Chase target for Wednesday, January 12
Chase target:
Coffeyville, KS.
Timing:
Storm initiation 11AM.
Storm type:
Isolated “low-topped†supercells early in storm evolution, which will track rapidly to the NE at nearly 50mph. Hail to golfball size, and a few weak (F0-F1) tornadoes will be possible. By early afternoon, storms will evolve into a squall-line with severe wind to 70mph the primary severe threat. By 00Z, this line will be approaching a Harrison, AR; to Hot Springs, AR; to Dallas line. All-in-all, not an ideal chasing day given the rapid storm speed and extensive low cloud cover that will be in place.
Discussion:
00Z analysis shows a 150kt jet streak approaching SRN CA which will round the base of the WRN US trough tomorrow. By 12Z-18Z tomorrow, the left-exit region of this streak will lift into the FA. Associated with this feature will be a 700mb-trough axis aligned along a Grand Island, NE; to Dodge City line. Surface low-pressure will track along the OK/KS border during the day along the strong temperature gradient there. The FA will remain strongly capped until mid-day as cold mid-level temperatures approach with the mid-level trough/shortwave, and 700mb temperatures drop to –0C, and 500mb temps drop to nearly –20C.
The $1,000,000 question is that of the degree of thermodynamic instability that can be achieved in the FA. The large negative factor is the shallow cold and damp airmass that is in place on all but SERN OK that will be very difficult to scrub out despite the WAA that has commenced. A strong LLJ is already in place just above the BL: 00Z 850mb analysis already shows a 40kt SWRLY LLJ transporting 16C(61F) temperatures as far north as I-40 between AMA and OUN. Even the 925mb level shows a 35kt LLJ nosing into OUN where T=10C. The OUN sounding also shows Td=10C at 925mb; while LMN shows T/Td=9C/9C at 900mb, with a surface T/Td of –2C/-2C. The 00Z Eta has initialized a few degrees cool in SWRN OK with temperatures and dewpoints well initialized elsewhere. It has also initialized well with regard to 00Z temperatures throughout OK. Based on this and the fact the Eta does best at handling shallow cold airmasses, will go with that model. A marginally unstable MLCAPE approaching 700J/kG is suggested during the afternoon hours. Even if surface temperatures verify a few degrees cooler then guidance, the excellent mid- and upper-level dynamics which will be very conducive to rotating updrafts should be able to make up for January CAPEs.
- bill