-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 271446
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1046 AM EDT SUN JUL 27 2014

.SYNOPSIS...
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UPPER DISTURBANCES WILL CONTINUE TO WORK INTO THE AREA THIS
AFTERNOON AND EVENING IN ADVANCE OF A STRONG COLD FRONT THAT WILL
BE APPROACHING FROM THE NORTHWEST THIS EVENING. THESE FEATURES
MAY TRIGGER STRONG TO POTENTIALLY SEVERE THUNDERSTORMS THIS
AFTERNOON INTO EARLY TONIGHT. THE COLD FRONT WILL MOVE ACROSS THE
REGION BY EARLY MONDAY...RESULTING IN COOLER WEATHER INTO THE
MIDDLE OF THE WORK WEEK.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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AS OF 1020 AM EDT SUNDAY...

FORECAST REMAINS COMPLICATED INTO THIS EVENING GIVEN TIMING
ISSUES OF IMPULSES ALOFT AND MODEL UNCERTAINTY WITH THESE
FEATURES. CURRENT SHORTWAVE CROSSING THE REGION THAT CAUSED THE
EARLIER ARRIVAL OF SHRA/TSRA EARLY THIS MORNING CONTINUES TO
PRODUCE BANDS OF SHOWERS AND STORMS OVER THE WEST BUT ALSO A QUITE
EXTENSIVE AREA OF CLOUD COVER WITHIN THE APPARENT LEFTOVER COOL
POOL. NEXT UPSTREAM VORT AHEAD OF THE FRONT THAT LOOKS TO BE THE
MAIN PLAYER FOR STRONGER STORMS LATER ON WILL WORK AROUND THE
UPSTREAM UPPER TROF THIS AFTERNOON AND EVENTUALLY MERGE WITH THE
SURFACE COLD FRONT EARLY TONIGHT. FORECAST SHEAR AND HELICITY
QUITE LARGE AS WELL AS LAPSES BUT ALL DEPENDENT UPON INSTABILITY
WHICH WILL BE THE DRIVING FORCE FOR ORGANIZED COVERAGE LATER ON.
LATEST 12Z GUIDANCE CONTINUES TO SHIFT THE BETTER LIFT TO LATER IN
THE DAY AND MORESO THIS EVENING AS WILL LIKELY TAKE LONGER TO GET
AT LEAST DECENT HEATING AND CAPES REACHING 1-2K J/KG. THUS MAY
HAVE A SITUATION WHERE INITIALLY WILL SEE MORE ELEVATED CONVECTION
ESPCLY NORTH/CENTRAL SECTIONS...WITH MORE SURFACE BASED STORMS
TAKING SHAPE ACROSS THE FAR SW PER BETTER THETA-E AND HEATING
UNDER THE INCREASING SW JET. OTRW COMBO OF WESTERLY FLOW ALOFT AND
EARLY CLOUDS/SHRA LIKELY TO CAUSE LESS EARLY ON...SO LOWERED POPS
SOUTHERN/EAST TO INIT...THEN INCREASED WEST FOR LEAST MORE SHRA
EARLY AFTERNOON AHEAD OF THE NEXT MCS BEFORE THINGS PERHAPS COME
TOGETHER FOR DEEPER CONVECTION ESPCLY WEST- NORTH LATE IN THE DAY.
CONSIDERED A FLOOD WATCH OVER THE FAR WEST/NW WHERE 12Z GUIDANCE
SHOWING IN EXCESS OF AN INCH OF RAIN BUT GIVEN UNCERTAINTY AND
LIGHT AMOUNTS OVERNIGHT WILL CONTINUE TO HOLD OFF FOR NOW.

TEMPS REMAIN QUITE TRICKY AS SEEING LITTLE RISE ATTM AND WITH
LATEST LAV MO COOLER...EXPECT MORE LATE DAY HIGHS SO LOWERED A
CAT OR SO MOST SPOTS WHICH MAY NOT BE COOL ENOUGH OVER THE NW.

PREVIOUS DISCUSSION AS OF 500 AM EDT SUNDAY...

