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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1139 AM EDT FRI SEP 19 2014

.SYNOPSIS...
A WEAK TROUGH OF LOW PRESSURE WILL SHIFT WEST ACROSS THE MOUNTAINS
TODAY AHEAD OF STRONG HIGH PRESSURE BUILDING IN FROM THE NORTH BY
THIS AFTERNOON. THE HIGH WILL WEDGE SOUTH ALONG THE EASTERN
SLOPES OF THE APPALACHIANS TONIGHT INTO SUNDAY KEEPING DRY
WEATHER IN PLACE. A COLD FRONT SHOULD CROSS THE AREA FROM THE
NORTHWEST LATER SUNDAY NIGHT INTO MONDAY FOLLOWED BY COOLER AND
DRIER WEATHER INTO NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1139 AM EDT FRIDAY... 
MADE SOME QUICK ADJUSTMENTS IN POPS TO EXPAND COVERAGE OF LIGHT
POPS FURTHER NORTH OF HIGHWAY 460 FOR THIS AFTERNOON. ALSO
ADJUSTED TEMPERATURES AND DEW POINTS FOR THIS AFTERNOON INTO
TONIGHT. CUT BACK ON MENTION OF THUNDERSTORMS FOR THIS AFTERNOON.

AS OF 933 AM EDT FRIDAY...

THIS MORNINGS 12Z RNK SOUNDING DISPLAYED PLENTY OF LOW LEVEL 
MOISTURE TRAPPED BELOW THE SUBSIDENCE INVERSION WITH A EASTERLY FLOW 
FROM SFC UP TO 1KFT. KFCX 88D IMAGES HIGHLIGHTED A FEW SHOWERS THIS 
MORNING ESPECIALLY ALONG THE FOOTHILLS OF THE BLUE RIDGE MOUNTAINS. 
THIS ACTIVITY IS BEING SUPPORTED BY THE COMBINATION OF A WEAK 
SURFACE TROUGH ACROSS THE PIEDMONT AND LOW LEVEL THETA-E RIDGING 
EAST OF THE BLUE RIDGE. A BLEND OF THE HRRR AND HI RESW-ARW CAPTURED
THIS MORNING POPS. 

TWO CHALLENGES FOR THIS AFTERNOON FORECAST ARE HOW FAST/DEEP CAD IS 
AND WHATS THE WESTERN EXTENT OF CLOUD COVER. MODEL GUIDANCE STILL 
SHOWS AN AXIS OF INSTABILITY ALONG THE I-77 CORRIDOR THIS AFTERNOON 
WITH THE WESTERN MOVING SURFACE TROUGH. INCLUDED AN ISOLATED TSRA
MENTION IN NORTHWEST NORTH CAROLINA RIDGES/FOOTHILLS THIS
AFTERNOON WHERE BEST LOW LEVEL CONVERGENCE LINES UP WITH THE
PASSING TROUGH UNDER DECENT 85H THETA-E RIDGING.

TEMPERATURES WILL LIKELY TO BE STUCK MOSTLY IN THE 60S UNDER LOW 
DECK AND EASTERLY FLOW. HOWEVER THE FAR WEST COULD ACTUALLY SEE 
READINGS PUSH INTO THE 70S GIVEN THE SLOWER WEDGING.

MADE SOME MINOR ADJUSTMENTS IN TEMPERATURES...POPS AND CLOUD COVER 
FOR THIS MORNING INTO THIS AFTERNOON. 


AS OF 230 AM EDT FRIDAY...

