Wednesday, March 22, 2023

Warming Up, Stormy Friday Night

Today (High 69): Partly to mostly cloudy, a little breezy at times. Widely scattered showers are possible throughout the day. 

Thursday (High 80, Low 54): Partly to mostly sunny. Breezy.

Friday (High 81, Low 62): Quite breezy with increasing clouds and isolated showers and thunderstorms possible during the day. Thunderstorms are likely late at night, and some of those may become severe. 

Saturday (High 79, Low 61): Mostly sunny.

Sunday (High 76, Low 50): Partly cloudy with a 30% chance of showers and thunderstorms.

Monday (High 73, Low 59): Thunderstorms likely.

Tuesday (High 67, Low 53): Mostly sunny with a 20% chance of lingering showers. 

At 11:15 PM it is mostly clear tonight in Cullman, but we do have a few clouds, bringing the visibility down to 8 miles for now. The temperature is 54 degrees. The dewpoint is 30, making the relative humidity 41%. Winds are from the South at 9 miles per hour, gusting to 16 mph at times. The barometric pressure is 30.25 inches and holding steady. It was breezy with partly to mostly sunny skies overall today, a High of 63 and a Low of 30. Jasper saw a High of 64 and a Low of 28 today. Haleyville saw a High of 61 and a Low of 29. 


And we actually have some showers moving through the region now. Looks like it is one of those cases where I owe the American GFS model an apology for my usual flippancy about its output. Looks like it picked up on this rain a couple days ago before any other models were very much. Though I think the timing was more for Wednesday. This time of year is very active, as most of us know. We just got through the Spring equinox, so whether you go by meteorology or astronomy now, it is springtime. 


Noticed some lightning earlier West of Memphis, around the Arkansas/Tennessee/Mississippi state line. 


Our upper-level wind flow is more-or-less zonal from the West for now, and I think I made a mistake the other day in emphasizing the southwesterly component to the 500 millibar winds. Was reading back over that. They won't really turn to the Southwest in any meaningful way until the next day or two, ahead of our next storm system Friday. 
 



So we've got rain going on through a lot of the Ohio River Valley and Midwest. Got some thunderstorms in the mix for mainly Missouri, Eastern Arkansas, Western Tennessee, Northern Mississippi. They've got snow back in the Rockies and points West, also up in the Dakotas and the Great Lakes region. Things are pretty active over most the country. Even the Desert Southwest is having some rain. 

The main frontal system is going to move into our region over the next three days. But like a lot of times, especially this time of year, it is not all cut-and-dried. Our weather will be bit of a mix of things. So let's get into details after looking at those broad brushstrokes. 

Tomorrow will feature some rain chances after all. And as mentioned above, some of it arrived early tonight. The GFS picked up on this a couple days ago, or could have been more like three days ago. I remember dismissing it as a wild goose chase, and I have to remember, that model did finally get an upgrade in recent years. Need to start showing it more respect. It used to really come up with some doosies from time to time. One forecaster told me that even though it technically stood for Global Forecast System, some of them came up with other nicknames for it when it messed up their forecasts. And I came to agree with that over a long period of time. I've noticed some improvement after the upgrade. 

Looks like the rain today will be (Wednesday I mean, we are after midnight now, I can be slow at putting these things together sometimes) widely scattered and that we'll be partly to mostly cloudy, light to moderate winds, not as breezy as Tuesday probably. Winds from the South. High getting up to about 68 or 69. 

By Thursday it looks like we'll be dry again, this initial trough will have done its thing, and we'll be warming up ahead of Friday's system. Which will affect the Great Plains on Thursday, bringing a chance of severe weather, and more of a risk for some flash flooding issues up into parts of the Midwest and Ohio Valley. 

We'll see a High near 80, Low about 53 or 54. We'll have a pretty good southerly breeze again. Should see more sunshine than clouds overall.


