SPC AC 040657
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0157 AM CDT SAT JUL 04 2009
VALID 061200Z - 071200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE CENTRAL/SRN HIGH
PLAINS...
...SYNOPSIS...
LONG WAVE PATTERN IS FORECAST TO PROGRESS SLOWLY EWD ON MONDAY AS
THE ERN ONTARIO UPPER LOW MOVES EWD INTO THE ST LAWRENCE
VALLEY...WHILE THE UPSTREAM RIDGE MOVES EWD ACROSS THE NRN HIGH
PLAINS AS A VORTICITY MAX EJECTS NEWD FROM THE ERN PACIFIC LOW
ACROSS THE PACIFIC NW/SERN BC INTO ALBERTA. THE FASTER GFS/ECMWF
SOLUTION OVER THE NWRN STATES IS FAVORED OVER THE SLOWER NAM
FORECAST.
AT THE SURFACE...A LOW WILL MOVE EWD ACROSS MT. A WARM FRONT
EXTENDING SEWD FROM THE LOW WILL LIFT NWD INTO THE NRN PLAINS...AND
TRAILING COLD FRONT WILL MOVE EWD ACROSS THE NRN INTERMOUNTAIN
REGION. A LEE TROUGH WILL PERSIST OVER THE HIGH PLAINS. OVER THE
SRN STATES...A WEAKENING FRONT WILL MOVE SLOWLY SWD FROM SRN SC
ACROSS THE LOWER MS VALLEY AND SERN TX.
...CENTRAL/SRN HIGH PLAINS...
PERSISTENT WEAK SELY UPSLOPE FLOW IS EXPECTED AGAIN DURING THE
AFTERNOON AND EVENING...MAINTAINING AMPLE LOW LEVEL MOISTURE WITH
SURFACE DEW POINTS IN THE 50S. STEEP MID LEVEL LAPSE RATES COUPLED
WITH STRONG DIURNAL HEATING WILL CONTRIBUTE TO MLCAPE OF 1000-1500
J/KG DURING THE LATE AFTERNOON AND EVENING. THUNDERSTORMS ARE
EXPECTED TO DEVELOP DURING THE AFTERNOON AND MOVE SEWD WITHIN NWLY
FLOW REGIME. PRONOUNCED DIRECTIONAL SHEAR WILL CONTRIBUTE TO 30-40
KT DEEP LAYER SHEAR ACROSS THE AREA...PROMOTING DEVELOPMENT OF
STRONG/SEVERE STORMS INCLUDING A FEW SUPERCELLS CAPABLE OF PRODUCING
LARGE HAIL AND DAMAGING WIND GUSTS.
...MT INTO THE DAKOTAS...
THUNDERSTORM ACTIVITY MAY INCREASE OVER PARTS OF WRN/CNTRL MT DURING
THE AFTERNOON IN RESPONSE TO ENHANCED DYNAMIC FORCING IN ADVANCE OF
THE VORTICITY MAX/SHORT WAVE TROUGH LIFTING NEWD ACROSS THE NRN
INTERMOUNTAIN REGION. ELY COMPONENT TO THE LOW LEVEL FLOW NORTH OF
THE SURFACE LOW AND WARM FRONT WILL TRANSPORT MOISTURE WWD...WITH
MLCAPE OF 500-1000 J/KG EXPECTED ACROSS PARTS OF WRN/NRN MT. MODEL
GUIDANCE IS INCONSISTENT WITH THE EXTENT OF CONVECTIVE COVERAGE
ASSOCIATED WITH A CAPPING INVERSION IN THE WARM SECTOR. THERE IS
POTENTIAL FOR A FEW STRONG THUNDERSTORMS TO DEVELOP...INITIALLY OVER
WRN MT THEN SPREADING EWD ACROSS NRN MT AND POSSIBLY INTO WRN ND BY
THE END OF THE PERIOD. OTHER ISOLATED STORMS MAY DEVELOP OVER PARTS
OF THE DAKOTAS TO THE NORTH OF THE WARM FRONT DURING THE LATE
AFTERNOON/EVENING...BUT CONSIDERABLE SPREAD IN THE
LOCATION/INTENSITY OF THE WARM FRONT LOWERS CONFIDENCE IN THIS
ACTIVITY.
...SERN TX ACROSS SERN STATES...
MODERATE INSTABILITY IS EXPECTED TO DEVELOP IN AREAS ALONG/SOUTH OF
THE FRONT EXTENDING ACROSS THE REGION...AND MODELS INDICATE THAT
WIDESPREAD CONVECTION WILL DEVELOP BY AFTERNOON. STRONG STORMS
CAPABLE OF PRODUCING A FEW WET MICROBURSTS ARE POSSIBLE... BUT
SEVERE PROBABILITY WILL BE LIMITED TO 5% AT THIS TIME GIVEN THE WEAK
WINDS ALOFT AND MINIMAL VERTICAL SHEAR ACROSS THE AREA.
...ERN NY INTO NEW ENGLAND...
UPPER LOW FORECAST TO MOVE NEWD ACROSS THE NRN PARTS OF THE AREA IS
ASSOCIATED WITH RELATIVELY COOL MID LEVEL TEMPERATURES /-14 TO -18C
AT 500 MB/. THIS WILL RESULT IN MODEST INSTABILITY...ESPECIALLY IF
AREAS OF STRONGER HEATING CAN DEVELOP DURING THE DAY. MULTIPLE
BANDS OF LOW-TOP CONVECTION ARE EXPECTED TO MOVE EWD THROUGH THE
EVENING HOURS...WITH STRONGER CELLS CAPABLE OF PRODUCING HAIL GIVEN
THE LOW ENVIRONMENTAL FREEZING LEVELS FORECAST.
..WEISS.. 07/04/2009
CLICK TO GET WUUS03 PTSDY3 PRODUCT
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
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