Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 191530
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1130 AM EDT SUN APR 19 2015

.SYNOPSIS...
HIGH PRESSURE CENTERED OVER QUEBEC WILL TRACK EAST TO MAINE TODAY.
LOW PRESSURE OVER THE MID-SOUTH STATES WILL TRACK NORTHEAST TO THE
OHIO VALLEY TODAY AND GREAT LAKES TONIGHT...BRINGING A WARM FRONT
ACROSS THE MID-ATLANTIC TONIGHT. A COLD FRONT WILL MOVE THROUGH
THE AREA LATE MONDAY. AN UPPER LOW BRINGS COOLER THAN NORMAL
TEMPERATURES TO THE NORTHEASTERN STATES FOR THE MIDDLE AND LATE
PORTION OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
EXPANDED FLOOD WATCH TO INCLUDE GREATER BALTIMORE-WASHINGTON METRO
(NOT SRN MD WHERE FLOOD GUIDANCE IS HIGHER)...THE REST OF THE
SHENANDOAH VALLEY...AND MORE OF N-CNTRL VA AND THE ALLEGHENY
HIGHLANDS. THREE START TIMES...CONTINUED 2PM FOR SWRN ZONES...5PM
FOR CENTRAL...AND 7PM FOR BALT-WASH. 1.5 INCHES IS NEAR OR
EXCEEDING THE 6HR FLOOD GUIDANCE. WILL BUMP UP QPF A BIT BASED ON
LATEST HI-RES GUIDANCE. 2 INCHES STILL GENERALLY CONTAINED TO THE
EAST SIDE OF CNTRL VA BLUE RIDGE.

PREVIOUS...
AS OF 14Z...1029MB SFC HIGH CENTERED OVER WRN QUEBEC WITH A SFC
RIDGE ARCING ACROSS NEW ENGLAND TO THE MID-ATLANTIC COAST. 1002MB SFC
LOW IS OVER THE MID-SOUTH AND WILL DEVELOP AS IT LIFTS NORTH TO
SRN MICHIGAN THIS EVENING.

GULF MOISTURE AHEAD OF THIS LOW WILL LIFT FROM THE SERN STATES
THIS MORNING TO THE MID-ATLANTIC AND ERN OHIO VALLEY THROUGH
TONIGHT. THIS MOISTURE WILL OVERRUN THE RATHER DRY AIRMASS
CURRENTLY BEING REINFORCED BY ELY FLOW OF 15 TO 20 MPH. RAIN IS
DRIFTING NORTH TO CENTRAL VA AND WILL SLOWLY PROGRESS NORTH...
REACHING DC BY 6PM OR SO. INTENSITY WILL INCREASE TO HEAVY WITHIN
A COUPLE HOURS OF ONSET...ACROSS THE AREA.

AS THE LOW DEEPENS INTO THE GREAT LAKES...AND A MESOLOW DEVELOPS
AND LIFTS NORTH ACROSS THE AREA (ROUGHLY ALONG THE PIEDMONT) A
STRONG SE LLVL JET WILL DEVELOP BY THIS EVENING...TRANSPORTING
COPIOUS MOISTURE INTO THE REGION. PWATS WILL CLIMB TO NEAR MAXIMUM
CLIMO VALUES FOR THIS TIME OF YEAR (UPWARDS OF 1.5 INCHES) AND
WARM CLOUD DEPTHS ARE FORECAST TO AOA 3 KM...ESPECIALLY EAST OF
THE BLUE RIDGE. COMBINED WITH THE UPSLOPE COMPONENT...EXPECT
HIGHEST RAIN TOTALS APPROACHING 2 INCHES TO BE FOCUSED NEAR THE
CENTRAL BLUE RIDGE. WILL BE RAISING A FLOOD WATCH IN THIS AREA AS
6 HR FFG IS AROUND 1.5 INCHES IN SPOTS. HOWEVER THE ENTIRE AREA
WILL GET A GOOD SOAKING RAIN AS THE WARM FRONTAL BAND LIFTS
THROUGH TONIGHT...WITH MANY SPOTS TOPPING AN INCH. WILL ALLOW THE
DAYSHIFT TO ASSESS THE NEED TO EXPAND THE WATCH...WITH THE MOST
LIKELY CANDIDATES BEING INTO THE URBAN AREAS. HOWEVER...WOULD
EXPECT PONDING OF WATER WOULD BE THE MAIN CONCERN.

