The SPC is forecasting ...significant severe thunderstorms expected over parts of the southern plains into lower mississippi valley today into tonight.... Please read the latest public statement about this event.
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SPC AC 121959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT FRI JUN 12 2009
VALID 122000Z - 131200Z
...THERE IS A MDT RISK OF SVR TSTMS FROM ERN AR INTO WRN TX/NRN
MS/NWRN AL...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN PLAINS EWD INTO
THE ATLANTIC COAST STATES...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CO FRONT RANGE AND
VICINITY...
...MID MS VALLEY REGION...
WELL-ORGANIZED MCS CONTINUES MOVING ESEWD ACROSS NRN AND CENTRAL AR
ATTM...THROUGH A MODERATELY-UNSTABLE AIRMASS WHICH EXTENDS ESEWD
DOWNSTREAM OF THE ONGOING STORMS ALONG A SURFACE COLD FRONT. OTHER
CONVECTION IS DEVELOPING AHEAD OF THE MCS OVER NRN MS AND NWRN AR.
WIDESPREAD DAMAGING WINDS HAVE OCCURRED WITH THE ESEWD-MOVING
MCS...AND WILL LIKELY CONTINUE DOWNSTREAM ACROSS ERN AR...PARTS OF
WRN TN...AND INTO NRN MS AND LATER NRN AL AS THIS MCS CONTINUES
SHIFTING ESEWD THROUGH THE EVENING AND INTO THE OVERNIGHT HOURS.
PRIOR TO THE ARRIVAL OF THIS STORM CLUSTER...OTHER DEVELOPING
CONVECTION WILL ALSO BE CAPABLE OF PRODUCING DAMAGING WINDS AND
LARGE HAIL...AS MODERATE WNWLY FLOW ALOFT PERSISTS ACROSS THIS
REGION.
...OK SWD INTO CENTRAL TX...
WEAK RIDGING ALOFT CONTINUES ACROSS THE SRN PLAINS...WHICH CONTINUES
TO CAP AN OTHERWISE EXTREMELY UNSTABLE ENVIRONMENT. GIVEN THE
DEGREE OF INSTABILITY AND SHEAR FAVORABLE FOR SUPERCELLS...SEVERE
THREAT CONTINUES ACROSS THIS REGION. THE THREAT IS CONDITIONAL UPON
STORM DEVELOPMENT...AND ATTM ISOLATED DEVELOPMENT IS STILL EXPECTED
-- BOTH ALONG THE CENTRAL TX DRYLINE...AND OVER THE SRN HALF OF OK
INVOF THE REMNANT OUTFLOW BOUNDARY LEFT OVER FROM EARLIER MCS. ANY
STORMS WHICH DO DEVELOP WILL BE CAPABLE OF PRODUCING VERY LARGE HAIL
AND DAMAGING WINDS...AND AN ISOLATED TORNADO WILL ALSO BE POSSIBLE.
STORMS MAY ALSO INCREASE ACROSS OK -- PARTICULARLY N OF THE OUTFLOW
-- LATER THIS EVENING...AS SLY LOW-LEVEL JET INCREASES. SEVERE
POTENTIAL WOULD EXIST WITH THE DEVELOPING STORMS...GIVEN THE OVERALL
KINEMATIC AND THERMODYNAMIC ENVIRONMENT.
...ERN CO...
CONVECTION IS DEVELOPING INVOF THE PALMER DIVIDE...WITH TCU
INCREASING ELSEWHERE ALONG THE FRONT RANGE SWD TO NERN NM -- IN
BROAD ZONE OF WEAK ELY LOW-LEVEL UPFLOPE FLOW. STORMS SHOULD
CONTINUE TO INCREASE THROUGH THE AFTERNOON AS WEAK DESTABILIZATION
CONTINUES...AND WITH VEERING FLOW BENEATH MID-LEVEL WLYS...SHEAR
SUFFICIENT FOR STORM ORGANIZATION/ROTATION APPEARS TO EXIST.
THUS...EXPECT ISOLATED SEVERE STORM DEVELOPMENT THIS
AFTERNOON...INCLUDING THE THREAT FOR LARGE HAIL AND LOCALLY-DAMAGING
WINDS...AND PERHAPS AN ISOLATED TORNADO.
...CENTRAL PLAINS...
CONVECTION CONTINUES TO DEVELOP FROM SERN NEB SWWD INTO CENTRAL
KS...ALONG A WEAK SURFACE TROUGH ASSOCIATED WITH AN UPPER VORT MAX
CROSSING THE MID MO VALLEY REGION. WITH 500 TO 1000 J/KG
MIXED-LAYER CAPE AND MODERATE WLY MID-LEVEL FLOW...A FEW
MARGINALLY-SEVERE CELLS MAY EVOLVE THIS AFTERNOON.
FARTHER WEST...STORMS MOVING OFF THE HIGHER TERRAIN OF CO LATER THIS
AFTERNOON/EVENING MAY BRING A LIMITED SEVERE THREAT TO PORTIONS OF
WRN KS.
...MID-ATLANTIC REGION SWWD INTO GA...
