Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 181444 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1044 AM EDT MON AUG 18 2014 .SYNOPSIS... LOW PRESSURE WILL PASS ACROSS THE REGION THIS AFTERNOON...TRIGGERING WIDESPREAD SHOWER ACTIVITY AND A FEW THUNDERSTORMS. EXPECT SHOWERS AND ISOLATED THUNDERSTORMS TO AFFECT THE REGION THROUGH THE WEEK AS A SERIES OF UPPER LEVEL DISTURBANCES PASS ACROSS THE AREA. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1005 AM EDT MONDAY... UPPER WAVE OVER NE KY WILL CONTINUE TO SLIDE EAST ACROSS THE CENTRAL PORTION OF THE CWA THIS AFTERNOON TAKING THE CORE OF THE MORE WIDESPREAD PRECIP ALONG HIGHWAY 460 AND POINTS NORTH. HOWEVER JUST SOUTH OF THE VORT TRACK WILL SEE MORE BANDED CONVECTIVE NATURE SHRA/ISOLATED TSRA ESPCLY WHERE LIKELY TO SEE A BIT MORE INSTABILITY PER LATEST HRRR. BEST LOCATIONS FOR HEAVY RAIN APPEAR TO BE OVER SW VA INTO THE SOUTHERN HALF OF SE WVA ALTHOUGH RAINFALL RATES THE FARTHER NORTH LOOK TO BE LESS. GIVEN SLOW MOVEMENT AND HIGH PWATS OF NEARLY 2 INCHES WONT TAKE MUCH TO SEE A QUICK COUPLE INCHES OF RAIN ACROSS THE REGION. HOWEVER SINCE ALREADY SEEING RAIN OVER THE REGION AND THE BACK EDGE JUST TO THE WEST...WONT HOIST A FLOOD WATCH OVER THE WEST AT THIS POINT AND HANDLE LOCAL ISSUES WITH STATEMENTS/WARNINGS. OTRW KEEPING POPS CAT TO LIKELY ACROSS THE REGION BUT MORE SCATTERED...OR IN BANDS TOWARD NW NC WHERE DEEPER CONVECTION POSSIBLE PER MORE BREAKS CURRENTLY SEEN ON THE LATEST VISIBLE IMAGES. SOME ISOLATED SEVERE CANT TOTALLY BE RULED OUT OVER THE FAR SOUTH LATER ON PENDING DEGREE OF INSTABILITY AS MID LEVEL WINDS QUITE DECENT IF SOME BREAKS ARE REALIZED. HIGH TEMPS REMAIN QUITE TRICKY WITH POTENTIAL TO ZOOM WELL INTO THE 80S SOUTH WHILE STAYING STUCK IN THE LOWER 70S WEST. FOR NOW BOOSTED HIGHS A FEW DEGREES ACROSS NW NC INTO SOUTHSIDE VA AND KEPT ELSEWHERE SIMILAR TO PREVIOUS FOR NOW. PREVIOUS VALID DISCUSSION... RADAR INDICATES SPOTTY SHOWER ACTIVITY MOVING EAST ACROSS THE NORTH CAROLINA MOUNTAINS AND THE MOUNTAIN EMPIRE THIS MORNING... THE LEADING EDGE OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS THAT WILL AFFECT THE AREA TODAY. THE UPPER LEVEL DISTURBANCE TRIGGERING THIS ACTIVITY IS WELL DEFINED IN WATER VAPOR IMAGERY AS IT APPROACHES THE APPALACHIANS...AND THE ASSOCIATED SURFACE LOW IS DRIFTING EAST ALONG A STATIONARY BOUNDARY SITUATED NEAR THE OHIO RIVER. EAST OF THE APPALACHIANS...WE SEE WEAK HIGH PRESSURE WEDGING SOUTHWARD INTO THE MID ATLANTIC FROM THE GREAT LAKES REGION. THROUGH THE MORNING...BANDS OF SHOWER ACTIVITY WILL CONTINUE TO ENTER OUR AREA FROM THE WEST...STARTING US OFF WITH OCCASIONAL RAINFALL THAT WILL BECOME SCATTERED TO WIDESPREAD DURING THE AFTERNOON AS DAYTIME HEATING INCREASES AND THE UPPER DISTURBANCE DRAWS CLOSER. BECAUSE OF THE VERY MOIST ATMOSPHERIC CONDITIONS ALREADY IN PLACE...WITH PRECIPITABLE WATER VALUES APPROACHING TWO INCHES ACROSS MUCH OF THE FORECAST REGION...LOCALLY HEAVY RAIN CAN BE EXPECTED...ESPECIALLY ACROSS THE MOUNTAINS. FLOODING THREAT STILL APPEARS MINIMAL DUE TO THE DRY ANTECEDENT CONDITIONS OVER THE PAST SEVERAL WEEKS...BUT CANNOT RULE OUT LOCAL MINOR FLOODING IF CELLS BEGIN TO TRAIN. ALSO FEEL THAT THUNDERSTORM ACTIVITY WILL BE MINIMAL DUE TO THE LACK OF SUBSTANTIAL INSTABILITY ASSOCIATED WITH WEAK WEDGING...BUT BELIEVE THE BEST CHANCES FOR