7/21/2004 FCST: MIDWEST / GREAT LAKES

[Robert Dewey]

The 12Z ETA is looking good. DTX mentions severe weather is likely tomorrow. Looking at he ETA, here is what I come up with:

Positives:
Temps in the upper 80's
Dewpoints in the mid 70's
CAPE in excess of 3500J/KG
SW SFC winds
30-35knts in the 850-700MB layer (WNW flow)
0-3KM SRH ~300M2/S2
ETA actually outputs precip across the region

Cons:
Lack of a significant trigger (other than 500mb shortwave energy, outflow boundaries)
500mb winds <40knts
700MB Temps climbing through the day, maybe capping everything off

Given that, it looks like there could be some decent supercells tomorrow afternoon, given the warming at 700mb/instability/helicity.

 

[nickgrillo]

I will be chasing tomorrow... yet it will be extremely difficult for me, sadly... as my laptop is broke and I'll have to use those dang piece of crap "old-fashioned" maps. :?

Looks very good to me... Not sure about tornadoes... but very good for large hail and damaging winds.

 

[Bob Hartig]

I'm swamped with work, but hopefully the weather will hold off till after five. I'm keeping my fingers crossed and waiting to see how things shake out over the next 24 hours.

 

[Steve Fitzsimmons]

06:05 PM CDT Tue-Jul-20 - The National Weather Service has issued a
SEVERE THUNDERSTORM WATCH until 10:00 PM CDT
Wisconsin counties
Dane, Green, Iowa, Jefferson, Lafayette, Rock, Walworth

 

[Steve Fitzsimmons]

Issued at: 7:32 AM CDT 7/21/04, expires at: 8:30 AM CDT 7/21/04

Severe thunderstorm warning continues for iowa lafayette, green and dane counties until 830 am cdt,
At 732 am cdt, national weather service doppler radar continued to indicate a severe thunderstorm along a line extending from 3 miles west of arena to 4 miles north of gratiot, or along a line extending from 15 miles southwest of sauk city to 5 miles southeast of darlington, moving east at 40 mph.

 

[David Draun]

Looks to be a derecho event setting up today. That MCS in IA is moving into an environment where there is moderate uniderectional wind shear. There is also a low level jet moving ENE into that area.

Update: MD up for Chicago/Milwaukee area cites isolated wind damage potential as thunderstorm complex approaches from NW. No weather watch expected.... yet.

 

[David Draun]

Chicgao radar showing that MCS hauling butt. It was just entering IL 45 min ago, now it's about to hit Rockford. Tail end of the line continues to strengthen. Looking for impact on NW suburbs within next two hours.

 

[nickgrillo]

Chicgao radar showing that MCS hauling butt. It was just entering IL 45 min ago, now it's about to hit Rockford. Tail end of the line continues to strengthen. Looking for impact on NW suburbs within next two hours.

I think we should start a NOW thread...

 

[Robert Dewey]

Havn't checked all the data just yet, but the 12Z RUC is looking very good! The latest data indicates good wind fields at 850-700MB, compared to yesterdays runs, with 0-3km helicity of >300m2/s2. This is all combined with CAPES in excess of 3500J/KG, and the RUC actually outputs some sig. precip, so the chances are looking good.

Gonna check the rest of the data now... Hopefully, it paints as good of a picture as the RUC does...

 

[rdale]

I'm abandoning the supercell threat and instead worried about this line to the west... I would imagine this is going to enter western MI about prime time for winds to be an issue. GRR however says winds are too light through the column - I see they aren't "maxed" but I'd hesitate to blow them off!

- Rob

 

[Robert Dewey]

I'm abandoning the supercell threat and instead worried about this line to the west... I would imagine this is going to enter western MI about prime time for winds to be an issue. GRR however says winds are too light through the column - I see they aren't "maxed" but I'd hesitate to blow them off!

- Rob

I agree with the squall event (Im happy with just about any kind of SVR)... I believe that 30-40knts in the 850-700MB layer, when combined with forecast CAPES in excess of 4000J/KG (by the RUC) should be sufficient. Not sure, but I think previous model runs (of the ETA and RUC) showed much weaker low level winds, which may be what GRR was looking at. I am also noticing the 0-3KM helicity of 300M2/S2 on the RUC at 12HRS, though if things are completely linear, this wouldn't matter all that much...

 

[Amos Magliocco]

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