Wednesday, June 23, 2010

Updated forecast for today (6/23)

Not quite as gungho as I was yesterday about the tornado potential in Illinois this afternoon, but that could be my morning MCS goggles. What gives me trouble is the convection training along the target area across northern Illinois into central Iowa. Rather than one single bow echo moving thru the area laying down an OFB and leaving clearing skies in it's wake, we've had a very disorganized training east-west line along Interstate 80. Thus, confidence in the location of the OFB and the extent of destabilization are somewhat in question at this point in the morning.

That said, the risk still exists and I will be paying close attention to any areas of significant destabilization ahead of the low today near the OFB. Extensive WAA should help lift the OFB north slowly thru the afternoon, but ultimately it should end up very near Interstate 80, not overly far from where it sits now. After a couple waves of convection, destabilization should begin to occur in southeast Iowa, and eventually extend into northern Illinois. Initially, convection should begin to develop in southeast Iowa but rapidly explode into northwest Illinois during the early-mid afternoon hours. My current target time for initiation is 2-3 PM CDT from near Quincy, IL to the Quad Cities. While low level shear will again remain fairly unidirectional, early in the afternoon hodographs will have some slight turning, which coupled with potentially significant destabilization and the aid of one or more boundaries could favor early storm mode in the form of supercells. This remains conditional, as line segments or multicell clusters are easily a plausible scenario as well which would favor a damaging wind threat. Should initial storm mode take the form of quasi-discrete supercells, a few tornado reports would be possible, likely very near Interstate 80 in northern Illinois. My target for tornado development is between Interstate 88 and 80 in northwest Illinois from the Quad Cities toward Mendota, IL... or a triangle from Moline, IL to LaSalle, IL to Rochelle, IL. Should the currently forecast extreme instability be realized along with the unseasonably strong wind fields associated with the wave, perhaps we can begin talking about a strong tornado or two with any storm initially interacting with the boundary in this area. Storm speeds will also be faster than you'd normally expect in mid-late June, so this is something to consider.

Eventually, congealment into a linear storm mode seems more than likely across central into northeast Illinois as storms move into northern Indiana. Given unseasonably strong wind fields, isolated embedded tornadoes would remain a legitimate threat through the evening.

I'll be hanging here in DeKalb for the afternoon, waiting to see how things unfold but may eventually drop slightly SW to intercept initial convection.

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