647  
FXUS61 KRNK 240900  
AFDRNK  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BLACKSBURG VA  
500 AM EDT THU AUG 24 2017  
   
SYNOPSIS
 
 
A LARGE AREA OF HIGH PRESSURE OVER CENTRAL CANADA WILL MOVE  
INTO NEW ENGLAND AND WEDGE DOWN EAST OF THE APPALACHIANS THIS  
WEEKEND. THIS WILL BRING A HINT OF FALL TO THE REGION WITH  
BELOW NORMAL TEMPERATURES THROUGH SUNDAY, ALONG WITH A CHANCE  
FOR SHOWERS MAINLY ALONG AND WEST OF THE BLUE RIDGE.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AS OF 300 AM EDT THURSDAY...  
 
WEAK LOW LEVEL CONVERGENCE AND MOISTURE LINGER BEHIND THE COLD  
FRONT EAST OF THE BLUE RIDGE. KFCX RADAR HAS SHOWN ISOLATED  
SHOWERS POPPING UP FROM TIME TO TIME TONIGHT AND EXPECT THIS  
WILL CONTINUE TO BE THE CASE UNTIL A LARGE AREA OF HIGH PRESSURE  
MOVING OUT OF CENTRAL CANADA SLIDES INTO THE NORTHEASTERN US  
AND STARTS TO WEDGE DOWN EAST OF THE APPALACHIANS.  
 
SATELLITE IMAGERY SHOWS GOOD COVERAGE OF CLOUDS EAST OF THE  
RIDGE, BUT LESS COVERAGE TO THE WEST WILL ALLOW FOR SOME PATCHY  
FOG TO DEVELOP BY DAYBREAK. WITH DIURNAL HEATING THIS AFTERNOON AND  
SUPPORT FROM A DIGGING SHORT WAVE PASSING BY TO OUR NORTH  
EXPECT A ROBUST CUMULUS FIELD THIS AFTERNOON. OVERALL, EXPECT  
TODAY WILL BE GENERALLY DRY BUT WITH THE COMBINATION OF  
CONVECTIVE FORCING AND LINGERING LOW LEVEL CONVERGENCE WILL  
MENTION A SLIGHT CHANCE FOR SOME SPOTTY SHOWERS ALONG AND EAST  
OF THE BLUE RIDGE.  
 
DIURNAL CLOUDINESS WILL DISSIPATE WITH LOSS OF HEATING THIS  
EVENING AND WITH GOOD RADIATIONAL COOLING EXPECTED FOG TO  
DEVELOP LATE TONIGHT ESPECIALLY IN THE VALLEYS WEST OF THE BLUE  
RIDGE.  
 
IT WILL BE NOTICEABLY COOLER TODAY WITH HIGHS IN THE LOWER 80S  
EAST OF THE RIDGE TO MIDDLE 70S WEST. LOWS TONIGHT WILL BE  
REFRESHING WITH READINGS GENERALLY AROUND 60 EAST TO LOW/MID 50S  
WEST AND SOME UPPER 40S IN THE VALLEYS.  
 

 
   
SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/
 
 
AS OF 400 AM EDT THURSDAY...  
 
