791  
FXUS62 KGSP 041450  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
950 AM EST WED MAR 4 2015  
   
SYNOPSIS
 
 
VERY WARM AND MOIST AIR WILL RETURN TO THE AREA TODAY AHEAD OF AN  
APPROACHING COLD FRONT. THIS FRONT IS FORECAST TO PASS THROUGH THE  
AREA ON THURSDAY...WITH COOL AND DRY HIGH PRESSURE RETURNING FOR  
FRIDAY AND INTO THE WEEKEND.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AS OF 0945AM...REMNANT COOL POOL STILL STUBBORNLY HANGING ON OUTSIDE  
OF THE MOUNTAINS DESPITE SW WINDS. MOUNTAIN TEMPS STILL REMAIN CLOSE  
TO 15 DEGREES WARNER THAN THE PIEDMONT. ALL SHORT TERM GUIDANCE  
CONTINUES TO INDICATE THAT THE WARM AIR WILL EVENTUALLY PREVAIL  
TODAY. STILL EXPECT THAT THE LOW STRATUS AND FOG WILL MIX OUT IN THE  
EARLY AFTERNOON. WILL LET THE FOG ADVISORY EXPIRE AT 1000L BUT  
FOLLOW IT UP WITH A SPS FOR PATCHY DENSE FOG UNTIL MIDDAY. STILL  
LOOKS LIKE MAX TEMPS WILL TOP OUT IN THE UPPER 60S TO LOWER 70S  
OUTSIDE THE MOUNTAINS WITH MID 60S MOUNTAIN VALLEYS. TRIMMED POPS  
BACK SOME TODAY OVER THE MOUNTAINS BASED ON CURRENT RADAR.  
 
AS OF 650 AM...QUITE THE FASCINATING SITUATION OVER THE FORECAST  
AREA THIS MORNING...AS THE MTN VALLEYS ARE AS MUCH AS 20 DEGREES  
WARMER THAN THE ADJACENT ERODING DAMMING AIR MASS OVER THE PIEDMONT.  
SOME OF THIS WARMTH IS BEGINNING TO SPREAD INTO THE FOOTHILLS...  
RESULTING IN IMPROVING VISBY (ALBEIT WITH STILL VERY LOW CEILINGS).  
THE DENSE FOG ADVISORY WILL BE ALLOWED TO CONTINUE AS ADVERTISED...  
BUT IT APPEARS THAT DENSE FOG WILL BE PATCHY AT WORST ACROSS THE  
FOOTHILLS THROUGH THE REMAINDER OF THE MORNING. OTHERWISE...PATCHY  
RAIN/SHOWERS CONTINUE NEAR THE TENN BORDER...WITH THE BULK OF  
ACTIVITY REMAINING WEST OF THE FORECAST AREA.  
 
DENSE FOG IS SLOWLY BUT SURELY EXPANDING ACROSS THE PIEDMONT THIS  
MORNING WITHIN WARM/MOIST ADVECTIVE/DECAYING WEDGE REGIME. AS  
SUCH...THE DENSE FOG ADVISORY APPEARS TO BE VERY WELL PLACED...AND  
WILL REMAIN IN EFFECT UNTIL 15Z.  
 
THE BULK OF SHOWER ACTIVITY CONTINUES TO DEVELOP ACROSS THE GREAT  
TENN VALLEY AND CUMBERLAND PLATEAU AREAS THIS MORNING...LIFTING  
PRIMARILY WEST OF THE APPALACHIANS WITHIN DEEP SW FLOW ALOFT. THIS  
PROBABLY ISN/T GOING TO CHANGE A WHOLE LET OVER THE NEXT 12-18  
HOURS...AS THIS IS WHERE THE BETTER FORCING AND MOISTURE PROFILES  
WILL REMAIN THROUGH THE DAY...UNDER PERSISTENT DEEP SW FLOW.  
STILL...CHANCE POPS APPEAR WARRANTED ALONG THE TENN BORDER THROUGH  
THE DAY...WITH 50-60 POPS RESERVED PRIMARILY FOR THE SMOKIES AND  
SURROUNDING AREAS...WHICH IS SLIGHTLY MORE ALONG THE TRAJECTORY OF  
THE SHOWER GENERATION AREA...AND STANDS THE BEST CHANCE OF SEEING  
SHOWERS INITIATE IN RESPONSE TO MECHANICAL LIFT ASSOCIATED WITH THE  
SW FLOW.  
 
