Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 080515 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1215 AM EST MON FEB 8 2016 .SYNOPSIS... DEEP LOW PRESSURE OFF THE CAROLINAS WILL CONTINUE TO SHIFT SLOWLY NORTHEAST AND AWAY FROM THE REGION OVERNIGHT INTO EARLY MONDAY. ANOTHER AREA OF UPPER LEVEL LOW PRESSURE ACROSS THE GREAT LAKES WILL SWING A STRONG COLD FRONT ACROSS THE MID ATLANTIC MONDAY...FOLLOWED BY A SECONDARY SURGE OF ARCTIC AIR TUESDAY INTO WEDNESDAY. WEAK IMPULSES COMBINED WITH NORTHWEST FLOW AND DEEP MOISTURE WILL THEN RESULT IN A PROLONGED SNOW SHOWER EVENT ESPECIALLY OVER THE MOUNTAINS INTO MIDWEEK. && .NEAR TERM /THROUGH MONDAY/... AS OF 925 PM EST SUNDAY... THE REGION IS CURRENTLY BETWEEN SYSTEMS WITH CIRRUS SHIELD FROM LARGE STORM BOMBING OUT OFF THE COAST COVERING THE EASTERN PART OF OUR AREA...WHILE THE APPROACHING ARCTIC FRONT IS STILL A WAYS OFF TO OUR WEST. DO NOT EXPECT MUCH IN THE WAY OF PRECIPITATION TO REACH THE WESTERN SLOPES BEFORE DAYBREAK AND INCREASING LOW CHANCE POPS FOR THE FAR WEST LATE TONIGHT HAVE THE SITUATION COVERED. PREVIOUS AFD... DEEP LOW PRESSURE OFF THE CAROLINAS HAS CONTINUED TO FAN A DEFORMATION MID/HIGH CLOUD CANOPY ACROSS THE REGION THIS AFTERNOON BUT FINALLY SEEING SIGNS OF THINNING WITH DRY AIR WORKING IN FROM THE NORTH. EXPECT AS THE SYSTEM CONTINUES TO WRAP UP WILL SEE THIS AXIS OF CLOUDS FINALLY SHIFT EAST...EXITING THE EASTERN ZONES LATER THIS EVENING PER LATEST GFS CLOUD FORECAST. THIS SHOULD ALLOW FOR A BRIEF PERIOD OF SUBSIDENCE CLEARING BETWEEN THE EXITING OFFSHORE SURFACE LOW AND THE NEXT UPSTREAM UPPER TROUGH FOR MUCH OF THE NIGHT. THUS WENT BELOW MOS TEMPS GIVEN A PERIOD OF CLEAR SKIES AND DIMINISHING WINDS LATE BEFORE CLOUDS ARRIVE ACROSS THE FAR WEST LATE. STRONG UPPER LOW ACROSS THE GREAT LAKES PIVOTS EAST MONDAY ALLOWING AN ASSOCIATED COLD FRONT TO WORK EAST INTO THE REGION MONDAY AFTERNOON. THIS WILL BRING AN AXIS OF LIFT INTO THE WEST BY MIDDAY MONDAY WITH THIS PRE-FRONTAL BAND OF MOISTURE POSSIBLY WORKING ACROSS THE CWA BY THE END OF THE DAY. CONCERNS REMAIN WITH TIMING AND THE DEGREE OF BOUNDARY LAYER WARMING THAT COULD OCCUR...AND JUST HOW MUCH QPF WILL BE ABLE TO BE GENERATED AS MOISTURE WORKS INTO LEFTOVER SUBSIDENCE BEHIND THE OFFSHORE LOW. LATEST GFS REMAINS THE WETTEST WITH OVER A QUARTER INCH LIQUID OVER THE NORTH/WEST WHILE THE NAM QUITE DRY AND THE SREF/12Z EC IN THE MIDDLE. SINCE THERE IS SOME GOOD BACKING AHEAD OF THE BOUNDARY...AND A RATHER STRONG BUT BRIEF PERIOD OF