Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 250246
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1046 PM EDT TUE MAR 24 2015

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE EAST COAST WEDNESDAY. A COLD FRONT
WILL APPROACH THE REGION FROM THE WEST ON THURSDAY AND CROSS THE
AREA THURSDAY NIGHT. A STRONG UPPER LEVEL DISTURBANCE WILL MOVE OVER
THE APPALACHIANS FRIDAY THROUGH FRIDAY NIGHT...WITH COOL HIGH
PRESSURE SETTLING IN OVER THE WEEKEND. A LOW PRESSURE CLIPPER SYSTEM
WILL CROSS THE AREA FROM THE NORTHWEST EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 1030 PM EDT TUESDAY...TOUCHED UP THE NEAR TERM A BIT BY
BLENDING IN LATEST CONSSHORT FOR SKY/TEMPS/DEWS THROUGH THE NIGHT
WHICH DIDNT YIELD ANY SIGNIFICANT CHANGES.  OTHERWISE...LEADING EDGE
OF THE HIGH PRESSURE WEDGE BOUNDARY STARTING TO INTRUDE ACROSS THE
REGION AS SELECT NC PIEDMONT/TRIAD LOCATIONS STARTING TO BACK SFC
WINDS AROUND TO THE NORTHEAST.  LIKEWISE...SKY OBS CONTINUE TO
INDICATE INCREASING LOW LEVEL VFR STRATUS WORKING THROUGH THE
REGION...WHICH IS STILL EXPECTED TO EXPAND SOUTHWARD THROUGH THE
REMAINDER OF THE AREA OVERNIGHT.  AS FAR AS FCST MOIST
UPGLIDE...LATEST 00Z NAM 295K SURFACE ANALYSIS INDICATES THE BEST
ISENTROPIC LIFTING WILL SPREAD IN FROM THE SOUTH BEFORE DAYBREAK.
MOST RECENT RAP/HRRR RUNS CONTINUE TO HIGHLIGHT INITIAL PRECIP ONSET
AROUND THE 3-5AM TIMEFRAME ALONG THE INTRUDING HIGH PRESSURE
PERIPHERY...WHICH WILL MOST LIKELY BE ALONG THE BLUE RIDGE SOUTHWARD
INTO NORTHEAST GA AND THE WESTERN UPSTATE.  ALL SAID...CURRENT POP
TRENDS REMAIN IN LINE THUS NO CHANGES WERE MADE ON THAT FRONT.

PREVIOUS DISCUSSION...

AS OF 245 PM...SAT PIX SHOW QUITE A BIT OF CONVECTIVE CU ACROSS THE
MTNS. RADAR IS STILL QUIET...BUT ISOLATED SHRA STILL POSSIBLE ACROSS
THE MTNS INTO THE EVENING WITH THE WEAK INSTABILITY IN PLACE. CLEAR
SKIES OUTSIDE OF THE MTNS...BUT EXPECT CLOUDS TO SLOWLY INCREASE
INTO THE EVENING. CONDITIONS CHANGE DRAMATICALLY AFTER MIDNIGHT AS
COPIOUS LOW LEVEL MOISTURE MOVES IN AND WIDESPREAD ISENTROPIC LIFT
DEVELOPS. EXPECT CLOUDY SKIES AND INCREASING RAIN AND DRIZZLE
COVERAGE AS A WEAK IN SITU CAD OR COOL POOL DEVELOPS. QPF WILL BE
LIGHT...WITH HIGHEST AMOUNTS NEAR THE BLUE RIDGE. LOWS WILL BE
AROUND 10 DEGREES ABOVE NORMAL WITH THE CLOUDS AND INCREASING DEW
POINTS.

