Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 280843
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
343 AM EST SAT FEB 28 2015

.SYNOPSIS...
COLD HIGH PRESSURE WILL PERSIST THROUGH THE WEEKEND. MOISTURE
WILL INCREASE AHEAD OF AN APPROACHING COLD FRONT THAT WILL CROSS THE
AREA ON MONDAY. ANOTHER HIGH WILL MOVE OVER THE REGION BEHIND THE
FRONT. ANOTHER COLD FRONT WILL CROSS THE REGION LATE WEDNESDAY OR
EARLY THURSDAY...FOLLOWED BY MORE HIGH PRESSURE.

&&

.NEAR TERM /THROUGH TONIGHT/...
AT 245 AM EST SATURDAY...A BROAD LOW AMPLITUDE UPPER TROUGH WAS OVER
THE CONUS THIS MORNING...WITH A WELL DEFINED CLOSED UPPER LOW MOVING
INTO IT ALONG THE WEST COAST...AND NEARLY ZONAL FLOW OVER THE
SOUTHERN TIER OF STATES. HEIGHTS RILL RISE ALOFT OVER THE SOUTHERN
TIE OF STATES TODAY AND TONIGHT AS THE CLOSED LOW DIVES S ALONG THE
CA COAST...RESULTING IN A FLAT RIDGE FORM TN TO THE CAROLINAS.

AT THE SURFACE...HIGH PRESSURE OVER THE NE WILL NOSE DOWN THE
EASTERN SEABOARD IN A WEDGE CONFIGURATIONS. MOIST ISENTROPIC UPGLIDE
OVER THIS WEDGE WILL SPREAD PRECIPITATION OVER OUR AREA TONIGHT.
MODEL SOUNDINGS AND SURFACE TEMPERATURES SUPPORT FREEZING RAIN ACROSS
THE SOUTHERN MOUNTAINS THIS EVENING...SPREADING SOUTH AND EAST
ACROSS THE PIEDMONT OVERNIGHT. BY DAYBREAK ONLY OUR NON MOUNTAIN GA
COUNTIES WILL BE IN AN ALL RAIN SCENARIO. WITH UPGLIDE RATHER
WEAK...QPF IS EXPECTED OT BE RATHER LIGHT...AND ICE ACCUMULATIONS
WILL BE MINIMAL THROUGH DAYBREAK.

MAXIMUM TEMPERATURES WILL RUN NEARLY 20 DEGREES BELOW NORMAL TODAY
IN COOL NE FLOW UNDER CLOUDS COVER. MINIMUM TEMPERATURES TONIGHT
WILL RUN AROUND 7 DEGREE BELOW NORMAL IN RAIN COOLED AIR.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 3 AM SATURDAY...WHILE IT APPEARS RATHER CERTAIN THAT SOME
LOCATIONS ACROSS THE FORECAST AREA WILL SEE A PERIOD OF FREEZING
RAIN AND/OR DRIZZLE SUNDAY MORNING...THE AND EXTENT OF ANY ICING IS
STILL NOT AT ALL CERTAIN. WHILE THE NAM REMAINS QUITE WET...
DEPICTING WIDESPREAD QPF OF AROUND .25 INCH THROUGH THE MORNING
HOURS...SOME OF THE OTHER GUIDANCE...INCLUDING THE SREF SYSTEM IS
TRENDING IN THAT DIRECTION. THIS IS SOMEWHAT DISCONCERTING...AS THE
NAM TYPICALLY DOES A REASONABLE JOB IN HANDLING MOISTURE-RETURN/
UPGLIDE PRECIP EVENTS. HOWEVER...EVEN A PREFECT PROG OF THE NAM...
WHICH CAN PROBABLY BE VIEWED AS A /WORST-CASE/ SCENARIO WOULD
SUGGEST ANY ICING WOULD REMAIN SOLIDLY AT ADVISORY-LEVELS...EVEN IF
SOME LOCATIONS SEE AN ALL-FREEZING RAIN EVENT. AND THIS SEEMS FAIRLY
UNLIKELY...AS THE MODELS WARM/MOISTEN THE AIR MASS QUITE QUICKLY
SUNDAY IN RESPONSE TO STRONG WAA...AND A SURFACE PATTERN THAT WILL
BECOME INCREASINGLY UNFAVORABLE FOR STRONG HYBRID CAD. IN FACT...
IT/S INTERESTING THAT THE NAM...WHICH ONE WOULD TYPICALLY EXPECT TO
HAVE A SUPERIOR HANDLE ON THE DECAYING CAD AIR MASS THAN THE GLOBAL
MODELS...IT ACTUALLY THE WARMEST MODEL. EVEN SO...THE OFFICIAL
FORECAST WILL HOLD ON TO SUB-FREEZING TEMPS FOR A FEW HOURS LONGER
THAN SUGGESTED BY THE MODELS...WHICH WOULD SEE MUCH OF THE AREA
NORTH OF I-85 EXPERIENCING AT LEAST A BRIEF PERIOD OF -FZRA.
STILL...WITH UNCERTAINTY LINGERING REGARDING QPF AND THE RESIDENCE
TIME OF COLD AIR...HAVE OPTED TO ABSTAIN FROM ISSUING AN ADVISORY
ATTM.

