05/19/05 FCST: MIDWEST

As SPC Day 2 Outlook shows 15% severe probability over large portion of the midwest, midsouth, and extending into southern plains, a discussion is introduced.

Of particular interest may be western and southern MO, with dewpoints expected to reach 70-74td on Thursday. Another feature which catches the eye are LCL heights from 1,000 m in W Central MO, down to 400 m in extreme southern MO, together w/ low LFC heights and minimal convective inhibition across the area. 0-3km ML CAPE values peak out at nearly 3,000 j/kg from extreme SW MO to S Central MO. Up, up above this juice at 250mb will be a jet nosing in at 100 kts from the NNW, w/ 500mb flow out of NW at 30-40 kts.

As was the case Wed, surface forcing mechanism - and therefore prediction of time and location of initiation - is a little tough to pin down. Surface wind fields and moisture convergence across the area look like a plate of limp noodles. SPC Outlook speaks timidly of a secondary surface front perhaps forming along I-70 corridor early on in the day, and beyond that we need to look for outflow boundaries from tonight's convection. If I had to pick a target now, I would say Springfield, MO where wind direction crossovers with height look closest to ideal, but possibilities exist over a very wide area of the midwest so flexibility will be key for chase prospects tomorrow.
 
Most of the models are consistant with good instability near sw mo, ne ok. Given strong cape and weak frontal boundry, any storm that can form could be very descrete. Small cluster of storms near Chanute should lay down some adequate outflow boundrys for tommows action.

HWO for spf and tulsa seem to hint that if anything can initiate things could really get going. I will have to agree with Mike as Joplin to Just east of SGF looks like a good target. This looks like a last shot for awhile as next week gets very hot and dry...
 
I like the KS, MO boarder south of Kansas City. Partially because I am near there. The low LCL level is a nice feature, as are the outflow from yesterdays storms.

HWO for this area is not caller for spotter activation because the action is likely to be discrete rather than widespread. They are requesting that spotters stay alert however, good enough for me.

I imagine the action will be further east but I assume MO becomes unchaseable as we go east.

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Tom Hanlon
 
Myself, I'll be partial to central IL. 16Z RUC Analysis shows a nice CAPE axis extending from DVN-PIA-ILX-swrd into east-central MO. The helicity is rather poor, but closer to 0Z, the CAPE and helicity meet up from ORD-IKK-DNV. Already starting to get warm and moist in the target area: 72/67 in CMI, 79/67 at SPI (17Z obs). Vis sat shows clear skies over the western half of IL, and the clouds are moving out to the east. Wolcott, IN profiler looks mainly unidirectional, but theres some hint of veering winds at Winchester, IL. I may bail on work early, depending on how trends continue. Looks like a decent prospect today.


Ben
 
Ben, I agree with you that there is some potential for severe storms - even supercells, later today across portions of northern IL in to IN. central IL I think is a bit too far south - but as the surface low sweeps southeastward it will at least clip parts of east central IL. Fairly discretet convection already developing with the main push - cell in Jones county IA just went svere warned- and certainly looks pretty good on radar. There is some drier air in west central IL that could hamper the southernmost cell's potential in the 1-3 hr time frame - but I think the area around Kankakee to Watseka could be interesting - and perhaps even sooner if moisture holds across northern IL. Certainly north of the I-80 corridor of IL could hold low 60 dewpoints this afternoon - and the small corridor of backed winds ahead of the low could support a rogue tornado or two. I'm pretty well stuck close to home today, unfortunately, but I'd probably be chasing this later today if it continues to look like supercells would be the favored mode.

Suspect a T box will be issued - mostly owing to the potential threat to the Chicago metro area. If lapse rates are what the RUC advertises - along with the strength of straightline shear - could see some exceptionally large hail by IL standards later today.

[edit]Ha! and SPC proves me wrong. Oh well. Svr box it is.[/edit]

Glen
 
Very unstable airmass seems to be developing today across a large target area. As we saw yesterday, RUC seems to be missing the mark on td's. Example: 3:00pm forecast has Topeka KS in the 55 td range; actual observation at 1:00pm already 65 td.

Although current discussion focuses on SO IL and SE MO, I would not totally discount W and N MO, or even E KS today. Although the various surface boundaries around the broad area are difficult to pin down, the relatively sharp dewpoint gradient never really worked its way out of central KS last night, so we see - for example - 64td in McPherson, KS and 48td in Great Bend two counties apart. Even Kansas City HWO has now introduced talk of discrete supercells and mentioned tornadoes, citing the upper level flow expected to nose southeastward into MO later today. Seems like because chances are so discrete and cover such a broad area today, official public forecasts are not sounding a big alarm bell. But, with this airmass, weak cap, falling LFC heights and effective deep layer bulk shear already reading 40 to 50 kts, there could be some fireworks today.
 
Looks like today will be another waiting game. :( Spc has tornado threat further to the east. All forecast discussions suggest that initiation, if any, could be from N. MO to SE KS and even in NE OK. Thinking of sitting in KC or a point to the south....
 
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