Convective Addiction

FCST: 05/24/12 – Western Great Lakes and Upper Mississippi Valley Regions

Posted on 24. May, 2012 by Jesse in Uncategorized

There’s not much change in thinking to the post that we made on Facebook last night, but just as a heads up, if you live in the Upper Mississippi river valley and western Great Lakes region, strong upper-level dynamics are taking aim on this corridor as the surface low presently over the Plains deepens and moves towards NW WI by 00z/FRI, dragging the cold front into E IA and N MO. A potent mid-level jet core AOA 80 kts will take aim on the region as the trough lifts across the eastern prairie provinces of Canada (SK and MB), rendering SFC-500 mb deep layer shear profiles on the order of 70-80 kts across parts of E MN/NW WI/W MI (upper peninsula).

Though the aereal extent of more substantial instability may be the one limiting factor in the norther regions today, favorable lapse rates, dynamic forcing, and ample dry air aloft, coupled with seasonably strong wind shear, should foment a more demonstrable risk for damaging winds and large hail, with tornadoes also possible (perhaps one or two strong if storms can remain discrete given the forcing), namely east of the frontal boundary and proximal to the surface low where horizontal vorticity values will likely be maximized (cf. 00z/24 NAM, 21z/23 SREF and 12z/23 ECMWF)

Due to the nature of there being a fairly strong cold front, a widespread tornado outbreak doesn’t presently appear as likely, given forecast Skew-t/Log-p profiles looking more unidirectional than not; nevertheless shear profiles are very favorable for damaging winds, with large hail a lesser threat due to slightly higher WBZ profiles than may otherwise be optimal . However, a deepening surface low with 50-60 kts of shear at 850 mb, coupled with strongly backed surface winds oriented very perpendicular to the boundary, especially S/E of the triple point, could well produce some short-lived, albeit stronger tornadoes, especially if more magnanimous instability materializes.

Further south, a threat may exist ahead of the cold front in parts of MO and IL, as instability values are progged to be better than further north due to potentially better moisture, and a pre-frontal trough may be something to watch in that region by late afternoon as conditions become more favorable for damaging winds in what will likly be a more linear complex that forms between 3 PM and 7 PM west of the Mississippi River.

(cf. 00z/24 NAM, 03z/24 SREF and 00z/24 ECMWF)

JLR