Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 131954
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
354 PM EDT SAT SEP 13 2014

.SYNOPSIS...
HIGH PRESSURE WILL PASS FROM THE GREAT LAKES TO NEW ENGLAND
TONIGHT...AND THEN BUILD SWEETHEART ACROSS THE MID ATLANTIC FOR
SUNDAY. WARMER WEATHER RETURNS FOR MONDAY AS HIGH PRESSURE MOVES
OFFSHORE...ALLOWING WINDS TO SHIFT SOUTHWESTERLY. THE NEXT COLD
FRONT MOVES THROUGH EARLY TUESDAY MORNING BRINGING COOLER THAN
NORMAL TEMPERATURES FOR THE REMAINDER OF THE WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 345 PM EDT SATURDAY...

FORECAST AREA REMAINS IN THE ZONAL FLOW SOUTH OF THE ACTIVE NORTHERN
JET STREAM. NO ORGANIZED SYNOPTIC SYSTEMS TONIGHT OR SUNDAY WITH
ONLY A SLIGHT COOLING TREND. 850 MB TEMPERATURES DROP INTO THE +10
TO +12 RANGE ON SUNDAY.

DRIER AIR SEEN ON WATER VAPOR LOOP MOVES INTO THE NORTHERN COUNTY
WARNING AREA TONIGHT. ZONAL FLOW KEEPS MOISTURE...ESPECIALLY BELOW
700 MB...OVER EXTREME SOUTHERN VIRGINIA AND NORTHERN NORTH CAROLINA.
WONT SEE MUCH DRYING AT LOW LEVEL EITHER. MODELS KEEP MOISTURE OVER
THE MOUNTAINS THROUGH SUNDAY...BUT DO SHOW SOME POSSIBLE DRYING IN
THE EAST BY SUNDAY AFTERNOON.

AFTER A BRIEF PERIOD OF SURFACE AND LOW LEVEL WEST WINDS
TONIGHT...HIGH PRESSURE WILL BUILDING BACK SOUTH DOWN THE EAST COAST
SUNDAY. BUFKIT FROM THE NAM/SREF SUGGEST A SHALLOW LAYER OF LOW
LEVEL UPSLOPE WINDS...MAINLY BELOW 850 MB...WILL DEVELOP SHORTLY
AFTER MIDNIGHT AND CONTINUE THROUGH MIND MORNING.

FOR SUNDAY AFTERNOON MODELS VEER SHOWING MOISTURE MOVING BACK NORTH
AND A RETURN OF INSTABILITY INTO THE FAR SOUTHWEST COUNTY WARNING
AREA. WILL KEEP PROBABILITY OF PRECIPITATION IN THE SOUTHWEST AND
REMOVE IN THE SOUTHEAST AND NORTHWEST.

LOCAL WRF BRINGS LOWER TO MID 50S SURFACE DEW POINTS INTO THE
SOUTHERN COUNTY WARNING AREA BY SUNDAY AFTERNOON. BUT IT HAS GONE
DOWN THAT PATH BEFORE. MORE BELIEVABLE WOULD BE DRIER DEW POINTS IN
THE NORTH AND A MUCH SMALLER DROP IN THE SOUTH.
&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF 345 PM EDT SATURDAY...

WITH WEAK HIGH PRESSURE BUILDING INTO THE AREA SUNDAY NIGHT...ANY
LINGERING EVENING PRECIPITATION SHOULD WANE. SKIES WILL REMAIN
MOSTLY CLOUDY...WHICH SHOULD KEEP LOW TEMPS WARMER THAN GUIDANCE
VALUES.

