Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 301433
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1033 AM EDT TUE JUN 30 2015

.SYNOPSIS...
LOW PRESSURE WILL SLIDE EASTWARD OVER THE EASTERN GREAT LAKES
TODAY. A COLD FRONT WILL SLIDE SOUTHEAST INTO THE MID ATLANTIC ON
WEDNESDAY...AND THEN STALL ACROSS THE REGION ON THURSDAY. THE
STALLED FRONT WILL LINGER IN THE AREA THROUGH THE WEEKEND BEFORE
LIFTING NORTHWARD AGAIN ON MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
SFC ANALY DEPCITS SUBTLE FETURES TODAY. TOUGH TO PIN DOWN
SPECIFICALLY WHERE THE WMFNT IS...BUT CLERLY THERES CNVGNC INVOF
THE BALT/DC CRRDR BASED ON SELY FLOW ACRS NERN MD VS S/SWLY FLOW
ELSW WITHIN THE CWFA. THAT HAS RESULTED IN A PATCH OF CLDS IN THE
METROS. A CLUSTER OF SHRA HV BEEN ABLE TO DVLP UNDER CLD DECK...
WITH A HINT OF A LINE BGNG STRETCHING DOWN TO CHO.

LWX 12Z RAOB DEPICTS WARM LYRS H10-8 AND AGN H6-5. HWVR...THE
CURRENT RADAR SUGGESTS THAT MAY NOT BE A DETERRENT. THE MTNS/SHEN
VLY SEEM TO BE GETTING ENUF HEATING...SO WUD XPCT INSTBY TO
INTENSIFY. A MODIFIED SNDG...BASED ON LAMP AND A TEMP/DEWPT FCST
OF 85/65F...SUGGESTS 1500-2000 J/KG SBCAPE AVBL. SHEAR MEASURED
AT 30 KT...WHICH MDL PROGS RETAIN THRU THE DAY.

IN TERMS OF EVOLUTION...OBVIOUSLY THE CNVGNC WL DOMINATE FOR THE
MRNG. LWX WRF-ARW4 CAPTURING IT. HWVR...BELIEVE THAT TRRN
CIRCUALTION SHUD DVLP IN THE BLURDG OR IN THE CRRDR OF HEATING IN
THE SHEN VLY. HV POPS IN THE FORMER LOCATION FOR THE MORNING...
THEN EXPAND CHC POPS ELSW BY ELY AFTN.

SOME STRONG TO SEVERE STORMS COULD DEVELOP BASED ON MODIFIED RAOB
AND THE MORE AGGRESSIVE MDL GDNC. THE PRIMARY THREAT WOULD BE
LOCALIZED DAMAGING WIND GUSTS. HWVR THE SHEAR SUGGESTS A CPL
SUPERCELLS NOT OUT OF THER QUESTION.

WHILE THERE SHOULD BE AN OVERALL EASTWARD PROGRESSION AND DIURNAL
WEAKENING OF ACTIVITY THIS EVENING...MODELS MAINTAIN ELEVATED INSTBY
OVERNIGHT...AND MID/UPPER LEVEL TROUGH WILL BE APPROACHING TOWARD
DAYBREAK. THEREFORE SOME SHOWERS AND STORMS MAY LINGER WELL INTO THE
OVERNIGHT PERIOD. MIN TEMPS IN THE LOWER/MID 60S WEST AND UPPER
60S/LOWER 70S EAST.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
MID LEVEL TROUGH AXIS WILL BE LIFTING NORTH DURING THE MORNING
HOURS. SFC COLD FRONT WILL BE APPROACHING FROM THE NORTHWEST BUT
LIKELY WON/T ENTER THE AREA DURING THE DAYTIME HOURS. TIMING AND
COVERAGE OF PRECIP QUITE UNCERTAIN WITHOUT STRONG FORCING
MECHANISMS. IF FORECAST SOUNDINGS ARE CORRECT IN DECREASING INSTBY
BEHIND THE TROUGH PASSAGE IN THE AFTERNOON...CONVECTION MAY BE
RATHER LIMITED. HAVE MAINTAINED LOW CHANCE POPS THROUGHOUT DAY.

