951  
FXUS61 KLWX 200135  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
935 PM EDT MON APR 19 2021  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL BUILD ALONG THE MID-ATLANTIC COAST TONIGHT  
AND TUESDAY. A STRONG COLD FRONT WILL CROSS THE AREA WEDNESDAY.  
CANADIAN HIGH PRESSURE WILL BUILD TO FROM THE WEST WEDNESDAY  
NIGHT THROUGH THURSDAY BEFORE SETTLING TO THE SOUTH LATE IN THE  
WEEK. LOW PRESSURE MAY AFFECT THE AREA OVER THE WEEKEND.  
 

 
   
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
 
 
DRY CONDITIONS ARE EXPECTED EVERYWHERE TONIGHT AS SUBSIDENCE  
IS TAKING OVER BEHIND THE DEPARTING THE DISTURBANCE. THERE MAY  
BE SOME FOG, ESPECIALLY IN AREAS THAT RECEIVED HEAVIER RAINFALL  
(CENTRAL VA TO SOUTHERN MD). HOWEVER, MOST GUIDANCE ISN'T  
LATCHING ON TO FOG JUST YET, PROBABLY DUE TO A LIGHT BUT  
PERSISTENT SOUTH FLOW. MIN TEMPS WILL BE IN THE 40S FOR MOST  
PLACES TONIGHT TO NEAR 50 IN DOWNTOWN WASHINGTON AND BALTIMORE.  
SOME UPPER 30S ARE POSSIBLE IN COLDER VALLEYS.  
 

 
   
SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/
 
 
HIGH PRESSURE WILL REMAIN OFF THE MID-ATLANTIC COAST TUESDAY  
WHILE A TROUGH DIGS OVER THE CENTRAL CONUS AND MIDWEST ALONG  
WITH ITS ASSOCIATED COLD FRONT. A SOUTHERLY FLOW BETWEEN THESE  
SYSTEMS WILL DEVELOP BY AFTERNOON. ALONG WITH WHAT SHOULD BE A  
FAIR AMOUNT OF SUNSHINE, TEMPERATURES SHOULD REACH THE 70S IN  
MANY LOCATIONS. MOISTURE RETURN COULD RESULT IN AN ISOLATED  
SHOWER OVER THE APPALACHIANS BY LATE AFTERNOON, BUT MOST AREAS  
WILL BE DRY.  
 
THE COLD FRONT WILL APPROACH TUESDAY NIGHT AS THE UPPER-LEVEL  
TROUGH STRENGTHENS A BIT. MOST OF TUESDAY NIGHT SHOULD BE DRY,  
BUT A FEW SHOWERS ARE POSSIBLE, ESPECIALLY ACROSS WESTERN AREAS  
CLOSER TO THE FRONT. TUESDAY NIGHT WILL TURN OUT MILD DUE TO THE  
SOUTHERLY FLOW AHEAD OF THE APPROACHING COLD FRONT.  
 
THE POTENT UPPER-LEVEL TROUGH WILL DIG OVERHEAD WEDNESDAY  
THROUGH WEDNESDAY NIGHT. THE SURFACE LOW ASSOCIATED WITH THIS  
WILL STRENGTHEN AND TRACK TO OUR NORTH WHILE A COLD FRONT PASSES  
THROUGH OUR AREA WEDNESDAY BEFORE MOVING OFFSHORE WEDNESDAY  
EVENING. SHOWERS WILL LIKELY DEVELOP ALONG THE FRONT (WITH A  
POSSIBLE MINIMUM IN THE IMMEDIATE LEE OF THE APPALACHIANS DURING  
THE MORNING), WITH SOME EMBEDDED THUNDERSTORMS POSSIBLE AS THE  
FRONT ENCOUNTERS HIGHER INSTABILITY EAST OF THE BLUE RIDGE  
DURING THE MIDDAY HOURS. THE FORCING ALONG THE FRONT WILL BE  
STRONG, SO A LINE OF GUSTY SHOWERS ARE POSSIBLE WITH THE FRONTAL  
PASSAGE MAINLY EAST OF THE BLUE RIDGE AND CATOCTIN MOUNTAINS,  
AND THE HIGHEST CHANCE WILL BE CLOSER TO THE BALTIMORE METRO  
WHERE FORCING/INSTABILITY WILL ULTIMATELY BE HIGHEST. THE SEVERE  
WEATHER THREAT WILL BE DEPENDENT ON THE TIMING OF THE FRONT.  
CURRENTLY, THE TIMING IS FAIRLY FAST, RESULTING IN LIMITED  
INSTABILITY. HOWEVER, SUBTLE CHANGES COULD RESULT IN A GREATER  
RISK OF STRONG/DAMAGING WINDS WITH THE SHOWERS AND STORMS, SO  
STAY TUNED. REGARDLESS OF PRECIPITATION, STRONG WEST TO  
NORTHWEST WINDS WILL FOLLOW THE FRONTAL PASSAGE, AND  
TEMPERATURES WILL START FALLING. FREQUENT GUSTS AROUND 25 TO 40  
MPH ARE EXPECTED, AND IT'S NOT OUT OF THE QUESTION A WIND  
ADVISORY COULD BE NEEDED FOR SOME AREAS. ANY LINGERING  
PRECIPITATION ALONG/WEST OF THE ALLEGHENY FRONT COULD START  
MIXING WITH/CHANGING OVER TO SNOW. ACCUMULATIONS WILL BE  
MINIMAL, HOWEVER.  
 