COMBINATION OF A WEAK SURFACE TROUGH ACROSS THE PIEDMONT AND LOW LEVEL 
THETA-E RIDGING EAST OF THE BLUE RIDGE CONTINUES TO LEAD TO ISOLATED 
SLOW MOVING SHOWERS IN SPOTS EARLY THIS MORNING. EXPECT THIS TO PERSIST 
A WHILE LONGER PER LATEST HRRR BEFORE THE DEVELOPING WEDGE STARTS TO 
ENHANCE FROM NE TO SW BUT A BIT SLOWER THAN EARLIER THOUGHT. THIS 
SHOULD START TO PRODUCE SOME SPOTTY -DZ ALONG THE EASTERN SLOPES AS 
SHOWERS WANE PER INCREASING STABILITY BUT LOOKS LESS THAN PREVIOUS 
GIVEN DRY AIR SAGGING IN FROM THE NORTH OFF MSAS. HOW FAST/DEEP ANY OF 
THE LOW CLOUDS CAN BANK IN ALONG THE EASTERN SLOPES KEY TO CLOUDS/TEMPS 
THIS AFTERNOON WITH MODELS NOW SLOWER IN INITIALLY PUSHING THE CAD 
SOUTH AND WEST. THIS MAY LEAD TO AN AXIS OF MODEST INSTABILITY ESPCLY 
ALONG THE I-77 CORRIDOR EARLY THIS AFTERNOON WHERE GUIDANCE REDEVELOPS 
SHRA ALONG THE WESTWARD MOVING SURFACE TROUGH. SINCE THIS IN LINE WITH 
CONSENSUS...BUMPED UP CHANCE POPS ACROSS NW NC...AND SW VA LATER WHILE 
TRIMMING ANY -DZ/-RA TO ISOLATED -SHRA BLUE RIDGE...AND LITTLE MORE 
THAN CLOUDS EAST-NE AS BUILDING HIGH PRESSURE START TO ENHANCE INLAND 
FROM THE MID ATLANTIC COAST. ALSO INCLUDED AN ISOLATED -TSRA MENTION NW 
NC RIDGES/FOOTHILLS WHERE BEST LOW LEVEL CONVERGENCE LINES UP WITH THE 
PASSING TROUGH UNDER DECENT 85H THETA-E RIDGING.

OTRW CLOUD COVER AND TEMPS THE MAIN ISSUES ESPCLY BLUE RIDGE WHERE 
LIKELY TO BE STUCK MOSTLY IN THE 60S UNDER LOW DECK AND EASTERLY FLOW. 
HOWEVER COULD ACTUALLY SEE READINGS PUSH INTO THE 70S FAR WEST GIVEN 
THE SLOWER WEDGING...AS WELL AS OVER THE SOUTH/EAST IF CAN GET MORE 
SUNNY BREAKS AS MOISTURE STARTS TO DECREASE FROM THE EAST LATE. 

SURFACE RIDGING STRENGTHENS FROM THE NE OVERNIGHT HELPING PUSH THE 
RESIDUAL AXIS OF MOISTURE FARTHER WEST WHICH SHOULD BRING AN END TO 
POPS DURING THE EVENING. BANKED UP LOW LEVEL MOISTURE THOUGH LIKELY TO 
REDEVELOP OR PERSIST BLUE RIDGE WHERE LOTS OF LOW CLOUDS/FOG POSSIBLE. 
APPEARS AREAS OVER THE EAST/SE FROM HIGHWAY 29 EAST COULD SEE SOME 
CLEARING AS MOISTURE GETS PINCHED FARTHER WEST AHEAD OF THE DRIER 
EASTERLY FLOW. OTRW VARYING DEGREE OF CLOUDS FROM THE BLUE RIDGE WEST 
WITH LOWS MAINLY IN THE 50S PER LATEST SIMILAR MAV/MET MOS.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 300 AM EDT FRIDAY...

