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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1012 PM EDT FRI APR 17 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD INTO THE AREA TONIGHT AND SATURDAY BRINGING 
DRY AND WARM WEATHER FOR THE START OF THE WEEKEND. A COMPLEX STORM 
SYSTEM PASSING TO THE WEST WILL RESULT IN MORE WIDESPREAD RAIN 
SUNDAY INTO SUNDAY NIGHT BEFORE A COLD FRONT CROSSES THE REGION WITH 
A CHANCE OF SHOWERS AND POTENTIALLY STRONG STORMS ON MONDAY. DRY AND 
COOL CONDITIONS WILL PREVAIL FOR THE MIDDLE PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 1012 PM EDT FRIDAY...

ISOLD SHOWERS HAVE DISSIPATED AND SEE NO REASON FOR ANY NEW ONES
TO FIRE UP OVERNIGHT...OTHER THAN ONE OR TWO ACROSS NORTHERN NC
GIVEN MUCAPE VALUES STILL AROUND 300-500 J/KG. ALSO KEEPING AN EYE
ON THE NORTHERN EDGE OF AREA OF SHOWERS INTO SW NC...WHICH IS
AHEAD OF A SHORT WAVE NEAR CHATTANOOGA...AS SOMETHING COULD SNEAK
INTO OUR NW NC MTNS AFTER MIDNIGHT...BUT MOST GUIDANCE AGREES
THIS WILL STAY JUST TO OUR SOUTH. LEFT SLIGHT CHC POP ACROSS
SOUTHERN EDGE OF FCST AREA THROUGH MUCH OF THE NIGHT...BUT REMOVED
MENTION EVERYWHERE ELSE. TRENDS LOOK BETTER FOR MORE CLEARING FROM
WEST LATE...AND THUS POSSIBILITY OF SOME PATCHY VALLEY FOG WITH
WET GROUND SO ADDED THAT AS WELL...MAINLY TO MTN VALLEYS.
OVERNIGHT TEMPS LOOK ON TRACK AT THIS POINT.

PREV DISC AS OF 635 PM EDT FRIDAY...

UPDATE TO REFLECT CURRENT MAINLY ISOLD COVERAGE OF
SHOWERS FROM FOOTHILLS INTO SOUTHSIDE VA. INCLUDED A COUPLE HOURS
OF CHC POPS ACROSS SOUTHSIDE THROUGH EARLY EVENING WITH CLUSTER
OF SHOWERS THERE...AND SO FAR NOT SEEING ANY SIGNS OF EVEN
INTERCLOUD LIGHTNING WITH CELLS NEAR MTV AND DAN...BUT KEEPING
ISOLD THUNDER IN FCST GIVEN SBCAPES OF 500-800 J/KG....AND SOME
ISOL LTG IN CELLS JUST NORTHEAST OF BUCKINGHAM COUNTY. ALL THIS
ACTIVITY SHOULD SLOWLY DIMINISH AS IT DRIFTS SOUTHEASTWARD INTO
FAR NORTHERN NC BY 8 OR 9PM...AND RECENT HRRR RUNS SEEM TO BE
DOING A BETTER JOB CAPTURING THE SPARSITY OF THE SHALLOW
CONVECTION AND WEAKENING INTO THE EVENING HOURS WITH LOSS OF
HEATING.

SOME OF THE MORE WIDESPREAD LIGHT RAIN OVER FAR SW NC AND UPSTATE
SC WILL SLIDE TO THE NORTHEAST IN ADVANCE OF WEAK SHORT WAVE
HEADING EAST OUT OF TN...BUT PREVIOUS THINKING THAT IT WILL REMAIN
SOUTH OF THE FCST AREA STILL LOOKS ON TRACK. WE DO KEEP A
LINGERING SLIGHT CHC POP ACROSS NW NC MTNS UNTIL A LITTLE AFTER
MIDNIGHT JUST IN CASE...BUT THEN DROP ALL POPS TOWARD MORNING.

PREVIOUS DISCUSSION AS OF 235 PM EDT MONDAY...

