Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 291126
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
726 AM EDT FRI MAY 29 2015

.SYNOPSIS...
HIGH PRESSURE OFFSHORE WILL MAINTAIN A MOIST SOUTHERLY FLOW ACROSS
THE REGION TODAY 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 DRIER CONDITIONS WILL
THEN BUILD IN FROM THE NORTH BY THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 220 AM EDT FRIDAY...

OVERALL PERSISTENCE FORECAST LOOKS IN ORDER TODAY WITH CONTINUED
MOISTURE FEED ON SE FLOW BETWEEN HIGH PRESSURE WELL OFFSHORE AND THE
NEXT UPPER TROUGH WELL TO THE WEST. FOCUS AGAIN OTHER THAN FOR
OROGRAPHICS AND RESIDUAL OUTFLOW LOOKS WEAK WITH ONLY A FAINT
BOUNDARY ACROSS THE NORTH TO HELP WITH ADDED FORCING THIS
AFTERNOON. HOWEVER MOST LATEST SHORT TERM GUIDANCE SHOWS A BIT
FASTER DEVELOPMENT MAINLY ACROSS THE NW AND BLUE RIDGE BY EARLY
AFTERNOON...WITH BEST COVERAGE PROGGED OVER THE VA HIGHLANDS INTO
THE GREENBRIER VALLEY WHERE CLOSER TO THE RESIDUAL FRONT. IN
ADDITION...GOOD POOLING OF HIGHER 85H THETA-E PROGGED ALONG THE
EASTERN SLOPES OF THE BLUE RIDGE GIVEN SE FLOW...BUT MORE DRYING
SE AS WEAK SUBSIDENCE TOWARD THE COAST WORKS TO THE NW. THUS WILL
BUMP UP TO A PERIOD OF LIKELY POPS WEST-NW BY MID AFTERNOON GIVEN
COMBO OF MOISTURE...WEAK CONVERGENCE AND PROGGED CAPES OF 1-2K
J/KG LATER ON. OTRW MAINLY MID TO HIGH CHANCE POPS ELSEWHERE...EXCEPT
ONLY ISOLATED COVERAGE FAR SE. WEAK STEERING AGAIN UNDER HIGH
PWATS SUGGESTS MORE HEAVY RAIN POTENTIAL WITH PERHAPS A BIT HIGHER
CHANCE OF A FEW STRONGER PULSE NATURE CELLS PER SOME DRYING ALOFT
SEEN ON FORECAST RAOBS. KEPT TEMPS CLOSER TO THE WARMER MET MOS
EAST WHERE EXPECT LESS CONVECTION AFTER EARLY ISOLATED SHRA
FADE...WHILE TRENDING A LITTLE MORE TOWARD THE MAV VALUES BLUE
RIDGE...AND POINTS NORTH GIVEN SE FLOW AND ANTICIPATED BETTER
SHOWER COVERAGE.

MODELS SUGGEST SWATH OF DEEPER MOISTURE TO PUSH NW THIS EVENING AS
BETTER CONVERGENCE DEVELOPS WELL WEST OF THE MOUNTAINS AHEAD OF THE
NEXT COLD FRONT. THIS SHOULD ALLOW AN AREA OF WEAK SINKING MOTION TO
ADVECT OVER MOST OF THE REGION ESPCLY AFTER MIDNIGHT BRINGING AN END TO
ANY EVENING CONVECTION MAINLY NW. HOWEVER PENDING AFTERNOON
COVERAGE...WILL LEAVE IN SOME DECENT CHANCE POPS MOUNTAINS TO INIT THIS
EVENING BEFORE CUTTING BACK TO JUST PC INCLUDING SOME PATCHY FOG LATE.
LOWS MOSTLY IN THE 60S BUT LIKELY NOT QUITE AS MUGGY GIVEN SOME SLIGHT
DECREASE IN DEWPOINTS OVERNIGHT AS DEEP MOISTURE EXITS.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
AS OF 230 AM EDT FRIDAY

THE UPPER RIDGE ACROSS THE EASTERN U.S. EARLY SATURDAY GRADUALLY
FLATTENS BY EARLY NEXT WEEK AS SHORTWAVE ENERGY MOVES INTO THE
NORTHERN GREAT LAKES.

FOR SATURDAY...CONVECTION SHOULD BE DIURNALLY DRIVEN...BUT COVERAGE
IS EXPECTED TO BE LESS AS DRY AIR SEEN ACROSS SOUTH GEORGIA AND N.
FLORIDA LIFTS NORTH INTO OUR AREA AROUND THE LARGE ATLANTIC HIGH. AS
A RESULT...PWAT VALUES ARE EXPECTED TO BE SLIGHTLY LOWER.  THIS
SLIGHTLY DRIER AIRMASS COMBINED WITH WARMING 850MB TEMPS IN ADVANCE
OF AN APPROACHING SFC FRONT SHOULD ALLOW TEMPS TO BE A COUPLE OF
DEGREES WARMER THAN FRIDAY.

