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.



Storm-Chaser Wx said...

Hey Andrew,I am curious about where you got the derecho probability map, I can't seem to find it. Thanks for the coverage of this week's storms, but what are your thoughts on this weekend?

Andrew said...

The map comes from the Storm Prediction Center's SREF system- if you search it you should be able to find it after exploring the different parameters.

I'm kind of wrapped up in tomorrow's events for the time being, but come Thursday I'll be sure to look into the weekend.

Anonymous said...

Ok will this storm be a significant severe weather outbreak in the Mid-Atlantic region and will the storms be widespread cells (Tornado Outbreak) or lines, or collections of strong t-storms? Please make a post on the severe weather coming up in the near future...Thanks, Justin

Anonymous said...

They've got a 15% and "significant" tornado potential over Chicago. The models depict SB CAPES approaching 5500 J/KG right over the city and into northern Indiana, with helicity on the order of 500-600. Think this could be upgraded to a high risk? From what I've seen, any time you have parameters this extreme you get widespread damage. Since we're free of significant convection this morning over the moderate risk area, that instability should be quickly realized. Once this strong cap breaks, all hell is going to break loose with it. Keep up the work!

Eric (weather advance) said...

@ Andrew
Nice post, but I will make a warning against predicting a full-blown derecho here, because the conditions we have at hand are not the same, in fact I have noticed through a little research that derechos are much more likely when there is a large focus of surface heating, like there was last year, however, we are nowhere near as warm. Another thing to consider is that when you look at the 500 millibar charts, we are unusually cold aloft (a reoccurring theme this year), and this does not tend to favor derechos, but rather this is a much more prominent signature for tornadoes and potentially large hail. Thus, in general when you look for derechos, you should look for the largest region of instability to be near the surface associated with large surface heating, however this time we are cold aloft, which suggests much different scenario apart from derechos.

Eric (weather advance) said...

Another thing to remember about Derechos is that they are a self-sustaining mesoscale complex of thunderstorms, and last year they formed because of the dramatic surface heating & instability that was around, in fact there was no significant trough feature in their vicinity. This time, we have a major trough (by June standards) giving dynamic support for these systems, which suggests that there are different processes at work to produce these thunderstorms, and this also suggests that the most favorable environment will be underneath the significant trough feature. Thus implying that any storms that develop will have a tendency to stay underneath the support aloft, rather than move well out ahead of any support aloft (because of them characteristically being self-sustaining, being relatively independent of other atmospheric processes) like a derecho is known to do. Given this evidence, I don't think it's a good idea to be forecasting a derecho.

Anonymous said...

Nothing but heat, dryness and deadly wildfires here, it hasn't rained in weeks.
It's June 2012 all over again :(