SCATTERED STORMS CONTINUE DEVELOPING INVOF THE WEAK COOL FRONT
DRAPED ACROSS THIS REGION...WHERE MODERATE DESTABILIZATION HAS
OCCURRED. WHILE RELATIVELY WEAK DEEP-LAYER WIND FIELD SHOULD
CONTINUE TO LIMIT STORM ORGANIZATION/LONGEVITY...BRIEFLY-STRONGER
STORM PULSES WILL CONTINUE TO OCCUR THROUGH EARLY EVENING...WITH
MARGINAL HAIL/LOCALLY-DAMAGING WINDS POSSIBLE.
..GOSS.. 06/12/2009
.PREV DISCUSSION... /ISSUED 1100 AM CDT FRI JUN 12 2009/
...SYNOPSIS...
DYNAMIC FEATURE OF INTEREST AS RELATED TO SEVERE CONVECTIVE
POTENTIAL THIS FORECAST PERIOD IS THE MID LEVEL S/WV TROUGH
CURRENTLY MOVING EWD CENTRAL KS TO NRN OK EMBEDDED IN RELATIVELY
FAST MID/UPPER WLY FLOW THAT EXTENDS EWD TO ATLANTIC COAST. A
DERECHO HAS DEVELOPED IN ADVANCE OF THE TROUGH AND IS TRACKING
RAPIDLY E/ESEWD ACROSS NERN OK ON INTO LWR MS VALLEY THIS AFTERNOON.
A S/WV TROUGH ROTATES INLAND SWRN U.S. BY TONIGHT WITH DOWNSTREAM
RIDGING OVER THE SRN HIGH PLAINS.
...ERN OK/AR/NRN MS/WRN TN...
REF MCD 1074
HAVE UPGRADED AREA IN ADVANCE OF THE SEVERE MCS/DERECHO OVER NERN OK
TO MDT RISK AS THE COMBINATION OF 40-50KT OF SHEAR COUPLED WITH
DEVELOPMENT OF VERY TO EXTREMELY UNSTABLE AIRMASS DOWNSTREAM ACROSS
LOWER MS RIVER VALLEY EXPECTED TO RAPIDLY INCREASE THE DAMAGING WIND
POTENTIAL ALONG WITH THE ONGOING VERY LARGE HAIL THREAT. WITH
DEWPOINTS AOA 70F...SURFACE TEMPERATURES WELL INTO THE 80S...AND
STEEP MID LEVEL LAPSE RATES...MLCAPES AOA 3500 J/KG... A SWATH OF
POSSIBLY SIGNIFICANT DAMAGING WINDS WILL TRACK EWD ACROSS NRN HALF
OF AR INTO WRN TN/NRN MS BY LATER THIS AFTERNOON.
...CAROLINAS/GA/AL...
FARTHER EAST...SCATTERED THUNDERSTORMS WILL FORM THIS AFTERNOON FROM
EAST TN/AL EASTWARD INTO THE CAROLINAS. SUFFICIENT VERTICAL SHEAR
WILL BE PRESENT FOR A FEW SEVERE STORMS...ALBEIT LESS ORGANIZED THAN
FARTHER WEST. LATE TONIGHT...SOME POTENTIAL EXISTS FOR LONG-LIVED
MCS MOVING INTO THIS REGION FROM THE WEST.
...OK/TX ALONG AND JUST E OF DRYLINE...
AN EXTREMELY UNSTABLE AIRMASS IS EXPECTED TO DEVELOP THIS AFTERNOON
ALONG AND EAST OF THE SURFACE DRYLINE ACROSS CENTRAL/EASTERN OK AND
NORTH CENTRAL TX. FORECAST SOUNDINGS SUGGEST A WEAK CAPPING
INVERSION WILL SUPPRESS CONVECTION FOR MOST OF THE DAY AS HEIGHTS
GRADUALLY RISE IN ADVANCE OF THE RIDGING.
HOWEVER...ENHANCED CONVERGENCE ALONG THE REMNANT OUTFLOW BOUNDARY
FROM THIS MORNINGS STORMS ACROSS NORTHERN OK MAY HELP TO INITIATE
ISOLATED STORMS. ALSO...MOST MODELS SHOW ISOLATED CELLS FORMING
DURING THE HEAT OF THE DAY OVER NORTH CENTRAL AND NORTHEAST TX. ANY
STORM THAT FORMS IN THIS ENVIRONMENT WILL HAVE A CONDITIONAL RISK OF
BECOMING A SUPERCELL AND WILL POSE A RISK OF VERY LARGE HAIL AND
DAMAGING WINDS.
HAVE EXTENDED THE THREAT OF AT LEAST ISOLATED INITIATION INTO SWRN
TX GIVEN THE EXPECTED EXTREMELY UNSTABLE AIR MASS THAT IS EXPECTED E
OF DRY LINE. ANY STORM THAT IS ABLE TO OVERCOME THE WEAK CINH BY
LATER THIS AFTERNOON WILL QUICKLY BECOME SEVERE/SUPERCELL WITH
POTENTIAL FOR VERY LARGE HAIL.
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z