Area Forecast Discussion
Issued by NWS Greer, SC

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814
FXUS62 KGSP 011540
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1140 AM EDT SUN MAY 1 2016

.SYNOPSIS...
A WAVY FRONTAL BOUNDARY ACROSS THE REGION THIS MORNING IS EXPECTED
TO LIFT NORTH AS A WARM FRONT TODAY. MEANWHILE...A SLOW MOVING COLD
FRONT APPROACHING FROM THE WEST WILL KEEP A WARM AND HUMID AIR MASS
ACROSS THE REGION THROUGH MONDAY AND MONDAY NIGHT. THE FRONT WILL
FINALLY MOVE ACROSS THE REGION ON TUESDAY. A SECOND STRONGER COLD
FRONT WILL PASS ON THURSDAY AND WILL BRING DOWN A MASS OF COLD AIR
FROM CANADA FOR LATE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1010 AM...PER LATEST WV IMAGERY...A SHORT WAVE TROUGH IS
BEGINNING TO MOVE EAST OF THE FORECAST AREA THIS MORNING...TAKING
THE AREA OF WIDESPREAD SHOWERS/THUNDERSTORMS ALONG WITH IT.
MEANWHILE...THE OLD CAD BOUNDARY HAS LIFTED TO NEAR THE NC/SC
BORDER...WITH SW SFC WINDS NOW BEING OBSERVED ACROSS MUCH OF UPSTATE
SC AND NORTHEAST GA. QUITE A FEW BREAKS IN THE OVERCAST HAVE BEEN
DEVELOPING ACROSS THE WESTERN HALF OF THE AREA THIS MORNING...
ALTHOUGH CUMULUS TENDS TO FILL IN PRETTY QUICKLY WITHIN THE MOIST
ENVIRONS. SBCAPE IS CURRENTLY RANGING FROM 500-1000 J/KG IN DEEPER
INTO THE WARM SECTOR (ACROSS THE SOUTHERN UPSTATE AND THE SOUTHWEST
NC MTNS). ALTHOUGH MANY AREAS WILL PROBABLY SEE A FEW PEAKS OF
SUN...IT APPEARS THE BULK OF THE DAY WILL BE MOSTLY CLOUDY. THAT
BEING THE CASE...IT STILL SEEMS THE 2000+ SBCAPE DEPICTED IN SOME
SHORT TERM GUIDANCE IS A BIT OVERDONE...BUT SUFFICIENT BUOYANCY
SHOULD NEVERTHELESS EXIST TO ALLOW FOR STRONG TO A PERHAPS A HANDFUL
OF SEVERE STORMS.

HAVING SAID THAT...IT/S NOT AT ALL CLEAR HOW CONVECTIVE TRENDS ARE
GOING TO EVOLVE LATER TODAY. WEAK SUBSIDENCE OVERSPREADING THE AREA
IN THE WAKE OF THE SHORT WAVE SHOULD PRECLUDE ANYTHING MORE THAN A
FEW ISOLATED CELLS...AT LEAST INTO EARLY AFTERNOON. OTHER THAN
TERRAIN EFFECTS...THERE WILL BE LITTLE IN THE WAY OF SOURCES OF LIFT
TO FOCUS CONVECTION. THE SURFACE BOUNDARY IS EXPECTED TO BECOME
INCREASINGLY DIFFUSE...SO IT/S NOT CLEAR AS TO WHETHER THERE WILL BE
ADEQUATE LIFT ALONG THIS BOUNDARY. SOME OF THE LATEST HIRES/
MESOSCALE GUIDANCE SUGGESTS THE CONVECTIVE LULL WILL PERSIST WELL
INTO THE AFTERNOON...WHILE THE LATEST HRRR DOES EXPAND COVERAGE OVER
THE AREA THIS EVENING...WITH THE APPROACH OF ANOTHER WEAK MID-LEVEL
SHORT WAVE TROUGH (IT/S THE ONLY HIRES MODEL THAT/S REALLY DOING
THIS). BASED UPON THE EXPECTED DEGREE OF INSTABILITY...IT SEEMS
REASONABLE THAT SCATTERED CONVECTION WILL DEVELOP NEAR THE BLUE
RIDGE THIS AFTERNOON INTO THE EVENING...AND WILL ALLOW POPS TO
INCREASE TO LIKELY THERE BY EARLY EVENING...WITH SOLID CHANCES
ADVERTISED ACROSS MUCH OF THE REMAINDER OF THE AREA. IN ADDITION TO
THE POTENTIAL FOR ISOLATED SEVERE WEATHER...WILL HAVE TO KEEP AN EYE
ON PORTIONS OF THE EASTERN UPSTATE/SC PIEDMONT AND SOUTHWEST NC
PIEDMONT FOR HYDRO ISSUES...AS SEVERAL INCHES OF RAIN HAVE FALLEN
ACROSS A FAIRLY WIDE SWATH SINCE SAT EVENING.

