DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211243
SWODY1
SPC AC 211241

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0741 AM CDT MON MAY 21 2012

VALID 211300Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR PORTIONS OF NERN/E-CNTRL
NM...WRN PARTS OF THE TX PANHANDLE AND TX SOUTH PLAINS...FAR WRN
PARTS OF THE OK PANHANDLE...EXTREME SERN CO...

...SYNOPSIS...
IN THE MID LEVELS...A LOOSELY ORGANIZED SHORTWAVE TROUGH EXTENDING
FROM LAKE SUPERIOR SSWWD INTO THE MID-MISSISSIPPI VALLEY WILL SHIFT
EWD TOWARD THE GREAT LAKES AND OHIO VALLEY THROUGH TONIGHT...WHILE
ITS SRN EXTENT DIGS SEWD AS IT BECOMES ENTRENCHED WITHIN A BROAD
AREA OF CYCLONIC FLOW ANCHORED ACROSS THE SERN STATES. ELSEWHERE IN
THE MID-LEVELS...A RIDGE AXIS WILL SHIFT EWD FROM THE NRN/CNTRL
ROCKIES TO THE NRN/CNTRL PLAINS...WITH A BROAD AREA OF NWLY FLOW
COVERING THE CNTRL/SRN PLAINS. MEANWHILE...A STRONG PACIFIC TROUGH
WILL CONTINUE MOVING ONSHORE OVER THE PACIFIC NW COAST EXTENDING EWD
ACROSS THE NRN GREAT BASIN AND NRN ROCKIES.

AT THE SFC...A COLD FRONT ASSOCIATED WITH THE SHORTWAVE TROUGH
STRETCHES FROM THE NRN LOWER PENINSULA OF MI SSWWD INTO THE NWRN MS
DELTA REGION WHERE IT ARCS WWD INTO NORTH TX AND E-CNTRL NM. IN
RESPONSE TO SFC PRESSURE FALLS IN THE LEE OF THE CNTRL ROCKIES...THE
INCREASING SLY COMPONENT OF THE LOW-LEVEL FLOW WILL FORCE THE WRN
EXTENT OF THE FRONT TO ADVANCE NWD OVER THE CNTRL/SRN HIGH
PLAINS...WHILE THE N-CNTRL TX FRONTAL SEGMENT REMAINS
QUASI-STATIONARY...AND THE ERN/NRN EXTENT OF THE FRONT GRADUALLY
SHIFTS EWD/SEWD.

...CNTRL/SRN HIGH PLAINS INTO PARTS OF NERN TX THIS AFTERNOON INTO
TONIGHT...
ONGOING WEAK WAA IN ASSOCIATION WITH THE NOCTURNAL BOUNDARY LAYER
WIND MAX CONTINUES TO FOSTER AREAS OF ELEVATED CONVECTION FROM FAR
NERN NM EWD ACROSS THE TX PANHANDLE AND INTO OKLAHOMA. THIS ACTIVITY
MAY WEAKEN/DISSIPATE THROUGH THE MORNING AS THE WAA DECREASES. AN
EXCEPTION COULD BE ACROSS THE TX PANHANDLE WHERE A MODESTLY
INTENSIFYING LOW LEVEL JET STREAM /IN RESPONSE TO LEE TROUGHING/
WOULD REINFORCE WAA/ISENTROPIC ASCENT NORTH OF THE NWD-ADVANCING SFC
FRONT.

BY EARLY/MID AFTERNOON...ADDITIONAL ISOLATED TO SCATTERED CONVECTION
WILL LIKELY DEVELOP IN RESPONSE TO /1/ MOIST/UPSLOPE FLOW OVER THE
SRN/CNTRL ROCKIES.../2/ LOW-LEVEL ASCENT ALONG CONVECTIVELY
AUGMENTED SEGMENTS OF THE QUASI-STATIONARY FRONT...AND /3/ ASCENT
OVER SWRN FLANKS OF NWRN TX CONVECTION /AND ASSOCIATED BOUNDARIES/
THAT PERSIST INTO THE EARLY AFTERNOON. BOUNDARY-LAYER DEWPOINTS IN
THE 50S TO AROUND 60 F WILL CONTRIBUTE TO THE DEVELOPMENT OF MLCAPE
VALUES OF 500-1500 J/KG.

