SWODY1
SPC AC 081249
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 AM CDT SUN MAY 08 2011
VALID 081300Z - 091200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF THE NRN HIGH
PLAINS SEWD THROUGH THE MID MO VALLEY...
...NRN HIGH PLAINS EWD/SEWD INTO THE UPPER MS AND MID/LOWER MO
VALLEYS...
MORNING WATER VAPOR IMAGERY SHOWS A WEAK VORTICITY MAXIMUM OVER SWRN
NEB WHICH SHOULD CONTINUE NEWD TODAY...GRADUALLY WEAKENING WITH TIME
AS A LONGER WAVELENGTH RIDGE BUILDS OVER THE UPPER MS VALLEY/UPPER
GREAT LAKES REGION. IN IT/S WAKE...THERE IS SOME SUGGESTION BY
MODEL GUIDANCE THAT A WEAK UPSTREAM SYSTEM MAY MOVE OUT OF THE SRN
ROCKIES INTO THE CNTRL PLAINS LATER TODAY. IN THE LOW
LEVELS...ELONGATED LEE CYCLONE WILL BE MAINTAINED FROM ERN WY/WRN SD
SWD INTO ERN CO/WRN KS. ASSOCIATED DRYLINE WILL BECOME
BETTER-DEFINED BY AFTERNOON...EXTENDING FROM WY/SD LOW THROUGH WRN
NEB INTO CNTRL KS. MEANWHILE...WARM FRONT CURRENTLY LIFTING NWD
THROUGH KS SHOULD CONTINUE TO MOVE/DEVELOP NWD...LIKELY EXTENDING
FROM SURFACE LOW OVER WRN SD SEWD THROUGH CNTRL NEB INTO NERN KS.
LATEST SUITE OF MESOSCALE AND CONVECTION-ALLOWING MODEL GUIDANCE HAS
CAST CONSIDERABLE UNCERTAINTY ON TSTM EVOLUTION THIS AFTERNOON AND
EVENING. THIS IS LIKELY DUE IN PART TO THE TENDENCY FOR LARGE-SCALE
RIDGING OVER THE N-CNTRL CONUS...DOWNSTREAM FROM AMPLIFYING TROUGH
OVER THE WRN STATES. NONETHELESS...THE MAINTENANCE OF A 30-40 KT
SLY LLJ ACROSS THE GREAT PLAINS WILL SUPPORT THE NWD FLUX OF AN
INCREASINGLY MOIST BOUNDARY LAYER WITH AFTERNOON DEWPOINTS RANGING
FROM MID/UPPER 50S OVER S-CNTRL SD TO MID 60S ALONG WARM FRONT IN
CNTRL/ERN NEB. WHEN COUPLED WITH MIDLEVEL LAPSE RATES APPROACHING
DRY ADIABATIC AND STRONG DAYTIME HEATING...EXPECT WARM SECTOR AIR
MASS TO BECOME MODERATELY TO STRONGLY UNSTABLE WITH MLCAPE VALUES
RANGING FROM 1000-1500 J/KG IN WRN SD TO AS HIGH AS 3000-3500 J/KG
ACROSS S-CNTRL/SERN NEB.
GIVEN THE ABSENCE OF A WELL-DEFINED SHORT WAVE TROUGH APPROACHING
THE REGION DURING PEAK HEATING /AND THE TENDENCY FOR LONGWAVE
RIDGING TO OCCUR/...MODEL GUIDANCE HAS TRENDED TOWARD A LOWER
PROBABILITY OF SURFACE-BASED STORM DEVELOPMENT WITHIN THE WARM
SECTOR THIS AFTERNOON INTO EVENING. SHOULD ISOLATED STORM
DEVELOPMENT OCCUR...THE DEGREE OF INSTABILITY AND VERTICALLY VEERING
WIND PROFILES WITH 30-40 KT OF DEEP-LAYER SHEAR WILL PROMOTE
SUPERCELLS CAPABLE OF VERY LARGE HAIL...DAMAGING WINDS AND A FEW
TORNADOES.
