northeast Mississippi. In agreement with that, a FLOOD WATCH has been issued to cover all of our Tennessee coverage area counties that’s valid until 7:00 AM Monday. The main threats with storms tonight continue to be the potential for damaging straight-line winds of 50-70 mph and localized areas of flooding and flash flooding. However, a few tornadoes WILL be possible areawide, as will the potential for a few storms to produce hail as large as quarters or half dollar size. There may be an isolated storm or two with larger hail than that if we see anything more cellular ahead of the main line. Of course, frequent cloud-to-ground lightning will be an important risk to remember with ANY storm, regardless of whether it is severe warned or not!
Overnight runs of the HRRR model aren’t perfect, but they seem to have a reasonable decent grasp on what is happening now as well as the basic and general idea of timing and evolution of the storms tonight; so, we’re going to use that to give you a basic “Futurecast” type generalized breakdown of the overall timing…
A stray shower or thundershower from that spotty activity we talked about in west Tennessee may try to clip our area west of the Natchez Trace Parkway between now and around 8-9am. The overall chance of that is low, and should it happen, it shouldn’t be a big deal, but we can’t rule that out. Otherwise, much of the rest of the daytime hours of today will likely be quiet, partly cloudy, hot, and muggy as the upper-level ridge temporarily builds in across the area. Dewpoints will stay in the upper 60s to as high as the mid 70s, and as temperatures climb into the upper 80s to lower 90s this afternoon, that will shoot heat index values into the 95 to 100 degree range for a few hours in the mid to late afternoon! There is an uncertain chance of a few ISOLATED, SPOTTY, HIT-OR-MISS thunderstorms this afternoon. IF one of these were to develop between 2:00pm-6:00pm, they may grow briefly strong with gusty winds and hail, simply because of how hot and unstable the atmosphere will be. However, it’s very uncertain these will be able to break through the cap to even develop, and IF they do, they would be very isolated. This means that you ARE going to be able to do outdoor activities today! Read that again. We’ve had a few people accuse us of ruining their holiday weekend when we’ve repeatedly said all week until we’ve turned blue in the face that folks wouldn’t have to cancel plans as long as they pay attention to the radar. You WILL be able to do outdoor activities during the daytime today! WITH THAT SAID, you ALSO still need to pay attention to the radar this afternoon in case one of these isolated thunderstorms does pop up near you, and you need to be ready to quickly head indoors if one approaches! But overall, if you are able to do that, you WILL be able to have outdoor activities and functions during the daytime hours today!
As we get near and especially after sunset, some of the modeling is trying to pop off a few cellular storms across the area, most likely in the 9-11pm timeframe but some data has hinted it’s possible as early as 7-9pm. IF this is able to happen, we will have to watch these storms carefully. The atmosphere will still be very unstable, despite the sun going down. The big change near sunset and afterwards is that the low-level jet about 5,000 ft above ground level will start rapidly strengthening as it always does at night. This will rapidly increase the wind shear and spin in the atmosphere as this happens. IF we are able to get these more scattered and cellular storms to develop during that timeframe, the strengthening wind shear profiles combined with the unstable atmosphere will be favorable for these storms to have the potential to become supercells with a tornado threat, a damaging wind threat of 60-70 mph gusts, and the risk of hail that may be half dollar to as large as golfball size. It’s just a big question mark of whether or not they will be able to break the cap in the atmosphere and develop. We will be watching the data carefully through the day to assess this potential!
Once we get into the 11pm-1am timeframe overnight, the main line of storms itself will start moving into the area from the northwest and then work through the ENTIRE viewing area from northwest to southeast from that timeframe on through about 3-5am early Monday morning. The main threats with the main line of storms will be potentially more widespread damaging wind gusts of 50-70 mph, the chance of a few embedded spin-up type tornadoes, a few spots of hail to quarter or half dollar size, and the potential for localized flooding and flash flooding. IF those evening supercells are able to develop, that would possibly increase the flooding and flash flooding threat a little more with the main line of storms overnight because of multiple rounds of heavy rain within that short amount of time. The flooding threat would be a bit more limited if there are no even supercells to form ahead of the main overnight line.
We have been urging everyone for the past several days to take time while the weather is quiet to review safety plans and make sure you have reliable ways of receiving watches and warnings. If you have not done so, take the time during the quiet daytime hours today to make sure you are ready for tonight’s storms. This is nothing you have to be afraid of or panic over, but you do have to take the storm threat seriously and pay attention to weather information, and then act immediately to shelter appropriately if you area is issued a warning. Remember, a WARNING means TAKE ACTION NOW. The WATCH means to pay attention and be ready, but you don’t have to shelter at the moment. With flooding and flash flooding a threat, especially during the overnight, it’s important that you take particular care in that respect as well, especially if you are traveling. Do not attempt to cross a flooded roadway. Turn around and find an alternate route. The roadway may be damaged or washed away under the water, and it only takes 6 inches of fast moving flood waters to sweep you away!
We will be fully staffed in the weather center to provide live updates on all platforms as the weather situation makes it necessary. Please see the map above to see the counties included in our viewing area service territory. If a Tornado Watch is issued for any of these counties, we will have live short-duration updates at the top of every hour on all platforms until the threat has ended. If a Severe Thunderstorm Warning is issued, we will have immediate live updates on all platforms to provide the warning and storm tracking information. The seriousness of that severe thunderstorm warning threat will dictate whether it’s a short-duration live update or if it’s live continuous coverage. If a Tornado Warning is issued for any of those 14 coverage area counties, or we see a suspicious radar signature that signals an elevated danger of an immediately developing tornado, we will have LIVE NON-STOP CONTINUOUS COVERAGE ON ALL PLATFORMS until the warning has expired, the warning has been canceled, or the danger is over (either by the storm weakening or it moving out of the coverage area).
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