2/24/11 FCST: OK, TX, LA, AR, MO

[Greg Blumberg]

A few things. I don't trust the models right now because of their lack of good data regarding the shortwave trough south of Arizona, so I'm sticking to the 00 UTC observations for most of this discussion. I don't think CAPE will be a problem at all tomorrow. Looking at the Tucson, AZ 00 UTC 500 mb temperatures, (which I'd say the location well represent the temperatures of the shortwave trough), I see a -26 C. If this is representative of what kinds of temperatures will be aloft tomorrow, I'd say that the instability fears that we've seen in the past few days will vanish. With some surface heating and the moisture we already have, I believe that CAPE values in the 1,500 J/kg seems reasonable, maybe even more. This is new upper level data is probably the reasoning behind the 00 UTC NAM's CAPE solution Donovan mentioned.

I'll throw this into the mix. We've already got 70 F dewpoints just a bit off of the Texas coast. Advect those up to our target area (which I'll add doesn't seem too unreasonable given 40 knot 1.5 km winds out of the south per the current profilers in TX), and you've probably got somewhere in the 2,000 J/kg of CAPE near the Eastern border of OK. The 00 UTC NAM doesn't even have 70 F dewpoints anywhere near the TX Coast or have the 40 knot winds I was mentioning about. Keep in mind that I'm mostly estimating this, but my main point is that CAPE may be much larger that what we've been thinking. It's possible the 00 UTC NAM is underestimating CAPE.

It's really hard to track the vorticity max using water vapor right now. It's right between the division line between GOES-E and GOES-W on the composite maps. Just from my observations, it looks like it's lifting north ever so slightly. I'm watching the potential for a new surface low developing in southwest Kansas right now via the 3-hr pressure tendency maps and am hoping that the front over OK retreats a bit.

Just from looking at these observations, the MDT risk the SPC has put out seems very well warranted.

 

[Lanny Dean]

Interesting 00z run...still holding on my original target area between Cushing and Perkins to start for my CWA. CAPE values increasing to over 1000 with very nice Lifted Index of -6 to -8. Decent looking sounding to boot....now if it would just slow a little more and deepen up further I think we could really see something!

 

[Brandon Sullivan]

You know, my thoughts on what I plan to do tomorrow are rather simple.. Most Hi Res short term numerical guidance continues to tell me to play on the low, across eastern/northeastern OK and hope for any enhanced warm front interactions.. This is where the models show the most instability, where the region sits in enhanced low level lapse rates. Im hoping there are some more mesoscale effects, and some locally backed winds, but we will find that out tomorrow.

Im having a hard time getting excited about playing what I feel like will be a damaging wind event, in the afternoon and evening across Arkansas.. Sub cloud instability is a little better with the 00z models, but still nothing to write home about. VWP's and PWAT values just scream line with HP's to me.. With a setup like Sunday on the horizon, my desire to go all out for that risk is low.

4km WRF from 12z today and 00z show a few discrete cells breaking out in the vicinity of the low, which makes sense to me.

I am not hopeful for tornadoes anywhere tomorrow, especially my target in northeast/east oklahoma.. But I would like to see a nice supercell like the WRF indicates.

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/refc_f22.gif

http://www.emc.ncep.noaa.gov/mmb/mpyle/cent4km/conus/00/mxuphl_f22.gif

http://wxcaster4.com/nam/CONUS_ETA212_ATMOS_SIGSVR_21HR.gif

 

[Bill Tabor]

For any potential TX/OK daytime chasing my area would be central OK onward toward the Tulsa area. I see OKC region and perhaps a bit south down toward Ardmore around 12z to 15z then headed toward TUL region by 18z with perhaps extended activity 18z to 21z toward se KS and sw MO, nw AR. Appears there could be precip (widespread?) breaking out early across OK before 12z
adding to the mess and due to early small mid level leading influence. Not
that crazy about 850's in OK and they seem worse in TX.

TX may see a little activity early near DFW, but not sure how decent
supercell / tornado wise it will be.

Precip model shows a squall or possible line of individual cells extended
into TX down I35 and moving east quickly with hugely veered 850's pushed by
raging westerly sfc wind. I'll keep and eye out for those and may go out to
see one just to see a storm if they are decent enough and close.

