SWODY1
SPC AC 271959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT SAT JUN 27 2009
VALID 272000Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS ND/NRN SD INTO NWRN
MN...
...THERE IS A SLGT RISK OF SVR TSTMS FROM UPPER MS VALLEY SWWD TO
SRN PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS CAROLINAS TO NRN GA...
...ND/SD/MN...
SMALL ADJUSTMENTS MADE TO THE WRN AND SRN PORTIONS OF THE SLIGHT
RISK AREA ACROSS THIS REGION. EARLY AFTERNOON SURFACE ANALYSIS
SHOWED A COLD FRONT EXTENDING FROM SWRN MANITOBA THROUGH WRN ND INTO
WY. TSTMS HAVE FORMED ALONG THIS BOUNDARY...WITH VISIBLE IMAGERY
ALSO INDICATING SEVERAL WEAK PRE-FRONTAL BOUNDARIES FOCUSING ONGOING
TSTMS. ENVIRONMENTAL CONDITIONS AS INDICATED BY SPC MESOSCALE
DISCUSSION 1351 WILL SUPPORT ADDITIONAL STRONG TO SEVERE TSTMS
SPREADING EWD ACROSS ND/NRN SD AND INTO WEST CENTRAL/NW MN...WITH
ACTIVITY TENDING TO WEAKEN EARLY THIS EVENING.
...UPPER MS VALLEY...
EARLY AFTERNOON SURFACE ANALYSES INDICATED COLD FRONT EXTENDING SWD
FROM NERN MN THROUGH FAR WEST CENTRAL WI/SERN MN TO NWRN MO. GIVEN
CURRENT LOCATION OF THIS FRONT...SLIGHT RISK HAS BEEN ADJUSTED EWD
ACROSS CENTRAL IA AND SERN MN. OTHERWISE...MOISTURE ADVECTION AND
SURFACE HEATING WITHIN WARM SECTOR ARE AIDING IN AIR MASS
DESTABILIZATION FROM S-N ACROSS MUCH OF THE SLIGHT RISK AREA.
EFFECTIVE BULK SHEAR IS STRONGEST ACROSS SERN MN/NERN IA INTO SRN
WI. SHEAR VALUES ARE EXPECTED TO INCREASE FARTHER S INTO NRN MO/IL
BY LATE AFTERNOON/EARLY EVENING AS WLY MID LEVEL FLOW STRENGTHENS
AHEAD OF AMPLIFYING NRN PLAINS TROUGH. ALTHOUGH LOW LEVEL WINDS
WILL CONTINUE TO VEER ALONG AND AHEAD OF THE COLD FRONT...THE
INCREASE IN EFFECTIVE BULK SHEAR WILL SUPPORT ORGANIZED STORMS
PRODUCING MAINLY STRONG WIND GUSTS AND HAIL.
FARTHER S/SW THROUGH SRN EXTENT OF SLIGHT RISK AREA...STRONGER SWLY
MID LEVEL WINDS/EFFECTIVE BULK SHEAR WERE LOCATED ACROSS
POST-FRONTAL AIR MASS. DESPITE WEAK SHEAR ALONG SRN EXTENT OF COLD
FRONT...AIR MASS IS BECOMING MODERATELY UNSTABLE AND CONDUCIVE FOR
TSTM DEVELOPMENT. GIVEN THAT SIMILAR ATMOSPHERIC CONDITIONS EXIST
OVER THE TX PANHANDLE AS COMPARED TO AREAS ENE INTO NRN OK/SRN KS...
THE SLIGHT RISK HAS BEEN EXTENDED FURTHER TO THE SW. FOR ADDITIONAL
MESOSCALE DETAILS...REFER TO SPC MESOSCALE DISCUSSION 1354.
...CAROLINAS INTO PARTS OF NRN/CENTRAL GA...
MODERATELY UNSTABLE AIR MASS AND EFFECTIVE BULK SHEAR /30-40 KT/
WILL CONTINUE TO SUPPORT STRONG TO SEVERE STORMS ACROSS MUCH OF SRN
NC THROUGH SC AND PARTS OF NRN/CENTRAL GA. FOR ADDITIONAL MESOSCALE
DETAILS...REFER TO WW 526 AND ASSOCIATED MESOSCALE DISCUSSIONS.
..PETERS.. 06/27/2009
.PREV DISCUSSION... /ISSUED 1051 AM CDT SAT JUN 27 2009/
...ND/SD/MN...
MORNING WATER VAPOR LOOPS SHOW A WELL-DEFINED SHORTWAVE TROUGH
MOVING EASTWARD ACROSS EASTERN MT/WESTERN ND. SCATTERED
THUNDERSTORMS ARE EXPECTED TO CONTINUE TO DEVELOP IN VICINITY OF
THIS FEATURE THROUGH MID AFTERNOON OVER CENTRAL ND...SPREADING
EAST-SOUTHEASTWARD INTO PARTS OF SD/MN DURING THE EVENING. COOL
TEMPERATURES ALOFT AND STEEP LAPSE RATES...COUPLED WITH SUFFICIENT
EFFECTIVE VERTICAL SHEAR FOR ORGANIZED MULTICELL OR ISOLATED
SUPERCELL STRUCTURES...WILL POSE A RISK OF LARGE HAIL AND GUSTY
WINDS IN STRONGER CELLS.
