Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 270100
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
900 PM EDT SUN JUL 26 2015

.SYNOPSIS...
A WEAK COLD FRONT WILL APPROACH THE REGION FROM THE
NORTHWEST LATE TONIGHT INTO MONDAY BEFORE WASHING OUT OVER THE
REGION INTO MIDWEEK. ANOTHER FRONT WILL MOVE INTO THE AREA FROM
THE WEST THURSDAY...THEN STALL JUST TO THE SOUTHEAST OF THE REGION
FRIDAY INTO THE WEEKEND...BRINGING A BETTER CHANCE OF SHOWERS AND
THUNDERSTORMS TO THE AREA. OTHERWISE...IT WILL REMAIN WARM AND
HUMID THROUGHOUT THE WEEK WITH MORE DIURNAL NATURE SHOWERS AND
STORMS.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 830 PM EDT SUNDAY...

HEAVIER SLOW MOVING CONVECTION HAS BEEN CONFINED MOSTLY TO
OROGRAPHICS THIS EVENING WITH CELLS POPPING UP OFF THE RIDGES THEN
REDEVELOPING WITH OUTFLOW ALLOWING SLOW PROPAGATION. HOWEVER MOST
ONLY PRODUCING HEAVY RAIN WITH LITTLE LIGHTNING AS SUPPORTED BY
SHALLOW INSTABILITY OFF EVENING SOUNDINGS AND STILL SOME CAPPING
ABOVE 7H THEREBY LIMITING DEPTH TO MOST CELLS. BETTER WINDS ALOFT
REMAIN TO THE NW CLOSER TO THE FRONT AND WITH AN APPARENT WEAK
WAVE THAT WILL SLIDE TO THE NORTH OF THE CWA LATE TONIGHT. THIS
MAY ALLOW FOR SOME ADDED COVERAGE TO REDEVELOP OVER THE NORTH
AFTER MORE DIURNAL SHOWERS FADE IN THE NEXT FEW HOURS. THIS
SIMILAR TO THE LATEST HRRR/NAM SO ADDING IN MORE LOW POPS OVER THE
FAR NORTH/NE OVERNIGHT...WITH ISOLATED COVERAGE NEAR THE BLUE
RIDGE UNTIL RESIDUAL INSTABILITY FADES BY MIDNIGHT. ALSO APPEARS
DEBRIS CLOUDS LIKELY A BIT MORE OVERNIGHT WHICH SHOULD LIMIT FOG
TO POCKETS WHERE HEAVIER RAINFALL OCCURRED AND IN THE VALLEYS FOR
THE MOST PART. OTRW MORE OF A WARMER AND MORE HUMID OVERNIGHT WITH
MOIST PWATS IN PLACE...AND HIGH DEWPOINTS SUPPORTING LOWS CLOSER
TO 70-73 EXCEPT FOR 60S WESTERN VALLEYS.


PREVIOUS DISCUSSION AS OF 330 PM EDT SUNDAY...

SURFACE HIGH REMAINS OVER THE REGION WITH WEAK SOUTHERLY FLOW ACROSS
THE PIEDMONT AND SOUTHEASTERLY FLOW ACROSS THE FOOTHILLS AND BLUE
RIDGE. THERE STILL EXIST AN UPPER LEVEL TROUGH WITH WEAK STEERING
CURRENTS FROM THE WEST-NORTHWEST. THIS PATTERN IS SIMILAR TO
YESTERDAY. EXPECT ISOLATED AFTERNOON SHOWERS AND THUNDERSTORMS TO
DEVELOP ACROSS THE MOUNTAINS...MORESO ALONG THE BLUE RIDGE...THEN
DRIFT EASTWARD INTO THE FOOTHILLS AND POSSIBLY THE PIEDMONT THIS
EVENING. ANY OF THESE DIURNAL STORMS THIS AFTERNOON/EVENING SHOULD
REMAIN SMALL BUT COULD PRODUCE VERY LOCALIZED HEAVY DOWNPOURS AS
PWATS HAVE INCREASED TO OVER AN INCH.

