Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 272013
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
413 PM EDT FRI MAR 27 2015

.SYNOPSIS...
AN UPPER LEVEL DISTURBANCE WILL CROSS THE REGION FROM THE WEST
TONIGHT. COLD AND DRY HIGH PRESSURE WILL SETTLE IN OVER THE WEEKEND.
A LOW PRESSURE CLIPPER SYSTEM AND ASSOCIATED COLD FRONT WILL PASS
OVER THE AREA ON SUNDAY NIGHT OR MONDAY. MOISTURE WILL RETURN MID TO
LATE WEEK AHEAD OF THE NEXT APPROACHING COLD FRONT.

&&

.NEAR TERM /THROUGH SATURDAY/...
2015 UTC UPDATE...POPS WERE INCREASED BASED ON RADAR TRENDS...AND
SNOW TOTALS INCREASED SLIGHTLY AT HIGH ELEVATIONS OF THE NC
MOUNTAINS.

AS OF 230 EDT FRIDAY...SHOWER ACTIVITY HAS INCREASED ALONG THE
FOOTHILLS IN RESPONSE TO CONTINUED VERY WEAK ISENTROPIC LIFT AT THE
LOWER THETA LEVELS. THESE LIGHT SHOWERS SHOULD CONTINUE TO SLIDE
EAST WITH THE SHORTWAVE AND DIMINISH THIS EVENING. WIDESPREAD
CLOUDINESS CONTINUES ACROSS THE AREA WHICH HAS KEPT TEMPS DOWN
ACROSS MOST OF THE AREA...WITH ONLY A FEW PEEKS OF SUNSHINE IN
EXTREME WESTERN ZONES. AS THE EVENING PROGRESSES AND THE SHORTWAVE
AND ATTENDANT FRONT CONTINUE TO SLIDE EAST...LOW CLOUDS WILL BEGIN
TO LIFT AND SKIES GRADUALLY CLEAR TOWARDS THE OVERNIGHT HOURS FOR
ALL BUT THE MOUNTAINS AS WINDS BACK TO THE NORTHWEST AND DOWNSLOPING
OFF THE HIGHER ELEVATIONS INCREASES...ACTING TO REDUCE SATURATION IN
LOW LEVELS AND CLEAR THE CLOUDS ACROSS THE PIEDMONT. THE TWO MAIN
CONCERNS FOR THE NEAR TERM PERIOD REMAIN OVERNIGHT LOW TEMPERATURES
WITH FREEZE POTENTIAL AND POSSIBLE ACCUMULATING SNOW IN THE
MOUNTAINS.

STRONG CAA BEHIND THE FRONT ESPECIALLY AS SKIES CLEAR TOWARD MORNING
WILL ALLOW TEMPERATURES TO DROP SIGNIFICANTLY TONIGHT...WITH
WIDESPREAD 20S IN THE MOUNTAINS /A FEW TEENS AT HIGHER ELEVATIONS/
AND SOLIDLY IN THE 30S ELSEWHERE. THE FROST/FREEZE PROGRAM FOR AREAS
SOUTH OF I-40 HAS BEEN ACTIVATED STARTING TONIGHT...AND BASED ON
UPDATED LOW TEMPS WILL EXTEND THE CURRENT FREEZE WARNING ANOTHER
TIER OF COUNTIES SOUTH INTO NORTHEAST GEORGIA...UPSTATE SOUTH
CAROLINA...AND THE PIEDMONT OF NORTH CAROLINA JUST WEST OF
CHARLOTTE. WINDS DO DIMINISH ACROSS UPSTATE SOUTH CAROLINA OVERNIGHT
BUT SHOULD REMAIN GENERALLY BETWEEN 5-10MPH INHIBITING FROST
FORMATION SO AT THIS TIME DO NOT PLAN TO ISSUE A FROST ADVISORY FOR
AREAS SOUTH OF THE FREEZE WARNING...BUT WINDS WILL NEED TO BE
MONITORED CLOSELY.

