Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 300559
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
159 AM EDT SAT APR 30 2016

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN ACROSS THE SOUTHEAST REGION...BEFORE A
COLD FRONT PUSHES IN FROM THE NORTHWEST SATURDAY NIGHT. THIS FRONT
WILL BECOME STATIONARY ACROSS THE CAROLINAS AND NORTHEAST GEORGIA
THROUGH TUESDAY. CANADIAN HIGH PRESSURE WILL THEN BUILD INTO THE
AREA AND PERSIST THROUGH FRIDAY.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 130 AM EDT SATURDAY...STILL QUIET ACROSS THE REGION WITH
MAINLY MID/HIGH LEVEL CLOUDS THICKENING. NOT YET SEEING ANY
ENCROACHMENT OF LOW CLOUDS OR LIGHT PRECIP FROM THE NE AS SUGGESTED
BY NEW MODEL RUNS. TEMPS WILL REMAIN SEASONALLY MILD.

BY SATURDAY MORNING...AN AREA OF SURFACE HIGH PRESSURE CENTERED NEAR
HUDSON BAY...AND EXTENDING OVER MUCH OF EASTERN CANADA AND THE
NORTHEAST CONUS IS EXPECTED TO FORCE A BACK DOOR COLD FRONT THROUGH
THE MID-ATLANTIC AND THROUGH MUCH OF NORTH CAROLINA BY SAT
AFTERNOON. AS USUAL...EXACTLY HOW FAR SOUTHWEST THIS BOUNDARY
PENETRATES INTO OUR FORECAST AREA IS THE SUBJECT OF MUCH UNCERTAINTY
AT THIS POINT. INCREASING LOW-LEVEL SOUTHERLY FLOW DEVELOPING IN
RESPONSE TO LARGE SCALE HEIGHT FALLS TO OUR WEST WILL RESULT IN WEAK
ISENTROPIC LIFT NORTH OF THE BOUNDARY...WHICH COULD SUPPORT SOME
PRECIP DEVELOPMENT BY LATE IN THE DAY.

OF LARGER CONCERN WILL BE WHAT HAPPENS IN THE WARM SECTOR SAT
AFTERNOON. IT APPEARS APPRECIABLE MOISTURE/CLOUDS WILL HOLD OFF
UNTIL LATE IN THE DAY...WHILE DEWPOINTS WILL BE ON THE INCREASE
THROUGHOUT THE DAY. MEANWHILE...RESPECTABLE MID-LEVEL LAPSE RATES OF
AROUND 6.5 C/KM ARE EXPECTED ACROSS THE REGION SAT AFTERNOON. WARM
SECTOR INSTABILITY IS THEREFORE EXPECTED TO BECOME PRETTY
RESPECTABLE BY THE END OF THE DAY...WITH SBCAPE LIKELY REACHING THE
1500-2000 J/KG RANGE ACROSS THE WESTERN HALF OF THE AREA BY LATE
AFTERNOON. MEANWHILE...AS A MID-LEVEL SHORT WAVE RIDGE PUSHES
NORTHEAST OF THE AREA...WEAK LARGE SCALE LIFT WILL INCREASE...WITH
SHORT TERM GUIDANCE DEPICTING THE APPROACH OF A SHORT WAVE TROUGH.
AS THIS OCCURS...AT LEAST SCATTERED CONVECTION SHOULD DEVELOP ALONG
THE BOUNDARY AND ACROSS THE HIGH TERRAIN BY LATE AFTERNOON. POPS IN
THE 40-60 PERCENT RANGE (HIGHEST ACROSS THE WEST) WILL BE FEATURED
DURING THIS TIME. WIND FIELDS WILL BE INCREASING THROUGHOUT THE
DAY...WITH DEEP LAYER SHEAR INCREASING TO 35-40 KTS BY THE END OF
THE DAY. WHILE HELICITY WILL BE RELATIVELY WEAK IN A LARGE SCALE
SENSE...ENHANCED HELICITY WILL EXIST ALONG THE SURFACE
BOUNDARY...POSSIBLY SUPPORTING A WEAK TORNADO THREAT WITH ANY CELLS
CROSSING THE BOUNDARY.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
AS OF 200 PM EDT FRIDAY...THE SHORT TERM FCST PERIOD KICKS OFF
SATURDAY EVENING WITH BROAD UPPER RIDGING OVER THE SOUTHEAST...WHILE
AN H5 CYCLONE ROTATES OVER THE CENTRAL PLAINS.  AT THE
SURFACE...CYCLOGENESIS IS EXPECTED BENEATH SAID H5 LOW WITH A COLD
FRONT EXTENDING SOUTHWARD THROUGH CENTRAL TX...WHILE AN EAST/WEST
ORIENTED WARM FRONT EXTENDS ACROSS THE TN/OH VALLEYS.
MEANWHILE...HIGH PRESSURE OVER NEW ENGLAND WILL LIKELY WEAKEN AND
SLIDE OUT TO SEA EFFECTIVELY FORCING THE RETREAT OF A WEAK CAD WEDGE
OVER MUCH OF NORTHEAST GA AND THE WESTERN CAROLINAS...ESPECIALLY AS
THE WARM FRONT SURGES NORTH.  THUS...AM EXPECTING ONGOING CONVECTION
TO CONTINUE THROUGH THE EARLY/MID EVENING HOURS AMONGST THE BUILDING
WARM SECTOR...WHILE WEAK UPGLIDE COULD ALLOW FOR SHRA NORTH OF THE
FRONT.

