Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 192012 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 412 PM EDT SUN APR 19 2015 .SYNOPSIS... LOW PRESSURE OVER WESTERN KENTUCKY WITH A WARM FRONT EXTENDING EAST AND COLD FRONT TRAILING SOUTHWARD FROM THE LOW WILL LIFT NORTHEAST TONIGHT INTO MONDAY. A COLD FRONT CROSSES THE REGION ON MONDAY...THEN HIGH PRESSURE BUILDS IN FOR TUESDAY. && .NEAR TERM /THROUGH MONDAY/... AS OF 333 PM EDT SUNDAY... FLOOD WATCHES REMAIN IN EFFECT INTO TONIGHT. A WARM FRONT TO OUR SOUTH WILL LIFT NORTH THIS EVENING AND CROSS THE FORECAST AREA TONIGHT. DEEPER MOISTURE AND HIGHER PWATS WILL INCREASE IN THE WARM ADVECTION WITH THE NORTHWARD ADVANCE OF THE FRONT. THE REGIONAL RADAR IMAGE SHOWED WIDESPREAD CONVECTION ACROSS THE MID ATLANTIC REGION SOUTHWARD TO THE SOUTHEAST US. THERE ARE SOME CONCERNS OF STRONG CONVECTION ACROSS GEORGIA THIS AFTERNOON MAY TAKE SOME OF THE MOISTURE AWAY FROM OUR AREA. OUR LOCAL RNK WRFARW...HIRESW-ARW...NAM AND GFS WAIT UNTIL AFTER 00Z BEFORE BRINGING IN HEAVIER CONVECTION THIS EVENING...WHILE HRRR AND ECMWF ARE A LITTLE FASTER WITH TIMING. THE HRRR AND HIRESW-ARW LIFTS THE PRECIPITATION NORTHEAST WITH MOST OF RAIN PULLING OUT BY 06-08Z. USED A BLEND OF HRRR AND NAM FOR POPS...TAPERING POPS BACK AFTER 06Z TONIGHT INTO MONDAY MORNING. NOT EXPECTING ANY STRONG THUNDERSTORMS THIS AFTERNOON INTO TONIGHT WITH CLOUD COVER HINDERING INSTABILITIES. HOWEVER...THE LOW LEVEL JET INCREASING TO 50-60 KNOTS FROM THE SOUTHEAST WILL RESULT IN STRONG UPSLOPE AND ISENTROPIC LIFT. THE STRONG WINDS THROUGH A DEEP LAYER WILL PROVIDE LARGE HELICITY VALUES LATE THIS AFTERNOON INTO THIS EVENING. THE DAY ONE CONVECTIVE OUTLOOK (SWODY1) PLACED A MARGINAL (5 PERCENT CHANCE OF WIND) ACROSS SOUTHWEST PORTION OF CWA. PLAYED LOW TEMPERATURES CLOSE TO ADJMAV WITH READINGS FROM THE UPPER 40S IN THE NORTHWEST MOUNTAINS TO AROUND 60 DEGREES IN THE PIEDMONT. A WARM...MOIST AND UNSTABLE AIRMASS EXPECTED MONDAY. THE ATMOSPHERE WILL DESTABILIZE AHEAD OF THE APPROACHING COLD FRONT WITH SHOWERS AND THUNDERSTORMS DEVELOPING MONDAY. INITIALLY CUT BACK POPS CLOSER TO NAM FOR MONDAY MORNING...THEN INCREASED TO LIKELY BY MONDAY AFTERNOON. SPC CONTINUES OUR SLIGHT RISK FOR MONDAY ACROSS MOST OF OUR CWA. THIS IS SUPPORTED BY THE DYNAMIC ENVIRONMENT WITH HEALTHY SHEAR AND DECENT CAPES AROUND 2K. IT WILL ALSO BE QUITE BREEZY WITH EFFICIENT DOWNWARD MOMENTUM TRANSFER IN A WELL MIXED BOUNDARY LAYER. THE FRONT SHOULD BE CLEARING MONDAY NIGHT. HIGH TEMPERATURES MONDAY WILL RANGE FROM THE MID 60S IN THE MOUNTAINS TO THE LOWER 80S IN THE PIEDMONT. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
