Area Forecast Discussion
Issued by NWS Blacksburg, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KRNK 170521 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 121 AM EDT FRI APR 17 2015 .SYNOPSIS... A WEDGE OF COOL HIGH PRESSURE WILL REMAIN OVER THE REGION INTO THIS MORNING BEFORE WEAKENING AS A WEAK TROUGH OF LOW PRESSURE CROSSES THE AREA FROM THE WEST DURING THE AFTERNOON. HIGH PRESSURE FOLLOWS THIS SYSTEM FRIDAY NIGHT INTO SATURDAY BRINGING DRIER AND WARMER WEATHER TO START THE WEEKEND. A COMPLEX STORM SYSTEM PASSING TO THE WEST WILL RESULT IN MORE WIDESPREAD RAIN SUNDAY INTO SUNDAY NIGHT BEFORE A COLD FRONT CROSSES THE REGION WITH CHANCES OF SHOWERS AND STORMS ON MONDAY. && .NEAR TERM /THROUGH TODAY/... AS OF 1030 PM EDT THURSDAY... COOL DAMP CONDITIONS LIKELY THROUGH FRIDAY MORNING AS SHALLOW WEDGE OF HIGH PRESSURE REMAINS LOCKED IN PLACE ALONG EASTERN SLOPES OF THE APPALACHIANS. OCCASIONAL DRIZZLE AND FOG WILL BE MOST PRONOUNCED ALONG THE EASTERN SLOPES OF THE BLUE RIDGE WHERE SHALLOW ISENTROPIC LIFT WILL BE THE GREATEST. VERY LITTLE CHANGE IN TEMPERATURES IS EXPECTED OVERNIGHT WITH TEMPERATURES REMAINING IN THE U40S-M50S. FRIDAYS HIGH TEMPERATURES HOWEVER...WILL BE A LITTLE TRICKY...ESPECIALLY IN AREAS WHERE THE WEDGE HANGS ON. TEMPERATURES FOR LOCATIONS OUTSIDE OF THE WEDGE COULD SEE HIGH TEMPERATURES IN THE LOW TO MID 70S. THOSE AREAS REMAINING IN THE WEDGE MAY ONLY SEE TEMPERATURES WARMING INTO THE LOW TO MID 60S WITH A LATE DAY SURGE IF THE WEDGE BREAKS. && .SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... AS OF 330 PM EDT THURSDAY... SOUTHWEST FLOW ALOFT WILL TRANSITION TO NORTHWEST FLOW ALOFT AT THE BEGINNING OF THE SHORT TERM AS AN UPPER SHORT WAVE MOVES OFF THE MID-ATLANTIC COAST. ANY LINGER SHOWERS ACROSS THE BLUE RIDGE SHOULD MOVE OUT OF THE REGION QUICKLY AFT 00Z SAT. UPPER-LEVEL SHORT WAVE RIDGING WILL EVOLVE ACROSS THE OH/TN VALLEY SUNDAY AS THE FLOW AMPLIFIES IN RESPONSE TO A DEEP UPPER TROUGH SHIFTING SLOWLY EAST FROM THE CENTRAL/SOUTHERN PLAINS. THIS PATTERN WILL BRING DRY/SEASONABLE CONDITIONS TO THE REGION SATURDAY. BY SUNDAY...THE AFOREMENTIONED UPPER TROUGH BEGINS TO LIFT OUT OF THE MID-SOUTH INTO THE MID-ATLANTIC REGION...WHILE TAKING ON A STRONG NEGATIVE TILT. ANTECEDENT SURFACE HIGH PRESSURE WILL MOVE OFF THE MID-ATLANTIC COAST INTO YET AGAIN ANOTHER FAVORABLE WEDGE POSITION. STRONG PVA/ISENTROPIC LIFT WILL ENSUE QUICKLY OVER THE SHALLOW WEDGE SUNDAY BRINGING WIDESPREAD RAIN...SOME HEAVY DURING THE AFTERNOON/EVENING...INTO THE WEDGE AIR MASS. THE WEDGE WILL BE REINFORCED WITH THE PRECIPITATION...HOLDING