Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 290940 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 540 AM EDT WED OCT 29 2014 .SYNOPSIS...
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A COLD FRONT WILL MOVE ACROSS THE MID ATLANTIC REGION TODAY WITH A PERIOD OF LIGHT RAIN...RAIN AMOUNTS OF A QUARTER INCH OR LESS. TEMPERATURES WILL RETURN TO MORE SEASONABLE LEVELS AFTER THE PASSAGE OF THIS COLD FRONT. A SHOT OF COLDER AIR WILL ARRIVE THIS WEEKEND...ASSOCIATED WITH A FAST MOVING CLIPPER SYSTEM FROM CANADA THAT WILL RESULT IN THE SPIN UP OF A STRONG AREA OF LOW PRESSURE IN THE UPPER LEVELS OF THE ATMOSPHERE AS IT REACHES THE MID ATLANTIC REGION SATURDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 500 AM EDT WEDNESDAY... COLD FRONT IS SLOWLY CROSSING THE FORECAST AREA. AS OF 5AM THIS FRONT WAS ALIGNED WITH THE SPINE OF THE APPALACHIAN MOUNTAINS. WINDS BEHIND THE FRONT HAVE WEAKENED...THE FRONT LOSING FORWARD MOMENTUM...WHICH SUGGESTS IT WILL TAKE MUCH OF THE DAY TO WORK ITS WAY ACROSS THE ENTIRE CWA. A 50 TO 75 MILE WIDE BAND OF LIGHT RAIN AND RAIN SHOWERS EXTENDED ALONG THE LENGTH OF THE FRONT. RAINFALL AMOUNTS OF ABOUT A HALF INCH WERE OBSERVED AS THE FRONT CROSSED KY/TN. THE SHOWERS HAVE BEEN WEAKENING WITH TIME...THUS THINK AMOUNTS FOR OUR CWA WILL BE LESS ROBUST...WITH FORECAST AMOUNTS RANGING FROM A QUARTER OF AN INCH IN THE WEST TO A TENTH OF AN INCH IN THE EAST. AREAL COVERAGE HAS BEEN SOLID ENOUGH TO MAINTAIN CATEGORICAL POPS IN THE WEST...AND TO A LESSER DEGREE IN THE EAST...ALTHOUGH CONFIDENCE STILL GREATER THAN 50 PERCENT THAT FOLKS EAST OF THE BLUE RIDGE WILL RECEIVE AT LEAST AN HOUR OR TWO OF WETTING SHOWERS. FRONT IS PROGGED BY ALL MODELS TO CLEAR THE CWA BY THIS EVENING. SHOULD SEE SOME CLEARING IN OUR WESTERN CWA MID/LATE AFTERNOON...FOLLOWED BY CLEARING IN THE EAST THIS EVENING OR EARLY TONIGHT. CLEAR SKIES AND DIMINISHING WINDS LATE TONIGHT COULD LEAD TO SOME PATCHY FOG. TEMPERATURES TODAY WILL STILL BE RELATIVELY MILD AHEAD OF THE FRONT WITH THE PIEDMONT SNEAKING BACK INTO THE 70S. HOWEVER... TEMPERATURES WILL STRUGGLE IN THE MOUNTAINS DUE TO THE ABUNDANT CLOUD COVER...EARLY DAY RAINFALL. THE AIRMASS BEHIND THIS FRONT IS SEASONAL...SO TEMPERATURES WILL TREND BACK CLOSER TO WHERE WE SHOULD BE FOR LATE OCTOBER WITH HIGHS 55 TO 65 AND LOWS 35 TO 45. A MORE PRONOUNCED COOL DOWN WILL TAKE PLACE THIS WEEKEND.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
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AS OF 500 AM EDT WEDNESDAY... HIGH PRESSURE WILL CONTROL OUR WEATHER PATTERN ON THURSDAY... RESULTING IN MOSTLY CLEAR SKIES UNDER LIGHT NORTHERLY WINDS. EXPECT AFTERNOON TEMPERATURES TO BE A FEW DEGREES BELOW NORMAL AS SUBTLE UPPER LEVEL TROUGHING TAKES SHAPE ALONG THE APPALACHIAN CHAIN...WITH HIGHS RANGING FROM THE MID 50S FOR THE MOUNTAINS...TO THE LOW 60S ACROSS THE PIEDMONT. CLOUDS