Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 021235 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 835 AM EDT THU JUL 2 2015 .SYNOPSIS... A FRONTAL BOUNDARY WILL REMAIN DRAPED ACROSS THE AREA FOR THE NEXT SEVERAL DAYS. THERE WILL BE SEVERAL WAVES OF LOW PRESSURE PASSING ACROSS THE BOUNDARY KEEPING THE THREAT OF SHOWERS AND THUNDERSTORMS IN OUR FORECAST THROUGH THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 400 AM EDT THURSDAY... WE CONTINUE TO BE LOCKED IN TO THE SAME PATTERN WITH A LONG SERIES OF SHORT WAVES MOVING THROUGH AN UPPER TROF OVER THE EASTERN US...AS AN EAST TO WEST FRONTAL BOUNDARY STRETCHES ACROSS THE AREA. THIS WILL KEEP OUR WEATHER QUITE UNSETTLED AND SHOWERS/STORMS CAN NOT BE RULED OUT AT ANY TIME...THOUGH DIURNAL HEATING WILL KEEP THE BULK OF ACTIVITY BIASED TO THE AFTERNOON/EVENING HOURS. INSTABILITY AND SHEAR ARE MODEST AT BEST AND THIS WILL HELP LIMIT ANY SEVERE THREAT...BUT IF WE MANAGE TO GET MORE SUN THROUGH THE EARLY CLOUDS TODAY WE MAY DESTABILIZE MORE THAN ANTICIPATED. THE MAIN THREAT WILL BE INCREASING PRECIPITABLE WATER VALUES LEADING TO A HYDRO THREAT FROM TRAINING HEAVY DOWNPOURS. ALL MODELS DEVELOP VARYING DEGREES OF AN MCS AND MOVE IT EASTWARD ALONG THE FRONTAL BOUNDARY...BUT THEY ALL HAVE ENOUGH DIFFERENCES IN LOCATION AND TIMING TO LOWER CONFIDENCE IN WHERE HEAVY PRECIPITATION IS MOST LIKELY BELOW THE THRESHOLD NECESSARY FOR ISSUING ANY SORT OF FLOOD WATCH. WILL CONTINUE TO HIGHLIGHT THE POTENTIAL FOR HEAVY PRECIPITATION AND POSSIBLE FLOODING ISSUES IN THE HWO AND WAIT TO SEE IF A THREAT AREA REVEALS ITSELF WITH TIME. AFTER A DOWNTURN IN ACTIVITY EARLY TONIGHT INDICATIONS ARE THAT ANOTHER WAVE WILL BE SET TO MOVE THROUGH THE REGION LATE TONIGHT/TOWARD DAYBREAK FRIDAY. EXTENSIVE CLOUD COVER WILL HELP KEEP TEMPERATURES A FEW DEGREES COOLER TODAY THAN YESTERDAY WITH LOW TO MID 80S FOR THE PIEDMONT/SOUTHSIDE AND LOW TO MID 70S WEST OF THE BLUE RIDGE. LOWS TONIGHT REMAIN MILD WITH UPPER 60S EAST TO LOWER 60S WEST. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... AS OF 420 AM EDT THURSDAY... BROAD TROUGHING AND NORTHWEST FLOW ALOFT REMAINS IN PLACE AT THE BEGINNING OF THE PERIOD. A REMNANT MCS...MOST LIKELY IN THE FORM OF WIDESPREAD LIGHT TO MODERATE RAIN AND EMBEDDED THUNDER APPEARS LIKELY AT THE START OF THE DAY FRI...ONE OF TWO POTENTIAL CONVECTIVE COMPLEXES OR THE REMNANTS OF SUCH TO DRIFT INTO THE AREA FROM THE TN VALLEY. GIVEN TIME OF DAY...THREAT OF SEVERE SHOULD BE LITTLE TO NONE. MAIN CONCERN WOULD BE HEAVY RAINFALL ON TOP OF RAINFALL EXPECTED THU. MODEL AND WPC QPC AMOUNTS OVER THE 24-48 HOUR PERIOD ARE MOSTLY IN THE 1.5 