Tuesday, May 21, 2024

Warm and Unsettled Pattern Late This Week Through Memorial Day

FORECAST:

Today (High 87): Sunny. Rather warm.

Wednesday (High 87, Low 63): Mostly sunny. Warm.

Thursday (High 86, Low 66): Partly cloudy. Isolated showers and thunderstorms are possible. 

Friday (High 86, Low 68): Partly cloudy. Widely scattered showers and thunderstorms are possible.

EXTENDED OUTLOOK:

Saturday (High 87, Low 68): Partly cloudy with a 20% chance of showers/thunderstorms. 

Sunday (High 87, Low 69): Mostly cloudy with a 30% chance of thunderstorms - a few could be strong. 

Memorial Day (High 86, Low 69): Partly to mostly cloudy with a 40% chance of showers/thunderstorms. 

Tuesday (High 85, Low 70): Mostly cloudy with a 50% chance of showers/thunderstorms. 

PRONÓSTICO:

Hoy (Máxima 87): Soleado. Bastante cálido.

Miércoles (Máxima 87, Mínima 63): Mayormente soleado. Cálido.

Jueves (Máxima 86, Mínima 66): Parcialmente nublado. Es posible que se produzcan lluvias y tormentas aisladas.

Viernes (Máxima 86, Mínima 68): Parcialmente nublado. Es posible que se produzcan lluvias y tormentas eléctricas ampliamente dispersas.

PERSPECTIVA EXTENDIDA:

Sábado (Máxima 87, Mínima 68): Parcialmente nublado con un 20 % de probabilidad de lluvias/tormentas eléctricas.

Domingo (Máxima 87, Mínima 69): Mayormente nublado con un 30 % de probabilidad de tormentas eléctricas; algunas podrían ser fuertes.

Día de los Caídos (Máxima 86, Mínima 69): Parcialmente a mayormente nublado con un 40% de probabilidad de lluvias/tormentas eléctricas.

Martes (Máxima 85, Mínima 70): Mayormente nublado con un 50 % de probabilidad de lluvias/tormentas eléctricas.

NOTES:

The National Weather Service in Huntsville has a work-in-progress page about the May 8-9 tornado outbreak this year. And the National Weather Service in Nashville also has a page about their counties that were affected. 

And the National Weather Service in Mobile has a page about rip currents. Going to the beach sounds great right about now, would if I had the chance, but seriously, it's a good idea to have a plan for basic hazards like that, in case you were to ever get caught by one. A family I know that was taking a vacation in California had two of the three of them get caught up in a current a few years ago. The stepfather had to be rescued by a lifeguard, so it's good that there was a lifeguard there. And the daughter managed to swim out of it herself. That's why I encourage people to read up on it or watch some of the videos, so maybe if it ever happens, and there is no lifeguard nearby, you can stay calm and get yourself back to safety. 

DISCUSSION:




At 10 AM, skies are fair and sunny in Cullman. The temperature is 79 degrees. The dewpoint is 66 degrees, making the relative humidity 65%. Winds are from the Southwest at 10 miles per hour. The pressure is 30.05 inches and steady. The Low this morning was 61. Actually it was 60.8 degrees, but I'm rounding to the nearest whole number. Good to remember those things from math class . . . We did have a little fog this morning too but not for very long, about 4:30 to 5 AM. 

Fair skies in Jasper too and also 79 degrees there. The dewpoint is 70, making the relative humidity 74%. Winds are totally calm at this hour. The pressure is 30.03 inches and rising slowly. The Low this morning was 59. And I didn't even have to round it from a decimal place. 

It is also sunny in Haleyville with a temperature of 79 degrees. The dewpoint is 63, making the relative humidity 58%. Winds are South at 12 mph. The pressure is 30.05 inches/1016 millibars and rising slowly. 

It is sunny and 81 degrees in Huntsville. The dewpoint is 64, making the relative humidity 57%. Winds are Southwest at 6 mph. The pressure is 30.02 inches/1015.9 millibars and rising slowly. 

It is mostly sunny in Nashville with a temperature already at 83 degrees this morning. They saw 90 degrees yesterday, today looks like another hot one. The dewpoint is 61, making the relative humidity 48%. Winds are from the South at 13 mph. The pressure is 29.98 inches/1014.6 millibars and actually falling slowly at the moment. The pressure has been pretty steady over the past few hours at all the sites, but I'm making note of even minor fluctuations, like it's rising a little, falling a little. 

