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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 180902
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
502 AM EDT TUE JUN 18 2013

.SYNOPSIS...
-- Changed Discussion --
LOW PRESSURE OVER THE TENNESSEE VALLEY WILL MOVE EAST ACROSS THE
SOUTHERN APPALACHIANS TODAY AND OFFSHORE TONIGHT. THIS WILL BRING
ADDITIONAL SHOWERS AND STORMS BACK TO THE REGION TODAY INTO THIS
EVENING. WEAK HIGH PRESSURE WILL BUILD NORTH OF THE AREA
WEDNESDAY AND THURSDAY RESULTING IN SOMEWHAT DRIER WEATHER INTO
THE END OF THE WEEK.
-- End Changed Discussion --
&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 240 AM EDT TUESDAY...

CLUSTERS OF CONVECTION HAVE CONTINUED TO LINGER ACROSS THE NW
OVERNIGHT WHERE SUPPORTED BY EARLIER OUTFLOW AND A WEAK WAVE
ALOFT ZIPPING EAST FROM THE MAIN SYSTEM BACK ACROSS THE WRN TN
VALLEY. EXPECT CURRENT SHRA/TSRA TO THE NW TO FADE OUT TOWARD
DAYBREAK BEFORE LIFT WITH THE STRONGER SHORTWAVE TO THE SW STARTS
TO ARRIVE BY 12Z. MODELS CONTINUE TO HAVE DIFFERENCES IN EXACTLY
WHERE THE MAIN SURFACE FEATURE TRACKS BUT DO HAVE THE 85H LOW
COMING ACROSS THE CENTRAL CWA THIS AFTERNOON. HIGH PWATS AND GOOD
LIFT COMBO WITH A STRONG UPPER JET/DIFFLUENCE ACROSS THE LOW LEVEL
THETA-E GRADIENT SUPPORTS VERY EFFICIENT RAINFALL BUT LOTS OF
QUESTIONS WITH RATES AND HOW MUCH DEEPER CONVECTION MIXES IN. THIS
SEEN IN MANY MODEL SOLUTIONS WITH EARLY ARRIVAL NIXING MUCH OF THE
INSTABILITY EXCEPT OVER THE SE WHILE A MORE SHUNTED SCENARIO WOULD
PUT THE BETTER RATE RAINFALL JUST SOUTH OF THE AREA. SINCE THIS
WOULD BE IN AREAS THAT HAVE HIGHER FFG VALUES AND GIVEN LOTS OF
UNCERTAINTY...WILL HOLD OFF ON ANY FLOOD/FLASH FLOOD WATCHES PER
COORDINATION WITH SURROUNDING WESTERN OFFICES. HOWEVER THE NEXT
SHIFT MAY NEED TO HOIST A SHORT TERM HEADLINE PENDING EXACTLY
WHERE IT APPEARS THE HEAVIER RAIN AND/OR CONVECTION MAY SET UP.
THUS ADDING HEAVY RAIN MENTION WHILE BUMPING UP QPF AND RUNNING
WITH CAT POPS MOST OF THE DAY.

ALSO CUT BACK ON TEMPS PER EARLY ARRIVAL OF SHRA AND TREND OF
THE LOW LEVEL FLOW TURNING MORE NE FROM SOUTH TO NORTH AS THE
WAVE PASSES LATER. THIS COULD CAUSE SOME SPOTS OVER THE WEST TO
REMAIN IN THE 60S WITH RISES ONLY INTO THE LOW/MID 70S OUT TO THE
BLUE RIDGE AND PERHAPS CLOSE TO 80 PIEDMONT IF CLOUDS HOLD OFF
LONGER.

ANY HEAVIER RAIN SHOULD BE EXITING OFF TO THE SOUTH AND EAST BY
LATER THIS EVENING WITH ONLY SOME SCATTERED -RA OR SHOWERS
REMAINING AFTER MIDNIGHT AS THE LOW HEADS OFFSHORE. POPS WILL
REMAIN AT LIKELY OR HIGHER SOUTHERN HALF EARLY THEN CUTTING BACK
TO JUST SLIGHTS OR LOW CHANCES LATE AS ALL LIFT EXITS. SHOULD
BE A BIT COOLER BEHIND THE SYSTEM WITH NORTH/NW TRAJECTORIES
DEVELOPING AND DEWPOINTS FALLING JUST A BIT BY DAYBREAK ALLOWING
SOME 50S IN THE VALLEYS.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
-- Changed Discussion --
AS OF 445 AM EDT TUESDAY...

