Wednesday, June 17, 2009

Big Day Thursday

Looking for a potential big severe event in central Illinois and eastern Iowa tomorrow. We may see somewhat of a wind threat overnight if storms in Nebraska currently manage to congeal into a bow echo and progress eastward along the instability gradient into central Illinois.

In the early afternoon tomorrow, a warm front should extend primarily along Interstate 74 from Iowa City, IA to Champaign, IL. The 4 km WRF shows extreme instability with surface cape values pushing 6500 j/kg and low level helicities averaging around 250 m2/s2 along the warm front where surface winds back to the SE. Looks like the cap erodes along the warm front in eastern Iowa and northwest to central Illinois. If this happens, explosive supercell development would be favored. Another favored area will be northern Iowa, but I will cap bust all day before heading to Iowa for this one.

At this point for Thursday I'll be targeting anywhere between Iowa City, IA to Peoria, IL. If the mcs scenario does not play out completely different than the models are currently hinting at and we see something like the models showed on the 12z runs, I'd look for a couple significant tornadoes in eastern Iowa and NW Illinois.

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