LIFT...THINK THERE COULD BE A DECENT BAND OF SNOW OVER THE WESTERN THIRD IF ARRIVAL IS AS FAST AS THE GFS. ELSEWHERE MAY SEE PRECIP START AS A BRIEF PERIOD OF RAIN CLOSER TO THE BLUE RIDGE...WITH MOSTLY LIQUID HEADING EAST EXCLUDING THE HIGHER ELEVATIONS SUCH AS THE SOUTHERN SHENANDOAH VALLEY CTYS AND SKYLINE DRIVE WHERE MORE SNOW POSSIBLE UP TOP. THEREFORE TRENDING POPS WITH A BAND OF LIKELY/CATEGORICAL WORKING EAST...REACHING THE BLUE RIDGE AROUND MIDDAY...AND THE PIEDMONT MID/LATE AFTERNOON. PROVIDED TOO MUCH WARMING DOESN`T OCCUR AND THE BAND STAYS TOGETHER CROSSING THE HIGHER ELEVATIONS...EXPECT A RANGE FROM 1-3 INCHES FAR WEST TO UP TO AN INCH OUT TO PARTS OF THE BLUE RIDGE AND LITTLE ELSEWHERE. GIVEN AMOUNTS BASICALLY NEAR ADVISORY LEVELS...WILL GO AHEAD AND INCLUDE A SECOND PERIOD ADVISORY FOR THE FAR WESTERN SLOPE COUNTIES FOR MONDAY FOR NOW. HIGH TEMPS TRICKY WITH POTENTIAL TO RISE WELL INTO THE 40S OR WARMER EAST GIVEN WARM ADVECTION...WHILE PERHAPS GETTING STUCK IN THE LOW/MID 30S FAR WEST IF PRECIP IS FASTER. THIS SUPPORTS RUNNING WITH A BLEND WHILE NUDGING VALUES CLOSER TO THE WARMER MOS OUT EAST. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... AS OF 340 PM EST SUNDAY... MODELS SHOWING NEXT SURGES OF COLDER AIR COMING IN ON MONDAY NIGHT...THEN AGAIN ON WEDNESDAY NIGHT. PERSISTENT NORTHWEST WINDS FROM THE SURFACE THROUGH AROUND 700 MB...THEREFORE RESULTING GIN SNOW SHOWERS. THERE MAY BE OCCASIONAL LULLS IN THE SNOW SHOWERS...BUT ANTICIPATE MORE TIME WITH PRECIPITATION THAN WITHOUT. MORE QUESTIONABLE IS WHEN AND HOW FAR EAST BANDS OF SNOW SHOWERS MAY DEVELOP DURING THIS TIME FRAME. WITH GOOD COLD AIR ADVECTION AND FORECAST SOUNDINGS SHOWING PRIME ICE CRYSTAL GROWTH...WILL TREND TOWARD AT LEAST SOME PROBABILITY OF SNOW SHOWERS OR FLURRIES NEARLY AS FAR EAST AS THE BLUE RIDGE. APPEARS THAT DEEPER MOISTURE WILL ERODE FROM SOUTH TO NORTH ON WEDNESDAY AND WEDNESDAY NIGHT...WITH THE SNOW SHOWERS ENDING FIRST IN THE NORTHWEST NORTH CAROLINA MOUNTAINS AND EVENTUALLY IN SOUTHEAST WEST VIRGINIA. ALSO ENHANCING THE AVAILABLE MOISTURE...HYSPLIT TRAJECTORIES OFF THE GFS SHOWED BETWEEN AIR 2000 AND 300 FEET AGL MAY BE PICKING UP SOME MOISTURE FROM LAKE MICHIGAN. ISSUED A WINTER STORM WATCH FOR SEVERAL COUNTIES IN THE FAR WESTERN COUNTY WARNING AREA...SINCE TOTAL SNOWFALL FROM MONDAY NIGHT THROUGH WEDNESDAY NIGHT WILL BE ENOUGH TO IMPACT TRAVEL. PLUS...ENOUGH COLD AIR...COMBINED WITH MODERATE WINDS...TO RESULT IN HAZARDOUS WIND CHILL VALUES. HIGHEST SNOW AMOUNTS WILL BE ON THE HIGHER WEST FACING SLOPES AND COLDEST WIND CHILLS WILL BE AT HIGHER ELEVATIONS WEDNESDAY NIGHT. STAYED AS COLD OR SLIGHTLY COLDER THAN GUIDANCE THROUGH WEDNESDAY NIGHT. