186  
FXUS61 KRNK 212316  
AFDRNK  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BLACKSBURG VA  
716 PM EDT MON AUG 21 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL GRADUALLY MOVE OFF THE MID ATLANTIC COAST  
TONIGHT, ALLOWING WINDS TO TURN SOUTHERLY AND BRING A RETURN OF  
DEEPER MOISTURE TO THE REGION ALONG WITH A CHANCE FOR SHOWERS  
AND THUNDERSTORMS MAINLY ALONG AND WEST OF THE BLUE RIDGE. A  
COLD FRONT WILL PASS OVER THE AREA WEDNESDAY, BRINGING A BETTER  
CHANCE FOR SHOWERS AND STORMS TO THE APPALACHIANS AND CENTRAL  
MID ATLANTIC REGION.  
 

 
   
NEAR TERM /THROUGH TUESDAY/
 
 
AS OF 716 PM EDT MONDAY...SURFACE METARS AND SPC MESOANALYSIS  
GRAPHICS DEPICTS SURFACE CONVERGENCE BOUNDARY/TROUGH WHICH  
EXTENDS ESSENTIALLY ALONG MUCH OF THE BLUE RIDGE. THIS IS  
HELPING TO SPARK WIDELY SCATTERED THUNDERSTORMS IN CONJUNCTION  
WITH MODERATELY UNSTABLE AIR MASS (~2000 J/KG MUCAPE) IN THE  
PIEDMONT. COVERAGE AND STRENGTH OF STORMS WERE MORE LIMITED  
ALONG THE SOUTHERN BLUE RIDGE IN WILKES AND WATAUGA COUNTIES IN  
NC. CELLS THIS AFTERNOON HAVE BEEN SLOW EAST-SOUTHEAST MOVERS  
AND A FEW HAVE PRODUCED LOCALLY HIGH RAINFALL RATES,  
PARTICULARLY IN CENTRAL BEDFORD COUNTY AND EARLIER IN NORTHERN  
AMHERST COUNTY IN VA. MAY CONTINUE TO SEE POP-UP ISOLATED TO  
WIDELY SCATTERED STORMS THROUGH SUNSET, A FEW WHICH COULD BECOME  
LOCALLY STRONG BUT SEVERE IS NOT PRESENTLY ANTICIPATED ATTM. AN  
EXPECTED DECREASE IN COVERAGE AND INTENSITY IS EXPECTED BY 10  
PM WITH STABILIZATION OF THE PBL. INDICATION FROM RAP-BASED RH  
CROSS SECTIONS SHOWS CLEARING AND, AS PBL DECOUPLES, THAT SHOULD  
ENCOURAGE A GOOD COVERAGE OF PATCHY RADIATION FOG. OUTSIDE OF  
THE WESTERN RIVER VALLEYS, AREAS WHICH SAW RAIN THIS AFTERNOON  
POSE THE BEST CHANCE AT SEEING PATCHY FOG. NO CHANGES MADE TO  
LOWS.  
 
PREVIOUS NEAR-TERM DISCUSSION ISSUED AT 200 PM FOLLOWS...  
 
SURFACE HIGH PRESSURE WILL CONTINUE TO MOVE OFF THE VIRGINIA  
AND CAROLINA COAST TONIGHT. RETURN SOUTHWESTERLY FLOW WILL  
MAINTAIN AN INFLUX OF HEAT AND HUMIDITY INTO THE REGION. UNDER A  
WEAKLY CAPPED ENVIRONMENT THIS AFTERNOON, UPSLOPE FLOW HAS  
GENERATED ISOLATED SHOWERS AND THUNDERSTORMS ACROSS THE EASTERN  
SLOPES OF THE NORTH CAROLINA HIGH COUNTRY AND SOUTHWEST VIRGINIA  
BLUE RIDGE. SOME INSTABILITY SHOWERS HAVE ALSO POPPED ACROSS  
THE PIEDMONT. SOME LACK IN COVERAGE IS DUE TO THE ECLIPSE AS  
HEATING IS TEMPORARILY HALTED. SOME STORMS MAY CONTINUE INTO  
THIS EVENING AS THEY TRACK EAST IN ZONAL FLOW, BUT WILL FADE  
WITH LOSS OF HEATING. SKIES SHOULD BE MOSTLY CLEAR THROUGH  
MIDNIGHT THEN HIGH CLOUDS WILL ADVANCE OVER THE AREA THROUGH THE  
EARLY MORNING HOURS. THESE HIGH CLOUDS SHOULD NOT BE THICK  
ENOUGH TO DETER PATCHY FOG FROM FORMING IN MOUNTAINS AND RIVER  
VALLEYS. OVERNIGHT CONDITIONS WILL REMAIN MUGGY WITH LOWS IN THE  
60S.  
 