AT 18Z...A WEAK SURFACE TROF WAS NOTED JUST EAST OF THE BLUE 
RIDGE...AND WEAK CONVERGENCE ALONG THIS BOUNDARY COMBINED WITH SOME 
MODEST INSTABILITY (DCAPES 500-700 J/KG) SHOULD GENERATE ISOLATED 
SHOWERS AND STORMS ALONG THE BLUE RIDGE AS WELL AS AREAS NORTH OF I-
64 WHERE VISIBLE SATELLITE SHOWS SOME ENHANCED CUMULUS FORMING IN 
ADVANCE OF A FAINT UPPER LEVEL DISTURBANCE.

MESOSCALE MODELS ARE OVERDONE ON THIS COVERAGE OF THIS PRECIP...BUT 
GENERALLY HAVE A GOOD HANDLE ON THE LOCATION OF DEVELOPMENT.

ANY ISOLATED/WIDELY SCATTERED PRECIP THAT DEVELOPS SHOULD GRADUALLY 
DIMINISH TONIGHT...BEFORE AN UPPER LEVEL SHORTWAVE IN WEST TENNESSEE 
ZIPS ACROSS NRN NC LATE TONIGHT. THIS SYSTEM WILL BRING AN INCREASE 
IN CLOUD COVER...ESPECIALLY ACROSS THE SOUTHERN PORTION OF OUR 
FORECAST AREA LATE TONIGHT...AND A FEW SHOWERS MAY BE POSSIBLE.

AT THE SFC...HIGH PRESSURE WILL SLOWLY NOSE SOUTH INTO THE EASTERN 
OHIO VALLEY BRINGING A LIGHT NORTH WIND. A SHALLOW LAYER OF MOISTURE 
NEAR THE SURFACE WILL REMAIN...WHICH WILL RESULT IN POCKETS OF 
FOG...ESPECIALLY WHERE CLOUDS ARE ABSENT TO THE NORTH. LEANED TOWARD 
THE WARMER GUIDANCE VALUES WITH CLOUDS.

FOR SATURDAY...HEIGHTS BUILD IN ADVANCE OF A DEEP UPPER LEVEL TROF 
IN THE WEST AND TEMPS SHOULD AGAIN WARM WELL INTO THE 70S AND THE 
80S IN THE EAST.

A WEAK LOW LEVEL EAST FLOW COMBINED WITH A NOSE OF HIGHER THETA-E 
AIR IN NW NC INTO FAR SW VA MAY SPARK ISOLATED SHOWERS/STORMS.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 330 PM EDT FRIDAY...

FOCUS THROUGH THIS PERIOD REMAINS ON A STRONG NEGATIVELY TILTED
UPPER TROUGH PROGGED TO LIFT RAPIDLY NORTHEAST ACROSS THE REGION
SUNDAY INTO EARLY MONDAY. MEANWHILE...ANTECEDENT HIGH PRESSURE
WILL MOVE OFF THE MID-ATLANTIC COAST INTO A NEAR CLASSIC WEDGE
POSITION. STRONG PVA/ISENTROPIC LIFT INDUCED RAINFALL INTO THE
WEDGE AIR MASS WILL ENHANCE/INTENSIFY THE WEDGE SUNDAY.
RAINFALL/QPF WILL BE THE MAIN CONCERN AS THE WEDGE KEEPS A VERY
STABLE/COOL AIR MASS IS PLACE. MOIST SOUTHEAST...UPSLOPE FLOW
ALONG THE BLUE RIDGE WILL ENHANCE RAINFALL...ESPECIALLY ACROSS
WATAUGA NORTHEAST TOWARD FLOYD. AS NOTED YESTERDAY...HOWEVER...THE
SYSTEM WILL REMAIN HIGHLY PROGRESSIVE...LIMITING THE PERIOD OF
HEAVIER RAINFALL TO 12 HOURS OR LESS. WPC HAS PARTS OF THE NC/VA
SOUTHERN VA PIEDMONT OUTLOOKED FOR EXCESSIVE RAINFALL. THE MAIN
CONCERN WITHIN THIS AREA WOULD BE WATAUGA THROUGH
ASHE/WILKES...WITH LESS CONCERN TOWARD THE DANVILLE AREA WHERE
ANTECEDENT CONDITIONS ARE RELATIVELY DRY. IN ADDITION...THE
CONVECTIVE THREAT THROUGH THE HEAVIER RAIN PERIOD AS NOTED ABOVE
IS MINIMAL TO NONE...WHICH SHOULD FURTHER REDUCE THE FLASH FLOOD
THREAT. WILL RE-EVALUATE AGAIN TOMORROW...BUT AT THIS POINT NO
NEED FOR A FLOOD/FLASH FLOOD WATCH. ONE MAY EVENTUALLY BE NEEDED
FOR A SMALL AREA INCLUDING THE NW NC MOUNTAINS AND THE ADJACENT
FOOTHILLS. WENT WELL BELOW GUIDANCE ON MAX TEMPS IN THE WEDGE
SUNDAY...BUT AT OR ABOVE GUIDANCE ON MONDAY IN THE WARM SECTOR.
MAX TEMPS MONDAY WILL BE A GOOD 20 DEGREES WARMER IN MOST AREAS
THAN ON SUNDAY.

