Sep 20, 2014 1630 UTC Day 1 Convective Outlook
Updated: Sat Sep 20 16:30:43 UTC 2014 (20140920 1630Z Day 1 shapefile | 20140920 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20140920 1630 UTC Day 1 Outlook Graphic
Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 198,961 31,315,579 Chicago, IL...Detroit, MI...Milwaukee, WI...Minneapolis, MN...St. Paul, MN...
Probabilistic Tornado Graphic
20140920 1630 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.
Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
2 % 134,348 23,579,004 Chicago, IL...Detroit, MI...Minneapolis, MN...Grand Rapids, MI...Aurora, IL...
Probabilistic Damaging Wind Graphic
20140920 1630 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.
Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
30 % 20,040 2,598,771 Minneapolis, MN...Bloomington, MN...Plymouth, MN...Brooklyn Park, MN...Eden Prairie, MN...
15 % 180,046 28,606,565 Chicago, IL...Detroit, MI...Milwaukee, WI...St. Paul, MN...Fort Wayne, IN...
5 % 270,389 17,073,730 Indianapolis, IN...Kansas City, MO...Wichita, KS...St. Louis, MO...Toledo, OH...
Probabilistic Large Hail Graphic
20140920 1630 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.
Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 196,123 31,089,888 Chicago, IL...Detroit, MI...Milwaukee, WI...Minneapolis, MN...St. Paul, MN...
5 % 274,354 17,189,178 Indianapolis, IN...Kansas City, MO...Wichita, KS...St. Louis, MO...Toledo, OH...
   SPC AC 201630

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1130 AM CDT SAT SEP 20 2014

   VALID 201630Z - 211200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF MN AND THE UPPER
   MS VALLEY...

   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDWEST/SOUTHERN
   GREAT LAKES...

   ...SUMMARY...
   SEVERE THUNDERSTORM GUSTS AND HAIL ARE MOST PROBABLE TODAY OVER
   PORTIONS OF MINNESOTA AND THE EASTERN DAKOTAS...AS WELL AS FROM
   NORTHERN MISSOURI ACROSS CENTRAL AND NORTHERN ILLINOIS TO SOUTHERN
   LOWER MICHIGAN.  A MARGINAL THREAT OF SEVERE WEATHER EXISTS ACROSS
   NEVADA...NORTHWESTERN ARIZONA AND WESTERN UTAH.

   ...EASTERN DAKOTAS ACROSS MN THIS AFTERNOON AND EVENING...
   A POTENT AND COMPACT SHORTWAVE TROUGH EVIDENT IN SATELLITE IMAGERY
   AND SHORT-TERM MODEL DATA WILL TRACK QUICKLY SOUTHEAST FROM ND AND
   ACROSS THE UPPER MS VALLEY THROUGH TONIGHT. LATEST INDICATIONS
   SUPPORT AT LEAST AN 80KT 500MB JET AIDING IN THE RAPID SOUTHEASTWARD
   TRANSLATION OF THIS IMPULSE ACROSS MN THIS AFTERNOON AND EVENING.
   STRONGLY FORCED DEEP-LAYER ASCENT WITHIN/BENEATH LEFT EXIT REGION OF
   THE MID/UPPER JET WILL BE REALIZED ALONG A SECONDARY COLD
   FRONT/WIND-SHIFT THAT IS FORECAST TO TRACK EAST-SOUTHEAST FROM ND/MN
   BORDER TO EXTREME SOUTHEAST MN AND WESTERN WI THROUGH EVENING.
   DESPITE LIMITED BOUNDARY LAYER MOISTURE AHEAD OF THE FRONTAL SURGE
   WITH SURFACE DEWPOINTS GENERALLY IN THE LOW-MID 50S F...THE
   MAGNITUDE OF FORCING/LIFT WILL COINCIDE PREFERENTIALLY WITH THE
   DIURNAL HEATING CYCLE TO SUPPORT DEVELOPMENT OF STRONG LOW-TOPPED
   LINEAR CONVECTION...AND POSSIBLY EMBEDDED SUPERCELL STRUCTURES
   ACROSS WESTERN MN BY EARLY AFTERNOON. GIVEN INTENSITY OF MESO-BETA
   SCALE FORCING...HIGH RES MODELS ARE QUITE CONSISTENT IN THE
   EVOLUTION OF A LINEAR MCS MOVING RAPIDLY SOUTHEAST ACROSS CENTRAL
   AND SOUTHEAST MN THROUGH THE DAYLIGHT HOURS. WITH LATEST VISIBLE
   SATELLITE IMAGERY INDICATING NEARLY CLOUDLESS CONDITIONS FROM
   EASTERN DAKOTAS ACROSS THE SOUTHERN HALF OF MN...CONFIDENCE IS
   INCREASING THAT SUFFICIENT HEATING/INSTABILITY WILL DEVELOP TO
   CONTRIBUTE TO A CORRIDOR OF STRONG TO DAMAGING THUNDERSTORM WIND
   GUSTS AS STORMS MOVE OVER THESE AREAS THROUGH THE AFTERNOON. HAIL UP
   TO AN INCH ALSO APPEARS LIKELY TO OCCUR WITH A FEW OF THE MORE
   ROBUST UPDRAFTS OR EMBEDDED SUPERCELLS WITH THIS CONVECTIVE SYSTEM.

