Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 030308 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1008 PM EST MON MAR 2 2015 .SYNOPSIS... HIGH PRESSURE WILL MOVE EAST INTO THE MID ATLANTIC REGION TONIGHT. MEANWHILE...A WARM FRONT WILL PUSH NORTH THROUGH THE AREA LATE TONIGHT INTO TUESDAY...THEN FOLLOWED BY A COLD FRONT TUESDAY NIGHT INTO WEDNESDAY. COLD HIGH PRESSURE WILL RETURN FOR THURSDAY INTO THE WEEKEND. && .NEAR TERM /THROUGH TUESDAY/...
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AS OF 1000 PM EST MONDAY... 1033 MB SURFACE HIGH WAS CENTERED OVER OHIO. THIS HIGH WILL CONTINUE TO DRIFT EAST OVERNIGHT PROVIDING MAINLY DRY CONDITIONS. A STATIONARY FRONT WAS OVER THE DEEP SOUTH...EXTENDING FROM CENTRAL SOUTH CAROLINA SOUTHWEST TO JACKSON MS. THIS STATIONARY FROM IS EXPECTED TO BEGIN MOVING NORTH OVERNIGHT AS A WARM FRONT RESULTING IN THE RETURN OF LOW LEVEL MOISTURE TO THE AREA BY DAYBREAK TUESDAY. QUESTION TO BE ANSWERED IS WHETHER THERE WILL BE ENOUGH MOISTURE FOR PRECIPITATION. THE CLOSEST THING ON RADAR AT THE MOMENT IS OVER THE SOUTHERN APPALACHIANS BETWEEN ASHVILLE NC AND ATLANTA GA. THE SURFACE HIGH WILL CERTAINLY BE IN A POSITION TO PROVIDE ENOUGH COLD AIR FOR A WINTRY FORM OF PRECIPITATION TUESDAY MORNING. THE QUESTION IS WHETHER THERE WILL BE ENOUGH DEPTH TO THE MOISTURE TO PRODUCE PRECIPITATION. BOTH THE HRRR AND RNKWRF SUGGEST ONLY TRACE AMOUNTS TO OCCUR BETWEEN NOW AND NOON TUESDAY WITH THE LARGER SCALE MODELS PRODUCING A FEW HUNDREDTHS OF AN INCH. TRACE ICE IS CERTAINLY ENOUGH TO BE A NUSCIANCE...BUT THIS IS NOT GOING TO BE A WIDESPREAD EVENT. THE MAIN PROBLEM WITH PRECIP PRODUCTION FOR TUESDAY IS THE LACK OF UPPER LEVEL MOISTURE WITHIN THE M8-M12 DEG C DENDRITIC GROWTH ZONE. FORECAST MODEL SOUNDINGS ARE DRY WITHIN THIS LAYER...ALL OF THE SATURATION TAKING PLACE IN A LOWER LAYER BETWEEN +3 DEG C AND -3 DEG C. UNLESS THERE IS SOME SEEDER FEEDER PROCESS THAT DEVELOPS INOF THE WARM FRONT...THE MODEL SOUNDINGS SUGGESTS THE PYTYPE WILL BE EITHER DRIZZLE OR FREEZING DRIZZLE PENDING SURFACE TEMEPRATURE AT THE TIME. THE CRITICAL WINDOW FOR THE FREEZING PRECIPITATION WILL BE DURING THE MORNING...SO STILL SEE THE NEED FOR WINTER WEATHER ADVISORIES TO ACCOUNT FOR THE POTENTIALLY LIGHT ICING THAT MAY OCCUR...KEEPING IN MIND THAT EVEN A VERY LIGHT COATING OF ICE ON AN UNTREATED SURFACE CAN POSE A TRAVEL/WALKING HAZARD. LOW TEMPERATURES OVERNIGHT WILL RANGE FROM THE MID 20S IN THE COLDEST VALLEYS TO THE LOWER 30S IN THE PIEDMONT. WARM AIR WILL MOVE IN FROM THE SOUTHWEST TUESDAY CHANGING PRECIPITATION OVER TO ALL LIQUID TUESDAY AFTERNOON. AREAS ACROSS THE NORTH AND NORTHEAST WILL BE THE SLOWEST TO TRANSITION. HIGH TEMPERATURES TUESDAY WILL RANGE FROM THE MID 30S IN THE NORTHEAST TO THE LOWER 50S IN THE SOUTHWEST.