Apr 27, 2015 2000 UTC Day 1 Convective Outlook
Updated: Mon Apr 27 19:57:31 UTC 2015 (20150427 2000Z Day 1 shapefile | 20150427 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20150427 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 70,336 16,442,091 Houston, TX...Dallas, TX...Fort Worth, TX...New Orleans, LA...Arlington, TX...
MARGINAL 72,971 14,946,769 Tampa, FL...St. Petersburg, FL...Shreveport, LA...Mobile, AL...Fort Lauderdale, FL...
Probabilistic Tornado Graphic
20150427 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
5 % 19,736 4,965,872 Dallas, TX...Fort Worth, TX...Arlington, TX...Irving, TX...Grand Prairie, TX...
2 % 84,712 22,691,081 Houston, TX...New Orleans, LA...Tampa, FL...Plano, TX...St. Petersburg, FL...
Probabilistic Damaging Wind Graphic
20150427 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
15 % 69,686 16,406,115 Houston, TX...Dallas, TX...Fort Worth, TX...New Orleans, LA...Arlington, TX...
5 % 73,395 15,028,759 Tampa, FL...St. Petersburg, FL...Shreveport, LA...Mobile, AL...Fort Lauderdale, FL...
Probabilistic Large Hail Graphic
20150427 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
15 % 69,689 16,396,059 Houston, TX...Dallas, TX...Fort Worth, TX...New Orleans, LA...Arlington, TX...
5 % 51,717 4,796,576 Shreveport, LA...Mobile, AL...Waco, TX...College Station, TX...Longview, TX...
   SPC AC 271957

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0257 PM CDT MON APR 27 2015

   VALID 272000Z - 281200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM N-CNTRL TX TO THE CNTRL 
   GULF COAST...

   ...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLIGHT RISK 
   OVER THE GENERAL AREA...

   ...THERE IS A MRGL RISK OF SVR TSTMS FOR PORTIONS OF CNTRL AND SRN
   FL...

   ...SUMMARY...
   ISOLATED STRONG TO SEVERE STORMS WITH HAIL...LOCALLY DAMAGING
   WIND...AND PERHAPS A TORNADO OR TWO MAY AFFECT PARTS OF
   NORTH-CENTRAL INTO EASTERN TEXAS AND PERHAPS SOUTHWEST LOUISIANA.  A
   FEW STRONG TO POSSIBLY SEVERE STORMS ALSO MAY OCCUR OVER CENTRAL AND
   SOUTHERN FLORIDA.

   THE ONLY SUBSTANTIAL CHANGES THIS OUTLOOK UPDATE INCLUDE...
   1) THE REMOVAL OF 5 PERCENT TORNADO PROBABILITIES OVER SERN LA.  THE
   EARLY DAY MCS HAS MOVED INTO THE GULF AND THE AIRMASS HAS BECOME
   LESS UNSTABLE IN ITS WAKE.  ANOTHER ROUND OF STORMS IS EXPECTED TO
   MOVE INTO SERN LA LATER TODAY/TONIGHT AND STRONG WIND PROFILES WILL
   SUPPORT A CONDITIONAL SEVERE THREAT FOR ORGANIZED STORMS.
   2) ADDED LOW SEVERE PROBABILITIES FOR MUCH OF THE SRN HALF OF THE FL
   PENINSULA AS RECENT ITERATIONS OF CONVECTION-ALLOWING MODELS SHOW
   THE NRN GULF OF MEXICO MCS CONTINUING ESEWD AND AFFECTING THE FL
   PENINSULA TONIGHT.

   ..SMITH.. 04/27/2015

   .PREV DISCUSSION... /ISSUED 1118 AM CDT MON APR 27 2015/

   ...SYNOPSIS...

   A MID TO UPPER-LEVEL LOW WILL EDGE SLOWLY EWD ACROSS THE SRN PLAINS
   IN RESPONSE TO AN AMPLIFYING UPSTREAM RIDGE OVER THE GREAT BASIN
   INTO NRN ROCKIES.  A MID-LEVEL JET STREAK OBSERVED WITHIN THE BASE
   OF THE UPPER LOW PER 12Z OBSERVED SOUNDINGS WILL PROGRESS GENERALLY
   EWD INTO THE CNTRL GULF COAST.