   ...NORTHEAST MO/EASTERN IA TO SOUTHERN WI/NRN IL/IND AND LOWER MI...

   SOMEWHAT LOWER CONFIDENCE EXISTS REGARDING THUNDERSTORM
   DEVELOPMENT/EVOLUTION ACROSS THESE AREAS COMPARED TO FARTHER NORTH.
   ISOLATED...MOSTLY WEAK...CONVECTION HAS PERSISTED NEAR THE LEADING
   FRONTAL WIND-SHIFT ACROSS PARTS OF IA AND EXTREME SOUTHEAST NEB THIS
   MORNING. CI/DEBRIS CLOUDS AHEAD OF THIS ACTIVITY WERE THINNING AND
   THIS SHOULD CONTRIBUTE TO SURFACE HEATING/DESTABILIZATION THROUGH
   THE AFTERNOON. AS WEAK INHIBITION IS OVERCOME EXPECT MORE ROBUST
   STORM DEVELOPMENT TO OCCUR ALONG SOUTHWEST-NORTHEAST ORIENTED WEAK
   CONFLUENCE ZONES ASSOCIATED WITH 1) LEADING FRONT...AND 2)
   PRE-FRONTAL TROUGH/RESIDUAL OUTFLOW BOUNDARY...FROM NORTHERN MO TO
   SOUTHERN WI/NORTHERN IL. MODEST TO LOCALLY STRONG INSTABILITY
   /SBCAPE 2000-2500 J PER KG/ IS FORECAST TO EXIST NEAR/AHEAD OF THE
   INCREASE CONVECTION OVER MO/IL...WITH A GENERAL DECREASE IN CAPE TO
   UNDER 1000 J PER KG WITH EAST-NORTHEASTWARD EXTENT INTO LOWER MI.
   GREATEST SUPPORTIVE JUXTAPOSITION OF INSTABILITY AND STRENGTHENING
   DEEP-LAYER VERTICAL SHEAR FOR SEVERE STORMS THROUGH EARLY EVENING IS
   LIKELY TO EVOLVE FROM NEAR THE SOUTHERN TIP OF LAKE MICHIGAN
   SOUTHWESTWARD TO NEAR THE KS/MO BORDER. THIS ACTIVITY WILL HAVE A 
   CHANCE TO PRODUCE DAMAGING GUSTS AND SPORADIC LARGE HAIL. A COUPLE
   OF SUPERCELLS MAY DEVELOP A BRIEF OPPORTUNITY FOR A TORNADO IF
   STORMS CAN RETAIN DISCRETE CHARACTER AND ENCOUNTER LOCALLY ENHANCED
   LOW LEVEL SHEAR NEAR ANY LAKE BREEZES...OR RESIDUAL BOUNDARIES.
   SEVERE THREAT SHOULD DIMINISH FROM LATE EVENING INTO OVERNIGHT HOURS
   AS AIRMASS BECOMES MORE STABLE.

   ...GREAT BASIN...
   WIDELY SCATTERED AFTERNOON AND EVENING STORMS ARE EXPECTED TO TRACK
   NORTHWARD/NORTHEASTWARD OVER NV THROUGH TONIGHT. ACTIVITY WILL BE
   SPURRED/SUSTAINED BY A SLOW INCREASE IN BOTH MID-UPPER LEVEL WINDS
   AND LARGE-SCALE ASCENT AS DEEP-LAYER CLOSED LOW DEVELOPS EASTWARD
   FROM CA. MOISTURE WILL REMAIN MARGINAL FOR MORE ROBUST STORMS BUT
   DEEPENING/WELL-MIXED SUBCLOUD LAYER WILL DEVELOP WITH NEARLY
   DRY-ADIABATIC LAPSE RATES EVOLVING COINCIDENT WITH GENERALLY WEAK
   MLCAPE AOB 500 J PER KG. ALTHOUGH DEEP-LAYER SHEAR VALUES ARE MODEST
   FOR MORE ORGANIZED STORMS...SUFFICIENT AND STRENGTHENING FLOW
   THROUGH THE CLOUD-BEARING LAYER...IN COMBINATION WITH THE INCREASE
   IN LARGE SCALE FORCING FOR ASCENT....SHOULD CONTRIBUTE TO MODEST
   STORM ORGANIZATION INTO THIS EVENING WITH LOCALIZED SEVERE WIND AND
   HAIL POSSIBLE.

   ..CARBIN/JEWELL.. 09/20/2014

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z