Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210640 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 240 AM EDT THU AUG 21 2014 .SYNOPSIS... A WEAK STATIONARY FRONT WILL REMAIN IN THE AREA THROUGH THE REST OF THE WEEK. UPPER LEVEL DISTURBANCES TRACKING EAST AND SOUTHEAST ACROSS THE BOUNDARY WILL BRING SCATTERED SHOWERS AND STORMS TO THE REGION EACH DAY. THE FRONT SHOULD SHIFT BACK SOUTH OF THE REGION SATURDAY BRINGING A RETURN TO COOLER WEATHER FOR THE WEEKEND. && .NEAR TERM /THROUGH TODAY/... AS OF 1120 PM EDT WEDNESDAY... MLCAPES OVER 1500 J/KG STILL LINGERING OVER THE PIEDMONT LATE THIS EVENING KEEPING CONVECTION ONGOING FROM THE NC/VA LINE NORTH INTO BUCKINGHAM COUNTY. AIRMASS HAS BEEN WORKED OVER ACROSS THE MTNS...AND DESPITE A STRONGER WAVE DEPICTED BY LATEST RAP ANALYSIS OVER KY...NOT SEEING MUCH OF ANYTHING EXCEPT ISOLATED/WIDELY SCATTERED SHOWER THREAT THROUGH 3 AM OUT OVER FAR SW VA INTO NW NC. THINK THE CONVECTION OUT EAST WILL EXIT THE CWA BY 1 AM. SKIES WILL BE VARIABLY CLOUDY WITH LOTS OF HIGH CLOUDINESS ACROSS THE WEST AND SOUTH. CLEARING TAKES PLACE INTO EARLY MORNING OUT EAST...WITH MORE CLOUDS ARRIVING INTO THE APPALACHIANS AHEAD OF THE NEXT SHORTWAVE MOVING OVER ILLINOIS THIS EVENING. MODELS HAVE SLOWED TIMING DOWN SOME WITH ONSET OF NEXT ROUND OF SHOWERS IN THE MTNS...SO DELAYED CHANCES A COUPLE OF HOURS. FOG MAY BE MORE OF AN ISSUE OUT EAST IF/WHEN IT CLEARS ESPECIALLY WHERE IT RAINED. FOR NOW KEPT IN PATCHY FOG...WITH AREAS CLOSER TO BUCKINGHAM COUNTY. LOW TEMPS REMAIN MUGGY IN THE 60S. WEAK RESIDUAL FRONT WILL LIFT BACK NE ON THURSDAY AS THE WAVE CHANNEL ALOFT AROUND THE RIDGE TO THE SW AMPLIFIES A BIT AND STARTS TO SHIFT NORTH AS WELL. MODELS BRING ANOTHER IMPULSE QUICKLY SE OUT OF THE UPSTREAM CONVEYER BELT AND DRIVE IT TOWARD THE NW COUNTIES THURSDAY MORNING SIMILAR TO TODAY...PERHAPS JUST A BIT SLOWER. HOWEVER LIFT WILL BE ENCOUNTERING DEEP NW FLOW SO UNCERTAIN AS TO HOW FAR THIS COMPLEX MAY GET BEFORE FADING. THUS RUNNING WITH INCREASING CHANCE POPS THURSDAY MORNING...MAINLY BLUE RIDGE WEST...WITH HIGHEST ACROSS SE WEST VA. EXPECT EARLY CONVECTION TO AGAIN FADE CROSSING THE RIDGES AS WE SLIP IN BETWEEN WAVES BEFORE BETTER INSTABILITY/OUTFLOW HELPS REDEVELOP AT LEAST SCATTERED AFTERNOON COVERAGE MOUNTAINS...AND ISOLATED OUT EAST WHERE DOWNSLOPE ALOFT WILL BE STRONGER. THEREFORE TRIMMED BACK POPS TO MORE CHANCE NATURE GIVEN TRENDS OF LATE AND LACK OF MUCH LIFT THURSDAY AFTERNOON WITH THE NEXT WAVE IN OHIO. WARMING ALOFT AND WESTERLY WINDS SHOULD COMBINE WITH SUNSHINE TO PUSH TEMPS ABOVE 90 SE WITH 80S MOST OTHER SPOTS PENDING EARLY CLOUDS. && .SHORT TERM /TONIGHT THROUGH SATURDAY/... AS OF 245 PM EDT WEDNESDAY... FORECAST AREA STAYS IN BROAD NORTHWEST SYNOPTIC FLOW. PROBABILITY OF PRECIPITATION WILL DEPEND ON WHEN SHORT WAVES COME THROUGH. SHOWERS AND THUNDERSTORMS THAT CROSS THE COUNTY WARNING AREA DURING THE LATE NIGHT OR EARLY MORNING...OR UPSTREAM CLUSTERS OF STORMS THAT SPREAD CLOUDS DOWNSTREAM OVER US WILL DIMINISH THE AVAILABLE INSTABILITY. MODELS HAVE AXIS OF BEST LIFT SHIFTING JUST NORTH OF THE FORECAST AREA ON FRIDAY. THIS MAY LIMIT THE COVERAGE OF PRECIPITATION FOR FRIDAY THROUGH SATURDAY. BUT SURFACE BOUNDARY POSSIBLY MOVING SOUTH THROUGH THE EASTERN PART OF THE FORECAST AREA ON FRIDAY MAY TRIGGER SHOWERS AND THUNDERSTORMS. PRECIPITABLE WATER VALUES REMAIN HIGH THROUGH THE PERIOD. LARGE RAINFALL RATES WILL BE POSSIBLE IN ANY OF THE STORMS. EXPECTING MUGGY CONDITIONS OVERNIGHT WITH DEW POINTS REMAINING WELL INTO THE 60S. 850 TEMPERATURES ON THE EASTERN SIDE OF THE FORECAST AREA WILL BE COOLER THAN IN THE WEST. OVERALL PRECIPITATION AND CLOUD COVER WILL HOLD TEMPERATURES AT OR JUST BELOW NORMAL FOR MAXIMUM TEMPERATURES. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... AS OF 300 PM EDT WEDNESDAY... LARGE UPPER RIDGE BUILDS FROM THE LOWER MISSISSIPPI VALLEY. 500 MB HEIGHTS OVER THE FORECAST AREA BEGIN TO RISE ON TUESDAY WITH THE RIDGE CENTERED OVER THE TENNESSEE VALLEY. SURFACE HIGH PRESSURE WILL BE OVER NEW ENGLAND AND WEDGED DOWN THE APPALACHIANS THROUGH TUESDAY. BY THURSDAY A STRONG BERMUDA HIGH WILL BE IN PLACE. CHALLENGING TO TIME SHORT WAVES COMING OVER THE TOP OF THE RIDGE. WPC WAS FAVORING A BLEND OF ENSEMBLE GFS AND ECMWF THROUGH THE PERIOD. THIS KEEPS FORECAST AREA IN A PERSISTENT CHANCE OF PRECIPITATION THROUGH MONDAY NIGHT. AT THIS TIME WILL BE EMPHASIZING SUNDAY NIGHT AS THE BEST CHANCE IN THIS TIME FRAME. WILL BE WARMING UP CLOSER TO ABOVE NORMAL TEMPERATURES ASSOCIATED WITH THE UPPER RIDGE ON WEDNESDAY. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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AS OF 230 AM EDT THURSDAY... PATCHY MORNING FOG ANTICIPATED AREAWIDE...MAINLY MVFR...BUT CAN`T RULE OUT BRIEF PERIOD OF IFR/LIFR FOR A FEW HOURS AROUND DAYBREAK. ANY FOG AND STRATUS THAT FORMS WILL DISSIPATE AFTER SUNRISE WITH WIDESPREAD VFR CONDITIONS DEVELOPING AFTER 13Z/9AM. SHALLOW EASTERLY SURFACE WINDS THIS MORNING WILL GIVE WAY TO WEST NORTHWEST WINDS LATER THIS MORNING. THE LOW LEVEL FLOW WILL BE FROM THE NORTHWEST TODAY...WINDS 6-12 KTS...AND GUSTY NEAR THE RIDGE CRESTS. THE DEEPER FLOW...WELL ALOFT...IS ALSO FROM THE NORTHWEST. THIS WILL TRANSPORT DEBRIS CLOUDINESS DOWNSTREAM FROM THUNDERSTORMS OVER THE MIDWEST AND OHIO VALLEY REGIONS...CLOUD LAYERS MAINLY ABOVE 10KFT. WITH WINDS OUT OF THE WEST TODAY...THIS WILL CREATE DOWNSLOPE COMPRESSIONAL WARMING AND SUBSIDENCE. DO NOT EXPECT MUCH IN THE WAY OF LOCAL STORM ACTIVITY...DEEP CONVECTION...DUE TO THIS DOWNWARD VERTICAL MOTION. THE SUBSIDENCE IS EXPECTED TO WEAKEN TOWARD SUNSET...THUS POTENTIAL FOR STORM ACTIVITY WILL INCREASE...BUT MAINLY CONFINED LATER IN THE TAF PERIOD. THUNDERSTORMS ARE EXPECTED TO DEVELOP TODAY VCNTY OF STALLED FRONTAL BOUNDARY OVER THE OHIO VALLEY. STORMS WHICH DEVELOP VCNTY OF THIS BOUNDARY...ACROSS IL/IN/OH/KY...WILL MOVE DOWNSTREAM TOWARD THE MID ATLANTIC REGION THIS EVENING AND DURING THE OVERNIGHT TONIGHT. HIGHEST CONFIDENCE FOR STORMS THIS AFTERNOON WILL BE FROM WEST VIRGINIA INTO THE OHIO VALLEY...THE THREAT TRANSITIONING DOWNSTREAM INTO VIRGINIA AND NORTH CAROLINA TONIGHT. INTRODUCED VCNTY TSRA FOR ALL THE TERMINALS AFTER 22Z/6PM...THE STORM THREAT PERSISTING THROUGH THE OVERNIGHT. CONFIDENCE IS HIGHER FOR THE WV TERMINALS. EXTENDED AVIATION... UPPER LEVEL DISTURBANCES WILL BE MOVING THROUGH PERIODICALLY AND INTERACTING WITH A STATIONARY FRONT OVER THE AREA FOR THE NEXT FEW DAYS...RESULTING IN PERIODS OF SHOWERS AND THUNDERSTORMS. DUE TO THE HIGH MOISTURE CONTENT OF THE AIR...EXPECT STRATUS AND FOG DURING THE OVERNIGHT PERIODS WITH AREAS OF MVFR/IFR MOST PRONOUNCED BETWEEN MIDNIGHT AND 9AM EACH DAY. MODELS ARE INDICATED THAT A DEEPER EASTERLY SORT OF WIND FLOW WILL SETUP FOR THIS UPCOMING WEEKEND. THIS SUGGEST THAT LOW CIGS MAY PERSIST EVEN DURING THE DAYTIME PERIODS...SATURDAY AND SUNDAY...WITH WIDESPREAD MVFR CONDITIONS ACROSS THE AREA THIS WEEKEND DUE TO MOISTURE BANKING UP AGAINST THE EAST SIDE OF THE APPALACHIANS.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...JH/WP SHORT TERM...AMS LONG TERM...AMS AVIATION...PM

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