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Area Forecast Discussion

006
FXUS62 KGSP 281814
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
114 PM 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/...
AS OF 935 AM EST SATURDAY...CLOUD COVER HAS BEEN DIMINISHING SOME
OVER THE PAST FEW HOURS WITH THE DAYTIME HEATING...YET MOST
LOCATIONS ARE STILL SCT TO OVC WITH MID LVL CIGS. ANY ADDITIONAL
CLEARING SHOULD BE MINIMAL AS DEWPTS SLOWLY CREEP UP AND THE WEDGE
PATTERN STRENGTHENS TO OUR NE. I LOWERED HIGH TEMPS A FEW DEGREES
OVER MOST OF THE CWFA AS MODEL GUIDANCE TENDS TO BE TOO WARM WITH
THESE CAD REGIMES...ESPECIALLY OVER THE NC FOOTHILLS AND PIEDMONT
AREAS. MOST OF THOSE AREAS WILL STRUGGLE TO REACH 40 DEGREES THIS
AFTERNOON. I KEEP THINGS DRY THRU 00Z SUN WITH POPS RAMPING UP FROM
THE SOUTH BEYOND THAT TIME.

PREVIOUS DISCUSSION...

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 SATURDAY/...
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 /18Z SATURDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...OVER THE PAST FEW HOURS...CLOUDS HAVE
SCATTERED OUT A BIT MORE THAN ANTICIPATED WITH MOST LOCATIONS SEEING
FEW TO SCT BETWEEN 8000 AND 12000 FT. COVERAGE SHOULD GRADUALLY
INCREASE AS WE GO INTO THE EVENING HOURS AND DEEPER LYR MOISTURE
FILLS IN. BY 23Z OR SO...I HAVE ALL 6 SITES WITH MVFR CIGS AND BY
10Z TOMORROW CIGS DROP BELOW 1000FT WITH CLT DROPPING LAST. AS A
COMBINATION OF RAIN AND FZ RAIN OVERSPREAD THE AREA...CIGS SHOULD
REMAIN IFR THRU THE TAF PERIOD WITH SOME VISBY RESTRICTIONS ALSO
POSSIBLE DURING THE LAST 4 TO 6 HOURS OR SO. I WAS NOT CONFIDENT
ENOUGH TO INCLUDE ANY VISBY RESTRICTIONS IN THE 18Z TAFS...HOWEVER
THIS MAY BE NEEDED FOR THE 00Z ISSUANCE ESPECIALLY FOR KCLT. WINDS
SHOULD MAINTAIN A TYPICAL CAD TYPE ORIENTATION FROM THE NE THRU THE
PERIOD WITH KAVL MAINTAINING A MORE SELY DIRECTION. SOME GUSTS IN
THE 15 TO 20KT RANGE ARE POSSIBLE THRU THE PERIOD...BUT THEY SHOULD BE
SPORADIC AND NOT PREVAILING.

OUTLOOK...COLD AIR DAMMING REGIME WILL WEAKEN AS WE MOVE INTO LATE
SUNDAY AND EARLY MONDAY WITH ANOTHER CANADIAN HIGH SLIDING NORTH OF
THE CAROLINAS. AS THE HIGH MOVES NE OF THE REGION...ANOTHER BRIEF
CAD PATTERN IS POSSIBLE. THIS WILL LIKELY RESULT IN ADDITIONAL
PRECIP AND FLIGHT RESTRICTIONS FOR TUES AD WED...HOWEVER EXACT
TIMING REMAINS CHALLENGING.

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...JPT
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...JPT



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