INCREASING CLOUDS TODAY LIMIT TEMPS TO THE UPPER 50S/LOWER 60S.
TEMPS HOLD STEADY OR PERHAPS RISE A LITTLE IN EASTERN AREAS TONIGHT
WITH THE RAIN. LOWS IN THE 50S.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
AFTER THE WARM FRONTAL BAND PASSES EARLY MONDAY MORNING...THERE MAY
BE A FAIRLY PROLONGED BREAK INTO THE MIDDAY HOURS AS THE AREA
BECOMES WARM SECTORED...AND THERE MAY BE A CAP IN PLACE AS WELL.
TEMPERATURES WILL WARM INTO THE 70S...AND FAIRLY GOOD AGREEMENT ON
60S DEW POINTS ESPECIALLY EAST OF BLUE RIDGE. DECENT PROBS OF
MUCAPE GREATER THAN 1000 J/KG AND DEEP LAYER SHEAR AOA 30 KT. HI-
RES GUIDANCE SUGGEST STORMS FIRST FIRE ALONG THE MOUNTAINS NEAR A
PRE- FRONTAL TROUGH...WITH ADDITIONAL STORMS ALONG THE COLD FRONT
TO THE WEST. SPC HAS HIGHLIGHTED MOST OF THE AREA FOR A SLIGHT
RISK OF SEVERE STORMS. UNIDIRECTIONAL WINDS SUGGEST POTENTIAL FOR
LINEAR FEATURES. GIVEN SOME MID LEVEL DRYING AND STEEP LLVL LAPSE
RATES...THINK DMG WINDS WILL BE MORE LIKELY THAN LARGE HAIL.

COLD FRONT SWEEPS OFFSHORE OVERNIGHT...BRINGING AN END TO ANY
SHOWERS AND THUNDERSTORMS FROM WEST TO EAST...LIKELY BY AROUND
MIDNIGHT. SLIGHT CHANCE A FEW SHOWERS LINGER NEAR THE BAY INTO THE
WEE HOURS OF THE MORNING TUESDAY. OTHERWISE...BREEZY AND DRIER
OVERNIGHT BEHIND THE FRONT.

PRESSURE SURGE BEHIND THE COLD FRONT COULD BRING DOWN STRONG GUSTY
WINDS NEAR ADVISORY LEVELS ESPECIALLY OVER THE RIDGELINES MONDAY
NIGHT.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
A LARGE AND DEEP UPPER-LEVEL LOW PRESSURE SYSTEM WILL DIVE OUT OF
CANADA AND SET UP SHOP ACROSS THE NORTHEASTERN CONUS FOR MUCH OF
THE MIDDLE AND LATER PART OF THE WEEK. A REINFORCING COLD FRONT
WILL MOVE ACROSS THE AREA WEDNESDAY. MOISTURE MAY BE SOMEWHAT
LIMITED SO KEPT POPS AT CHANCE FOR NOW. SEEMS LIKE A SCATTERED
SHOWER/ISOLATED THUNDERSTORM DAY ENHANCED OVER TERRAIN
AREAS...MORE ISOLATED FURTHER EAST.

BEHIND THIS FRONT WILL COME A MUCH COOLER AND DRIER DURING THE
SECOND HALF OF THE WEEK. TEMPERATURES WILL BE AROUND 10 DEGREES
BELOW NORMAL...WITH HIGHS STRUGGLING TO GET OUT OF THE 50S THURSDAY
THROUGH NEXT WEEKEND.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
VFR CONDITIONS THROUGH MOST OF THE DAY WITH ELY WINDS GUSTING
AROUND 20 KT. RAIN WILL SPREAD S TO N THIS AFTERNOON AND
EVENING...WITH FLIGHT CONDITIONS DETERIORATING FIRST AT CHO. AS
THE RAIN SPREADS THROUGH TONIGHT...MDT TO LOCALLY HEAVY RAIN IS
POSSIBLE. THUNDER CHANCES LOOK BEST SOUTHEAST OF DC LATE TONIGHT. IFR
OR LOWER CIGS AND IFR VSBYS ARE LIKELY. CONDITIONS WILL IMPROVE
MONDAY MORNING AS THE RAIN EXITS AND WINDS BECOME SOUTHERLY.
THUNDERSTORMS WILL BE POSSIBLE MONDAY AFTERNOON AND EVENING AHEAD
OF AN APPROACHING COLD FRONT. STRONG WIND GUSTS AND BRIEF CIG/VSBY
REDUCTIONS POSSIBLE.