THE UPPER-LEVEL TROUGH WILL REMAIN OVERHEAD WEDNESDAY NIGHT  
ALLOWING FOR MORE BLUSTERY AND CHILLY CONDITIONS FOR THIS TIME  
OF YEAR. A FEW MOUNTAIN SNOW SHOWERS ARE POSSIBLE, AND ISOLATED  
SNOW OR RAIN SHOWER MAY EVEN SPILL EAST OF THE MOUNTAIN. ANY  
ACCUMULATION SHOULD BE LIGHT DUE TO LIMITED MOISTURE AND  
CONFINED TO THE RIDGES. MIN TEMPERATURES WILL END UP IN THE  
LOWER AND MIDDLE 30S FOR MOST PLACES WITH 20S IN THE MOUNTAINS.  
FREEZE HEADLINES MAY BE WARRANTED.  
 

 
   
LONG TERM /THURSDAY THROUGH MONDAY/
 
 
AN ANOMALOUS UPPER-LEVEL TROUGH WILL LINGER OVERHEAD MOST OF  
THURSDAY BEFORE FINALLY MOVING OFFSHORE THURSDAY NIGHT. FORECAST  
850 MB TEMPS ARE -5 TO -9 C MUCH OF THURSDAY. AT THE SURFACE,  
THIS TRANSLATES TO HIGHS IN THE 50S FOR MUCH OF THE REGION, WITH  
UPPER 30S AND LOW 40S ACROSS THE HIGHER TERRAIN. THE WELL BELOW  
NORMAL APRIL TEMPERATURES COUPLED WITH BLUSTERY WNW WINDS WILL  
MAKE IT FEEL LIKE LATE FEBRUARY OR EARLY MARCH. A FEW LINGERING  
UPSLOPE SNOW SHOWERS ARE POSSIBLE THURSDAY MORNING ACROSS THE  
HIGHER RIDGES OF THE ALLEGHENY FRONT.  
 
TEMPERATURES REBOUND CLOSER TO AVERAGE FRIDAY DUE TO A RETURN  
FLOW AS HIGH PRESSURE BUILDS TO THE SOUTH. FRIDAY SHOULD REMAIN  
DRY. REMAINING SEASONABLE ON SATURDAY AS THE REGION OF HIGH  
PRESSURE MOVES OFFSHORE.  
 
THE NEXT SYSTEM MOVES IN SATURDAY NIGHT AS AN UPPER-LEVEL  
TROUGH SWINGS EAST INTO THE GREAT LAKES. ENSEMBLE GUIDANCE IS IN  
AGREEMENT WITH A REGION OF LOW PRESSURE FORMING AHEAD OF THE  
TROUGH AND MOVING EITHER OVER OR JUST SOUTH OF THE REGION  
SATURDAY NIGHT INTO SUNDAY. THIS SYSTEM COULD BE ONE OF THE  
BIGGER RAIN PRODUCERS IN RECENT WEEKS WITH ENSEMBLE GUIDANCE  
SHOWING 0.50-1.00" AREAWIDE. THE EXACT TRACK OF THE LOW WILL  
ULTIMATELY DETERMINE QPF AMOUNTS, BUT THERE IS SOME GULF  
MOISTURE TO WORK WITH. DO NOT CURRENTLY ANTICIPATE WIDESPREAD  
FLOODING ISSUES DUE TO PRECEDING DRY CONDITIONS. STRONG WINDS  
ARE ALSO POSSIBLE WITH THIS SYSTEM. TEMPERATURES WILL NOT  
DECREASE BEHIND THIS SYSTEM AS MUCH AS THE WEDNESDAY/THURSDAY  
SYSTEM DUE TO THE PACIFIC ROOTS OF THIS SYSTEM.  
 