THE MAIN CHANGE TO THE FORECAST DURING THE SUN AFTERNOON/SUN NIGHT/
MONDAY TIME FRAME WAS TO LOWER POPS ACROSS MUCH OF THE AREA...AS
FORCING FOR UVV/PRECIP WILL BE MINIMAL DURING THIS TIME. IN FACT...
UPGLIDE WILL SHUT OFF RATHER ABRUPTLY SUN AFTERNOON...AS LOW LEVEL
FLOW VEERS TO W-NW...AS A COLD FRONT PUSHES INTO THE AREA.
THUS...FRONTAL CONVERGENCE WILL BE VIRTUALLY NON-EXISTENT...AND
INDEED MODEL QPF RESPONSE IS VIRTUALLY NIL OUTSIDE THE MTNS DURING
THIS TIME. DELAY OF COLD ADVECTION AND DOWNSLOPE FLOW SHOULD RESULT
IN SOME OF THE WARMEST TEMPS IN SEVERAL WEEKS ACROSS THE PIEDMONT
MONDAY AFTERNOON...WITH 60S EXPECTED ON MOST LOCATIONS. MEANWHILE...
1030+ MB SURFACE HIGH BUILDING INTO THE MID-ATLANTIC WILL SEND
COOLER AND DRIER AIR INTO THE NORTHERN ZONES BY THE END OF MONDAY...
WHICH WILL FUNNEL THROUGH THE REMAINDER OF THE FORECAST AREA MONDAY
NIGHT. THIS WILL SET THE STAGE FOR ANOTHER HYBRID CAD EVENT AND
INCREASING CHANCES FOR UPGLIDE PRECIP BY EARLY TUESDAY. ANOTHER
BRIEF PERIOD OF -FZRA WILL BE POSSIBLE TUE MORNING...PRIMARILY
ACROSS THE BLUE RIDGE AREA OF THE NORTHERN NC MTNS/FHILLS.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 330 AM SATURDAY...THE PRIMARY MEDIUM RANGE STORY CONTINUES TO
REVOLVE AROUND THE ANTICIPATED PATTERN CHANGE TOWARD A WARMER/WET
REGIME...AS A DEVELOPING WESTERN TROUGH FORCES HEIGHT RISES ALONG
THE EAST COAST. THUS...AFTER ANOTHER DAY OF BELOW-NORMAL TEMPS
WITHIN HYBRID CAD/LIGHT PRECIP REGIME ON TUESDAY...TEMPS WILL
REBOUND WELL INTO THE 60S ON WEDNESDAY IN ADVANCE OF A VERY WET COLD
FRONT...WHICH WILL BRING THE POTENTIAL FOR THUNDERSTORMS AND HEAVY
RAINFALL TO THE EASTERN STATES DURING MID-WEEK. COOL WEATHER IS
ANTICIPATED TO RETURN BY WEEKS END...AS LOW AMPLITUDE UPPER
TROUGHING RETURNS TO THE EASTERN CONUS.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...HIGH CLOUDS WILL SPREAD IN FROM THE WEST OVERNIGHT...
     BUT BEFORE DAYBREAK A MODEL BLEND WOULD BRING AN MVFR CIG TO THE
FIELD. THE CIG WOULD RISE TO LOW VFR BY MIDDAY...REMAINING THERE
THROUGH THIS EVENING. GUIDANCE DOES NOT SUPPORT A VSBY RESTRICTION.
WINDS WILL FAVOR THE NE THROUGH THE FORECAST AS COOL HIGH PRESSURE
REMAINS ALONG THE EASTERN SEABOARD.

ELSEWHERE...INCREASING HIGH CLOUD COVER FROM WEST WILL OCCUR EARLY
IN THE FORECAST. GUIDANCE BRING MVFR CIGS TO KAVL AND THE SC SITES
BEFORE DAWN...WITH LOW VFR AT KHKY. BY MIDDAY THE SC SITES AND KAVL
RISE TO LOW VFR...WHILE KHKY FALLS TO MVFR. THE KHKY CIG RISES TO
LOW VFR THIS EVENING...WHILE KAVL AND KAND FALL TO MVFR. MOIST FLOW
FROM THE SOUTH OVER COOL HIGH PRESSURE WILL SPREAD PRECIPITATION
OVER THE SAVANNAH RIVER VALLEY LATE THIS EVENING...BUT THE CHANCE OF
RAIN AT KAND IS TOO LOW TO MENTION. GUIDANCE DOES NOT FAVOR VSBY
RESTRICTIONS. WINDS WILL FAVOR THE NE AT FOOTHILLS SITES AS HIGH
PRESSURE REMAINS ALONG THE EAST COAST. KAVL WINDS WILL FAVOR THE SE.

OUTLOOK...COLD AIR DAMMING STRENGTHENS INTO SUNDAY. FLIGHT
RESTRICTIONS WILL BE POSSIBLE DURING THIS TIMEFRAME...PARTICULARLY
LATE SAT NIGHT AND SUN DUE TO INCREASING MOISTURE AND LIFT OVER THE
WEDGE. RAIN CHANCES LINGER INTO WEDNESDAY AS SEVERAL FRONTS CROSS
THE AREA...BUT CONFIDENCE IS LIMITED ON RESTRICTIONS.

CONFIDENCE TABLE...

            13-19Z        19-01Z        01-07Z        07-12Z
KCLT       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   74%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       MED   77%     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 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...JAT
NEAR TERM...JAT
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...JAT


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