Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 201402
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1002 AM EDT SUN JUL 20 2014

.SYNOPSIS...
A WEAK WEDGE OF HIGH PRESSURE WILL REMAIN OVER THE AREA TODAY
BEFORE SLIDING OFF THE MID ATLANTIC COAST OVERNIGHT. A RESIDUAL
WEAK FRONTAL BOUNDARY ACROSS THE CAROLINAS WILL LIFT SLOWLY NORTH
INTO THE REGION ON MONDAY RESULTING IN CONTINUED UNSETTLED
WEATHER INTO EARLY NEXT WEEK.
&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 930 AM EDT SUNDAY...

WEAK WEDGE OF COOL AIR REMAINS IN PLACE EARLY THIS MORNING BUT NOT
AS STRONG AS SATURDAY GIVEN LACK OF RE-ENFORCING PRECIP...WITH
EVEN SOME BREAKS SHOWING UP JUST WEST OF THE NEW RIVER VALLEY.
THIS MAY ALLOW FOR A PERIOD OF SUNSHINE ESPCLY FAR SW VA INTO SE
WVA WHERE LACK OF LOW CLOUDS BEFORE THE FAINT SHORTWAVE NOW WEST
OF THE MOUNTAINS SLIDES EAST LATER IN THE DAY AND CAUSES
CLOUDS/SHRA TO FILL BACK IN. LATEST GUIDANCE ALSO SHOWS SOME
WIDELY SCTD SHRA/TSRA DEVELOPMENT MOUNTAINS WITH THIS FEATURE
ESPCLY AFTER 18Z WHEN MODELS INDICATE SOME MODEST 1000-1500 J/KG
CAPE OVER THE FAR WEST. THEREFORE CUT BACK ON POPS TO INIT BASED
ON CURRENT RADAR TRENDS AND ADDED IN A BIT MORE TSRA I-77 CORRIDOR
LATER ON PER LATEST HRRR AND NCEP WRF. CANT TOTALLY RULE OUT
ISOLATED -TSRA SE PIEDMONT BUT APPEARS LACK OF MUCH INSTABILITY
AND BETTER LIFT REMAINING SOUTH CLOSER TO THE OLD FRONT SHOULD
PRECLUDE MUCH MORE THAN SHOWERS AT THIS POINT. OTRW KEEPING SLIGHT
TO CHANCE POPS WITH HIGHEST ENDING UP FAR WEST LATER ON AND LEAST
ACROSS THE NE UNDER THE WEAKENING WEDGE. EVEN WITH SOME
SUN...COOLER MET MOS TEMPS STILL LOOK BEST SO KEPT VALUES CLOSE TO
THE CURRENT FORECAST WHICH KEEPS MOST IN THE 70S...ALTHOUGH THE NW
NC BLUE RIDGE SPOTS MAY STRUGGLE IN THE 60S MOST OF THE DAY.

PREVIOUS VALID DISCUSSION...

