000
FXUS61 KLWX 121450
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1050 AM EDT WED JUN 12 2013

.SYNOPSIS...
A COLD FRONT WILL STALL OUT NEAR THE MASON-DIXON LINE TODAY. LOW
PRESSURE WILL RIDE ALONG THE BOUNDARY...IMPACTING THE AREA TONIGHT
AND THURSDAY. THE COLD FRONT ASSOCIATED WITH THE LOW WILL PASS
THROUGH LATE THURSDAY AND HIGH PRESSURE WILL BUILD TOWARD THE
REGION FRIDAY AND THIS WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
THE MID-ATLANTIC REGION IS SITUATED IN BETWEEN LOPRES OVER THE
GULF OF ME AND A BROAD HIGH OVER THE GULF STATES. SFC ANALYSIS
REVEALS A PRESSURE TROUGH DEVELOPING OVER THE HIGHLANDS THIS
MRNG. CONVERGENCE BETWEEN LGT SWLY FLOW AHEAD OF THE TROUGH AND
NWLY FLOW AROUND THE NEW ENGLAND LOW WILL RESULT IN DEVELOPMENT OF
A WEAK FRONTAL BOUNDARY NEAR THE M-D LINE. A FEW LGT SHOWERS HAVE
DEVELOPED NEAR THIS BOUNDARY THIS MRNG AND WILL CONTINUE TO MOVE
SEWD INTO NORTH-CENTRAL MD.

STRONG DAYTIME HEATING SOUTH OF THE BOUNDARY WILL BE AIDED FURTHER
BY DOWNSLOPING WINDS AND WAA. RAISED AFTN TEMPS A COUPLE OF
DEGREES BASED ON MODIFIED 12Z IAD RAOB. MAX TEMPS RANGE FROM THE
UPPER 80S IN THE MTS AND NORTH- CENTRAL MD TO LOWER 90S ELSEWHERE.
DESPITE SUFFICIENT DESTABILIZATION TDA...COVERAGE OF SHOWERS AND
STORMS WILL BE LOW THRU AT LEAST MID AFTN WITH A LACK OF ORGANIZED
LIFT.

LEADING SHORTWAVE ENERGY THAT IS CURRENTLY OVER THE UPPER MIDWEST IS
FCST TO ROTATE SEWD AROUND THE UPPER RIDGE AND INTO THE MID-ATLANTIC
STATES THIS EVE AND OVNGT. WILL NEED TO MONITOR UPSTREAM
CONVECTIVE TRENDS AND POSSIBLE DEVELOPMENT OF AN MCS OVER THE OH
VLY LATE TDA. WITH STEEPENING MID-LVL LAPSE RATES AND
STRENGTHENING MID-LVL NW WINDS...THERE IS A THREAT FOR SEVERE
WEATHER INTO THE NGT IF THE MCS HOLDS UP AFTER CROSSING THE
APPALACHIANS. MAJORITY OF HI-RES MODELS WEAKEN THIS MCS AS IT
CROSSES THE APPALACHIANS AND INTO THE CWA LATE THIS EVE OR OVNGT
BUT THERE MAY BE SUFFICIENT INSTABILITY DOWNSTREAM OF THE MTS TO
MAINTAIN SOME DEGREE OF THIS MCS. ACCORDINGLY...THERE IS PLENTY OF
CAUTION WITH THESE MODELS AND LOW CONFIDENCE WITH THE FCST TNGT.
WILL CONTINUE TO HIGHLIGHT THE THREAT OF SEVERE STORMS IN ADDITION
TO FLASH FLOODING TNGT...ESPECIALLY OVER THE MTS AND NEAR THE M-D
LINE. A FLASH FLOOD WATCH MAY BE NEEDED.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
POTENTIAL FOR A SIGNIFICANT SEVERE WEATHER EVENT AND FLASH
FLOODING THURSDAY...

THURSDAY BEGINS WITH SOME UNCERTAINTY REGARDING THE FATE OF A
MESOSCALE CONVECTIVE SYSTEM AFFECTING THE OHIO VALLEY TONIGHT. IT IS
UNCLEAR WHAT THE STRENGTH OF THIS SYSTEM WILL BE AT THE BEGINNING OF
THURSDAY...WHETHER IT MAY STILL BE SEVERE AND AFFECT THE WESTERN
PORTION OF THE CWA EARLY THURSDAY MORNING /WITH DAMAGING WINDS AND
HEAVY RAINFALL/ OR WHETHER IT WILL BE IN A WEAKENING/DECAYING STATE
DURING THE MORNING. WILL NEED TO FURTHER ADDRESS THIS ISSUE AS THE
MCS DEVELOPS TODAY AND THE MODELS ARE BETTER ABLE TO RESOLVE DETAILS
OF THIS MCS AND ITS EVOLUTION THROUGH THE DAY AND NIGHT.

