2017-04-02 EVENT: TX/LA

[Ben Holcomb]

SPC has gone with an Enhanced risk on Sunday with some pretty good parameters in place for a gulf coast severe weather event. NAM is showing upwards of 4000-5000 MLCAPE and dewpoints well into the 70s across E TX and Louisiana, although I'll be interested to see if any of that actually is realized/verified.

It seems like an early wave may kick off storms earlier in the afternoon, but the atmosphere still seems supportive of severe weather. Timing issues like Saturday, but this seems like the better chance at something big.

As usual, the terrain there is terrible, so I am still on the fence of chasing this one.

 

[Ethan Schisler]

I'm watching this one for a potential chase as well. I haven't had a lot of time to delve into this one, however the 12km NAM seems to be less aggressive with morning convection, at least further south. This allows a favorable CAPE/shear environment setting up over a large chunk of Eastern Texas into Louisiana. Awful terrain as OP mentioned, so if could see this shift west, it could be more favorable from a chasing standpoint. If you look at the 3km NAM though, it allows morning convection to form into a vigorous MCS and wipes the environment out almost to the gulf coast. Which one is going to be correct? We won't be able to hone in on that until probably this time tomorrow or maybe even later. A similar scenario existed on the models for last Tuesday in the Panhandle as to how aggressive morning convection was going to be. If we don't have to deal with a lot of aggressive convection in the AM hours, the setup would definitely favor something big occurring somewhere in Eastern Texas and perhaps Louisiana.

 

[Matt Hunt]

In spite of the terrible terrain in East Texas, things are shaping up for a significant event tomorrow morning/afternoon. A very moist and unstable warm sector will be present with dewpoints hitting 70° in SE TX by lunch time. It seems like every sounding I pull is a "PDS Tornado" with a large clockwise curved hodograph, and SRH >300. I may do more spotting than chasing, given the terrain, and just drop down I-45, following down the line of storms. Wouldn't be surprised at all if there are a couple significant tornadoes tomorrow.

 

[Andy Wehrle]

I dunno, seems like the GFS and NAM soundings across the area of greatest instability in Texas have an awful lot of veer-back. Instability drops off (although it remains strong, especially for early April) east into LA as wind profiles and hodographs get much more impressive.

 

[Ethan Schisler]

I plan on chasing tomorrow in Eastern Texas myself. I'll probably be leaving Illinois within a few hours. I have two potential target areas defined for tomorrow. Its not going to be an easy chase with a lot of storms going up in the warm sector. However potential moisture/instability/shear are quite significant for the first week of April in this region. A quick look at most of the guidance shows potential for at least 3000 J/KG of MLCAPE to develop across Eastern Texas into Louisiana by late morning into afternoon. This is in conjuction with at least 300 m2/s2 of ESRH that should develop over a large portion of the warm sector. Even higher amounts are being shown closer to the warm front in the northern edge of the target area. Any storms that can take advantage of this parameter overlap could produce strong tornadoes given the right storm mode. So going back to what I said earlier about target areas, I have 2 in mind.....


1) College Station to Houston, TX area. I like this area along the southern edge of any morning convection where discrete supercells could potentially develop and foster in the high instability/shear environment. While the low level shear this far south isn't going to be as great as further north along the warm front, lapse rates are around ~8C/KM which is pretty good and I think this would be the best shot of anything "photogenic" if that is what you're after. Oh and storms will be firing by mid to late morning as well and probably already be surface based ready to produce tornadoes, so no sleeping in.

2) TX/LA border....potentially as far north as the AR border. This will be the area along the warm front further east that I think could also see a shot at significant tornadic supercells, perhaps later in the day. This may be the target I'm more apt to go after driving from Illinois. I've been looking at both the 12km NAM and the HRW-WRF and its showing quite a bit of semi-discrete (intiially) convection developing in this regime (particularly the later model). The problem is, after a couple hours, storms will have the tendency to congeal into a damaging MCS as it pushes eastward.

On a final note, this setup kind of reminds me of April 26, 2011 in much of the same area. I don't think the outcome will be nearly the same, especially the very significant overnight event, however I could definitely see a few strong/potentially longer lived tornadoes tomorrow if storms can take advantage of this somewhat rare CAPE/shear overlap region. Its going to be a very difficult chase....normally I wouldn't chase something like this, but I think its worth giving a shot, given how things look at the moment. Its one of those setups, either you stay home and regret going and miss something huge or you go and nothing happens and you regret going lol. Gotta love storm chasing!