I forgot to mention the Low temperatures for the last three sites, but probably not many people care about such details anyway. 

We have such clear skies and drier air right now because we've come under a ridge of high pressure for the moment, a lot like we'd have if it was a few weeks later and we were properly into summer already.





The action today is mainly in the Midwest, where they have potential for organized severe thunderstorms, some of which could end up doing significant damage. Especially in Iowa, there is potential for supercell thunderstorms capable of damaging winds, large hail, and tornadoes. They could end up with an outbreak of severe weather sort of similar to what we had a couple weeks ago in Tennessee and into North Alabama. It looks like the hot spot will mainly be in Iowa, but some risk does extend all the way from the Great Lakes back down through Missouri and even Eastern parts of Oklahoma and Texas. 

Around here we should stay sunny and make it up to about 87 degrees today. 



Tomorrow it looks like that ridge holds strong even though the front moves along and tries to bring some showers and thunderstorms to the Tennessee counties anyway. 


The NAM is more conservative with the moisture around here, and I think that's right. Forecasting a High of about 86-87, Low about 63-64 and mostly sunny skies.







And tomorrow features another widespread risk of severe thunderstorms in the country, stretching from the Ohio Valley back through the Mid-South, Arkansas, back into Northeast Texas. The threat for damaging winds or hail look a little enhanced above average, but the tornado threat looks like the standard isolated threat and is focused on those areas of the Mid-South like Arkansas back into Southeast Oklahoma and mainly Northeastern Texas. 

It would not be impossible to see an isolated storm go severe in Middle Tennessee, but the risk is very low. The better chance of any thunderstorms producing damaging wind gusts or severe hail is going to be over about the Western third of Tennessee. Certainly anybody around Memphis would need to pay attention to this, but overall for Tennessee, at least the people likely to read this blog, this probably is not going to be a big deal. Most places in Tennessee probably will not even see a drop of rain tomorrow, much less any storminess. 



But if you want to get nitpicky, the very low risk of an isolated thunderstorm reaching severe limits does include places like Waynesboro, Nashville in Tennessee, and Corinth, Mississippi. It clips Northwest Alabama but only the very rural parts of Lauderdale County in the far corner there. 



Thursday looks like around here we'll have to bring back the chance for isolated rain and thunderstorms, 20% chance, about like you'd see on a typical summer day. High should be about 85-87 range, Low about 66-68. 



The severe thunderstorm chances on Thursday look to move back more into the Plains, but Arkansas could still be having some organized activity too. This is just the basic 15% chance for severe storms and some low-end 5% marginal probabilities out around that, still sort of clips Memphis, but for the most part, Tennessee is just expected to have general thunderstorms and rain. And even that should stay isolated like down here on the Alabama wide, or at least pretty widely scattered across the map. If I was forecasting for somewhere close to Nashville, I might bump the rain chance up to 30-40%. 



On Friday, even the GFS guidance has come down in the rain chances to more like 30%. So I'll stick with that from previous forecasts. I think yesterday I might have gone with 40%. But this is a summerlike pattern in a way, even though we're not quite into summer yet. Where a front is running into a ridge of higher pressure. And we'll have some rain but not a lot like in the Spring. Friday is looking like showers and any thunderstorms will stay widely scattered, a lot like in the Summer. High should be in the mid-to-upper-80's and the Low in the mid-to-upper-60's. 



The GFS is currently showing a decrease in rain chances, or at least shifting them more into Central Alabama, on Saturday. But the guidance has been wishy-washy on this. And it is not a pattern where the models tend to handle the details all that great. So I'm definitely keeping the rain chances in but cutting them back to 20% for Saturday, High more toward the upper 80's, Low more toward upper 60's. 


On Saturday the risk for any organized severe thunderstorms looks like it will be mainly over Arkansas back into Southeast Oklahoma and Northeast Texas. That area has a chance for multiple rounds of severe weather over the next few days, so I wouldn't be surprised if somebody ends up with some damage out there. The severe weather tends to shift more out West as we get farther into May and June. 



Sunday looks mostly dry around here via the GFS. 


Like I said though, the models don't always handle summer convection so great. You have to second-guess them more when the pattern is even vaguely summerlike around here. The ECMWF shows more moisture available around here Sunday to fuel showers and thunderstorms. 