THUNDERSTORM DEVELOPMENT WILL BE OVER NORTHERN NORTH CAROLINA WHERE STRONGER HEATING WILL OCCUR. WIDESPREAD CLOUD COVER AND RAINFALL WILL KEEP A LID ON HEATING...HOLDING HIGHS IN THE MID 70S IN THE MOUNTAINS AND THE LOW 80S ACROSS THE SOUTHSIDE. MAIN UPPER LEVEL SUPPORT WILL SHIFT EAST LATE IN THE EVENING... ALLOWING LOW PRESSURE DEVELOPING OVER THE COASTAL PLAIN TO DEEPEN...AND EVENTUALLY TAKE OVER AS THE MAIN LOW PRESSURE SYSTEM. EVEN THEN...THERE IS NO SUBSTANTIAL PUSH OF COLD AIR IN THE WAKE OF THE SYSTEM...AND EXPECT THE FRONT TO REMAIN STALLED NEAR THE INTERSTATE 64 CORRIDOR INTO TUESDAY. THAT STATED...THE LACK OF UPPER LEVEL ENERGY AND DAYTIME HEATING WILL CAUSE SHOWER ACTIVITY TO DIMINISH TO ISOLATED SHOWERS OVER THE MOUNTAINS BY EARLY TUESDAY MORNING. WARM AND MUGGY CONDITIONS WILL PERSIST OVERNIGHT... AND EXPECT LOCALLY DENSE FOG TO OCCUR IN SOME AREAS WHERE SKIES CLEAR. OVERNIGHT LOWS WILL RANGE FROM THE MID 60S TO THE LOW 70S. && .SHORT TERM /TUESDAY THROUGH THURSDAY/... AS OF 400 AM EDT MONDAY... WAVY FRONTAL BOUNDARY WILL STRETCH FROM THE CENTRAL/SOUTHERN PLAINS TO THE MID ATLANTIC COAST. SCATTERED SHOWERS/THUNDERSTORMS WILL BE FOUND ALONG THIS BOUNDARY WITH POTENTIAL FOR ORGANIZED MESOSCALE CONVECTIVE SYSTEMS IN ADDITION TO THE DIURNALLY DRIVEN ACTIVITY. HAVE MAINTAINED CHANCE THREAT POPS THROUGH THE WEEK WITH LOW CONFIDENCE ON THE TIMING. WITH THE FRONTAL BOUNDARY STALLED OVER THE AREA...COULD JUST AS EASILY EXPERIENCE NIGHTTIME SHOWERS/STORMS ASSOCIATED WITH AN MCS AS IT SLIDES DOWNSTREAM ALONG THE FRONTAL BOUNDARY. THERE IS SOME POTENTIAL FOR EXCESSIVE RAINFALL. ATTM NOT SURE HOW TRANSIENT THESE MCS SORT OF FEATURES WILL BE. TENDENCY MAY BE FOR THEM TO BACKBUILD ALONG THE SURFACE FRONT INTO THE OH/TN VALLEY WHERE DEEPER MOISTURE FROM THE GULF OF MEXICO WILL BE INTERACTING WITH THE FRONTAL BOUNDARY. IF THIS OCCURS...WILL HAVE TO WATCH FOR REPEAT HEAVY RAINFALL. THE GREATEST RISK FOR THIS SORT OF SETUP APPEARS TO BE THE WESTERN CWA...CLOSER TO THE UPSTREAM INSTABILITY THAT WILL EXIST OVER THE OH/TN VALLEYS DURING THE PERIOD. IN SPITE OF THE THREAT FOR SHOWERS...TEMPERATURES SHOULD PAN OUT NEAR NORMAL. THE FORECAST WESTERLY WIND ALOFT SHOULD HELP GIVE TEMPERATURES A BOOST WEDNESDAY AND THURSDAY PER COMPRESSIONAL WARMING LEE OF THE BLUE RIDGE. && .LONG TERM /THURSDAY NIGHT 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 /14Z MONDAY THROUGH FRIDAY/... AS OF 745 PM EDT SUNDAY... LOW PRESSURE OVER EASTERN KENTUCKY WILL ADVANCE EAST TODAY WITH WIDESPREAD SHOWERS AND EMBEDDED THUNDERSTORMS PASSING OVER THE CENTRAL APPALACHIANS AND INTO CENTRAL VA/NC TODAY. PER RADAR IMAGERY WHICH INDICATES RAIN CURRENTLY ADVANCING OVER THE MOUNTAINS...HIGH CONFIDENCE FOR LOWERING CIGS/VSBYS ASSOCIATED WITH WIDESPREAD SHOWERS TODAY. SHOWERS WILL GRADUALLY COME TO AN END THIS EVENING AS THE AREA OF LOW PRESSURE MOVES EAST. VERY MOIST ATMOSPHERE WILL REMAIN IN PLACE TONIGHT WITH LOW CIGS/VSBYS CONTINUING WITH AREAS OF FOG. HIGH CONFIDENCE FOR MVFR CONDITIONS DURING THE TAF PERIOD WITH MODERATE CONFIDENCE FOR IFR. EXTENDED AVIATION... A SURFACE FRONT IS EXPECTED TO REMAIN STALLED 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. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...JH/NF SHORT TERM...PM LONG TERM...SK AVIATION...PM

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