Severe Thunderstorm Warning 159, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
248 PM EDT TUE JUN 9 2009

.SYNOPSIS...
WEAK HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH WEDNESDAY. A
SURFACE BOUNDARY WILL APPROACH THE MOUNTAINS THURSDAY...BEFORE
PUSHING INTO THE REGION FRIDAY AND LINGERING THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
CONVECTION IS FINALLY FIRING OFF OF THE HIGHER TERRAIN THIS
AFTERNOON...WITH A COUPLE OF CELLS HAVING DEVELOPED OVER THE
NORTHERN MTNS AS OF 18Z. COVERAGE SHOULD CONTINUE TO EXPAND...AND
ISOLATED TO WIDELY SCATTERED COVERAGE SHOULD BE ATTAINED BY LATE IN
THE AFTERNOON. WITH FREEZING LEVEL AT AROUND 13KFT...A HIGH
REFLECTIVITY CORE UP TO AROUND 30KFT SHOULD BE GOOD ENOUGH TO
PRODUCE LARGE HAIL AND MICROBURSTS. CONVECTION WILL DIMINISH ACROSS
MOST OF THE AREA BY MIDNIGHT.

WEDNESDAY SHOULD BE VERY SIMILAR TO TODAY...WITH MAX TEMPS REACHING
THE LOWER 90S ACROSS MOST OF THE PIEDMONT...AND ANOTHER AFTERNOON
WITH MODERATE DESTABILIZATION. SCATTERED COVERAGE OF DIURNAL
CONVECTION IS ANTICIPATED OVER THE MTNS ONCE AGAIN...WITH ISOLATED
TO WIDELY SCATTERED STORMS EXPECTED OVER THE FHILLS/PIEDMONT.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
AS OF 245 PM TUESDAY...MODELS STILL IN GENERAL AGREEMENT DURING THE
SHORT RANGE WITH NEARLY ZONAL FLOW ALLOWING A SERIES OF SHORT WAVES
TO MOVE ACROSS THE AREA. THE DETAILS DIFFER ON TIMING AND LOCATION
OF MCS ACTIVITY...RESULTING OUTFLOW BOUNDARIES AND FRONTAL TIMING
AND LOCATION. WED NITE CONVECTION SHOULD BE DIURNAL OUTSIDE OF THE
MTNS...BUT COULD LINGER ACROSS THE MTNS...ESP IF MCS TRACK IS CLOSE
TO THE AREA. LOWS ABOVE NORMAL.

FOR THURSDAY...THE SFC FRONT STILL REMAINS TO OUR NORTH...BUT CLOSE
ENUF THAT WITH WLY FLOW...LIKELY COVERAGE OF CONVECTION SHOULD
DEVELOP OVER THE MTNS AND NRN FOOTHILLS. ALTHOUGH LEE TROF WILL BE
EAST OF THE AREA DURING THE AFTERNOON...MODERATE INSTABILITY IS
LIKELY. THEREFORE...HAVE INCLUDED SCT CONVECTION ALL AREAS OUTSIDE
OF THE MTNS...BUT LEAST LIKELY SOUTH OF I-85 IN THE UPSTATE AND NE
GA. HIGHS REMAIN WELL ABOVE NORMAL. THU NITE...CONVECTION SHOULD
AGAIN BE MAINLY DIURNAL OUTSIDE OF THE MTNS...WITH POTENTIAL
LINGERING CONVECTION OVER THE NC MTNS DUE TO MCS ACTIVITY. LOWS
AGAIN ABOVE NORMAL.

FRIDAY...LOOKS TO BE THE DAY THE FRONT SLIDES ACROSS THE AREA.
MODERATE INSTABILITY LIKELY AGAIN...SO WITH INCREASED LOW LEVEL
CONVERGENCE SCT CONVECTION SHOULD DEVELOP ALL AREAS...WITH HIGHER
CHC OVER THE MTNS. HIGHS DOWN A LITTLE FROM THURSDAY. CONVECTION
SHOWS DIURNAL TREND FRI NITE...WITH LOWS A TAD COOLER.

