Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 171745 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 145 PM EDT WED SEP 17 2014 .SYNOPSIS... A COOL WEDGE OF HIGH PRESSURE SETTLES IN FROM THE NORTH THIS AFTERNOON 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. && .NEAR TERM /THROUGH TONIGHT/... AS OF 115 PM EDT WEDNESDAY... MADE ADJUSTMENTS TO SKY COVER BASED ON SAT TRENDS AND MODEL TRENDS. NOT REALLY SEEING GOOD SIGNALS FOR RAIN SHOWERS THIS AFTERNOON...EXCEPT FOR INCREASING THETA-E AT THE SFC WITH SOME CONVERGENCE OVER THE MOUNTAINS OF NC/SW VA. KEPT SPOTTY POPS IN THE SOUTHERN CWA THIS AFTERNOON BUT NOT REALLY SEEING A LOT OF COVERAGE AT THIS POINT. TEMPS WERE BUMPED A LITTLE MORE WHERE MORE SUN HAS ALLOWED THEM TO RISE ABOVE FORECAST. PREVIOUS VALID DISCUSSION... WEAK WAVE ALOFT SHOULD PASS TO THE SOUTH TODAY AS WELL WITH ANOTHER NEARING THE WESTERN SLOPES THIS EVENING. 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. && .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... 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. && .LONG TERM /SUNDAY THROUGH TUESDAY/... 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. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 125 PM EDT WEDNESDAY... CIGS HAVE BEEN RISING THROUGH THE DAY AND MOST LOCATIONS ARE VFR OR HIGH END MVFR. THINK VFR WILL CARRY US INTO THIS EVENING WHEN THE INVERSION SETS UP AGAIN WITH EAST-SE FLOW ALLOWING FOR SOME STRATUS LAYER TO FORM. QUESTION IS HOW MUCH COVERAGE. MODELS ARE FAVORING SUB VFR AT ALL SITES ALONG WITH FOG...SO MADE THE TAFS SIMILAR TO THE PREVIOUS ISSUANCE AND WENT PESSIMISTIC ON VSBYS AT ALL BUT ROANOKE. WILL SEE SOME RECOVERY BACK TOWARD MVFR/VFR AFTER 12Z...WITH VFR IN THE AFTERNOON THURSDAY AHEAD OF THE NEXT TROUGH. EXTENDED AVIATION DISCUSSION... TROUGH IN THE EAST LIFTS LATE THIS WEEK INTO SATURDAY BUT WEAKNESS ALOFT TO LINGER OVER THE SOUTHEAST. HIGH PRESSURE AT THE SFC WILL WEDGE SOUTHWEST INTO OUR AREA DURING THIS TIME. EXPECT MAINLY VFR CONDITIONS OUTSIDE ANY FOG AT NIGHT AND POTENTIAL FOR SOME STRATUS ALONG AND EAST OF ROA/BCB...THOUGH THE HIGH PRESSURE SHOULD BE STRONG ENOUGH TO KEEP MOISTURE LIMITED. NEXT UPSTREAM TROUGH AND FRONT EXPECTED TO ARRIVE BY EARLY NEXT WEEK WITH A THREAT OF SHOWERS. MAY SEE SOME MVFR CIGS/VSBYS BUT APPEARS MOST OF THE TIME WILL CONTINUE TO SEE VFR. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/WP NEAR TERM...JH/WP SHORT TERM...RAB LONG TERM...AMS/RAB AVIATION...JH/WP

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