Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 030136
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
936 PM EDT SUN AUG 2 2015

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN ACROSS THE AREA TONIGHT INTO MONDAY
KEEPING MAINLY DRY WEATHER IN PLACE. A COLD FRONT DROPS SOUTHEAST
INTO THE REGION BY TUESDAY BEFORE STALLING OUT DURING MIDWEEK.
LOW PRESSURE WILL RIDE ALONG THE FRONT BRINGING A BETTER CHANCE
FOR MORE WIDESPREAD SHOWERS AND STORMS THURSDAY INTO FRIDAY.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 930 PM EDT SUNDAY...

NO MAJOR CHANGES ARE BEING MADE TO THE FORECAST FOR THE OVERNIGHT
PERIOD. THE AREA STILL LOOKS TO HAVE A RELATIVELY COOL NIGHT WITH
A MIX OF MID TO UPPER 50S ACROSS THE MOUNTAINS...AND AROUND 60 TO
LOWER 60S ACROSS THE PIEDMONT. PATCHY FOG IS EXPECTED TO DEVELOP
LATE TONIGHT INTO EARLY MONDAY MORNING. HAVE MADE SOME MINOR
ADJUSTMENTS TO THE TEMPERATURE...DEW POINT AND SKY COVER THROUGH
THE NEXT FEW HOURS BASED UPON THE LASTEST OBSERVATIONS AND
EXPECTED TRENDS.

AS OF 630 PM EDT SUNDAY...

HEADING INTO THE EVENING HOURS...THE FORECAST IS ON TRACK FOR
WINDS TO BECOME CALM WITH DECREASING CLOUD COVER. BY 1000 PM...TEMPERATURES
WILL FALL INTO THE MID TO UPPER 60S ACROSS THE MOUNTAINS AND THE
LOWER 70S ACROSS THE PIEDMONT. NO PRECIPITATION IS EXPECTED.

AS OF 310 PM EDT SUNDAY...

HIGH PRESSURE OVER THE REGION WILL BRING QUIET WEATHER TO THE
REGION ONCE AGAIN TONIGHT. EXPECTED LIGHT WINDS...SCANT CLOUD
COVER...AND LOW DEW POINTS WILL MAKE FOR GOOD RADIATIONAL COOLING
AND A REPEAT OF CHILLY TEMPERATURES BY DAYBREAK MONDAY. MOST
GUIDANCE FROM THE 12Z RUN SEEMS TOO WARM BASED ON THE LOWS THAT
OCCURRED UNDER SIMILAR CONDITIONS LAST NIGHT...SO WILL BE USING
MOS GUIDANCE FOR TONIGHT WHICH IS NOTABLY COOLER THAN OTHER
SOLUTIONS. EXPECT UPPER 50S/LOWER 60S EAST OF THE BLUE RIDGE WITH
LOW/MID 50S WEST AND SOME COOLER READINGS IN THE COLDEST VALLEYS.
ALSO EXPECT SOME VALLEY FOG TO DEVELOP WEST OF THE BLUE RIDGE AND
BECOME LOCALLY DENSE NEAR THE RIVERS BY DAYBREAK.

THE REGION WILL BE GETTING SQUEEZED BETWEEN SYSTEMS ON MONDAY AS A COLD
FRONT APPROACHES FROM THE NORTHWEST AND A TROF/FRONTAL BOUNDARY TO OUR
SOUTHEAST GETS A PUSH BACK IN OUR DIRECTION AS LOW PRESSURE DEVELOPS
OVER THE CAROLINAS. BEST CHANCE FOR ORGANIZED STORMS WILL BE WITH
BETTER DYNAMICS OUTSIDE OF OUR AREA TO THE NORTH AND TIMING OF FRONT IS
LATE SO SLGT/LOW CHANCE POPS FOR A LATE DAY THUNDERSTORM ACROSS
SOUTHEAST WV SHOULD BE SUFFICIENT. SWLY FLOW EAST OF THE BLUE RIDGE
WILL ALLOW FOR HIGHER DEWPOINTS TO MOVE IN AND HELP GENERATE SOME
INSTABILITY DURING THE AFTERNOON. WHILE THE OVERALL ENVIRONMENT FEATURES
WEAK DYNAMICS...OROGRAPHIC FORCING JUST EAST OF THE RIDGE COMBINED
WITH CONVERGENCE ASSOCIATED WITH THE TROF/FRONTAL BOUNDARY WILL BE
ENOUGH TO JUSTIFY MORE SLGT/LOW CHC POPS FOR A THUNDERSTORM TO THE
EAST. THE END RESULT WILL BE DRY EARLY WITH THE CHANCE FOR A LATE
DAY THUNDERSTORM MAINLY EAST OF THE BLUE RIDGE AND ACROSS
SOUTHEAST WV. IT WILL ALSO BE WARMER AS TEMPERATURES REBOUND INTO
THE LOWER 90S EAST WITH GENERALLY MID 80S WEST.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
AS OF 230 PM EDT SUNDAY...

