Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 130204
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1004 PM EDT SAT JUL 12 2014

.SYNOPSIS...
HIGH PRESSURE WILL GIVE WAY TO RETURN SOUTHWEST FLOW AND
INCREASING MOISTURE THROUGH SUNDAY. THEN A STRONG COLD FRONT
APPROACHES FROM THE WEST ON MONDAY AND CROSS THE REGION ON
TUESDAY. COOL HIGH PRESSURE FOLLOWS THE FRONT FOR THE LATTER
HALF OF NEXT WEEK.

&&

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

PATCHY FOG OVERNIGHT...MAINLY IN THE MOUNTAIN VALLEYS WHERE SOME
ISOLATED SHOWERS OCCURRED LATE SATURDAY AFTERNOON. OTHER THAN
THAT...ANTICIPATE A QUIET OVERNIGHT...WITH NEAR NORMAL
TEMPERATURES.

EVENING RNK SOUNDING REVEALED MODEST CAPE...1100 J/KG...ENOUGH TO
DRIVE SHOWER ACTIVITY VCNTY OF THE LATE DAY WIND CONVERGENCE ALONG
THE MOUNTAINS. DID NOT HAVE ANY SEVERE REPORTS. BEST COVERAGE WAS
OVER THE NC HIGH COUNTRY...AND OVER THE HIGHER RIDGES JUST
NORTHWEST OF ROANOKE. PRETTY DESCENT STORM OCCURRED IN EASTERN
CRAIG COUNTY VA...EAST OF NEW CASTLE. THIS STORM DEPOSITED A
HEALTHY 1.50 INCH OF RAIN...A NARROW CORE...MOST OF THIS FALLING
IN THE NATIONAL FOREST. THIS SAME STORM CELL HAD THE HIGHEST
CONCENTRATION OF CLOUD TO GROUND LIGHTNING OF ALL THE STORMS THAT
OCCURRED IN THE CWA TODAY. OF THE OFFICIAL REPORTING STATIONS...WE
MEASURED 0.11 IN THE GAGE HERE AT THE NWS OFFICE IN BLACKSBURG...A
10 MINUTE THUNDERSHOWER. THERE WAS NO CLOUD TO GROUND LIGHTNING
OBSERVED WITH THIS SHOWER...BUT WE DID HEAR SOME IN-CLOUD
RUMBLINGS.

THUNDERSTORMS ASSOCIATED WITH AN UPPER LEVEL TROUGH OVER THE UPPER
MIDWEST WILL RESULT IN AN ADVANCING AREA OF CIRRUS CLOUDS...THIS
DEBRIS CLOUDINESS MOVING DOWNSTREAM AND POTENTIALLY IMPACTING OUR
CWA LATE TONIGHT.  THE RESULT WILL BE THE POTENTIAL FOR LESS NET
RADIATIONAL COOLING WHICH MAY REDUCE THE AMOUNT OF FOG DEVELOPMENT.
LOW TEMPERATURES TONIGHT WILL BE JUST SLIGHTLY HIGHER THAN THOSE
REALIZED SATURDAY MORNING THANKS TO THE POTENTIAL FOR MORE CLOUD
COVER.

ON SUNDAY...WE EXPECT GREATER COVERAGE OF SHOWERS AND STORMS AS
COMPARED TO WHAT IS OCCURRING TODAY. WHILE DAYTIME HEATING WILL HELP
FUEL CONVECTION...AN ADDED FEATURE WILL BE INCREASED JET DYNAMICS
ALOFT WITH THE APPROACH OF AN UPPER TROUGH. WE STILL EXPECT THE
GREATEST COVERAGE ACROSS THE MOUNTAINS...HOWEVER...ISOLATED
CONVECTION WILL BE POSSIBLE EVEN ACROSS THE PIEDMONT. HIGH
TEMPERATURES SUNDAY IN THE WEST MAY BE SLIGHTLY COOLER THAN THOSE
REALIZED TODAY THANKS TO A GREATER POTENTIAL FOR PRECIPITATION AND
MORE CLOUD COVER. ACROSS THE PIEDMONT...READINGS MAY BE SLIGHTLY
HIGHER THAN THOSE OF TODAY.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF 355 PM EDT SATURDAY...

