Severe Weather Discussion for October 14, 2007.
– Active severe weather day is possible on Sunday for western and central Oklahoma northward into KS/NE.
– Isolated thunderstorms are possible today through early Sunday for the panhandles and western Kansas.
– Chase Status is increased to Level 2.
12z models continue to agree on the general setup for Sunday and I see no reason to revisit those issues. I will note there remains some differences of opinion regarding the evolution of the longwave trof as it progresses eastward into the central U.S. I think the result has little impact on this forecast and I'm not really qualified to debate if it is trying to phase with the northern stream or not. The models seem to keep it separate more so than yesterday's runs.
The issue at hand is really the differences between the NAM-WRF and GFS regarding instability. The NAM-WRF is now more robust with moisture return, showing 16C at 850mb and near 65F at the surface. Hence it develops CAPE values near 2500 J/Kg and LIs to -8. The GFS is a little lower with CAPE values to 2000 J/Kg and LIs to -6. This can be seen partially in the moisture fields with the GFS dewpoints in the low 60s. The NAM's 0-30mb dewpoints are also slightly higher. There doesn't seem to be a huge difference at other levels. The GFS did not initialize very well this morning on dewpoints and this may be impacting the overall forecast. The NAM-WRF dewpoint fields better represent the current environment across west Texas.
Small differences remain in the jet structure, but not enough to really scream. In fact I'm pretty happy the models agree so well. The NAM-WRF is rather dry through 06z with very little QPF, while the GFS shows convection. I certainly think a blend of the models may be best for this forecast as I can't find everything I think right in one model. I do disagree with Day 3, I'm not really sure what rules out southern Oklahoma. The lift won't be as good, but it will be the prime moisture source area. Obviously there will be a lot of lift north with the best 500mb height falls and strong PVA during the early afternoon hours. Moisture may be an issue, as noted ad nauseum by SPC.
PRIND: Early morning activity may occur on Sunday generally in northwest Oklahoma northward into KS/NE. More robust activity is expected during the afternoon hours as temperatures warm into the upper 70s across western Oklahoma and parts of northwest Texas. If storms can remain discrete, a tough sell in such a dynamic environment, then supercells are likely with attendant threats. I'm not going with SPC's Day 3 product, I think the threat extends farther south into northwest Texas. Lack of moisture can be compensated for by dynamics. The new Day 2 should be interesting and if I'm wrong, well that's why forecasting isn't easy. I'm keeping the moderate risk prob a little higher since it would seem plausible from I-40 to southwest Kansas. The best spot to me appears to be Sayre.
Risk area for any part of OK/TX (valid: 10/12, Day 2):
Level 2 – Monitoring Sunday
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