MONDAY IS A DIFFERENT STORY. A SIGNIFICANT WARM SECTOR WILL SURGE
NORTHWARD INTO THE REGION MONDAY AFTERNOON BEHIND THE DEPARTING
UPPER TROUGH AND AN APPROACHING STRONG COLD FRONT ASSOCIATED WITH
A DEEPENING BROAD UPPER TROUGH ACROSS THE GREAT LAKES. SEVERAL OF
THE MODELS CONTINUE TO ADVERTISE GOOD POTENTIAL FOR STRONG
THUNDERSTORMS MONDAY AFTERNOON...WITH SIGNIFICANT SVR PARAMETER
NEAR 20000 ACROSS THE PIEDMONT...CAPES NEARING 2000 J/KG WITH AT
LEAST 20-30KTS OF 0-2KM LOW-LEVEL SHEAR AND LIS NEAR -4C. SPC DAY
4 OUTLOOK SUGGESTS THAT DAMAGING WINDS WOULD BE THE MAIN CONCERN
WITH ANY CONVECTION...MOST LIKELY LINEAR ORIENTED...THAT DEVELOPS
ALONG/IN ADVANCE OF THE COLD FRONT MONDAY AFTERNOON/EVENING. THIS
ACTIVITY QUICKLY MOVES EAST OF THE REGION MON AFTERNOON.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 345 PM EDT FRIDAY...

A TRANSITION TO A PATTERN MORE REMINISCENT OF WINTER CONTINUES TO
BE IN THE CARDS FOR THE EARLY AND MID PART OF NEXT WEEK AS A DEEP
AND BROAD UPPER TROUGH BUILDS INTO THE CENTRAL/EASTERN U.S. BY
TUESDAY...500MB HEIGHTS DROP INTO THE 560DM RANGE AND 850MB TEMPS
PLUNGE TOWARD THE 0C MARK ACROSS THE NORTH BY MIDWEEK.
ANTICYCLONIC FLOW...A SERIES OF EMBEDDED UPPER DISTURBANCES...AND
COLD ADVECTION WILL KEEP VARIABLE CLOUDINESS AND POTENTIALLY
UPSLOPE SHOWERS IN PLACE ACROSS THE MOUNTAINS. THE CLOUDS AND
CYCLONIC FLOW WILL HOLD MAX TEMPS INTO THE 50S AND LOWER 60S ACROSS
THE MOUNTAINS THROUGH MUCH OF THE LATER HALF OF NEXT WEEK...WHILE
60S TO 70S PREVAIL TO THE EAST WITH DOWNSLOPE NORTHWEST FLOW AND
SIGNIFICANTLY GREATER AMOUNTS OF SUNSHINE. AT THIS POINT A
DISTURBANCE ON WED APPEARS TO BE THE MOST SIGNIFICANT IN
POTENTIALLY BRINGING SHOWERS EAST OF THE MOUNTAINS. HAVE NOT
INTRODUCED ANY THUNDER AT THIS POINT GIVEN THE LOW-LEVEL
COLD/STABLE AIR MASS.

