9/21/05: FCST upper MS valley

Plenty of instability and shear for Iowa along with MN and Wisconson for Wednesday.

If the cap breaks early enough things could get interesting.

Curious what the next model runs bring, might be an interesting and surprising day.

--
Tom Hanlon
 
The potiental is certainly there for an interesting night. I've passed up taking the day off though as it looks like storms will form after dark/slightly elevated. Seems like the best chance for surface based convection would be in SW MN/SC MN. With 50+ kts of Effective Shear and 2500-3500 MLCAPE. Pretty good late-night severe potiental for E MN and W WI. With 45-50 kts LLJ feeding into the region though not backing significantly.
 
The 12Z NAM shows excellent SFC moisture advecting in WED afternoon as the cold front swings through. Given the extreme instability (SBCAPE AOA 3500J/KG) and a ridge of theta-e + combined with a 500MB jet of +50KNTS with strong southerly SFC inflow yields a favorable airmass for severe thunderstorms. Strong veering with height indicates the potential for supercells - Along with a couple tornadoes, particularly where the warm front sits. I haven't looked at much at the moment, but will pay close attention to tonight's run...
 
Chase target for September 21

Chase target:
20 mi north of Mankato, MN.

Timing:
Storm initiation 6 PM CDT.

Discussion:
Morning soundings showed very strong capping, with convective temperatures generally in the mid-90’s in the upper Midwest. Optimum insulation is also a concern, with a band of CI that will lift through the area during the peak heating hours today. By late afternoon, however, strong mid-level UVV’s in association with the exit region of a 50kt H5 jetlet should provide sufficient forcing to overcome strong capping. Meanwhile, surface low pressure will develop and strengthen in SWRN MN along SFC boundary along FSD/MSP line.

- bill
 
I have to agree with the SPC outlooking Northern Wisconsin in a 5% tornado risk.... with 0-6 KM deep layer shear between 50-65 kts, 0-1 km helicity at 200 m2/s2, SB cape at 1500-2000 j/kg, I am expecting a few tornadoes over the area.... looking like a very good late summer/early autumn setup...

Wisconsin season tornado count stands at 60 at the moment, if we can get 10 tors today that will bump us over 70... being optimistic, I think its possible, but reality tells me it won't happen. Our previous record year was 43 tors in 1980, our seasonal average is 21. Very happy with this chase year in WI.

I would be out chasing today, except Northern WI is highly wooded and I have to work :(. If I didn't have to work though, I might take the chance in a wooded area, I did on 8/18/05 and caught a beautiful F2.
 
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