9/22/05 FCST: GREAT LAKES

[Robert Dewey]

Decent setup for severe thunderstorms tomorrow across the Great Lakes region, yet again.

A nice boundary/cold front will be laid across the region... NAM and GFS are pretty much similar with the general synoptic layout, though there is some rather significant differences in timing and overall jet dynamics. GFS is quite a bit stronger with wind fields, bringing in nearly 70KNTS at 700MB, while the NAM is a bit more conservative with 55KNTS or so. Either way, shear values will be more than supportive of severe thunderstorms. In fact, NAM has 0-3KM helicity of nearly 400M2/S2 ahead of the cold front.

Hopefully Td's can manage to pool up into the upper 60's, and looking upstream into IA, this looks quite possible. NAM outputs CAPE of 1500-2000J/KG, and the GFS is actually pretty unstable as well. Hopefully, anything that develops upstream today will remain further west, and limit any potential debris tomorrow morning. Given that, I think tomorrows convection will be based strongly on what happens to convection tonight - as a matter of fact, I think it may be an MCV (or left over activity) that will initiate things for tomorrow.

 

[nickgrillo]

Strong moisture/theta-e advects in right in time for the cold front... Combined with SFC temps of 80F will yield strong instability (SBCAPE 2000-3000) efficiant for severe thunderstorms. Strong flow is present at every level (including excellent +40KNT southwesterly 850MB flow) and combined with strong instability/moisture, spells out severe thunderstorms - mainly capable of large hail (and perhaps a few damaging wind reports).

Not getting too exicted at all... Although, it could give a nice local "hailer" chase :wink:

 

[Robert Dewey]

Originally posted by nickgrillo
Strong moisture/theta-e advects in right in time for the cold front... Combined with SFC temps of 80F will yield strong instability (SBCAPE 2000-3000) efficiant for severe thunderstorms. Strong flow is present at every level (including excellent +40KNT southwesterly 850MB flow) and combined with strong instability/moisture, spells out severe thunderstorms - mainly capable of large hail (and perhaps a few damaging wind reports).

Not getting too exicted at all... Although, it could give a nice local \"hailer\" chase :wink:

Actually, if we do hit 80F and things become SFC based, damaging wind gusts would most likely be the primariy threat. Right now, SPC is calling for large hail being the main threat given the expected elevated nature of the convection, with the general thought being that instability won't be all that great.

The thing concerning me right now is the junk over WI. It's a bit further south and east than I had anticipated, and the IR imagery (before cutting out) showed a massive amount of debris. This can be confirmed, however, using the METAR data - which shows extensive overcast over much of central and southern WI, into northern IL. This looks like it's on the nose of the 850MB LLJ, which appears to decrease in strength over the next 0-6HRS, meaning we might see a reduction in this activity.

The RUC cloud algorithms and 500MB RH values suggest that only very high cirrus clouds will be present at times through 15Z (decreasing somewhat, actually). This would be good news for any insolation, but I'm not ready to be 100% confident in the RUC forecast at 12 hours out.

Anyway, unless we see sun, and actually hit 80F tomorrow, I'm not too excited. Hail in MI usually equals less than pea sized - not enthralling at all.

 

[rdale]

Feeling a little better for extreme southern MI / northern IN IL this afternoon with clear skies allowing for some nice warming... If we can get rid of this junk in MI the threat might even come north of I94, but if I were desperate for a chase I might head towards the Turnpike.

 

[rdale]

Temps well into the 80's along with dew points approaching 70 should lead to severe weather in southern MI / extreme nourthern IN OH later this afternoon. 90's in IL but 18Z sounding from ILX appears to be too capped.

- Rob

 

[Andrew Khan]

It looks to me like, if there were to be any supercells, they would be isolated into the SW MI area. I don't think there is really to much of a chance for tornadoes, but if there were, they would also be in the SW MI area. Extreme SW MI, is showing 3000-4000 J/KG of SBCAPE.