ANY SCATTERED CONVECTION WILL DISSIPATE IN THE EVENING...ALTHOUGH
LEFT A SMALL AREA OF SLIGHT CHC POPS IN NW NC MTNS AREA DUE TO
SOME WEAK CONVERGENCE AND LIGHT PRECIP SUGGESTED BY NAM. WHILE
THERE IS LIKELY TO BE A BREAK IN THE FAR WEST BETWEEN DYING
EVENING SHOWERS AND WHEN CHANCES INCREASE AGAIN TOWARD MORNING
WITH LEFT-OVER ACTIVITY TRYING TO REACH WESTERN SLOPES FROM
OVERNGIHT CONVECTION FAR TO THE WEST...KEPT A LOW CHC POP GOING
IN FAR WEST...INCREASING TO MID CHC TOWARD MORNING SINCE
CONFIDENCE IS LOW IN TERMS OF EXCATLY WHEN SOME OF THIS MIGHT
ARRIVE. MOST LIKELY IT WILL NOT BE UNTIL AFTER 12Z MONDAY
MORNING...BUT NAM SUGGESTING FASTER TIMING IF ENOUGH OF A COLD
POOL DEVELOPS WITH AN ORGANIZED LINE WELL UPSTREAM OVERNIGHT...THE
DYING REMNANTS COULD SNEAK IN EARLIER. CERTAINLY NOT CONFIDENT
ENOUGH TO DROP POPS ENTIRELY FOR THE OVERNIGHT BACK ON WESTERN
SLOPES. LOWS SUNDAY NIGHT WILL BE BIT MILDER IN THE WEST GIVEN
ARRIVAL OF CLOUDS OVERNIGHT AHEAD OF CONVECTION...AND GOING ON
WARM SIDE OF GUIDANCE THERE...AND WITH COOLER GUIDANCE IN EAST
WHERE SKIES WILL BE PARTLY TO MOSTLY CLEAR. RIGHT NOW AHVE BLF AND
DAN WITH SAME LOW TEMP...AND WOULD NOT BE SURPRISED IF BLF IS
WARMER.

MONDAY THE FRONT APPROACHES FROM THE WEST WITH INCREASING SHEAR
AND MOISTURE...BUT BIG QUESTION IS INSTABILITY AND AMOUNT OF ANY
DRY AIR TO AID IN DOWNBURST PRODUCTION. MUCH DEPENDS ALSO ON HOW
MUCH LINGERING SHOWER ACTIVITY CAN GET INTO THE WEST IN THE
MORNING...WHICH WOULD REDUCE INSTABILITY FURTHER. SOME
CONVERGENCE IN LEE TROUGH DEVELOPS LATER IN THE DAY TOO...AND WITH
FCST SOUNDINGS SUGGESTING BETTER MIXING AND DIFFERENCE IN TEMP AND
DEW PT OUT THERE...WONDERING NOW IF THE BETTER SEVERE POTENTIAL
WILL BE ALONG AND EAST OF THE BLUE RIDGE VS. IN THE MOUNTAINS.
WITH SFC FRONT STILL TO THE WEST THOUGH...AND HEATING AHEAD OF IT
COULD STILL CAUSE SOME TROUBLE...SO AT THIS POINT DONT WANT TO TRY
AND DIFFERENTIATE SEVERE THREAT BETWEEN WEST AND EAST...BUT AM
LEANING TOWARD A MINIMAL THREAT OVERALL...WITH A LITTLE BETTER
POTENTIAL IN THE EAST. WILL NOT KNOW MUCH MORE UNTIL WE GET A
BETTER HANDLE ON WHAT COULD BE LINGERING MONDAY MORNING AND HOW
MUCH HEATING WILL OCCUR TO HELP INCREASE INSTABILITY BEYOND WHAT
MODELS ARE SUGGESTING NOW. BUMPED UP HIGHS A BIT IN EAST WITH THE
IDEA OF MORE SUNSHINE EARLY...AND GUDIANCE STILL GOING WITH SOME
MID 90S. MUCH BIGGER DIFFERENCE IN DAYTIME HIGHS FROM WEST TO EAST
MONDAY COMPARED TO LAST COUPLE OF DAYS.