LINGERING UPPER TROUGH WELL TO THE NORTH WILL SWING ANOTHER COLD FRONT
TOWARD THE REGION FROM THE NW MONDAY NIGHT WITH THIS BOUNDARY BASICALLY
JUMPING TO THE EASTERN LEE TROUGH ON TUESDAY. FRONT LIKELY TO BE
PRECEDED BY A BROKEN BAND OF CONVECTION JUST NW OF THE CWA EARLY MONDAY
EVENING BEFORE LIKELY SPLITTING/WEAKENING UPON CROSSING THE WESTERN
RIDGES INTO DRIER AIR DURING LOSS OF HEATING. HOWEVER WITH GUIDANCE
SHOWING SOME LEFTOVER INSTABILITY NW COUNTIES AND POTENTIAL FOR MOMENTUM
TO CARRY CONVECTION A BIT FARTHER TO THE SE PENDING ORGANIZATION...INCLUDING
SOME LOW CHANCE POPS NW THIRD TUESDAY NIGHT BUT DRY ELSEWHERE.

GUIDANCE SHOWING MUCH OF THE AREA IN A SUBSIDENCE REGION TUESDAY INTO
TUESDAY NIGHT ALONG/BEHIND THE FRONT AIDED BY DEEP WESTERLY FLOW AND
LITTLE FOCUS. CANT TOTALLY RULE OUT ISOLATED SHRA/TSRA FAR WEST/SW WITH
THE LOW LEVEL CONVERGENT FLOW AND HIGHER THETA-E...AS WELL AS THE FAR
EASTERN PERIMETER WHERE WILL BE CLOSER TO THE BETTER INSTABILITY NEAR
THE LEE TROUGH. THIS AREA ALSO WHERE MAY BE FAR ENOUGH REMOVED
FROM DOWNSLOPING AND BETTER MIXING IN THE EVENING TO POP A SHOWER
OR TWO SO RUNNING WITH 20ISH POPS IN THESE LOCATIONS. OTRW
PARTLY/MOSTLY SUNNY BUT QUITE WARM/HOT VIA COMPRESSION TUESDAY
WITH HIGHS MID/UPPER 80S WEST AND LOW/MID 90S EAST.

NEXT RATHER STRONG SHORTWAVE WILL APPROACH FROM THE MIDWEST WEDNESDAY
AND ATTEMPT TO LIFT THE BOUNDARY BACK NORTH THROUGH THE REGION WEDNESDAY
NIGHT AS WARM FRONT AS THE WAVE PASSES TO THE NW. BEST INSTABILITY
AND DEEPER MOISTURE WILL BE OVER THE FAR WEST LATER WEDNESDAY WITH
MORE OVERRUNNING OF THE FRONT POSSIBLE WEDNESDAY NIGHT PENDING
JUST HOW FAR WEST THIS WAVE ENDS UP TRACKING. LATEST MODELS SUGGEST
COULD BE TOO FAR REMOVED FOR MUCH MORE THAN MID RANGE CHANCE POPS
FAR NORTH-WEST FROM LATER WEDNESDAY INTO WEDNESDAY NIGHT WITH LACK
OF DEEP CONVECTION PER ONLY WEAK LIFT/INSTABILITY. HOWEVER FOR NOW
WILL LEAVE IN SOME CHANCES ACROSS THE REGION AND SEE HOW LATER
RUNS EVOLVE GIVEN SUCH UNCERTAINTY. SHOULD AGAIN BE QUITE WARM/MUGGY
WEDNESDAY WITH THE 850 MB BOUNDARY SLIDING BACK NORTH ALLOWING
MORE OF A SW TRAJECTORY WHICH SHOULD AT LEAST HOLD HIGHS A CATEGORY
OR SO BELOW VALUES SEEN ON TUESDAY.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 1245 PM EDT SUNDAY...

TRANSITION TO MORE ZONAL FLOW ALOFT WILL OCCUR EARLY IN THE PERIOD AS
THE REGION GETS CAUGHT UNDER THE SURFACE-850 MB BAROCLINIC ZONE AND
WITHIN A NEARBY FRONTAL ZONE STRETCHED BACK INTO THE MIDWEST. A COUPLE
OF SHORTWAVES RIDING ALONG THESE FEATURES TO AID CONVECTIVE CHANCES...ESPCLY
NORTH/WEST THURSDAY INTO THURSDAY NIGHT AS DECENT LOW PRESSURE PASSES
JUST NORTH...SUPPORTIVE OF HIGH CHANCE/LOW LIKELY POPS. STRONGER
ENERGY ALOFT DROPPING OVER THE CENTRAL STATES UPPER RIDGE WILL THEN
START TO DIG OUT ANOTHER RATHER STRONG 5H TROUGH TO THE NW FRIDAY...WITH
AN ASSOCIATED SURFACE WAVE HELPING TO DRIVE THE NEXT COLD FRONT
THROUGH THE REGION BY FRIDAY EVENING. EARLIER MODELS AGREED ON QUITE
A BIT OF DEEP MOISTURE BEING PULLED NORTH AHEAD OF THE FRONT/WAVE
ON FRIDAY WITH GOOD DYNAMICS AND JET FEATURES ALOFT. THIS WOULD
SUPPORT MORE WIDESPREAD SHOWERS/STORMS FRIDAY UNLESS THE FRONT IS
FASTER SIMILAR TO THE LATEST GFS WHICH WOULD TREND THE BEST
COVERAGE THURSDAY INTO THURSDAY NIGHT. THUS HAVE TRENDED THE
HIGHEST CHANCE TO LIKELY POPS LATE THURSDAY INTO THURSDAY NIGHT
WHILE KEEPING HIGH CHANCES FRIDAY FOR CONSISTENCY AND LINE WITH
THE CURRENT CMC AND EARLIER ECMWF. WILL BE A BIT COOLER BUT STILL
HUMID PER MORE CLOUDS/SHRA WITH HIGHS MOSTLY 80S THURSDAY...
LOWERING TO 70S WEST TO MID 80S EAST FRIDAY.

