Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 161957 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 357 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 130 PM EDT THURSDAY... THE HIGH PRESSURE CENTER OF THE COOL WEDGE WILL DRIFT OUT TO SEA THROUGH THE PERIOD. HOWEVER...BAGGY HIGH LEFT BEHIND WILL KEEP COOL...CLOUDY AND DAMP CONDITIONS INTO FRIDAY MORNING. FROM THE MORNING RNK/GSO SOUNDINGS...THE WEDGE WAS 4-5KFT THICK OVER THE FORECAST AREA AND STRETCHED SOUTH INTO THE PANHANDLE OF FLORIDA. WITH NO SIGNIFICANT FORCING OR PRESSURE RISES NEAR THE IMMEDIATE AREA...THE WEDGE WILL LIKELY HANG AROUND THROUGH MUCH OF THE DAY FRIDAY...ESPECIALLY ACROSS THE FOOTHILLS AND PIEDMONT COUNTIES. A WARM FRONT...ASSOCIATED WITH A WEAK DISTURBANCE IN THE OHIO VALLEY...WILL OVERRUN THE WEDGE LATE THIS AFTERNOON AND EVENING. ISENTROPIC LIFT WILL SPREAD ANOTHER ROUND OF LIGHT RAIN ACROSS THE FORECAST AREA THROUGH MIDNIGHT. THIS LIFT TRACKS NORTHWARD AND THE FORECAST AREA WILL THEN BE IN A LULL OF MEASURABLE PRECIPITATION INTO FRIDAY MORNING. HOWEVER...WITH SATURATED CONDITIONS AND EASTERLY FLOW...LOW CLOUDS...FOG AND DRIZZLE HIGHLY POSSIBLE ALONG EASTERN SLOPES...PARTICULARLY ALONG THE BLUE RIDGE. VERY LITTLE CHANGE IN TEMPERATURES OVERNIGHT FROM THIS AFTERNOON WITH LOWS ONLY IN THE MID 40S TO LOWER 50S. FRIDAY AFTERNOONS TEMPERATURES 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 SURGE TOWARDS 70F. && .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 /20Z THURSDAY THROUGH TUESDAY/... AS OF 130 PM EDT THURSDAY... HIGH PRESSURE WILL REMAIN BANKED AGAINST THE APPALACHIANS INTO TONIGHT...WITH WINDS BECOMING MORE SOUTHEASTERLY ALOFT BY LATE IN THE DAY. ADDED FAINT UPPER LEVEL ENERGY PASSING ACROSS THE AREA WILL SUPPORT CONTINUED PATCHY RAINFALL...AS WELL AS CAUSE CEILINGS TO GRADUALLY LOWER AS EARLIER RAINFALL ADDS MOISTURE TO THE LOW LEVELS OF THE ATMOSPHERE. CONFIDENCE IN TIMING OF LOWER CIGS THOUGH REMAINS LOW GIVEN UNCERTAINTY IN THE DEGREE OF RAINFALL GIVEN SUCH WEAK FEATURES PASSING THROUGH THE WEDGE. THUS TRENDING TOWARD WIDESPREAD MVFR FROM MID AFTERNOON ONWARD BUT WITH ONLY SPOTTY PRECIP FOR NOW. LOW LEVEL WEDGE STARTS TO BREAK DOWN TONIGHT AS THE FLOW VEERS FROM SOUTHEAST TO MORE SOUTHERLY OVERNIGHT. THIS MAY ACTUALLY HELP MOISTEN THINGS FURTHER PROVIDING FOR OVERALL SUB-VFR AND RESIDUAL SPOTTY SHOWERS WITH POTENTIAL FOR MORE IN THE WAY OF LOW END IFR/LIFR IN STRATUS/FOG/DZ OVERNIGHT. ON FRIDAY...LOW LEVEL FLOW TURNS TO THE SOUTHWEST IN ADVANCE OF A COLD FRONT. ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE IN THE AFTERNOON...ESPECIALLY ONCE HIGH PRESSURE WEDGED AGAINST THE EASTERN FACE OF THE APPALACHIANS MOVES AWAY. 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...RCS SHORT TERM...RAB LONG TERM...RAB AVIATION...RCS

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