Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 032002
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
402 PM EDT THU SEP 3 2015

.SYNOPSIS...
A BACKDOOR COLD FRONT WILL APPROACH THE REGION TONIGHT AND FRIDAY
AND CROSS THE AREA FRIDAY NIGHT INTO SATURDAY. ANTICIPATE INCREASING
CHANCES OF SHOWERS AND STORMS ON FRIDAY...THAT WILL CONTINUE INTO
EARLY SATURDAY. COOLER AND SOMEWHAT DRIER WEATHER IS EXPECTED
TOWARDS THE END OF THE WEEKEND INTO EARLY NEXT WEEK. A RESURGENCE OF
ATLANTIC MOISTURE RETURNS TO THE AREA BY THE MIDDLE PART OF NEXT
WEEK.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 230 PM EDT FRIDAY...

ISOLATED TO SCATTERED SHOWERS AND STORMS CONTINUE TO DEVELOP ALONG
AND WEST OF THE CREST OF THE BLUE RIDGE WHERE SURFACE BASED CAPE HAS
INCREASED INTO THE 2000 - 2500 JOULES PER KILOGRAM RANGE. EAST OF
THE CREST OF THE BLUE RIDGE...VALUES WERE MAINLY STILL UNDER 1000
JOULES PER KILOGRAM. OUR UPCOMING FORECAST WILL CONTINUE TO REFLECT
THAT OF THE ONGOING FORECAST. WE ARE EXPECTING A GENERAL TREND FOR
THE ACTIVITY TO CONTINUE IS SOUTHERLY PROGRESSION THROUGH THE
EVENING WITH ISOLATED COVERAGE EXPECTED EAST OF THE CREST OF THE
BLUE RIDGE BY THIS EVENING. AT THE SAME TIME...THE SCATTERED
COVERAGE ACROSS THIS MOUNTAINS WILL ALSO BE TRENDING TO ISOLATED
COVERAGE.

OVERNIGHT INTO FRIDAY...WE ARE EXPECTING THE LOW LEVEL FLOW TO TREND
MORE NORTHEAST...AND EVENTUALLY MORE EASTERLY TOWARDS LATE IN THE
DAY FRIDAY. THIS WILL HAVE THE INFLUENCE OF EVENTUALLY BRINGING
INCREASING ATLANTIC MOISTURE INTO THE REGION. THE RESULT WILL BE A
TREND TOWARDS MORE CLOUD COVER...AND PATCHY RAIN SHOWERS VERY LATE
TONIGHT INTO EARLY FRIDAY MORNING BECOMING MORE NUMEROUS THROUGHOUT
FRIDAY. TRAJECTORIES BY THE AFTERNOON WILL ALLOW FOR OROGRAPHIC
INFLUENCE ALONG THE BLUE RIDGE...WITH LIKELY PROBABILITY OF
PRECIPITATION BY THE LATE AFTERNOON.

MOUNTAIN AND RIVER VALLEY FOG WILL DEVELOP AGAIN
TONIGHT...ESPECIALLY IN THOSE AREA THAT RECEIVE RAIN TODAY AND THIS
EVENING.

TEMPERATURES WILL CONTINUE TO BE ON THE WARM/HOT SIDE TONIGHT AND
THURSDAY. LOWS TONIGHT WILL RANGE FROM THE LOW TO MID 60S ACROSS THE
MOUNTAINS TO THE MID TO UPPER 60S ACROSS THE FOOTHILLS AND PIEDMONT.
HIGH TEMPERATURES FRIDAY WILL RANGE FROM THE MID 80S ACROSS THE
MOUNTAINS TO THE UPPER 80S TO LOWER 90S ACROSS THE FOOTHILLS AND
PIEDMONT.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 345 PM EDT THURSDAY...

