Severe Weather Discussion for September 15 – 17, 2006.
– Isolated severe thunderstorms are expected later today across the Texas/Oklahoma Panhandles and far western Oklahoma northward into South Dakota. Primary threats are large hail and strong winds, however an isolated tornado or two remains possible.
– Active severe weather day is expected from Kansas northward to Minnesota on Saturday. Primary threats are tornadoes, large hail, and strong winds.
– Severe thunderstorms are possible across parts of Oklahoma on Sunday. The exact area is in question, however the primary threats are large hail and strong winds.
No change to the forecast reasoning for today. Deep layer moisture return is under way across the panhandles and far western OK, per mid 60s dewpoints. Models have done well with expected moisture return and see no reason to deviate at this point. Severe thunderstorms may develop later this afternoon as upper system traverses the region. I agree with OUN and SPC about lack of surface boundary being a limiting threat. However, any storm that can sustain itself will have the potential to become a supercell.
General idea for Saturday remains the same, other than the most concentrated severe threat is expected to be north of Oklahoma. Isolated severe thunderstorms are possible in northern Oklahoma and a small slight risk has been issued for that area. 12z models are in decent agreement of the large closed low moving eastward over the next few days. Said models prog the upper system to be located in eastern Montana Saturday afternoon with the PVA moving into South Dakota and Nebraska. The best chance for severe thunderstorms will be in these areas with decent opportunities in Kansas as strong deep layer shear overspreads Gulf moisture. The 17:30z Day 2 looks good and I certainly agree on the conditional upgrade to a moderate for part of the threat area.
Sunday remains a very tough forecast. Bowling ball low should slowly translate eastward during Saturday. This reduction in speed from earlier forecasts has had a dramatic change in the cold front location. Models now bring the cold front into NW OK late Saturday where it stalls until late Sunday when the secondary push moves through as the low progresses far enough east. Models have really backed off on the cold front, but it will be big change given the 90F temperatures expected on Saturday. The big implication is for severe thunderstorms on Sunday in a larger part of Oklahoma than originally thought. SPC Day 3 looks good for now and plenty of time to make changes. Current indications are that storms would be linear, but directional shear and slow speed of the cold front may serve to enhance helicity values in discrete storms.
Risk area for any part of OK/TX (valid: 09/16 Day 1, Day 2):
Slight: 100%, 100%
Moderate: 0%, 15%
High: 0%, 0%
Level 1 – Normal
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