THE STRONG UPPER DISTURBANCE...RESPONSIBLE FOR THE HEAVY RAIN
TUESDAY...WILL BE EXITING THE REGION WEDNESDAY MORNING.  BROAD
TROUGHING WILL PERSIST ACROSS THE EASTERN U.S...BUT THE OVERALL
TROUGH AXIS WILL SHIFT SLIGHTLY EASTWARD AS UPPER RIDGING BUILDS
ACROSS THE CENTRAL U.S. A LARGE AREA OF SFC HIGH PRESSURE WILL
SPREAD SOUTHEAST TOWARD THE NORTHERN MID-ATLANTIC REGION THROUGH
THU. ECMWF/GFS IN REASONABLE AGREEMENT ON THE EVOLUTION OF THE
SYNOPTIC PATTERN. OVERALL...THE WEATHER DURING THE WED-SAT TIME
FRAME WILL BE MORE TRANQUIL THAN RECENT DAYS. HOWEVER...THERE ARE
SOME POTENTIAL WEAK WEATHER SYSTEMS THAT WILL PREVENT IT FROM BEING
TOTALLY QUIET DURING THESE PERIODS. WED SHOULD BE THE QUIETEST DAY
WITH FAIRLY GOOD SUBSIDENCE BEHIND THE DEPARTING UPPER SHORT WAVE
AND ANY REMAINING SHOWERS LIMITED GENERALLY TO THE MORNING HOURS.
ISSUES TO KEEP AN EYE ON REVOLVE AROUND A FAIRLY DIRTY UPPER RIDGE
TO OUR WEST...ALLOWING A SERIES OF WEAK NW FLOW DISTURBANCES TO
CONTINUE TO TRACK SE ACROSS THE REGION AND A PERSISTENT AREA OF
WEAK LOW PRESSURE ALOFT ACROSS GA...THAT EVENTUALLY DRIFTS NORTH
TOWARD THE SOUTHERN APPALACHIANS AS WE APPROACH THE WEEKEND. AS WE
APPROACH THE WEEKEND...THE MID-ATLANTIC HIGH PRESSURE AREA GRADUALLY
SINKS SOUTHWARD TOWARD A BERMUDA POSITION...BRINGING INCREASINGLY
MOIST SOUTHERLY FLOW INTO THE AREA WHILE THE UPPER RIDGE CONTINUES A
SLOW EASTWARD PROGRESSION. THE COMBINATION OF ALL OF THESE
FEATURES...ALBEIT WEAK...WILL ALLOW FOR INCREASING DIURNAL
CONVECTION FOCUSED MAINLY ALONG THE SPINE OF THE ALLEGHANYS
FROM EASTERN WV SOUTHWARD TOWARD NW NC. WITHIN THIS AREA...INITIALLY
THE FOCUS SHOULD BE GREATEST ACROSS THE SW PART OF THE
CWA...EXPANDING NORTHWARD TOWARD THE WEEKEND. LIMITED CONVECTIVE
ACTIVITY IS EXPECTED TOWARD THE PIEDMONT...WHICH WILL BE MORE
STRONGLY INFLUENCED BY HIGH PRESSURE ALONG THE COAST LINE AND AN
ATTENDANT DRIER AIR MASS.

TEMPERATURES SHOULD REMAIN BELOW SEASONAL NORMALS WED-THU...THEN
GRADUALLY INCREASE TO NORMAL OR EVEN SLIGHTLY ABOVE BY THE WEEKEND
AS 850MB TEMPS CREEP TOWARD +2OC AS THE BROAD UPPER RIDGE EXPANDS
EASTWARD.
-- End Changed Discussion --
&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 400 PM EDT MONDAY...