A SECONDARY SHORTWAVE PUSHING THROUGH THE SOUTHERN APPALACHIANS
TONIGHT WILL RESULT IN STRONG NORTHWEST FLOW PROVIDING UPSLOPE
COMPONENT TO THE RIDGES...ESPECIALLY ALONG THE SMOKIES. NAM REMAINS
A LITTLE MORE AGGRESSIVE WITH BULLSEYE OF MOISTURE ALONG THE SMOKIES
BUT EVEN RESULTANT SREF PROBS HAVE AT BEST 50-60 PERCENT CHANCE OF
>1 INCH SNOW...LINING UP WELL WITH WPC PROBS. AS TEMPERATURES FALL
THIS EVENING AND NORTHWEST FLOW INCREASES...DESPITE DRYING
ALOFT...SHOULD BE ENOUGH LIFT TO GET LIGHT TO OCCASIONALLY MODERATE
SNOW SHOWERS WITH BEST CHANCES OF ACCUMULATIONS GENERALLY AT
ELEVATIONS 2500FT OR GREATER. DEEP LEVEL MOISTURE PRETTY MUCH GONE
BY 09Z WITH ONLY LOW LEVEL MOISTURE AT 850MB AND BELOW REMAINING
THROUGH ABOUT 12Z...AND THUS BEST CHANCE OF ACCUMULATING SNOW LIKELY
BETWEEN 00-06Z. STORM TOTAL SNOW IS JUST UNDER 2 INCHES AT THE
HIGHEST PEAKS OF THE SMOKIES ALONG THE TENNESSEE STATE LINE SO NO
ADVISORY PLANNED AT THIS TIME.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 145 PM FRIDAY...THE MAIN STORY FOR THE SHORT TERM WILL BE THE
ABNORMALLY COLD TEMPS FOR SATURDAY NIGHT INTO SUNDAY. CP HIGH
PRESSURE WILL SETTLE OVER THE REGION SAT NIGHT PRODUCING IDEAL
RADIATIONAL COOLING CONDITIONS. ALL GUIDANCE HAS BEEN CONSISTENT IN
ADVERTISING FREEZING TEMPS ACROSS THE BOARD SAT NIGHT...WITH UPPER
TEENS TO MID 20S IN THE MOUNTAINS AND MID 20S TO AROUND 30
ELSEWHERE. THEREFORE...WILL POST A FREEZE WATCH FOR ALL OF THE AREA
WHERE THE FROST/FREEZE PROGRAM HAS BEEN TURNED ON. THE HIGH WILL
MOVE SOUTHEAST OF THE AREA DURING SUNDAY ALLOWING FOR WEAK WARM
ADVECTION TO KICK IN. EVEN SO...MAX TEMPS ON SUNDAY WILL CONTINUE TO
BE A COUPLE CATEGORIES BELOW CLIMO.

ANOTHER UPPER TROUGH WILL MOVE THROUGH THE GREAT LAKES SUNDAY NIGHT
WHICH WILL DRIVE A COLD FRONT INTO THE MOUNTAINS BY 12Z MONDAY AND
ACROSS THE REMAINDER OF THE AREA MONDAY. THE FRONT WILL NOT HAVE A
GREAT DEAL OF MOISTURE TO WORK WITH...SO PRECIP SHOULD BE ON THE
LIGHT SIDE AND SPOTTY EAST OF THE MOUNTAINS. PRECIP THAT DOES FALL
SHOULD BE MAINLY LIQUID AS TEMPS ARE FORECAST TO REMAIN ABOVE
FREEZING SUNDAY NIGHT INTO EARLY MONDAY. THE EXCEPTION MY BE THE
OVER THE HIGHEST ELEVATIONS OF THE NC MOUNTAINS WHERE A RAIN/SNOW
MIX MAY OCCUR. DRYER AIR IS FORECAST TO OVERSPREAD THE AREA MONDAY
AFTERNOON AS HIGH PRESSURE BUILDS IN FROM THE WEST. AN UPTICK TEMPS
IS ALSO EXPECTED ON MONDAY THANKS TO DOWNSLOPE FLOW BEHIND THE FRONT.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 205 PM FRIDAY...THE MID-WEEK PERIOD WILL FEATURE A TRANSITION
TOWARD A WARMER AND DRIER PATTERN...AS THE UPPER TROUGH AXIS SHIFTS
OFF THE EAST COAST. IN FACT...WITH HEIGHTS FALLING IN THE WEST AND
RISING IN THE EAST...THE CONUS IS IN STORE FOR A SUBSTANTIAL PATTERN
SHIFT DURING THE LATTER HALF OF NEXT WEEK. AS SUCH...IT IS NOT
SURPRISING THAT THE GLOBAL MODELS ARE STRUGGLING A BIT WITH THE
SHORT WAVE DETAILS DURING THIS TIME FRAME. THE FIRST AREA OF
UNCERTAINTY REGARDS A (LIKELY DAMPENING) SHORT WAVE TROUGH EJECTING
OUT OF THE ARKLATEX SOMETIME AROUND WED...WITH THE MORE PROGRESSIVE
GFS SPREADING UPGLIDE PRECIP INTO THE CWA BY THE END OF THE DAY
WED...WHILE THE ECMWF IS AT LEAST 12 HOURS SLOWER. WE OPTED TO GO
WITH SOMEWHAT OF A BLEND...WITH SLIGHT/LOW CHANCE POPS OVERSPREADING
THE AREA BY THE END OF WED.

