10/21/09 FCST: KS/OK/TX

[Mike Smith]

A little surprised that a thread has not been started for Wednesday, so here it is.

SPC has a 5% area in Texas and Oklahoma. The 12Z NAM forecasts, at the moment my talk is supposed to begin in Greensburg, a nice size blob of convection over the Greensburg-Pratt area.
www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/12/images/nam_slp_060l.gif

Given Murphy's Law...

 

[Bart_Comstock]

The models have practically no CAPE over the forecast area for this day and really it looks like day two of a wasted system where nothing will happen. The surface winds also look near stagnate and I just see a rainy day over areas along the front in the forecast area.

The one thing I am concerned about is more rain over my area here in NW Ark as we certainly don't need any more but may get over an inch which might not seem like a lot but we are still pretty well saturated here.

 

[Jeff House]

Severe weather will happen from southeast OK to central TX. Now I am selling tornadoes but would buy wind and hail all day. Might be an isolated torn or two but looks like another squall line to enjoy from my Dallas living room. Before even analyzing the setup, I have concerns about moisture return after the cold front that blasted through the entire Gulf last week. What makes for a beautiful Texas weekend means moisture issues now.

Should be quite a bit of ongoing rain and storms on and behind the front. Additional convection should develop along a pre-frontal trough or just in the free warm sector. Lack of a even a weak cap probably elimiates the Miller Type I loaded gun sounding; therefore, will downplay torn threat. GFS still slower than WRF/NAM and has a more defined pre-frontal trough and less veered 850 winds. Despite these nice GFS traits, I trust the WRF more and it is bearish for storm chasing. ECMWF is similar to the WRF.

If things improve will start planning for a southern Plains chase. Otherwise, this will be another fun squall line. SPC should have slight because the squall line should materialize, but we shall see. Cheers!

 

[W. Grant Dade]

Main concern for this event will be the return of moisture. With most of the Gulf moisture pushed well to the south, it will take quite some time to get it in the area. Also, we could see a lot of mid and high level clouds thanks to the remains of Rick. However, if enough moisture does return to get surface based convection, this looks to be a low instability high shear set up. Many times these events have produced devastating tornadoes across the southeast. I by no means am calling for this at this time but a couple of areas of interest:

• Very high 0-1 and 0-3 km SRH values across central and northeast Texas.
• Right rear quadrant of a strong jet streak wrapping around the base of the trough.

With current MLCAPE values forecast to be in the 250 to 500 range and LI s around or just less than 1, there is very little instability to work with. If we see a little sun and a little more moisture, could be very interesting. There have been a few tornadoes develop in extremely low instability if there is enough shear and a little dynamic support, which this system may have.

 

[cdcollura]

Good day all,

I see - again - moisture return / instability to be a major problem with this setup. A cold front has completely cleared the Gulf (it actually was in the mid 50's here in Miami), so most moisture has been flushed out.

It will take a lot of upper lift / dynamics to work with the limited moisture we have. At best, you may have elevated stuff as the speed max / lift overspreads the area (TX / OK).

 

[Jeff Duda]

Good day all,

I see - again - moisture return / instability to be a major problem with this setup. A cold front has completely cleared the Gulf (it actually was in the mid 50's here in Miami), so most moisture has been flushed out.

It will take a lot of upper lift / dynamics to work with the limited moisture we have. At best, you may have elevated stuff as the speed max / lift overspreads the area (TX / OK).

In looking at the current moisture and low level winds, I think it looks entirely plausible that sufficient moisture return will occur. 60s Tds are already on the SE TX coast and surface winds are coming right off the gulf. Even as per H925 and H85 12Z analyses, flow is fairly "off the Gulf", which leads me to believe moisture return will probably be good enough.

I checked the setup last night and again this morning with the new 12Z runs and noticed a trend here: the upper level support is moving farther northwest. Also, winds for this system, especially for the time of year, are kind of weak. Only a meager 80 - 90 kt streak at 300 mb, but the best upward motion from it looks to be over far NC TX and into OK. At 500 mb, winds were more like they would be in a late-spring/early-summer setup. Looks like it will be difficult to squeeze out an area of even 50 kts at that level. Although there will be a sufficient SLY LLJ with good backed surface winds, so low level shear/helicity will be large. The other thing is it looks like starting Wednesday afternoon the upper level low begins to close off and stall, thus ending the PVA/UVV aid.

It looked like capping was going to be an issue before, but latest runs show some cooling at 700 mb as the low approaches, so it may not be as big of a factor. In summary, it looks sufficient thermodynamically (I saw up to 1000 J/kg of CAPE in the 12Z WRF), and low level shear will be there, but it seems upper level support will be lacking somewhat.