Before you read further please know there will be plenty of changes between now and this time Wednesday. Please check back for the latest as the greatest risk area and scope of severity may shift either north or south
All of Central Indiana is under a heightened risk for severe weather between Wednesday 7am and Thursday 7am. During that time we’re anticipating multiple rounds of storms…beginning as early as the morning commute Wednesday.
One of the contributing factors to the severe weather set up is what will be a sharp temperature gradient across the state. From the 70s & 80s Central/Northeast to near 100 degrees in southwestern Indiana.
The warm front that delineates the differing air masses also serves as a “track” for storm clusters which will most likely be in a northwest to southeast fashion.
With little movement in the “track” or front early in the day this allows “training storms” to drop very high rainfall over a specific region. This is why flash flooding is a big concern I have tomorrow.
Precipitable Water Values (PWATs) will already by 1-1.5″ early tomorrow and peak Wednesday evening over 2″.
Precipitable Water Values (PWATs) will already by 1.5″+ early tomorrow and peak Wednesday evening over 2″.
So any storms in this highly tropical environment would easily be able to achieve Flash Flood Guidance in Central Indiana… which is around 1-2″ for one hour and 1.5-2″ for three hours in areas that got walloped last night.
Storms Wednesday morning will be primarily be heavy rain-makers and prolific lightning producers but could also drop severe hail in the strongest cells. These storms may either linger into midday or new clusters develop along a warm front that will be draped across the viewing area… both of which impede the ability of the atmosphere to destabilize quickly.
It should be noted that if the modeled morning storms do not materialize then the local atmosphere will destabilize quicker and severe storms will be likely area wide from the afternoon into predawn Thursday morning.
We’ll have to wait and watch for new storm initiation during late afternoon and early evening. It’s unknown at this time exactly where the warm front will be late in the day and how morning convection will influence it. The “modeled” atmosphere suggests Central/Northern Illinois will be the initiation point closer to the center of low pressure.
But supercelluar development in Central/Northern Indiana is also a possibility and this discrete storms that develop during peak heating have the best chance to produce tornadoes before eventually congeal into a larger complex.
Another wildcard in late day development is location of the atmospheric “cap”… or where it’s too warm in the mid-levels to support vertical storm development.
The “cap” or lid as it’s also called can limit storm development under it, but also aid in explosive storm development on its edge in a similar fashion to steam around a saucepan lid on a stove.
If the cap establishes over the I-70 corridor then the Indy metro area may miss the secondary storm show. We just don’t know for sure at this juncture.
For now the higher probabilities of severe wind and flash flooding remain along and north of I-70… with a possible bullseye along a line from Chicago to Fort Wayne.
The expected evening storm complex most likely yields a widespread swath of damaging wind in excess of 70mph and flash flooding rain of 3″+.
Please don’t just focus on tornado headlines. Flash flooding and lightning are dangerous, formidable (and likely) weather headlines with this set up… and deserves your attention.
Please be weather aware tomorrow and have a way to get watches and warnings. You can download the free Skytrak13 Weather app (http://www.wthr.com/category/225686/wthr-skytrak-weather-app) for local watches and warnings, forecast updates and live streaming of newscast. The severe threat should be east of the state by 7am Thursday Stay tuned for updates – Sean Ash