 
   
AVIATION /02Z TUESDAY THROUGH SATURDAY/
 
 
VFR CONDITIONS ARE EXPECTED MOST OF THE TIME TONIGHT THROUGH  
TUESDAY NIGHT. LOW CLOUDS AND FOG CANNOT BE RULED OUT LATE  
TONIGHT, ESPECIALLY AT DCA/BWI/MTN, BUT GUIDANCE REMAINS FAIRLY  
STRONGLY AGAINST IT, AS SOUTHERLY FLOW HAS ALREADY DEVELOPED AND  
MAY HELP KEEP IT MIXED ENOUGH TO LIMIT LOW LEVEL MOISTURE  
POOLING.  
 
A STRONG COLD FRONT WILL PASS THROUGH WEDNESDAY, LIKELY  
BRINGING SOME SHOWERS AND PERHAPS EVEN A THUNDERSTORM (BEST  
CHANCE ACROSS THE I-95 CORRIDOR). GUSTY WINDS ARE EXPECTED  
BEHIND THE COLD FRONT LATER WEDNESDAY INTO WEDNESDAY NIGHT.  
FREQUENT GUSTS OF 25 TO 35 KNOTS ARE EXPECTED DURING THIS TIME.  
 
VFR CONDITIONS AT THE TERMINALS THURSDAY AND FRIDAY WITH A  
GUSTY WESTERLY WIND.  
 

 
   
MARINE
 
 
THE GRADIENT HAS WEAKENED FOR TONIGHT AND WILL REMAIN WEAK THROUGH  
TUESDAY MORNING, BUT WINDS SHOULD PICK UP OUT OF THE SOUTHWEST  
TUESDAY AFTERNOON THROUGH TUESDAY NIGHT. AN SCA IS NOW IN  
EFFECT FOR PORTIONS OF THE WATERS DURING THIS TIME. GUSTY WEST  
TO NORTHWEST WINDS ARE EXPECTED BEHIND A STRONG COLD FRONT  
WEDNESDAY AFTERNOON INTO WEDNESDAY NIGHT AND A GALE WATCH IS NOW  
IN EFFECT. THERE'S ALSO POTENTIAL FOR A LINE OF GUSTY  
SHOWERS/ISOLATED THUNDERSTORMS AROUND MIDDAY WEDNESDAY WITH THE  
COLD FRONT.  
 
GALES MAY PERSIST AT TIMES THURSDAY, SO GALE WATCH INCLUDES  
THURSDAY. SCA CONDITIONS COULD LAST INTO FRIDAY AS A WEAKER,  
BUT STILL GUSTY SOUTHERLY WIND DEVELOPS.  
 

 
   
TIDES/COASTAL FLOODING
 
 
ANOMALIES HAVE DECLINED SOME THIS EVENING, BUT LIKELY RISE AGAIN  
WITH RETURNING SOUTHERLY FLOW LATE TONIGHT AND TUESDAY. WATER  
LEVELS COULD REACH CAUTION STAGES FOR SENSITIVE AREAS WITH THE  
HIGH TIDE CYCLES TUESDAY AND WEDNESDAY MORNINGS. MINOR FLOODING  
CANNOT BE RULED OUT, BUT CONFIDENCE IS LOW DUE TO THE LIGHT  
FLOW.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...GALE WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY AFTERNOON  
FOR ANZ530>543.  
SMALL CRAFT ADVISORY FROM 3 PM TUESDAY TO 6 AM EDT WEDNESDAY  
FOR ANZ532>534-539>541-543.  
SMALL CRAFT ADVISORY FROM 6 PM TUESDAY TO 6 AM EDT WEDNESDAY  
FOR ANZ531-537-538.  
SMALL CRAFT ADVISORY FROM MIDNIGHT TUESDAY NIGHT TO 6 AM EDT  
WEDNESDAY FOR ANZ530-536-542.  
 

 
 

 
SYNOPSIS...ADS/RCM  
NEAR TERM...ADS/RCM  
SHORT TERM...ADS  
LONG TERM...CPB  
AVIATION...ADS/CPB/RCM  
MARINE...ADS/CPB/RCM  
TIDES/COASTAL FLOODING...ADS/RCM  
 
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