DECREASED THUNER POTENTIAL LATE OVERNIGHT MONDAY NIGHT BUT NOT
ELIMINATING ENTIRELY...WITH MID CHC POPS GIVEN PLENTY OF MOISTURE
AND FRONTAL BOUNDARY MOVING INTO WEST. BY DAYTIME...MODELS
SUGGESTING A MUCH STRONGER LEE TROUGH DEVELOPING AND IDEA THAT
THE SFC FRONT WILL EVENTUALLY JUMP INTO THIS POSITION BY LATE IN
THE DAY. INITIALLY...THERE COULD BE SOME ACTIVITY ALONG WEAKENING
SFC BOUNDARY ACROSS WEST...BUT INSTABILITY IS VERY MINIMAL.
AGAIN...BETTER IN EAST. ANY SEVERE CHANCES SHOULD BE ACROSS
EAST...AND DEPENDING ON WHERE THE BOUNDARY IS BY MID
AFTERNOON...IT COULD ACTUALLY BE JUST SOUTHEAST OF THE FCST AREA.
COOLER WITH HIGHS DUE TO EXTENSIVE CLOUD COVER AND SCATTERED TO
NUMEROUS SHOWERS/THUNDERSTORMS.

SOME COOLER AND SLIGHTLY DRIER AIR TO BEGIN PUSHING IN FROM WEST
OVERNIGHT TUES NIGHT...BUT TRENDS ARE TO SLOW THIS MOISTURE
BOUNDRY DOWN A BIT...AND STILL THINK THERE COULD BE LINGERING
SHOWERS IN THE EAST MUCH OF THE NIGHT WITH SLOWLY MOVING
BOUNDARY...BUT LEFT IT NO HIGHER THAN CHC POPS IN FAR EAST BY
EVENING. WE HAVE BEEN RUNNING MUCH COOLER THAN GUIDANCE FOR
OVERNIGHT LOWS...AND THIS MAY BE THE CASE IN FAR WEST...BUT NOT SO
SURE ABOUT EAST WITH LINGERING SHOWERS AND UNCERTAINTY IN HOW FAR
EAST BOUNDARY WILL BE...SO BUMPED UP LOWS A BIT IN THE EAST.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 1230 PM EDT SATURDAY...

BY 12Z WEDNESDAY MORNING THE COLD FRONT WILL BE ACROSS EASTERN VA.
HIGH PRESSURE BUILDS IN BRINGING DRIER AND MUCH COOLER CONDITIONS.
AS THE HIGH SHIFTS TO THE EAST TOWARDS THE NE STATES BY THE END OF
THE WEEK OUR WIND DIRECTION WILL GRADUALLY SHIFT FROM NW TO AN E/SE
FLOW. THERE WILL BE A NOTICEABLE DROP IN HUMIDITY BEHIND THE FRONT
AS DEWPTS CRASH INTO THE 40S AND 50S. 850MB TEMPS WILL RANGE FROM
+11-15C WHICH WILL COORDINATE TO SURFACE TEMPS 5-10F BELOW NORMAL.
HIGHER ELEVATIONS OF THE MOUNTAINS MAY NOT MAKE IT OUT OF THE 60S ON
WEDNESDAY AND THURSDAY...WHILE EVEN LOWER LYING AREAS WILL ONLY
RANGE FROM THE LOW 70S TO NEAR 80 EAST OF THE BLUE RIDGE. NIGHT TIME
LOWS WILL ALSO BE 5-10F BELOW NORMAL. WHILE ITS TOO SOON TO TALK
ABOUT ANY POTENTIAL RECORD LOWS...SEVERAL OF THEM MAY BE WITHIN
REACH SHOULD WE GET SUFFICIENT RADIATIONAL COOLING.