UPPER LOW OVER THE SOUTHEAST UNITED STATES AND WEDGE ALONG THE EAST
SLOPES OF THE APPALACHIANS WILL RESULT IN DEEP EASTERLY WINDS FRIDAY
NIGHT AND SATURDAY. WINDS WILL NOT BE PARTICULARLY STRONG BUT BUFKIT
FORECAST SOUNDINGS AT LYNCHBURG AND DANVILLE INDICATE EAST WINDS
FROM THE SURFACE THROUGH AT LEAST 500MB. BUFKIT WAS ALSO SHOWING
SOME MID LEVEL DRYING ON SUNDAY NIGHT AND MONDAY BUT OVERALL MODELS
WERE NOT AS AGGRESSIVE WITH THE PUSH OF DRIER AIR BEHIND THE BACKDOOR
COLD FRONT AS IN PAST FEW RUNS.

BEST LIFT THROUGH THE PERIOD WILL BE FROM THE UPSLOPE WITH VORTICITY
ADVECTION AND INSTABILITY NOT AS MUCH OF A CONTRIBUTING FACTOR. THIS
WILL MEAN THE HIGHEST PROBABILITY OF PRECIPITATION WILL BE ALONG THE
BLUE RIDGE AND OVER THE FOOTHILLS.

12Z GFS WAS FARTHER EAST WITH RETURN OF LOW LEVEL MOISTURE INTO THE
EASTERN COUNTY WARNING AREA ON SUNDAY. WILL BE FOLLOWING THE GFS
TRENDS FOR CLOUD COVER ON SATURDAY NIGHT AND SUNDAY. WILL BE
TRIMMING BACK THE CHANCE OF THUNDER ON SATURDAY NIGHT AND SUNDAY
WITH THE GUIDANCE SHOWING THE STABLE AIR BEHIND THE FRONT WELL INTO
THE FORECAST AREA. STAYED CLOSER TO COOLER MAV GUIDANCE NUMBERS FOR
MAXIMUM AND MINIMUM TEMPERATURES IN THE WEDGE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 100 PM EDT THURSDAY...

STARTING WITH A BROAD UPPER LOW OVER THE SOUTHEAST UNITED STATES AND
A STRONG RIDGE IN THE SOUTHERN PLAINS ON SUNDAY NIGHT. 500 MB
HEIGHTS FALL OVER THE NORTHEAST UNITED STATES MONDAY THROUGH
WEDNESDAY. BY THURSDAY THE NORTHERN STREAM BECOMES MORE DOMINANT WITH
MORE TROUGHING ACROSS ALL OF THE EAST.

AT THE SURFACE AND LOW LEVELS FORECAST AREA WILL BE IN A DEEP WEDGE
COVERING THE EAST SIDE OF THE APPALACHIANS FRIDAY NIGHT THROUGH
MONDAY WITH EAST TO SOUTHEAST WINDS. THE WEDGE WILL BREAK DOWN ON
TUESDAY. THEN SOUTHWEST FLOW WILL BRING A RETURN OF MOISTURE AND
WARMER 850 MB TEMPERATURES TUESDAY NIGHT AND WEDNESDAY.

A WELL DEFINED COLD FRONT AND THE LEADING EDGE OF COOLER AIR WILL
REACH THE FORECAST AREA ON THURSDAY. WAVES OF LOW PRESSURE ALONG THE
FRONT IN THE CENTRAL UNITED STATES MAY SLOW DOWN THE TIMING AND THE
EASTWARD MOVEMENT OF THE FRONT FOR WEDNESDAY AND THURSDAY.
TEMPERATURES WILL AGAIN BE ABOVE NORMAL IN THE WARM SECTOR AHEAD OF
THE COLD FRONT ON WEDNESDAY AND THURSDAY.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
AS OF 135 PM EDT THURSDAY...