MEANWHILE...THERE IS A GOOD CONSENSUS THAT REGARDLESS OF THE FATE OF
AN EARLY MORNING MCS...THE ATMOSPHERE ACROSS THE MID-ATLANTIC WILL
SUFFICIENTLY DESTABILIZE AND BE PRIMED FOR WHAT COULD BE A
SIGNIFICANT SEVERE WEATHER EVENT DURING THE AFTERNOON AND EARLY
EVENING.

AN UNSEASONABLY STRONG SURFACE LOW WILL MOVE FROM THE OHIO VALLEY
INTO SOUTHERN PENNSYLVANIA THURSDAY AFTERNOON. WARM FRONTAL BOUNDARY
LOOKS BE DRAPED ACROSS NORTHEAST MARYLAND...WHILE A COLD FRONT
APPROACHES THE APPALACHIANS. MODELS SHOW STRONG SYNOPTIC LIFT
ACROSS THE CWA...JOINED BY DECENT DESTABILIZATION DURING THE
AFTERNOON AND LIKELY CONTRIBUTING TO STRONG LAPSE RATES AND CAPE
AOA 2000 J/KG. MODELS ALSO INDICATE STRONG VERTICAL WIND SHEAR
ACROSS THE CWA /BULK SHEAR GTE 50 KT/. THESE FACTORS WILL RESULT
IN WIDESPREAD THUNDERSTORMS DURING THE AFTERNOON...SOME PRODUCING
DAMAGING/DESTRUCTIVE WIND GUSTS...LARGE HAIL AND ALSO A FEW
TORNADOES.

IN ADDITION...THUNDERSTORMS WILL BE CAPABLE OF PRODUCING FLASH
FLOODING. PRECIPITABLE WATER VALUES ARE NOT FORECAST TO BE QUITE AS
HIGH AS A FEW DAYS AGO...BUT RECENT RAINFALL HAS RESULTED IN LOW
FLASH FLOOD GUIDANCE ACROSS MUCH OF THE CWA /EXCEPT PERHAPS THE
NORTHWEST CORNER/. THIS ANTECEDENT CONDITION COMBINED WITH THE
EXPECTATION FOR HEAVY DOWNPOURS FROM THUNDERSTORMS MAY LEAD TO
FLASH FLOODING IN SOME AREAS. A FLASH FLOOD WATCH MAY BECOME
NECESSARY.

LOW PRESSURE MOVES OFF THE DELMARVA THURSDAY EVENING...WITH A COLD
FRONT PUSHING EAST ACROSS THE CWA/CHESAPEAKE BAY AREA EARLY IN THE
EVENING. THIS WILL EFFECTIVELY END THE SEVERE WEATHER/FLASH FLOODING
THREAT.

ANOTHER HAZARD TO CONSIDER WILL BE GRADIENT WINDS. NAM IS MORE
AGGRESSIVE THAN THE GFS...BUT BOTH SHOW GUSTY WINDS ESPECIALLY
BEHIND THE COLD FRONT WITH 850 MB WINDS OF 40 TO 50 KT. THIS COULD
RESULT IN WIND ADVISORY GUSTS FOR A PERIOD THURSDAY EVENING/NIGHT.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
EVEN THOUGH THE COLD FRONT WILL BE WELL OFFSHORE FRIDAY...MODELS
SHOW A VORT MAX ROTATING AROUND THE BACK SIDE OF THE UPPER LOW. THIS
WILL LEAD TO PARTLY TO MOSTLY CLOUDY SKIES AND PERHAPS EVEN ISOLATED
SHOWERS PER THE NAM/GFS.

IN ADDITION...BREEZY CONDITIONS ARE EXPECTED TO CONTINUE ON FRIDAY
WITH A TIGHT GRADIENT IN PLACE. GUSTS OF 35 MPH MAY BE POSSIBLE.
ALSO OF NOTE WILL BE A COOL DOWN INTO THE MID TO UPPER 70S FOR
MAXIMA ON FRIDAY.

HIGH PRESSURE BUILDS IN OVER THE WEEKEND FOR WHAT SHOULD BE A QUIET
WEEKEND. SATURDAY LOOKS SUNNY AND SEASONABLE. TEMPERATURES CREEP UP
ON SUNDAY AS A WARM FRONT MOVES THROUGH. THERE MAY BE MORE
CLOUDS...BUT THE CURRENT THINKING IS THAT ANY CONVECTION REMAINS TO
THE NORTHWEST OF THE CWA.

