Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 291758 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 158 PM EDT SAT AUG 29 2015 .SYNOPSIS... HIGH PRESSURE WILL REMAIN CENTERED OVER THE DELMARVA REGION FOR MUCH OF TODAY. A WEAK UPPER LEVEL DISTURBANCE WILL LIFT NORTH ALONG THE APPALACHIANS SUNDAY INTO MONDAY AHEAD OF A WEAK COLD FRONT TO THE WEST. UPPER LEVEL HIGH PRESSURE WILL STRENGTHEN IN THE WAKE OF THIS FEATURE...RESULTING IN MORE DIURNAL NATURE SHOWERS AND STORMS INTO THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 945 AM EDT SATURDAY... MORNING VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS INDICATE VALLEY FOG HAS JUST ABOUT DISSIPATED BUT MID CLOUDS HAVE BLOSSOMED AND HIGH CLOUDS ARE STREAMING UP FROM THE SOUTH. BELIEVE THIS EXTRA CLOUD COVER WILL FILTER INSOLATION JUST ENOUGH TO SLIGHTLY INHIBIT WARMING...SO WILL ADJUST MAX TEMPS DOWN JUST A HAIR. THE REST OF THE FORECAST WILL REMAIN UNCHANGED WITH SLGT/LOW CHC POPS WARRANTED IN THE FAR WEST FOR DIURNAL OROGRAPHICALLY DRIVEN ISOLATED SHOWERS...MAINLY FROM THE MOUNTAIN EMPIRE OF VA INTO THE GREENBRIER VALLEY AND ALLEGHANY HIGHLANDS. PREVIOUS AFD... INSTABILITY REMAINS LIMITED...HOWEVER MAY SEE A FEW SHOWERS DEVELOP FROM THE ALLEGHANY HIGHLANDS THROUGH THE MOUNTAIN EMPIRE. WITH SUBTROPICAL RIDGING NUDGING ITS WAY CLOSER TO THE MID ATLANTIC...WE CAN EXPECT SLIGHTLY WARMER TEMPERATURES FOR TODAY... WITH HIGHS RANGING FROM THE LOW 80S ACROSS THE MOUNTAINS...TO THE UPPER 80S ACROSS THE PIEDMONT. HIGH CLOUDS WILL INCREASE DURING THIS EVENING...MAKING FOR MOSTLY CLOUDY SKIES FOR TONIGHT. WARMER AND MUGGIER...OVERNIGHT LOWS WILL GENERALLY FALL INTO THE LOW TO MID 60S...WITH UPPER 50S FOR A FEW OF THE DEEPER VALLEYS ACROSS THE MOUNTAINS. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 230 AM EDT SATURDAY WATER VAPOR SATELLITE IMAGERY DEPICTS A BROAD UPPER LEVEL AREA OF LOW PRESSURE OVER THE NORTHERN GULF OF MEXICO WITH A PLUME OF MOISTURE IN ADVANCE OF THIS SYSTEM STREAMING INTO THE SOUTHEAST U.S. MOST OF THE DETERMINISTIC MODELS ARE IN GENERAL AGREEMENT THAT THIS LOW OPENS AND LIFTS INTO OUR AREA SUNDAY NIGHT/EARLY MONDAY BEFORE PUSHING EAST OF THE REGION BY LATE MONDAY...BEFORE UPPER HEIGHTS AND HIGHER PWAT VALUES BUILD TUESDAY. MODEL TRENDS HAVE BEEN SLIGHTLY SLOWER AND FURTHER WEST WITH THIS FEATURE. FOR SUNDAY...A WEAK UPPER LEVEL SHORTWAVE IN ADVANCE OF THE AFOREMENTIONED LOW ENTERS FAR SOUTHWEST VA ON SUNDAY. FORECAST SOUNDINGS STILL INDICATE A DRY