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.

Please feel free to use the sharing links below to share this information with others via social networks, etc. Also, if you have an comments or questions, please use the comment link under the post title.

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.

The northern Indiana office of the National Weather Service issued an updated “Hazardous Weather Outlook” at 3:34 p.m. EDT in which it advises SKYWARN storm spotters to “be prepared to send in reports as storms move through the area.” The full text appears below.

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NORTHERN INDIANA
334 PM EDT FRI SEP 5 2014

INZ004>009-012>018-020-022>027-032>034-MIZ078>081-OHZ001-002-004-005-
015-016-024-025-061945-
ST. JOSEPH IN-ELKHART-LAGRANGE-STEUBEN-NOBLE-DE KALB-STARKE-PULASKI-
MARSHALL-FULTON IN-KOSCIUSKO-WHITLEY-ALLEN IN-WHITE-CASS IN-MIAMI-
WABASH-HUNTINGTON-WELLS-ADAMS-GRANT-BLACKFORD-JAY-CASS MI-
ST. JOSEPH MI-BRANCH-HILLSDALE-WILLIAMS-FULTON OH-DEFIANCE-HENRY-
PAULDING-PUTNAM-VAN WERT-ALLEN OH-
INCLUDING THE CITIES OF...SOUTH BEND...MISHAWAKA...ELKHART...
GOSHEN...LAGRANGE...TOPEKA...ANGOLA...KENDALLVILLE...LIGONIER...
AUBURN...GARRETT...KNOX...NORTH JUDSON...WINAMAC...FRANCESVILLE...
PLYMOUTH...BREMEN...ROCHESTER...WARSAW...WINONA LAKE...
COLUMBIA CITY...SOUTH WHITLEY...FORT WAYNE...MONTICELLO...
BROOKSTON...LOGANSPORT...PERU...WABASH...NORTH MANCHESTER...
HUNTINGTON...BLUFFTON...OSSIAN...DECATUR...BERNE...MARION...
HARTFORD CITY...MONTPELIER...PORTLAND...DOWAGIAC...CASSOPOLIS...
STURGIS...THREE RIVERS...COLDWATER...HILLSDALE...BRYAN...WAUSEON...
ARCHBOLD...DEFIANCE...NAPOLEON...PAULDING...ANTWERP...OTTAWA...
PANDORA...VAN WERT...DELPHOS...LIMA
334 PM EDT FRI SEP 5 2014 /234 PM CDT FRI SEP 5 2014/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHWEST OHIO...
NORTHERN INDIANA AND SOUTHWEST LOWER MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND TONIGHT. SOME OF
THESE STORMS MAY BE SEVERE. THE MAIN RISK WILL BE WIND GUSTS UP
TO 65 MPH...BUT LARGE HAIL MAY ALSO BE POSSIBLE. LOCALLY HEAVY
RAINFALL IS EXPECTED WITH THESE STORMS AS WELL.

AFTERNOON TEMPERATURES WILL CLIMB TO THE LOWER 90S TODAY. COMBINED
WITH HIGH HUMIDITY...THIS WILL LEAD TO HEAT INDEX VALUES AROUND
100.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THUNDERSTORMS ARE POSSIBLE TUESDAY AND WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS SHOULD BE PREPARED TO SEND IN REPORTS AS STORMS MOVE
THROUGH THE AREA. 

&&

STAY TUNED TO NOAA WEATHER RADIO FOR FURTHER DETAILS OR UPDATES...OR
CHECK OUR WEB SITE AT WEATHER.GOV/IWX

$$

INZ003-MIZ077-061945-
LA PORTE-BERRIEN-
INCLUDING THE CITIES OF...MICHIGAN CITY...LA PORTE...NILES...
BENTON HARBOR...ST. JOSEPH...BUCHANAN
334 PM EDT FRI SEP 5 2014 /234 PM CDT FRI SEP 5 2014/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHERN INDIANA
AND SOUTHWEST LOWER MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND TONIGHT. SOME OF
THESE STORMS MAY BE SEVERE. THE MAIN RISK WILL BE WIND GUSTS UP
TO 65 MPH...BUT LARGE HAIL MAY ALSO BE POSSIBLE. LOCALLY HEAVY
RAINFALL IS EXPECTED WITH THESE STORMS AS WELL.

AFTERNOON TEMPERATURES WILL CLIMB TO AROUND 90 DEGREES TODAY.
COMBINED WITH HIGH HUMIDITY...THIS WILL LEAD TO HEAT INDEX VALUES
FROM THE MID 90S TO AROUND 100.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

DANGEROUS SWIMMING CONDITIONS DUE TO HIGH WAVES AND STRONG RIP
CURRENTS ARE EXPECTED ALONG THE LAKE MICHIGAN SHORELINE ON
SATURDAY.

