Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 170827 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 427 AM EDT WED SEP 17 2014 .SYNOPSIS...
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A COOL WEDGE OF HIGH PRESSURE SETTLES IN FROM THE NORTH TODAY BEFORE WEAKENING OVERNIGHT INTO THURSDAY. ANOTHER LARGER AREA OF HIGH PRESSURE WILL STRENGTHEN TO THE NORTH OF THE REGION FRIDAY INTO SATURDAY BEFORE PASSING OFFSHORE ON SUNDAY. A COLD FRONT WILL CROSS THE AREA FROM THE NORTHWEST ON MONDAY BRINGING A BETTER CHANCE OF SHOWERS TO START THE WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 245 AM EDT WEDNESDAY... MSAS SHOWING THE COLD FRONT NOW WELL TO THE SOUTH WITH SURFACE HIGH PRESSURE STARTING TO NOSE IN FROM THE NORTH ALLOWING AN INITIAL SHOT OF LOW LEVEL DRY ADVECTION PER CURRENT DEWPOINTS. AS THE CENTER OF THE RIDGE PASSES NORTH THIS MORNING...AND TO THE MID ATLANTIC COAST THIS AFTERNOON...WILL SEE BETTER WEDGING TAKE PLACE EARLY THIS MORNING AND LIKELY PERSIST AT LEAST BLUE RIDGE EAST INTO THIS EVENING. HOWEVER DEGREE OF STRATUS AND DRIZZLE STILL IN QUESTION THIS MORNING GIVEN THE DRY AIR AND DELAYED SETUP OF THE WEDGE UNDER A RATHER HIGH LEVEL STRATO- CU CANOPY TO INIT. THIS MAY TEND TO ALLOW MORE BREAKS THIS AFTERNOON ESPCLY IF LOW CLOUDS ARE SLOWER. THUS CUT BACK ON CLOUDS/DRIZZLE EARLY SIMILAR TO THE DRIER GFS AND TRENDED WITH MORE CLOUDS DURING THE MORNING. WEAK WAVE ALOFT SHOULD PASS TO THE SOUTH TODAY AS WELL WITH ANOTHER NEARING THE WESTERN SLOPES THIS EVENING. MAY SEE SOME WEAK INSTABILITY DEVELOP WEST OF THE BLUE RIDGE THIS AFTERNOON SO INCLUDED AN ISOLATED SHRA MENTION I-77 INTO NW NC AND OVER THE SE ON THE TAIL OF THE PASSING IMPULSE. ELSW...KEEPING SOME MENTION IN FOR -RA BLUE RIDGE PENDING DEPTH OF THE WEDGE BUT MAY END UP PC FAR WEST AND NE WITH MOSTLY CLOUDY CENTRAL/SOUTH BUT EVEN THERE SOME BREAKS POSSIBLE LATER. HIGH TEMPS REMAIN TRICKY GIVEN TIMING OF THE WEDGE/LOW CLOUDS AND CURRENT SPREAD IN MOS GUIDANCE. SINCE ALREADY RUNNING WARMER AND HAVE POTENTIAL FOR MORE SUN IN SPOTS...BUMPED UP GOING VALUES MORE IN LINE WITH THE ECMWF 2M TEMPS WHICH GETS SOME LOCATIONS ALONG THE WEDGE PERIMETER ABOVE 70 WITH MOSTLY 60S WITHIN THE CAD. WEAK WEDGE LINGERS ESPCLY EAST OVERNIGHT WITH ADDED CLOUDS WEST AHEAD OF ANOTHER SHORTWAVE DIVING SE IN THE NW FLOW ALOFT. HOWEVER SETUP NOT TOTALLY IDEAL FOR GOOD WEDGING GIVEN WEAKENING OF THE MID ATLANTIC SURFACE HIGH AND MORE NORTH/NW FLOW JUST ABOVE THE BOUNDARY LAYER MOIST LAYER. THIS ALONG WITH PLENTY OF DRY AIR ALOFT SUPPORTS LITTLE MORE THAN CLOUDS/PATCHY DRIZZLE EASTERN SLOPES LATE ALONG WITH SOME FOG IN SPOTS SO TRIMMED POPS. LOWS MAINLY 50S UNDER THE LOW LEVEL COOL POOL WITH SOME 40S POSSIBLE VALLEYS ESPCLY IF MORE CLEARING DEVELOPS.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
