Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 201719
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
119 PM EDT WED AUG 20 2014

.SYNOPSIS...
A WEAK STATIONARY FRONT WILL REMAIN IN THE AREA THROUGH THE REST
OF THE WEEK. UPPER LEVEL DISTURBANCES TRACKING EAST AND SOUTHEAST
ACROSS THE BOUNDARY WILL BRING SCATTERED SHOWERS AND STORMS TO THE
REGION EACH DAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
AS OF 955 AM EDT WEDNESDAY...

BAND OF DEEP CONVECTION CONTINUES TO PUSH SE OUT OF THE MOUNTAIN
EMPIRE REGION INTO THE BLUE RIDGE ATTM AND EXPECT THIS AXIS TO
PERSIST UNTIL PERHAPS TOPPING THE FOOTHILLS IN THE NEXT HOUR OR
SO. THIS DESPITE LACK OF INSTABILITY AHEAD OF THE SHRA/TSRA
COMPLEX AS FEED OF BETTER CAPES AND THETA-E ADVECTION OFF TO THE
WEST PROVIDING SUPPORT. THIS AHEAD OF THE MID LEVEL SHORTWAVE
TROUGH THAT IS CURRENTLY APPROACHING THE WESTERN SLOPES AND ALONG
THE RESIDUAL SURFACE FRONT THAT HAS BACKDOORED SW INTO SW VA EARLY
THIS MORNING.

ALTHOUGH EXPECTING THIS PRECIP TO FADE...COMBINATION OF EARLY
CLOUDS/SHRA OVER THE WEST AND LINGERING FOG/STRATUS IN THE EASTERN
WEDGE WILL MAKE THINGS TRICKY IN REGARDS TO POSSIBLE RENEWED
AFTERNOON CONVECTION. MOST EARLIER GUIDANCE AND CURRENT SHORT TERM
SOLUTIONS WANT TO REDEVELOP TSRA ALONG THE BLUE RIDGE BEFORE
SLIDING THIS EAST INTO EARLY EVENING AS THE TROUGH AXIS LIFTS NE.
HOWEVER THE LATEST HRRR ONLY SHOWS ISOLATED COVERAGE BLUE RIDGE
AFTER CURRENT SHRA FIZZLES WHILE THE 12Z NAM SLOWER IN HOLDING OFF
MOST NEW CONVECTION UNTIL LATE OR EARLY EVENING EAST WITH SOME
WEAK CAPPING ALOFT UNDER RESIDUAL CLOUDS IN THE WAKE OF THE
CURRENT COVERAGE. THUS HAVE ADJUSTED POPS DOWN SOME IN THE FAR
WEST AND TRIMMED LIKELYS DOWN BLUE RIDGE BEHIND THE ONGOING
COVERAGE BEFORE BEEFING UP OUT EAST MID/LATE AFTERNOON AS CAPES
RECOVER LATE TO 1-2K J/KG. HIGH TEMPS WILL AGAIN GET OFF TO A
SLOW START IN SPOTS WITH LATE DAY HIGHS MOST SPOTS PENDING ADDED
SHRA/TSRA WITH PERHAPS THE FAR WEST BEING THE WARMEST WITH MORE
SUN EARLIER BEHIND THE CURRENT COVERAGE.

PREVIOUS VALID DISCUSSION...

AN UPPER LEVEL TROUGH OF LOW PRESSURE IS MOVING THROUGH THE GREAT
LAKES WITH LOBE OF VORTICITY TRAILING SOUTH INTO THE OHIO VALLEY.
THIS FEATURE HAS RESULTED IN A PERSISTENT AREA OF LIFT ASSOCIATED
WITH SHOWERS AND THUNDERSTORMS. AS OF 08Z/4AM...NUMEROUS SHOWERS
AND STORMS WERE OCCURRING FROM WESTERN PA INTO EASTERN OHIO AND
NORTHEAST KY. OUTFLOW FROM THIS COMPLEX OF THUNDERSTORMS IS
EXPECTED TO MAKE ITS WAY OVER THE MOUNTAINS TODAY.

