Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 270514
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1214 AM EST TUE JAN 27 2015

.SYNOPSIS...
IN THE WAKE OF A STRONG DEPARTING LOW...DRY HIGH PRESSURE WILL
SPREAD BACK OVER THE REGION FROM THE NORTHWEST TONIGHT AND TOMORROW.
ANOTHER COLD FRONT IS EXPECTED TO CROSS THE REGION LATE THURSDAY
INTO EARLY FRIDAY WITH ANOTHER ROUND OF HIGH PRESSURE IN ITS WAKE.

&&

.NEAR TERM /THROUGH TODAY/...
0515 UTC UPDATE...WINDS WERE UPDATED WITH A TWO TO ONE BLEND OF NAM
AND ADJMAV...FAVORING THE FORMER FOR GREATER WINDS IN THE MOUNTAINS.
WINDS WERE MANUALLY INCREASED SLIGHTLY IN GSP AREA WHERE A MINOR GAP
WIND EVENT IS IN PROGRESS. SKY COVER WAS UPSTATE FROM INFRARED
SATELLITE IMAGERY.

915 PM UPDATE...LIGHT SHOWER ACTIVITY CONTINUES TO STREAM FROM
THE GREAT LAKES REGION DOWN THE BACK SIDE OF THE UPPER TROUGH AND
INTO EAST TN...N GA...AND AT LEAST THE SMOKY MTNS PER RADAR
RETURNS. SFC OBS CONTINUE TO REFLECT PERIODIC LIGHT SNOW SHOWERS IN
ASHE/WATAUGA COUNTIES NORTH OF THE CWFA. IN OUR NRN MTNS THE
ACTIVITY APPEARS TOO SHALLOW TO BE SEEN ON RADAR. WE SOLICITED
SOME REPORTS FROM COUNTIES ALONG THE TENN BORDER...INDICATING
GENERALLY VERY LIGHT ACCUMS AND ONLY MINOR ROAD ISSUES.

GOING FORWARD INTO THE NIGHT...LLVL WIND/MOISTURE FIELDS INDICATE
LITTLE CHANGE ALONG THE SPINE OF THE MTNS UNTIL JUST BEFORE DAYBREAK
WHEN A BETTER SLUG OF MOISTURE ARRIVES IN THE SMOKIES AND VICINITY.
SO I REVISED POPS TO INDICATE A FAIRLY STEADY SITUATION UNTIL THAT
TIME WHEN CHANCES INCREASE SOMEWHAT IN THE SOUTH...AND BEGIN TO
TAPER OFF IN THE NORTH. FOR QPF...I USED OUR SHORT TERM CONSENSUS
PRODUCT WHICH REFLECTS THE TRENDS IN THE HRRR...RAP AND
NAM...KEEPING LIQUID ACCUMS MINIMAL UNTIL AROUND THAT TIME AS WELL.
A LITTLE EARLIER THIS EVENING A COCORAHS OBSERVER FROM AVERY CO
REPORTED A SNOW RATIO OF ABOUT 7 TO 1. THIS MAKES SENSE GIVEN PROG
SOUNDINGS SHOWING THE SATURATED LAYER NOT REACHING VERY FAR AT ALL
INTO THE DENDRITIC GROWTH ZONE. I GENERATED SNOW TOTALS BASED ON AN
8 TO 1 RATIO WHICH PUTS TOTALS A BIT LOWER THAN PREV FCST. THE
ADVISORY LOOKS GOOD AS A HEADLINE...BUT I WILL UPDATE THE TEXT
PRODUCT SHORTLY TO DETAIL THE LATEST EXPECTATIONS.

AS OF 245 PM EST MONDAY...BROAD FULL LATITUDE LONGWAVE UPPER TROF
REMAINS ACROSS THE EASTERN CONUS WITH SHARP RIDGING ACROSS THE WEST.
CLOSER TO HOME...BRISK NORTHWEST FLOW AMONGST THE AMPLIFIED UPPER
PATTERN AND POOLED LOW LEVEL MOISTURE CONTINUES TO YIELD LIGHT
UPSLOPE SNOW SHOWERS ALONG THE TN BORDER.  FURTHER EAST...FCST
FEATURES DECREASING POPS ACROSS NC PIEDMONT AS EARLIER SHOWER
ACTIVITY HAS DIMINISHED WITH ONLY A FEW LIGHT ECHOES EVIDENT ON
RADAR.  MODELS CONTINUE TO TREND TOWARDS A BRIEF LULL IN NORTHWEST
FLOW SNOW SHOWER ACTIVITY ALONG THE TN BORDER COUNTIES BEFORE A
SECOND ROUND OF CHANNELED VORTICITY SLIDES THROUGH THE REGION
TONIGHT. IN ADDITION TO THE SNOWFALL...GUSTY NORTHWEST WINDS WILL
PREVAIL THROUGH MUCH OF THE NIGHT WITH SOME OF THE HIGHER ELEVATIONS
SITES EXPERIENCING GUSTS NEAR 40MPH...WHILE THE LOWER ELEVATIONS TOP
OUT WITH GUSTS NEARING 25-30MPH.