SHOWERS AND SCATTERED THUNDERSTORMS ARE OBSERVED ACROSS THE
FORECAST REGION THIS MORNING AS AN UPPER LEVEL DISTURBANCE PASSES
OVERHEAD. RAINFALL AMOUNTS HAVE BEEN OBSERVED AROUND A HALF INCH
ACROSS SOUTHEAST WEST VIRGINIA...WITH AMOUNTS TAPERING DOWN TO A
FEW HUNDREDTHS FURTHER EAST. IN ADDITION TO THE ACTIVITY CURRENTLY
AFFECTING OUR AREA...ALSO KEEPING AN EYE ON TWO OTHER AREAS OF
THUNDERSTORM ACTIVITY...ONE ENTERING WESTERN KENTUCKY AND ANOTHER
OVER EASTERN ILLINOIS.

RAPID UPDATE FORECAST MODELS APPEAR TO BE IN GOOD AGREEMENT THAT
THE THUNDERSTORMS OVER WESTERN KENTUCKY WILL SHIFT EAST SOUTHEAST...
PUSHING INTO THE NORTH CAROLINA MOUNTAINS LATE MORNING TO AROUND
NOON. WHILE THE DISTURBANCE TRIGGERING THESE STORMS MAY REMAIN
STRONG ENOUGH TO PRODUCE SOME GUSTY WINDS ACROSS THE MOUNTAINS...
WONDERING IF THE CLOUD COVER IT PRODUCES WILL ALSO LIMIT
INSTABILITY FOR AREAS SOUTH OF HIGHWAY 460 DURING THE AFTERNOON AS
THE SECOND...MORE POTENT DISTURBANCE PUSHES EAST ALONG THE OHIO
RIVER.

THE SECOND DISTURBANCE WILL BRING WITH IT AN UNSEASONABLY STRONG
MID LEVEL WINDS IN THE RANGE OF 50KT TO 60KT. WITH CLOUD COVER
EXPECTED TO BE MORE DIMINISHED HEADING INTO THE AFTERNOON NORTH OF
HIGHWAY 460...EXPECT GREATER INSTABILITY IN THIS AREA. MODELS ARE
IN AGREEMENT ON BRINGING THE SECOND LINE OF STORMS INTO SOUTHEAST
WEST VIRGINIA DURING THE 6PM TO 8PM TIME FRAME...WITH CONVECTION
QUICKLY SPREADING EAST THEREAFTER. THE MAIN THREAT WITH THESE
STORMS WILL BE POTENTIALLY DAMAGING WINDS AS THE DOWNDRAFTS PULL
THE STRONG MID LEVEL WINDS TO THE SURFACE. HAIL WILL ALSO BE
POSSIBLE IN SOME OF THE STRONGER CELLS...AS WILL BE LOCALLY HEAVY
RAIN DUE TO THE UNUSUALLY HIGH ATMOSPHERIC MOISTURE POOLING AHEAD
OF THE SYSTEM. DUE TO THE STRONG SHEAR PRESENTED BY THIS SYSTEM...
CANNOT EVEN RULE OUT AN ISOLATED TORNADO...ALTHOUGH BELIEVE THE
THREAT IS HIGHER WEST OF THE APPALACHIANS...OUTSIDE OUR FORECAST
AREA.

THUNDERSTORM ACTIVITY WILL BEGIN TO DIMINISH DURING LATE EVENING
AS THE LINE PASSES EAST OF THE MOUNTAINS AND BEGINS TO MOVE
DOWNSLOPE...ALTHOUGH SOME POTENTIAL FOR GUSTY WINDS WILL REMAIN
THROUGH MIDNIGHT EAST OF THE BLUE RIDGE. WINDS WILL THEN SHIFT
WESTERLY EARLY MONDAY AS A STRONG COLD FRONT MOVES EAST ACROSS THE
FORECAST REGION...LEAVING ONLY UPSLOPE SHOWERS ACROSS THE
MOUNTAINS.

