370  
FXUS62 KGSP 180309  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
1009 PM EST SUN FEB 17 2019  
   
SYNOPSIS
 
 
A MOIST WARM FRONT WILL CONTINUE TO MOVE NORTH FROM GEORGIA  
TONIGHT AS LOW PRESSURE CROSSES TENNESSEE. EXPECT CANADIAN HIGH  
PRESSURE RIDGE DOWN INTO OUR AREA FROM NORTH DAKOTA BY LATE MONDAY  
GIVING US A SHORT DRY PERIOD. RAIN RETURNS ON TUESDAY AS A SERIES  
OF LOW PRESSURE SYSTEMS WILL TRACK FROM SOUTHWEST TO NORTHEAST  
ACROSS THE REGION, RESULTING IN A PERSISTENT MOIST PATTERN THROUGH  
MOST OF THE WEEK.  
 

 
   
NEAR TERM /THROUGH MONDAY/
 
 
AS OF 945 PM EST SUNDAY: REGIONAL RADARS LATE THIS EVENING DEPICT A  
FAIRLY SOLID MODERATE TO HEAVY RAIN SHIELD EXTENDING TO THE  
SOUTHWEST ACROSS NORTHERN ALABAMA AND GEORGIA IN ADVANCE OF H5  
VORTICITY LOBES EMBEDDED IN THE WSW FLOW ALOFT, AND AHEAD OF A WEAK  
SURFACE COLD FRONT. ISENTROPIC LIFT AND MOISTURE ARE MAXIMIZING  
ACROSS THE FORECAST AREA AT PRESENT, BUT UPGLIDE SHOULD DIMINISH  
FROM THE WEST AFTER 06Z AND THE UPPER DPVA SHOULD PASS BY 09Z, SO  
THE DURATION OF THE HEAVIEST PART OF THE EVENT WILL BE FAIRLY SHORT-  
LIVED. SOME 1 TO 1.5 INCH RAINFALL TOTALS WILL BE POSSIBLE ALONG THE  
TN BORDER AND IN SOUTHWEST MOUNTAIN UPSLOPE FLOW AREAS THROUGH  
DAYBREAK, BUT STREAM AND RIVER RISES HAVE BEEN FAIRLY MODEST SO FAR.  
THE CURRENT THINKING IS THAT ANY OVERNIGHT HYDRO ISSUES IN THE  
SOUTHWEST MOUNTAINS WILL BE ISOLATED. THUS, NO FLOOD WATCHES WILL BE  
POSTED FOR THE REMAINDER OF THIS EVENT. THIS WILL CERTAINLY PRODUCE  
MOIST CONDITIONS, HOWEVER, FOR SUBSEQUENT RAINFALL THROUGH THE WEEK.  
 
MEANWHILE, COLD AIR DAMMING WILL CONTINUE TO WEAKEN OVERNIGHT AS THE  
PARENT HIGH PRESSURE SLIPS FARTHER OFFSHORE. DEVELOPING WESTERLY  
FLOW BY DAYBREAK WILL LEAD TO DOWNSLOPING AND SCOURING OF THE  
SURFACE WEDGE LAYER. THIS WILL CAUSE TEMPERATURES TO RISE SLIGHTLY  
OVERNIGHT AND THEN SHARPLY THROUGH TOMORROW AS THE LOW CLOUDS  
FINALLY SCATTER OUT AND INSOLATION IMPROVES WITHOUT ANY SIGNIFICANT  
THICKNESS FALLS FROM THE PASSING FRONT. THE DOWNSLOPE WARMING AND  
IMPROVING SUNSHINE SHOULD PERMIT A NICE WARMUP TO 60S HIGH  
TEMPERATURES IN MOST AREAS EAST OF THE MOUNTAINS MONDAY AFTERNOON.  
THIS BREAK IN THE RAINFALL FOR MOST OF MONDAY AND INTO MONDAY NIGHT  
COULD WELL BE THE LAST SIGNIFICANT DRY WEATHER OF THE UPCOMING WEEK.  
 

 
   
SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/
 
 
AS OF 255 PM EST SUNDAY: THE FCST WILL START OFF DRY ACROSS THE AREA  
AS A BROAD CANADIAN HIGH BUILDS SOUTH ACROSS THE GLAKES REGION  
AND BEGINS TO RIDGE DOWN THE EAST COAST. TEMPS WILL DROP TO ARND  
FREEZING ACROSS THE NC MTNS WHILE A DEVELOPING WARM FRONT BEGINS TO  
APPROACH THE AREA ARND DAYBREAK. THERE IS SOME UNCERTAINTY WITH THE  
LEVEL OF MOISTURE WITH THIS FRONT AS THE NAM CONTINUES TO HAVE VERY  
LITTLE QPF RESPONSE BY 12Z TUE. LIKELY A NULL CHANCE OF ANY WINTRY  
PRECIP TUE MORNING AS ANY LIGHT PRECIP SHUD NOT ARRIVE UNTIL TEMPS  
WARM ABV FREEZING. TEMPS WONT RISE MUCH DURING THE DAY...PROBABLY  
REMAINING 40S ALL LOCALES AS SFC-BASED CAA CONTINUES AND CLOUD COVER  
INCREASES.  
 
