145  
FXUS61 KLWX 071856  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
256 PM EDT TUE JUL 7 2020  
   
SYNOPSIS
 
 
HIGH PRESSURE REMAINS OFFSHORE THROUGH WEDNESDAY, PUMPING WARM AND  
HUMID AIR INTO THE REGION, ALONG WITH DAILY CHANCES FOR SHOWERS AND  
THUNDERSTORMS. CUTOFF LOW PRESSURE WILL DEVELOP TO THE SOUTH ON  
WEDNESDAY AND IT MAY IMPACT THE AREA LATER IN THE WEEK. AN  
UPPER-LEVEL TROUGH WILL MOVE INTO AREA SATURDAY WHILE A COLD  
FRONT PASSES THROUGH. THE UPPER-LEVEL TROUGH WILL HANG AROUND  
FOR EARLY NEXT WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
THIS MORNING'S CLOUD DECK HAS ERODED TO NORTHEAST MARYLAND. A  
CUMULUS FIELD HAS DEVELOPED WHERE INSOLATION HAS BEEN STRONGEST...  
ACROSS CENTRAL VIRGINIA, THE SHENANDOAH VALLEY AND THE POTOMAC  
HIGHLANDS. SOME OF THE MORE ENERGETIC UPDRAFTS APPEAR TO NEAR  
HARDY AND GRANT COUNTIES.  
 
WHILE AMPLE INSTABILITY PRESENT (2000-3000 J/KG SBCAPE) WHERE  
HEATING HAS BEEN THE BEST AND A WIDESPREAD 1000 J/KG DCAPE,  
FORCING FACTORS REMAIN DISORGANIZED AND HIGHLY MESOSCALE-  
DRIVEN... NAMELY BOUNDARIES FROM DIFFERENTIAL HEATING, BAY  
INTERACTIONS, AND TERRAIN CIRCULATIONS. FLOW WEAK AND MEAN LAYER  
LAPSE RATES THUS FAR UNIMPRESSIVE. STILL BELIEVE THAT SCATTERED  
TO NUMEROUS THUNDERSTORMS WILL CONTINUE TO DEVELOP. GIVEN THE  
AVAILABLE FUEL, A FEW STRONG THUNDERSTORMS POSSIBLE. WIND GUSTS  
APPEARS TO BE THE BIGGEST SEVERE CONCERN, AND THAT'S LIKELY TO  
BE LOCALIZED. HEAVY RAINFALL MAY BE THE GREATER CONCERN GIVEN  
WEAK FLOW WOULD LEAD TO SLOW MOVERS. IF STORMS DEVELOP ALONG  
I-95, WHERE ANTECEDENT CONDITIONS NEARLY SATURATED, THAT COULD  
BE A PARTICULAR CONCERN. AT THIS POINT, CONFIDENCE IN COVERAGE  
INSUFFICIENT TO JUSTIFY A FLOOD WATCH. WE WILL CONTINUE TO  
MONITOR FOR THAT.  
 
SINCE THIS ACTIVITY WILL HAVE A SIZEABLE DIURNAL COMPONENT,  
BELIEVE THERE WILL BE FAIRLY RAPID DISSIPATION THIS EVENING.  
WILL KEEP FORECAST DRY AFTER MIDNIGHT. SINCE DEWPOINTS IN THE  
UPPER 60S-LOWER 70S, LOW TEMPERATURES WILL REMAIN LIKEWISE.  
 

 
   
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
 
 
WEDNESDAY AND THURSDAY LOOK RATHER DISORGANIZED FROM A SYNOPTIC  
STANDPOINT. THERE WILL BE BROAD RIDGING ACROSS THE GREAT  
LAKES/NORTHEAST/MID ATLANTIC WHILE AN UPPER LEVEL LOW DEVELOPS  
OVER THE SOUTHEAST. CONSEQUENTLY DIURNAL CONVECTION REMAINS A  
POSSIBILITY. HOWEVER, IF SURFACE LOW PRESSURE DEVELOPS OFFSHORE,  
WHICH GUIDANCE IS HINTING AT FOR THURSDAY, THE LOCAL AREA WOULD  
BE WITHIN A SUBSIDENT REGION. THEREFORE, WILL BE MAINTAINING  
CHANCE POPS FOR WEDNESDAY, GREATEST IN THE MOUNTAINS WITH  
OROGRAPHIC INFLUENCE, AND A SLIGHT CHANCE ON THURSDAY. SINCE  
THERE ISNT A SOURCE FOR THERMAL ADVECTION, KEPT TEMPERATURE  
FORECASTS SIMILAR.  
 

 
   
LONG TERM /FRIDAY THROUGH TUESDAY/
 
 
THE FRIDAY THROUGH THIS WEEKEND PERIOD WILL BE FAIRLY ACTIVE AS  
MULTIPLE SYSTEMS POTENTIALLY IMPACT OUR REGION. A COASTAL LOW WILL  
BE TRACKING NORTHWARD ALONG THE EAST COAST THIS WEEK AND WILL BE  
SITUATED NEAR OUR REGION TO THE EAST ON FRIDAY. THERE REMAINS SOME  
UNCERTAINTY ON THE EXACT TRACK OF THIS SYSTEM AND IF IT TRACKS  
FURTHER WESTWARD, THE HEAVY RAIN THREAT WILL INCREASE FOR PARTS OF  
OUR REGION. AS THERE WILL BE CONTINUE CHANCES FOR SHOWERS AND  
THUNDERSTORMS THROUGHOUT THIS WEEK AND COUPLED WITH THE HEAVY RAIN  
WE RECEIVED OVER THE PAST 36 HOURS, ANY ADDITIONAL RAINFALL TOWARD  
THE END OF THE WEEK COULD LEAD TO AN INCREASED FLOOD THREAT. AS OF  
RIGHT NOW WE ARE FORECAST TO BE ON THE WEST SIDE OF THE STORM WHICH  
WILL MEAN A MORE NORTHERLY FLOW AND COOLER, DRIER CONDITIONS WHICH  
SHOULD LIMIT THE THREAT FOR THUNDERSTORMS ESPECIALLY WITH THE LACK  
OF AN UPPER LEVEL LIFTING MECHANISM.  
 
