Thursday, May 23, 2024

Unsettled Weekend, Then Thunderstorms Could Become Severe Sunday Night

FORECAST:

Friday (High 84, Low 70): Partly cloudy. Widely scattered showers and thunderstorms are possible, and storms could be strong where they form. 

Saturday (High 86, Low 70): Partly cloudy. Widely scattered showers and thunderstorms are possible, and storms could be strong where they form. 

Sunday (High 89, Low 69): Partly cloudy with an isolated shower possible during the day. Thunderstorms are likely at night and may become severe. 

EXTENDED OUTLOOK:

Memorial Day (High 85, Low 70): Decreasing clouds with a 40% chance of lingering showers/thunderstorms. 

Tuesday (High 80, Low 61): Mostly sunny. 

Wednesday (High 78, Low 56): Sunny. 

Thursday (High 81, Low 58): Sunny. 

PRONÓSTICO:

Viernes (Máxima 84, Mínima 70): Parcialmente nublado. Es posible que haya lluvias y tormentas eléctricas muy dispersas, y las tormentas podrían ser fuertes donde se forman. 

Sábado (Máxima 86, Mínima 70): Parcialmente nublado. Es posible que haya lluvias y tormentas eléctricas muy dispersas, y las tormentas podrían ser fuertes donde se forman. 

Domingo (Máxima 89, Mínima 69): Parcialmente nublado con posible lluvia aislada durante el día. Es probable que haya tormentas eléctricas por la noche y pueden volverse severas. 

PERSPECTIVA EXTENDIDA:

Día de los Caídos (Máxima 85, Mínima 70): Nubes en disminución con un 40% de probabilidad de lluvias/tormentas eléctricas persistentes. 

Martes (Máxima 80, Mínima 61): Mayormente soleado. 

Miércoles (Máxima 78, Mínima 56): Soleado. 

Jueves (Máxima 81, Mínima 58): Soleado.

NOTES:

Since we have some severe weather potential Sunday night/Monday morning, it is a good time to go over your safety plan

If you would like to donate to the tornado relief in Iowa, here is a link to the Greater Greenfield Community Foundation. A meteorologist I trust and respect told me privately that this was probably the best way to help those folks out. So I appreciate that information and pass it along here. 
 
DISCUSSION:

It was a mostly sunny day in the Tennessee Valley overall with only scattered showers and thunderstorms. A few did get strong enough to prompt warnings, at least in Tennessee, though I haven't seen any damage reports yet for today. The High in Cullman was 82 with a morning Low of 70. Jasper saw a High of 84 and Low of 71. Haleyville saw a High of 81 and Low of 69. Huntsville saw a High of 86 and Low of 72. And Nashville saw a High of 85, Low of 67. 

Interesting that the Low temperatures are so much balmier than the models have been showing lately. Will take that into account for this forecast. 






Our weather for now continues to be a standoff between the front draped across the Ohio Valley and the Plains and this ridge of high pressure here in the Southeast and Tennessee Valley. Right now that front is lifting northward again as a warm front. 



The severe thunderstorms it produced today were isolated compared to what it did yesterday, across a good bit of the country, not just some stuff in Tennessee. 



The GFS shows another day tomorrow of a good chance of rain and thunderstorms, at least scattered. 


I trust the NAM more this time, especially in light of what we ended up seeing today. 

Forecasting a rain chance of only 30% tomorrow with a High of about 84, Low of about 70 tonight. 


And there is a risk of isolated severe thunderstorms tomorrow, but the risk is low. 



And again the GFS looks too aggressive with rain chances for Saturday. 


So I'm going more with the NAM guidance. Forecasting a 30% chance of rain and thunderstorms with a High of about 85, maybe 86. The Low should be about 69 or 70. The model guidance wants it cooler than that, but I'm leaning more toward the actual temperatures this setup has produced around here lately. 


Again we have a very low chance of one or two storms around here producing enough winds or hail to be considered severe. But the main severe weather threat on Saturday will be out in the Plains. Places like Wichita, Oklahoma City, and Tulsa may be dealing with another outbreak. I saw where the office in Norman is really keeping an eye on this and advising people to be prepared, even though everybody is tired of so many stormy days this year. 



The chance of rain during the day Sunday is looking very low, about 20%. Expecting a High in the upper 80's and Low in the upper 60's. 