THE GUIDANCE SUGGESTS THAT PRECIP CHANCES WILL DIMINISH BY LATE
EVENING OR SO. TONIGHT/S LOWS WILL REMAIN SEASONALLY MILD.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300AM EDT SUNDAY...CHANCES FOR THUNDERSTORMS CONTINUE ON
MONDAY AS SOUTHWESTERLY BOUNDARY LAYER FLOW PERSISTS AROUND A
SURFACE TROUGH WEST OF THE APPALACHIANS AHEAD OF AN UPPER CENTRAL
CONUS TROUGH THAT MAKES GRADUAL EASTWARD PROGRESS.  MONDAY AFTERNOON
SOUNDINGS SHOW PWATS AROUND 1.5 INCHES...MODEST INSTABILITY...AND
MODEST BULKSHEAR...CONDITIONS SIMILAR TO SATURDAY AND SUNDAY.
RESULT WILL BE CONTINUED CHANCES FOR THUNDERSTORMS ON MONDAY WITH
THE POTENTIAL FOR LOW-END SEVERE AND LOCAL FLOODING IF CELLS SHOULD
TRAIN OVER ONE AREA.

TROUGH REACHES THE CWA WITH A COLD FRONT AS UPPER SYSTEM CONTINUES
TO PROGRESS MONDAY NIGHT.  LIGHTER NON-THUNDER SHOWERS MAY PERSIST
TUESDAY MORNING...DESPITE DECLINING PWATS...DUE TO FORCING FROM
UPPER SYSTEM.  SOME UPSLOPE SHOWERS ON THE WEST SIDE OF THE
MOUNTAINS MAY ALSO CONTINUE INTO TUESDAY...BUT TUESDAY WILL HAVE
MOSTLY DRYER CONDITIONS AND AN END TO RAINFALL.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 300AM SUNDAY...FOLLOWING PASSAGE OF MAJOR FRONT EARLY
TUESDAY...MOISTURE PLUMMETS ACROSS THE AREA AND SIGNIFICANT
ADDITIONAL PRECIP IS NOT EXPECTED WEDNESDAY THROUGH SATURDAY.
TEMPERATURES ALSO DECLINE TO 5 TO 10 DEGREES BELOW NORMAL.  SOME
ISOLATED RAIN SHOWERS...AND POSSIBLY EVEN AN ISOLATED THUNDERSHOWER
ARE POSSIBLE...ESPECIALLY WEDNESDAY AFTERNOON WHEN MODELS HAVE A
SHORTWAVE TRAVERSING THE AREA BUT GREATLY REDUCED BL MOISTURE LIMITS
POTENTIAL.

