-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 211416
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1016 AM EDT TUE MAY 21 2013

.SYNOPSIS...
-- Changed Discussion --
HIGH PRESSURE OVER THE ATLANTIC WILL CONTINUE TO AID A SOUTHERLY
FLOW THROUGH THURSDAY...BRINGING WARM AND HUMID CONDITIONS.
AFTERNOON AND EVENING THUNDERSTORMS ARE POSSIBLE EACH DAY. A
COLD FRONT WILL PASS THROUGH THE REGION THURSDAY NIGHT INTO
FRIDAY. COOLER CONDITIONS ARE EXPECTED OVER THE WEEKEND.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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WEAK UPPER-LEVEL LOW PRESSURE REMAINS OVER SOUTHERN VIRGINIA INTO
THE CAROLINAS THIS MORNING WHILE SURFACE HIGH PRESSURE REMAINS
CENTERED OVER THE ATLANTIC OCEAN. PLENTY OF CLDS BANKED UP ALONG
AND EAST OF THE BLURDG...WHILE MOSUN SKIES PREVAIL TO THE W. 12Z
LWX RAOB INDICATES AN INVERSION ASSOCD W/ THE LOW CLDS UP TO ABT
H9. ABV THAT SNDG UNSTBL...W/ APPROX 1850 J/KG CAPE. HWVR CNVCTV
TEMPS /89F/ WL BE HARD TO REACH UNDER THE CLD CVR.

LAMP TEMPS RUNNING LWR THAN FCST MAXT. WHILE LAMP HAS HAD A GOOD
FEEL FOR ERODING LOW CLDS PAST CPL DAYS AND LIKE ITS HANDLING TDA
/SCT OUT LLVL MSTR BTWN 15-18Z/...TEMP HV BEEN RUNNING A LTL ON
THE COOL SIDE. INDEED...OUR OBSVD SNDG CUD WARM UP IN A HURRY.
THEREFORE...WL BE HOLDING ONTO GOING TEMP FCST.

THAT LEADS TO THE PCPN FCST. THE WARM AND HUMID AIR WILL LEAD TO
HIGH AMOUNTS OF INSTABILITY. NAM/GFS BUFKIT ARE INDICATING AROUND
2000-2500 J/KG OF MLCAPE THIS AFTERNOON. GOT SIMLR RSLTS IN SBCAPE
MODIFYING OBSVD SNDG TO 85/65. HWVR...THERE WAS ALSO ABT 50 J/KG
CINH. THIS INHIBITION WILL MAKE IT DIFFICULT FOR CONVECTION TO
DEVELOP. LIKE PRVS FCST...WHICH CONCENTRATED ON TERRAIN
CIRCULATIONS...A SURFACE TROUGH AND THE UPPER-LEVEL LOW ACTING AS
LIFTING MECHANISMS. MAIN PREMISE OF POPS REMAIN UNCHGD. WILL ALSO
HAVE TO MONITOR CONVECTION OVER THE MIDWEST. THIS MAY SURVIVE OFF
ITS COLD POOL AND BRING A THREAT FOR MORE WIDESPREAD CONVECTION
ALONG THE ALLEGHENY AND POTOMAC HIGHLANDS THIS EVENING. THE
HIGHEST POPS ARE LOCATED ACROSS THESE AREAS FOR THAT REASON.

THE THREAT FOR SEVERE T-STORMS THIS AFTERNOON AND EVENING SHOULD BE
LOW DUE TO THE STRONG CAPPING INVERSION. HOWEVER...IF THE LIFTING
MECHANISMS END UP BEING STRONG ENOUGH TO ERODE THE INVERSION...THEN
GUSTY WINDS AND HAIL ARE POSSIBLE.

