Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 211718
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
118 PM EDT MON JUL 21 2014

.SYNOPSIS...
A WEAK WEDGE OF HIGH PRESSURE ALONG THE MID ATLANTIC COAST WILL
CONTINUE TO EXTEND INLAND ACROSS THE AREA THIS AFTERNOON THROUGH
TUESDAY. EAST TO SOUTHEAST WINDS AROUND THE HIGH WILL COMBINE
WITH DEEP MOISTURE LIFTING NORTH WITH A RESIDUAL FRONTAL BOUNDARY
TO PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS INTO TUESDAY
EVENING. A STRONGER COLD FRONT WILL APPROACH THE REGION FROM THE
NORTHWEST WEDNESDAY...AND PUSH THROUGH THE AREA THURSDAY...RESULTING
IN MORE WIDESPREAD SHOWERS AND STORMS.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 935 AM EDT MONDAY...

AXIS OF HEAVIER SHRA/TSRA REMAINS CONFINED OVER THE SE EDGE OF
THE VA PIEDMONT THIS MORNING IN A BELT OF HIGHER THETA-E AND NORTH
OF A WEAK WAVE ALONG THE RESIDUAL FRONT TO THE SOUTH. ALSO SEEING
A SMALL BAND OF SHRA STUCK ALONG THE CENTRAL BLUE RIDGE JUST SOUTH
OF ROA PER LOW LEVEL UPSLOPE OFF THE MORNING RNK RAOB. OTRW
SOUNDINGS SHOW AN INCREASE IN LOW LEVEL MOISTURE THIS MORNING WITH
MORE TROPICAL NATURE PWATS OFF TO THE SOUTH AND EAST CLOSER TO THE
OLD FRONT. HOWEVER HEADING NORTH...RAOBS REMAIN RATHER DRY ALOFT
AND CAPPED IN THE MID LEVELS WITH LATEST VISIBLE PICS SHOWING LESS
CLOUDS WEST OF THE BLUE RIDGE WHERE THERE IS LITTLE LEFTOVER
WEDGING. LATEST GUIDANCE TENDS TO PICK UP ON THIS DRIER AIR ALOFT
AND SHIFT CURRENT PIEDMONT COVERAGE EAST WHILE GRADUALLY
DEVELOPING AT LEAST SCATTERED SHRA/TSRA OVER THE SOUTHERN THIRD
WITH ADDED SHRA ESPCLY OUTFLOW HEADING UP FROM N CAROLINA. SOME
OF THESE LIKELY TO PRODUCE HEAVY RAINFALL GIVEN SLOW MOVEMENT AND
INCREASING MOISTURE. THUS BUMPING UP POPS SOUTHERN HALF THIS
AFTERNOON...WITH OVERALL LOW CHANCES NORTH/WEST...WHERE
INSTABILITY WILL ACTUALLY BE HIGHER WHILE THE OVERALL SEVERE
THREAT REMAINS LOW.

OTRW ENOUGH OF A WEDGE TO HOLD CLOUDS IN AGAIN OVER THE EAST
WHICH SHOULD HOLD TEMPS DOWN TO THE MUGGY 70S TO PERHAPS LOW 80S
WHERE SEE A FEW PEAKS OF SUN. APPEARS WARMEST TEMPS OVER THE FAR
WEST GIVEN INSOLATION WITH SOME LOW 80S POSSIBLE INTO SE WEST VA.


PREVIOUS VALID DISCUSSION AS OF 400 AM EDT MONDAY...

WILL START THE DAY WITH A BROAD UPPER LEVEL TROUGH SITUATED OVER
THE OHIO RIVER VALLEY...WHILE WEAK HIGH PRESSURE REMAINS IN PLACE
ACROSS NEW ENGLAND INTO THE MID ATLANTIC. DEWPOINT TEMPERATURES
ARE NOTICEABLY HIGHER THIS MORNING THANKS TO THE EASTERLY WIND
FLOW AROUND THE HIGH CARRYING ATLANTIC MOISTURE INTO OUR AREA.
ALSO KEEPING AN EYE ON WEAK UPPER LEVEL DISTURBANCES PUSHING INTO
OUR AREA FROM THE SOUTH...RESULTING IN SHOWERS AND OCCASIONAL
THUNDERSTORM ACTIVITY ACROSS THE SOUTHSIDE AND NORTHERN NORTH
CAROLINA.

