Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 231946
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
246 PM EST SUN NOV 23 2014

.SYNOPSIS...
WIDESPREAD RAIN WILL TAPER OFF LATER TONIGHT WITH A COLD FRONT
MOVING ACROSS THE REGION ON MONDAY. A COASTAL LOW IS THEN EXPECTED
TO DEVELOP OFF THE SOUTHEAST COAST AND MOVE UP THE ATLANTIC SEABOARD
ON WEDNESDAY. DRIER HIGH PRESSURE WILL SPREAD BACK OVER THE REGION
ON THURSDAY AND FRIDAY AND LINGER WELL INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 230 PM EST SUNDAY...WIDESPREAD MODERATE TO HEAVY RAIN WILL
CONTINUE ACROSS MUCH OF THE CWA THIS AFTERNOON INTO TONIGHT AS UPPER
DIVERGENCE JET STREAK COMBINED WITH ONGOING ISENTROPIC UPGLIDE ATOP
THE PERSISTENT IN-SITU COLD AIR DAMMING PROMOTE IMPRESSIVE SYNOPTIC
LIFT. THE SPC HOURLY MESOSCALE ANALYSIS TREND SHOWS AREAS OF
100-300J/KG MUCAPE OVER CENTRAL GA AND MIDLANDS SC LIFTING
NORTHEASTWARD INTO OUR SW ZONES OF THE CWA THIS AFTERNOON. IN
FACT...MULTIPLE BANDS OF SHOWERS EMBEDDED WITH THUNDER WERE
APPROACHING THE NE GA. HENCE...HAVE MADE SOME ADJUSTMENTS TO THE WX
GRID TO INCLUDE THUNDER COVERING NE GA...UPSTATE SC AND WESTERN PART
OF THE NC PIEDMONT THIS AFTERNOON THRU THIS EVENING. THIS ELEVATED
BUOYANCY SHOULD SUPPORT BETTER RAINFALL RATES...WITH ADDITIONAL
0.75-1.5" CAN BE EXPECTED ACROSS MUCH OF OUR FORECAST AREA. DESPITE
THE PRESENCE OF ELEVATED BUOYANCY AND STRONG LLV WIND
SHEAR...PERSISTENT IN-SITU CAD SHOULD LIMIT OUR POTENTIAL FOR SEVERE
WEATHER. IN FACT...THE LATEST 12Z GFS/NAM KEEPS THE CAD AT LEAST
THROUGH 00Z MON...BEFORE ERODING BY LATE TONIGHT AS A WARM FRONT
LIFTS NORTH ACROSS THE AREA. ALSO...BOTH THE NAM/GFS SUGGEST THAT
AREAS OF SBCAPE SHOULD REMAIN WELL TO OUR SOUTH. LATEST SPC
CONVECTIVE OUTLOOK IS WELL IN LINE WITH THIS...KEEPING OUR AREA FREE
OF MARGINAL THREAT. HOWEVER...IF AREAS OF SBCAPE PUSH FARTHER NORTH
INTO OUR AREA BY THE TIME CAD ERODES TONIGHT...THE RISK FOR SEVERE
WEATHER INCREASES ACCORDINGLY. DUE TO THE UNCERTAINTY...WILL
CONTINUE TO MENTION NON-ZERO CHANCE FOR SEVERE WEATHER IN OUR HWO
MAINLY OVER THE SOUTHERN ZONES OF OUR CWA.

POPS SHOULD TAPER OFF FROM WEST TO EAST TONIGHT INTO EARLY MON
MORNING AS THE WARM FRONT LIFT NORTH OF THE AREA AND DRY AIRMASS
MOVES IN FROM THE WEST. CONDITIONS FOR MONDAY LOOK MOSTLY DRY UNDER
A WARM SECTOR AHEAD OF AN APPROACHING COLD FRONT FROM THE
MISSISSIPPI VALLEY. THEREFORE...MAX TEMPS ON MONDAY WILL BE AROUND
20-25 DEGREES WARMER THAN TODAY...REACHING THE LOW 70S EAST OF THE
MTNS. POPS REMAIN ON THE LOW SIDE AS MOISTURE APPEARS TO BE SHALLOW
AND GOOD DOWNSLOPING WSW WINDS WILL LIMIT THE BUOYANCY. WITH
TIGHTENING PRESSURE GRADIENT...WE WILL SEE GUSTY SW WINDS OF 20-25
MPH BY EARLY MON AFTERNOON.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 PM SUNDAY...ONCE OUR CURRENT SYSTEM IS OUT OF THE WAY BY
LATE MONDAY...OUR ATTENTION TURNS TO THE NEXT INTERESTING
DEVELOPMENT IN THE MODEL GUIDANCE. EXPECT MONDAY NIGHT AND TUESDAY
TO BE FAIRLY BENIGN WITH A SW FLOW ALOFT AND COOLER HIGH PRESSURE
BUILDING IN FROM THE WEST. THE MOST NOTABLE THING WILL BE THAT HIGH
TEMPS ON TUESDAY WILL DROP BACK TO SOMETHING MORE LIKE A CATEGORY OR
SO BELOW NORMAL. THERE SHOULD BE A GOOD AMOUNT OF HIGH CLOUDS AS
WELL AS THE JET CORE REMAINS JUST TO OUR NW.