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AS OF 400 AM EDT WEDNESDAY... A WEAK SHORT WAVE WILL MOVE THROUGH THE REGION EARLY THU. THE TRACK WILL TAKE THE BEST LIFT/MOISTURE FROM EASTERN KY/EASTERN TN TOWARD FAR SW VA/NW NC. AT THIS POINT ONLY EXPECTING SOME MID CLOUDS AND POSSIBLY A PASSING SPRINKLE...BUT NOT ENOUGH SUPPORT TO INCLUDE ANY -SHRA IN THE GRIDS AT THIS POINT. FOLLOWING THIS TROUGH...THE BROAD UPPER LOW ANCHORED OVER HUDSON BAY WILL DEEPEN BRIEFLY. A STRONG CANADIAN SFC HIGH WILL TRANSLATE EASTWARD TOWARD NEW ENGLAND BY EARLY FRI AND INTO A VERY FAVORABLE WEDGE POSITION. AS THE SFC HIGH STRENGTHENS TOWARD 1030MB...DEEPENING EASTERLY FLOW WILL SPREAD DOWN THE EAST SIDE OF THE APPALACHIANS INTO THE SOUTHEAST STATES. GFS/ECMWF/NAM ALL IN GOOD AGREEMENT ON UPSLOPE WINDS ALONG THE BLUE RIDGE/ALLEGHANY FRONT LIKELY SQUEEZING OUT -DZ FRI MORNING...WHICH TRANSLATES FURTHER W-SW BY AFTERNOON TOWARD THE VA/TN/NC BORDER REGION. ABUNDANT LOW CLOUDS...ESPECIALLY BLUE RIDGE WESTWARD...WILL HOLD TEMPS BELOW NORMAL. BY SAT...THE FLOW QUICKLY BECOMES MORE ZONAL AS HEIGHTS RISE IN RESPONSE TO A BROAD UPPER RIDGE BUILDING ACROSS THE SOUTH CENTRAL/SOUTHEAST STATES. MEANWHILE...ANOTHER SHORT WAVE DIGS SOUTHWARD THROUGH THE GREAT LAKES WITH THE ASSOCIATED FRONTAL SYSTEM REACHING THE REGION BY SUN. THUS...WITH THE WEDGE ERODING QUICKLY SAT AND SW FLOW DEVELOPING IN ADVANCE OF THE NEXT SHORT WAVE...WE SHOULD SEE WARMER TEMPERATURES AND MORE SUNSHINE THAN WILL BE THE CASE FRI. FOR TEMPERATURES...LESS IMPRESSED WITH THE POTENTIAL WEDGE SETUP FOR THU...IF ANY. THE FIRST SFC HIGH IS VERY WEAK AND DISSIPATES AS OVERALL NW FLOW ALOFT PREVAILS. HAVE REMOVED MENTION OF DRIZZLE FOR EARLY THU AND ALSO WARMED TEMPERATURES SOMEWHAT THU IN ANTICIPATION OF RETURNING SW SFC FLOW...OR AT LEAST SOUTHERLY FLOW...AND LIKELY SOME SUNSHINE BY AFTERNOON WITH THE DISSIPATING WEAK WEDGE. ADJUSTMENT TO MOS GUIDANCE WAS NEEDED FOR MAX TEMPS ALL THREE DAYS. FOR MAX TEMPS THU...HAVE USED A COMPROMISE BETWEEN THE WARMEST MAV MOS AND THE COLDEST MET MOS...THUS JUST A TAD WARMER THAN THE ECMWF MOS. FOR FRI...HOWEVER...HAVE UNDERCUT ALL MODEL GUIDANCE...ESPECIALLY THE MAV MOS WHICH IS WAY TO WARM AND IN DISAGREEMENT WITH THE CLOUD FIELD AND -DZ/-RA IT GENERATES. POTENTIALLY...SOME AREAS FRI MAY NOT GET OUT OF THE MID TO UPPER 60S WEST OF THE BLUE RIDGE. BY SAT...SOUTHWEST FLOW...MORE SUNSHINE...AND NOTABLY HIGHER HEIGHTS/TEMPERATURES ALOFT...585DM AT 500MB...SHOULD SUPPORT LOW 80S ACROSS THE PIEDMONT TO THE LOWER 70S IN THE MOUNTAINS. AGAIN...GUIDANCE DOES NOT HAVE A GOOD HANDLE ON THIS AND IS TOO COOL.
