Apr 17, 2013 2000 UTC Day 1 Convective Outlook
Updated: Wed Apr 17 20:03:41 UTC 2013
Probabilistic to Categorical Outlook Conversion Table
Public Severe Weather Outlook

The SPC is forecasting ...a significant severe weather episode is expected over parts of the southern/central plains later today and tonight....   Please read the latest public statement about this event.  View What is a Watch? clip.

Categorical Graphic
20130417 2000 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20130417 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.
Probabilistic Damaging Wind Graphic
20130417 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.
Probabilistic Large Hail Graphic
20130417 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.
Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MODERATE 74,540 4,788,441 Oklahoma City, OK...Tulsa, OK...Norman, OK...Columbia, MO...Wichita Falls, TX...
SLIGHT 298,910 36,774,942 Chicago, IL...Dallas, TX...Ft. Worth, TX...Nashville, TN...Louisville, KY...
   SPC AC 171959
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0259 PM CDT WED APR 17 2013
   
   VALID 172000Z - 181200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS FOR FAR NWRN TX...MOST OF
   OK...SERN KS...SWRN/CNTRL MO...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN PLAINS TO THE
   MID-MS/TN VALLEYS...
   
   ...SRN PLAINS TO THE MID-MS/TN VALLEYS...
   PRIMARY CHANGE THIS OUTLOOK IS TO ADD HIGHER WIND PROBABILITIES
   WHICH EXTENDS THE MODERATE RISK FARTHER NE INTO CNTRL MO.
   HERE...PRONOUNCED DESTABILIZATION HAS OCCURRED /AS SAMPLED BY 18Z
   SGF RAOB/ WITH THE SURFACE WARM FRONT ARCING INTO NRN MO. WITH AN
   IMPULSE EVIDENT IN WATER VAPOR IMAGERY EJECTING INTO THE CNTRL/SRN
   PLAINS...TSTMS FROM CNTRL KS TO SWRN OK SHOULD GROW UPSCALE THIS
   EVENING. WITH LOW/MID-LEVEL S/SWLYS EXPECTED TO STRENGTHEN E OF THE
   PIVOTING FRONT...A FEW QLCS/CLUSTERS SHOULD EVOLVE ACROSS THE OZARK
   PLATEAU TO THE MID-MS VALLEY WITH ALL SEVERE HAZARDS EXPECTED.
   
   FARTHER SW...MAIN ADJUSTMENT WAS TO SHIFT TORNADO PROBABILITIES
   BASED ON THE CURRENT POSITION OF THE STATIONARY FRONT.
   
   ..GRAMS.. 04/17/2013
   
   .PREV DISCUSSION... /ISSUED 1132 AM CDT WED APR 17 2013/
   
   ...SYNOPSIS...
   
   A POSITIVELY TILTED LONG-WAVE TROUGH FROM THE CANADIAN PRAIRIE
   PROVINCES TO LOWER CO VALLEY WILL MOVE EWD THIS PERIOD IN RESPONSE
   TO THE PROGRESSION OF A SERIES OF LOWER-AMPLITUDE PERTURBATIONS
   THROUGH THE NERN PACIFIC.  WITHIN THIS BROADER-SCALE PATTERN...A
   MIDLEVEL JET STREAK AND ASSOCIATED VORTICITY MAXIMUM WITHIN THE
   LONG-WAVE TROUGH BASE OVER THE LOWER CO VALLEY WILL REACH THE
   CNTRL/SRN HIGH PLAINS LATER TODAY INTO THIS EVENING...PRIOR TO
   MOVING INTO THE MID MO VALLEY BY THURSDAY MORNING.
   
   IN RESPONSE TO THESE UPPER-AIR DEVELOPMENTS...A LEE CYCLONE OVER
   N-CNTRL NM WILL DEVELOP SEWD ALONG AN ASSOCIATED STATIONARY BOUNDARY
   INTO NWRN TX BY 18/00Z BEFORE ACCELERATING NEWD INTO THE LOWER MO
   VALLEY BY 18/12Z.  THE BAROCLINIC ZONE ATTENDANT TO THIS MIGRATORY
   CYCLONE WILL LIFT NWD THROUGH THE OZARKS AND LOWER MO/OH VALLEYS AS
   A WARM FRONT.  UNCERTAINTY STILL REMAINS ON THE EXACT LOCATION OF
   THE WRN EXTENSION OF THIS BOUNDARY OVER THE SRN PLAINS THIS
   AFTERNOON.  CURRENT INDICATIONS ARE THAT IT WILL STRETCH FROM CNTRL
   THROUGH SWRN OK INTO THE SRN TX PNHDL BY THE 17/21-18/00Z TIME
   FRAME.  A DRYLINE WILL MIX EWD THROUGH WRN TX TODAY...LIKELY
   REACHING NWRN TX INTO THE TX BIG COUNTRY BY PEAK HEATING.  BY
   TONIGHT...EXPECT THE WRN EXTENSION OF THIS BOUNDARY TO SURGE SEWD
   ACROSS WRN/CNTRL PARTS OF OK/TX AS A COLD FRONT.
   
   ...SRN/CNTRL PLAINS INTO THE OZARKS...
   
