Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 280227
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
927 PM EST SAT DEC 27 2014

.SYNOPSIS...
A SERIES OF SMALL LOW PRESSURE WILL MOVE NORTHEAST ALONG A COLD
FRONT AS THE FRONT SLOWLY CROSSES OUR REGION FROM THE WEST THROUGH
MONDAY. COOLER HIGH PRESSURE WILL BUILD OVER OUR REGION IN THE MID
TO LATTER PART OF THE WEEK. ANOTHER LOW PRESSURE WILL GET ORGANIZED
OVER TEXAS AND REACH OUR AREA NEXT WEEKEND.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 920 PM...LATEST RADAR IMAGES FROM KGSP INDICATED LIGHT SHOWERS
ACROSS THE LAKELANDS OF SC. UPSTREAM ACROSS CENTRAL AND NRN
GA...COVERAGE OF LIGHT RAIN WAS INCREASING...ESPECIALLY NEAR THE
AL/GA LINE. RECENT SATELLITE IMAGES INDICATED BKN TO OVC MID TO HIGH
CLOUDS ACROSS THE CWA. THE THICK CLOUD COVER HAS LIKELY CONTRIBUTED
TO KEEPING TEMPS ONE TO TWO DEGREES WARMER THAN THE CURRENT
FORECAST. I WILL UPDATE THE FORECAST TO ADJUST POPS TO RECENT RADAR
TRENDS...INCREASE SKY COVER...AND WARM HRLY TEMPS TO OBS.

AS OF 710 PM...I WILL UPDATE TO FINE TUNE CLOUDS....TEMPS...AND
POPS. WIDELY SCATTERED SHOWERS WILL LIKELY DEVELOP ACROSS THE UPPER
SAVANNAH RIVER VALLEY THIS EVENING. OTHERWISE...MOIST SOUTHWEST LLVL
WINDS WILL INCREASE ACROSS THE MTNS AND ADJACENT FOOTHILLS DURING
THE PRE DAWN HOURS. THE COMBINATION OF UPSLOPE FLOW IN INCREASING
LLVL LIFT SHOULD SUPPORT AN EXPANDING AREA OF LIGHT RAIN AND LOW
CIGS TOWARD SUNRISE.

AS OF 515 PM...LIGHT AND HIGH RADAR RETURNS WERE TRACKING ACROSS NRN
GA. THESE RETURNS HAVE NOT BEEN ASSOCIATED WITH SFC OBS OF
RAIN...EXPECTING RETURNS FROM VIRGA. HOWEVER...A LARGE PATCH OF
LIGHT RAIN WAS DRIFTING ACROSS THE AL/GA LINE...THIS AREA SHOULD
RESULT IN RAIN ACROSS THE CWA LATER TONIGHT. I WILL UPDATE TO ADJUST
POP TIMING AND ALIGN TEMP/DWPT WITH OBSERVATIONS.

AS OF 240 PM EST SATURDAY...THE LATEST SATELLITE IMAGE SHOWS A DEEP
AND MOIST WARM CONVEYOR BELT EXTENDING FROM THE GREAT LAKES REGION
DOWN TO THE WESTERN GULF...AND TO THE EASTERN PACIFIC...WITH BROAD
AREAS OF CONVECTION DEVELOPING ACROSS THE DEEP SOUTH AS OF THIS
AFTERNOON HOURS. AS AN EASTERN CONUS UPPER RIDGE AXIS PUSHES OFF THE
ATLANTIC COAST AND MOIST SWLY FLOW ALOFT SETS UP OVER THE SOUTHEAST
US...MID TO LOW LEVEL CLOUDS WILL SPREAD OVER THE PIEDMONT THROUGH
THE AFTERNOON HOURS.THE LATEST SHORT TERM MODELS CONTINUE TO
INDICATE THAT A COLD FRONT WILL SLOWLY MOVE EAST ACROSS THE
MISSISSIPPI VALLEY AND INTO THE TN VALLEY TONIGHT INTO SUN
MORNING...REACHING THE SOUTHERN APPALACHIANS BY SUN AFTERNOON. AHEAD
OF THIS FRONT...A DEEP PLUME OF GULF MOISTURE WILL BE DRAWN UP INTO
THE REGION AS A WAVE OF LOW OVER THE WESTERN GULF LIFTS NE ACROSS
AL/MI TONIGHT. THEREFORE...POPS QUICKLY RAMP UP FROM WEST TO EAST
INTO THE CATEGORICAL RANGE OVER THE WESTERN MTNS ZONES AND NE
GA...WITH LIKELY RANGE OVER THE REST OF THE WESTERN HALF OF THE CWA.
THE BEST RAINFALL RATES WILL OCCUR BETWEEN 12Z-18Z SUN WHEN THE
SURFACE WAVE OF LOW LIFTS NE ACROSS THE CWA AND A SERIES OF UPPER
DISTURBANCES RIPPLES ACROSS THE MTNS ZONES IN SWLY FLOW ALOFT.
ALSO...HAVE MENTIONED A CHANCE OF THUNDER ACROSS MUCH OF THE REGION
EARLY SUN AFTERNOON DUE TO THE PRESENCE OF 100-200J/KG MUCAPE PER
LATEST NAM/GFS/ECMWF. POPS RAMP DOWN TO THE LIKELY RANGE OVER THE
MTN ZONES AND SOLD CHANCE RANGE OVER THE SOUTHERN TIER OF THE REGION
18Z THRU 00Z MON AS THE UPPER FORCING AND THE SURFACE WAVE OF LOW
MOVES OFF TO THE NE. WITH MODELS TRENDING A BIT WETTER FOR THE
UPCOMING EVENT...HAVE GONE WITH THE HPC QPF GUIDANCE RESULTING IN
0.75-1.0" OVER THE WESTERN NC MTNS AND NE GA... WITH AROUND
0.25-0.5" ELSEWHERE THRU SUN EVENING.