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&& .LONG TERM /SUNDAY THROUGH TUESDAY/...
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AS OF 400 AM EDT WEDNESDAY... UPPER TROUGH WILL MOVE THROUGH THE REGION SUNDAY...ACCOMPANIED BY A CHANCE OF SHOWERS. WITH PREVAILING NW FLOW...THE BEST CHANCE WILL BE WEST OF THE ALLEGHANY FRONT ACROSS EASTERN WV. LATEST MODELS PROG ENOUGH INSTABILITY TO CONSIDER THUNDER...ALSO GIVEN CURRENT EXPECTED TIMING OF THE CONVECTION REACHING THE CWA LATE AFTERNOON/EARLY EVENING. HOWEVER...OUR ONLY NEIGHBOR TO MENTION THUNDER AT THIS POINT IS IN EAST TN...SO WILL LEAVE OUT AT THIS POINT. AT ANY RATE...THIS WOULD APPEAR TO BE ONE OF THE MORE TYPICAL EVENTS WE OFTEN SEE AS THE SYSTEM CROSSES THE MOUNTAINS WHERE MOST PRECIPITATION WANES RATHER QUICKLY AFTER IT PASSES EAST OF THE BLUE RIDGE. THE MAIN STORY BEHIND THE UPPER TROUGH SATURDAY WILL BE A DEEPENING TROUGH ACROSS EASTERN CANADA AND THUS DRASTICALLY LOWER HEIGHTS/TEMPERATURES ALOFT ACROSS THE EASTERN U.S. THIS WILL DOMINATE THE REGION THROUGH THE FIRST HALF OF NEXT WEEK AS IT SLOWLY TRANSLATES TOWARD THE CANADIAN MARITIMES. A REINFORCING SHORT WAVE WILL DRIVE WHAT APPEARS TO BE ONE OF THE COOLEST AIR MASSES OF THE FALL SEASON SO FAR THROUGH THE REGION MON-TUE. 850MB TEMPS DROP INTO THE +2C TO +6C RANGE BY TUE WITH MIN TEMPS POTENTIALLY INTO THE 30S IN THE MOUNTAINS AND 40S ELSEWHERE BY MID-WEEK NEXT WEEK. THE GFS TENDS TO BE SLIGHTLY COLDER THAN THE ECMWF. PRECIPITATION BEYOND SAT APPEARS TO BE PRETTY SCANT...BUT LIKELY EXTENSIVE UPSLOPE CLOUDS ACROSS THE ALLEGHANYS WITH NW UPSLOPE FLOW AND STRONG CAA. STILL TOO EARLY TO MENTION ANY -SHRA OR POTENTIALLY EVEN -SHSN AT THE HIGHEST ELEVATIONS WITH THE COLD AIR MASS MID PART OF NEXT WEEK...ESPECIALLY SINCE THE BEST UPPER SUPPORT REMAINS NORTH OF THE CWA WITH THE SECONDARY REINFORCING UPPER TROUGH. THUS...HAVE NOT MADE ANY SIGNIFICANT ADJUSTMENTS TO THE LONG TERM GRIDS AT THIS TIME.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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AS OF 1255 AM EDT WEDNESDAY... MAINLY VFR CIGS IN THE WAKE OF THE PASSING WAVE/FRONT TO THE SE WILL SLOWLY LOWER OVERNIGHT PER INCREASING NE FLOW UNDER THE DEVELOPING WEDGE. THIS SHOULD BRING CIGS DOWN TO MVFR ACROSS THE EAST IN THE NEXT FEW HOURS