03/21/05 FCST: OK/TX/MO/AR/LA

[Melissa Moon]

I'm looking at the ETA right now. I'm sure this all will have changed by the time anyone reads this with new model runs..

I really haven't been following this event too well because I've been busy this weekend, but right now I am looking at the 48 hr runs (valid 0z Tues). I'm not sure what I like best right now. There are much higher CAPE and LI values in Texas, but I think that the high values in Texas may be a little overbearing, which may do more harm than good. The helicities improve farther east (the CAPE is okay, but not the greatest), and the dewpoint depression decreases farther east into Louisiana (the temp are higher in Texas, but the dewpoint stays close to constant from E Texas into LA). My favorite place as far as wind shear goes is NW Louisiana. Too hard to pick a spot right now, but I think that I like the Louisiana area (think Shreveport) the best based on the ETA. Glancing 6 hours ahead, it looks like this event could very well go into the night too. I think Eastern LA and Western MS up into SE Arkansas has a shot of having some extreme weather at night.

Looking at the GFS...the surface low looks to be right over Wichita in this run, or close to it as aforementioned. Both the GFS and the ETA seem to be consistent with having good winds in far NE Texas into NW LA and into S Ark. One noteworthy thing is that in the latest GFS, the Lifting Indexes at oz Tuesday in places like Louisiana and Arkansas are positive, whereas the ETA predicts them to be between -2 and -4. It only shifts east enough to cover not even half of Louisiana by 6z. Just an interesting observation...

It's only 10:50 PM here, so I think I will stay up a bit later to get a comparative glimpse of the new run coming out soon. I see a possibility of this being a big day, but I am not sold on it yet.

 

[George Tincher]

I can't be out there tomorrow, so I hope you don't mind if I post my current cyberchase target and assessment here.

Based on the latest data (probably dated data by the time this is posted....lol), I have narrowed down 2 potential target areas: Durant, OK and Hugo, OK (depending on whether the next runs keep this system the same or slow it down just a tad. I'm not sure what this terrain is like, but I like this area as having the best chance for tornadic supercells. Also, being I am not yet convinced how far N the WF is going to make it, I'd prefer to stay near the Red River. From Hugo and Durant, you could easily adjust N, S, E or W as well as get across the river into TX if need be. I like all of those options.

Looking at the latest NAM (which I am favoring over the GFS), there's a nice 40-50 knot LLJ punching in right over my target. I am thinking the ETA may be a little too conservative with moisture. But even so, I'll stick with staying near the Red River just in case. At any rate, I would want to position as close as I could to where the best combo of helicity and instability exists, so for now I will stick with Durant or Hugo, OK (leaning more toward Hugo). Helicity approaches 500 m2/s2 over SERN OK by 18z and adequate (though not dramatic) CAPE will be in place.

If there's one concern I have with this setup, it would be the strength of the forcing. Considering the shear to CAPE ratio, I'm a bit worried this stuff may congeal into a line too quickly. But if slightly higher CAPE can be realized, then this could get very, very interesting....and may anyway. I guess as so often happens, much will depend on ongoing precip, clouds, boundaries and other factors we won't have a handle on until tomorrow.

But I have a gut feeling the main show will occur during the evening and overnight across SRN AR, LA, and MS. This could get rather scary. I wouldn't be surprised to see a bit of everything down there, including a nasty squall line with bows, embedded sups and rotating comma heads....all the way to isolated supercells firing ahead of the line. With the strong shear and instability that's forecast to be in place across this region, this could get downright hairy.Hopefully those folks down there will keep on alert tomorrow and tomorrow night.

Edited to add: Just read the latest AFD out of KJAN and it sure sounds rather ominous.

http://kamala.cod.edu/ms/latest.fxus64.KJAN.html

-George

 

[Larry J. Kosch]

First MOD!

Don't look now but we have a MODERATE :shock: Risk area being forcasted by the SPC for Monday. The area hightlighted by the moderate risk is the Southern Mississippi Valley area bordered by TX, LA, MS, OK and AR.

That's what you get when we had a severe weather symposium in Lincoln NE yesterday. You get severe weather in 1-2 days!! 8)

 

[Alex Lamers]

I think they drew up the Moderate Risk wonderfully. The WRF/NAM support supercellular development in that region as the warm sector expands northward with time. SE surface flow with WNW flow aloft...looks like some excellent curved hodographs. Instability and moisture should not be difficult to achieve so svr wx is looking increasingly likely. I would say supercellular storms will evolve in the SE OK/Arklatex vicinity in the late afternoon and into the early evening before consolidating into a complex of tstms perhaps taking on bowing characteristics as it races across far N LA and into much of AR.

