Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 291514
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1014 AM EST MON DEC 29 2014

.SYNOPSIS...
A COLD FRONT WILL SLOWLY CROSS OUR REGION TODAY...THOUGH SOME
MOISTURE WILL LINGER UNTIL TUESDAY. DRIER AND COOLER HIGH PRESSURE
WILL MOVE ACROSS THE AREA WEDNESDAY AND THURSDAY. ANOTHER LOW
PRESSURE SYSTEM THEN SHOULD BEGIN TO TAKE SHAPE AT THE END OF THE
WEEK...BRINGING PRECIPITATION BACK TO THE AREA BY FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
1015 EST UPDATE...POPS HAVE BEEN ADJUSTED PER RADAR TRENDS...AND
AREAS OF FOG HAVE BEEN UPDATED FROM OBSERVATIONS.

AT 0930 EST MONDAY...A BROAD UPPER TROUGH WAS OVER THE CENTER OF THE
NATION...WITH SW FLOW ALOFT OVER THE EAST. CHANNELED VORTICITY WAS
WAS OVER GA AND THE CAROLINAS...AND ASSOCIATED WIDESPREAD
PRECIPITATION WAS MOVING EAST ACROSS THE INTERSTATE 77 CORRIDOR...
WELL BEHIND A SLOW MOVING COLD FRONT OVER THE COASTAL PLAIN. SURFACE
OBSERVATIONS ACROSS THE AREA SHOWED A WIDE RANGE OF SURFACE
VISIBILITY. ALTHOUGH CLOUD COVER WAS EXTENSIVE THIS MORNING...
HEIGHTS ALSO DISPLAYED A WIDE RANGE OF VARIABILITY.

PRECIPITATION IS EXPECTED TO DECREASE FURTHER THIS MORNING AS THE
UPPER VORT MAX DEPARTS TO THE EAST...HOWEVER VEERING LOW LEVEL WINDS
WILL SET UP ISENTROPIC UPGLIDE OVER THE AND UPSLOPE FLOW THIS
AFTERNOON...RESULTING IN AN INCREASE IN LIGHT PRECIPITATION...
MAXIMIZED ALONG THE BLUE RIDGE. HIGH TEMPERATURES WILL RUN SLIGHTLY
ABOVE NORMAL AS POST FRONTAL COLD ADVECTION WILL BE DELAYED...AND
HEIGHTS ALOFT REMAIN ABOVE NORMAL.

PREVIOUS DISCUSSION...AS OF 640 AM...SFC FRONT IS LAID OUT ACRS THE
SC MIDLANDS AND NC SANDHILLS. A 500MB DISTURBANCE HAS DEPARTED THE
AREA AND TAKEN WITH IT THE MIDLEVEL FRONTOGENESIS THAT DROVE MUCH OF
THE OVERNIGHT PRECIP. AT THE SFC...DRIER AIR HAS ALREADY WORKED INTO
THE AREA AS EXPANSIVE CONTINENTAL HIGH PRESSURE BUILDS THRU THE
CENTRAL/ERN CONUS AND DOWN THE EAST SIDE OF THE APPALACHIANS. COLD
ADVECTION WITH THIS FLOW WILL AMPLIFY OVER THE NRN NC
FOOTHILLS/PIEDMONT. TIGHT 925MB AND 850MB THERMAL GRADIENTS ARE
STILL SEEN NEAR THE NC/SC BORDER THRU MUCH OF THE DAY. IT APPEARS
THE CURRENT PRECIP ACTIVITY WILL TAPER OFF SLOWLY UNTIL MIDDAY.
HOWEVER THE LLVL GRADIENTS CONTINUE TO REFLECT A BROAD AND NEARLY
STATIONARY BAROCLINIC ZONE INTO TONIGHT...AND THE FORCING AND
MOISTURE ARE SUFFICIENT TO KEEP CHANCE POPS ACRS THE AREA MOST OF
THE DAY. MEANWHILE...THE COOL NELY BDY LAYER FLOW CONTINUES INTO THE
ERN FACING BLUE RIDGE THRU THE AFTN. BY THE END OF THE DAY MOST OF
THE AVBL GUIDANCE IS FOCUSING THE REMAINING QPF OVER THE FOOTHILLS.
WILL REINTRODUCE LKLY POPS FOR THESE AREAS FOR A TIME THIS EVENING
AS A RESULT...BUT GUIDANCE DOES SUPPORT A STEADY IF NOT SLOW DECLINE
IN CHANCES FOR THE SRN HALF OF THE AREA INTO TMRW MRNG.

