Area Forecast Discussion
Issued by NWS Greer, SC

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133
FXUS62 KGSP 041049
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
649 AM EDT WED MAY 4 2016

.SYNOPSIS...
IN THE WAKE OF A COLD FRONT... COOLER AND DRIER AIR MASS WILL MOVE
IN ACROSS THE REGION TODAY.  ANOTHER COLD FRONT WILL CROSS THE
REGION TONIGHT AND USHER IN AN EVEN COOLER AIR MASS FROM CANADA
FOR THE END OF THE WORK WEEK. HIGH PRESSURE SHOULD RETURN WITH A
WARMING TREND FOR THE BALANCE OF THE WEEKEND...WITH A FRONT SLOWLY
APPROACHING FROM THE NORTH.

&&

.NEAR TERM /THROUGH TONIGHT/...
OF 645 AM...LATEST RADAR IMAGES INDICATED A FEW WEAK SHOWERS OVER
THE FRENCH BROAD VALLEY NEAR THE TN/NC LINE. THESE SHOWERS WILL
LIKELY COME AND GO THROUGH THE MORNING HOURS. SHOWER COVERAGE SHOULD
INCREASE THIS AFTERNOON WITH THE DEVELOPMENT OF WEAK INSTABILITY. I
WILL UPDATE THE FORECAST TO MAKE MINOR ADJUSTMENTS TO THE
TEMPS...WINDS...AND POPS.

AS OF 345 AM...NEAR TERM GUIDANCE INDICATES THAT A CLOSED LOW WILL
SLIDE SE ACROSS THE OHIO RIVER VALLEY LATE THIS AFTERNOON. AS THE
LOW CROSSES THE SOUTHERN APPALACHIANS TONIGHT...A MID LEVEL OMEGA
BLOCKING PATTERN WILL DEVELOP. AT THE SFC...THE FIRST COLD FRONT
WILL SLIDE TOWARD THE ATLANTIC OCEAN EARLY THIS MORNING...A
SECONDARY COLD FRONT WILL CROSS THE SC FOOTHILLS LATE TONIGHT.
DOWNSLOPE FLOW AND NEAR NORMAL LLVL THICKNESSES SHOULD SUPPORT
TEMPERATURES CLOSE TO NORMALS.

THE PASSAGE OF THE COLD FRONT AND MID LEVEL LOW SHOULD SLOW AND PROVIDE
STEEP LAPSE RATES ACROSS THE REGION DURING THE EVENING HOURS. I WILL
FORECAST 30% COVERAGE TONIGHT AND OVER THE TN BORDER COUNTIES. BROAD
LOW PRESSURE WILL SETTLE ACROSS THE REGION THROUGH THE REST OF THE
NIGHT. LOW TEMPERATURES MAY RANGE FROM THE LOW 30S ACROSS THE MTN
RIDGES TO NEAR 50 ACROSS EASTERN CLT METRO. A ROTATING LOW CENTER
WILL TRACK NORTHWARD. RIDGE TOP SHOWER COULD FALL AS A PERIOD OF
SNOW ACROSS THE HIGHEST ELEVATIONS.

