FCST: 06/01/10 – NE/IA/MO | Convective Addiction

FCST: 06/01/10 – NE/IA/MO

Posted on 31. May, 2010 by Jesse in Forecasts, Uncategorized

The next chance for significant severe weather appears to be developing across the Upper Midwest for late Tuesday afternoon, extending into the evening and overnight hours. It should be noted that the forecast dynamics associated with this event are presently pointing towards the ontogenesis of a potent MCS-type scenario (per 12z model runs on 05/31), featuring straight-line winds and large hail as the preeminent headlines, with a secondary threat of isolated tornadoes early in the evolution of this severe weather episode.

The GFS is not as lusty in lifting the warm front northward; however, given ongoing convective trends, the NAM appears to currently have a better handle on the evolution of this severe weather episode. Both models show CAPE values AOA 3000 J/KG across a broad warm sector extending from NE KS into southern Nebraska and points eastward, though the GFS confines the best instability to NE KS, SE NE and NW MO.

The absence of both a stalwart surface low and relatively stronger 500 mb flow, which is circumscribed to the northern Great Lakes region, will likely preclude the evolution of an otherwise momentous severe weather episode. However, modest 500 mb flow of 40-50kts will be present across the region at 21z on Tuesday, along with a strengthening LLJ on the order of 40-50kts propagating into northern MO and southern IA overnight Tuesday into Wednesday morning. This will aggrandize the nocturnal threat for a robust, organized MCS to continue propagating ESE into early Wednesday morning.

Current thinking is that one or two squall lines will develop near the I-29 corridor Tuesday afternoon and march ESE towards northern Missouri and SE Iowa through Tuesday evening and into Wednesday morning. The tornado threat will become more peripheral once the storms congeal into a linear mode, though rotating updrafts embedded within an otherwise linear structure will remain a distinct possibility as the LLJ intensifies after 00z.

While the large, begirding hodographs that are present in very favorable tornadic environments are not progged to exist tomorrow, a sample sounding from Red Oak, IA at 00z Wednesday (see KRDK SKEW-T image below) does indicate that conditions will be favorable for some tornadic activity across the region IF storms remain discrete for a short window of time after initiation.

Forecast written by Convective Addiction’s Jesse Risley and Ryan Wichman (Monday, May 31, 2010 at 3 p.m.)