Severe weather possible tomorrow, Saturday

Probability map from Day 2 Convective Outlook
Probability of severe weather within 25 miles of a point between 8 a.m. Friday and 8 a.m Saturday.

Update: The risks for tomorrow are pretty much the same in the updated convective outlook that the SPC issued at 1:30 p.m. EDT. In the new version, the 30 percent probability area dips just south of the Indiana-Michigan state line. The next outlook for tomorrow will be the first Day 1 Outlook of the day, scheduled for about 2 a.m. EDT.

The northern third of Indiana, as well as all of lower Michigan and parts of Illinois and Wisconsin have a slight risk of severe weather between 8 a.m. EDT tomorrow and 8 a.m. EDT Saturday, according to the Day 2 Convective Outlook that the National Weather Service (NWS) Storm Prediction Center (SPC) issued this morning. The slight risk area includes all 37 Indiana, Michigan and Ohio counties that receive warnings from the northern Indiana NWS office. All of those counties have at least a 15 percent probability of severe weather within 25 miles of any point (see an explanation of outlook probability numbers). But as you can see on the map at left, the probability is twice as high (30 percent) in the Chicago and Milwaukee areas, as well as in much of lower Michigan.

In the area covered by the northern Indiana NWS office, thunderstorms are most likely late Friday into Saturday, according to the Hazardous Weather Outlook that the office issued this morning.

According to the convective outlook, numerous episodes of strong to severe storms seem possible in the Great Lakes region through the day Friday. The greatest severe weather potential is damaging wind around the time of maximum daytime heating (i.e. around 3 p.m. EDT). Conditions such as high atmospheric instability and strong changes in wind speed with altitude could support relatively fast-moving and longer-lived linear storm segments. We could see some line echo wave patterns (bulges in thunderstorm lines that produce wave-shaped “kinks” in the lines) and bowing lines of storms. These could result in a greater potential for damaging winds and perhaps a brief tornado or two in any areas where they occur.

Later in the evening, especially in the eastern Great Lakes region, conditions should support one or two longer-lived lines of thunderstorm complexes. Damaging winds might accompany these storms into early Saturday morning.

Our next look at the risk of severe weather tomorrow comes when the SPC issues an updated Day 2 Convective Outlook at around 1:30 p.m. EDT.

Risk map from Day 3 Convective Outlook
Yellow area: Slight risk of severe weather between 8 a.m. EDT Saturday and 8 a.m. EDT Sunday. Green area: non-severe thunderstorms.

Also, much of Indiana has a slight risk of severe weather between 8 a.m. Saturday and 8 a.m. Sunday, according to today’s Day 3 Convective Outlook. As you can see on the map at left, the slight risk area includes the Indiana Counties of Allen and Whitley, as well as counties to the south and west and Ohio Counties to the east (Van Wert and Allen). In those areas, there’s a 15 percent probability of severe weather within 25 miles of a point on Saturday.