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AS OF 345 PM EDT SUNDAY... TAIL END OF COLD FRONT AND ASSOCIATED CONVECTION WILL BE EXITING THE AREA JUST AFT 00Z. HOWEVER...A BROAD UPPER TROUGH...ALMOST WINTERLIKE PATTERN CONTINUES TO EVOLVE AND DEEPEN ACROSS THE GREAT LAKES WITH NUMEROUS SPOKES OF PVA/SHORT WAVES REMAINING UPSTREAM. THIS LEAVES THE REGION...ESPECIALLY THE MOUNTAINS...WITH A VERY UNSETTLED PATTERN. AT A MINIMUM...EXPECT VARIABLE CLOUDINESS. TIMING OF EMBEDDED DISTURBANCES WILL BE THE KEY TO THE TIMES FOR THE BETTER CHANCES OF SHOWERS. FOR SEVERAL DAYS...THE GFS HAS INSISTED ON A SIGNIFICANT DISTURBANCE MOVING THROUGH THE REGION WED WITH WIDESPREAD -SHRA AS A RESULT. THE OTHER MODELS REMAIN LACKLUSTER WITH THIS FEATURE...BUT DO SUGGEST AT LEAST SOME SMALL CHANCE WITHIN THIS TIME FRAME. GIVEN THE UNSETTLED NATURE OF THE PATTERN WITH UPSLOPE FLOW AND VERY DIFFICULT TO TIME UPPER DISTURBANCES...CANNOT REALLY DROP POPS AT ANY TIME. BEST FOCUS THROUGH THE PERIOD WILL REMAIN WEST OF THE BLUE RIDGE...AND ESPECIALLY ACROSS THE MOUNTAINS OF WV/FAR SW VA. IN ADDITION...ENOUGH INSTABILITY SUGGESTED WITH COLD AIR ALOFT...TO INTRODUCE ISOLD TSRA WITH THE WED DISTURBANCE AS WELL. 850MB TEMPS DROP TO NEAR 0C ACROSS THE NORTHERN PART OF THE FORECAST AREA BY WED...BUT THE BETTER COLD ADVECTION COMES IN THE EXTENDED PERIOD BEHIND THE WED DISTURBANCE.A
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
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AS OF 400 PM EDT SUNDAY... BROAD UPPER TROUGH REMAINS IN PLACE AND DOMINATES THE EXTENDED FORECAST...GRADUALLY SHIFTING FURTHER ESE LATE IN THE PERIOD. THIS KEEPS THE REGION IN AN UNSTABLE/UNSETTLED NORTHWEST FLOW WITH NUMEROUS EMBEDDED SHORT WAVES. MODELS VARY CONSIDERABLY AS TO THE TIMING AND PLACEMENT OF THESE DISTURBANCES...BUT ENOUGH AGREEMENT THAT POPS CANNOT BE DROPPED REALLY AT ANY TIME THE OVERALL TREND IS TO PUSH THE BETTER MOISTURE FURTHER SOUTH OF THE REGION AS THE WEEK PROGRESSES AND 850MB TEMPS DROP BELOW 0C IN THE NORTHERN COUNTIES. THE ENTIRE PERIOD SHOULD FEATURE BELOW NORMAL TEMPERATURES WITH LOW CHC POPS...HIGHEST ACROSS THE MOUNTAINS AND TOWARD THE SOUTHERN COUNTIES...WITH THE NORTHERN PIEDMONT THE DRIEST. ALTHOUGH TEMPERATURES WILL BE BELOW NORMAL THROUGHOUT THE PERIOD...NO REAL CLEAR CONCERN AT THIS POINT FOR FROST/FREEZE BECAUSE OF CYCLONIC FLOW AND CLOUDS.
