376  
FXUS61 KRNK 240116  
AFDRNK  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BLACKSBURG VA  
916 PM EDT FRI JUN 23 2017  
   
SYNOPSIS
 
 
A COLD FRONT, ENERGIZED BY THE REMNANTS OF WHAT WAS TROPICAL  
STORM CINDY, WILL PROGRESS EAST ACROSS THE FORECAST AREA  
TONIGHT. SHOWERS AND EMBEDDED THUNDERSTORMS ARE ANTICIPATED INTO  
THE OVERNIGHT, A FEW OF WHICH MAY PRODUCE GUSTY WINDS AND HEAVY  
DOWNPOURS. THE COLD FRONT WILL SLOWLY PUSH SOUTHEASTWARD INTO  
EASTERN VIRGINIA AND NORTH CAROLINA ON SATURDAY, FOLLOWED BY A  
COOLER AND MUCH DRIER AIR MASS FOR THE REST OF THE WEEKEND.  

 
   
NEAR TERM /THROUGH SATURDAY/
 
 
AS OF 855 PM EDT FRIDAY...  
 
LEADING EDGE OF WEAKENING CONVECTION TO THE WEST SLOWLY HEADING  
EAST TOWARD THE WESTERN COUNTIES ATTM IN ASSOCIATION WITH THE  
CINDY REMNANT RACING THROUGH NE KENTUCKY AND INTO WEST VA. ONCE  
THE LOW PASSES SHOULD SEE SHRA/TSRA GET A BIT BETTER PUSH OFF TO  
THE SOUTHEAST WITH PERHAPS LOW TOPPED BANDS IMPACTING THE  
MOUNTAINS INTO THE EARLY MORNING HOURS. HOWEVER LATEST REGIONAL  
RADAR LOOPS SHOW A WEAKER AREA OF SHOWERS WITHIN THE LINE  
HEADING TOWARD SOUTHWEST VA LIKELY DUE TO STRONG LIFT JUST NORTH  
AND A PASSING STORM CLUSTER TO THE WEST. THIS MAY TEND TO FILL  
IN AND INTENSIFY GIVEN THE PASSAGE OF THE MAIN CORE OF 850 MB  
WINDS ACROSS THE WESTERN SECTIONS IN THE NEXT FEW HOURS AND LOW  
LEVEL INSTABILITY OFF EVENING SOUNDINGS BUT IFFY.  
 
OTHER CONCERN IS WITH THE HEAVY RAIN POTENTIAL MAINLY NORTHWEST  
SECTIONS AS THE PERSISTENT BAND OF HEAVY RAIN NOW NORTHWEST OF  
RLX DROPS SOUTHEAST ONCE THE REMNANT LOW PASSES. SOME SOLUTIONS  
INCLUDING THE HRRR DO BRING BETWEEN 1 AND 2 INCHES TO PORTIONS  
OF GREENBRIER COUNTY BETWEEN 03-09Z WHILE OTHERS WEAKEN THE  
HEAVIER RAINFALL ONCE BETTER SUPPORT EXITS. GIVEN UNCERTAINTY  
AND ISOLATED NATURE TO POSSIBLE HEAVY RAIN, WONT HOIST A WATCH  
AND HANDLE WITH SHORT TERM PRODUCTS IF NEEDED AT THIS POINT.  
MAY ALSO SEE SOME OF THE SHOWERS PUSH EAST OF THE MOUNTAINS  
AFTER MIDNIGHT BUT IN A MUCH WEAKER STATE. THUS MAIN UPDATE WAS  
WITH TIMING OF HIGHER POPS NORTHWEST AND TO BUMP UP QPF MAINLY  
GREENBRIER/SUMMERS INTO BATH COUNTY. OTHERWISE EXPECTING A  
BREEZY AND VERY MUGGY OVERNIGHT WITH HIGHER GUSTS POSSIBLE IN  
SHOWERS DESPITE LACK OF THUNDER. LOWS 60S WEST TO LOW/MID 70S  
EAST.  
 
APPEARS EXODUS OF SHOWERS WILL OCCUR A BIT FASTER LATER TONIGHT  
WITH DECENT DRYING DEVELOPING BY EARLY SAT. SINCE THIS SUPPORTED  
BY MOST SOLUTIONS, OPTED TO LOWER POPS BY DAYBREAK SAT AND  
REMOVE MOST CHANCES DURING THE MORNING FOR NOW.  
 