THE FCST BECOMES QUITE TRICKY TUE NIGHT AS A PARENT 1040 MB HIGH  
SETS UP ACROSS THE ERN GLAKES. THE HIGH CONFIG LOOKS TO BE CLASSICAL  
IN NATURE AND BAD FOR WINTRY PRECIP ACROSS THE COLDER NC MTN AREAS  
AS A STG LLVL SW/LY JET BRINGS IN A SIGFNT WARM NOSE ALOFT. MODEL  
TEMP GUIDANCE HAS TRENDED DOWN OVERALL SO MIXED IN LOWER VALUES WITH  
THE PREVIOUS FCST NUMBERS. THIS GAVE MORE AREAS FOR ACCUM FZRA OVER  
THE NC MTNS AND EVEN A -RA/FZRA MIX ACROSS THE NRN FTHILLS AND NRN  
NC PIEDMONT. TEMPS LOOK TO HOVER JUST NORTH OF FREEZING GENERALLY  
OUTSIDE THE NRN MTNS...BUT A DEGREE OR TWO DIFFERENCE IN SFC TW/S  
COULD CREATE WINTRY/ICY PRECIP.  
 
THE AMT OF PRECIP IS NOT TOTALLY CERTAIN AS THERE COULD BE ROBBING  
CONVEC SOUTH AND THE OVERALL DEPTH OF SATURATION WILL LIKELY BE  
LIMITED TO ARND H7. THEREFORE...ICE NUCLEI MAY NOT BE ACTIVATED ESP  
AS THE MORNING PROGRESSES...PER THE LATEST GFS/NAM SOUNDINGS.  
THUS...WILL ANTICIPATE AN ONSET OF FREEZING PRECIP ARND 02Z WITH  
LIKELY A SWITCH TO -FZDZ...BEFORE A CHANGEOVER TO ALL RAIN OCCURS  
ARND 14Z. EXPECT A LIGHT GLAZE OF ICE AT MOST ACROSS THE  
NON/MTNS...AND THE BEST ICE ACCUM POTENTIAL OF A COUPLE TENTHS OVER  
THE NRN NC MTNS AND HIGH ELEV NRN FTHILLS...AND PERHAPS EVEN FURTHER  
SOUTH ACROSS THE BLACK MTNS. RIGHT NOW...THIS EVENT IS CERTAINTY ADV  
LEVEL AND AS THE FCST CHANGES WARNING LEVEL CONDS COULD DEVELOP. A  
LIGHT COLD RAIN WILL CONTINUE THRU PERIOD WITH TEMPS ONLY REACHING  
THE L40S NORTH AND L50S OVER THE FAR SW/RN ZONES AS THE WEDGE IS  
SLOW TO LIFT OUT OF THE AREA.  
 
ANOTHER ISSUE TUE NIGHT INTO WED WILL BE THE POTENTIAL FOR STREAM  
FLOODING ACROSS THE SW/RN NC MTNS. WPC HAS THE AREA IN A DAY 3  
SLIGHT RISK OF FLOODING THE FAVORED UPSLOPE SW-FACING REGIONS WILL  
LIKELY RECIEVE ARND 2 INCHES TO NEAR 3 INCHES BY THEN IN CONTINUED  
HIGH SATURATED SOILS.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
 
 
AS OF 200 PM SUN: AN ACTIVE PATTERN IS STILL DEPICTED ACROSS THE CWFA  
THROUGHOUT THE MEDIUM RANGE, STILL WITH A STRONG RIDGE CENTERED OVER  
THE EASTERN CARIBBEAN AND DEEP TROUGHING OVER THE SOUTHERN ROCKIES  
AND VICINITY. AS LOW PRESSURE TRAVERSES THE GREAT LAKES REGION EARLY  
THURSDAY, A COLD FRONT WILL MOVE THRU THE LOWER MISSISSIPPI VALLEY,  
THEN PIVOT ACROSS THE APPALACHIANS AS THE SFC LOW MOVES THRU NEW  
ENGLAND. THAT WILL PROMOTE EROSION OF THE MIDWEEK CAD AFFECTING OUR  
AREA, THOUGH WITH THE BOUNDARY LINGERING, UNSETTLED WEATHER WILL  
PERSIST. FURTHERMORE, GLOBAL MODELS DEPICT YET ANOTHER SEASONABLY  
STRONG SFC HIGH MOVING EASTWARD NORTH OF THE BOUNDARY, SUGGESTING CAD  
WILL RETURN BY FRIDAY. TEMPERATURES WITHIN THE WEEKEND CAD EVENT  
CURRENTLY DO NOT LOOK COLD ENOUGH FOR WINTRY PRECIP, SO THE MAIN  
IMPACT INITIALLY MAY JUST BE TO PROLONG THE ALREADY CLOUDY/DAMP  
CONDITIONS.  
 