Further south along the dryline in Texas we could see more isolated svr wx with a few supercells still possible. Best threat looks to be in the most dynamic environment invof maximum warm air advection.

The squall line that evolves across Arkansas even appears to have the potential to race northeastward during the overnight and could be ongoing at the beginning of the next period into NW MS/W TN.

If I were chasing I would probably set up somewhere in Far NE TX perhaps a point between Texarkana and Tyler. Obviously you want to catch these storms before they go too linear...looks like the supercells will be nicely evolved by the time they reach LA/AR borders with TX/OK.

Unfortunately I live way up here in Wisconsin so I can merely watch on radar. If you live in the Arklatex region though, you could have some interesting storms to chase Monday.

...Alex Lamers...

 

[Andrea Griffa]

New ETA run looks like worsen a little bit with a slight decreasing of the rich in cape zone but there's nothing worry: the good low level shear zone is mantained.
As to me NE TX is going to be the best zone along the border with AR. Fortunely the I 20 with his W-E orientation could help chasers to be faster in that zone and could be very useful.

 

[Aaron Kennedy]

Although there is a lack of moisture (classic for early systems), I'm not too worried. 17 March 2003 had sub 60degree dewpoints, but there were some amazing storms that day. The main problem I see is getting any insolation... precip earlier in the period may hose the potential for substantial heating.

Aaron

 

[Adam Atkins]

Svr Wx

I really like the setup for tomorrow due to the lack of extreme forcing. The cold air is lagging quite a bit behind so they dynamics aren't extreme in the mid and upper levels. My concern is the lack of a strong cap, according the the GFS, which shows a little CAA at 850 mb by mid-day tomorrow. If things light up too quickly, the possibility of discrete cells is less because of storm interaction. I'm hoping the NAM is more correct in placement of the surface low because SE OK has awful terrain for chasing. I wouldn't be surprised to see the MOD risk area shifted a bit west towards I-35 by tomorrow. Happy chase season 2005 stormtrackers.

 

[Ben Cotton]

Were this about 5 days earlier, I think I'd make the drive from Indiana to go after this. Granted, it is March, but I'm storm-deprived. It's encouraging to see a MDT anywhere in the country though, and I'd have to agree that it's well placed. If I were to chase, I'd probably pick Tyler, TX as a starting point (it's the only town I know in that part of the world). Although the SRH is better closer to the surface low, I think the location of the CAPE axis and the LLJ supports ern TX/wrn LA better. My main concern is will the LCLs be low enough to support tornadogenesis?

It looks like the LCLs will be too high around Tyler, but SHV LCLs are pretty low -- unfortunately not til after dark. I'll be interested to see how things play out, but this definitely has potential to make the evening news.

 

[Blake Naftel]

I'll remain optimistic on the pending event based on what ETA/NAM trends have been. Aside from the SHV region; another interesting area to watch for a convective surprise may be around NC/NE OK and SE KS in vicinity of the surface low. CAPE on the order of 1500/2000 J/kg (discounting CIN) along with low 60 Tds could allow for a lone LT supercell or two to anyone venturing around Ponca City early in the day. Winds are not great in the aforementioned region; and if I could chainsaw chase would favor Texarkana to Shreveport. Storms will be fast moving and through poor chase terrain; still will be interested to see how this system plays out.

..Blake..

 

[Alex Lamers]

Looks like everything is shaping up nicely over the Arklatex Region. Thought I'd highlight some tidbits from local NWS offices (several sentences each) before I launch into my own analysis.

WFO Lake Charles Special Weather Statement 249 PM CST

THE MOST LIKELY AREA OF DAMAGING TORNADOES AND LARGE HAIL IS ALONG AND WEST OF A PORT ARTHUR...LAKE CHARLES...OBERLIN...ST. LANDRY... AND MARKSVILLE LINE. -and- AS THE FRONT SWEEPS THROUGH THE AREA...AN INTENSE LINE OF STORMS WILL FORM THAT WILL ALSO CONTAIN HAIL...HIGH WINDS...AND ISOLATED TORNADOES.

