SPC AC 092001
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0301 PM CDT SAT APR 09 2011
VALID 092000Z - 101200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS FAR SOUTHEAST SOUTH
DAKOTA...FAR NORTHEAST NEBRASKA...THE NORTHWESTERN HALF OF
IOWA...SOUTHERN MINNESOTA...AND PARTS OF FAR WESTERN WISCONSIN...
...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN SD/ERN NEB/CENTRAL KS
NEWD INTO THE WRN UPPER GREAT LAKES...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL AND SRN
APPALACHIANS REGION AND SEWD TO THE SC COAST...
...MID MO VALLEY INTO THE SWRN UPPER GREAT LAKES...
CONVECTIVE INITIATION HAS YET TO OCCUR ACROSS THIS REGION...BUT
EXPECT STORMS TO DEVELOP LATE THIS AFTERNOON INVOF THE MID MO
VALLEY. SUBSTANTIAL SEVERE WEATHER THREAT REMAINS EVIDENT...WITH THE
THREAT FOR LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES IN
THIS AREA. STORMS WILL ALSO EXPAND -- AND THEN SHIFT EWD -- THIS
EVENING AS LOW-LEVEL JET INCREASES. ALONG WITH THREAT FOR DAMAGING
WINDS...VERY LARGE HAIL SHOULD BE A SIGNIFICANT SEVERE CONCERN.
...CENTRAL AND SRN APPALACHIANS TO COASTAL SC AND VICINITY...
ORGANIZED CLUSTER OF STORMS CONTINUES SHIFTING ACROSS FAR ERN KY AND
SRN WV...ALONG WITH WRN PORTIONS OF VA AND NC. STORMS SHOULD
CONTINUE TO INCREASE WITH TIME ACROSS ERN TN...WRN NC...AND NRN
GA...AND THEN SPREAD ACROSS SC AND NERN GA WHERE MODERATELY UNSTABLE
AIRMASS RESIDES. STORMS MOVING EWD TOWARD CENTRAL VA/CENTRAL NC
SHOULD WEAKEN SLOWLY WITH TIME AS THEY SHIFT ATOP A COOL BOUNDARY
LAYER...WITH THE MAIN SEVERE THREAT LIKELY TO SHIFT SWD INTO THE
NERN GA/SC REGION INTO THE EVENING. ALONG WITH THREAT FOR LARGE
HAIL AND DAMAGING WINDS...A COUPLE OF TORNADOES REMAIN POSSIBLE.
..GOSS.. 04/09/2011
.PREV DISCUSSION... /ISSUED 1121 AM CDT SAT APR 09 2011/
...SYNOPSIS...
MAJOR WRN TROF WILL START ITS EWD MOVE WITH A VERY STRONG JET
DRIVING NEWD ACROSS THE HIGH PLAINS TOWARD THE UPPER MS VALLEY
OVERNIGHT. SURFACE LOW DEVELOPING OVER CENTRAL HIGH PLAINS WILL
DEEPEN NEWD ACROSS NEB BY THIS EVENING MOVING INTO SWRN MN BY 12Z
SUN. STRONG SLY FLOW WILL CONTINUE TO SPREAD A MOIST AND
POTENTIALLY VERY UNSTABLE AIR MASS NWD THRU THE SRN/CENTRAL PLAINS
AS WARM FRONT CURRENTLY SRN NEB TO NRN MO LIFTS NWD.
FURTHER EAST A WELL DEVELOPED MCS OVER LOWER OH VALLEY WILL TURN S
OF E ON THE E SIDE OF RIDGE MOVING ACROSS CENTRAL U.S. A MOIST AND
VERY UNSTABLE AIR MASS DOWNSTREAM SEWD ACROSS APPALACHIANS INTO
CAROLINAS COUPLED WITH THE OBSERVED MID LEVEL JET OF 50-60KT WILL
SUPPORT AN ACTIVE SEVERE THUNDERSTORM PERIOD THIS AFTERNOON AND
EVENING.
...ERN KY/TN SEWD THRU THE CAROLINAS...
AS THE AIR MASS HEATS DOWNSTREAM FROM THE MCS AIR MASS EXPECTED TO
BECOME STRONGLY UNSTABLE SEWD ACROSS ERN KY/TN INTO CAROLINAS TO THE
S OF THE BACKDOOR COLD FRONT. COLD FRONT CURRENTLY AGAINST THE
MOUNTAINS NRN NC THEN SEWD ALONG SC/NC BORDER SHOULD SLOW AND BE THE
NWD LIMIT OF THE GREATER SEVERE THUNDERSTORM THREAT THIS AFTERNOON.
