Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 252345 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 745 PM EDT MON AUG 25 2014 .SYNOPSIS... STRONG HIGH PRESSURE WILL CONTINUE TO EXTEND SOUTH ALONG THE EASTERN FACE OF THE APPALACHIANS THIS EVENING THROUGH MID WEEK. THIS SYSTEM WILL BRING COOL AND DRY AIR TO THE REGION OVER THE NEXT COUPLE OF DAYS. ANOTHER COLD FRONT WILL APPROACH THE AREA LATE IN THE WORK WEEK...RESULTING IN THE NEXT CHANCE OF SHOWERS AND THUNDERSTORMS. && .NEAR TERM /THROUGH TUESDAY/... AS OF 330 PM EDT MONDAY... SATELLITE IMAGERY AND SURFACE OBSERVATIONS INDICATE SCATTERED FAIR WEATHER CLOUDS ACROSS MUCH OF THE FORECAST AREA THIS AFTERNOON AS HIGH PRESSURE STRETCHING FROM NEW ENGLAND SOUTHWARD ALONG THE EASTERN FACE OF THE APPALACHIANS REMAINS OUR DOMINANT LOW LEVEL WEATHER FEATURE. THE COOL NORTHEASTERLY FLOW AROUND THIS HIGH HAS OFFSET THE WARMING ASSOCIATED WITH UPPER LEVEL RIDGING BUILDING UP THE OHIO RIVER VALLEY...KEEPING HIGHS TODAY SOME 5 TO 7 DEGREES BELOW NORMAL. SCATTERED CLOUDS ACROSS THE AREA WILL DISSIPATE QUICKLY TOWARD SUNSET...AND EXPECT TO ENTER THE LATE EVENING UNDER MOSTLY CLEAR SKIES. WITH HIGH PRESSURE CONTINUING TO BUILD SOUTHWARD TO SETTLE ACROSS OUR AREA...THE COMBINATION OF LIGHT WINDS AND MINIMAL CLOUD COVER WILL MAKE FOR STRONG RADIATIONAL COOLING...BRINGING OVERNIGHT LOWS TO SOME OF THE COOLEST OUR AREA HAS EXPERIENCED IN QUITE A WHILE. EXPECT LOWS TO DIP TO THE MID/UPPER 50S ACROSS THE PIEDMONT...WHILE LOW 50S AND UPPER 40S CAN BE EXPECTED ACROSS THE MOUNTAINS...MAYBE EVEN LOW 40S IN SOME OF THE DEEPER MOUNTAIN VALLEYS. FACTOR IN MOIST SOIL CONDITIONS IN ADDITION TO THE RADIATIONAL COOLING...AND WE CAN ALSO EXPECT AREAS OF FOG TO DEVELOP OVERNIGHT ACROSS MUCH OF THE REGION. FOG MAY BE DENSE BY SUNRISE IN SOME AREAS...ESPECIALLY THE DEEPER RIVER VALLEYS ACROSS THE MOUNTAINS...WHICH MAY MAKE FOR HAZARDOUS MORNING TRAVEL. FOG WILL BEGIN TO DISSIPATE AFTER 9 AM ACROSS THE REGION AS DAYTIME HEATING COMMENCES...BUT MAY SEE A FEW FOG BANKS LINGER UNTIL AROUND 11 AM ACROSS THE MOUNTAINS BEFORE THEY TOO MIX OUT. MUCH OF THIS FOG WILL TRANSITION TO ANOTHER ROUND OF AFTERNOON FAIR WEATHER CLOUDS DURING THE AFTERNOON. THE AXIS OF THE UPPER LEVEL RIDGE WILL BE SITUATED MORE ACROSS THE MID ATLANTIC AND CENTRAL APPALACHIANS ON TUESDAY...AND THEREFORE EXPECT SLIGHTLY WARMER AFTERNOON TEMPERATURES...WITH HIGHS REACHING INTO THE UPPER 70S AND LOW 80S MOST LOCATIONS. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... AS OF 325 PM EDT MONDAY... HIGH PRESSURE SHOULD MAINTAIN CONTROL OVER THE APPALACHIAN MOUNTAINS THROUGH TUESDAY NIGHT. CLEAR SKIES AND LIGHT WINDS SHOULD SET UP GOOD RADIATIONAL COOLING INITIALLY...BUT THE MOIST GROUND MAY ALLOW AREAS OF FOG TO DEVELOP TOWARD SUNRISE. THE LATEST MOS GUIDANCE RAISED HIGHS ON WEDNESDAY BY A FEW DEGREES COMPARED TO PREVIOUS RUNS...BUT THE MAV SEEMS A LITTLE AGGRESSIVE WITH THE DAYTIME HEATING. DEWPOINTS WILL ALSO BEGIN TO CREEP UPWARD...AS HIGH PRESSURE DRIFTS TOWARD THE SOUTHEAST. BY WEDNESDAY NIGHT...THE GFS AND ECMWF MODELS AGREE ON A WEAK COLD FRONT ARRIVING FROM THE NORTHWEST THAT MAY SPARK A FEW SHOWERS BY EARLY MORNING IN SOUTHEAST WEST VIRGINIA. THE FRONT WILL CROSS OVERHEAD ON THURSDAY...BUT SHOULD WASH OUT ALONG THE VIRGINIA AND NORTH CAROLINA BORDER BY THURSDAY NIGHT. CHANCE POPS WERE KEPT FOR THURSDAY AFTERNOON IN THE NORTHERN AND WESTERN PARTS OF THE CWA...WITH ONLY SLIGHT CHANCE POPS ELSEWHERE. INSTABILITY AND LIFT PARAMETERS SUGGEST THAT ONLY SCATTERED SHOWERS AND THUNDERSTORMS SHOULD BE EXPECTED...WHICH WILL DIMINISH DURING THURSDAY NIGHT. && .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 /00Z TUESDAY THROUGH SATURDAY/... AS OF 730 PM EDT MONDAY... HIGH CONFIDENCE OF VFR CONDITIONS THIS EVENING. VIS SAT AND SURFACE OBS CONFIRM THAT LOW CLOUDS CONTINUE TO ERODE...JUST A FEW CU REMAIN. EXPECT CLEAR SKIES FOR MUCH OF THE EVENING. RADIATIONAL COOLING WILL ALLOW TEMPS TO DROP QUICKLY OVERNIGHT AND APPROACH SURFACE DEWPTS EARLY TUESDAY MORNING. CONFIDENCE IS 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. FOG IS MENTIONED IN A TEMPO GROUP FOR A FEW HOURS IN THE MORNING. AFTER SUNRISE TUESDAY WHATEVER FOG THERE IS WILL BURN OFF QUICKLY AND SHOULD BE GONE BY 14-15Z. VFR CONDITIONS WILL RETURN FOR ALL TAF LOCATIONS THROUGH THE END OF THE PERIOD. WINDS WILL CONTINUE TO BE LIGHT AND OUT OF THE EAST. EXTENDED DISCUSSION... HIGH PRESSURE STRETCHING FROM NEW ENGLAND SOUTHWARD ALONG THE EASTERN FACE OF THE APPALACHIANS WILL MAINTAIN DRY CONDITIONS THROUGH MIDWEEK. 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 WITH ONLY BRIEF PERIODS OF SUB VFR EXPECTED FOR NOW. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...NF SHORT TERM...PW LONG TERM...SK AVIATION...CF/MBS/NF

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