Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 280516
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1216 AM EST WED JAN 28 2015

.SYNOPSIS...
DRY HIGH PRESSURE WILL REMAIN ACROSS THE REGION THROUGH WEDNESDAY.
ON THURSDAY...A COLD FRONT WILL CROSS THE FORECAST AREA WITH ANOTHER
HIGH PRESSURE SYSTEM BUILDING IN FRIDAY THROUGH SATURDAY. A MOIST
LOW PRESSURE SYSTEM IS EXPECTED TO AFFECT THE REGION ON SUNDAY INTO
MONDAY.

&&

.NEAR TERM /THROUGH TODAY/...
0515 UTC UPDATE...POPS HAVE BEEN LOWERED NEAR THE TN BORDER PER
RADAR TRENDS. SKY COVER HAS BEEN UPDATED FROM INFRARED SATELLITE
IMAGERY. WINDS WERE UPDATED FORM THE LATEST NAM AND ADJMET.

AS OF 915 PM TUE...WITHIN THE LAST HOUR WE HAVE GOTTEN SOME REPORTS
FROM THE WAYNESVILLE AND ASHEVILLE AREAS THAT INDICATE SNOW IS
FALLING OUT OF THE REMAINING UPSLOPE-FORCED CLOUD COVER. I REVISED
FLURRY/SHSN MENTION IN THE FCST BASED ON CLOUD TOP TEMPS...WITH THE
RESULT BEING SHSN OVER THE FRENCH BROAD VALLEY AND SMOKIES WHERE THE
TOPS ARE COLDEST...WITH LESS WIDESPREAD COVERAGE TOWARD THE NORTH
WHERE MOISTURE IS EVIDENTLY MORE SHALLOW. FLURRIES WERE MENTIONED IN
TOWARD THE EDGES OF THE CLOUD DECK...WHERE THE FLOW IS MORE
DOWNSLOPE ANYWAY. SHORT TERM GUIDANCE...WHICH HAS DONE PRETTY GOOD
IN THIS PATTERN...SHOWS QPF ENDING BEFORE MIDNIGHT...SO I MAINTAINED
A DOWNWARD TREND WITH TIME. LITTLE TO NO ADDITIONAL ACCUMS ARE
EXPECTED EXCEPT PERHAPS IN THE HIGHEST ELEVATIONS.

HIGHLY AMPLIFIED UPPER PATTERN CONTINUES TO PREVAIL ACROSS THE
UNITED STATES WITH A SHARP FULL LATITUDE TROF AXIS SLIDING OFFSHORE
INTO THE WESTERN ATLANTIC...WHILE H5 RIDGING BUILDS ACROSS THE
SOUTHERN PLAINS. A DRY FCST PREVAILS LATE TONIGHT AND TMRW WITH
SKIES NEARLY CLEAR...BUT THE HIGH TERRAIN REMAINING AT LEAST PARTLY
CLOUDY THROUGH SUNRISE WEDNESDAY.  HEIGHTS WILL RISE ALOFT AS THE
AFORE MENTIONED UPPER RIDGE SLIDES EAST WITH SURFACE HIGH PRESSURE
BUILDING JUST TO THE NORTH.  THIS WILL LEND ITSELF TO SLIGHTLY
WARMER TEMPERATURES ON WEDNESDAY DUE TO ABUNDANT INSOLATION AND
DOWNSLOPING FLOW...ALTHOUGH STILL A TAD BELOW CLIMO. RH LEVELS ON
WEDNESDAY AFTERNOON WILL FALL TOWARDS CRITICAL LEVELS AS
TEMPERATURES RISE AND DEWPOINTS MIX OUT.  THAT SAID...AS THE SURFACE
RIDGE BUILDS OVERHEAD...PRESSURE GRADIENT FORCES WILL REMAIN WEAK
ENOUGH TO INHIBIT ANY GUSTING THEREFORE THESE FIRE WX CONCERNS
REMAIN MARGINAL AT THIS POINT.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
AS OF 230 PM TUESDAY...THE MAIN STORY FOR THE SHORT RANGE WILL BE
THE PASSAGE OF A STRONG COLD FRONT THURSDAY NIGHT...AND SUBSEQUENT
COLD ADVECTION FLOW BEHIND THE FRONT THROUGH FRIDAY. BEFORE WE GET
THERE...THE AXIS OF AN UPPER RIDGE WILL MOVE OVERHEAD WEDNESDAY
NIGHT AND THURSDAY MORNING...WHICH WILL SUPPORT DRY HIGH PRESSURE.
ON THURSDAY...THE MODELS CONTINUE TO SHOW A LEAD SHORT WAVE MOVING
UP THE OH VALLEY AND DAMPENING OUT. ALTHO THERE IS SOME DPVA
ASSOCIATED WITH THIS FEATURE IN THE AFTERNOON...AND SOME WEAK UPPER
DIVERGENCE THAT MOVES OVERHEAD...THERE WILL BE VERY LITTLE MOISTURE
TO WORK WITH. AS A RESULT...NONE OF THE OPERATIONAL MODELS RESPOND
WITH ANY LIGHT PRECIP E OF THE MTNS. IN FACT...THE MODELS DELAY THE
ONSET OF PRECIP OVER THE MTNS UNTIL THE AFTERNOON. SO...THE PRECIP
CHANCES HAVE BEEN PUSHED BACK IN TIME...AND ELIMINATED OVER THE
PIEDMONT.

