SPC AC 120555
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1255 AM CDT SUN JUL 12 2009
VALID 121200Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL HIGH
PLAINS...CNTRL PLAINS AND MID-MO VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MID-MS AND
TN VALLEYS...
...CNTRL HIGH PLAINS/CNTRL AND NRN PLAINS/MID-MO VALLEY...
AN UPPER-LEVEL RIDGE WILL MOVE SLOWLY EWD ACROSS THE HIGH PLAINS
SUNDAY WITH NORTHWEST FLOW IN PLACE ACROSS THE CNTRL AND NRN PLAINS.
A COUPLE OF MARGINALLY SEVERE CONVECTIVE CLUSTERS SHOULD BE ONGOING
THIS MORNING...ONE COMING SEWD OUT OF ERN ND AND ANOTHER IN ECNTRL
NEB AND NRN KS. AT THE SFC...A COLD FRONT IS FORECAST TO BE LOCATED
FROM SERN CO EXTENDING EWD TO A LOW IN SRN KS. NORTH OF THE
FRONT...A WELL-DEFINED MOIST AXIS SHOULD BE PRESENT IN NRN KS WITH
SFC DEWPOINTS FROM 65 TO 75 F. THUNDERSTORMS SHOULD AGAIN DEVELOP
THIS AFTERNOON ON THE WRN EDGE OF THE MOIST TONGUE IN THE HIGHER
TERRAIN OF ERN CO AND SE WY WITH THIS ACTIVITY MOVING EWD ACROSS THE
HIGH PLAINS. FURTHER EAST ACROSS THE PLAINS...THE MODELS ARE QUITE
VARIED. THE MOST LIKELY SCENARIO WOULD BE FOR CONVECTION INITIATION
TO OCCUR ON THE NORTH EDGE OF THE INSTABILITY AXIS IN NRN NEB OR
SERN SD WITH A CLUSTER OF STORMS MOVING SEWD ALONG THE GRADIENT
THROUGH EARLY THIS EVENING.
FORECAST SOUNDINGS FROM NERN CO NEWD INTO CNTRL AND ERN NEB SHOW
MODERATE VERTICAL SHEAR PROFILES MAINLY ASSOCIATED WITH DIRECTIONAL
SHEAR IN THE BOUNDARY LAYER AND STRONG SPEED SHEAR IN THE
MID-LEVELS. THIS COMBINED WITH MUCAPE VALUES AGAIN FORECAST ABOVE
4000 J/KG ALONG MUCH OF THE MOIST AXIS SHOULD BE SUPPORTIVE OF
SUPERCELLS WITH LARGE HAIL. THE GREATEST POTENTIAL FOR LARGE HAIL
SHOULD BE IN NE CO AND WRN NEB WHERE MID-LEVEL LAPSE RATES ARE
FORECAST TO BE STEEPEST. AN ISOLATED TORNADO COULD OCCUR IF A
SUPERCELL CAN BECOME DOMINANT LATE THIS AFTERNOON. WITH THE MOIST
BOUNDARY LAYER...CONVECTIVE CLUSTERS SHOULD ALSO BE CAPABLE OF
PRODUCING ISOLATED WIND DAMAGE. A GREATER WIND DAMAGE THREAT COULD
EXIST IN ERN NEB AND NE KS EARLY THIS EVENING IF A SMALL MCS CAN
ORGANIZE ON THE NOSE OF THE LOW-LEVEL JET.
...MID-MS/TN VALLEYS...
A LARGE UPPER-LEVEL HIGH WILL REMAIN ACROSS MUCH OF THE SCNTRL U.S.
TODAY. AN AXIS OF MODERATE TO STRONG INSTABILITY SHOULD BE IN PLACE
BY MIDDAY ON THE ERN EDGE OF THE HIGH PRESSURE SYSTEM EXTENDING SEWD
INTO THE TN VALLEY. MODEL FORECASTS ARE CONSISTENT DEVELOPING
NUMEROUS THUNDERSTORMS ALONG THIS INSTABILITY AXIS FROM SERN MO SEWD
INTO CNTRL MS AND NRN AL THIS AFTERNOON. FORECAST SOUNDINGS IN THIS
CORRIDOR AT 21Z SHOW VERY STEEP LOW-LEVEL LAPSE RATES WITH MUCAPE
VALUES ABOVE 2500 J/KG AND ABOUT 30 KT OF VERTICAL SHEAR. THIS
SHOULD BE SUPPORTIVE OF ISOLATED SEVERE STORMS CAPABLE OF PRODUCING
WIND DAMAGE ESPECIALLY IF A LINE-SEGMENT CAN ORGANIZE AROUND PEAK
HEATING.
...ERN CAROLINAS/SE VA/SRN MD...
AN UPPER-LEVEL TROUGH IS FORECAST TO MOVE EWD ACROSS THE NERN STATES
TODAY AS A QUASI-STATIONARY FRONT REMAINS IN PLACE EWD FROM THE
CNTRL APPALACHIANS INTO THE MID-ATLANTIC. ALONG AND SOUTH OF THE
BOUNDARY...MODERATE INSTABILITY IS FORECAST AND SEVERAL MODELS
DEVELOP THUNDERSTORMS ALONG THE INSTABILITY AXIS THIS AFTERNOON.
FORECAST SOUNDINGS LATE THIS AFTERNOON ACROSS SERN VA AND ERN NC
SHOW 30 TO 40 KT OF VERTICAL SHEAR SUGGESTING AN ISOLATED SEVERE
THREAT MAY DEVELOP. A FEW ORGANIZED SEVERE STORMS WITH HAIL AND
ISOLATED WIND DAMAGE WILL BE POSSIBLE ESPECIALLY IF THE FORECAST OF
MODERATE INSTABILITY VERIFIES.
...PACIFIC NW/NRN ROCKIES...
AN UPPER-LEVEL TROUGH IS FORECAST TO MOVE INTO THE PACIFIC NORTHEAST
TODAY WITH SOUTHWEST FLOW IN PLACE ACROSS THE NRN ROCKIES.
THUNDERSTORMS SHOULD DEVELOP IN THE HIGHER TERRAIN OF ID AND WRN MT
AS SFC TEMPS WARM AROUND MID-DAY WITH SEVERAL STORM CLUSTERS
PERSISTING INTO THE LATE AFTERNOON AND EARLY EVENING. FORECAST
SOUNDINGS IN THE NRN ROCKIES THIS AFTERNOON SHOW STRONG VERTICAL
SHEAR PROFILES AND STEEP MID-LEVEL LAPSE RATES. THIS COULD SUPPORT A
FEW MARGINALLY SEVERE STORMS WITH HAIL POTENTIAL. STRONG GUSTY WINDS
WILL ALSO BE POSSIBLE WITH THE FASTER MOVING STORMS IN AREAS WITH
MAXIMIZED INSTABILITY.
..BROYLES.. 07/12/2009
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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