Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 290519 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 119 AM EDT FRI MAY 29 2015 .SYNOPSIS... HIGH PRESSURE OFFSHORE WILL MAINTAIN A MOIST SOUTHERLY FLOW ACROSS THE REGION INTO THE WEEKEND. A COLD FRONT WILL APPROACH FROM THE NORTHWEST LATE IN THE WEEKEND BEFORE DIPPING SOUTH OF THE AREA EARLY NEXT WEEK RESULTING IN MORE WIDESPREAD SHOWERS AND STORMS LATER SUNDAY INTO MONDAY. COOLER AND SOMEWHAT DRIER CONDITIONS WILL THEN BUILD IN FROM THE NORTH BY THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TODAY/... AS OF 755 PM EDT THURSDAY... PREVIOUS FORECAST FOR OVERNIGHT PERIOD STILL ON TRACK AND VERIFYING WELL...ALTHOUGH HAVE MADE A FEW ADJUSTMENTS TO GRIDS OVER THE PAST SEVERAL HOURS TO KEEP UP WITH SIGNIFICANT CHANGES TO HOURLY TEMPERATURES IN TIME AND SPACE ASSOCIATED WITH SHOWER/THUNDERSTORM OUTFLOW BOUNDARIES. ALSO BUMPED UP THREAT OF PRECIPITATION ACROSS PIEDMONT FROM CAMPBELL COUNTY VA EAST...WHERE LARGE AREA OF SLOW MOVING CONVECTIVE ACTIVITY HAS SET UP. TRENDS DURING THE PAST HOUR HAVE BEEN TOWARD SLOW STRATIFICATION OF AIRMASS AND DECREASING INTENSITY/COVERAGE AS LOSS OF DAYTIME HEATING AND BOUNDARY LAYER INCREASINGLY BECOMING OVERWHELMED BY COOL OUTFLOW BOUNDARIES. WILL UPDATE GRIDS AGAIN SHORTLY TO REFLECT AREA THAT WILL HAVE THE GREATEST THREAT FOR SOME LATE NIGHT FOG...SPECIFICALLY WHERE RAIN HAS FALLEN AND SKIES CLEAR. OTHERWISE...FORECAST FOR LATER TONIGHT AS FAR AS TEMPS/DEW POINTS AND DIMINISHING THREAT OF ANY ADDITIONAL RAIN STILL LOOKS GOOD. AS OF 330 PM EDT THURSDAY... AMORPHOUS WEATHER PATTERN WITH AMPLE INSTABILITY BUT WEAK DYNAMICS CONTINUES TO AFFECT THE REGION THROUGH THE SHORT TERM. A DIFFUSE FRONT TO OUR NORTHWEST WILL SAG IN OUR DIRECTION AND ADD A LITTLE SUPPORT TO OROGRAPHIC FORCING OF DIURNAL CONVECTION TO GENERATE THE BETTER CHANCES OF PRECIPITATION FROM THE BLUE RIDGE WEST. HOWEVER...SCATTERED ACTIVITY IS EXPECTED TO SPILL INTO THE UNSTABLE AIR OVER THE PIEDMONT AS. WITH LACK OF DYNAMIC SUPPORT THE OVERALL SEVERE THREAT IS LOW BUT OUTFLOW BOUNDARY INTERACTION MAY GENERATE A PULSE STORM OR TWO THAT WARRANT ATTENTION. MAINLY EXPECTING RELATIVELY SLOW MOVING HEAVY RAINERS BUT QUITE DRY ANTECEDENT CONDITIONS WILL PROHIBIT ANY HYDRO ISSUES. ACTIVITY WILL QUIET DOWN WITH LOSS OF HEATING AFTER SUNSET SO EXPECTING MAINLY DRY CONDITIONS FOR THE OVERNIGHT. BY TOMORROW...HIGH PRESSURE CENTERED OFF THE COAST WILL BRING SOUTHEASTERLY WINDS TO THE REGION AND PUSH THE WASHED OUT FRONTAL BOUNDARY BACK NORTHWARD. THIS WILL AGAIN BRING THE GREATEST CHANCES FOR SHOWERS AND THUNDERSTORMS TO AREAS FROM THE BLUE RIDGE WEST WITH THE PIEDMONT/SOUTHSIDE LOOKING MOSTLY DRY. NO AIRMASS CHANGE SO CONDITIONS WILL REMAIN WARM AND A BIT HUMID WITH MINS TONIGHT AROUND 60 WEST OF THE RIDGE TO LOW/MID 60S EAST...AND HIGHS FRIDAY GENERALLY UPPERS 70S/LOWER 80S WEST TO MIDDLE 80S