A SECONDARY SHORT WAVE IS STILL EXPECTED TO DRIVE THE COLD FRONT
ACROSS THE REGION THURSDAY EVENING AND EARLY FRIDAY MORNING. THE
MODEL GUIDANCE SHOWS A STRONG SIGNAL FOR PRECIP WITH THE FRONT AND
THEN BEHIND THE FRONT FROM THURSDAY NIGHT THRU FRIDAY MORNING OVER
THE MTNS...AND IN PARTICULAR...THE TN BORDER. PRECIP CHANCES WERE
NUDGED UPWARD A BIT MORE. STRONG COLD ADVECTION WILL BRING SNOW
LEVELS DOWN TO THE VALLEY FLOORS VERY QUICKLY THURSDAY EVENING SUCH
THAT THE BULK OF THE PRECIP WILL FALL AS SNOW. PRESENT INDICATIONS
ARE FOR AN ADVISORY-LEVEL ACCUMULATION OVER PARTS OF THE TN BORDER
COUNTIES...MAINLY BECAUSE OF THE DURATION. THE LOW LEVEL NW FLOW
UPSLOPE MOISTURE DRIES UP DURING MIDDAY ON FRIDAY...LIMITING THE
SNOW ACCUMULATION. THE OTHER CONCERN WILL BE THE WIND. BEHIND THE
FRONT...A VERY STRONG PRESSURE GRADIENT WILL RAISE THE WIND
SIGNIFICANTLY. THE NAM IN PARTICULAR SHOWS WINDS AT THE TOP OF A
SHALLOW MIXED LAYER AT AROUND 50KT. THE HIGHEST RIDGETOPS WILL STICK
UP INTO A VERY FAST FLOW. THE QUESTION IS HOW MUCH OF THIS HIGH
MOMENTUM AIR WILL REACH THE GROUND. THE COLD ADVECTION SUGGESTS A
SURFACE-BASED MIXED LAYER THAT SHOULD ALLOW SOME OF IT TO HAPPEN.
WILL MENTION THE HIGH WIND POTENTIAL IN THE HWO ACROSS THE MTNS AND
ADJACENT BLUE RIDGE FOR FRIDAY. TEMPS SHOULD FALL BACK BELOW NORMAL.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 230 PM EST TUESDAY...FLAT RIDGING WILL BUILD OVER THE REGION
FROM THE WEST FRI NIGHT INTO SAT. LITTLE MORE THAN MID AND HIGH
CLOUDS SPILLING OVER THE RIDGE AXIS ARE EXPECTED ON SAT. 1034 MB SFC
HIGH PRES WILL BUILD EASTWARD FROM THE SRN SHORES OF THE GREAT LAKES
TO UPSTATE NY THROUGH THROUGH THE MIDDLE OF THE WEEKEND.

THE NEXT CLIPPER DIGGING SE THROUGH THE NRN PLAINS SAT NIGHT WILL
BECOME MORE AMPLIFIED FROM THE OH VALLEY TO THE MS RIVER VALLEY BY
LATE SUNDAY. GOOD CONSENSUS EXISTS ON A SFC REFLECTION DEEPENING
OVER ERN TX LATE SAT NIGHT AND ROCKETING UP THE FRONTAL
ZONE...MAINLY W OF THE APPALACHIANS SUN/SUN NIGHT. THE GFS REMAINS A
BIT FASTER THAN THE ECMWF WITH THE MAIN TROUGH AND ASSOCIATED COLD
FRONT. FOLLOWING AN ENSEMBLE COMPROMISE BRINGS THE DEEPEST MOISTURE
ACROSS OUR AREA FROM EARLY SUNDAY THROUGH SUNDAY EVENING...WITH DRY
SLOTTING THEN EXPECTED LATE SUNDAY NIGHT WITH THE FAST MOVING
SYSTEM. THE PEAK OF WARM CONVEYOR BELT LIFT AND UPPER DIVERGENCE
SHOULD YIELD THE BEST PERIOD OF LIKELY POPS BY SUNDAY EVENING.