THE AIR MASS ABOVE THE DRAINING COOL POOL IS VERY WARM...WITH H8  
TEMPS OF +10 TO +13 REPORTED ACROSS THE REGION AT 00Z. ONCE THE FOG  
AND LOW STRATUS BURN OFF...TEMPS WILL SOAR ACROSS THE AREA...LIKELY  
REACHING THE 70S ACROSS MUCH OF THE PIEDMONT THIS AFTERNOON . IN  
FACT...IF THE GRUNGE DISSIPATES EARLIER THAN CURRENTLY  
ANTICIPATED...EVEN THIS MAY PROVE TO BE TOO COOL...AND WOULD NOT BE  
SURPRISED TO SEE EXTREME SOUTHERN PIEDMONT AREAS TOP OUT NEAR 80.  
 
POPS WILL GRADUALLY RAMP UP ACROSS THE MTNS THIS EVENING...AS  
COLD/ANAFRONT GRADUALLY BUILDS INTO THE FORECAST AREA. DUE TO THE  
ANAFRONT NATURE OF THE BOUNDARY...TIMING OF THE WIND SHIFT INTO THE  
AREA WILL DICTATE HOW SOON LIKELY/CATEGORICAL CHANCES FOR RAIN WILL  
DEVELOP OVER THE FORECAST AREA...AND THESE THINGS NEVER SEEM TO MOVE  
AS FAST AS THE MODELS SUGGEST. THEREFORE...THE HIGHEST POPS HAVE  
BEEN DELAYED UNTIL AFTER MIDNIGHT...CATEGORICAL ACROSS THE  
MTNS...TAPERING TO HIGH CHANCE/LIKELY ACROSS THE PIEDMONT BY  
DAYBREAK THU.  
 
COLD AIR MAY BEGIN FILTERING INTO THE FAR WESTERN MTN VALLEYS BY  
DAYBREAK THU...WITH PROFILES EXHIBITING A TREMENDOUS WARM NOSE...AND  
FREEZING RAIN BEING THE PRIMARY WINTRY P-TYPE. WHILE IT APPEARS THAT  
FREEZING RAIN WILL BE LIKELY AT SOME POINT DURING THIS EVENT ACROSS  
THE WESTERN MTN VALLEYS...TIMING OF THE ARRIVAL OF COLD AIR IS STILL  
HIGHLY UNCERTAIN...AND SUSPECT DAYBREAK THURSDAY IS THE  
EARLIEST THAT THIS WOULD OCCUR. THEREFORE...NO ADVISORIES WERE  
ENTERTAINED ON THIS SHIFT.  
 

 
   
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
 
 
AT 300 AM EST WEDNESDAY...ON THURSDAY MORNING AN UPPER TROUGH WILL  
EXTEND FRONT EASTERN CANADA TO THE SOUTHERN PLAINS...WITH A WELL  
DEFINED SHORTWAVE MOVING THROUGH IT OVER THE UPPER MS RIVE VALLEY  
AND SOUTHERN PLAINS. THE TROUGH DEAMPLIFIES SOMEWHAT BY  
FRIDAY...WHILE AN UPPER LOW CLOSES OFF IN NW MEXICO. THE SHORTWAVE  
MOVING THROUGH BECOMES MORE CHANNELED...APPROACHING THE SOUTHERN  
APPALACHIANS IN THE MORNING. A SECOND AND MORE ROBUST SHORTWAVE  
APPROACHES THE MOUNTAINS LATER IN THE DAY...CROSSING THE MOUNTAINS  
BY FRIDAY EVENING...AND MOVING TO THE SOUTHERN EDGE OF OUR AREA LATE  
SATURDAY NIGHT.  
 
