Apr 29, 2013 1300 UTC Day 1 Convective Outlook
Updated: Mon Apr 29 12:55:38 UTC 2013
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20130429 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20130429 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
20130429 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
20130429 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 25,592 1,764,171 Cedar Rapids, IA...Davenport, IA...Ottumwa, IA...Platteville, WI...
   SPC AC 291252
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0752 AM CDT MON APR 29 2013
   
   VALID 291300Z - 301200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN IA TO ADJACENT AREAS
   OF EXTREME NW IL AND SW WI...
   
   ...SYNOPSIS...
   LARGE-SCALE TROUGH AMPLIFICATION IS UNDERWAY FROM SRN BC/AB TO THE
   NRN ROCKIES.  WITHIN THIS STRENGTHENING CYCLONIC FLOW REGIME...A
   PRONOUNCED SHORTWAVE TROUGH/JET STREAK WILL PROGRESS EWD FROM WA
   THIS MORNING TO THE DAKOTAS BY TUESDAY MORNING.  THIS STRONGER
   TROUGH WILL BE PROCEEDED BY WEAKER LEAD TROUGHS EJECTING GENERALLY
   EWD FROM THE UPPER MS VALLEY TO THE UPPER GREAT LAKES...AND FROM THE
   CENTRAL HIGH PLAINS TO THE UPPER MS VALLEY.  THE SURFACE PATTERN
   THIS MORNING FEATURES A WEAKENING FRONTAL ZONE FROM WI TO KS...AND
   ANOTHER WEAKENING BOUNDARY ACROSS THE GULF COAST STATES.  BOTH
   BOUNDARIES WILL BECOME DIFFUSE TODAY AS CYCLOGENESIS OCCURS IN THE
   LEE OF THE CENTRAL/NRN ROCKIES...WITH A PRIMARY CYCLONE DEVELOPING
   TO NRN MN BY THE END OF THE PERIOD.
   
   ...CENTRAL PLAINS TO MID MS VALLEY THROUGH TONIGHT...
   A SMALL CLUSTER OF THUNDERSTORMS IS ONGOING IN CENTRAL IA NEAR THE
   STALLED SURFACE FRONT AND IMMEDIATELY ESE OF THE LEAD EJECTING
   SHORTWAVE TROUGH.  THIS CONVECTION SHOULD MOVE INTO WI AND WEAKEN BY
   EARLY AFTERNOON AS LOW-LEVEL CONVERGENCE WEAKENS AND THE FRONT
   BECOMES DIFFUSE...AND AS THE MIDLEVEL WAVE MOVES ENEWD. 
   THEREAFTER...GRADUAL LOW-LEVEL MOISTENING AND SURFACE HEATING WILL
   OCCUR BENEATH STEEP MIDLEVEL LAPSE RATES FROM IA TO KS.  THE
   DESTABILIZATION WILL COINCIDE WITH THE ARRIVAL OF THE SECOND WEAK
   SHORTWAVE TROUGH NOW CROSSING THE CENTRAL HIGH PLAINS. 
   HOWEVER...THE PROSPECTS FOR ADDITIONAL THUNDERSTORM INITIATION THIS
   AFTERNOON ARE CLOUDED BY WEAKENING OF THE SURFACE FRONT AND
   ASSOCIATED ASCENT...AS WELL AS THE WARMTH OF THE EML AND A LIKELY
   OVER-FORECAST OF LOW-LEVEL MOISTURE IN THE OPERATIONAL MODELS.  THE
   CONTINUED DEPICTION OF UPPER 60S DEWPOINTS INTO THE KC AREA BY THIS
   EVENING APPEARS TO BE THE RESULT OF THE LAND SURFACE TREATMENT IN
   THE MODELS...WHEREAS THE CLOSEST OBSERVED UPPER 60S DEWPOINTS RESIDE
   ALONG THE TX COAST AS OF 12Z.
   
   THE MORE PROBABLE SCENARIO IS FOR A FEW MORE STORMS TO FORM LATER
   THIS AFTERNOON INTO EARLY TONIGHT ACROSS IA IN CONJUNCTION WITH THE
   SECOND SHORTWAVE TROUGH.  RATHER MODEST BUOYANCY /MLCAPE CLOSE TO
   1000 J PER KG/ IS EXPECTED ON THE NE EDGE OF THE WARMER EML...WITH
   BOUNDARY LAYER DEWPOINTS IN THE MID-UPPER 50S.  STILL...VERTICAL
   SHEAR WILL BE SUFFICIENT FOR SUPERCELLS WITH MARGINALLY SEVERE HAIL
   AND ISOLATED DAMAGING GUSTS.  STORM DEVELOPMENT IS MUCH MORE
   QUESTIONABLE FARTHER SW INTO NW MO/NE KS WHERE STRONG SURFACE
   HEATING/DEEP MIXING ALONG THE DIFFUSE BOUNDARY IN NE KS COULD
   SUPPORT ISOLATED HIGH-BASED STORM DEVELOPMENT THIS EVENING.
   
   ...CENTRAL/ERN FL PENINSULA THIS AFTERNOON...
   A DIFFUSE MIDLEVEL TROUGH MOVING OVER FL FROM THE NE GULF OF
   MEXICO...IN CONCERT WITH DAYTIME HEATING AND INCREASING LOW-LEVEL
   MOISTURE...WILL PROMOTE THUNDERSTORM DEVELOPMENT ACROSS THE CENTRAL
   PENINSULA BY EARLY AFTERNOON.  THE STORMS WILL THEN MOVE EWD/NEWD
   TOWARD THE ATLANTIC COAST LATER THIS AFTERNOON AND ENCOUNTER A WEAK
   E COAST SEA BREEZE.  LOW-LEVEL AND DEEP-LAYER SHEAR WILL BE
   SUFFICIENT FOR ORGANIZED MULTICELL CLUSTERS WITH A FEW
   STRONG/DAMAGING GUSTS...AND PERHAPS MARGINAL SUPERCELLS ALONG THE E
   COAST WHERE LOW-LEVEL FLOW WILL BE SOMEWHAT BACKED.  LAPSE RATES
   ALOFT AND BOUNDARY LAYER DEWPOINTS IN THE 60S WILL LIMIT MLCAPE TO
   AOB 1500 J/KG...WHICH WILL LIKEWISE TEMPER THE THREAT FOR LARGE
   HAIL.
   
   ...LOWER RIO GRANDE VALLEY TODAY...
   A WEAK MIDLEVEL TROUGH WILL MOVE SLOWLY SEWD TODAY FROM NEAR DRT TO
   DEEP S TX.  THOUGH MIDLEVEL LAPSE RATES ARE NOT AS STEEP AS PREVIOUS
   DAYS...WEAKENING OF A TROUGH ALONG THE LOWER TX COAST WILL ALLOW
   MID-UPPER 60S DEWPOINTS TO SPREAD INLAND WITH DAYTIME
   HEATING...RESULTING IN MLCAPE OF 1000-1500 J/KG.  GIVEN EFFECTIVE
   BULK SHEAR NEAR 40 KT...A FEW ORGANIZED/SUPERCELL STORMS WILL BE
   POSSIBLE...WITH AN ATTENDANT RISK FOR ISOLATED LARGE HAIL/DAMAGING
   GUSTS.
   
   ..THOMPSON/COHEN.. 04/29/2013
   
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