   12Z OBSERVED SOUNDINGS SHOWED A POTENT COMBINATION OF RICH BOUNDARY
   LAYER MOISTURE /I.E. LOWEST 100-MB MEAN MIXING RATIOS OF 13-14 G PER
   KG/ BENEATH A PRONOUNCED EML WHERE 700-500-MB LAPSE RATES WERE
   APPROACHING 8.5-9.0 C/KM.  WHERE STRONGER HEATING CAN OCCUR...THESE
   PARAMETERS WILL YIELD A MODERATELY TO STRONGLY UNSTABLE WARM SECTOR
   BY AFTERNOON WITH MLCAPE VALUES APPROACHING 2000-3000 J/KG.
   
   TODAY/S SEVERE WEATHER SCENARIO REMAINS COMPLICATED BY VARYING MODEL
   SOLUTIONS ON FRONTAL PLACEMENT...AND THE POTENTIAL FOR EARLY DAY
   STORMS IN CONJUNCTION WITH AN APPARENT WEAK IMPULSE CURRENTLY
   PROGRESSING NEWD THROUGH THE SRN PLAINS.  CURRENT INDICATIONS ARE
   THAT INITIAL SURFACE-BASED STORM DEVELOPMENT WILL OCCUR LATE THIS
   MORNING OR EARLY THIS AFTERNOON ALONG THE RETREATING WARM FRONT OVER
   ERN KS INTO MO.  HERE...A RAPIDLY MOISTENING/DESTABILIZING AIR MASS
   WILL COINCIDE WITH A STRONGLY SHEARED ENVIRONMENT...WHICH WILL BE
   SUPPORTIVE OF SUPERCELLS CAPABLE OF VERY LARGE HAIL...TORNADOES
   /SOME POSSIBLY STRONG/...AND DAMAGING WINDS.  SEE RECENTLY ISSUED
   TORNADO WATCH 114 FOR DETAILS.
   
   STORMS MAY GROW UPSCALE INTO CLUSTERS OR LINE SEGMENTS BY THIS
   EVENING INTO TONIGHT WITH A CONTINUED RISK FOR DAMAGING
   WINDS...HAIL...AND PERHAPS A FEW TORNADOES.
   
   FARTHER SWWD ALONG THE FRONT FROM N-CNTRL OK INTO NWRN TX...STRONGER
   CAPPING IS EXPECTED TO DELAY STORM INITIATION UNTIL LATER THIS
   AFTERNOON INTO EVENING WITH THE HIGHEST PROBABILITY OF DEVELOPMENT
   OCCURRING NEAR THE DRYLINE-FRONT TRIPLE POINT.  DESPITE AN INITIAL
   WEAKNESS IN FORECAST HODOGRAPHS IN THE 2.5-4 KM AGL LAYER...THE
   ENVIRONMENT WILL BE VERY SUPPORTIVE OF INTENSE SUPERCELLS CAPABLE OF
   VERY LARGE HAIL AND TORNADOES /SOME POTENTIALLY SIGNIFICANT AND
   LONG-TRACKED/.  AN ENHANCED TORNADO THREAT IS EXPECTED TO PERSIST
   INTO TONIGHT ALONG THE I-44 CORRIDOR OF OK WHERE HODOGRAPHS WILL
   GROW INCREASINGLY LARGE AND THE BOUNDARY LAYER WILL REMAIN VERY
   MOIST AND MODERATELY UNSTABLE.
   
   STORMS SHOULD EVENTUALLY CONSOLIDATE INTO A BROKEN LINE ALONG THE
   SURGING COLD FRONT OVERNIGHT WITH A CONTINUED RISK FOR DAMAGING
   WINDS...LARGE HAIL...AND A FEW TORNADOES.  
   
   ...SRN IA/NRN MO/IL INTO TONIGHT...
   
   CLUSTERS OF ELEVATED TSTMS ARE ONGOING ACROSS THE REGION WITH
   ACTIVITY LIKELY BEING FORCED BY LOW-LEVEL WAA/ISENTROPIC ASCENT AT
   THE TERMINUS OF A 40-50 KT LLJ...AND DCVA ATTENDANT TO A VORTICITY
   MAXIMUM OVER CNTRL IA /PER RADAR DATA/.  EXPECT THESE STORMS TO
   CONTINUE EWD TODAY WITH AN ASSOCIATED RISK FOR LARGE HAIL AND
   DAMAGING WINDS.  
   
   ...PARTS OF KY/TN THROUGH THIS EVENING...
   
   REGIONAL RADAR DATA INDICATE STORM REGENERATION OCCURRING FROM CNTRL
   KY INTO NERN TN...ALONG THE WRN EDGE OF A RESIDUAL COLD POOL
   ATTENDANT TO A NOCTURNAL MCS.  MODIFICATION OF THE 12Z NASHVILLE
   SOUNDING FOR CURRENT CONDITIONS INDICATES THAT THE AMBIENT
   ENVIRONMENT IS ALREADY MODERATELY UNSTABLE WITH MLCAPE OF AROUND
   2500 J/KG...WHICH SHOULD PROMOTE FURTHER STORM INTENSIFICATION. 
   THIS IS SUPPORTED BY 12Z CONVECTION-ALLOWING MODEL GUIDANCE WHICH
   DEVELOPS A SWWD/SWD-PROPAGATING MCS ACROSS THE REGION INTO THIS
   EVENING.  THOUGH VERTICAL SHEAR WILL REMAIN WEAK...THE DEGREE OF
   INSTABILITY WILL FOSTER INTENSE UP/DOWNDRAFTS CAPABLE OF DAMAGING
   WINDS AND SEVERE HAIL.
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

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