Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 190638 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 238 AM EDT TUE AUG 19 2014 .SYNOPSIS... A LOW PRESSURE AREA WILL MOVE EAST OF THE APPALACHIANS EARLY TONIGHT...LEAVING ONLY SCATTERED SHOWERS AND A FEW THUNDERSTORMS LINGERING BEHIND IT. A SERIES OF UPPER LEVEL DISTURBANCES WILL PASS ACROSS THE AREA DURING THE WEEK...BRINGING A CHANCE FOR SHOWERS AND THUNDERSTORMS JUST ABOUT EVERY DAY. && .NEAR TERM /THROUGH TODAY/... AS OF 1000 PM EDT MONDAY... STRONG UPPER SHORT WAVE HAS MOVED ESE OF THE CWA...BUT UNSTABLE NW FLOW LINGERS AND WILL DO SO FOR THE NEXT SEVERAL DAYS. HOWEVER...THERE DO NOT APPEAR TO BE ANY MORE SUCH SIGNIFICANT UNTIL THU NIGHT/FRI. NONETHELESS...WEAK SHORT WAVES WILL IMPINGE ON AN INCREASINGLY UNSTABLE AIR MASS AS HEIGHTS AND 850MB TEMPS SLOWLY RISE OVER THE NEXT FEW DAYS. THUS...EXPECT SCATTERED POP UP SHRA/TSRA NEXT SEVERAL DAYS...MAINLY AFTERNOON/EVENING. FOR TONIGHT...MODIFIED POPS EARLIER TO TREND DOWNWARD...BUT SCT -SHRA WILL CONTINUE TO TRAVERSE THE REGION FROM NW-SE THROUGH THE NIGHT. FOR THIS REASON HAVE MAINTAINED SLIGHT CHC TO LOW CHC POPS MOST AREAS OVERNIGHT. REMOVED ALL MENTION OF THUNDER UNTIL EARLY AFTERNOON TUE. WILL UPDATE HWO TO REMOVE ANY MENTION OF HAZARDS. AS OF 315 PM EDT MONDAY... STRONG MID LEVEL WAVE AND ASSOCIATED SURFACE LOW ACROSS WEST VA LATE THIS AFTERNOON WILL WORK EAST JUST NORTH OF THE STALLED FRONT ACROSS THE CENTRAL CWA THIS EVENING BEFORE REACHING THE COAST AFTER MIDNIGHT. THIS WILL KEEP PERIODIC ROUNDS OF LIGHT TO MODERATE RAIN GOING ESPCLY ALONG AND NORTH OF HIGHWAY 460 INTO THIS EVENING WITH MORE SCATTERED/BANDED CONVECTIVE NATURE COVERAGE OVER NORTHERN N CAROLINA INTO SOUTHSIDE VA WHERE WEAK INSTABILITY RESIDES JUST SOUTH OF THE WIDESPREAD CLOUD CANOPY. STILL SOME POTENTIAL TO SEE SOME ISOLATED MINOR FLOODING OR A PULSE SEVERE CELL GIVEN DIFFERENTIAL HEATING SOUTH...OTRW GOING WITH A GRADUAL DECREASE IN HIGH POPS FROM WEST TO EAST THIS EVENING. WAVE SLIDES OFFSHORE LATER TONIGHT TAKING BEST LIFT TO THE EAST WHILE THE LINGERING BOUNDARY REMAINS STUCK ACROSS THE SOUTHERN CWA INTO EARLY TUESDAY. LITTLE IN THE WAY OFF ADDED SUPPORT ALOFT BUT MODELS INDICATE A TRAILING AXIS OF DEEPER MOISTURE JUST NORTH OF THE FRONT WHICH MAY KEEP A FEW SHRA GOING THROUGH MORNING SO HOLDING ONTO SOME LOW POPS AFTER MIDNIGHT. OTRW HIGH PWATS AND LOW LEVEL MOISTURE LIKELY TO LEAD TO FOG AS WELL AS PATCHY DRIZZLE OVER MUCH OF THE REGION. TEMPS NOT TO FALL MUCH GIVEN SATURATED CONDITIONS WITH MOSTLY 60S FOR LOWS. WILL BASICALLY BE IN BETWEEN THE DEPARTING LOW TO THE EAST TUESDAY AND THE NEXT UPSTREAM IMPULSE TO THE NW. GUIDANCE SHOWS SOME WEAK SUBSIDENCE SPILLING IN ON WEAK NW FLOW BEHIND THE EXITING SHORTWAVE BUT WITH ONLY SLIGHT DRYING ALOFT SEEN ON FORECAST SOUNDINGS MAINLY OVER THE WEST. ABUNDANT RESIDUAL LOW LEVEL MOISTURE WILL PERSIST ESPCLY EAST AND WITH THE LEFTOVER FRONT AROUND EXPECT TO GET ISOLATED TO WIDELY SCATTERED COVERAGE AIDED BY OROGRAPHICS NORTH AND WEAK LOW LEVEL CONVERGENCE EAST WHERE WINDS WILL BE QUITE LIGHT. THIS ALSO DEPENDENT UPON GETTING ENOUGH INSTABILITY AFTER EARLY LOW CLOUDS/FOG AS GUIDANCE SHOWING 1-2K J/KG CAPES WHICH WOULD BE ENOUGH TO POP AT LEAST SOME SHALLOW CONVECTION SO RUNNING WITH CHANCE TO SLIGHT POPS OVERALL. LOWERED HIGHS SLIGHTLY BASED ON EARLY CLOUDS AND COOLER EC 2M TEMPS BUT SHOULD BE ENOUGH WARMING ALOFT AND INSOLATION TO PUSH 80 WEST AND MID/UPPER 80S EAST. