Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180208 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1008 PM EDT SUN AUG 17 2014 .SYNOPSIS... A WEAK COLD FRONT WILL MOVE THROUGH THE APPALACHIANS FROM THE WEST ON MONDAY. THIS WEAK BOUNDARY WILL GENERALLY LINGER OVER OUR AREA THROUGH MUCH OF THE WEEK KEEPING A GOOD CHANCE FOR SHOWERS AND THUNDERSTORMS EVERY DAY. && .NEAR TERM /THROUGH MONDAY/...
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AS OF 1000 PM EDT SUNDAY... REDUCED POPS FURTHER FOR THE NEXT 6 HRS OR SO AS PRECIPITATION HAVING A VERY DIFFICULT TIME SPREADING EAST OF THE CUMBERLAND PLATEAU INTO THE MUCH MORE STABLE AIR MASS TO THE EAST. MODELS...IN GENERAL...KEEP A FAIRLY STABLE AIR MASS OVER US THROUGH MON...SO NOT SEEING A WHOLE LOT OF THUNDER EVEN MONDAY. REMOVED ALL MENTION OF TSRA THROUGH 12Z...ALTHOUGH AN ISOLD LIGHTNING STRIKE NOT COMPLETELY OUT OF THE QUESTION TOWARD SMYTH/MERCER COUNTIES LATE TONIGHT...JUST COULD NOT SUPPORT IT BASED ON MODEL INSTABILITY. STILL FEEL CLOUDS/PRECIPITATION WILL SPREAD INTO THE REGION TOWARD DAYBREAK FROM THE WEST WITH THE BEST CHANCE OF RAIN REMAINING WEST OF THE ALLEGHANY FRONT THROUGH DAYBREAK. SHOWERS DEVELOPING NOW BETWEEN KBNA AND KTYS ARE INCREASING AND THIS COULD WELL BE THE ACTIVITY THAT REACHES OUR AREA AFT 06Z. NO OTHER SIGNIFICANT CHANGES AT THIS TIME. AS OF 700 PM EDT SUNDAY... AS NOTED EARLIER...INSTABILITY LACKING ACROSS OUR REGION...WHICH WHEN COMBINED WITH EXTENSIVE RESIDUAL CLOUD COVER...MAKING IT VERY DIFFICULT FOR MUCH CONVECTION THIS EVENING. LATEST NSSL WRF SUGGESTS WE WILL SEE LITTLE CONVECTION THROUGH THE EVENING...JUST A FEW SPOTTY LIGHT RAIN SHOWERS. ALTHOUGH A POTENT UPPER SHORT WAVE IS MOVING THIS DIRECTION AND WILL ARRIVE LATER TONIGHT/EARLY MON...INSTABILITY REMAINS MINIMAL AT BEST. 18Z RUN OF THE GFS IN AGREEMENT WITH 12Z RUN OF ECMWF IN SUGGESTING THAT WIDESPREAD CLOUD COVER AND SHOWERS WILL MOVE THROUGH THE REGION LATE TONIGHT/EARLY MONDAY...LINGERING TOWARD THE PIEDMONT INTO THE LATE MORNING. THIS SUGGESTS THAT AGAIN THE ENVIRONMENT MONDAY AFTERNOON WILL ONLY SUPPORT MINIMAL CONVECTION DUE TO LACK OF INSTABILITY. REMNANT CONVECTION WILL DRIFT TOWARD THE SE PART OF THE CWA BY AFTERNOON...WHICH ALL MODELS AGREE ON. DEPENDING ON AMOUNT OF ANTECEDENT SUNSHINE...THAT COULD END UP BEING THE MOST FAVORABLE AREA FOR AFTERNOON/EVENING CONVECTION AND ANY CHANCE OF SEVERE...ALBEIT VERY MINIMAL. HAVE ADJUSTED POPS IN ACCORDANCE WITH THINKING AND GENERAL MODEL AGREEMENT THAT DIMINISHING AREA OF CONVECTION OR MCS WILL REACH WESTERN AREAS BEFORE DAYBREAK...THEN DRIFT TOWARD THE EASTERN PART OF THE CWA BY EARLY AFTERNOON. ONLY MINOR CHANGES TO T/TD READINGS NEEDED AT THIS TIME. AS OF 245 PM EDT SUNDAY... CONVECTION REMAINS AT A MINIMUM LATE THIS