Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 042017 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 317 PM EST WED MAR 4 2015 .SYNOPSIS... A COLD FRONT WILL EAST ACROSS THE REGION THIS EVENING INTO TONIGHT...BEFORE MOVING OFFSHORE LATE THURSDAY. HIGH PRESSURE OVER THE MISSISSIPPI VALLEY WILL MOVE INTO THE AREA FOR FRIDAY THROUGH SUNDAY. WIDESPREAD RAIN IS EXPECTED TODAY WITH WINTER PRECIPITATION TONIGHT AND THURSDAY. && .NEAR TERM /THROUGH THURSDAY/... AS OF 311 PM EST WEDNESDAY... EROSION OF THE COLD AIR AND SOME SUNSHINE HAS ALLOWED TEMPERATURES TO CLIMB INTO THE MID 60S TO LOWER 70S ACROSS SOUTHERN LOCATIONS OF FORECAST AREA THIS AFTERNOON. FRONTAL BOUNDARY REMAINS TO OUR WEST AS SEVERAL WAVES OF LOW PRESSURE SLOWING PROGRESS EAST THIS AFTERNOON. ONCE THE AREA OF LOW PRESSURE PUSHES NORTHEAST...COLD FRONT WILL TRAVEL EAST THIS AFTERNOON INTO TONIGHT. MODELS ARE IN REASONABLE AGREEMENT ON TIMING OF COLDER AIR AND PRECIPITATION ALTHOUGH SOME FLUCTUATIONS ON QPF. MODEL BLEND OF THE 00Z ECMWF/12Z GFS AND PREVIOUS FORECAST WAS USED. NOT BUYING INTO THE AMOUNT OF SNOW THE NAM IS SHOWING...THOUGH THIS SETUP IS VERY TRICKY AS WE USUALLY DO NOT GET HEAVY SNOW POST FRONTAL. THE NAM HAS A BETTER HISTORY THIS WINTER...THOUGH WETTER THAN THE OTHER MODELS. NONETHELESS THE BLEND OF THE GFS/ECMWF FAVOR EXPANDING THE WARNING SOUTHWEST AND EAST TO INCLUDE THE REST OF SE WV...AS WELL AS NORTH OF THE JAMES RIVER IN AMHERST TO SOUTH OF RIVER IN BUCKINGHAM. GIVEN THE IMPACT OF SLEET IN CUTTING SNOW TOTALS...USED AN INCH LESS THAN WHAT WE NORMALLY USE FOR SNOW AMOUNTS FOR THE HEADLINES. STILL LOOKS LIKE THE SETUP FAVORS 4-8 INCHES OF SNOW ACROSS THE MOUNTAINS OF SE WV INTO THE ALLEGHANY HIGHLANDS...AND WOULD NOT BE SURPRISED FOR DOUBLE DIGITS IN THE NW CORNER OF GREENBRIER COUNTY AND THE HIGHEST RIDGES OF BATH COUNTY. AS YOU HEAD SOUTHWARD...AMOUNTS WILL BE MORE LIMITED...BUT ENOUGH FOR ADVISORY. ONLY THE NC PIEDMONT AND FOOTHILLS WILL STAY UNDER AN INCH FOR SNOW/SLEET. THE COLDER WILL BE ARRIVING BY THU AFTERNOON IN THE SOUTHEAST WHICH SHOULD LIMIT ACCUMULATIONS SOMEWHAT. THE PTYPE WILL BE RAIN THIS EVENING...THEN LOOK FOR SLEET MOVING INTO THE MOUNTAINS OF WV/FAR SW VA BY LATE EVENING...REACHING THE I- 81 CORRIDOR TOWARD DAWN AND EAST OF THE BLUE RIDGE BY MIDDAY/EARLY AFTERNOON. THE SNOW WILL REACH THE WV MTNS BY DAWN...THE NEW RIVER VALLEY/ROANOKE AREA BY LATE MORNING AND THE PIEDMONT THROUGH THE AFTERNOON. THE BIG QUESTION WILL BE HOW FAR SOUTHEAST THE FRONT MOVES AND HOW QUICK THE COLD AIR PUSHES IN WITH HOW MUCH MOISTURE REMAINS. THIS SCENARIO FAVORS A SMALLER TRANSITION ZONE...SO FREEZING RAIN WILL BE LIMITED FOR AN HOUR OR TWO AT MOST IN THE MOUNTAINS AND PORTIONS OF THE NEW RIVER VALLEY LATE TONIGHT/THURSDAY MORNING. TEMPERATURES TONIGHT WILL BE TRICKY BEHIND THE FRONT BUT THINK BY MORNING THE COLDER AIR WILL BE IN THE MOUNTAINS WITH 20S TO NEAR 30...WITH LOWER 40S SOUTHSIDE. TEMPERATURES DURING THURSDAY WILL CONTINUE TO FALL. && .