Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180212 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1012 PM EDT FRI APR 17 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD INTO THE AREA TONIGHT AND SATURDAY BRINGING DRY AND WARM WEATHER FOR THE START OF 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 A CHANCE OF SHOWERS AND POTENTIALLY STRONG STORMS ON MONDAY. DRY AND COOL CONDITIONS WILL PREVAIL FOR THE MIDDLE PART OF NEXT WEEK. && .NEAR TERM /THROUGH SATURDAY/...
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AS OF 1012 PM EDT FRIDAY... ISOLD SHOWERS HAVE DISSIPATED AND SEE NO REASON FOR ANY NEW ONES TO FIRE UP OVERNIGHT...OTHER THAN ONE OR TWO ACROSS NORTHERN NC GIVEN MUCAPE VALUES STILL AROUND 300-500 J/KG. ALSO KEEPING AN EYE ON THE NORTHERN EDGE OF AREA OF SHOWERS INTO SW NC...WHICH IS AHEAD OF A SHORT WAVE NEAR CHATTANOOGA...AS SOMETHING COULD SNEAK INTO OUR NW NC MTNS AFTER MIDNIGHT...BUT MOST GUIDANCE AGREES THIS WILL STAY JUST TO OUR SOUTH. LEFT SLIGHT CHC POP ACROSS SOUTHERN EDGE OF FCST AREA THROUGH MUCH OF THE NIGHT...BUT REMOVED MENTION EVERYWHERE ELSE. TRENDS LOOK BETTER FOR MORE CLEARING FROM WEST LATE...AND THUS POSSIBILITY OF SOME PATCHY VALLEY FOG WITH WET GROUND SO ADDED THAT AS WELL...MAINLY TO MTN VALLEYS. OVERNIGHT TEMPS LOOK ON TRACK AT THIS POINT. PREV DISC AS OF 635 PM EDT FRIDAY... UPDATE TO REFLECT CURRENT MAINLY ISOLD COVERAGE OF SHOWERS FROM FOOTHILLS INTO SOUTHSIDE VA. INCLUDED A COUPLE HOURS OF CHC POPS ACROSS SOUTHSIDE THROUGH EARLY EVENING WITH CLUSTER OF SHOWERS THERE...AND SO FAR NOT SEEING ANY SIGNS OF EVEN INTERCLOUD LIGHTNING WITH CELLS NEAR MTV AND DAN...BUT KEEPING ISOLD THUNDER IN FCST GIVEN SBCAPES OF 500-800 J/KG....AND SOME ISOL LTG IN CELLS JUST NORTHEAST OF BUCKINGHAM COUNTY. ALL THIS ACTIVITY SHOULD SLOWLY DIMINISH AS IT DRIFTS SOUTHEASTWARD INTO FAR NORTHERN NC BY 8 OR 9PM...AND RECENT HRRR RUNS SEEM TO BE DOING A BETTER JOB CAPTURING THE SPARSITY OF THE SHALLOW CONVECTION AND WEAKENING INTO THE EVENING HOURS WITH LOSS OF HEATING. SOME OF THE MORE WIDESPREAD LIGHT RAIN OVER FAR SW NC AND UPSTATE SC WILL SLIDE TO THE NORTHEAST IN ADVANCE OF WEAK SHORT WAVE HEADING EAST OUT OF TN...BUT PREVIOUS THINKING THAT IT WILL REMAIN SOUTH OF THE FCST AREA STILL LOOKS ON TRACK. WE DO KEEP A LINGERING SLIGHT CHC POP ACROSS NW NC MTNS UNTIL A LITTLE AFTER MIDNIGHT JUST IN CASE...BUT THEN DROP ALL POPS TOWARD MORNING. PREVIOUS DISCUSSION AS OF 235 PM EDT MONDAY... AT 18Z...A WEAK SURFACE TROF WAS NOTED JUST EAST OF THE BLUE RIDGE...AND WEAK CONVERGENCE ALONG THIS BOUNDARY COMBINED WITH SOME MODEST INSTABILITY (DCAPES 500-700 J/KG) SHOULD GENERATE ISOLATED SHOWERS AND STORMS ALONG THE BLUE RIDGE AS WELL AS AREAS NORTH OF I- 64 WHERE VISIBLE SATELLITE SHOWS SOME ENHANCED CUMULUS FORMING IN ADVANCE OF A FAINT UPPER LEVEL DISTURBANCE. MESOSCALE MODELS ARE OVERDONE ON THIS COVERAGE OF THIS PRECIP...BUT GENERALLY HAVE A GOOD HANDLE ON THE LOCATION OF DEVELOPMENT. ANY ISOLATED/WIDELY SCATTERED PRECIP THAT DEVELOPS SHOULD GRADUALLY DIMINISH TONIGHT...BEFORE AN UPPER LEVEL