WITH CONSIDERABLE CLOUD COVER AND WAA SOUTHERLY FLOW...OVERNIGHT
TEMPS WILL STAY 7-10 DEGREES ABOVE NORMAL. WITH ONGOING
PRECIP...AFTERNOON HIGHS ON SUN WILL BE AROUND 3-5 DEGREES COOLER
THAN TODAY.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 200 PM SATURDAY...THE MODELS SUGGEST THAT WE WILL BE IN A LULL
OF SORTS AT THE START OF THE SHORT RANGE PERIOD SUNDAY EVENING...AS
WE WILL BE IN A MINIMUM OF FORCING. THAT CHANGES QUICKLY BY LATE
EVENING AS THE RIGHT ENTRANCE REGION OF THE UPPER JET TRANSLATES
OVERHEAD BETWEEN ROUGHLY 03Z AND 09Z...AND THE MAIN SHORT WAVE AXIS
MOVES THROUGH IN THE 06Z TO 12Z MONDAY TIME FRAME. ALTHO THE WAVE
SHEARS AND DEAMPLIFIES AS IT CROSSES THE REGION...THE FORCING SHOULD
STILL BE SUFFICIENT TO INCREASE PRECIP PRODUCTION...COMBINED WITH
IMPROVED MOIST ISENTROPIC LIFT. SO...PRECIP CHANCES RAMP BACK UP TO
CATEGORICAL MAINLY OVER THE AREA ALONG AND N/W OF I-85...AND LIKELY
TO THE S...BY 06Z OR SO. THE MAIN FORCING SHOULD SHIFT E OF THE AREA
MONDAY MORNING. THE HIGHEST PRECIP PROBABILITY WILL BE OVER THE WRN
NC PIEDMONT ON MONDAY MORNING. POP WAS LIMITED TO LIKELY OUT OF
UNCERTAINTY WITH TIMING THE DEPARTURE OF THE FORCING...BUT COULD
EASILY HAVE TO BE KEPT CATEGORICAL BEYOND 12Z MONDAY WITH THE
SLIGHTEST DELAY. THE REST OF MONDAY WILL HAVE A SLOW RAMP DOWN
THROUGH THE CHANCE RANGE AS FORCING GRADUALLY WEAKENS BEHIND THE
SURFACE FRONT THAT CROSSES FIRST THING IN THE DAY. FOR MONDAY NIGHT
AND TUESDAY...THERE IS UNCERTAINTY REGARDING THE EXTENT/CHANCE OF
PRECIP. THE LOW LEVEL FLOW COMES AROUND TO SOMETHING NW MONDAY NIGHT
AND TUESDAY WHICH SHOULD FORCE SOME SHOWER ACTIVITY NEAR THE TN
BORDER. THE PASSAGE OF ANOTHER SHORT WAVE COMBINED WITH SOME LOW
LEVEL FRONTOGENESIS APPEARS TO BE RESPONSIBLE FOR THE REDEVELOPMENT
OF PRECIP ON TUESDAY OFF TO OUR N...WHICH SOME OF THE GUIDANCE
BLEEDS DOWN INTO NC. PREFER TO KEEP THE BETTER CHANCES IN THE
UPSLOPE AREAS OF THE NRN MTNS AND TO KEEP THE AREA E OF THE BLUE
RIDGE DRY FOR THE TIME BEING. TEMPS SHOULD DROP BACK DOWN TO NEAR
NORMAL ON TUESDAY.


