Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 301807
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
207 PM EDT SAT APR 30 2016

.SYNOPSIS...
AN UPPER LOW WILL APPROACH THE AREA WITH A FRONTAL PASSAGE MONDAY
MORNING.  A SECOND MAJOR FRONT AHEAD OF A MASS OF COLD AIR FROM
CANADA IS EXPECTED BY THURSDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 200 PM EDT SATURDAY...CONVECTIVE INITIATION IS UNDERWAY ACROSS
NORTHEAST GA AS EXPECTED WITH CELLS ALREADY APPROACHING
STRONG/SEVERE LIMITS.  CURRENT FCST IS UNCHANGED WITH THE FULLY
UPDATED PACKAGE/DISCUSSION TO FOLLOW WITHIN THE HOUR.

HIGH PRESSURE OVER EASTERN CANADA THIS MORNING WILL CONTINUE TO
EXPAND...WHICH IS EXPECTED TO PUSH A BACK DOOR COLD FRONT OF SORTS
FARTHER TO THE SOUTH AND WEST INTO THE WESTERN PART OF NC DURING
THE DAY. ASSUMING THIS HAPPENS...ALL SORTS OF SUBTLE COMPLICATIONS
ARISE. EXTENSIVE LOW CLOUDS BEHIND THE BOUNDARY WOULD KEEP TEMPS
COOLER WELL INTO THE DAY AND DELAY OR PERHAPS EVEN PREVENT MUCH
IN THE WAY OF DESTABILIZATION TO THE NORTH OF IT. MEANWHILE...TO
THE SOUTH OF THE BOUNDARY...WE EXPECT SOME DESTABILIZATION TO
OCCUR BY MIDDAY. HOWEVER...IT MIGHT NOT BECOME AS UNSTABLE AS
PREVIOUSLY THOUGHT...PERHAPS ONLY ON THE ORDER OF 1000-1500 J/KG
OF CAPE BASED ON THE NEW NAM/SREF...WITH THE BETTER CAPE AND LAPSE
RATES REMAINING TO OUR WEST. SHEAR STILL INCREASES LATE IN THE DAY
TO SOMETHING ON THE ORDER OF 35-40 KT SO THERE REMAINS A DISTINCT
POSSIBILITY OF ORGANIZED THUNDERSTORMS. WHAT WE LACK IN INSTABILITY
MIGHT BE COMPENSATED BY A STRONGER SURFACE BOUNDARY WITH BETTER
SHEAR AND STORM RELATIVE HELICITY IN ITS VICINITY. BOTTOM LINE IS
WE MIGHT NOT HAVE QUITE AS GOOD A CHANCE AT SEVERE STORMS ACROSS
MUCH OF THE REGION...STILL ENOUGH TO WARRANT THE MARGINAL IN THE
NEW DAY 1 CONVECTIVE OUTLOOK...BUT AT THE SAME TIME WE MIGHT HAVE
A SLIGHTLY BETTER CHANCE AT SEVERE STORMS NEAR THE BOUNDARY. THIS
WILL BE MENTIONED IN THE HWO. THE CONVECTION-ALLOWING MODEL GUIDANCE
DEVELOPS NUMEROUS COVERAGE...SO A RELATIVELY HIGH PRECIP PROBABILITY
WILL BE KEPT...AND IT RAMPS UP THROUGH THE CHANCE RANGE AND INTO
THE LIKELY RANGE THROUGH THE AFTERNOON AND EVENING...AIDED BY THE
PASSAGE OF A SHORT WAVE TROF AND UPPER DIVERGENCE ALOFT. TEMPS
WILL DEPEND ON HOW STRONG THE BOUNDARY IS...WITH PERHAPS NEAR
NORMAL TEMPS OVER THE NW PIEDMONT AND ABOVE NORMAL ELSEWHERE.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
AS OF 1205 PM EDT SATURDAY...UPPER HEIGHTS ATOP THE SE CONUS WILL
BEGIN TO FALL ON MONDAY AS SOUTHERN PLAINS ENERGY TRANSLATES
EASTWARD. THE RECENTLY POSTED OP RUNS OF THE 30/12 UTC NAM/GFS
SUPPORT THE 30/00 UTC ECMWF TREND OF THE MAIN LLVL BAROCLINIC
ZONE LINGERING NEAR OR NW OF THE CWFA. HENCE...IN CONJUNCTION WITH
THE DEVELOPING FAVORABLE UPPER LEVEL DYNAMICS...CHANCES FOR
DIURNALLY ENHANCED DEEP CONVECTION WILL BE INCREASING. INITIAL
THOUGHTS WILL BE FOR ON AN UPWARD BUMP IN TSTM PROBABILITIES MONDAY
AFTERNOON. CONTINUED UNSETTLED BUT LESS WARM WX CONDITIONS ARE
EXPECTED ON TUESDAY GIVEN THE PROGGED SLOW EVOLUTION OF THE MEAN
PATTERN FEATURING BROAD/DEEP SW FLOW AND THE SLOW SE SAGGING OF
ATTENDANT FRONTAL SYSTEM. WILL PLAN AND KEEPING SOLID MID-CHANCE
POP IF NOT AN UPWARD NUDGE TO LIKELY.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 130 PM SATURDAY...THE EXT RANGE WILL FEATURE A DEVELOPING
UNSEASONAL AND BROAD ERN CONUS ULVL TROF. THIS TROF WILL INTERACT
WITH A STATIONARY FRONT TRAPPED IN A DEEP MEAN SW/LY FLOW. THERE ARE
SIGFNT MODELED DIFFERENCES AS TO THE AMOUNT OF S/W ENERGY TRAVERSING
THE TROF...THE DEGREE OF ATL CYCLOGENESIS...THE AMOUNT OF LLVL COLD
AIR MAKING IT TO THE CAROLINAS...TILT OF THE ULVL TROF...AND
AVAILABLE MOISTURE. WITH THIS SAID...WILL MAINTAIN GRIDS CLOSE TO
THE PREVIOUS FCST. SINCE THE SYSTEM IS OUTSIDE THE NORMS FOR THIS
TIME OF YEAR WILL ALSO SIDE MORE WITH THE DYNAMICAL SOLNS AS OPPOSED
TO MOS GUIDANCE.

