6/18/09 FCST: IA/MN/NE/WI/IL

[Jeff Snyder]

The 00z soundings are interesting... The 00z DVN sounding has 400 m/s 0-1km SRH with >7000 j/kg SBCAPE! There is some CINH near 850 mb, apparently enough to hold back initiation. The 100mb MLCINH is too high for sfc-based initiation unless the capping layer cools, but I think a 75 mb MLCINH calculation would be similar to the SBCINH calculation showing not a lot of capping after one applies the virtual temperature correction (which is huge given the amt of moisture in place). Regardless, a 58 supercell composite parameter and 4.9 STP represents the very supercell- and tornado-favorable environment that awaits any updraft that can utilize it. The 00z OAX sounding looks pretty good in terms of sfc-based initiation in areas with 3-4 F higher Tds.

 

[Josh Richardson]

Cap definitely finally breaking over Chickasaw County, cell going up to 37,000 ft. now and rising quickly.

 

[David Draun]

Tornado watch likely needed from SE MN down to the Chicago area very shortly. Cirrus canopies have also been preventing initiation but the MD suggests that Cbs will be breaking through it very soon.

And now the radar lights up, bye bye CAP!!

 

[J West]

Cells finally starting to show some life invof Decoah, IA up towards LaCrosse WI. Hopefully the steel-plated cap is starting to erode and let this show get on the road, which MKX seems confident of per the latest guidance.

 

[Jacob Ferden]

A word of caution from someone who grew up in SE Minnesota: If you're planning on chasing after dark the terrain is horrendous along and east of US 52 approaching the Mississippi River all the way from Rochester, MN to Dubuque, IA. Also, the population of deer in the vicinity is comparable to anywhere in the upper midwest. Just a concern in light of recent events.

 

[Bill Schintler]

The 00z soundings are interesting... The 00z DVN sounding has 400 m/s 0-1km SRH with >7000 j/kg SBCAPE!

Indeed, the 00Z DVN sounding was sweet. I wasn't chasing today - at work in Cedar Rapids (60 miles west of the DVN NWS), and the cap appeared close to breaking during the early evening hours - there were a number of CU trying to go up around here... According to the SPC mesoanalysis, the MLCIN was mostly eroded over western and central IA for several hours, while capping remained stronger in the eastern part of the state owing to slower air mass recovery after the morning MCS. I think surface-based initiation would have taken place in western or northwestern IA by late afternoon or early evening had the CI not overspread those areas while probably robbed them of a few degrees of surface heating.

- bill