SURFACE HIGH PRESSURE WILL LOSE ITS INFLUENCE ON OUR WEATHER BY  
TUESDAY AFTERNOON. A LEE TROUGH AND SOUTHERLY UPSLOPE FLOW MAY  
HELP GENERATE A FEW STORMS ACROSS THE MOUNTAINS THROUGH THE  
AFTERNOON, BUT COVERAGE MAY BE LIMITED WITH INCREASE MIXING  
AHEAD OF AN APPROACHING FRONT. ANY DIURNAL SHOWERS WILL FADE  
WITH LOSS OF HEATING. THERE IS A SMALL CHANCE THAT PREFRONTAL  
SHOWERS MAY MAKE IT TO THE WESTERN SLOPES OF SE WV AND SW VA BY  
EVENING, HOWEVER THE BULK OF THE SHOWERS WILL COME WITH THE  
FRONT WEDNESDAY. WITH LIMITED COVERAGE OF SHOWERS, ABUNDANT  
SUNSHINE AND SOUTHERLY FLOW, AFTERNOON TEMPERATURES TUESDAY WILL  
WARM INTO THE MID TO UPPER 80S ACROSS THE MOUNTAINS TO THE  
LOWER 90S ACROSS THE FOOTHILLS AND PIEDMONT.  
 

 
   
SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/
 
 
AS OF 230 PM EDT MONDAY...  
 
SHORT WAVE CROSSES THROUGH THE BASE OF A BROAD, SOMEWHAT FLAT  
UPPER TROUGH OF MONDAY NIGHT. THIS WILL RESULT IN A CHANCE OF  
SHOWERS TUESDAY NIGHT. BETTER UPPER DIFFLUENCE AND COVERAGE OF  
PRECIPITATION WILL BE APPROACHING SOUTHEAST WEST VIRGINIA BY  
8AM/12Z WEDNESDAY MORNING.  
 
00Z ECMWF WAS BRINGING A PRE-FRONTAL TROUGH AND FRONT THROUGH  
SOUTHERN WEST VIRGINIA, VIRGINIA AND NORTHERN NORTH CAROLINA ON  
WEDNESDAY, WITH REASONABLE AGREEMENT FROM THE 12Z NAM AND GFS.  
THE EARLIER IN THE DAY THE FRONT CROSSES THROUGH, THE LESS  
INSTABILITY WILL BE AVAILABLE FOR SHOWERS AND THUNDERSTORMS  
UNTIL THE FRONT GETS FARTHER EAST. CLOUD COVER FROM ONGOING  
PRECIPITATION UPSTREAM WEDNESDAY MORNING WILL ALSO LIMIT  
INSTABILITY IN THE MOUNTAINS. HIGHER PROBABILITY OF SHOWERS AND  
THUNDERSTORMS TUESDAY NIGHT AND WEDNESDAY WILL REMAIN OVER THE  
MOUNTAINS DUE TO THE WEST WIND THAT WILL BE IN PLACE AHEAD OF  
THE FRONT. BY WEDNESDAY EVENING THE FOCUS WILL SHIFT TO THE  
PIEDMONT OF VIRGINIA AND NORTH CAROLINA.  
 
THE FRONT AND DEEPER MOISTURE MAY BE SLOW TO EXIT SOUTHERN  
VIRGINIA AND NORTHERN NORTH CAROLINA. CLEARING IN THOSE  
LOCATIONS MAY NOT OCCUR UNTIL LATE THURSDAY.  
 

 
   
LONG TERM /FRIDAY THROUGH MONDAY/
 
 
AS OF 130 PM EDT MONDAY...  
 
DEEPER UPPER TROF DEVELOPS IN THE EASTERN UNITED STATES WITH  
THE CANADIAN, ECMWF, AND GFS SHOWING ANOTHER STRONG SHORT  
WAVE/POTENTIAL UPPER LOW RE-ENFORCING THE TROF OVER THE GREAT  
LAKES ON MONDAY.  
 
FOR THE MID ATLANTIC REGION THE PRIMARY LONG WAVE TROF AXIS  
WILL CROSS THROUGH THE AREA ON FRIDAY. THEN NOT MUCH RECOVER IN  
500 MB HEIGHTS THROUGH MONDAY. BY FRIDAY MORNING 850MB  
TEMPERATURES ARE DOWN TO AROUND +12. AT THE SURFACE A LARGE HIGH  
PASSES THROUGH THE GREAT LAKES ON FRIDAY, THEN WEDGES DOWN THE  
EAST SIDE OF THE APPALACHIANS ON SATURDAY THROUGH MONDAY.  
SURFACE DEW POINTS AND PRECIPITABLE WATER VALUES ALSO DROP BY  
FRIDAY, DOWN UNDER AN INCH FOR PRECIPITABLE WATER AND INTO THE  
50S FOR DEW POINTS.  
 
