663  
FXUS61 KLWX 051850  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
250 PM EDT WED AUG 5 2020  
   
SYNOPSIS
 
 
A COLD FRONT STALLED JUST TO THE SOUTH OF THE REGION TODAY  
WILL BEGIN TO SLOWLY PUSH BACK NORTH ACROSS THE REGION THROUGH  
THE END OF THE WEEK. BRIEF HIGH PRESSURE BUILDS IN FOR THE FIRST  
HALF OF THE WEEKEND, BEFORE UNSETTLED CONDITIONS RETURN LATER  
SUNDAY INTO THE BEGINNING OF NEXT WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
A WEAK FRONTAL BOUNDARY HAS PUSHED SOUTH OF THE REGION AND IS  
DRAPED ACROSS THE DELMARVA PENINSULA, THEN DOWN ALONG THE NC/VA  
BORDER. MEANWHILE, SURFACE HIGH PRESSURE IS PUSHING INTO THE  
OHIO VALLEY. ALOFT, A CLOSED UPPER LOW REMAINS OVER  
QUEBEC/ONTARIO, WITH A TROUGH EXTENDING DOWN INTO THE OHIO  
VALLEY.  
 
WITH THE STATIONARY BOUNDARY LINGERING JUST SOUTH OF THE  
FORECAST AREA, MUCH OF THE AREA REMAINS DRY FOR MUCH OF THE  
AFTERNOON. WITH HIGH TEMPERATURES IN THE 80S AND DEW POINTS IN  
THE 60S MOST OF THE DAY, IT WILL FEEL RELATIVELY COMFORTABLE AS  
WELL.  
 
LATER THIS AFTERNOON INTO THIS EVENING, COULD SEE SOME SHOWERS  
AND STORMS FIRE IN OUR SOUTHWEST ZONES OVER CENTRAL VA ALONG A  
WEAK PRESSURE TROUGH RELATED TO THE HIGHER TERRAIN. OTHERWISE,  
A VERY WEAK DAY IN TERMS OF FORCING. THINK WE ARE TOO DRY OVER  
NORTHERN VA, NORTHERN/CENTRAL MD, AND DC (SEE THE 12Z IAD RAOB,  
WHICH DEPICTS SUBSTANTIAL DRY AIR ABOVE 600MB). EITHER WAY, NOT  
SEEING MUCH OF A SEVERE THREAT, AS THE BEST MID-UPPER LEVEL FLOW  
IS OFF TO THE NORTH AND EAST. THERE WILL BE CAPE IN THE  
NEIGHBORHOOD OF 1000-1500 J/KG TO WORK WITH, BUT THIS WILL  
LIKELY RESULT IN JUST SOME HEAVIER SHOWERS, AND PERHAPS A FEW  
WEAKER THUNDERSTORMS.  
 
THINGS GET A LITTLE INTERESTING OVERNIGHT, AS MOST HI-RES  
GUIDANCE BRINGS A WEAK PIECE OF UPPER-LEVEL ENERGY ACROSS THE  
REGION, WHILE THE AFOREMENTIONED FRONTAL BOUNDARY BEGINS TO  
DRIFT NORTHWARD. THIS SHOULD RESULT IN A GREATER RISK OF  
SHOWERS AND PERHAPS SOME ISOLATED THUNDERSTORMS SPREADING NORTH  
ACROSS MOST OF THE REGION OVERNIGHT, AND ESPECIALLY EARLY  
THURSDAY MORNING. LOWS WILL BE IN THE 60S TO LOW 70S.  
 

 
   
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
 
 
THE BOUNDARY WILL CONTINUE TO LIFT NORTHWARD THROUGHOUT THE DAY  
ON THURSDAY, AND LIKELY STALL SOMEWHERE OVER CENTRAL VA INTO  
SOUTHERN MD. WITH UPPER-LEVEL ENERGY APPROACHING FROM THE WEST,  
AND THE SURFACE FRONTOGENESIS OVER THE AREA, SHOWERS AND STORMS  
ARE LIKELY ON THURSDAY AFTERNOON EVENING NEAR/ALONG THIS FRONTAL  
BOUNDARY. MOIST AIR WILL BE FUNNELING BACK INTO THE REGION SOUTH  
OF THIS BOUNDARY, AND GIVEN THE ORIENTATION OF THE FRONTAL  
BOUNDARY COMPARED TO THE MID-UPPER LEVEL FLOW, FLOODING COULD  
BECOME AN ISSUE (MORE ON THAT IN THE HYDROLOGY SECTION BELOW).  
 
