Target:
10 miles south of Shattuck, OK (At the junction of US-283 and US-60, or about 30 miles SW of Woodward).
Timing:
High-based storm (or virga) initiation should take place at around 4 PM CDT in the Pampa, TX to Perryton, TX areas. Storms should become surface-based and reach severe limits as they cross the TX/OK border and enter an environment with deeper moisture and better low-level shear. The first severe warning, for Ellis CO. in OK, should be issued at around 5:30 PM CDT.
Comments:
Discrete, high-based supercell storms during the early evening hours, with an evolution into an MCS by mid-evening. Hail to 2.5†will be the primary severe SVR threat, while wind gusts to 80mph will also be likely.
Discussion:
Generally zonal ULVL pattern across the CONUS, and storms should fire in the vicinity of a dryline during the afternoon in OK as a compact wave approaches the area. MDL guidance suggests a compact H5 vort max at the exit region of a 45kt H5 streak, with an associated H7 short wave lifting into the target area by late afternoon.
The primary FCST concern is the amount and depth of SFC moisture and resulting instability. 00Z DDC and OUN soundings, both of which are N of a SFC WF, are fairly dry in the low levels; with the OUN indicating a 200mb deep moist layer with a mean Td of about 10C through this layer. FWD indicates a 140mb deep layer with a mean Td of 14C. Overnight, the veering LLJ will not assist in transporting any of this moisture into NWRN OK. The latest (00Z) NAM does seem to have a good handle on both the SFC and H85 dewpoints in OK. Still, it is my gut feeling to adjust the WWRD extent of the deep moisture during the afternoon hours as the MDLs may not resolve the shallow moist layer in the vicinity of the DL. Given a 20-25kt SWRLY flow of SFC and H85 temperatures in the mid-80s F by mid afternoon, expect that the DL should advance to the OK/TX border through 5 PM.
In any event, cloud bases will be high with SFC depressions of nearly 30F. This will result in LCL's in the 1600m to 2200m range from N to S across WRN OK with a deep and well mixed BL. Expect fairly steep mid-level lapse rates, with H7 temps of around 9C and H5 temps of around -14C. This will support MLCAPE's (100mb) in excess of 1500J/kG. Shear parameters will also be favorable, including LLVL hodographs with SRH's (0-3km) to 250m^2/s^2 and bulk shear to 45kts, under the aforementioned H5 streak. All of these parameters will support storm organization and supercells. Later in the evening, a developing 70kt LLJ will result in an evolution into a large MCS.
- bill