CLOUDS WILL BE SLOW TO SCATTER TODAY DUE TO THE UPPER LEVEL
TROUGHING...AND EXPECT MOSTLY CLOUDY SKIES WITH OCCASIONAL BREAKS
OF SUNSHINE FOR MUCH OF OUR AREA. SHOWER AND THUNDERSTORM ACTIVITY
WILL REMAIN CONFINED MAINLY ACROSS OUR SOUTHEAST THROUGH LATE
MORNING... BUT EXPECT SHOWER ACTIVITY TO INCREASE AREAWIDE BY
EARLY AFTERNOON IN SPOTTY...HIT AND MISS FASHION...WITH SOME OF
THE SHOWERS INTENSIFYING INTO THUNDERSTORMS BY LATE AFTERNOON.
DESPITE THE INCREASED INSTABILITY...BELIEVE THE WEAKENING HIGH
PRESSURE WEDGE WILL STILL HAVE ENOUGH INFLUENCE TO PREVENT STORMS
FROM BECOMING SEVERE. RATHER...THE BIGGER CONCERN WILL BE SLOW
MOVING AND LOCALLY HEAVY RAINFALL DUE TO WEAK WINDS ALOFT. BELIEVE
THE THREAT OF ANY SORT OF FLOODING IS VERY REMOTE...BUT ONE THAT
CANNOT BE RULED OUT. SHOWER AND THUNDERSTORM ACTIVITY WILL
DIMINISH DURING THE EVENING... BUT STILL EXPECT A FEW AREAS OF
RAINFALL TO LINGER INTO EARLY TUESDAY.

AFTERNOON HIGHS FOR TODAY WILL BE A FEW DEGREES WARMER THAN
SUNDAY...BUT STILL SEVERAL DEGREES BELOW AVERAGE FOR THE SECOND
HALF OF JULY...WITH MID 70S TO LOW 80S AREAWIDE. THE RETURN OF
SUBTROPICAL AIR WILL MAKE FOR WARM AND MUGGY CONDITIONS TONIGHT...
WITH PATCHES OF FOG AS LOWS BOTTOM OUT IN THE MID 60S TO THE LOW
70S.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
AS OF 415 AM EDT MONDAY...

MODELS IN GOOD AGREEMENT ON THE OVERALL SYNOPTIC PATTERN WITH A
MAMMOTH NEAR 600DM RIDGE BUILDING ACROSS THE INTERMOUNTAIN WESTERN
U.S....A SIMILAR RIDGE BUILDING ACROSS THE WESTERN ATLANTIC...
AND AN UPPER TROUGH LINGERING ACROSS THE SOUTHEASTERN U.S. STUCK
BETWEEN THE TWO AFOREMENTIONED UPPER RIDGES. THIS PATTERN WILL
KEEP THE HOT WEATHER WELL TO OUR WEST. THE PERSISTENT SE U.S.
UPPER TROUGH WILL DRIFT/RETROGRADE TO THE NW WITH TIME IN RESPONSE
TO THE BUILDING WESTERN ATLANTIC UPPER RIDGE. THIS SYSTEM HAS SOME
PSEUDO TROPICAL CHARACTERISTICS WITH PWS NEARING 2.0 INCHES IN THE
ASSOCIATED AIR MASS. AS THIS SPREADS NORTHWEST TUE-WED...EXPECT
AN INCREASE IN DIURNALLY DRIVEN CONVECTION...ESPECIALLY ALONG THE
EAST FACING SLOPES OF THE BLUE RIDGE FROM NW NC NORTHEASTWARD INTO
SOUTHWEST/SOUTH CENTRAL VA. WITH SUCH HIGH PWS AND WEAK STEERING
CURRENTS ALOFT...THE THUNDERSTORMS WILL BE VERY EFFICIENT RAIN
PRODUCERS AND AS SUCH COULD RESULT IN LOCALIZED FLOODING.
FORTUNATELY...MUCH OF THE CWA IS IN A MILD DROUGHT...SO THE
RAINFALL WILL BE WELCOME. BUT IN MOUNTAINOUS TERRAIN...AN INCH OR
TWO IN AN HOUR CAN BECOME PROBLEMATIC RATHER QUICKLY.
HOWEVER...CERTAINLY NOT ENOUGH CONCERN FOR ANY FLOOD/FLASH FLOOD
WATCH AT THIS POINT DUE TO THE LOCALIZED NATURE OF THE EXPECTED
THUNDERSTORMS. HOWEVER...A MENTION OF LOCALIZED HEAVY RAIN IN THE
HWO ACROSS MAINLY THE NC COUNTIES IN COLLABORATION WITH OUR
NEIGHBORS IS WARRANTED. MEANWHILE...THE SEVERE THREAT SHOULD BE
NEAR NIL WITH AN INCREASING TROPICAL AIR MASS...HENCE MOIST
ADIABATIC SOUNDING...AND VERY WEAK WINDS ALOFT. NEVER CAN TOTALLY
RULE OUT AN ISOLD WET DOWNBURST...BUT NOT ENOUGH CONFIDENCE TO
EVEN MENTION IN THE HWO AT THIS POINT.

