Severe weather threat south this evening

Posted at 1:30 PM, Jun 22, 2016
and last updated 2016-06-22 13:30:06-04

WEST MICHIGAN — FOX 17 Meteorologists have been mentioning the possibility of strong to severe thunderstorms late this afternoon and through the early overnight hours for the past few days. With each computer forecast model run (there are several through the day), the real threat continues to be SOUTH of our entire viewing area across northern Illinois and northern Indiana. That said, a few of these severe storms may clip our southern counties along/south of the I-94 corridor. Damaging straight line or microburst winds at 70 mph or stronger are the primary threat, with other threats such as large hail, frequent lightning, heavy rain, and an isolated tornado also possible across our southern counties.

There are several factors we look at to determine if severe weather is feasible in our area. Mainly moisture, lift, and instability (the ability for the air to rise). One may be something called CAPE…convective available potential energy…the ability to provide fuel for these storms to fire. The best CAPE is actually south of our border. Next, the real atmospheric moisture is lacking over Michigan. Dew point temperatures, a measure of moisture in the atmosphere, are only in the upper 50s to low 60s (south). We really like to see those higher…in the upper 60s or better to provide more moisture for these storms. Third, we need lift! That lift will be provided by an arriving low pressure area and warm front…neither of which will ever reach southern lower Michigan. They may come close, but both are expected to remain SOUTH of the border. That said, areas closer to the low and the warm front such as Van Buren, Berrien, Cass, and St. Joseph counties are under a “moderate risk” for severe weather development. The threat diminishes further north and is only a “slight risk” for Grand Rapids and a “marginal risk” north of Grand Rapids.

I believe the “biggest” threat or bulls-eye with this system will be south of Michigan. Again, the best chance of severe storms in West Michigan will be along/south of I-94, with isolated chances up to and including the Grand Rapids and vicinity locations. Note the image attached to this story is from the Storm Prediction Center. These meteorologists are responsible for issuing severe weather outlooks and watches. The moderate threat exists across southern Van Buren, Berrien, Cass, and southern St. Joseph County. An enhanced risk can be found a bit further north, which graduates to a slight risk in to Grand Rapids (yellow). So the threat/chance of severe weather diminishes the farther north you are, and increases the farther south you go.

The greatest time frame for severe storms is anywhere from 8 PM through 4 AM. Make sure to have a NOAA severe weather radio or mobile device that can broadcast watches/warnings/advisories if it’s overnight and you’re sleeping. Storms like these tend to produce heavy rain and wind that typically cause trees/branches to fall on houses and injure people. Make sure if a warning is issued you can retreat to a safe place like a basement or shelter. Get the complete forecast