AFTERNOON GIVEN LACK OF DEEP INSTABILITY PER SPC ANALYSIS AND RESIDUAL CLOUD COVER. APPEARS COULD STILL POP A SHOWER IN THE NEAR TERM ACROSS THE MOUNTAINS DUE TO HEATING...OTRW MAIN CONCERN WITH THE LEADING EDGE PRECIP OVER EASTERN KY/TN WELL AHEAD OF THE UPSTREAM WAVE BACK OVER SOUTHERN INDIANA. MODELS NOT HANDLING THIS WELL BUT AGAIN WILL BE MOVING INTO AN AREA OVER THE FAR WEST WHERE CAPE VALUES ARE LOW...AND LOW LEVEL THETA-E LACKING AROUND THE TIME OF LOSS OF INSOLATION. THUS WILL ONLY KEEP LOW POPS MAINLY I-77 CORRIDOR INTO THIS EVENING AND SHOW A DECREASE BY MIDNIGHT WITH COMBO OF THIS INITIAL AXIS FADING AND LOSS OF ANY RESIDUAL INSTABILITY. POTENT WAVE ALOFT MOVES EAST ALONG THE FRONT OOZING IN FROM THE NORTH OVERNIGHT TO ACROSS THE OHIO RIVER BY MORNING. GUIDANCE BRINGING THE NEXT ROUND OF LIFT INTO THE WEST BY DAYBREAK IF NOT A BIT SOONER BASED ON PAST EVENTS IN WESTERLY FLOW ALOFT. THUS PUSHED CAT/LIKELY POPS INTO THE FAR WEST LATE...WITH DECENT CHANCE POPS OUT TO THE BLUE RIDGE AND SLIGHTS ACROSS THE PIEDMONT BY 12Z. OTRW PARTLY TO BECOMING MOSTLY CLOUDY WITH MILDER LOWS MOSTLY IN THE 60S PER MOISTENING DEWPOINTS. STRONG VORT CENTER PUNCHES EAST ACROSS THE AREA MONDAY WITH MODEL DIFFERENCES ON WHERE THE SURFACE GOES AND WHETHER OR NOT A SECONDARY WAVE FORMS ALONG THE TRAILING TROUGH AXIS TO THE SOUTH. SOLUTIONS STILL RANGE FROM A FLATTER ECMWF WITH HEAVIER RAINFALL GOING OVER SOUTHERN VA/NW NC TO THE SLOWER NAM WHICH TAKES THE BEST LIFT UP ALONG THE NW SLOPES AND THEN EAST NORTH OF HIGHWAY 460 LATER MONDAY. LATEST ENSEMBLE RUN REMAINS IN BETWEEN WITH AN AXIS OF HEAVIER SHOWERS NW THEN DIPPING SOUTH ALONG THE BLUE RIDGE INTO NW NC AS PERHAPS A SECOND WAVE DEVELOPS SO FOLLOWED THIS SCENARIO A BIT CLOSER. COMBO OF DECENT LIFT...HIGH PWATS OF NEARLY 2 INCHES AND VEERING ALOFT WOULD SUGGEST A PERIOD OF MODERATE TO HEAVY RAIN ACROSS MUCH OF THE AREA MONDAY...WITH EMBEDDED CONVECTION LIKELY ESPCLY NW AND OVER THE EAST WHERE MAY SQUEEZE OUT A LITTLE MORE INSTABILITY. GIVEN A FEW DAYS OF DRYING SINCE THE LAST HEAVY RAIN EVENT WILL TAKE HIGHER RAINFALL RATES OR PROLONGED BANDS OF SHRA/TSRA TO PRODUCE FLOODING EXCEPT OVER PARTS OF SE WEST VA WHERE FFG REMAINS RATHER LOW. SINCE IFFY AS TO RATES...WILL HOLD OFF ON A WATCH FOR NOW BUT A GOOD 1- 2 INCHES POSSIBLE WHERE THE CORE OF THE WAVE TRACKS ON MONDAY SO WIDESPREAD CAT/LIKELY POPS. HIGH TEMPS REMAIN QUITE TRICKY PENDING EXPANSE OF HEAVY RAIN AS MAY SEE A WEAK WEDGE FORM IF RAIN ARRIVES EARLIER SO TRIMMED BACK HIGHS TO MOSTLY 70S...EXCEPT LOW/MID 80S FAR SOUTH WHICH MAY BE TOO WARM.