Sep 20, 2013 1300 UTC Day 1 Convective Outlook
Updated: Fri Sep 20 12:51:41 UTC 2013 (20130920 1300Z Day 1 shapefile | 20130920 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20130920 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20130920 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probabilistic Damaging Wind Graphic
20130920 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probabilistic Large Hail Graphic
20130920 1300 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 23,745 7,353,114 Detroit, MI...Toledo, OH...Warren, MI...Sterling Heights, MI...Ann Arbor, MI...
   SPC AC 201247

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0747 AM CDT FRI SEP 20 2013

   VALID 201300Z - 211200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE ERN UPPER GREAT LAKES
   AREA AND VICINITY...

   ...SYNOPSIS...
   A RELATIVELY PROGRESSIVE UPPER FLOW FIELD IS EXPECTED THROUGH THE
   END OF THE PERIOD...AS A LARGE ERN PACIFIC TROUGH APPROACHES THE W
   COAST AND A SECOND/AMPLIFYING TROUGH CROSSES THE GREAT
   LAKES/MIDWEST/OH VALLEY AREA.

   WHILE A COLD FRONT ASSOCIATED WITH THE WRN TROUGH IS FORECAST TO
   SHARPEN WITH TIME AND MOVE INTO THE WRN GREAT BASIN...THE MORE
   ACTIVE FRONT FROM A CONVECTIVE PERSPECTIVE WILL CROSS THE UPPER
   GREAT LAKES AND THE LOWER OH/MID AND LOWER MS VALLEYS DURING THE
   DAY.  BY THE END OF THE PERIOD...THE FRONT -- AND ASSOCIATED BAND OF
   CONVECTION -- SHOULD REACH THE LOWER GREAT LAKES/UPPER OH VALLEY AND
   THE W SLOPES OF THE APPALACHIANS.

   ...ERN UPPER GREAT LAKES SWWD...
   A BAND OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS -- EXTENDING
   FROM THE GREAT LAKES REGION SWD ACROSS THE MIDWEST REGION AND THEN
   ON SWWD INTO TX WILL CONTINUE THROUGH THE PERIOD...SHIFTING
   GRADUALLY EWD WITH TIME.  WIDESPREAD CONVECTION AND HEAVY RAIN CAN
   BE EXPECTED ACROSS SRN PORTIONS OF THIS AREA...BUT SLIGHTLY ENHANCED
   SEVERE RISK IS EXPECTED FARTHER N INTO THE MID MS/LOWER OH VALLEY
   AND NWD INTO THE ERN UPPER GREAT LAKES VICINITY.  HERE...POCKETS OF
   HEATING SHOULD YIELD MODEST DESTABILIZATION AND A CORRESPONDING
   INCREASE IN THUNDERSTORM COVERAGE.

   AS THE UPPER TROUGH ADVANCES AND STRENGTHENS WITH TIME...INCREASING
   MID-LEVEL SWLYS MAY PROVIDE SUFFICIENT SHEAR FOR A FEW STRONGER
   STORMS TO EVOLVE -- MAINLY DURING THE AFTERNOON HOURS.  LOCALLY
   GUSTY WINDS -- PERHAPS REACHING SEVERE LEVELS IN A COUPLE OF AREAS
   -- WILL BE POSSIBLE BEFORE STORMS DIMINISH IN INTENSITY OVERNIGHT.

   ..GOSS/ROGERS.. 09/20/2013

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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z