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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 190744
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
344 AM EDT SUN MAY 19 2013

.SYNOPSIS...
-- Changed Discussion --
A STATIONARY BOUNDARY WILL REMAIN SOUTH OF THE AREA THROUGH
TONIGHT BEFORE LIFTING NORTH OF THE AREA MONDAY. A WEAK MID-LEVEL
TROUGH WILL MOVE THROUGH MONDAY. HIGH PRESSURE BUILDS OVER THE
WESTERN ATLANTIC MIDWEEK...WITH SOUTHERLY RETURN FLOW PROVIDING
WARM TEMPERATURES TO THE REGION. A COLD FRONT WILL APPROACH FROM
THE GREAT LAKES LATE THIS WEEK.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
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NEARLY STATIONARY BOUNDARY ALONG THE COASTAL VIRGINIA/NORTH CAROLINA
BORDER WAS SNAKING ITS WAY WESTWARD THROUGH THE CENTRAL APPALACHIANS
AND INTO THE OHIO VALLEY EARLY THIS MORNING. MEANWHILE...HIGH
PRESSURE WAS LOCATED OVER THE NORTH ATLANTIC.

SURFACE SYNOPTIC FEATURES ARE FORECAST TO REMAIN NEARLY STATIC
TODAY. FRONTAL BOUNDARY MAY SLIGHTLY OSCILLATE NORTH-SOUTH...BUT
BOUNDARY IS FORECAST TO REMAIN SOUTH OF THE CWA. RESULT WILL BE A
CONTINUATION OF EAST-SOUTHEAST FLOW IN THE LOW LEVELS WITH CLOUDY
AND COOLER THAN NORMAL CONDITIONS.

BASED ON RADAR TRENDS...HAVE BACKED OFF ON POPS FOR THE REMAINDER OF
THE NIGHT. IF PRECIPITATION FALLS FROM THE SKY THROUGH DAYBREAK IT
WILL MORE THAN LIKELY BE DRIZZLE THAN ANYTHING ELSE.

HOWEVER...MEASURABLE RAINFALL ASSOCIATED WITH SHOWERS WAS NOTED
ACROSS SOUTHERN VIRGINIA AT 07Z...AND THESE ARE FORECAST TO MOVE TO
THE NORTH AND FURTHER DEVELOP NORTHWARD THROUGH THE DAY. POPS FROM
21Z SREFS HAVE BEEN OVERDONE AND GENERALLY DISCOUNTED AT LEAST
INITIALLY. TODAYS FORECAST REFLECTS POPS WEIGHTED MORE TOWARD RADAR
TRENDS INITIALLY THEN BLENDING WITH GUIDANCE FROM RECENT RUNS OF THE
HRRR AND WRF-ARW WHICH ARE NOT TOO TERRIBLY DIFFERENT FROM WHAT THE
00Z NAM SUGGESTS.

NAM ALSO SUGGESTS SOME INSTABILITY...LIKELY ELEVATED IN
NATURE...BEING PRESENT ACROSS SOUTHWEST PORTIONS OF THE CWA THIS
AFTERNOON. HAVE INCLUDED MENTION OF THUNDER IN THESE AREAS. ANY OF
THESE THUNDERSTORMS MAY PRODUCE LOCALLY HEAVY RAINFALL. KEPT GREATER
BALTIMORE/WASHINGTON AREA FREE OF THUNDER GIVEN RELATIVELY STABLE
ONSHORE FLOW.

GUIDANCE WAS TOO WARM FOR MAXIMA YESTERDAY...AND AM FEARFUL THAT
GUIDANCE IS ALSO TOO WARM FOR TODAY WITH BOTH MAV AND MET GENERATING
MID 70S. HAVE BLENDED BIAS CORRECTED MAV/MET AS A BASIS AND
MANUALLY ADJUSTED MAXIMA DOWNWARD SEVERAL DEGREES PARTICULARLY EAST
OF THE BLUE RIDGE AS ONSHORE FLOW...CLOUDS AND EVENTUALLY RAINFALL
ARE EXPECTED.