OUTSIDE OF THE MOUNTAINS...CONDITIONS WILL GRADUALLY IMPROVE THROUGH
THE OVERNIGHT WITH SKIES BEGINNING TO SCT NEAR MIDDAY TUESDAY.
DOWNSLOPING FLOW WILL YIELD TEMPERATURES JUST BELOW NORMAL DESPITE
COLD ADVECTION PATTERN.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
AS OF 230 PM MONDAY...THE FIRST PART OF THE SHORT RANGE LOOKS LIKE
THE QUIETEST PART OF THE ENTIRE FCST. ANY REMAINING NW FLOW SNOW
SHOWERS OVER THE NRN MOUNTAINS OF NC SHOULD TAPER OFF RIGHT AWAY
TUESDAY EVE. THE AXIS OF THE UPPER TROF SHOULD MOVE SLOWLY OFF THE E
COAST TUESDAY NIGHT...WHICH WILL KEEP A DRY NW FLOW OVERHEAD. AN
UPPER RIDGE WILL SLOWLY BUILD IN FROM THE WEST ON WEDNESDAY WITH THE
AXIS OF THE UPPER RIDGE MOVING OVERHEAD WEDNESDAY NIGHT. THIS WILL
SUPPORT DRY AND COOL HIGH PRESSURE THAT WILL KEEP TEMPS GENERALLY A
CATEGORY OR SO BELOW NORMAL.

ON THURSDAY...THE MODELS SHOW A PAIR OF SHORT WAVES MOVING THRU THE
MIDWEST AND AROUND A MEAN TROF OVER THE EAST. THE FIRST WAVE SHOULD
STAY OVER THE OH VALLEY ON THURSDAY AFTERNOON. WARM ADVECTION AHEAD
OF THE WAVE MAY HELP TO DEVELOP SOME LIGHT PRECIP ACROSS THE FCST
AREA...WITH THE BEST CHANCE OVER THE MTNS. FCST SOUNDINGS SUGGEST
THIS WILL BE AN ELEVATION-DEPENDENT RAIN OR SNOW SITUATION. THERE
SHOULD BE A SMALL CHANCE FOR PRECIP OUTSIDE THE MTNS THAT SHOULD
FALL AS RAIN. TEMPS WERE UNDERCUT FROM THE GUIDANCE...WITH THE
EXPECTATION THAT INCREASING CLOUDS AND SOME LIGHT PRECIP WILL
CONTINUE TO KEEP TEMPS BELOW NORMAL. THE SECOND WAVE SHOULD HELP TO
DRIVE A COLD FRONT ACROSS THE WESTERN CAROLINAS THURSDAY NIGHT. MOST
OF THE PRECIP WITH THIS FEATURE WILL BE CONFINED TO THE MTNS.
IMPROVING MOIST UPSLOPE FLOW BEHIND THE FRONT SHOULD MAINTAIN A
CHANCE OF PRECIP ON THE TN BORDER THROUGH AT LEAST DAYBREAK ON
FRIDAY. THIS SHOULD BE IN THE FORM OF SNOW SHOWERS OWING TO THE COLD
ADVECTION BEHIND THE FRONT. MIN TEMPS E OF THE MTNS SHOULD BE ABOVE
NORMAL BECAUSE OF LINGERING CLOUDS.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 215 PM MONDAY...A PROMINENT TROUGH AXIS WILL MOVE QUICKLY EAST
OF THE FORECAST AREA FRI MORNING AND THEN OFF THE ERN SEABOARD
THROUGH THE DAY. SHALLOW MOISTURE IN THE NW FLOW COLD ADVECTION
BEHIND THE TROUGH COULD LINGER THROUGH LATE FRI MORNING...BUT WITH
LITTLE TO NO ADDITIONAL SNOW ACCUMULATIONS IN ANY UPSLOPE SHOWERS IN
THE WRN MTNS. MAXES WILL FALL BELOW CLIMO...PERHAPS 10 DEGREES OR
MORE BELOW CLIMO IN THE NC MOUNTAINS.

