000
FXUS61 KLWX 170113
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
913 PM EDT THU MAY 16 2013

.SYNOPSIS...
A FRONTAL BOUNDARY WILL DRIFT SOUTH THROUGH TONIGHT THEN REMAIN
STALLED OVER THE SOUTHERN MID-ATLANTIC THROUGH THE WEEKEND...WITH
SURFACE HIGH PRESSURE BUILDING OFF THE NEW ENGLAND COAST. HIGH
PRESSURE WILL BUILD OVER THE MID-ATLANTIC EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH FRIDAY/...
A WEAK COLD FRONT IS MOVING THROUGH THE CWA THIS EVENING WHILE
SHOWERS AND THUNDERSTORMS MOVED ACROSS CENTRAL VIRGINIA...SOUTHERN
MD AND SURROUNDING WATERS THIS AFTERNOON.  THREAT OF SVR HAS PUSHED
SOUTH OF THE AREA THIS EVENING. MOST AREAS WILL STAY DRY
OVERNIGHT WITH THE EXCEPTION OF CENTRAL VA AND THE SHENANDOAH
VALLEY AS COLD FRONT CONTINUES TO MOVE SOUTHWARD. THUNDERSTORM
DEVELOPMENT IS STILL POSSIBLE THIS EVENING AND OVERNIGHT FOR AREAS
IN CENTRAL VIRGINIA PER 00Z RNK RAOB BUT MOST LIKELY BE SOUTH OF
THE CWA. FURTHER NORTH...CLOUDS WILL BREAK OVERNIGHT AND TEMPS ARE
EXPECTED TO DROP TO THE UPPER 50S LOW 60S. WINDS WILL SLOWLY BACK
TO THE NORTH OVERNIGHT AND EVENTUALLY TO THE EAST BY FRIDAY
AFTERNOON AS HIGH PRESSURE SLOWLY MOVES TOWARDS THE MID ATLANTIC
FROM THE NORTH.

WEAK COLD FRONT WILL STAY TO THE SOUTH OVER THE COURSE OF FRIDAY.
SHOWERS WILL MOVE INTO THE POTOMAC HIGHLANDS AND CENTRAL VA
FOOTHILLS FRIDAY AFTERNOON. A STABLE AIRMASS WILL BE IN PLACE FOR
AREAS EAST OF THE BLUE RIDGE TOMORROW SO SHOWERS AND ISOLATED
THUNDERSTORMS SHOULD STAY TO THE WEST. HIGH TEMPERATURES WILL BE
NEAR CLIMATOLOGICAL NORMS FRIDAY.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
SFC HIGH PRESSURE BUILDS SOUTHEAST ACROSS NEW ENGLAND INTO THE NORTH
ATLANTIC WEEKEND. THIS HIGH...COMBINED WITH A STALLED BOUNDARY WILL
RESULT IN A SELY SFC FLOW FOR THE CWA. SLY FLOW ACROSS THE ERN CONUS
WILL PUMP MOISTURE INTO THE REGION AS A DEEP RIDGE BUILDS OVER THE
MIDWEST. PRECIP STILL LOOKS CONTAINED TO THE SWRN HALF OF THE CWA ON
SATURDAY AS WITH THE BOUNDARY IS ALONG THE NC/VA BORDER. THE DIFFUSE
BOUNDARY SEEMS TO DRIFT NORTH INTO THE SWRN ZONES WHERE TERRAIN
WOULD AID DEVELOPMENT...SO LIKELY POPS (WITH THUNDER) WERE ADDED S/W
OF KCHO. ONGOING SHOWERS SATURDAY NIGHT AS THE MOIST FLOW EXPANDS
ACROSS THE CWA. RAISED POPS TO LIKELIES FOR SUNDAY ALL BUT FAR NERN
MD WHERE INFLUENCE FROM THE HIGH OFFSHORE MAY LIMIT COVERAGE. WITH
PLENTY OF CLOUDS AND PRECIP...MAINTAINED BELOW NORMAL MAX
TEMPERATURES LOW 70S (WITH MID 70S SOUTH OF DC) ON SATURDAY AND
UPPER 60S FOR SUNDAY (WITH LOW 70S ALONG THE TIDAL POTOMAC).

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
THE 00Z ECMWF STILL PROGS A LONG WAVE (WARM) RIDGE TO BUILD OVER THE
OHIO VALLEY...WITH SUBSIDENCE FOR MON/TUE ACROSS THE CENTRAL
MID-ATLANTIC. LOWERED WPC GUIDANCE TO LOW CHANCE POPS FOR BOTH DAYS
WHICH IS UNDERSTANDABLE AS THE 12Z GFS STILL PROGS INSTABILITY FROM
THE SLY FLOW ACROSS THE REGION. WENT NEAR NORMAL (GENERALLY MID 70S)
FOR MONDAY GIVEN MIX OF CLOUDS AND 850MB TEMPS 12-14C. MID 80S ON
TUESDAY WITH MORE SUNSHINE AND 14-18C 850MB TEMPS.

LOW PRESSURE LINGERS OVER THE NRN PLAINS INTO THE MIDDLE OF NEXT
WEEK AS THE UPR RIDGE PERSISTS OVER THE ERN CONUS WITH CONTINUED
WARMTH.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
MAINLY VFR CONDITIONS EXPECTED THIS EVENING. THUNDERSTORMS MOVED
THROUGH CHO THIS AFTERNOON AND CALM WINDS AND LOW LEVEL MOISTURE
MAY CAUSE VSBY TO DROP TO 6SM ALTHOUGH CLOUDS SHOULD KEEP CHO FROM
DROPPING TO MVFR OR LESS.

WINDS WILL SLOWLY BACK TO THE NORTH OVERNIGHT AND EVENTUALLY TO
THE EAST BY FRIDAY AFTERNOON AS HIGH PRESSURE SLOWLY MOVES TOWARDS
THE MID ATLANTIC FROM THE NORTH.

VFR CONDS PREVAIL THROUGH SATURDAY BEFORE A SELY FLOW LOWERS CIGS
INTO THE MVFR RANGE SATURDAY NIGHT. THUNDER WEST OF THE BLUE RIDGE
ON SATURDAY EXPANDS EAST INTO THE DC METROS ON SUNDAY WITH GREATER
COVERAGE OF RAIN THAT DAY.

&&

.MARINE...
WINDS WILL SLOWLY BACK TO THE NORTH OVERNIGHT AND EVENTUALLY TO THE
EAST BY FRIDAY AFTERNOON AS HIGH PRESSURE SLOWLY MOVES TOWARDS THE
MID ATLANTIC FROM THE NORTH.  SCA CONDITIONS ARE NOT POSSIBLE AT THE
TIME.

NO SCAS EXPECTED THROUGH THIS WEEKEND...THOUGH SELY FLOW 10 TO 15 KT
IS EXPECTED THROUGH THE WEEKEND. SLY FLOW EARLY NEXT WEEK STILL
GENERALLY 10 TO 15 KT.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

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