DO BELIEVE IT WILL BE A FAIRLY ACTIVE PERIOD WITH THE FRONTAL ZONE
BISECTING THE CWFA PROVIDING A FOCUSING MECHANISM FOR -SHRA AND
PERHAPS A COUPLE GENERAL TSTMS WED/THU AFTERNOONS. SOME DRIER AIR
LOOKS TO WORK IN AHEAD OF DEVELOPING OMEGA RIDGE FRI/SAT WHILE THE
SFC LOW PULLS NE OF THE AREA. THIS WILL CONFINE THE BETTER MOISTURE
ACROSS THE NC MTNS AND PERHAPS PRODUCE NON/ACCUM -SNSH THU NIGHT
ACROSS THE HIGHEST ELEVATIONS AS H85 TEMPS DROP TO -2 C ACCORDING TO
THE ECMWF...YET ONLY DOWN TO ARND ZERO GOING BY THE GFS. THU NIGHT
WILL BE THE COLDEST AT THE SFC AS WELL WITH HIGH ELEV TEMPS
DROPPING TO JUST ABOVE FREEZING. THIS SCENARIO WILL BE WATCHED FOR
POSSIBLE FROST/FREEZE CONCERNS. WITH CLOUD COVER LIKELY REMAINING
MCLDY/CLDY AND COOLER CP AIR MIXING BEGINNING THU...MAX TEMPS WILL
REMAIN NEAR NORMAL WED...WITH A DECREASE BY A COUPLE CATS THU/FRI
THEN A RETURN TO NORMAL LEVELS SAT AS SFC RIDGING ENGULFS THE SE
STATES.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
AT KCLT...MVFR IMPROVING TO LOW VFR THROUGH THE AFTERNOON.
EXPECTING CURRENT WEDGE INDUCED STRATUS TO RETREAT NE OVER THE NEXT
HOUR ALLOWING FOR MVFR TO SCT OUT.  WINDS WILL BE A BIT TRICKY AS
THE BOUNDARY ITSELF CONTINUES TO HOVER IN THE VICINITY...THUS
STARTED TAF NE...HOWEVER THINK VEERING TO SE IS LIKELY BY MID
AFTERNOON.  CONVECTION IS ALREADY STARTING TO INITIATE TO THE
WEST...AND WILL CONTINUE TO DEVELOP ALONG I85 IN THE UPSTATE IN THE
NEAR TERM.  THUS...CARRIED NO WX MENTION IN THE PREVAILING LINE
BEFORE INTRODUCING A 4HR TEMPO AT 21Z TO ACCOUNT FOR TSRA AND GUSTY
WINDS AS WELL AS MVFR STRATUS.  BEYOND THAT...SCT SHRA WILL REMAIN
IN THE AREA THROUGH AT MIDNIGHT THUS CARRIED SHRA...WITH VCSH
PREVAILING SHORTLY AFTER MIDNIGHT AMIDST LOWERING MVFR THEN IFR
CIGS/VISB.  THESE RESTRICTIONS WILL CARRY UNTIL AROUND DAYBREAK WITH
VISB IMPROVING FIRST...THEN CIGS TO FOLLOW AN HOUR OR SO AFTER
SUNRISE.  BY THAT TIME WINDS WILL BE SOLIDLY OUT OF THE SE BENEATH
MVFR CIGS.