MODEL DISCREPANCY AND FORECAST UNCERTAINTY AMPLIFIES LATER IN THE
WEEK...AS THE GFS IS MUCH MORE AMPLIFIED WITH A NORTHERN STREAM
SHORT WAVE TROUGH LATE IN THE WEEK. THE RESULT IS THE CARVING OF
ANOTHER EASTERN LONG WAVE TROUGH BY THE END OF THE PERIOD.
MEANWHILE...THE LESS AMPLIFIED ECMWF ALLOWS FOR MORE SUBSTANTIAL
UPSTREAM SHORT WAVE ENERGY...ADVERTISING ANOTHER FRONT LOADING UP
ACROSS THE MISS VALLEY BY FRIDAY. OUR CURRENT COURSE OF ACTION IS TO
RESERVE THE HIGHEST POPS FOR THURSDAY...WHEN BOTH MODELS DEPICT SOME
QPF RESPONSE (ALBEIT FOR DIFFERENT REASONS)...WHILE MOST PERIODS
PAST WED WILL SEE AT LEAST A SLIGHT CHANCE. TEMPS SHOULD MODERATE TO
AT LEAST NORMAL LEVELS DURING THE PERIOD.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT...MVFR CIGS CONTINUE FOR CLT AT TAF TIME BUT WITH LOW VFR
CIGS JUST TO THE WEST. STILL SOME -SHRA ACROSS THE AREA BUT MAINLY
WEST OF CLT SO WILL HOLD OFF ON SHRA/VCSH MENTION IN THE TAF FOR
NOW. EXPECT THAT CLT WILL REMAIN MVFR THROUGH 21-22Z WITH A SLOW
LIFTING TREND TO VFR AT THAT TIME. N WINDS AROUND 10KT WITH GUSTS
BETWEEN 15-20KT WILL LOSE GUSTINESS AND DECREASE LATE THIS EVENING
AND OVERNIGHT...BACKING MORE NW OVERNIGHT. CIGS WILL CONTINUE TO
GRADUALLY LIFT BUT REMAIN GENERALLY BELOW 6KFT UNTIL DOWNSLOPING
KICKS IN MORE SIGNIFICANTLY AFTER MIDNIGHT WITH THE WIND SHIFT TO
NW...WHEN CIGS SHOULD LIFT RAPIDLY AND SCATTER OUT. SOME HINTS AT
LOW LEVEL MOISTURE...BETWEEN 60-70 PERCENT RH...AFTER 15Z SATURDAY
SO HAVE INTRODUCED FEW035 FOR LATE IN THE PERIOD WITH WINDS BACK UP
TO AROUND 10KT.

ELSEWHERE...VERY SIMILAR TREND TO CLT BUT INITIALIZING MAINLY LOW
VFR WITH ONLY SPOTTY MVFR. CANNOT RULE OUT BRIEF -SHRA THROUGH THE
AFTERNOON BUT WITH LIFTING TREND IN CIGS CHANCES WILL CONTINUE TO
DIMINISH. CIGS SHOULD REMAIN VFR THROUGH THE PERIOD WITH N WINDS
BACKING TO NW ALLOWING SKIES TO CLEAR FOR THE MOST PART OVERNIGHT
FOR ALL BUT KAVL...WHERE SOME LOW VFR CIGS MAY REMAIN THROUGH AROUND
SUNRISE. CAA AND NORTHWEST FLOW BEHIND THE FRONT WILL LEAD TO -SHSN
ALONG THE TN LINE AND CANNOT RULE OUT ISOLATED FLURRIES AT KAVL BUT
CONFIDENCE NOT HIGH ENOUGH TO INCLUDE IN TAF AT THIS TIME.

OUTLOOK...DRY HIGH PRESSURE WILL PREVAIL THROUGH THE WEEKEND WITH
ANOTHER FRONT APPROACHING FOR MONDAY. RAIN CHANCES INCREASE THROUGH
MIDDAY MONDAY WITH BEST CHANCES FOR WESTERN TAFS...WITH CIG/VSBY
RESTRICTIONS FOLLOWING A SIMILAR TREND BUT CANNOT BE RULED OUT AT
ANY SITE ON MONDAY BEFORE THE FRONT CLEARS THE AREA.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       HIGH  91%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH  92%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH  96%     HIGH 100%     HIGH 100%
KHKY       HIGH  98%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  96%     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

&&

.CLIMATE...
RECORD MINIMUM TEMPERATURES FOR MARCH 28TH...

GSP  26  1982
CLT  25  1982
AVL  11  1887

RECORD MINIMUM TEMPERATURES FOR MARCH 29TH...

GSP  26  1899
CLT  26  2013
AVL  19  1982

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING
     FOR GAZ010-017-018-026-028-029.
     FREEZE WARNING FROM MIDNIGHT TONIGHT TO NOON EDT SATURDAY FOR
     GAZ010-017.
NC...FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING
     FOR NCZ048-051>053-058-059-062>065-068>072-082-507>510.
     FREEZE WARNING FROM MIDNIGHT TONIGHT TO NOON EDT SATURDAY FOR
     NCZ048-051>053-058-059-062>065-068>070-507>510.
SC...FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING
     FOR SCZ001>014-019.
     FREEZE WARNING FROM MIDNIGHT TONIGHT TO NOON EDT SATURDAY FOR
     SCZ001>003.

&&

$$
SYNOPSIS...HG
NEAR TERM...JAT/TDP
SHORT TERM...LG
LONG TERM...JDL
AVIATION...TDP
CLIMATE...



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