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... AS OF 345 PM EDT SUNDAY... TIMING OF WAVE EXITING FORECAST AREA IS TRICKY FOR MONDAY EVENING...BUT LEANING TOWARD THE SLOWER NAM SOLUTION AT THIS POINT PARTLY DUE TO CURRENT POSITION OF SURFACE AND UPPER LOW STILL BACK OVER SRN ILLINOIS WHICH IS MORE IN LINE WITH 18Z POSITION IN NAM VS FASTER GFS. THUS LEFT SOME HIGH LIKELY TO LOW CATEGORICAL POPS IN FOR THE NORTHEAST FOR MONDAY EVENING...BEFORE EXITING LATE...BUT STILL SOME LINGERING UPSLOPE SHOWERS IN FAR WEST. BEHIND THIS WAVE THERE APPEARS TO BE SOME SUBSIDENCE AND ALSO THE OVERNIGHT SHOWERS COULD LEAVE ATMOS FAIRLY STABLE FOR TUES...SO THINK THIS WILL BE A BIT OF A DOWN DAY FOR PRECIP CHANCES BUT LEFT SOME LOW CHANCE POPS IN MAINLY BLUE RIDGE AND WEST. MAY NEED TO LOWER THESE EVEN MORE BUT FOR NOW TRENDED DOWNWARD. UNCERTAINLY AS FAR AS HOW MUCH CLOUD COVER WILL REMAIN BEHIND THIS WAVE...BUT EVEN WITH SOME PARTIAL CLEARING ODDS ARE THAT CU WILL REFORM QUICKLY SO NOT A GREAT DEAL OF SUN. STILL...MUCH WARMER THAN MONDAY WITH LACK OF PRECIP...PERHAPS BRIEF SUN...AND DOWNSLOPE INTO PIEDMONT. STILL GOING JUST A TAD BELOW GUIDANCE THOUGH WHICH NOW HAS LOWER 90S FOR DAN. STICKING WITH UPPER 80S FOR WARMEST TEMPS. TIMING OF SHOWERS AND ANY THUNDERSTORMS THEN BECOMES CHALLENGING WITH MODELS VERY DIFFERENT ON ARRIVAL OF CONVECTIVELY DRIVEN DISTURBANCES FROM UPSTREAM...AS WELL AS THEIR TRACKS. SEEMS NOW MOST LIKELY TIMING IS THE NEXT SIGNIFICANT WAVE COMING BY TUES NIGHT OR EARLY WED MORNING...SO THIS MIGHT MEAN A BETTER CHANCE FOR SHOWERS...PERHAPS THUNDER...IN THE WEST OVERNIGHT TUES NIGHT AND LESS OF A CHANCE DURING THE DAY WED. NEW 12Z ECMWF A LITTLE SLOWER AND SUGGEST THIS NEXT WAVE MAYBE EARLY WED MORNING. STILL..DAYTIME HEATING MAY BE ENOUGH TO KICK OF ADDITIONAL ACTIVITY DURING THE DAY WED BUT THIS MAY BE MAINLY IN THE MOUNTAINS. GIVEN THE COMPLEX AND HIGHLY UNCERTAIN NATURE OF THESE WAVES AND LINGERING FRONTAL BOUNDARY...WE REALLY WILL NOT GET A DECENT HANDLE ON THE TIMING AND LOCATION OF WHERE TO PUT HIGH CHANCES OR LIKELY POPS VERSUS LOW CHANCES OR SLIGHT CHANCE UNTIL MAYBE 24 HRS IN ADVANCE...SO AT THIS POINT AM STICKING WITH SHOWING THE BEST CHANCES IN MOUNTAINS...BUT LINGERING CHANCES OVERNIGHT AND EVEN WELL AFTER MIDNIGHT...GIVEN THE FORCING FROM THESE DISTURBANCES AND SURFACE BOUNDARY...ALTHOUGH VERY HARD TO SAY REALLY HOW MUCH INFLUENCE THAT WILL HAVE. 850 WESTERLY FLOW WILL HELP AID CHANCES IN MOUNTAINS VS PIEDMONT AS WELL. BEST CHANCES FOR THUNDER DURING THE AFTERNOON AND EVENING...BUT LEFT A SLIGHT CHANCE LATE AT NIGHT AND EARLY MORNING. DESPITE ONGOING PRECIP CHANCES THROUGH THE PERIOD...INCLUDING OVERNIGHT...DO NOT SEE A HIGH THREAT FOR ESPECIALLY HEAVY RAINFALL RATES OR THE SAME AREAS GETTING HIT DAY AFTER DAY AS THE WAVES AND BOUNDARY ARE LIKELY TO SHIFT AROUND EACH DAY AND PRECIP WATER VALUES ACTUALLY A LITTLE BELOW CLIMATOLOGY...SO NO MAJOR CONCERNS FOR FLASH FLOODING...BUT WORTH KEEPING AN EYE ON. