929  
FXUS61 KLWX 180121  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
921 PM EDT WED AUG 17 2022  
   
SYNOPSIS
 
 
AN UPPER LEVEL LOW WILL REMAIN OFF TO THE NORTH BRINGING COOLER  
WEATHER AND CONTINUED CHANCES FOR PRECIPITATION THROUGH EARLY  
THURSDAY. HIGH PRESSURE WILL BUILD OVER THE REGION THURSDAY  
THROUGH THE EARLY PARTS OF THIS WEEKEND. A SURFACE LOW IS  
EXPECTED TO FORM ALONG A STALLED BOUNDARY OVER SE US AND PASS  
OFF TO SOUTH OF THE REGION THIS WEEKEND. A STRONGER COLD FRONT  
WILL IMPACT THE REGION BY EARLY NEXT WEEK BRINGING THE NEXT  
CHANCE FOR STRONG THUNDERSTORMS.  
 

 
   
NEAR TERM /UNTIL 9 AM THURSDAY MORNING/
 
 
9:15 PM UPDATE: SHOWERS AND THUNDERSTORMS ARE CONTINUING TO  
DIMINISH ACROSS THE AREA FROM NORTH TO SOUTH. A FEW SHOWERS AND  
RUMBLES OF THUNDER REMAIN NEAR THE NORTHERN NECK AND LOWER TIDAL  
POTOMAC RIVER. THESE WILL CONTINUE TO DISSIPATE OVER THE NEXT  
HOUR OR SO. BEHIND THESE SHOWERS, CLEARING SKIES AND CALM  
CONDITIONS EXPECTED FOR THE REMAINDER OF THE OVERNIGHT HOURS.  
THE UPPER LOW WILL CONTINUE TO MOVE FURTHER NORTH ACROSS THE  
NORTHEAST AND EVEN INTO THE PROVINCES OF CANADA LATER TONIGHT.  
 
PREVIOUS DISCUSSION FOLLOWS:  
 
CLOUDS WILL START BREAKING UP OVERNIGHT WITH WINDS SLOWLY BECOMING  
LIGHT AND VARIABLE. THE COMBINATION OF LIGHT WINDS AND CLEAR SKIES  
MAY LEAD TO SOME ISOLATED INSTANCES OF DENSE FOG FOR AREAS WEST  
OF THE BLUE RIDGE MTNS. MODEL GUIDANCE HAS WIDESPREAD DENSE FOG  
IN AREAS IN THE SHENADOAH VALLEYS AND WESTWARD WHICH SUGGESTS  
THAT DENSE FOG MAY BE POSSIBLE OVERNIGHT BUT CONFIDENCE REMAINS  
LOW. OVERNIGHT LOWS WILL BE COOL IN THE MID TO UPPER 50S TO  
LOWER 60S.  
 

 
   
SHORT TERM /9 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/
 
 
THE UPPER LEVEL LOW WILL LIFT NORTHEASTWARD, AWAY FROM OUR  
REGION ON THURSDAY AS WEAK RIDGING BUILDS IN FROM THE WEST. A  
WARMING TREND THAT WILL CONTINUE INTO THIS WEEKEND WILL BEGIN ON  
THURSDAY. RISING HEIGHTS ALONG WITH INCREASING SOUTHERLY  
ADVECTION WILL LEAD TO TEMPERATURES TRENDING UP INTO THE MID 80S  
ON THURSDAY AND INTO THE UPPER 80S BY FRIDAY. MAINLY DRY  
CONDITIONS ARE EXPECTED FOR MOST OF THE REGION ON THURSDAY BUT  
AN ISOLATED SHOWER COULD FORM ALONG THE ALLEGHENY FRONT DUE TO  
LOCAL TERRAIN CIRCULATIONS AND CONVERGENCE.  
 