MODELS DO NOT SEEM OVERLY CONFIDENT THIS OUTFLOW WILL MAKE IT
OVER THE MOUNTAINS...INDICATING WEAKENING AND A GRADUAL DEMISE OF
ACTIVITY. MATTER OF FACT THE SYNOPTIC MODELS DON`T PRODUCE MUCH IN
THE WAY OF RAINFALL AT ALL ACROSS OUR CWA...MOS POPS GENERALLY LESS
THAN 40 PERCENT.

ATTM PREFER NOT TO IGNORE THE OBVIOUS...WHICH IS A MODEST LOOKING
UPPER LEVEL TROF...ASSOCIATED WITH A HEALTHY LOOKING AREA OF
SHRA/TSRA...THE OUTFLOW OF WHICH SHOULD PASS THROUGH OUR FORECAST
AREA TODAY. THE ONLY THING THAT KEPT ME FROM GOING WITH
CATEGORICAL POPS IS THE POTENTIAL TIMING OF THE ACTIVITY AS IT
CROSSES THE MOUNTAINS. BASED ON CURRENT PROGRESSION...SHOWERS WILL
MOVE INTO THE WV MOUNTAINS DURING THE MORNING...THEN PROGRESS EAST
REACHING THE BLUE RIDGE TOWARD NOON...THEN EAST OF THE MTNS EARLY
THIS AFTERNOON. THIS EARLIER SORT OF TIMING SUGGESTS DEBRIS CLOUDS
WILL OVERSPREAD THE CWA EARLY AND LIMIT FULL INSOLATION THUS
LIMITING INSTABILITY.

THAT SAID...THINK AREA OF SHOWERS WITH EMBEDDED THUNDER WILL
CROSS THE FORECAST AREA...BUT IN A WEAKENED STATE. GREATEST
COVERAGE WILL BE FROM THE VIRGINIAS NORTHWARD CLOSER TO THE UPPER
SUPPORT FROM THE SHORT WAVE TROUGH...THE STRONGER DYNAMIC LIFT
MOVING FROM THE OHIO VALLEY INTO PA/NY. HAVE PLACED THE HIGHEST
POPS ACROSS WV/VA CLOSER TO THE SUPPORT FROM THE UPPER TROF...AND
WHERE THE OUTFLOW WILL HAVE THE BEST CHANCE OF MAKING IT OVER THE
MOUNTAINS AND HELP FOCUS RENEWED DEEP CONVECTION. FARTHER
SOUTH...FROM THE VA/NC BORDER SOUTHWARD...COVERAGE WILL BE LESS
AND MORE SCATTERED IN NATURE. WITH LESS COVERAGE COMES THE
OPPORTUNITY FOR MORE SUN. MORE SUN SUGGESTS WARMER
TEMPERATURES...AND WARMER TEMEPERATURES WILL YIELD GREATER
INSTABILITY PROVIDING STRONGER UPDRAFTS. AS SUCH CAN`T RULE OUT A
STRONG PULSE STORM OR TWO...ESPECIALLY WHERE MORE SUN
MATERIALIZES.

WENT BLO MOS GUIDANCE FOR TEMPERATURES ACROSS THE VIRGINIAS WHERE
MORE CLOUD COVER IS ANTICIPATED TODAY. THE WARMEST TEMPERATURES
WILL BE ACROSS NORTH CAROLINA WHERE MORE SUN IS ANTICIPATED.

PASSAGE OF THE UPPER TROUGH WILL BRING AN END TO MOST OF THE STORM
ACTIVITY THIS EVENING...FOLLOWED BY ANOTHER FOGGY NIGHT WITH
AREAS OF FOG AND PATCHY DENSE FOG DEVELOPING ACROSS THE FORECAST
AREA. IF SKIES CAN COMPLETELY CLEAR...THIS WOULD BE MOST IDEAL FOR
RADIATION FOG. THERE WERE SEVERAL REPORTS IN THE NEW RIVER VALLEY
WITH DENSE FOG EARLY WEDNESDAY MORNING. THINK IT WILL BE A REPEAT
AGAIN EARLY THURSDAY MORNING.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
AS OF 330 AM WEDNESDAY...

