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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 180134
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
934 PM EDT FRI MAY 17 2013

.SYNOPSIS...
A FRONTAL BOUNDARY OVER THE CENTRAL APPALACHIANS AND SOUTHERN
MID-ATLANTIC WILL REMAIN STALLED THROUGH THE WEEKEND AS AN ONSHORE
FLOW DEVELOPS WITH SURFACE HIGH PRESSURE BUILDING OFF THE NORTHERN
MID-ATLANTIC COAST. HIGH PRESSURE WILL BUILD OVER THE EASTERN STATES
THROUGH THE FIRST HALF OF NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
-- Changed Discussion --
HIGH PRESSURE WILL CONTINUE TO SPREAD EASTWARD OVER NEW ENGLAND AND
EVENTUALLY ANCHOR ITSELF OFF THE ATLANTIC COAST SATURDAY. A STATIONARY
FRONT THAT HAS BEEN THE ZONE OF SHOWER AND THUNDERSTORM ACTIVITY
IN THE PAST FEW DAYS HAS POSITIONED ITSELF ALONG THE APPALACHIANS
AND IN SOUTHERN VIRGINIA TONIGHT. TO THE EAST OF THIS BOUNDARY MID TO
HIGH LEVEL CLOUDS HAVE INCREASED AS A STABLE AIR MASS HAS MOVED
INTO THIS REGION TODAY. ALONG THE BOUNDARY... SHOWERS ARE PRESENT
ACROSS THE POTOMAC HIGHLANDS AND CENTRAL VA ZONES. THIS ACTIVITY
WILL CONTINUE AND SLOWLY FILL IN AS AN UPPER LEVEL DISTURBANCE
APPROACHES THE MID ATLANTIC FROM THE SOUTHWEST. ISENTROPIC LIFT
WILL INCREASE IN THE SW OVERNIGHT AND BY SAT MORNING SHOWERS AND
CLOUDS WILL HAVE INCREASED OVER THE ENTIRE REGION. BEST CHANCE FOR
SHOWERS WILL BE IN CENTRAL VIRGINIA AND THE POTOMAC HIGHLANDS
THROUGH SATURDAY. THUNDERSTORMS SHOULD STAY SOUTH OF OUR REGION
CLOSER TO THE STATIONARY BOUNDARY DURING THE DAY ON SATURDAY BUT
AN ISO THUNDERSTORM IS POSSIBLE IN CENTRAL VA AND THE POTOMAC
HIGHLANDS IN THE AFTERNOON. MINIMAL INSTABILITY AND A STABLE AIR
MASS WILL MAKE IT DIFFICULT FOR UPDRAFTS TO FORM. SHOWER ACTIVITY
WILL MOVE NORTH AND OVERSPREAD NOVA AND WASHDC METRO BY SATURDAY
AFTERNOON.

EASTERLY WINDS WILL PERSIST THROUGH MUCH OF THE WEEKEND LEADING TO
LOW CEILINGS INTO SATURDAY EVENING. DUE TO THE CLOUD COVER AND SHOWER
ACTIVITY TEMPS WILL NOT HAVE AS BIG OF A DIURNAL CURVE AS FRIDAY.
UPPER 60S AND POSSIBLY 70 ARE EXPECTED SAT.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
AN UPR TROUGH EJECTING FROM THE NORTHERN INTERMOUNTAIN WEST TO THE
GREAT PLAINS AND AN AMPLIFYING TROUGH OVER THE CANADIAN MARITIMES
WILL AMPLIFY A LONG-WAVE RIDGE OVER THE MIDWEST THIS WEEKEND. AT THE
SFC...HIGH PRESSURE WILL BUILD OFF THE NRN MID-ATLANTIC COAST WITH
THE STALLED BOUNDARY PERSISTING OVER THE SRN MID-ATLANTIC. AS A
RESULT...AN ONSHORE FLOW IS EXPECTED SATURDAY THROUGH SUNDAY NIGHT.
EXPECT WIDESPREAD SHOWERS TO SPREAD NORTHEAST TO THE BALT-WASH METRO
SATURDAY NIGHT AS MOIST SLY LLVL FLOW EXPANDS ACROSS THE CWA. CLOUDS
AND ONSHORE FLOW MAKE FOR A MILD SATURDAY NIGHT WITH MIN TEMPS MID
TO UPR 50S...LOW 60S URBAN/NEAR SHORE. WAA OVERRIDES THE CLOUDS
MAKING FOR MAX TEMPS ONLY ABOUT 5 DEGREES BELOW NORMAL (LOW 70S).

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
A LONG WAVE (WARM) RIDGE WILL PERSIST OVER THE ERN STATES MONDAY
THROUGH MOST OF NEXT WEEK WITH A SLY FLOW AND ABOVE NORMAL
TEMPERATURES. GENERALLY 80S MAX TEMPS THROUGH THE WEEK WITH MID TO
UPR 60 FOR MINS IN THE HUMID AIR. AT LEAST DIURNALLY DRIVEN
CONVECTION IS EXPECTED WITH ANY DISTURBANCE MAKING FOR ALL-DAY
THUNDERSTORM POTENTIAL.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
VFR CONDITIONS EXPECTED THIS EVENING AND FOR MOST OF THE OVERNIGHT.
INCREASED COVERAGE IN SHOWERS AND CLOUDS WILL OCCUR OVERNIGHT WITH
CIGS DROPPING TO MVFR AT CHO BY THE MORNING. CONDITIONS WILL
DETERIORATE SATURDAY AS EASTERLY FLOW CONTINUES AT THE SFC AT ALL
TERMINALS.


MVFR/IFR CIGS SATURDAY NIGHT THROUGH SUNDAY NIGHT AS AN ONSHORE FLOW
BRINGS AMPLE MOISTURE ACROSS THE REGION. PASSING SHOWERS THROUGH
THIS TIME COULD CAUSE IFR VSBYS DURING THE HEAVIEST RAINFALL.
UNSTABLE PATTERN CONTINUES THROUGH AT LEAST THE MIDDLE OF NEXT
WEEK.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
SCA IS IN EFFECT FOR THE LOWER TIDAL POTOMAC AND PORTIONS OF THE
CHESAPEAKE BAY.  EASTERLY FLOW WILL CONTINUE FOR THE MOST OF THE
WEEKEND. A PRESSURE GRADIENT WILL TIGHTEN OVER THE WATERS SATURDAY
AND GUSTS AROUND 20 KNOTS WILL BE POSSIBLE IN TEH LOWER TIDAL
POTOMAC AND CHESAPEAKE BAY. VSBYS OVER THE WATERS WILL BE REDUCED
AT TIMES IN RAIN/SHOWERS.

ONSHORE FLOW 10 TO 15 KT SATURDAY NIGHT THROUGH SUNDAY
NIGHT...BECOMING SLY MONDAY MORNING. PERHAPS AN SCA FOR SLY
CHANNELING MONDAY AFTERNOON/EVENING...OTHERWISE WINDS STAY BELOW 18
KT. SWLY FLOW AROUND 10 KT THEN TUESDAY THROUGH WEDNESDAY.
-- End Changed Discussion --

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 AM TO 8 PM EDT SATURDAY FOR
     ANZ534-537-543.
-- End Changed Discussion --

&&

$$
SYNOPSIS...HAS
NEAR TERM...HAS
SHORT TERM...BAJ
LONG TERM...BAJ
AVIATION...BAJ/HAS
MARINE...BAJ/HAS