&&

.SHORT TERM /THURSDAY/...
AS OF 245 AM EDT WEDNESDAY...THE BIG STORY WITH THE LATTER PART OF
THE WEEK WILL BE THE PASSAGE OF A DEEP UPPER LOW THAT MOVES ACROSS
THE CAROLINAS ON THURSDAY. MODEL GUIDANCE DOES NOT SHOW MIXING TO BE
AS DEEP AS FCST SOUNDINGS ARE A BIT WARMER IN THE 850-700MB LAYER...
BUT EXPECT ENUF INSTABILITY THAT SHALLOW CONVECTION WILL DEVELOP BY
MIDDAY ACROSS MOST OF THE FCST AREA...EXCEPT FOR PROBABLY AREAS OF
UPSTATE SC AND NE GEORGIA TO THE IMMEDIATE LEE OF THE BLUE RIDGE.
THUS...THE FCST WILL STILL FEATURE A CHANCE OF SHOWERS MAINLY OVER
THE NC PART OF THE FCST AREA...AND PARTS OF THE UPSTATE WHERE
CONVERGENCE DOWNSTREAM OF THE MTNS SHOULD PROVIDE LOW LEVEL FORCING
FOR A BAND OF SHOWERS. UPSLOPE FLOW ON THE W SIDE OF THE MTNS WILL
SUPPORT A LIKELY POP ON THE TN BORDER. TEMPS WILL BE ON THE ORDER OF
10-15 DEG BELOW NORMAL FOR HIGHS. STILL THINK PRECIP CHANCES E OF
THE BLUE RIDGE WILL DIMINISH WITH LOSS OF HEATING ON THURSDAY
EVENING...SO PRECIP PROB GRADUALLY TAPERS BACK TO THE UPSLOPE AREAS
ON THE TN BORDER. MIN TEMPS WILL BE COOL AGAIN...BUT NOT NEARLY
CLOSE TO RECORDS...OR COLD ENOUGH TO WORRY ABOUT A FREEZE. A STEADY
NW WIND WILL PROBABLY ALSO PRECLUDE ANY FROST DEVELOPMENT. NO
SIGNIFICANT CHANGES ARE SUGGESTED FOR FRIDAY...EITHER...AS THE UPPER
LOW SPINS AWAY ACROSS THE MID-ATLANTIC. THE WESTERN EDGE OF THE COLD
POOL ALOFT WILL REMAIN ACROSS THE PIEDMONT...SO A SMALL PRECIP
CHANCE WAS KEPT ALONG AND E OF I-77. THAT TOO SHOULD END WITH LOSS
OF HEATING. TEMPS SHOULD REBOUND A BIT AS THE AIR MASS MODIFIES AND
THE UPPER LOW MOVES AWAY. FRIDAY NIGHT SHOULD BE DRY WITH TEMPS
ABOUT FIVE DEGREES WARMER THAN PREVIOUS NIGHTS.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
AS OF 320 AM EDT WEDNESDAY...THERE IS A GROWING CONSENSUS WITH
RUN-TO-RUN CONTINUITY REGARDING THE OLD UPPER LOW LIFTING NWD ON
SATURDAY NIGHT/SUNDAY AND BEING ABSORBED INTO THE NEXT UPPER LOW
DROPPING OUT OF CANADA. THE REINFORCING OF THE DEEP EASTERN UPPER
TROF SHOULD HELP TO PUSH A SURFACE FRONT DOWN INTO THE FCST AREA ON
SUNDAY THAT COULD SERVE AS THE FOCUS FOR SOME PRECIP...MAINLY ON THE
W SIDE OF THE MTNS. AT ANY RATE...WITH THE MODELS HANDLING THIS
FAIRLY CONSISTENTLY...PERHAPS NOW IT IS TIME TO START INCREASING THE
PRECIP CHANCES OVER MAINLY THE NC MOUNTAINS FOR SATURDAY NIGHT AND
INTO SUNDAY. THE BOUNDARY SHOULD LIFT BACK NWD ON MONDAY...PUTTING
THE FCST AREA BACK INTO A WARM SECTOR WITH WEAK HIGH PRESSURE OFF
THE SOUTHEAST COAST AND THE NEXT FRONT OFF TO OUR WEST.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT AND ELSEWHERE EAST OF THE MTNS...VFR THROUGH THE PERIOD. A
COLD FRONT HAS SLIDE EAST OF THE CWA EARLY THIS MORNING. NW WINDS SHOULD
DEVELOP IN THE WAKE OF THE FRONT...INCREASING TO AROUND 10KTS DURING
THE HEAT OF THE AFTERNOON. IT IS POSSIBLE THE KAND WILL DEVELOP
MARGINAL WIND GUSTS DURING THE HEAT OF THE AFTERNOON. A SECONDARY
COLD FRONT WILL APPROACH THE FOOTHILLS AND PIEDMONT DURING THE
EVENING HOURS...RESULTING IN WINDS TO BACK FROM THE SW. WINDS WILL
LIKELY VEER BACK FROM THE NW IN THE WAKE OF A LATE NIGHT FROPA.

AT KAVL...WINDS CHANNELED WITHIN THE FRENCH BROAD VALLEY SHOULD
YIELD WINDS FROM THE 350 DEGREES THROUGH MOST OF THE TAF PERIOD.
WINDS ARE FORECAST TO FREQUENTLY GUST INTO THE MID 20S DURING THE
AFTERNOON. WEAK INSTABILITY...FALLING MID LEVEL HEIGHTS...AND THE
APPROACH OF A SECONDARY COLD FRONT WILL SUPPORT SCT SHRAS/TSRAS
DURING THE 23Z TO 5Z PERIOD...I WILL HIGHLIGHT WITH A PROB30. THE
ARRIVAL OF LLVL MOISTURE ON THE WEST SIDE OF THE MTNS SHOULD YIELD
PERIODS OF MVFR UPSLOPE CEILINGS BY 5Z...RETURNING TO VFR DURING THE
LATE NIGHT.

OUTLOOK...A STRONG UPPER LOW WILL SWING THRU THE AREA THRU
FRIDAY...AND WILL BRING SHRA AND TSRA MAINLY ACROSS THE NC SITES
BOTH THU AND FRI AFTN.

CONFIDENCE TABLE...

            10-16Z        16-22Z        22-04Z        04-06Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   69%     HIGH 100%     HIGH 100%     HIGH  87%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
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...PM
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...PM
AVIATION...NED



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