Sep 3, 2015 2000 UTC Day 1 Convective Outlook
Updated: Thu Sep 3 19:53:38 UTC 2015 (20150903 2000Z Day 1 shapefile | 20150903 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20150903 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MARGINAL 22,850 12,632,580 Chicago, IL...Toledo, OH...Aurora, IL...Naperville, IL...Joliet, IL...
Probabilistic Tornado Graphic
20150903 2000 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.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
20150903 2000 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.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 22,850 12,632,580 Chicago, IL...Toledo, OH...Aurora, IL...Naperville, IL...Joliet, IL...
Probabilistic Large Hail Graphic
20150903 2000 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.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
   SPC AC 031953

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0253 PM CDT THU SEP 03 2015

   VALID 032000Z - 041200Z

   ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PORTIONS OF THE LOWER
   GREAT LAKES REGION...

   ...SUMMARY...
   ISOLATED STRONG/DAMAGING WIND GUSTS WILL BE POSSIBLE ACROSS PORTIONS
   OF THE LOWER GREAT LAKES REGION THIS AFTERNOON INTO EARLY THIS
   EVENING. OTHER STORMS WITH GUSTY WINDS MAY ALSO OCCUR THIS
   AFTERNOON/EVENING ACROSS SOUTH CENTRAL ARIZONA.

   ...DAY-1 CONVECTIVE OUTLOOK UPDATE...

   THE MRGL HAS BEEN SHIFTED SWD/SWWD TO ACCOUNT FOR ONGOING TRENDS IN
   DESTABILIZATION S OF CONVECTIVELY OVERTURNED AIR FROM CNTRL TO SERN
   LOWER MI. THE AIR MASS S OF A RELATED BOUNDARY IS BECOMING
   MARGINALLY TO STRONGLY UNSTABLE AS LOW-LEVEL LAPSE RATES STEEPEN
   AMIDST UPPER 60S/LOWER 70S DEWPOINTS. ADDITIONAL CONVECTION MAY
   DEVELOP/INTENSIFY IN THIS ENVIRONMENT ON THE SWRN RIM OF A MID-LEVEL
   CYCLONE CROSSING LOWER MI...OFFERING ISOLATED SVR-WIND POTENTIAL.
   SIMILAR ACTIVITY MAY ALSO DEVELOP WWD INTO NRN INDIANA/NERN IL WHERE
   THE LAKE-BREEZE BOUNDARY MAY OFFER SUFFICIENT ASCENT FOR CONVECTIVE
   DEVELOPMENT AMIDST 2000-3000 J/KG OF MLCAPE.

   OTHERWISE...STRONG-TSTM POTENTIAL WILL PERSIST THROUGH THE
   AFTERNOON/EVENING IN S-CNTRL AZ...PORTIONS OF THE SERN CONUS...AND
   PORTIONS OF THE NERN CONUS...THOUGH THE SVR RISK SHOULD REMAIN TOO
   LIMITED IN COVERAGE IN EACH CASE FOR MRGL DELINEATION.

   ..COHEN.. 09/03/2015

   .PREV DISCUSSION... /ISSUED 1130 AM CDT THU SEP 03 2015/

   ...SYNOPSIS...
   AN AMPLIFIED PATTERN OVER THE CONUS CONSISTS OF A DEEP TROUGH OVER
   THE PAC NW AND A RIDGE FROM TX TO ONTARIO.  SEVERAL SMALLER-SCALE
   TROUGHS ARE TRANSLATING AROUND THE ERN PERIPHERY OF THE RIDGE OVER
   LOWER MI AND AL...AND THE WRN PERIPHERY OF THE RIDGE FROM THE NRN
   GULF OF CA TO SRN AZ AND FROM SW CO TOWARD THE NRN HIGH PLAINS.  

   ...S/SE LOWER MI THIS AFTERNOON...
   CONVECTION ASSOCIATED WITH THE LOWER MI TROUGH WILL SPREAD SLOWLY
   SEWD THROUGH THE AFTERNOON ON CONVECTIVE OUTFLOW...MAINTAINED BY
   SURFACE HEATING AND THE MOISTURE/BUOYANCY NOTED IN THE 12Z DTX
   SOUNDING.  MODEST ENHANCEMENT OF MIDLEVEL WLY/NWLY FLOW WITH THE
   TROUGH...MLCAPE AOA 2000 J/KG...AND DCAPE NEAR 1000 J/KG COULD
   SUPPORT STRONG/ISOLATED DAMAGING OUTFLOW GUSTS WITH THE CONVECTION
   ACROSS S/SE LOWER MI THIS AFTERNOON. 

   ...S CENTRAL AZ THIS AFTERNOON/EVENING...
   WATER VAPOR LOOPS SUGGEST THAT A WEAK MID-UPPER SPEED MAX IS MOVING
   NNEWD FROM THE NRN GULF OF CA TOWARD SRN AZ.  AN INCREASE IN
   MOISTURE FROM THE S WILL CONTRIBUTE TO AN INCREASE IN CONVECTION
   COMPARED TO YESTERDAY...THOUGH THE CLOUDS WILL ALSO KEEP SURFACE
   TEMPERATURES COOLER.  THERE WILL BE SOME POTENTIAL FOR STORMS WITH
   GUSTY OUTFLOW WINDS LATER THIS AFTERNOON/EVENING ACROSS S CENTRAL
   AZ...JUST W OF THE THICKER CLOUDS WHERE SURFACE TEMPERATURES WILL BE
   WARMER.  AS OF NOW...IT IS NOT CLEAR THAT LOW DAMAGING WIND
   PROBABILITIES ARE NECESSARY...BUT THIS AREA WILL BE MONITORED IN
   LATER UPDATES.

   ...SRN MAINE/NH THIS AFTERNOON...
   A FEW STORMS WITH GUSTY OUTFLOW WINDS WILL BE POSSIBLE THIS
   AFTERNOON AS CONVECTION FORMS OVER THE HIGHER TERRAIN AND MOVES SEWD
   TOWARD THE COAST.  THE 12Z GYX SOUNDING SUPPORTS MODERATE BUOYANCY
   THIS AFTERNOON...BUT THE OVERALL RISK APPEARS TOO MARGINAL TO ADD
   DAMAGING WIND PROBABILITIES.

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z