And actually the reason I decided to post this forecast at all is that I noticed this: The Storm Prediction Center has included all of Southern Middle Tennessee (actually just about the entire state of Tennessee, all but the far Eastern counties) in a basic 15% severe thunderstorm risk on Sunday. And I just got through saying yesterday that it looked like our severe weather season had just about played out until November. So this got my attention, and we'll look at it. The risk also clips far Northern Alabama, mainly around the Shoals. And it extends up into Kentucky and other parts of the Ohio Valley, also parts of Arkansas and Missouri. 


Zooming in on this area, basically everybody in Tennessee is included. And the risk does clip all the way down to Huntsville, Decatur, Russellville, includes Athens and Florence for sure. And this many days in advance, it's a good idea to pay attention when this general idea is brought to the table. The forecaster who wrote the extended outlook this morning tends to be one of their better ones too, recognized the name. 





Guidance for specific parameters varies in how reliable it is 5-6 days out, often is not all that reliable, but can give you some ideas of the general trends if you know how to interpret it. And the combination of unstable air and wind shear does start to look concerning for us Sunday afternoon. This is valid at 4 PM. Took a forecast sounding for the hot spot around Ardmore or maybe a little East of there, along the AL/TN state line, where the Energy-Helicity-Index got up to a value of 5 or so. And it's showing insanely high CAPE values of over 4,000 j/kg, which looks more like July levels of unstable air. And the Helicity values are in the 200's up to 3 kilometers, actually approaching 300 m2/s2. And then the value at the lowest kilometer is below 150. The Significant Tornado Parameter is showing 2-4 range. This is a setup where we might have just enough wind shear to work with for a tornado potential, and the strong instability could overcome the wind shear not being too strong at the lowest levels of the atmosphere. 

The problem is, I have a hard time buying this forecast sounding. It looks overblown and could be an example of the models not handling this pattern too well. Then again Tennessee will be closer to the surface Low, so could end up with decent wind shear. 


This forecast sounding from Cullman County at the same time makes more sense in this pattern. It shows about 2,000 of CAPE, which is high for the Spring around here but common for the Summer. And the wind shear doesn't look supportive of a tornado threat at the lowest levels. This would be more a setup for large hail and damaging straight-line winds. 

And I guess Tennessee might have a little more wind shear, being closer to the center of low pressure, but I wouldn't get too hung up on it. If there is a tornado threat, I tend to think it would stay on the lower end with this one. If you're shaken up by the May 8-9 event (and I'll admit that I am . . . I had family in TN and AL who had a strong tornado pass within just a few miles in the same evening . . . in the heat of the moment, seemed like they could take a hit), then I would just monitor future forecasts and see how this unfolds. At the moment it looks like it's worth paying attention to but not worth a lot of worry. The only thing that does make it more concerning to me is the holiday weekend. Plus it's a Sunday, and a lot of people are going to and from church. If we have problems though, looks likely to be in the afternoon. But there again, lots of people are out eating fried chicken or taking a nap. And actually, a lot of people will be working to serve at those restaurants and probably won't care about the weather. 

It doesn't look like a big severe weather event around here to me. But still have to respect that potential here at the tail end of our severe weather season. The center of low pressure will pass close to Chicago. It's a close call for Southern Middle Tennessee. Coverage of thunderstorms will probably be a little higher there, at least a 40-50% chance of rain as you get up close to Nashville especially, further into Middle Tennessee. It's one of those things to keep an eye on, but please do not get bent out of shape this far in advance. 

For North Alabama, it looks like the chance for thunderstorms will be more like 20-30% again, High in upper 80's, Low in upper 60's. 

This reminds me of sometimes in the summer when we'll get a 15% severe weather risk, and I might or might not mention it, because it's sort of understood that our summer storms can always ramp up and produce some hail or strong winds. But then for the Tennessee counties, that surface Low might be just close enough to make the threat a little more organized, with an isolated tornado threat. I guess I just don't want to rule out a few problems here at the end of May. Once in a while we'll have an event at the very end of the season. This doesn't look like a really significant, widespread event around here though, not even in Southern Middle Tennessee. But I'll show the setup enough respect to say we might want to keep an eye out for a lower-end event around here, just in case. All it takes is one damaging storm, or a few isolated storms that get out of hand, and people have got problems. I figure it's worth spending some time looking at because it's coming on the Sunday right before Memorial Day. If we did have any issues, probably not many people would be paying attention, because it's getting toward summer, and the pattern overall is looking pretty calm. 

It's still five or six days out, so I'll just keep an eye on it. 



