Thursday Forecast.... Severe Weather Threat for Friday

Thursday: The day will start mostly cloudy with temps in the mid-upper 30s. Clouds will thin out some what in the afternoon. A partly-mostly cloudy wording will do. Temps will rise in the afternoon to around 50º. Winds will diminish through the day from 15-20mph in the morning to 5-10mph before nightfall. Skies will remain partly cloudy during the evening hours. Temps will be around 40º.

Friday: Friday looks like it will get interesting. I will do a general forecast then I will get into a more detail. Friday will start with rain and a few embedded thunderstorms. Temps will be in the low 40s. Winds will gradually increase through the day maxing out at 10-15mph later in the day.  A line of thunderstorms looks to move through our area in the time frame of 1-7p.m. (more on this below) Highs will max out in the mid 60s. As night falls, cloudy skies will dominate the sky with a few lingering showers. Temps overnight will be around 40º.

Friday Severe Weather Threat:

Here are some simulated images of the potential squall line.

 Dew point map

CAPE or instability at the ground level

High winds in all levels of the atmosphere suggest a linear storm mode. This is also known as wind shear.

Helicity or spin in the atmosphere can indicate tornadoes. The higher the helicity, the more spin there is.

CAPE Inhibition: The higher the CINH the harder it is for thunderstorms to get going. There is no sign of CINH in this map, so thunderstorms should pop in Illinois without too much trouble.

Here is the overall outlook for severe weather Friday evening:

Overall, I believe a squall line will develop in central Illinois and will race West- Southwestward. The storms may start super-cellular in Illinois and may produce a couple tornadoes.  As it progresses to Indiana, it will begin to become more linear and more intense. It will be fueled by the 1000 J/
kg Surface CAPE in front of the line. You can thank the dew points near 60º for the high surface CAPE. We may see a weather watch as early as 3 Friday afternoon. It will be pretty intense when the line moves into our area. Squall lines have a tendency to spawn weak tornadoes in the line and winds in excess of 80mph. The main threats will be high winds, large hail, and a few tornadoes. Especially from central Indiana southward. This weather system will need to be watched closely. I will update tomorrow with more information regarding this weather system.