LOW LEVEL ATMOSPHERE WITH LITTLE TO NO CAPE. KEPT A SMALL CHANCE FOR SHOWERS AND STORMS IN THE FAR WEST WHERE BEST UVM IS FORECAST ALONG WITH HIGHEST FORECAST THETA-E VALUES. NUDGED TEMPS DOWN A DEGREE OR TWO WITH THE EXPECTED INCREASED CLOUD COVER. BETTER CHANCE FOR PRECIPITATION APPEARS TO BE SUNDAY NIGHT WITH SURGE OF DEEPER MOISTURE AND BEST UPPER DYNAMICS ARRIVE. AS A RESULT...INCREASED POPS DURING THE OVERNIGHT HOURS SUNDAY NIGHT/MONDAY MORNING. IT SHOULD BE NOTICEABLY MORE HUMID MONDAY AND WARMER THANKS TO AN INCREASE IN 1000-850MB THICKNESSES...AND LEANED TOWARD THE WARM NAM MOS VALUES FOR HIGHS ON MONDAY. WHILE THE INITIAL UPPER LEVEL SHORT WAVE WILL BE EXITING OUR AREA DURING THE DAY...AND TAKING MOST OF THE PRECIPITATION WITH IT...LINGERING INSTABILITY AND WEAK LOW LEVEL CONVERGENCE IN THE MOUNTAINS SHOULD TRIGGER DIURNALLY DRIVEN WIDELY SCATTERED SHOWERS AND STORMS. PWAT VALUES CONTINUE TO SURGE TUESDAY AS AN UPPER RIDGE BUILDS... LEADING TO A HUMID AND WARM DAY WITH MORE AFTERNOON/EVENING SHOWERS AND STORMS. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 1240 PM EDT FRIDAY... OVERALL PERSISTENCE FORECAST AT LEAST EARLY ON AS UPPER RIDGING STRENGTHENS ACROSS THE REGION IN THE WAKE OF THE PASSING WAVE ALOFT AND IN INCREASING SUBSIDENCE WELL NORTH OF ERIKA. THIS SHOULD RESULT IN A MORE DIURNALLY DRIVEN TREND OF DAILY SHOWERS AND ISOLATED STORMS EACH AFTERNOON/EVENING WITH A GRADUAL INCREASE IN COVERAGE/EXPANSE FROM TUESDAY THROUGH THURSDAY GIVEN BETTER PWATS/MOISTURE AND SLIGHT COOLING ALOFT. HOWEVER THINK LOW/MEDIUM CHANCE POPS CONFINED MAINLY ALONG/WEST OF THE BLUE RIDGE PER OROGRAPHICS...AND MORE ISOLATED ELSEWHERE ESPECIALLY GIVEN MOISTURE OVER TOP A LINGERING SURFACE RIDGE. THUS FOLLOWED CLOSER TO TRENDS FROM WPC WITH A GRADUAL BOOST IN POPS EACH DAY BUT LITTLE DURING THE OVERNIGHTS INTO THURSDAY. THINGS BECOME MORE UNCERTAIN BY DAY7 WITH MODELS LOWERING HEIGHTS ACROSS THE APPALACHIANS AND FROM THE NE WITH A POSSIBLE ASSOCIATED BACKDOOR COOL FRONT. THIS COULD HELP FOCUS MOISTURE GIVEN A BETTER EASTERLY TRAJECTORY TO THE NORTH OF ERIKA OR ITS REMNANTS ON FRIDAY. THEREFORE GOING WITH MORE WIDESPREAD CHANCE POPS PER POTENTIAL TROPICAL TYPE PWATS OVER THE AREA DURING HEATING FRIDAY AFTERNOON. OTHERWISE LITTLE CHANGE IN DAILY TEMPS GIVEN SUCH A HUMID/WARM AIRMASS...SUPPORTING HIGHS MOSTLY IN THE 80S AND LOWS IN THE 60S EXCEPT PERHAPS A BIT COOLER FRIDAY PENDING CLOUDS/SHOWERS. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... AS OF 150 PM EDT SATURDAY... SYNOPTIC PATTERN REMAINS UNCHANGED WITH SOME RIDGING ALOFT FROM THE EAST WITH HIGH PRESSURE AT THE SURFACE. THIS IS KEEPING THE REGION IN A LIGHT WIND ENVIRONMENT WITH A CHANCE FOR DIURNAL OROGRAPHICALLY INDUCED SHOWERS. SATELLITE IMAGES ARE SHOWING CU FIELD BLOOMING EARLY THIS AFTERNOON AS HIGHER CLOUDS RIDE UP OVER THE TOP FROM THE SOUTH. ANY SHOWER ACTIVITY WILL BE ISOLATED TO WIDELY SCATTERED SO WILL GENERALLY KEEP TAFS DRY AND ONLY USE VCSH AT KBLF/KLWB WHERE THE BEST CHANCE POPS ARE LOCATED DEEPER INTO THE TERRAIN. MODEL SOUNDINGS SHOW A GOOD AMOUNT OF MOISTURE IN THE COLUMN THROUGH THE PERIOD SO DIURNAL CLOUDS WILL BE IN NO GREAT HURRY TO DISSIPATE WITH THE LOSS OF HEATING. WITH THIS IN MIND...EXPECTING MULTILAYERED VFR CLOUDS AT ALL SITES THROUGH THIS TAF PERIOD. BELIEVE THE LOWEST CIGS WILL BE IN AND OUT FOR VARIOUS PERIODS OVERNIGHT BUT WITHOUT A CHANGE IN FLIGHT CATEGORY WILL KEEP TAFS AS SHORT AND SIMPLE AS POSSIBLE AND NOT INDICATE CHANGES IN VFR CIGS. THERE SHOULD BE ENOUGH RADIATIONAL COOLING TO ALLOW FOR SOME FOG FORMATION AGAIN TONIGHT PRIMARILY AT KBCB AND KLWB...BUT KBCB LOOKS TO BE AFFECTED BY MORE CLOUDINESS SO WILL USE A TEMPO FOR MVFR VSBY TOWARD DAYBREAK. KLWB WAS AN OVERACHIEVER LAST NIGHT AND WENT TO LIFR DESPITE SOME CLOUDS AROUND SO WILL GO WITH THIS TREND AGAIN FOR TONIGHT AND INDICATE LIFR CONDITIONS TOWARD DAYBREAK. ANY FOG DISSIPATED AFTER DAYBREAK SUNDAY AND IT LOOKS LIKE SHOWER ACTIVITY WILL BE MORE WIDESPREAD SUNDAY AFTERNOON AS A GOOD DOSE OF SHORT WAVE ENERGY RISES OUT OF THE GULF COAST AND INTO THE REGION. BELIEVE THE BEST CHANCES FOR PRECIPITATION WILL BE BEYOND THIS TAF PERIOD SO WILL ONLY INCLUDE VCSH AT KBLF/KLWB WHERE TERRAIN INFLUENCES MAY GET CONVECTION OFF TO AN EARLIER START. EXTENDED AVIATION DISCUSSION... SHORT WAVE ENERGY MOVING UP FROM THE SOUTH WILL SUPPORT AN INCREASED CHANCE FOR CONVECTIVE ACTIVITY INTO MONDAY. GENERALLY EXPECT THE BEST CHANCES FOR MVFR/IFR TO BE LATE NIGHT/EARLY MORNING DUE TO FOG AND STRATUS DEVELOPMENT FROM THE BLUE RIDGE WEST ESPECIALLY AT KLWB/KBCB. WILL THEN REMAIN IN A WEAKLY FORCED SYNOPTIC ENVIRONMENT THROUGH MIDWEEK WITH CHANCES FOR DIURNAL CONVECTION MAINLY FROM THE BLUE RIDGE WEST...AND SOME MVFR/IFR FOG/STRATUS DEVELOPMENT AT NIGHT ESPECIALLY AT KBCB AND KLWB. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...MBS/NF SHORT TERM...PH LONG TERM...JH AVIATION...MBS/NF

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