EDIT: I should also note my target choices is based completely off meteorology and not so much as terrain, I know the terrain further east is.....well it sucks lets face it....but based on meteorological data, this is how I would play it right now, so just a disclaimer here

 

[KenMcWatters]

I used to live in Houston and drive to College Station a lot. Here's an important tip about the terrain:

Avoid the East Texas piney woods if at all possible! They are south and east of a line from roughly Hempstead north to College Station to Huntsville to Tyler. You go from relatively open terrain to the west of that line, to 100 ft tall pine forests with a few breaks here and there.

Most of the Houston metro is south of those woods, along the coastal plain. If I were chasing tomorrow I would start somewhere west of Houston and work eastward toward Houston or northward toward College Station. Because it's a Sunday, traffic won't be too congested if you end up in Houston as long as you stay on the main highways. Good luck!

 

[Manuel Salgado]

My plan is currently to make a decision rather early about whether to ride the WF north as it passes me here in College Station or play the arm sector. I will likely do whatever keeps me west of I45 as the trees once you start going east of that area are far too thick to see anything - especially a relatively low LCL base.

The HRRRx has been consistent with firing off some warm sector super cells right around College Station. That would likely be the best case for me. As great as the parameters might be further east of here, I am not confident about being able to safely chase within the piney woods. I'm not really keen on heading SE too far as the traffic in the Houston Metro an be wildly unpredictable and thick at times. Terrain is likely the most important factor for me on this chase.

 

[Jeff Duda]

Man, the 00Z soundings from deep south Texas show some serious low level moisture content (mean mixing ratios of 14-16 g/kg) . The upstream soundings have PBLs about 200 mb thick, so we should expect to see some pretty decent lapse rates in the region tomorrow. I have no doubts some serious CAPE will materialize...

IF

...tonight's convection doesn't expand into a large MCS that moves slowly enough to wipe out the moisture through morning or early afternoon. Granted, the area is so close to a rich moisture source that even if the moisture does get scoured, it doesn't have far to go to be replenished. However, clouds could still limit destabilization.

I've only taken a deep look at the afternoon model runs. Other than what I commented on above, my only remaining concern keeping this from becoming a severe weather/tornado outbreak is storm mode. The main surface forcing appears to be a cold front, as the models don't seem to want to fire off a ton of convection along the warm front (probably because there isn't a ton of focused convergence at the front...the wind shift is pretty gradual). Mid-level flow is parallel to the front, so I'm wondering if things are going to go linear pretty quickly along the front. If we can get some discrete storms, especially if they're out ahead of the front, then there certainly appears to be well more than sufficient instability and shear (both deep and low-level) to get some long-tracked supercells and significant tornadoes. But, getting discrete storms seems to be the major term of uncertainty here.

 

[Troy Scheiber]

http://its.txdot.gov/ITS_WEB/FrontEnd/default.html?r=BRY&p=Bryan&t=map

For chasers today, good luck and be safe. Rare early afternoon setup in south eastern Texas to bring large hail - forecasts are for 3-6" diameter. Large instability with 3k of cape should be interesting. Wanted to share the Texas DOT site at the top of this post. It will give you road conditions, stationary camera feeds on the highways, construction closures. Extras you don't have with your GPS, Atlas.

Troy


Sent from my iPhone using Stormtrack

 

[Jeff Duda]

I know it's still a little early and we have a tornadic supercell in progress across LA at the moment, but this event feels like a high risk bust to me. As I mentioned in my previous post, the storm mode has really not allowed for a lot in the way of tornadoes. I'm sure there will be a few sig tors today (we may have already had one), but this doesn't look anywhere close to a widespread outbreak with multiple tornadic supercells or significant long track tornadoes or anything like that. The western portion of the current high risk is already behind the now squall line crossing into LA, and the atmosphere is definitely overturned basically in all of TX except for the immediate Gulf coast portion. I think as this line continues to plow east across LA it will certainly clear out the rest of the air mass for the day. Unless there is significant discrete cellular development ahead of it, which at this point will have to be in eastern LA or into MS, I don't see too many more tornado miles coming out of this (i.e., I suspect this event will be dominated by spin-ups along the leading edge of the squall line).

It will be interesting to see what SPC does with the 20Z update.