Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 181337 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 937 AM EDT THU SEP 18 2014 .SYNOPSIS... HIGH PRESSURE OVER THE AREA WILL WEAKEN AND SLIDE OFFSHORE THIS AFTERNOON AHEAD OF A WEAK COOL FRONT THAT SHOULD PASS ACROSS THE REGION THIS EVENING. STRONG HIGH PRESSURE WILL BUILD TO THE NORTH LATE TONIGHT INTO SATURDAY BEFORE PASSING OFFSHORE ON SUNDAY. A COLD FRONT WILL CROSS THE AREA FROM THE NORTHWEST ON MONDAY BRINGING A BETTER CHANCE OF SHOWERS TO START THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 928 AM EDT THURSDAY... BROAD UPPER-LEVEL TROUGH WILL REMAIN OVER THE REGION THROUGH TONIGHT...WHILE A WEAK UPPER-LEVEL DISTURBANCE PASSES THROUGH IN THE FLOW ALOFT. A WEAK COLD FRONT WILL SLIDE SOUTH ACROSS THE REGION THIS EVENING. MORNING FOG IS SLOWLY LIFTING AND SHOULD BURN OFF BY LATE MORNING. HIRESW-ARW...RAP13 AND NAM SUPPORT MENTION OF A FEW SHOWERS AS THE WEAK COLD FRONT PASS THROUGH OUR AREA. MADE SOME MINOR ADJUSTMENTS IN TEMPERATURES AND CLOUD COVER FOR THIS MORNING INTO THIS AFTERNOON. MORE CHANGES LATER TODAY. AS OF 235 AM EDT THURSDAY... FOG AND LOW CLOUDS THE MAIN ISSUES EARLY THIS MORNING AS EXPECT QUITE A BIT OF DENSE FOG COVERAGE ESPCLY MOUNTAINS GIVEN THE WEAK FLOW AND FAINT CONVERGENCE. MAY NEED TO HOIST AN ADVISORY PENDING TRENDS BUT WILL LET RIDE FOR NOW WITH GRIDS/ZFP MENTION AND SEE HOW WIDESPREAD COVERAGE GETS TOWARD SUNRISE. OTRW AREA WILL BE IN TRANSITION TODAY BETWEEN THE WEAK WEDGE SEEN OVER THE PAST 24 HOURS AND THE ONSET OF A MUCH STRONGER CAD EVENT THAT WILL UNFOLD LATE TONIGHT. THIS SCENARIO TO TAKE SHAPE IN THE WAKE OF THE PASSING OF THE CENTER OF THE UPSTREAM 5H TROUGH THIS AFTERNOON AND ITS ASSOCIATED WEAK SURFACE TROUGH/FRONT THAT WILL PIVOT THROUGH FROM THE NW LATER TODAY. MOST GUIDANCE NOW SHOWING AN AXIS OF WEAK LOW LEVEL CONVERGENCE JUST AHEAD OF THIS FEATURE...MAINLY ALONG/EAST OF THE BLUE RIDGE THIS AFTERNOON...AND ACROSS THE SOUTH THIS EVENING. HOWEVER MOISTURE LOOKS QUITE SHALLOW FOR THE MOST PART WHILE FORECAST CAPES REACH 500-1K J/KG UNDER AN AXIS OF WEAK 85H THETA-E RIDGING. THUS APPEARS SOME LOW TOPPED CONVECTION POSSIBLE PROVIDED ENOUGH HEATING WITH MOST TURNING PARTLY SUNNY AFTER EARLY LOW DECK. SINCE MOISTURE DEPTH AND LIFT NOT CONDUCIVE TO MUCH DEEP CONVECTION...WILL LEAVE OUT THUNDER MENTION SIMILAR TO THE SHALLOW NATURE OF SHRA SEEN OFF THE NCEP WRF...BUT CANT COMPLETELY RULE OUT PER DECENT FORECAST LAPSES OUT EAST. OTRW WILL RUN WITH A SHOTGUN...MAINLY ISOLATED TYPE COVERAGE...BLUE RIDGE EAST INTO THIS EVENING WITH LITTLE POP NW WHERE DRIER NW FLOW SHOULD PREVAIL. LEFT HIGHS IN LINE WITH THE LATEST MOS EXCEPT PERHAPS COOLER BLUE RIDGE AS LIGHT SE FLOW DEVELOPS INCLUDING AFTERNOON CLOUDS. SHOWERS SHOULD SINK SOUTH OR SW AND FADE LATE THIS EVENING