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 100 PM EDT SUNDAY... FORECAST FOR LATE IN THE WEEK INTO NEXT WEEKEND REMAINS HIGHLY UNCERTAIN STARTING WITH A SOMEWHAT PROGRESSIVE PATTERN AND LOW AMPLITUDE TROUGH MOVING ACROSS NE US...THEN TRYING TO BECOME HIGHER AMPLITUDE WITH BUILDING RIDGE INTO GREAT LAKES REGION AND THE TROUGH OFF NEW ENGLAND COAST DEEPENING AND SLOWING DOWN. THIS GENERAL PATTERN WOULD INITIALLY HAVE OUR REGION IN WESTERLY TO NW FLOW WITH A WEAK FRONTAL BOUNDARY SHIFTING ACROSS THE REGION THE REMAINING NEARLY STATIONARY...BEFORE EVENTUALLY GETTING PUSHED SOUTH OF THE AREA BY A BACK DOOR PUSH AS NEARLY STATIONARY TROUGH OFF NEW ENGLAND DEEPENS. LAST NIGHTS GFS RUNS SHOWED HIGHER AMPLITUDE PATTERN THEN ECMWF AND GFS ENSEMBLES WERE IN DECENT AGREEMENT. THIS WOULD ARGUE FOR STRONGER PUSH OF THE BACK DOOR FRONT AND THUS COOLING OFF BY AT LEAST LATE IN THE WEEKEND WITH DEEPER MOISTURE AND HEAVIER RAINFALL RATES DROPPING TO OUR SOUTH...OR AT LEAST FAR SW PART OF FORECAST AREA. NOW THE NEW 12Z GFS IS EVEN WEAKER AMPLITUDE THAN 00Z ECMWF AND ALLOWS MORE RIDGING INTO WESTERN PART OF FORECAST AREA. THIS WOULD LEAVE A NEARLY STATIONARY BOUNDARY MORE OVER THE HEART OF THE FORECAST AREA. AND KEEP CHANCES FOR CONTINUED SHOWERS AND STORMS FAIRLY HIGH. ALSO WARMER ACROSS AT LEAST THE SOUTHWEST PART OF AREA. GIVEN ALL THIS UNCERTAINTY...BEST APPROACH IS TO LEAN TOWARD CLIMATOLOGY AND KEEP AT LEAST LOW CHANCE POPS UP THROUGH THIS ENTIRE PERIOD...AND WHILE A DIURNAL TREND IS STILL LIKELY...NEED TO KEEP CHANCE POPS UP OVERNIGHT WITH BOUNDARY HANGING AROUND. USUALLY WHEN HIGHER AMPLITUDE FLOW BEGINS TO DEVELOP...THE MODELS DONT BRING BACK DOOR FRONT IN STRONGLY ENOUGH AND GIVEN THE KIND OF SUMMER WE HAVE ALREADY HAD...WILL STILL PUT SOME WEIGHT TOWARD THIS HIGHER AMPLITUDE IDEA LIKE PREVIOUS GFS RUN. THUS A BIT COOLER OVER THE WEEKEND...MORE SO SUNDAY...AND A BIT OF SHIFT IN HIGHER POPS TOWARD SOUTHWEST VA AND NW NC MOUNTAINS. BUT OVERALL WILL HAVE GENERALLY HIGHER POPS IN MTNS AND LOW CHANCE TO SLIGHT CHANCE POPS IN PIEDMONT. BOTTOM LINE GIVEN ALL THIS UNCERTAINTY IN PATTERN...AND ALSO POSSIBILITY THAT NOCTURNAL CONVECTION COULD CONTINUE WITH AID OF FRONTAL BOUNDARY AND UPSTREAM WAVES FROM MIDWEST CONVECTION...JUST NEED TO KEEP POPS UP THROUGH THIS ENTIRE PERIOD AND DO NOT FEEL CONFIDENT TO GO LIKELY POPS ANYWHERE YET...NOT NOT AS LOW AS SLIGHT CHANCE IN TOO MANY PLACES EITHER. IF FRONTAL BOUNDARY HANGS AROUND ALL WEEKEND...WE MAY BE DEALING WITH SOME SIGNIFICANT PRECIP AMOUNTS IN SOME AREAS...BUT HOPEFULLY THIS STRONGER BACKDOOR PUSH OF THE BOUNDARY WITH HIGHER AMPLITUDE PATTERN WILL PUSH IT OFF TO THE SOUTH AS THE WEEKEND PROGRESSES. EXPECT QUITE A FEW CHANGES AS THAT TIME FRAME DRAWS NEAR. && .AVIATION /02Z MONDAY THROUGH FRIDAY/...