WEAK CAD REMAINS IN PLACE WED AS LOW LEVEL MOISTURE CONTINUES TO
STREAM IN AND ISENTROPIC LIFT REMAINS IN PLACE. THIS WILL KEEP RAIN
AND DRIZZLE ACROSS THE AREA THRU THE MORNING...WITH RAIN CONTINUING
INTO THE AFTERNOON. GIVEN THAT THE CAD WILL BE SHALLOW AND WEAK...
SOME INSTABILITY MAY DEVELOP ACROSS THE NC MTNS WEST OF THE FRENCH
BROAD VALLEY WHERE BETTER HEATING OCCURS. HAVE LIMITED ANY THUNDER
MENTION TO THAT AREA IN THE SLIGHT CHC RANGE FOR THE AFTERNOON. KEPT
PRECIP AS RAIN ELSEWHERE. THIS ALSO MEANS THE HIGHS WILL BE
RELATIVELY MILD FOR A CAD...WITH VALUES ONLY A LITTLE BELOW NORMAL.
BEST POP AND QPF WILL AGAIN BE NEAR THE BLUE RIDGE...WITH AMOUNTS
REMAINING LIGHT.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 245 PM EDT TUESDAY...ANY LINGERING IN SITU CAD EAST OF THE
BLUE RIDGE WED NIGHT WILL GRADUALLY ERODE IN SRLY FLOW DURING THE
DAY ON THU. MEANWHILE...THE DEEPENING UPPER TROUGH OVER THE PLAINS
WED NIGHT WILL SWING THROUGH THE MS RIVER VALLEY ON THU AND THEN
BOTTOM OUT OVER THE APPALACHIANS THROUGH FRI NIGHT. THE TROUGH WILL
DRIVE A SFC COLD FRONT ACROSS TN ON THU. 850 MB FLOW WILL STEADILY
INCREASE AHEAD OF THE FRONT...BUT WITH WINDS VEERING MORE SWLY
WITH TIME. THERE IS STILL FAIRLY LARGE DISPARITY BETWEEN THE LEAST
UNSTABLE GFS AND MOST UNSTABLE NAM REGARDING PIEDMONT PROFILES LATE
THU. SFC TO 3 KM SHEAR VALUES WILL LIKELY REACH 30 TO 35 KT DURING
THE BEST PERIOD OF OVERLAP WITH THE LATE DAY INSTABILITY TO CREATE A
VERY MARGINAL CASE FOR SHALLOW CONVECTIVE LINE FEATURES. IT IS
POSSIBLE THAT THE MAIN FRONTAL FORCING WILL ARRIVE TOO LATE IN THE
PERIOD TO TAP INTO THE BEST LATE DAY INSTABILITY.

