Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 210739
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
239 AM EST SUN DEC 21 2014

.SYNOPSIS...
LOW LEVEL MOISTURE WILL LINGER ACROSS THE REGION TODAY THROUGH
MONDAY. DEEPER MOISTURE WILL ARRIVE FROM THE WEST ON TUESDAY AHEAD
OF A STRONG COLD FRONT. THE COLD FRONT WILL CROSS THE REGION ON
WEDNESDAY. COLD AND WINDY CONDITIONS WILL SET UP IN THE MOUNTAINS
THROUGH THURSDAY...WITH DRIER CONDITIONS EXPECTED EAST OF THE
MOUNTAINS THROUGH LATE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AT 230 AM EST SUNDAY...A MEAN UPPER TROUGH AXIS WAS LOCATED OVER THE
CENTER OF THE NATION EARLY THIS MORNING...WITH LOW AMPLITUDE RIDGING
DOWNSTREAM OVER THE SOUTHEAST AND LOWER GREAT LAKES. WEAK SHORTWAVE
ENERGY WAS MOVING OUT OF THE BASE OF THE TROUGH OVER THE GULF
STATES. AT THE SURFACE...A HIGH PRESSURE RIDGE EXTENDED FORM QUEBEC
TO THE GULF STATES. A STATIONARY FRONT WAS LOCATED FROM OFF THE
CAROLINA AND GA COASTS...ACROSS N FL...TO THE CENTRAL GULF OF MEXICO.

LIGHT MOIST UPSLOPE FLOW INTO THE BLUE RIDGE THIS MORNING MAY RESULT
IN SOME VERY LIGHT PRECIPITATION...SOME OF WHICH MAY FALL AS
FREEZING RAIN OF FREEZING DRIZZLE...BUT ACCUMULATIONS ARE EXPECTED
TO BE VERY LIGHT AND RATHER SPOTTY.

THE MODELS SHOW A WEAK SURFACE WAVE DEVELOPING ALONG THE COASTAL
FRONT TODAY...WHICH WILL BRING MOIST ISENTROPIC UPGLIDE NW OVER THE
SURFACE RIDGE AND ACROSS OUR AREA. THIS WILL KEEP CLOUD COVER IN
PLACE OVER THE AREA...AND SUPPORT LIGHT RAIN BY THIS EVENING...
ESPECIALLY OVER THE PIEDMONT. HIGH TEMPERATURES WILL RUN SLIGHTLY
BELOW NORMAL DUE TO CLOUDS...DESPITE ABOVE NORMAL HEIGHTS ALOFT.
MINIMUM TEMPERATURES TONIGHT WILL RUN AROUND SEVEN DEGREES ABOVE
NORMAL. THERE MAY BE A FEW AREAS AT HIGH ELEVATIONS OF THE MOUNTAINS
THAT SEE SOME FREEZING RAIN TOWARD DAWN MONDAY...BUT THE DURATION
WILL BE TOO SHORT FOR MUCH ICE ACCUMULATIONS.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 220 AM EST SUNDAY...WEAK SFC CAD WILL BE ESTABLISHED ACROSS
THE REGION ON MON...WITH 1026 MB HIGH PRES NOSING SWD EAST OF THE
APPALACHIANS...AND SRLY 850 MB FLOW DEVELOPING AHEAD OF FALLING
HEIGHTS BACK ACROSS THE PLAINS STATES. THE PRECIPITATION WILL LIKELY
BE VERY LIGHT...WITH DRIZZLE EXPECTED AT TIMES. WILL FEATURE BELOW
GUIDANCE MAX TEMPS FOR MONDAY AFTERNOON.

VERY LITTLE MOVEMENT IN THE SFC CAD LAYER IS EXPECTED THROUGH MONDAY
NIGHT. UPGLIDE AND SRN TIER MTN UPSLOPE FLOW WILL STEADILY IMPROVE
TUE THROUGH TUE NIGHT...WITH WIDESPREAD RAIN/SHOWERS GRADUALLY
DEVELOPING. CONSIDERABLE GULF COAST AND SE COASTAL PLAIN CONVECTION
IS STILL FEATURED IN THE MODELS TUE TO TUE NIGHT...WHICH MAY SERVE
TO INHIBIT THE TRANSPORT OF DEEPER MOISTURE AND ASSOCIATED HIGHER
QPF INTO THE SRN APPALACHIANS AND SURROUNDING AREAS. MODERATE TO
OCCASIONALLY HEAVY RAINFALL COULD STILL RESULT...BUT LITTLE OR NO
HYDRO PROBLEMS ARE EXPECTED. THIS PERIOD SHOULD ALSO SEE STEADY
EROSION/PINCHING OF THE SFC CAD LAYER BACK TOWARD THE NRN NC BLUE
RIDGE THROUGH LATE TUE NIGHT...WITH NON DIURNAL WARMING OF PIEDMONT
TEMPERATURES.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 230 AM EST SUNDAY...THE POTENTIAL FOR HIGH SHEAR LOW CAPE
CONVECTION ALONG THE IMMEDIATE COLD FROPA WED WILL DEPEND ON SEVERAL
FACTORS. A SLOW STEADY EROSION OF THE SFC CAD IS EXPECTED...BUT SFC
BASED INSTABILITY MAY ONLY BUBBLE UP TO A COUPLE HUNDRED J/KG OF
CAPE BY MIDDAY WED IN THE UNCOVERED PIEDMONT. THERE ARE TIMING
DIFFERENCES...WITH THE BEST DEEP LAYER FORCING ON THE GFS TOWARD WED
EVENING...WHILE THE ECMWF IS FASTER TOWARD MIDDAY. FINALLY THE GULF
COASTAL CONVECTION MAY DISRUPT ANY DEVELOPING SHALLOW CONVECTIVE
LINE SEGMENTS FARTHER INLAND. THE POTENTIAL FOR ISOLD SEVERE
CONVECTION WILL HAVE TO BE MONITORED...BUT CONFIDENCE IS TOO LOW FOR
ANY HWO MENTION AT THIS POINT.