THE COASTAL LOW IS FORECAST TO LIFT TO OUR NORTHEAST EARLY ON  
SATURDAY. AN UPPER LEVEL TROUGH IS FORECAST TO DROP DOWN INTO OUR  
AREA FROM THE UPPER PLAINS/MIDWEST. A COLD FRONT ASSOCIATED WITH  
THIS SYSTEM WILL MOVE EASTWARD THROUGH OUR REGION SATURDAY INTO  
SUNDAY. AHEAD OF THIS BOUNDARY, WINDS WILL BECOME SOUTHERLY LEADING  
A RETURN FLOW OF WARM AND MOIST AIR INTO OUR REGION. INCREASING  
MOISTURE AND TEMPS WILL LEAD TO INCREASED INSTABILITY AND COUPLED  
WITH THE LIFT FROM THE FRONT COULD LEAD TO A THUNDERSTORM THREAT FOR  
THIS WEEKEND. THE MODELS HAVE THE FRONT THROUGH OUR REGION BY SUNDAY  
MORNING BUT THE UPPER LEVEL TROUGH OVERHEAD COULD LEAD TO CONTINUE  
CHANCES FOR PRECIP INTO THE AFTERNOON PERIODS SUNDAY.  
 
HIGH PRESSURE TRIES TO BUILD OVER OUR REGION BRIEFLY ON MONDAY  
BEFORE ANOTHER POTENTIAL LOW APPROACHES FROM THE SOUTH.  
 

 
   
AVIATION /18Z TUESDAY THROUGH SUNDAY/
 
 
LOW CLOUDS STARTING TO BREAK (CEILINGS REMAIN AT DCA/BWI/MTN)  
AND CONVECTION CUMULUS BEGINNING TO DEVELOP. SCATTERED  
SHOWERS/THUNDERSTORMS REMAIN A POSSIBILITY FOR LATE AFTERNOON  
INTO EARLY EVENING. HAVE A FEW HOURS WINDOW (2100-2400 UTC)  
WHERE THE RISK IS THE GREATEST IN THE TAF. HOWEVER, BASED ON  
COVERAGE, THE CONFIDENCE IN A DIRECT IMPACT ON THE LOWER SIDE.  
BRIEF IFR POSSIBLE IF IT DID.  
 
LOCAL FOG A POSSIBILITY TONIGHT, BUT ULTIMATELY THAT WILL BE  
BASED ON CONVECTIVE EVOLUTION. AT THIS POINT HAVE A BRIEF MVFR  
RISK AT MRB/CHO WHICH ARE PREFERRED WRT CLIMO.  
 
FORECAST THREATS SIMILAR WED-THU, ALTHOUGH THE RISK OF  
THUNDERSTORMS PERHAPS A PINCH LESS EACH DAY.  
 
PERIODS OF SUBVFR CONDITIONS WILL BE POSSIBLE FRIDAY THROUGH THIS  
WEEKEND AS MULTIPLE SYSTEMS BRING INCREASE CHANCES FOR RAIN AND  
THUNDERSTORMS.  
 

 
   
MARINE
 
 
MOST MESOSCALE GUIDANCE SUGGESTING THAT THERE WILL BE A RISK OF  
SOUTH CHANNELING IN MID SECTION OF THE CHESAPEAKE BAY/TANGIER  
SOUND/MOUTH OF THE POTOMAC, WITH 20-25 KT PRESENT IN THE LOW  
LEVEL FLOW. IT'S A BIT UNCERTAIN ON MOMENTUM TRANSFER, BUT  
BELIEVE THE RISK IS SUFFICIENT TO RAISE A SMALL CRAFT ADVISORY  
LATE THIS AFTERNOON INTO THIS EVENING BETWEEN SANDY POINT AND  
THE MARYLAND-VIRGINIA LINE.  
 
OVERALL FLOW WILL REMAIN WEAK WEDNESDAY-THURSDAY, ALTHOUGH THERE  
ARE SUBTLE SIGNALS AT CHANNELING IN THE DRUM POINT-SMITH POINT  
AND TANGIER SOUND AREA NIGHTLY.  
 
SMALL CRAFT ADVISORIES MAY BE NEEDED FRIDAY DUE TO A NORTHERLY FLOW  
AND COASTAL LOW OFF TO THE EAST. SUBSCA CONDITIONS EXPECTED AT THIS  
TIME FOR SATURDAY.  
 

 
   
TIDES/COASTAL FLOODING
 
 
WATER LEVELS WILL REMAIN ELEVATED OVER THE NEXT COUPLE OF DAYS.  
HOWEVER, CONFIDENCE IN ANY INUNDATION REMAINS LOW. CAUTION  
STAGES MAY BE REACHED, ESPECIALLY DURING THE MORNING CYCLE WHICH  
IS THE HIGHER ASTRONOMICAL TIDE.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EDT WEDNESDAY FOR ANZ532>534-  
537-543.  
 

 
 

 
SYNOPSIS...BJL  
NEAR TERM...HTS  
SHORT TERM...HTS  
LONG TERM...JMG  
AVIATION...HTS/JMG  
MARINE...HTS/JMG  
TIDES/COASTAL FLOODING...HTS  
 
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