Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 230145
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
945 PM EDT TUE JUL 22 2014

.SYNOPSIS...
UPPER TROUGH OVER THE GULF COAST STATES SHIFTS WEST THROUGH
WEDNESDAY LEAVING A RESIDUAL WEAK BOUNDARY AND LOW LEVEL MOISTURE
OVER THE AREA INTO MID WEEK. A COLD FRONT WILL BE ARRIVING
THURSDAY FROM THE NORTHWEST...THEN EXITING BY THURSDAY NIGHT. HIGH
PRESSURE BUILDS IN ON FRIDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 940 PM EDT TUESDAY...

LOW LEVEL WEDGE THAT HAS BEEN IN PLACE FOR THE PAST FEW DAYS HAS
SHOWN SIGNS OF BREAKING DOWN...AS SFC WINDS HAVE BEEN GRADUALLY
VEERING TO THE SOUTH THIS EVENING. MODELS ARE IN GOOD AGREEMENT
THAT AS AN UPPER LEVEL SHORT WAVE MOVES OVER THE GREAT LAKES BY
12Z WEDNESDAY...LOW LEVEL WINDS IN OUR AREA WILL CONTINUE TO VEER
TO THE WEST/NORTHWEST OVERNIGHT. WITHOUT AN UPSLOPE FLOW TONIGHT
CLOUD COVER SHOULD BE LIMITED AND ADJUSTED SKY CONDITIONS
ACCORDINGLY IN THE FORECAST.

PATCHY FOG IS STILL POSSIBLE TONIGHT WITH A MOIST AIRMASS IN THE
LOW LEVELS...AS THE 00Z RNK SOUNDING SHOWING A FAIRLY MOIST
ATMOSPHERE BELOW 700MB...AND LIGHT WINDS. WITH THE GSO SOUNDING
SHOWING MUCH HIGHER PWATS (1.85 INCHES VS. 1.2 AT RNK)...CANNOT
RULE OUT A STRAY SHOWER IN THE SOUTHERN PORTION OF THE FORECAST
AREA OVERNIGHT.

WITH LESS COVER...BROUGHT TEMPS DOWN A COUPLE OF DEGREES FOR
TONIGHT.

THE NEXT STRONG 5H TROF AND ASSOCIATED COLD FRONT WILL BE
APPROACHING ON WED AS HIGH PRESSURE SHIFTS FARTHER SOUTH ALLOWING
DEEPENING WESTERLY FLOW AND A SUBSEQUENT LEE TROF WELL EAST OF THE
BLUE RIDGE. MODELS SPARK MOST AFTERNOON CONVECTION ALONG THE
SOUTHERN BLUE RIDGE GIVEN THE WEAK BOUNDARY LAYER SW FLOW AND
BETTER DIFFERENTIAL HEATING BUT STILL IFFY GIVEN WESTERLY FLOW
ALOFT AND ONLY FAINT LIFT. ELSW APPEARS RATHER ISOLATED DESPITE
LINGERING MOISTURE GIVEN DRY AIR ALOFT AND DOWNSLOPING WEST WINDS
ACROSS THE EAST SO KEEPING SHOTGUN CHANCE POPS. HOWEVER THE
UPSTREAM PRE- FRONTAL BAND OF TSRA WILL LIKELY BE NEARING THE NW
SLOPES LATE. THUS KEPT IN LOW LIKELYS EXTREME WEST...BUT MOSTLY
TOWARD SUNSET AT THIS POINT. SOME ISOLATED SEVERE POSSIBLE IF
PULSE STORMS ORGANIZE MORE EARLY...AND UPSTREAM ACTIVITY MOVES
INTO THE WEST IN MORE OF A LINE FEATURE...ALTHOUGH THIS MAY BE
AFTER INSTABILITY IS STARTING TO FADE. OTRW SHOULD SEE CLOUDS
BREAK QUICKER UNDER THE WESTERLY FLOW ALLOWING INSOLATION AND 85H
TEMPS AROUND +20C TO AID WEAK COMPRESSION IN PUSHING HIGHS INTO
THE 80S WEST AND 90-95 EAST.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 345 PM EDT TUESDAY...