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... AS OF 330 PM EST MONDAY... COMPLICATED SHORT TERM FORECAST WITH MULTIPLE CONCERNS. TO BEGIN TUESDAY NIGHT...ANY REMNANTS OF EARLIER WEDGE WILL BE LONG GONE TO THE NORTHEAST WITH THE AREA SOLIDLY IN THE WARM SECTOR. TEMPERATURES WILL BE WELL ABOVE FREEZING AND CONTINUING TO RISE DURING THE OVERNIGHT HOURS ON THE HEELS OF A STRONG SOUTHWESTERLY LLJ. CONSEQUENTLY...ANY ASSOCIATED WARM FRONTAL PRECIPITATION WILL ALSO HAVE LIFTED WELL NORTHEAST OF THE REGION. NOW...THE ATTENTION SHIFTS TO THE ARCTIC FRONT APPROACHING FROM THE WEST. A BROAD UPPER RIDGE ACROSS THE CENTRAL/EASTERN GULF...590+ DM AT THAT...WILL AMPLIFY INTO THE SOUTHEAST WHILE A DEEP UPPER TROUGH DIGS INTO THE SOUTHERN PLAINS. A SIGNIFICANT SURGE OF ARCTIC AIR WILL PLUNGE INITIALLY SOUTH INTO THE CENTRAL/SOUTH CENTRAL U.S. AS THE ASSOCIATED ARCTIC FRONT SLOWS ITS PUSH INTO THE MID- ATLANTIC/SOUTHEAST STATES THANKS TO THE AFOREMENTIONED UPPER RIDGE AND THE APPALACHIAN MOUNTAINS. THIS HOLDS THE HEAVIEST RAINFALL WEST OF OUR CWA THROUGH WEDNESDAY MUCH OF THE DAY WEDNESDAY...MAINLY ACROSS THE OH/TN VALLEYS. FINALLY...WEDNESDAY AFTERNOON/EVENING...THE FRONT WILL BEGIN A BETTER SOUTHEASTWARD PUSH AS SHORT WAVE ENERGY KICKS OUT OF THE CENTRAL PLAINS. WOULD EXPECT HEAVIER RAIN TO MOVE INTO THE WESTERN PARTS OF THE CWA BY 00Z WED...THEN BEGIN TO SPREAD EASTWARD OVERNIGHT. MEANWHILE...PART OF THE UPPER TROUGH LAGS BEHIND AND SURFACE LOW PRESSURE DEVELOPS ACROSS THE SOUTHEAST STATES IN RESPONSE. THIS WILL FURTHER DELAY THE PUSH OF THE PRECIPITATION INTO/THROUGH THE CWA...BUT PERHAPS NOT THE SHALLOW COLD ARCTIC AIR ONCE IT MANGES TO CROSS THE APPALACHIANS. QUITE A VARIETY OF SOLUTIONS PRESENTED BY THE MODELS AND WPC AS TO THE WINTER WEATHER THREAT THURSDAY GIVEN THAT THIS IS FAR FROM A NORMAL SYNOPTIC SITUATION FOR A SNOW EVENT IN THIS REGION. THE BIG QUESTION IS NOT WHETHER OR NOT THERE WILL BE PRECIPITATION...BUT HOW QUICKLY WILL THE COLD AIR SPREAD INTO THE REGION BEHIND THE FRONT...BEFORE THE HEAVIER PRECIPITATION MOVES OUT...AND HOW QUICKLY WILL THE COLD AIR BECOME DEEP ENOUGH TO CHANGE THE PRECIPITATION TO SNOW. AM INCLINED AT THIS POINT TO THROW OUT RAIN TO FREEZING RAIN SCENARIOS...NOT ONLY BECAUSE IT IS NOT CLIMATOLOGICALLY OR SYNOPTICALLY FAVORABLE IN THIS SITUATION...BUT THINKING IS THAT COLD AIR WILL BECOME DEEP ENOUGH QUICKLY ENOUGH TO CHANGE RAIN OVER TO SNOW...OTHER THAN A BRIEF PERIOD OF SLEET ALONG THE LEADING EDGE OF THE CHANGEOVER. FURTHERMORE...GROUND TEMPS WILL NOT SUPPORT FZRA AT THE CHANGEOVER TIME AS THE SOUNDING COLUMN COOLS ISOTHERMALLY. FINALLY...THIS IS YET AGAIN A SIGNIFICANT ARCTIC AIR MASS...SO ONCE IT ENTERS THE REGION...COOLING WILL BE QUICK...ESPECIALLY WEST OF I-81. FOR SNOW AMOUNTS...A PRELIMINARY ESTIMATE...FAIRLY CONSISTENT WITH WPC WWD...IS 4-5 INCHES NORTH...2-4 INCHES CENTRAL/WESTERN AREAS...1-2 INCHES VA PIEDMONT...LITTLE TO NONE NC PIEDMONT. SEE THE HYDROLOGY SECTION BELOW FOR FURTHER DETAILS ON THE FLOOD THREAT ASSOCIATED WITH COMBINED RAINFALL AND SNOW MELT. DID ADVERTISE A PERIOD OF MODERATE RAIN WEDNESDAY EVENING FROM WEST TO EAST...BUT HAVE REDUCED THE TIME PERIOD OF SUCH COMPARED TO PREVIOUS FORECAST