Haven't checked the weekend yet.

Based on the above I'm not planning on trying to be in central OK at 12z. It
could be an option for someone really hungry - there and TUL but I'm not
THAT excited about tornado chances. Hmm maybe 5% torn in OK and 2% for
northern TX near DFW region and extending east toward TXK.

 

[ahaberlie]

My analysis + forecast based on what is going on now. What worries me is this area of the country is prone to deadly tornadoes. Heres to a bunch of pretty looking, but weak, tornadoes guys!* Notice how current surface winds are perpendicular to my magical outflow boundary line.. could play a factor was well as storm motion.

*If they are strong, please be in open fields.

 

[cwachal]

I still think there will be 1 or 2 EF2 or higher tornadoes today

The reasoning behind this is there is enough sheer that even if it is short lived there will be a very high tornado threat for 3-6 hours tonight

 

[Jeff House]

Wish I could see that chart above (work browser settings); but, yes parts of the Mississippi Valley prone to deadly tornadoes are at risk tonight. Appears East Texas and southeast OK low clouds may not break in time as the CF/DL approaches. Arkansas triple point looks like the focal point for tornadoes, but it is unchasable. Mix of terrain and fast storm motions is a real challenge. Anyway sun is breaking through there, and winds are backing as the WF lifts. The clock on daylight may run out before storms reach the eastern flat part of Arkansas. Unfortunately it will probably be dark when supercells reach Mississippi and Western Tenn. By unfortunate, I am referring to the human risk more than the chase ending. Should go mainly high winds a couple counties east of the Mississippi River, at least I hope so for local residents at night.

Though I'm not chasing this event, I will be watching closely on radar. Y'all chasing out there be safe. If one gets away remember there will be other better events this year. Cheers!

 

[ahaberlie]

Sorry I will include my updated opinion and also a text based analysis.

The "crapvection" associated with the low pressure in OK is a little worrysome, but could be due to 1) the storms are starting to fire as the SPC has issued a tornado watch or 2) the areas west of Arkansas couldn't get the temperature/dewpoint gap to be sufficient, and the cap will be a little stronger further east as daytime heating increases temperatures as the morning MCS moves out of the way. Haven't changed my mind much.. as there is a SW to NE area around the outflow from SW Arkansas to the Missouri border and into SW Tennessee that seems to be not only the area most likely to see warm/moist advection, but also good lift from the boundaries in place.

Disagreement/Criticism is welcome.

 

[Greg Blumberg]

I wouldn't say it's weaker convergence, but rather the lack of strong instability and surface heating. There's a lot of clouds down there right now.

http://www.spc.noaa.gov/exper/soundings/11022416_OBS/

From the sounding I see it's not difficult to get parcels to their LFC, especially with upper level lifting and the dryline you've pointed out. Strength of low level convergence isn't something you can diagnose well using surface winds. What you're seeing here is confluence, which is the directional component of convergence. You have to assess the speed part of it too to diagnose convergence. It's just that there's a lack of instability I believe. No real strong surface heating anywhere in the warm sector east of the dryline. Also, if you look at some of the 12 UTC soundings from today, you'll see that the CRP area is pretty well capped.

Edit: Don't worry about it ahaberlie. The convergence/confluence is something that is confusing sometimes. Nice graphics btw. That's a great way to make posts here and provide a diagnosis of the atmosphere.

 

[Greg Blumberg]

Wow. Looks like the surface low pressure system near SE OK is really starting to deepen. I'm getting readings of strong pressure falls from these two links:

Time sensitive:
http://weather.unisys.com/surface/sfc_con.php?image=3p&inv=0&t=cur&expanddiv=hide_bar
http://www.mesonet.org/index.php/weather/map/3_hr_pressure_change/pressure

I would expect surface winds to back more as a response to this deepening. This'll be good because we'll need all the directional shear we can get while the sun's still around.

Also, special 18 UTC soundings are out for Shreveport and Little Rock:

http://www.spc.noaa.gov/exper/soundings/11022418_OBS/

Better directional shear further south, and I'm guessing east of Shreveport. Looks like that's the better target area, just based on a quick look at the soundings.