Severe Weather Discussion for June 6 – 8, 2007.
– Active severe weather periods expected Wednesday and Thursday, with some potential for continued activity into Friday.
– Excessive rainfall will become an increasing threat by Friday and through the weekend.
12z models remain in agreement with each other and prior runs. Setup for Wednesday through Friday looks the same with potential for at least a medium-end event and most likely a high-end event across northern Kansas into Minnesota. Thursday, the threat will shift south as progressive shortwave trof moves into the northeast U.S. and synoptic scale front drops south behind it. This front will also be aided by convective outflow. Friday is quite muddied as winds aloft will start to weaken and issues from Thursday convection may make things tough.
Unfortunately Wednesday looks to be well north of the region as a significant cap will be in-place across OK/TX. This is not unusual this time of year, just disappointing. Wednesday is one of the better setups I've seen this year. Despite the very strong cap, one or two isolated thunderstorms may develop in Oklahoma. As such, I'm keeping the slight risk up and a little bit in the moderate risk area. Any sustained storms that can develop on Wednesday will likely be severe. Tornadoes may be tough to come by with no boundaries and high T/Td spreads. I'm not looking for a chase on Wednesday at this point, but will monitor in case it appears the cap will be breached.
Thursday appears to be a more likely day for the cap to be breached. The surface pattern should be characterized by a synoptic cold front in southern Kansas with a dryline through western Oklahoma. Extreme instability should once again develop near these features. The cap is progged to weaken during the day and the NAM does create QPF in northern Oklahoma. Wind fields aloft will remain strong and quite favorable for rotating storms. Storms that develop on Thursday will produce severe weather and tornadoes appear more likely given stalled cold front and potential for convective outflow boundaries around the region. Thursday will lack the jet max and shortwave trof from Wednesday, but the weakening cap should be sufficient for storm initiation. I've gone pretty high on the moderate risk, as I think we should get one. I'm not sure about a higher threat given time of year. Thursday is a possible chase day.
Friday will have to be watched as wind fields remain supported of organized severe thunderstorms. Wind speeds decrease 400mb and up in southern Oklahoma, but low-level values are sufficient. Ultimate placement of the cold front will determine how much of a threat we face on Friday. For now I'm going to leave it as conditional.
Risk area for any part of OK/TX (valid: 06/05 Day 2, Day 3):
Slight: 100%, 100%
Moderate: 15%, 80%
High: 0%, N/A
Level 1 – Normal
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