PACKAGES. TEMPERATURE WISE...A LOT OF NON-DIURNAL TEMPERATURE TRENDS THROUGH THIS FORECAST PERIOD. TEMPERATURES CONTINUING TO RISE TUESDAY NIGHT/WEDNESDAY MORNING AND REMAINING MILD/ABOVE FREEZING UNTIL THE ARCTIC FRONT ARRIVES IN THE WEST WEDNESDAY NIGHT. THE PIEDMONT WILL LIKELY REMAIN ABOVE FREEZING FROM TUESDAY AFTERNOON UNTIL THURSDAY MORNING. LIKEWISE...A NON-DIURNAL COOLING TREND EXPECTED THROUGHOUT THE DAY THURSDAY AS ARCTIC AIR SPREADS INTO THE REGION. THE GFS IN PARTICULAR SHOW SFC TEMPS BELOW ZERO IN OUR WESTERN COUNTIES BY FRIDAY MORNING. GIVEN THAT IT IS EARLY MARCH AND THE 850MB TEMPS ARE ONLY AROUND -16C...AS COMPARED TO -26C A COUPLE OF WEEKS AGO...I FIND THIS SOMEWHAT EXTREME. NONETHELESS...IT IS A VERY COLD AIR MASS AND WELL BELOW NORMAL FOR THIS TIME OF YEAR. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 145 PM EST MONDAY... HIGH PRESSURE WILL BUILD OVER THE REGION ON FRIDAY...AND BE IN CONTROL OF OUR WEATHER PATTERN THROUGH AT LEAST SATURDAY NIGHT. THE HIGH WILL GRADUALLY BUILD INTO THE AREA FROM THE WEST...AND MAKE ITS WAY TO THE COAST BY SATURDAY. THIS WILL ALLOW FOR A TREND TOWARD MILDER CONDITIONS AS THE LOW LEVEL FLOW ACROSS THE AREA BECOMES GRADUALLY MORE SW-W...WHILE A SHORTWAVE RIDGE AND RISING 850 TEMPS TAKE PLACE. SUNDAY INTO MONDAY A GENEROUS AMOUNT OF VARIATIONS IN THE MODELS TAKE PLACE. WHILE BOTH THE GFS AND THE NAM EVENTUALLY COME INTO AGREEMENT OF A LONG WAVE TROUGH OVER THE EASTERN THIRD OF CONUS BY MONDAY OR TUESDAY OR NEXT WEEK...HOW THE SOLUTIONS COME TO BE THAT WAY HAVE NOTABLE DIFFERENCES. THE GFS IS MORE PROGRESSIVE IN ESTABLISHING THE TROUGH IN THE EAST BY SUNDAY...AND ANY SOUTHERN STREAM SYSTEMS EASILY BYPASS OUR REGION EXITING THE U.S. NEAR THE GA/FL BORDER. THE ECWMF IS NOT A QUICK TO ESTABLISH AN EAST COAST TROUGH...AND A SUCH...SOUTHERN STREAM SYSTEMS HAVE A BETTER OPPORTUNITY TO PROGRESS NORTHEAST THROUGH OUR REGION ON THE EAST SIDE OF AN APPROACHING SHORTWAVE TROUGH. OUR FORECAST FOR SUNDAY INTO MONDAY WILL BE A CONSENSUS OF THESE TWO...WITH IT RESEMBLING A WATERED DOWN VERSION OF THE ECWMF IN TERMS OF PRECIPITATION POTENTIAL ON SUNDAY AND SUNDAY NIGHT...AND ALSO STAYING ON MORE OF THE MILD SIDE THAN COLD IN REGARDS TO MONDAY. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... AS OF 630 PM EST MONDAY... VFR CONDITIONS WILL CONTINUE ACROSS THE ENTIRE REGION THROUGH ROUGHLY 04Z/11PM. AFTER THIS TIME...MVFR CIGS WILL START PROGRESSES NORTHEAST ACROSS THE REGION IN CONJUCTION WITH A WARM FRONT HEADING TOWARD THE AREA. ALONG WITH THE FRONT WILL COME LIGHT WINTRY PRECIPITATION IN THE FORM OF PATCHY LIGHT FREEZING RAIN AND SLEET. BY DAYBREAK TUESDAY...MANY AREAS WILL HAVE LOWERED TO LIFR/IFR CIGS AND MVFR VSBYS DUE TO THE PRECIPITATION AND MIST. THE BULK OF THE WINTRY PRECIPITATION WILL BE CONFINED TO NORTH A LINE FROM KBLF-KROA-KLYH DURING THE LATE MORNING. BY THE AFTERNOON...SURFACE TEMPERATURES SHOULD BE MILD ENOUGH FOR A WIDESPREAD AREA OF PLAIN RAIN. LIFR/IFR CIGS AND IFR/MVFR VSBYS WILL BE THE