-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 111915
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
315 PM EDT TUE JUN 11 2013

.SYNOPSIS...
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A SURFACE TROUGH WILL MOVE EAST OF THE AREA THROUGH THIS EVENING.
HIGH PRESSURE BRIEFLY BUILDS IN TONIGHT. LOW PRESSURE IS THEN
EXPECTED TO RIDE ALONG A STATIONARY BOUNDARY OVER THE MID-ATLANTIC
REGION...IMPACTING THE AREA LATE WEDNESDAY AND THURSDAY. THE COLD
FRONT WITH THIS LOW PASSES THROUGH BY THURSDAY EVENING. HIGH
PRESSURE RETURNS FOR FRIDAY THROUGH THE WEEKEND.
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&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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UPPER SHORTWAVE TROUGH CURRENTLY PROGRESSING TOWARD THE MID-ATLANTIC
COAST. W-NW FLOW ALOFT IN WAKE OF THE EXITING TROUGH HAS PRODUCED
DOWNSLOPING OFF THE MTS WITH MT WAVE CLOUDS OVER MUCH OF THE CWA.
SFC REFLECTION OF THE TROUGH LAGS BEHIND THE UPPER TROUGH AND IS
CURRENTLY LOCATED TO THE LEE OF THE BLUE RIDGE. BOUNDARY-LAYER
MOISTURE AND INSTABILITY IS SLIGHTLY HIGHER AHEAD OF THE SFC TROUGH
NEAR THE BAY. AN ISO SHOWER IS STILL POSSIBLE THIS AFTN EAST OVER
THE WRN SHORE BUT ANY CONVECTION THAT DEVELOPS WILL HAVE TO OVERCOME
A STRENGTHENING SUBSIDENCE INVERSION IN WAKE OF THE MID-LVL TROUGH.

SFC HIPRES BUILD IN FROM THE SRN APPALACHIANS TNGT. SKIES WILL CLEAR
TNGT ALTHOUGH HI CLOUDS WILL STREAM IN FROM THE NW LATE TNGT. MIN
TEMPS GENERALLY IN THE 60S ALTHOUGH LOCALES IN THE CITES AND ALONG
THE WRN SHORE MAY STAY AOA 70F.
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&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
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THE SHORT-TERM PERIOD LOOKS TO BE VERY ACTIVE WITH THE POTENTIAL FOR
MULTIPLE EPISODES OF SEVERE THUNDERSTORMS AND FLASH FLOODING.

ON WED AND WED NGT...THE CWA WILL BE SITUATED IN SRN PERIPHERY OF
STRONG MID-LVL WESTERLIES WHILE A NRN STREAM UPPER LOW MOVES INTO
THE CANADIAN MARITIMES AND AN EXPANSIVE RIDGE DOMINATES THE SRN
CONUS. AT THE SFC...A BACKDOOR FRONT WILL DEVELOP BY WED MRNG OVER
PA AND SAG SWD NEAR THE MASON-DIXON LINE WED AFTN. THE BOUNDARY
WILL STALL OVER THE AREA WED NGT. CLOUDS WILL OVERSPREAD THE AREA
DURING THE DAY WED AS MOISTURE MOVES IN FROM THE OH VLY. LLVL
CONVERGENCE AND ISENTROPIC LIFT MAY PRODUCE LGT SHOWERS OVER THE
MTS IN THE MRNG. SPC HAS PLACED ENTIRE CWA IN A SLGT RISK FOR SVR
STORMS ON WED. THERE IS STILL UNCERTAINTY REGARDING THE AMT OF
DESTABILIZATION THOUGH THE BEST OPPORTUNITY WILL RESIDE IN THE
WARM SECTOR OVER CENTRAL VA. STORMS MAY INITIALLY DEVELOP OVER
THE APPALACHIANS DURING THE PEAK HEATING HRS AND SPREAD EWD LATE
IN THE DAY. THERE IS ALSO A POTENTIAL THAT AN MCS DEVELOPS OVER
THE MIDWEST/OH VLY BEFORE CROSSING THE MTS WED NGT. TIMING OF
THAT IS UNCERTAIN BUT IF THE POTENTIAL MCS MOVES INTO THE CWA
EARLIER IN THE NGT...THEN ENOUGH INSTABILITY WOULD BE AVAILABLE
TO MAINTAIN STRONG TO SVR STORMS. LARGE HAIL...DAMAGING WINDS AND
FLASH FLOODING WOULD BE POSSIBLE WITH THESE STORMS.

