Tuesday, August 3, 2010


Well, if there's any positive right now it's that skies are almost entirely clear along and south of the outflow boundary and warm front left in the wake of morning thunderstorms that rocked us here in DeKalb from about 4 AM - 7 AM. Doppler estimates have around 1-3 inches of rain having fallen in the area, due to the slow moving nature and east-west formation I discussed last night.

My guess is that the better part of the day is ruled by subsidence and weak forcing leading to a mostly thunderstorm free day across the forecast target area of NW and NC Illinois. If there were a target, I'd still place it around the Peoria to LaSalle area sometime after 6-7 PM. The NAM among others are still insistent on the eventual development of an isolated thunderstorm or two along the residual boundary likely draping itself around the Interstate 80 corridor. Turning is present, but speed shear and lack of surface flow will likely prevent this from being a tornado day. That said, should a severe cell be able to root to a boundary an isolated tornado is possible with any brief mini-supercell storm. I don't have my hopes up, and will not be making the trip down there unless things appear much more certain.

It should be toasty, with temperatures south of the boundary easily reaching the low to mid 90's in central Illinois, with dew points in the mid-upper 70's. While overdone, the RUC estimates about 8,500 j/kg of surface based cape by evening. While not exactly representative of what will actually be present to work with, it's apparent the juice will be there. It's subsidence and capping, along with weak surface convergence that will keep a lid on things, and prevent explosive severe development that may otherwise be possible. I'll keep an eye on that Peoria to LaSalle line, but I don't expect much at all until at least very near sunset. That's when I believe an isolated storm or two is possible along that line.

The more likely scenario is that things remain dry through the daylight period, and we see another gradual increase in thunderstorm activity after sunset and another noisy and wet evening along the warm front in eastern Iowa and northern Illinois.

... and cue the 10 AM / First Tuesday test of the local tornado sirens! If only that were an omen...!

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