A LARGE AREA OF HIGH PRESSURE WILL SLIDE SLOWLY EASTWARD FROM  
THE GREAT LAKES TOWARD NEW ENGLAND THROUGH THE PERIOD. AS IT  
TRANSLATES EASTWARD ACROSS PA, A NOTABLE WEDGE PATTERN WILL  
SETUP ACROSS THE MID-ATLANTIC THROUGH THE WEEKEND. THE WEDGE  
WILL BEGIN TO DEVELOP FRIDAY AND MAXIMIZE THROUGH THE WEEKEND.  
THIS WILL RESULT IN INCREASING UPSLOPE CLOUDS ALONG THE BLUE  
RIDGE AND WESTWARD TOWARD THE ALLEGHANYS WITH LIGHT RAIN SHOWERS  
DEVELOPING, ESPECIALLY SATURDAY AND SUNDAY. FRIDAY SHOULD BE  
MOSTLY DRY WITH JUST INCREASING CLOUDS, ESPECIALLY ALONG THE  
SOUTHERN BLUE RIDGE. SATURDAY AND SUNDAY SHOULD BRING MOSTLY  
CLOUDY SKIES TO MUCH OF THE AREA WEST OF THE BLUE RIDGE. LIGHT  
SHOWERS ARE EXPECTED FROM WATAUGA COUNTY NORTHEAST TOWARD  
ROANOKE BY AFTERNOON/EVENING. FOR SUNDAY, THE AXIS OF DEEPER  
CLOUDS AND SHOWERS SHOULD SHIFT SLIGHTLY FURTHER WEST IN  
RESPONSE TO THE SURFACE HIGH STRENGTHENING AND PUSHING SLIGHTLY  
DRIER AIR SOUTHWEST THROUGH VIRGINIA. THUS, THE BEST AXIS FOR  
CLOUDS AND SHOWERS ON SUNDAY SHOULD BE NEAR THE TN/NC/VA BORDER.  
NEAR THE SOUTHWEST EDGE OF THE WEDGE ACROSS EXTREME WESTERN NC  
AND FAR SOUTHWESTERN VA INTO SOUTHERN WV, ISOLATED THUNDERSTORMS  
WILL BE POSSIBLE PRIMARILY SATURDAY AFTERNOON AS THIS PORTION  
OF THE CWA WILL BE JUST OUTSIDE THE WEDGE AND ALONG AN AXIS OF  
BETTER INSTABILITY. INSTABILITY PARAMETERS SUGGEST INCLUDING A  
SLIGHT CHANCE OF THUNDER SATURDAY AFTERNOON IN THE FAR SOUTHWEST  
AND SUNDAY AFTERNOON IN THE EXTREME WEST IS REASONABLE, AND  
THUS HAS BEEN INCLUDED IN THE GRIDS.  
 
THE DEVELOPMENT OF THE WEDGE AND INCREASING UPSLOPE FLOW AND  
ASSOCIATED CLOUD COVER AND LIGHT PRECIPITATION WILL LEAD TO  
WELL BELOW NORMAL TEMPERATURES INTO THE WEEKEND. TEMPERATURES  
WILL ALREADY BE BELOW NORMAL FRIDAY THANKS TO THE CANADIAN AIR  
MASS OVERSPREADING THE REGION. THIS WILL BE ENHANCED BY THE  
NORTHEAST FLOW EVEN MORE SO SATURDAY INTO SUNDAY. HAVE LEANED  
TOWARD THE COOLER METMOS GUIDANCE, AND EVEN UNDERCUT THAT IN  
SOME AREAS LIKE BLACKSBURG AND LEWISBURG. WE COULD END UP SEEING  
TEMPERATURES WELL BELOW NORMAL SUNDAY IF RAIN AND/OR DRIZZLE  
AND DENSE CLOUD COVER REMAINS IN PLACE. FOR NOW, HAVE ADVERTISED  
HIGH TEMPERATURES MAINLY IN THE 70S, RANGING FROM NEAR 70 WEST  
TO NEAR 80 EAST. LOWS WILL NOT BE AS FAR BELOW NORMAL WITH  
DEWPOINTS REMAINING IN THE 50S WEST TO LOWER 60S PIEDMONT.  
 

 
   
LONG TERM /MONDAY THROUGH WEDNESDAY/
 
 
AS OF 450 AM EDT THURSDAY...  
 
