Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 260625 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 225 AM EDT TUE AUG 26 2014 .SYNOPSIS... STRONG HIGH PRESSURE WILL CONTINUE TO EXTEND SOUTH ALONG THE EASTERN FACE OF THE APPALACHIANS THROUGH MID WEEK. THIS SYSTEM WILL BRING COOL AND DRY AIR TO THE REGION THROUGH TONIGHT BEFORE WARMER TEMPERATURES AND HIGHER HUMIDITY RETURN FOR THURSDAY AND FRIDAY. ANOTHER COLD FRONT WILL APPROACH THE AREA LATE IN THE WORK WEEK...RESULTING IN THE NEXT CHANCE OF SHOWERS AND THUNDERSTORMS...MAINLY OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 200 AM EDT TUESDAY... MAINLY ANOTHER TEMPERATURE FORECAST OVER THE NEXT 24 HOURS AS HIGH PRESSURE BOTH SURFACE AND ALOFT REMAINS ACROSS THE REGION INTO TONIGHT. THIS SHOULD MAINTAIN A DRY EAST/NE FLOW OVER THE AREA ALLOWING FOR CONTINUED LOW HUMIDITY AND COMFORTABLE TEMPERATURES UNDER MAINLY SUNNY/CLEAR SKIES. HOWEVER WILL AGAIN HAVE PATCHY DENSE FOG AROUND EARLY THIS MORNING ALONG WITH SOME RESIDUAL STRATO-CU BANDS ACROSS THE SOUTH. HOWEVER THE AIR TODAY WILL BE DRIER THAN MONDAY SO EXPECT A QUICK EROSION TO ANY EARLY CLOUDS/FOG WITH ONLY SOME CU/CI AROUND THIS AFTERNOON. SURFACE RIDGING WILL BEGIN TO SINK TO THE SOUTH LATER TONIGHT AS 5H HEIGHTS START TO FALL IN RESPONSE TO THE APPROACH OF THE NEXT UPSTREAM SHORTWAVE/FRONT FROM THE NW LATE. THIS MAY SPILL SOME MID/HIGH CLOUDS IN OVER THE NW LATE OTRW OVERALL CLEAR PER DRY AIR WITH ANOTHER ROUND OF PATCHY OVERNIGHT FOG. EXPECT HIGH TEMPS TO BE SLIGHTLY WARMER TODAY GIVEN A BIT OF WARMING ALOFT ALONG WITH HEATING OF DRY AIR. THIS AGAIN SHOULD MAKE FOR UNIFORM HIGHS OF 75-80 WEST AND OVERALL LOW 80S EAST. COOL AGAIN TONIGHT GIVEN GOOD RADIATIONAL COOLING WITH LOWS MOSTLY IN THE 50S...EXCEPT CLOSER TO 60 RIDGES...AND SOME 40S DEEPER VALLEYS PENDING FOG LATE. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 150 AM EDT TUESDAY... CRISTOBAL WILL BE IN THE VICINITY OF BERMUDA WEDNESDAY. EVEN THOUGH THIS TROPICAL SYSTEM IS WELL OFFSHORE...IT WILL ALLOW A WEAK COOL FRONT TO SLIDE INTO THE REGION LATE WEDNESDAY AFTERNOON/EVENING. HOWEVER...WITH CRISTOBAL PULLING MOISTURE AWAY FROM THE AREA AND AN UPPER LEVEL RIDGE EDGING INTO THE REGION FROM THE WEST...DO NOT THINK SHOWER ACTIVITY WILL GO HIGHER THAN ISOLATED. IF A FEW ROGUE STORMS DO DEVELOP...THEY WILL NOT LAST LONG. ON THURSDAY...CRISTOBAL IS OUT OF THE PICTURE. A STRONG HOT AND HUMID UPPER LEVEL RIDGE WILL BE DRIFTING OVER THE SOUTHEASTERN USA STRETCHING BACK INTO THE TENNESSEE AND OHIO VALLEYS...NORTH ACROSS THE MID ATLANTIC STATES. THIS RIDGE WILL PUSH AFTERNOON HIGHS ABOVE NORMAL WITH LOWER 90S IN THE EAST AND M/U 80S IN THE WEST. MODELS DEVELOPING A LEE TROUGH/REFLECTION OVER THE CAROLINA PIEDMONT THURSDAY AFTERNOON. THIS TROUGH AND/OR WASHED OUT COOL FRONTAL BOUNDARY WILL CREATE ENOUGH CONVERGENCE FOR SCATTERED SHOWERS AND THUNDERSTORMS TO DEVELOP. IF STORMS CAN OVERCOME A STRONG CAP...THEY ARE LIKELY TO START ALONG THE BLUE RIDGE IN THE AFTERNOON THEN DRIFT TO THE FOOTHILLS AND PIEDMONT THROUGH THE EVENING. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 200 PM EDT MONDAY... GOING INTO LABOR DAY WEEKEND THE PATTERN WILL FEATURE A LOW AMPLITUDE RIDGE WHICH WILL ALLOW FOR SLOW RETURN OF GULF MOISTURE AROUND WEST EDGE INTO APPALACHIANS...WHICH WILL THEN LIKELY BE BROKEN DOWN BY APPROACHING UPPER TROUGH BY LATE IN THE WEEKEND OR EARLY NEXT WEEK. SOME DIFFERENCES IN TIMING BETWEEN 12Z GFS AND ENSEMBLE RUNS FROM 00Z...AS WELL AS 00Z ECMWF...AND INTERESTINGLY SOME OF THESE DIFFERENCES MAY HAVE TO DO WITH HOW THIS CURRENT FEATURE...DROPPING SOUTHWARD