Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 171712 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 112 PM EDT SUN AUG 17 2014 .SYNOPSIS... A WARM FRONT LIFTS NORTH TO NORTHERN VIRGINIA TODAY...THEN A COLD FRONT ENTERS FROM THE NORTHWEST MONDAY. THIS FRONT WILL GENERALLY LINGER OVER OUR AREA INTO MIDWEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 945 AM EDT SUNDAY... SPOTTY SPRINKLES CONTINUE ACROSS PARTS OF THE REGION...MAINLY ALONG THE BLF-PSK-DAN CORRIDOR THIS MORNING. THIS IN AN AREA OF WEAK LIFT JUST NORTH OF THE WARM FRONT TO THE SOUTH AND IN THE WAKE OF AN INITIAL WAVE ALOFT THAT HAS SLIPPED TO THE EAST EARLY ON. NEXT FAINT IMPULSE ALOFT TO FOLLOW FROM THE NW THIS AFTERNOON AS THE BOUNDARY LIFTS NORTH AND SLOWLY FADES WITH TIME. HOWEVER LIFT WITH THE SHORTWAVE LOOKS QUITE WEAK ESPCLY GIVEN COMPLEX TO THE WEST AND LEFTOVER RIDGING IN PLACE. MODELS CONTINUE TO ERODE ONGOING MID DECK RATHER QUICKLY THIS AFTERNOON ALLOWING SOME MODEST CAPES OF 500-1K J/KG TO DEVELOP WHILE ALSO BOOSTING PWATS TO ABOVE 1.5 INCHES. HOWEVER MOST SOLUTIONS NOT PRODUCING MUCH COVERAGE WITH MOSTLY ISOLATED CONVECTION NORTH AND WEST WHERE HEATING ALONG WITH SOME CONVERGENCE LOOKS A BIT BETTER. APPEARS TSRA CHANCES IFFY GIVEN SHALLOW INSTABILITY AND CLOUDS EARLY BUT KEPT MENTION AS EXPECT DIFFERENTIAL HEATING/STEEPER LAPSES MAY AID DEVELOPMENT IN SPOTS. OTRW KEEPING OVERALL SLIGHT TO LOW CHANCE POPS FOR NOW. HIGHS REMAIN TRICKY PENDING EROSION OF THE MID DECK BUT APPEARS WILL HAVE ENOUGH HEATING ESPCLY LATER TO PUSH 75-80 MOUNTAINS AND 80S OUT EAST. TONIGHT...THE BREAK IN BETWEEN UPPER WAVES OCCURS...WITH NEXT SHARPER WAVE MOVING INTO ERN KY BY DAWN MONDAY...WITH FRONTAL BOUNDARY WORKING OVER THE OHIO RIVER INTO NRN VA. WILL KEEP POPS IN THE WEST THROUGH THE EVENING...THOUGH NO HIGHER THAN 30...BUT INCREASE THEM TO LIKELY BY DAWN MONDAY AS THE UPPER WAVE INCREASES UPPER DIVERGENCE BY THEN WITH SOLID SHIELD OF SHOWERS MOVING INTO ERN KY BY 12Z MONDAY. LOWS WILL BE ELEVATED AND MOISTURE INCREASES TO ONLY HAVE LOWS IN THE 60S CWA WIDE. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... AS OF 400 AM EDT SUNDAY... EXPECT TO START SUNDAY OFF WITH A STATIONARY FRONT SITUATED JUST NORTH OF THE INTERSTATE 64 CORRIDOR ACROSS THE MOUNTAINS AND POSSIBLY DIPPING AS FAR SOUTH AS LYNCHBURG ACROSS THE PIEDMONT...AS HIGH PRESSURE WEDGES SOUTHWARD FROM THE GREAT LAKES. RAIN CHANCES WILL INCREASE THROUGH THE MORNING AS OUR NEXT UPPER LEVEL DISTURBANCE AND ASSOCIATED SURFACE LOW PRESSURE SYSTEM RIDES EAST ALONG THE FRONT DURING THE AFTERNOON. MODEL PRESENTATION