FOR TONIGHT...MODELS ARE SUGGESTIVE THAT THE STATIONARY FRONT WILL
START TO MAKE ITS WAY NORTH. EVEN IF LOW LEVEL FLOW TURNS MORE TO
THE SOUTH...AM NOT CONVINCED THAT ENOUGH WIND IN THE BOUNDARY LAYER
WILL BE ABLE TO PUSH THE FRONT THIS FAR TO THE NORTH. THEREFORE
FORECAST REFLECTS THIS BOUNDARY REMAINING SOUTH OF THE CWA...KEEPING
LOW CLOUD COVER OVER THE CWA. NORTH OF THE BOUNDARY...LIFT ENHANCED
BY A SHORTWAVE AT 500 MB IS LIKELY TO BRING AT LEAST SCATTERED
SHOWERS OVER THE CWA. STAYED CLOSE TO BIAS CORRECTED MAV/MET FOR
MINIMA.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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LLVL RIDGE WILL AMPLIFY OVER THE WRN ATLANTIC DURING THE FIRST HALF
OF THE WORK WEEK. BROAD SLY RETURN FLOW ON THE WRN PERIPHERY OF THE
HIGH WILL KEEP WHATEVER IS LEFT OF THE REMNANT SFC WARM FRONT NORTH
OF THE AREA DURING THIS TIME. SOUTH OF THIS FRONT...A WARM AND A
MODESTLY HUMID AIRMASS WILL BE IN PLACE. MAX TEMPS IN THE 80S EACH
DAY ALTHOUGH CLOUDS MAY INHIBIT TEMPS FROM REACHING 80F IN SOME
LOCATIONS ON MON.

BOTH THE 00Z NAM/GFS PROG A MID-LVL SHORTWAVE TROUGH THAT IS
CURRENTLY OVER THE TN VLY TO SLOWLY MOVE WD THRU THE MID-ATLANTIC
REGION ON MON. LIFT/MOISTURE AHEAD OF THE TROUGH IN CONJUNCTION WITH
DAYTIME HEATING WILL SUPPORT DIURNAL CONVECTION OVER THE CWA. POPS
HIGHEST TOWARD CENTRAL VA/SRN MD BUT STILL IN CHANCE RANGE.

MID-LVL RIDGE BUILDS OVERHEAD TUE AND WED AFTER THE SHORTWAVE
TROUGH EXITS THE AREA. COVERAGE OF SHOWERS AND STORMS WILL BE LOW
TUE AND WED DUE TO AN ABSENCE OF ORGANIZED LIFT AND A
STRENGTHENING SUBSIDENCE INVERSION. KEPT FCST DRY FOR MOST OF THE
I-95 CORRIDOR AND CHSPK BAY AS WEAK STEERING FLOW WILL LIMIT HOW
FAR EAST CONVECTION PROPAGATES ONCE INITIATED OVER THE MTS.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
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SHORTWAVE TROUGH AND ASSOCIATED COLD FRONT WILL APPROACH FROM THE
GREAT LAKES/MIDWEST REGIONS WED NGT AND THU BEFORE PASSING THRU
THE AREA ON FRI. CHANCES FOR SHOWERS AND STORMS WILL ACCORDINGLY
INCREASE LATE IN THE WEEK AND WILL BE HIGHEST WITH FROPA. ABOVE
NORMAL TEMPS AHEAD OF THE COLD FRONT WILL TREND MUCH COOLER IN
WAKE OF FROPA FRI INTO THE WEEKEND.
-- End Changed Discussion --