ON MONDAY...OUR FOCUS TURNS TO AN APPROACHING UPPER LEVEL SHORTWAVE
THAT WILL MOVE INTO THE GREAT LAKES BY 00Z (8 PM EDT) TUESDAY. IN
ADVANCE OF THIS FEATURE...PWAT VALUES VALUES SURGE AND INSTABILITY
INCREASES. IN ADDITION...NAM/ECMWF/GFS ALL SHOW A WEAK UPPER LEVEL
WAVE PASSING OVER OUR AREA IN ADVANCE OF THE GREAT LAKES WAVE. ALL
OF THIS SPELLS SCATTERED SHOWERS AND EVEN A FEW
THUNDERSTORMS....ESPECIALLY ACROSS THE SOUTHERN BLUE RIDGE WHERE LOW
LEVEL CONVERGENCE WILL BE THE GREATEST.

DESPITE A PARTLY SUNNY SKY...PUSHED HIGHS UP A COUPLE OF DEGREES
WITH GOOD WAA IN ADVANCE OF THE APPROACHING SYSTEM.

HIGHEST POPS DURING THE SHORT TERM PERIOD WILL BE MONDAY
NIGHT...ASSOCIATED WITH THE COLD FRONT THAT MOVES THROUGH OUR AREA.
PRECIP WILL ALSO BE AIDED BY UPPER LEVEL SUPPORT IN THE FORM OF RR
QUAD OF DEPARTING UPPER LEVEL JET. THE NAM WAS CONSIDERABLY SLOWER
COMPARED TO THE SREF/GFS/ECMWF AND WAS NOT USED.

NORTHWEST WINDS BEHIND THE FRONT WILL GENERATE A FEW UPSLOPE SHOWERS
IN SE WV EARLY...BUT A LARGE MAJORITY OF THE FORECAST AREA WILL BE
DRY ON TUESDAY. COLD AIR WILL BE LACKING BEHIND THIS FRONT...AND
WITH DOWNSLOPING WINDS FOR THE EASTERN PORTION OF OUR FORECAST
AREA...PUSHED HIGHS UP A COUPLE OF DEGREES EAST OF THE BLUE RIDGE.&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 345 PM EDT FRIDAY...

MEDIUM RANGE MODELS...AS WELL AS THE GFS/ECMWF MODEL ENSEMBLE MEANS
AGREE THAT A BROAD UPPER TROF WILL COVER THE EASTERN U.S. THROUGH
THE LONG TERM PERIOD. THERE ARE DIFFERENCES IN THE
MODELS...HOWEVER...ON THE AMPLITUDE OF THE TROF. THIS LOOKS TO KEEP
A WEDGE OF HIGH PRESSURE IN PLACE THROUGH MUCH OF THE LONG TERM
PERIOD...WITH A LOW LEVEL EASTERLY FLOW.

AS HIGH PRESSURE BUILDS ON WEDNESDAY...A LOW LEVEL EASTERLY FLOW
DEVELOPS...ADVECTING HIGHER THETA-E AIR INTO REGION. LOW LEVEL
CONVERGENCE IN THE MOUNTAINS...MAY SPARK SCATTERED SHOWERS. ON THE
WEST SIDE OF THE EAST FLOW...ISOLATED THUNDER ALSO BE POSSIBLE. THIS
PATTERN CONTINUES ON THURSDAY. TEMPS FOR WEDNESDAY AND THURSDAY WILL
BE HIGHLY DEPENDENT ON CLOUD COVER. WITH THE POTENTIAL FOR LOW
CLOUDS IN EASTERLY FLOW...TRENDED TOWARD THE COOLER ECMWF GUIDANCE
FOR TEMPS DURING THIS PERIOD.

ECMWF AND GFS BOTH STRENGTHEN THE WEDGE ON FRIDAY...WHICH WILL BRING
COOLER TEMPS TO THE AREA...AND PUSHES MOISTURE SOUTH AND WEST.
CONTINUED TO LEAN TOWARD COOLER ECMWF VALUES FOR HIGHS. MODELS HINTS
AT ANOTHER UPPER LEVEL SYSTEM MOVING INTO THE REGION EARLY NEXT
WEEKEND...THAT WOULD REINFORCE THE UPPER LEVEL TROF OVER OUR AREA.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
AS OF 100 PM EDT SATURDAY...

