Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 041827
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
227 PM EDT TUE AUG 4 2015

.SYNOPSIS...
A WEAK COLD FRONT WILL CROSS THE AREA TODAY...THEN STALL ACROSS
THE CAROLINAS WEDNESDAY. AN AREA OF LOW PRESSURE IS EXPECTED TO
FORM ALONG THE FRONT THURSDAY AND MOVE NORTHEAST ACROSS THE MID
ATLANTIC REGION FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
MORNING SATELLITE IMAGES SHOW FEW CLOUDS ACROSS THE REGION AND THE
RADAR IS QUIET. HOWEVER...A FRONTAL BOUNDARY LIES NOT TOO FAR OFF
TO THE NORTHWEST AND CONTINUES TO APPROACH THE REGION. BELIEVE THE
ABUNDANT EARLY SUN WILL COOK UP ENOUGH INSTABILITY TO HELP THE
FRONT TRIGGER SHOWERS AND THUNDERSTORMS THIS AFTERNOON. WITH
WESTERLY FLOW CREATING DOWNSLOPE EAST OF THE BLUE RIDGE THERE WILL
LIKELY BE A GAP IN CONVECTIVE DEVELOPMENT WITH ONE AREA FURTHER TO
THE EAST AND ANOTHER AREA FAR WEST. CURRENT SPC OUTLOOK FOR A
MARGINAL SEVERE THREAT CLIPPING THE FAR NORTHEASTERN SECTION OF
OUR AREA LOOKS GOOD BUT ALSO FEEL CONDITIONS ARE MARGINAL FAR WEST
AS THE LOW LEVEL WIND FIELD INCREASES LATE IN THE DAY AND SOME
SHORT WAVE ENERGY ALSO STREAMS IN...AND CURRENT ACTIVITY UPSTREAM
IN IN/KY BOLSTER THIS LINE OF THINKING. EXPECTING THE MAIN THREAT
WITH ANY STRONG CELLS THAT DEVELOP TO BE GUSTY WINDS WITH
UNIDIRECTIONAL FLOW AND STRONG HEATING HELPING TO GENERATE HIGHER
DCAPE VALUES.

HIGH TEMPERATURES TODAY WILL BE AIDED BY DOWNSLOPE EAST OF THE
RIDGE WITH READINGS IN THE LOW TO MID 90S EXPECTED...A BIT COOLER
WEST WITH GENERALLY MIDDLE 80S.

PREVIOUS AFD...

AS OF 500 AM EDT TUESDAY...

A WEAK SURFACE FRONT EXTENDS FROM NORTHERN VA...SOUTHWEST THROUGH
SOUTHERN WVA AND INTO CENTRAL KY. THIS FRONT WILL CONTINUE TO MOVE
SOUTHEAST...CROSSING OUR REGION TODAY. GREATEST FORECAST CAPE IS
PROGGED FROM LYH/DAN INTO EASTERN VA...WESTERLY DOWNSLOPE WINDS
LIMITING INSTABILITY VCNTY OF THE MTNS. FARTHER WEST...BETTER
CONVERGENCE AND CAPE WILL BUILD INADV OF FRONT AS IT DROPS SOUTH
FROM KY INTO TN AND WRN NC.

GIVEN THE WESTERLY WIND FLOW ALONG THE FRONT...ANTICIPATING TWO
AREAS OF DEEP CONVECTION TODAY. ONE OVER THE VA/NC PIEDMONT...AND
THE OTHER IN THE UPPER TN VALLEY. AS SUCH...HAVE FOCUSED THE
HIGHEST POPS TODAY IN THE EASTERN CWA MAINLY EAST OF HIGHWAY 29
AND IN THE FAR WEST...WEST OF I77. WESTERLY DOWNSLOPE WINDS SHOULD
LIMIT ACTIVITY IN BETWEEN.

THERE IS A MARGINAL RISK...5% CHANCE FOR SEVERE STORMS EAST OF
HIGHWAY 29...THREAT FOR DAMAGING WIND GUSTS. THE GREATER
THREAT...SLIGHT RISK OR 15% CHANCE FOR SEVERE STORMS...IS
CONFINED TO THE DELMARVA AND NEW ENGLAND COAST.

TEMPERATURES TODAY SHOULD BE SIMILAR TO YESTERDAY WITH READINGS
CLIMBING WELL INTO THE 80S ACROSS THE MOUNTAIN VALLEYS AND INTO
THE LOWER 90S EAST OF THE BLUE RIDGE. ONLY THE HIGHEST
ELEVATIONS... ABOVE 3500 FEET WILL ESCAPE THE HEAT...WITH HIGHS IN
THE 70S.