HIGH TEMPERATURES SUN AFTERNOON POTENTIALLY IN THE 50S. RAINFALL IN EXCESS OF 1 INCH ACROSS MUCH OF THE CWA APPEARS LIKELY WITH THIS EVENT. THE GOOD NEWS IS THAT THE SYSTEM IS MOVING VERY QUICKLY AS A NORTHERN STREAM UPPER LOW QUICKLY DIGS INTO THE NORTHERN PLAINS HELPING TO PUSH THE SOUTHERN STREAM UPPER TROUGH NORTHEAST OF THE REGION BY SUN NIGHT/EARLY MON. THIS SHOULD CONFINE THE PERIOD OF HEAVY RAIN TO ABOUT 12 HOURS OR LESS...WHICH SHOULD HELP LIMIT ANY POTENTIAL FLOOD ISSUES. WILL CONTINUE TO HIGHLIGHT IN THE HWO AS THE GROUND IS WELL SATURATED NOW FROM ALL OF THE RECENT RAINFALL. IT STILL APPEARS THAT THE HEAVIEST RAINFALL WILL FALL ALONG THE EAST FACING SLOPES OF THE BLUE RIDGE WITH PRONOUNCED SOUTHEAST FLOW IN THE WEDGE AIR MASS AS THE STRONG NEGATIVELY TILTED UPPER SHORT WAVE TRAVERSES THE REGION LATE SUN/SUN NIGHT. CANNOT RULE OUT A FLOOD WATCH AS WE GET CLOSER TO THAT PERIOD. WE WILL NEED TO ALSO WATCH...AS NOTED BEFORE...STRONG SOUTHEAST WINDS ARRIVING ACROSS THE USUAL AREAS OF SOUTHEAST WV/SOUTHWEST VA...EARLY SUN PRIOR TO THE HEAVIER RAIN MOVING INTO THE REGION. BOTTOMLINE...THIS WILL BE A SIGNIFICANT RAIN EVENT...BUT TIME DURATION SHOULD LIMIT PROBLEMS. THE SEVERE THREAT APPEARS TO BE NIL WITH MUCH OF THE CWA IN A STRONG WEDGE AND VERY STABLE. HAVE OPTED NOT TO INTRODUCED THUNDER AT THIS POINT. && .LONG TERM /MONDAY THROUGH THURSDAY/... AS OF 345 PM EDT THURSDAY... A TRANSITION TO A PATTERN MORE REMINISCENT OF WINTER APPEARS TO EVOLVE THROUGH THE MID AND LATER PART OF NEXT WEEK AS A DEEP UPPER TROUGH BUILDS INTO THE CENTRAL/EASTERN U.S. IN THE WAKE OF THE STRONG UPPER SHORT WAVE ON SATURDAY. PRIOR TO THE ARRIVAL OF THE COLDER AIR MON NIGHT/TUE...A WARM SECTOR WEDGE SURGES INTO THE REGION DURING PEAK HEATING MON AFTERNOON. CAPE VALUES EXCEED 1000 J/KG ACROSS AREAS EAST OF THE BLUE RIDGE AND ARE NOTABLE IN MOST OF THE CWA MON AFTERNOON. THE SIGNIFICANT SVR PARM RISES TOWARD 20000 ACROSS THE PIEDMONT WITH LIS DROPPING INTO THE -4C RANGE ON SOME MODELS. THUS...MON AFTERNOON APPEARS TO BE THE BEST CHANCE FOR THUNDERSTORM ACTIVITY...AND POTENTIALLY EVEN A FEW STRONG/APPROACHING SEVERE LIMITS ACROSS EAST OF THE BLUE RIDGE. BY TUESDAY...500MB HEIGHTS DROP INTO THE 560DM RANGE AND 850MB TEMPS PLUNGE TOWARD THE 0C MARK ACROSS THE NORTH BY MIDWEEK. ANTICYCLONIC FLOW 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 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. EMBEDDED SHORT WAVES ROTATING THROUGH THE UPPER TROUGH MAY ENHANCE CLOUD AND RAIN SHOWERS AT TIMES...ESPECIALLY ACROSS THE MOUNTAINS...BUT NO SIGNIFICANT RAINFALL