334  
FXUS61 KLWX 211421 AAA  
AFDLWX  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
1021 AM EDT SAT OCT 21 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL MOVE EAST INTO THE WESTERN ATLANTIC THROUGH  
MONDAY. LOW PRESSURE AND ITS ATTENDANT COLD FRONT WILL SWEEP  
THROUGH THE AREA TUESDAY. TROUGHING WILL REMAIN OVERHEAD FOR  
MUCH OF THE SECOND HALF OF THE WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
HIGH PRESSURE WILL REMAIN IN CONTROL THROUGH THE WEEKEND. HIGHS  
IN THE MID 70S WITH INCREASING HIGH CLOUDS IN THE AFTERNOON.  
 

 
   
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/
 
 
RIDGING SHIFTS EASTWARD INTO THE NORTH ATLANTIC DURING THE  
SECOND HALF OF THE WEEKEND. MEANWHILE, AN AMPLIFYING RIDGE OVER  
WESTERN NOAM WILL RESULT IN LOWERING HEIGHTS OVER THE EASTERN  
HALF OF THE CONUS BY LATE MONDAY. SOUTHERN STREAM SHORTWAVE  
MOVING NORTHEASTWARD OUT OF THE LOWER MISSISSIPPI RIVER VALLEY  
WILL INTERACT/PHASE WITH DIGGING NORTHERN STREAM WAVE CROSSING  
THE GREAT LAKES RESULTING IN THE DEVELOPMENT OF A SURFACE LOW  
WHICH WILL BRING WIDESPREAD (MUCH NEEDED) RAIN TO THE AREA  
STARTING LATE MONDAY NIGHT. UNTIL THEN, ONLY A MODEST AND  
GRADUAL INCREASE IN CLOUDS WITH ABOVE NORMAL TEMPERATURES WILL  
CONTINUE.  
 

 
   
LONG TERM /TUESDAY THROUGH FRIDAY/
 
 
THE BIG STORY IN THE LONG TERM WILL HAPPEN RIGHT OFF THE BAT AS  
A COLD FRONT CROSSES THE REGION. HAVE UPPED THE POPS TO 90%. THE  
QUESTION AT THE MOMENT IS ONE OF TIMING - MODELS ACTUALLY APPEAR  
TO FAVOR THE FIRST PART OF THE DAY FOR PRECIP WHILE THE  
NUMERICAL GUIDANCE IS MORE IN THE AFTERNOON. FOR NOW WILL KEEP  
POPS AT 90 FOR THE ENTIRE PERIOD. FINE TUNING WILL COME LATER.  
IF THIS DOES COME THROUGH EARLIER THIS WILL LIMIT THUNDERSTORM  
CHANCES.  
 
HIGHS TUESDAY SHOULD REACH THE LOWER 70S. AFTERWARDS MID  
ATLANTIC WILL BE ON THE BACKSIDE OF UPPER LEVEL CYCLONIC FLOW.  
THIS WILL BRING TEMPERATURES BACK DOWN TO MORE NORMAL LATER  
OCTOBER VALUES: HIGHS IN THE 60S, LOW IN THE 40S.  
 

 
   
AVIATION /14Z SATURDAY THROUGH WEDNESDAY/
 
 
LOWER CEILINGS POSSIBLE BY LATE MONDAY NIGHT AS LOW PRESSURE  
APPROACHES AND ATMOSPHERE MOISTENS. SHOWERS DEVELOP WEST TO EAST  
LATE MONDAY NIGHT. LOW-LEVEL WIND SHEAR IS POSSIBLE AS WELL BY  
TUESDAY MORNING AS A SOUTHERLY LOW-LEVEL JET (~40 KNOTS AT 2KFT)  
DEVELOPS. LATEST MODEL GUIDANCE REMAINS CONSISTENT AND IN  
REASONABLY GOOD AGREEMENT AT THIS TIME RANGE.  
 
TUESDAY WILL BE AN INTERESTING DAY AS A COLD FRONT BRINGS  
SHOWERS AND ISOLATED THUDERSTORMS TO ALL TAF SITES. PERIODS OF  
SUB-VFR CEILINGS WILL BE LIKELY, AS WELL AS THE POTENTIAL FOR  
LOW LEVEL SPEED SHEAR AS WELL AS A WIND SHIFT.  
 
CONDITIONS SHOULD IMPROVE TUESDAY NIGHT AND WEDNESDAY.  
 

 
   
MARINE
 
 
LIGHT WINDS ARE EXPECTED AS HIGH PRESSURE REMAINS IN CONTROL  
OF THE WEATHER OVER THE WATERS THROUGH THE WEEKEND. SMALL CRAFT  
ADVISORIES MAY BE NEEDED AS EARLY AS MONDAY AFTERNOON DUE TO  
TIGHTENING PRESSURE GRADIENT/INCREASING SOUTHERLY WINDS AHEAD OF  
DEVELOPING LOW PRESSURE.  
 
TUESDAY WINDS WILL DEFINITELY REACH SCA LEVELS WITH THE  
POTENTIAL FOR GALES, ESPECIALLY ON THE WIDER PART OF THE MD  
CHES BAY. SCA WILL CONTINUE TO BE POSSIBLE TUESDAY NIGHT AND  
WEDNESDAY.  
 

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

 
 

 
UPDATE...LFR  
PRODUCTS...DFH/WOODY!  
 
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