But it looks like a line of storms will be pushing into the region late Sunday night, probably actually after Midnight, as we go into the dark hours of Monday morning. Keep in mind that this is Memorial Day, so a lot of people are going to be paying even less attention to the weather than they would on an ordinary Sunday night. 



This system is now just barely within the reach of the NAM, and it is showing (like the GFS has for days, except the instability is not as crazy-high as the GFS a few days ago) fairly strong instability and more than enough wind shear to support a threat for severe thunderstorms, capable of large hail, damaging winds, and isolated tornadoes. This forecast sounding is from near Huntsville. 


The SREF does not show the strong Helicity values as the NAM, and it shows the onset time as more toward 10 PM Sunday night, when the atmosphere will become favorable for severe thunderstorms. It does show CAPE values between 1,000-2,000 j/kg like the NAM does. And the Helicity down at 1 kilometer is expected to be about 150 m^2/s^2, which is enough to support at least a low-end tornado threat along with a damaging thunderstorm wind potential. 



Notice the Supercell Composite numbers creeping up a little, and the Significant Tornado Parameter is about 1-2. So we'll see how things look tomorrow, but all the signals point toward there being an isolated tornado threat involved here as well as a threat for damaging thunderstorm winds and large hail. Credit where it is due, the Storm Prediction Center, particularly Forecaster Leitman, picked up on this sooner than any other source I saw, two or three days ago. And I was inclined to downplay it then. Now I'm paying more attention and having to admit, this could be an organized severe weather event. The only thing left to figure out is the most likely timing and placement of specific threats. 


And notice the dewpoints are expected to be in the 65-70 range, even though this is in the middle of the night. You have to pay attention even seeing that in the daytime, if a cold front is approaching with strong storm potential. 


The ECMWF also is showing upper-60's dewpoints between 7 PM Sunday night and 1 AM Monday morning. 


And we will have to keep an eye on this. Right now the SPC outlook has a 15% basic risk over North Alabama and the bordering counties of Southern Middle Tennessee. But as you get up to about Shelbyville, Tennessee and points Northward, that increases to the enhanced 30% risk. Which extends up into Kentucky and back to places like St. Louis and even into Southern Indiana and Illinois. This is the area where more significant storm damage is expected to be more likely. But we are still three days away from the event. These areas will need to be refined today and tomorrow. And actually the SPC refines them even the day of the event at specific times throughout the day. But this gives you a general idea for now. I would respect this risk, especially since it is coming overnight on a holiday weekend. 



Then we should see an actual frontal passage on Monday, Memorial Day. Not expecting any further problems with severe weather after the stuff clears out in the morning, atmosphere should not be able to recover in North Alabama enough for that. Model guidance has waffled up and down for rain chances, but I think 40%, scattered showers lingering, is reasonable. The High should be in the mid, maybe upper 80's, the Low near 70. Looks like a muggy night going into Monday morning. 



We should clear out pretty well on Tuesday behind the front. Should be mostly sunny with a High of 80 or so, Low near 60 or so. 



Wednesday we have high pressure strongly over the region still. And skies will be sunny. High should be near 80 again, and we might even have only upper 70's here. The morning Low should be in the upper 50's with really dry air in place, about as cool a morning as you're going to get in late May. 



And basically the same for Thursday. The High should be in the lower 80's, but the Low probably will still drop below 60 degrees. And this will be May 30th, one day from the very end of the month. 

If anybody paid attention to the 8-10 day model guidance I showed this morning, it looks even more of an outlandish mess this evening. And I am not going to waste time on trying a 10-Day-Outlook. It would be worthless if I did post it. You'd probably do just as well to read the Farmer's Almanac. 


Please do take this severe weather threat Sunday night/Monday morning seriously, and let people know it is there. Because it could get organized. And while the better chances of significant storm damage (based on the data we have right now) look more likely to occur further North into Tennessee or Kentucky, we can't rule out an isolated event that does significant damage even in far Southern Tennessee or down in North Alabama, in the basic 15% risk area. 

So whether you're in the 15% or the 30% area, my advice is to have a reliable way to get alerts and to have a safety plan that you can put into action within five minutes of getting a Tornado Warning. A lot of people may be travelling and staying with somebody else. Wherever you are, identify the safest place you could get to. 

That needs to be a small central room (or hallway) on the lowest floor of a sturdy house or other strong building, away from windows. 

You can't stay in a mobile home if a tornado is coming, and it's really better to be in a sturdier shelter if a storm is producing damaging straight-line winds, especially if there are trees around. 