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 250 PM EST SUNDAY... CLOSED 500 MB LOW REMAINS OVER SOUTHEAST CANADA BUT HEIGHTS RISE OVER THE REGION. LONG WAVE TROUGH REMAINS OVER THE EAST THROUGH SUNDAY WITH MODELS SHOWING DIFFERENCE IN TIMING AND INTENSITY OF SHORT WAVES EMBEDDED WITHIN THE TROUGH. SURFACE HIGH PRESSURE WILL BE CENTERED OVER THE FORECAST AREA ON FRIDAY MORNING. MORE ARCTIC AIR COMES IN SATURDAY AND SUNDAY. BOTH GFS AND ECMWF ARE SHOWING VARIATIONS OF A 1040 MB HIGH BUILDING WELL INTO THE OHIO VALLEY AND MID ATLANTIC REGION DURING THAT TIME FRAME. SNOW SHOWERS WILL BE ENDING IN THE NORTHWEST COUNTY WARNING AREA. WILL HAVE A LOW PROBABILITY OF SNOW IN THE FORECAST FOR FRIDAY OR SATURDAY THAT IS ASSOCIATION WITH A SOMEWHAT STRONGER SHORT WAVE TRACKING THROUGH THE BASE OF THE UPPER TROF. BUT AT THAT TIME FRAME...LOCATION AND TIMING ARE LIKELY TO CHANGE. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 1150 PM EST SUNDAY... THROUGH THE NIGHT...THE CWA SHOULD GENERALLY BE SANDWICHED IN BETWEEN THE DEPARTING COASTAL SYSTEM AND A DEEP UPPER LOW SAGGING SOUTHWARD THROUGH THE GREAT LAKES. THIS SYSTEM ALSO APPEARS TO BE SOMEWHAT SLOWER THAN EXPECTED YESTERDAY. CONSEQUENTLY...DEEPER ASSOCIATED MOISTURE SHOULD NOT REACH THE WESTERN CWA UNTIL AROUND DAYBREAK...AFTER DAYBREAK EAST OF THE BLUE RIDGE. SO LARGELY...ALL TAF SITES WILL SEE VFR CIGS/VSBYS THROUGHOUT THE FIRST 12 HOURS OF THE TAF VALID PERIOD. CIGS WILL BEGIN TO LOWER INTO THE MVFR CATEGORY KBLF-KLYH AND KBCB IN THE 12Z-15Z TIME FRAME WITH -SN ASSOCIATED WITH A BAND OF STRONGER DYNAMIC FORCING AND INITIAL FRONTAL BOUNDARY. ALTHOUGH THIS INITIAL BAND OF PRECIPITATION WILL SPREAD INTO THE PIEDMONT...TEMP PROFILES SUGGEST THAT IT MAY LARGELY BE RAIN IN THOSE AREAS. HAVE CARRIED ONLY -RA FOR KDAN AND KLYH...WITH A -RASN MIX KROA...WITH LOW CONFIDENCE IN SNOW THERE. KBCB SHOULD SEE MOSTLY -SN...BUT SOME -RA POSSIBLE AT THE ONSET. THE INITIAL BAND OF FRONTAL FORCED PRECIPITATION SHOULD MOVE EAST OF THE CWA BY AFTERNOON. AT THAT POINT...AND WITH COLDER ARCTIC AIR BEGINNING TO FILTER INTO THE REGION FROM THE WEST...PRECIPITATION SHOULD GENERALLY END EAST OF THE ALLEGHANY FRONT EXCEPT FOR A FEW FLURRIES LATER IN THE EVENING...BUT -SHSN SHOULD COMMENCE IN EARNEST ACROSS THE ALLEGHANYS WITH MVFR CIGS LOWERING TO