Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210414 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1114 PM EST SAT DEC 20 2014 .SYNOPSIS... HIGH PRESSURE WILL BRING SOME IMPROVEMENT TO OUR WEATHER ON SUNDAY...BEFORE A WEAK AREA OF LOW PRESSURE MOVING UP THE COAST BRINGS PRECIPITATION BACK TO OUR FORECAST FOR SUNDAY NIGHT AND MONDAY. AFTER A BRIEF BREAK ON TUESDAY...A VERY STRONG COLD FRONT WILL MOVE THROUGH THE REGION ON WEDNESDAY...BRINGING RAIN AND GUSTY WINDS TO THE AREA FOR CHRISTMAS EVE. && .NEAR TERM /THROUGH SUNDAY NIGHT/...
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AS OF 1100 PM EST SATURDAY... LOW LEVEL MOISTURE REMAINS OVER THE FORECAST AREA WITH SOLID OVERCAST BEING REPORTED ACROSS THE FCST AREA. RADAR INDICATES SOME VERY LIGHT PRECIP FALLING OVER THE NEW RIVER VALLEY. SURFACE REPORTS INDICATE DRIZZLE OR DRIZZLE MIXED WITH A LITTLE BIT OF LIGHT SNOW...JUST TRACE AMOUNTS. FOR THE OVERNIGHT...LITTLE CHANGE EXPECTED WITH MOSTLY CLOUDY SKIES. MOISTURE IN THE SOUNDING PROFILE IS VERY SHALLOW SO ANY PRECIP SHOULD REMAIN LIGHT. PROSPECTS FOR ANYTHING MORE THAT A TRACE IS 10 PERCENT OR LESS. UPPER FLOW IS ESSENTIALLY ZONAL OVER US AND THIS IS KEEPING ANY DECENT ENERGY LOCKED UP TO OUR NORTH AS A SHORT WAVE MOVES THROUGH THE FLOW OVERNIGHT. HOWEVER...WEDGE ALONG THE EASTERN SEABOARD WILL BE SHARPENING THROUGHOUT THE WEEKEND WHICH WILL LEAD TO SOME UPSLOPE ALONG THE EASTERN SLOPES OF THE BLUE RIDGE WITH LIGHT SOUTHEASTERLY SURFACE WINDS. THIS WILL HELP SQUEEZE OUT SOME SNIZZLE...DRIZZLE/FLURRIES...TONIGHT. THERE MAY BE SOME FREEZING FOG AROUND AS MODEL SOUNDINGS SHOW SATURATED CONDITIONS IN THE BOUNDARY LAYER IN AREAS WHERE TEMPERATURES WILL BE BELOW FREEZING. DO NOT BELIEVE ANY HEADLINES ARE CALLED FOR SINCE IT LOOKS TO BE A FACTOR FOR ONLY A VERY SMALL WINDOW OF TIME JUST BEFORE DAYBREAK BUT WILL MENTION IN THE HWO. MODEST IMPROVEMENT FOR SUNDAY AS MOISTURE SLOWLY ERODES...BUT WILL REMAIN POOLED ALONG THE MOUNTAINS. WE WILL NOT HAVE TO WAIT LONG FOR OUR NEXT BOUT WITH WINTER AS A WEAK SHORT WAVE MOVES OVER THE AREA SUNDAY NIGHT AND COMBINES WITH WEAK ISENTROPIC LIFT TO GENERATE LIGHT PRECIPITATION. PTYPE WILL BE A STRUGGLE WITH THIS SINCE COLD AIR WEDGE WILL HAVE NEAR SURFACE TEMPS NEAR FREEZING AS TEMPERATURES ALOFT WARM. TOP DOWN METHODOLOGY CURRENTLY YIELDS MOSTLY LIQUID WITH SLEET AND FREEZING RAIN MAINLY FOR THE GREENBRIER VALLEY AND ALLEGHANY HIGHLANDS...WITH ADDITIONAL POCKETS OF MIXED PRECIPITATION ELSEWHERE. OVERALL QPF LOOKS TO BE RATHER LIGHT SO THIS DOES NOT LOOK TO BE A VERY SIGNIFICANT EVENT THOUGH IT DOES NOT TAKE MUCH FREEZING RAIN TO MAKE TRAVEL HAZARDOUS.