Then on Friday is when it gets interesting. Synoptically this looks like a fairly impressive setup for some organized severe weather potential. But of course it is the mesoscale features that will determine the details. We're just getting into the window where we can start to look at those, over the next day. But the position of this front and Low pressure system are favorable for severe storms around here. 



Now the GFS has started to show the Low going well up into the Midwest, maybe even the Great Lakes region. And this has started to look more like a late Friday night event too, by all models. This position of the Low would lessen our severe weather threat some with better wind fields and forcing staying to our North. 


And it's worth noticing that the ECMWF is in reasonable agreement with the positioning. 


Those are global models. The mesoscale model for North America (NAM) shows a much more favorable position of the Low to support severe weather around here on Friday night. Actually all these graphics I am showing of these models are valid for 1 AM Friday morning. Since we are on Daylight time now. The UTC or Greenwich Mean Time of 06 hours translates to 1 AM CDT. 

I am paying attention to this, but also have to consider that it is 78 hours out. And for a mesoscale model, even something as reliable as the NAM sometimes is, that's pretty far out there, since it is only working with data from North America. It is zeroed in on local conditions. So it is better for up to 72 hours out or less. The global models tend to be more reliable for the longer-range. And here this event is right on the borderline of the time period the mesoscale or global models are better at. 

We'll see a High near 80 again (so the air may still be soupy late at night), morning Low near 60 or so. Looks like a breezy day with increasing clouds. Might see an isolated shower or two somewhere on the map, but more likely the rain will hold off into late Friday night into early Saturday morning. And we'll probably see some thunderstorms in the mix, some of which could become severe. 




And this mainly looks like a typical squall line event. This is the NAM I'm showing, but I checked it against the GFS and ECMWF to see if they were projecting anything that looked a lot different. Looked about the same to me. 



The NAM is showing a decent combination of instability and wind shear (two of the ingredients we need for severe storms - third ingredient is the lift associated with the cold front moving in) over Mississippi and then moving into Alabama during the pre-dawn hours on Saturday. So this is very late Friday night into wee hours of Saturday morning, this potential. 


Forecast sounding from roughly around Blountsville shows what is sort of unusual for spring time, unstable air really struggling to even reach the baseline of 500 j/kg of CAPE and unusually high wind shear values of more than 400 m2/s2 of helicity, rotation as you go down in the atmosphere. The significant tornado parameter is about 1-2. This feels more like an event where we are still in the cold season. 

So let's look at the SREF.




It is showing the same basic ideas, but is a little more conservative than the NAM. And this is typical, another model bias. A lot of times when the NAM looks a little too aggressive in warning of danger, I'll go to the SREF, the in-house model for the Storm Prediction Center, to see if it is quite as alarming. And usually it doesn't show things looking quite as bad. Neither one of them shows a really big severe weather threat here, but they are both showing some. The SREF sells it a little calmer, but the output is not that much different. Which makes me more confident in believing it. 

Especially considering that the GFS and ECMWF agree on bringing the Low further to our North than the NAM is showing. This looks like a situation where things may be out of phase, out of sync, to bring together a full-blown severe weather outbreak. 

The CAPE values are staying below 500 joules on the SREF data. And the helicity at the lowest level of the atmosphere is about 200 units or greater. That is weak instability, maybe not enough to work with, which would fit with this coming through at night and being mainly a big squall line of storms (rather than a lot of supercells getting going ahead of a line). That is strong wind shear though, and the kind that would particularly favor tornadoes developing if the other ingredients were coming together right. So again, I am humbled from some of the stuff I said the other day. I thought the wind shear would decide this, but now it looks like due to the timing and a few nitpicky factors, the instability may be what is lacking to make this a more significant severe weather event. 

