Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 220934 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 434 AM EST MON DEC 22 2014 .SYNOPSIS...
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HIGH PRESSURE WILL REMAINED WEDGED EAST OF THE APPALACHIANS TODAY THROUGH TUESDAY NIGHT. A STRONG COLD FRONT WILL MOVE THROUGH ON WEDNESDAY. HIGH PRESSURE WILL THEN BUILD OVER THE EASTERN UNITED STATES THROUGH THE END OF THE WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 400 AM EST MONDAY... 500 MB PATTERN WILL AMPLIFY TODAY AND TONIGHT. THE EASTERN UNITED STATES REMAINS BETWEEN DIGGING TROUGH IN THE CENTRAL UNITED STATES AND DOWNSTREAM RIDGE OVER THE WESTERN ATLANTIC. AT THE SURFACE... HIGH PRESSURE WEDGE WAS FIRMLY IN PLACE THIS MORNING AND WILL HOLD OVER THE FORECAST AREA THROUGH TONIGHT. PRECIPITATION WILL SPREAD INTO THE AREA THIS MORNING WITH THE BEST FORCING MAINLY BEFORE 18Z. ISENTROPIC LIFT CONTINUES TODAY AND TONIGHT AND COMBINED WITH THE WEDGE PATTERN AND UPSLOPE LOW LEVEL WINDS...WILL KEEP THE REGION CLOUDY TODAY AND TONIGHT. MORE PRECIPITATION WILL RETURN TO THE AREA TONIGHT...WITH A SHORT WAVE ROUNDING THE EAST SIDE OF THE UPPER TROF AND STRONGER WARM AIR ADVECTION ABOVE THE WEDGE. SURFACE DEW POINTS WERE AT OR ABOVE FREEZING FROM THE NEW RIVER VALLEY INTO THE NORTHWEST NORTH CAROLINA MOUNTAINS AND FOOTHILLS AND IN THE UPPER 20S TO AROUND 30 ACROSS THE REST OF THE COUNTY WARNING AREA. EXPECT TEMPERATURES TO LOWER DOWN TO NEAR THE DEW POINT AS THE PRECIPITATION ADVANCES INTO THE FORECAST AREA AND THERE IS SOME EVAPORATIVE COOLING. SOME LOCATIONS WERE ALREADY BELOW FREEZING. OTHER SPOTS WILL DROP BELOW FREEZING WITH THE ONSET OF THE RAIN THIS MORNING. NO CHANGES PLANNED TO FREEZING RAIN ADVISORY AT THIS TIME BUT WILL CONTINUE TO MONITOR. ONCE TEMPERATURES REACH THEIR LOW POINT AROUND 12Z/7AM THIS MORNING...THERE WILL BE LITTLE TO NO RISE DURING THE DAY. SIMILAR TEMPERATURE TREND OVERNIGHT. HIGHEST ELEVATIONS MAY RISE A COUPLE OF DEGREES DEPENDING ON DEPTH OF THE WEDGE.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
