Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 071953 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 353 PM EDT MON JUL 7 2014 .SYNOPSIS...
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A COLD FRONT WILL APPROACH FROM THE NORTHWEST TUESDAY AND SPILL SLOWLY SOUTHEAST INTO THE AREA ON WEDNESDAY. THIS COMBINED WITH DAYTIME HEATING AND INCREASING MOISTURE...WILL BRING AN INCREASING THREAT FOR SCATTERED SHOWERS AND THUNDERSTORMS...FIRST IN THE FAR WEST TUESDAY...AND THEN FOR MUCH OF THE AREA BY WEDNESDAY. THE FRONT WILL STRUGGLE TO CLEAR THE PIEDMONT AREAS ON THURSDAY.
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&& .NEAR TERM /THROUGH TUESDAY/...
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AS OF 350 PM EDT MONDAY... INCREASING MOISTURE IN SW FLOW THIS AFTERNOON WITH EXPANSICE CU FIELD ACROSS MOST AREAS...BUT AT 330 PM EDT RADAR SHOWING NO ECHOES IN BLACKSBURG CWA...CLOSEST IN FAR SOUTHERN NC. WILL KEEP A SLIGHT CHC POP FOR LATE AFTERNOON THROUGH SOME OF EVENING AND EXPAND A LITTLE FARTHER NORTH MAINLY ALONG BLUE RIDGE AND ALSO HIGHER ELEVATIONS OF GREENBRIER AND ALLEGHANY HIGHLANDS GIVEN WHERE MAX SBCAPES ARE THIS AFTERNOON AND LATEST HRRR SUGGESTING ANY ISOLD POP UPS NOW MORE ACROSS CENTRAL PART OF FCST AREA. LOW CONFIDENCE THAT ANYTHING WILL ACTUALLY POP UP...AND ANY CELLS MAY NOT EVEN BE ABLE TO PRODUCE THUNDER...BUT DO NOT FEEL COMFORTABLE WITH NOTHING MENTIONED IN THESE AREAS THROUGH THIS EVENING. OTHERWISE ANY CONVECTION WILL DIE QUICKLY WITH LOSS OF HEATING AND LOOKING AT TRENDS IN CONVECTION UPSTREAM VIA SATELLITE AND RADAR...THINKING THAT MOST MODELS OVERDOING AMOUNT OF CONVECTION AND THUS DEBRIS CLOUDINESS THAT COULD REACH INTO FAR WESTERN PORTIONS LATER TONIGHT. ONLY MODELS THAT SUGGESTION SOME LINGERING ACTIVITY SNEAKING INTO FAR WEST ARE THE ONES THAT TEND TO OVERDUE IT...AND INSTABILITY AFTER MIDNIGHT IS NON-EXISTANT...SO MAINTAINING ONLY A VERY SLIGHT CHC POP FAR NW LATE TONIGHT AND TRENDED DOWN ON CLOUD COVER A BIT MOST OF THE OVERNIGHT ACROSS THE WEST...WITH MOSTLY CLEAR ALL FAR BUT FAR WESTERN FRINGES. WENT WITH COOLER GUIDANCE AGAIN FOR LOWS...BUT STILL A BIT MILDER THAN PREVIOUS NIGHT...ESPECIALLY WEST WHERE THERE WILL BE A LITTLE CLOUD COVER MOVING IN LATE. TUESDAY CONVECTIVE CHANCES AND TIMING IS TOUGH WITH FRONT APPROACHING FROM WEST LATE BUT EFFECTIVE DAYTIME HEATING EARLY WITH LITTLE CAP TO HOLD CONVECTION BACK. THINKING THAT SOME ISOLATED CONVECTION COULD FIRE OVER HIGHER TERRAIN FROM BLUE RIDGE WEST RATHER EARLY...PERHAPS BY NOON...BUT MID LEVEL DRY AIR INITIALLY WILL KEEP THIS