UPPER LEVEL TROUGH OVER THE EASTERN U.S. WILL REMAIN IN PLACE TODAY
AND TONIGHT WITH WEAK RIDGING FROM NEW ENGLAND CONTINUING TO
MAINTAIN A WEAK EASTERLY LOW-LEVEL WIND COMPONENT INTO THE MID-
ATLANTIC AND CENTRAL APPALACHIANS PRODUCING SUBTLE COOL-AIR
DAMMING. WITH VERY LITTLE FORCING EXPECTED AT THE SURFACE AND
ALOFT THERE SEEMS TO BE LITTLE OBVIOUS TRIGGER FOR SHOWER ACTIVITY
BUT THE AIR MASS THE OVERHEAD WILL REMAIN QUITE MOIST WITH PWATS
HOLDING NEAR 1.5 INCHES ACROSS MOST OF THE CWA...00Z/20 RAOB FROM
KRNK HAD 1.48 INCHES WHICH IS ABOUT THE 75TH PERCENTILE FOR DATE
IN JULY...ALSO RIGHT AT THE CLIMATOLOGICAL MAXIMA FOR THE YEAR.
THAT SAID THE QUESTION REMAINS WHETHER WE CAN DEVELOP ANY
CONVECTION AT ALL TODAY AND THAT MAY DEPEND ON SOME BREAKS IN THE
PERSISTENT OVERCAST. BEST CHANCES FOR ANY SHOWERS OR EVEN A
THUNDERSTORM TO DEVELOP WILL BE IN FAR WEST WHICH WILL BE LESS
UNDER THE INFLUENCE OF THE WEDGE. MODEL CAPES FROM ARW_RNK REACH
1000 J/KG BY LATE AFTERNOON AT BLUEFIELD SO PUT ISOLATED THUNDER
CHANCES IN THE WEST ALONG WITH CHANCE POPS GENERALLY FROM BLUE
RIDGE WESTWARD AND ONLY SLIGHT CHANCE EAST. BEST SYNOPTIC FORCING
FOR PRECIPITATION WILL BE WELL SOUTH OF OUR CWA IN ASSOCIATION
WITH SHORT-WAVE AND WEAK LOW DOWN ALONG THE GULF COAST. SOME OF
THIS ACTIVITY MAY REACH OUR SOUTHERN COUNTIES BUT AMOUNTS SHOULD
BE QUITE MODEST...GENERALLY UNDER 0.25 INCHES ON A MEAN AREAL
BASIS. TEMPS TRICKY AS WELL TODAY WITH CLOUDS/JULY SUN GAME IN
FULL SWING. USED MODEL BLEND BUT A FEW HOURS OF EXTRA HEATING
COULD PLAY HAVOC WITH CURRENT MID-70S WEST TO LOW 80S EAST
FORECAST.
&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
AS OF 430 AM EDT SUNDAY...

FOCUS THROUGH THIS PERIOD WILL EVOLVE AROUND A PERSISTENT TROUGH
ALONG THE SOUTHEAST U.S. COAST LEFT BEHIND FROM THE CURRENT UPPER
TROUGH AS IT LIFTS OUT. WITH TIME...THIS SYSTEM ASSUMES A PSEUDO
TROPICAL CHARACTERISTIC AND DRIFTS SLOWLY NORTHWESTWARD AS A
MAMMOTH UPPER RIDGE BUILDS ACROSS THE WESTERN U.S. AND RIDGES
EASTWARD TOWARD THE GREAT LAKES WHILE ANOTHER UPPER RIDGE
AMPLIFIES IN THE WEST ATLANTIC. THIS WILL FORCE THIS FEATURE TO
RETROGRADE FROM THE GA/SC COAST NORTHWESTWARD TOWARD THE SOUTHERN
APPALACHIANS THROUGH THE PERIOD. FINALLY...THE LONG RANGE MODELS
HAVE COME INTO REASONABLY GOOD AGREEMENT ON THE EVOLUTION AND
TRACK OF THIS SYSTEM. AS THIS SYSTEM DRIFTS NORTHWEST TOWARD THE
REGION DURING THE FIRST HALF OF THE WEEK...PWS WILL RISE TO NEAR
2.0 INCHES. THIS ALONG WITH INCREASING HEAT AND INSTABILITY SHOULD
SUPPORT AN INCREASE IN DIURNAL CONVECTION. THE BEST CHANCES FOR
SUCH SHOULD REMAIN FOCUSED ACROSS NW NC/FAR SW VA WHERE MOIST
SOUTHEAST UPSLOPE FLOW WILL BE ENHANCED ALONG THE BLUE RIDGE.
EXPECT SCATTERED DIURNAL CONVECTION AREA WIDE...WITH NUMEROUS
AFTERNOON/EVENING SHRA/TSRA ACROSS NW NC AND FAR SW VA THROUGH THE
PERIOD. CONSEQUENTLY...HAVE ADVERTISED HIGH CHC TO LOW LIKELY POPS
IN THESE AREAS THROUGH THE PERIOD DURING THE AFTERNOON HOURS. FOR
MUCH OF THE AREA THIS WILL RESULT IN INCREASING CHANCES OF
BENEFICIAL RAIN...BUT SLOW MOVING/TRAINING
THUNDERSTORMS...ESPECIALLY ACROSS THE MOUNTAINS TERRAIN OF NW
NC/FAR SW VA COULD BECOME MORE PROBLEMATIC AS THE WEEK PROGRESSES.
ALTHOUGH INSTABILITY WILL BE HIGH...DYNAMICS/SHEAR ARE WEAK.
HOWEVER...AN ISOLATED PULSE SEVERE WITH STRONG WIND GUSTS COULD
NOT BE COMPLETELY RULED OUT THROUGH THE PERIOD ANYWHERE IN THE CWA
FOR THAT MATTER.

