Wednesday, April 26, 2023

Could Get a Little Stormy Tomorrow, Clearing and Turning Cooler As We Head Into May

Thursday (High 72, Low 54): Cloudy and breezy with rain and thunderstorms likely, mainly in the afternoon through the dark hours. A few thunderstorms may become severe. 

Friday (High 76, Low 59): Gradually decreasing clouds throughout the day, some sunshine breaking out. Widely scattered showers and thunderstorms are still possible, mainly in the morning. 

Saturday (High 78, Low 52): Partly to mostly sunny. Isolated showers or a stray thunderstorm are possible, mainly at night. 

Sunday (High 69-72, Low ~55): Partly to mostly sunny with a 20% chance of showers.

May Day (High ~65, Low 40-43): Sunny.

Tuesday (High ~70, Low 39-44): Sunny.

Wednesday (High 72-77, Low ~45): Sunny.

We have had an overcast day in the Tennessee Valley with periods of light rain, fog, and mist. The fog was mostly this morning. It has been breezy at times, but winds generally light and from the East/Northeast. The High in Cullman was 63 after a morning Low of 50. Jasper saw a High of 66 and Low of 62. Haleyville has gotten up to 64 this afternoon after a morning Low of 48. The High was 61 in Fort Payne after a morning Low of 52. Decatur is up to 66 at the 3 PM hour after a morning Low of 48. It is 64 degrees and overcast at the Huntsville/Madison County Airport, the High so far today, probably will end up being today's High, had a Low of 49 this morning. Had a High of 63, Low of 48, up in Fayetteville, across the Tennessee border. And over in Winchester, it is 59 degrees with overcast skies and Southeast winds at 9 miles per hour, looks like 59 will be the High there, had a Low of 48 degrees this morning. 



The rain around here continues to be light and spotty for now. The heavier showers, widespread coverage, is staying out in the Mid-South region for now, mainly along the state borders of Arkansas, Louisiana, Texas, and Oklahoma. 



That's also where most of the thunderstorms are, also a few down around the Gulf Coast, Southeast Alabama into Florida, where the air is a little less stable than up this way. 


That upper-level trough is riding westerly winds aloft through Colorado. At the surface, we have a couple of fronts further East, one down along the Gulf Coast, and another stretched across Tennessee and through the Mid-Atlantic back out to the Plains. 


Tomorrow that storm system will shift to the East and affect us more. 

The NAM has it faster-moving and more robust than the GFS.

We'll probably see a High of about 71-72 tomorrow after a morning Low of about 54-55, thunderstorms and rain likely in the afternoon. The threat for severe thunderstorms is low, but worth keeping an eye on, more on that below the main discussion. 

And it will be breezy tomorrow even outside of any thunderstorms that might try to produce damaging winds, winds generally from the South and East. 



Still expecting a clearing trend on Friday.


As usual, the ECMWF is slower in moving the moisture and rain out of here. The NAM, which I forgot to show with graphics, was in between the two, but closer to the faster GFS solution. Will decrease rain chance to 30% for Friday seeing that two of the models are trending drier, High in mid-70's, Low near 60 or at least upper 50's with some moist air overnight between Thursday and Friday.

Still southerly winds on Friday and not as breezy, also the clouds should be diminishing and more sun breaking out as the day goes on, some places may get into upper 70's.



Saturday is starting to look like it may actually be dry. Expecting mostly sunny skies overall and a High in mid/upper 70's, Low down near 50. 



Looks like there may be a window at least Saturday night into Sunday where isolated rain is possible again, especially in Eastern counties. So will blanket Saturday and Sunday with a minimal 20% rain chance. The global models have not handled this unsettled pattern all that well, and you have to throw in some personal memories/experience and local climatology to balance out what the supercomputers are telling you. This kind of a pattern, better to just blanket both days with a minimal rain chance. Looking at lower 70's for the High, mid-50's for the Low. We finally get a passage of that second cold front on Sunday. 



Both the ECMWF and the GFS have us high and dry for Monday, and the passage of the front on Sunday means that Monday morning will be cooler again. We'll have good radiational cooling conditions as the High pressure moves in from the West. Starting the day in the lower 40's and warming to the mid-60's in the afternoon under abundant sunshine.



