Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 181335 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 935 AM EDT SAT APR 18 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD INTO THE AREA TODAY. A COMPLEX STORM SYSTEM PASSING TO THE WEST WILL RESULT IN WIDESPREAD RAIN SUNDAY INTO SUNDAY NIGHT...BEFORE A COLD FRONT CROSSES THE REGION WITH A CHANCE OF SHOWERS AND POTENTIALLY STRONG THUNDERSTORMS ON MONDAY. HIGH PRESSURE...ALONG WITH DRY AND COOLER WEATHER...RETURNS FOR TUESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 930 PM EDT SATURDAY... TEMPERATURES ARE RAPIDLY CLIMBING UNDER ABUNDANT SUNSHINE THIS MORNING AND 13Z TEMPS ARE ALREADY RUNNING A FEW DEGREES HIGHER THAN FORECAST. AS A RESULT...CONTINUED THE TREND OF INCREASING TEMPS TODAY AND NUDGED HIGHS UP A COUPLE OF DEGREES. MODELS ARE IN GOOD AGREEMENT THAT THE AXIS OF SFC HIGH PRESSURE SHIFTS EAST...ALLOWING LOW LEVEL WINDS TO VEER TO THE EAST LATER TODAY. ALOFT...WEAK AREAS OF SHEARED VORTICITY WILL DRIFT ACROSS NC OVER A BUILDING RIDGE. WEAK LOW LEVEL CONVERGENCE...INCREASING PWATS...FORECAST CAPES OF 100-500 J/KG AND THESE SUBTLE UPPER DISTURBANCES...SHOULD GENERATE SOME ISOLATED SHOWERS/STORMS...ESPECIALLY ALONG THE EAST SLOPES OF THE SOUTHERN BLUE RIDGE. FOR TONIGHT...WINDS CONTINUE TO VEER TO THE SOUTHEAST WIT BUFKIT SHOWING A LOW LEVEL SOUTHEAST JET INCREASING INTO THE 35 TO 40 KNOT RANGE AFTER 06Z/2AM. WITH INCREASING UPSLOPE AND DEEPER MOISTURE...RAIN WILL ALSO SPREAD INTO THE COUNTY WARNING AREA FROM THE SOUTHWEST AFTER MIDNIGHT. CLOUDS AND THE LACK OF ANY ADVECTION WILL MEAN LOW TEMPERATURES WILL AGAIN BE MILD OVERNIGHT. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... AS OF 330 AM EDT SATURDAY... MODELS ARE FAIRLY CONSISTENT WITH HANDLING THE UPCOMING RAIN EVENT WITH THE MAIN DIFFERENCES BEING TIMING AS THE GFS IS A FEW HOURS FASTER THAN OTHER SOLUTIONS. HIGH PRESSURE WILL WEDGE DOWN THE EASTERN SEABOARD ON SUNDAY AS DEEPENING LOW PRESSURE MOVES UP THE MISSISSIPPI VALLEY AND PUSHES A WARM FRONT INTO THE REGION. SIGNIFICANT ISENTROPIC LIFT WILL DEVELOP AS THE WARM AIR RUNS OVER THE WEDGE AND DEEP MOISTURE TRANSPORT CONTINUES TO BRING ANOMALOUSLY HIGH PRECIPITABLE WATER VALUES INTO THE REGION. THE LOW LEVEL WIND FIELD WILL ALSO STRENGTHEN MARKEDLY FROM THE SOUTHEAST SUNDAY AFTERNOON...ALLOWING FOR ENHANCED OROGRAPHIC LIFT ALONG THE EASTERN SLOPES OF THE BLUE RIDGE. ALL OF THESE FACTORS WILL COMBINE TO BRING A SOAKING RAIN TO THE REGION SUNDAY INTO SUNDAY NIGHT. DOWNSLOPING WILL HELP LIMIT RAINFALL AMOUNTS ACROSS THE FAR