THE RELATIVELY NARROW ZONE OF DEEPER FRONTAL MOISTURE WILL CROSS THE
REGION PRIMARILY THU EVENING...ACCOMPANIED BY GOOD FORCING ALOFT
NEAR A 140 KT UPPER JETLET SHARPENING UP WEST OF THE APPALACHIANS.
ANTICIPATE FROPA TO OCCUR THROUGH 06Z FRI...BUT WITH CONSIDERABLE
POST FRONTAL MOISTURE THROUGH DAYBREAK FRIDAY. SNOW LEVELS WILL
LIKELY UNCOVER THE HIGHEST RIDGES OF THE NC MTNS TO PERMIT SCATTERED
SNOW SHOWERS TO DEVELOP IN THE NW UPSLOPE FLOW. THE BEST DEEP LAYER
Q VECTOR CONVERGENCE AHEAD OF THE UPPER TROUGH WILL THEN ARRIVE
FRIDAY TO KEEP POST FRONTAL SCATTERED SHOWERS GOING ACROSS THE
REGION. MOST OF THE OPERATIONAL MODELS ALLOW SOME SNOW SHOWERS TO
BREAK CONTAINMENT EAST OF THE MTNS FRI AFTN...BUT PROFILES SUGGEST
THAT THE BOUNDARY LAYER WILL BE TOO WARM TO BE OVERCOME BY ANY
SCATTERED SNOW SHOWERS. NW FLOW MOISTURE AND COLD TEMPERATURES WILL
SUPPORT ADDITIONAL LIGHT HIGH MTN ACCUMULATIONS OF SNOW THROUGH FRI
NIGHT...ASSISTED BY THE PASSAGE OF THE STRONG H5 COLD POOL. ANY
ACCUMS ARE CURRENTLY EXPECTED TO BE SUB ADVISORY.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 145 PM TUESDAY...THE MEDIUM RANGE FEATURES A NW FLOW ALOFT
COURTESY OF A MEAN TROF OVER EASTERN NORTH AMERICA...BUT THE TROF
GRADUALLY DEAMPLIFIES LATE IN THE PERIOD. WE BEGIN AT 12Z SATURDAY
WITH THE AXIS OF THE EASTERN UPPER TROF JUST TO THE EAST AND MOVING
AWAY. THINK ANY LEFTOVER NW FLOW PRECIP WILL HAVE ENDED AROUND
DAYBREAK SATURDAY. A SHORT WAVE RIDGE WILL BRING COLD HIGH PRESSURE
DOWN ACROSS THE REGION ON SATURDAY THAT SHOULD HAVE TEMPS WELL BELOW
NORMAL. THE CENTER OF HIGH PRESSURE WILL MOVE DOWN ACROSS THE
WESTERN CAROLINAS AROUND SUNRISE ON SUNDAY...PERFECT TIMING TO ALLOW
FOR CLEAR SKY AND CALM WIND THAT PERMITS RADIATIONAL COOLING DOWN
BELOW FREEZING ACROSS MOST OF THE FCST AREA. THIS WILL MISS THE
OPENING OF OUR FROST/FREEZE PROGRAM BY TWO DAYS...TOO EARLY. THE AIR
MASS SHOULD MODERATE A BIT ON SUNDAY. A SHORT WAVE DROPPING DOWN IN
THE NW FLOW SHOULD AFFECT MAINLY THE MTNS EARLY NEXT WEEK. THE
PROBLEM IS THAT THE OPERATIONAL 12Z GFS AND 00Z ECMWF ARE MORE THAN
12 HRS OFF WITH THE TIMING. ALTHO PRECIP POTENTIAL SHOULD BE LIMITED
TO THE HIGHER TERRAIN NEAR THE TN BORDER...THE TIMING DISCREPANCY
HAS THE SLIGHT CHANCE/CHANCE OF PRECIP SMEARED OUT ACROSS SUNDAY
NIGHT BECAUSE OF THE EARLIER GFS THROUGH MONDAY EVENING BECAUSE OF
THE LATER ECMWF.  ONCE THIS SYSTEM MOVES THROUGH...TUESDAY SHOULD BE
QUIET...WITH TEMPS RETURNING ABOVE NORMAL.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...VFR/MVFR/IFR CONDITIONS WILL PREVAIL THROUGH THIS TAF
PERIOD.  HIGH PRESSURE SLIDING EAST ACROSS THE MID ATLANTIC WILL
WEDGE DOWN ACROSS THE REGION BY MORNING.  IN RESPONSE...CURRENT SSW
WINDS WILL BACK TO THE NE AND CIGS WILL LOWER AS MOIST UPGLIDE
REGIME INITIATES.  INITIALIZED TAF AT VFR THROUGH 08Z BEFORE CIGS
BEGIN TO LOWER TO MVFR AS WINDS BACK NE...THEN TO IFR JUST BEFORE
DAYBREAK.  SPED UP ONSET OF RADZ FROM PREVIOUS FCST BY AN HOUR OR
SO...THUS TAF FEATURES IFR CONDITIONS AMIDST WX MENTION BY
12Z...LASTING THROUGH THE PERIOD DESPITE MODELS BEING OPTIMISTIC
REGARDING IMPROVEMENT LATE IN THE DAY.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH ADJUSTMENTS REGARDING
TIMING OF PRECIP ONSET...AND DURATION.  INITIALIZED ALL TAFS VFR
BEFORE INTRODUCING RESTRICITIONS BY EARLY MORNING IN THE WAY OF
CIGS/VISB...ALONG WITH BACKED NE FLOW AT ALL SITES ASIDE FOR KAVL.
EXPECTING THESE CONDITIONS TO CONTINUE AS MOIST UPGLIDE REMAINS
OVERHEAD LEADING TO PERSISTENT RADZ THROUGH THE DAY.  DID REMOVE
MENTION OF WX AT KAND LATE IN THE PERIOD AS BEST UPGLIDE REGION
ADVECTS SLIGHTLY NORTH BY PERIODS END.

OUTLOOK...LOW LEVEL MOISTURE REMAINS ACROSS THE REGION FOR THE
BETTER PART OF THIS WEEK...WHICH COULD RESULT IN PERIODIC FLIGHT
RESTRICTIONS. A COLD FRONT WILL KEEP CHANCES OF PRECIPITATION ACROSS
THE AREA THU...POSSIBLY LINGERING INTO FRI.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       HIGH 100%     MED   64%     MED   71%     MED   73%
KGSP       HIGH 100%     MED   64%     HIGH  88%     HIGH  90%
KAVL       HIGH 100%     HIGH  93%     HIGH  86%     HIGH 100%
KHKY       HIGH 100%     MED   60%     MED   77%     HIGH  90%
KGMU       HIGH 100%     MED   64%     HIGH  88%     HIGH  90%
KAND       HIGH 100%     MED   71%     HIGH  86%     HIGH  80%

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...NONE.
SC...NONE.

&&

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


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