Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 181147 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 747 AM EDT SAT OCT 18 2014 .SYNOPSIS... A COLD FRONT CROSSING THROUGH THE MID ATLANTIC REGION THIS MORNING WILL BE OFF THE COAST TONIGHT...FOLLOWED BY HIGH PRESSURE FOR SUNDAY. ON MONDAY AND TUESDAY LOW PRESSURE WILL TRACK FROM THE GREAT LAKES TO OFF THE VIRGINIA COAST. && .NEAR TERM /THROUGH TONIGHT/... AS OF 430 AM EDT SATURDAY... WELL DEFINED SHORT WAVE ON WATER VAPOR LOOP NEAR LAKE SUPERIOR WILL TRACK SOUTHEAST THROUGH THE OHIO VALLEY TODAY AND ACROSS THE COUNTY WARNING AREA THIS EVENING. THE NAM/ECMWF WERE SLIGHTLY SLOWER WITH THE TROF AXIS THAN THE GFS. WPC WAS FAVORING THE NAM/ECMWF TIMING. SURFACE COLD FRONT WAS CROSSING THROUGH THE EASTERN COUNTY WARNING AREA EARLY THIS MORNING. WILL HAVE MODEST 850 COLD AIR ADVECTION TODAY AND TONIGHT WITH 850 MB TEMPERATURES LOWERING TO 0 TO +5 BY LATE TONIGHT. ANY SUNSHINE AND MIXING WILL BE OFFSET BY COLD AIR ADVECTION TODAY. NET RESULT WILL BE ONLY A SMALL RISE IN TEMPERATURES. BUT WINDS AND CLOUDS WERE LIMITING DROP IN TEMPERATURES EARLY THIS MORNING. STARTING OUT MILD ENOUGH IN SOME LOCATIONS THAT EVEN WILL A SMALL RISE IN TEMPERATURES WILL BE WARMER THAN SOME THE GUIDANCE SUGGESTS FOR MAXIMUM TEMPERATURES. WILL BE TRIMMING BACK ON CHANCE OF PRECIPITATION AFTER MIDNIGHT. AIR POSSIBLY COLD ENOUGH TO SUPPORT SNOW COMES IN AT THE VERY TAIL END OF THE CHANCE OF PRECIPITATION. ALONG THE SAME LINES...CLOUDS DO NOT CLEAR OUT AND WIND DOES NOT DIMINISH UNTIL LATE TONIGHT. THIS WILL LIMIT THE AREAL COVERAGE OF ANY FROST. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... AS OF 400 AM EDT SATURDAY... TO BEGIN...STRONG SHORT WAVE WILL QUICKLY ROTATE OUT OF THE REGION SUNDAY MORNING...WITH SFC HIGH PRESSURE BUILDING IN RAPIDLY FROM THE NORTHWEST IN ITS WAKE. GUSTY NW WINDS AND STRONG CAA EARLY WILL QUICKLY GIVE WAY TO DIMINISHING WINDS AND WAA ALOFT BY AFTERNOON. UPSLOPE CLOUDS MAY LINGER FOR A FEW HOURS ACROSS THE ALLEGHANYS...BUT ALL BUT THE NAM SHOW THIS MOISTURE GONE BY EARLY AFTERNOON...AND THE NAM BY 00Z MON. THUS...WE SHOULD SEE AMPLE AMOUNTS OF SUNSHINE ALL AREAS BY AFTERNOON AND IT WILL BE CLEAR NEARLY ALL DAY EAST OF THE BLUE RIDGE. TEMPERATURES WILL BE ON THE COOL SIDE...AND AMONG SOME OF THE COOLEST SO FAR IN THIS YOUNG FALL SEASON. WITH MORNING LOWS IN THE WESTERN MOUNTAINS IN THE LOW TO MID 30S AND GUSTY NW WINDS...IT WILL FEEL LIKE A LITTLE WINTERLIKE FOR A FEW HOURS SUN MORNING WITH WIND CHILLS 20 TO 25 NW GREENBRIER FOR A AROUND SUNRISE. SUNSHINE AND WEST WINDS...ESPECIALLY EAST OF THE ALLEGHANY FRONT...WILL YIELD A MUCH NICER AFTERNOON WITH HIGHS RANGING FROM THE UPPER 40S HIGHER ELEVATIONS OF WESTERN GREENBRIER TO THE MID 60S SOUTHSIDE AND OUR NC PIEDMONT COUNTIES. THE MAIN CONCERN THROUGH THIS PERIOD WILL BE THE FROST/FREEZE POTENTIAL LATE SUNDAY NIGHT/EARLY MONDAY MORNING. WHILE CONDITIONS ARE EXPECTED TO BE THE MOST CONDUCIVE TO SUCH SINCE THE OCT 5 EVENT...THEY ARE FAR FROM IDEAL. PROGRESSIVE FLOW ALOFT