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000
FXUS61 KLWX 181453
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1053 AM EDT SAT MAY 18 2013

.SYNOPSIS...
A FRONTAL BOUNDARY WILL REMAIN STALLED TODAY OVER THE CENTRAL
APPALACHIANS AND SOUTHERN MID- ATLANTIC STATES WHILE ONSHORE FLOW
KEEPS THE FORECAST AREA SEASONABLY COOL. THE FRONTAL BOUNDARY WILL
LIFT NORTH INTO THE AREA SUNDAY..THEN INTO THE NORTHERN MID-
ATLANTIC ON MONDAY. HIGH PRESSURE WILL THEN BUILD OVER THE
EASTERN STATES THROUGH MIDWEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 14Z...FRONTAL BOUNDARY ESTIMATED FROM SFC OBS TO BE LOCATED
OVER NERN NC...THEN EXTENDING WEST ALONG THE VIRGINIA/NORTH
CAROLINA BORDER. MEANWHILE...HIGH PRESSURE IS SHIFTING SOUTH FROM
THE NEW ENGLAND COAST.

UPDATED POPS BASED ON RADAR UNTIL MIDDAY...THEN BASED
AFTERNOON/EVENING GRIDS ON THE 03Z SREF. BLEND OF MAV/MET/SREF WAS
ADJUSTED DOWN FOR SRN CWA ZONES WHERE CLOUDS AND PRECIP SHOULD
KEEP MAX TEMPS IN THE MID 60S.

COOL WEDGE WILL BE PRESENT ACROSS MUCH OF THE CWA TO PRECLUDE
THUNDER EXCEPT FOR THE SOUTHWEST CWA THIS AFTERNOON/EARLY EVENING
WHERE ELEVATED INSTABILITY WILL SPREAD NORTH ALONG WITH BATCH OF
PRECIP CURRENTLY OVER WRN NC/VA. THEREFORE...CONTINUE TO INCLUDE
CHANCE OF THUNDER IN THIS AREA AND ANY CONVECTION MAY BE EFFICIENT
RAINFALL PRODUCERS FOR LOCALLY HEAVY RAINFALL.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
FRONTAL BOUNDARY WILL REMAIN STALLED ACROSS SRN VA ON SUN WHILE SFC
RIDGE FROM HIPRES OFF THE NEW ENGLAND COAST WILL EXTEND WWD INTO NJ
AND PA. SFC PATTERN WILL YIELD A CONTINUED ONSHORE FLOW ACROSS THE
CWA ON SUN. REMNANT MID-LVL SHORTWAVE TROUGH WILL MEANDER OVER THE
CENTRAL APPALACHIANS AS IT REMAINS EMBEDDED WITHIN WEAK STEERING
PATTERN OF THE ERN CONUS RIDGE. FLOW VEERS WITH HEIGHT WITH SLY FLOW
AT H8-7 PROMOTING ISENTROPIC LIFT. CLOUDS AND PERIODS OF SHOWERS
EXPECTED ON SUN. THE HEAVIEST QPF AND CAT POPS RESIDE OVER CENTRAL
VA AND LWR SRN MD...WHERE LIFT MAY BECOME ENHANCED NEAR THE BOUNDARY
AND NORTH OF THE MID-LVL TROUGH. MOST OF THE CWA WILL BE WEDGED IN
STABLE MARINE AIRMASS ALTHOUGH LOCATIONS IN CENTRAL VA MAY TAP INTO
SOME INSTABILITY CLOSER TO THE BOUNDARY. WILL NEED TO MONITOR THE
CONDITIONAL RISK FOR FLOODING OVER THESE AREAS IF CONVECTION
DEVELOPS. WPC HAS HIGHLIGHTED CENTRAL VA WITH A SLIGHT RISK FOR
EXCESSIVE RAINFALL ON SUN.

