FCST: 06/05/10 – IA/IL/MO/IN | Convective Addiction

FCST: 06/05/10 – IA/IL/MO/IN

Posted on 04. Jun, 2010 by Jesse in Forecasts, Uncategorized

Saturday could be another day of potentially active weather across the Central Lowlands. A 1004 mb low is progged to be situated near the IA/NE border region by Saturday morning (per the NAM, GFS and ECMWF), though exact placement varies slightly by model choice.

A nearly stationary frontal boundary should be present from south central Iowa into central Illinois and Indiana. The NAM keeps the frontal boundary confined to roughly the I-80 corridor, whereas the GFS is much more aggressive in driving the frontal boundary well north of the I-80 corridor by 00z Sunday. A robust warm sector will likely develop south of the front, with CAPE values AOA 2,000 J/KG in some areas. While the NAM has a slightly more picayune warm sector confined to southern IA, northern Missouri and west central Illinois, the GFS depicts a much more capacious warm sector engrossing the southern third of Iowa, most of Illinois and the southwest third of Indiana by 00z Sunday.

Of greater significance will be the evolution of an overnight MCS that is currently forecast by models to track somewhere between I-80 and US 136. The actual evolution and track of this system, as well as its timely exit from the region, will determine the amount of instability that is able to evolve prior to convective initiation Saturday afternoon, as well as the ultimate location of any OFBs. A belt of 90-100 kt winds at 250 mb will be juxtaposed with 500 mb longitudinal flow on the order of 60-70 kts, along with modest southwesterly winds of 25-30kts, yielding SFC-500 mb bulk shear value AOA 50 kts (70 kts across far N IL).

Current thinking is that storm initiation will occur by late afternoon INVO remnant OFBs, though with zonal flow aloft, any shortwave has the potential to either spark convection spasmodically or contravene convective chances altogether. As is typically the case, a good morning forecast based on surface features will be on order to ensure successful intercepts on Saturday, should the severe threat materialize. All modes of severe weather are possible on Saturday, including tornadoes, severe hail and damaging winds. Given the potential strength of shear near the frontal boundary, any storm that becomes rooted in the boundary layer and peregrinates parallel to the front could have an enhanced tornado potential. The greatest threat for damaging winds > 70 mph and an enhanced tornado threat appears to lie along an axis roughly parallel to and immediately north of the US 36 corridor from KUIN to KIND.

Forecast written by Convective Addiction’s Jesse Risley and Ryan Wichman at 11:30 p.m. June 4th.