WEDNESDAY NIGHT...PREFRONTAL MCS LIKELY TO IMPACT AT LEAST THE
WESTERN HALF OF THE CWA...ACTIVITY FADING WITH LOSS OF DAYTIME
HEATING. REMNANT OUTFLOW MAY REACH PIEDMONT BY DAYBREAK THURSDAY
AND DEBRIS CLOUDINESS WILL LIKELY REMAIN TO START THE DAY
THURSDAY. MODELS ARE IN AGREEMENT THE ACTUAL COLD FRONT WILL
ENTER OUR SOUTHEAST WEST VIRGINIA COUNTIES LATE MORNING/EARLY
AFTERNOON ON THURSDAY...AND CONTINUE EAST THROUGH THE DAY. ATTM
THINK ABUNDANT CLOUDINESS EARLY THURSDAY MAY INHIBIT SOLAR
INSOLATION...LIMITING INSTABILITY OVER ALL BUT THE FAR
SOUTHEASTERN CWA...THE GREATEST CHC FOR SHOWERS/STORMS OCCURRING
FROM OUR PIEDMONT EASTWARD INTO THE TIDEWATER OF VA/NC.

FOR NOW WILL MAINTAIN HIGH POPS BOTH WEDNESDAY NIGHT AND
THURSDAY...THEN END THE PRECIP THREAT QUICKLY FROM WEST TO EAST
WITH THE PASSAGE OF THE FRONT...LEAVING MAINLY DRY CONDITIONS
FOR THE AREA BY FRIDAY.

WEAK HIGH PRESSURE WILL BUILD INTO THE AREA BEHIND THE
FRONT...AND SHOULD PROVIDE A DAY...MAYBE TWO...OF PRECIP FREE
CONDITIONS.

TEMPERATURES THURSDAY WILL BE TEMPERED BY CLOUDS ASSOCIATED WITH
THE FRONT...THEN TREND DOWN A FEW DEGREES FOR FRIDAY. THE AIRMASS
CHANGE IS NOT OVERLY DRY NOR COOL...SO WHEN THE SUN POPS OUT
FRIDAY...READINGS MAY FEEL JUST AS WARM AS THURSDAY...ALTHOUGH THE
DEWPOINTS WILL NOT BE AS ROBUST.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 400 PM EDT TUESDAY...

FOR THE WEEKEND AND INTO EARLY NEXT WEEK...THE AREA REMAINS
VULNERABLE TO NW FLOW DISTURBANCES TRACKING AROUND THE LARGE
WESTERN/CENTRAL CONUS UPPER RIDGE. A PARTICULARLY STRONG
DISTURBANCE...NOTED BY ALL THE MODELS...PROMISES TO AMPLIFY THE
EASTERN LONG WAVE TROUGH...A FEATURE THAT SHOULD KEEP
CONDITIONS UNSETTLED WITH NEAR TO SLIGHTLY BELOW NORMAL
TEMPERATURES WHILE THE EXTREME HEAT REMAINS WELL TO OUR WEST AND
WELL AWAY FROM OUR PART OF THE COUNTRY.

THE BEST CHANCE FOR SHOWERS/STORMS LOOKS TO BE SUNDAY AS THE
SURFACE FRONT ASSOCIATED WITH THE STRONG DISTURBANCE CROSSES THE
FORECAST AREA FROM THE NORTHWEST. POTENTIAL EXISTS FOR STORMS TO
BE ORGANIZED WITH UPSTREAM MCS IMPACTING THE FORECAST AREA.