THAT BRINGS US TO TUESDAY NIGHT AND WEDNESDAY. THE GFS AND ECMWF
HAVE BEEN FAIRLY CONSISTENT WITH THE PAST FEW RUNS IN DEVELOPING A
BAND OF MID LEVEL FRONTOGENESIS ORIENTED SW-NE ACROSS THE FCST AREA
LATE TUESDAY NIGHT AND WEDNESDAY MORNING AS A SRN STREAM SHORT WAVE
INDUCES CYCLOGENESIS ON THE OLD COLD FRONT OFF THE SOUTHEAST COAST.
THE INCREASING FRONTOGENESIS ON THE NW SIDE OF THE DEVELOPING LOW
SHOULD FORCE THE DEVELOPMENT OF LIGHT PRECIP EARLY WEDNESDAY
MORNING. THE TREND HAS BEEN TO DEVELOP THE LOW A BIT FURTHER W WITH
EACH RUN...WHICH SPEAKS FAVORABLY TO AN INCREASING TREND IN PRECIP
PROBABILITY. WILL BUMP POP INTO THE CHC RANGE ACROSS NEARLY THE
ENTIRE MTNS BY SUNRISE WEDNESDAY...AND INTO THE LIKELY RANGE OVER
THE NC PIEDMONT/CLT METRO AREA. OF NOTE IS THE NAM SOLUTION...WHICH
IS MUCH FARTHER E AND CONSIDERED AN OUTLIER AT THIS TIME...AND THUS
DISCOUNTED. THE PRECIP TYPE IS THE PROBLEM...AS THE PARTIAL
THICKNESS FROM THE ECMWF IS LOWER AND MORE BORDERLINE OVER THE NW
PIEDMONT. CONSIDERING A BLEND OF THICKNESS FROM THE GFS AND ECMWF...
THERE COULD BE SOME PROBLEMS...BUT THINK THEY WILL BE CONFINED TO
THE HIGHER ELEVATIONS. FCST SOUNDINGS DO NOT SHOW A WARM
NOSE...WHICH SUGGESTS AN ELEVATION-DEPENDENT RAIN/SNOW SITUATION. IF
THE GFS IS THE MODEL OF CHOICE...THEN WE MUST CONSIDER THE MODEL
DEPICTION OF FREEZING LEVEL REMAINING ABOVE ABOUT 3K FEET AND THE
SFC DEWPOINT BOTTOMING OUT ONLY IN THE MID-30S OUTSIDE THE MTNS.
THAT SIMPLY WILL NOT CUT IT IF WE WANT SNOW TO REACH THE GROUND
OUTSIDE THE MTNS. THAT COMBINED WITH THE MODEL TREND OF MOVING THE
SYSTEM A BIT FARTHER W EACH RUN SUGGESTS THAT PRECIP TYPE IS LIKELY
TO TREND EVEN MORE TOWARD RAIN VERSUS SNOW OUTSIDE THE MTNS.
SO...WENT WITH A COLD RAIN. THE MTNS ARE STILL LOOKING LIKE AN
ELEVATION DEPENDENT SNOW/RAIN DEAL...WITH THE ONLY THING UP IN THE
AIR BEING THE SNOW LEVEL. THERE IS THE POTENTIAL FOR A FEW INCHES OF
WET SNOW MAINLY ABOVE 4K FEET. THAT BEING SAID...CONFIDENCE IS A BIT
BELOW AVERAGE BECAUSE OF THE POOR AGREEMENT BETWEEN THE NAM AND
GFS...AND THE POSSIBILITY THAT THERE IS TIME FOR SOME PHASING OF SRN
AND NRN STREAM WAVES...WHICH MIGHT TRACK THE SYSTEM SO FAR W SO AS
TO BRING WARMER AIR OVER THE MTNS. WILL NOT MENTION THIS IN THE HWO
YET BECAUSE OF THE LIMITED SCOPE OF THE SNOW ACCUM POTENTIAL. PRECIP
SHOULD TAPER OFF FROM THE SW IN THE AFTERNOON AS THE FRONTOGENESIS
LIFTS OFF TO THE NE.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
AS OF 2 PM SUNDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
THURSDAY WITH THE UPPER TROF AXIS JUST TO OUR NW AND STEEP UPPER
RIDGING BUILDING OVER THE WESTERN CONUS. OVER THE NEXT 24 TO 36
HRS...THE TROF IS EXPECTED TO LIFT NE OF THE FCST AREA WITH THE
PATTERN FLATTENING IN THE TROFS WAKE. OVER THE PAST COUPLE OF
RUNS...THE ECMWF IS LOOKING MORE LIKE THE GFS WRT MAINTAINING A MORE
ZONAL UPPER PATTERN THRU THE REMAINDER OF THE PERIOD. THE MODELS DO
AMPLIFY ANOTHER LONGWAVE TROF ON SAT/SUN...HOWEVER IT REMAINS WELL
TO OUR NORTH AND SHOULD HAVE VERY LITTLE IMPACT ON OUR SENSIBLE WX.