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... AS OF 305 PM TUESDAY... ON THURSDAY NIGHT...THE MOISTURE EXITS QUICKLY BUT COULD SEE LINGERING SNOW ACROSS THE PIEDMONT UNTIL 9 PM. HIGH PRESSURE WORKS IN BY LATE THURSDAY NIGHT...THOUGH COULD SEE JUST ENOUGH WIND FOR WIND CHILLS TO ZERO OR JUST BELOW OVER THE SE WV MTNS...INTO THE ALLEGHANY HIGHLANDS. STRONG RADIATIONAL COOLING WILL PUSH ACTUAL OVERNIGHT LOW TEMPERATURES TO AROUND ZERO IN SPOTS ACROSS THE MOUNTAINS...AND TO THE UPPER TEENS/LOW 20S ACROSS THE NORTH CAROLINA PIEDMONT. THE SAME HIGH PRESSURE SYSTEM WILL REMAIN ACROSS THE REGION ON FRIDAY...KEEPING TEMPERATURES ON THE CHILLY SIDE. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 300 PM EST WEDNESDAY... SATURDAY...HIGH PRESSURE BUILDS OVER THE REGION...WITH ITS CENTER SHIFTING EAST OF THE AREA BY SATURDAY NIGHT. THE RESULT WILL BE A DRY FORECAST...WITH MODERATING TEMPERATURES. AFTER HIGHS ON FRIDAY IN THE UPPER 20S TO MID 30S ACROSS THE FORECAST AREA...HIGHS ON SATURDAY WILL RANGE MORE IN THE 40S WEST TO LOWER 50S EAST. THERE HAS BEEN CONSIDERABLE VARIATION IN THE MODEL GUIDANCE DURING THE SUNDAY THROUGH TUESDAY TIME PERIOD. WHILE EACH IS FAIRLY CONSISTENT THAT A LONG WAVE TROUGH WILL DEVELOP ACROSS THE EASTERN THIRD OF CONUS...THERE HAVE BEEN INCONSISTENCIES AS TO WHETHER OR NOT...AND WHEN...AND WHAT TRACK A SOUTHERN STREAM SYSTEM MAY GET PICKED UP ON THE EAST SIDE OF THIS TROUGH AND PROGRESS NORTHEAST ACROSS OUR AREA. THE GFS HAS NOT BEEN FAVORABLE OF THIS OCCURRENCE. THE ECMWF WAS OPTIMISTIC ON AN ARRIVAL A SOUTHERN SYSTEM ON MONDAY. OUR FORECAST TODAY WILL REFLECT TEMPERATURES CONTINUING TO MODERATE THROUGH MONDAY...WITH THE THINKING THAT THE DEVELOPING TROUGH AXIS WILL REMAIN TO OUR WEST...AND WE WILL CONTINUE IN WARM AIR ADVECTION AT THE SURFACE. IT WILL ALSO REFLECT THE POTENTIAL FOR SOME ISOLATED TO SCATTERED UPSLOPE SNOW SHOWERS ACROSS SOUTHEAST WEST VIRGINIA WHERE 850 MB FLOW WILL BE MORE W-NW. IT WILL ALSO ALLOW FOR A SLIGHT CHANCE OF A SOUTHERN STREAM SYSTEM IMPACTING THE AREA ON TUESDAY WITH RAIN OR FREEZING RAIN. THE LATEST GUIDANCE FOR THE EARLY TO MIDDLE PART OF NEXT WEEK CONTINUES TO FLUCTUATES IN REGARDS TO THE TIMING AND TRACK OF A SOUTHERN STREAM SYSTEM. THE LATEST TRENDS BRING THE GFS INTO PLAY NOW FOR BRINGING A SYSTEM THROUGH THE AREA ON WEDNESDAY...THE CANADIAN AND ECWMF STILL A LITTLE EARLIER. IN ADDITION TO THE SMALL CHANCE OF PRECIPITATION ON TUESDAY...WE WILL ALSO ADD WEDNESDAY INTO THE MIX TO REFLECT THE MODEL VARIATIONS AND A SMALL POTENTIAL EACH DAY FOR A LOW AND ITS ASSOCIATED PRECIPITATION TO PROGRESS OVER OR NEAR THE REGION. WHILE MOST OF THE REGION SHOULD EXPERIENCE RAIN ON WEDNESDAY...A FEW SPOTS IN THE SOUTHEAST WEST VIRGINIA MAY BE COLD ENOUGH FOR A BRIEF PERIOD OF FREEZING RAIN. HIGH TEMPERATURES ON WEDNESDAY WILL BE MILDER THAN THOSE OF TUESDAY. EXPECT A RANGE OF LOW TO MID 50S ACROSS THE MOUNTAINS WITH UPPER 50S TO LOWER 60S ACROSS THE PIEDMONT. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... AS OF 1245 PM EST WEDNESDAY... MVFR CONDITIONS WITH POCKETS OF IFR/LIFR IN LOW CLOUDS...FOG AND RAIN THIS AFTERNOON INTO TONIGHT. SOUTHWESTERLY WINDS WILL GRADUALLY MIX TO THE SURFACE THIS AFTERNOON...RESULTING IN AN INCREASE OF WIND SPEEDS TO AROUND 10KTS WITH UP TO 20KT GUSTS. A COLD FRONT WILL PASS ACROSS THE MOUNTAINS THIS AFTERNOON INTO TONIGHT. THIS BOUNDARY SHOULD REACH KDAN AFTER 05/00Z. ARCTIC AIR WILL BUILD IN BEHIND THE FRONT...WHICH WILL CAUSE TEMPERATURES TO FALL TONIGHT. RAIN WILL TRANSITION TO SLEET AND FREEZING RAIN...THEN OVER TO SNOW IN MOST LOCATIONS. FOR TIMING EXPECT RAIN CHANGING TO SLEET BY AROUND 05/05Z FOR KBLF/KLWB...BEFORE CHANGING TO SNOW BY AROUND 05/10Z. CHANGE OVER TO SLEET FOR KBCB/KROA WILL HAPPEN CLOSER TO 05/10Z...WITH THE CHANGE TO SNOW NOT TAKING PLACE UNTIL AFTER SUNRISE THURSDAY. WITH THE CHANGE TO SNOW... SIGNIFICANT REDUCTIONS IN VISIBILITY CAN BE EXPECTED. CEILINGS WILL FALL TO IFR/LIFR LEVELS BEHIND THE FRONT. SLEET WILL CHANGE TO SNOW FROM NORTHWEST TO SOUTHEAST ON THURSDAY. ROUNDS OF HEAVY SNOW WILL BE POSSIBLE IN THE VICINITY OF THE BLUE RIDGE LATE THURSDAY MORNING AND DURING THE AFTERNOON AS A WAVE OF LOW PRESSURE PASSES ALONG THE COASTAL PLAIN. LOW MVFR/IFR CONDITIONS WILL BE WIDESPREAD THROUGH THE DAYTIME...WITH CLEARING DURING THE EVENING. MEDIUM CONFIDENCE ON CEILINGS...VISIBILITIES AND WINDS DURING THE TAF PERIOD. EXTENDED FORECAST... FRIDAY TO SUNDAY WILL SEE A RETURN TO HIGH PRESSURE AND VFR WEATHER. SOME RAIN AND SNOW SHOWERS ARE POSSIBLE ON MONDAY IN THE WESTERN MOUNTAINS. && .HYDROLOGY... AS OF 300 PM EST WEDNESDAY FLOODING HAS BEEN WIDESPREAD ACROSS MAINLY TAZEWELL AND MERCER COUNTIES TODAY AS RAINFALL OF 0.50 TO 0.75 INCHES OVERNIGHT AND THIS MORNING COMBINED WITH SNOW MELT FROM THE REMAINS OF THE SNOWPACK TO CAUSE A RAPID HYDROLOGIC RESPONSE. IN TERMS OF RIVERS THE BLUESTONE AND CLINCH HAVE BEEN THE MOST AFFECTED ALONG WITH SHARP RISES ON THE EAST RIVER AND BRUSH CREEK IN MERCER COUNTY AND INDIAN CREEK IN MONROE...ALONG WITH NUMEROUS SMALLER AND UNGAGED STREAMS. BOTH THE BLUESTONE AND CLINCH SHOULD CREST IN THE NEXT FEW HOURS A FEW FEET ABOVE MINOR FLOOD STAGE. THE BREAK IN RAINFALL THAT HAS TAKEN PLACE SINCE LATE THIS MORNING THROUGH AFTERNOON HAS BEEN A HUGE BLESSING SINCE ALMOST EVERY DROP THAT FELL SEEMED TO BE RUNNING OFF INTO THE RIVERS AND CREEKS. THE BIG QUESTION IS HOW MUCH MORE LIQUID PRECIPITATION OCCURS BEFORE THE TRANSITION TO FROZEN. AT THIS POINT ABOUT AN ADDITIONAL ONE QUARTER TO ONE-HALF INCH OF RAIN /0.25 TO 0.50 INCHES/ IS FORECAST WHICH COULD EXTEND THE FLOODING SOMEWHAT BUT IS UNLIKELY TO REVERSE A FALLING TREND ONCE IT IS ESTABLISHED. THE ENTIRE HYDROLOGIC SITUATION SHOULD STABILIZE ONCE THE FREEZING TEMPERATURES AND PRECIPITATION TAKES OVER LATE TONIGHT. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 7 PM EST THURSDAY FOR VAZ007-009>018-022-034. WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 7 PM EST THURSDAY FOR VAZ019-020-023-024. WINTER WEATHER ADVISORY FROM 6 AM TO 10 PM EST THURSDAY FOR VAZ032-033-043>046-058-059. WINTER STORM WARNING FROM 3 AM TO 7 PM EST THURSDAY FOR VAZ035- 047. NC...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 7 PM EST THURSDAY FOR NCZ001-002-018. WV...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 7 PM EST THURSDAY FOR WVZ042>044-507-508. && $$ SYNOPSIS...AMS/KK NEAR TERM...KK/WP SHORT TERM...NF/WP LONG TERM...DS AVIATION...AMS/KK HYDROLOGY...PC

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