THE BEST FOCUS FOR CONVECTION TODAY SHOULD BE ACROSS NORTHWEST/NORTH
CENTRAL NC INTO THE ADJACENT COUNTIES OF SOUTHWEST/SOUTH CENTRAL
VA...SHIFTING MORE TOWARD SW VA/SE WV ON THU.

FOR THU...MODELS GENERALLY IN GOOD AGREEMENT IN BRINGING A FRONT
INTO THE REGION FROM THE NORTHWEST AS A STRONG UPPER DISTURBANCE
TRACKS ATOP THE WESTERN/CENTRAL U.S. UPPER RIDGE TOWARD THE GREAT
LAKES. THE LINGERING DISTURBANCE ACROSS THE SOUTHERN/CENTRAL
APPALACHIANS WILL SHEAR OUT IN ADVANCE OF THIS FEATURE...BUT LEAVE
AMPLE MOISTURE FOR THE FRONTAL SYSTEM TO ACT UPON. FOR A
CHANGE...THE ECMWF IS ACTUALLY SLIGHTLY FASTER THAN THE GFS IN
BRINGING THIS SYSTEM THROUGH THE CWA...WITH MOST FAVORED TIMING TO
ENTER THE WESTERN SECTIONS WED NIGHT/EARLY THU...TRACKING ACROSS THE
CWA THU...SHIFTING TO THE SOUTH OF THE AREA FRI. AGAIN...THE MAIN
CONCERN WITH THIS FRONT WILL BE LOCALIZED HEAVY RAINFALL AS IT
INTERACTS WITH THE VERY MOIST AIR MASS IN PLACE ACROSS THE REGION.
OVERALL PROGGED INSTABILITY AND SHEAR SUGGEST THAT THE SEVERE THREAT
IS MINIMAL AND CURRENTLY SPC DOES NOT HAVE ANY AREAS OUTLOOKED. EVEN
SO...USUALLY THE DYNAMICS/BETTER FORCING EVIDENT ALONG A FRONT OFFER
AT LEAST A SLIGHT INCREASE IN THE SEVERE THREAT.