THUNDERSTORMS ARE POSSIBLE TUESDAY AND WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS SHOULD BE PREPARED TO SEND IN REPORTS AS STORMS MOVE
THROUGH THE AREA. 

&&

STAY TUNED TO NOAA WEATHER RADIO FOR FURTHER DETAILS OR UPDATES...OR
CHECK OUR WEB SITE AT WEATHER.GOV/IWX

$$

LMZ043-046-061945-
NEW BUFFALO MI TO ST JOSEPH MI-MICHIGAN CITY IN TO NEW BUFFALO MI-
334 PM EDT FRI SEP 5 2014

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE NEARSHORE WATERS OF
SOUTHEASTERN LAKE MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND TONIGHT. SOME OF
THESE STORMS MAY BE SEVERE WITH STRONG WIND GUSTS...HAIL...AND
LOCALLY HIGHER WAVES.

CONDITIONS HAZARDOUS TO SMALL CRAFT ARE EXPECTED LATE TONIGHT.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

HAZARDOUS CONDITIONS FOR SMALL CRAFT ARE EXPECTED TO CONTINUE
INTO SATURDAY.

THERE IS A CHANCE FOR THUNDERSTORMS TUESDAY AND WEDNESDAY.

&&

STAY TUNED TO NOAA WEATHER RADIO FOR FURTHER DETAILS OR UPDATES...OR
CHECK OUR WEB SITE AT WEATHER.GOV/IWX/?N=MARINE

The National Weather Service has issued a severe thunderstorm watch, in effect until 9 p.m. EDT, for much of northern Indiana and nearby states. It includes all of IMO SKYWARN quadrant two except for Blackford and Jay Counties. The verbatim watch announcement appears below.

URGENT - IMMEDIATE BROADCAST REQUESTED
   SEVERE THUNDERSTORM WATCH NUMBER 495
   NWS STORM PREDICTION CENTER NORMAN OK
   305 PM EDT FRI SEP 5 2014

   THE NWS STORM PREDICTION CENTER HAS ISSUED A

   * SEVERE THUNDERSTORM WATCH FOR PORTIONS OF 
     NORTHERN ILLINOIS
     NORTHERN INDIANA
     SOUTHERN AND EASTERN LOWER MICHIGAN
     NORTHWEST OHIO
     LAKE ERIE
     LAKE HURON
     LAKE MICHIGAN

   * EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 305 PM UNTIL
     900 PM EDT.

   * PRIMARY THREATS INCLUDE...
     SCATTERED DAMAGING WIND GUSTS TO 70 MPH LIKELY
     ISOLATED LARGE HAIL EVENTS TO 1.5 INCHES IN DIAMETER POSSIBLE

   THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 75
   STATUTE MILES NORTH AND SOUTH OF A LINE FROM 15 MILES EAST
   SOUTHEAST OF MOUNT CLEMENS MICHIGAN TO 65 MILES WEST OF
   VALPARAISO INDIANA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE
   THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU5).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
   FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
   AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
   THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
   AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
   DO PRODUCE TORNADOES.

   &&

   DISCUSSION...TSTMS EXPECTED TO INCREASE IN COVERAGE/STRENGTH ALONG
   AND AHEAD OF ESE-MOVING COLD FRONT NOW APPROACHING THE WRN SUBURBS
   OF CHICAGO AND WRN LWR MI. DEVELOPMENT ALSO MAY OCCUR ALONG
   PRE-FRONTAL CONFLUENCE AXES AND LAKE BREEZE BOUNDARIES IN NRN IN/SRN
   MI. BAND OF ELEVATED STORMS NOW FORMING E OF ROCKFORD IL MAY
   INTENSIFY AS IT OUTPACES SFC COLD FRONT AND ENCOUNTERS GREATER
   LOW-LVL INSTABILITY IN THE CHICAGO AREA OVER THE NEXT 1-2 HRS. THESE
   STORMS...AND THOSE FORMING FARTHER E...WILL HAVE A TENDENCY TO
   ORGANIZE INTO N-S LINES. ASSOCIATED EMBEDDED BOWS WILL POSE A RISK
   FOR DMGG WIND AND POSSIBLY SVR HAIL THOUGH EARLY TNGT GIVEN VERY
   WARM/MOIST LOW-LVL ENVIRONMENT...RESIDUAL EML...AND 35+ KT WSWLY
   UNIDIRECTIONAL 700-500 MB FLOW.

   AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
   TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
   KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM
   MOTION VECTOR 26035.

