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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 180301
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1101 PM EDT FRI MAY 17 2013

.SYNOPSIS...
A COLD FRONT WILL CONTINUE TO MOVE SOUTH THIS EVENING AND
TONIGHT ACROSS THE EASTERN HALF OF THE FORECAST REGION...ALLOWING
WEAK HIGH PRESSURE TO WEDGE AGAINST THE MOUNTAINS. AN UPPER LEVEL
DISTURBANCE WILL ADVANCE TOWARD THE CENTRAL APPALACHIAN CHAIN ON
SATURDAY...INCREASING THE CHANCE OF SHOWERS AND THUNDERSTORMS
ACROSS THE AREA. A DEEP UPPER LEVEL LOW PRESSURE SYSTEM WILL
APPROACH THE AREA TOWARD THE END OF THE COMING WEEK...WHICH MAY
BRING A RETURN OF COOLER WEATHER.

&&

.NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --
AS OF 1030 PM EDT FRIDAY...

SCATTERED SHOWERS WITH EMBEDDED THUNDERSTORMS CONTINUE ACROSS THE
FORECAST AREA. SURFACE FRONT IS GRADUALLY BACKDOORING IN FROM THE
NORTHEAST...BOUNDARY LAYER WINDS GRADUALLY SHIFTING AROUND AND
COMING FROM AN EASTERLY DIRECTION. ALOFT HOWEVER...WINDS IN BOTH
THE GSO/RNK SOUNDINGS WERE FROM THE SOUTH. WITH THIS WARM MOIST
AIR RIDING UP AND OVER THE FRONT...EXPECT SHOWER THREAT TO
CONTINUE THROUGH THE OVERNIGHT. CAN`T RULE OUT A RUMBLE OF THUNDER
AS THERE IS SOME ELEVATED CAPE...BOTH THE GSO/RNK SOUNDINGS
SHOWING CAPE OF ABOUT 1000-1500 J/KG. WINDS ALOFT ARE RELATIVELY
WEAK...MEAN WIND OF ABOUT 10KTS/12MPH. AS SUCH STORM MOVEMENT IS
SLOW...THUS RESULTING IN PERSISTENCE OF HEAVY RAIN WHERE IT
HAPPENS TO OCCUR...SOME CASES RESULTING IN AN INCH OF RAIN IN LESS
THAN AN HOUR.

THROUGH THE OVERNIGHT...WILL SEE GREATEST CONCENTRATION OF
SHOWERS AND A FEW THUNDERSTORMS OVER THE PIEDMONT AS THE FRONT
ENTERS THE AREA AND WINDSPEEDS ALOFT DIMINISH. EXPECT THAT THE
ACTIVITY WILL REMAIN PULSY IN NATURE...ALTHOUGH WOULD NOT BE
SURPRISED TO SEE CLUSTERS OF SEMI-ORGANIZED CELLS WHERE OUTFLOW
BOUNDARIES MERGE. RAINFALL SHOULD DECREASE IN COVERAGE HEADING
INTO THE EARLY HOURS OF SATURDAY...THEN INCREASE AGAIN BY SATURDAY
AFTERNOON.

SHOWER AND THUNDERSTORM ACTIVITY WILL BECOME MORE WIDESPREAD
GOING INTO SATURDAY AFTERNOON AS THE UPPER LEVEL TROUGH MOVES
CLOSER. INCREASED CLOUD COVER AND SCATTERED RAINFALL WILL LIMIT
SURFACED BASED INSTABILITY...WITH AFTERNOON HIGHS HOLDING MAINLY
IN THE UPPER 60S TO MID 70S...SO DO NOT FORESEE A LARGE THREAT OF
SEVERE THUNDERSTORM ACTIVITY DURING THE AFTERNOON. HOWEVER...WEAK
UPPER LEVEL WINDS WILL RESULT IN SLOW MOVEMENT OF ANY STRONGER
SHOWERS AND STORMS...WHICH MAY LEAD TO LOCALLY HEAVY RAIN. BELIEVE
WE WILL HAVE A FEW AREAS OF LOCALIZED NUISANCE FLOODING WHERE
HEAVY RAIN DEVELOPS...BUT DO NOT FORESEE THE THREAT TO BE
WIDESPREAD ENOUGH AT THIS TIME TO GO WITH ANY SORT OF FLOOD WATCH.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 330 PM EDT FRIDAY...

