Off and on active storms today through the Memorial Day weekend. Watching a more elevated severe storm threat for Sunday PM.

We are temporarily quiet across the Tennessee Valley early on this Thursday morning. Enjoy it while it lasts! Thunderstorms coming out of the Arklatex to Arklamiss area overnight have fizzled (as expected) on their approach to east Mississippi and west Alabama. Spotty thunderstorms closer to the stalled frontal boundary are currently staying north of our area over northern Tennessee and northern Kentucky. Meanwhile, additional thunderstorms are ongoing from southeast Oklahoma into western Arkansas. The remnant cloud shield from the former thunderstorm complexes has our area mostly cloudy to overcast, and this combined with a southerly wind and dewpoints up into the mid to upper 60s has our temperatures this morning ranging from the mid to upper 60s over parts of middle Tennessee where there was some rain-cooled air last evening, to the low to mid 70s over north Alabama where areas never got rain-cooled yesterday.

As we did with yesterday’s forecast discussion, we’re going to start with the general overview first and then breaks things down one day at a time because there is a lot to talk about. The good news is that the rain/storm chances do go away in the extended forecast and we dry out for a time beginning on Tuesday of this coming week. We also get into slightly cooler air with daytime highs as low as the upper 70s by next Tuesday and Wednesday! But between now and then, we are locked into an active weather pattern today through Sunday in which there will be off and on periods of showers and thunderstorms likely. There’s at least some chance of showers and thunderstorms continuing into Monday, although a lot of that will depend on how Sunday night evolves (Sunday night’s storms could help speed the cold front across Monday morning faster than models currently show). From now through Sunday night, there will also be (at minimum) low chances for a few storms to be strong to severe. The Sunday afternoon and Sunday night period, however, offers a more elevated threat of severe storms that we will be talking in more detail about further into this discussion. Overall, while it isn’t necessary to full-on cancel outdoor plans for your Memorial Day weekend, it’s going to be very important to have alternate indoor plans you can switch to on short notice, and it’s also going to be just as important that you remain weather aware as we head through the holiday weekend!

Let’s start with today and tonight first. The latest outlook update from the NWS Storm Prediction Center maintains the low-end Level 1 of 5 risk of severe storms for today and tonight across all of our viewing area in southern middle Tennessee, northwest Alabama, and northeast Mississippi. This is part of a larger severe weather risk zone that stretches from the East Coast, through the Tennessee and Lower Ohio Valleys, and back into the Plains. There are higher severe weather risk levels off to the west from the Plains into the Arklamiss. This is one running theme that you will notice for today, Friday, and Saturday… while we have low-end severe storm risks here each of those days, the higher risk zones will stay west of us. Within our local area, this is because of a low-end threat that a couple of the storms this afternoon and evening could be briefly strong to severe with gusty winds and small hail. While the tornado threat is never 100% completely zero any time a severe thunderstorm is present, the tornado threat for today and tonight will be VERY MINIMAL across our area. Storms this afternoon may also produce localized street flooding, but a more organized flooding threat doesn’t look that likely.

Above is the best attempt possible at a “Futurecast” type breakdown of the timing and evolution of the storm chances for today and tonight. This is using the overnight data from the HRRR model. It is not perfect, and that means that you cannot try to translate the exact specific location of where a storm is or isn’t located on the model at an exact specific time and then expect that to perfectly verify (we know some of you do despite us repeatedly telling you not to do that, and then you get mad at us when it doesn’t work out! lol), but it will give you a general guideline of the rough idea of when/where to expect storms to evolve through the day. Of the high-resolution models, the overnight HRRR data has been the data that’s most closely modeled the reality of how the overnight storm complexes have behaved. That gives us at least reasonable confidence that it has the basic idea of things on the right track. You can see it has mostly cloudy skies this morning with a spotty showers possible through the morning or midday, but the better chances under heavier storms hold off until 2:00-3:00pm or after this afternoon. Don’t take that timing down to the exact, but that general idea looks right. From there, scattered strong storms will remain possible through the rest of the afternoon on into the late evening or so before we lose daytime heating about an hour or two after sunset. Additional spotty showers and thunderstorms will be possible into the late night, but they are not likely to be strong to severe.

We have a similar situation for Friday, although Friday’s storms will likely get going as early as the morning hours. The NWS Storm Prediction Center maintains a low-end Level 1 of 5 risk of severe storms across all of our viewing area for Friday. As with Thursday, there are higher chances off to the west, with a broad Level 2 of 5 risk of severe storms stretching from the Lower Great Lakes area down to central Texas. This will be closer to the stalled frontal boundary to our north and where the jet stream will be located, giving more energy and dynamics for a slightly higher severe threat off to our west. With storms in our area, the main threat will once again be a few being strong to marginally severe with gusty winds and hail. The tornado threat again on Friday won’t be completely zero, but it will be VERY LOW. We may have a slightly higher chance of some localized flooding with heavy rainfall on Friday, but we still don’t expect an organized or widespread flooding/flash flooding threat at this time.

Again, if the overnight data from the HRRR model is correct, there could very well be rain and thunderstorms in the area (especially northeast Mississippi and northwest Alabama) as early as the morning hours. From there, we look to have the potential for showers and storms to continue off and on through the rest of the day into the evening. At any point in there, we could have a storm grow strong to marginally severe with the threats we talked about earlier. There’s not going to be a specific cute 2-hour time window to give you because of this. You just need to have a way to listen out for a severe thunderstorm warning and be ready to head inside away from windows if one is issued or if you hear thunder from an approaching storm. Again, while the tornado threat for Friday isn’t zero it is VERY LOW. It’s not a situation where you’re going to have to sit on pins and needles all day! One thing I will note is that the model shows a lot of repeated widespread showers and storms through the day. If this is indeed how things are to play out, that may help reduce the daytime heating and instability a bit and help somewhat lower (BUT NOT REMOVE) the severe storm threat for Friday. Still, don’t let your guard down though! The model data has things go quiet as we head into the overnight Friday night. If we do have repeated widespread action during the day, the atmosphere may get worked over enough for this to happen, but we aren’t yet brave enough to lower rain chances for Friday night!

