Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 170245 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1045 PM EDT THU APR 16 2015 .SYNOPSIS... AN AREA OF COOL HIGH PRESSURE WILL REMAIN OVER THE REGION INTO FRIDAY MORNING. ONCE THIS WEDGE BREAKS...TEMPERATURES WILL WARM BACK INTO THE 70S. TEMPERATURES WILL DROP AS RAIN CHANCES INCREASE WITH THE PASSING OF A COLD FRONT ON SUNDAY. && .NEAR TERM /THROUGH FRIDAY/... 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 /FRIDAY NIGHT 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 /03Z FRIDAY THROUGH TUESDAY/... AS OF 720 PM EDT THURSDAY... IFR TO MVFR CEILINGS WERE NOTED ACROSS THE MOUNTAIN TAF SITES...INCLUDING KBCB...KLWB AND KBLF...AND EVEN AT KROA CIGS WERE MVFR. AS LOW LEVEL WINDS TURN TO A MORE SOUTHERLY DIRECTION...MOISTURE WILL ADVECT INTO THE REGION DURING THIS EVENING AND OVERNIGHT HOURS. THIS MOISTURE ADVECTION IN COMBINATION WITH A WEAK UPPER LEVEL DISTURBANCE MOVING OVER THE AREA TONIGHT WILL KEEP LOW CLOUDS AND LIGHT PRECIP IN PLACE. EXPECT FLYING CONDITIONS TO CONTINUE TO WORSEN TONIGHT WITH ALL TAF SITES FALLING INTO IFR OR LIFR FLIGHT CATEGORIES THROUGH EARLY FRIDAY. 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. THIS MORE UNSTABLE AIRMASS WILL SPAWN WIDELY SCATTERED TO SCATTERED SHOWERS AND STORMS...BUT THE COVERAGE IS NOT EXPECTED TO BE GREAT ENOUGH TO ADD PRECIP AT ANY TAF SITES. A COLD FRONT WILL PASS ACROSS THE AREA FRIDAY NIGHT...WITH DRIER HIGH PRESSURE BUILDING IN BEHIND FOR SATURDAY. 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. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...RCS NEAR TERM...PM/RCS SHORT TERM...RAB LONG TERM...RAB AVIATION...PH/RCS

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