2/16/08 FCST: TX/LA

[Paul Knightley]

After a chance of a few storms Friday, it looks like moisture return to TX could set up a decent shot at severe wx on Saturday.

Latest ECMWF suggesting ~1000J/Kg CAPE for southern/central parts of TX, with a deepening surface low ahead of approaching upper trough. Pretty good low-level shear in place, and adequate 0-6 shear for supercells.

Problem could be boundary layer moisture as cold front pushes through Friday night, and the moisture only looks set to return as surface low starts to develop/deepen through the day on Sat.

Thus big hail looks a pretty good bet, but tornado risk somewhat lower. From current ECMWF/GFS (and I know it's a long way out yet!), I would favour the Austin to Hearne area.

This is interesting from my point of view as I've just got hold of a couple of new ECMWF parameters, viz. CAPE and LI700hPa - the latter being the lifted index at 700hPa (as opposed to 500 hPa) - I think this will give me a better idea of lower-level instability, and the only parts of TX on Sat with a -ve LI at 700 hPa are in the Austin - Hearne area.

I should imagine Sunday could be a bigger day, for the SE states - different thread needed for that though.

 

[Paul Redmond]

Oh so promising for the desperate. Granted its still early in the season. It seems that central texas is pegged for a slight risk both friday and saterday.

One of the questions will be how much low level moisture will penetrate north and west. Looks like I will have to look into my chasing kit tonight, lest I be caught with my pants down. Will monitor further.

 

[Mikey Gribble]

I wouldn't be surprised to see southern Texas get a moderate risk. The setup for tornadoes is quite good given the time of year. I am moving into a new apartment tomorrow so I have very little time for forecasting. If it wasn't for moving tomorrow I would more than likely be heading for San Antonio. I would target a little further South than that though.
Everything looks pretty good for tornadoes, especially the strong 850mb winds. With that good of low level shear, good deep layer shear, respectable CAPE, and more discrete storms in southern Texas, I think that area is in for some tornadoes on Saturday afternoon. Once again I can't post a forecast now since I am crunched on time, but I will get one posted tomorrow night or Saturday morning on my blog http://loadedgunchasing.com/blog.html
Damnit I wish I could chase!

 

[Paul Knightley]

ECMWF generates areas of showers/thunderstorms tonight as the cold front slowly moves southwards, which is likely to spawn various outflow boundaries.

Best moisture will obviously be the further south you go, but both GFS and ECMWF take 60+F dewpoints towards the region east of DFW by 2100-0000, along with several hundred J/Kg of CAPE. With the deepening surface low in this region, I am interested in the chance of some low-topped type supercells to the east of DFW on Saturday afternoon/evening.

Other than that, I still like the Hearne area, perhaps a bit east of there...better 850 hPa flow here compared to areas further SW, and somewhat backed surface flow, along with some decent lower atmosphere instability should give a fairly good chance of tornadoes.

Actually, ECMWF is showing a pretty good shot at severe weather for the Houston area towards evening, with backed flow remaining there for some time. The main problem, of course, is trying to get storms to form in the backed flow of the warm sector...the cold front will probably squall out pretty quickly.

 

[Brian Emfinger]

The combination of the likelihood of severe storms (at least) and storm speeds that aren't too bad (well they are slower than everything Ive chased so far this year) make me very interested in chasing this. All the models I have glanced through show really nice backed winds with 0-3km Helicity of at least 300 and CAPE of as much as 2000. The main questions which the SPC addressed well is whether or not we can get storms to form out ahead of the front. Even if storms don't fire ahead of the line or can't form far enough out that they won't be engulfed by the line, at the worst there will be a severe line of storms. I am 80% going right now. If someone (from Oklahoma or Arkansas or can drive there) wants to come with I would definitely go if I had some cost-splitting but I will probably go regardless.

 

[Jim Bishop]

From interpretting the latest WRF model, I'd say a broken line of supercells is going to develop along the I-35 corridor early in the afternoon Saturday from Dallas south to I-10. Initially this line could be quite broken, with rather discrete supercells possibly. The backed surface winds and strong southerly 850mb jet will cause amazing low level hodraphs, supportive of tornadoes - some strong. This looks like it may be a big tornado day for the southeast third of Texas. Of course if the storms go straight to a squall line, the tornado threat will be significantly decreased.

My main concern would be how much warm air advection precip develops during the morning to midday along the 850mb jet. That will limit instability. But storms should fire along the front and race north-northeast. Of course any discrete storms that fire from warm advection alone and become surface based will pose a high tornado threat.

Not very long after the broken line forms it will fill into a massive full blown squall line with imbedded supercells. There will still be a tornado threat with this line as it races eastward through East Texas.

I don't like chasing in these areas, but it's close to home, so I'll give it my best. The road network stinks and the terrain only gets worse as you drive east.

 

[Mikey Gribble]

We might want to start a list of available nowcasters for tomorrow since this could be pretty sloppy and fast moving it is an ideal situation to have somebody helping out with nowcasting. I should be available if anybody needs any help. I haven't had time to do more than glance over the models this morning, but damn it looks good for a February chase. It is going to be extremely tough chasing with fast storm motions, crappy roads/terrain, and lots of convection, but I would still be chasing this for sure if I wasn't moving into my apartment today.

