re: Let's Do It Again: Severe Threat 3/30 - Line of Severe Storms leaving SELA. AL in it now

Nick's post from Sunday afternoon... as we get closer to this potential event

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Meteorologist Nick Mikulas
This long paragraph is me explaining in very simple terms, what high resolution models are, and why they matter. Skip it if you just want the forecast.

Severe weather remains a good possibility, with only subtle differences showing up in models. Higher resolution model data is starting to trickle in, and will increase over the next few days. I always say high resolution models, and just now realize I’ve never really explained it. I hate when I do stuff like that. I’ll try and simplify. Models spit out a pretty picture to us, but they are run at different resolutions for different reasons. The regularly used GFS model runs out to 16 days, and runs on a grid space of around 27 kilometers for the first 7 of those 16 days. That means we are getting data in that first week that forecasts for points that are 27 kilometers apart, then the model generates a blend of that data that we see as different model parameters, like wind, precipitation, and temperature, at the surface, and many layers above the surface. The HRRR model runs on a 3 kilometer resolution, but only goes out 48 hours. The finer resolution allows us to see details that the GFS would never be able to resolve. The HRRR will actually forecast the evolution of individual thunderstorms, which is great for seeing what storm mode might be, or timing when a squall line will move through. So why don’t we just run all models on very fine resolutions, and completely solve the weather forecasting game? First off, there are always small errors in the initial data of a model. These might not cause a big problem 12 hours out, but that small error in data can cause big issues down the road. It also takes an incredible amount of computing power to run these models. We aren’t just looking at “will it rain?”. These models are forecasting a three dimensional picture of what the atmosphere will look like, and with global models like the GFS, that means a 3D representation of the entire world. It’s all connected, and fascinating, and I’m always amazed that these models can even hint at a big weather event 8-10 days out. I didn’t expect to rattle on that long. I’ll note that up top, in case you want me to shut up and tell you the weather.

There aren’t many differences from yesterday, though it seems models might be slowing things down by an hour or two. That doesn’t seem like a huge deal, but any slowing will allow a bit more instability as we warm up slowly on Wednesday. I think storms will evolve in a fairly similar fashion to what we saw last week, with a main line kind of gobbling up cells that form just ahead of the main line. It’s possible we get those isolated cells far enough ahead of the line to become individual supercells, but that’s a less likely scenario that one fairly solid line, with some cell mergers happening as the line engulfs those nearby storms. This will be a quick hitter, with most areas only seeing a couple hours of action between 10:00 AM and 4:00 PM. The earlier storms will be out west, with things crossing the Mississippi River around 4:00 PM. The quick motion of this system actually has me backing off a bit on rain totals. I’m thinking 1/2 to 2 inches, with isolated areas maybe seeing 3 inches. The main severe threat will be damaging wind, with 40-50 mph gusts widespread across the area. There should be scattered gusts in stronger storms in the 50-75 mph range, so there will be some limbs coming down, and at least some brief power outages. Tornadoes are also possible. I think the main chance will be quick moving, and perhaps brief tornadoes along that main line. Those are tough to warn, as they evolve quickly. Of course, if anything can take off ahead of the line, it would have a high severe potential. For now, I’m thinking the line is our main threat. Hail will be possible, but it’s a distant third as threats go from what I’m seeing now.

I’ll update things tomorrow, and probably do a video since I like talking about this stuff. For now, the threat is areawide, and you can see on the map I posted where SPC has the highest risk for severe weather. The avocado has evolved a bit, but it still looks like we are making guacamole on Wednesday.

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Nick's updated take from Monday morning

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Meteorologist Nick Mikulas
Another round of strong and severe thunderstorms is on the way for Wednesday. It’ll be a quick, but hard hit across the area. Here’s how I see things going.

SPC has a large part of the area in an enhanced, level 3 of 5 risk for Wednesday. They’ve also included most of the area in a 10% risk for significant severe weather. That means there is a 10% chance for greater than 75 mph wind gusts, or EF2+ tornadoes within a point. Significant severe can technically also include a risk for 2+ inch hail, but I don’t see that as a significant part of the threat this time. Some hail is possible, but getting hail that large will be pretty difficult. Once again, very strong wind shear will combine with adequate instability, and a strong upper level feature to produce a quick moving, and potentially intense round of severe weather across Central Louisiana.

It still looks like roughly 10:00 AM until 4:00 PM is prime time for severe weather in our area. The earlier threat will be along the Texas border, and it will exit across the Mississippi River in the afternoon. This should only last an 1-3 hours for most, with a quick 1/2 to 2 inches of rain likely. Our main threat will be damaging wind. The normally conservative GFS ensemble shows widespread 45-50 mph wind gusts across most of the area. The stronger storms will have no problem bringing 50-75 mph gusts, so there will very likely be at least some power outages. There will also be a threat for tornadoes. As usual, if we get storms to form, and stay ahead of the main line, those will have a higher threat for tornadoes. At this point, I think the line will continue to surge ahead and absorb those storms in our area, though it’s always possible that one takes hold, and causes big problems. As these cells merge with the line, we could see tornadoes spin up quickly, so you’ll want to monitor your area for warnings. I’ll do a live stream later today with the latest on this next round of severe weather.

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Makes sense they'd co-locate.

That line is gonna be salty. I do have some questions of tornado risk on the southern end since the line is a little more broken on some of the models. Still think its just too far south but worth watching.

Also, I expect half the posts in here Wednesday to be asking WTF is the wind all about. Gusts up to 40 even 50 seem reasonable ahead of the front.

ETA: The blog has over 1000 views in the last two weeks and 915 unique visitors. My data says most of that is coming from the posters and lurkers of Tigerdroppings. So all yall for the support.

Good luck Duke

Gumbo Weather - My Blog

oh shite man - whats the blog address and ill got check it out too

Flying to DEN out of MSY early Wednesday morning and have to be there by the evening. Am I screwed and looking at some delays here?

Delays probably but wont be an all day thing. Just might get in a little later than expected.

Reasonable enough, though 50 mph gusts is probably the ceiling and would expect most of the hourly highs to be near 40.

Wind is gonna be blowing Wednesday.

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I can only imagine the turbulence for people flying on Wednesday

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Oh yeah, and landing/taking off is going to be big fun too. MSY at least has a N/S runway.