MODELS ARE AGGRESSIVE WITH BRINGING FRONTAL SHOWERS...CURRENTLY OVER
THE OHIO VALLEY...IN ACROSS CENTRAL AND NORTHERN VIRGINIA OVERNIGHT.
WITH VERY LITTLE UPPER LEVEL SUPPORT AND LACK OF MOVEMENT FROM
CURRENT CONVECTION...WILL LOWER CHANCES FOR PRECIPITATION OVERNIGHT
AND KEEP A MAINLY DIURNAL THEME. THIS FRONT MAY WASHOUT BEFORE
CROSSING OVER THE AREA ON MONDAY. IF THIS IS FACT...WE WILL HAVE
ANOTHER DAY OF DIURNALLY DRIVEN SHOWERS AND THUNDERSTORMS FOR THE
AREA. COVERAGE SHOULD BE MORE WIDESPREAD ON MONDAY COMPARED TO THIS
WEEKEND.

WITH NO FRONTAL PASSAGE AND JUST EXPECTING DIURNAL
CONVECTION...INCREASED TEMPERATURES A FEW DEGREES WITH MORE
SUNSHINE EXPECTED.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
AS OF 333 PM EDT SUNDAY...

WILL SEE THE HEAT RETURN AND ESPECIALLY THE HUMIDITY AS 5H HEIGHTS
BUILD FROM THE SOUTHERN PLAINS RIDGE. WILL SEE A WEAK FRONTAL
BOUNDARY WITH SHORTWAVE IMPULSE SET UP FROM THE OHIO VALLEY INTO THE
CAROLINAS THIS PERIOD. QUESTION WILL BE STRENGTH OF WARMING ALOFT
AND WEAKENING OF CAP IN THE EVENING FOR STORM DEVELOPMENT. MODELS
ALL ADVERTISE SCATTERED CONVECTION ACROSS MOST OF THE FA MONDAY
EVENING BEFORE WEAKENING OVERNIGHT.


TUESDAY WILL SEE THE IMPULSE WORK SWD INTO KY/NE TN AND NC...WITH
THE GFS/ECMWF HINTING AT CONVECTION FIRING UP ACROSS THE SRN
CWA....WHILE THE 12Z NAM IS SCATTERED WITH CONVECTIVE FEEDBACK
BULLSEYES ACROSS THE MTNS. WILL MAINTAIN CLOSE TO WHAT THE ECMWF/GFS
SHOW WITH 30-40 POPS SOUTH OF HIGHWAY 460 AND ROANOKE RIVER WITH
LOWER THREAT NORTH.

CONVECTION WANES TUESDAY NIGHT WITH HEIGHTS BUILDING MORE THAN
TUESDAY AND THINK WEDNESDAY WILL BE OUR HOTTEST DAY THIS WEEK WITH
LESS CONVECTION. WILL LIMIT STORMS TO THE MOUNTAINS...MAINLY SW
VA/NW NC. BY WED NIGHT THE UPPER LOW OVER CENTRAL CANADA WORKS EAST
TOWARD THE JAMES BAY AREA WITH TROUGH OFFERING LOWER HEIGHTS AND
PUSH OF FRONTAL BOUNDARY TOWARD THE OHIO VALLEY BY 12Z THURSDAY.
WILL KEEP A FEW EVENING STORMS AROUND IN THE SW...THEN DRY
LATE...THINKING ANY FRONTAL CONVECTION WILL WAIT TIL THURSDAY.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 220 PM EDT SUNDAY...

OVERALL NOT TOO MUCH CHANGE IN THE FORECAST THIS PERIOD. LOOKS LIKE
FRONT WILL SLIDE SOUTHEAST THROUGH OUR AREA BY FRIDAY MORNING.
QUESTION ARISES ON HOW FAR SOUTHEAST THIS FRONT GETS AS UPPER FLOW
WEAKENS AND BECOMES PARALLEL TO THE FRONT. MODELS SHOWING SEVERAL
WAVES OF LOW PRESSURE THIS WEEKEND GOING FROM THE GULF COAST TO THE
SOUTHEAST COAST...SUCH THAT THIS COULD PUSH THE FRONT NW TOWARD
CENTRAL NC. SWING IN THE UPPER TROUGH FAVORS MOST OF THE DEEPER
MOISTURE TO STAY OVER THE ATLANTIC COAST INTO THE COASTAL PLAINS
SOUTHWEST TOWARD UPSTATE SC. STILL WILL MAINTAIN LOW CHANCE POPS
THIS WEEKEND MAINLY FROM THE SOUTHEAST TO UP ACROSS THE BLUE RIDGE
OF VA...WITH LITTLE TO NO CHANCE IN THE VIRGINIA/WEST VIRGINIA
MOUNTAINS.