TO 2.0 INCH RANGE...WHICH SHOULD BE HANDLED WITHOUT ANY SIGNIFICANT PROBLEMS. LOCALIZED PROBLEMS ARE ENTIRELY POSSIBLE...BUT THIS SHOULD LARGELY BE THE RESULT OF COMBINED RAINFALL FROM THU INTO FRI MORNING RATHER THAN NEW EVENTS FRI MORNING...GIVEN THE EXPECTED LACK OF HEAVIER CONVECTION DURING THE MORNING. BY AFTERNOON...WEAK SFC LOW PRESSURE DRIFTS TOWARD THE VA/MD COAST AND THE BETTER THREAT FOR DIURNAL CONVECTION SHIFTS EAST WITH THE MORNING MCS. HOWEVER...AMPLE MOISTURE REMAINS IN PLACE AND BROAD TROUGHING ALSO REMAINS IN PLACE...WITH THE AXIS STILL TO THE WEST ACROSS THE TN/OH VALLEY. WILL NEED TO KEEP AT LEAST CHANCE POPS ALL AREAS...KEEPING THE HIGHER POPS EAST AND SOUTH. ANOTHER MCS APPEARS LIKELY TO DEVELOP UPSTREAM LATE SATURDAY AND TRANSLATE ACROSS MUCH OF THE SOUTHERN PART OF THE CWA SATURDAY NIGHT/SUNDAY MORNING BEFORE THE UPPER TROUGH FINALLY WEAKENS AND BEGINS TO DRIFT ESE INTO THE CAROLINAS...WHILE A SHORT WAVE RIDGE RIDES OVER THE TOP OF THE TROUGH INTO THE OH VALLEY/PA REGION. THE FOCUS FOR CONVECTION SUNDAY SHOULD BE MAINLY EAST-SOUTH OF THE BLUE RIDGE AS DEEPER MOISTURE IS SHOVED SLIGHTLY SOUTHWARD. OVERALL...AS NOTED YESTERDAY...POPS CANNOT BE REDUCED BEYOND MENTIONABLE 15 PERCENT VALUES ANYTIME DURING THIS PERIOD. HOWEVER...THE EXACT TRACK AND TIMING OF CONVECTIVE COMPLEXES OR THE REMNANTS OF SUCH WILL REMAIN DIFFICULT TO DETERMINE AND WILL ONLY BE RESOLVED NEAR THE EVENT AND ON THE MESOSCALE...NOT THE SYNOPTIC SCALE LEVEL. ABUNDANT CLOUD COVER AND LIMITED DAYTIME HEATING WILL HOLD MAX TEMPS BELOW NORMAL. HOWEVER...HIGH HUMIDITY LEVELS/DEWPOINTS WILL RESULT IN WELL ABOVE NORMAL MAX TEMPS. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... AS OF 430 AM EDT THURSDAY... A SURFACE BOUNDARY WILL STALL ACROSS THE CAROLINAS OVER THE WEEKEND. MEANWHILE...THE TAIL END OF THE LONGSTANDING EASTERN UPPER TROUGH WILL BECOME CUTOFF ACROSS SOUTHEAST VA/NORTH NC AND SLOWLY DRIFT SOUTH INTO SOUTH CAROLINA. THE GFS ADVERTISES THIS TO A MUCH GREATER EXTENT THAN THE OTHER MODELS. MEANWHILE...A SHORT WAVE RIDGE DRIFTS OVER THE TOP OF THIS WEAK CUTOFF UPPER LOW/TROUGH. CONVECTION SHOULD BECOME MUCH MORE DIURNAL IN NATURE AS THE FAVORABLE MCS PATTERN OF THE CURRENT WEEK FADES GIVEN THE CHANGE IN THE SYNOPTIC PATTERN AND AN END TO THE STRONG WNW-NW FLOW ALOFT. AREAS SOUTH AND EAST OF THE BLUE RIDGE SHOULD SEE THE BEST CHANCE OF CONVECTION THROUGH THIS PERIOD CLOSER TO THE SURFACE BOUNDARY...UPPER LOW...AND DEEPER MOISTURE. BEYOND MON...THE MODELS TO VARYING DEGREES DEPICT A COLD FRONT APPROACHING THE REGION FROM THE NORTHWEST...THEN LIKELY STALLING IN/NEAR THE REGION BY WED AS BROAD UPPER