CLOUDS AND ONSHORE FLOW WILL LIMIT DIURNAL HEATING/COOLING SUN-SUN
NGT. HIGHS NEAR 70F ON SUN AND LOWS IN THE 60S SUN NGT WILL BE
COMMON.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
THE MID-ATLANTIC REGION WILL BE SITUATED ALONG WRN PERIPHERY OF AN
UPPER RIDGE THROUGH MIDWEEK. PERSISTENT AND DEEP RETURN FLOW AROUND
THE RIDGE WILL CONTINUE TO SUPPLY WARM/MOIST AIR FOR OUR AREA. WITH
THE PREVIOUSLY STALLED FRONTAL BOUNDARY LIFTING NORTH OF THE AREA ON
MON...INSTABILITY AND MOISTURE WILL BE GREATER IN WARM SECTOR. DAILY
CHANCES FOR SHOWERS AND TSTMS WILL BE HIGHEST DURING THE PEAK
HEATING HRS. DURING THE FIRST HALF OF THE WORK WEEK...MON EXPECTED
TO HAVE THE BEST COVERAGE OF PRECIP WITH THE LINGERING MID-LVL
SHORTWAVE TROUGH NEARBY. POPS TUE AND WED WERE CONFINED TO THE
HIGHER TERRAIN WITH OROGRAPHIC LIFT THE PRIMARY DRIVING MECHANISM
FOR DIURNAL CONVECTION. MAX TEMPS NEAR 80F ON MON AND MU80S TUE/WED.

CHANCES FOR SHOWERS AND STORMS INCREASE LATE WEEK WITH THE APPROACH
OF A MIDWEST TROUGH. WARM/HUMID AIRMASS REMAINS IN PLACE DURING THIS
TIME.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
MVFR CIGS CONTINUE TO SPREAD NE TODAY WITH IFR/LIFR TONIGHT AND
PROBABLY THROUGH SUNDAY.LIFR CONDITIONS AFTER MIDNIGHT. PASSING
LIGHT SHOWERS WILL CONTINUE INTO THE AFTERNOON. A LULL EXPECTED IN
PRECIP THIS AFTERNOON...THEN SHOWERS EXPAND ACROSS THE DC METROS.
ANY THUNDER CHANCE DOWN BY KCHO AT THIS POINT.

MVFR CIGS SUN WITH ONSHORE FLOW CONTINUING. CIGS LIKELY RETURN TO
IFR SUN NGT. WARM FRONT EVENTUALLY LIFTS NORTH OF THE REGION ON MON.
FLIGHT RULES RETURN TO VFR ERY NEXT WEEK...ALTHOUGH BRIEF
RESTRICTIONS POSSIBLE IN SHRA/TSRA.

&&

.MARINE...
SOUTHEAST FLOW FROM HIGH PRESSURE MOVING OFF THE NEW ENGLAND
COAST AND A FRONTAL BOUNDARY STALLED TO THE SOUTH OF THE
WATERS. EXPANDED SCA TO SOUTH OF NORTH BEACH AND THE MIDDLE TIDAL
POTOMAC WHERE SELY FLOW OFTEN ENHANCES. A LULL TO AROUND 15 KT IS
EXPECTED THROUGH MIDDAY WITH GUSTS INCREASING TO AROUND 20
KT THIS AFTERNOON AND EVENING.

ELY FLOW 10-15 KT ON SUN. WINDS BECOME SLY ONCE A WARM FRONT PASSES
THRU ON MON. SCA MAY BE NEEDED MON FOR THE MARINE ZONES THAT ARE
SUSCEPTIBLE TO SLY-CHANNELING.

&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES WILL REMAIN ABOUT 3/4 FT TODAY AS ONSHORE FLOW
MAINTAINS THE LEVEL. SELY FLOW BECOMES SLY MONDAY WHEN A WARM
FRONT LIFTS NORTH OF THE AREA. WILL NEED TO MONITOR TIDAL LVLS
THOUGH THE THREAT OF COASTAL FLOODING WILL BE RELATIVELY LOW JUST
PAST HALF MOON.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR ANZ533-
     534-536-537-543.

&&

$$
UPDATE...JACKSON
PREVIOUS DISCUSSION...BPP/JRK