Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 301714
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
114 PM EDT THU OCT 30 2014

.SYNOPSIS...
MOISTURE WILL INCREASE ON FRIDAY OUT AHEAD OF AN APPROACHING COLD
FRONT. THIS FRONT...AND A STRONG MID LEVEL AREA OF LOW PRESSURE IS
FORECAST TO TRACK ACROSS THE REGION FRIDAY NIGHT INTO SATURDAY. A
STRONG SURFACE LOW PRESSURE SYSTEM WILL DEVELOP OFFSHORE ON
SATURDAY...THEN TRACK QUICKLY NORTH BY SATURDAY NIGHT. CIRCULATION
AROUND THE COASTAL LOW WILL BRING A CANADIAN AIR MASS TO THE REGION
INTO MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
1715 UTC UPDATE...SKY COVER WAS ADJUSTED DOWN PER SATELLITE IMAGERY.
WINDS WERE UPDATED TO INCORPORATE THE LATEST NAM DATA. TEMPERATURES
WERE UPDATED WITH A BLEND OF THE LATEST ADJMAV AND ADJMET. POPS AND
AREAS OF SNOW WERE ADJUSTED LATE FRIDAY BASED ON THE LATEST MODEL
DATA AND TO CONCUR WITH NEIGHBORING OFFICES.

AT 1000 AM EDT THURSDAY...AN UPPER TROUGH WAS OVER EASTERN NORTH
AMERICA...WITH AN UPPER RIDGE OVER THE WESTERN PORTION OF THE
CONTINENT. A PAIR OF SHORTWAVE WERE MOVING THROUGH THE BASE OF THE
TROUGH...ONE OVER CA...AND THE OTHER OVER THE GULF STATES...WHILE
ADDITIONAL SHORTWAVE ENERGY WAS NOTED OVER THE NORTHERN PLAINS.

AT THE SURFACE...A COLD FRONT WAS LOCATED OFF THE CAROLINA AND GA
COASTS...AND EXTENDED TO THE NORTHERN GULF OF MEXICO. A SURFACE HIGH
WAS CENTERED OVER THE OH RIVER VALLEY. THE PRESSURE GRADIENT BETWEEN
THIS HIGH AND THE COASTAL FRONT WILL KEEP WINDS A BIT GUSTY FROM THE
NORTH TODAY. MODEL TIME HEIGHTS SHOW VERY LIMITED LOW LEVEL MOISTURE
TODAY...AND UPPER LEVEL MOISTURE ASSOCIATED WITH A SURFACE LOW
ENTERING THE MID MS RIVER VALLEY ONLY REACHES THE MOUNTAINS TOWARD
SUNSET. TEMPERATURES WILL RUN AROUND 5 DEGREES OR SO BELOW NORMAL IN
COLD ADVECTION BEHIND THE FRONT.

TONIGHT...THE AXIS OF A DEEP L/W TROF WILL REACH THE SOUTHERN
APPALACHIANS BY 12Z FRI. HEIGHTS WILL FALL ACROSS THE CWA
TONIGHT...HOWEVER...H85 TEMPS WILL NOT COOL BY MORE THAN TWO
DEGREES. AS THE TROF APPROACHES...CIRRUS LEVEL MOISTURE WILL BEGIN
TO BUILD ACROSS THE WESTERN CAROLINAS. LOWER MOISTURE/CLOUDS ARE
FORECAST TO ARRIVE ACROSS THE WEST FACING MTN SLOPES LATE
TONIGHT...SUPPORTING INCREASING UPSLOPE CLOUD COVER. MIN
TEMPERATURES SHOULD RANGE FROM MID TO UPPER 30S ACROSS THE MTNS TO
LOW TO MID 40S EAST.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 315 AM THURSDAY...THE 00Z GUIDANCE (EXCEPT THE CMC)...HAVE
COME INTO BETTER AGREEMENT ON A VERY POTENT COMPACT VORTMAX/CLOSED
500 MB LOW...DIVING SOUTH OUT OF CANADA FRIDAY...AND ROUNDING THE
BASE OF A SHARP/DEEP TROF OVER THE CWFA ON SATURDAY. THE ENERGY OF
THE SYSTEM WILL LIKELY INDUCE CYCLOGENESIS EAST OF THE OUTER BANKS
DURING THE DAY ON SATURDAY...WITH A DEFORMATION ZONE SETTING UP ACRS
CENTRAL VA/NC. A SURGE OF VERY COLD AIR WILL ALSO ACCOMPANY THE
SYSTEM...WITH 850 MB TEMPS PLUMMETING TO -6 TO -8C ALONG THE TN LINE
AND GENERALLY 0 TO -4C ACRS THE PIEDMONT. THE LLVL WINDS WILL BE
AROUND 40-50 KTS OUT OF THE NW...AS THE MID-UPR LOW SWINGS BY...WITH
STRONG CAA...SHUD RESULT IN PROBABLY WIND ADV LVL WINDS IN THE MTNS
(EVEN HIGHER AT THE HIGHEST PEAKS). BREEZY TO WINDY CONDITIONS WILL
THEN SPREAD ACRS THE PIEDMONT DURING THE DAY ON SATURDAY...AS THE
LLVL SYSTEM DEEPENS NEAR THE OUTER BANKS...AND CONTINUED NLY CAA
FLOW PERSISTS. THIS EVENT IS ONLY 48-60 HOURS AWAY...AND YET
CONFIDENCE IS LOW ON THE DETAILS ON SENSIBLE WX. IF THE 00Z GFS
VERIFIES...IT/S 500 MB HEIGHTS WILL BE ABOUT 5.5 STANDARD DEVIATIONS
BELOW NORMAL (OR ABOUT A 50-YEAR RETURN INTERVAL). HOWEVER...ONE
THING SEEMS ALMOST A SLAM DUNK...AND THAT IS ACCUMULATING SNOW ALONG
THE TN BORDER...AS A VERY GOOD NW FLOW SNOW SET UP SHUD OCCUR.