AS MENTIONED BEFORE...CLOUD COVER AND SHOWERS ARE ADDING TO THE
UNCERTAINTY OF MANY ASPECTS OF THE FORECAST...INCLUDING AFTERNOON
HIGHS. HAVE UNDERCUT MAV/MET GUIDANCE BY A FEW DEGREES...OPTING
FOR THE COOLER MOS GUIDANCE.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300 AM EDT SUNDAY...

BY 12Z (8 AM EDT) MONDAY...THE DYNAMIC UPPER LEVEL SHORTWAVE WILL
HAVE LIFTED INTO THE NORTHEAST U.S. LEAVING A DEEP LOW LEVEL
NORTHWEST FLOW IN PLACE. FAIR PRESSURE RISES AND 40+ KT 850MB WINDS
SHOULD GENERATE GUSTY WINDS...BUT SPEEDS REMAINING BELOW ADVISORY
CRITERIA.

RESIDUAL MOISTURE BELOW 4K FT SHOWN ON FORECAST SOUNDINGS FORCED UP
ALONG THE WESTERN SLOPES...COMBINED WITH LAPSE RATES GREATER THAN
6.5 C/KM WILL HELP GENERATE UPSLOPE SHOWERS MONDAY AND INTO MONDAY
EVENING.

LEANED TOWARD THE COOLER GUIDANCE FOR HIGHS MONDAY...HOWEVER...WITH
DOWNSLOPING WINDS...TEMPS EAST OF THE BLUE RIDGE WILL STILL MANAGE
TO REACH WELL INTO THE 80S.

CHANCE FOR UPSLOPE SHOWERS DIMINISH TUESDAY AND UPSLOPE FLOW WEAKENS
AND LOW LEVEL DRYING CONTINUES.  AS THE DOWNSLOPE FLOW EAST OF THE
BLUE RIDGE ALSO WEAKENS...COOLING TREND CONTINUES AND WENT SLIGHTLY
BELOW GUIDANCE FOR HIGHS TUESDAY. ENERGY ROUNDING THE BASE OF THE
UPPER LEVEL EASTERN U.S. TROF HELPS DEVELOP A WEAK SFC LOW ACROSS
THE CAROLINAS LATE TUESDAY. MODELS HINT THAT THIS MAY PRODUCE A WEAK
EAST/NORTHEAST FLOW IN THE FAR EAST AND PERHAPS BRING SOME CLOUDS TO
THIS REGION.  ACROSS THE WEST...HOWEVER...SFC HIGH PRESSURE BUILDS
WHICH SHOULD ALLOW TEMPS TUESDAY NIGHT TO DROP INTO THE 40S ACROSS
PORTIONS OF THE MOUNTAINS.

&&

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

THE PERIOD STARTS OFF WITH A COLD FRONT WELL OFF THE ATLANTIC COAST.
A 1020MB SURFACE HIGH OVER SE MO SHIFTS TO THE NE STATES THURSDAY
AND FRIDAY. AT THE MID LEVELS...A RIDGE WILL PERSIST ACROSS THE
WESTERN US...WHILE A TROUGH WILL PERSIST ACROSS THE EASTERN US. VERY
LITTLE MOISTURE IS AVAILABLE FOR WEDNESDAY AND THURSDAY. THE ONLY
PLACE THAT MAY BE ABLE TO SQUEAK OUT A SHOWER OR TWO IS ACROSS THE
FAR SW...OTHERWISE MUCH OF THE REGION WILL REMAIN DRY. MOISTURE AND
LOW LEVEL CONVERGENCE INCREASE FOR FRIDAY AND SATURDAY...THUS
INCREASING THE THREAT FOR SHOWERS AND THUNDERSTORMS. GREATEST CHANCE
POPS ARE ACROSS THE WEST WHERE THE CONVERGENCE IS MAXIMIZED.

850MB TEMPS OF +13-15C AND A PERSISTENT WEDGING EASTERLY WIND WILL
ALLOW SURFACE HIGH TEMPS TO BE 5-10 DEGREES BELOW NORMAL. THURSDAY
WILL BE THE COOLEST MORNING OF THE PERIOD WITH UPPER 40S POSSIBLE
ACROSS SOME OF THE MOUNTAIN VALLEY LOCATIONS. LOW TEMPS WILL
MODERATE FRIDAY THROUGH THE WEEKEND AS SURFACE DEWPTS INCREASE.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
AS OF 720 AM EDT SUNDAY...

