Thursday, May 12, 2011

May 12 Severe Weather

Today's overall risk of severe weather
Significant closed low to weaken and eject southeast from the Central Plains. That low will be the focus of storms for today.

DISCUSSION
Weak to Moderate instability will once again develop as high temperatures and high dewpoints combine for a hot, sticky day. This system will impact the Eastern Plains into the Appalachians, and the Appalachians southward along the Coast.
A big factor is how these storms are becoming more unclear. Shearing fields are becoming more modest than predicted, which would lower the already low tornado threat and some wind threat.
Convective outflow from earlier storms has stabilized the atmosphere in the South/East Texas region into the Mid Missouri Valley.
However, should a cluster of storms develop, strong mixed layer CAPE would support a threat for hail and wind.

In the Plains northeast to the MS valley, convective development is also hazy. Early clouds ongoing in these areas are stopping instability from developing. It can be expected these clouds should remain at least an hour more in the Plains.
Although surface wind will be weakening, marginal shearing will give some potential to supercellular development. Should expected steep lapse rates and pockets of some mixed layer CAPE come through, an impulse will provide the forcing for storm development. This would contain large hail and damaging winds. However, in my own view, I would tone down this forecast, as current infrared imagery indicates some sort of disturbance and cloud cover in the Plains.

In the Lower Great Lakes and Upper Ohio Valley, a moist boundary layer may become fairly unstable from daytime heating. Shearing will be weak, as will deep layer flow. However, a shortwave will provide forcing for potentially substantial storms to fire up in this area. The expected initiation times would occur 7am- 4pm or 8am- 10pm CDT.

Risk for hail

Today's risk for tornadoes

Today's risk for damaging winds


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