190  
FXUS61 KLWX 260120  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
920 PM EDT TUE JUL 25 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL BUILD INTO THE MID ATLANTIC TONIGHT BEFORE  
MOVING OFFSHORE WEDNESDAY. A COLD FRONT WILL APPROACH THE AREA  
THURSDAY BEFORE PASSING THROUGH FRIDAY INTO FRIDAY NIGHT. HIGH  
PRESSURE IS EXPECTED TO RETURN FOR THE WEEKEND.  
 

 
   
NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
 
 
HIGH PRESSURE IS CENTERED OVER THE EASTERN GREAT LAKES THIS  
EVENING, AND WITH ITS EASTWARD PROGRESS TONIGHT, A LIGHT ONSHORE  
FLOW WILL EVENTUALLY DEVELOP. UPPER TROUGH AXIS IS MOVING  
OFFSHORE NOW, AND WHILE STRATOCU HAS RETREATED CLOSER TO THE PA  
BORDER, IT MAY NOT COMPLETELY EXIT NORTHEAST MARYLAND. THE  
ONSHORE FLOW BENEATH THE SUBSIDENCE INVERSION MAY ALLOW THE  
CLOUDS TO SPREAD BACK WESTWARD, BUT IT LOOKS LIKE THEY WILL  
REMAIN EAST OF THE BLUE RIDGE (IF EVEN THAT FAR WEST). PATCHY  
FOG MAY DEVELOP WHERE THERE ARE CLEAR SKIES AND LIGHT WINDS  
(MOST LIKELY WESTERN VALLEYS), ALTHOUGH THERE'S NOT A STRONG  
SIGNAL IN MODEL DATA.  
 
LIGHT SHOWERS WHICH HAVE BEEN OBSERVED OVER NEW JERSEY AND  
SURROUNDING AREAS MAY EVENTUALLY SPREAD WESTWARD TO THE  
CHESAPEAKE BAY LATE TONIGHT INTO WEDNESDAY MORNING, WHERE THE  
DEEPEST MOISTURE (ALBEIT STILL ONLY 500 FT OR SO DEEP) WILL  
RESIDE. SPRINKLES MAY BE A BETTER EXPECTATION. LOW TEMPERATURES  
WILL BE IN THE 60S FOR MOST LOCATIONS.  
 

 
   
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/
 
 
LOW FOG/STRATUS WILL MIX OUT DURING THE LATE MORNING OR EARLY  
AFTERNOON WED. NO WX IS EXPECTED IN THE AFTERNOON AS SUBSIDENCE  
INVERSION WILL REMAIN QUITE STRONG. A WARM FRONT WILL LIFT  
THROUGH THE AREA THU WITH WARM HUMID AIR MOVING IN. SCATTERED  
SHOWERS/T-STORMS EXPECTED IN THE AFTERNOON MAINLY IN THE WEST,  
THEN WIDESPREAD SHOWERS/T-STORMS THU NIGHT INTO AT LEAST THE  
FIRST HALF OF FRI AS WAVE OF LOW PRESSURE MOVES ACROSS. STILL  
UNCERTAINTY IN TIMING OF FRONTAL WAVE MOVING ACROSS AND  
INSTABILITY AVAILABLE GIVEN EXPECTED WIDESPREAD CLOUDS AND  
SHOWERS. BOTH A SEVERE AND FLASH FLOODING RISK ARE PRESENT WITH  
FLASH FLOODING HAVING HIGHER ODDS AT THIS TIME GIVEN POTENTIAL  
FOR REPEATED ACTIVITY.  
 

 
   
LONG TERM /SATURDAY THROUGH TUESDAY/
 
 
A CLOSED UPPER LEVEL LOW IS FORECAST TO SWING ACROSS THE MID-  
ATLANTIC REGION SATURDAY. LOW PRESSURE ALONG A COLD FRONT WILL  
LIKELY BE MOVING SOUTH OF THE MID-ATLANTIC REGION. SHOWERS MAY  
LINGER INTO SATURDAY UNTIL THE UPPER LEVEL TROUGH AXIS SWINGS  
THROUGH BY SATURDAY EVENING. HIGH PRESSURE WILL MOVE INTO THE REGION  
BEHIND THE DEPARTING SFC LOW SATURDAY NIGHT. HIGH PRESSURE WILL  
LIKELY BE IN CONTROL INTO THE START OF THE WORK WEEK.  
 

 
   
AVIATION /01Z WEDNESDAY THROUGH SUNDAY/
 
 
BKN STRATOCU MAY NEVER COMPLETELY EXIT BALTIMORE AREA. THE  
QUESTION IS WHETHER MVFR CIGS IN NJ/NE PA WILL MOVE INTO THE  
AREA WITH THE INTRODUCTION OF ONSHORE FLOW. FEEL THIS IS MOST  
LIKELY AT MTN, WITH A CONDITIONAL THREAT (SCT IN TAF) AT BWI,  
DCA, AND IAD. PATCHY LIGHT FOG ALSO POSSIBLE AT CHO AND MRB,  
ALTHOUGH THERE'S NOT A STRONG SIGNAL IN GUIDANCE.  
 
VFR ON WEDNESDAY, WITH ANOTHER CHANCE OF FOG NEAR MRB/CHO  
WEDNESDAY NIGHT.  
 
SHOWERS AND T-STORMS LIKELY THU NIGHT AND FRI WITH FLYING  
RESTRICTIONS LIKELY AT SOME POINT.  
 
IMPROVING WEATHER SATURDAY NIGHT INTO SUN.  
 

 
   
MARINE
 
 
WINDS WILL CONTINUE TO DIMINISH THROUGH WED NIGHT AND  
BEGIN TO STRENGTHEN THU AFTERNOON INTO SAT. SCA CONDITIONS ARE  
POSSIBLE DURING THIS TIME. SMWS MAY ALSO BE REQUIRED DUE TO  
POTENTIAL FOR CONVECTION.  
 
SMALL CRAFT CONDITIONS POSSIBLE SATURDAY INTO SUNDAY, BUT WINDS  
SHOULD BE ON THE DOWNWARD TREND BY SAT NIGHT.  
 

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

 
 

 
SYNOPSIS...LFR  
NEAR TERM...ADS/LFR  
SHORT TERM...LFR  
LONG TERM...HSK  
AVIATION...ADS/HSK/LFR  
MARINE...HSK/LFR  
 
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