MODELS BEGINNING TO COME INTO BETTER AGREEMENT ON THE EVOLUTION  
OF TROPICAL SYSTEMS, ONE OFF THE SOUTHEAST U.S. COAST AND HARVEY  
IN THE TX/LA AREA. GFS AND ECMWF ARE TRENDING TOWARD EACH OTHER  
WITH A GENERAL CONSENSUS THAT HARVEY WILL STILL AND LINGER  
ALONG THE UPPER TX COAST AND THEN EVENTUALLY THE WESTERN LA  
COAST BEFORE BECOMING CAUGHT UP IN A NORTHERN STREAM TROUGH  
DURING THE MIDDLE TO LATER PART OF NEXT WEEK. THIS WOULD TAKE  
THE REMNANTS OF HARVEY JUST TO OUR WEST THROUGH THE TN AND OH  
VALLEY DURING THE LATER PART OF NEXT WEEK. CONFIDENCE IN THIS OR  
ANY SOLUTION REMAINS LOW BECAUSE OF THE WEAKNESS OF THE UPPER-  
LEVEL PRESSURE PATTERN IN PLACE. WHAT WILL LIKELY BE MORE  
SIGNIFICANT FOR OUR CWA DURING THIS TIME FRAME IS THE TROPICAL  
SYSTEM OFF THE NC/SC COAST THAT WILL KEEP A COOL NORTHEAST  
MARITIME FLOW ACROSS OUR REGION WITH ENHANCED CLOUDS, LIGHT  
PRECIPITATION THROUGH THE MOUNTAINS, AND MUCH BELOW NORMAL  
TEMPERATURES. THIS COULD WELL PERSIST THROUGH MOST OF THIS  
PERIOD. AS A RESULT OF THE CONSIDERABLE UNCERTAINTIES, HAVE NOT  
MADE ANY SIGNIFICANT CHANGES TO TEMPERATURES OR POPS IN THE  
EXTENDED DAYS 6-8 PERIOD WITH THIS UPDATE.  
 

 
   
AVIATION /08Z THURSDAY THROUGH MONDAY/
 
 
AS OF 230 AM EDT THURSDAY...  
 
WEAK LOW LEVEL CONVERGENCE AND MOISTURE LINGER BEHIND THE COLD  
FRONT EAST OF THE BLUE RIDGE. ISOLATED SHOWERS HAVE BEEN POPPING  
UP FROM TIME TO TIME THIS EVENING AND EXPECT THIS WILL CONTINUE  
TO BE THE CASE UNTIL A LARGE AREA OF HIGH PRESSURE MOVING OUT OF  
CENTRAL CANADA SLIDES INTO THE NORTHEASTERN US AND STARTS TO  
WEDGE DOWN EAST OF THE APPALACHIANS. WITH AN ABSENCE OF  
DISCRETE FEATURES TO CORRELATE WITH SHOWERS AND EXPECTED SPARSE  
ISOLATED COVERAGE WILL NOT MENTION VCSH AT ANY SITE.  
 
EXPECT A GOOD AMOUNT OF VFR CLOUD COVER EAST OF THE BLUE RIDGE  
TODAY, WITH SOME MVFR CIGS THROUGH THIS MORNING AT KDAN. LESS  
CLOUD COVER THROUGH DAYBREAK WEST OF THE RIDGE WILL ALLOW FOR  
SOME PATCHY FOG AND BELIEVE THERE MAY BE A WINDOW FOR KLWB TO GO  
DOWN TO LIFR VSBY/CIG SO WILL COVER THIS WITH A TEMPO AROUND  
DAYBREAK. WITH DIURNAL HEATING AND DIGGING SHORT WAVE PASSING BY  
TO OUR NORTH EXPECT A ROBUST VFR CU FIELD THIS AFTERNOON.  
DIURNAL CLOUDS WILL DISSIPATE WITH LOSS OF HEATING THIS EVENING  
AND WITH GOOD RADIATIONAL COOLING EXPECTED FOG WILL START TO  
DEVELOP BY THE END OF THE VALID PERIOD.  
 
WINS WILL GENERALLY BE LIGHT THROUGH THE PERIOD.  
 
EXTENDED AVIATION DISCUSSION...  
 
GENERALLY VFR CONDITIONS ARE EXPECTED INTO THE WEEKEND AS HIGH  
PRESSURE BUILDS OVER THE REGION. THERE WILL ALSO BE A DIURNAL  
TREND FOR LATE NIGHT FOG/STRATUS ESPECIALLY WEST OF THE BLUE  
RIDGE WITH KLWB AND KBCB THE MOST LIKELY TAF SITES TO BE  
AFFECTED. ISOLATED CONVECTION MAY BE POSSIBLE ACROSS THE  
MOUNTAINS SATURDAY INTO MONDAY.  
 

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

 
 

 
SYNOPSIS...MBS  
NEAR TERM...MBS  
SHORT TERM...RAB  
LONG TERM...AMS/RAB  
AVIATION...AL/MBS  
 
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