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... AS OF 355 PM EDT MONDAY... TIMING INDIVIDUAL UPPER LEVEL WAVES REMAINS TRICKY DURING THE PERIOD...ALTHOUGH CONSENSUS AGREEMENT IS THAT THE NEXT BEST WAVE ROUNDING THE BOTTOM OF GREAT LAKES AREA UPPER TROUGH WILL BE APPROACHING WESTERN SLOPES LATE TUES NIGHT INTO WED MORNING...AND MAY BE BRINGING WITH IT WEAKENING CONVECTION INTO WESTERN SLOPES. WHAT HAPPENS DURING THE DAY MAY DEPEND ON AMOUNT OF HEATING...AND IF THERE IS ANY KIND OF OUTFLOW FROM WHATEVER MOVES IN THE FROM THE WEST EARLY. ONE POSSIBLE SCENARIO IS AN AREA OF SHOWERS MAKES IT ALL THE WAY ACROSS BLUE RIDGE INTO PIEDMONT DURING THE MORNING BUT STABILIZES THE ATMOS FOR THE AFTERNOON. IF IT DOESNT MAKE IT ACROSS...THE CHANCES FOR AFTERNOON SCATTERED CONVECTION ARE A LITTLE HIGHER...AND MODEL FCST INSTABILITY RANGES FROM 1000-1500 J/KG...WITH NAM AND ECMWF SHOWING A LITTLE BETTER SW LOW LEVEL FLOW IN PIEDMONT COMPARED TO GFS...BUT STILL WESTERLY DOWNSLOPE AT RIDGE TOP LEVEL. WILL KEEP CHANCE POPS ALL DAY IN WEST BUT A LITTLE HIGHER IN MORNING...AND SLIGHT CHANCE FAR EAST. NEXT DISTURBANCE LOOKS LIKE IT WILL ARRIVE DURING THE DAY THURSDAY...WHICH TIMED WITH DAYTIME HEATING WOULD GIVE BETTER CHANCES FOR DEEPER CONVECTION AND MAYBE MORE WIDESPREAD COVERAGE. IF THIS COMES IN A LITTLE SOONER IT COULD BE A REPEAT OF WEDNESDAY WITH SHOWERS AND A FEW STORMS CROSSING IN THE MORNING AND THEN NOT MUCH ELSE DEVELOPING LATER IN THE DAY. LEANING POPS TOWARD THE SLOWER IDEA. BOTH WED AND THUR TEMPS WILL BE WARMER WITH MORE CHANCES FOR AT LEAST A COUPLE HOURS OF SUN...ESPECIALLY PIEDMONT. THE RIDGE MAY ALSO TRY TO BUILD A LITTLE INTO THE FAR SOUTHWEST AS WELL. WENT PRETTY CLOSE TO GUIDANCE NUMBERS FOR HIGHS. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 100 PM EDT MONDAY... TREND OF BUILDING UPPER RIDGE INTO GREAT LAKES REGION SPREADING INTO OHIO VALLEY WITH DEEPENING AMPLITUDE TROUGH OVER NEW ENGLAND AND ALONG MID ATLANTIC COAST IS STILL ADVERTISED BY EXTENDED MODELS...AND TREND LAST 24 HRS HAS BEEN A BIT DEEPER AMPLITUDE AND POSSIBLY A BIT OF RETROGRESSION OF THE TROUGH BY LATE IN WEEKEND. AT LEAST A GOOD BET THAT FLOW WILL BECOME BLOCKED AND CONFIDENCE A LITTLE HIGHER THAT MUCH OF BLACKSBURG CWA WILL BE INFLUENCED BY BACK DOOR PUSH OF FRONTAL BOUNDARY OFF TO THE SOUTH BY AS EARLY AS FRI OR AT LEAST BY SAT AND THUS WEDGE OF COOLER AIR FOR MUCH OF WEEKEND AND POSSIBLY INTO MONDAY. SO WHILE STRONG RIDGE AND MORE TYPICAL AUGUST LIKE TEMPERATURES WILL BE ON OUR DOOR STEP AND AT TIMES THIS WARMER AIRMASS MAY INFLUENCE PARTS OF THE SOUTHWEST FCST AREA...LOOKS LIKE MOST LOCATIONS WILL BE BACK IN THE WELL BELOW NORMAL