PREVIOUS DISCUSSION AS OF 339 PM EDT FRIDAY...  
 
WHILE CURRENTLY ON THE QUIET SIDE, HEADING INTO A MORE ACTIVE  
EVENING WITH SEVERAL POTENTIAL ISSUES TO CONTEND WITH, OWING TO THE  
APPROACHING COLD FRONT WHICH HAS MERGED WITH CINDY'S REMNANTS.  
 
THROUGH THE REST OF THE AFTERNOON.... WE CONTINUE TO CAREFULLY  
MONITOR THE POTENTIAL FOR ISOLATED THUNDERSTORMS. VISIBLE  
SATELLITE REVEALS SOME CLOUD BREAKS TAKING PLACE FROM THE  
CENTRAL/SOUTHERN BLUE RIDGE EASTWARD. LAPS-BASED CAPE VALUES ARE  
ON THE ORDER OF 1000-1500 J/KG, AND WE DO HAVE STRONG LOW-LEVEL  
WINDS ALREADY IN PLACE (40-50 KTS ARE COMMON PER AREA VWPS).  
THE STRONG LOW-LEVEL WINDS CONTRIBUTING TO DEEP LAYER SHEAR  
VALUES NEAR 40 KTS PER SPC MESOANALYSIS. IF ANY ISOLATED STORMS  
DO DEVELOP, AS REFLECTED IN RECENT RUNS OF THE HRRR AND THE 3-KM  
NAM, THEY MAY PRODUCE LOCALIZED GUSTY WINDS AS THEY MOVE  
NORTHEASTWARD OFF THE BLUE RIDGE. OTHERWISE, LOOKING AT  
GENERALLY QUIET CONDITIONS INTO THE EARLY EVENING.  
 
FOR TONIGHT... WEATHER TURNS INCREASINGLY MORE ACTIVE, AS WE  
WILL WATCH ONGOING STORMS ACROSS THE OHIO AND TENNESSEE VALLEYS  
PROGRESS EASTWARD ACROSS THE FORECAST AREA. PRESENT INDICATION  
FROM A CONSENSUS OF HIGH-RESOLUTION GUIDANCE IS TO BRING AN  
EVOLVING LINE OF HEAVY SHOWERS AND EMBEDDED THUNDERSTORMS INTO  
OUR WESTERN WV/VA/NC DOORSTEP BY AROUND 01Z, PROGRESSING  
EASTWARD TO THE BLUE RIDGE FOOTHILLS TOWARD MIDNIGHT. WHILE IT  
IS A DIURNALLY UNFAVORABLE PERIOD OF TIME FOR STRONG CONVECTION,  
WIND SHEAR VALUES BOTH THROUGH THE LOWEST 0-3KM AND DEEP LAYER  
OWING TO CINDY'S WIND FIELD ONLY INCREASE. THOUGH IT'S DIFFICULT  
TO FULLY TRUST HIGHER-RESOLUTION GUIDANCE LATER IN THE MODEL  
CYCLE, THROUGH MIDNIGHT SEVERAL MEMBERS DO DEPICT SOME  
CONCERNING RADAR STRUCTURES AS STORMS MOVE INTO FAR WESTERN  
COUNTIES. I SUSPECT THAT WE'LL HAVE A HIGH-SHEAR/LOW-CAPE  
ENVIRONMENT IN PLACE TONIGHT, EVEN WELL AFTER DARK. IN THAT  
ENVIRONMENT, EVEN HEAVY SHOWERS COULD OFFER THE POTENTIAL TO  
PRODUCE GUSTY WINDS WHICH MAY TOPPLE DEAD OR SHALLOW-ROOTED  
TREES. BASED ON 0-1 KM SHEAR VALUES PROGGED TO BE IN THE 40 TO  
50 KT NEIGHBORHOOD, THIS ALSO POSES A CONCERN FOR ISOLATED  
EMBEDDED SPIN-UPS IN STRONGER CONVECTIVE ELEMENTS IN THE LINE.  
GIVEN THOSE REASONS, TO RAISE AWARENESS OF THE POTENTIAL THREAT  
I'VE ADDED ENHANCED WORDING FOR GUSTY WINDS IN THE ZONE FORECAST  
THROUGH MIDNIGHT AT LEAST, ROUGHLY FROM THE BLUE RIDGE  
FOOTHILLS WESTWARD INTO SOUTHEAST WV. AFTER MIDNIGHT, HEAVIER  
SHOWERS AND STORMS SEEM TO LOSE STRUCTURE AS THEY DRIFT INTO THE  
PIEDMONT AREAS, SO I'VE KEPT THE GUSTY WIND WORDING TO CENTRAL  
AND WESTERN COUNTIES AWAY FROM THE VA/NC PIEDMONT AREAS.  
 
