FXUS61 KLWX 190744
AFDLWX

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TONIGHT/...
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. 

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
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.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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.

&&

.MARINE...
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.

&&

.TIDES/COASTAL FLOODING...
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.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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.

&&

$$
PELOQUIN/KLEIN