REGIME AGAIN. NEVERTHELESS TEMP FCST STILL TRICKY SINCE BACK DOOR FRONT COULD TAKE DEEPER MOISTURE SOUTH AND THUS DRY THINGS OUT ENOUGH TO GET MORE SUN THAN OTHERWISE MIGHT. FCST TEMPS IN GENERAL CLOSER TO ECMWF GUIDANCE...BUT LATEST 12Z MEX/GFS GUIDANCE SHOWING THE LOWERING TREND COMPARED TO PREVIOUS 00Z GUIDANCE. THE PRECIP FCST ALSO REMAINS CHALLENGING THROUGH THIS PERIOD...ALL DEPENDENT ON HOW FAR SOUTH BOUNDARY PUSHES AND TIMING OF UPSTREAM SHORT WAVE ENERGY FROM NORTHWEST. CHANCES ARE HIGHER FRIDAY INTO SATURDAY WITH BOUNDARY CLOSER TO SW PART OF FCST AREA AND WILL CONTINUE CARRYING A MID CHANCE POP FOR MTNS...LINGERING INTO OVERNIGHT GIVEN THIS BOUNDARY AND UNKNOWN TIMING OF DISTURBANCES COMING FROM NW. BUT WILL THEN INDICATE SOMEWHAT LOWERING CHANCES SUNDAY AND ESPECIALLY BY MONDAY AS BOUNDARY LIKELY TO PUSH WELL SOUTH...BUT KEEPING A SLIGHT CHANCE SINCE BY THIS TIME RIDGING COULD ACTUALLY BUILD BACK IN TO THE WEST...WHICH OF COURSE IS ANOTHER CHALLENGE FOR TEMPERATURES AS WELL. OVERALL...STILL A FAIR AMOUNT OF UNCERTAINTY WITH THIS PATTERN...AND WOULD ALMOST LIKE TO SEE A RETURN TO RIDGE AND TYPICAL DIURNAL PATTERN TO CONVECTION...AT LEAST FROM A FCST CHALLENGE PERSPECTIVE...AND THERE ARE SOME GOOD SIGNS OF THAT HAPPENING AS WE GET FARTHER INTO NEXT WEEK. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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AS OF 200 AM EDT TUESDAY... SURFACE OBSERVATIONS INDICATE MVFR/IFR CEILINGS ARE WIDESPREAD THIS MORNING ACROSS THE REGION AS TROPICAL MOISTURE POOLS JUST SOUTH OF A STATIONARY FRONT SITUATED ALONG A LINE FROM KLWB/KROA/KAVC. LOCALLY DENSE FOG IS ALSO BEING OBSERVED ACROSS THE MOUNTAINS AND FOOTHILLS IN THE FEW LOCATIONS WHERE CLOUDS HAVE SCATTERED. LOW CLOUDS AND PATCHY DENSE FOG WILL PERSIST OVERNIGHT...ALTHOUGH CEILINGS AND VISIBILITIES WILL FLUCTUATE UP AND DOWN AT TIMES. VISIBILITIES WILL IMPROVE QUICKLY AFTER 13Z AS DAYTIME HEATING INCREASES...WITH CLOUD BASES ALSO GRADUALLY IMPROVING THROUGH THE REMAINDER OF THE MORNING. EXPECT A MIXTURE OF BROKEN LOW END VFR CLOUDS AND HIGH MVFR CLOUDS TO AFFECT THE AREA DURING THE AFTERNOON. WILL ALSO SEE A REDEVELOPMENT OF SPOTTY SHOWER AND THUNDERSTORM ACTIVITY ACROSS THE MOUNTAINS BY 16Z AS ANOTHER UPPER LEVEL DISTURBANCE APPROACHES THE REGION. THIS ACTIVITY WILL SPREAD EAST THROUGH LATE AFTERNOON TO AFFECT THE PIEDMONT. SHOWER ACTIVITY WILL LINGER INTO MID EVENING BEFORE DIMINISHING WITH THE LOSS OF DAYTIME HEATING. EXPECT A RETURN OF MVFR AND IFR CEILINGS TUESDAY NIGHT...ALONG WITH PATCHY DENSE FOG. EXTENDED AVIATION... A SURFACE FRONT IS EXPECTED TO REMAIN STALLED NORTH OF THE AREA THROUGH THE MIDDLE OF THE WEEK AS A SERIES OF UPPER LEVEL DISTURBANCES TRACK FROM WNW-ESE ACROSS THE REGION...TRIGGERING SHOWERS AND THUNDERSTORMS...WITH BEST CHANCES OCCURRING DURING THE AFTERNOON AND EVENING. ABUNDANT TROPICAL MOISTURE AND MOIST SOIL CONDITIONS WILL ALSO RESULT IN LATE NIGHT/EARLY MORNING 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...NF/RCS

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