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AS OF 745 PM EDT SUNDAY... UNSETTLED WEATHER PATTERN WILL CONTINUE THROUGH THE OVERNIGHT HOURS WITH A SERIES OF SCATTERED RAIN SHOWERS PROGRESSING EASTWARD ACROSS THE AREA. CONDITIONS WILL BE MAINLY VFR WITH THE ROUND OF ACTIVITY THAT WILL PASS THROUGH THE REGION PRIOR TO 06Z/2AM MONDAY. AFTER THAT POINT...EXPECT AN INCREASING NUMBER OF AREAS WITH MVFR VSBYS FOR LIGHT FOG WITH A LESSER EXTENT DUE TO THE INTENSITY OF THE PRECIPITATION. STARTING AROUND 10Z/6AM MONDAY IN THE WEST...AND PROGRESSING EASTWARD AS THE DAY PROGRESSES...ANTICIPATE WORSENING FLIGHT CONDITIONS AS A PRECIPITATION AND LOWERING CLOUDS ASSOCIATED WITH AN APPROACHING WARM FRONT...AND LOW PRESSURE ALONG THE FRONT...PROGRESS INTO THE REGION. MOST AREAS BY 18Z/2PM WILL EXPERIENCE MVFR CONDITIONS FOR BOTH CLOUDS HEIGHTS AND VISIBILITIES DUE TO A MIX OF PRECIPITATION AND LIGHT FOG. ISOLATED IFR CONDITIONS ARE ALSO ANTICIPATED. CONDITIONS WILL REMAIN RELATIVELY STABLE IN AND AROUND THE AREA OF THE BLUE RIDGE ALONG AND NORTH OF ROUGHLY KROA. THE FARTHER WEST...SOUTH...AND EAST AN AREA IS FROM THIS STABLE ZONE THE BETTER CHANCE OF ENOUGH INSTABILITY FOR ISOLATED TO SCATTERED THUNDERSTORMS. HAD GREATEST CONFIDENCE IN THE AREA NEAR KBLF TO INCLUDE MENTION IN ANY OF THE TAFS AT THIS POINT. AS OF 100 PM EDT SUNDAY... EXTENDED AVIATION... FRONT IS EXPECTED TO STALL NEAR OUR AREA THROUGH THE MIDDLE OF THE WEEK AS A SERIES OF UPPER-LEVEL DISTURBANCES TRACK FROM WNW-ESE ACROSS THE REGION. MAIN ACTIVITY EXITS THE EAST BY TUESDAY MORNING...WITH MAINLY DIURNALLY DRIVEN SHOWERS AND THUNDERSTORMS ANTICIPATED FOR THE REMAINDER OF THE WEEK. INCREASED MOISTURE AND RAIN CHANCES WILL RESULT IN A DAILY THREAT FOR LATE NIGHT/EARLY IFR- LIFR CONDITIONS IN FOG AND LOW CLOUDS AT THE USUAL SITES...LWB/BCB/LYH...WITH MVFR POSSIBLE AT OTHER LOCATIONS.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...SK NEAR TERM...JH/RAB SHORT TERM...SK LONG TERM...SK AVIATION...DS/MBS

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