OF THIS NEXT SYSTEM DOES NOT APPEAR AS STRONG AS IT DID 24 HOURS AGO...HOWEVER BELIEVE THERE WILL STILL BE ENOUGH INSTABILITY TO TRIGGER AT LEAST OFF AND ON RAINFALL THAT WILL AFFECT MOST OF THE FORECAST REGION. ATMOSPHERIC MOISTURE WILL BE ABUNDANT...WITH PRECIPITABLE WATER VALUES FOR MOST OF THE AREA RANGING FROM 1.75 TO 2 INCHES. AS SUCH...WILL HAVE TO KEEP AN EYE OUT FOR LOCALLY HEAVY RAIN WHICH MAY CAUSE MINOR FLOODING IF SHOWERS AND STORMS BEGIN TO PASS REPEATEDLY ACROSS THE SAME LOCATIONS. STUCK CLOSER TO THE COOLER MET GUIDANCE FOR AFTERNOON HIGHS CONSIDERING RAINFALL AND CLOUD COVER MOVING IN EARLY IN THE DAY...ALTHOUGH THE SOUTHSIDE MAY RECEIVE ENOUGH HEATING TO REACH INTO THE UPPER 80S. UPPER 70S TO MID 80S CAN BE EXPECTED ELSEWHERE. WE WILL NOT SEE MUCH MOVEMENT OF THE FRONTAL BOUNDARY MONDAY NIGHT AND TUESDAY. THE UPPER LEVEL DISTURBANCE WILL CONTINUE EAST MONDAY NIGHT...WEAKENING AS IT PROGRESSES...WITH A SURFACE LOW DEVELOPING OVER THE COASTAL PLAIN STARTING TO TAKE OVER AS THE MAIN SURFACE LOW ON TUESDAY MORNING. WITH LITTLE UPPER SUPPORT TO PUSH THE LOW EASTWARD...IT WILL ONLY DRIFT TOWARD THE COAST THROUGH THE DAY... PROVIDING THE FOCUS FOR ON AND OFF SHOWERS AND THUNDERSTORMS ACROSS THE MID ATLANTIC TUESDAY AND TUESDAY NIGHT. WITH THE LOW OFF THE COAST BY SUNRISE WEDNESDAY...WE CAN TURN OUR ATTENTION TO ANOTHER UPPER LEVEL DISTURBANCE PASSING SOUTHEAST ACROSS THE GREAT LAKES AS UPPER LEVEL RIDGING BUILDS OVER THE GULF COAST REGION...SHIFTING WINDS OVER THE MID ATLANTIC FROM THE NORTHWEST. THIS DISTURBANCE WILL BRING MORE SPOTTY SHOWERS AND THUNDERSTORMS AS FAR SOUTH AS THE CENTRAL APPALACHIANS...MAINLY WITH DAYTIME HEATING. WITH A LITTLE MORE SUNSHINE EXPECTED...LOOK FOR HIGHS TO REACH INTO THE 80S MOST LOCATIONS. BECAUSE OF THE ABUNDANT TROPICAL MOISTURE RESIDING ACROSS THE MID ATLANTIC...OVERNIGHT LOWS WILL HOLD IN THE MID 60S TO AROUND 70 EACH NIGHT. && .LONG TERM /THURSDAY THROUGH SATURDAY/... AS OF 100 PM EDT SATURDAY... RATHER UNCERTAIN PATTERN THROUGH THE EXTENDED WITH RESIDUAL WEAK UPPER TROUGHINESS IN PLACE AND A LEFTOVER SURFACE BOUNDARY DANGLING ACROSS PARTS OF THE REGION INTO FRIDAY. THIS ALONG WITH HIGH MOISTURE LEVELS WILL KEEP THINGS UNSETTLED FOR THE MOST PART PENDING DEGREE OF DAILY CONVECTION...AND SUBSEQUENT MOVEMENT OF THE BOUNDARY ESPCLY DURING THE WEEK. LATEST OPERATIONAL SOLUTIONS CONTINUE TO DIFFER ON THE AMPLITUDE OF THE UPPER PATTERN WITH A BLENDED WEAKER ECMWF CONSENSUS APPEARING BEST GIVEN LATE AUGUST CLIMO. THIS ALONG WITH UNCERTAINTY IN LOCATIONS OF ADDED SHORTWAVE ENERGY RIDING INTO THE