THE HIGH PRESSURE CENTER THAT WAS OVER NEW ENGLAND WILL MOVE OUT 
INTO THE ATLANTIC OVER THE WEEKEND. HOWEVER...THIS RIDGE WILL REMAIN 
WEDGE BACK OVER THE MID ATLANTIC AND SOUTHEASTERN STATES INTO 
SATURDAY NIGHT. A GULF STREAM DISTURBANCE WILL HELP KEEP THIS WEDGE 
IN THE AREA AND ALSO PROVIDE SUBSIDENCE TO KEEP THE FORECAST AREA 
DRY SATURDAY. THESE DISTURBANCE WILL HAVE MOST OF ITS RAIN FALLING 
ON ITS EASTERN FLANK AS DRY AIR IS ENTRAINED INTO THE WESTERN SIDE. 
THIS DISTURBANCE WILL TRACK TO THE NORTHEAST AND WILL REMAIN 
OFFSHORE THROUGH THE WEEKEND.

MODELS HAVE SPED UP THE TIMING OF THE NEXT FRONTAL PASSAGE FROM 
MONDAY TO SUNDAY. THIS FRONT STILL LOOKS LIKE A TYPICAL FALL FRONTAL 
PASSAGE WITH RAIN FALLING ALONG WESTERN SLOPES...LOSING THEIR 
INTENSITY MOVING TO THE BLUE RIDGE. THIS PRECIPITATION MAY THEN JUMP 
THE FOOTHILLS AS A WEAK LINE OF CONVECTION DEVELOPS OVER THE 
PIEDMONT WHERE A LEE TROUGH WILL RESIDE SUNDAY AFTERNOON. THE NAM 
AND ECM LOOK SIMILAR WITH KEEPING BULK OF THE RAIN OVER THE 
MOUNTAINS. THE GFS PROGRESSIVELY MOVES THE FRONT AND RAINFALL ACROSS 
THE ENTIRE FORECAST AREA...DISREGARDING DOWNSLOPE. THE FORECAST DID 
NOT DISCREDIT THE GFS...BUT MORE WEIGHT WAS PLACED WITH THE NAM/ECM 
FOR SUNDAY.

SATURDAY TEMPERATURES WILL RUN WARMER THAN NORMAL WITH UPPER 70S TO 
LOWER 80S. AREAS NOT SEEING RAIN UNTIL LATER IN THE DAY SUNDAY 
SHOULD HAVE TEMPERATURES IN THE LOWER TO MID 80S. WESTERN SLOPES 
SHOULD HAVE RAIN FALLING BY THE AFTERNOON AND MAY SEE HIGHS IN THE 
MID 70S SUNDAY.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 200 PM EDT THURSDAY...

THIS PERIOD IS SHAPING UP TO BE DRY AND SEASONAL. ANOTHER SHORTWAVE 
DROPS SOUTHEAST ACROSS THE TN VALLEY MONDAY AND COULD BRING ISOLATED 
SHOWERS TO THE ENTIRE AREAS AS FLOW BACKS ALOFT SOME. THEN HIGH 
PRESSURE ACROSS THE MIDWEST PUSHES EAST OVER THE MID ATLANTIC
TUE- WED. TEMPS BEHIND THIS SYSTEM EARLY NEXT WEEK WILL COOL DOWN
SOME...BUT NOT LOOKING AS CHILLY AS EARLIER THOUGHT...WITH 8H
TEMPS +10-12C.

HIGHS WILL RUN FROM THE 60S WEST TO 70S EAST...WITH LOWS MAINLY IN 
THE 40S...WITH SOME 50S ACROSS THE PIEDMONT.

&&

.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
AS OF 650 AM EDT FRIDAY...