ON SUNDAY...HIGHER PWAT AIR SURGES BACK INTO THE REGION IN ADVANCE
OF A COLD FRONT. MEDIUM RANGE MODELS DIFFER ON THE FORECAST LOCATION
OF THE FRONT...WITH THE NAM MUCH SLOWER COMPARED TO THE GFS AND 12Z
ECMWF. INCREASING FORCING ASSOCIATED WITH THIS BOUNDARY WILL BRING
INCREASED COVERAGE IN PRECIP TO THE REGION...AND MORE ORGANIZED
STORMS. THEREFORE PUSHED POPS INTO HIGH CHANCE TO NEAR LIKELY ON
SUNDAY.

TEMPS COULD AGAIN BE VERY WARM WITH WARMING AHEAD OF THE LOW LEVEL
BOUNDARY AND 850MB THERMAL RIDGE OVER THE REGION...ESPECIALLY IN THE
EAST WHERE CLOUD COVER IS EXPECTED TO BE LESS. BUMPED UP TEMPS A
COUPLE OF DEGREES FOR HIGHS.

IF THE LATEST GFS VERIFIES...HIGH PRESSURE WEDGING SOUTH WILL PUSH
THE COLD FRONT SOUTH OF OUR AREA MONDAY...LEAVING BEST CONVERGENCE
AND  CHANCES FOR PRECIP TO THE SOUTH ALONG WITH COOLER TEMPS. FOR
NOW...LEANED TOWARD THE ECMWF WHICH KEEPS THE BOUNDARY IN OUR AREA
AND LEAVING THE SOUTHERN HALF OF OUR AREA IN THE WARM SECTOR. EVEN
WITH THE MORE AGGRESSIVE GFS...PRECIP COVERAGE SHOULD BE FAIRLY
WIDESPREAD WITH WEAK OVERRUNNING...AND A WAVE OF LOW PRESSURE
MOVING ALONG THE BOUNDARY THROUGH OUR AREA.

&&

.LONG TERM /MONDAY NIGHT 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 /12Z FRIDAY THROUGH TUESDAY/...
AS OF 650 AM EDT FRIDAY...

FOG REMAINS QUITE SPOTTY ACROSS THE REGION WITH VARYING DEGREES OF
LOWER VSBYS RANGING FROM MVFR/IFR IN SPOTS NEAR THE TAF SITES TO
UNLIMITED VSBY UNDER MID DECK IN OTHERS. MAY STILL SEE FOG DRIFT
ACROSS ANY OF THE VALLEY LOCATIONS DURING THE NEXT HOUR OR TWO
RESULTING IN BRIEF IFR/LIFR VSBY BEFORE THE FOG QUICKLY BURNS OFF
BY MID MORNING IF NOT SOONER.

THIS 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 APPEARS BASED ON LATEST
GUIDANCE THAT THE WEST WILL HAVE THE BEST SHOT AT SEEING THE MORE
WIDESPREAD CONVECTION...KEPT A PREVAILING MVFR SHRA GROUP WITH
VCTS MENTION AT BOTH KBLF/KLWB THIS AFTERNOON...AND LEFT IN VCTS
AT ALL SITES EXCEPT FOR KDAN WHERE THINK CHANCES ARE LESS WITHIN
THE SE FLOW.

A FEW SHRA/TSRA MAY LINGER ALONG THE KBLF-KLWB CORRIDOR THIS
EVENING BEFORE MOISTURE DECREASES OVERNIGHT. THIS MAY RESULT IN
SOME LINGERING MVFR IN SHRA OVER THE WEST THIS EVENING BEFORE ALL
BRIEFLY RETURN TO VFR IN SCTD/BKN STRATO-CU AND MID DECK. ONCE THE
SHOWERS END AND SKIES CLEAR A BIT EXPECTING ANOTHER ROUND OF FOG
ESPCLY IN THE VALLEYS AND WHERE EARLIER RAINFALL OCCURRED. THIS
SUPPORTS MORE WIDESPREAD IFR/LIFR ACROSS THE WESTERN VALLEYS WITH
ONLY PATCHY COVERAGE IN THE EAST INCLUDING KROA.

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 MONDAY NIGHT WITH LOWER
CIGS/VSBY REDUCTIONS DUE TO SHOWERS/STORMS DURING THE DAY...AND IN
FOG OVERNIGHT INTO THE EARLY MORNING HOURS EACH DAY. MAY SEE
ENOUGH DRYING TO BRING AN END TO SHOWERS ON TUESDAY WHILE LOWER
MVFR/IFR CIGS LIKELY SLOW TO IMPROVE WITH EASTERLY FLOW AND
WEDGING IN PLACE.

&&

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

&&

$$
SYNOPSIS...JH
NEAR TERM...JH
SHORT TERM...PH
LONG TERM...AMS
AVIATION...JH/MBS/WERT


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