NORM DURING THE DAY TUESDAY. WINDS WILL REMAIN LIGHT THROUGH THE NIGHT AND GRADUALLY VEER NORTH TO SOUTHEAST. ON TUESDAY...WINDS WILL INCREASE DURING THE DAY FROM THE SOUTHWEST...AND WINDS AT 850 MB WILL INCREASE TO AROUND 45 TO 50 KTS. LOW LEVEL WIND SHEAR WILL BE POSSIBLE DURING THE AFTERNOON...ESPECIALLY AT TERMINALS AT HIGHER ELEVATION. MEDIUM CONFIDENCE IN CEILINGS...VISIBILITIES AND WINDS DURING THE PERIOD. EXTENDED FORECAST... ANOTHER LOW PRESSURE SYSTEM THAT WILL IMPACT ALL OF THE REGION WILL TRACK FROM THE CENTRAL PLAINS INTO NEW ENGLAND TUESDAY NIGHT INTO WEDNESDAY. THIS WILL RESULT IN SUB-VFR CONDITIONS WEDNESDAY AND THURSDAY WITH WIDESPREAD RAIN AHEAD OF THE FRONT ON WEDNESDAY AND WINTER PRECIPITATION BEHIND THE FRONT WEDNESDAY NIGHT AND THURSDAY. FRIDAY SHOULD SEE A RETURN TO HIGH PRESSURE AND VFR WEATHER. && .HYDROLOGY... AS OF 300 PM EST MONDAY LIKELY TO SEE SOME SUBSTANTIAL RISES ON AREA RIVERS AND STREAMS IN RESPONSE TO UPCOMING RAIN EVENT AND SNOWMELT IN THE MOUNTAINS...QUESTIONS REMAIN ABOUT HOW SUBSTANTIAL. SIGNIFICANT SNOW AMOUNTS ARE NOW CONFINED TO PARTS OF THE UPPER JAMES AND GREENBRIER RIVER BASINS WHERE THE LATEST AVAILABLE ESTIMATES FROM THE NATIONAL OPERATIONAL REMOTE SENSING CENTER SHOW ROUGHLY 1 TO 3 INCHES OF SNOW WATER EQUIVALENT WITH ISOLATED 4 INCHES IN THE HIGHEST ELEVATIONS OF THE GREENBRIER. IN THE OTHER MAJOR RIVER BASINS...NEW...ROANOKE/DAN AND TENNESSEE... MELTING OVER THE WEEKEND AND TODAY HAS REDUCED THE SNOW TO LESS THAN 1 INCH OF SNOW WATER AND IN MOST PLACES ZERO. THE OTHER ELEMENT OF COURSE IS THE QPF. 12Z MODELS (INCLUDING LATEST EC) HAVE NUDGED THE HEAVIEST QPF A LITTLE MORE TO THE WEST...REDUCING AMOUNTS IN THE JAMES AND GREENBRIER SOME. IT STILL APPEARS AS IF 1 TO 2 INCHES COULD FALL ACROSS THE WESTERN BASINS BY 12Z THURSDAY AND COMBINED WITH SNOWMELT THIS COULD PRODUCE AT LEAST MINOR RIVER FLOODING ALONG THE GREENBRIER AND POSSIBLY THE UPPER JAMES. GUIDANCE RECEIVED FROM OHRFC THIS MORNING SUGGESTED MINOR FLOOD STAGE AT ALDERSON WV ON THE GREENBRIER LIKELY BY EARLY THURSDAY WITH THE COMBINED SNOWMELT AND QPF. HOWEVER...GIVEN THE CONTINUED UNCERTAINTIES WILL HOLD OFF ON A FLOOD WATCH AT THIS POINT. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...WINTER WEATHER ADVISORY FROM 7 AM TO 1 PM EST TUESDAY FOR VAZ018>020-022>024-034-035-045>047. WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR VAZ007-009- 010-012-015-016. WINTER WEATHER ADVISORY FROM 4 AM TO 1 PM EST TUESDAY FOR VAZ011-013-014-017-032-033-043. NC...WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR NCZ001-002- 018. WV...WINTER WEATHER ADVISORY FROM 7 AM TO 1 PM EST TUESDAY FOR WVZ507-508. WINTER WEATHER ADVISORY UNTIL NOON EST TUESDAY FOR WVZ042. WINTER WEATHER ADVISORY FROM 4 AM TO 1 PM EST TUESDAY FOR WVZ043-044.
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&& $$ SYNOPSIS...KK/RAB NEAR TERM...KK/PM SHORT TERM...RAB LONG TERM...DS AVIATION...DS/KK HYDROLOGY...PC

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