IN ADDITION TO SHORTWAVES ROTATING AROUND MAJOR UPPER TROUGH
DEVELOPING OVER THE NORTHEAST CONUS...MODELS CONTINUE TO SHOW A SHOT
OF COOL CANADIAN AIR DESCENDING WITH THIS UPPER TROUGH WITH A MAJOR
COLD FROPA ON THURSDAY...AND THE COLDEST POINT IN THE FORECAST BEING
REACHED FRIDAY MORNING.  GFS STILL HAS 850MB TEMPS DOWN TO -2C OVER
THE MOUNTAINS BEHIND THE FRONT...WITH THE EC SLIGHTLY WARMER AT
-1C.  FRONT COULD GENERATE SOME LIGHT SHOWERS...ESPECIALLY WITH
UPSLOPE ENHANCEMENT ON THE WEST SLOPE OF THE MOUNTAINS...BUT SURFACE
TEMPERATURES SHOULD BE JUST WARM ENOUGH EVERYWHERE TO STILL PRECLUDE
ANY WINTER PRECIP. TYPES.  GFS-EC AGREEMENT IS QUITE GOOD THROUGH
THURSDAY...INCLUDING DETAILS ABOUT SHORTWAVE PASSAGE ON WEDNESDAY.
COOL AIR INTRUSION FRIDAY IS SEASONALLY SHORT-LIVED WITH
TEMPERATURES REBOUNDING TO NORMAL SATURDAY AFTERNOON.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...A MIXED BAG THROUGH THE MID-MORNING HOURS
WITH VARIABLE CEILING AND VISIBILITY DEPENDING ON LOCATION RELATIVE
TO WAVES OF SHOWERS AND THUNDERSTORMS MOVING ACROSS THE REGION. MOST
PLACES WILL BE MVFR OR IFR/LIFR THROUGH THAT TIME...WITH THE THOUGHT
THAT IFR WILL PREVAIL MAINLY OVER THE NC PIEDMONT AS THE MAIN AREA
OF STORMS MOVES THROUGH. THINK THE BIGGER PROBLEM WILL BE CEILING
AND NOT VISIBILITY. MEANWHILE...THERE WILL BE SOME VFR HOLES IN THE
LOW CLOUD CEILING. WIND GENERALLY SHOULD BE SE TO THE SOUTH OF AN
OLD BOUNDARY RUNNING ROUGHLY ALONG I-85...AND NORTHEAST TO THE NORTH
OF THE BOUNDARY. THIS IS EXPECTED TO WASH OUT WITH SE WIND TAKING
SHAPE AT ALL PLACES BY MID MORNING. THE LATEST GUIDANCE FROM
CONVECTION ALLOWING MODELS SUGGESTS THERE WILL BE A BIT OF A LULL IN
THE WAKE OF THE CURRENT ACTIVITY...THEN ANOTHER DEVELOPMENT OF
STORMS IN THE MIDDLE PART OF THE DAY.  THE TSRA CHANCE WILL BE
HANDLED WITH A TEMPO AT ALL SITES. ENDED PRECIP/RESTRICTION THREAT
EVERYWHERE BY 00Z BASED ON GUIDANCE SHOWING A WAVE MOVING PAST
AROUND THAT TIME. MOST DETAIL BEYOND 00Z MONDAY WAS ELIMINATED FOR
BREVITY.

OUTLOOK...UNSETTLED WEATHER/OCCASIONAL CONVECTION/RESTRICTIONS ARE
EXPECTED TO CONTINUE INTO EARLY NEXT WEEK...AS A FRONT BECOMES
STALLED NEAR THE AREA. DEFINITIVE DRYING DOES NOT APPEAR LIKELY
UNTIL AT LEAST MID-WEEK.

CONFIDENCE TABLE...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       MED   70%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       MED   68%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  81%     HIGH 100%     HIGH 100%     HIGH  94%
KHKY       LOW   53%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH  83%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  88%     HIGH 100%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE 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...PM
NEAR TERM...JDL/PM
SHORT TERM...WJM
LONG TERM...WJM
AVIATION...PM



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