EAST. && .SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... AS OF 330 PM EDT THURSDAY... CONVECTION SHOULD CONTINUE TO HAVE A STRONG DIURNAL TENDENCY WITH ANY WEAK FORCING LIFTING WELL TO NORTH FRIDAY NIGHT AND ONLY WEAK SOUTHERLY FLOW TO KEEP A FEW SHWRS GOING INTO THE EVENING NEAR THE BLUE RIDGE. OTHERWISE REDUCING POPS BELOW SLIGHT CHANCE BY MIDNIGHT OR SOON THEREAFTER. MODELS IN AGREEMENT THAT SOME DRIER AIR WRAPS CLOCKWISE AROUND THE SURFACE HIGH OFF THE MID ATLANTIC COAST FRIDAY NIGHT INTO SATURDAY AND THIS CAN BE SEEN READILY IN THE PRECIPITABLE WATER FORECASTS AND MODEL SOUNDINGS. THUS INSTABILITY LOOKS MUCH MORE LIMITED FOR SATURDAY AFTERNOON AND OTHER THAN THE HIGHEST RIDGES PERHAPS GETTING ENOUGH LIFT FOR SOME SHOWER OR ISOLD THUNDER...MAINLY IN WEST VIRGINIA...THINK MOST AREAS WILL ACTUALLY BE DRY AND ALSO FAIRLY WARM FOR SATURDAY. LOWERED POPS TO SLIGHT CHC FROM BLUE RIDGE AND NORTHWESTWARD...WITH LOW CHC CONFINED TO WEST VIRGINIA COUNTIES AND ALONG STATE BORDER WITH VIRGINIA...INCLUDING ALLEGHANY HIGHLANDS. MAY HAVE TO WATCH PIEDMONT AREAS OVERNIGHT SAT NIGHT FOR A STRAY SHOWERS AS MOISTURE BEGINS TO RETURN AGAIN...BUT FOR NOW LEAVING POPS BELOW MENTIONABLE THRESHOLD THERE FROM SAT THROUGH SAT NIGHT. BY SUNDAY MOISTURE CONTINUES TO INCREASE SLIGHTLY FROM THE SOUTH BUT THEN ALSO FROM THE NORTHWEST AS INCREASED CONVERGENCE ALONG A SLOWLY APPROACHING WEAK FRONTAL BOUNDARY BEGINS TO SQUEEZE DEEPER MOISTURE BACK INTO AREA. THUS LOOKING LIKE A RETURN TO MORE ACTIVE DAY FOR CONVECTION...BUT GIVEN THE GENERALLY WEAK FORCING AM STILL NOT CONVINCED THAT COVERAGE WILL BE ALL THAT WIDESPREAD...AND THUS THINK CHANCE POPS MAY STILL BE ADEQUATE TO DESCRIBE EXPECTED COVERAGE IN MOST AREAS. LOWERED POPS SOMEWHAT...BUT STILL LEAVING SOME LOW LIKELY VALUES IN MOUNTAINS...BUT HOLDING OFF ON ANY MENTION IN PIEDMONT UNTIL AFTERNOON AND KEEPING LOW CHANCE THERE. NAM DEPICTS SLIGHTLY MORE SOUTHERLY FLOW WITH GFS A BIT MORE SW...THUS SOME QSTN HOW FAR EAST OF BLUE RIDGE STORMS MAY DRIFT BY LATE AFT/EVE...BUT WITH THE CONVERGENCE FROM WEAK BOUNDARY THIS COULD BE AN OVERNIGHT WHERE SOME SHOWERS OR EVEN A THUNDERSTORM OR TWO LINGER MUCH OF THE NIGHT...SO KEPT POPS UP IN THE CHC CATEGORY SUNDAY NIGHT. && .LONG TERM /MONDAY THROUGH THURSDAY/... AS OF 330 PM EDT THURSDAY... MODELS HAVE CLUSTERED AROUND A BASIC SOLUTION OF BUILDING A DECENT SUMMER WEDGE BUILDS ON OVER THE FORECAST AREA MONDAY NIGHT INTO WEDNESDAY. WILL TRIM BACK MAXIMUM TEMPERATURES A CATEGORY OR TWO BUT AMOUNT OF HEATING WILL DEPEND ON AMOUNT OF CLOUDS. PLUS THE WEDGE WILL BE SHALLOW. THE BOUNDARY AT 850 NEVER MAKES IT SOUTH THROUGH THE REGION AND WITHOUT A BIG CHANGE IN AIRMASS...MOIST DEW POINTS WILL LIMIT HOW COOL IT GETS AT NIGHT AND SO EACH DAY WILL BE STARTING WITH MILD TEMPERATURES. THE EAST TO SOUTHEAST SURFACE WINDS WILL PROVIDE SOME UPSLOPE COMPONENT FOR INCREASED PROBABILITY OF PRECIPITATION ALONG THE BLUE RIDGE THROUGH TUESDAY NIGHT. BY WEDNESDAY AND THURSDAY AREA WILL BE UNDER RIDGING ALOFT WITH LOW LEVEL FLOW GENERALLY OUT OF THE SOUTHEAST. SURFACE BOUNDARY AND WEDGE TRICKY TO DISTINGUISH BY DAY 7. WILL HAVE DRY WX ON THURSDAY. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... AS OF 100 AM EDT FRIDAY... SHOWERS REMAIN ISOLATED ACROSS THE REGION TONIGHT WITH MOSTLY RESIDUAL VFR STRATO-CU AND MID DECK LINGERING ESPCLY SOUTHERN SECTIONS. CANT TOTALLY RULE OUT ADDED SHRA DEVELOPING THROUGH DAYBREAK GIVEN MOISTURE AROUND A WEAK BOUNDARY TO THE NORTH BUT NOT ENOUGH TO INCLUDE MENTION IN ANY OF THE TAF LOCATIONS FOR NOW. OTRW...SLOW CLEARING AND MOIST GROUND NOW IN MANY AREAS...SHOULD LEAD TO DEVELOPMENT OF LATE NIGHT FOG...AND THIS HINTED WELL IN LAMP GUIDANCE. SHOULD SEE LATE NIGHT PERIOD OF IFR TO LIFR RESTRICTIONS...AT LEAST TO VISIBILITY...AT KLYH...KDAN...KBCB...KLWB WHERE RAIN FELL EARLIER THIS EVENING...WITH MVFR RESTRICTIONS POSSIBLE AT KBLF. FOR NOW...HEAT ISLAND EFFECT AROUND KROA SHOULD KEEP VISIBILITY OUT OF MVFR RANGE...BUT BRIEF INTRUSION TO 4-5SM POSSIBLE RIGHT AROUND SUNRISE CAN`T ENTIRELY BE RULED OUT. ANY LATE NIGHT FOG/STRATUS WILL BURN OFF RAPIDLY AFTER DAYBREAK ON FRIDAY...TO BE FOLLOWED BY ANOTHER ROUND OF DIURNALLY-DRIVEN CONVECTION BY OR SHORTLY AFTER NOON IN THE MOUNTAINS AND FOOTHILLS...PERHAPS A COUPLE-FEW HOURS LATER OUT ACROSS THE PIEDMONT TERMINAL FORECAST SITES. SINCE BASED ON LATEST GUIDANCE THAT THE WEST WILL HAVE THE BEST SHOT AT SEEING THE MORE WIDESPREAD CONVECTION...ADDED IN A PREVAILING SHRA WITH VCTS MENTION AT BOTH KBLF/KLWB FRIDAY AFTERNOON AND LEFT IN VCTS AT ALL SITES EXCEPT FOR KDAN WHERE THINK CHANCES ARE LESS WITHIN THE SE FLOW. EXTENDED AVIATION DISCUSSION... THROUGH THE UPCOMING WEEKEND...A MOIST UNSTABLE AIR MASS WILL REMAIN IN PLACE ACROSS THE REGION WITH ONLY WEAK FORCING. THIS WILL RESULT IN MAINLY SLOW MOVING DIURNALLY DRIVE DEEP CONVECTION DURING THE AFTERNOON AND EVENING HOURS FOLLOWED BY STABLE CONDITIONS AT NIGHT. A FRONTAL SYSTEM WILL APPROACH FROM THE NORTH DURING THE WEEKEND...BUT WILL LIKELY REMAIN WELL NORTH OF THE FORECAST AREA THROUGH SUNDAY. THUS...NO CHANGE IN AIR MASS IS EXPECTED THROUGH THE PERIOD. THIS BOUNDARY SHOULD FINALLY SINK SOUTH INTO THE REGION EARLY NEXT WEEK RESULTING IN MORE WIDESPREAD CONVECTION POSSIBLY AS EARLY AS SUNDAY EVENING...FOLLOWED BY ADDITIONAL ROUNDS OF SHRA/TSRA INTO AT LEAST MONDAY NIGHT BEFORE PERHAPS THE BOUNDARY SINKS TO THE SOUTH. THIS SHOULD MAKE FOR MORE FREQUENT PERIODS OF SUB-VFR FROM LATER SUNDAY INTO TUESDAY WITH LOWER CIGS/VSBY REDUCTIONS DUE TO SHOWERS/STORMS DURING THE DAY...AND IN FOG OVERNIGHT INTO THE EARLY MORNING HOURS EACH DAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...MBS/WERT SHORT TERM...SK LONG TERM...AMS AVIATION...JH/MBS/PM/WERT

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