HIGH PRESSURE IS FORECAST TO BUILD OVER OUR REGION LATE THURSDAY AND  
REMAIN IN PLACE THROUGH FRIDAY. DRY AND NEAR AVERAGE CONDITIONS  
SHOULD CONTINUE ON FRIDAY BUT THE NEXT CHANCE FOR WIDESPREAD SHOWERS  
WILL COME LATE FRIDAY INTO SATURDAY. A COASTAL LOW IS FORECAST TO  
FORM IN SOUTHERN STREAM ENERGY OVER SE US AND LIFT NORTHEASTWARD  
THROUGH THE SOUTHERN MID-ATLANTIC LATE FRIDAY INTO SATURDAY.  
DEPENDING ON THE TRACK OF THIS SURFACE LOW, OUR REGION COULD  
EXPERIENCE SOME PRECIPITATION OVER THE SOUTHERN HALF OF OUR  
REGION EARLY ON SATURDAY. THERE REMAINS A LOT OF UNCERTAINTY ON  
THE TIMING AND POSITIONING OF THE SURFACE LOW AND HOW FAR NORTH  
PRECIPITATION WILL REACH EARLY THIS WEEKEND.  
 

 
   
LONG TERM /SATURDAY THROUGH WEDNESDAY/
 
 
A BROAD TROUGH IS LOCATED OVER THE GREAT PLAINS AND WILL BEGIN TO  
SLOWLY MOVE EASTWARD THROUGH THE LONG TERM PERIOD. AN UPPER LEVEL  
LOW WILL DEVELOP OVER THE GREAT LAKES ON SUNDAY. THROUGHOUT THE LONG  
TERM PERIOD, WE WILL REMAIN IN THE EASTERN PORTION OF THE TROUGH  
BRINGING SOUTHERNLY FLOW AND INSTABILITY. TEMPERATURES WILL BE  
SEASONABLE WITH HIGHS IN THE 80S AND LOWS IN THE 60S TO 70S.  
 
A SHORTWAVE WILL MOVE NORTHEAST OVER THE MID-ATLANTIC REGION  
SATURDAY MORNING. THERE WILL BE PLENTY OF MOISTURE IN THE ATMOSPHERE  
WITH PRECIPITABLE WATER VALUES NEARING 2 INCHES. SHOWERS AND  
POSSIBLY A FEW THUNDERSTORMS ARE FORECASTED. SOME MODELS HAVE  
INCREASED PRECIPITATION TOTALS WHICH COULD LEAD TO HYDRO ISSUES.  
AFTER THE PASSING OF THE SHORTWAVE, THERE WILL BE TIME FOR DIURNAL  
DRIVEN SHOWERS AND THUNDERSTORMS SATURDAY AFTERNOON.  
 
THE UPPER LEVEL LOW CENTERED OVER THE GREAT LAKES WILL BEGIN  
TRACKING EASTWARD SUNDAY AND INTO NEXT WEEK. A FEW SHOWERS AND A  
POSSIBLE THUNDERSTORM CANNOT BE RULED OUT DUE TO DIURNAL HEATING,  
BUT THE CHANCE FOR HAZARDOUS WEATHER IS DECREASED COMPARED TO  
SATURDAY AND THE REST OF THE LONG TERM PERIOD.  
 
GOING INTO THE WORK WEEK, CHANCES FOR HAZARDOUS WEATHER INCREASE ON  
MONDAY. AS THE AFOREMENTIONED TROUGH MOVES CLOSER TO THE AREA,  
INSTABILITY, MOISTURE, AND FLOW ALOFT WILL INCREASE. SOUTHERLY FLOW  
WILL PROVIDE PLENTY OF MOISTURE WITH PRECIPITABLE WATER VALUED  
GREATER THAN 2 INCHES. OF THE LONG TERM PERIOD, MONDAY HAS THE  
GREATEST THREAT FOR HAZARDOUS WEATHER INCLUDING STRONG THUNDERSTORMS  
AND ISOLATED FLOODING. THERE IS A CHANCE OF DIURNALLY DRIVEN SHOWERS  
AND THUNDERSTORMS ON TUESDAY, BUT THERE IS STILL UNCERTAINTY ABOUT  
THE DETAILS GIVEN HOW FAR OUT IT IS.  
 