MAINLY VISUAL FLIGHT RULE CONDITIONS EXIST ACROSS THE REGION
CURRENTLY. THE EXCEPTION WILL BE UNDER THE HEAVIER CORES OF THE
ISOLATED TO SCATTERED SHOWERS AND STORMS THAT ARE PROGRESSING
SOUTH THROUGH PARTS OF THE REGION. AS THE REGION CONTINUES TO
DESTABILIZE WITH DAYTIME HEATING...CONFIDENCE HAS INCREASED
ENOUGH TO INCLUDE SUCH A LOWERING OF FLIGHT CATEGORIES AT ROANOKE
BETWEEN 19Z/3PM AND 20Z/4PM WITH THE CLUSTER OF SHOWERS AND STORMS
THAT IS CURRENTLY PROGRESSING SOUTH THROUGH ALLEGHANY COUNTY
VIRGINIA. FOR THE OTHER TERMINAL SITES SAVE DANVILLE...HAVE
INCLUDED ONLY VICINITY OF SHOWERS OR VICINITY OF THUNDER THROUGH
THIS AFTERNOON. IF CONFIDENCE INCREASES THE ACTIVITY TO PASS OVER
A GIVEN AIRPORT...AN ADMENDMENT WILL BE ISSUED.

COVERAGE IS EXPECTED TO INCREASE AS THE AFTERNOON PROGRESSES...AND
GRADUALLY ENTER INTO EASTERN AND SOUTHEASTERN PARTS OF THE REGION
BY THE LATE AFTERNOON AND EARLY EVENING. AT THIS POINT COVERAGE
WILL BEGIN TO WANE...LEAVING ISOLATED COVERAGE BY THE LATE
EVENING.

OVERNIGHT AND INTO EARLY FRIDAY...THE LOW LEVEL FLOW WILL BEGIN TO
TREND NORTHEAST OR EAST...EVENTUALLY ALLOWING FOR A MOISTURE FETCH
OFF THE ATLANTIC. THIS WILL HELP ADVECT CLOUD COVER INTO THE
REGION AND ALSO ALLOW FOR UPSLOPE CLOUD DEVELOP ALONG THE CREST OF
THE BLUE RIDGE. SHOWER AND THUNDERSTORM DEVELOPMENT IS EXPECTED
TO INITIATE BY THE LATE MORNING TO AROUND NOONTIME ON FRIDAY.
CEILINGS WILL MOSTLY BE VISUAL FLIGHT RULES WITH POCKETS OF
MARGINAL VISUAL FLIGHT RULES. MOUNTAIN AND RIVER VALLEY FOG OR
MIST IS AGAIN EXPECTED LATE TONIGHT INTO EARLY FRIDAY...WITH
COVERAGE MORE LIKELY WHERE PRECIPITATION OCCURS THE AFTERNOON AND
EVENING.

EXTENDED AVIATION DISCUSSION...

WILL SEE A WEAK FLOW PATTERN WITH AN UPPER TROUGH EXTENDING FROM
EAST-WEST OVER OUR AREA FRIDAY INTO SUNDAY. THIS ALONG WITH HIGH
PRESSURE TO THE NORTHEAST WILL CAUSE THE LOW LEVEL FLOW TO TURN
MORE EASTERLY IN TIME. AS OF NOW...THE TERMINALS WILL BE VFR
DURING THE DAY...WITH POSSIBLE MVFR OR WORSE WITH FOG AT NIGHT
INTO FRIDAY NIGHT. THE EASTERLY FLOW EXPECTED BY SATURDAY WILL
BRING LOWER CLOUDS IN AND POTENTIAL FOR MVFR CIGS AT LEAST FOR THE
MOUNTAINS...AND LOW END VFR AT KROA/KLYH/KDAN. WITH THIS UPPER
TROUGH THERE WILL BE A DAILY THREAT OF SHOWERS...SO SUB VFR IN
THESE WILL BE POSSIBLE.

BY SUNDAY-MONDAY THE WEAK TROUGH ALOFT MOVES OVER THE SOUTHEAST
COAST WHILE UPPER RIDGING ELONGATES OVER THE MID ATLANTIC. WE WILL
SEE SOME DRYING TAKE PLACE SO VFR SHOULD OCCUR SUNDAY-TUESDAY WITH
THE STILL A THREAT OF FOG AT NIGHT AT KBCB/KLWB.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.

&&

$$
SYNOPSIS...DS
NEAR TERM...DS
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...DS/JH



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