   AT THE SURFACE...AN AREA OF LOW PRESSURE OVER N-CNTRL TX WILL
   DEVELOP SEWD INTO SRN LA ALONG A COLD FRONT ADVANCING SEWD THROUGH
   CNTRL AND SRN PARTS OF TX.  MEANWHILE...VISIBLE SATELLITE AND
   SURFACE OBSERVATIONS AS OF MID MORNING INDICATE AN OUTFLOW BOUNDARY
   ASSOCIATED WITH THE BOW ECHO OVER SERN LA EXTENDING WWD THROUGH THE
   UPPER TX COAST BEFORE CURVING NWWD ALONG A BAZ-SEP LINE WHERE IT
   LINKS WITH THE SURFACE LOW AND ASSOCIATED COLD FRONT.

   ...SERN TX INTO THE CNTRL GULF COAST TODAY INTO TONIGHT...

   A WELL-DEFINED BOW ECHO WITH A HISTORY OF FAIRLY WIDESPREAD DAMAGING
   WINDS SHOULD CONTINUE ESEWD THROUGH THE REMAINDER OF FAR SERN LA
   LATE THIS MORNING INTO EARLY AFTERNOON WITH A RISK FOR DAMAGING
   WINDS AND PERHAPS A TORNADO OR TWO OVER THOSE LOCATIONS.  IN THE
   WAKE OF THIS MCS...IT APPEARS THAT WAA/ISENTROPIC ASCENT ATOP THE
   TRAILING OUTFLOW BOUNDARY COUPLED WITH DEEPER-LAYER FORCING FOR
   ASCENT RELATED TO THE ABOVE-MENTIONED MID-LEVEL JET STREAK MAY
   SUPPORT THE DEVELOPMENT OF TSTMS THIS AFTERNOON INTO TONIGHT FROM
   SERN TX EWD INTO LA.  

   BASED ON THE 12Z SOUNDINGS AT CRP AND BRO...AMPLE LOW-LEVEL MOISTURE
   SURMOUNTED BY A WELL-DEFINED EML WILL SUPPORT MODERATE AFTERNOON
   INSTABILITY AND THE POTENTIAL FOR ORGANIZED STORM MODES INCLUDING
   SUPERCELLS GIVEN 40-50 KT OF DEEP-LAYER SHEAR.  WHILE LARGE HAIL
   APPEARS TO BE THE PRIMARY HAZARD...LOCALLY DAMAGING WINDS AND
   PERHAPS A BRIEF TORNADO OR TWO ARE POSSIBLE.

   ...N-CNTRL INTO ERN TX THIS AFTERNOON/EVENING...

   AS MENTIONED ABOVE...CONSIDERABLE OVERTURNING OF THE AIR MASS HAS
   OCCURRED OVER ERN INTO N-CNTRL TX IN THE WAKE OF THE MCS NOW OVER
   LA.  HOWEVER...COLD MID-LEVEL TEMPERATURES COUPLED WITH A WARMING
   BOUNDARY LAYER SHOULD SUPPORT AIR MASS DESTABILIZATION BY AFTERNOON
   AHEAD OF THE SURFACE LOW AND COLD FRONT WITH MLCAPE APPROACHING
   1000-1500 J/KG.  FORCING FOR ASCENT IN ADVANCE OF THE DEEP-LAYER
   CYCLONE IS EXPECTED TO FOSTER THE DEVELOPMENT OF SURFACE-BASED
   STORMS BY AFTERNOON AMIDST A KINEMATIC ENVIRONMENT FEATURING
   VERTICALLY VEERING AND STRENGTHENING WINDS WITH HEIGHT.  AS
   SUCH...SUPERCELLS ARE POSSIBLE WITH THE RISK FOR LARGE
   HAIL...DAMAGING WINDS AND A COUPLE OF TORNADOES SPREADING SEWD INTO
   PARTS OF ERN TX.  THIS SEVERE WEATHER THREAT SHOULD BEGIN TO WANE BY
   MID TO LATE EVENING AS THE BOUNDARY LAYER BEGINS TO COOL AND
   STABILIZE.

   ...FL PENINSULA THIS AFTERNOON...

   PRONOUNCED WLY DEEP-LAYER FLOW OBSERVED BY 12Z SOUNDINGS WILL
   PERSIST TODAY WITH DIURNAL STORM DEVELOPMENT LIKELY REMAINING
   CONFINED TO THE EAST COAST SEA BREEZE.  WHILE MID-LEVEL LAPSE RATES
   WILL REMAIN POOR...DAYTIME HEATING COUPLED WITH A MOIST BOUNDARY
   LAYER WILL YIELD MODERATE AFTERNOON INSTABILITY AND THE POTENTIAL
   FOR A FEW STRONG TO MARGINALLY SEVERE STORMS THIS AFTERNOON WITH A
   RISK FOR LOCALLY DAMAGING WIND GUSTS.

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