MOVING ALONG...THE WARM FRONT WILL HAVE PUSHED THROUGH THE ENTIRE
FCST AREA BY SUNDAY THEREBY ALLOWING THE REGION TO SIT FIRMLY IN THE
WARM SECTOR AS THE ASSOCIATED COLD FRONT CROSSES THE MS RIVER
VALLEY.  GUIDANCE CONTINUES TO FAVOR CONVECTIVE INITIATION THROUGH
THE DAY AS HEATING LEADS TO DESTABILIZATION.  STEEP LOW/MID LEVEL
LAPSE RATES AND ABUNDANT DRY AIR ALOFT YIELD FCST SOUNDINGS THAT ARE
SOMEWHAT IMPRESSIVE WITH CAPES APPROACHING/EXCEEDING 2K J/KG WITH
DEEP LAYER SHEAR IN THE 25-30KTS RANGE.  THEREFORE WOULDNT BE
SURPRISED TO SEE SCATTERED/NUMEROUS TSRA WITH SOME CELLS REACHING
STRONG/SEVERE LIMITS ON SUNDAY WITH LARGE HAIL AND DAMAGING WINDS
BEING THE PRIMARY THREATS...WITH LOCALIZED HEAVY RAINFALL AS A
SECONDARY THREAT. MONDAY LOOKS FAIRLY SIMILAR TO SUNDAY HOWEVER WITH
A BIT WEAKER SHEARING AND STEERING FLOW ALBEIT STILL FAIRLY UNSTABLE
AHEAD OF THE APPROACHING COLD FRONT...THEREFORE ISOLATED/SCATTERED
TSRA LOOKS POSSIBLE OVER REGION.  IN SUMMARY...THE FCST FEATURES
WIDESPREAD ELEVATED CHANCE/LIKELY POPS ON SUNDAY...LOWERING TO
CHANCE LEVELS FOR MONDAY.  TEMPERATURES THROUGH THE PERIOD WILL
HOVER A FEW DEGREES ABOVE NORMAL ON AVERAGE.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AT 230 PM FRIDAY, ON MONDAY NIGHT ZONAL UPPER FLOW WILL BE OVER THE
SOUTHEAST USA, WHILE AN UPPER TROUGH WILL EXTEND FROM EASTERN CANADA
TO THE MIDWESTERN USA, AND AN UPPER RIDGE WILL BE OVER WESTERN
CANADA AND THE WESTERN USA. THE UPPER TROUGH AMPLIFIES OVER THE
EASTERN USA BY WEDNESDAY, PROGRESSING CLOSER TO THE EAST COAST BY
FRIDAY WHILE THE RIDGE UPSTREAM REACHES THE PLAINS.