ON WEDNESDAY NIGHT...THE COLD FRONT WILL STALL OUT OVER THE MID
ATLANTIC JUST TO OUR SOUTH. SUPPORT ALOFT WILL WANE AS THE TROUGH
PASSES SO EXPECT CONVECTION TO QUICKLY DISSIPATE OR MOVE AWAY.
WITH THE FRONT STALLED IN THE AREA...GUIDANCE IS BEGINNING TO HONE
IN ON A WAVE OF LOW PRESSURE MOVING EAST ALONG THE FRONT FROM THE
MID MISSISSIPPI VALLEY THURSDAY OR THURSDAY NIGHT.
HOWEVER...TIMING IS STILL MUCH IN QUESTION...SO GENERALLY KEEP
CHANCE POPS AROUND WITH LIKELYS TO THE SOUTH CLOSER TO THE STALLED
FRONT. WITH THE FRONT TO THE SOUTH AND INCREASED CLOUD
COVER...TEMPS SHOULD BE COOLER ON THURSDAY.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
THROUGH THE LONG TERM THE PATTERN WILL REMAIN FAIRLY STATIC WITH A
BROAD TROUGH OVER CANADA...AND A STRONG RIDGE OUT WEST. THIS WILL
KEEP FUNNELLING DISTURBANCES SOUTHEAST AND EAST ACROSS OUR AREA AS
A FRONTAL BOUNDARY REMAINS STALLED OUT OVER THE REGION. SHOWERS
AND THUNDERSTORMS WILL BE POSSIBLE EACH DAY WITH THE FRONT NEARBY
BUT TIMING DISTURBANCES WILL BE INCREASINGLY DIFFICULT AS WE GO
FURTHER OUT. RIGHT NOW ONE SYSTEM MAY AFFECT US SATURDAY...AND
ANOTHER MONDAY...BUT CONFIDENCE ON TIMING IS NOT HIGH.
SO...GENERALLY HAVE KEPT TEMPS A BIT BELOW NORMAL...WITH A CHANCE
OF SHOWERS AND THUNDERSTORMS IN THE FORECAST EACH DAY. AS WE GET
CLOSER...WE SHOULD HAVE BETTER CLARITY AS FAR AS DAYS WHICH WILL
TURN OUT MOSTLY RAIN-FREE...AND THOSE WHICH WILL BE PRETTY WET.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
SOUTHERLY WINDS WILL INCREASE DURING THE MIDDAY WITH OCNL GUSTS
TO 20 KT. THUNDERSTORM COVERAGE AND TIMING STILL LOWER CONFIDENCE
TODAY. CONVERGENCE DVLPG SOME STORMS INVOF DCA/IAD/BWI THIS MRNG.
THINK THE ACTIVITY SHUD JUMP TO THE BLURDG DURING THE AFTN.
HWVR...CANNOT RULE ANYTHING OUT IN TERMS OF TIMING AND PLACEMENT.
RESTRICTIONS WUD BE BRIEF...BUT MVFR/IFR POTL EXISTS. STRONG WIND
GUSTS COULD ACCOMPANY ANY STORM.

DISTURBANCE CROSSES AREA LATE TONIGHT/WED MORNING...SO A SHOWER OR
STORM WILL REMAIN POSSIBLE...BUT LOWER POTENTIAL FOR CIG/VSBY
REDUCTIONS. QUESTIONABLE HOW MUCH OF THIS ACTIVITY
LINGERS/REDEVELOPS WED AFTERNOON...LOW CHANCE OF IMPACTS.

MAIN CONCERN THROUGH EXTENDED IS POTENTIAL FOR SCATTERED
THUNDERSTORMS EACH DAY. WINDS WILL BE UNCERTAIN GIVEN THE FRONT
WILL CONTINUE TO MEANDER IN THE AREA AFTER ARRIVING WEDNESDAY.
WAVE OF LOW PRESSURE MAY PROVIDE A MORE CONCENTRATED PERIOD OF
RAIN AND IFR CIGS/VIS AT SOME POINT THURSDAY...FRIDAY OR SATURDAY
BUT LOW CONFIDENCE RIGHT NOW ON WHEN THIS IS...OR IF IT EVEN
HAPPENS.

&&

.MARINE...
S/SE CHANNELING OCCURING OVER THE WATERS. SCA IN EFFECT.
THUNDERSTORMS WILL DEVELOP WITH THE POTENTIAL FOR STRONG WIND
GUSTS-- SOME SMW/S ARE POSSIBLE. GRADIENT WINDS WILL DIMINSH
OVERNIGHT. SW FLOW THROUGH WED AROUND 10 KT...ALTHOUGH MAY BE
SLIGHTLY STRONGER TOWARD TANGIER SOUND. LOWER CHANCE OF STORMS
THROUGH WED.

WINDS EXPECTED TO REMAIN BELOW SCA CRITERIA THROUGH THE
EXTENDED...THOUGH WILL NEED TO MONITOR AS FRONT WILL BE NEAR AREA
EACH DAY. SHOWERS AND TSTMS ARE ALSO POSSIBLE EACH DAY...WHICH
COULD IMPACT MARINE CONCERNS.

&&

.TIDES/COASTAL FLOODING...
WATER LVLS WL BE INCREASING THRU MID WEEK. THE WATER LVLS TOPPED
OUT ON THE EDGE OF ADVY CRITERIA THIS MORNING AT WASD2 AND AXTV2.
BETTER CHC TMRW DURING THE SAME TIME CYCLE...MIDNGT THRU NOON.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EDT WEDNESDAY FOR ANZ531>534-
     536-537-539>543.
     SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ530-
     535-538.

&&

$$
SYNOPSIS...RCM
NEAR TERM...ADS/HTS
SHORT TERM...ADS/RCM
LONG TERM...RCM
AVIATION...ADS/RCM/HTS
MARINE...ADS/RCM/HTS
TIDES/COASTAL FLOODING...HTS


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