...UPPER MS VALLEY...
A SURFACE COLD FRONT IS MOVING EASTWARD ACROSS IA THIS MORNING...AND
WILL BE THE FOCUS FOR SCATTERED THUNDERSTORMS THIS AFTERNOON.
RELATIVELY STRONG HEATING AHEAD OF THE FRONT ALONG WITH DEWPOINTS IN
THE 60S TO NEAR 70F WILL YIELD MLCAPE VALUES OF 1500-2500 J/KG AND A
RELATIVELY WEAK CAP. STORMS ARE EXPECTED TO INITIATE ALONG THE
FRONT OVER CENTRAL IA/SOUTHEAST MN BY LATE AFTERNOON AND SPREAD INTO
WI/IL/MO DURING THE EVENING. LINEAR FORCING AND MARGINAL VERTICAL
SHEAR AHEAD OF THE FRONT SUGGEST THE RISK OF A MULTICELL SQUALL LINE
CAPABLE OF DAMAGING WINDS AND HAIL.
...MO/KS/OK...
ALL MODEL GUIDANCE IS IN GENERAL AGREEMENT THAT A TRAILING COLD
FRONT EXTENDING FROM MO INTO NORTHWEST OK WILL BECOME CONVECTIVELY
ACTIVE BY EARLY EVENING. STORMS ARE LIKELY TO DEVELOP FIRST IN THE
DEEPLY MIXED BOUNDARY LAYER AIRMASS OF THE TX/OK PANHANDLES. STORMS
WILL THEN PROPAGATE/DEVELOP EASTWARD ALONG THE FRONT INTO NORTHWEST
OK AND EVENTUALLY ACROSS KS. STORMS MAY ALSO DEVELOP SOUTHWESTWARD
FROM IA/IL ACTIVITY INTO MO. THUNDERSTORMS ALONG THIS AXIS WILL BE
IN REGION OF HOT SURFACE TEMPERATURES AND SUFFICIENT CAPE FOR STRONG
UPDRAFTS/DOWNDRAFTS AND A RISK OF LOCALLY DAMAGING WINDS. THE
SEVERE THREAT SHOULD SUBSIDE BY LATE EVENING AS DIURNAL COOLING
ENSUES.
...CAROLINAS...
AN UPPER TROUGH REMAINS OVER THE EASTERN STATES TODAY...WITH A
SERIES OF SHORTWAVE TROUGHS ROTATING SOUTHEASTWARD FROM THE OH
VALLEY INTO THE WESTERN ATLANTIC. STRENGTHENING NORTHWESTERLY
DEEP-LAYER FLOW WILL LIKELY LIMIT INLAND PUSH OF CAROLINA SEA BREEZE
TODAY. ALSO...TIMING OF SHORTWAVE TROUGHS SUGGEST WEAK SUBSIDENCE
WILL BE OVER THE REGION UNTIL LATE AFTERNOON OR EARLY EVENING WHICH
MAY LIMIT AREAL COVERAGE OF STORMS UNTIL LATER. AROUND 00Z...MORE
NUMEROUS THUNDERSTORMS MAY DEVELOP BOTH ALONG THE SEABREEZE AND THE
HIGHER TERRAIN OF UPSTATE SC. MODERATE INSTABILITY AND RATHER
STRONG VERTICAL SHEAR WILL SUPPORT A RISK OF ORGANIZED SEVERE STORMS
CAPABLE OF DAMAGING WINDS AND HAIL. OVERALL COVERAGE OF SEVERE
THREAT IS UNCERTAIN...BUT WILL MAINTAIN CATEGORICAL SLIGHT.
...FL EAST COAST...
SCATTERED THUNDERSTORMS ARE OCCURRING THIS MORNING OVER THE CENTRAL
FL PENINSULA. OTHER STORMS ARE LIKELY LATE THIS AFTERNOON ALONG THE
EAST COAST AS WESTERLY LOW LEVEL WINDS ENHANCE CONVERGENCE ALONG
THAT SEA BREEZE. MORNING RAOBS AT TBW/MFL SHOW SUBSTANTIAL CAPE/PW
VALUES AND THE PRESENCE OF SOME DRY AIR AT MID LEVELS. THIS WILL
HELP TO PROMOTE STRONG DOWNDRAFTS AND POTENTIAL WET MICROBURSTS THIS
AFTERNOON ALONG THE SEA BREEZE. SLIGHTLY LOWER WBZ/MELTING LEVELS
MAY ALSO AID IN THE RISK OF HAIL IN THE STRONGEST STORMS.
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