Basically the same thing for Tuesday except the High should get back up to about 70 degrees, sunny skies again. Low temperature might not modify much thanks to the dry air and strength of the high pressure system moving through the region, probably still around 44 or 45 at the most.



And that strong High pressure system holds over the region on Wednesday, sunny skies and High expected to stay in lower 70's, the Low in the mid-40's.


We should see an average of about an inch of rainfall around here for this forecast period, while a few locally heavier amounts are possible here and there, still probably staying well under two inches for most places. Any storms that were to become severe tomorrow could dump a lot of rain in a short time span, that's always a possibility.

So let's talk about that. 



The NAM is actually showing the best combination of unstable air and wind shear around here between 7-10 PM tomorrow evening/night. Though a lot of other data has suggested we could be seeing storms in the afternoon hours. 


Still, taking a sounding from Walker County tomorrow evening, forecast sounding, there is marginal instability but more than enough wind shear to support severe thunderstorms capable of damaging winds, maybe some large hail, or even an isolated tornado or two. I'm surprised at how much the forecast helicity values at the lowest 1 kilometer of the atmosphere have enhanced with this run of the NAM. Yesterday it was looking like not a lot of low-level rotation possible. Still at the worst times and places for severe potential, the significant-tornado-parameter is only making it up to a 1 or 2 value. The more likely threat is damaging straight-line winds, but with suggestions of better low-level wind shear, have to keep an eye on it, considering the time of year. 


The SREF is showing instability values getting in place by afternoon, marginal, but enough to support severe thunderstorms if there is enough wind shear. Remember we already have the third ingredient of lift with a fairly strong low pressure system moving through and a front associated with it. 


The low-level helicity is not looking concerning on the SREF model, is only about a third of what we saw on the NAM. 


But we do still see a solid 40 knots of bulk wind shear, good speed shear even if not strong directional shear showing up here. I think the SREF is closer to having this right. It fits this overall pattern better.


The Storm Prediction Center has outlooked a Level 1 Marginal threat for severe weather around here tomorrow/tomorrow night, and that outlined area does not include the counties of Southern Middle Tennessee as well as North Alabama.



The main threat is going to be from damaging straight line winds in thunderstorms, or maybe some outflow winds ahead of them. And even that is a minimal 5% risk, about what you'd see on a summer's day when those random popcorn thunderstorms happen. (Or one particularly taciturn meteorologist from the Plains calls those "bird-fart thunderstorms". Scientific term is "airmass thunderstorms", for the kinds you get in summer. But they carry a low risk of becoming severe in the heat and humidity . . . those rain themselves out quickly and are a lot different than any organized threats for severe we have in the Spring.)


The threat for large hail is very low with this, but SPC has included a 5% risk of it around the Shoals where it looks like a short-lived supercell thunderstorm might try to develop and pack a little more of a punch if it does. 

Most of our severe threat should come from a squall line in the afternoon or evening. 


Again allowing for the possibility of a discrete supercell thunderstorm up around Muscle Shoals approximately, the Storm Prediction Center has introduced a marginal 2% risk of an isolated tornado in that general area. The more organized severe thunderstorm/isolated tornado threat is expected to stay down along the Gulf Coast. 

This is not expected to be a big severe weather threat for the Tennessee Valley. This is one of those deals where one or two storms may try to get out of hand, either within the squall line or developing out ahead of it. If they do, main threat is damaging winds, but can't rule out a stronger cell that produces some large hail or maybe even a tornado somewhere . . . best chance of that happening is up around Muscle Shoals into adjacent parts of Tennessee, Arkansas, and there in Northern Mississippi. 

Any severe weather threat is worth respecting, but if this sort of thing makes you nervous, please understand that our severe weather threat tomorrow is very low. We might not even see any storms become severe. 

If we do though, need to have a reliable way to get warnings (not an outdoor siren, think more like wireless alerts on your cell phone, radio/television, or best is a NOAA weather radio or service like WeatherCall), and have a plan. 