 
   
AVIATION /01Z THURSDAY THROUGH MONDAY/
 
 
VFR CONDITIONS ARE EXPECTED FOR THE TERMINALS TONIGHT WITH LIGHT  
WINDS. LIGHT WINDS AND CLEAR SKIES MAY LEAD TO SOME ISOLATED  
INSTANCES OF DENSE FOG, MAINLY AFFECTING THE MRB AND CHO  
TERMINALS. MVFR TO IFR VISIBILITIES WILL BE POSSIBLE AT MRB  
BETWEEN 6Z AND 13Z TOMORROW. WINDS ARE EXPECTED TO BEGIN OUT OF  
THE WEST TO NORTHWEST THIS AFTERNOON AND THEN SLOWLY BECOME MORE  
SOUTHWESTERLY BY THURSDAY AFTERNOON. PATCHY DENSE FOG WILL BE  
POSSIBLE AGAIN THURSDAY EVENING WITH MRB MAINLY AT RISK FOR  
OVERNIGHT RESTRICTIONS. VFR CONDITIONS AND LIGHT WINDS ARE  
EXPECTED FOR FRIDAY.  
 
SUB-VFR CONDITIONS MAY BE POSSIBLE SATURDAY MORNING WITH THE  
POSSIBILITY OF SHOWERS AND STORMS. VFR CONDITIONS ARE EXPECTED  
SATURDAY AFTERNOON AND SUNDAY, BUT AFTERNOON SHOWERS AND STORMS ARE  
POSSIBLE.  
 

 
   
MARINE
 
 
SUBSCA CONDITIONS EXPECTED THROUGH THURSDAY. SMALL CRAFT  
ADVISORIES MAYBE NEEDED ON FRIDAY DUE TO A WEAK CHANNELING FLOW.  
 
WINDS WILL LIKELY STAY BELOW SCA LEVELS SATURDAY AND SUNDAY WITH THE  
EXCEPTION BEING DURING STORMS. IN THE EVENT OF A LOCALIZED STORM,  
INCREASED WINDS ARE POSSIBLE. THUNDERSTORMS ARE POSSIBLE SATURDAY  
MORNING WITH POTENTIAL FOR GUSTY WINDS.  
 

 
   
TIDES/COASTAL FLOODING
 
 
COASTAL FLOODING IS ONGOING OR EXPECTED FOR A FEW AREAS  
(ANNAPOLIS, ST. MARYS, DC SW WATERFRONT), YIELDING COASTAL FLOOD  
ADVISORIES TO BE HOISTED. ST. MARYS LOCATION HAS REACHED MINOR  
FLOOD STAGE AS OF 8 PM WITH THE EXPECTATION OF THE OTHER TWO  
SENSITIVE LOCATIONS TO HIT MINOR FLOOD STAGE TONIGHT AND INTO  
THE OVERNIGHT HOURS. ANOMALIES ARE COMING DOWN A BIT WHICH MAY  
KEEP DC SW WATERFRONT FROM TOUCHING MINOR BUT WE WILL CONTINUE  
TO MONITOR THE TRENDS OVER THE NEXT SEVERAL HOURS. AFTER  
TONIGHT, ANOMALIES CONTINUE TO COME DOWN AND ALLEVIATE TIDAL  
FLOODING CONCERNS FOR THE FORESEEABLE FUTURE.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...COASTAL FLOOD ADVISORY UNTIL 3 AM EDT THURSDAY FOR DCZ001.  
MD...COASTAL FLOOD ADVISORY UNTIL 2 AM EDT THURSDAY FOR MDZ014.  
COASTAL FLOOD ADVISORY UNTIL 10 PM EDT THIS EVENING FOR MDZ017.  
VA...NONE.  
WV...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...JMG/ADM  
NEAR TERM...JMG/ADM  
SHORT TERM...JMG  
LONG TERM...AVS  
AVIATION...AVS/JMG/ADM  
MARINE...AVS/JMG/ADM  
TIDES/COASTAL FLOODING...ADM  
 
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