AT KHKY...VERY SIMILAR TO KCLT ABOVE REGARDING AFTERNOON/OVERNIGHT
RESTRICTIONS...HOWEVER WITH SOME TIMING ADJUSTMENTS OF SHRA...WITH
LESS CHANCES FOR TSRA AS THE AIRMASS IS A BIT MORE STABLE.
NEVERTHELESS...UPSTREAM CONVECTION COULD IMPACT THE SITE LEADING TO
AMDS AT A LATER TIME THIS AFTERNOON.

AT KAVL AND THE SC SITES...SIMILAR CONVECTIVE TRENDS TO KCLT ABOVE
HOWEVER WITH SLIGHT TIMING ADJUSTMENTS AS CONVECTION WILL DEVELOP
CLOSER TO THESE SITES.  OTHERWISE...WINDS WILL REMAIN ESE...VEERING
SE OVERNIGHT TO REMAIN THROUGH THE PERIOD.  TEMPOS ARE FAVORED AT
ALL SITES FOR TSRA...WITH VCTS CARRIED THROUGH MUCH OF THE
EVENING/OVERNIGHT...EVENTUALLY GIVING WAY TO SHRA AMIDST IFR
CIGS/VISB...BEFORE NO WX IS MENTIONED JUST AHEAD OF SUNRISE WHEN
RESTRICITIONS IMPROVE.

OUTLOOK...UNSETTLED WEATHER/OCCASIONAL CONVECTION/RESTRICTIONS ARE
EXPECTED TO CONTINUE INTO EARLY NEXT WEEK...AS A FRONT BECOMES
STALLED NEAR THE AREA. DEFINITIVE DRYING DOES NOT APPEAR LIKELY
UNTIL AT LEAST MID-WEEK.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       MED   78%     MED   70%     HIGH  86%     HIGH  80%
KGSP       HIGH 100%     HIGH  85%     MED   79%     HIGH  83%
KAVL       HIGH  97%     HIGH  85%     HIGH  90%     HIGH  80%
KHKY       MED   77%     MED   76%     HIGH  90%     HIGH  86%
KGMU       HIGH 100%     HIGH  94%     MED   73%     HIGH  80%
KAND       HIGH 100%     HIGH  95%     HIGH  80%     HIGH  83%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...SBK/WJM
NEAR TERM...CDG/PM
SHORT TERM...CSH
LONG TERM...SBK
AVIATION...CDG


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