698  
FXUS61 KLWX 010138  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
938 PM EDT SUN APR 30 2017  
   
SYNOPSIS
 
 
A FRONT WHICH IS DRAPED ACROSS THE AREA WILL LIFT NORTH AS A  
WARM FRONT TONIGHT. A STRONG COLD FRONT WILL CROSS THE REGION  
LATE MONDAY AND MONDAY NIGHT. HIGH PRESSURE WILL BRING COOLER  
AND DRIER WEATHER DURING THE MIDDLE OF THE WEEK. LOW PRESSURE  
WILL MOVE INTO THE AREA LATE IN THE WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM MONDAY MORNING/
 
 
CURRENTLY, THE NEARLY STATIONARY BACKDOOR FRONT HAS RETREATED  
SLIGHTLY, STRETCHING FROM NEAR CAMP DAVID SOUTHEAST TOWARDS  
COLLEGE PARK AND ON TO CHESAPEAKE BEACH. NORTH OF THE FRONT,  
TEMPERATURES ARE GENERALLY IN THE MID TO UPPER 60S, WITH MID TO  
UPPER 70S COMMONS SOUTH OF IT. SCATTERED THUNDERSTORMS WHICH  
DEVELOPED PRIMARILY OVER THE HIGHER TERRAIN, BUT WERE ABLE TO  
TAKE ADVANTAGE OF THE HIGH SHEAR, HAVE NOW DISSIPATED WITH THE  
LOSS OF INSOLATION, AND NO FURTHER STORMS ARE EXPECTED TONIGHT.  
AS SOUTHERLY WINDS INCREASE AHEAD OF THE APPROACHING COLD FRONT,  
THE BACKDOOR FRONT IS EXPECTED TO VERY SLOWLY RETREAT NORTHWARD  
OVERNIGHT. DESPITE THE FRONT'S PASSAGE, THE REMAINDER OF THE  
NIGHT SHOULD BE DRY, BUT LOWER CLOUDS MAY ONCE AGAIN DEVELOP  
TOWARD DAWN. CAN'T RULE OUT PATCHY FOG IN AREAS THAT REMAIN  
CLEARER. IT WILL BE VERY MILD ONCE AGAIN WITH LOWS IN THE 60S  
FOR MOST LOCATIONS.  
 

 
   
SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/
 
 
ON MONDAY, A WELL DEFINED COLD FRONT WILL BE APPROACHING THE  
AREA. THERE REMAINS SOME DIFFERENCES IN SOLUTIONS REGARDING THE  
EVOLUTION OF CONVECTION. SOME CONVECTION LOOKS TIED TO A  
PREFRONTAL TROUGH, WITH ADDITIONAL CONVECTION ALONG THE ACTUAL  
FRONT. WHILE COVERAGE/TIMING IS A LITTLE UNCERTAIN, THE WIND  
FIELDS ARE NOT. THERE WILL BE PLENTY OF WIND THROUGHOUT THE  
COLUMN, AND IT WILL BE A BREEZY DAY EVEN OUTSIDE OF THE STORMS.  
WE LIKELY REMAINED CAPPED MOST OF THE DAY, AS WELL AS MOSTLY  
CLOUDY. THUS INSTABILITY IS LIKELY TO REMAIN ON THE LOWER END OF  
THE SCALE, BUT NEVERTHELESS ENOUGH TO SUPPORT CONVECTION WHICH  
COULD PULL DOWN THE STRONG WINDS. SPC HAS MAINTAINED THE SLIGHT  
RISK ACROSS PARTS OF THE AREA. TEMPERATURES WILL REACH THE 70S  
TO MID 80S.  
 
CONVECTION WILL BE EXITING THE AREA DURING THE EVENING HOURS,  
WITH MOST AREAS LIKELY DRYING OUT AFTER MIDNIGHT. COOLER  
(COMPARED TO THE PAST FEW DAYS) AND DRIER AIR MOVE IN BEHIND THE  
FRONT, WITH GUSTY WINDS LIKELY CONTINUING INTO TUESDAY (GUSTS  
25-35 MPH). VORT MAX WILL SKIM NORTHWESTERN AREAS DURING THE  
DAY, WITH PERHAPS A SHOWER OR SPRINKLE IN THE POTOMAC HIGHLANDS.  
THE LOW WILL PULL FARTHER AWAY TO THE NORTHEAST TUESDAY NIGHT,  
LIKELY ALLOWING WINDS TO RELAX.  
 