AT THE END OF THE PERIOD...THE GFS CONTINUES TO HINT AT A SHORTWAVE
DISTURBANCE PIVOTING TOWARDS THE REGION FROM THE SOUTHERN PLAINS FOR
FRIDAY AND SATURDAY. THE FLOW BECOMES MORE SOUTHERLY AND MOISTURE
INCREASES AHEAD OF THE DISTURBANCE. PLACED A BROAD AREA OF LOW
CHANCE POPS ACROSS THE AREA FOR THOSE TWO DAYS.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
AS OF 10 PM EDT SATURDAY...

QUIET NIGHT...ISOLATED DEEP CONVECTION HAS ENDED. A SHOWER
OCCURRED AT THE BCB AIRPORT...AND THIS WILL LIKELY RESULT IN
PATCHY FOG VCNTY OF THE AIRPORT FOR THE REMAINDER OF THE
NIGHT...AND MAY RESULT IN PERIOD OF IFR/LIFR TOWARD DAYBREAK
SUNDAY. ELSEWHERE THINK BRIEF PD OF MVFR RESTRICTION POSSIBLE DUE
TO LIGHT FOG/HAZE BUT SINCE NO RAIN WAS OBSERVED AT THESE
TERMINALS...CONDITIONS SHOULD REMAIN PRIMARILY VFR.

SUNDAY WILL BE COMPARABLE TO SATURDAY WITH MAINLY VFR
CONDITIONS. CLOUD BUILD-UPS EXPECTED BY EARLY AFTERNOON...WITH
SCATTERED MID/LATE AFTERNOON SHOWERS...PRIMARY DEVELOPMENT VCNTY
OF THE MOUNTAINS.

EXTENDED AVIATION DISCUSSION...

MONDAY NIGHT THROUGH TUESDAY NIGHT...A BETTER CHANCE OF SHOWER
AND THUNDERSTORM ACTIVITY...ALONG WITH THE POTENTIAL FOR A GREATER
COVERAGE OF SUB-VFR CONDITIONS WILL EXIST THANKS TO AN UPPER LEVEL
LOW/TROUGH AND ITS ASSOCIATED DYANAMICS PROGRESSING EASTWARD
THROUGH THE GREAT LAKES REGION AND THEN INTO NEW ENGLAND. ITS
ASSOCIATED SURFACE FEATURES WILL OFFER A COLD FRONTAL PASSAGE
TUESDAY AFTERNOON OR EVENING ALONG WITH A SLIGHT CHANCE OF SEVERE
WEATHER AS OFFERED BY THE STORM PREDICTION CENTER.

HIGH PRESSURE WILL TRY TO WORK ITS WAY INTO THE AREA WEDNESDAY
INTO THURSDAY. THERE IS SOME QUESTION AS TO JUST HOW FAR SOUTH OF
THE AREA THE COLD FRONT WILL MAKE IT BEFORE THE REGION IS ON THE
WEST SIDE OF THE HIGH...AND THUS WE RETURN TO A SOUTHERLY FLOW OF
MOISTURE INTO THE AREA. EITHER WAY...LOW LEVEL MOISTURE WILL
LIKELY NOT COMPLETELY DRY OUT...AND THE POTENTIAL FOR OVERNIGHT
IFR/MVFR FOG IS PROMISING...ESPECIALLY FOR AREAS THAT RECEIVE THE
MOST RAINFALL MONDAY INTO TUESDAY.

BY FRIDAY...MOST GUIDANCE IS IN AGREEMENT THAT A WAVE WILL MOVE
ALONG THE STALLED FRONT AND BRING ANOTHER SUBSTANTIAL ROUND OF
SHOWERS AND STORMS TO THE AREA.

&&

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

&&

$$
SYNOPSIS...AMS/SK
NEAR TERM...DS/PM
SHORT TERM...SK
LONG TERM...CF
AVIATION...PM



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