WINDS TURN WLY BEHIND COLD FRONT MON NIGHT...10-20 KT W/
VFR LIKELY BY AROUND MIDNIGHT. GUSTY TUE IN CONTINUED WLY FLOW AND
VFR. SWLY FLOW 10-15 KT TUE NIGHT-WED...W/ SUB-VFR POSSIBLE IN ISO
SHOWER/TSTM...HIGHEST PROBABILITY N&W OF BLUE RIDGE WED PM. VFR THU
WLY FLOW 10 KT.

&&

.MARINE...
SCA FOR ALL WATERS THROUGH TONIGHT FOR ELY FLOW CURRENTLY GUSTING
TO 20 22KT...THEN FOR SELY/SLY FLOW TONIGHT THAT COULD GUST 25 TO
30 KT. MODERATE TO HEAVY RAIN TONIGHT. ISOLATED THUNDER POSSIBLE
LATE TONIGHT...PARTICULARLY FOR SRN MD WATERS. STRONG GUSTS COULD
MIX DOWN AND WARRANT SPECIAL MARINE WARNINGS OR A GALE WARNING.

S WINDS CONTINUE MONDAY. SCA THROUGH THE DAY OR BAY/LOWER
POTOMAC DUE TO CHANNELING. BREAK IN ACTIVITY EXPECTED MONDAY LATE
MORNING INTO THE AFTERNOON...BUT THEN THUNDERSTORMS POSSIBLE WITH
A CHANCE OF STRONG WIND GUSTS AND SMW/S.

SCA CONDITIONS LIKELY IN WESTERLY SURGE MONDAY NIGHT INTO
TUESDAY...WITH GALE GUSTS POSSIBLE DURING THIS TIME. SCA GUSTS
POSSIBLE AGAIN WEDNESDAY AHEAD OF A SECONDARY COLD FRONT.

&&

.TIDES/COASTAL FLOODING...
STRONG EASTERLY FLOW CONTINUES TODAY...THEN SELY TONIGHT. WATER
LEVELS WILL INCREASE ACROSS THE BAY...PARTICULARLY TONIGHT. MINOR
COASTAL FLOODING IS POSSIBLE BY THE HIGH TIDES EARLY MONDAY.

&&

.EQUIPMENT...
AUDIO DEGRADATION AT THE NOAA WEATHER RADIO CHARLOTTESVILLE
TRANSMITTER IS EXPECTED TO CONTINUE THROUGH THIS WEEKEND.
TECHNICIANS ARE SCHEDULED TO PERFORM MAINTENANCE AT THE
TRANSMITTER SITE MONDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLOOD WATCH FROM 7 PM EDT THIS EVENING THROUGH MONDAY MORNING
     FOR DCZ001.
MD...FLOOD WATCH FROM 7 PM EDT THIS EVENING THROUGH MONDAY MORNING
     FOR MDZ004>006-011-013-014-503>508.
VA...FLOOD WATCH THROUGH LATE TONIGHT FOR VAZ025-026-029-036>040-
     503-504-507-508.
     FLOOD WATCH FROM 7 PM EDT THIS EVENING THROUGH MONDAY MORNING
     FOR VAZ052>054-505-506.
     FLOOD WATCH FROM 5 PM EDT THIS AFTERNOON THROUGH LATE TONIGHT
     FOR VAZ027-028-030-031-050-051-055-056-501-502.
WV...FLOOD WATCH THROUGH LATE TONIGHT FOR WVZ505-506.
     FLOOD WATCH FROM 7 PM EDT THIS EVENING THROUGH MONDAY MORNING
     FOR WVZ053.
     FLOOD WATCH FROM 5 PM EDT THIS AFTERNOON THROUGH LATE TONIGHT
     FOR WVZ050-055.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT MONDAY FOR ANZ530>534-
     537>543.
     FLOOD WATCH FROM 7 PM EDT THIS EVENING THROUGH MONDAY MORNING
     FOR ANZ535.
     SMALL CRAFT ADVISORY UNTIL 8 AM EDT MONDAY FOR ANZ535-536.

&&

$$
SYNOPSIS...BAJ/ADS
NEAR TERM...BAJ/ADS
SHORT TERM...ADS/DFH
LONG TERM...DFH
AVIATION...BAJ/ADS/DFH
MARINE...BAJ/ADS/DFH
TIDES/COASTAL FLOODING...BAJ
EQUIPMENT...LWX



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