THE REGION WILL REMAIN IN AN ACTIVE WEATHER PATTERN DURING THIS
PORTION OF THE FORECAST. A STRONG UPPER HIGH PRESSURE WILL BE
SITUATED ACROSS THE MID-MISSISSIPPI VALLEY. A DEEPENING UPPER
LOW/TROUGH WILL BE POSITIONED OFF THE COAST OF NEW ENGLAND. OUR AREA
OF THE COUNTRY WILL BE SANDWICHED BETWEEN THE TWO WITHIN NW-SE
ORIENTED MID-LEVEL BAROCLINIC ZONE...WITH AN ASSOCIATED SURFACE
BACKDOOR COLD FRONT EITHER OVER...OR VERY CLOSE TO THE REGION BY THE
START OF THE WEEKEND.

THE ABOVE SCENARIO POINTS TOWARD A PERIOD WITH AT LEAST SCATTERED
SHOWERS IN THE FORECAST EACH DAY AND NIGHT...AND SOME AFTERNOON AND
EVENING STORMS. WHAT IS A LITTLE HARDER TO NAIL DOWN WILL BE THE
WINDOWS OF OPPORTUNITY FOR LIKELY TO CATEGORICAL CHANCES OF
PRECIPITATION IN ASSOCIATION WITH PERIODICAL UPPER LEVEL SHORTWAVE
TROUGHS HEADING SOUTHEAST ALONG THIS BAROCLINIC ZONE AND THROUGH OUR
REGION. EACH MODEL SEEMS TO HAVE A DIFFERENT TAKE ON TIMING AND
TRACK.

EYEBALLING A CONSENSUS OF THE GUIDANCE POINTS TOWARD THURSDAY
AFTERNOON AND EVENING AS ONE POTENTIAL TIME THAT WOULD WARRANT
HIGHER POPS...ESPECIALLY ACROSS THE WESTERN AND NORTHERN PARTS OF
THE REGION. ANOTHER OPPORTUNITY MAY BE FRIDAY NIGHT ACROSS MAINLY
NORTHERN AND EASTERN PARTS OF THE AREA. FINALLY...SATURDAY NIGHT MAY
PROVE TO BE A THIRD OPPORTUNITY FOR ALL OF THE REGION...ESPECIALLY
CENTRAL AND WESTERN PORTIONS.

AT THIS TIME...CONFIDENCE IS NOT THERE TO OFFER A CATEGORICAL...75
PERCENT OR HIGHER...CHANCE OF PRECIPITATION FOR ANY ONE OF THE THREE
SCENARIOS LISTED ABOVE. HOWEVER...WILL CONTINUE...OR ADD...A
FORECAST OF LIKELY POPS TO THE FIRST AND SECOND SCENARIOS. FOR THE
THIRD SCENARIO...WILL OFFER A FORECAST JUST SHY OF LIKELY POPS.

TEMPERATURES THROUGH THE PERIOD ARE EXPECTED TO GRADUALLY COOL AS
THE BAROCLINIC ZONE MAKES PROGRESS WESTWARD. THE COMBINATION OF MORE
CLOUD COVER AND MORE PRECIPITATION...ALONG WITH LOWER HEIGHTS WILL
CONTRIBUTE TO THIS. BY SATURDAY...THE SURFACE COLD FRONT MAY BE
BISECTING THE REGION FROM NW-SE...THUS YIELDING NOTABLY COOLER
TEMPERATURES AT LEAST FOR THE CENTRAL AND NORTHEAST PARTS OF THE
AREA.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 130 PM EDT TUESDAY...