Wherever you shelter, it's good to shield your body in some way from debris that could fall or go flying around, especially protect your head. Protecting the head and neck can save people's lives in some cases. It can be the deciding factor in a worst-case scenario where there is a lot of damage. And usually that doesn't happen. But once in a while it does. And you could be glad you took an extra precaution. 

Best way to get warnings overnight is a NOAA Weather Radio with battery backup. But every cell phone has Wireless Emergency Alerts. If you can make sure they are set to wake you up at night, that might be all you need to get your attention. 

And please remember that you can always gather more information from a safe place. If you wait to gather information before taking shelter, you may be wasting valuable time. 

To lighten the mood, I'll tell the story of an old man who was some kind of college professor that I knew from a church my dad went to when I was a kid. I was fascinated that he had actually seen a tornado and had to go down and check out the storm cellar he went to. 

He was one of the calmest and driest people I've ever met. He drawled out, "Well, we were watchin' James Spann, and he made it sound like it was gettin' pretty close to here. And then Paula said, `Listen.' And we could hear the wind roarin'. And by the time we went out on the porch to look, it was right over there behind that house and those trees." 

He continued to drawl casually, "So . . . I went and . . . got my shoes on . . . and we headed on down to the storm pit."

If you're reading this, especially from Tennessee, you probably do not have a storm pit. But almost everyone can get out of a mobile home and shelter in that lowest, most central part of a sturdy house. Even if it takes some effort, it is worth the effort. And even if you're as laid-back as that professor and his wife, you'd be better off sheltering as soon as you get the warning than watching anybody's video stream and waiting until you can see or hear the tornado. That guy mentioned James Spann, and I'll remind everybody that the Spann-man always says: Respect the polygon. If you're anywhere in that warning, it's really better if you go ahead and get to a safe place. 

For Severe Thunderstorm Warnings, it's kind of a judgement call. I wouldn't sit there and not do anything at all. Even if you don't want to take shelter like you would from a tornado, I'd move away from windows and anything that might easily conduct electricity. And especially if you have trees around the house, if you've got more than one floor, try not to be up on that top floor. 

A lot of this may sound like common sense, but before you go "DUH!", I'd like to remind everybody that common sense often goes out the window at the holidays. Just being realistic, some people may be getting together who served in the military, maybe a friend of theirs got killed, and it's Memorial Day coming up. They could be having a few drinks and telling old stories and then just want to go to sleep. 

So that's why I'm spending some time on this, other than having a totally free day and needing to distract myself from some neighborhood drama that I've tried to stay out of, but has still taken its toll on my nerves, as it has for many others. One person actually moved out of the neighborhood recently, and I hated to see her go. But I didn't blame her. I'm trying to take an example from my cats, Salem and Stormy. They are sharing a dish and litter box, and sleeping in the same cat-tower, even though Stormy is new here and won't let any cat (or human) within two or three feet of her without growling and getting ready to attack. Salem has lived here since last August. (He actually showed up when the power was out, after a really bad thunderstorm. There was a warning, but our weather radio transmitter was out, which I'd forgotten about, so the storm damage itself woke me up for that one.) And he watches her patiently while she threatens him. And occasionally makes that little chirrup noise that cats do when they are trying to say hello and be friendly. I'm pretty sure he is telling her in cat language, "Chill out, I don't bite . . . because you're another cat. I only bite Matt. We could have lots of fun tearing up his new roll of paper towels if you just wouldn't be s' grouchy! Oh and by the way, I'd totally mate with you if he hadn't had me neutered ... but it is what it is." 

For anyone who thinks I'm portraying my male cat as too much of a pervert, let it be known that he used to try to mate with my arm before that trip to the vet. And I honestly hate to do that to pets, although it's required for city living and is probably for the best, just being practical. I only got that done because he was already having an operation for a broken hip. And we got him his rabies shot and everything. 

I like to think Stormy finds him mildly amusing, same as I do. 

And I really hope I don't end up sheltered in a small space with the both of them Sunday night. 


Rainfall totals will average an inch or two for this forecast period, with most of the rain coming Sunday night into Monday. 

And let's not totally discount the risk of flash flooding, even with isolated stronger storms. Even if the risk is low, a daycare had to be evacuated in Erin, TN yesterday because of flash flooding. 

The weather next week after Tuesday looks great. But until then, we need to have a healthy respect for the storms. The risk of anything severe through Saturday is very low. But Sunday night into Monday morning, I would definitely watch and be prepared for. 

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