WILL INCREASE DURING LATE EVENING AS OUR NEXT LOW PRESSURE SYSTEM APPROACHES...WITH WINDS SHIFTING SOUTHWESTERLY AFTER MIDNIGHT. THURSDAY NIGHT LOWS WILL BE GENERALLY IN THE MID TO UPPER 30S...WITH A FEW AREAS OF FREEZING TEMPERATURES...MAINLY IN THE MOUNTAIN VALLEYS. SHOWERS WILL ENTER OUR WESTERN SLOPES AROUND SUNRISE FRIDAY...AND SPREAD EAST THROUGH THE MORNING AS A DEEP UPPER LEVEL TROUGH DROPS SOUTH FROM THE WESTERN GREAT LAKES...BECOMING A CLOSED LOW AS IT CROSSES THE OHIO RIVER NEAR CINCINNATI FRIDAY EVENING. FROM THERE... WEATHER FORECAST MODELS DIFFER ON THE TRACK THE LOW TAKES...WITH THE NAM MODEL FARTHEST WEST OF OUR AREA AND WARMEST...WHILE THE ECMWF TAKES THE LOW DIRECTLY ACROSS OUR PORTION OF THE APPALACHIANS...AND IS COLDEST/DEEPEST. THE GFS FORECAST MODEL SPLITS THE DIFFERENCE BETWEEN THE OTHER TWO...AND SINCE THE MODELS ARE STILL TRYING TO GET A HANDLE ON THE EVOLUTION OF THIS SYSTEM...HELD CLOSEST TO THE GFS SOLUTION. ALL MODELS ARE IN AGREEMENT THAT THIS SYSTEM WILL BRING THE COLDEST AIR WE HAVE SEEN THIS AUTUMN...AND THAT THE SYSTEM WILL PASS RAPIDLY ACROSS OUR AREA. RAIN SHOWERS WILL BECOME WIDESPREAD FRIDAY AFTERNOON. 850MB TEMPERATURES WILL GRADUALLY DROP THROUGH THE DAY AS THE UPPER LOW APPROACHES...WITH THE AIR BECOMING COLD ENOUGH BY AROUND SUNSET FOR A FEW SNOW FLAKES TO MIX IN FOR ELEVATIONS ABOVE 3000 FEET. FROM THERE...TEMPERATURES WILL NOSEDIVE FRIDAY NIGHT... CAUSING RAIN TO BECOME MIXED WITH...AND EVENTUALLY CHANGE OVER TO... SNOW ACROSS MUCH OF THE AREA BY EARLY SATURDAY. SNOWFALL ACCUMULATIONS WILL BE HIGHEST ACROSS THE NORTH CAROLINA MOUNTAINS AND THE MOUNTAIN EMPIRE...CLOSEST TO THE UPPER LOW...WHERE UP TO AN INCH OF SNOW IS POSSIBLE. ACCUMULATIONS WILL TAPER DOWN TO A FEW TENTHS OF AN INCH FOR THE REST OF THE MOUNTAINS FOR FRIDAY NIGHT...WITH NO ACCUMULATION EXPECTED EAST OF THE BLUE RIDGE. TEMPERATURES WILL WARM INTO THE UPPER 30S ACROSS THE MOUNTAINS ON SATURDAY...WITH SNOW BECOMING MIXED WITH OR CHANGING BACK TO RAIN...DEPENDING ON ELEVATION. AS SUCH...NEW SNOWFALL ACCUMULATIONS SHOULD BE LIMITED TO THE HIGHEST ELEVATIONS. BY EARLY SATURDAY AFTERNOON...THE UPPER LOW WILL PUSH OFF THE NORTH CAROLINA COAST... CAUSING PRECIPITATION TO FADE FROM EAST TO WEST OVER OUR AREA AS WINDS BECOME NORTHWESTERLY. WIND SPEEDS WILL INCREASE DRASTICALLY AS THE PRESSURE GRADIENT BETWEEN THE DEPARTING LOW AND HIGH PRESSURE APPROACHING FROM THE WEST INCREASES TO 10MB TO 12MB. WIND SPEEDS WILL DECREASE AGAIN DURING THE EVENING AS THE PRESSURE GRADIENT BEGINS TO RELAX. SNOW SHOWER ACTIVITY WILL BE LIMITED TO THE MOUNTAINS SATURDAY NIGHT...WITH SNOW SHOWERS FADING QUICKLY IN THE NORTHWESTERLY DOWNSLOPE FLOW EAST OF THE BLUE RIDGE. MOISTURE WILL BECOME INCREASINGLY SHALLOW THROUGH THE NIGHT ACROSS THE WESTERN RIDGES... SO ACTUALLY MAY SEE PRECIPITATION TRANSITION MORE TO LIGHT FREEZING DRIZZLE AS OPPOSED TO SNOW SHOWERS.