This looks most likely to be an overnight thing, mainly between Midnight and Daybreak on Saturday actually, where we'll have a squall line of severe thunderstorms moving through. The main threat is just thunderstorms with strong enough winds to be considered severe (that's 50 knots or more - at least 58 mph). Probably will not be every storm in the line, but some of them may go severe. Could also have some hail, but with such weak instability, that threat is pretty low, for any really large hail. And even though the chance is looking on the lower end, there is some chance of isolated tornadoes along this line or embedded within the line. And remember, we are getting into the core of our usual tornado season. This looks more like something we'd see in November or one of our cold-season severe events, but this time of year, it can pay to play it safe rather than sorry. Especially because any time something is coming during the dark hours, it is more dangerous. The idea of weather radio has still not caught on all that much, and a lot of people don't like waking up at 3 AM for something like a flash flood warning (that includes me). So a lot of people are not aware of severe storms that happen at night, or a lot of times, they just don't care, thinking it'll never hit them. 

Some of the analog events that were showing up over the last few days, similar setups in the past, were fairly significant outbreaks of severe weather, if not for our region, at least for places close to us, like more in the Mississippi into Ohio Valley. One that has kept showing up a lot as an analog was the Super Tuesday outbreak of 2008. That happened in February. We only got grazed by it in the Tennessee Valley, but we still had two F-4 tornadoes that night. I believe one was in Northeast Alabama, way ahead of where the main action was expected to be. Now these parameters do not support that sort of an event. And most of the analogs show a more general or low-end severe wind/isolated tornado threat event. But I do pay attention when things like that show up. It is a reminder that if one or two ingredients change just a little bit, those mesoscale features, then the severe weather threat can be enhanced. Right now it is looking more likely that this will be a routine or even lower-end severe weather threat. It seems like we've had a lot of these dicey/borderline setups lately, even after getting into the month of March. A lot of times the Spring events are more clear-cut. 

Or maybe that's selective memory on my part. There are so many severe weather threats in the spring season, many of which do not play out, or don't do as much as expected. Maybe we should be grateful for these more messy setups, because a lot of times, the ones that are easier to predict end up doing a lot more damage and upheaval in people's lives. 

For now I'm going to post the most recent SPC outlook which has trimmed back the basic 15% severe thunderstorm outlook to mainly Northwest Alabama. A couple days ago, they had all of the Tennessee Valley included. And I suspect in another hour, when the new Day 3 Outlook comes out, they'll have all of us included again. The local Birmingham office does their own outlooks, as several local offices do across the country. And they've gone ahead and included all counties from West to East in a severe weather risk. I agree with that. 


So this outlook is really outdated, but it'll probably be another hour (it's 1:35 AM now) before they issue the new one. This is what we've got for now. Just be aware that there will probably be a basic or at least low-end risk for severe storms over all of North Alabama and Southern Middle Tennessee by the next outlook. If any area ends up being enhanced, I'd expect it to include North and Central Mississippi. Looking at some of the forecast soundings there, it was more unstable and more favorable for tornadoes to develop. Most likely we will see that basic 15% risk. If you see a "slight" level 2 out of 5 risk, same thing. The jargon confuses the general public sometimes. If you do get confused, pay attention to the percentages, and you can use common sense from there and figure it out. 


Saturday after we get some daylight, looks like this will clear out pretty quickly. Does not look like temperatures cool down much behind this front though, Low near 60 again, High in upper 70's, maybe not quite making 80 again despite mostly sunny skies. It'll probably be a breezy day as it usually is behind a front. 

By the way, one reason I slow-poked my way through gathering data and writing all this up, so much rambling, is that I was hoping I could time it right to get the new SPC outlook for Friday/Friday night before I was done. I misjudged the timing. I'm still thinking like we're on standard time. I guess I'll post that separately or as a footnote at the bottom of this post later. 


Warm front will start to move northeast back through the area on Sunday. Looks like a High in 70's, Low near 50, rain during day probably staying scattered, and then becoming likely Sunday night into Monday. 


Monday may get stormy again. Looks like a High in lower 70's and Low in upper 50's. Usually it is best to take these severe thunderstorm potentials one at a time. The atmosphere after the first one can affect how the next one sets up. But it won't hurt to take a peek. 