ANOTHER CONCERN IN THIS HUMID, TROPICAL AIR MASS WILL BE HEAVY  
RAINFALL POTENTIAL. EVEN SHOWERS SHOULD BE EFFICIENT RAINFALL  
PRODUCERS. POTENTIAL FOR HOURLY RAIN RATES TO BE ENHANCED BY  
CONVECTIVE ELEMENTS AS WELL. I'VE MAINTAINED HEAVY RAINFALL WORDING  
IN THE ZONES FOR THE TONIGHT PERIOD. FORTUNATELY, RAINFALL WE DID  
RECEIVE LAST NIGHT WAS NOT SUBSTANTIAL. AND THE FAST-MOVING NATURE  
TO TONIGHT'S RAIN/THUNDERSTORMS WILL PROBABLY KEEP FLOODING MORE  
LOCALIZED. GUIDANCE QPF VALUES CONTINUE TO GENERALLY PAINT SOME  
CONSENSUS IN DEPICTING THE HIGHEST FORECAST VALUES NORTHWEST OF OUR  
FORECAST AREA, AND OFFICIAL FORECAST RANGED FROM A HALF TO ONE INCH  
WEST OF I-81, A QUARTER TO THIRD OF AN INCH TO THE BLUE RIDGE  
ESCARPMENT, TAPERING TO A COUPLE TENTHS OR LESS EAST. FOR THOSE  
REASONS, CONFIDENCE WAS TOO LOW ON AN ISSUANCE OF A FLASH FLOOD  
WATCH WITH THIS FORECAST PACKAGE. FOR MORE ON HYDRO, SEE THE  
HYDROLOGY SECTION BELOW.  
 
COLD FRONT WILL HAVE ADVANCED EAST OF THE BLUE RIDGE TOWARD SATURDAY  
MORNING. HOWEVER, THE 12Z NAM, ECMWF AND GFS SUGGEST THAT THE FRONT  
MAY MAKE MORE SLOW SOUTHEASTWARD PROGRESS INTO THE NC PIEDMONT AND  
FOOTHILLS AREAS. WHILE MUCH DRIER, MORE REFRESHING AIR FILTERS INTO  
THE NORTHWESTERN TWO-THIRDS OF THE FORECAST AREA ON SATURDAY, I'VE  
KEPT LOWER CHANCE LEVEL POPS THROUGH THE DAY FOR SHOWERS AND  
THUNDERSTORMS FOR THE SOUTHEASTERN THIRD.  
 
WITH THE FRONT ROUGHLY BISECTING THE FORECAST AREA, LOWS TONIGHT  
RANGE FROM THE LOWER TO MIDDLE 60S WEST OF THE BLUE RIDGE BUT WILL  
BE A MUGGY LOWER TO MID 70S FROM THE ROANOKE VALLEY EASTWARD. HIGHS  
TOMORROW SHOULD TOP OUT IN THE MID 70S TO LOWER TO MIDDLE 80S.  
 

 
   
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
 
 
AS OF 339 PM EDT FRIDAY...  
 
BY 00Z SUNDAY (8 PM SATURDAY NIGHT), MOST OF THE MEDIUM RANGE MODELS  
FORECAST THE POSITION OF THE COLD FRONT ACROSS THE FAR SOUTHEAST  
PORTION OF OUR FORECAST AREA. THIS BOUNDARY INTERACTING WITH  
LINGERING INSTABILITY WILL RESULT IN KEEPING A SLIGHT CHANCE FOR  
STORMS FROM SOUTH BOSTON TO YANCEYVILLE EARLY SATURDAY EVENING.  
 
DRY CONDITIONS ARE EXPECTED FOR THE REMAINDER OF THE SHORT TERM  
PERIOD AS A DEEP NORTHWEST-WEST FLOW PREVAILS ACROSS OUR REGION  
THROUGH MONDAY.  
 