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AS OF 330 AM EST MONDAY... LOOKING INTO TUESDAY...HIGH PRESSURE WILL STILL BE FIRMLY WEDGED AGAINST THE EASTERN FACE OF THE APPALACHIANS...MAINTAINING A CHILLY NORTHEASTERLY FLOW INTO THE MID ATLANTIC REGION. MAY STILL SEE A FEW POCKETS OF FREEZING RAIN AS SOUTHERLY WINDS OFF THE SURFACE CARRY GULF MOISTURE INTO OUR REGION...BUT THESE POCKETS ARE EXPECTED TO CHANGE OVER TO RAIN BY LUNCHTIME. LOW CLOUDS WILL BE WIDESPREAD THROUGH THE DAY...WITH SUBTLE UPPER LEVEL DISTURBANCES MOVING ACROSS THE AREA SUPPORTING OCCASIONAL BANDS OF RAIN. THE NORTHEASTERLY WINDS AND CLOUD COVER WILL ALLOW FOR ONLY MODEST DAYTIME HEATING... WITH HIGHS RANGING FROM THE LOW 40S ACROSS THE PIEDMONT...TO THE UPPER 40S ACROSS MOST OF THE MOUNTAINS. THE EXCEPTION WILL BE PORTIONS OF THE MOUNTAIN EMPIRE...WHICH ARE SEPARATED BY TERRAIN FROM THE AFFECTS OF THE HIGH PRESSURE WEDGE...WHERE TEMPERATURES WILL CLIMB INTO THE MID 50S. WILL NOT SEE MUCH OF A DROP IN TEMPERATURES FOR TUESDAY NIGHT...WITH RAIN CHANCES INCREASING DURING LATE EVENING AS A DEEP LOW PRESSURE SYSTEM PUSHES RAPIDLY NORTHWARD FROM THE CENTRAL GULF OF MEXICO. FOR WEDNESDAY...LOW PRESSURE WILL ADVANCE NORTH FROM CENTRAL TENNESSEE TOWARD THE GREAT LAKES...DEEPENING AS IT PROGRESSES. STRONG SOUTHERLY WIND FLOW WILL PUSH PRECIPITABLE WATER VALUES ACROSS OUR AREA INTO THE 1.1 TO 1.3 INCH RANGE...SIGNIFICANTLY ABOVE NORMAL FOR THIS TIME OF YEAR. AS SUCH...LOCALLY HEAVY RAIN WILL BE POSSIBLE...ESPECIALLY WHERE RAIN BANDS BEGIN TO PASS REPEATEDLY OVER THE SAME LOCATIONS. IN ADDITION...MAY SEE GUSTY WINDS AS THE 45 TO 55 MPH WINDS BLOWING JUST ABOVE THE SURFACE REACH THE HIGHER TERRAIN FROM TIME TO TIME. BY SUNSET ON WEDNESDAY...THE LOW WILL BEGIN TO DRAG A COLD FRONT ACROSS THE NORTH CAROLINA HIGHLANDS AND FAR WESTERN VIRGINIA. WE MAY SEE ONE MORE SHOT OF HEAVY RAIN AS THE FRONT PASSES...HOWEVER RAINFALL SHOULD DIMINISH QUICKLY AS DRY AIR WORKS IN BEHIND THE FRONT. THE COLD FRONT WILL WORK EAST QUICKLY...PASSING OUT OF OUR AREA SHORTLY AFTER MIDNIGHT. AS THE SUPPORTING UPPER LEVEL TROUGH PASSES ACROSS THE REGION LATE WEDNESDAY NIGHT/EARLY THURSDAY...MAY SEE ANOTHER SHOT OF STRONG WINDS ACROSS THE MOUNTAINS...AND WOULD NOT BE SURPRISED TO SEE GUSTS REACH 50 MPH ALONG THE HIGHER RIDGES FOR A FEW HOURS UNTIL THE TROUGH MOVES EAST. GUSTY WINDS WILL REMAIN IN PLACE THROUGH MUCH OF CHRISTMAS DAY... WITH DRY COOLER AIR WORKING ITS WAY INTO OUR REGION. PRECIPITATION WILL BE RELEGATED TO RESIDUAL SNOW SHOWERS ACROSS THE WESTERN RIDGES...PARTICULARLY WESTERN GREENBRIER COUNTY...WITH ONLY MODEST SNOW ACCUMULATIONS. HIGH PRESSURE WILL SETTLE ACROSS THE AREA FROM THE SOUTH CHRISTMAS NIGHT.
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&& .LONG TERM /FRIDAY THROUGH SUNDAY/...