 
   
LONG TERM /WEDNESDAY THROUGH SUNDAY/
 
 
HIGH PRESSURE BUILDS OVER OUR REGION ON WEDNESDAY WITH W TO NW  
WINDS OVER OUR REGION. A STORM SYSTEM WILL DEVELOP ACROSS THE  
MISSISSIPPI VALLEY WEDNESDAY NIGHT INTO THURSDAY. AN INCREASE IN  
CLOUDS AND PRECIPITATION COULD BEGIN OVERNIGHT WEDNESDAY AND  
STRETCH INTO FRIDAY NIGHT AS THIS SYSTEM MOVES NE. THUNDERSTORMS  
AND HEAVY RAIN POSSIBLE... WITH GUIDANCE SUGGESTING PW VALUES  
ABOVE ONE INCH... AND EVEN HIGHER FOR SOME AREAS.  
 
THE WARM FRONT ASSOCIATED TO THIS SYSTEM WILL PUSH NORTH  
THROUGH OUR AREA THURSDAY NIGHT WITH SOUTHERLY FLOW ADVECTING  
MOISTURE OVER OUR AREA INTO FRIDAY NIGHT. THE UPPER LEVEL AND  
SURFACE LOW WILL PUSH NE NEAR OR OVER OUR CWA SOMETIME FRIDAY OR  
SATURDAY. CONDITIONS START TO DRY OUT FRIDAY NIGHT INTO  
SATURDAY WITH SOME SHOWERS INTO SUNDAY AS UPPER LEVEL TROUGH  
AXIS MOVES ACROSS.  
 
HIGH TEMPERATURES WILL BE MAINLY IN THE 60S AND 70S WITH...  
SOME 50S AT HIGHER ELEVATIONS.  
 

 
   
AVIATION /01Z MONDAY THROUGH FRIDAY/
 
 
PRECIPITATION ISN'T EXPECTED TONIGHT, BUT LOW CLOUDS ARE LIKELY  
TO REDEVELOP LATE, WITH MVFR CIGS POSSIBLE. THESE CLOUDS MAY  
STICK AROUND MUCH OF MONDAY MORNING.  
 
A STRONG COLD FRONT WILL PUSH INTO THE AREA DURING THE LATE  
AFTERNOON TO EVENING, LIKELY TO BE ACCOMPANIED BY AT LEAST A  
BROKEN LINE OF THUNDERSTORMS. THESE STORMS COULD CONTAIN STRONG  
WIND GUSTS. EVEN OUTSIDE THUNDERSTORMS, WINDS COULD GUST TO 25  
KT. FRONT PUSHES EAST LATE MONDAY NIGHT, ENDING PRECIPITATION  
CHANCES, BUT GUSTY WSW WINDS OF 20-30 KT WILL CONTINUE THROUGH  
TUESDAY.  
 
VFR EXPECTED FOR WEDNESDAY OVER THE TERMINALS... THEN AN  
EXTENDED PERIOD OF SUB-VFR CONDITIONS POSSIBLE STARTING  
WEDNESDAY NIGHT AND INTO FRIDAY AS A STORM SYSTEM APPROACHES.  
GUSTS AS HIGH AS 20 KT POSSIBLE.  
 

 
   
MARINE
 
 
GRADIENT FLOW (SOUTHERLY) WILL INCREASE OVERNIGHT INTO MONDAY AS  
THE BACKDOOR FRONT LIFTS BACK TO THE NORTH AHEAD OF A STRONGER  
COLD FRONT APPROACHING FROM THE WEST. A SMALL CRAFT ADVISORY  
IS IN EFFECT FOR THE SOUTHERN WATERS OVERNIGHT, AND THEN FOR  
ALL WATERS ON MONDAY. THE FRONT ITSELF WILL IMPACT THE MARINE  
AREA MONDAY NIGHT. THUNDERSTORMS WITH GUSTY WINDS WILL LIKELY  
AFFECT THE WATERS AHEAD OF THE FRONT.  
 
BEHIND THE FRONT FLOW TURNS WESTERLY. MIXED PROFILES APPEAR  
DEEP, AND THE SCA CONTINUES INTO TUESDAY. WINDS GRADUALLY  
DIMINISH TUESDAY NIGHT, BUT SCA MAY NEED TO BE CONTINUED ON  
PORTIONS OF THE BAY.  
 