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&& .LONG TERM /SUNDAY THROUGH TUESDAY/...
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AS OF 500 AM EDT WEDNESDAY... TEMPERATURES WILL MODERATE OVER THE FIRST FEW DAYS OF NEXT WEEK AS THE UPPER LOW MOVES AWAY FROM OUR AREA. HIGH PRESSURE WILL PASS OVERHEAD ON SUNDAY NIGHT...SO TEMPERATURES STILL PRETTY CHILLY SUNDAY AND SUNDAY NIGHT. AS THE HIGH SHIFTS TOWARD THE CAROLINA COAST ON MONDAY...WINDS WILL SHIFT SOUTHWESTERLY... WHICH WILL BEGIN TO CARRY WARMER AIR FROM THE GULF OF MEXICO NORTHWARD ALONG THE APPALACHIAN CHAIN.
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&& .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
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AS OF 300 AM EDT WEDNESDAY... COLD FRONT WILL MOVE FROM WEST TO EAST ACROSS THE FORECAST AREA TODAY. MAIN CONCERN THROUGH THE TAF VALID PERIOD WILL BE PASSAGE OF THIS FRONT AND ASSOCIATED -SHRA ACTIVITY. MODELS IN GENERAL CONSENSUS THAT MUCH OF THIS ACTIVITY WILL PASS THROUGH THE MOUNTAINS THIS MORNING...THEN EAST OF THE MOUNTAINS THIS AFTERNOON. THERE ARE SOME DISCREPANCIES BETWEEN OBSERVED TIMING AND MODEL TIMING...BUT ONLY BY A FEW HOURS. AT ANY RATE...LOOK FOR A PERIOD...ABOUT A 4-8 HOUR WINDOW OF TIME...WHERE -SHRA AND LOWERING CIGS WILL OCCUR BEFORE THE FRONT CLEARS THE AREA AND CONDITIONS IMPROVE. PRIOR TO THE FRONTAL PASSAGE...SFC WINDS WILL BE PRETTY LIGHT...OUT OF THE SOUTHWEST AT 3-7KTS. FRONTAL PASSAGE WILL BRING A WIND SHIFT TO THE NORTHWEST...SPEEDS INCREASING INTO THE 6 TO 10 KT RANGE WITH GUSTS OF 15 TO 20KTS. STRONGEST WINDS WILL OCCUR VCNTY OF THE RIDGE CRESTS AND JUST LEE OF THE BLUE RIDGE VCNTY OF KBCB AND KROA. EXTENDED AVIATION DISCUSSION... VFR CONDITIONS TO RETURN TO ALL SITES THURSDAY. A DEEP LOW PRESSURE AREA IS THEN SLATED TO DIVE SOUTHWARD INTO THE REGION OVER THE WEEKEND PROVIDING A LONGER PERIOD OF POTENTIALLY IFR-LIFR CIGS AND PRECIPITATION...POTENTIALLY EVEN -SHSN OR -SN BLF/LWB AREA...WITH -RA ELSEWHERE. CONSIDERABLE UNCERTAINTY REGARDING THIS NEXT EVENT AT THIS POINT BECAUSE OF MODEL FLIP-FLOPS FROM RUN-TO- RUN. WINDS WILL ALSO BE QUITE STRONG AS CANADIAN AIR FILTERS INTO THE SYSTEM AND ANY POTENTIAL COASTAL LOW DEVELOPMENT ALSO EVOLVES WITH TIME. OVERALL...VERY POOR AVIATION CONDITIONS EXPECTED FRI- SUN.
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&& .EQUIPMENT... THE AC UNITS FOR THE RADAR SHELTER ARE BAD. RADAR OPERATION WILL BE INTERMITTENT UNTIL SUCH TIME THE AC UNITS ARE FIXED. IF SHELTER TEMPERATURES RISE ABOVE CRITICAL LEVELS WE WILL BE FORCED TO PLACE THE RADAR INTO STANDBY TO AVOID DAMAGE TO THE TRANSMITTER. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...NF LONG TERM...NF AVIATION...PM EQUIPMENT...PM

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