WILL ALLOW THE COLD SFC HIGH TO QUICKLY SHIFT EAST OF THE REGION SUN NIGHT AS THE NEXT UPSTREAM/ALBERTA CLIPPER SYSTEM RAPIDLY APPROACHES FROM THE NW. TEMPERATURES MAY ACTUALLY BOTTOM OUT AROUND MIDNIGHT AND THEN SLOWLY RISE AFTERWARDS AS WAA ENSUES FAIRLY QUICKLY WITH RETURN SW FLOW EVIDENT. THE EXCEPTION WILL BE THE DECOUPLED AREAS IN DEEPER VALLEYS. AT THIS POINT...GIVEN THE PATTERN...THE POTENTIAL FOR FROST OR A VERY LIGHT FREEZE MAY BE GREATEST EAST OF THE ALLEGHANY FRONT IN DECOUPLED AREAS OF THE GREENBRIER VALLEY/NEW RIVER VALLEY.SOUTHERN SHENANDOAH VALLEY...AND EVEN SOME AREAS OF THE PIEDMONT CLOSER TO THE HIGH CENTER WITH LIGHTER WINDS. FROST POTENTIAL IS LIKELY GREATER THAN FREEZE POTENTIAL GIVEN MOIST GROUND FROM ALL OF THE RECENT RAIN. HAVE DECIDED NOT TO ISSUE ANY HEADLINES AT THIS POINT IN COORDINATION WITH NEIGHBORING OFFICES AND ONLY PATCHY GRID PIXELS OF 30-32. A FROST ADVISORY FOR MUCH OF THE CWA...AND PERHAPS SOME COUNTIES...E.G. EASTERN GREENBRIER COUNTY...MAY NEED A FREEZE WARNING...BUT NOT ENOUGH CERTAINTY OR AGREEMENT TO ISSUE THE HEADLINE AT THIS POINT. WILL CONTINUE TO HIGHLIGHT IN THE HWO AND LIKELY INCLUDE MUCH IF NOT ALL OF THE CWA GIVEN AFOREMENTIONED POSSIBILITIES EVEN ACROSS THE PIEDMONT. ON OCT 5...LYH WAS ACTUALLY COOLER THAN BCB/BLF WITH A LOW OF 33F. FOR THE REMAINDER OF THE SHORT TERM...THE FOCUS WILL BE ON THE NEXT CLIPPER/UPPER TROUGH TO DIVE SOUTHEAST TOWARD THE AREA LATE MON-TUE. MODELS HAVE CONVERGED ON A MORE NORTHERN SOLUTION AND...INITIALLY AT LEAST... A LESS CLOSED LOW SOLUTION WITH THIS EVENT. THIS WILL LEAVE THE RNK CWA LARGELY ON THE SOUTHWEST/DRIER SIDE OF THIS SYSTEM...RESULTING IN LESS RAINFALL THAN PREVIOUSLY EXPECTED WITH THIS EVENT. INSTEAD OF THE UPPER LOW CLOSING OFF OR MIGRATING ACROSS SW VA/SE WV INTO CENTRAL VA...IT APPEARS DESTINED FOR A MUCH MORE NORTHERN LOCATION SUCH AS PA/NY/MD. STILL...THOUGH THIS WILL LEAVE AN UNSETTLED CYCLONIC FLOW SETUP ACROSS THE REGION WITH VARIABLE CLOUDINESS...SCATTERED MAINLY DAYTIME SHOWERS...AND COOL TEMPERATURES...FAIRLY TYPICAL FOR BEING ON THE SOUTHWEST/SOUTH SIDE OF A COLD CORE CLOSED LOW. THE POTENTIAL FOR RAINFALL SHOULD END SOONER WITH THESE LATEST MORE N/NE SOLUTIONS. THROUGHOUT THE PERIOD...THE BEST POTENTIAL FOR -SHRA WILL BE ACROSS THE MOUNTAINS OF SE WV. TEMPERATURES WILL BE TOO COOL TO SUPPORT ANY INSTABILITY...HENCE THUNDER...BUT ON THE OTHER HAND WILL BE TOO WARM...850MB TEMPS GENERALLY AOB +1C THROUGHOUT THE EVENT AT THE COLDEST...TO SUPPORT ANY WINTER PRECIPITATION. USED A MODEL BLEND FOR TEMPERATURES THROUGHOUT THE SHORT TERM...AS THE GFS MOST WAS TOO COLD AND THE ECMWF MOS WAS TOO WARM. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... AS OF 430 AM EDT SATURDAY... MOST...IF NOT ALL OF THE PERIOD...WILL BE DOMINATED BY THE AFOREMENTIONED DEEP CLOSED LOW ACROSS THE NE STATES. WITH A HIGH AMPLITUDE UPPER RIDGE ACROSS THE WESTERN STATES...THE UPPER LOW WILL BE SLOW TO MOVE OUT. THE CENTRAL/SOUTHERN APPALACHIAN REGION WILL THUS BE LOCATED FOR SEVERAL DAYS ON THE SW SIDE OF THE UPPER LOW...AN INCREASINGLY DRY POSITION AS THE LOW DRIFTS FURTHER NE. BETWEEN WED AND FRI THE UPPER LOW ONLY DRIFTS VERY SLOWLY FROM CENTRAL/SOUTHERN PA TO OFF THE DELMARVA PENINSULA. SFC HIGH PRESSURE WILL SLOWLY APPROACH FROM THE CENTRAL U.S. EXPECT VARIABLE CLOUDS TO CONTINUE...SLIGHTLY LESS EACH DAY AND GREATEST ACROSS THE MOUNTAINS WITH SLIGHTLY ABOVE NORMAL MIN TEMPS AND BELOW NORMAL MAX TEMPS. OVERALL...A RELATIVELY BENIGN...QUIET WEATHER PERIOD. AGAIN...USED A BLEND OF MODEL TEMPS THROUGHOUT THE PERIOD. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... AS OF 740 AM EDT SATURDAY... SURFACE COLD FRONT WAS CROSSING THROUGH THE MID ATLANTIC REGION EARLY THIS MORNING...TURNING WINDS TO THE WEST. A SHARP UPPER TROUGH WAS APPROACHING FROM THE NORTHWEST FOR LATE TODAY/TONIGHT. EXTENSIVE CLOUDS HAVE DEVELOPED FROM THE COMBINATION OF UPSLOPE WEST WINDS WEST OF THE ALLEGHANY FRONT...SPREADING TOWARD THE BLUE RIDGE...AND THE APPROACHING STRONG PVA CENTER. MVFR CIGS HAVE ALREADY SPREAD INTO BLF/LWB AND WILL BE APPROACHING BCB THROUGH THE MORNING. EXPECT GENERALLY LOW END VFR CIGS TO DEVELOP TOWARD ROA/LYH AND POSSIBLY EVEN DAN THROUGH THE DAY. SOME -SHRA CAN BE EXPECTED ACROSS EASTERN WV TOWARD AFTERNOON IN ADVANCE OF THE SHARP UPPER TROUGH...BUT IT IS UNLIKELY THAT ANYTHING MORE THAN A -RA WILL REACH ANY FARTHER THAN BCB THROUGH THE TAF VALID PERIOD. AS THE FRONT MOVES THROUGH...CIGS WILL IMPROVE TO VFR EAST OF THE BLUE RIDGE WITH SKIES CLEARING AFT 06Z. WEST OF THE BLUE RIDGE AND ESPECIALLY IN UPSLOPE AREAS OF THE ALLEGHANYS...EXPECT MVFR CIGS TO PREVAIL OVERNIGHT INTO EARLY SUN...BUT -SHRA OR ANY HIGH ELEVATION -SHSN WILL REMAIN AWAY FROM THE TAF SITES. NO RESTRICTIONS TO VISIBILITY EXPECTED THROUGH THE TAF VALID PERIOD AS ANY PRECIPITATION WILL BE TOO LIGHT TO RESTRICT VISIBILITY AND THE SFC LEVELS ARE TOO DRY ALONG WITH STRONG GUSTY WINDS AND TURBULENT MIXING TO ALLOW FOR ANY FOG DEVELOPMENT THROUGH THE PERIOD. MAIN CONCERN THROUGH THE TAF VALID PERIOD WILL BE WIND. SUCH A DYNAMIC...NEGATIVELY TILTED SHORT WAVE WILL YIELD WSW-WNW WINDS THROUGH MUCH OF THE TAF VALID PERIOD OF SUSTAINED 10-15KTS WITH GUSTS 25-30KTS...ESPECIALLY BLF/BCB/ROA. WINDS WILL GRADUALLY DIMINISH AFT 06Z...BUT REMAIN ABOVE NORMAL FOR LATE NIGHT HOURS. MEDIUM TO HIGH CONFIDENCE IN CIG THROUGH THE TAF VALID PERIOD. HIGH CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. HIGH CONFIDENCE IN WIND DIR/SPD THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... HIGH PRESSURE BUILDS IN SATURDAY NIGHT AND SUNDAY. WINDS WILL DIMINISH AND CLOUD COVER WILL ERODE. VFR CONDITIONS ARE EXPECTED SUNDAY INTO MONDAY. ANOTHER UPPER LOW WILL SETTLE INTO THE REGION FROM THE NORTH LATE MON AND LINGER THROUGH MID-WEEK WITH SCT -SHRA AND MOSTLY MVFR CIGS AND BRIEF PERIODS OF MVFR VSBYS IN -SHRA. IMPROVING CONDITIONS EXPECTED TOWARD THE VERY END OF THE WEEK. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...RAB LONG TERM...DS/RAB AVIATION...AMS/RAB

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