THE UPPER LEVEL FLOW PATTERN WILL BECOME ZONAL THROUGH SAT WITH SFC
HIGH PRESSURE LIKELY BUILDING OVER TO THE N OF THE REGION. A STEADY
INCREASE IN MID AND HIGH CLOUDS IS EXPECTED. MODEL DIFFERENCES THEN
APPEAR THROUGH THE LATTER HALF OF THE WEEKEND...WITH THE GFS
GENERALLY FASTER THAN RECENT ECMWF RUNS IN FEATURING A NRN STREAM
WAVE DIGGING INTO THE MIDWEST ON SUNDAY. THE 00Z OPERATIONAL ECMWF
WAS A BIT SLOWER...BUT THE 12Z RUN IS NOW CLOSER TO THE GFS TIMING
ON THE WAVE. THE MAIN SENSIBLE WEATHER DIFFERENCE FOR SUNDAY IS THAT
THE FASTER GFS TIMING ALLOWS PRECIPITATION TO ARRIVE BY
DAYBREAK...WITH A SRN TIER FREEZING RAIN/NRN TIER SNOW AND SLEET
THREAT...WITH RELATIVELY PROMINENT CAD SETTING UP FROM THE NE.
PROFILES WOULD THEN WARM FOR THE PEAK OF THE WARM ADVECTION...WITH
MAINLY A RAIN PTYPE EXCEPT FOR LINGERING FZRA IN ANY COLD POCKETS
JUST E OF THE BLUE RIDGE. THE ECMWF HAS A SLOWER ONSET OF
PRECIPITATION...WITH LESS MORNING FREEZING RAIN THREAT...MUCH WEAKER
CAD...BUT THEN MORE OF A RAIN VERSUS SNOW PTYPE ISSUE THROUGHOUT THE
WHOLE EVENT. SUNDAY TEMPS HAVE BEEN LOWERED SLIGHTLY...AND PTYPES
REMAIN RAIN/SNOW.

DIFFERENCES ARE MORE STARK SUN NIGHT INTO MONDAY. THE GFS DRIVES A
COLD FRONT THROUGH THE REGION AND DRIES THINGS OUT...OTHER THAN ANY
LINGERING NW FLOW MOISTURE IN THE WRN MTNS. THE ECMWF...ON THE OTHER
HAND...DEVELOPS A SFC WAVE OVER THE SE AND KEEPS HEAVY PRECIPITATION
IN THE REGION SUNDAY NIGHT INTO MONDAY. ASSOCIATED PTYPE ISSUES
WOULD CONTINUE DEPENDING ON THE SFC LOW TRACK. WILL CONTINUE TO KEEP
ALL PTYPES RAIN VERSUS SNOW THROUGHOUT GIVEN ALL THE UNCERTAINTY IN
THERMAL PROFILES.

&&

.AVIATION /05Z TUESDAY THROUGH SATURDAY/...
AT KCLT...GUIDANCE SUGGESTS A LOW VFR CIG RETURNING AROUND
DAYBREAK...AND LASTING INTO LATE MORNING...BEFORE CLOUD COVER
DECREASES. NW WINDS ARE EXPECTED TO DIMINISH TOWARD DAWN...THEN PICK
BACK UP AND GET A BIT GUSTY DURING THE DAY. WINDS TAKE THEIR TIME
DIMINISHING ON TUESDAY NIGHT.

ELSEWHERE...GUIDANCE SUPPORTS VFR CIGS RETURNING TO THE FOOTHILLS
BEFORE DAWN...WITH MVFR AT KAVL. CIGS WOULD END IN THE MORNING AT
FOOTHILLS SITES AS CLOUDS COVER DECREASES...BUT THE MVFR CIGS AT
KAVL WOULD PERSIST INTO THE AFTERNOON BEFORE ERODING. GUSTY NW WINDS
WILL PERSIST OVERNIGHT AT KAVL AND KGSP...THE LATER DUE TO MOUNTAIN
GAP WINDS. AFTER DAYBREAK MODEST WIND GUSTS PICK UP AT OTHER
FOOTHILLS SITES. WINDS WILL SLOWLY DIMINISH TUESDAY NIGHT IN THE
FOOTHILLS. KAVL APPEARS TO BE ON THE SE FRINGE OF LIGHT SNOW SHOWERS
OVERNIGHT...AND THE CHANCE OF SNOW IS TOO LOW TO MENTION IN THE TAF.

OUTLOOK...A SERIES OF CLIPPER SYSTEMS WILL BRING PERIODIC CHANCES
FOR SNOW SHOWERS...MAINLY TO THE MOUNTAINS THROUGH THE WEEK. MOST OF
THESE SNOW SHOWERS WILL REMAIN WEST AND NORTH OF KAVL...BUT BRIEF
PERIODS OF RESTRICTIONS AND SNOW SHOWERS CANNOT BE RULED OUT THERE.
OTHERWISE...MAINLY VFR CONDITIONS ARE EXPECTED.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       HIGH 100%     MED   62%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     LOW   57%     MED   62%
KHKY       HIGH 100%     LOW   31%     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 NOON EST TODAY FOR NCZ033-
     048>052-058-059.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...CDG/JAT/WIMBERLEY
SHORT TERM...PM
LONG TERM...HG
AVIATION...JAT



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