 

[Evan Stubbart]

Things are shaping up to look pretty good tomorrow. I think the best chance for a target area is going to be out of the Austin area. I will be in Houston on a family trip with our kids, but might have to see how things shape up for some family fun chasing. My guess is that by the time these storms reach the Houston area they will have turned into a squal line. Good luck to anyone going out and have a good road map handy as the road system sucks for chasing...

 

[Karen Politte]

At $3/gallon gas and in February - we'll be sitting this one out for sure. Of course if it were in my backyard I'd jump at the chance to get out and chase - but it's just too far and we're not even in March.

Like others though my main concern would be for the interference from day-long precip. and grunge over the target area from waa as advertised by the ETA-NAM and others. It looks to be an ongoing wet event for most of the day until the energy kicks out after 0Z and sends the whole mess rocketing east-northeast into the horrid chase terrain of the Arklatex/TXK area.

On paper this is a strong-looking southern U.S. system but it's for sure less than ideal in many ways, and I don't foresee anything photogenic enough happening to cause me to rush hundreds of miles on my weekend. Good luck to those who do chase, however, the road network and terrain is going to suck quite badly but it's not as bad as the Ozarks so maybe someone can pull a rabbit out of the hat.

KL

 

[Paul Redmond]

Looking at the postions of the front, I am wondering if this event maybe farther south than proged. I am most curious about the SPC predictions for severe weather in west texas today, when the front is clearly to the south and east. I understand that the front is pegged for a slow passage until late saterday. Are they expecting a backwards movement? That does not seem likely to me.

 

[Mitchell Daszewski]

I may or may not go out depending on how my schedule plays out, but I would target SAT and south. That's where the best destabalization will occur and actual CAPE with maybe a peak of sunshine before development occurs...if we're lucky. Anything north will be swampish with all the rain showers.

This reminds me of a similar event last year and I targeted too far north and the all the morning muck completely nixed the afternoon prefront development. I'd rather get south and stick with the higher CAPE.

 

[Matt Haworth]

Looking at the postions of the front, I am wondering if this event maybe farther south than proged. I am most curious about the SPC predictions for severe weather in west texas today, when the front is clearly to the south and east. I understand that the front is pegged for a slow passage until late saterday. Are they expecting a backwards movement? That does not seem likely to me.

I have been rather busy with school this week, so I haven't really had much time to forecast this event, but I was under the impression that the front was originally going to make it all the way to the coast, before retreating north as a warm front.

Some of the private mets here in Houston were forecasting it to make it close to Galveston tonight before backing up as a warm front tomorrow morning...actually, there are still a few that think the front will make it to Houston around midnight; however it looks like most of the cold air is sliding more south than east.

 

[Rich Thompson]

The outlook extends to W/NW TX to cover the threat for thunderstorms with hail. A flow of moisture from the south, above the shallow cool air, and steep mid level lapse rates should support instability based above about 850 mb. Given forecast wind profiles, you might even see an elevated supercell or two overnight.

Rich T.

 

[Bill Tabor]

Ah, so chilly outside in Austin right now - brrrrr. The front has passed and is south of us. It was certainly feeling more chase like earlier today as we were south of the warm front with decent humidity. Hard to imagine a revival tomorrow, but I suppose it is possible. I was under the impression that this is a fairly strong cold front. It will be interesting to see what the latest model run (coming out right now) has to say about this. I had my eye on Seguin, Tx earlier as a target but we'll see, the upper air dynamics last run I checked seem very strong. For tornadoes the lower level jet to 850mb seems impressive particularly if it stays backed around the low.

 

[Mikey Gribble]

I did some quick forecasting and I think I would be heading to La Grange tomorrow if I was chasing. I think that will be the northern end of where convection becomes more discrete. It will be easy to drop South on the storms tomorrow, but nearly impossible to catch them if they are already North of you and I took that into consideration with my target. I would probably drop a bit South of there, but that is a good starting point. It puts you far enough ahead of the boundary to have plenty of time to get into position once you see how storms are evolving, which is going to be key tomorrow IMO.

Not much to say that hasn't been said already. I really like the strong 850mb winds. Strong 1km SR winds (around 30kts), good 0-1km helicity, low LCL's, good deep layer shear, and respectable CAPE (especially for February) should create an environment favorable for tornadoes. I also think there will be the possibility of a few strong tornadoes. Crappy terrain/road networks, fast storm motions, questions with convective mode, and more questions with insolation obviosly make this a less than ideal setup. You can't ask for a whole lot in February though IMO. I can't chase tomorrow, but if I could I would. One more big worry is that historically these early season outbreak scenarios don't seem to come together as anticipated. What can you do though? Go chase and whatever happens happens. If I was forecasting at SPC I would stick with the moderate risk. Good luck to all chasing tomorrow. I didn't do much forecasting this afternoon. It was about a 30 minute job so you can probably ignore this post. I plan on doing my in-depth forecasting tomorrow. I have a little longer forecast on my blog if you're interested http://loadedgunchasing.com/blog.html
BTW I'm really looking forward to the WRF radar simulation coming out. If it has more discrete storms South of La Grange (which is what I'm thinking now), then it will greatly increase my confidence in a few good tornadoes tomorrow.