LIMITED. THEN WITH INCREASING SHEAR AND FORCING BACK ALONG FRONT TO THE WEST...MORE ORGANIZZED CONVECTION EXPECTED TO MOVE IN LATE. SOME HIGH RES MODELS AS WELL AS NAM SUGGEST TWO SEPARATE WAVES...WITH ONE BROKEN LINE OR CLUSTERS MOVING IN TO SE WV BY LATE AFTERNOON BUT WEAKENING QUICKLY ON WESTERN SLOPES...WITH ANOTHER PERHAPS MORE SIGNIFICANT LINE OF STORMS MOVING THROUGH KENTUCKY BY EVENING AND APPROACHING FAR SW VA AND NW NC LATER IN THE EVENING...BUT ALSO WEAKENING QUICKLY DUE LARGELY TO LOSS OF INSTABILITY. OVERALL LOW CONFIDENCE IN THESE DETAILS...BUT TRENDED TOWARD SLOWER ARRIVAL OF MID CHC TO LIKELY POPS UNTIL VERY LATE IN THE DAY...WITH OTHERWISE SLIGHT CHC FROM FOOTHILLS WEST FROM MIDDAY ON. GIVEN LATE TIMING AND WEAKENING NATURE OF STORMS...THINK SEVERE POTENTIAL IS LOW...BUT NOT ZERO. SPC SLIGHT RISK INTO WESTERN THIRD OF AREA WOULD BE MAINLY FOR EVENING...AND THINK THIS WOULD MAINLY BE FOR DAMAGING WINDS AS MOST DEEPER CORES WILL BE COLLAPSING AS THEY MOVE INTO OUR AREA...AND LINE CLUSTERS AND BOWING SEGMENTS ARE MOST LIKELY STORM MODE. ANY ISOLD CONVECTION AHEAD OF THIS EARLIER IN UNCAPPED ENVIRONMENT IS NOT LIKELY TO REACH SEVERE LIMITS. ANOTHER HOT DAY IN THE EAST WITH HIGHS AGAIN IN THE 90S AIDED BY SOME DOWNSLOPE AND LITTLE CHANCE FOR PRECIP AND MUCH IN THE WAY OF CLOUD COVER...AND LOW TO MID 80S IN WEST WITH LESS CONFIDENCE IN SOME OF THESE HIGHS SINCE IT WILL DEPEND ON CLOUD COVER AND CONVECTIVE COVERAGE AND TIMING.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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AS OF 330 EDT MONDAY... ALTHOUGH A BULK OF THE BEST VORTICITY ADVECTION REMAINS NORTHWEST OF THE FORECAST AREA...UPPER TROF AXIS CROSSES THE REGION ON WEDNESDAY AND MODELS STILL SHOWED FORECAST AREA IN THE RIGHT REAR QUADRANT OF THE UPPER JET TUESDAY NIGHT AND WEDNESDAY. WILL KEEP THESE TWO PERIODS AS THE TIME WITH THE HIGHEST PROBABILITY OF PRECIPITATION. CLOUDS WILL LIMIT TEMPERATURE DROP TUESDAY NIGHT AND AMOUNT OF INSTABILITY ON WEDNESDAY. WHILE THE SYNOPTIC FORCING IS GOOD...THE LACK OF HEATING WEDNESDAY MORNING AND DOWNSLOPING FROM A WEST WIND MAY SUPPRESS THE COVERAGE OF THUNDERSTORMS IN ALL BUT THE FAR SOUTHEAST COUNTY WARNING AREA...DEPENDING ON WHERE OUTFLOW FROM THUNDERSTORMS ON TUESDAY END UP. HAVE LOWERED CHANCE IN THE NORTHWEST. BY WEDNESDAY NIGHT THE COLD FRONT WILL BE THROUGH THE FORECAST AREA ENOUGH TO CONFINE PROBABILITY OF PRECIPITATION TO THE FAR SOUTHEAST BUT DURING THE DAY THURSDAY WEAK EAST FLOW MAY BE ENOUGH TO TRIGGER SHOWERS AND THUNDERSTORMS ALONG THE FOOTHILLS AND INTO THE PIEDMONT.