850MB TEMPS WILL BE ON THE INCREASE AS HEIGHTS ALOFT RISE AS WELL.
HOWEVER...INCREASING DEWPOINTS/PWS AND PERSISTENT TROUGHINESS
ACROSS THE REGION WILL TEMPER ANY EXCESSIVE HEAT AND SHOULD KEEP
MOST AREAS IN THE 80S FOR HIGHS...70S IN THE MOUNTAINS...NEAR 90
ACROSS THE PIEDMONT. WEDNESDAY WILL BE THE WARMEST DAY IN ADVANCE
OF THE FRONT/UPPER TROUGH APPROACHING FROM THE NORTHWEST.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
AS OF 445 PM EDT SATURDAY...

UPPER RIDGE IS FORECAST TO REMAIN OVER THE WESTERN CONUS THROUGH
THE LONG TERM...WITH A PERSISTENT UPPER TROUGH OVER THE EASTERN
CONUS. A STRONG SHORT WAVE TRACKS FROM SOUTH CENTRAL CANADA ATOP
THE UPPER RIDGE TOWARD THE GREAT LAKES. THIS DRIVES A FRONTAL
SYSTEM INTO THE EASTERN U.S. AND OUR REGION BY THURSDAY. ECMWF/GFS
ARE IN REASONABLE AGREEMENT ON THE PROGRESSION AND TIMING OF THESE
FEATURES. THE FRONT SHOULD PUSH JUST SOUTH OF THE AREA BY
FRI...ALTHOUGH AT THIS TIME OF YEAR THERE IS ALWAYS SOME
UNCERTAINTY AS TO HOW FAR SOUTH THE FRONT WILL GO BEFORE STALLING.
THE STRENGTH OF THE NORTHWEST FLOW ALOFT IN OUR REGION OWING TO
THE STRONG UPPER RIDGE OUT WEST SHOULD SUPPORT THE FRONT PUSHING
SOUTH OF THE CWA AT A MINIMUM. THE GREATEST CHANCE FOR SHOWERS/STORMS
WILL BE THURSDAY AND THERE IS SOME CHANCE THAT THE LINGERING
PSEUDO TROPICAL SYSTEM ACROSS THE CENTRAL/SOUTHERN APPALACHIANS
AND ASSOCIATED MOISTURE COULD ENHANCE SHRA/TSRA CHANCES ALONG THE
FRONT. FRIDAY STILL LOOKS LIKE A DRY DAY WITH THE FRONTAL BOUNDARY
SOUTH OF THE CWA. MOISTURE COULD RETURN TO WESTERN AREAS BY
SAT...BUT HAVE KEPT POPS LOW AT THIS POINT WITH TOO MUCH
UNCERTAINTY ON ANY UPSTREAM NW FLOW DISTURBANCES.

AFTER A VERY WARM DAY WED...THURSDAY WILL BE A TRANSITION DAY
WITH THE FRONTAL PASSAGE...FOLLOWED BY A 4 TO 7 DEGREE DOWNWARD
TREND IN TEMPERATURES FOR FRIDAY AND SATURDAY. USED A GFS/ECMWF
MOS MODEL BLEND THROUGH THE PERIOD.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
AS OF 735 AM EDT SUNDAY...