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&& .SHORT TERM /MONDAY/... AS OF 300 PM EST SATURDAY... COMPLEX FORECAST FOR THE EARLY TO MID-WEEK WITH TWO SYSTEMS TO DEAL WITH. FIRST WILL BE EARLY MONDAY EVENT WITH A WEAK LOW ALONG THE NC COAST AT 12Z AND THE FAMILIAR WEDGE BUILDING DOWN THE EASTERN SLOPES OF THE APPALACHIANS FROM A PARENT 1030-ISH SURFACE HIGH OVER FAR NORTHERN NEW ENGLAND. NOT A PARTICULARLY STRONG OR EVEN COLD WEDGE BUT ENOUGH TO BRING AT LEAST SURFACE TEMPS CLOSE TO FREEZING IN SOME COLDER LOCATIONS WHILE THE 0C H85 LINE IS GENERALLY ALREADY WELL NORTH OF THE CWA..DEPENDING OF COURSE ON WHICH MODEL. 12Z GFS AND NAM ARE BOTH ABOVE FREEZING AT H85 FROM 12Z ONWARD. SURFACE LOW LIFTS NORTHEAST DURING THE DAY TO A POSITION OFF THE VA CAPES BY 00Z TUE TAKING WHATEVER PRECIP DOES FALL WITH IT OFF TO THE EAST. QPF FROM THIS EVENT LIKELY TO BE QUITE MODEST...FROM LESS THAN 0.10 INCHES FAR NORTHWEST TO POSSIBLY 0.25 TO 0.50 INCHES FAR EAST. ALTHOUGH SEVERAL HOURS OF FREEZING RAIN IS POSSIBLE FOR THE COLDER WESTERN VALLEYS NOT EXPECTING IT TO LAST VERY LONG AND ALL LIQUID SHOULD FALL EAST OF THE MOUNTAINS AND THEN ALL AREAS TRANSITION TO RAIN DURING THE DAY. HIGHS MONDAY WILL REMAINS CHILLY IN THE 30S TO LOW 40S. THERE WILL BE A BRIEF BREAK IN THE ACTION OVERNIGHT MONDAY AS THE WEAK ATLANTIC LOW DEPARTS BUT WITH FLOW REMAINING SOUTHWEST THERE IS BARELY ANY COLD ADVECTION BEHIND IT WHICH SHOULD LEAVE TEMPS ACTUALLY FAIRLY MILD...GENERALLY ABOVE FREEZING BY TUESDAY MORNING. THE FLOW REMAINS SOUTH TO SOUTHWEST THROUGH THE DAY WITH PLENTY OF AMBIENT MOISTURE AND SEVERAL WEAK BUT HARD TO TIME DISTURBANCES SO KEPT MAINLY CHANCE POPS BUT QPF AGAIN QUITE LOW...BELOW 0.05 INCHES WITH POSSIBLY SOME ENHANCEMENT ALONG THE BLUE RIDGE. PRECIPITATION SHOULD BE ALL RAIN AS HIGHS IN THE 40S EXPECTED CWA-WIDE AND WEDGE REMOVED FROM THE EQUATION. SOUTHERLY FLOW AND WARM ADVECTION BECOMES FAIRLY IMPRESSIVE AHEAD OF THE MUCH STRONGER LOW DEVELOPING OVER THE LOWER MISSISSIPPI VALLEY MID- TO LATE DAY TUESDAY. POPS AND QPF WILL INCREASE OVERNIGHT TUESDAY AS AVAILABLE MODELS SHOW A WIDESPREAD PRECIP EVENT WITH AMOUNTS APPROACHING A HALF-INCH BY EARLY WEDNESDAY AS THE SURFACE LOW DEEPENS AND RAPIDLY LIFTS NORTH TOWARD THE GREAT LAKES BY 12Z WED. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... AS OF 300 PM EST SATURDAY... UPPER TROUGH OVER THE MISSISSIPPI VALLEY WILL EJECT A NEGATIVELY TILTED THROUGH THE SOUTHEAST U. S. WEDNESDAY. SFC LOW PRESSURE NEAR CINCINNATI WITH TRAILING COLD FRONT WILL LIFT NORTHEAST INTO THE GREAT LAKES BY WEDNESDAY EVENING AND INTO EASTERN CANADA BY WEDNESDAY NIGHT. A STRONG COLD FRONT WILL MOVE EAST ACROSS OUR REGION WEDNESDAY INTO WEDNESDAY NIGHT. THERE IS THE POTENTIAL FOR OUR REGION TO HAVE ACTIVE WEATHER WEDNESDAY WITH PLENTY OF SHOWERS...PERHAPS VERY GUSTY WINDS AND A FEW THUNDERSTORMS. HOWEVER THE BEST INSTABILITY AS SEEN IN THE LI FIELDS REMAINS SOUTH AND EAST OF OUR AREA. THE DAY 5 CONVECTIVE OUTLOOK FROM SPC HAS PLACED THE STRONG TO SEVERE THUNDERSTORMS POTENTIAL FURTHER SOUTH ALONG EASTERN CAROLINA TO FLORIDA. HIGHS ON WEDNESDAY WILL RANGE THE MID 40S IN THE WEST TO THE MID AND UPPER 50S IN THE EAST. 850MB TEMPERATURES ARE STILL INDICATING THE COLD AIR PUSHES IN QUICKLY IN WAKE OF THE COLD FRONT. RAIN AND SNOW SHOWERS WILL CHANGEOVER TO SNOW SHOWERS AND SNOW FLURRIES IN THE WEST WEDNESDAY NIGHT. SOME LIGHT SNOW ACCUMULATIONS MAY BE POSSIBLE CHRISTMAS EVE NIGHT IN THE WESTERN UPSLOPE FAVORED LOCATIONS. BUT A WARM GROUND AND SHARP RICH MOISTURE CUTOFF MAY HINDER SNOW ACCUMULATIONS. LOW TEMPERATURES WEDNESDAY NIGHT WILL DROP INTO THE LOWER TO MID 20S IN THE MOUNTAINS TO THE LOWER 30S IN THE PIEDMONT. WEST TO NORTHWEST UPPER FLOW WILL CONTINUE INTO THURSDAY WITH MOUNTAIN RAIN AND SNOW SHOWERS. HIGHS CHRISTMAS DAY WILL VARY FROM AROUND 30 DEGREES IN THE NORTHWEST MOUNTAINS TO AROUND 50 DEGREES IN PIEDMONT. WINDS WILL BE QUITE STRONG ON THURSDAY AS A 50 TO 55 KNOT 850MB JET PIVOTS ACROSS THE REGION. AT THIS TIME...LOOKS LIKE VALUES SHOULD REMAIN BELOW WIND ADVISORY LEVELS. AS HIGH PRESSURE SLIDES OFF THE COAST...DRY WEATHER IS EXPECTED CHRISTMAS NIGHT/THURSDAY NIGHT WITH LOW TEMPERATURES GENERALLY IN THE UPPER 20S AND LOWER 30S. THE UPPER FLOW SHIFTS TO THE SOUTHWEST FRIDAY INTO FRIDAY NIGHT AS TROF CURVES OUT IN THE CENTRAL US WITH SFC LOW PRESSURE DEVELOPING OVER THE MIDWEST WITH A FRONTAL BOUNDARY TRAILING SOUTH. HIGHS ON FRIDAY WILL VARY FROM THE LOWER 40S IN THE MOUNTAINS TO THE MID 50S IN THE PIEDMONT. MOISTURE SLOWLY RETURN FRIDAY NIGHT INTO SATURDAY AS FRONTAL BOUNDARY APPROACHES. LOWS FRIDAY NIGHT DROP INTO THE LOWER AND MID 30S IN MOST LOCATIONS. A COLD FRONT MOVES ACROSS OUR REGION SATURDAY INTO SATURDAY NIGHT. && .AVIATION /04Z SUNDAY THROUGH THURSDAY/...