GENERALLY FOLLOWED HPC GUIDANCE THROUGH THE PERIOD. TRENDED POPS
UP FOR SUNDAYS FROPA...THEN DOWN FOR A DAY OR TWO AFTER SUNDAYS
FRONTAL PASSAGE. TENDENCY FOR FRONTAL PASSAGES IS TO BRING SOME
DOWNTIME AS WITH RESPECT TO POPS BEFORE MOISTURE AND INSTABILITY
CAN RETURN.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
AS OF 715 PM EDT TUESDAY...

ONLY ISOLATED STORMS WERE NOTED ON RADAR...MAINLY NEAR KDAN AND
ACROSS THE HIGHER TERRAIN OF SOUTHEAST WV. THIS SMALL AREA OF
CONVECTION WILL DISSIPATE SHORTLY AFTER SUNSET...AND INCLUDED ONLY
AN HOUR OR TWO OF VCSH AT KDAN/KLWB/KBLF THIS EVENING.

AS WEAK HIGH PRESSURE CONTINUES TO BUILD SOUTHWEST...LIGHT SFC
WINDS WILL VEER TO THE SOUTH AND SOUTHWEST. THIS SHOULD RESULT IS
LESS CLOUD COVER COMPARED TO WHAT HAS BEEN EXPERIENCED FOR THE
PAST FEW MORNINGS. HOWEVER...LIGHT WINDS AND A MOIST LOW LEVEL
AIRMASS WILL LEAD TO THE DEVELOPMENT OF FOG AFTER 05Z.
THOSE CLIMATOLOGICAL FAVORED AREAS...KLWB AND KBCB...WILL HAVE
THE BEST CHANCE OF SEEING IFR VISIBILITIES LATE TONIGHT/EARLY
TOMORROW DUE TO FOG. MVFR VISIBILITIES ARE POSSIBLE AT KLYH AND
KDAN.

ANY FOG WILL QUICKLY BURN OFF EARLY WEDNESDAY...THANKS TO A
SOUTHWEST LOW LEVEL FLOW IN ADVANCE OF AN APPROACHING COLD FRONT.
HOWEVER...THIS WILL USHER IN DEEPER MOISTURE AND EXPECT BETTER
COVERAGE WITH AFTERNOON SHOWERS AND STORMS...ESPECIALLY ACROSS THE
SOUTHERN BLUE RIDGE. AS A RESULT...INTRODUCED VCTS FOR THE
MOUNTAIN TAF SITES WEDNESDAY AFTERNOON.

EXTENDED AVIATION DISCUSSION...

NEXT NORTHERN STREAM UPPER TROUGH AND ITS ASSOCIATED COLD FRONT
WILL APPROACH WEDNESDAY NIGHT AND WORK THROUGH THE REGION ON
THURSDAY. THIS WILL BRING THE BEST CHANCES OF MORE WIDESPREAD
SHOWERS TO THE MOUNTAINS AND PERHAPS SOME DEEPER CONVECTION EAST
OF THE BLUE RIDGE PENDING TIMING OF THE BOUNDARY THURSDAY
AFTERNOON. AIRMASS WILL DRY OUT BEHIND THE FRONT GOING INTO FRIDAY-
SATURDAY. OVERALL EXPECT SUB VFR AT TIMES THURSDAY WITH SHRA/TSRA
AND MAYBE SOME FOG THU NIGHT...FOLLOWED BY VFR FRI- SAT OUTSIDE OF
ANY VALLEY FOG AT KLWB/KBCB EACH MORNING.

&&

.EQUIPMENT...
AS OF 945 PM EDT TUESDAY...

KFCX RADAR IS BACK UP...BUT IN A DEGRADED MODE. TECHNICIANS WILL
AGAIN BE WORKING ON THE RADAR WEDNESDAY...AND AS A RESULT...THE
RADAR WILL BE DOWN AGAIN TOMORROW FOR AN UNKNOWN PERIOD OF TIME.

&&

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

&&

$$
SYNOPSIS...JH/WP
NEAR TERM...JH/PH
SHORT TERM...PM
LONG TERM...PM
AVIATION...JH/PH/WP
EQUIPMENT...PH


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