IN THE UPPER LEVELS, A BROAD UPPER TROF WILL GRADUALLY DEEPEN ACROSS  
THE GREAT LAKES INTO THE NORTHERN U.S., WHICH WILL ALLOW DEW POINTS  
TO DROP THROUGH THE PERIOD RESULTING IN COOLER TEMPERATURES MONDAY  
MORNING COMPARED TO SUNDAY MORNING. LEANED TOWARD THE COOLER  
GUIDANCE VALUES OR LOWS MONDAY MORNING. HIGHS WILL ALSO BE COOLER  
MONDAY AS 1000-850MB THICKNESSES CONTINUE TO FALL. FOR LATE JUNE,  
HUMIDITY LEVELS WILL BE QUITE COMFORTABLE.  
 

 
   
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
 
 
AS OF 339 PM EDT FRIDAY...  
 
THE LONG RANGE MODELS ARE IN GOOD AGREEMENT WITH THE OVERALL UPPER  
AIR PATTERN DURING THIS PERIOD WITH AN ANOMALOUSLY DEEP UPPER TROF  
OVER THE EASTERN U.S. EARLY IN THIS PERIOD, WITH 500MB HEIGHTS 2-3  
STANDARD DEVIATIONS BELOW NORMAL,TRANSITIONING TO A ZONAL FLOW BY  
MID WEEK, WITH RIDGING BUILDING BY THE END OF THE WEEK.  
 
THE 12Z GFS IS STILL FASTEST WITH THE EASTWARD PROGRESSION OF THE  
UPPER TROF TUESDAY NIGHT INTO WEDNESDAY, BUT THIS HAS LITTLE IMPACT  
ON THE TRANQUIL WEATHER EXPECTED DURING THIS TIME. A WEAK FRONTAL  
BOUNDARY MOVING THROUGH EARLY TUESDAY MORNING MAY GENERATE SOME  
SPOTTY SHOWERS IN THE MOUNTAINS, BUT FORECAST RAOBS INDICATE THERE  
WILL BE VERY LITTLE MOISTURE AVAILABLE. OTHERWISE, PWAT VALUES WILL  
REMAIN BELOW AVERAGE UNTIL THURSDAY NIGHT/FRIDAY SO EXPECT A  
PROLONGED PERIOD OF DRY WEATHER. BY LATE IN THE WEEK...A DEEP  
SOUTHWEST FLOW DEVELOPING ON THE WEST SIDE OF AN UPPER RIDGE AND  
AHEAD OF AN APPROACHING UPPER TROF IN THE UPPER MID WEST WILL  
INCREASE MOISTURE AND PROVIDE THE OPPORTUNITY FOR WEAK UPPER LEVEL  
DISTURBANCES TO PASS OVER OUR AREA. THIS WILL RESULT IN INCREASE  
CHANCES FOR SCATTERED THUNDERSTORMS DURING THIS PERIOD.  
 
AS FOR TEMPERATURES, FORECAST 850MB TEMPS FROM THE GEFS ARE 2-3  
STANDARD DEVIATIONS BELOW AVERAGE, WHICH WILL LEAD TO SOME COOL  
MORNINGS TUESDAY AND WEDNESDAY. ADJUSTED LOW TEMPERATURES DOWN A  
COUPLE OF DEGREES BELOW GUIDANCE DURING THIS PERIOD. TEMPERATURES  
WILL MODERATE LATE IN THE WEEK.  
 

 
   
AVIATION /01Z SATURDAY THROUGH WEDNESDAY/
 
 
AS OF 650 PM EDT FRIDAY...  
 
OVERALL ACTIVE AVIATION FORECAST PERIOD IN THE FIRST 12 HRS.  
 
VFR CONDITIONS SHOULD PREVAIL INTO EARLY THIS EVENING ACROSS THE  
MOUNTAINS AND OUT EAST THROUGH ABOUT MIDNIGHT. AREAS OF  
MECHANICAL TURBULENCE ALONG THE SPINE OF THE BLUE RIDGE ARE  
LIKELY TO CONTINUE INTO THIS EVENING AS THE LOW LEVEL JET RAMPS  
UP TO AROUND 50 KTS AHEAD OF CONVECTION TO THE WEST. SURFACE  
WINDS SHOULD ALSO REMAIN GUSTY AT TIMES WITH KBLF PERHAPS  
GUSTING TO 30 KTS AT TIMES.  
 