WITH RESPECT TO TEMPERATURES...850MB TEMPS WILL CREEP UP SLIGHTLY
INTO THE +18C RANGE AS 500MB HEIGHTS RISE TOWARD 590DM.
HOWEVER...INCREASING MOISTURE CONTENT...ABUNDANT CLOUD COVER...AND
SCT-NMRS SHRA/TSRA EACH AFTERNOON SHOULD KEEP TEMPERATURES FROM
BECOMING OPPRESSIVELY HOT. HOWEVER...HUMIDITY LEVELS WILL BE NOTABLY
HIGHER THAN RECENT DAYS...SO EVEN WITH HIGHS MOSTLY IN THE 80S WEST
TO NEAR 90 PIEDMONT...DEWPOINTS 65 TO 70 WILL YIELD SOME RATHER
UNCOMFORTABLE AFTERNOONS COMPARED TO RECENT DAYS WITH RECORD LOW
HIGHS IN THE 60S. WEDNESDAY SHOULD BRING THE WARMEST TEMPERATURES TO
THE REGION IN ADVANCE OF THE FRONT...ESPECIALLY ACROSS THE
PIEDMONT...WHICH SHOULD SEE A SLIGHT DECREASE IN CONVECTION AT THAT
TIME...THUS POTENTIALLY SEEING MAX TEMPS IN THE LOW 90S LYH-DAN AND
VICINITY.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
AS OF 445 AM EDT TUESDAY...

FRONTAL SYSTEM SHOULD SHIFT JUST SOUTH OF THE REGION FRI...ALTHOUGH
ALWAYS UNCERTAINTY IN MID-SUMMER REGARDING AS TO HOW FAR SOUTH THE
FRONT WILL GO BEFORE STALLING. WITH STRONG UPPER RIDGE TO THE WEST
AND STRONG NW FLOW ALOFT ACROSS OUR REGION AS A RESULT...FEEL IT
WILL AT LEAST GET FAR ENOUGH SOUTH OF THE CWA TO ENSURE ONE MOSTLY
DRY DAY. HAVE HELD ONTO SLIGHT CHC POPS ACROSS THE FAR SE
COUNTIES...MAINLY THE NC COUNTIES...TO ACCOUNT FOR THE SLIGHTLY LESS
SOUTHWARD MOVEMENT ADVERTISED BY THE ECMWF. DRYING AND COOLING
BEHIND THE FRONT COMPARED TO THE PAST TWO SUCH EVENTS IS MINOR AND
WE SHOULD STILL SEE HIGHS IN THE 80S...70S MOUNTAINS. HUMIDITY
LEVELS/DEWPOINTS WILL DROP SLIGHTLY...BUT WITH PWS STILL NEAR 1.5
INCHES...SIGNIFICANT DRYING IS NOT EXPECTED WITH THIS FRONTAL
PASSAGE.

FOR THE WEEKEND AND INTO EARLY NEXT WEEK...THE AREA REMAINS
VULNERABLE TO NW FLOW DISTURBANCES TRACKING AROUND THE LARGE
WESTERN/CENTRAL U.S. UPPER RIDGE. THERE ARE SEVERAL SUCH STRONG
DISTURBANCES NOTED IN THE MODELS DURING THIS TIME FRAME...THE MOST
NOTABLE ON SUN...THAT COULD BRING THUNDERSTORMS BACK INTO THE AREA.
HAVE RETAINED EXISTING CHC POPS THAT WERE ADVERTISED WITH EARLIER
FORECAST PACKAGES...BUT CLEARLY THESE COULD POTENTIALLY BECOME
LIKELY AT SOME POINT AS THE DEVELOPMENT OF AN UPSTREAM MCS BECOMES
MORE APPARENT. BY EARLY THE FOLLOWING WEEK...MODELS IN GOOD
AGREEMENT ON THE UPPER TROUGH REAMPLIFYING ACROSS THE EASTERN
U.S...WHICH 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 COUNTY...FORTUNATELY.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
AS OF 1250 PM EDT MONDAY...

