Wed. severe weather probability reaches 45%

Probabilities of any form of severe weather within 25 miles of a point between 8 a.m. EDT Wednesday, Sep. 10 and 8 a.m. EDT Thurs., Sep. 11. Purple: 45 percent. Red: 30 percent. Yellow: 15 percent. Brown: 5 percent. Highlighted counties: Northern Indiana NWS office county warning area. Source: SPC "Day 2 Convective Outlook" issued at 1:36 a.m. EDT.
Probabilities of any form of severe weather within 25 miles of a point between 8 a.m. EDT Wednesday, Sep. 10 and 8 a.m. EDT Thurs., Sep. 11. Purple: 45 percent. Red: 30 percent. Yellow: 15 percent. Brown: 5 percent. Highlighted counties: Northern Indiana NWS office county warning area. Source: SPC “Day 2 Convective Outlook” issued at 1:36 a.m. EDT.

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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