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000
FXUS61 KLWX 160401 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1201 AM EDT THU MAY 16 2013

.SYNOPSIS...
A COLD FRONT WILL SAG SOUTHWARD ACROSS THE AREA LATE TONIGHT AND
THURSDAY. THE FRONT WILL STALL JUST SOUTH OF THE REGION THROUGH
THE WEEKEND WHILE HIGH PRESSURE TO OUR NORTH CREATES AN ONSHORE
FLOW. HIGH PRESSURE WILL BUILD OVER THE MID-ATLANTIC EARLY NEXT
WEEK...AIDING A SOUTHERLY FLOW.

&&

.NEAR TERM /THROUGH THURSDAY/...
UPDATE...EXTENDED SCA FOR THE LOWEST COUPLE BAY ZONES FOR ANOTHER
FEW HRS.

FROM PREV DISC...THE MID-ATLANTIC REGION IS SITUATED IN WLY BELT
AROUND THE NRN PERIPHERY OF AN UPPER RIDGE OVER THE SOUTHEAST
STATES AND LOPRES SOUTH OF HUDSON BAY. STRONG HEATING AIDED BY
DOWNSLOPING WINDS THIS AFTN HAD PROMOTED A DEEP MIXED LAYER AS
SEEN ON THE 00Z IAD AND OTHER REGIONAL RAOB SOUNDINGS. A WEAK COLD
FRONT OVER THE OH VLY WILL GRADUALLY ADVANCING SEWD TNGT.

SOUTH OF THE FRONT...DIURNALLY-DRIVEN SHOWERS AND STORMS DEVELOPED
NEAR THE MASON-DIXON LINE BUT NEVER REALLY GOT GOING AS A EML
CAP...LACK OF ORGANIZED LIFT AND A RELATIVELY DRY BOUNDARY LAYER
WORKED AGAINST CONVECTIVE DEVELOPMENT. HAVE REMOVED SEVERE WX THREAT
FROM HWO AS THE ATMOSPHERE STABILIZES WITH THE LOSS OF HEATING AND A
STRONGER CAP FARTHER SOUTH. EVE POPS REFLECT A TIGHT GRADIENT WITH
CHANCE POPS CONFINED TO THE ERN WV PANHANDLE AND NRN MD. ADDITIONAL
SHOWERS ARE POSSIBLE OVNGT NEAR THE ALLEGHENY FRONT WHEN THE COLD
FRONT APPROACHES. MODEL GUIDANCE HAS BEEN OVERDOING FRONTAL
CONVECTION...SO KEPT POPS LOW.

BELT OF MID-LVL CLOUDS AHEAD OF THE FRONT WILL GRADUALLY PROGRESSES
SWD ACROSS THE CWA TNGT. ADJUSTED MIN TEMPS UP A FEW DEGREES SINCE
THESE CLOUDS WILL CURB RADIATIVE COOLING.

CLOUD COVER IS EXPECTED TO HOLD IN FOR MUCH OF THURSDAY...OCCASIONAL
BREAKS STILL POSSIBLE WITH FRONTAL BOUNDARY IN VICINITY. SCATTERED
SHOWERS AND THUNDERSTORMS AGAIN POSSIBLE ON THURSDAY JUST ABOUT
ANYWHERE...BUT THE HIGHEST POPS RESIDE CLOSER TO THE BOUNDARY ACROSS
CENTRAL VA. THESE SLIGHTLY COOLER WITH HIGHS IN THE 60S IN THE WRN
HIGHLANDS TO LOWER 80S ALONG AND EAST I-95.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/...
THE COLD FRONT SHIFTS SOUTH OF DC THURSDAY EVENING...SHUNTING
SHOWERS/THUNDERSTORMS TO THE SRN PERIPHERY OF THE LWX CWA (INCL
KCHO). NWLY FLOW FILLS IN BEHIND THE COLD FRONT AND SINCE THIS MIXES
DOWN ON FRIDAY...THERE SHOULD BE LITTLE CHANGE IN THE TEMPERATURES
(MAX TEMPS FRIDAY AROUND 80F...PERHAPS MID 80S SOUTH OF DC).
SCATTERED THUNDERSTORMS POSSIBLE IN THE TERRAIN W/SW OF KCHO
FRIDAY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
ONSHORE FLOW OR CAD WEDGE THIS WEEKEND WITH HIGH PRESSURE EITHER
STALLED ALONG THE NEW ENGLAND COAST OR OFF THE MID-ATLANTIC COAST. A
QUICK LOOK AT THE 12Z ECMWF SUGGESTS THE HIGH STALLS ALONG THE NEW
ENGLAND COAST AND GIVES A CAD WEDGE FOR THE MID-ATLANTIC. MAX
TEMPERATURES WERE KNOCKED DOWN 5-10 DEGREES BELOW NORMAL...LOW 70S
(WITH MID 70S SOUTH OF DC) ON SATURDAY AND SOME UPPER 60S FOR SUNDAY
(WITH LOW 70S SRN MD). PRECIP LOOKS TO REMAIN SHUNTED TO THE FAR
SWRN ZONES FOR LWX (WEST FROM KCHO).


LONG WAVE (WARM) RIDGE BUILDS OVER THE MIDWEST EARLY NEXT WEEK.
SLY/SELY FLOW WILL BRING QUITE A WARMUP TO THE REGION WITH
TEMPERATURES BACK ABOVE NORMAL BY MON OR TUE. MOISTURE INFLUX ACROSS
THE REGION IN THE SLY FLOW SHOULD BRING SOME INSTABILITY ACTIVITY
THROUGH THE EARLY AND MID PARTS OF NEXT WEEK.

&&

.AVIATION /04Z THURSDAY THROUGH MONDAY/...
VFR EXPECTED TNGT. SHOWERS WILL PASS IN VC OF MRB THIS EVE AND
POSSIBLE BWI/MTN CLOSER TOWARD MIDNIGHT.

ADDITIONAL CHANCES FOR SHRA AND EVEN AN ISO TSRA ON THURSDAY.
GENERALLY VFR EXPECTED ALTHOUGH ANY SHRA/TSRA COULD BE ACCOMPANIED
BY BRIEF RESTRICTIONS.

VFR CONDS PREVAIL THURSDAY NIGHT INTO THE WEEKEND. SCATTERED
THUNDERSTORMS WANE AND SHIFT SOUTH FROM THE DC METROS THURSDAY
EVENING AND PERSIST NEAR KCHO INTO THE EARLY MORNING HOURS.
THUNDERSTORMS ON FRIDAY LOOK TO BE WEST FROM THE BLUE RIDGE.

&&

.MARINE...
SLY WINDS HAVE WEAKENED AFTER SUNSET...BUT MARGINALLY REMAIN AT
SCA THRESHOLD IN THE LWR-MID TIDAL POTOMAC RVR AND SRN CHSPK BAY.
WINDS BECOME WLY AND DROP TO BELOW SCA LVLS OVNGT AND ON THU.

NO SCAS EXPECTED THURSDAY NIGHT THROUGH THIS WEEKEND. NWLY FLOW
10 TO 15 KT THURSDAY EVENING BECOMES NLY THURSDAY NIGHT...THEN
VEERING SELY THROUGH FRIDAY. EXPECT AN ONSHORE FLOW THROUGH THIS
WEEKEND.

&&

.TIDES/COASTAL FLOODING...

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EDT THURSDAY FOR ANZ534-537-
     543.

&&

$$
UPDATE...GMS
PREV DISCUSSION...JRK/BAJ/KRW