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Monday, July 18, 2011

July 18 Severe Weather Discussion- Conditional Storm Action Day

Today's Hail Outlook

Today's Tornado Outlook

Today's Wind outlook

Overall Severe Risk
Area outlined in severe risk will become focus for severe thunderstorms in Lower Great Lakes this afternoon as the atmosphere destabilizes from the heat and humidity.
Thunderstorms ongoing this morning will provide the base for thunderstorms this afternoon on the remnant outflow boundaries, presence of cold front and weak warm air advection.

Vorticity Generation Potential is a parameter that indicates spinning updrafts, or spinning columns of rising air that create thunderstorms. Normally, the air naturally spins horizontally in the atmosphere. When these updrafts rise up, they tilt the natural rising air on its side, providing vertical spinning air for tornadoes.
Looking at models, the VGP parameter increases as the day goes on. While it does weaken into the noon hours, it is still substantial that the threat remains.
A better model to look at for spinning air is the EHI, or Energy Helicity Index. EHI's will increase in the area in question (South WI/North IL) as the days go on.
This is more worrying than the VGP. Well, I guess the VGP and EHI combined are more worrisome. But with the EHI at such a high level forecast, one can only wonder if tornadoes are possible. Below s just one of the images of EHI forecast.
This forecast is for 3 PM CDT today.

The EHI is combined of both Helicity AND Energy. The Energy is the CAPE values.
Below is an image of CAPE at 3 PM CDT today.
In this image we see a very large area of extremely high CAPE values.
With the spinning and energy in place, it seems that the stage is set for tornadoes.
There's just one issue- Storm Relative Helicity, a parameter that goes into the EHI, will be low. Very low in the areas mentioned.
There is still potential for tornadoes despite this setback, so we will be on the StormWatch all day.

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