ANY LEFTOVER CONVECTION WILL DISSIPATE OVERNIGHT DUE TO THE LOSS OF
DAYTIME HEATING. LOW CLOUDS AND AREAS OF FOG MAY DEVELOP AS MOISTURE
GETS TRAPPED UNDERNEATH THE NOCTURNAL INVERSION. HOWEVER...LOW
CLOUDS/FOG SHOULD NOT BE AS WIDESPREAD AS RECENT NIGHTS DUE TO A
HIGHER TEMP/DEWPOINT DEPRESSION AND A STRONGER GRADIENT. MIN TEMPS
WILL BE IN THE 60S ACROSS MOST AREAS TO THE LOWER 70S IN DOWNTOWN
WASHINGTON/BALTIMORE.
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&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
CNTRL MID-ATLANTIC IN WARM SECTOR OF MIDWEST LOW UNTIL A COLD FRONT
IN THE THURSDAY NIGHT TIMEFRAME. SFC HIGH WELL OFF ERN SEABOARD AIDS
SLY FLOW/MOISTURE ADVECTION. TEMPS ABOUT 10 DEGREES ABOVE NORMAL
WITH UPR 60S TO NEAR 70F DEWPOINTS. EXPECT A DIURNAL TREND IN PRECIP
COVERAGE WITH PREFRONTAL FORCING ENTERING THE AREA THURSDAY. SLIGHT
RISK FOR WEDNESDAY DUE TO POTENTIAL FOR STRAIGHT LINE WINDS FROM
ONGOING MCS ACTIVITY OVER THE OHIO VALLEY PUSHING EAST.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
12Z ECMWF PROGS THE CD FROPA AS THURSDAY NIGHT (THERE HAS BEEN
FLUCTUATION FROM LATE THURSDAY TO FRIDAY MORNING). CANADIAN HIGH
PRESSURE BUILDS IN WITH A CRYSTAL CLEAR AND COOL WITH TEMPS 5-10
DEGREES BELOW NORMAL. SHORTWAVE OVER THE TN VLY ON SUNDAY SHOULD
REMAIN WEST OF THE LWX CWA...WILL HAVE TO MONITOR FOR INCREASED
POPS. AS OF NOW EXPECT SOME HIGH CLOUDS SUNDAY WITH A WARMING TREND
STARTING THAT CONTINUES INTO MID NEXT WEEK.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
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LOW-LEVEL MOISTURE IS TRAPPED UNDERNEATH THE STILL PRESENT
NOCTURNAL INVERSION. LOW CLOUDS AND FOG JUST BGNG TO ERODE...AND
WILL IMPROVE TO VFR BY/ARND NOON. ISOLD SHOWERS AND T-STORMS ARE
POSSIBLE THIS AFTERNOON AND EVENING. THREAT TOO SLIM FOR TAF
INCLUSION. AREAS OF LOW CLOUDS/FOG MAY IMPACT THE TERMINALS LATE
TONIGHT.

DIURNAL THUNDERSTORM ACTIVITY WED/THUR WITH IFR CONDS POSSIBLE IN
THE HEAVIEST ONES. SLY FLOW UNTIL A COLD FROPA THURSDAY NIGHT. NWLY
FLOW WITH CLEAR CONDS SATURDAY. JUST SOME HIGH CLOUDS ON SUNDAY.
-- End Changed Discussion --

&&

.MARINE...
SOUTHERLY WINDS ARE EXPECTED OVER THE WATERS THROUGH TONIGHT. WIND
GUSTS WILL BE CLOSE TO SCA CRITERIA THIS AFTERNOON AND TONIGHT. HAVE
CAPPED GUSTS AROUND 15 KNOTS FOR NOW DUE TO THE RELATIVELY COOLER
WATERS. SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE THIS
AFTERNOON AND EVENING.

SLY FLOW WITH HIGH PRESSURE OFFSHORE AHEAD OF A COLD FRONT THAT
COMES THROUGH THURSDAY NIGHT. SLY CHANNELING TO 20 KT POSSIBLE WED
EVENING...AND THURSDAY. NWLY FLOW TO 20 KT POSSIBLE FRIDAY. LIGHT
AND VARIABLE FLOW THIS WEEKEND.

&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES HAVE INCREASED TO AROUND ONE QUARTER FOOT ABOVE
NORMAL. ANOMALIES MAY INCREASE A BIT MORE DUE TO THE SOUTHERLY
FLOW...BUT WATER LEVELS SHOULD REMAIN BELOW THRESHOLDS FOR MINOR
FLOODING THROUGH TONIGHT. WILL HAVE TO WATCH SOUTHERLY FLOW
WEDNESDAY AND THURSDAY AS IT MAY SUPPORT AN INCREASE IN DEPARTURES
AGAIN.

&&

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

&&

$$
SYNOPSIS...BJL
NEAR TERM...HTS/BJL
SHORT TERM...BAJ
LONG TERM...BAJ
AVIATION...HTS/BJL/BAJ
MARINE...BAJ/BJL
TIDES/COASTAL FLOODING...BJL