MODEL CONSENSUS SHOWS PATTERN CHANGE FINALLY OCCURRING NEXT WEEKEND  
AS A SHORTWAVE EJECTS FROM THE ROCKIES, CYCLOGENESIS OCCURS SOMEWHERE  
TO OUR NORTHWEST, AND A COLD FRONT SWINGS THRU THE SOUTHEAST. THIS  
FRONT IS MOST LIKELY TO REACH OUR AREA ON SUNDAY. THE EUROPEAN AND  
CANADIAN SOLUTIONS DEPICT A STRONGER LOW AND BETTER DEFINED COLD  
FRONT THAN DOES THE GFS, THOUGH ALL OF THEM SHOW AT LEAST MODEST  
INSTABILITY IN THE WARM SECTOR PRECEDING THE FRONT, WHILE CAD  
PERSISTS FOR SOME OF OUR AREA. THESE TRENDS ARE WORTH WATCHING AS  
THEY IMPLY SOME SEVERE WEATHER THREAT MAY RESULT FOR THOSE PARTS OF  
OUR AREA ALONG/SOUTH OF THE WEDGE BOUNDARY.  
 
ALL IN ALL IT IS DIFFICULT TO IDENTIFY ANY MEANINGFUL BREAK IN PRECIP  
CHANCES BETWEEN WEDNESDAY EVENING AND SATURDAY MORNING, SO WE WILL  
ADVERTISE AT LEAST LIKELY POPS FOR NEARLY THE WHOLE AREA DURING THAT  
TIMEFRAME. A LIMITED DIURNAL RANGE IS EXPECTED DUE TO CLOUD COVER  
AND/OR WEDGING, BUT OVERALL TEMPS WILL REMAIN NEAR CLIMO. CHANCES  
WERE ALLOWED TO DROP A BIT BY SATURDAY AFTERNOON AS WARM FRONT SHIFTS  
NORTHWARD AHEAD OF THE DEVELOPING LOW.  
 

 
   
AVIATION /03Z MONDAY THROUGH FRIDAY/
 
 
AT KCLT AND ELSEWHERE: STEADIER RAINFALL ACROSS THE TERMINAL  
FORECAST AREA HAS PRODUCED MOSTLY IFR CIGS LATE THIS EVENING, BUT  
WITH SOME LOCATIONS BRIEFLY SCATTERING TO MVFR, WHILE OTHERS SINK TO  
LIFR. ANTICIPATE MORE WIDESPREAD LIFR THROUGHOUT FOR AT LEAST THE  
EARLY OVERNIGHT HOURS WHILE THE STEADY PRECIP FALLS THROUGH 09Z.  
CONDITIONS WILL BEGIN TO IMPROVE FROM THE WEST BEFORE DAYBREAK AS  
FLOW TURNS WESTERLY AND A LIGHT DOWNSLOPE FLOW DEVELOPS EAST OF THE  
MOUNTAINS. IT MAY TAKE SOME TIME, PERHAPS UNTIL LATE MORNING, TO  
FINALLY SCATTER THE MOISTURE IN THE BOUNDARY LAYER, BUT ONCE IT  
STARTS HAPPENING IT SHOULD SCATTER QUICKLY THROUGH NOON. STEADY BUT  
LIGHT WINDS WILL BECOME NW OVERNIGHT AND THEN WESTERLY THROUGH  
MONDAY MORNING. ANTICIPATE SOME LOW END GUSTS DEVELOPING IN THE  
WESTERLY FLOW WITH MIXING FOR MUCH OF MONDAY, WITH PERHAPS MORE  
ROBUST GUSTS WELL INTO THE 20S AT KAVL IN THE FRENCH BROAD VALLEY  
FLOW.  
 
OUTLOOK: AFTER BRIEF IMPROVEMENT LAST THROUGH MOST OF MONDAY NIGHT,  
A SERIES OF LOW PRESSURE SYSTEMS WILL MOVE THROUGH OR NEAR THE  
REGION THROUGH MUCH OF THE REST OF THE WEEK. THIS WILL PRODUCE  
PRECIPITATION AND ASSOCIATED RESTRICTIONS FOR LONG PERIODS OF TIME  
DURING EACH WAVE OF PRECIPITATION.  
 
CONFIDENCE TABLE...  
 
03-09Z 09-15Z 15-21Z 21-00Z  
KCLT HIGH 85% MED 60% HIGH 100% HIGH 100%  
KGSP HIGH 81% LOW 52% HIGH 100% HIGH 100%  
KAVL MED 79% MED 60% HIGH 100% HIGH 100%  
KHKY MED 75% MED 68% HIGH 100% HIGH 100%  
KGMU MED 77% LOW 52% HIGH 100% HIGH 100%  
KAND MED 77% MED 60% 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:  
 
WWW.WEATHER.GOV/GSP/AVIATION  
 

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

 
 

 
SYNOPSIS...DEO  
NEAR TERM...HG/PM  
SHORT TERM...SBK  
LONG TERM...WIMBERLEY  
AVIATION...HG/PM  
 
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