637  
FXUS61 KLWX 211420  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
1020 AM EDT MON MAY 21 2018  
   
SYNOPSIS
 
 
A FRONT WILL REMAIN OVER THE CAROLINAS INTO THE APPALACHIAN  
MOUNTAINS TODAY THROUGH TONIGHT. THE FRONT WILL RETURN NORTH AS  
A WARM FRONT ON TUESDAY WITH A COLD FRONT EXPECTED TO PASS  
THROUGH THE AREA ON WEDNESDAY. WEAK HIGH PRESSURE WILL BUILD  
OVER THE AREA FOR THE SECOND HALF OF THE WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
FRONTAL BOUNDARY IS STALLED OUT SOUTH OF THE REGION TODAY ACROSS  
CENTRAL VA AND INTO CENTRAL WV. A WEAKENING CLUSTER OF SHOWERS  
AND ISOLATED THUNDERSTORMS MOVED INTO PORTIONS OF EASTERN WV AND  
WESTERN VA THIS MORNING, AND SOME ADDITIONAL PROGRESS  
SOUTHEASTWARD IS LIKELY BEFORE DISSIPATION THIS AFTERNOON. BY  
LATER THIS AFTERNOON, SOME ADDITIONAL SHOWER/THUNDERSTORM  
DEVELOPMENT IS LIKELY NEAR THE FRONTAL BOUNDARY AND ACROSS THE  
HIGHER TERRAIN. LOCALLY HEAVY RAIN IS POSSIBLE, AND THERE IS A  
LOW RISK FOR AN ISOLATED FLOODING INCIDENT OR TWO, ALTHOUGH THE  
MAJORITY OF THE CONVECTION SHOULD BE SOUTH/WEST TOWARDS  
BLACKSBURG/ROANOKE/CHARLESTON ON THE WARM SIDE OF THE BOUNDARY.  
 
OTHERWISE, A GENERAL INCREASE IN CLOUDS IS ANTICIPATED, WITH  
HIGHS IN THE 70S TO LOW 80S.  
 
THE FRONT WILL BEGIN TO LIFT NORTHWARD TONIGHT.  
ANY SHOWERS/THUNDERSTORMS SHOULD SEE A WEAKENING TREND. LOW  
CLOUDS AND PATCHY FOG MAY ALSO DEVELOP. WARM AIR ADVECTION WILL  
ALLOW FOR LOW TEMPERATURES TO BE AROUND 10 DEGREES ABOVE NORMAL  
ACROSS THE REGION TONIGHT.  
 

 
   
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
 
 
THE BOUNDARY WILL RETURN NORTH AND EAST AS A WARM FRONT TUESDAY,  
AND A SOUTHWEST FLOW ALOFT WILL CONTINUE AROUND HIGH PRESSURE  
OVER THE ATLANTIC. THE SOUTHWEST FLOW WILL USHER IN MORE  
MOISTURE ACROSS OUR AREA, AND INSTABILITY WILL RETURN DUE TO THE  
MOISTURE AND DAYTIME HEATING. THE BOUNDARY WILL ACT AS THE  
LIFTING MECHANISM FOR SHOWERS AND THUNDERSTORMS TO DEVELOP,  
WITH THE BEST CHANCE FOR CONVECTION COMING DURING THE AFTERNOON  
AND EVENING HOURS. PWATS OVER 1.5 INCHES SUGGEST THAT THERE WILL  
BE ENOUGH MOISTURE FOR THUNDERSTORMS TO CONTAIN HEAVY RAINFALL,  
AND MODERATE TO PERHAPS HIGH AMOUNTS OF INSTABILITY  
THUNDERSTORMS MAY CONTAIN GUSTY WINDS OR HAIL. HOWEVER, THE  
THREAT FOR SEVERE THUNDERSTORMS IS STILL LIMITED DUE TO THE LACK  
OF DEEP LAYER SHEAR.  
 
A WEAK COLD FRONT WILL APPROACH THE REGION TUESDAY NIGHT BEFORE  
PASSING THROUGH WEDNESDAY INTO WEDNESDAY EVENING. A DRIER  
NORTHWEST FLOW WILL LIMIT CONVECTION BEHIND THE BOUNDARY  
WEDNESDAY, BUT WILL STILL CARRY THE SLIGHT CHANCE TO CHANCE FOR  
SHOWERS AND THUNDERSTORMS WEDNESDAY AFTERNOON, WITH THE HIGHEST  
POPS ACROSS SOUTHERN AREAS.  
 

 
   
LONG TERM /THURSDAY THROUGH SUNDAY/
 
 
WEAK HIGH PRESSURE WILL BUILD OVERHEAD THURSDAY BEFORE MOVING  
OFFSHORE FRIDAY. A NORTH TO NORTHWEST FLOW WILL ALLOW FOR DRY  
AND LESS HUMID CONDITIONS THURSDAY ALONG WITH SUNSHINE. THE  
HUMIDITY MAY CREEP BACK A BIT FRIDAY DUE TO A RETURN FLOW, BUT  
MAINLY DRY CONDITIONS ARE EXPECTED TO REMAIN IN PLACE.  
 