DETERIORATION TO SUB-VFR FLIGHT CONDITIONS WILL OCCUR FROM WEST  
TO EAST AFTER SUNSET WITH MOST OF THE SHOWERS EITHER PASSING  
EAST OR DISSIPATING DURING THE EARLY MORNING HOURS OF SATURDAY.  
THIS AHEAD OF A COLD FRONT ALONG WITH THE REMNANTS OF CINDY THAT  
ARE LIKELY TO PRODUCE AT LEAST A BROKEN BAND OF MODERATE TO  
HEAVY SHOWERS AND EMBEDDED THUNDERSTORMS. MODELS HAVE CONTINUED  
TO SLOW DOWN THE EASTWARD PROGRESS OF THIS LINE WHILE SHOWING A  
WEAKER SCENARIO WITH BEST ENERGY PASSING BY TO THE NORTHWEST.  
THUS HAVE ONLY INCLUDED A PREVAILING PERIOD FOR SHOWERS AT  
KBLF/KLWB WITH CONTINUED VCSH/VCTS AND TEMPO ELSEWHERE ALTHOUGH  
THUNDER CHANCES LOOK RATHER SMALL AT THIS POINT. APPEARS SOME  
LOW CLOUDS MAY DEVELOP ACROSS THE MOUNTAINS AS THE SHOWERS EXIT  
WITH POTENTIAL IFR/LIFR MAINLY AROUND KBLF LATE. STRONG WIND  
GUSTS TO 35 KTS MAY ALSO ACCOMPANY ANY OF THE HEAVIER SHOWERS.  
 
FOR SATURDAY, THE FRONT SHOULD MAKE SLOW BUT STEADY PROGRESS  
SOUTHWARD, WITH STEADILY IMPROVEMENT TO VFR CONDITIONS ALONG  
WITH A WESTERLY WIND AT 8-15 KTS WITH POTENTIAL GUSTS TO AROUND  
25 KTS DURING SATURDAY AFTERNOON.  
 
EXTENDED AVIATION DISCUSSION...  
 
VFR CONDITIONS TO THEN PREVAIL SATURDAY NIGHT THROUGH SUNDAY NIGHT.  
POTENTIAL FOR RADIATION FOG AND RELATED VISIBILITY RESTRICTIONS  
SUNDAY NIGHT.  
 
A COLD FRONT PASSING ON MONDAY MAY PRODUCE VFR/POSSIBLE MVFR  
CONDITIONS AND BREEZY NORTHWEST WINDS BEHIND IT. VFR THEN LASTS  
THROUGH WEDNESDAY.  
 

 
   
HYDROLOGY
 
 
AS OF 911 PM EDT FRIDAY...  
 
RAINFALL FORECAST/MODELS/ENSEMBLE RIVER FORECASTS SUGGESTS GREATER  
THREAT FOR FLOODING WILL REMAIN NORTHWEST OF OUR FORECAST AREA  
INTO TONIGHT. AVERAGE RAINFALL AMOUNTS OF .50 TO 2 INCHES  
EXPECTED FROM THE NC MOUNTAINS TO MOUNTAIN EMPIRE OF SW VA TO  
SOUTHEAST WV WITH 2 TO 4 INCHES FURTHER WEST INTO THE KY/TN/OH  
CORRIDOR.  
 
NOT SEEING ENOUGH SIGNALS TO WARRANT A WATCH, BUT GIVEN EFFICIENT  
RAINFALL RATES, ANY CONVECTIVE ELEMENTS OR TRAINING WILL INCREASE  
THE THREAT ESPECIALLY ACROSS THE GREENBRIER VALLEY OF WEST  
VIRGINIA INTO THE OVERNIGHT WHERE THE HEAVIEST RAINFALL IS  
EXPECTED. TIMING OF HEAVY RAIN WILL BE IN A 3 TO 6 HOUR WINDOW  
FROM LATE THIS EVENING INTO EARLY SATURDAY MORNING WITH DRIER  
AIR QUICKLY RETURNING SATURDAY.  

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

 
 

 
SYNOPSIS...AL/JH  
NEAR TERM...AL/JH  
SHORT TERM...PH  
LONG TERM...PH  
AVIATION...AL/AMS/JH  
HYDROLOGY...AL/AMS  
 
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