GENERALLY POOR AVIATION CONDITIONS EXPECTED TO CONTINUE WEST OF
THE BLUE RIDGE...WITH MARGINAL AVIATION CONDITIONS EAST OF THE
BLUE RIDGE. UPPER TROUGH WILL LINGER ACROSS THE EASTERN U.S.
THROUGH THE PERIOD. A PSUEDO TROPICAL UPPER DISTURBANCE WILL
DEVELOP ALONG THE GA/SC COAST TODAY INTO MONDAY...THEN RETROGRADE
NW BETWEEN EXPANDING WESTERN ATLANTIC UPPER RIDGE AND WESTERN
CONUS UPPER RIDGE. SYSTEM WILL REMAIN TRAPPED ACROSS THE
SOUTHERN-CENTRAL APPALACHIANS THROUGH MID-WEEK. LATEST MODEL RUNS
SUPPORT -SHRA SKIRTING KDAN THROUGH MID-MORNING WITH LOW END VFR
OR HIGH END MVFR CIGS...LIKELY VFR VSBYS. BY AFTERNOON...EXPECT
SHRA AND EVEN A FEW TSRA TO DEVELOP ACROSS THE
ALLEGHANYS...INCLUDING LWB/BLF/BCB...SPREADING EAST TOWARD ROA
AROUND SUNSET. FOR NOW...HAVE CONFINED MENTION OF TSRA TO BLF
WHERE BEST INSTABILITY WILL EXIST. OVERNIGHT...THIS ACTIVITY
SHOULD GRADUALLY DISSIPATE...BUT EXPECT LOWERING CIGS/VSBYS MOST
AREAS AFT 06Z IN STRATUS/FOG TO MVFR...WITH POTENTIAL FOR IFR
BCB/BLF/LWB AFT 08Z. DEEPER MOISTURE SPREADING NORTH AND WEAK SE
FLOW SHOULD PROMOTE DRIZZLE THROUGH THE NEW
RIVER...GREENBRIER...AND POTENTIALLY EVEN THE ROANOKE VALLEYS LATE
TONIGHT/EARLY MON. WINDS THROUGH THE PERIOD REMAINING LIGHT SE
5KTS OR LESS.

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

EXTENDED AVIATION DISCUSSION... THE AFOREMENTIONED UPPER
DISTURBANCE WILL TRACK TOWARD NW NC MON AND STALL/SHEAR OUT ACROSS
THE SOUTHERN-CENTRAL APPALACHIANS TUE-WED IN ADVANCE OF AN
APPROACHING COLD FRONT FOR THU. EXPECT SCT-NMRS DIURNAL CONVECTION
EACH DAY...WITH THE BEST CHANCE/COVERAGE THROUGH THE ALLEGHANYS
AND WEST OF THE BLUE RIDGE. FRONTAL SYSTEM THU WILL BRING MORE
WIDESPREAD SHRA/TSRA TO ALL AREAS. PERIODS OF MVFR WITH LOCALIZED
IFR CIGS CAN BE EXPECTED THROUGH THU. THE HIGH MOISTURE CONTENT IN
THE ATMOSPHERE AND DAILY -SHRA WILL PROMOTE DEVELOPMENT OF LATE
NIGHT/EARLY MORNING FOG...ESPECIALLY IN THE USUAL SUCH PRONE
LOCATIONS...NAMELY LWB/BCB/LYH. IMPROVED AVIATION CONDITIONS ARE
EXPECTED FRIDAY BEHIND THE FRONT WITH CLEARING SKIES AND LITTLE
TO NO PRECIPITATION...EXPECT POSSIBLY KDAN.

&&

.CLIMATE...
THE PERSISTENT LOW CLOUD COVER...DRIZZLE AND EASTERLY FLOW
COMBINED TO PRODUCE THREE NEW RECORD LOW MAXIMA FOR THE DATE
YESTERDAY JULY 19 2014. BLACKSBURG...LEWISBURG AND BLUEFIELD ALL
SET NEW DATE RECORDS...BY 6 DEGREES F IN THE CASE OF BLACKSBURG.
SEE WBCRERRNK FOR DETAILS.

&&

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

&&

$$
SYNOPSIS...JH/PC
NEAR TERM...JH/PC
SHORT TERM...RAB
LONG TERM...PM/RAB
AVIATION...PC/RAB
CLIMATE...PC


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