AS THE ONSET OF A DEEPENING EAST/SE FLOW TAKES SHAPE IN RESPONSE TO STRONG HIGH PRESSURE BUILDING IN FROM THE NORTH LATE. MOST SOUNDINGS SHOW QUITE A BIT OF MOISTURE BANKED UP ALONG THE MOUNTAINS WITH DEPTH EVEN ENOUGH TO SUPPORT SOME SPOTTY -RA AND CERTAINLY DRIZZLE/FOG BY DAYBREAK. HOWEVER TRENDS APPEAR A BIT SLOWER THAN BEFORE SO TRIMMED BACK ONSET TIME A BIT WHILE RUNNING WITH ISOLATED POPS AND MOST WIDESPREAD DRIZZLE ALONG THE EASTERN SLOPES LATE. WILL BE COOL/MOIST WITH LOWS MOSTLY IN THE 50S EXCEPT CLOSER TO 60 SE ESPCLY IF THE WEDGE IS SLOWER TO SPILL SOUTH. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... AS OF 300 AM EDT THURSDAY... A BROAD AREA OF HIGH PRESSURE WILL MOVE OVER NEW ENGLAND AND WEDGE SOUTH DOWN THE EAST COAST ON FRIDAY. BUFKIT DISPLAYING A SATURATED SOUNDING THROUGH 10KFT AND WITH AN EASTERLY FLOW...AREAS OF FOG AND DRIZZLE LIKELY ALONG EASTERN SLOPES OF THE BLUE RIDGE INTO THE EARLY AFTERNOON. DRIER AIR BEGINS TO PUSH INTO THE AREA LATE IN THE AFTERNOON BUT NOT ENOUGH TO COMPLETELY END LIGHT PRECIPITATION OR REMOVE CLOUD COVER...ESPECIALLY ACROSS THE NORTH CAROLINA HIGHLANDS. ALTHOUGH LIMITED...AFTERNOON HEATING MAY ERASE DRIZZLE/FOG THROUGH THE AFTERNOON...WHILE SOME LIGHT SHOWERS MAY PASS OVER THE REGION INTO THE EVENING. FRIDAY AFTERNOON TEMPERATURES WILL BE COLDER THAN NORMAL WITH AREAS KEEPING PRECIPITATION THROUGH THE DAY NOT LIKELY TO MAKE IT OUT OF THE 60S. LOW LEVEL DRY AIR CONTINUES TO SURGE SOUTHWARD FRIDAY NIGHT BUT WITH MOISTURE TRAPPED UNDER THE INVERSION...STRATUS CLOUDS SHOULD LINGER INTO SATURDAY MORNING. BY SATURDAY AFTERNOON...A DISTURBANCE DEVELOPS AND BECOMES STRONGER OVER THE GULF STREAM. SINCE THIS SYSTEM IS TO THE SOUTH...NORTHEASTERLY FLOW WILL HELP THE RIDGE TO THE NORTH PULL MORE DRY AIR INTO THE FORECAST AREA. LOW CLOUDS ARE EXPECTED TO BREAK IN THE AFTERNOON WITH TEMPERATURES RECOVERING TO NEAR NORMAL. THE GULF STREAM DISTURBANCE REMAINS OFF SHORE AND WITH CONTINUED SUBSIDENCE AND DRY NORTHEASTERLY FLOW...SUNDAY WILL BE ANOTHER RAIN FREE DAY WITH TEMPERATURES AGAIN TOPPING OUT NEAR NORMAL. A COLD FRONT IS ALSO EXPECTED TO TRACK OVER THE OHIO VALLEY ON SUNDAY. THIS MAY TURNS THE WINDS TO THE SOUTHWEST AND COULD PUSH TEMPERATURES WARMER THAN NORMAL ON SUNDAY. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... AS OF 300 PM EDT WEDNESDAY... A STRONG FALL FRONT WILL APPROACH THE REGION SUNDAY NIGHT...CROSSING OVER THE REGION ON MONDAY. BY THE TIME THIS FRONT ARRIVES...WINDS WILL BECOME WESTERLY. WE SHOULD SEE RAIN FALLING ALONG WESTERN SLOPES...LOSING THEIR INTENSITY MOVING TO THE BLUE RIDGE EARLY MONDAY MORNING. THIS PRECIPITATION MAY THEN JUMP THE FOOTHILLS AS A WEAK LINE OF CONVECTION DEVELOPS OVER THE PIEDMONT WHERE A LEE TROUGH WILL RESIDE ON MONDAY. SHOWERS LEAVE THE AREA BY MONDAY EVENING WITH HIGH PRESSURE BUILDING IN FROM THE WEST. A VERY LARGE 1025MB HIGH WILL COVER MUCH OF THE UNITED STATES EAST OF THE MISSISSIPPI RIVER TUESDAY AND WEDNESDAY. AHEAD OF THE FRONT 85H TEMPERATURES WARM TO NEAR +16C ON SUNDAY. BEHIND THE FRONT 85H TEMPERATURES ARE AROUND +8C TUESDAY AND WEDNESDAY. TUESDAY AND WEDNESDAY HIGH TEMPERATURES WILL RUN 5F-10F COLDER THAN NORMAL. OVERNIGHT LOWS ARE EXPECTED TO DROP INTO THE 40S. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... AS OF 650 AM EDT THURSDAY... QUITE VARIABLE CIGS AND VSBYS EARLY THIS MORNING WITH POCKETS OF MVFR TO LIFR IN FOG...MAINLY ACROSS THE MOUNTAINS...AND WIDESPREAD MVFR CLOUD BASES EXCEPT FOR PERIODS OF VFR WHERE SOME BREAKS OCCUR. LATEST IR PICS INDICATE THIS SCENARIO WILL PERSIST UNTIL AT LEAST MID MORNING AND PERHAPS LONGER BLUE RIDGE UNTIL BETTER HEATING/MIXING DEVELOPS. THUS WILL TREND IMPROVING CIGS TO BE A BIT SLOWER AND INCLUDE UP AND DOWN CHANGEABLE BASES WITHIN BRIEF TEMPO GROUPS UNTIL MID MORNING. AFTER 14-15Z/10-11AM...CONDITIONS SHOULD IMPROVE BACK INTO THE VFR CATEGORY...WITH MOST LOW CIGS LIFTING INTO THE 40-60 KFT RANGE FOR THIS AFTERNOON. HOWEVER HEATING MAY PROMOTE SOME BUILDUPS OF CU ACROSS THE MOUNTAINS WHERE ISOLATED AFTERNOON SHRA POSSIBLE BUT SINCE IFFY WONT MENTION AT THIS POINT. HOWEVER DO EXPECT LOCALIZED MVFR NEAR ANY CONVECTION THIS AFTERNOON. OTRW LOOKING AT CU FIELDS SCATTERING OUT BY EVENING UNDERNEATH A LEFTOVER MID DECK. THIS SUPPORTS MAINLY VFR INTO EARLY TONIGHT AS THE WEAK BOUNDARY SHIFTS SOUTH AND HIGH PRESSURE STARTS TO BUILD IN FROM THE NORTH. FLOW TURNS MORE EASTERLY LATER TONIGHT AS STRONGER HIGH PRESSURE BUILDS IN WITH WIDESPREAD MVFR/IFR CIGS LIKELY DEVELOPING AFTER MIDNIGHT WITH THE ONSET OF STRONGER WEDGING. THINK SOME DRIZZLE ALSO POSSIBLE ALONG THE BLUE RIDGE ESPCLY KROA/KBCB NEAR DAWN WITH PATCHY DENSE FOG MIXED IN AND ACROSS THE DEEPER WESTERN VALLEYS LATE. EXTENDED AVIATION DISCUSSION... HIGH PRESSURE WILL DOMINATE THE WEATHER THROUGH THE END OF THE WEEK WITH LITTLE OR NO PRECIPITATION. EXPECT MAINLY VFR CONDITIONS OUTSIDE ANY FOG AT NIGHT AND POTENTIAL FOR SOME LOW LEVEL STRATUS ALONG AND EAST OF ROA/BCB...THOUGH THE HIGH PRESSURE SHOULD BE STRONG ENOUGH TO KEEP MOISTURE LIMITED. PRESENCE OF SUBSIDENCE INVERSION ALOFT WILL LIKELY RESULT IN CLOUD LAYER PERSISTING BETWEEN 040-060KFT...SO IT WILL NOT BE ENTIRELY CLEAR. NEXT UPSTREAM TROUGH AND FRONT EXPECTED TO ARRIVE BY EARLY NEXT WEEK WITH A THREAT OF SHOWERS MAINLY LATE SUNDAY NIGHT INTO MONDAY. MAY SEE SOME MVFR CIGS/VSBYS WITHIN A BAND OF SHOWERS DURING THAT PERIOD BUT APPEARS MOST OF THE TIME WILL CONTINUE TO SEE VFR. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/WP NEAR TERM...JH/KK SHORT TERM...RCS LONG TERM...AMS/RCS AVIATION...JH/PM

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