SATURDAY, SUNDAY AND MONDAY SOME TRAPPED OR RETURN LOW LEVEL  
MOISTURE IN THE NORTHWEST NORTH CAROLINA MOUNTAINS, SPREADING  
NORTH, WEST OF THE APPALACHIANS EACH CONSECUTIVE DAY. SUNDAY  
ALSO HAS THE POTENTIAL FOR SCATTERED TO BROKEN MID AND HIGH  
CLOUDS ALONG WITH THE PASSAGE OF A WARM FRONT FROM THE WEST.  
WILL KEEP THE FORECAST DRY FRIDAY AND FRIDAY NIGHT WITH BELOW  
NORMAL TEMPERATURES THROUGH SUNDAY.  
 

 
   
AVIATION /00Z TUESDAY THROUGH SATURDAY/
 
 
AS OF 716 PM EDT MONDAY...  
 
GENERALLY VFR ACROSS MOST OF THE TAFS THROUGH MIDNIGHT. SHORT-  
LIVED/TEMPO MVFR RESTRICTIONS IN WIDELY SCATTERED THUNDERSTORMS  
AT ROANOKE AND LYNCHBURG POSSIBLE THROUGH 02Z. SCATTERED  
THUNDERSTORMS MAINLY FIRING ALONG OR JUST EAST OF THE BLUE  
RIDGE, SLOWLY MOVING EAST- SOUTHEAST. NOTED WINDS HAVE FLIPPED  
TO EASTERLY AT ROANOKE BEING AFFECTED BY CONVECTIVE OUTFLOW TO  
THE EAST. SHOULD BE A TEMPORARY CONDITION WITH WINDS GENERALLY  
PREVAILING SOUTH TO SOUTHWEST 4-6 KTS.  
 
AFTER MIDNIGHT, SHOULD SEE DEVELOPMENT OF PATCHY FOG AT  
LEWISBURG AND BLACKSBURG, AND LYNCHBURG AND DANVILLE ALSO STAND  
A GOOD SHOT AT FOG AS WELL GIVEN THAT THESE AREAS SAW  
SHOWERS/STORMS NEARBY TODAY. INDICATED IFR GENERALLY, WITH TEMPO  
LIFR FG AT LEWISBURG. ASIDE FROM THOSE, EXPECT VFR ELSEWHERE  
WITH WINDS LIGHT/VARIABLE.  
 
FOR TUESDAY, GENERALLY VFR WITH BUILDING CUMULUS AS ATMOSPHERE  
DESTABILIZES. POTENTIAL AGAIN EXISTS FOR ISOLATED TO WIDELY  
SCATTERED SHOWERS AND THUNDERSTORMS TO RE-DEVELOP IN THE MID TO  
LATE AFTERNOON THOUGH MORE WEST TO SOUTHWEST WINDS MAY LIMIT  
COVERAGE EVEN MORE SO THAN TODAY. THEREFORE, LEFT OUT OF THE  
TAFS ATTM. WINDS SOUTHWEST 4-7 KTS.  
 
EXTENDED AVIATION DISCUSSION...  
 
MOISTURE WILL CONTINUE TO INCREASE ON TUESDAY AS HIGH PRESSURE  
MOVES FARTHER OFFSHORE AHEAD OF ANOTHER COLD FRONT THAT WILL  
ARRIVE FROM THE NORTHWEST WEDNESDAY. THIS WILL AGAIN LEAD TO  
MORE AFTERNOON CLOUDS AND ISOLATED CONVECTION ACROSS THE  
MOUNTAINS TUESDAY AFTERNOON BUT OVERALL VFR AT THIS POINT.  
BETTER POTENTIAL FOR SUB- VFR WILL COME WEDNESDAY WHEN MORE  
WIDESPREAD SHOWERS AND STORMS ARRIVE WITH THE NEXT COLD FRONT.  
FLYING CONDITIONS SHOULD SLOWLY IMPROVE BEHIND THE PASSING COLD  
FRONT ON THURSDAY ALTHOUGH SUB-VFR CIGS MAY LINGER ACROSS  
SOUTHERN/WESTERN SECTIONS A WHILE LONGER.  
 

 
   
EQUIPMENT
 
 
AS OF 930 AM EDT MONDAY...  
 
KFCX DOPPLER RADAR IS EXPECTED TO BE BACK IN OPERATIONS AS EARLY  
AS WEDNESDAY EVENING (AUG 23RD). TECHNICIANS HAVE REPLACED THE  
BULL GEAR AND ARE REASSEMBLING THE RADAR TODAY AND TOMORROW  
WITH CALIBRATION WORKED ON WEDNESDAY.  
 

 
   
RNK WATCHES/WARNINGS/ADVISORIES
 
 
VA...NONE.  
NC...NONE.  
WV...NONE.  
 

 
 

 
SYNOPSIS...RCS  
NEAR TERM...AL/RCS  
SHORT TERM...AMS  
LONG TERM...AMS  
AVIATION...RCS  
EQUIPMENT...RCS  
 
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