THE SLOWEST OPERATIONAL GFS HAS SFC WAVES DEVELOPING ALONG THE FRONT
AND DELAYING FROPA INTO WED EVENING...WHILE OTHER SOLUTIONS ARE A
BIT FASTER WITH EARLIER COOLING ACROSS THE MTNS WED NIGHT. A BRIEF
PERIOD OF UPSLOPE SNOW SHOWERS SHOULD DEVELOP POST FROPA IN THE WRN
MTNS THROUGH THU MORNING...BUT A LESS THAN FAVORABLE WESTERLY
DIRECTION TO THE LOW LEVEL FLOW SHOULD CURTAIL THE FORCING A BIT.
SNOW ACCUMS CHRISTMAS MORNING ARE EXPECTED TO BE SUB ADVISORY GIVEN
THE LIMITED DURATION OF THE DEEPER MOISTURE AND THE LESS THAN
FAVORABLE WIND COMPONENT.

OTHERWISE...ANTICIPATE ZONAL FLOW IN THE WAKE OF THE PASSING TROUGH
THU THROUGH THU NIGHT. A GRADUAL RETURN TO DEEPER LAYER SW FLOW IS
EXPECTED FRI/FRI NIGHT AS ANOTHER TROUGH DEEPENS OVER THE PLAINS AND
MOVES EAST THROUGH MS RIVER VALLEY. THE ASSOCIATED FRONTAL SYSTEM
SHOULD REACH THE FORECAST AREA ON SAT...BUT WITH MORE LIMITED
MOISTURE THAN THE MID WEEK SYSTEM.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
AT KCLT...GUIDANCE FAVORS KEEPING CIG AT MVFR UNTIL AROUND
MIDDAY...THEN FAVORS LOW VFR INTO TONIGHT. WITH A LOW DEW POINT
DEPRESSION...THE FORECAST LEANED TOWARD MORE PESSIMISTIC GUIDANCE
WITH REGARD TO VSBY...CARRYING MVFR IN FOG AROUND DAYBREAK. LIGHT
RAIN SHOULD MOVE IN LATE TONIGHT AS A LOW MOVES UP THE COAST.

AT KAVL...LOW IFR CIG SHOULD PERSIST...WITH VSBY LOWERING FROM MVFR
TO IFR AROUND DAYBREAK. SOME LIGHT DRIZZLE IS POSSIBLE OVERNIGHT IN
LIGHT UPSLOPE FLOW...BUT ODDS ARE TOO LOW TO MENTION THIS. GUIDANCE
FAVORS VFR THIS AFTERNOON...WITH A RETURN TO MVFR THIS EVENING...AND
LIGHT RAIN LATE THIS EVENING...AS LOW PRESSURE MOVES UP THE COAST.

ELSEWHERE... WITH MANY CIGS JUST ABOVE IFR...CHANCES SEEM GOOD FOR
IFR AROUND DAYBREAK. DEW POINT DEPRESSIONS SEEM RIPE FOR IFR FOG AS
WELL. THE MODELS SUPPORT IMPROVEMENT TO VFR LATE THIS AFTERNOON...
WITH A RETURN TO MVFR THIS EVENING WITH RAIN...AS A LOW MOVES UP THE
COAST.

OUTLOOK...LINGERING LOW LEVEL MOISTURE IS LIKELY TO KEEP LOW STRATUS
AND NIGHT TIME FOG AROUND THRU MONDAY...WITH SOME IMPROVEMENT DURING
THE DAYLIGHT HOURS. A COLD FRONT WILL APPROACH ON TUESDAY FROM THE
WEST AND MOVE THROUGH ON WED. WIDESPREAD SHOWERS WITH RESTRICTIONS
SHOULD ARRIVE TUESDAY AFTERNOON AND WILL CONTINUE UNTIL THE FRONT
CLEARS THE AREA LATE WEDNESDAY.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       HIGH  88%     MED   78%     HIGH 100%     HIGH  94%
KGSP       MED   73%     MED   78%     HIGH  85%     HIGH  88%
KAVL       MED   78%     MED   76%     HIGH  91%     HIGH  90%
KHKY       MED   76%     HIGH  88%     HIGH  83%     HIGH  90%
KGMU       MED   73%     HIGH  81%     HIGH  83%     HIGH  88%
KAND       HIGH  83%     MED   78%     HIGH  85%     HIGH  90%

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...HG
NEAR TERM...JAT
SHORT TERM...HG
LONG TERM...HG
AVIATION...JAT


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