SIMILAR TO THE LAST WEEK OR TWO...APPEARS ANOTHER SURGE OF MUCH DRIER/COOLER
AIR LIKELY BEHIND THE FRONT NEXT WEEKEND AS YET ANOTHER 5H TROUGH
CARVES ITSELF OUT ACROSS THE EAST. GUIDANCE EVEN COOLER ALOFT
WITH THIS SYSTEM GIVEN PROGGED 850 MB TEMPS AS COOL AS +12C MOUNTAINS
BUT MAY BE TOO COOL THAT FAR OUT. HOWEVER STILL ENOUGH TO DROP
HIGHS BACK IN THE 70S MOUNTAINS AND ONLY LOW/MID 80S OUT EAST AS
HIGH PRESSURE BUILDS/WEDGES IN FROM THE NORTH. RESIDUAL POPS A BIT
TRICKY TOWARD DAYS 6/7 BUT SHOULD BE DRIER WITH PERHAPS SOME
LEFTOVER UPSLOPE SHOWERS WEST SATURDAY AND ONLY ISOLATED FAR
SOUTHWEST ON SUNDAY.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
AS OF 745 PM EDT SUNDAY...

GENERALLY VFR CONDITIONS EXPECTED THROUGH THE TAF VALID PERIOD AS
A RELATIVELY DRY AIR MASS REMAINS OVER THE REGION. LOW-LEVEL
MOISTURE WILL SLOWLY BE INCREASING THROUGH THE PERIOD ON THE HEELS
OF SOUTHWEST FLOW EXPECTED TO EVOLVE MORE EARNESTLY ACROSS THE
REGION MONDAY AS SFC HIGH PRESSURE DRIFTS TO THE SOUTHEAST OF THE
REGION AND A TROUGH OF LOW PRESSURE TRACKS EASTWARD THROUGH THE
GREAT LAKES. AN ASSOCIATED FRONTAL BOUNDARY WILL BE APPROACHING
FROM THE NORTHWEST LATE IN THE DAY. CONVECTION IS EXPECTED TO
ACCOMPANY THE FRONT INTO EASTERN KY...FAR WESTERN WV...BEFORE
DISSIPATING AS THE ACTIVITY ATTEMPTS TO CROSS THE MOUNTAINS
DURING THE EVENING AND INTO A MUCH MORE STABLE AIR MASS IN OUR
REGION. HAVE NOT ADVERTISED ANY PRECIPITATION THIS TAF VALID
PERIOD.

FOG CONCERNS ARE MINIMAL AS AIR MASS IS VERY DRY. HOWEVER...AS IS
OFTEN THE CASE FOR LWB IN THE GREENBRIER VALLEY...RADIATIONAL
COOLING SHOULD SUPPORT FOG DEVELOPMENT LATE TONIGHT/EARLY MONDAY
MORNING AND THUS HAVE ADVERTISED A PERIOD OF 1/4SM FG VV001.
ELSEWHERE...CONFIDENCE IN ANY FOG IS LOW...PERHAPS A PERIOD OF
MVFR BR AND BCB/LYH.

WINDS...MOSTLY CALM OVERNIGHT...BECOMING SOUTHWEST MONDAY MID-
MORNING AND INCREASING INTO THE 7-8KT RANGE MOST SITES BY LATE
MORNING. SOME LOW END GUSTS POSSIBLE BLF AND ROA...BUT HAVE NOT
INCLUDED THOSE IN THE TAF JUST YET.

HIGH CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD.
MEDIUM TO HIGH CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD.
MEDIUM TO HIGH CONFIDENCE IN WIND SPD/DIR THROUGH THE TAF
VALID PERIOD.

EXTENDED AVIATION FORECAST...
MOSTLY VFR OUTSIDE OF ANY CONVECTION THROUGH THE PERIOD. A FRONT
WILL SET UP IN THE MID ATLANTIC WHICH COULD BRING A FEW SHRA/TSRA
BY TUESDAY...WITH PERHAPS A BIT MORE COVERAGE LATER WEDNESDAY AT
THIS POINT. THUS THE THREAT OF SUB-VFR REMAINS LOW UNTIL AROUND
MIDWEEK...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...JH
NEAR TERM...DS/MBS
SHORT TERM...JH
LONG TERM...JH
AVIATION...MBS/RAB


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