SHORTWAVE IN WEST TENNESSEE ZIPS ACROSS NRN NC LATE TONIGHT. THIS SYSTEM WILL BRING AN INCREASE IN CLOUD COVER...ESPECIALLY ACROSS THE SOUTHERN PORTION OF OUR FORECAST AREA LATE TONIGHT...AND A FEW SHOWERS MAY BE POSSIBLE. AT THE SFC...HIGH PRESSURE WILL SLOWLY NOSE SOUTH INTO THE EASTERN OHIO VALLEY BRINGING A LIGHT NORTH WIND. A SHALLOW LAYER OF MOISTURE NEAR THE SURFACE WILL REMAIN...WHICH WILL RESULT IN POCKETS OF FOG...ESPECIALLY WHERE CLOUDS ARE ABSENT TO THE NORTH. LEANED TOWARD THE WARMER GUIDANCE VALUES WITH CLOUDS. FOR SATURDAY...HEIGHTS BUILD IN ADVANCE OF A DEEP UPPER LEVEL TROF IN THE WEST AND TEMPS SHOULD AGAIN WARM WELL INTO THE 70S AND THE 80S IN THE EAST. A WEAK LOW LEVEL EAST FLOW COMBINED WITH A NOSE OF HIGHER THETA-E AIR IN NW NC INTO FAR SW VA MAY SPARK ISOLATED SHOWERS/STORMS.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... AS OF 330 PM EDT FRIDAY... FOCUS THROUGH THIS PERIOD REMAINS ON A STRONG NEGATIVELY TILTED UPPER TROUGH PROGGED TO LIFT RAPIDLY NORTHEAST ACROSS THE REGION SUNDAY INTO EARLY MONDAY. MEANWHILE...ANTECEDENT HIGH PRESSURE WILL MOVE OFF THE MID-ATLANTIC COAST INTO A NEAR CLASSIC WEDGE POSITION. STRONG PVA/ISENTROPIC LIFT INDUCED RAINFALL INTO THE WEDGE AIR MASS WILL ENHANCE/INTENSIFY THE WEDGE SUNDAY. RAINFALL/QPF WILL BE THE MAIN CONCERN AS THE WEDGE KEEPS A VERY STABLE/COOL AIR MASS IS PLACE. MOIST SOUTHEAST...UPSLOPE FLOW ALONG THE BLUE RIDGE WILL ENHANCE RAINFALL...ESPECIALLY ACROSS WATAUGA NORTHEAST TOWARD FLOYD. AS NOTED YESTERDAY...HOWEVER...THE SYSTEM WILL REMAIN HIGHLY PROGRESSIVE...LIMITING THE PERIOD OF HEAVIER RAINFALL TO 12 HOURS OR LESS. WPC HAS PARTS OF THE NC/VA SOUTHERN VA PIEDMONT OUTLOOKED FOR EXCESSIVE RAINFALL. THE MAIN CONCERN WITHIN THIS AREA WOULD BE WATAUGA THROUGH ASHE/WILKES...WITH LESS CONCERN TOWARD THE DANVILLE AREA WHERE ANTECEDENT CONDITIONS ARE RELATIVELY DRY. IN ADDITION...THE CONVECTIVE THREAT THROUGH THE HEAVIER RAIN PERIOD AS NOTED ABOVE IS MINIMAL TO NONE...WHICH SHOULD FURTHER REDUCE THE FLASH FLOOD THREAT. WILL RE-EVALUATE AGAIN TOMORROW...BUT AT THIS POINT NO NEED FOR A FLOOD/FLASH FLOOD WATCH. ONE MAY EVENTUALLY BE NEEDED FOR A SMALL AREA INCLUDING THE NW NC MOUNTAINS AND THE ADJACENT FOOTHILLS. WENT WELL BELOW GUIDANCE ON MAX TEMPS IN THE WEDGE SUNDAY...BUT AT OR ABOVE GUIDANCE ON MONDAY IN THE WARM SECTOR. MAX TEMPS MONDAY WILL BE A GOOD 20 DEGREES WARMER IN MOST AREAS THAN ON SUNDAY. MONDAY IS A DIFFERENT STORY. A SIGNIFICANT WARM SECTOR WILL SURGE NORTHWARD INTO THE REGION MONDAY AFTERNOON BEHIND THE DEPARTING UPPER TROUGH AND AN APPROACHING STRONG COLD FRONT ASSOCIATED WITH A DEEPENING BROAD UPPER TROUGH ACROSS THE GREAT LAKES. SEVERAL OF THE MODELS CONTINUE TO ADVERTISE GOOD POTENTIAL FOR STRONG THUNDERSTORMS MONDAY AFTERNOON...WITH SIGNIFICANT SVR PARAMETER NEAR 20000 ACROSS THE PIEDMONT...CAPES NEARING 2000 J/KG WITH AT LEAST 20-30KTS OF 0-2KM LOW-LEVEL SHEAR AND LIS NEAR -4C. SPC DAY 4 OUTLOOK SUGGESTS THAT DAMAGING WINDS WOULD BE THE MAIN CONCERN WITH ANY CONVECTION...MOST LIKELY LINEAR ORIENTED...THAT DEVELOPS ALONG/IN ADVANCE OF THE COLD FRONT MONDAY AFTERNOON/EVENING. THIS ACTIVITY QUICKLY MOVES EAST OF THE REGION MON AFTERNOON. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 345 PM EDT FRIDAY... A TRANSITION TO A PATTERN MORE REMINISCENT OF WINTER CONTINUES TO BE IN THE CARDS FOR THE EARLY AND MID PART OF NEXT WEEK AS A DEEP AND BROAD UPPER TROUGH BUILDS INTO THE CENTRAL/EASTERN U.S. BY TUESDAY...500MB HEIGHTS DROP INTO THE 560DM RANGE AND 850MB TEMPS PLUNGE TOWARD THE 0C MARK ACROSS THE NORTH BY MIDWEEK. ANTICYCLONIC FLOW...A SERIES OF EMBEDDED UPPER DISTURBANCES...AND COLD ADVECTION 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 AND LOWER 60S 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. AT THIS POINT A DISTURBANCE ON WED APPEARS TO BE THE MOST SIGNIFICANT IN POTENTIALLY BRINGING SHOWERS EAST OF THE MOUNTAINS. HAVE NOT INTRODUCED ANY THUNDER AT THIS POINT GIVEN THE LOW-LEVEL COLD/STABLE AIR MASS. BY MID-WEEK...THE GFS/ECMWF BEGIN TO DIVERGE ON THE OVERALL PATTERN...WITH THE ECMWF KEEPING THE DEEP UPPER TROUGH IN PLACE ACROSS THE NORTHEAST AND A STRONGER NW FLOW INTO OUR REGION AS WELL...WHILE THE GFS DEPICTS THE UPPER TROUGH LIFTING FURTHER NORTH AND PLACING A ZONAL FLOW WITH A BAROCLINIC ZONE STUCK ACROSS OUR CWA. THIS RESULTS IN SIGNIFICANT DIFFERENCES BETWEEN MOISTURE/POPS ACROSS OUR CWA BETWEEN THE TWO MODELS...WITH THE GFS VERY WET AND THE ECMWF MUCH DRIER...KEEPING THE BAROCLINIC ZONE MUCH FURTHER SOUTH. HAVE JUST ADVERTISED CHC POPS FOR NOW UNTIL A BETTER HANDLE ON THIS PATTERN AND TIMING IS OBTAINED. TEMPERATURES ARE EXPECTED TO REMAIN BELOW NORMAL THROUGH THE MID PART OF THE WEEK...GRADUALLY TRENDING CLOSER TO NORMAL BY THE END OF THE PERIOD. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... AS OF 750 PM EDT FRIDAY... ISOLD SHOWERS NOT EXPECTED TO IMPACT ANY AIRPORTS THIS EVENING...AND FOR MOST OF THE OVERNIGHT EXPECTING VFR CONDITIONS AND LIGHT TO CALM WINDS WITH HIGH PRESSURE IN CONTROL. SOME MOISTURE OFF TO SOUTH SHOULD REMAIN THERE WITH WEAK SHORT WAVE MOVING IN FROM THE WEST ACROSS TENNESSEE AND SHUNTING AN AREA OF SHOWERS EASTWARD. THIS WAVE WILL ALSO EVENTUALLY TAKE MID TO HIGH CLOUDS EAST AND WITH CLEARING THERE IS LIKELY TO BE SOME RADIATION FOG FORMING...LOWERED CONDITIONS TO IFR AT BLF...LWB...BCB...AND LYH BY 08-09Z...BUT MOST CONFIDENT IN IFR CONDITIONS AT LWB AND BCB. ANY FOG AND LOW STRATUS DISSIPATES BY 13Z OR SO...FOR WIDESPREAD VFR CONDITIONS FOR THE DAY SATURDAY...WITH LIGHT EAST TO NORTHEAST WINDS AS SFC HIGH PRESSURE REMAINS TO THE NORTH AND WEAK SFC TROUGH WILL LINGER ACROSS NORTH CAROLINA. THIS MAY RESULT IN ENOUGH WEAK CONVERGENCE AND UPSLOPE TO KICK OFF A FEW ISOLD SHWRS OR TSTORMS BY AFTERNOON...ESPECIALLY NEAR BLUE RIDGE ALONG OR SOUTH OF VA/NC BORDER...BUT VERY UNLIKELY ANY ONE SHOWER OR STORM WILL IMPACT ANY AIRPORTS. 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 DURING THE DAY SUNDAY INTO 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...PH NEAR TERM...JH/PH/SK SHORT TERM...RAB LONG TERM...RAB AVIATION...JH/PH/SK

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