PRIOR TO THIS...FRONT SWINGS IN AND BOOSTS OUR THREAT OF SHRA/STORMS
THURSDAY INTO THURSDAY NIGHT. MAIN IMPACT LOOKS WEAK AS BETTER JET
DYNAMICS STAYS WELL NORTH OVER THE MID ATLANTIC/NORTHEAST...SO
FORCING WILL BE JUST WITH THE FRONT. SVR THREAT LOOKS LOW WITH THIS
FEATURE AND MODELS HAVE BACKED OFF ON RAINFALL AMOUNTS.

TEMPS THIS PERIOD WILL START OUT AT OR SLIGHTLY ABOVE NORMAL
THURSDAY THEN START TO GET AT OR JUST BELOW NORMAL FOR THE WEEKEND
AS WE STAY ON THE NORTHWEST SIDE OF THE FRONTAL BOUNDARY. DEWPOINTS
MAY SINK INTO THE 50S BY SATURDAY MORNING INTO WV/ALLEGHANYS.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
AS OF 800 PM EDT SUNDAY...

CURRENT RADAR IMAGERY INDICATES A FEW SLOW MOVING SHOWERS...
DEVELOPING MAINLY ALONG/NEAR THE CREST OF THE BLUE RIDGE. HEAVY
DOWNPOURS ARE OCCURRING BENEATH THESE CELLS HOWEVER...AND WILL
REDUCE VISIBILITIES TO ABOUT 1SM FOR UP TO AN HOUR UNTIL THE CELL
EXITS. OUTSIDE CONVECTION...VFR CONDITIONS OBSERVED AREAWIDE WITH
LIGHT SOUTHERLY WINDS.

OVERNIGHT...MAY SEE A FEW SHOWERS LINGER AS LATE AS 27/03Z. WE CAN
EXPECT LOCALIZED MVFR/IFR CONDITIONS AS PATCHY FOG REDEVELOPS...
PARTICULARLY IN THE DEEPER MOUNTAIN RIVER VALLEYS AND ACROSS SPOTS
THAT RECEIVED SIGNIFICANT RAINFALL THIS EVENING. ANY SUB VFR
CONDITIONS WILL IMPROVE RAPIDLY AFTER 27/13Z AS DAYTIME HEATING
RAMPS UP.

CU FIELD WILL REDEVELOP DURING LATE MORNING...MAINLY MOUNTAINS
FIRST BEFORE SPREADING ACROSS THE PIEDMONT. BELIEVE WE WILL SEE
WIDER COVERAGE OF SHOWER/THUNDERSTORM ACTIVITY ON MONDAY THANKS TO
INCREASED SURFACE CONVERGENCE AND INSTABILITY AS A COLD FRONT
APPROACHES FROM THE NORTH. CONVECTION WILL STILL BE PULSEY IN
NATURE...CAPABLE OF PRODUCING PROLONGED LOCALIZED HEAVY DOWNPOURS
AND GUSTY WINDS. STRONGER UPPER LEVEL WINDS WILL OFFER BETTER
SUPPORT HOWEVER...AND MAY SEE A COUPLE STORMS BECOME STRONG TO
SEVERE FOR SHORT PERIODS OF TIME. BEST COVERAGE WILL OCCUR ACROSS
THE MOUNTAINS...BEGINNING EARLY AFTERNOON...WITH SOME SHOWERS/
STORMS DRIFTING EAST SOUTHEAST ACROSS THE PIEDMONT BY LATER
AFTERNOON/EARLY EVENING.

EXTENDED AVIATION FORECAST...
MODELS APPEAR IN DECENT AGREEMENT THAT THE COLD FRONT WILL STALL
JUST NORTH OF THE FORECAST AREA MONDAY EVENING...BEFORE RETREATING
BACK TO THE NORTH ON TUESDAY. EXPECT MAINLY VFR CONDITIONS
THROUGH THE WORKWEEK OUTSIDE OF SPOTTY CONVECTION EACH AFTERNOON/
EVENING...AND LOCALIZED FOG/STRATUS EARLY EACH MORNING. SHOWER AND
THUNDERSTORM CHANCES INCREASE TOWARD THE END OF THE WEEK AS
ANOTHER COLD FRONT APPROACHES.

&&

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

&&

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


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