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AS OF 245 PM EST SUNDAY... HIGH PRESSURE WILL PASS ACROSS THE SOUTHEAST STATES ON FRIDAY... ALLOWING FOR A RAPID RETURN OF SOUTHWESTERLY WIND FLOW. UPPER LEVEL RIDGING AND ABUNDANT SUNSHINE WILL ALLOW AFTERNOON HIGHS TO RANGE FROM THE MID/UPPER 40S WEST TO THE MID 50S EAST. THE NEXT FRONT IS SCHEDULED TO ARRIVE SATURDAY. THIS FRONT WILL NOT HAVE MUCH MOISTURE AS DRY HIGH PRESSURE TRACKS ACROSS THE SOUTHERN STATES...BLOCKING GULF MOISTURE FROM RETURNING INTO THE REGION. ANY SHOWERS WITH THIS FRONT SATURDAY WILL BE ALONG WESTERN SLOPES AS WINDS BECOME WESTERLY RATHER QUICKLY. TEMPERATURES AND BOUNDARY LAYER WARM ENOUGH TO KEEP ANY PRECIPITATION AS RAIN. BY THE TIME THE COLD AIR ARRIVES...MOISTURE IS GONE. ALSO WITH A MOSTLY DRY FRONT...BREEZY AND GUSTY CONDITIONS ARE EXPECTED SATURDAY. THE 12Z ECM STALLS THE FRONT ACROSS THE SOUTHERN APPALACHIANS SATURDAY. A DEEP UPPER LEVEL TROUGH DIGGING INTO TEXAS WILL DEVELOP A SURFACE LOW NEAR THE MOUTH OF THE MISSISSIPPI SATURDAY...TRACKING ACROSS THE CAROLINAS ON SUNDAY. THE ECM SCENARIO WILL BRING RAIN WHEREAS THE GFS IS DRY. WILL LEAN THIS WEEKEND`S FORECAST TOWARDS WPC AND KEEP POPS LOW IN THE 20-30 PERCENT RANGE. WITH EITHER MODEL...BEHIND THE FRONT SATURDAY OR SUNDAY...ANOTHER AREA OF HIGH PRESSURE WILL TRACK ALONG THE GULF STATES...KEEPING THE REGION DRY INTO EARLY NEXT WEEK.
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&& .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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AS OF 1130 PM EST SUNDAY... HIGH PRESSURE WILL REMAIN WEDGED AGAINST THE EASTERN SIDE OF THE APPALACHIAN MOUNTAINS WHILE AN AREA OF LOW PRESSURE ADVANCES NORTHEAST ALONG THE SOUTHEAST ATLANTIC COAST. THIS AREA OF LOW PRESSURE WILL CAST MOISTURE INTO THE MID ATLANTIC REGION OVERNIGHT. MVFR CIGS WILL ADVANCE NORTHWARD FROM THE CAROLINAS...OVERSPREADING VIRGINIA AND WEST VIRGINIA DURING THE OVERNIGHT. ONSET OF PRECIPITATION IS EXPECTED TO BEGIN BETWEEN 2-5AM TIME FRAME. LIGHT RAIN/DRIZZLE IS ADVANCING NORTHWARD THROUGH THE CAROLINAS. WHILE THERE IS HIGH CONFIDENCE THAT THE MAIN PRECIPITATION TYPE WILL BE RAIN...A PERIOD OF FREEZING RAIN AND SLEET IS LIKELY NORTH OF HIGHWAY 460...ALONG AND NORTH OF A BLF- BCB-ROA-LYH LINE. MODELS ARE FORECASTING ABOUT A TENTH OF AN INCH OF QPF...SO ITS NOT OUT OF THE QUESTION TO HAVE UP TO A TENTH OF AN INCH OF ICE ACCRETION ON ELEVATED SURFACES MONDAY MORNING. A FREEZING RAIN ADVISORY IS IN EFFECT FROM 5AM TO NOON MONDAY TO ACCOUNT FOR THE FREEZING RAIN. SOME OF THE FORECAST