Area Forecast Discussion
Issued by NWS Blacksburg, VA

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991 FXUS61 KRNK 030130 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 830 PM EST TUE FEB 2 2016 .SYNOPSIS... HIGH PRESSURE IS CENTERED OVER EASTERN CANADA AND WILL REMAIN WEDGED AGAINST THE EAST SIDE OF THE APPALACHIANS THROUGH TONIGHT. MEANWHILE...A STRONG WINTER STORM WILL MOVE THROUGH THE PLAINS AND INTO THE UPPER MIDWEST...THE ASSOCIATED COLD FRONT MOVING EAST ACROSS THE MISSISSIPPI VALLEY THIS EVENING AND INTO THE OHIO AND TENNESSEE VALLEYS TONIGHT. THIS COLD FRONT WILL CROSS THE APPALACHIANS WEDNESDAY AS THE WINTER STORM ADVANCES NORTHEAST THROUGH THE GREAT LAKES AND INTO EASTERN CANADA. && .NEAR TERM /THROUGH WEDNESDAY/... AS OF 830 PM EST TUESDAY... EXPANDED WIND ADVISORY TO INCLUDE MERCER SOUTHWARD TO WATAGUA COUNTY IN NORTHWEST NORTH CAROLINA FOR THE SOUTHEAST WINDS INTO WEDNESDAY MORNING. THESE COUNTIES TEND TO BE OUR FAVORED LOCATIONS FOR THE STRONG SOUTHEAST WINDS. A VERY STRONG LOW LEVEL JET WILL PIVOT NORTHWARD ACROSS THE REGION. THE BEST LOCATIONS FOR THE POTENTIAL OF WIND ADVISORY CRITERIA WINDS WOULD BE AT THE HIGHEST ELEVATIONS. ONE OF THE HINDERING FACTORS WILL BE IF THE LOW-LEVEL INVERSION/CLOUD LAYER WILL STOP SOME OF THE STRONGEST WINDS FROM MIXING DOWN. ADJUSTED TEMPERATURES THIS EVENING INTO TONIGHT WITH THE CURRENT OBS AND MODEL TRENDS. THE HIRESW-ARW AND RNK WRFARW AND HRRR HAVE A SLOW THE DEVELOPMENT OF THE RAIN TONIGHT. DECIDED TO LOWER POPS FOR THIS EVENING INTO THE OVERNIGHT. PRECIPITATION WILL SLOWLY INCREASE TONIGHT IN COVERAGE AND INTENSITY AS ISENTROPIC LIFT INCREASES AHEAD OF AN APPROACHING COLD FRONT. BY WEDNESDAY MORNING...RAIN WILL ARRIVE FOR THE WEST AND SPREAD EAST ACROSS FORECAST AREA. MORE CHANGES LATER TONIGHT.... AS OF 330 AM EST TUESDAY... WEDGE OF HIGH PRESSURE IS NOSED DOWN THE EAST SIDE OF THE APPALACHIANS WITH SHALLOW STABLE LAYER PROMOTING NEAR SATURATED CONDITIONS BELOW 800 MB. CLOUDS ARE THE LOWEST AND THICKEST ALONG THE APPALACHIAN CREST FROM THE HIGH COUNTRY OF NC NORTHWARD THROUGH THE NRV OF VA AND INTO SOUTHEAST WV. CLOUD BASES WERE HIGHER ACROSS THE FOOTHILLS AND INTO THE PIEDMONT...THE DRY NORTHEAST WIND EVEN PROMOTING SOME CLEARING ACROSS PARTS OF NORTHERN AND EASTERN VA. RAIN THREAT TO THIS POINT HAS BEEN MINIMAL WITH THE ONLY REPORTS OF PRECIPITATION COMING FROM THE RIDGE TOPS NEAR THE APPALACHIAN CREST WHERE DRIZZLE WAS OCCURRING. AS WE PROGRESS THROUGH THE OVERNIGHT...THE WEDGE OF HIGH PRESSURE WILL REMAIN IN PLACE BUT WEAKEN AS WARM AIR ADVECTION INCREASES IN ADVANCE OF AN APPROACHING