FRIDAY SHUD SEE INCREASING CLOUDS...AS THE SYSTEM APPROACHES FROM
THE NW. SHOWERS MAY START AS EARLY AS MID AFTN IN THE NRN
MTNS...THEN SPREAD ACRS THE MUCH OF THE AREA...AS DEEP LYR RH WILL
ACCOMPANY VERY STRONG QG FORCING. MODELS IN DECENT AGREEMENT ON SNOW
LEVELS FALLING TO THE VALLEY FLOORS BY DAYBREAK SATURDAY...WITH
PERHAPS A LULL IN SHWR ACTIVITY OUTSIDE THE USUAL NW FLOW AREAS.
HIGHS WILL BE 1-2 CATEGORIES BELOW NORMAL ON FRIDAY...THEN DROP WITH
ONSET OF CAA...ESP IN THE HIGH TERRAIN FRIDAY NIGHT...WITH LOWS IN
THE 20S TO MID 30S MTNS...AND UPR 30S TO LWR 40S PIEDMONT.
ELEVATIONS ABOVE 3500 FT ALONG THE TN BORDER MAY SEE A FEW INCHES OF
SNOW...DEPENDING ON HOW ROBUST THE SHOWER ACTIVITY IS.

SATURDAY...TAKING A GFS/ECMWF BLEND...IT LOOKS LIKE THERE SHUD BE A
PERIOD OF WRAP-AROUND RAIN/SHWR ACTIVITY ACRS THE I-77
CORRIDOR...WHILE THE NW FLOW SNOW SHWRS CONTINUE ALONG THE TN
BORDER. TEMPS/POPS FOR THE DAY ARE LOW CONFIDENCE...GIVEN THE
DYNAMIC NATURE OF THE SYSTEM. SNOW LEVELS MAY RISE BACK UP TO ABOUT
3500 FT...AS THE COMPACT MID LVL LOW EXITS TO THE EAST. SOME
PORTIONS OF THE NC FOOTHILLS/PIEDMONT MAY SEE A FEW SNOW FLAKES
EARLY SATURDAY MORNING...BUT IT LOOKS LIKE THE DEFORMATION ZONE
PRECIP SHUD REMAIN LIQUID...AS THE SFC LAYER IS JUST TOO WARM. EVEN
IF SOME SNOW FALLS OUTSIDE THE MTNS ON SATURDAY...ANY SIGNIFICANT
ACCUMS LOOKS HIGHLY UNLIKELY...AS SOIL TEMPS ARE RUNNING MID 50S TO
MID 60S AHEAD OF THE SYSTEM. CHARLOTTE HAS NOT HAD MEASURABLE SNOW
EARLIER THAN NOV 11TH GOING BACK TO 1878. I BLENDED IN THE STRAIGHT
GFS TEMPS TO ACCOUNT FOR THE ANOMALOUSLY LOW THICKNESSES AND
LINGERING DEFORMATION ZONE IN THE EAST. HIGHS IN THE MTNS MAINLY IN
THE 30S TO LWR 40S...AND MID 40S EAST TO MID 50S WEST IN THE
PIEDMONT.

SATURDAY NIGHT...SNOW SHWR ACTIVITY SHUD SUBSIDE...AND GUIDANCE
AGREES ON POPS TAPERING OFF BY 12Z SUNDAY. MIN TEMPS WILL BE
TRICKY...AS LOW PRES EXITS TO THE EAST...ALLOWING SKIES TO CLEAR AND
WINDS TO DIMINISH...BUT TO WHAT EXTENT? SO DEPENDING ON HOW GOOD THE
RADIATIONAL COOLING CONDITIONS CAN GET...MAY A LIGHT FREEZE ACRS
MUCH OF THE PIEDMONT. THE GOING FCST IS FOR MAINLY LWR TO MID 30S
ACRS THE PIEDMONT. MTNS WILL BE MAINLY IN THE 20S.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 345 AM THURSDAY...GIVEN THE FCST CONCERNS IN THE SHORT
TERM...THERE WAS NO TIME TO MAKE ANY CHANGES TO THE EXTENDED THIS
MORNING. DRY CANADIAN HIGH PRES WILL BUILD IN FOR SUNDAY AND
MONDAY...WITH GENERALLY CLEAR SKIES AND WELL BELOW NORMAL TEMPS. A
WARMING TREND IS EXPECTED EARLY TO MIDDLE OF NEXT WEEK AS THE HIGH
SLIDES EAST AND AN UPPER RIDGE BUILDS IN FROM THE WEST.