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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WITH MOIST ONSHORE FLOW IN PLACE...CONFIDENCE IS HIGH IN THE
PRESENCE OF IFR/LIFR FLIGHT RESTRICTIONS THROUGH THIS MORNING.
CONFIDENCE LOWERS TO MODERATE REGARDING THE ENDING TIME OF THESE
FLIGHT RESTRICTIONS. HAVE FAVORED LAMP GUIDANCE ON KEEPING IFR UNTIL
17-18Z. DESPITE HIGH SUN ANGLE...THESE CONDITIONS COULD LINGER
LONGER GIVEN EASTERLY FLOW. ANY IMPROVEMENT THAT OCCURS LATER THIS
AFTERNOON IS EXPECTED TO BE BRIEF AS A STALLED FRONTAL BOUNDARY IS
FORECAST TO REMAIN TO THE SOUTH OF THE AREA TONIGHT. EVEN IF
EASTERLY FLOW BECOMES MORE SOUTH-SOUTHEAST...A DEGRADATION TO
IFR/LIFR CONDITIONS IS EXPECTED OVERNIGHT PER GUIDANCE. THE ONLY TAF
SITE WITH THE INCLUSION OF THUNDER IN THE GRIDS IS CHO...REST OF THE
SITES ARE EXPECTED TO BE TOO STABLE FOR THUNDER AND ONLY SHRA WAS
MENTIONED IN TAFS.

IFR CONDITIONS LIKELY TO START THE DAY MON BEFORE MRNG STRATUS/
FOG MIX OUT FROM W TO E. PREDOMINATELY VFR CONDITIONS EXPECTED MON
AFTN ALTHOUGH BRIEF RESTRICTIONS IN SHRA/TSRA ARE POSSIBLE.
DIURNAL FOG/LOW CLOUDS POSSIBLE AT NGT AND ERY IN THE MRNG EACH
DAY IN THE MIDWEEK. CHANCES FOR SHRA/TSRA WILL BE LOW DURING THIS
TIME.
-- End Changed Discussion --

&&

.MARINE...
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EASTERLY FLOW STARTS TO BECOME SOUTHEAST LATER THIS AFTERNOON AND
EVENING. MODELS FORECAST WINDS TO INCREASE...AND SOUTHEAST WINDS
TEND TO BE ENHANCED OVER THE LOWER TIDAL POTOMAC RIVER AND UP THE
BAY. SCA IN EFFECT THIS AFTERNOON/EVENING FOR THESE AREAS. ITS
POSSIBLE THAT THE SCA COULD NEED TO BE EXTENDED INTO THE OVERNIGHT
FOR SOME OF THESE AREAS.

LGT SLY FLOW ERY IN THE WEEK WILL STRENGTHEN LATER IN THE WEEK. SCA
CONDITIONS POSSIBLE BY THU...WHEN A COLD FRONT APPROACHES FROM THE
NW.
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&&

.TIDES/COASTAL FLOODING...
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DEPARTURES WERE ABOUT 1/2 FT ON THE BAY AND CLOSE TO 1 FT ON THE
UPPER TIDAL POTOMAC EARLY THIS MORNING. THESE ANOMALIES ARE NOT
EXPECTED TO RESULT IN TIDAL FLOODING DURING THE NEXT HIGH TIDE. AND
IF THESE ANOMALIES REMAIN THE SAME...NO FLOODING SHOULD OCCUR WITH
THE SUBSEQUENT HIGH TIDE CYCLE EITHER. THIS IS IN LINE WITH THE
LATEST CBOFS FORECAST. HOWEVER...AS WINDS TURN MORE TO THE SOUTHEAST
AND THEN SOUTH...DEPARTURES MAY INCREASE MONDAY INCREASING THE RISK
FOR MINOR TIDAL FLOODING AT SENSITIVE LOCATIONS.

WATER LEVELS SHOULD TICK UPWARD ERY NEXT WEEK WITH SLY FLOW
PERSISTING AND A WAXING GIBBOUS MOON. THIS FAR OUT...STILL SOME
UNCERTAINTY IF POSITIVE ANOMALIES INCREASE ENOUGH TO REACH MINOR
THRESHOLD.
-- End Changed Discussion --

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT EDT
     TONIGHT FOR ANZ531-532-539-540.
     SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO MIDNIGHT EDT
     TONIGHT FOR ANZ533-534-537-541-543.
-- End Changed Discussion --

&&

$$
PELOQUIN/KLEIN