COLD FRONT. THE ACTUAL FRONT IS IN THE PROCESS OF CROSSING THE MS RIVER VALLEY...TRAILING FROM LOW PRESSURE CENTERED OVER IOWA. THE PARENT LOW PRESSURE WILL BE MOVING NORTHEAST OVERNIGHT...REACHING THE GREAT LAKES BY DAWN WEDNESDAY...THE COLD FRONT WILL BE PROGRESSING EAST ACROSS THE OHIO AND TENNESSEE VALLEYS. AS THE FRONT GETS CLOSER TO OUR REGION...STRONG WARM AIR ADVECTION PER INCREASING SOUTHERLY FLOW WILL BEGIN TO OVERRUN THE COOL WEDGE OF HIGH PRESSURE RESULTING IN THE DEVELOPMENT OF RAIN ACROSS OUR FORECAST AREA...WELL IN ADVANCE OF THE FRONTAL SHOWERS. THE WARM AIR ADVECTION WILL ALSO BEGIN THE PROCESS OF ERODING THE COOL WEDGE. THIS WILL RESULT IN STEADY OR RISING TEMPERATURES OVERNIGHT...ESPECIALLY AT RIDGE TOP LEVEL CLOSER TO THE TOP OF THE INVERSION. THE MAIN EMPHASIS FOR RAIN WILL BE LATE TONIGHT AND DURING THE DAY WEDNESDAY AS 800MB LOW LVL JET STREAKS ACROSS THE CENTRAL APPALACHIANS FEEDING HIGHER PWATS INTO THE AREA. AS SUCH WILL SEE THE DEVELOPMENT OF RAIN PER INCREASING UPSLOPE AND OVERRUNNING WIND FLOW...AND IN ADDITION TO THE ARRIVAL OF A LINE OF SHOWERS ASSOCIATED WITH THE APPROACHING COLD FRONT...WHICH SHOULD BE NEARING OUR WRN CWA BORDER BY 12Z WEDNESDAY. LOOK FOR COVERAGE OF RAIN TO INCREASE FROM SOUTH TO NORTH ALONG AND EITHER SIDE OF THE BLUE RIDGE OVERNIGHT...WITH MOST OF THE FORECAST AREA ENGULFED IN A WIDESPREAD WETTING RAIN BY 12Z/7AM WED. DONT BE SURPRISED TO HEAR A RUMBLE OF THUNDER WITH THE PASSING LINE OF CONVECTION ON WEDNESDAY. THIS IS A VERY DYNAMIC SYSTEM...BUT THE OVERALL INSTABILITY APPEARS LIMITED FOR OUR CWA PER THE LINGERING STABLE WEDGE OF HIGH PRESSURE ON THE EAST SIDE OF THE APPALACHIANS. ATTM WILL ENTERTAIN A WIND THREAT PRIMARILY PRIMARILY FOR NON CONVECTIVE CONCERNS ON THE WEST SIDE OF THE APPALACHIAN DIVIDE...SPECIFICALLY TAZEWELL AND SMYTH COUNTIES WHERE WIND GUSTS OF 40 TO 50 MPH ARE CERTAINLY POSSIBLE DUE TO SOUTHEAST DOWNSLOPE FLOW AHEAD OF THE APPROACHING FRONT. THERE MAY ALSO BE SOME RIDGETOP GUSTS OF THIS MAGNITUDE FARTHER EAST ABOVE THE STABLE WEDGE...BUT IT APPEARS THERE WILL NOT BE ENOUGH COVERAGE TO JUSTIFY A WIND ADVISORY ATTM. MODEL QPF HAS BEEN TRENDING UP WITH THIS SYSTEM. PLEASE SEE HYDRO SECTION OF THIS AFD FOR DETAILS. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... AS OF 330 PM EST TUESDAY... THE COLD FRONT WILL BE WELL EAST OF THE CWA ON WEDNESDAY NIGHT...WHICH WILL ALLOW THE RAIN SHOWERS TO SUBSIDE IN THE PIEDMONT. MEANWHILE...COLD AIR ADVECTION SHOULD ENSUE...AND SOME UPSLOPE SNOW SHOWERS OR FLURRIES WILL DEVELOP AROUND MIDNIGHT ALONG THE WESTERN SLOPES. THE 12Z GFS AND ECMWF MODELS SHOW THAT THE WIND WILL NOT QUITE BE FROM THE NORTHWEST...BUT RATHER FROM THE NORTH- NORTHWEST. THIS SETUP IS NOT AS IDEAL FOR UPSLOPE SNOW SHOWERS...SO ONLY A LITTLE ACCUMULATION IS ANTICIPATED. BY THURSDAY...CLOUDS SHOULD GRADUALLY DECREASE...ALTHOUGH NOT SO QUICKLY IN THE WESTERN SLOPES AND IN THE PIEDMONT EAST OF A LINE FROM LYNCHBURG TO DANVILLE. THE ECMWF SOLUTION MOVES THE COLD FRONT SLOWER TOWARD THE EAST COAST THAN THE GFS...AND ALSO TRIES TO DEVELOP A WAVE OF LOW PRESSURE TO BUCKLE SOME MOISTURE BACK TOWARD THE PIEDMONT BY EARLY THURSDAY NIGHT. IT SEEMS THAT THE ECMWF MAY BE TOO SLOW...SO THE FASTER AND MORE PROGRESSIVE GFS SOLUTION WAS FAVORED IN THIS FORECAST. AS A RESULT...JUST DRY CONDITIONS WITH SOME LINGERING CLOUD COVER IS EXPECTED TO THE EAST. HIGH PRESSURE SHOULD FINALLY BUILD OVERHEAD AFTER MIDNIGHT ON THURSDAY NIGHT. SKIES WILL EVENTUALLY CLEAR EVERYWHERE IN THE CWA...WHICH SHOULD PROVIDE A GOOD RADIATIONAL COOLING SITUATION. FRIDAY LOOKS TO BE SUNNY BUT STILL COOL. THE HIGH SHOULD SHIFT OVER THE PIEDMONT ON FRIDAY NIGHT...WHICH WILL PROVIDE ANOTHER GOOD NIGHT FOR RADIATIONAL COOLING. LOCATIONS WEST OF THE BLUE RIDGE MAY NOT COOL AS MUCH DUE TO A FEW HIGH CLOUDS AND THE FLOW SLOWLY TURNING AROUND TO THE SOUTHWEST. THROUGHOUT THIS PERIOD...HIGH TEMPERATURES WERE GENERALLY HELD ON THE COOLER SIDE OF MOS GUIDANCE...WHILE LOW TEMPERATURES WERE KEPT BELOW MOS GUIDANCE. && .LONG TERM /SATURDAY THROUGH TUESDAY/... AS OF 400 PM EST TUESDAY... HIGH PRESSURE SHOULD DRIFT OFFSHORE ON SATURDAY...WHICH WILL START A PERIOD OF WARM AIR ADVECTION OVER THE MID ATLANTIC. TEMPERATURES SHOULD MODERATE SOMEWHAT ON SATURDAY...BUT THERE WILL BE AN INCREASE IN CLOUDINESS THAT WILL WEAKEN THE WARMING TREND. BY SATURDAY NIGHT...TWO UPPER LEVEL SHORT WAVE TROUGHS APPROACH THE EASTERN UNITED STATES. THE NORTHERN ONE WILL CROSS OVER QUEBEC AND THE NEW ENGLAND STATES...WHILE A SOUTHERN ONE SHOULD MOVE ALONG THE GULF COAST. THE LATEST GFS AND ECMWF MODELS KEEP THIS SPLIT FLOW PATTERN IN PLACE. THE SOUTHERN TROUGH WILL GENERATE A LOW PRESSURE SYSTEM OFF THE CAROLINA COAST...AND TRACK IT TO THE NORTHEAST AS THE SYSTEM INTENSIFIES. THE LOW PRESSURE SYSTEM APPEARS TO STAY JUST OFFSHORE AND NOT IMPACT THE CWA. BY SUNDAY...A BROAD UPPER LEVEL TROUGH WILL EMERGE WITHIN THE NORTHERN STREAM OVER THE DAKOTAS...AND DIG SOUTHWARD TOWARD THE MID ATLANTIC DURING MONDAY AND TUESDAY. A WAVE OF LOW PRESSURE SHOULD ACCOMPANY THE LEADING EDGE OF THIS TROUGH...THAT WILL SPARK AN ALBERTA CLIPPER SYSTEM. TEMPERATURES SHOULD REMAIN ABOVE FREEZING ON MONDAY...TO KEEP THE APPROACHING MOISTURE