THE CURRENT LINE OF SEVERE THUNDERSTORMS ASSOCIATED WITH THE MCS OH
RIVER INTO NRN KY EXPECTED TO REDEVELOP SEWD INTO AREA OF GREATEST
INSTABILITY THIS AFTERNOON. WITH MLCAPES RANGING UPWARDS TO 2500
J/KG AND THE 50-60KT OF BRN SHEAR THUNDERSTORMS SHOULD INCREASE AND
EVOLVE INTO LINE SEGMENTS AND BOWS. ALONG WITH THE WIND DAMAGE
CONCERN...LARGE HAIL WILL ALSO ACCOMPANY THE STRONGEST UPDRAFTS.
SHEAR SUFFICIENT FOR SUPERCELL STRUCTURES INCLUDING A TORNADO
THREAT...PARTICULARLY WITH ANY MORE DISCRETE STORM THAT DEVELOPS.
ONE FAVORED AREA WOULD BE THE ENHANCED LOW LEVEL CONVERGENCE
VICINITY BACKDOOR FRONT CAROLINAS.
...SD/IA/MN/NEB...
MODELS ARE IN GOOD AGREEMENT REGARDING DEEPENING THE CENTRAL HIGH
PLAINS SURFACE LOW AND TRACKING IT EAST-NORTHEASTWARD INTO SD/NEB BY
EVENING. SOUTHERLY LOW LEVEL WINDS IN THE WARM SECTOR WILL HELP TO
TRANSPORT GULF MOISTURE NORTHWARD AND YIELD AFTERNOON MLCAPE VALUES
OF 2000-3000J/KG. A STRONG CAPPING INVERSION WILL LIKELY LIMIT THE
NUMBER OF SURFACE-BASED STORMS THAT CAN FORM...WITH ISOLATED
DEVELOPMENT IN VICINITY OF THE DRYLINE BEING THE MAIN CONCERN
THROUGH 00Z. THOSE STORMS THAT DO FORM WILL LIKELY BE SUPERCELLS
CAPABLE OF VERY LARGE HAIL AND DAMAGING WINDS. STORMS WILL HAVE A
RISK OF TORNADOES AS THEY INTERACT WITH THE WARM FRONT NEAR THE
MN/IA BORDER LATE THIS AFTERNOON AND EVENING.
HAVE ADJUSTED THE MDT RISK A LITTLE S INTO WRN IA/NERN NEB AS HIGH
RES MODELS SUGGEST SURFACE STORM INITIATION LIKELY VICINITY ERN
NE/IA BORDER BY 00Z. IF SO THESE STORMS WOULD QUICKLY BECOME
SUPERCELLS AND SEVERE INCLUDING VERY LARGE HAIL ALONG WITH
TORNADOES.
AFTER 00Z...THE INCREASING LOW LEVEL JET WILL ENHANCE WARM ADVECTION
AND LIFT ALONG AND NORTH OF THE WARM FRONT. THIS SHOULD RESULT IN
AN EXPANDING AREA OF SEVERE STORMS CAPABLE OF VERY LARGE HAIL ACROSS
THE MODERATE RISK AREA.
...KS/OK/TX...
LITTLE CHANGE IN EARLIER IDEA OF DRY LINE POTENTIAL. IT IS VERY
CONDITIONAL BASED ON THE STRENGTH OF THE CAP. HOWEVER ANY STORM
THAT INITIATES WOULD QUICKLY BECOME AT LEAST A LARGE HAIL THREAT.
THE SURFACE DRYLINE IS FORECAST TO EXTEND FROM EAST-CENTRAL KS
SOUTHWARD INTO WESTERN OK AND WEST-CENTRAL TX BY LATE AFTERNOON.
STRONG HEATING ALONG THIS AXIS WILL HELP TO WEAKEN THE CAP AND YIELD
AFTERNOON MLCAPE VALUES OVER 2500 J/KG. VERTICAL SHEAR PROFILES
WILL ALSO BE QUITE FAVORABLE IN THIS REGION FOR SUPERCELLS CAPABLE
OF LARGE HAIL AND DAMAGING WINDS. DESPITE THIS CONDITIONAL
RISK...ONLY WEAK LARGE SCALE FORCING ASSOCIATED WITH A SMALL
SHORTWAVE PERTURBATION ROUNDING THE BASE OF THE CA TROUGH IS
EXPECTED IN THIS AREA...MAINLY AFTER 00Z. SOME OF THE EXPERIMENTAL
MODEL SOLUTIONS ARE SUGGESTING A THREAT OF ISOLATED THUNDERSTORM
DEVELOPMENT AS FAR SOUTH AS NORTHWEST TX...SO HAVE USED THAT AS THE
SOUTHERN EXTENT OF THE SLIGHT RISK.
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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