THE WEEKEND THROUGH EARLY NEXT WEEK WILL BE CHARACTERIZED BY THE
BATTLE BETWEEN LARGE UPPER RIDGE TO OUR WEST TRYING TO BUILD INTO
SOUTHERN APPALACHIANS...WHILE TROUGH OFF NEW ENGLAND COAST DEEPENS
WHILE CLOSING OFF AND CONTINUES TO APPEAR THAT IT WILL SET UP CLOSE
ENOUGH TO COAST TO PUSH BACK DOOR FRONT THROUGH AND WELL SOUTH OF
THE AREA THROUGH THE WEEKEND...BEFORE LIKELY WEAKENING AND ALLOWING
MORE INFLUENCE OF THE RIDGE TO BE FELT BY TUES...ESPECIALLY ACROSS
WESTERN PARTS OF THE AREA IF WEAK/SHALLOW BOUNDARY LAYER WEDGE IS IN
PLACE EARLY IN THE DAY BEFORE MIXING OUT OVER THE EAST.  WHILE
SURFACE WEDGE FRONT MAY BE WELL TO THE SOUTH DURING MUCH OF THIS
PERIOD...WITH STRONGEST SOUTHWARD PUSH ON SATURDAY...THE 850
BOUNDARY AND MOST LIKELY TRACK FOR UPPER S/WV ENERGY FROM THE NW IS
LIKELY TO BE RIGHT OVER THE BLACKSBURG FORECAST AREA...AND THUS GOOD
CHANCE FOR SHOWERS/THUNDERSTORMS THROUGH THIS ENTIRE PERIOD.  TIMING
MOST LIKELY WINDOWS REMAINS TRICKY...AS MANY OF THESE WAVES ARE
STRONGLY INFLUENCE BY CONVECTIVE COMPLEXES THAT WILL DEVELOP WELL
UPSTREAM. LIKE THE TRENDS OVERALL THAT 12Z GFS IS TAKING...NOT ONLY
WITH RETURN TO SHARPER AMPLITUDE PATTERN...BUT IDEA OF TWO DISTINCT
WAVES HEADING FOR THE WESTERN PART OF OUR FORECAST AREA...ONE
SATURDAY AND ANOTHER ONE SUNDAY. EXACT TIMES MAY HELP DETERMINE IF
THERE WILL BE ENOUGH INSTABILITY...WHICH WOULD LIKELY BE LIMITED TO
THE FAR WEST NEAR EDGE OF WEDGE BOUNDARY...BUT PERHAPS THE BIGGER
CONCERN IS RAINFALL THAT IS LIKELY TO IMPACT THE SAME AREAS AT LEAST
A COUPLE OF DAYS IN A ROW.

THERE COULD BE ANOTHER WAVE FOR MONDAY...BUT AS RIDGE ATTEMPTS TO
BUILD IN AND TROUGH TO THE EAST AND ASSOCIATED WEDGE WEAKEN WHAT MAY
TEND TO OCCUR IS MORE DIURNAL POP-UP CONVECTION ALONG AND NEAR THE
WESTERN PERIPHERY OF THE WEDGE BOUNDARY IN OUR WESTERN FORECAST AREA
AS THE ATMOS DESTABILIZES MORE. BY TUESDAY THE SUPPORT TO KEEP WEDGE
IN PLACE SHOULD BE WEAKENING AS TROUGH LIFTS AND SFC HIGH SHIFTS
MORE EAST OF THE AREA...AND OVERALL IT LOOKS A LITTLE DRIER...BUT
NOT SURE ALL POPS CAN BE REMOVED.