SUBTROPIAL RIDGE IS EXPECTED TO BUILD NORTH...FLOODING THE MID
ATLANTIC REGION WITH WARM TEMPERATURES AND INCREASING DEWPOINTS.
ATTM...NO REAL FOCUS FOR DEEP CONVECTION EXCEPT FOR CONVERGENCE OVER
THE MTNS...SO KEPT ANY PRECIP THREAT MAINLY DIURNAL WITH PRIMARY
TARGETED TO THE MTNS.  TRENDS SUGGEST TEMPS WILL CLIMB BACK ABOVE
NORMAL FOR THE WEEKEND...BUT NOTHING MAJOR...SHOULD NUDGE 90 FOR THE
URBAN AREAS.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
AS OF 1235 AM EDT TUESDAY...

WIDELY SCATTERED THUNDERSTORMS CONTINUE ALONG AN AXIS BETWEEN
KBLF AND KHSP WITH THE MOST WIDESPREAD COVERAGE JUST SOUTH OF
KLWB. EXPECT THESE TO PERSIST AND MEANDER ACROSS THE NW SECTIONS
INTO THE OVERNIGHT BEFORE FADING WITH OTHER ADDED SHRA MOVING UP
FROM THE SW. THUS WILL INCLUDE AN HOUR OR TWO OF MVFR IN TSRA OR
TEMPO MENTION AT KLWB PENDING RELEASE COVERAGE WHILE LEAVING OUT
CONVECTION ELSW GIVEN ISOLATED NATURE OVERNIGHT. FOG REMAINS QUITE
TRICKY GIVEN SOME SPOTS HAVING SEEN SHRA/TSRA NEARBY DURING THE
EVENING WHILE STILL HAVE QUITE A MID DECK CANOPY IN PLACE TO
NEGATE RADIATIONAL COOLING THROUGH DAYBREAK. THINK THIS WILL LIMIT
FOG MOST SPOTS EXCEPT KLWB WHERE MAY SEE ENOUGH BREAKS AFTER SHRA
TAPERS OVERNIGHT TO SEE AT LEAST MVFR IN FOG IF NOT A PERIOD OF
IFR AT DAYBREAK. BOTH KLYH/KBCB COULD ALSO EXPERIENCE SOME FOG BUT
LOOKS LESS THAN EARLIER UNLESS CLOUDS DIMINISH SOME.

FOR TUESDAY...A STALLED BOUNDARY WILL SERVE AS A FOCUSING
MECHANISM FOR SIGNIFICANT LIFT THAT WILL BEGIN IN EARNEST EARLY
TUESDAY. A STRONGER UPPER SHORTWAVE WILL APPROACH FROM THE
NORTHWEST RENEWING SHRA/TSRA ACTIVITY TO OUR SOUTH...WHICH WILL
SPREAD UP/OVER THE REGION TUESDAY...WITH WIDESPREAD SHOWERS AS A
RESULT. THIS IS NOT EXPECTED TO REACH OUR SOUTHERN CWA BORDER
UNTIL AFTER DAYBREAK TUE. OVERALL...WIND SPEEDS ON TUESDAY WILL
BE LIGHT WITH NORTHWEST TO WEST DIRECTION FAVORED IN THE
MOUNTAINS.

MEDIUM TO HIGH CONFIDENCE IN CIGS THROUGH TAF VALID PERIOD.
LOW TO MEDIUM CONFIDENCE IN VSBYS THROUGH TAF VALID PERIOD.
MEDIUM TO HIGH CONFIDENCE IN WIND SPD/DIR THROUGH TAF VALID
PERIOD.

EXTENDED AVIATION DISCUSSION...CLOUDS ALONG WITH A FEW SHOWERS
MAY LINGER INTO WEDNESDAY BEFORE DRIER AIR BRINGS A RETURN TO
OVERALL VFR THURSDAY INTO FRIDAY...WITH ONLY ISOLATED DIURNAL
MOUNTAIN CONVECTION. HIGH PRESSURE ALOFT BUILDS EAST SATURDAY WITH
CONTINUED OVERALL VFR OUTSIDE OF ISOLATED CONVECTION ALONG THE
MOUNTAINS.

&&

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

&&

$$
SYNOPSIS...JH
NEAR TERM...JH
SHORT TERM...RAB
LONG TERM...PM
AVIATION...JC/JH/KK