Nearly the entire state of Indiana has a slight risk of severe weather between 9 a.m. EDT today and 8 a.m. EDT tomorrow, according to the “Day 1 Convective Outlook” that the National Weather Service (NWS) Storm Prediction Center issued at 8:56 a.m. EDT today. The slight risk area also includes about half of the 37-county warning area of the northern Indiana NWS office and all of IMO SKYWARN quadrant two.

The primary threat is damaging straight-line thunderstorm winds or gusts of 58 mph or stronger, although an isolated tornado cannot be ruled out. As you can see on the maps at right, the probability of damaging straight-line winds in northeastern Indiana is 15 percent, which is about 7.5 times the average probability for this time of year (2 percent). The probability of a tornado is 2 percent, which is about 20 times the average probability for this time of year (0.1 percent).

The severe weather risk is conditional, because it depends largely on sunshine. If cloud cover remains heavy all day, the threat of severe weather will be much lower than if the area sees sunshine. This is because the sun’s heating of the earth’s surface would increase atmospheric instability.

SKYWARN storm spotter activation might be needed this afternoon and early this evening, according to a “Hazardous Weather Outlook” issued by the northern Indiana NWS office at 5:27 a.m. EDT.

Residents of the slight risk area should be sure they have a reliable way to be aware of any watches or warnings the NWS might issue today, such as a weather alert radio. You can also keep up to date on weather developments by subscribing to this blog, following the northern Indiana NWS office on Twitter (@NWSIWX) and/or liking the northern Indiana NWS office on Facebook.

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The northern Indiana National Weather Service office has postponed until Thursday the weekly weather radio test that it normally conducts on Wednesdays between 11 a.m. and noon EDT time, due to the threat of severe weather as well as transmitter problems at South Bend.

The National Weather Service has issued a flash flood watch for most of northern Indiana and northwestern Ohio from early this afternoon through this evening.

A flash flood watch means that conditions may develop that lead to flash flooding. Flash flooding is a very dangerous situation.

View the full statement on the NWS website.

No part of the country has a severe weather probability of greater than 30 percent, according to an updated “Day 2 Convective Outlook” that the National Weather Service Storm Prediction Center issued at 1:18 p.m. EDT. The entire state of Indiana and all 37 counties in the county warning area of the northern Indiana NWS office continue to have a slight risk of servere weather between 8 a.m. EDT tomorrow and 8 a.m. EDT Thursdsay, with probabilities ranging form 15 to 30 times higher than a normal day for this time of year.

At midday, forecast models indicated a weaker low pressure system than previously expected. The latest thinking is that an organized squall line or multiple line segments will be the primary storm mode. Extensive clouds and precipitation early in the day should limit atmospheric instability and hamper the development of severe storms. Even so, damaging straight-line thunderstorm winds remain a possibility.

The SPC’s next outlook for tomorrow comes early tomorrow morning, when it issues it’s first “Day 1 Convective Outlook” of the day.

Update: NWS has published a multimedia briefing on this situation.

Much of northern Indiana and surrounding parts of Illinois, Michigan and Ohio have a 45 percent probability of some form of severe weather within 25 miles of a point tomorrow, according to the “Day 2 Convective Outlook” that the National Weather Service (NWS) Storm Prediction Center (SPC) issued at 1:36 a.m. EDT.

To put that in perspective, the historical average probability of severe weather in that area at this time of year is only one percent, according to the SPC website. That means that tomorrow’s probability of severe weather is 45 times the normal probability. Here’s a link to a Web page that will provide a better understanding of outlook probabilities,

There is a chance that morning cloud cover tomorrow will limit atmospheric instability and therefore limit severe weather potential. But if that doesn’t happen, widespread swaths of severe wind gusts with peak gusts approaching 75 mph are possible. A couple of tornadoes are also possible as are heavy rainfall and localized flooding.

The area of 45 percent probability includes essentially all of the 37-county warning area of the northern Indiana NWS office and therefore all four quadrants of IMO SKYWARN.

SKYWARN storm spotters should spend some time today reviewing reporting criteria and methods, charging device batteries and generally preparing for possible activation tomorrow.

All residents of the area depicted in the map above who plan outdoor activities tomorrow should make sure they have a way of receiving notification of any severe thunderstorm or tornado warnings that the NWS issues (don’t rely on being able to hear an outdoor warning siren!). They should also identify in advance how they’ll notify others of a warning and where and how everyone will take shelter.

The northern Indiana NWS office plans to issue a multimedia briefing regarding tomorrow’s severe weather possibilities later this morning. I’ll post it on the “W9LW’s Ramblings blog” when it’s available.

The SPC will issue an updated “Day 2 Convective Outlook” by 1:30 p.m. today. I plan to update the blog after it comes out.

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The entire state of Indiana and the entire 37-county warning area (CWA) of the northern Indiana National Weather Service (NWS) office have a slight risk of severe weather between 8 a.m. EDT Wednesday and 8 a.m. EDT Thursday, according to a “Day 3 Convective Outlook” that the NWS Storm Prediction Center issued at 3:30 a.m. EDT.

“Severe storms are possible Wednesday across southern portions of the Great Lakes region into parts of the middle Mississippi and lower Ohio valleys. This will be accompanied by the risk for damaging wind gusts, possibly a couple of tornadoes, and could impact the Chicago, Detroit, Indianapolis and Cleveland metropolitan areas,” SPC meteorologists wrote.

As you can see in the map above, the probabilities of severe weather within 25 miles of a point are highest in northern Indiana, where they reach 30 percent, the high end of the SPC’s “slight risk” criteria. Day three outlooks provide combined probabilities and therefore indicate the likelihood of any of the following forms of severe weather:

• Tornadoes.
• Damaging straight-line thunderstorm winds of at least 58 mph.
• Large hail of at least one inch in diameter.

Our next look at the severe weather outlook for Wednesday comes early tomorrow morning, when the SPC issues its first “Day 2 Convective Outlook” of the day.

Approximately the northern two thirds of Indiana has a slight risk of severe weather between 8 a.m. EDT Wednesday, Sep. 10 and 8 a.m. EDT Thursday, according to a “Day 4-8 Convective Outlook” issued by the National Weather Service Storm Prediction Center at 5 a.m. EDT today. The risk area includes portions of other states near Indiana and all 37 counties of the northern Indiana NWS office’s county warning area (and therefore all of IMO SKYWARN’s quadrants).

Forecast conditions indicate “an increasing potential for a regional severe weather event,” which could include supercells and the evolution of an organized thunderstorm system, “accompanied by the risk for damaging wind gusts and a few tornadoes,” according to the SPC outlook.

The SPC will next update its outlook for the period by 5 a.m. EDT tomorrow.

…STRONG THUNDERSTORMS MOVING TOWARD SOUTHERN DEFIANCE…PAULDING… NORTHWESTERN VAN WERT…NORTHERN BLACKFORD…NORTHWESTERN JAY… NORTHERN GRANT…WELLS…NORTHERN ADAMS…SOUTHEASTERN MIAMI… HUNTINGTON…SOUTHEASTERN WABASH…SOUTHEASTERN WHITLEY AND ALLEN COUNTIES… AT 924 PM EDT…NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
View the full statement on the NWS website.