DRY CONDITIONS EXPECTED FOR WEDNESDAY OVER THE WATERS... THEN  
AN EXTENDED PERIOD OF RAIN COULD START WEDNESDAY NIGHT AND INTO  
FRIDAY AS A STORM SYSTEM APPROACHES. WIND GUSTS WILL BE NEAR THE  
SMALL CRAFT ADVISORY THRESHOLD... THEREFORE EXPECT ADVISORIES  
FOR PARTS OF THIS PERIOD.  
 

 
   
TIDES/COASTAL FLOODING
 
 
WATER LEVELS ARE RUNNING VERY CLOSE TO ASTRONOMICAL NORMALS  
THIS EVENING. TIDAL ANOMALIES MAY INCREASE THROUGH TONIGHT DUE  
TO AN ONSHORE FLOW...BUT WATER LEVELS SHOULD REMAIN BELOW MINOR  
FLOODING THRESHOLDS SINCE THE FLOW WILL BE LIGHT.  
 
SOUTHERLY FLOW WILL STRENGTHEN AHEAD OF A COLD FRONT MONDAY  
INTO MONDAY NIGHT. TIDAL ANOMALIES WILL CONTINUE TO INCREASE  
DURING THIS TIME AND MINOR TIDAL FLOODING IS POSSIBLE FOR  
SENSITIVE AREAS. HOWEVER...CONFIDENCE IS LOW SINCE THE HIGHER OF  
THE TWO ASTRONOMICAL HIGH TIDES WILL OCCUR MONDAY MORNING INTO  
EARLY MONDAY AFTERNOON. THIS WILL NOT LINE UP WITH THE HIGHEST  
ANOMALIES WHICH ARE MOST LIKELY LATE MONDAY AFTERNOON INTO  
MONDAY NIGHT...DURING THE LOWER OF THE TWO ASTRONOMICAL HIGH  
TIDES.  
 
SOME GUIDANCE SUGGEST ELEVATED LEVELS COULD LINGER INTO  
TUESDAY, AS WINDS WILL TURN GUSTY BUT WILL BE FROM THE  
WEST...AND THUS WON'T PROMPT A BLOWOUT.  
 
LOW PRESSURE WILL COME UP THE COAST THURSDAY, WHICH LIKELY WILL  
INCREASE WATER LEVELS FROM WHEREVER THEY STAND UP TO THAT  
POINT.  
 

 
   
CLIMATE
 
 
RECORD HIGHS WERE SET AT DCA AND IAD YESTERDAY, AND RECORD WARM  
LOWS WERE SET AT ALL THREE AIRPORTS (DCA, IAD, AND BWI). THE  
RECORD WARM LOW AT DCA WAS ALSO A RECORD FOR THE MONTH OF APRIL.  
 
RECORDS HIGHS ARE LESS LIKELY TODAY AS A BACKDOOR FRONT DROPS  
DOWN. HOWEVER, THE RECORD WARM LOWS ARE A POSSIBILITY. HERE ARE  
THE RECORD HIGHS/WARM LOWS FOR SUNDAY:  
 
WASHINGTON DC... HIGH 92 (IN 1942); WARM LOW 67 (IN 1983).  
BWI AIRPORT... HIGH 92 (IN 1910); WARM LOW 63 (IN 1983).  
DULLES AIRPORT.. HIGH 86 (IN 2007); WARM LOW 64 (IN 1983).  
 
APRIL 2017 IS LIKELY GOING TO GO DOWN AS THE WARMEST ON RECORD  
AT DCA AND IAD, AND ONE OF THE THREE WARMEST AT BWI. THE  
CURRENT RECORDS ARE:  
51.9 DEGREES IN 1981 AT DCA/WASHINGTON DC  
46.4 DEGREES IN 1994 AT IAD/DULLES VA  
50.7 DEGREES IN 1941 AT BWI/BALTIMORE MD  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...SMALL CRAFT ADVISORY FROM 6 AM MONDAY TO 6 AM EDT TUESDAY FOR  
ANZ530>532-535-536-538>540-542.  
SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ533-534-537-  
541-543.  
SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ535-536.  
 

 
 

 
SYNOPSIS...ADS  
NEAR TERM...ADS  
SHORT TERM...ADS  
LONG TERM...IMR  
AVIATION...ADS/IMR  
MARINE...ADS/IMR  
TIDES/COASTAL FLOODING...BJL  
CLIMATE...HTS/RCM  
 
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