THE FARTHER WEST SFC LOW TRACK ALONG THE FRONT WILL SUPPORT MORE
RAPID WARMING OF PROFILES THROUGH THE DAY ON SUNDAY. STILL...MOST
PROFILES SUPPORT WINTRY PTYPES AT ONSET GIVEN THE COOL WET
BULBS...WITH 850 MB TEMPS THEN RISING TO +3 TO +5 DEGREES C DURING
THE PERIOD OF BEST QPF LATER SUNDAY. ALTHOUGH THE HIGH PRES TO THE
NE MOVES OFFSHORE QUICKLY...A LINGERING SHALLOW HYBRID CAD
CONFIGURATION WILL LIKELY PERSIST INTO SUNDAY NIGHT...WITH
ASSOCIATED COOLER THAN GUIDANCE TEMPERATURES EXPECTED...ESPECIALLY
ALONG THE NRN TIER. WILL KEEP THE CURRENT RAIN VERSUS SNOW PTYPES
SINCE ANY TRANSITION ZONE LOOKS PRETTY NARROW. SOME INSTABILITY
COULD WRAP UP AROUND THE EDGE OF THE WEDGE LATE SUNDAY NIGHT...BUT
WITH TOO SMALL A CHANCE OF THUNDER TO MENTION IT IN THE LOWER
PIEDMONT AT PRESENT.

BRIEF NW FLOW SNOWFALL WILL BE POSSIBLE LATE SUNDAY NIGHT INTO
MONDAY. IN ADDITION...A TIGHT PRES GRADIENT WILL SET UP BEHIND THE
DEPARTING WAVE. HIGH WINDS COULD BE A PROBLEM WITH THE 850 MB JET
PROGGED TO RUN 50 TO 60 KT DURING THE PEAK OF THE COLD ADVECTION
AROUND 12Z MONDAY. AN HWO MENTION MAY BE NEEDED. DRY NW TO W FLOW IS
EXPECTED MON THROUGH TUE. STRONG AND DRY SFC HIGH PRESSURE WILL
BUILD OVER TO THE N...WITH VERY CHILLY THICKNESSES AND ASSOCIATED
TEMPERATURES.

&&

.AVIATION /05Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...VFR. LIGHT N WINDS WILL PERSIST THROUGH THIS AFTERNOON...
THEN VEER TO SE....REMAINING UP SOMEWHAT AS THE PRESSURE GRADIENT
TIGHTENS AHEAD O THE NEXT FRONT. THE DRY AIR MASS MOVING OVER THE
REGION DOES NOT SUPPORT VSBY RESTRICTIONS. HIGH CLOUDS WILL MOVE
INTO THE AREA TONIGHT IN ADVANCE OF THE NEXT SYSTEM...BUT CLOUD
COVER WILL NOT BE GREAT ENOUGH FOR A HIGH LEVEL CIG.

ELSEWHERE...VFR. GUSTY NW WINDS WILL BE SLOW TO DIMINISH OVERNIGHT
AT KAVL. WINDS VEER NE AFTER DAYBREAK AT SC SITES...THEN BECOME
S EVERYWHERE BY THIS EVENING..STAYING UP SOMEWHAT AS THE PRESSURE
GRADIENT TIGHTENS AHEAD OF ANOTHER FRONT. HIGH CLOUDS MOVE IN
TONIGHT AHEAD OF THE FRONT...BUT NOT TO THE EXTEND THAT A HIGH CIG
WOULD SET UP.

OUTLOOK...A PAIR OF CLIPPER SYSTEMS WILL BRING CHANCES FOR RAIN OR
SNOW SHOWERS TO THE NC MTNS THU AND FRI. MOST OF THESE SHOWERS WILL
REMAIN WEST AND NORTH OF KAVL...BUT BRIEF PERIODS OF RESTRICTIONS
CANNOT BE RULED OUT. OTHERWISE...MAINLY VFR CONDITIONS ARE EXPECTED
ACROSS THE AREA UNTIL MOISTURE BEGINS TO RETURN SUNDAY.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       LOW   57%     MED   62%     MED   64%     HIGH 100%
KHKY       HIGH 100%     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...SBK
NEAR TERM...CDG/JAT/WIMBERLEY
SHORT TERM...PM
LONG TERM...HG
AVIATION...JAT


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