Area Forecast Discussion
Issued by NWS Greer, SC

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151
FXUS62 KGSP 271421
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1021 AM EDT WED APR 27 2016

.SYNOPSIS...
WARM ATLANTIC HIGH PRESSURE WILL PERSIST OVER THE SOUTHEAST THROUGH
MIDWEEK. AFTER A WEAK COLD FRONT MOVES IN FROM THE WEST THURSDAY
NIGHT...WEAK HIGH PRESSURE WILL RETURN BRIEFLY ON FRIDAY. A LOW
PRESSURE SYSTEM WILL MOVE IN FROM THE WEST OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1020 AM...HAVE UPDATED POP AND SKY COVER TRENDS TO BE IN LINE
WITH LATEST RADAR AND SATELLITE PIX. UPDATED REST OF THE FIELDS TO
BE IN LINE WITH LATEST OBS.

OTHERWISE...THE FORECAST REMAINS ON TRACK WITH A WEST TO EAST
ORIENTED FRONT DRAPED ACROSS THE MID ATLANTIC REGION THIS MORNING.
OUTFLOWS FROM EARLIER CONVECTION ALONG THIS BOUNDARY ARE GENERATING
SHOWERS AND EMBEDDED THUNDERSTORMS FARTHER SOUTH FROM SOUTHERN KY TO
SOUTHERN VA AROUND DAYBREAK. HOWEVER...THE FRONT IS EXPECTED TO
REMAIN NORTH OF OUR FORECAST AREA THROUGH THE NEAR TERM PERIOD.
MEANWHILE...SOUTHWESTERLY FLOW AT LOW LEVELS WILL PERMIT MOISTURE TO
GRADUALLY RETURN TO THE REGION TODAY ALONG WITH WARMER TEMPERATURES.
THIS WILL RESULT IN SLIGHTLY BETTER INSTABILITY IN VERTICAL PROFILES
THAN WERE OBSERVED ON TUESDAY...WITH MLCAPE VALUES LIKELY PEAKING AT
1500 TO 2000 J/KG LATE IN THE DAY. LOW LEVEL WIND CONVERGENCE WILL
BE GREATEST OVER THE MOUNTAINS THIS AFTERNOON...BUT WITH ADDITIONAL
WEAK FORCING OVER THE NORTHERN FOOTHILLS/PIEDMONT. WILL FEATURE
SOLID CHANCES FOR TSRA IN NORTHERN AND WESTERN SECTIONS LATE IN THE
DAY AND TAPER DOWN TO SLIGHT CHANCES SOUTHEAST. MAXES SHOULD REACH
THE MID 80S OUTSIDE OF THE MOUNTAINS AND EVEN AROUND 80 IN THE LOWER
MOUNTAIN VALLEYS DESPITE SOME HIGH CLOUDS.

CONVECTIVE OUTFLOWS WILL GET A BIT CLOSER FOR TONIGHT...BUT WITH
DIURNAL ACTIVITY TO THE NORTH AND WEST LIKELY DIMINISHING BEFORE
REACHING THE SOUTHERN APPALACHIANS. EXPECT A MILD NIGHT WITH MINS
GREATER THAN 10 DEGREES ABOVE CLIMO AND CONTINUED NOCTURNAL
CONVECTIVE CHANCES...HIGHEST IN NW SECTIONS AND LOWEST SE.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 245 AM WEDNESDAY...THURSDAY STILL LOOKS LIKE THE DAY WITH
HIGHEST CONVECTIVE COVERAGE WITH A MARGINAL SEVERE TSTM THREAT. A
POTENT VORT MAX WILL EJECT OUT OF THE WESTERN CONUS TROUGH AND
RIPPLE AROUND THE NORTHERN PERIPHERY OF THE SOUTHEAST FLAT RIDGE.
THIS WILL INCREASE THE MID AND UPPER FLOW ENOUGH TO PRODUCE 0-6 KM
BULK SHEAR OF 30-40 KTS...HIGHEST IN THE NORTHERN TIER. INSTBY
SHOULD MANAGE TO TOP OUT WITH SBCAPE OF 1000-1500 J/KG BY PEAK
HEATING. A COLD FRONT WILL BE APPROACHING FROM THE WEST...BUT MODELS
HAVE TRENDED SLOWER WITH ITS ARRIVAL...STILL SHOWING IT OVER THE
CUMBERLAND PLATEAU THRU 00Z FRIDAY. SO POPS JUST MAY BE OVERDONE ON
THURSDAY...ESP EAST OF THE MTNS. WHATEVER CONVECTION DOES FIRE MAY
NOT PUSH INTO THE PIEDMONT UNTIL THURSDAY EVENING.  WILL CONTINUE TO
FORECAST SOLID CHC TO LOW-END LIKELY POPS THU-THU NIGHT. TEMPS WILL
BE ABOVE NORMAL.