WEAK SFC FRONT CONTINUES TO PUSH THROUGH THE AREA AS HIGH PRESSURE
BUILDING INTO THE OHIO VALLEY FLOPS OVER THE TOP OF US THROUGH
TOMORROW. THIS WILL GIVE US A BIT OF NW FLOW WEATHER EARLY...WITH
WINDS ONCE AGAIN BECOMING E/NELY AND SOME MOISTURE RETURN ALONG THE
BLUE RIDGE.

EAST OF THE BLUE RIDGE FOR KLYH AND KDAN...EXPECT CIGS TO RISE AOA
VFR LEVELS DURING THE FIRST PART OF THE TAF PERIOD WITH KDAN TAKING
THE LONGEST. OVERNIGHT NELY FLOW RETURNS BUT INDICATIONS ARE THAT
LOWER CIGS WILL SKIRT THE AREA. WILL GO OPTIMISTIC AND INDICATE
ONLY VFR BUT KDAN STANDS THE BETTER CHANCE OF SEEING SOME MVFR
CIGS OVERNIGHT.

ALONG THE BLUE RIDGE FOR KBCB AND KROA...EXPECTING SOME IMPROVEMENT TO
VFR THIS AFTERNOON. BUT AS LIGHT WIND BECOMES E/NELY MOISTURE RUNNING UP
THE SLOPES WILL LIKELY GENERATE A RETURN TO LOWER CIGS. KBCB MAY ALSO SEE
SOME DRIZZLE AND -SHRA AS THE MOISTURE LOOKS TO BE GREATER HERE AND WILL
COMBINE WITH SOME WAA ALOFT TO SQUEEZE OUT SOME PCPN.

WEST OF THE BLUE RIDGE...EXPECT KBLF TO STAY LOCKED INTO LOW CIGS WITH A
SLIGHT LIFT FROM IFR TO MVFR THIS EVENING BEFORE GOING BACK TO IFR AS DEEPER
MOISTURE AND PREVIOUSLY MENTIONED WAA ARRIVE. KLWB MAY SCATTER OUT THIS
EVENING...LEADING TO THE QUESTION OF HOW MUCH RADIATION CAN TAKE PLACE TO
GENERATE FOG/STRATUS. IT SEEMS LIGHT NE FLOW WILL ENTER KLWB DURING PRIME
FOG TIME SO THIS MAY KEEP THINGS FROM BOTTOMING OUT. WILL INDICATE THIS BUT
THE SITUATION COULD GO EITHER WAY.

EXTENDED AVIATION DISCUSSION...
BUT OVERALL CONDITIONS SHOULD BE MOSTLY MVFR...WITH LESS IFR OR
WORSE CIGS/VSBYS. BEYOND SUNDAY...BROAD UPPER TROUGH DEVELOPING
ACROSS THE NORTHERN STATES...WITH THE RNK CWA ON THE SOUTHERN EDGE
OF THIS BROAD UPPER TROUGH...LEADING TO PRIMARILY CONTINUED ZONAL
FLOW. LATEST MODEL TRENDS BEGINNING TO FAVOR POTENTIAL CHANGE TO A
MORE NW FLOW ALOFT AS THE WEEK PROGRESSES...WHICH SHOULD ATTEMPT
TO PUSH THE PESKY DEEP MOISTURE FURTHER SOUTH AWAY FROM THE
REGION. OVERALL...EXPECT MVFR CONDITIONS TO PERSIST INTO MONDAY AS
AFOREMENTIONED UPPER TROUGH BRINGS MORE CLOUDS AND SHOWERS TO THE
REGION.

&&

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

&&

$$
SYNOPSIS...PH
NEAR TERM...AMS
SHORT TERM...PH
LONG TERM...PH
AVIATION...MBS



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