Sunday, July 11, 2010

Marginal Potential 7/11

Scott Weberpal shot me a text this evening, and after taking a brief glance I tend to concur with the idea of a marginal shot at an isolated tornado or two tomorrow, generally across eastern Iowa into northwest Illinois and maybe even far southern Wisconsin tomorrow evening.

A fairly robust shortwave is currently making it's way thru the northern plains overnight, with several convective complexes moving across Minnesota and Iowa associated with the wave. Some of this convection will likely be ongoing thru the morning hours across portions of central Iowa and northern Missouri. In the early morning hours, the shortwave and a potential MCV which if presence could warrant a heightened severe potential across the mid-Mississippi Valley region should be located over central Iowa. There is considerable disagreement among the operational models to the location and track of the shortwave, but a movement into eastern Iowa early and into northwest Illinois by peak heating seems reasonable to me. Convection should continue and likely die out during the late morning and early afternoon across Iowa southward into Missouri. Re-intensification of the tail end of this complex into a forward propagating MCS across southern Missouri during the afternoon is possible, which could pose a severe wind threat into the evening as it moves east south east into southern Illinois into the night time hours.

Further north, as convection begins to decay and destabilization occurs ahead of the wave and potential MCV in far eastern Iowa into northern Illinois, new convention should begin to develop toward late afternoon. While directional shear will pose favorable turning, speed shear may not be all that impressive which may favor either a multi-cell pulse severe threat or brief HP supercell mode, the presence of an MCV and slightly stronger than forecast deep layer speed shear could present a brief window for isolated tornado development with any stronger cells that manage to develop ahead of the wave, likely in northwest Illinois. Good lapse rates, and good low level turning could be enough to squeeze out a surprise.

This is certainly a very conditional, and best case scenario only presents a marginal tornado risk, but for mid-July still certainly warrants a mention and half an eye tomorrow afternoon. Tia and I are celebrating an anniversary tomorrow, but being the broke college students we are, have no major set-in-stone plans beyond spending the day together in some fashion. Being the sport she is, she has already given the green light to the potential for a local chase should things fall into place. That said, I'm not interested in wasting a potential relaxation day to sit and do nothing only to spend hours in the car for no reason, but it's been a while and should stuff go locally we may venture out for a looksie.

Best time frame and region for any "violently" rotating columns of air to make their way toward ground level would be right around peak heating from 3-6 PM in an area from Galesburg to Sterling, Illinois. I'll enter a disclaimer however that with such model disparity on the outcome of such a complex convective scenario that this target area is subject to change, or completely disappear by tomorrow morning.

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