Tuesday, June 11, 2013

Derecho Likely Tomorrow; Moderate Risk Issued

The likelihood for a derecho is on the rise tomorrow, as new model data and an upgrade from the Storm Prediction Center launch Wednesday into a significant weather event status.

The Storm Prediction Center has issued a moderate risk of severe weather for much of Illinois, nearly all of Indiana and the western half of Ohio in anticipation of a potentially significant weather event tomorrow. Latest reasoning from the SPC cites abundant and high instability in the highlighted areas, as well as high moisture content in the lower levels of the atmosphere as supportive for a significant damaging wind event. Expectation is for isolated supercells to grow into a bowing line segment, with the potential for a derecho to evolve.

Model probabilities for derecho formation tomorrow afternoon into the evening hours are pretty high, with upwards of a 70 percent chance of derecho formation across nearly all of the moderate risk area. My personal expectation is for the moderate risk to be modified slightly further east to account for increasing derecho parameters late Wednesday into early Thursday, however if the moderate risk were to remain unchanged I would understand the reasoning.

Evolution of this significant weather event should commence with multiple cells in northern and western Illinois before coagulation of these cells brings about a line segment of storm cells. With time, this segment should easily bow out and develop the danger for some serious damaging winds. Derecho formation is most likely to commence in east-central Illinois, throughout Indiana and into western Ohio. High resolution models initiate convection in the early afternoon hours, roughly around 4 PM Central time. Upscale development into a sustained bowing segment should ramp up going into the evening hours of 6 or 7 PM central.

 Oddly enough, this bow segment is expected to follow an almost identical path as the June 2012 derecho that left thousands upon thousands with damaged property across a wide swath of this country.  While the environment is not conducive for an incredibly damaging derecho like the one observed last year, it is very possible we could see a weaker derecho move through Indiana and Ohio after commencing in Illinois. Damage is possible.