THE INITIALLY DEEPLY SATURATED COLUMN BEGINS TO DRY OUT FROM THE TOP
THIS MORNING. SOME OF THE SW MTNS AND SAVANNAH RIVER VALLEY MAY SEE
SOME THIN PATCHES OR EVEN BREAKS IN CLOUD COVER COME THIS AFTN...BUT
THE REST OF THE AREA SHOULD REMAIN OVC THRU THE DAY AND ALL NIGHT.
FAVORED A BLEND OF RAW GUIDANCE FOR MAX TEMPS...ALSO BLENDING IN A
BIT OF THE BIAS CORRECTED VERSION THEREOF GIVEN THE PLENTIFUL CLOUDY
WEATHER WE HAVE SEEN LATELY WHICH SHOULD BE REFLECTED IN THE BIASES.
BY TONIGHT ALL MOISTURE IS CONCENTRATED LOW ENOUGH THAT THERE IS NO
OVERLAP WITH THE ICE NUCLEATION LAYER. MIN TEMPS WILL BE NOTICEABLY
COOLER TONIGHT...THOUGH STILL TWO OR THREE CATEGORIES ABOVE NORMAL.
SOME OF THE MTN PEAKS/RIDGES MIGHT MAKE IT BRIEFLY BELOW FREEZING
NEAR DAYBREAK BUT PROFILES SUGGEST FZRA/FZDZ WOULD RESULT IF PRECIP
IS STILL OCCURRING THEN.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 3 AM MONDAY...WITH DAMPENING SHORT WAVE TROUGH PASSING NORTH
OF THE AREA EARLY TUESDAY...WITHIN QUASI-ZONAL UPPER FLOW PATTERN...
COLDER AIR WILL GRADUALLY FILTER INTO THE AREA FROM THE NORTH
THROUGHOUT TUE... WHILE THERE REALLY WON/T BE A GOOD MECHANISM TO
RAPIDLY SCOUR THE LOW LEVEL MOISTURE. HOWEVER...MOISTURE WILL BECOME
INCREASINGLY SHALLOW THROUGHOUT THE DAY...SO WHILE LOW CLOUDS SHOULD
REMAIN MORE OR LESS ENTRENCHED ACROSS MUCH OF THE AREA...PRECIP
CHANCES MAY TEND MORE TOWARD THE DRIZZLE END OF THE SPECTRUM. BY THE
TIME THE TRULY COLD AIR ARRIVES TO THE NORTHERN ZONES LATE IN THE
DAY...MOISTURE SHOULD BE MORE OR LESS ANKLE DEEP...THUS WINTRY
PRECIP OF ANY STRIPE HAS BEEN REMOVED FROM THE FORECAST DURING THIS
TIME. TEMPS SHOULD BE BELOW NORMAL ON TUE IN CLOUDY/WEAK COLD
ADVECTION REGIME.

