-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 181140
AFDRNK

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TONIGHT/...
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.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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.

&&

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

SUBTROPICAL 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.
-- End Changed Discussion --

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
AS OF 730 AM EDT TUESDAY...

AREA OF WIDESPREAD -SHRA/ISOLD TSRA WITH MVFR-IFR CIGS AND MVFR
VSBYS...LOCALLY IFR...SPREADING INTO THE CWA FROM THE WEST NOW.
ALREADY IMPACTING THE BLF/LWB TAFS...AND WILL REACH LYH/DAN IN THE
14Z-16Z TIME FRAME. SYSTEM WILL BEGIN TO EXIT THE REGION FROM THE
WEST AFT 00Z...BUT EXPECT LOW-LEVEL AIR MASS TO REMAIN VERY MOIST
AND AREAS OF MVFR-IFR CIGS/VSBYS IN -DZ/BR LIKELY TO PERSIST
THROUGHOUT THE NIGHT...ESPECIALLY LWB AND DAN. BOTTOMLINE...POOR
AVIATION CONDITIONS EXPECTED THROUGHOUT THE TAF VALID PERIOD.
ISOLD TSRA CAN ALSO BE EXPECTED...BUT INSTABILITY IS MINIMAL...SO
NOT EXPECTING A LOT OF TSRA...BEST CHANCE DAN. WINDS LIGHT SW OR
CALM THROUGH MIDDAY...THEN BECOMING W-NW BEHIND UPPER SHORT
WAVE/ASSOCIATED SFC TROUGH LATE AFTERNOON/EVENING FROM W-E.

EXTENDED AVIATION CONDITIONS...FOR WED...LOW IFR CIGS/VSBYS MAY
PERSIST THROUGH MID-MORNING...BUT EXPECT IMPROVED CONDITIONS AS
THE DAY PROGRESSES WITH LITTLE TO NO SHRA ACTIVITY. CIGS/VSBYS
SHOULD IMPROVE TO VFR BY AFTERNOON. FOR THU INTO THE
WEEKEND...INCREASED DIURNAL CONVECTION...ESPECIALLY ALONG THE
APPALACHIANS...WITH LOCALLY BRIEF MVFR-IFR CIGS/VSBYS IN TSRA.
AREAS OF MVFR-IFR VSBYS BR...LOCALLY IFR FG...ALSO POSSIBLE DURING
THE MORNING HOURS.

MEDIUM CONFIDENCE IN CIGS THROUGH TAF VALID PERIOD.
MEDIUM CONFIDENCE IN VSBYS THROUGH TAF VALID PERIOD.
MEDIUM TO HIGH CONFIDENCE IN WIND SPD/DIR THROUGH TAF VALID
PERIOD.
-- End Changed Discussion --

&&

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

&&

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