WITH PERIODIC IFR OVER THE WEST WHERE MOISTURE REMAINS TRAPPED AT KBLF/KLWB. LOW CONFIDENCE IN HOW FAST STRATUS/FOG AND/OR DRIZZLE DEVELOP OVERNIGHT BUT APPEARS THAT LOCATIONS ALONG THE BLUE RIDGE INCLUDING KBCB/KROA WILL SEE CIGS AND PERHAPS VSBYS DROP RIGHT BEFORE DAYBREAK...WITH SIMILAR TRENDS ALSO POSSIBLE AT KLYH/KDAN. HOWEVER THINK CURRENT HIGHER CLOUD BASES WILL DELAY THE OVERALL FOG FORMATION WITH THIS OCCURRING AS CIGS LOWER BY DAWN. THUS CONTINUED LEANING TOWARD MORE IFR/MVFR LATE TONIGHT WITH SOME FOG...THOUGH THINK FOG WILL BE LESS THAN THE LOWER CIGS. SOME DEGREE OF LOW LEVEL MOISTURE WILL REMAIN STUCK ACROSS THE REGION WEDNESDAY MORNING AND JUST HOW FAST THIS ERODES TRICKY PENDING JUST HOW DEEP THE LOW CLOUDS GET OVERNIGHT. LATEST GUIDANCE REMAINS SPREAD FROM ERODING MUCH OF THE LOW CIGS PER THE GFS TO AT LEAST MVFR HOLDING FOR MUCH OF THE DAY ESPCLY BLUE RIDGE AND POINTS EAST LIKE THE NAM/CMC. FOR NOW GIVEN THE POTENTIAL FOR CIGS TO HANG LONGER WITHIN THE WEDGE...TRENDED TOWARD HOLDING MVFR IN LONGER ESPCLY KROA AND POINTS EAST WITH RETURN TO VFR SE WEST VA SITES BY AFTERNOON AND AT KBCB AROUND 18Z/2PM. ANY IMPROVEMENT IN THE EAST LIKELY TO BE SHORT AS THE WEDGE FLOPS BACK AFTER DARK WITH POSSIBLE MVFR CIGS OR LOWER REDEVELOPING DURING WEDNESDAY EVENING. EXTENDED AVIATION DISCUSSION... BROAD UPPER TROUGH REMAINS IN PLACE ACROSS THE EASTERN STATES FOR THE REMAINDER OF THE WEEK ALLOWING A LARGE AREA OF HIGH PRESSURE TO REMAIN WEDGED ACROSS THE MID ATLANTIC THROUGH THE WEEKEND. THIS SHOULD PUSH THE PESKY DEEP MOISTURE FURTHER SOUTH AWAY FROM THE REGION. HOWEVER BIGGER CONCERN WILL BE WITH TRAPPED RESIDUAL LOW LEVEL MOISTURE THAT MAY KEEP SOUTHERN/WESTERN LOCATIONS STUCK IN PERIODS OF MVFR CIGS INTO FRIDAY AS THE LOW LEVEL EAST/SE FLOW TAKES SHAPE. HIGH PRESSURE MAY BE STRONG ENOUGH TO PUSH THE LOW LEVEL MOISTURE TO THE SOUTHWEST SATURDAY AND WITH HEATING/MIXING COULD SEE THINGS RETURN TO OVERALL VFR FOR EARLY IN THE WEEKEND...BUT NOT UNTIL SATURDAY AFTERNOON AT THIS POINT. FLOW TURNS MORE SW BY SUNDAY AHEAD OF THE NEXT FRONT ALLOWING FOR WIDESPREAD VFR WITH ANY WESTERN SHOWERS LIKELY NOT ARRIVING UNTIL OVERNIGHT.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...RAB LONG TERM...AMS/RAB AVIATION...JH

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