HIGH PRESSURE WILL SET UP OVER THE ATLANTIC FOR SATURDAY AND  
SUNDAY AND A SOUTHWEST FLOW WILL ALLOW FOR MOISTURE TO RETURN,  
INCREASING THE CHANCES FOR POPUP SHOWERS AND THUNDERSTORMS.  
TROPICAL MOISTURE HAS THE CHANCE TO GET DRAWN NORTH INTO THE  
AREA, BUT CONFIDENCE IS STILL LOW AT THIS TIME. IF IT DOES, THEN  
SHOWERS AND THUNDERSTORMS WILL BE MORE WIDESPREAD.  
 

 
   
AVIATION /14Z MONDAY THROUGH FRIDAY/
 
 
A WEAK FRONT WILL STALL TO THE SOUTH AND WEST TODAY. VFR  
CONDITIONS ARE EXPECTED THROUGH TODAY. THE BOUNDARY WILL BEGIN  
TO LIFT NORTHWARD TONIGHT, WITH WARM AIR ADVECTION INCREASING  
ALOFT, AND THIS MAY RESULT IN LOW CLOUDS AND AREAS OF FOG  
TOWARD MORNING.  
 
THE FRONT WILL MOVE INTO THE AREA TUESDAY BEFORE A WEAK COLD  
FRONT PASSES THROUGH WEDNESDAY. POPUP SHOWERS AND THUNDERSTORMS  
ARE LIKELY TUESDAY AFTERNOON AND EVENING, BUT COVERAGE WILL  
DIMINISH OVERNIGHT. DRIER AIR SHOULD ALLOW FOR ANY CONVECTION TO  
BE ISOLATED OR WIDELY SCATTERED WEDNESDAY AND CONFINED MAINLY  
TOWARD THE SOUTH NEAR KCHO. EVEN THERE, MUCH OF THE DAY MAY BE  
DRY.  
 
HIGH PRESSURE WILL RETURN FOR THURSDAY AND FRIDAY WITH VFR  
CONDITIONS MOST LIKELY.  
 

 
   
MARINE
 
 
A WEAK COLD FRONT WILL STALL TO THE SOUTH AND WEST THROUGH  
TONIGHT. A NORTHEAST FLOW THIS MORNING WILL TURN TO THE  
SOUTHEAST LATER TODAY INTO TONIGHT. WINDS SHOULD REMAIN BELOW  
SCA CRITERIA DURING THIS TIME.  
 
A WARM FRONT WILL APPROACH THE WATERS TUESDAY INTO TUESDAY NIGHT  
BEFORE A COLD FRONT PASSES THROUGH WEDNESDAY. SHOWERS AND  
THUNDERSTORMS ARE LIKELY TUESDAY, ESPECIALLY DURING THE  
AFTERNOON AND EVENING HOURS. SOME STORMS MAY CONTAIN GUSTY  
WINDS. SOUTH TO SOUTHEAST WINDS MAY APPROACH SCA CRITERIA  
TUESDAY AND A NORTHWEST FLOW BEHIND THE COLD FRONT MAY CAUSE  
WINDS TO APPROACH SCA CRITERIA WEDNESDAY, BUT CONFIDENCE IS LOW  
FOR TUESDAY DUE TO THE RELATIVELY COOLER WATERS.  
 
HIGH PRESSURE WILL RETURN FOR THURSDAY BEFORE MOVING OFFSHORE  
FRIDAY INTO THE WEEKEND.  
 

 
   
TIDES/COASTAL FLOODING
 
 
FRESHWATER CONTINUES TO DECREASE AS WATER LEVELS ON THE POTOMAC  
RIVER UPSTREAM HAVE CRESTED AND THEY CONTINUE TO FALL.  
THEREFORE, THE THREAT FOR MODERATE FLOODING HAS ENDED. MINOR  
FLOODING IS STILL EXPECTED NEAR TIMES OF HIGH TIDE THROUGH  
TONIGHT, AND IT IS POSSIBLE TUESDAY FOR WASHINGTON DC. WILL  
CONTINUE WITH THE ADVISORY THROUGH TONIGHT, AND IT MAY NEED TO  
BE EXTENDED INTO TUESDAY AS WELL.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...COASTAL FLOOD ADVISORY UNTIL 6 AM EDT TUESDAY FOR DCZ001.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...BJL  
NEAR TERM...MM/IMR  
SHORT TERM...BJL  
LONG TERM...BJL/IMR  
AVIATION...BJL/MM/IMR  
MARINE...BJL/MM/IMR  
TIDES/COASTAL FLOODING...BJL  
 
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