FCST: 06/04/10 – WI/IA/MO/IL | Convective Addiction

FCST: 06/04/10 – WI/IA/MO/IL

Posted on 03. Jun, 2010 by Jesse in Forecasts, Uncategorized

A shortwave trough that currently resides over the south-central prairie province region of Canada will promulgate a ~ 1000mb low pressure system from the northern High Plains into the Great Lakes region by 02z Saturday. However, the exact placement of surface features associated with this attendant low pressure system vary according to the several different 12z model runs from Thursday morning.

While the NAM has the surface low presaged to tarry across southern Wisconsin at 00z Saturday, the GFS and the JMA are fairly congruous in having the surface low progged to move from eastern Minnesota to the Superior Uplands near the Wisconsin and Michigan border by 00z Saturday. The ECMWF is slightly more progressive, ostensibly centering the low pressure system over Lower Michigan state by 00z Saturday, whereas the Canadian GEM has a slightly less stalwart 1003 mb low centered over central Lake Michigan at 00z Saturday.

Further complicating matters will be a MCS that is expected to traverse across IA, MN, WI and IL overnight. The 00z HRRR moves the MCS across NC IA into S WI and far N IL through 14z Friday morning, whereas the 12z 4km WRF initiates the MCS in N IA and MN, propagating the system as far south as the Missouri border before exiting the region by late Friday morning. Regardless of which model solution, if any, accurately verifies, the location, timing and southward extent of the MCS will play a significant role in determining how much the atmosphere can recover by late Friday afternoon, as well as where any remnant OFBs may reside to help reinitiate convection.

By 21z Friday, the nose of the 100kt 250 mb winds should reach far NW IL, though the GFS is more progressive than the NAM in the placement of the best upper level support between 21z Friday and 00z Saturday. Synchronously, longitudinal 500 mb flow of 45-55 kts will sit atop broad southwesterly flow of 30+ kts as sfc-500 mb bulk shear values spike to over 30kts (per both the GFS and the NAM) between 21z Friday and 00z Saturday. If the atmosphere is indeed able to recover, the GFS has CAPE values AOA 2000 J/KG across the entire central third of Illinois by late Friday, whereas the NAM confines the best instability values AOA 2000 J/KG from southern Wisconsin into Missouri, roughly WNW of the I-55/I-94 corridor.

At 18z Friday 0-1 km SRH values are progged to agglomerate AOA 200 m2/s2 across an area from KEOK northeast to KJVL and points northward. As the frontal boundary begins to advect eastward, a remnant OFB from overnight/morning convection should serve as the atmospheric nitroglycerine to kindle convection Friday afternoon. Current thinking is that storms will initiate somewhere in NW IL and/or far southern WI by 21z INVO the Mississippi River, tracking ESE across NC and NW IL before congealing into possibly a quasi-linear structure.

If instability can materialize in the wake of earlier convection, preventing the setup from essentially falling to detritus, all modes of severe weather are possible on Friday afternoon across far southern WI, NW, NC and central IL, far northern MO, and far eastern Iowa, including tornadoes, especially when storms initiate and remain discrete, possibly interacting with remnant boundaries, along with damaging winds and severe hail.

Forecast written by Convective Addiction’s Jesse L. Risley Thursday, June 3rd at 8:00 p.m.