THE NEXT FRONT IS FORECAST TO AFFECT THE CWA MONDAY-TUESDAY OF NEXT
WEEK WITH A CHANCE OF SHOWERS AND THUNDERSTORMS.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
AN ISO SHOWER OR STORM MAY POP UP DURING AFTER 18Z. COVERAGE MAY
BE SCT IN VC OF MRB. ANY THUNDERSTORMS THAT DO DEVELOP THIS
AFTERNOON WILL PROVIDE TEMPORARY FLIGHT RESTRICTIONS AND
POTENTIALLY GUSTY WINDS.

SHOWER AND THUNDERSTORM COVERAGE EXPECTED TO BECOME MORE
WIDESPREAD TONIGHT AS AN UPPER-LEVEL DISTURBANCE PASSES THROUGH
THE AREA. A FEW THUNDERSTORMS WILL HAVE THE POTENTIAL TO BE
SEVERE. THE CERTAINTY IN THUNDERSTORM TIMING AND COVERAGE TONIGHT
REMAINS LOW DUE TO LOW CERTAINTY IN TIMING THE UPPER-LEVEL
DISTURBANCE.

EXPECT SHOWERS AND THUNDERSTORMS TO AFFECT THE TERMINALS ON
THURSDAY...MOST LIKELY IN THE AFTERNOON. THUNDERSTORMS MAY PRODUCE
VERY STRONG WIND GUSTS AND HEAVY DOWNPOURS. FRONT MOVES THROUGH BY
EARLY THURSDAY EVENING. WEST WINDS WITH THE FROPA AND BEHIND IT MAY
BE GUSTY...PERHAPS AOA 40 MPH THROUGH THE NIGHT. GUSTY WINDS COULD
LINGER INTO FRIDAY...THEN HIGH PRESSURE BUILDS IN OVER THE WEEKEND.

&&

.MARINE...
A WEST-SOUTHWEST FLOW MAY TURN ONSHORE THIS AFTERNOON. WIND SPEEDS
WILL REMAIN BELOW SCA CRITERIA. SHOWERS AND THUNDERSTORMS MAY IMPACT
THE WATERS MAINLY LATE TONIGHT THOUGH AN ISO STORM CANNOT BE RULED
OUT LATE IN THE DAY. ANY THUNDERSTORMS THAT DO DEVELOP WILL HAVE
THE POTENTIAL TO PRODUCE GUSTY WINDS AND HAIL.

SOUTHERLY WINDS INCREASE AHEAD OF A COLD FRONT ON THURSDAY...LIKELY
UP TO 30 KT. WILL RAISE A SMALL CRAFT ADVISORY. THUNDERSTORMS ARE
EXPECTED AHEAD OF A COLD FRONT THURSDAY AFTERNOON...AND MAY PRODUCE
LARGE HAIL AND STRONGER WIND GUSTS.

IN ADDITION...BEHIND THE COLD FRONT AT LEAST SCA WINDS ARE EXPECTED
INTO THURSDAY NIGHT. SOME GUIDANCE HOWEVER SUGGESTS THAT WINDS MAY
ACTUALLY BECOME GALES THURSDAY NIGHT. THEREFORE WILL NOT DRAG THE
SCA INTO THURSDAY NIGHT...AS SUBSEQUENT SHIFTS MAY NEED TO RAISE A
GALE WARNING.

GUSTY WINDS CONTINUE ON FRIDAY...THEN LESS WIND IS EXPECTED OVER THE
WEEKEND AS HIGH PRESSURE BUILDS IN.

&&

.HYDROLOGY...
MORE RAIN IS ON THE WAY TO THE MID-ATLANTIC AS A SERIES OF
DISTURBANCES MOVES ACROSS THE REGION TNGT AND THURSDAY.
DEEPER MOISTURE RETURNS AS WELL...WHICH WILL RESULT IN HEAVY
RAINFALL. A COLD FRONT WILL STALL NEAR THE MASON-DIXON LINE
TODAY. 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 /AND A FLASH FLOOD WATCH MAY BECOME NECESSARY/...BUT
ISOLATED FLASH FLOODING CANNOT BE RULED OUT AS EARLY AS THIS EVE.
AS WE SAW MONDAY...AN INCH OF RAIN IN A SHORT PERIOD OF TIME IS
MORE THAN ENOUGH TO CAUSE A PROBLEM.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM TO 6 PM EDT THURSDAY FOR
     ANZ530>543.

&&

$$
UPDATE...KLEIN
PREV DISC...BJL/BPP