EVENTS APPEAR THROUGH THIS PERIOD WITH DEEP CYCLONIC NORTHWEST FLOW IN PLACE. BY THE END OF THE WEEK...THE UPPER FLOW DEAMPLIFIES AND BECOMES MORE ZONAL. AN EMBEDDED SHORT WAVE MAY BRING A MORE SIGNIFICANT THREAT OF RAIN TO THE REGION THU NIGHT/FRI...SO HAVE RETAINED CHC POPS TOWARD DAY 8 AS A RESULT. INSTABILITY MAY SUPPORT ISOLD THUNDER...BUT HAVE NOT INTRODUCED JUST YET. TEMPERATURES ARE EXPECTED TO BE BELOW NORMAL THROUGH MOST OF THE PERIOD...WITH THE EXCEPTION OF MONDAY...WHEN SOME LOWER 80S ARE POSSIBLE ACROSS THE PIEDMONT. CLOUDS AND WIND SHOULD PREVENT ANY FROST/FREEZE CONCERN THROUGH THIS TIME FRAME. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... AS OF 1253 AM EDT FRIDAY... MVFR TO OCNL IFR CIGS CONTINUE ACROSS THE REGION TONIGHT WITH SPOTTY AREAS OF -DZ/FOG MAKING FOR PERIODS OF MVFR TO IFR VSBYS AS WELL ESPCLY ACROSS THE MOUNTAIN LOCATIONS. INCREASING WARM ADVECTION OVER THE SLOWLY ERODING LOW LEVEL COLD POOL SHOULD CONTINUE TO MAKE FOR POOR FLYING CONDITIONS OVERNIGHT INTO EARLY FRIDAY WITH CONDITIONS DETERIORATING TO MORE WIDESPREAD IFR/LIFR IN STRATUS/FOG AND DRIZZLE BY DAYBREAK. ON FRIDAY...LOW LEVEL FLOW TURNS TO THE SOUTHWEST IN ADVANCE OF A COLD FRONT. THIS SHOULD ALLOW CEILINGS TO RISE AND EVEN BRING SOME CLEARING TOMORROW...ESPECIALLY BY AFTERNOON. HOWEVER TIMING OF WHEN THIS STUCK LOW LEVEL MOISTURE EXITS STILL IN QUESTION GIVEN LATEST BUFKIT SOUNDINGS SHOWING A BIT SLOWER EROSION ON FRIDAY. THUS DELAYED THE RETURN TO VFR A COUPLE HOURS ESPCLY BLUE RIDGE SITES AND POINTS EAST. ONCE MORE CLEARING/HEATING DEVELOPS...A MORE UNSTABLE AIRMASS WILL SPAWN WIDELY SCATTERED SHOWERS AND STORMS. HOWEVER THE COVERAGE IS NOT EXPECTED TO BE GREAT ENOUGH TO ADD PRECIP AT ANY TAF SITES WITH MAINLY A PERIOD OF BKN VFR CIGS AS A WEAK TROUGH CROSSES THE REGION LATER IN THE DAY. DRIER HIGH PRESSURE WILL BUILD IN BEHIND THIS FEATURE FRIDAY NIGHT AND SATURDAY WITH A RETURN TO VFR EXPECTED TO START THE WEEKEND. EXTENDED AVIATION... A COMPLEX STORM SYSTEM WILL BEGIN TO AFFECT THE REGION LATER IN THE WEEKEND WITH A WARM FRONT BRINGING WIDESPREAD MVFR/IFR CONDITIONS IN RAIN SUNDAY/SUNDAY NIGHT FOLLOWED BY ANOTHER COLD FRONTAL PASSAGE MONDAY. THIS LIKELY TO KEEP PERIODS OF MVFR IN PLACE UNTIL THE FRONT POSSIBLY CLEARS THE REGION LATER MONDAY. VFR RETURNS LATER MONDAY NIGHT AND TUESDAY WITH HIGH PRESSURE BUILDING IN BEHIND THE FRONT WITH GOOD DRYING EXPECTED. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...RCS NEAR TERM...PM/RCS SHORT TERM...RAB LONG TERM...RAB AVIATION...JH/PM/RCS

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.