Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 271940
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
240 PM EST TUE JAN 27 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 WEDNESDAY/...
AS OF 200 PM EST TUESDAY...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.  BRISK NORTHWEST FLOW WILL
PREVAIL THROUGH THE REMAINDER OF THE DAY AS LOW LEVEL MOISTURE
CONTINUES TO POOL ALONG THE WESTWARD FACING SLOPES OF THE SMOKIES.
THUS...OPTED TO CONTINUE WITH WW ADVISORY THROUGH 6PM WHEN WINDS
VEER/WEAKEN AND LOW LEVEL MOIST LAYER THINS.  FCST CONTINUES WITH
CHANCE/LIKELY LEVEL POPS ALONG THE TN LINE THIS AFTERNOON GIVING WAY
TO A SLOW DECLINE TOWARDS MIDNIGHT.  QPF REMAINS RATHER LOW IN THE
NEAR TERM THEREFORE STORM TOTAL SNOWFALL AMOUNTS OF GENERALLY LESS
AND AN INCH OR TWO ARE FCST.  ALL POPS ARE REMOVED FROM THE REGION
NLT 03Z.

BEYOND THE LINGERING SNOWFALL MENTIONED ABOVE...A DRY FCST PREVAILS
WITH SKIES SLOWLY SCATTERING OUT FROM THE EAST WITH 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 /WEDNESDAY NIGHT 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 /20Z TUESDAY THROUGH SUNDAY/...
AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD.  MID
LEVEL STRATUS WILL LINGER THROUGH THE FIRST FEW HOURS OF THE TAF
CYCLE BEFORE SCT OUT TOWARDS SUNSET.  NORTHWEST WINDS WILL REMAIN
BRISK WITH GUSTS NEAR 20KTS LIKELY THROUGH THE AFTERNOON BEFORE
MIXING AND PGFS RELAX.  OTHERWISE...TAFS FEATURE LIGHT NORTHWESTERLY
WINDS THROUGH THE OVERNIGHT INTO WEDNESDAY MORNING AMIDST CLEAR
SKIES.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH VFR PREVAILING WITH THE
EXCEPTION OF AT KAVL WHERE UPSTREAM SNOW SHOWERS ADVECT MVFR CIGS UP
THE FRENCH BROAD VALLEY INTO KAVL.  THUS...KAVL TAF FEATURES BRIEF
WINDOW OF MVFR AT INITIALIZATION BEFORE INCREASING TO LOW VFR
THROUGH THE REMAINDER OF THE DAY.  OTHERWISE...GUSTY NW WINDS WILL
PREVAIL AT ALL SITES WITH MID LEVEL CIGS SCT OUT INTO THE EVENING
LEADING TO SKC THROUGH PERIODS END.  WINDS WILL SUBSIDE AFTER SUNSET
YIELDING LIGHT NORTHWEST FLOW FOR THE REMAINDER OF THE TAF CYCLE.

OUTLOOK...A SERIES OF CLIPPER SYSTEMS WILL BRING PERIODIC CHANCES
FOR RAIN OR SNOW SHOWERS...MAINLY TO THE MOUNTAINS LATE IN THE WEEK.
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.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  91%     HIGH 100%     HIGH 100%     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...WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS EVENING FOR NCZ048-
     051-052-058-059.
SC...NONE.

&&

$$
SYNOPSIS...SBK
NEAR TERM...CDG
SHORT TERM...PM
LONG TERM...HG
AVIATION...CDG


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