Ideally if you get a severe thunderstorm warning, you want to be in a sturdy house, rather than a mobile home (especially if there are trees around), away from any windows or anything electrical. And especially on the off-chance that it has to be upgraded to a tornado warning, or the storm is showing enough rotation to notice along with the strong straight-line winds, it is better to be in a smaller room like a bathroom, closet, or hallway, near the center of the house. And to be on the lowest floor. You don't have to have a basement to survive a severe thunderstorm or tornado, the vast majority of the time, even on a bigger severe weather day, but even with a low-end threat like this, if you live in a mobile home or a weakly built structure, it is good to have a plan to get to better shelter just in case of any problems. I'm being extra cautious because we have had numerous deaths and injuries from severe storms/tornadoes already this year, even if a lot of it was in other states. It is usually very easy to prevent being injured from a severe thunderstorm or even a storm that produces a tornado. Most of the time the serious injuries or deaths happen from something like a tree falling on someone, or a window blowing out where someone was too close to it, or someone not getting out of a mobile home soon enough and it being too heavily damaged for them to have any protection at all. 

So tomorrow is probably not a big deal for most of us, but please have a reasonable plan in place, just in case a few storms do become severe. It is better if you can leave a mobile home for a more substantial shelter before any severe thunderstorms get to you, even if they are only showing signs of straight-line wind damage. Those structures are just too easy to turn over in the winds or to be basically destroyed by falling trees. You have to prepare for the worst and hope for the best sometimes. For the most part I'd rather people relax, like tomorrow is not a big threat, but I'd also encourage anyone reading to take it seriously enough that if you do have the bad luck to go under a warning polygon tomorrow, you've got somewhere safe to be. 

Hopefully this advice is overkill. But some low risk of a severe thunderstorm or two is there. Maybe we'll luck out, but I am respecting what the weather has done so far this year and taking a "better safe than sorry" approach for anyone who chances to read this. Please be prepared, even though the risk is very low. I mean, you've probably got a tentative plan for if you ever woke up and your house was on fire. So think of it like that, hopefully you don't need it, but it's better to have that plan than to get caught off guard in a situation where you don't really have any good shelter. 

Having said that, overall the weather looks fine after tomorrow, even if some of the mornings are kind of chilly next week, it is just Springtime around here, and while our severe weather season lasts through the end of May, I'm cautiously optimistic that maybe we saw the worst of its storms earlier in the season this year. Toward the end of next week things will warm up, and we'll be getting into the month of May, but for now the forecast looks peaceful for a while, just have to watch this window tomorrow in case even one or two storms try to get a little rowdy. If you are worried by it being April 27, the anniversary of a terrible tornado outbreak, then you can relax: It is not going to be anywhere close to that level of a severe weather threat. But any thunderstorm that reaches severe limits is dangerous, even if it's the only one in the whole state or region all day. So don't get hung up on the date, but have a healthy respect for a very low-end threat for isolated severe storms. That event in April 2011 had the maximum High Risk threat level in the forecast and was basically in another galaxy as far as severe weather threats go. A lot of you may already know this, but if anybody tries to get you worked up by comparing the two, you can safely put that out of your mind. Even if we do have problems, it is not going to be anywhere close to that. But if we had one storm that produced severe enough winds to do damage to your house, and you were not in a safe place, and got hurt, then you might not care much how the two events compared. The bottom line would be that you got hurt by a falling tree or some broken glass or some such. And were probably within walking distance of a safe place that would have kept it from happening. That's all I'm getting at. The risk is very low tomorrow, but still worth respecting, as any severe weather threat is. I encourage you to respect it. But if anyone tries to scare you about it, shut 'em down. Stop listening. And tune in to a source that is more reliable. There is way too much hysteria online now, and not only about weather. Facts matter. And this is only a low-end severe weather threat. I think most sources are communicating that, but if you do come across anyone trying to make it sound like doomsday and the four horsemen of an apocalypse, they're wrong. And if we do have any problems tomorrow, it is easy to protect yourself with a basic safety plan - small central room on the lowest floor of a sturdy house if you go under a warning. 

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