THE WEAK FRONTAL BOUNDARY WILL CONTINUE SLOWLY MIGRATING  
NORTHWARD THURSDAY NIGHT THROUGH FRIDAY NIGHT AS IT GRADUALLY  
FALLS APART. HOWEVER, A SHORTWAVE WILL BE MOVING OVERHEAD. THUS,  
DESPITE THE DIMINISHED SURFACE FORCING, THE INCREASED UPPER  
LEVEL SUPPORT SHOULD RESULT IN MORE SHOWERS AND THUNDERSTORMS  
THROUGH THE END OF THE WEEK. THE RISK OF CLOUDS AND RAIN WILL  
CONTINUE TO KEEP TEMPS LOWER, WITH HIGHS IN THE LOW-MID 80S  
OVERALL. DESPITE THE COOLER TEMPS, DEW POINTS IN THE LOWER 70S  
WILL MAKE IT FEEL QUITE HUMID. THE HIGH MOISTURE CONTENT WILL  
CONTINUE TO RESULT IN A RISK OF ISOLATED FLOODING FROM  
THUNDERSTORMS.  
 

 
   
LONG TERM /SATURDAY THROUGH TUESDAY/
 
 
A STALLED BOUNDARY THAT HAS BEEN NEAR THE AREA STARTS TO SHIFT  
SOUTHEASTWARD AWAY FROM THE REGION ON SATURDAY. A FEW SHOWERS AND  
THUNDERSTORMS WILL CONTINUE TO BE POSSIBLE ON SATURDAY BUT THE MAIN  
THREAT AREA SHOULD BE FOCUSED OVER CENTRAL VIRGINIA AND SOUTHERN  
MARYLAND CLOSER TO THE BOUNDARY. THE FRONT SHOULD FINALLY SHIFT AWAY  
FROM OUR AREA BY SUNDAY AND HIGH PRESSURE BRIEF BUILDS OVER OUR  
REGION. A WESTERLY FLOW ALOFT COMBINED WITH A WEAK NORTHERLY FLOW AT  
THE SURFACE SHOULD HELP LIMIT TEMPERATURES THIS WEEKEND TO THE MID  
TO UPPER 80S WITH OVER NIGHT LOWS IN THE 60S AND LOWER 70S.  
 
ANOTHER BOUNDARY IS FORECAST TO MOVE INTO OUR AREA AND STALL DURING  
THE EARLY PARTS OF NEXT WEEK. MULTIPLE SHORTWAVES WILL LEAD TO  
CONTINUED CHANCES FOR SHOWERS AND THUNDERSTORMS BOTH MONDAY AND  
TUESDAY. A WESTERLY FLOW ALOFT MAY LIMIT THE COVERAGE OF STORMS AS  
DRY AIR GETS PULLED INTO THE SYSTEM. TEMPERATURES SHOULD TREND  
UPWARDS INTO THE LOWER 90S AS WE REMAIN MAINLY ON THE WARM SIDE OF  
THE BOUNDARY.  
 

V  
   
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
 
 
VFR FOR THE REST OF TODAY AT ALL TERMINALS. SHOWERS AND STORMS  
POSSIBLE AT CHO LATER THIS AFTERNOON/EVENING. TRIED TO NARROW  
DOWN A TIMEFRAME THERE IN THE LATEST TAFS. COULD SEE BRIEF  
RESTRICTIONS IF A STORM PASSES OVER THE TERMINAL. OUTSIDE OF  
CHO THOUGH, THINK ALL OTHERS REMAIN DRY.  
 
