4/27/07 FCST: TX / OK

[Ilya Neyman]

I've been eyeing the models and paying close attention to the rather strong shortwave progged to dive down the Rockies during the Thursday night-Friday timeframe. GFS and NAM are quite different in terms of their placement of this feature, which would have notable effects on the exact situation. Main things that are quite interesting is the strength/trajectory of this forecasted wave and the downstream flow development. Both models forecast a rather strong LLJ to get cranking overnight Thursday into Friday morning which would start advecting moisture back into the region. Though 850 winds do weaken during the day they show signs of strengthening again toward 00z, additionally there is good directional shear with height. Moisture is progged to possibly reach the low-mid 50s with NAM favoring more of the TX panhandle vs. OK on the GFS. 50 dewpoints would be more favorable for a panhandle solution. CAPE does not look all that high, but it does show up..and instability in the form of lapse rates and lifted indexes could be significant. Both GFS and NAM fire convection during the day. It may be elevated early on, however, but surface based would not be out of the question during the afternoon. SPC had a Day 3 see text for the area...which has NOW been upgraded to a Slight Risk (just checking now). Could be something to watch!

 

[Ilya Neyman]

May need to add OK to this thread. NAM has trended toward GFS placement of system across OK now, mid-upper 50 dewpoints are showing up on both models advecting into OK by Friday evening and convection fires south of possible morning elevated activity. 850 flow is a bit marginal but NAM has increased CAPE across southern OK now.

 

[Shane Adams]

Not real impressed with the flow from AG-h85....relatively non-existent per current WRF in the hotspot. If the new runs can find a solution that would stack the instability and shear hotspots, I'm definitely interested in this possible backyard chase opportunity.

 

[Ilya Neyman]

Yea, new runs have kind of toned down the prospects here. The real interesting solution was yesterday where the NAM diverged from the GFS and featured the shortwave diving down a more westerly track, with 50+ dews in the TX panhandle, great directional shear and decent speed shear, especially above 700mb...as well as firing convection, most likely surface-based toward mid-late afternoon. Today's runs trended toward more of a northerly/easterly course, which even then looked possibly marginal, particularly for southern OK and far northern TX with a nice front/boundary backing/focusing surface winds underneath some CAPE, decent LIs, and progged heating. Latest NAM showing more SW-WSW 850 winds, that aren't too weak but more veered. Ok, now looking more in detail and NAM has increased CAPE further 1,000-1,500 just south of Lawton while cap erosion takes place by 00z. Surface flow looks tremendously weak, but may be played around some from possible earlier elevated convection and associated outflow. The main thing is that the shear/instability don't quite coincide on this latest run, however. A See Text seems justified at this point in time, with a very localized Slight not out of the question.

 

[Bill Schintler]

Chase target for April 27

Chase target:
Lawton, OK

Timing:
Storms will move into the area at 4 PM CDT.

Storm mode:
A few discrete cells are possible but the overall storm mode should be linear or multicellular. Storms may produce marginally severe hail but should remain below severe limits for the most part.

Synopsis:

NWRLY flow at all levels is present over must of the WRN CONUS. A couple of noteworthy features in the UA charts were observed this evening. First was the Upper-low spinning away over the Baja California, while the second is an elongated wave analyzed on the H7/H5 charts from extending from CO into ERN MT which had an area of storms associated with it over ERN CO into SD. Both of these features show up well on WV imagery. In TX and OK, SFC moisture LLVL was rather meager this evening, with the 45F isodrotherm analyzed along a Sweetwater TX to Wichita Falls to Shamrock, TX line. At the SFC, weak SERLY return flow has commenced while a 20kt LLJ was transporting 8C dewpoints NWRD into the TX panhandle. The 00Z NAM initialized 5F too low with dewpoints in WRN OK although both the NAM and GFS initialized well to SFC and UA features otherwise, as well as the ongoing precipitation in CO into NEB and SD.

Discussion:

A moisture axis should develop along the Red River valley from Sherman, TX WWRD through Vernon, TX during the afternoon hours Friday. Precipitation will be ongoing early in the period along the CF and in association with the shortwave which will track towards the Red River area by mid-afternoon. The strongest forcing in association with the shortwave will remain north of the area however ongoing storms along the southern extent of the front should strengthen as they move in to an environment of 60F dewpoints, 1000J/kg SBCAPEs and 7C/km mid-level lapse rates. SERLY SFC flow of 10 kts beneath 25kt WNWRLY H7 flow will contribute towards (SFC-3km) SRH of 200m^2/s^2; while a 35kt NWRLY bulk shear vector will be present.

[FONT=&quot]- bill[/FONT]

 

[Ilya Neyman]

Heading down to Lawton...I know this is a bit marginal..but I'm off work, we've got a system moving in, ouflow boundaries are spreading out...and atmosphere is destabilizing in SW OK attm. Who knows!

 

[Jimmy Deguara]

I guess staying in Dallas, I will await any action heading down this way but the cumulus at this point seem to be staying put.