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AS OF 1100 PM EST SATURDAY... LOW LEVEL MOISTURE WILL REMAIN IN PLACE OVER THE MID ATLANTIC OVERNIGHT. MVFR WILL PERSIST AND POTENTIALLY BECOME IFR VCNTY OF THE MTNS WHERE RIDGES MAY BE OBCSD ATTMS. RESIDUAL BOUNDARY LAYER MOISTURE MAY ALSO LEAD TO SOME VERY LIGHT PRECIP...MIXED DRIZZLE/FLURRIES WITH THE POTENTIAL FOR RIME ICING. CONFIDENCE IS LOWER FOR THE EVENTUAL CLEARING OF FOG AND LOW CEILINGS ON SUNDAY...AS HIGH PRESSURE REMAINS WEDGED AGAINST THE EASTERN SIDE OF THE BLUE RIDGE. SOME OF THE GUIDANCE APPEARS TOO OPTIMISTIC AND DOES NOT ACCOUNT FOR THE REMAINING LAYER OF MOISTURE NEAR THE SURFACE...AS THEY PORTRAY SKIES CLEARING BY 18Z AT ALL TAF SITES. ALTHOUGH CONDITIONS SHOULD EVENTUALLY IMPROVE TO VFR SUNDAY AFTERNOON AT LYH/ROA/DAN...MVFR CEILINGS WERE LEFT AT BCB/LWB/BLF FOR THIS UPDATE AS IT MAY TAKE UNTIL MID/LATE AFTERNOON OR AFTER 18Z/1PM FOR THE LOW CLOUDS TO FINALLY SCATTER. EXTENDED DISCUSSION... A LOW PRESSURE SYSTEM ALONG THE GULF COAST WILL TRACK NORTHWARD ALONG THE EAST COAST DURING SUNDAY NIGHT INTO MONDAY...AND BRING PRIMARILY RAIN AND MVFR/IFR CONDITIONS OVER THE MID ATLANTIC. HOWEVER...THERE IS A POTENTIAL FOR PATCHY AREAS OF FREEZING RAIN ACROSS THE ALLEGHANY HIGHLANDS OF VIRGINIA AND SOUTHEAST WEST VIRGINIA...WHERE TEMPERATURES MAY STRUGGLE TO GET ABOVE FREEZING DURING EARLY MONDAY MORNING. LWB MAY BE IMPACTED...BUT THERE IS LOW CONFIDENCE DUE TO THE UNCERTAINTY OF THE THERMAL PROFILE IN THE MODEL SOUNDINGS. WARM AIR ADVECTION DURING MONDAY AND TUESDAY SHOULD END THE THREAT OF FROZEN PRECIPITATION...BUT PERIODS OF RAIN AND MVFR/IFR CONDITIONS COULD LINGER THROUGHOUT THIS TIME. A STRONG COLD FRONT WILL APPROACH FROM THE WEST BY TUESDAY NIGHT INTO WEDNESDAY. POOR FLYING WEATHER DUE TO MORE RAIN SHOWERS SHOULD ACCOMPANY THE FRONT...AND A STRONG LOW LEVEL JET MAY POSE A LOW LEVEL WIND SHEAR THREAT. GUSTY NORTHWEST WINDS AND A CONSIDERABLE TEMPERATURE DROP ARE EXPECTED BEHIND THE COLD FRONT ON WEDNESDAY NIGHT. UPSLOPE SNOW SHOWERS ARE POSSIBLE ALONG THE WESTERN SLOPES JUST IN TIME FOR CHRISTMAS DAY...WHILE VFR CONDITIONS SHOULD RETURN TO MOST LOCATIONS EAST OF THE BLUE RIDGE.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...MBS NEAR TERM...MBS/PM SHORT TERM...PC LONG TERM...KK AVIATION...PM/PW

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