BULLETIN - IMMEDIATE BROADCAST REQUESTED
   SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 495
   NWS STORM PREDICTION CENTER NORMAN OK
   305 PM EDT FRI SEP 5 2014

   SEVERE THUNDERSTORM WATCH 495 IS IN EFFECT UNTIL 900 PM EDT
   FOR THE FOLLOWING LOCATIONS

   ILC031-043-053-063-075-089-091-093-097-105-197-060100-
   /O.NEW.KWNS.SV.A.0495.140905T1905Z-140906T0100Z/

   IL 
   .    ILLINOIS COUNTIES INCLUDED ARE

   COOK                 DUPAGE              FORD                
   GRUNDY               IROQUOIS            KANE                
   KANKAKEE             KENDALL             LAKE                
   LIVINGSTON           WILL                


   INC001-003-007-017-033-039-049-069-073-085-087-089-091-099-103-
   111-113-127-131-141-149-151-169-179-181-183-060100-
   /O.NEW.KWNS.SV.A.0495.140905T1905Z-140906T0100Z/

   IN 
   .    INDIANA COUNTIES INCLUDED ARE

   ADAMS                ALLEN               BENTON              
   CASS                 DE KALB             ELKHART             
   FULTON               HUNTINGTON          JASPER              
   KOSCIUSKO            LAGRANGE            LAKE                
   LA PORTE             MARSHALL            MIAMI               
   NEWTON               NOBLE               PORTER              
   PULASKI              ST. JOSEPH          STARKE              
   STEUBEN              WABASH              WELLS               
   WHITE                WHITLEY             


   MIC005-015-021-023-025-027-037-045-049-057-059-063-065-067-075-
   077-087-091-093-099-115-125-145-147-149-151-155-157-159-161-163-
   060100-
   /O.NEW.KWNS.SV.A.0495.140905T1905Z-140906T0100Z/

   MI 
   .    MICHIGAN COUNTIES INCLUDED ARE

   ALLEGAN              BARRY               BERRIEN             
   BRANCH               CALHOUN             CASS                
   CLINTON              EATON               GENESEE             
   GRATIOT              HILLSDALE           HURON               
   INGHAM               IONIA               JACKSON             
   KALAMAZOO            LAPEER              LENAWEE             
   LIVINGSTON           MACOMB              MONROE              
   OAKLAND              SAGINAW             SANILAC             
   SHIAWASSEE           ST. CLAIR           ST. JOSEPH          
   TUSCOLA              VAN BUREN           WASHTENAW           
   WAYNE                


   OHC003-039-043-051-063-069-077-095-123-125-137-143-147-161-171-
   173-060100-
   /O.NEW.KWNS.SV.A.0495.140905T1905Z-140906T0100Z/

   OH 
   .    OHIO COUNTIES INCLUDED ARE

   ALLEN                DEFIANCE            ERIE                
   FULTON               HANCOCK             HENRY               
   HURON                LUCAS               OTTAWA              
   PAULDING             PUTNAM              SANDUSKY            
   SENECA               VAN WERT            WILLIAMS            
   WOOD                 

SEVERE THUNDERSTORM WATCH 495 IS IN EFFECT UNTIL 900 PM EDT FOR THE FOLLOWING LOCATIONS IN . INDIANA COUNTIES INCLUDED ARE ADAMS ALLEN BENTON CASS DE KALB ELKHART
View the full statement on the NWS website.

…HEAT ADVISORY REMAINS IN EFFECT UNTIL 6 PM EDT /5 PM CDT/ THIS EVENING… HAZARDOUS WEATHER… * THE HEAT INDEX IS EXPECTED TO REMAIN AROUND 100 DEGREES THIS AFTERNOON OVER NORTHERN INDIANA AND NORTHWEST OHIO. IMPACTS…
View the full statement on the NWS website.

A large part of Indiana and parts of nearby states continue to have a slight risk of severe thunderstorms this afternoon and tonight, according to an updated “Day 1 Convective Outlook” that the National Weather Service (NWS)  Storm Prediction Center (SPC) issued at 12:08 p.m. EDT.

The slight risk area continues to include almost all of the 37-county warning area of the northern Indiana NWS office. The SPC widened the slight risk area a bit since it’s 9 a.m. EDT outlook.

The latest outlook indicates that scattered strong to severe storms might produce locally damaging winds and marginally severe hail across parts of the lower Great Lakes and Midwest later this afternoon into tonight.

The atmospheric set-up appears favorable for the development of lines and/or small clusters of mainly multi-cell storms from parts of the mid-Mississippi Valley east-northeastward into Lower Michigan and the lower Great Lakes later today and into tonight, as surface heating further destabilizes the atmosphere along and ahead of an approaching cold front.

Storms that form will pose a conditional risk for damaging wind and possibly severe hail, given the very warm and humid environment near the Earth’s surface. Small bows and/or arcing line segments are possible. Although the strongest storms should occur before mid to late evening, strong activity could persist into late tonight and early Saturday over Ohio and the lower Great lakes.

An updated “Hazardous Weather Outlook” issued at 12:05 p.m. EDT by the northern Indiana NWS office continues to indicate that SKYWARN storm spotter activation might be needed this afternoon and tonight.

The next outlook update from the SPC is due out by 4 p.m. EDT.