GIVEN PATTERN WE`VE BEEN IN...REALLY DON`T HAVE CONFIDENCE TO DRY IT
OUT OR WARM IT UP TOO FAST...SO WILL LEAN TOWARD STRONGER INFLUENCE
OF THE WEDGE THROUGH THIS PERIOD AND BETTER CHANCES FOR
PRECIP...WHICH WILL HELP STRENGTHEN THE WEDGE TOO.  UNDERCUT EVEN
COOLER ECMWF A LITTLE BIT FOR HIGHS...WITH A BIT MORE WARMING FOR
TUESDAY. BUT IN THE FAR SOUTHWEST THINGS MAY BE ABLE TO WARM UP VERY
QUICKLY A DAY OR TWO EARLIER THAN THIS IF THE WEDGE CAN BREAK AND
SOME OF THE INFLUENCE OF THE BIG UPPER RIDGE CAN BE REALIZED.  THIS
WILL EVENTUALLY RESULT IN A SIGNIFICANT WARM UP FOR OUR ENTIRE
AREA...BUT AM THINKING IT WILL NOT COME UNTIL MIDDLE OF NEXT WEEK.

&&

.AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
AS OF 100 PM EDT WEDNESDAY...

ACTIVE AND VARIABLE WEATHER PATTERN CONTINUES THIS TAF PERIOD.
EARLY CONVECTION WITHERED ON THE VINE AS IT MOVED OFF THE BLUE
RIDGE AND HELPED STABILIZE THE ATMOSPHERE FOR A BIT. HOWEVER...
LATEST ANALYSES INDICATE INSTABILITY IS RECOVERING AND MESO MODELS
DO SHOW SOME CONVECTIVE DEVELOPMENT DURING THE AFTERNOON. EASTERN
AREAS ARE ON THE FRINGE OF HIGH PRESSURE WEDGING DOWN THE COAST
WHERE THERE WAS EXTENSIVE LOW CLOUD COVER THIS MORNING. BELIEVE
CONDITIONS WILL GENERALLY BE VFR BY ISSUANCE TIME AND WILL USE
VICINITY TO COVER EXPECTED SHOWER/STORM DEVELOPMENT. CONDITIONS
WILL DIP DOWN WITH ANY PRECIPITATION BUT FEEL A TEMPO GROUP WILL
BE TOO HEAVY HANDED SO WILL LEAVE OUT MENTION OF LOWER CONDITIONS.

TONIGHT WILL BE ANOTHER TOUGH CALL FOR FOG/LOW STRATUS DEVELOPMENT.
INDICATIONS IN MESO RH FIELDS ARE THAT IFR/LIFR WILL BE LESS
WIDESPREAD SO WILL TRY TO CONFINE LOW CONDITIONS TO A SMALLER PERIOD
TOWARD DAYBREAK...JUST IN TIME TO MENTION SOME ADDITIONAL SHOWER
ACTIVITY WITH THE NEXT WAVE OF ENERGY ENTERING FROM THE WEST. WINDS
WILL NOT BE PROBLEMATIC FOR AVIATION PURPOSES THROUGH THIS TAF PERIOD.

EXTENDED AVIATION...

UPPER LEVEL DISTURBANCES WILL BE MOVING THROUGH PERIODICALLY AND
INTERACTING WITH A STATIONARY FRONT OVER THE AREA FOR THE NEXT
FEW DAYS...RESULTING IN PERIODS OF SHOWERS AND THUNDERSTORMS. DUE
TO THE HIGH MOISTURE CONTENT OF THE AIR...EXPECT STRATUS AND FOG
DURING THE OVERNIGHT PERIODS WITH AREAS OF MVFR/IFR MOST PRONOUNCED
BETWEEN MIDNIGHT AND 9AM EACH DAY. MODELS ARE INDICATED THAT A DEEPER
EASTERLY SORT OF WIND FLOW WILL SETUP FOR THIS UPCOMING WEEKEND.
THIS SUGGEST THAT LOW CIGS MAY PERSIST EVEN DURING THE DAYTIME
PERIODS...SATURDAY AND SUNDAY...WITH WIDESPREAD MVFR CONDITIONS
ACROSS THE AREA THIS WEEKEND DUE TO MOISTURE BANKING UP AGAINST THE
EAST SIDE OF THE APPALACHIANS.

&&

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

&&

$$
SYNOPSIS...SK
NEAR TERM...JH/PM
SHORT TERM...DS
LONG TERM...SK
AVIATION...MBS


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