BY MID-WEEK...THE GFS/ECMWF BEGIN TO DIVERGE ON THE OVERALL
PATTERN...WITH THE ECMWF KEEPING THE DEEP UPPER TROUGH IN PLACE
ACROSS THE NORTHEAST AND A STRONGER NW FLOW INTO OUR REGION AS
WELL...WHILE THE GFS DEPICTS THE UPPER TROUGH LIFTING FURTHER
NORTH AND PLACING A ZONAL FLOW WITH A BAROCLINIC ZONE STUCK ACROSS
OUR CWA. THIS RESULTS IN SIGNIFICANT DIFFERENCES BETWEEN
MOISTURE/POPS ACROSS OUR CWA BETWEEN THE TWO MODELS...WITH THE GFS
VERY WET AND THE ECMWF MUCH DRIER...KEEPING THE BAROCLINIC ZONE
MUCH FURTHER SOUTH. HAVE JUST ADVERTISED CHC POPS FOR NOW UNTIL A
BETTER HANDLE ON THIS PATTERN AND TIMING IS OBTAINED. TEMPERATURES
ARE EXPECTED TO REMAIN BELOW NORMAL THROUGH THE MID PART OF THE
WEEK...GRADUALLY TRENDING CLOSER TO NORMAL BY THE END OF THE
PERIOD.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
AS OF 750 PM EDT FRIDAY...

ISOLD SHOWERS NOT EXPECTED TO IMPACT ANY AIRPORTS THIS
EVENING...AND FOR MOST OF THE OVERNIGHT EXPECTING VFR CONDITIONS
AND LIGHT TO CALM WINDS WITH HIGH PRESSURE IN CONTROL. SOME
MOISTURE OFF TO SOUTH SHOULD REMAIN THERE WITH WEAK SHORT WAVE
MOVING IN FROM THE WEST ACROSS TENNESSEE AND SHUNTING AN AREA OF
SHOWERS EASTWARD. THIS WAVE WILL ALSO EVENTUALLY TAKE MID TO HIGH CLOUDS
EAST AND WITH CLEARING THERE IS LIKELY TO BE SOME RADIATION FOG
FORMING...LOWERED CONDITIONS TO IFR AT BLF...LWB...BCB...AND LYH
BY 08-09Z...BUT MOST CONFIDENT IN IFR CONDITIONS AT LWB AND BCB.
ANY FOG AND LOW STRATUS DISSIPATES BY 13Z OR SO...FOR WIDESPREAD
VFR CONDITIONS FOR THE DAY SATURDAY...WITH LIGHT EAST TO NORTHEAST
WINDS AS SFC HIGH PRESSURE REMAINS TO THE NORTH AND WEAK SFC
TROUGH WILL LINGER ACROSS NORTH CAROLINA. THIS MAY RESULT IN
ENOUGH WEAK CONVERGENCE AND UPSLOPE TO KICK OFF A FEW ISOLD SHWRS
OR TSTORMS BY AFTERNOON...ESPECIALLY NEAR BLUE RIDGE ALONG OR
SOUTH OF VA/NC BORDER...BUT VERY UNLIKELY ANY ONE SHOWER OR STORM
WILL IMPACT ANY AIRPORTS. 

EXTENDED AVIATION...

A COMPLEX STORM SYSTEM WILL BEGIN TO AFFECT THE REGION LATER IN
THE WEEKEND WITH A WARM FRONT BRINGING WIDESPREAD MVFR/IFR
CONDITIONS IN RAIN DURING THE DAY SUNDAY INTO SUNDAY NIGHT...
FOLLOWED BY ANOTHER COLD FRONTAL PASSAGE MONDAY. THIS LIKELY TO
KEEP PERIODS OF MVFR IN PLACE UNTIL THE FRONT POSSIBLY CLEARS THE
REGION LATER MONDAY. VFR RETURNS LATER MONDAY NIGHT AND TUESDAY
WITH HIGH PRESSURE BUILDING IN BEHIND THE FRONT WITH GOOD DRYING
EXPECTED.

&&

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

&&

$$
SYNOPSIS...PH
NEAR TERM...JH/PH/SK
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...JH/PH/SK

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