WEST TO JUST UNDER ONE INCH...WITH MOST LOCATIONS EAST OF THE BLUE RIDGE PICKING UP 1.0 TO 1.5 INCHES. THE HIGHEST TOTALS WILL LIKELY BE FOUND ALONG THE EAST SLOPES OF THE BLUE RIDGE FROM NORTHWEST NC AND EXTENDING ACROSS THE BORDER INTO VA WHERE AMOUNTS MAY APPROACH 2.0 INCHES. THE LATEST ENSEMBLE HYDRO GUIDANCE INDICATES FORECAST POINTS IN THE ROANOKE RIVER BASIN WILL LIKELY EXCEED ACTIONS STAGE AND APPROACH FLOOD STAGE...AND SMALLER STREAMS AND CREEKS WILL ALSO EXPERIENCE SHARP RISES. THIS SITUATION WILL CONTINUE TO BE MONITORED FOR THE THREAT OF FLOODING AND FLOOD WATCHES MAY BE ISSUED LATER TODAY. INDICATIONS ARE THAT THE CORE OF THE SOUTHEASTERLY LOW LEVEL JET WILL MOVE JUST TO OUR WEST. THIS COMBINED WITH INEFFICIENT DOWNWARD MOMENTUM TRANSFER ONCE PRECIPITATION BEGINS SHOULD MITIGATE THE THREAT FOR ADVISORY LEVEL WINDS IN DOWNSLOPING AREAS WEST OF THE BLUE RIDGE ON SUNDAY. HOWEVER...IT WILL STILL BE QUITE GUSTY ESPECIALLY ALONG THE RIDGE. LATER SUNDAY NIGHT AND INTO MONDAY THERE WILL BE A BREAK IN THE ACTION AS WE GET SOLIDLY INTO THE WARM SECTOR AHEAD OF AN APPROACHING COLD FRONT. THERE WILL BE ENOUGH INSTABILITY FOR THUNDERSTORMS TO DEVELOP AHEAD OF THE FRONT ON MONDAY. THERE WILL BE ENOUGH SHEAR FOR A MARGINAL SEVERE THREAT ACROSS MOST OF THE AREA BUT CONDITIONS LOOK MORE FAVORABLE FROM THE PIEDMONT EASTWARD. WE WILL THEN REMAIN UNDER THE INFLUENCE OF COOL CYCLONIC FLOW ON TUESDAY AND CONDITIONS WILL BE UNSETTLED ENOUGH FOR A SLIGHT CHANCE OF SHOWERS WEST OF THE BLUE RIDGE. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... AS OF 345 PM EDT FRIDAY... A TRANSITION TO A PATTERN MORE REMINISCENT OF WINTER CONTINUES TO BE IN THE CARDS FOR THE EARLY AND MID PART OF NEXT WEEK AS A DEEP AND BROAD UPPER TROUGH BUILDS INTO THE CENTRAL/EASTERN U.S. BY TUESDAY...500MB HEIGHTS DROP INTO THE 560DM RANGE AND 850MB TEMPS PLUNGE TOWARD THE 0C MARK ACROSS THE NORTH BY MIDWEEK. ANTICYCLONIC FLOW...A SERIES OF EMBEDDED UPPER DISTURBANCES...AND COLD ADVECTION WILL KEEP VARIABLE CLOUDINESS AND POTENTIALLY UPSLOPE SHOWERS IN PLACE ACROSS THE MOUNTAINS. THE CLOUDS AND CYCLONIC FLOW WILL HOLD MAX TEMPS INTO THE 50S AND LOWER 60S ACROSS THE MOUNTAINS THROUGH MUCH OF THE LATER HALF OF NEXT WEEK...WHILE 60S TO 70S PREVAIL TO THE EAST WITH DOWNSLOPE NORTHWEST FLOW AND SIGNIFICANTLY GREATER AMOUNTS OF SUNSHINE. AT THIS POINT A DISTURBANCE ON WED APPEARS TO BE THE MOST SIGNIFICANT IN POTENTIALLY BRINGING SHOWERS EAST OF THE MOUNTAINS. HAVE NOT INTRODUCED ANY THUNDER AT THIS POINT GIVEN THE LOW-LEVEL COLD/STABLE AIR MASS. BY MID-WEEK...THE