SIMILAR TO SUNDAY...WIDESPREAD MVFR CIGS CONTINUE THIS AFTERNOON
WITH THE EXCEPTION OF KBLF WHERE SEEING VFR ON THE WESTERN
PERIMETER OF THE LOW LEVEL WEDGE. HOWEVER SHOWERS REMAIN VERY
ISOLATED ATTM WITH MOST OF THE BEST LIFT AND COVERAGE JUST SOUTH
OF THE REGION CLOSER TO THE OLD FRONT IN THE CAROLINAS. MOISTURE
SPREADING NORTH FROM THIS ACTIVITY LIKELY TO KEEP LOWER CIGS IN
PLACE THIS AFTERNOON WITH ONLY A SLOW IMPROVEMENT IN CLOUD BASES
AS THE LOW LEVEL MOISTURE STAYS TRAPPED UNDER THE CANOPY HEADING
IN FROM THE SOUTH. STILL SOME CHANCE AT SEEING BRIEF PERIODS OF
VFR ESPCLY ACROSS THE WESTERN LOCATIONS...WHILE OCNL IFR COULD
OCCUR NEAR OR WITHIN ANY DEVELOPING SHRA/TSRA THAT LOOK MOST
LIKELY AROUND KDAN AND PERHAPS OVER THE FAR SW FROM KHLX TO KBLF.
THUS WILL LEAVE IN THE GOING VICINITY SHRA/TSRA MENTION MOST
SPOTS BUT LOW CONFIDENCE GIVEN ONLY SPOTTY HEATING AND FORCING
ALOFT.

ANY CONVECTION SHOULD BE DIURNAL AND FADE FOR THE MOST PART AFTER
SUNSET...BUT LEAVE WIDESPREAD MVFR CIGS TRENDING TOWARD IFR AFT
MIDNIGHT WITH POCKETS OF -DZ BR AS WELL AS LIFR NEAR THE BLUE
RIDGE. ALSO SOME POTENTIAL TO SEE ADDED BANDS OF NOCTURNAL
SHOWERS REDEVELOP ALONG THE SOUTHERN BLUE RIDGE TOWARD KDAN GIVEN
THE SE FLOW AND OLD OUTFLOW UNDER SUCH DEEP MOISTURE. OTRW WINDS
SOUTHEAST THROUGH THE TAF VALID PERIOD AT SPEEDS OF 5-7KTS...LESS
AT NIGHT.

WEDGE WILL WEAKEN A BIT MORE ON TUESDAY AS THE LOW LEVEL FLOW
TURNS A LITTLE MORE SOUTHERLY PERHAPS ALLOWING LOW CIGS TO IMPROVE
A BIT FASTER TO VFR THAN THE LAST COUPLE OF DAYS. HOWEVER ANY
BREAKS WILL ONLY LEAD TO QUICKER DEVELOPMENT OF SHRA/TSRA BY
TUESDAY AFTERNOON WITH DECENT COVERAGE LIKELY ESPCLY BLUE RIDGE...AND
POINTS WEST ON TUESDAY...BUT MAINLY AFTER THE VALID TAF PERIOD.

EXTENDED AVIATION DISCUSSION...

UPPER SYSTEM IN THE BASE OF THE FADING SE TROUGH WILL CUTOFF AND
SHIFT WESTWARD INTO WEDNESDAY IN ADVANCE OF AN APPROACHING COLD
FRONT FOR THURSDAY. HOWEVER LEFTOVER DEEP MOISTURE WITH THE OLD
FRONT AROUND WILL RESULT IN MORE WIDESPREAD DIURNAL CONVECTION
WEDNESDAY AFTERNOON WITH EARLY FOG IN SPOTS GIVING WAY TO BRIEF
VFR...THEN PERIODIC MVFR IN CLOUDS/TSRA. A COLD FRONT LOOKS TO
PUSH THROUGH ON THURSDAY WITH BETTER COVERAGE OF MVFR/IFR
PRODUCING SHOWERS AND STORMS. IMPROVED AVIATION CONDITIONS ARE
EXPECTED FRIDAY BEHIND THE FRONT WITH CLEARING SKIES AND LITTLE TO
NO PRECIPITATION INTO SATURDAY.
&&

.EQUIPMENT...
AS OF 1000 AM EDT MONDAY...

KFCX RADAR IS DOWN. TECHNICIANS HAVE BEEN NOTIFIED AND WILL
INVESTIGATE LATER TODAY. NO ESTIMATED TIME FOR RETURN TO SERVICE.

&&

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

&&

$$
SYNOPSIS...JH/NF
NEAR TERM...CF/JH/NF
SHORT TERM...RAB
LONG TERM...PM/RAB
AVIATION...JH/NF/RAB
EQUIPMENT...CF


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