WIDELY SCATTERED SHOWERS WILL CREATING SPOTTY AREAS OF MVFR CIGS
AND VSBYS THIS MORNING. THIS FIRST ROUND OF PRECIPITATION WILL
DIMINISH BY LATE MORNING. WIND GUSTS TO 30 MPH IN THE NORTHWEST
NC MOUNTAINS AND FAR SOUTHWEST VIRGINIA EARLY THIS MORNING WILL
GRADUALLY DIMINISH AS THE MORNING PROGRESSES.

WHILE VFR CONDITIONS ARE EXPECTED THROUGH MUCH OF THE MORNING...A
COMPLEX OF STORMS IN KENTUCKY WILL SPREAD MID AND HIGH CLOUDS OVER
THE REGION...AS WELL AS SCATTERED SHOWERS AND STORMS...ESPECIALLY
IN NW NORTH CAROLINA.

THE GREATEST THREAT TO AVIATORS TODAY WILL BE YET ANOTHER COMPLEX
OF STORMS THAT WILL ENTER OUR AREA FROM THE NORTHWEST LATE THIS
AFTERNOON AND THIS EVENING...IN ADVANCE OF A STRONG UPPER LEVEL
DISTURBANCE MOVING INTO THE OHIO VALLEY.THERE STILL IS SOME
UNCERTAINTY ABOUT HOW MUCH INSTABILITY WILL BE IN PLACE BY EARLY
AFTERNOON...WHICH WILL DEPEND ON HOW MUCH CLOUD COVER REMAINS FROM
THE MORNING CONVECTION.

REGARDLESS...WITH AN IMPRESSIVE WIND FIELD ALOFT...CONFIDENCE IS
GROWING THAT THIS LARGE COMPLEX OF STORMS WILL IMPACT OUR AREA AND
MANY TAF SITES...BUT MOST LIKELY KBLF...KLWB...KBCB AND KROA.
AS A RESULT...INTRODUCED THUNDER WITH PROB30 OF WIND GUSTS TO
30-40KTS. IFR CONDITIONS WITH LOW CIGS/VSBYS EXPECTED WITH THIS
COMPLEX.

A COLD FRONT PASSES TONIGHT...LEAVING VFR CONDITIONS...BUT GUSTY
NORTHWEST WINDS...ESPECIALLY IN THE MOUNTAINS.

EXTENDED AVIATION DISCUSSION...
THREAT OF SUB VFR THROUGH MONDAY EXPECTED ACROSS SE WEST VA PER
NW FLOW...BUT LESS ELSEWHERE GIVEN DOWNSLOPE.

DRIER AIR PUSHING IN FOR TUESDAY-WEDNESDAY WILL BRING MAINLY VFR
CONDITIONS...BUT CANNOT RULE OUT LATE NIGHT FOG KBCB/KLWB BUT LOW
LVLS MAY STAY DRY ENOUGH FOR LESS FOG COVERAGE.

VARIABLE CIGS EXPECTED UNDER ANOMALOUS UPPER LOW THROUGHOUT THE
WEEK. A FEW -SHRA NOT COMPLETELY OUT OF THE QUESTION ACROSS
EASTERN WV...ALONG WITH OCCASIONAL MVFR CIGS. TYPICAL FOG
POTENTIAL LESS THAN NORMAL FOR THIS TIME OF YEAR THROUGHOUT THE
WEEK BECAUSE OF TURBULENT MIXING AND PREVAILING CYCLONIC FLOW.
TOWARD THE END OF THE WEEK...AS THE UPPER LOW RETROGRADES JUST
WEST OF THE REGION...INCREASING POTENTIAL FOR SHRA/TSRA...
ESPECIALLY IN THE FRI-SUN TIME FRAME.

&&

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

&&

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