Right now the GFS guidance makes it look like a marginal threat, and another overnight one in the wee hours of Monday morning. Interesting. 

Take that with a grain of salt. It's so far out, and with another storm system we haven't gotten out of the way yet, this is only speculating for fun. 

And you do have to keep an eye on every system this time of the year. 


Then next Tuesday, we might have a lingering shower or two, but for the most part I think skies will be clearing. Probably see a High in upper 60's and Low of 50 or so. 



We may see up to 2-3 inches of average rainfall totals over the next seven days. And the WPC does have most of us outlooked for a marginal risk of some flash flooding, about a 5% risk. And then for Northwest Alabama up into Tennessee, it's more of a basic 15% risk. 

Remember that if you get a severe thunderstorm or tornado warning on Friday night/Saturday morning, you need to be able to get into a small central room (or hallway) on the lowest floor of a sturdy house, away from any windows. It's best if you get there within five minutes of getting the warning, because tornadoes within a squall line tend to happen quickly, and actually so can instances of damaging winds. At night it is a little more challenging to issue those warnings, because forecasters are mostly relying on radar. If you can get good reports at night, sometimes they are delayed, even in the social media age. And they can be hard to sort out even if you get them. So if you do get a warning, please take it seriously, and encourage other people to. And then if you live in a mobile home, try to have a plan ahead of time. It's ideal if you can go stay with a trusted friend or family member who lives in a sturdier house or maybe even something like an apartment on the ground floor (not on the top floor - people there need a plan to get down lower too, before the storms get to them). But I know that things are often not ideal. So I'm just encouraging you to do the best you can. And if it puts a lot of wear on your nerves, try to take a deep breath and remember that most people survive even the really bad severe weather events by taking a few of the basic precautions. And frankly, a lot of the absolute idiots who take stupid chances and drive recklessly trying to catch video of tornadoes, also usually survive and get to post their antics online for other people to lap up. So that's my sarcastic way of trying to say something a bit gentler, like . . . try not to let it worry you too much. If you care enough to read something like this and think out a safety plan, you are more than likely going to be just fine, even whenever we have our next really bad severe weather day. 

And with all that stuff I just said, have to remember too, even if it's a lower-end threat, if the one tornado all night happens to come down your block, that's a big deal to you, even if the damage is rated as only average or relatively weak. I've seen a couple of tornadoes that were rated F-1, and they did not look weak in person. The second time I had that happen was actually on April 27, 2011. A lot of students and janitors stayed watching the tornado behind the trees until it got too close to us, and then they yelled and literally ran to the basement. It was kind of funny, but I could see where they were coming from. I got to the basement myself. Probably should have already been there, but it didn't look like we were in immediate danger. It was during the midday round that only affected a small part of North Alabama. Any tornado is rough to go through, and even damaging thunderstorm winds or the really bad gradient winds like we had a few weeks ago are rough to go through. The chances of being hit by the worst damage of any storm are low, but it is still good to have your precautions worked out ahead of time just in case you do draw the short straw, you know, you want to stay as safe as you can, and protect people around you. 

Tuesday (it is technically Wednesday now) was the anniversary of a similar event to 1974 or 2011, a tornado outbreak that happened in 1932. And on the latest episode of Weatherbrains, James Spann shared a link to J.B. Elliott's writeup about that event. He had some family members who were old enough to remember it. There were not very good weather records then, and people basically had to watch the skies and other simple signs, no technology to depend on like we have now. This was a terrible event where a lot of people died. But one thing I'll say that was better back then, was that more people had access to shelter. I remember stories from 1974 where people waited for hours hearing about tornadoes in Mississippi, they'd invite people to their storm pits and wait and watch the sky together. They did not have Doppler or Dual-Pol Radar, but they had a lot more common sense than I feel like most people have these days. And that included helping each other out when they did know that something was coming. One of my worst memories of 2011 was seeing a video of some guys amateur-chasing in Tuscaloosa and nearly getting rolled by that tornado, backing up on what I think was an interstate in a panic after they got too close. And I know of two guys personally who went sight-seeing after the morning Cordova tornado, and nearly got rolled by the stronger tornado in the afternoon. The morning one was rated F-3 (or EF-3 if I'm being proper and modern) and the afternoon tornado was rated F-4. Almost no chance of surviving that in a vehicle. So to put it bluntly, I think a lot of people are idiots now compared to in 1974 or 1932. It's a shame that better technology has not always been accompanied by greater wisdom. Sometimes it almost feels like there is an inverse relationship going on there. 