ON SUNDAY THE FAIRLY BROAD FRONTAL ZONE WILL
EXTEND FROM QUEBEC SWWD TO THE WRN GULF COAST...BISECTING THE TENN
VALLEY JUST TO OUR WEST. AT LEAST ONE WEAK WAVE IS PROGGED TO RIDE
UP THE FRONT DURING THE DAY AS A RESULT OF CYCLONIC UPPER FLOW OVER
THE BOUNDARY CONTAINING EMBEDDED WEAK VORTICES. THOUGH SUCH A WAVE
WOULD LIKELY PROVIDE LOCAL ENHANCEMENT TO LLVL WARM/MOIST ADVECTION
AHEAD OF THE FRONT...THE EXISTENCE OF ONE IS IN QUESTION GIVEN THE
POOR AGREEMENT AND CONSISTENCY FROM GUIDANCE ON HOW THIS OCCURS.
OVERALL THE FORCING SUNDAY IS JUST NOT ALL THAT IMPRESSIVE. LITTLE
TO NO INSTABILITY IS PROGGED OVER THE CWFA AND THOUGH A GOOD SLUG OF
MOISTURE TRANSPORT IS PRESENT ON NAM/GFS PROGS THE LLVL LIFT IS
LIMITED. AT ANY RATE...THRU SUNDAY THE FRONT REMAINS NEARLY
STATIONARY ACRS THE SOUTHEAST...THE PARENT LOW CONTINUING TO
PROGRESS EWD WITH THE ACTIVE NRN STREAM WHILE THE BROAD SRN STREAM
TROUGH IS HELD OFF BY THE BERMUDA HIGH. IT APPEARS THE FRONT WILL
NOT ACTUALLY ENTER THE AREA UNTIL MONDAY MRNG...WITH A DISTINCT
500MB SHORTWAVE ACCOMPANYING IT AS WELL AS UPPER DIVERGENCE ASSOC
WITH RR QUAD OF A JET STREAK.

TWO PEAKS OF PRECIP ACTIVITY ARE SUGGESTED WHEN THE TOTAL FORCING IS
MAXIMIZED...SUNDAY MRNG AND THEN EARLY MON MRNG. HOWEVER IT IS
DIFFICULT TO PICK OUT A POINT BETWEEN WHERE A LULL SHOULD BE
BETWEEN...WITH THE OVERALL PATTERN REMAINING FAVORABLE FOR AT LEAST
LIGHT PRECIP. WILL CONTINUE TO ADVERTISE LIKELY POPS MOST OF THE AREA
THROUGHOUT SUNDAY...BUT CONCENTRATING MORE QPF CLOSE TO THE
AFOREMENTIONED PEAKS. DESPITE CLOUDS AND RAIN...IN THE WARM AIRMASS
TEMPS SHOULD TOP OUT 5-9 DEGREES ABOVE NORMAL SUN AFTN...WITH MINS
MON MRNG BEING EVEN MORE ABOVE NORMAL...UPPER 40S AND LOWER 50S. MAX
TEMPS MONDAY WILL BE SLIGHTLY WARMER THAN SUNDAY OVER THE PIEDMONT
WITH THE FRONT NOT YET HAVING AN IMPACT.

