Apr 21, 2010 1300 UTC Day 1 Convective Outlook
Updated: Wed Apr 21 12:39:16 UTC 2010
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20100421 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20100421 1300 UTC Day 1 Tornado Probabilities Graphic
Torndao Legend Image
Probabilistic Damaging Wind Graphic
20100421 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Wind Legend Image
Probabilistic Large Hail Graphic
20100421 1300 UTC Day 1 Large Hail Probabilities Graphic
Hail Legend Image
   SPC AC 211236
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0736 AM CDT WED APR 21 2010
   
   VALID 211300Z - 221200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS
   PARTS OF THE CENTRAL AND SOUTHERN HIGH PLAINS...
   
   ...SYNOPSIS...
   A CLOSED LOW WITHIN THE SOUTHERN PORTION OF A SPLITTING UPPER TROUGH
   NEAR THE PACIFIC COAST APPEARS LIKELY TO BECOME INCREASINGLY CUT-OFF
   FROM STRONGER WESTERLIES TODAY.  ONLY A SLOW EASTWARD MIGRATION
   ACROSS THE SOUTHERN SIERRA NEVADA INTO THE GREAT BASIN IS
   EXPECTED...MAINLY IN RESPONSE TO SHORT WAVE PERTURBATIONS PIVOTING
   AROUND ITS CIRCULATION CENTER.  AS THIS OCCURS...MODELS GENERALLY
   INDICATE THAT DOWNSTREAM SHORT WAVE RIDGING WILL SHIFT EAST OF THE
   SOUTHERN ROCKIES...THROUGH THE CENTRAL AND SOUTHERN HIGH PLAINS BY
   12Z THURSDAY.  GRADUAL MID-LEVEL HEIGHT RISES ARE ALSO PROGGED EAST
   OF THE LOWER MISSISSIPPI VALLEY THROUGH THE SOUTHEAST STATES...BUT A
   COOL CYCLONIC MID/UPPER FLOW REGIME WILL PERSIST ACROSS MUCH OF
   EASTERN CANADA AND THE EASTERN U.S...TO THE SOUTHEAST OF A PROMINENT
   BLOCKING RIDGE.
   
   IN RESPONSE TO THE EVOLVING UPPER PATTERN...A SIGNIFICANT COLD FRONT
   IS EXPECTED TO ADVANCE EAST OF THE WASATCH AND LOWER COLORADO VALLEY
   THROUGH THE REMAINDER OF THE CENTRAL/SOUTHERN GREAT BASIN.  WHILE
   SURFACE TROUGHING SLOWLY DEEPENS TO THE LEE OF THE ROCKIES...A
   LOW-LEVEL BAROCLINIC ZONE IS EXPECTED TO BECOME BETTER DEFINED
   ACROSS SOUTHEAST COLORADO INTO NORTHWEST TEXAS...AS STRONG HEATING
   OCCURS ACROSS THE HIGH PLAINS TO THE SOUTH AND WEST OF IT BY LATE
   AFTERNOON.  AT THE SAME TIME...A RETURN FLOW OF MOISTURE APPEARS
   LIKELY TO CONTINUE DEVELOPING ACROSS THE SOUTHERN PLAINS ...BUT
   SURFACE DEW POINTS HIGHER THAN THE LOWER 60S MAY NOT ADVECT NORTH OF
   THE LOWER RIO GRANDE VALLEY UNTIL TOMORROW.
   
   ...CENTRAL/SOUTHERN HIGH PLAINS...
   21/03Z SREF GUIDANCE INDICATES MORE UNCERTAINTY CONCERNING SEVERE
   POTENTIAL THAN EARLIER RUNS...PERHAPS DUE TO THE INFLUENCE OF WEAK
   MID/UPPER SUPPORT FOR UPWARD VERTICAL MOTION...AND THE PRESENCE OF
   CONSIDERABLE LOWER/MID TROPOSPHERIC INHIBITION.  MOISTURE
   CONVERGENCE AND DAYTIME HEATING NEAR THE DEVELOPING LOW-LEVEL
   BAROCLINIC ZONE ARE STILL PROGGED TO CONTRIBUTE TO MODERATE CAPE OF
   1000-2000 J/KG.  AND...DESPITE FLOW FIELDS RATHER MODEST IN
   STRENGTH...VEERING PROFILES FROM EASTERLY AND SOUTHERLY AT
   LOW-LEVELS TO WESTERLY AT MID-LEVELS WILL PROBABLY PROVIDE
   SUFFICIENT SHEAR FOR SUPERCELLS.
   
   AT LEAST ISOLATED TO WIDELY SCATTERED LATE AFTERNOON STORM
   DEVELOPMENT STILL SEEMS PROBABLE...BUT HIGHEST PROBABILITIES PRIOR
   TO NIGHTFALL MAY BE IN FAVORABLE LOW-LEVEL UPSLOPE FLOW ACROSS
   SOUTHEAST COLORADO...BENEATH MORE STRONGLY DIFLUENT AND DIVERGENT
   UPPER FLOW.  POTENTIAL FOR BOUNDARY LAYER BASED STORMS MAY INCREASE
   FOR A PERIOD THIS EVENING ACROSS THE TEXAS/OKLAHOMA PANHANDLE
   REGION...NEAR THE NOSE OF A NOCTURNALLY STRENGTHENING LOW-LEVEL JET.
   THEREAFTER...AS THE BOUNDARY LAYER ALONG AND SOUTH OF THE FRONTAL
   ZONE COOLS AND STABILIZES...STORM DEVELOPMENT ROOTED IN AN ELEVATED
   WARM ADVECTION REGIME...NORTH OF THE FRONT INTO THE CENTRAL
   PLAINS...IS EXPECTED.  THIS MAY PERSIST AND SPREAD EAST
   NORTHEASTWARD THROUGH THE NIGHT...PERHAPS WITH INSTABILITY
   SUFFICIENT FOR A CONTINUING RISK FOR HAIL...BUT POTENTIAL FOR
   DAMAGING WIND GUSTS APPEARS LOW AT THE PRESENT TIME.
   
   ...GREAT BASIN...
   STRONG FORCING FOR UPWARD VERTICAL MOTION TO THE NORTHEAST OF THE
   CLOSED LOW MAY SUPPORT AN EVOLVING FRONTAL/PRE-FRONTAL BAND OF
   STORMS NEAR THE WASATCH AS EARLY AS LATE MORNING...BEFORE DEVELOPING
   NORTH/NORTHEASTWARD INTO THE UPPER SNAKE VALLEY AND WESTERN WYOMING.
   ADDITIONAL STORMS THEN APPEAR POSSIBLE AHEAD OF THE COLD FRONT
   ACROSS EASTERN UTAH LATER THIS AFTERNOON.  SOMEWHAT WEAK BOUNDARY
   LAYER WARMING...PARTICULARLY WITHIN THE STRONGER MEAN FLOW NEAR THE
   UPPER JET AXIS ACROSS UTAH...MAY BE A LIMITING FACTOR TO THE
   POTENTIAL FOR STRONG/SEVERE STORMS.  BUT...SUB-CLOUD TEMPERATURE/DEW
   POINT SPREADS MAY STILL BECOME LARGE ENOUGH TO CONTRIBUTE TO THE
   RISK FOR AT LEAST LOCALIZED STRONG GUSTS WITH THE MOST VIGOROUS
   CONVECTION.
   
   ..KERR/STOPPKOTTE.. 04/21/2010
   
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