AT 230 PM EDT WEDNESDAY...ON SATURDAY EVENING...A STRONG...ANOMALOUS
UPPER LOW WILL BE LOCATED OFF THE NC COAST...WHILE AN UPPER RIDGE
WILL BE OVER THE PLAINS. THE UPPER LOW WILL WEAKEN AND FILL AS IT
LIFTS NE OFF THE NEW ENGLAND COAST ON SUNDAY. BY MONDAY THE UPPER
RIDGE REACHED THE OH AND TN RIVER VALLEYS...AND ON TUESDAY THIS
RIDGE CROSSES THE EAST COAST. AN UPPER TROUGH PROGRESSES FROM THE
GREAT LAKES TO THE SOUTHERN AND CENTRAL APPALACHIANS BY WEDNESDAY IN
THE GFS...BUT IS LESS PROGRESSIVE IN THE ECMWF.

DRY HIGH PRESSURE WILL BUILD SOUTHEAST ACROSS OUR AREA FROM SATURDAY
NIGHT THROUGH MONDAY. AS A RESULT...VERY TIGHT PRESSURE GRADIENT
WILL GRADUALLY RELAX ON SATURDAY NIGHT AND SUNDAY. BY LATE
TUESDAY...A LIGHT MOIST UPSLOPE FLOW ON THE BACK SIDE OF THE
DEPARTING SURFACE HIGH WILL REACH OUR AREA...STARTING IN THE
MOUNTAINS...WHILE A COLD FRONT MOVES INTO THE OH AND MID MS RIVER
VALLEY. THIS COLD FRONT IS EXPECTED TO STALL TO OUR WEST BY
WEDNESDAY MORNING. POPS WILL BE ALLOWED TO RAMP UP LATE TUESDAY INTO
WEDNESDAY... HOWEVER PRECIPITATION ACCUMULATIONS WILL BE LIGHT...AND
MAINLY LIMITED TO THE MOUNTAINS.

TEMPERATURES WILL START OUT AROUND 15 DEGREES OR SO BELOW NORMAL IN
A COLD AIR MASS BEHIND THE DEPARTING UPPER LOW AND AN ASSOCIATED
COLD FRONT. TEMPERATURES WILL MODERATE TO NEAR NORMAL VALUES BY
MIDWEEK AHEAD OF THE NEXT FRONT.

&&

.AVIATION /17Z THURSDAY THROUGH MONDAY/...
AT KCLT..WINDS WILL PERSIST FROM THE NNE THIS AFTERNOON...WITH
MODEST GUSTS. GUSTS WILL DIMINISH THIS EVENING...WITH LITTLE CHANGE
IN WIND DIRECTION. HIGH AND LOW CLOUDS COVER WILL INCREASE OVERNIGHT
AHEAD OF AN APPROACHING COLD FRONT...BUT NO CIG IS EXPECTED UNTIL
MIDDAY...WHEN CIRRUS FORMS A HIGH LEVEL VFR CIG. WINDS WILL BACK TO
THE WNW ON FRIDAY MORNING...REMAINING RATHER LIGHT. PRECIPITATION IS
NOT EXPECTED DURING THE FORECAST TIME PERIOD.

ELSEWHERE...VFR. NNE WINDS WILL PERSIST THROUGH TONIGHT...WITH SOME
MODEST GUSTS POSSIBLE THIS AFTERNOON. MODEL TIME HEIGHTS SHOW
INCREASING LOW AND HIGH CLOUDS OVERNIGHT...AS A COLD FRONT
APPROACHES FROM THE WEST...BUT VFR CIGS ARE NOT EXPECTED UNTIL
MIDDAY FRIDAY...AND ONLY AT NC SITES. LIGHT WINDS WILL BACK TO THE
WNW AT SC SITES ON FRIDAY...BUT WILL BACK TO THE SW AT KHKY...AND
REMAIN CHANNELED UPVALLEY FROM THE NW AT KAVL. RAIN AHEAD OF THE
FRONT WILL REMAIN TO THE WEST OF THE TAF SITES THROUGH THIS FORECAST
PACKAGE.

OUTLOOK...ANOTHER COLD FRONT APPROACHES ON FRIDAY AFTERNOON BRINGING
CLOUDS AND A CHANCE FOR SHOWERS AS IT MOVES THROUGH BY FRIDAY
EVENING. SOME RESTRICTIONS ARE POSSIBLE...ESPECIALLY IN THE
MOUNTAINS WHERE EVEN SOME SNOW SHOWERS ARE EXPECTED FRIDAY NIGHT AND
SATURDAY.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY
     EVENING FOR NCZ033-048>053-058-059.
SC...NONE.

&&

$$
SYNOPSIS...NED
NEAR TERM...JAT/NED
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...JAT



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