We can tend to see the past (especially if it was before our time) through rose-colored glasses though. I remember during the 1974 outbreak (which mainly happened at night), a woman called up J.B. at the National Weather Service and offered to say a prayer with him. He was all right with that, but it soon became clear that she was not offering a good-natured prayer, but a passive-aggressive prayer that he would be forgiven for keeping people bothered at night with all the tornado warnings. So the way I remember him telling it, he was overworked and just told her that if she didn't get off the phone, he was going to use his super-powered radar to send the meanest storm right for her house. And she hung up. 

And it looks like my aimless rambling has paid off, in that I'll be able to post the new Storm Prediction Center outlook for Friday at the bottom here after all. It comes out in about 15 minutes. 

While we're waiting, I'll mention that the National Weather Service in Nashville is doing Weather101 classes again. The first one is this Thursday evening and is about upper-air balloons and how their data is used to plot weather maps and feed into the computer models so we can have way, way better forecasts. I wish we had more of those balloons, but you know how budgeting is. Most of it gets wasted on things that are pretty much meaningless, and the important stuff gets ignored. We need more radar too, especially around here. There is one really dead zone, afraid I'll say the wrong thing since I'm sleepy, but think it's down around Demopolis, they desperately need to put another radar site down there whenever anyone can find it in their hearts to fit that into some sort of budget. I'm guessing that probably won't happen until a tornado gets missed in that general area and kills someone. We're lucky around here to have a radar down at the Shelby County Airport, one at Hytop in Northeast Alabama, and another one at Columbus Airforce Base. Not to mention the one in Nashville. There are a few rough zones, but for the most part, we can tell what storms are doing around here. But you only have to go as far as South/Central Alabama to find a real problem in lack of radar data. And I wish we had more balloon launches across the country, around the world really. That UAH SWIRLL team has been really good about trying to get more data in Huntsville or when they go out chasing. I think Kevin Knupp is in charge of that. Glad to see that, just like I'm glad to see Nashville doing these classes. 

They might help me get back into studying this. I still have a few books on meteorology scattered in the shelves. Some I've never finished reading. It was awesome to get to take actual classes on it at one time. One class I had on severe weather, there were only three of us. So there was a lot of time for discussion and understanding things. 

While I continue to wait on the new outlook, I see that places like Sacramento and Oakland, California are dealing with large hail and enough of a windstorm to cause some power outages. 



About as expected, we are all in a basic 15% risk of severe weather in the Tennessee Valley for Friday night. Earlier in the day, storms will initially get going as supercell thunderstorms focused mainly over Louisiana, Southern Arkansas, and into about the Western two-thirds of Mississippi. As the dark hours get going and the storms move further east, they are expected to form into a line before moving into our neck of the woods. Damaging winds are expected to be the main threat around here, but isolated tornadoes may still be embedded within the squall line. Now back in that enhanced area, or where you see the hatching, where the supercell thunderstorms are expected to initially get going, the tornado threat is substantial, much higher than it is expected to be around here. And they may see some really large hail like you can get in some of those storms too. It looks like we will probably get a leftover squall line out of this event, but that is still dangerous happening at night if people don't know what is going on or do not take any precautions. So here was my long-winded heads up about it. Just in case we have some problems somewhere. Most of our severe weather threats are going to be these routine basic level threats. They should be respected as well as the major outbreaks that happen less often. 

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