THE REMAINDER OF THE SHORT TERM IS EXPECTED TO BE DRY/MOSTLY CLEAR
WITH TEMPS ABOUT 5-10 DEGREES BELOW CLIMO.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 310 AM MONDAY...THE LULL IN THE ACTIVE WEATHER REGIME WILL
PERSIST INTO THE EARLY PART OF THE MEDIUM RANGE...WITH UNSETTLED
WEATHER RETURNING BY THE WEEKEND...AS INTENSE UPPER LOW WOBBLES OUT
OF THE FOUR CORNERS REGION. THIS FEATURE APPEARS DESTINED TO WEAKEN
AND BECOME ABSORBED IN THE BROAD/LOW AMPLITUDE TROUGH AND CONFLUENT
FLOW REGIME AFFECTING MUCH OF EASTERN NORTH AMERICA OVER THE
WEEKEND. THE MAIN QUESTIONS WILL BE...HOW SOON WILL THIS
HAPPEN...AND HOW STRONG WILL THE SYSTEM BE WHEN IT MOVES INTO
POSITION TO AFFECT THE SOUTHEAST. AS IS TO BE EXPECTED...GLOBAL
MODEL SOLUTIONS ARE A BIT ALL OVER THE PLACE REGARDING THESE
QUESTIONS...WITH QUITE STARK DIFFERENCES IN SURFACE CYCLONE
TRACKS...AS WELL AS TIMING AND AMOUNTS OF PRECIPITATION OVER OUR
AREA. WITH SUCH INHERENT UNCERTAINTY...OPTED TO NOT MAKE MUCH CHANGE
TO THE FRI-SUNDAY PORTION OF THE FORECAST...WHEN ALL THREE DAYS
FEATURE SOME AMOUNT OF PRECIP PROBABILITY. ONE ITEM OF IMPORT THAT
THE MODELS DO SEEM TO AGREE ON...EVEN THE SOMEWHAT COLD ECMWF WOULD
SUGGEST VERY LITTLE CHANCE OF ANY WINTRY WEATHER ACROSS OUR AREA
DURING THIS PERIOD. IN FACT...TEMPS ARE EXPECTED TO MODERATE TO
ABOVE-NORMAL LEVELS BY THE WEEKEND.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
AT KCLT...TRICKY FCST WITH GUIDANCE HAVING DONE A VERY POOR JOB SO
FAR WITH THIS PRECIP EVENT AND ASSOCIATED RESTRICTIONS. SFC COLD
FRONT HAS PUSHED S OF THE FIELD...BUT A NEARLY STATIONARY BAROCLINIC
ZONE WILL REMAIN OVER THE AREA THRU THE DAY TODAY. WARM UPGLIDE IN
THIS ZONE WILL INCREASE LATER TODAY...WHILE AT THE SFC NELY FLOW
WILL TRY TO ADVECT IN A COOLER AND DRIER AIRMASS. THE EXPECTATION IS
THAT MVFR CIGS WILL FORM AGAIN LATER THIS MRNG AND LINGER THRU THE
DAY...BUT THE LLVL MIXING AFFORDED BY THE COLD ADVECTION WILL
MAINTAIN VFR VSBY. PERIODS OF RAIN WILL CONTINUE THRU THE MRNG
BEFORE CHANCES BEGIN TO TAPER OFF IN THE AFTN...AND STILL A SMALL
CHANCE TONIGHT THOUGH TOO LOW TO MENTION. CIGS ARE EXPECTED TO DROP
TO IFR AFTER SUNSET...WITH LIFR NOT OUT OF THE QUESTION ESP IF
RA/DZ DOES CONTINUE MUCH OF THE DAY.

ELSEWHERE...INITIAL SHIELD OF PRECIP WILL SHIFT EWD THRU THE MORNING
BUT WITH LLVL THERMAL BOUNDARY STILL PRESENT CONCURRENT WITH PLENTY
OF MOISTURE...SOME CHANCE WILL LINGER ACRS ALL SITES INTO TONIGHT.
USED SHRA TO REFLECT THE LOWER CHANCES LATER TODAY. AS NOTED FOR
KCLT...NELY TO ELY FLOW IN THE BOUNDARY LAYER WILL PREVAIL
TODAY...AND GUIDANCE SEEMS TO REFLECT ENOUGH UPSLOPING INTO THE BLUE
RIDGE...TRENDING CIGS DOWN FROM DAYBREAK TO MIDDAY. SOME MEMBERS
FAVOR IFR OR LIFR...BUT GIVEN THAT MOST AREAS HAVE SEEN CIGS
DISSOLVE EARLY THIS AM AS DRIER AIR MOVES IN AT THE SFC...I FELT IT
WAS BEST TO KEEP THE REDEVELOPING CIGS MVFR. HOWEVER...TONIGHT IT
DOES SEEM LIKELY TO DROP CIGS TO IFR/LIFR AGAIN WITH SOME FOG
FORMING AS WELL.

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

CONFIDENCE TABLE...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       HIGH  88%     HIGH  94%     MED   75%     HIGH  80%
KGSP       HIGH  83%     HIGH  94%     MED   75%     MED   74%
KAVL       HIGH  89%     HIGH  83%     MED   77%     HIGH  90%
KHKY       MED   72%     HIGH  94%     MED   75%     HIGH  80%
KGMU       HIGH  83%     HIGH  94%     MED   75%     MED   70%
KAND       HIGH  94%     HIGH 100%     HIGH  86%     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...JAT/WIMBERLEY
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...WIMBERLEY



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