SLOW MOVING UPPER LOW/TROUGH WILL MAKE ITS WAY EASTWARD ALONG A
STALLED FRONTAL BOUNDARY. ITS PASSAGE WILL ALLOW FOR DAILY ORGANIZED
SHOWERS AND STORMS TO OCCUR ACROSS THE AREA. SOME WILL BE DRIVEN BY
THE DYNAMICS OF THE SYSTEM...THOSE OCCURRING DURING THE DAY WILL
BENEFIT FROM DAYTIME INSTABILITY AS WELL. THE AXIS OF THE SYSTEM IS
PROGGED TO LIFT NORTHEAST OF THE AREA LATE IN THE DAY MONDAY. WE
EXPECTED A GRADUAL DECREASE IN COVERAGE DURING THIS TIME
PERIOD...WITH THE GREATEST COVERAGE ACROSS THE EASTERN PART OF THE
FORECAST AREA.

TEMPERATURES WILL AVERAGE NEAR NORMAL...IF NOT A SLIGHTLY ABOVE
NORMAL ON AVERAGE GIVEN ELEVATED DEW POINT VALUES OVERNIGHT.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 330 PM EDT FRIDAY...

MONDAY NIGHT...THE PROCESS OF DECREASING COVER THAT BEGAN ON MONDAY
WILL CONTINUE MONDAY NIGHT AS THE TROUGH CONTINUES HEADING OUT OF
THE REGION. ON TUESDAY...WE WILL BE BETWEEN SYSTEMS...WITH THE
POTENTIAL FOR A BRIEF PERIOD OF UPPER LEVEL RIDGING ACROSS THE
REGION. HOWEVER...LOW LEVELS WILL REMAIN ON THE ACTIVE SIDE AHEAD OF
THE NEXT APPROACHING SYSTEM.

THIS NEXT SYSTEM WILL BE AN UPPER LOW THAT WILL HAVE A MORE
NORTHERLY TRACK AS COMPARED TO THE ONE OVER THE WEEKEND.
HOWEVER...ITS PATH WILL ALLOW FOR A SOUTHERLY FETCH OF GULF OF
MEXICO MOISTURE TO STREAM INTO THE REGION WITH INCREASING CHANCE OF
SHOWERS AND STORMS THROUGH THE START OF FRIDAY. MODEL GUIDANCE
VARIES AS TO HOW QUICKLY THE ASSOCIATED COLD FRONT CROSSES THE
AREA...BUT CONSENSUS IS FAIRLY GOOD THAT LINGERING MOISTURE WILL
REMAIN OVER THE AREA ON THE BACKSIDE OF THE FRONT REGARDLESS OF THE
MODEL OF CHOICE. THIS EQUATES TO SHOWERS IN THE FORECAST THROUGH AT
LEAST FRIDAY.

TEMPERATURES WILL TREND MILDER THROUGH THE PERIOD THROUGH AT LEAST
WEDNESDAY...THEN START TO BE COOLER AS CLOUDS AND PRECIPITATION
BECOME MORE ABUNDANT.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
AS OF 1100 PM EDT FRIDAY...

SURFACE FRONT OVER THE AREA WILL COMBINE WITH AN UPPER LEVEL
TROUGH RESULTING IN SCATTERED TO NUMEROUS SHOWERS THROUGH THE TAF
PERIOD. AN EASTERLY WIND WILL ALSO DEVELOP OVER THE
AREA...RESULTING IN THE FORMATION OF LOW LEVEL STRATUS. MODELS
SUGGEST CIGS MAY DROP INTO IFR CATEGORY BY SATURDAY MORNING. ATTM
WILL ADVERTISE MVFR CIGS WITH THINKING THAT ENOUGH MIXING SHOULD
TAKE PLACE FROM THE SHOWER ACTIVITY TO LIFT CIGS A BIT HIGHER THAN
MODEL FORECAST. AT THE VERY LEAST...MAY BE LOOKING AT OBSCD RIDGE
TOPS FROM THE LOWERING CLOUD BASE.

.AVIATION EXTENDED...
SIMILAR CONDITIONS EXPECTED SUNDAY WITH MVFR CONDITIONS AND LCL
IFR. CONDITIONS LOOK TO IMPROVE MONDAY AS THE UPPER TROUGH MOVES
TO ALONG THE MID ATLANTIC COAST. EXPECT TUESDAY TO BE THE BEST
BET FOR DECENT FLYING CONDITIONS THOUGH MOUNTAINS ALTHOUGH AN
ISOLATED AFTERNOON AIRMASS SHOWER OR STORM IS STILL POSSIBLE.
NEXT LAZY FRONT APPROACHES ON WEDNESDAY WITH MORE SHOWERS/STORMS
DEVELOPING. THIS FRONT DOES NOT APPEAR TO BE IN A BIG HURRY AND
LOOKS TO BRING MVRF CONDITIONS...POSSIBLY IFR AT NIGHT...TO TAF
SITES FOR THE LATTER HALF OF THE WEEK.
-- End Changed Discussion --

&&

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

&&

$$
SYNOPSIS...NF
NEAR TERM...NF/PM
SHORT TERM...DS
LONG TERM...DS
AVIATION...PM