REGION WOULD SUPPORT MORE DIURNAL NATURE TO SHOWERS/STORMS DURING THE AFTERNOON/EVENING HOURS...AND TAPERING AT NIGHT DUE TO LOSS OF INSTABILITY. THUS WILL CONTINUE TREND OF MOSTLY CHANCE POPS THU-FRI WITH BEST COVERAGE MOUNTAINS AND SLIGHT TO LOW CHANCE COVERAGE OVERNIGHT. BY SATURDAY...THE APPROACH OF ANOTHER TROUGH/FRONT FROM THE NW MAY BE ENOUGH OF A KICKER TO PUSH THE INITIAL BOUNDARY FARTHER SE...WITH MORE OF AN IN BETWEEN SCENARIO...SO TRIMMED POPS TO LOW CHANCE/SLIGHT POPS ON DAY7 FOR NOW. TEMPS TO RETURN TO MORE NORMAL LEVELS THROUGH THE PERIOD GIVEN WEAK WESTERLY FLOW AND MOST OF THE 85H COOL ADVECTION STAYING NORTH. APPEARS WARMEST READINGS ALONG THE FRONT INTO MIDWEEK WHEN MOST WILL SEE 80S AND PERHAPS TOPPING 90 OVER THE SE. THIS BEFORE THINGS BECOME MORE OF THE WARM/MUGGY NATURE BY THE WEEKEND WITH HIGHER HUMIDITY MAKING FOR RATHER WARM LOWS IN THE 60S/NEAR 70...AND HIGHS 70S MOUNTAINS TO MID 80S PIEDMONT. && .AVIATION /17Z SUNDAY THROUGH THURSDAY/... AS OF 100 PM EDT SUNDAY... GOOD CONFIDENCE THROUGH FIRST PORTION OF TAF PERIOD...DECREASING THEREAFTER. WEAK DYNAMIC FORCING ASSOCIATED WITH A WEAK FRONTAL BOUNDARY OVER THE AREA WILL COMBINE WITH SOME LOW LEVEL INSTABILITY TODAY TO GET SOME ISOLATED SHOWERS GOING ACROSS THE AREA. HOWEVER...THE ISOLATED COVERAGE AND LACK OF A SPECIFIC FOCUS INDICATES GOING WITH VCSH FOR THE EARLY PART OF THE TAF PERIOD WOULD BE MOST REPRESENTATIVE FOR THE TAF SITES. AS TEMPS CLIMB INTO THE 80S...CONVECTIVE LIFTING SHOULD DEVELOP A VFR CIG OF CU GOING TO SC WITH SOME AC ABOVE...THEN LOSING THE LOWER CLOUD DECK AS WE HEAD INTO THE EVENING. UPPER DYNAMICS WHICH WERE HELPING TO DRIVE CONVECTION LAST NIGHT WILL BE LESSENING A BIT AS THEY APPROACH TAF SITES TONIGHT. BELIEVE THE OVERALL FLAVOR OF THE FORECAST WILL BE FOR CONDITIONS TO BECOME INCREASINGLY MORE UNSETTLED AS WE GET PAST MIDNIGHT. THIS WILL BRING AN INCREASING CHANCE OF SHOWERS ALONG WITH GRADUAL LOWERING OF CIGS TO THE EDGE OF VFR AS WE GET TOWARD DAYBREAK. BELIEVE THERE WILL BE ENOUGH HIGHER AC CLOUDS AROUND TO KEEP FOG FORMATION FROM BOTTOMING OUT VISIBILITIES SO WILL KEEP THEM IN THE MVFR RANGE FOR PREVAILING AND TEMPO GROUPS. THUNDER BECOMES MORE LIKELY AS INSTABILITY INCREASES LATE IN THE TAF PERIOD. WINDS WILL BE ON THE LIGHT SIDE AND WILL NOT POSE A SIGNIFICANT PROBLEM FOR AVIATION THROUGH THE TAF PERIOD. ...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. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...WP NEAR TERM...JH/WP SHORT TERM...NF LONG TERM...JH AVIATION...MBS

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