THROUGH NRN CALIF...INTERACTS WITH HURRICANE MARIE MOVING NORTHWEST UP THE BAJA COAST. ECMWF IS SLOWER BRINGING THE FEATURE ACROSS THE CENTRAL US LATER THIS WEEK...AND ALSO A LITTLE FLATTER WITH THE RIDGE OVER EASTERN US WITH A VERY WEAK DISTURBANCE CUTTING ACROSS IT FRIDAY...AND ACTUALLY SLIDES A WEAK BACK DOOR FRONT DOWN FROM THE NORTH ON FRIDAY...TEMPORARILY COOLING IT OFF A COUPLE MORE DEGREES. AS OF THIS WRITING...HAVING NOT SEEN THE NEW 12Z ECMWF...I DO TEND TO LIKE THE IDEA OF SLOWER PROGRESSION OF TROUGH GIVEN THE STRENGTH OF THE SOUTHEAST US RIDGE...WHICH INCLUDES THE POTENTIAL FOR A FRIDAY BACK DOOR FRONT...BUT WILL HEDGE IN THAT DIRECTION FOR NOW WITH TEMPS IN CASE THE GFS IDEA WITH SHARPER RIDGE AHEAD OF MORE PROGRESSIVE TROUGH PANS OUT. TOO MUCH UNCERTAINTY GIVEN POTENTIAL ROLE OF THE PACIFIC HURRICANE. WHAT THIS MEANS FOR THE WEEKEND FCST IS KEEPING A VERY SMALL CHANCE FOR SCATTERED CONVECTION MAINLY MTNS FOR FRIDAY AND SATURDAY... BASICALLY JUST AIR MASS WITH WEAK SW FLOW AND POTENTIAL FOR WEAK BACK DOOR FRONT TO KEEP THINGS SUPPRESSED EAST OF BLUE RIDGE AND MAYBE EVEN PARTS OF THE MOUNTAINS AS WELL...AND INCREASING CHANCES BY SUNDAY AND MONDAY AS UPPER TROUGH APPROACHES. THIS WILL RESULT IN INCREASED MOISTURE AND SOMEWHAT STEEPER LAPSE RATES AND MORE WIDESPREAD CONVECTION...AGAIN MAINLY MOUNTAINS BUT WITH THE UPPER FORCING AT SOME POINT SPREADING INTO PIEDMONT ON EITHER OR BOTH OF THOSE DAYS. GOING WITH HIGH CHANCE POPS BUT THAT FAR OUT NOT READY TO GO LIKELY...BUT ONCE TIMING OF THE TROUGH PUSHING THROUGH IS BETTER KNOWN...THEN LIKELY POPS WILL PROBABLY BE APPROPRIATE. SO COULD HAVE A STORMY LATER HALF OF LABOR DAY WEEKEND...WITH NEAR SEASONABLE TEMPS OVERALL. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 1250 AM EDT TUESDAY... VFR TO PREVAIL OVERNIGHT WITH JUST SOME PASSING MID/HIGH CLOUDS AS WELL AS A FEW BANDS OF STRATO-CU EARLY AND THEN STRATUS IN SPOTS LATE. CONFIDENCE IS ALSO HIGH THAT THERE WILL BE SOME PATCHY FOG IN THE HOURS LEADING UP TO DAYBREAK...BUT THERE IS SOME UNCERTAINTY TO HOW WIDESPREAD IT WILL BE. DO EXPECT KLWB/KBCB TO SEE A PERIOD OF IFR WITH LIFR POSSIBLE AT BOTH LOCATIONS BEFORE DAWN. ELSW MORE SPOTTY NATURE MVFR AT MOST OTHER LOCATIONS EXCEPT FOR KBLF WHERE CIGS AND VSBYS MAY FALL ENOUGH TO MAKE FOR IFR. THUS INCLUDED PREVAILING DENSE FOG IN SPOTS WHERE MORE CERTAIN AND LEFT TEMPO GROUPS FOR MORE ISOLATED/BRIEF VSBY REDUCTIONS. AFTER SUNRISE TUESDAY WHATEVER FOG THERE IS WILL BURN OFF QUICKLY AND SHOULD BE GONE BY 14Z/10AM. VFR CONDITIONS WILL RETURN FOR ALL TAF LOCATIONS THROUGH THE DAY AND CONTINUE INTO TUESDAY NIGHT WITH AGAIN MORE PATCHY FOG AROUND LATE. EXTENDED DISCUSSION... HIGH PRESSURE STRETCHING FROM NEW ENGLAND SOUTHWARD ALONG THE EASTERN FACE OF THE APPALACHIANS WILL MAINTAIN DRY CONDITIONS THROUGH WEDNESDAY. THE MAIN CONCERNS DURING THIS TIME WILL BE LOCALIZED FOG DURING THE PREDAWN HOURS OF EACH MORNING DUE TO MOIST SOILS...LIGHT WINDS AND MINIMAL CLOUD COVER. THE OFFICIAL NHC FORECAST INDICATES THAT TROPICAL CYCLONE CRISTOBAL WILL REMAIN WELL OFF THE EAST COAST AND WILL NOT IMPACT THE LOCAL WEATHER. A COLD FRONT WILL SINK SOUTHWARD FROM THE GREAT LAKES ON THURSDAY AND WEAKEN ACROSS OR JUST NORTH OF THE REGION BY FRIDAY. THIS BOUNDARY MAY BRING WIDELY SCATTERED SHOWERS AND STORMS MAINLY TO THE MOUNTAINS FOR WEEKS END INTO THE START OF THE WEEKEND WITH ONLY BRIEF PERIODS OF SUB VFR EXPECTED FOR NOW. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/NF NEAR TERM...JH SHORT TERM...RCS LONG TERM...SK AVIATION...CF/JH/MBS/NF

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