Severe Weather Discussion 2008-7-2

Severe Weather Discussion for March 31, 2008.
Valid: 03/30/2008.

Highlights:

– Isolated severe thunderstorms are likely in northern Oklahoma and southern Kansas tonight. Primary threat is large hail, but isolated tornadoes will be possible with discrete storms.

– One or two severe thunderstorms may develop along the dryline in the Texas panhandle, but chances are low. Primary threat with this activity will be destructive hail.

– Active severe weather day is possible across eastern 2/3rds of Oklahoma into Kansas/Missouri on Monday. Primary threats are tornadoes, large hail, and damaging winds.

Discussion:

Little change to prior forecast reasoning and this issuance will serve to update some of the particulars. Day 1 event unfolding as expected and SPC Day 1 16:30z is a great product. Primary storm development is expected after dark as the 50-60kt low level jet strengthens across the developing warm front in northern Oklahoma. Storm development is expected from Sayre northward to Woodward eastward to Poncai City and northeast from that location into Missouri. Storms may develop near the surface low in the Texas panhandle, but this is unlikely given dewpoints below 50F. Storms should continue during the night with some convective training. Excessive rainfall may occur in isolated areas. Coordination with Andy and Greg yields primary zone for tornadoes to be from Enid to Ponca City. This will be on the nose of the surface and 850mb moisture tongue and in favorable area north of the CAPE max. While tornadoes are possible along the warm front, the primary threat is damaging hail to
golf ball size. Destructive hail is likely with any storms along the dryline, which will likely be LP supercells.

Monday continues to look very interesting, but one must really read between the lines (or bits) in the models. I can't say I'm that impressed with SPC's Day 2 product. I think it is too far east and downplays the supercell threat too much. The cap will certainly be strong and the models are still playing catchup with the cap strength. This is noted by the 700mb temperature progs from the 12z GFS/NAM as compared to the 00z runs with widespread 8C 700mb temperatures across the region @12z Monday. Day 1 convection across the warm sector does not appear to be a problem and model QPF fields remain in the 0.01 to 0.05 area, indicating little to no precip. Secondary issue becomes veered surface flow due to ejecting early morning shortwave trof. Models indicate that the winds will remain veered during the day and only back around or after sunset. I'm not convinced of this solution given the main system remaining west and a shortwave trof approaching during the early afternoon.
Models have been very consistent in their solutions regarding surface flow, but I'm going to disagree for now. Irrespective of the surface flow, the dryline is progged to be near or just west of I-35 at 00z Tuesday. Supercells may develop during the mid-afternoon hours with a squall line likely by late afternoon. The cap will be removed and widespread storm development should occur along the dryline. Any discrete storms that can develop ahead of the dryline will have supercell potential and attendant threat of tornadoes. Models are likely under-doing instability due to their persistent development of precip across the warm sector tonight. This would serve to limit CAPE values during the day Monday. Given that we'll be starting in the mid 60s on Monday, reaching the mid 70s should not be that tough. I think a moderate risk should be placed across the eastern 1/3rd of Oklahoma with a slight risk to HWY 81. Storms will likely start just west of OKC, whether supercells or squall
line by mid/late afternoon.

12z ECMWF has slowed the Thursday system down a little more, with it passing over the region by 12z Friday. The consistency of the ECMWF and placement of the upper system continues to hint at a medium-end event for Thursday. Moisture will not be pushed that far south and will be poised to surge northward Wednesday night into Thursday. This is indicated by the 12z GFS bringing 60-65F dewpoints into Oklahoma. Note that I've only used the GFS for surface values as its 500mb pattern remains suspicious, especially when compared to the ECMWF.

Probabilities:

Risk area for any part of OK/TX (valid: 03/31 Day 1):

Slight: 100%
Moderate: 80%
High: 0%

Chase Status:

Level 2 – Monitoring Monday, can't quite say yes yet given model differences and complex surface pattern.

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About Putnam Reiter

Putnam has been storm chasing since 1990 and is a co-founder of Hook-Echo.com. For his day job, Putnam works in emergency management for information technology.
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