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&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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AS OF 300 PM EDT MONDAY... UPPER PATTERN IS AGAIN BECOMING ZONAL THURSDAY NIGHT AND FRIDAY BUT MODELS WERE BRINGING A SHORT WAVE THROUGH THE BASE OF THE EASTERN TROF AND ACROSS THE MID ATLANTIC REGION THURSDAY NIGHT. THE 500 MB TROF DEEPENS AGAIN ON SUNDAY AND MONDAY. SURFACE FRONT IS WELL TO THE SOUTHEAST OF THE FORECAST AREA THURSDAY NIGHT AND FRIDAY BUT ANY WAVE ALONG THE FRONT MAY BRING DEEPER MOISTURE AND A HIGHER PROBABILITY OF PRECIPITATION BACK TOWARD THE SOUTHERN COUNTY WARNING AREA. FORECAST AREA WILL RETURN TO WARM...HUMID...UNSTABLE AIR...AND THE ASSOCIATED CHANCE OF THUNDERSTORMS...SUNDAY AND MONDAY AHEAD OF THE NEXT COLD FRONT.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/... AS OF 130 PM EDT MONDAY... MED/HIGH CONFIDENCE FORECAST THIS TAF PERIOD. COMMS ISSUES REMAIN AT KDAN DESPITE AN INTERMITTENT RETURN OF OBSERVATION DATA. AMD NOT SKED CONTINUED IN THE TAF...ALTHOUGH VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. LOOKS LIKE QUIET WEATHER WILL HOLD THROUGH THIS TAF PERIOD. THERE MAY BE SOME ISOLATED SHOWERS IN THE MTNS THIS AFTERNOON BUT HAVE NO EXPECTATIONS THAT ANYTHING WILL AFFECT TAF SITES. PREFER THE WAY NAM AND LOCAL WRF ARE HANDLING LOW LEVEL MOISTURE FIELDS SO WILL LEAN ON THEM FOR CLOUD TRENDS. EXPECT BURST OF CU THIS AFTERNOON TO SCATTER OUT BUT MAY SEE A PERIOD OF VFR CIGS FROM THE BLUE RIDGE WWD. LOW LEVEL THTE FIELDS SHOW A SEPARATION BETWEEN SOME MOISTURE RUNNING UP THROUGH THE PIEDMONT TONIGHT AND MOISTURE ASSOCIATED WITH APPROACHING FRONT FROM THE NW. KDAN MAY SEE A PERIOD OF BKN VFR CIGS OVERNIGHT WITH THE PIEDMONT MOISTURE AND BELIEVE SCT CLOUDS WILL HOLD ELSEWHERE...BUT KLWB AND KBLF WILL SEE BORDERLINE VFR CIGS BY DAYBREAK. ANTICIPATING LOW/MID LEVEL CLOUDS MOVING IN FROM THE WEST AND THIS MAY HELP KEEP FOG FORMATION IN CHECK TONIGHT AT KLWB AND KBCB...BUT IF CLOUDS DO NOT MATERIALIZE FOG MAY BE MORE AGGRESIVE THAN INDICATED. EXPECTING VARIABLE CLOUDS AFTER DAYBREAK TOMORROW BUT CU SHOULD DEVELOP INTO A BORDERLINE VFR CIG BY LATE MORNING KBCB/KBLF/KLWB. BELIEVE BETTER CHANCES FOR CONVECTIVE PCPN WILL BE VERY LATE IN THE TAF PERIOD AND BEYOND SO WILL NOT MUDDY THE WATERS AND KEEP THINGS DRY WITH THIS ISSUANCE. EXPECT LOW LEVEL FLOW FROM THE SW TO KEEP GUSTY CONDITIONS AT TAF SITES WITH A DIURNAL BIAS. SW IS A PREFERED DIRECTION FOR KBLF SO WILL KEEP WINDS UP A BIT THERE OVERNIGHT. EXTENDED AVIATION... BEST CHANCE FOR THUNDERSTORMS LOOKS TO BE ON WEDNESDAY WITH THE BEST PUSH OF UPPER DYNAMICS TO NUDGE THE SFC BOUNDARY THROUGH THE AREA. BUT THE FRONT WILL LINGER IN OUR VICINITY THROUGH THE END OF THE WEEK WITH IMPULSES RIDING ALONG IT. THIS WILL KEEP UNSETTLED CONDITIONS AT TAF SITES THROUGH THE END OF THE WEEK. EXPECT DIURNAL TRENDS FOR AFTERNOON CONVECTIVE PRECIPITATION WITH ASSOCIATED MVFR OR LOWER CONDITIONS... ESPECIALLY FOR KDAN/KLYH...AND POSSIBLE IFR FOG LATE NIGHTS...MAINLY KBCB AND KLWB. && .EQUIPMENT... COMMS ISSUES WITH KDAN ASOS TRANSMITTING OUT. THE FAA IS AWARE OF THE OUTAGE AND WILL BE WORKING ON IT...BUT NO ESTIMATED TIME OF WHEN IT WILL BE WORKING AGAIN. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/SK NEAR TERM...SK SHORT TERM...AMS LONG TERM...AMS AVIATION...JH/MBS/NF EQUIPMENT...WP

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