PROGRESSION OF THE UPPER PATTERN IS STILL PRETTY SLOW THRU MON
NIGHT...WITH THE CWFA NEAR THE INFLECTION POINT BETWEEN THE PLAINS
TROUGH AND THE ATLANTIC RIDGE. POPS DECLINE ONLY GRADUALLY THRU THE
END OF THE PERIOD WITH MOST OF THE GUIDANCE INDICATING SOME QPF
CONTINUING ON THE BACK SIDE OF ANOTHER FRONTAL WAVE DEVELOPING NEAR
THE GA/SC COAST. COLDER AIR WILL BEGIN TO RETURN TO ALL AREAS ON THE
ENSUING NLY FLOW MON NIGHT...THOUGH MIN TEMPS WILL STILL BE AROUND 10
DEGREES ABOVE CLIMO.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 215 PM SATURDAY...THE MEDIUM RANGE WILL START OUT WITH SPLIT
UPPER LVL FLOW...WITH A LARGE POLAR VORTEX SPINNING OVR HUDSON
BAY...AND A CUTOFF LOW INVOF CALIFORNIA. THE MODEL GUIDANCE HAS BEEN
SLOWLY CONVERGING ON THE TIMING OF THE CUTOFF LOW BEING EJECT ACRS
INTO THE SOUTHERN STREAM AROUND FRIDAY. HOWEVER...THERE IS STILL
SOME DISAGREEMENT ON THAT...WITH THE GFS CONSISTENTLY
FASTER/EARLIER...AND THE ECMWF SLOWER/DEEPER. THE LATEST WPC
PREFERENCE IS WITH THE ENSEMBLE MEAN...SLOWER THAN THE GFS...AND NOT
AS DEEP WITH THE RESULTED PROGRESSIVE SHORTWAVE TROF AS THE ECMWF.
AT THE SFC...A BROAD AREA OF CANADIAN HIGH PRES WILL ENCOMPASS ABOUT
3/4TH OF THE CONUS ON WEDNESDAY...GRADUALLY MODIFYING AND DRIFTING
EAST WITH THE CENTER CROSSING THE CWFA EARLY FRIDAY. DRY WEATHER AND
SLIGHTLY BELOW NORMAL TEMPS ARE EXPECTED WEDNESDAY THRU THURSDAY
NIGHT. AS THE EJECTING UPPER TROF FINALLY ENTERS THE SOUTHERN
PLAINS...A LOW PRES SYSTEM SHUD BEGIN TO ORGANIZE...TAPPING INTO
COPIOUS GULF MOISTURE. POPS WILL THEN RAMP UP BY NEXT WEEKEND. OF
COURSE...EXACT TIMING IS STILL THE MAIN QUESTION. THE 12Z GFS AND
ECMWF BOTH SHOW POSSIBLE WINTRY MIX PRECIP TYPE CONCERNS AT ONSET
FRIDAY MORNING...BUT THEN TURNING OVER TO ALL RAIN...AS STRONG SWLY
WAA SHUD DOMINATE ANY LINGERING IN SITU COLD AIR DAMMING.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
AT KCLT...VFR CONDITIONS EXPECTED THROUGH MOST OF TONIGHT. LLVL LIFT
AND DEEP MOISTURE WILL SPREAD ACROSS THE TERMINAL AROUND DAYBREAK
SUNDAY. THE ARRIVAL OF THE LIFT SHOULD RESULT IN WIDESPREAD MVFR
CEILINGS AND LIGHT RAIN. FORECAST SOUNDINGS INDICATE THAT CLOUD
BASES WILL CONTINUE TO LOWER THROUGH THE MORNING HOURS...REACHING
LIFR. IN ADDITION...A COLD FRONT WILL RUN ACROSS THE APPALACHIANS
SUN AFTERNOON...LIKELY SUPPORTING A BAND OF LIGHT TO MODERATE RAIN.
THE INCREASED RAINFALL RATES MAY LOWER VIS TO IFR DURING THE EARLY
AFTERNOON HOURS. RAINFALL INTENSITY SHOULD DECREASE LATER IN THE
AFTERNOON...ALLOWING VIS AND CIGS TO IMPROVE...BUT REMAINING IFR.

ELSEWHERE...MOIST SOUTHWEST LLVL WINDS WILL INCREASE ACROSS THE MTNS
AND ADJACENT FOOTHILLS DURING THE PRE DAWN HOURS. THE COMBINATION OF
UPSLOPE FLOW IN INCREASING LLVL LIFT SHOULD SUPPORT AN EXPANDING
AREA OF LIGHT RAIN AND LOW CIGS TOWARD SUNRISE. IFR TO LIFR WILL
REMAIN COMMON THROUGH THE REST OF THE TAF PERIOD. CONDITIONS MAY
IMPROVE SLIGHTLY DURING THE LATE AFTERNOON HOURS AS COLD FRONT
SHIFTS EAST OF THE MTNS...BUT REMAINING IFR. KAVL SHOULD SEE WINDS
SHIFT FROM THE NW BY 20Z...CIGS LIFTING TO MVFR.

OUTLOOK...PERIODS OF RAIN AND FLIGHT RESTRICTIONS ARE EXPECTED
THROUGHOUT SUNDAY...MONDAY...AND MONDAY NIGHT BEFORE GRADUAL
IMPROVEMENT OCCURS THROUGHOUT TUESDAY. DRY HIGH PRESSURE SHOULD
RETURN BY MID-WEEK.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       HIGH 100%     HIGH 100%     MED   75%     MED   75%
KGSP       HIGH 100%     HIGH  93%     LOW   58%     MED   79%
KAVL       HIGH 100%     HIGH  89%     LOW   37%     HIGH  83%
KHKY       HIGH 100%     HIGH  97%     LOW   56%     MED   62%
KGMU       HIGH 100%     HIGH  93%     LOW   54%     MED   70%
KAND       HIGH 100%     MED   68%     MED   64%     HIGH  80%

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...DEO
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...ARK
AVIATION...NED


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