Isolated severe thunderstorms possible this afternoon and evening

Yellow area: Slight risk of severe weather between 9 a.m. EDT today and 8 a.m. EDT Wednesday. Red area: moderate risk of severe weather during same period.

Almost all of Indiana, the southern half of Lower Michigan and all of Ohio have a slight risk for severe thunderstorms this afternoon and evening, according to the Day 1 Convective Outlook that the National Weather Service Storm (NWS) Prediction Center issued at 8:45 a.m. EDT. The main threats are large hail and damaging straight-line winds. The NWS might need to activate SKYWARN storm spotters this afternoon into this evening, according to the Hazardous Weather Outlook the northern Indiana NWS office issued at 4:47 a.m. EDT.

In the “slight risk” areas of Indiana, Michigan and Ohio (see map, above right), the convective outlook indicates a 15 percent probability of damaging thunderstorm winds of 50 knots (58 mph) or greater within 25 miles of a point. The outlook indicates the same probability of one-inch diameter or larger hail. The probability of a tornado in these areas is negligible at two percent or less. To understand these probabilities, remember how often 58 mph winds do damage or one-inch hail falls within 25 miles of your home. The normal probability of such phenomena is probably less than one percent, so today’s probability is at least 15 times greater than normal. Read more about the outlook probabilities.

Actions to take
Make sure your weather alert radio is plugged in and working and that you’ll hear it if the NWS issues a severe thunderstorm watch or warning today. During any times you won’t be near a weather alert radio, make sure you have other ways to receive such information, including keeping a broadcast radio or television on or signing up for text alerts from your favorite local TV station. Above all, don’t ignore a severe thunderstorm warning. Remember how much damage a severe thunderstorm did in the Fort Wayne area in June of 2012, when the now-famous “derecho” came through. Severe thunderstorms can do a lot of dangerous damage, even when they do not produce tornadoes!

If you’re a SKYWARN storm spotter, gas up your car, check your communications gear and review NWS reporting criteria, as you might need them this afternoon and evening.

Meteorological setup
Afternoon showers and thunderstorms are forecast to develop across the mid-Ohio Valley and northwestward into Lower Michigan, as the left exit region of a 120-plus knot jet stream rounds the southeast side of an upper low and spreads across the region. With 500 to 1000 joules per kilogram of relatively low-topped mixed-layer convective available potential energy forecast to develop, isolated severe storms are expected — with organization potential enhanced by strong flow through the mid and upper troposphere. Along with a risk for hail, locally damaging winds can be expected through early evening — after which a diminishing trend is expected in conjunction with the boundary-layer stabilization that happens every evening.

Mississippi, Alabama again targeted
Elsewhere, Mississippi and Alabama, which were clobbered by tornadoes yesterday, are again in the cross hairs today. Parts of both states have a 15 percent risk of tornadoes this afternoon and evening.