IFR. CIGS SHOULD GENERALLY IMPROVE TO MVFR OR BETTER EAST OF THE BLUE RIDGE. VISIBILITIES WILL BE MOSTLY MVFR DURING THE MORNING/AFTERNOON RAIN/SNOW...IMPROVING TO VFR ACROSS THE PIEDMONT DURING THE EVENING...DETERIORATING TO IFR OR PERHAPS EVEN LIFR IN THE WEST IN INCREASING SNOW SHOWERS AND PERHAPS EVEN SOME BLOWING SNOW...ALTHOUGH DID NOT ADVERTISE THAT JUST YET. WINDS WILL REMAIN CHAOTIC THROUGH THE OVERNIGHT HOURS AS THE REGION REMAINS SANDWICHED BETWEEN THE TWO LARGER SCALE SYNOPTIC SYSTEMS. GENERALLY A NNW WIND WILL PREVAIL IN MOST AREAS. TOWARD DAYBREAK...WINDS IN THE WEST SHOULD TRANSITION TO SW 5-7KTS AND THIS WILL SPREAD EAST THROUGH THE MORNING. BY EVENING...WINDS WILL BECOME WSW-WNW 10-12KTS WITH GUSTS 15-20KTS BEHIND THE FRONTAL BOUNDARY AND SLOWLY INCREASE THROUGH THE EVENING HOURS. HIGH CONFIDENCE IN CIGS THROUGH 12Z...THEN MEDIUM CONFIDENCE THROUGH THE REMAINDER OF THE TAF VALID PERIOD. HIGH CONFIDENCE IN VSBY THROUGH 12Z...THEN MEDIUM CONFIDENCE THROUGH THE REMAINDER OF THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN WIND DIRECTION...MEDIUM TO HIGH CONFIDENCE IN WIND SPEED THROUGH THE TAF VALID PERIOD. EXTENDED DISCUSSION... SUB-VFR SHOULD BECOME MORE CONFINED TO THE WESTERN SLOPES MONDAY NIGHT INTO MIDWEEK WITH PROLONGED MVFR/IFR CONDITIONS AT KBLF/KLWB IN SNOW SHOWERS THROUGH AT LEAST WEDNESDAY NIGHT AS ARCTIC AIR ARRIVES. POTENTIAL ALSO FOR PERIODS OF MVFR AT KBCB/KROA AS IMPULSES ROTATE ACROSS THE MOUNTAINS AND BANDS DEVELOP DURING THE OVERNIGHT HOURS. ACCUMULATING SNOW IS LIKELY IN THE MOUNTAINS WEST OF THE BLUE RIDGE. FLURRIES MAY ALSO OCCUR AS FAR EAST AS THE PIEDMONT WHERE INTERVALS OF VFR TO MVFR CIGS COULD ALSO OCCUR. CONDITIONS SHOULD BRIEFLY RETURN TO MAINLY VFR THURSDAY/THURSDAY NIGHT AS WEAK HIGH PRESSURE BUILDS IN AND MOISTURE DECREASES. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...WINTER STORM WATCH FROM MONDAY EVENING THROUGH THURSDAY MORNING FOR VAZ007-009>012-015-019-020. WINTER WEATHER ADVISORY FROM 7 AM TO 6 PM EST MONDAY FOR VAZ007-009-015. NC...WINTER STORM WATCH FROM MONDAY EVENING THROUGH THURSDAY MORNING FOR NCZ001-018. WINTER WEATHER ADVISORY FROM 7 AM TO 6 PM EST MONDAY FOR NCZ001-018. WV...WINTER STORM WATCH FROM MONDAY EVENING THROUGH THURSDAY MORNING FOR WVZ042>044-507-508. WINTER WEATHER ADVISORY FROM 7 AM TO 6 PM EST MONDAY FOR WVZ042-043-508. && $$ SYNOPSIS...JH/PM NEAR TERM...JH/MBS SHORT TERM...AMS LONG TERM...AMS AVIATION...JH/PM/RAB

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