FOR TONIGHT...THE SURFACE FRONT IS EXPECTED TO DRIFT INTO NORTH
CAROLINA...WINDS COMING AROUND TO THE NORTHWEST.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
AS OF 430 AM EDT TUESDAY...

THE COLD FRONT IS EXPECTED TO STALL ACROSS THE CAROLINAS BY
WEDNESDAY MORNING...WITH WEAK HIGH PRESSURE EXTENDING SOUTHWARD
FROM THE WESTERN GREAT LAKES BECOMING THE MAIN INFLUENCE OF OUR
WEATHER PATTERN. TRULY DRIER AIR BEHIND THE FRONT WILL REACH AS
FAR SOUTH AS THE HIGHWAY 460 CORRIDOR...WITH MID 60S DEWPOINTS
LINGERING ACROSS NORTHERN NORTH CAROLINA. COUNTER THAT WITH
NORTHWESTERLY DOWNSLOPE WINDFLOW HOWEVER...WHILE A WEAK SHORTWAVE
RIDGE PUSHES ACROSS THE CENTRAL APPALACHIANS DURING THE
AFTERNOON/EVENING...LIMITING INSTABILITY. WITH LITTLE CHANGE
EXPECTED IN THE PATTERN...OPTED TO MAINTAIN ONLY SLIGHT CHANCE OF
SHOWERS/STORMS WEDNESDAY AND WEDNESDAY NIGHT...MAINLY SOUTH OF
HIGHWAY 460.

THE CENTER OF HIGH PRESSURE WILL SHIFT EAST LATE WEDNESDAY NIGHT AND
THURSDAY...ALLOWING A WEAK WEDGING PATTERN TO DEVELOP AS A LOW
PRESSURE SYSTEM PUSHES UP THE OHIO RIVER VALLEY. AS SUCH...MAY START
THE DAY WITH A FEW OVERRUNNING TYPE SHOWERS...BUT AS THE LOW DRAWS
CLOSER DURING THE AFTERNOON...THE FRONTAL BOUNDARY ACROSS THE
CAROLINAS WILL LIFT NORTH AS A WARM FRONT...RESULTING IN MORE
WIDESPREAD RAINFALL FOR OF AREA HEADING INTO EVENING.

LOW PRESSURE WILL PASS JUST NORTH OF OUR AREA EARLY FRIDAY MORNING.
MODELS CONTINUE TO HINT AT MODEST SHEAR AND HELICITY...WITH HIGHEST
VALUES NEAR THE INTERSTATE 64 CORRIDOR. AS SUCH...CANNOT RULE OUT A
FEW STRONG STORMS OVERNIGHT...ALTHOUGH THE LACK OF STRONG MID/UPPER
LEVEL WINDS KEEPS THE THREAT MINIMAL.

NAM/ECMWF INDICATE THAT THE SYSTEM WILL TAKE ON A MILLER B
ORIENTATION EARLY FRIDAY...WHERE A SECONDARY LOW DEVELOPS ACROSS THE
NORTH CAROLINA PIEDMONT...PUSHES NORTHEAST AND EVENTUALLY TAKES OVER
AS THE MAIN LOW LATE FRIDAY MORNING. THIS WILL ACT TO DELAY THE
PASSAGE OF THE COLD FRONT ACROSS OUR AREA...ALLOWING SHOWER ACTIVITY
TO LINGER INTO THE AFTERNOON...MAINLY EAST OF THE BLUE RIDGE. WINDS
WILL GRADUALLY SHIFT NORTHWESTERLY THROUGH THE EVENING AS THE LOW
PUSHES AWAY AND THE COLD FRONT CLEARS OUR AREA TO THE EAST...
BRINGING DRIER AIR INTO OUR AREA...AND ENDING ALL RAINFALL ASIDE
FROM UPSLOPE SHOWERS ALONG THE WESTERN RIDGES.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
AS OF 430 AM EDT TUESDAY...

ANOTHER DIGGING 5H TROUGH WILL BRING THE ONSET OF THE NEXT ROUND OF
SLIGHTLY COOLER TEMPERATURES FOR THE COMING WEEKEND. HOWEVER NEW
GUIDANCE CONTINUES TO FLIP FLOP AS SOME SOLUTIONS NOW NOT AS DEEP OR
PROLONGED WITH THE EASTERN UPPER TROUGH IN HAVING A PASSING 5H COOL
POOL EARLY IN THE WEEKEND BEFORE RETURNING TO MORE ZONAL FLOW AND
SOME RETURN IN MOISTURE BY DAY7. THIS AHEAD OF ADDED UPSTREAM
CLIPPER TYPE ENERGY THAT SHOULD GIVE THE INITIAL SYSTEM A BIT OF A
BOOT TO START. THIS COULD ALSO KEEP MORE CLOUDS AROUND AT TIMES
DESPITE WEAK SURFACE RIDGING IN PLACE...ALONG WITH POSSIBLE ISOLATED
SHOWERS SW SUNDAY AND MAINLY OVER THE WEST MONDAY AHEAD OF THE NEXT
WAVE.