AT THE SURFACE...ON THURSDAY MORNING A STRONG COLD FRONT WILL BE  
LOCATED JUST SE OF OUR AREA...WITH A SURFACE WAVE MOVING ALONG IT  
OVER SC. MOISTURE WILL EXTEND WELL BEHIND THE FRONT INTO THE MS  
RIVER VALLEY...AND POST FRONTAL PRECIPITATION. THE NAM EVEN SHOWS  
SOME INSTABILITY AND SHEAR BEHIND THE BOUNDARY OVER UPSTATE SC AT  
MIDDAY. AS THE FRONT MOVES SE DURING THE DAY...COLD ADVECTION WILL  
SPREAD OVER THE NC MOUNTAINS. MODEL SOUNDINGS ARE INITIALLY TO WARM  
AT THE TOP OF THE MOIST LAYER TO SUPPORT ICE NUCLEATION...AND  
FREEZING RAIN IS EXPECTED BY LATE IN THE DAY. DRYING FROM THE TOP  
DOWN WILL RAPIDLY LESSEN THE CHANCE OF PRECIPITATION IN THE  
EVENING...BUT RAPID COOLING WILL BRING THE TOP OF THE MOIST LAYER TO  
THE POINT OF ICE NUCLEATION...SUPPORTING A CHANGEOVER FROM FREEZING  
RAIN TO SNOW BEFORE PRECIPITATION ENDS LATE THURSDAY NIGHT. FRIDAY  
AND FRIDAY NIGHT FEATURE DRY AND COOL CONDITIONS.  
 

 
   
LONG TERM /SATURDAY THROUGH TUESDAY/
 
 
AT 300 AM EST WEDNESDAY...ON SATURDAY MORNING A WELL AMPLIFIED UPPER  
TROUGH WILL EXTEND FROM NE CANADA TO THE SOUTHERN APPALACHIANS...  
WHILE A CLOSED UPPER LOW WILL BE OVER NW MEXICO. THE TROUGH LOSES  
SOME AMPLITUDE BY SUNDAY...WHILE THE UPPER LOW FILLS AND CROSSES  
NORTHERN MEXICO. THE REMAINS OF THE UPPER LOW CROSS THE SOUTHERN  
PLAINS ON MONDAY...RESULTING IN LOW AMPLITUDE RIDGING OVER THE  
SOUTHERN APPALACHIANS...WHILE NORTHERN STREAM FLOW BECOMES ZONAL. ON  
TUESDAY THE ECMWF AND GFS DIVERGE...WITH THE FORMER HAVING ZONAL  
FLOW OVER THE SE...AND THE LATER MAINTAINING A TROUGH IN THE LOWER  
MS RIVER VALLEY AND A RIDGE TO THE EAST.  
 
AT THE SURFACE...ON SATURDAY DRY HIGH PRESSURE WILL EXTEND FROM  
CHESAPEAKE BAY TO TX...WHILE A STATIONARY FRONT WILL EXTEND FROM S FL  
TO NEAR THE YUCATAN PENINSULA. MOISTURE AND PRECIPITATION ASSOCIATED  
WITH THIS FRONT IS EXPECTED TO REMAIN SOUTH OF OUR AREA. A DRY COLD  
FRONT RAPIDLY CROSSES OUR AREA SATURDAY NIGHT...REACHING THE GA  
COAST BY SUNDAY MORNING...WHILE THE STATIONARY FRONT REMAIN OVER S  
FL. ON MONDAY A SURFACE WAVE DEVELOPS ON THE STATIONARY FRONT IN THE  
WESTERN GULF OF MEXICO. MOISTURE IS EXPECTED TO SPREAD FARTHER NORTH  
OVER THE FRONT IN FL...PERHAPS SUPPORTING SMALL POPS AS FAR N AS OUR  
AREA. BY TUESDAY THE SURFACE WAVE REACHES THE SC COAST...WITH  
PRECIPITATION IN ISENTROPIC UPGLIDE EXTENDING BACK THE THE SOUTHERN  
APPALACHIANS.  
 