LOW CLOUDS ASSOCIATED WITH A SLOW MOVING FRONTAL BOUNDARY COULD  
CAUSE SOME RESTRICTIONS THURSDAY INTO FRIDAY. THINK THINGS STAY  
LOW END VFR IN TERMS OF CIGS, BUT COULD BRIEFLY DIP INTO MVFR AT  
TIMES AT ALL TERMINALS. ADDITIONALLY, MORNING FOG POSSIBLE EACH  
MORNING, ASSOCIATED WITH MOISTURE FROM RECENT RAINS. CHO WOULD  
BE THE BEST CANDIDATE FOR THIS.  
 
VFR CONDITIONS EXPECTED THIS WEEKEND AND INTO EARLY NEXT WEEK BUT  
SHOWERS AND THUNDERSTORMS MAY CAUSE BRIEF PERIODS OF  
RESTRICTIONS.  
 

 
   
MARINE
 
 
LIGHT WINDS EXPECTED THROUGH FRIDAY, OUTSIDE OF GUSTY WINDS IN  
THUNDERSTORMS THURSDAY AND FRIDAY. TODAY SHOULD REMAIN DRY OVER  
THE WATERS, AS SHOWERS AND STORMS SHOULD BE LIMITED TO THE  
HIGHER ELEVATIONS. HOWEVER, CAN'T COMPLETELY RULE OUT A ROGUE  
STORM OVER THE LOWER POTOMAC INTO THE CENTRAL BAY.  
 
GREATEST CHANCE FOR SHOWERS AND STORMS IS THURSDAY AND FRIDAY,  
AS THE FRONTAL BOUNDARY TO OUR SOUTH TODAY SLOWLY PUSHES  
NORTHWARD, AND AN UPPER TROUGH MOVES OVERHEAD INTO FRIDAY.  
 
NO SMALL CRAFT ADVISORIES EXPECTED AT THIS TIME FOR THIS  
WEEKEND.  
 

 
   
HYDROLOGY
 
 
THURSDAY AFTERNOON AND EVENING ARE GROWING A BIT MORE CONCERNING  
OVER CENTRAL/SOUTHERN MD AND NORTHEAST VA, MAINLY SOUTHEAST OF  
I-95. SEVERAL THINGS OF NOTE FOR THURSDAY AFTERNOON. FIRST, A  
STALLED /SLOW-MOVING BOUNDARY WILL BE SITUATED OVER CENTRAL  
VA/SOUTHERN MD. THIS BOUNDARY WILL BE ROUGHLY PARALLEL TO THE  
WSW MID-UPPER LEVEL FLOW, WHICH WILL FAVOR TRAINING STORMS ALONG  
THE FRONT. PWATS, WHILE NOT EXCEEDINGLY IMPRESSIVE, SHOULD BE  
CLOSE TO 2 INCHES NEAR/SOUTH OF THE BOUNDARY. GIVEN THE RECENT  
HEAVY RAINFALL FROM ISAIAS, FFG VALUES ARE QUITE LOW OVER  
CENTRAL/SOUTHERN MD. MANY AREAS SAW 4-6 INCHES OF RAIN TUESDAY,  
WITH SOME EVEN SEEING UP TO 7-8 INCHES. THE 12Z RUN OF THE HREF  
SHOW THE POTENTIAL FOR SEVERAL INCHES OF RAIN OVER THIS REGION  
IN ROUGHLY A 6 HOUR PERIOD THURSDAY AFTERNOON/EVENING. THIS  
WOULD EASILY EXCEED FFG IF REALIZED. WPC HAS INTRODUCED THE  
SLIGHT RISK OF EXCESSIVE RAINFALL OVER THIS AREA TOMORROW AS A  
RESULT OF ALL OF THIS. MONITOR THE LATEST FORECAST FOR UPDATES.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...RCM  
NEAR TERM...CJL  
SHORT TERM...CJL/RCM  
LONG TERM...JMG  
AVIATION...CJL/JMG  
MARINE...CJL/JMG  
HYDROLOGY...CJL  
 
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