FRIDAY...ALL THE MODELS EXCEPT FOR THE NAM PUSH THE FRONT THRU THE
AREA...AND BRING SOME DRY AIR AND LLVL CAA THRU THE DAY. I WILL
THROW OUT THE NAM WITH THIS FCST AND CONTINUE THE DRY FCST. ASSUMING
WE HAVE THE 20 KTS OR SO OF NWLY DOWNSLOPE FLOW...TEMPS WILL BE IN
THE MID TO UPR 80S EAST OF THE MTNS. OVERNIGHT SHOULD BE DRY WITH
LOWS STILL ABOUT 10 DEG ABOVE NORMAL.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 300 AM WEDNESDAY...THE MEDIUM RANGE GUIDANCE SHOWS A RATHER
COMPLEX UPPER LEVEL FLOW ACRS THE CONUS WITH DISAGREEMENTS ON THE
DETAILS. THIS MAKES FOR A BELOW AVERAGE CONFIDENCE FORECAST THRU THE
EXTENDED. ON SATURDAY...A LARGE AREA OF HIGH PRES WILL BUILD IN
ACROSS THE GREAT LAKES...WITH DRY ONSET CAD EXPECTED TO DEVELOP ATOP
THE CWFA. AS DEEP-LAYER SWLY FLOW DEVELOPS ATOP THE WEDGE...EXPECT
INCREASING CLOUDS AND POPS FROM SATURDAY AFTN THRU SUNDAY NIGHT.
WITH THAT SAID...MODELS ARE IN DISAGREEMENT ON HOW FAST WE MOISTEN
UP AND HOW MUCH QPF CAN BE EXPECTED. AT SOME POINT...A LOW PRESSURE
SYSTEM IS EXPECTED TO ORGANIZE OVER THE SOUTHERN PLAINS...THEN LIFT
NE INTO THE OH VALLEY. THIS SHOULD BRING A WARM CONVEYOR BELT OF
CLOUDS AND PRECIP ACRS THE AREA EITHER SUNDAY OR SUNDAY NIGHT. SO I
STILL THINK THE LIKELY POPS LOOK GOOD.

FOR MONDAY AND TUESDAY...THE CENTER OF THE LOW SHOULD BE INVOF THE
MID ATLANTIC OR NORTHEAST BY MONDAY AFTN...PLACING THE CWFA ON THE
NW FLOW/DRYING SIDE OF THE SYSTEM. THE GFS SLOWS THE LOW DOWN AND
MANAGES TO KEEP ENUF MOISTURE AROUND FOR BETTER INSTBY AND SOME
CONVECTION MONDAY. THE ECMWF IS FASTER AT PUSHING THE LOW OFF THE
EAST COAST...BUT SHOWS A STRONGER REINFORCING COLD FRONT APPROACHING
FROM THE NW. SO WILL FCST A SHOTGUN CHC POP FOR MONDAY...TAPERING
OFF TO MAINLY SLGT CHC TO LOW-END CHC FOR TUESDAY. TEMPS WILL
SLIGHTLY COOLER MONDAY...AND CLOSE TO NORMAL TUESDAY.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT AND ELSEWHERE...ALL AIRPORTS WILL REMAIN IN THE WARM SECTOR
TODAY THROUGH TONIGHT...SOUTH OF A STALLED FRONTAL ZONE OVER THE
VIRGINIAS AND A SLOWLY APPROACHING COLD FRONT FROM THE WEST NEAR THE
MS RIVER VALLEY. FEW TO SCATTERED CUMULUS WILL DEVELOP WITH HEATING
AND CIRRUS BLOWOFF FROM UPSTREAM CONVECTION MAY PROVIDE SOME
CEILINGS AT TIMES. THE BEST CHANCES OF SCATTERED THUNDERSTORMS
AFFECTING THE NC TERMINALS WILL OCCUR LATE DAY THROUGH EARLY
EVENING...WHILE CHANCES REMAIN EVEN LESS AT THE SC TERMINALS. EXPECT
MAINLY SW WINDS...WITH LOW END GUSTS AT TIMES...EXCEPT LIGHTER AND
MORE VARIABLE WINDS AT KAVL THROUGH THE PERIOD.

OUTLOOK...PRECIPITATION CHANCES AND ASSOCIATED RESTRICTIONS SHOULD
INCREASE ON THURSDAY AHEAD OF A COLD FRONT APPROACHING FROM THE
WEST. SOME DRYING IS EXPECTED ON FRIDAY...WITH BRIEF VFR
CONDITIONS...BEFORE UNSETTLED WEATHER AND POSSIBLE RESTRICTIONS
RETURN FROM THE WEST OVER THE WEEKEND.

CONFIDENCE TABLE...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  90%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  83%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  95%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

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

&&

$$
SYNOPSIS...ARK
NEAR TERM...HG/RWH
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...HG/RWH



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