MODELS...ESP THE NAM...SUGGEST A PERIOD OF IFR MAY ACCOMPANY THE PRECIPITATION MONDAY MORNING... SO THERE IS A CHC THAT CIGS COULD DROP TO BETWEEN 400-800 FT AGL WITH VSBYS BETWEEN 1-3SM. THE PRECIPITATION IS EXPECTED TO COME TO AN END MONDAY AFTERNOON. LINGERING MOISTURE...HOWEVER...WILL RESULT IN A PERSISTENT LOW CEILING...MAINLY MVFR...IN ADDITION TO SOME PATCHY DRIZZLE. EXTENDED DISCUSSION... A LOW PRESSURE SYSTEM ALONG THE NORTH CAROLINA COAST WILL HEAD OFFSHORE BY MONDAY NIGHT...BUT MVFR CEILINGS AND DRIZZLE MAY LINGER INTO TUESDAY DUE TO THE WEDGE OF HIGH PRESSURE EAST OF THE APPALACHIAN MOUNTAINS. BY WEDNESDAY...A STRONG COLD FRONT WILL SWEEP OVER THE MID ATLANTIC...AND ERODE THE WEDGE. MODEL SOUNDINGS CONTINUE TO SHOW THE POTENTIAL FOR LOW LEVEL WIND SHEAR AHEAD OF THIS FRONT...WITH A POTENT LOW LEVEL JET DEPICTED. RAIN AND MVFR CONDITIONS WILL ACCOMPANY THE FRONTAL PASSAGE. BEHIND THE COLD FRONT...SURFACE WINDS SHOULD TURN FROM THE SOUTHEAST TO THE NORTHWEST...AND BECOME RATHER GUSTY BY CHRISTMAS DAY. MEANWHILE...MVFR CEILINGS AND UPSLOPE RAIN/SNOW SHOWERS SHOULD PERSIST IN THE MOUNTAINS...WHILE VFR CONDITIONS WILL RETURN IN THE PIEDMONT. HIGH PRESSURE SHOULD BUILD OVER THE SOUTHEAST BY THURSDAY NIGHT...WHICH WILL PROVIDE GOOD FLYING WEATHER WITH LIGHTER WINDS ON FRIDAY.
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&& .HYDROLOGY... AS OF 245 PM EST SUNDAY... BIGGER STORY MAY BE THE RAINFALL WITH UPCOMING EVENT AS FORECAST STORM TOTAL QPF IS IN THE 1.00 TO 1.50 INCH RANGE ACROSS THE ENTIRE CWA. THIS WILL ACTUALLY BE WELCOME FROM A HYDROLOGIC STANDPOINT AS MUCH OF THE PIEDMONT HAS BEEN DRIER THAN NORMAL OVER SEVERAL MONTHS AND DECEMBER HAS HAD BELOW NORMAL PRECIPITATION IN MOST OF THE CWA. SHOULD NOT SEE ANY EXCESS RUNOFF ISSUES..I.E. FLOODING...ALTHOUGH SOME DITCHES WILL LIKELY FILL UP AND MAYBE A FEW PONDING ISSUES. RIVER FORECASTS FROM NORTH AMERICAN AND GEFS ENSEMBLES PORTRAY BASIN- AVERAGE QPF GENERALLY IN THE 0.75 TO 1.25 INCH RANGE WITH SOME OUTLIERS AS USUAL BUT ALL SOLUTIONS AT THIS POINT PRODUCE ONLY MINOR WITHIN-BANK RISES ON MAINSTEM RIVERS BY LATER IN THE WEEK. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...FREEZING RAIN ADVISORY UNTIL NOON EST TODAY FOR VAZ011-013-014- 016>020-022>024-034-035-045>047. NC...NONE. WV...FREEZING RAIN ADVISORY UNTIL NOON EST TODAY FOR WVZ044-507-508.
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&& $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...NF LONG TERM...RCS AVIATION...PM/PW HYDROLOGY...PC

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