ON THU...MODELS HAVE BEEN PERSISTENT WITH A STRONG SHORTWAVE TROUGH
AND COLD FRONT CROSSING THE MIDWEST WED NGT BEFORE MOVING THRU
MID-ATLANTIC STATES ON THU. SLY FLOW AHEAD OF A COLD FRONT AND
ASSOCIATED LOPRES WILL ALLOW THE BOUNDARY TO MOVE BACK NWD INTO PA
AS A WARM FRONT. 12Z MODELS HAVE TRENDED SLIGHTLY FASTER WITH THIS
SYSTEM. THERE IS STILL UNCERTAINTY WITH HOW MUCH HEATING OCCURS
AHEAD OF THE FRONT...BUT A FASTER SOLUTION WOULD THEORETICALLY
MEAN EARLIER DEVELOPMENT OF STORMS AND LESS OPPORTUNITY FOR
DAYTIME HEATING. THE BEST CHANCE FOR DESTABILIZATION THU MRNG WILL
BE ACROSS THE S/E PART OF THE CWA. SPC HAS OUTLOOKED EAST OF THE
BLUE RIDGE FOR A SLGT RISK WITH THE HIGHEST RISK /30 PERCENT/ OVER
SRN MD. GIVEN THE STRONG FORCING AND DEEP SHEAR PROFILES...THERE
IS A CONCERN FOR AN ORGANIZED SVR WX EVENT THU AFTN IF SUFFICIENT
HEATING OCCURS.
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&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
HIGH PRESSURE IS STILL FORECAST TO BUILD IN BEHIND THE FRONT ON
FRIDAY...AND CONTINUE INTO SATURDAY. GFS SHOWS THE NEXT SYSTEM
APPROACHING SUNDAY OR MONDAY WITH A CHANCE OF
SHOWERS/THUNDERSTORMS.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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WLY WINDS WILL CONT TO GUST 15-20 KT THRU SUNSET AS SFC TROUGH MOVES
EWD AND HIPRES BUILDS IN FROM THE SW. UNDER LGT WINDS TNGT AND
MAINLY CLEAR SKIES...PATCHY RADIATIONAL FOG MAY DEVELOP DURING THE
ERY MRNG MAINLY AT THE CHO/MRB.

FRONTAL BOUNDARY IS EXPECTED TO DROP SWD FROM PA AND STALL OVER THE
AREA WED AND WED NGT. SHRA/TSRA MAY DEVELOP OVER THE MTS AND SPREAD
SEWD INTO THE TERMINALS LATE WED AND WED NGT THOUGH THERE IS HIGH
UNCERTAINTY WITH HOW WIDESPREAD/STRONG THIS ACTIVITY WILL BE AND
WHEN IT WILL REACH THE TERMINALS.

COLD FRONT WILL MOVE THRU THE TERMINALS THU AFTN/EVE...BRINGING THE
RISK OF STRONG THUNDERSTORMS.

HIPRES BUILDS INTO THE TERMINALS FRI INTO THE WEEKEND.
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&&

.MARINE...
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WLY WINDS HAVE BECOME GUSTY OVER THE NRN CHSPK BAY AND UPPER TIDAL
POTOMAC...WHERE THE PRESSURE GRADIENT IS STRONGEST. SCA CONTINUES
THRU 10 PM FOR THESE ZONES. SCA-LVL GUSTS WILL BE MORE COMMON CLOSER
TO LAND...WHERE DEEPER MIXING OCCURS. WLY WINDS 5-10 KT TNGT WILL
INCREASE SLIGHTLY BY WED AFTN.

A BOUNDARY WILL PUSH SWD OVER THE WATERS WED AFTN AND EVE. SCT
SHOWERS AND STORMS MAY DEVELOP OVER THE MTS AND MOVE SEWD TOWARD THE
WATERS WED NGT. SLY FLOW INCREASES THU IN PRE-FRONTAL WARM SECTOR.
SCA CONDITIONS ARE LIKELY. SHOWERS AND STORMS ARE LIKELY THU AHEAD
OF THE APPROACHING COLD FRONT. THUNDERSTORMS HAVE THE POTENTIAL TO
PRODUCE STRONG WINDS AND LARGE HAIL.

WINDS BECOME NWLY BEHIND THE FRONT LATE THU AND THU NGT WITH SCA
CONDITIONS POSSIBLY CONTINUING. HIPRES BUILDS IN FRI INTO THE
WEEKEND.
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&&

.HYDROLOGY...
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SMALL STREAMS ARE SLOWLY RECEDING AFTER YESTERDAYS 2-3 INCH RAIN.
THE HEAVIEST SWATH OF PRECIPITATION STRETCHED FROM AUGUSTA COUNTY
VIRGINIA TO THE WASHINGTON AND BALTIMORE METRO AREAS. THE MAINSTEM
RIVERS ARE STILL RISING...BUT ARE NOT EXPECTED TO FLOOD.

MORE RAIN IS ON THE WAY AS A CONTINUING SERIES OF DISTURBANCES MOVES
ACROSS THE REGION. DEEPER MOISTURE RETURNS AS WELL...WITH PWATS
COMPARABLE TO YESTERDAY ACROSS THE REGION. A COLD FRONT WILL
APPROACH ON WEDNESDAY AND STALL NEAR THE AREA. STEADY HEAVIER RAIN
IS MORE LIKELY NORTH OF THIS BOUNDARY...WHICH LIKELY PUTS WIDESPREAD
HEAVY PRECIPITATION NORTH OF THE AREA. HOWEVER...EVEN CONVECTIVE
ACTIVITY THAT DEVELOPS SOUTH OF THE WARM FRONT WILL DEFINITELY BE
CAPABLE OF PRODUCING HEAVY RAIN IN A SHORT PERIOD OF
TIME...SIMILAR TO RECENT DAYS...LEADING TO A RENEWED FLASH FLOOD
THREAT. THE THREAT IS MAINLY ON THURSDAY...BUT ISOLATED FLASH
FLOODING CANNOT BE RULED OUT AS EARLY AS WEDNESDAY AFTERNOON. AS
WE SAW YESTERDAY...AN INCH OF RAIN IN A SHORT PERIOD OF TIME IS
MORE THAN ENOUGH TO CAUSE A PROBLEM.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR
     ANZ530>533-535-536-538>542.
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&&

$$
SYNOPSIS...JRK
NEAR TERM...JRK
SHORT TERM...JRK
LONG TERM...BPP
AVIATION...JRK
MARINE...JRK
HYDROLOGY...JE