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&& .AVIATION /20Z SUNDAY THROUGH FRIDAY/... AS OF 142 PM EDT SUNDAY... KFCX WSR-88D SHOWED RAIN SPREADING NORTHEAST ACROSS THE FORECAST AREA THIS AFTERNOON...AS A WARM FRONT LIFTS NORTH ACROSS THE REGION. CEILINGS WILL LOWER TO MVFR AND IFR WITH RAIN. A STRONG SOUTHEAST LOW LEVEL JET WILL CONTINUE TO INCREASE THIS AFTERNOON AND TONIGHT WHICH WILL BRING WIND GUSTS AS HIGH AS 30 KTS. WITH A WEDGE OF HIGH PRESSURE IN PLACE ALONG AND EAST OF THE BLUE RIDGE...AFTER SUNSET THESE STRONG WINDS ARE NOT EXPECTED TO REACH THE SURFACE. SHORTEN THE TIME WINDOW AND KEPT LLWS IN THE KLWB AND KBCB TAFS AFTER 00Z/8PM. CEILINGS WILL LOWER TO IFR THIS EVENING INTO TONIGHT AND WILL REMAIN LOW OVERNIGHT. A COLD FRONT APPROACHES LATER MONDAY WITH SOME THUNDERSTORMS POSSIBLE AHEAD OF AND ALONG THE FRONT...ESPECIALLY EAST OF THE BLUE RIDGE. THIS IS LIKELY TO KEEP PERIODS OF MVFR AND BRIEF IFR IN STORMS UNTIL THE FRONT CLEARS THE REGION MONDAY EVENING. MEDIUM CONFIDENCE IN CEILINGS...VISIBILITIES AND WINDS DURING THE TAF PERIOD. EXTENDED AVIATION... 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 AND THURSDAY. && .HYDROLOGY... AS OF 330 PM EDT SUNDAY... HAVE EXPANDED THE FLOOD WATCH FOR THE ALLEGHANY HIGHLANDS OF VIRGINIA. A DEEP LAYER FROM THE SURFACE THROUGH MID LEVELS OF THE ATMOSPHERE OF SOUTHEAST WINDS...WILL BE INCREASING TO AROUND 50 KNOTS LATER THIS AFTERNOON AND EVENING. PRECIPITABLE WATER VALUES JUST ABOVE 1.5 INCHES WILL BE ADVECTED INTO THE FORECAST AREA. THE STRONGEST LIFT AND HIGHEST RAINFALL AMOUNTS WILL BE FROM 18Z/2PM THROUGH 06Z/2AM SO HAVE ADDED HEAVY RAIN TO THE FORECAST ALONG THE BLUE RIDGE FOR THIS TIME FRAME. TOTAL RAINFALL AMOUNTS WILL RANGE FROM 1 TO 3 INCHES THROUGH 12Z/8AM MONDAY. FLASH FLOOD GUIDANCE VALUES WERE ROUGHLY 1.5 TO 2.5 INCHES FOR 3 HOURS. SO THIS AMOUNT OF RAINFALL HAS THE POTENTIAL TO PRODUCE FLOODING ON SMALL STREAMS AND CREEKS. PROBABILISTIC GUIDANCE FOR MAINSTEM RIVERS SUGGESTS A SMALL POSSIBILITY FOR MINOR FLOODING ALONG THE DAN RIVER AND NEW RIVER. HOWEVER...THE IS HIGHLY DEPENDENT ON THE AMOUNT OF RAINFALL THROUGH MONDAY MORNING. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...FLOOD WATCH THROUGH LATE TONIGHT FOR VAZ018>020-022>024- 033>035. FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR VAZ009-012>017-032. NC...FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR NCZ001>003-018>020. WV...NONE. && $$ SYNOPSIS...AMS/KK NEAR TERM...KK SHORT TERM...RAB LONG TERM...RAB AVIATION...AMS/KK HYDROLOGY...KK

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