FROM THE CLIPPER SYSTEM AS RAIN...EXCEPT FOR THE COLDER WESTERN SLOPES WHERE IT MAY START AS SNOW. ONCE A SHOT OF ARCTIC AIR ARRIVES FROM THE UPPER LEVEL TROUGH ON MONDAY NIGHT...THE PRECIPITATION WOULD TURN OVER TO ALL SNOW WEST OF THE BLUE RIDGE. SINCE THERE IS STILL CONSIDERABLE UNCERTAINTY DUE TO THE MODELS DIVERGING ON THE TRACK OF THIS CLIPPER SYSTEM...JUST CHANCE POPS WERE UTILIZED. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... AS OF 645 PM EST TUESDAY... MOIST EASTERLY FLOW WILL CONTINUE THROUGH THE EVENING. ALL TAF SITES ARE BELOW VFR AT THIS HOUR EXCEPT DANVILLE WHICH IS EXPECTED TO LOWER TO MVFR OVER THE NEXT FEW HOURS. WARMER AIR AHEAD OF A COLD FRONT WILL CONTINUE TO LOWER CEILINGS/VISBYS OVERNIGHT WITH ALL TAF LOCATIONS AT IFR CEILINGS BY DAYBREAK WEDNESDAY. RAIN WILL CROSS THE REGION WEDNESDAY MORNING AND AFTERNOON AND MAY BE HEAVY AT TIMES. A STRONG LOW LEVEL JET MOVING ACROSS THE CENTRAL APPALACHIANS WILL KEEP WINDS GUSTY AT BLF THROUGH THE TAF PERIOD AND GUSTY WINDS OF 15-25KTS WITH THE FRONTAL PASSAGE DURING THE DAY TOMORROW AT THE REMAINING TAF SITES. THE COLD FRONT ISNT EXPECTED TO CROSS THE ENTIRE FORECAST AREA UNTIL LATE WEDNESDAY NIGHT. AS THE COLD FRONT CROSSES...WIND DIRECTIONS WILL SWITCH AROUND TO THE W/SW WITH SPEEDS SLOWLY SUBSIDING. EXTENDED DISCUSSION... THE STRONG COLD FRONT WILL MOVE EAST OF THE APPALACHIANS LATE WEDNESDAY EVENING REACHING THE COAST BY EARLY THURSDAY. BY LATE THURSDAY...HIGH PRESSURE WILL BUILD OVERHEAD TO PROVIDE COLDER AND DRIER CONDITIONS... AND ALSO PROVIDE A RECOVERY TO VFR CONDITIONS AT ALL TAF SITES THROUGH SATURDAY. && .HYDROLOGY... MODELS HAVE BEEN TRENDING HIGHER FOR QPF WITH WEDNESDAYS FRONTAL PASSAGE...AMOUNTS RANGING FROM 0.75 TO 1.25...WITH SOME ISOLATED 1.50 INCH AMOUNTS NEAR THE BLUE RIDGE. THIS SORT OF RAINFALL WILL GENERATE SIGNIFICANT RISES ON AREA STREAMS...POTENTIALLY TO NEAR BANKFULL IN SOME INSTANCES. IF TRENDS CONTINUE TO GO HIGHER THEN A FLOOD WATCH MAY BE NEEDED FOR PARTS OF THE AREA ON WEDNESDAY. && .EQUIPMENT... AS OF 100 PM EST TUESDAY... MAINTENANCE HAS BEEN CONDUCTED ON THE KFCX RADAR. THE RADAR IS BACK UP AND RUNNING BUT MAY CONTINUE TO EXPERIENCE INTERMITTENT OUTAGES. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...WIND ADVISORY UNTIL 10 AM EST WEDNESDAY FOR VAZ007-009-015. NC...WIND ADVISORY UNTIL 10 AM EST WEDNESDAY FOR NCZ001-018. WV...WIND ADVISORY UNTIL 10 AM EST WEDNESDAY FOR WVZ042. && $$ SYNOPSIS...PM NEAR TERM...KK/PM SHORT TERM...PW LONG TERM...PW AVIATION...CF/PM HYDROLOGY...PM EQUIPMENT...PM

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