AT THE SURFACE, A COLD FRONT WILL DEPART THE WESTERN CAROLINAS AND
NORTHEAST GEORGIA ON MONDAY NIGHT, MOVING OFF THE CAROLINA COAST BY
TUESDAY MORNING. THE WESTERN END OF THIS FRONT STALLS NEAR THE GULF
COAST. MOIST FLOW OVER THIS BOUNDARY WILL SUPPORT CONTINUING
PRECIPITATION OVER OUR AREA. ON WEDNESDAY A SURFACE WAVE MOVING
ALONG THE FRONT WILL REACH THE LOWER SAVANNAH RIVER VALLEY, AND
MOIST FLOW AHEAD OF THIS SYSTEM WILL KEEP PRECIPITATION GOING OVER
OUR AREA. PRECIPITATION WILL FINALLY END LATE ON THURSDAY, AS
ANOTHER FRONT MOVES OVER THE SOUTHERN APPALACHIANS FROM THE
NORTHWEST AND BRINGS DRIER AIR INTO OUR AREA. TEMPERATURES WILL
INITIALLY EXHIBIT A REDUCED DIURNAL RANGE DUE TO MOISTURE ASSOCIATED
WITH THE STALLED FRONT AND APPROACHING SURFACE WAVE. TEMPERATURES
WILL FALL TO SLIGHTLY BELOW NORMAL IN THE WAKE OF THE SECOND COLD
FRONT.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT AND KHKY...VFR FOR MOST OF THE PRE-DAWN HOURS WITH MID/HIGH
CLOUDINESS STREAMING OVERHEAD. THINGS GET MORE COMPLICATED TOWARD
DAYBREAK AS THE MODELS SUGGEST THE ONSET OF COLD AIR DAMMING WITH
THE ARRIVAL OF A WEAK BACK DOOR FRONT. OBSERVATIONS SHOW MVFR/IFR
CLOUDS OVER VA AND NORTHEAST NC...WHICH WOULD DRIFT SW WITH THE
BOUNDARY SIMILAR TO THIS PAST MORNING. HOW FAR TO THE SW THE LOW
CLOUDS WOULD MOVE BEFORE RUNNING UP AGAINST A WARMING BOUNDARY LAYER
AFTER SUNRISE IS OPEN TO DEBATE. A CONSENSUS OF THE GUIDANCE WOULD
BRING AT LEAST A BKN/OVC LOW CLOUD DECK DOWN ACROSS THE NC PIEDMONT
AND FOOTHILLS WITH A CLOUD BASE IN THE MVFR RANGE...ALONG WITH A NE
WIND. SOME OF THE GUIDANCE SUGGESTS THIS COULD BE IFR OR LIFR. FOR
NOW...HAVE KEPT THE MVFR SIMILAR TO THE PREVIOUS TAF...WITH
SCATTERED CLOUDS BELOW THAT. WILL EVALUATE FURTHER AND PERHAPS
INTRODUCE A TEMPO FOR IFR IF TRENDS SUPPORT IT. THE LOW CLOUDS
SHOULD LIFT/ERODE IN THE MIDDLE OF THE DAY AND GIVE WAY TO
CONVECTIVE CLOUDS IN THE MID/LATE AFTERNOON...AT WHICH TIME
SHOWERS/THUNDERSTORMS BECOME A CONCERN. THIS WILL BE HANDLED WITH
PROB30S AT THIS POINT AS IT IS UNCLEAR HOW MUCH OF THIS AREA WILL
BREAK OUT AND WARM UP ENOUGH FOR CONVECTION. WIND SHOULD COME AROUND
TO SE AS THIS HAPPENS. EITHER WAY...EXPECT FLIGHT RESTRICTIONS
INSIDE THE PRECIP AREAS. CEILING MAY COME BACK DOWN LATE SATURDAY
EVENING BUT THIS DETAIL HAD TO BE LEFT OUT OF THE TAFS FOR NOW.

ELSEWHERE...WEAK COLD AIR DAMMING IS NOT EXPECTED TO EXPAND ACROSS
THE REST OF THE AREA...SO VFR CONDITIONS WILL PREVAIL AT LEAST THRU
MID-MORNING...AND WILL CONTINUE OUTSIDE OF SHOWERS/STORMS THAT
DEVELOP IN THE AFTERNOON/EVENING. WILL HANDLE CONVECTION WITH A
PROB30 TO START...AND TRANSITION TO A TEMPO IN THE EVENING WHEN
COVERAGE IS EXPECTED TO BE THE GREATEST. WIND SHOULD BE LIGHT NE
OVERNIGHT...THEN SE DURING THE DAY.

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...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH  99%     MED   75%     MED   66%     HIGH  84%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  93%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  95%
KHKY       HIGH  98%     HIGH  95%     LOW   53%     HIGH  93%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  90%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  97%

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...SBK
NEAR TERM...JDL/PM/TDP
SHORT TERM...CDG
LONG TERM...JAT
AVIATION...PM


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