AT THE SFC...BY 00Z THURS THINGS SHOULD BE DRYING OUT PRETTY QUICKLY
AS THE LOW TRACKS UP THE ATLANTIC SEABOARD. A WEAK SECONDARY
OCCLUDED FRONT IS EXPECTED TO PASS JUST TO OUR NORTH AS THE MAIN LOW
LIFTS NE AND SOME LINGERING PRECIP IS POSSIBLE OVER THE NORTHERN AND
WESTERN ZONES...HOWEVER IT SHOULD NOT AMOUNT TO MUCH AND I ONLY
CARRY SLIGHT CHANCE POPS FOR THAT PERIOD. BY FRI...ANOTHER ROUND OF
CANADIAN HIGH PRESSURE MOVES INTO THE REGION FROM THE NW AND KEEPS
THINGS DRY WELL INTO THE WEEKEND. THE 00Z RUN OF THE ECMWF TRIES TO
MOVE A PLUME OF DEEP MOISTURE OVER THE FCST AREA FROM THE NW ON SAT
AND THE GFS DOES SOMETHING SIMILAR...ONLY ABOUT 24 HRS LATER ON
SUN. THESE SCENARIOS LOOK SUSPICIOUS AND I WOULD NOT PLACE TOO MUCH
FAITH ON THE TIMING AND/OR EXTENT OF THE MOISTER RIGHT NOW. TEMPS
WILL REMAIN BELOW CLIMO THRU THE PERIOD WITH DAILY VALUES INCREASING
A FEW DEGREES THRU DAY 7.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
AT KCLT...IFR CIGS/VISBY SHOULD PERSIST THROUGH EARLY MONDAY MORNING
AS AREAS OF ISENTROPIC UPGLIDE INDUCED PRECIP ASSOCIATED WITH AN
UPPER SHORTWAVE TROUGH MOVE THROUGH THE REGION. WITH CONTINUED
IN-SITU COLD AIR DAMMING...ESE/NELY SURFACE WINDS WILL PREVAIL
THROUGH 02Z MONDAY WHILE PERSISTENT S/SELY LLVL JET SUPPORT LLVL
WIND SHEAR. LLVL JET THEN VEERS TO THE SW BY 02Z MON. HENCE...HAVE
MENTIONED WS020/12040KT AT 18Z AND WS020/20040KT AT AROUND 02Z MON.
OTHERWISE...EXPECT LIGHT TO MODERATE RAIN SHOWERS TO CONTINUE WITH
POSSIBLE THUNDER TOWARDS THE EVENING HOURS AS AREAS OF ELEVATED
BUOYANCY LIFT NORTHWARD INTO THE AREA ATOP THE SURFACE WEDGE. AS THE
SURFACE WEDGE ERODES TONIGHT...WINDS WILL VEER TO THE S/SSW. IFR
CIGS WILL CONTINUE TO AFFECT THE TERMINAL THRU MON MORNING BEFORE
IMPROVING TO VFR BY AROUND 15Z AS GUSTY SW WINDS DEVELOP.

ELSEWHERE...TRENDS MUCH LIKE KCLT WITH CONTINUED IFR IN PRECIP
TONIGHT INTO EARLY MON MORNING. WE WILL ALSO SEE THUNDER MAINLY OVER
THE PIEDMONT IN LIGHT OF AREAS OF ELEVATED BUOYANCY PUSHING
NORTHWARD INTO THE AREA. WITH STRONG S/SELY LLVL JET PUSHING THROUGH
ATOP THE SURFACE IN-SITU COLD AIR DAMMING...HAVE MENTIONED LLVL WIND
SHEAR AT ALL TERMINALS ACCORDINGLY. WIND CHANGES OVERALL ARE SIMILAR
IN PROGRESSION WITH THE EXCEPTION OF KAVL WHICH WILL SEE S/SSE WINDS
THROUGHOUT THE PERIOD.

OUTLOOK...BRIEF DRYING FOLLOWS A COLD FRONT MON-TUE...WITH RAIN
AND/OR WINTRY PRECIP POSSIBLY RETURNING WED. MORE SETTLED WEATHER
WILL RETURN TO END THE WEEK.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       HIGH 100%     HIGH  91%     MED   78%     HIGH  88%
KGSP       HIGH  96%     HIGH  86%     MED   76%     MED   77%
KAVL       HIGH  85%     MED   66%     HIGH  81%     HIGH  85%
KHKY       HIGH 100%     HIGH 100%     HIGH  88%     HIGH  85%
KGMU       HIGH  94%     HIGH  89%     MED   78%     MED   77%
KAND       HIGH  93%     MED   78%     MED   60%     MED   73%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

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

&&

$$
SYNOPSIS...JPT
NEAR TERM...JOH
SHORT TERM...PM
LONG TERM...JPT
AVIATION...JOH


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