CIGS CONTINUE TO SLOWLY LOWER THROUGH MVFR ALONG AND EAST OF THE
BLUE RIDGE EARLY THIS MORNING AS THE WEDGE STARTS TO SPILL
WESTWARD. THIS MAY LEAD TO AN AREA OF IFR CIGS ESPCLY AROUND
KBCB/KROA EAST TO KLYH THIS MORNING INCLUDING PATCHY -RA/-DZ.
OTHER HEAVIER SHOWERS JUST TO THE WEST OF KDAN SHOULD STAY MOSTLY
OUT OF THE KDAN VICINITY WHILE FEEDING NORTH UP TOWARD KROA SO
INCLUDING SOME PREVAILING LIGHT RAIN/DRIZZLE OR VCSH MENTION OVER
THE EAST THIS MORNING. CIGS REMAIN MORE VARIABLE TO THE WEST WITH
MOSTLY VFR TO HIGH END MVFR EXPECTED A WHILE LONGER AT KBLF/KLWB
BEFORE SHOWING SOME IMPROVEMENT LATER THIS MORNING INTO THE
AFTERNOON. SOME ADDED SHOWER DEVELOPMENT POSSIBLE MAINLY MOUNTAINS
THIS AFTERNOON BUT COVERAGE TOO WIDELY SCATTERED TO INCLUDE IN ANY
OF THE TAF LOCATIONS FOR NOW.

DEGREE OF LOW CIGS REMAINS IN QUESTION DURING THE AFTERNOON WITH
POTENTIAL TO SEE OTHER THE WESTERN AND EASTERN PERIMETER SITES
IMPROVE TO VFR WHILE STAYING STUCK IN MVFR OR WORSE ALONG THE BLUE
RIDGE UNTIL LATE. FOR NOW WILL KEEP THE SCENARIO OF SEEING A SLOW
RISE IN CLOUD BASES MOST SPOTS THIS AFTERNOON WITH MOST AT LEAST
GETTING INTO BRIEF VFR. EAST WINDS AT 7-12 KTS TODAY WITH POSSIBLE 
LOW END GUSTS IN USUALLY FAVORED SOUTHEAST WIND AREAS...SUCH AS
KBLF.

CIGS MAY LOWER AGAIN THIS EVENING PENDING DEGREE OF
EROSION/COVERAGE HEADING INTO LATE THIS AFTERNOON SO TRENDING
BACK TOWARD MVFR FROM THE BLUE RIDGE EAST EARLY TONIGHT BEFORE
DRYING FROM THE EAST OCCURS. OTRW ANOTHER ROUND OF LOW CIGS IN
FOG AND STRATUS LIKELY LATER TONIGHT INTO EARLY SATURDAY WITH
SOME ADDED PATCHY FOG LIKELY IN THE VALLEYS SUCH AS KLWB/KBCB BY
MORNING.

EXTENDED AVIATION DISCUSSION...

WEDGE SHOULD ERODE FAIRLY QUICKLY SATURDAY IN RESPONSE TO AN
UPSTREAM TROUGH. SOME LOW CLOUDS MAY LINGER THROUGH THE MORNING
ALONG WITH PATCHY FOG...BUT OVERALL VFR CONDITIONS EXPECTED SAT. A
FRONTAL SYSTEM WILL APPROACH SUN WITH -SHRA AND PERHAPS AN ISOLD
TSRA WEST OF THE ALLEGHANY FRONT. INSTABILITY IS QUITE LIMITED AND
SO IS DEEP MOISTURE. WITH A POSSIBLE TROPICAL SYSTEM DEVELOPING
OFF THE COAST AT THE SAME TIME...WE MAY BE IN A STRONG SUBSIDENCE
AREA AND SEE LITTLE MORE THAN -SHRA OR SPRINKLES EAST OF THE
ALLEGHANY FRONT. EXPECT MOSTLY VFR-PERIODS OF MVFR CIGS SUN-EARLY MON
AS THE TROUGH MOVES THROUGH. HIGH PRESSURE BUILDS IN FOR THE FIRST
HALF OF NEXT WEEK WITH DRY NW FLOW. THUS...EXPECT MOSTLY VFR
CONDITIONS THROUGH THE PERIOD WITH LOCAL EARLY MORNING MVFR-IFR
FOG CONDITIONS.

&&

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

&&

$$
SYNOPSIS...JH/KK
NEAR TERM...JH/KK
SHORT TERM...RCS
LONG TERM...WP
AVIATION...JH/KK/RAB

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