RIDGING DEVELOPS ACROSS THE SOUTHERN STATES. THUS...WE ARE LEFT IN A CONTINUAL UNSETTLED PATTERN. ANY DECREASE IN CONVECTION ACROSS THE CWA IN THE MON/TUE TIME FRAME WILL BE FOLLOWED BY AN UPTICK IN SUCH BY WED. TEMPERATURES SHOULD BE SLIGHTLY WARMER MON/TUE WITH DECREASED CLOUD COVER AND HENCE GREATER INSOLATION. OVERALL...TEMPERATURES SHOULD AVERAGE NEAR NORMAL FOR HIGHS...BUT CONTINUE TO BE QUITE A BIT ABOVE NORMAL FOR MIN TEMPS GIVEN CONTINUED HIGH MOISTURE CONTENT. && .AVIATION /13Z THURSDAY THROUGH MONDAY/... AS OF 730 AM EDT THURSDAY... DUE TO AN FAA RELATED OUTAGE...THE TAFS FOR LWB WILL NOT BE AMENDED DUE TO MISSING OBSERVATIONS. THE FIRST ROUND OF CLOUDS AND RAIN FROM AN UPSTREAM MCS DRIFTING INTO THE REGION NOW. MOST SITES REPORTING -RA NOW AND CIGS LOWERING INTO THE MVFR RANGE AT SEVERAL SITES...WITH VISIBILITIES DROPPING INTO THE MVFR RANGE AT BCB/BLF/LWB. EXPECT -SHRA TO CONTINUE TO INCREASE ACROSS THE REGION THROUGH THE EARLY AFTERNOON. BY MID-AFTERNOON...THE NEXT CONVECTIVE COMPLEX OR ASSOCIATED OUTFLOW/REMNANTS ARRIVE INTO THE CWA WITH AN INCREASING THREAT FOR WIDESPREAD -SHRA...EMBEDDED TSRA...AND ASSOCIATED MVFR-IFR CIGS/VSBYS. THUNDERSTORMS SHOULD DIMINISH AFTER 04Z- 06Z...BUT -SHRA WILL CONTINUE ALONG WITH PREVAILING MVFR CIGS/VSBYS AND POCKETS OF IFR-LIFR CIGS/VSBYS BCB/LWB/BLF. OVERALL...POOR AVIATION CONDITIONS EXPECTED THROUGH THE TAF VALID PERIOD. WINDS...LIGHT WSW-WNW THROUGH THE TAF VALID PERIOD AT SPEEDS OF 3-7KTS...OF COURSE VARIABLE AND POTENTIALLY GUSTY IN/NEAR THUNDERSTORMS. EXTENDED AVIATION DISCUSSION... THE REGION WILL BE IN A GENERAL NORTHWEST FLOW PATTERN THROUGH SATURDAY. WILL AGAIN SEE SHOWERS AND THUNDERSTORMS DEVELOP ON FRIDAY AND SATURDAY AS SEPARATE SHORTWAVE TROUGHS PROGRESS ACROSS THE FORECAST AREA WITHIN THE NORTHWEST FLOW. VFR CONDITIONS ARE EXPECTED FOR MOST OF THE AREA MUCH OF THE TIME. THE EXCEPTIONS WILL COME AS TEMPORARY DECREASES WITHIN ANY HEAVIER RAIN SHOWERS OR THUNDERSTORMS...AND THEN LATE AT NIGHT AND EARLY MORNING DUE TO RIVER OR MOUNTAIN VALLEY FOG...ESPECIALLY IN AREAS THAT RECEIVED PRECIPITATION THE DAY BEFORE. SUNDAY INTO MONDAY...WHILE UPPER LEVEL HEIGHTS RISE DURING THE PERIOD...THERE REMAINS AN UPPER TROUGH MOVING OVER THE MID ATLANTIC DURING THIS TIME...SO STORMS ARE NEVER OUT OF THE FORECAST. && .EQUIPMENT... AN OUTAGE EXISTS WITH SOME FAA AUTOMATED OBSERVATIONS IN THE AREA. THERE IS NO ESTIMATED TIME FOR RESTORATION. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...MBS NEAR TERM...MBS SHORT TERM...RAB LONG TERM...RAB/RCS AVIATION...MBS/NF/RAB/WP EQUIPMENT...WP

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