ACROSS THE SLIGHT RISK AREA...THE HIGHEST OF THE PREVIOUSLY
MENTIONED MLCAPE VALUES ARE FORECAST TO EXIST...WHERE RELATIVELY
STEEPER MID-LEVEL LAPSE RATES /7-8 C PER KM WITHIN THE 700-500 MB
LAYER ACCORDING TO 12Z RAOB DATA/ WILL BE PRESENT. WITHIN THIS
AREA...NOTABLE DIRECTIONAL SHEAR WITH MODERATE NWLY MID/HIGH-LEVEL
FLOW ATOP GENERALLY WEAK SSELY/SELY LOW-LEVEL FLOW WILL SUPPORT
30-40 KT OF DEEP SHEAR. WHILE NEUTRAL MID-LEVEL HEIGHT TENDENCIES
WILL BE ASSOCIATED WITH RELATIVELY LIMITED DEEP FORCING FOR
ASCENT...THE AFOREMENTIONED BUOYANCY/VERTICAL SHEAR COMBINATION WILL
SUPPORT ORGANIZED SEWD/SWD-MOVING STORM CLUSTERS/POSSIBLE SUPERCELLS
WITH SVR HAIL/WIND.

ELSEWHERE...COMPARATIVELY COOLER SFC TEMPERATURES NORTH OF THE
SLIGHT RISK AREA...AND WEAKER MID-LEVEL LAPSE RATES TO ITS
SOUTHEAST...WILL LIKELY CONTRIBUTE TO RELATIVELY WEAKER
UPDRAFTS/MORE LIMITED SVR THREAT.

...OHIO VALLEY SWD TO THE CNTRL GULF COAST THIS AFTERNOON INTO EARLY
THIS EVENING...
LOW-LEVEL ASCENT IN ASSOCIATION WITH /1/ THE FRONT.../2/ OUTFLOW
BOUNDARIES LEADING THE FRONT.../3/ OROGRAPHIC EFFECTS...AND /4/
DIFFERENTIAL HEATING ZONES AMIDST THE BROAD AREA OF MID/HIGH-LEVEL
CONVECTIVE DEBRIS CLOUDS AHEAD OF THE SHORTWAVE TROUGH WILL AID IN
THE DEVELOPMENT OF ISOLATED TO SCATTERED THUNDERSTORMS THIS
AFTERNOON. FORECAST SOUNDINGS SUGGEST THE DEVELOPMENT OF MODERATE
INSTABILITY IN AREAS WHERE INSOLATION/DIABATIC HEATING STEEPEN
LOW-LEVEL LAPSE RATES JUXTAPOSED WITH SFC DEWPOINTS IN THE UPPER 50S
TO THE LOWER 60S. CONVECTION SHOULD BE LARGELY DISORGANIZED...AS
ONLY 10-15 KT OF 500-MB FLOW ARE FORECAST TO OVERLAY MOST OF THE
WARM SECTOR...OFFERING VERY LITTLE DEEP SHEAR. HOWEVER...SUFFICIENT
DCAPE AND MODEST SFC TEMPERATURE-DEWPOINT SPREADS WILL SUPPORT A
LOW-END SVR WIND THREAT WITH THE STRONGEST STORMS.

A SOMEWHAT ENHANCED SVR THREAT COULD EVOLVE OVER PARTS OF
MS/AL...WHERE MID-LEVEL NWLY FLOW WILL BE SLIGHTLY STRONGER AHEAD OF
THE DIGGING SEGMENT OF THE SHORTWAVE TROUGH. A FEW ORGANIZED
MULTICELL CLUSTERS WITH DMGG WIND GUSTS AND PERHAPS MARGINALLY SVR
HAIL MAY OCCUR IN THIS AREA...FOCUSED ALONG OUTFLOW BOUNDARIES
EMANATING FROM MORNING CONVECTION. ONGOING CLOUD COVERAGE COULD
LIMIT SFC-BASED BUOYANCY TO SOME DEGREE.

...PORTIONS OF E-CNTRL ID INTO W-CNTRL/CNTRL MT THIS AFTERNOON INTO
THIS EVENING...
SFC HEATING BENEATH RELATIVELY COOLER MID-LEVEL TEMPERATURES WILL
SUPPORT THE DEVELOPMENT OF MARGINAL INSTABILITY. ISOLATED TO
SCATTERED THUNDERSTORMS ARE FORECAST TO DEVELOP OVER E-CNTRL ID AND
W-CNTRL MT THIS AFTERNOON OWING TO OROGRAPHIC ASCENT...ALONG WITH
INCREASING LARGE-SCALE ASCENT/MID-LEVEL HEIGHT FALLS. STORMS SHOULD
MOVE EWD/ENEWD INTO CNTRL MT LATE THIS AFTERNOON INTO THE
EVENING...INCLUDING THE POSSIBILITY OF ONE TO TWO
FORWARD-PROPAGATING ORGANIZED CONVECTIVE CLUSTERS GIVEN AROUND 35-50
KT OF EFFECTIVE SHEAR. LIMITED BUOYANCY OWING TO RELATIVELY MEAGER
LOW-LEVEL MOISTURE WILL MITIGATE THE OVERALL SVR THREAT...THOUGH A
FEW INSTANCES OF SVR WIND AND PERHAPS SVR HAIL WILL BE POSSIBLE.

..COHEN/CORFIDI.. 05/21/2012

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