April 29, 2008

4/25 Forecast

Full thread can be viewed here: http://stormtrack.org/forum/showthread.php?t=16164

4/23/08 - 12:17 PM

Potent shortwave trough with attendant surface low and cold front will slowly eject into the upper MS valley on Friday. Moderate instability will be present as far north as central WI owing largely to a very moist air mass. The triple point should be in eastern IA around 18z and lift ne into WI as the day progresses and the cold front should drift into the Chicago area by 00z/26. Amount of shear in the northern target should be sufficient for supercell structures if (as usual) we can get some cloud breaks and insolation after the morning convection moves out. My second concern is the 85ht LLJ veering progressively as the day goes on, so I'll be hoping for early clearing and initiation, which isn't unlikely given the meager forecast CINH.

4/24/08 - 5:05 PM
I'm losing hope in the potential tomorrow. Recent model runs have the sfc low screaming into northern WI in the mid-afternoon, taking the best shear profiles with it- far away from the best thermodynamics. My current thinking is that there will be a brief window of opportunity where tornadoes will be possible in the early afternoon near the MS river (Davenport, Dubuque area), and I can't rule out a rouge tornado in central WI before 00z, but that isn't exactly chaseable terrain. If we get enough sfc heating, the cap could be overcome out away from the cold front and produce a discrete storm before the cold front mashes it into a messy line, but that's very conditional.

4/25/08 - 11:41 AM
Decided to scrap the chase yesterday at 5 and it's looking like I might regret that decision. Things are looking up for eastern IA into northwestern IL with the MCS/ overnight convection moving out rapidly and the mid-level dry punch mixing out the low clouds behind that. I still believe there will be a brief window from 2-5pm where tornadoes will be possible in the e IA/nw IL/sw WI area. If I were chasing right now, I would be sitting in Davenport with the 77/70 surface ob.