Severe Weather Threat Discussion - 3/3/2020 - 3/5/2020

It’s very warm here this morning in Thibodaux, 73 degrees. And overcast.

yeah, feels like a spring morning...and my goodness it's muggy LOL

On any severe weather day, it's a good idea to get an idea of what's actually in place to start with. 

Surface:



I assume this image will update all day but this write up is for 12z. So obvious front is obvious looking at the surface obs. Wind out of the south below it, north (and weak) above. Low in central Texas will want to ride that boundary, as it gets it's power from feeding on temperature gradients. You can see this to be true with that second 1000 mb low sitting along the boundary near Atmore, AL. 

We need to watch how the front progresses today. Now where's the rain?


So comparing to the surface analysis we have an little squall riding the cold front on the south side of the low pressure system. Then the bulk of the rain would appear to be riding the isentropic lift train with warm gulf air riding over the front. South of the front, the marine layer is keeping a lid on it with no forcing mechanism close by. You can see how that might change later with both some sunlight getting through and warming the surface and the rain near Mobile thanks to a little help from that lead surface low nearby. 

The elevated showers near and north of the cold front have shown severe potential this morning, with some mesocyclones near our Texas low pressure and McDonald's sauce packet sized hail in Mississippi. 

So now, let's take a look at the upper air plots from the SPC. 



Upper low centered near big bend. Surface low in it's traditional position to the east of the upper low, feeding on that increasing vorticity advection. This upper low will progress east as the day goes along, moving the lifty dynamics along with it. 



Got us an upper jet streak rolling from Mexico to southern Texas and into north Louisiana, Mississippi, and Alabama. Look at all the upper divergence where all the rain is currently falling. Also, I'd call that the right entrance region, wouldn't you? Not a clean strong jet streak, but it's there. 



At 850 mb, you can see how the rain is lining up roughly with where the dew point gradient gets tight. You know, it's all getting squeezed out up there. 

Who wants more!? I'm sure the answer is nobody, but I'm doing it anyway. Deal with it. It's sounding time.

Shreveport:



Obvious frontal passage is obvious. Plenty of shear from the surface up to 700 mb, with all of it situated about 850-700 mb. Plenty enough for elevated rotations with some storms. Lapse rates over 6.5 C/km from 700 up above 500 mb and that's where the instability is. So hail potential is there. 

Slidell:



That's freakin' juicy. Kind of surprised at what's available already to be honest. 

Inversion at 850 mb noted to keep the cap on for a while. SRH from surface to 1 km a healthy 170 and even greater as we get up to about 700 mb. Absolutely could see surface based convection pop off with that temperature profile and there's plenty of spin to work with. The other thing that jumps out is the lapse rates. 7.4 C/km in the 700-500 range, and maxing out at 8.8 as it pushes up into the freezing level. So definitely need to watch for hail today because the uppers will cool some more as the upper low approaches the region. Some of it could be pretty big for this part of the world. Also enough a dry gap above 850 mb to bring down some stronger winds. 

Atmosphere has a lot of potential, but how our cap breaks (if it does) and convective interference can and probably will limit how many storms will fully take advantage of what's here. This is the story for the warm sector.

That's the right now. Next post, I'll look at the CAMs and how the front is projected to move as the day goes along and get the LIX discussion involved as well. 

Cold pool from the rain would appear to drive the frontal boundary south through the morning. That boundary will be the focus for the northshore. Lots of shear, not a lot of surface based potential for the I-12 crowd. Looking at the sounding for this morning though, it's obvious why the warm sector concern is there for us southshore and cajun people down by the coast. 

To note the difference, let's pull up the NAM soundings for noon today from the 12z run. 



New Orleans. That inversion hangs around on all the CAMs and they don't produce much in the way of storms in the danger area but damn if that isn't pretty loaded for trouble. 



Northshore. Boundary pushes through, totally cutting off surface based storms. A lot of twist to work with and stronger mid level winds there too. There is severe potential there but those storms will almost certainly be elevated. Don't discount that boundary though for a focus for some short lived severe storms today. 

So keep watching the surface analysis for front position and keep an ear out for warnings, especially south of I-10 this afternoon. 

If I'm reading Zack's latest FB post, correctly, today won't amount to much of anything for us in the BR area, which bums me out.

Not much of a warm nose left to hold convection back but also gotta say the little cells starting to pop aren't exactly impressive. Echo tops not showing much in the way of billowing cloud tops. 



Also in agreement with low tops. All of the convection is north of the surface boundary. So far, so good. Risk comes later in the afternoon for most though, so not sleeping on it yet. 





Yeah, so lots of potential but mostly lacking a spark to this point.