MORE PROBABLE STORM FORMATION APPEARS TO BE LATE THIS EVENING INTO
TONIGHT N OF SURFACE WARM FRONT FROM SERN MT EWD ACROSS ND...NRN SD
INTO CNTRL/SRN MN SEWD TOWARD THE MID MS VALLEY. THIS WILL BE IN
RESPONSE TO A BROAD SWATH OF INCREASING WAA/ISENTROPIC ASCENT
OCCURRING AT THE TERMINUS OF AN EXPANSIVE NOCTURNAL LLJ. GIVEN AN
INFLOW AIR MASS CHARACTERIZED BY MUCAPE VALUES OF 2000-3000 J/KG AND
35-45 KT OF EFFECTIVE BULK SHEAR...SETUP WILL FAVOR ORGANIZED
ELEVATED STORMS /INCLUDING SUPERCELLS/ CAPABLE OF SEVERE HAIL.
...SRN PLAINS...
INCREASING SWLY MID-TROPOSPHERIC FLOW IN ADVANCE OF AMPLIFYING WRN
U.S. TROUGH WILL SERVE TO STRENGTHEN EML AND ASSOCIATED CAP ACROSS
THE REGION TODAY. THIS STRENGTHENING CAP WILL BE OFFSET TO SOME
DEGREE BY STRONG DIABATIC WARMING ALONG/W OF THE DRYLINE WHERE
SURFACE TEMPERATURES WILL RISE THROUGH THE 90S TO 100-105 F. AIR
MASS E OF DRYLINE IS EXPECTED TO BECOME MODERATELY TO STRONGLY
UNSTABLE BY AFTERNOON WITH MLCAPE VALUES INCREASING TO 2000-3500
J/KG.
LATEST MODEL GUIDANCE REMAINS RATHER CONSISTENT IN SUGGESTING THAT
THE DRYLINE WILL REMAIN LARGELY INACTIVE THROUGH THIS EVENING. THIS
APPEARS REASONABLE GIVEN THE MID-TROPOSPHERIC WARMING FORECAST AND
THE ABSENCE OF ANY ROBUST FORCING MECHANISMS. AS SUCH...THE
CATEGORICAL SLIGHT RISK HAS BEEN REMOVED FROM THE AREA. SHOULD AN
ISOLATED STORM DEVELOP...THE THERMODYNAMIC ENVIRONMENT WILL BE
SUPPORTIVE OF LARGE HAIL AND LOCALLY DAMAGING WIND GUSTS THROUGH
THIS EVENING.
...TN VALLEY TO SERN ATLANTIC COAST...
BUILDING SURFACE RIDGE FROM THE LOWER GREAT LAKES SWD THROUGH THE
MID ATLANTIC STATES WILL RESULT IN THE SWD PROGRESSION OF A WEAK
BACKDOOR COLD FRONT THROUGH THE SRN APPALACHIANS WHICH WILL
EVENTUALLY MERGE WITH WARM FRONT LIFTING NWD THROUGH THE LOWER MS
VALLEY. THIS BOUNDARY IS EXPECTED TO SERVE AS THE FOCUS FOR
ISOLATED TO SCATTERED TSTM DEVELOPMENT THIS AFTERNOON.
12Z OBSERVED SOUNDINGS FROM AR EWD ACROSS THE GULF COAST SHOW THAT
AN EML HAS SPREAD EWD ACROSS THE REGION WITH MIDLEVEL LAPSE RATES OF
7.0-7.5 C/KM. WHEN COUPLED WITH A MOISTENING BOUNDARY LAYER AND
DAYTIME HEATING...ENVIRONMENT IS EXPECTED TO BECOME MODERATELY
UNSTABLE WITH MLCAPE VALUES RANGING FROM 1500-2500 J/KG OVER THE MID
SOUTH TO AROUND 1000 J/KG ALONG THE SAVANNAH RIVER. GIVEN THE
MODESTLY STRONG NWLY WIND FIELD OBSERVED THIS MORNING IN THE MID TO
UPPER-TROPOSPHERE...SETUP MAY YIELD A FEW FORWARD-PROPAGATING STORM
CLUSTERS CAPABLE OF DAMAGING WINDS AND SOME HAIL.
..MEAD/GRAMS.. 05/08/2011
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