SWODY1
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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