WFO Shreveport Area Forecast Discussion 250 PM CST

SO EXPECT THUNDER TO DEVELOP IN THE MORNING HOURS...WITH SEVERE THUNDERSTORMS SCATTERED TO NUMEROUS IN THE AFTERNOON AND EVENING HOURS

WFO Jackson Special Weather Statement 252 PM CST

IT APPEARS THAT PARAMETERS ARE COMING TOGETHER FOR A LARGE SEVERE WEATHER EVENT FOR THE LOWER MISSISSIPPI VALLEY.

WFO Jackson Special Weather Statement 330 PM CST

ONLY INGREDIENT THAT MAY BE LESS THAN IMPRESSIVE
WILL BE MOISTURE AT LOWEST LEVELS AS THE AIR MASS RECOVERS BUT DYNAMICS AND MOISTURE WILL BE MORE THAN SUFFICIENT FOR SIGNIFICANT ROTATING UPDRAFTS FOR THE POSSIBILITY OF TORNADOES...LARGE DAMAGING HAIL AND DAMAGING WIND GUSTS.

This is only a sampling and pretty much all offices agree on a major severe weather event now for tommorrow. Looks like development will occur during the early to mid afternoon along the dry line over South-Central/Southeastern Oklahoma and Eastern Texas as well as in the warm advection regime invof the warm front over Eastern Oklahoma and Arkansas. Additional isolated activity will be possible into Mississippi and Alabama. It looks like supercellular activity will be likely with SRH values of about 200-300 m2/s2 coinciding with MLCAPE values over 1000 j/kg and LCLs under 700m and as a result it appears as though a few of the supercells may produce tornadoes.

Any thoughts on potential for +F2 tornadoes??

...Alex Lamers...

 

[Karen Politte]

I would count seeing any kind of tornado as a major accomplishment tomorrow. Spring has sprung literally - and somebody has flicked the switch. The storm season has been turned ON.

Waiting on Monday morning's findings before making a decision whether or not to chase - things are still too difuse and besides we have a nice round of storms shaping up here overnight that I want to enjoy from home.

It'll be touch deciding whether tomorrow is worth spending $150+ on gas for.

KR

 

[Mark Sefried]

I think I am liking the areas bounded by Palestine, Centerville, and Crockett, TX the best according to the 12z data . Wind fields from 200 mb on up are "forecasted" to be the best across that area. Also, the storms should have a little more juice to play with as the dewpoints are suppose to be better across that general area than further North. I don't know how the chasing terrain is across the area as it might be a problem. It will be interesting to watch things Monday Afternoon and evening and see how things pan out.

 

[Bill Schintler]

RE: chase target 03/21/05

I'm not too excited about tomorrow. I do expect that we will see many storm reports - including weaker tornadoes, but I don't forsee it to be a good chasing day for the following reasons: 1) It looks like a big precipitation shield over the entire area of interest at 12Z - except down in LA, 2) Most of the severe weather and supercells will be imbedded in larger precipitation areas and extensive low cloud shield - the exception may be down in LA as some discrete supercells will likely form ahead of the more extensive precipitation areas and 3) that part of LA is not good for chasing because of trees everywhere. I know lots of folks have SDS pretty bad, but I'd save my gas tomorrow.

I'd be hard pressed to say anything intelligent about a forecast before looking at the radars and visible satellite tomorrow morning. Right now, I'd have to say western or northwestern LA, south of Shreveport, early to mid-afternoon. I've seen it before - big synoptic setup and lots of reports- but not good chasing conditions.

- bill

 

[Gabe Garfield]

This bit of info is way too small to justify a post, but I'll go ahead and do it.

The 00Z RUC forecasts the 60 F isodrosotherm will be near Austin by 12Z tommorow as opposed to the 12z NAM which forecasted the 60 isodrosotherm much further south (roughly around Corpus Christi). This could have a significant impact on this event if it verifies.

Gabe

 

[Mike Johnston]

If I weren't on a visit back to the east coast tomorrow, I would look to set up along an axis from just E of OKC, northeastward up to Joplin, MO - or just E of the approaching surface low. CAPE values, although not extremely high, should be sufficient. I like this area along a ridge of relatively higher forecast SRH values, along with some divergence in upper air winds, and steep lapse rates. Although dewpoints s/b in the 55-60 range, dewpoint depression from temperatures s/b less pronounced in this area than points to the west and southwest perhaps allowing for some lower LCL's, and initiation in this area should coincide fairly well with the diurnal cycle. Key factors to keep an eye on in this area tomorrow: forecast vs. actual dewpoints and cloud cover. (Am hoping a dry slot will nose far enough northeastward during early and mid-afternoon.)