GFS/ECMWF BEGIN TO DIVERGE ON THE OVERALL PATTERN...WITH THE ECMWF KEEPING THE DEEP UPPER TROUGH IN PLACE ACROSS THE NORTHEAST AND A STRONGER NW FLOW INTO OUR REGION AS WELL...WHILE THE GFS DEPICTS THE UPPER TROUGH LIFTING FURTHER NORTH AND PLACING A ZONAL FLOW WITH A BAROCLINIC ZONE STUCK ACROSS OUR CWA. THIS RESULTS IN SIGNIFICANT DIFFERENCES BETWEEN MOISTURE/POPS ACROSS OUR CWA BETWEEN THE TWO MODELS...WITH THE GFS VERY WET AND THE ECMWF MUCH DRIER...KEEPING THE BAROCLINIC ZONE MUCH FURTHER SOUTH. HAVE JUST ADVERTISED CHC POPS FOR NOW UNTIL A BETTER HANDLE ON THIS PATTERN AND TIMING IS OBTAINED. TEMPERATURES ARE EXPECTED TO REMAIN BELOW NORMAL THROUGH THE MID PART OF THE WEEK...GRADUALLY TRENDING CLOSER TO NORMAL BY THE END OF THE PERIOD. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... AS OF 145 AM EDT SATURDAY... STARTING THE TAF PERIOD WITH WEAK HIGH PRESSURE AND LIGHT WINDS OVER THE MID ATLANTIC REGION. LOCATIONS THAT HAVE SOME MVFR FOG WILL BECOME VFR BY 14Z/10AM THIS MORNING...THEN VFR CONDITIONS ARE EXPECTED FOR THE REST OF THE DAY. THERE MAY BE ENOUGH WEAK CONVERGENCE AND UPSLOPE TO TRIGGER A FEW ISOLD SHWRS OR TSTORMS THIS AFTERNOON...ESPECIALLY NEAR BLUE RIDGE ALONG OR SOUTH OF VA/NC BORDER...BUT PROBABILITY IS TOO LOW TO INCLUDE IN ANY OF THE TAFS AT THIS TIME. MODELS HAVE BEEN CONSISTENT WITH CLOUDS AND THEN RAIN WILL SPREAD INTO THE AREA FROM SOUTHWEST TO NORTHEAST TONIGHT. EXPECT CEILINGS TO LOWER TO MVFR AFTER MIDNIGHT/04Z. HIGHEST CONFIDENCE IN MVFR CEILINGS IS AT KBCB AFTER 06Z/2AM. A STRONG SOUTHEAST LOW LEVEL JET WILL DEVELOP JUST AFTER MIDNIGHT. WIND GUSTS UP TO 30 KNOTS ARE POSSIBLE AT KBLF BY 12Z. BUFKIT SOUNDINGS WERE SUGGESTING THAT STRONGER WINDS WOULD REMAIN JUST ABOVE THE SURFACE AT KBCB...RESULTING IN LOW LEVEL WIND SHEAR. CONFIDENCE IS LOW FOR HOW MUCH WIND WILL MIX DOWN TO THE SURFACE. EXTENDED AVIATION... A COMPLEX STORM SYSTEM WILL BEGIN TO AFFECT THE REGION SUNDAY WITH A WARM FRONT BRINGING WIDESPREAD MVFR/IFR CONDITIONS IN RAIN INTO SUNDAY NIGHT. THIS WILL BE FOLLOWED BY ANOTHER COLD FRONT MONDAY. THIS IS LIKELY TO KEEP PERIODS OF MVFR IN PLACE UNTIL THE FRONT POSSIBLY CLEARS THE REGION. VFR RETURNS LATER MONDAY NIGHT AND TUESDAY WITH HIGH PRESSURE BUILDING IN BEHIND THE FRONT WITH A DRIER AIRMASS. THEN THE NEXT CHANCE OF MVFR CONDITIONS AND PRECIPITATION WILL BE IN THE MOUNTAINS ON WEDNESDAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS NEAR TERM...AMS/PH SHORT TERM...MBS LONG TERM...RAB AVIATION...AMS/SK

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