It’s a similar song and dance for Saturday. The Storm Prediction Center (as we expected them to) has added in a low-end Level 1 of 5 risk of severe storms for Saturday across the entire viewing area. Just like the days before it, it’s part of a broad low-end threat that stretches as far east as the East Coast, with a higher threat (and what may be a potentially significant severe weather outbreak) off to the west over the Great Plains. This may be a significant tornado event over portions of Oklahoma into eastern Kansas Saturday afternoon into Saturday evening, carrying over into portions of Missouri and Arkansas overnight Saturday night. For our local area here, it’s the same situation as today and Friday… a few storms may grow strong to marginally severe with gusty winds, hail, lightning, heavy rain and localized low-end type flooding, but a VERY LOW tornado threat. As is the case with Friday, Saturday looks like a situation where storms could go as early as the morning hours and then carry on off and on during the rest of the day on into Saturday overnight and/or early Sunday morning. However, specific exact timing of rain chances for Saturday is going to be next to impossible to outline this far in advance today because of how a lot of that will be determined by 1.) How things evolve Friday and Friday night and 2.) Just the inner mechanics of the storm clusters themselves. It’s another case where you don’t have to fully cancel plans you may have, but you need to have alternate indoor plans, and you have to stay plugged in to weather information!

Sunday into Sunday night is when things ramp up and the severe storm threat becomes more elevated. The latest outlook update from the Storm Prediction Center maintains the risk of severe storms across the entire area for Sunday and Sunday night (with the general timing being the afternoon into the overnight hours), but they have now expanded their elevated/higher confidence area eastward in middle Tennessee to include some of our viewing area counties. This is the equivalent of a Level 3 of 5 risk already in place for those areas. With the outlook update that’s issued during the early morning hours of Friday, the Sunday system officially goes into their Level 1-5 ranking system. It’s very possible that, in future updates, there could be risk expansions/upgrades across more of the viewing area as details become more clear.

There may possibly be a few leftover showers and storms from Saturday overnight ongoing during the morning hours of Sunday, but if that’s the case, they aren’t expected to be much of a problem and will move out of the way during the morning hours. There will likely be a period during the late morning through some part of the afternoon where we see breaks in the cloud cover and get some sunshine to heat and destabilize the atmosphere. During the afternoon and evening hours, the upper support from the storm system arrives, and strong to severe storms are expected to develop that will carry over into the overnight hours. It’s too soon still to try to detail the specific timing of all of this. Because of the overall combination of ingredients that will be in place, this looks like a situation where all threat “types” will be in play. That means damaging winds, large hail, lightning, the potential for flooding (to some degree, at least), as well as some degree of a tornado threat. The “type” of tornado threat and its magnitude is still VERY uncertain at this time. During the late overnight hours, there will likely be a more solid line of storms that organizes and moves through the area that would have mainly a damaging wind and spin-up type tornado threat. This would reach as far south as north Mississippi and north Alabama. HOWEVER, during the afternoon and evening, there is going to be enough lift in the warm sector for supercell type storms to develop that would have a more elevated type of tornado threat. What we DON’T KNOW YET is how much of our viewing area is involved in that supercell threat. We don’t know if it just skirts our northern viewing area counties like the current outlook suggests, whether it extends down through the remainder of southern middle Tennessee, or if there’s enough lift in the evening hours for it to extend as far south as north Alabama and Mississippi (similar to how the supercells on May 8th developed farther south than the forecast a few days ahead of time showed and they extended into north Alabama). That’s something we simply do not have a handle on yet, but none of those three scenarios can be ruled out. Which one plays out, though, is what ultimately determines how much (or how little) of our viewing area is involved in the elevated tornado threat. We should start getting a better handle on that as we get into Friday evening and Saturday morning as some of the smaller scale details of the setup start making themselves more apparent in the data.

What do you do with this information? You plan and you prepare. We know it’s the Memorial Day weekend and you will be tempted to unplug from the outside world and go about your holiday weekend plans. Because of the storm threat, this simply isn’t the weekend to do that! You don’t have to cancel plans, but you do have to factor this information into your plans, and you have to stay updated with the latest forecast information. If you’re working with old information, you’re working with bad information! Just have your severe weather safety plans in place and ready to go, have multiple reliable ways of hearing watches and warnings, and then don’t be a hard-headed know-it-all and actually correctly react immediately when and if a warning is issued for your area, and we’ll all get through this together just fine! It’s spring in the Tennessee Valley. Don’t be scared of this. We are VERY cognizant of the fact that people have elevated storm anxiety after what happened earlier this month in our area, but there is no need to be anxious or to fear this. Take a deep calming breath, and look at this level headed. This is nothing new here. We have done this many times before. Severe storm and even tornado threats are nothing new here, even at the end of May. They don’t happen quite as frequently this late into spring as they do earlier in the season, but they do sometimes still happen here this late into the season! Just be prepared and remain weather aware, and we will get through it okay! We will certainly be fully staffed to cover whatever happens and provide live coverage as necessary! The good news…. as we discussed earlier toward the beginning of this blog, there IS light at the end of the tunnel with rain chances taking a break as we head into next week (Tuesday for sure, but they may trend down for Monday as we get closer and work out those details)!

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