Then on Monday, Memorial Day, it looks like some chances for showers and thunderstorms will linger. 

Now I do have to mention something that could really upset this forecast. If that ridge tries to build back northward, and the models are not picking up on it (and I've been looking at the European model too, it doesn't show that either), then our rain chances could end up being lower, or even just about nil. For now, since it's a holiday, I'm taking the models pretty much at their word, taking the rain chances seriously, even though I don't think it's going to rain as much as some forecasts I've seen. 

The most rain chance I feel right about putting in for Memorial Day is 40%, and 30% might be better here. Will have to look over the 7-day period as a whole now that we've gone through it day by day. And actually we still need to look at Tuesday. High Monday should be about the mid-80's, the Low in the upper 60's. 


Then on Tuesday it looks like we may get a frontal passage. If this works out, then later in the week next week could feature some pretty comfortable temperatures for the end of May and really dry air. We could get down into the lower 80's and see Lows near 60 or even in 50's. But for now, let's focus on Tuesday and speculate on beyond that more in future forecasts. Almost want to go with a 50% chance of rain here, but since it's so far out in this unsettled pattern, only going to put a 40% chance of rain in there, High in lower 80's, Low near 70. Between now and then, the timing of this front could change. And we'd have to adjust rain chances for that. Definitely interested to see if this plays out and if we get one last stretch of cool mornings before we get into June. That'd be an interesting variation on things. 


Rainfall totals will probably range anywhere from a half-inch to 1-2 inches for North Alabama and Southern Middle Tennessee, on average. Some isolated places and into West Tennessee may see higher amounts up to 3-4 inches or so. As we get into summer, rainfall guidance like this becomes less reliable. And we've got a combination this forecast period, where we sort of have an unsettled summer pattern going on but also have a front trying to push through here at the end of spring. But this WPC map gives a basic idea of where the heaviest rain is likely to be the next seven days. 

I found the extended part of this forecast challenging. Went with 50% chance of rain for Tuesday after all. In the end, my opinion on the Sunday severe thunderstorm potential is that it will probably be a chance for a few thunderstorms to produce large hail and winds strong enough to do some damage. Even for Middle Tennessee, based on the data I've looked at and understand, I think the tornado threat will be minimal, and might not end up being a concern at all. But since it's at the end of May, I'd keep an eye on it just to be on the safe side. And even straight-line winds in a severe thunderstorm can bring trees down or knock out a window. So we've kind of had a rough season, even if it was only that one event earlier this month, pretty rough evening and night. Might be good to err on the side of caution and pay attention to whatever it tries to do right here at the end, before we get into summer. But don't let it eat you up, just keep an eye on it and have a reasonable plan in case some storms do get out of hand. 

Sometimes I feel like the SPC overdoes severe weather outlook areas in our region in the summer months because they're not familiar with our local climatology and how that affects everything. But we are not quite into summer yet. And I always respect this particular forecaster's opinion. It's one of those borderline situations unfortunately. Was going to try to offer readers something clear-cut, but we'll just have to watch the trends over the next few days and try to be more specific. It is probably going to be a lower-end threat around here, at least if there ends up being any chance of tornadoes. But we do have to respect those lower-end threats too. Our severe weather season lasts for about another week or so. Once we get into June, then we're into summer in terms of meteorology. So if this system does do anything on Sunday, that's probably our last chance at any really organized severe thunderstorms until about November. 

Unless we get a hurricane coming inland, but let's not even worry about that right now. It does look like an active season, but nobody knows where those things will form or track. And neither do the best computer models at this point. 

A lot of times on here, I'm trying things out, like I'll hear meteorologists complain about certain aspects of forecasting, and how they can be improved. And I'll play around with how to make them better or easier to understand on here. Sometimes it's very subtle things that people wouldn't notice. But on weather radio, not sure if it is still this way, but they used to make a distinction between the basic forecast for the next 2-3 days and then the extended outlook, where they would give fewer details, more of a general idea, like High in the upper 80's or whatever. And I'm still trying to balance that out with the TV model we've all gotten used to. And the 10-day outlooks are sort of a new thing that came up within the last 10-15 years on the broadcast side. Sometimes I try them, but usually the last three days don't turn out to be very accurate. Not doing it this time because of the unsettled pattern and some doubt about how fast the front will pass on Tuesday, if we do get a full cold frontal passage like the models are suggesting. Once we get into June, we don't see many of those. More believable for late May. 

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