THUS...WILL HANG ONTO SOME ISOLATED TO LOW CHANCE POPS SATURDAY...
AND OVER THE FAR SW SUNDAY DESPITE THE SURFACE FRONT WELL TO THE
SOUTH. OTRW THINKING THAT MUCH OF THE WEEKEND INTO MONDAY WILL
REMAIN DRY PENDING LATER TRENDS WITH THE TIMING OF THE FRONTAL
PROGRESSION FROM LATE IN THE WEEK. TEMPS TO COOL BACK TO JUST BELOW
SEASONAL LEVELS BUT NOT QUITE AS COOL AS SEEN YESTERDAY FOR NOW.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
AS OF 215 PM EDT TUESDAY...

WEAK COLD FRONT IS MOVING THROUGH THE REGION THIS AFTERNOON AND
GENERATING SCATTERED SHOWERS AND THUNDERSTORMS. DO NOT EXPECT
EXTENSIVE COVERAGE SO WILL USE VCTS ALL SITES AND AMEND AS NEEDED
FOR SPECIFIC CELLS APPROACHING TAF SITES. OUTSIDE OF THIS
CONVECTIVE ACTIVITY CONDITIONS LOOK TO BE VFR.

POTENTIAL FOR FOG DEVELOPMENT OVERNIGHT IS ONCE AGAIN COMPLICATED
BY HOW MUCH MID/HIGH CLOUDS WILL DRIFT OVER FROM UPSTREAM
CONVECTION AND MODEL INDICATIONS FOR SOME LOW CLOUDS TO DEVELOP
OVERNIGHT IN LIGHT UPSLOPE WEST OF THE BLUE RIDGE BEHIND THE
FRONT. CURRENTLY BELIEVE THE SCALES TIP AWAY FROM FOG SO WILL NOT
INCLUDE ANY MENTION AT KBLF/KLWB/KBCB AND WILL INTRODUCE SOME BKN
MVFR CLOUDS TOWARD DAYBREAK. IF A TAF SITE GETS APPRECIABLE
RAINFALL FROM CONVECTION THIS AFTERNOON/EVENING OR ANTICIPATED
CLOUD DEVELOPMENT IS LESS THAN EXPECTED FOG WILL NEED TO BE ADDED
TO TAF SITES WEST OF THE BLUE RIDGE...POSSIBLY IFR/LIFR AT KLWB.

THE FRONT WILL NOT PASS CLEANLY THROUGH THE REGION AND WILL LINGER
TOMORROW AS UPPER LEVEL SHORT WAVE ENERGY APPROACHES FROM THE
WEST. THIS SHOULD LEAD TO ANOTHER ROUND OF SCATTERED SHOWERS AND
THUNDERSTORMS BY WEDNESDAY AFTERNOON. HOWEVER THE BULK OF THIS
ACTIVITY WILL BE BEYOND THIS TAF PERIOD SO WILL KEEP THE BACK END
OF THIS FORECAST DRY AND INDICATE VFR AT ALL SITES AFTER DAYBREAK.

WINDS WILL GENERALLY BE LIGHT WESTERLY TO NWLY THROUGH THE PERIOD
WITH SOME OCCASIONAL LOW END GUSTS.

EXTENDED AVIATION FORECAST...
MOSTLY VFR OUTSIDE OF ANY DEEP CONVECTION THROUGH THE PERIOD. A
FRONT WILL STALL ACROSS THE MID ATLANTIC BY LATE WEEK WHICH COULD
BRING A BIT MORE COVERAGE OF SHOWERS/THUNDERSTORMS THURSDAY AND
ESPECIALLY FRIDAY. THE THREAT OF SUB-VFR REMAINS LOW UNTIL
THURSDAY...EXCEPT FOR THE TYPICAL FOG POTENTIAL AT KLWB/KBCB EACH
MORNING BETWEEN 09-13Z.

&&

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

&&

$$
SYNOPSIS...PM
NEAR TERM...MBS/PM
SHORT TERM...NF
LONG TERM...JH
AVIATION...MBS/PM


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