LOW PRESSURE MOVING ALONG THE STALLED FRONT NEAR OR ACROSS THE AREA
SATURDAY BRINGS SCT DIURNAL CONVECTION ONCE AGAIN. HIGHS A LITTLE
COOLER THAN FRIDAY.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
AS OF 210 PM TUESDAY...THE MODELS CONTINUE TO OFFER VARYING SOLNS
WRT TO THE STATIONARY FRONT SUN THROUGH TUE. THE UPPER PATTERN
BECOMES MORE AMPLIFIED ON THE 00Z ECMWF THAN THE 12Z GFS...THUS
LEADING TO A MORE S/LY PLACEMENT OF THE FRONT AND ALLOWING LOW
THETA/E AIR INTO THE REGION MON THROUGH TUE. THE GFS ON THE OTHER
HAND KEEPS THE SFC BOUNDARY ACROSS THE MIDLANDS OR SOUTHERN
UPSTATE...WHICH WOULD KEEP THE ATMOS OVER THE CWFA UNSTABLE AND
HIGHLY MOIST. THE AMPLIFIED TROF PRESENTED BY THE ECMWF IS A NEW
IDEA FOR THAT MODEL AND THE GFS HAS BECOME LESS AMPLIFIED IN RECENT
RUNS. THIS DICHOTOMY HAS ADDED TO AN ALREADY UNCERTAIN FORECAST.
HOWEVER...A LOOK AT THE CMC AND NCEP ENS MEANS PORTENDS TO A FLATTER
UPPER PATTERN AND THIS WILL BE ACCOUNTED FOR IN THE GRIDS. THE OP
GGEM IS IN BETWEEN THE EC AND GFS...WHICH AGAIN POINTS TOWARD A LESS
AMPLIFIED PATTERN.

SO WITH ALL THIS SAID...LOW CONFIDENCE IS HAD IN POPS AND TEMPS AND
A SWING EITHER WAY OF THE GOING FCST COULD BE POSSIBLE WITH EQUAL
PROBABILITY. FOR NOW...WILL KEEP CHANCE POPS FOR SUN/MON AND GO FOR
A DRYING TREND TUE...WITH ONLY ISOL -SHRA/TS EXPECTED BY THEN. THE GFS
SOUNDINGS INDICATE A POSSIBLE HEAVY PRECIP EVENT SUN NIGHT...WITH PW
VALUES APPROACHING 1.8 INCHES...WHILE OPPOSING LLVL TO MLVL FLOWS
NORTH OF THE STATIONARY FRONT COULD BACK BUILD OR ANCHOR SOME
STORMS. TOO EARLY TO HAVE MUCH FAITH IN THIS SCENARIO...BUT ITS ONE
TO KEEP AN EYE ON. OTHER THAN THAT...THE ATMOS LOOKS REMAIN FAIRLY
UNSTABLE THROUGH THE PERIOD...PER THE GFS...AND AFTERNOON STORMS
COULD BE STRONG GIVEN THE DEEP LAYERED RH AND AVAILABLE LLVL
TRIGGER. HOWEVER...THE ECMWF DISPLAYS A HIGHLY STABLE ENVIRONMENT
WITH A POLAR AIRMASS COVERING THE REGION AND A DRY NE FLOW. SO...THE
LOW CHANCE POPS CONVEY EQUAL WEIGHT GIVEN TO BOTH SETS OF GUIDANCE.
TEMPS COULD BE HIGHLY VARIABLE TOO...WITH THE AMOUNT OF CLOUD COVER
OR AIRMASS EXPECTED...SO FOR NOW SEE NO REASON TO BUDGE MUCH FROM
NORMAL.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
CONVECTION IS GETTING A LATE START OVER THE AREA THIS AFTERNOON...
MUCH AS IT DID YESTERDAY. NEVERTHELESS...THE ATMOSPHERE HAS BECOME
QUITE UNSTABLE WITH DAYTIME HEATING...AND TERRAIN EFFECTS AND WEAK
LIFT WITHIN A LEE SIDE TROUGH SHOULD SPARK ISOLATED TO SCATTERED TS
BY LATE AFTERNOON. STILL...WE DO NOT THINK THE CHANCES OF A CELL
PASSING OVER AN AIRFIELD ARE GREAT ENOUGH TO WARRANT ANYTHING MORE
THAN A CB MENTION ATTM. THE TS THREAT SHOULD PASS BY LATE EVENING.
REDUCED VISBY (BR) IS EXPECTED AT A FEW TERMINALS EARLY WED
MORNING...ESP AT KAVL.

OUTLOOK...AREAS OF VISBY/PERHAPS CIG RESTRICTIONS ARE POSSIBLE EACH
DAY. CHANCES FOR AFTERNOON/EVENING THUNDERSTORMS WILL INCREASE
THROUGH THURSDAY...THEN PERSIST THROUGH THE WEEKEND AS A FRONT
STALLS OVER THE AREA.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

SYNOPSIS...SBK
NEAR TERM...JDL
SHORT TERM...RWH
LONG TERM...SBK
AVIATION...JDL

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