 
   
AVIATION /15Z WEDNESDAY THROUGH SUNDAY/
 
 
AT KCLT...LIFR CONDITIONS WILL CONTINUE UNTIL LATE MORNING.  
CONDITIONS HAVE BEEN WELL-BEHAVED IN NOT FALLING BELOW AIRPORT  
MINIMUMS...AND WILL TO KEEP THEM THAT WAY IN THE FORECAST. EXACT  
TIMING OF LIFTING OF THE FOG/CIGS IS UNCERTAIN AS USUAL...BUT 16Z  
SEEMS TO BE A REASONABLE GUESSTIMATE IN LIGHT OF THE SHALLOWNESS OF  
THE MOISTURE DEPTH...AND THE WARMING THAT IS OCCURRING ACROSS THE  
AREA. VFR CONDITIONS ARE EXPECTED BY EARLY AFTERNOON...ALONG WITH  
GUSTY SW WINDS. GUSTS WILL DIMINISH THIS EVENING...BUT SW WINDS WILL  
REMAIN AROUND 10 KTS THROUGH THE OVERNIGHT. CIGS SHOULD BEGIN TO  
LOWER AGAIN LATE TONIGHT...IN ADVANCE OF AN APPROACHING COLD FRONT.  
RAIN CHANCES WILL ALSO INCREASE...BUT THE BEST CHANCES ARE EXPECTED  
TO HOLD OFF UNTIL AFTER THE END OF THE FORECAST PERIOD.  
 
ELSEWHERE...WHILE PERIODS OF VLIFR VISBY ARE EXPECTED TO PERSIST AT  
KAND THROUGH 14Z OR SO...SIGNIFICANT IMPROVEMENT HAS BEEN NOTED AT  
THE FOOTHILLS SITES OVER THE PAST HOUR OR SO. NEVERTHELESS...LIFR  
CIGS WILL PERSIST THROUGH LATE-MORNING OR SO AT THE PIEDMONT/FHILLS  
TERMINALS. OTHERWISE...SIMILAR CONDITIONS TO KCLT . MEANWHILE...VFR  
CONDITIONS ARE EXPECTED TO PERSIST AT KAVL THROUGH AT LEAST THE  
DAYLIGHT HOURS...BEFORE LOWERING AGAIN TONIGHT IN ADVANCE OF A COLD  
FRONT. RAIN MAY ALSO APPROACH LATE TONIGHT...AS THE COLD FRONT DRAWS  
NEARER.  
 
OUTLOOK...A COLD FRONT WILL REMAIN OVER THE REGION THROUGH  
THURSDAY...BRINGING CHANCES FOR HEAVIER RAINFALL AND LOW CIGS/VSBYS  
TO THE AREA. VFR CONDITIONS ARE EXPECTED TO RETURN FOR FRIDAY  
THROUGH THE WEEKEND.  
 
CONFIDENCE TABLE...  
 
13-19Z 19-01Z 01-07Z 07-12Z  
KCLT HIGH 95% HIGH 100% HIGH 100% HIGH 100%  
KGSP HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KAVL MED 74% HIGH 100% HIGH 100% HIGH 100%  
KHKY MED 77% 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...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR GAZ010-017-  
018-026-028-029.  
NC...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR NCZ035>037-  
056-057-068>072-082-502-504-506-508-510.  
SC...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR SCZ001>014-  
019.  
 

 
 

 
SYNOPSIS...WIMBERLEY  
NEAR TERM...JDL/LG  
SHORT TERM...JAT  
LONG TERM...JAT/WIMBERLEY  
AVIATION...JDL  
 
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