377  
FXUS61 KLWX 141838  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
138 PM EST THU DEC 14 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL BUILD OVERHEAD THROUGH TONIGHT. LOW PRESSURE  
WILL DEVELOP ALONG THE NORTH CAROLINA COAST FRIDAY AND MOVE OUT  
TO SEA FRIDAY NIGHT. HIGH PRESSURE WILL RETURN FOR SATURDAY  
BEFORE WEAK LOW PRESSURE IMPACTS THE AREA EARLY NEXT WEEK.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
COLD FRONT HAS CROSSED THE REGION WITH BLUSTERY NORTHWEST FLOW  
OCCURRING THIS AFTERNOON AREA-WIDE. STRATO-CUMULUS HAS BEEN  
GRADUALLY SCATTERING OUT AND DIMINISHING, AND THIS TREND SHOULD  
CONTINUE FOR THE REST OF THE AFTERNOON. AT THE SAME TIME, HIGH  
CLOUDS WILL ONCE AGAIN BE INCREASING LATE IN THE DAY AND  
OVERNIGHT IN RESPONSE TO A DEVELOPING JET MAX AND NEXT FAST-  
APPROACHING SYSTEM. TEMPERATURES SHOULD STILL BE ABLE TO FALL  
QUITE A BIT OVERNIGHT WITH LOWS IN THE TEENS AND 20S.  
 

 
   
SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/
 
 
NORTHERN STREAM UPPER LEVEL TROUGH WILL BE QUICKLY APPROACHING  
THE REGION DURING THE MORNING FRIDAY. AT THE SAME TIME,  
ADDITIONAL SHORTWAVE ENERGY WILL BE RAPIDLY PUSHING EASTWARD  
FROM THE LOWER MISSISSIPPI RIVER VALLEY AND ACROSS THE  
APPALACHIANS BY THE AFTERNOON. THESE TWO SHORTWAVES ARE EXPECTED  
TO REMAIN UN-PHASED UNTIL WELL OFFSHORE, WHICH WILL KEEP  
ANY PRECIPITATION ON THE LOW SIDE. THAT BEING SAID, SURFACE LOW  
PRESSURE IS EXPECTED TO DEVELOP ALONG THE BAROCLINIC ZONE LEFT  
BY TODAY'S FRONTAL PASSAGE NEAR THE NORTH CAROLINA COASTLINE  
FRIDAY MORNING AND MOVE NORTHEASTWARD AND OFFSHORE FRIDAY  
AFTERNOON. THIS NOW LOOKS LIKE IT WILL BE JUST CLOSE ENOUGH,  
WHEN COMBINED WITH THE FORCING FROM THE NORTHERN STREAM TROUGH  
AND INTENSIFYING JET MAX TO BRING SOME LIGHT SNOW TO PORTIONS OF  
THE REGION ON FRIDAY. MODEL DIFFERENCES STILL EXIST WITH  
RESPECT TO WESTWARD EXTENT, BUT THE TRENDS TODAY HAVE BEEN FOR  
HIGH CHANCES FOR OUR REGION.  
 
HAVE INCREASED SNOW PROBABILITIES TO LIKELY ACROSS PORTIONS OF  
SOUTHERN MARYLAND AND TO CHANCE AS FAR WEST AS THE I-95 CORRIDOR  
FOR LATE FRIDAY MORNING, PEAKING IN THE AFTERNOON, AND ENDING  
DURING THE EARLY EVENING. HAVE SHOWN ACCUMULATIONS OF LESS THAN  
ONE INCH FOR THE MARYLAND COUNTIES THAT BORDER THE CHESAPEAKE  
BAY, GOING TO A TRACE OR LESS WEST OF I-95. HOWEVER, UNCERTAINTY  
IS STILL QUITE HIGH AT THIS TIME. HIGHS DURING THE DAYTIME  
REMAIN ON THE COLD SIDE, IN THE 30S AREA-WIDE.  
 
FLOW WILL TURN NORTHWEST FOLLOWING THE SYSTEM'S DEPARTURE FRIDAY  
NIGHT, WITH A BRIEF PERIOD OF UPSLOPE SNOW SHOWERS LIKELY ALONG  
THE ALLEGHENY FRONT. ACCUMULATIONS WILL BE LOW THOUGH AS  
MOISTURE WILL BE QUITE SHALLOW, UP TO ABOUT AN INCH OF SNOW OR  
SO. LOWS FRIDAY NIGHT IN THE 20S.  
 
HIGH PRESSURE WILL THEN BUILD IN SOUTH OF THE REGION ON  
SATURDAY, WITH DRY CONDITIONS EXPECTED. HIGHS SATURDAY IN THE  
UPPER 30S TO MID 40S AND LOWS SATURDAY NIGHT IN THE 20S.  
 

 
   
LONG TERM /SATURDAY THROUGH THURSDAY/
 
 
HIGH PRESSURE, CENTERED TO OUR SOUTH ON SUNDAY,  
WILL GENERATE SOUTHERLY FLOW OVER OUR REGION, ALLOWING FOR HIGH  
TEMPERATURES TO REACH THE MID TO UPPER 40S FOR MOST OF OUR CWA. A  
SHORTWAVE TROUGH WILL MOVE ACROSS THE AREA SUNDAY NIGHT INTO EARLY  
MONDAY. THIS WILL INCREASE POPS OVER OUR AREA, BUT STILL UNCERTAIN  
HOW MUCH QPF WILL BE ASSOCIATED WITH IT AND ANY P-TYPES.  
 
GUIDANCE SUGGESTS THAT MID TO UPPER LEVEL ENERGY COULD BRING A  
SLIGHT CHANCE OF PRECIPITATION BETWEEN MONDAY AND TUESDAY WITH  
STILL ABOVE NORMAL TEMPERATURES -REACHING THE 50S. A FRONT COULD  
BRING A CHANCE OF PRECIPITATION TUESDAY NIGHT INTO EARLY WEDNESDAY.  
HIGH PRESSURE BUILDS BEHIND THIS FRONT WEDNESDAY INTO THURSDAY  
BRINGING DRY AND MORE NEAR-NORMAL HIGH TEMPERATURES.  
 

 
   
AVIATION /18Z THURSDAY THROUGH TUESDAY/
 
 
PREDOMINANTLY VFR CONDITIONS ARE EXPECTED THROUGH SATURDAY  
NIGHT. GUSTY NORTHWEST WINDS UP TO AROUND 25 KNOTS ARE EXPECTED  
THROUGH TODAY, DIMINISHING BY SUNSET. A PERIOD OF LIGHT SNOW OR  
SNOW SHOWERS ARE POSSIBLE ACROSS THE EASTERN TERMINALS LATER  
FRIDAY...BUT CONFIDENCE IS LOW AT THIS TIME. THIS MAY BRING A  
PERIOD OF REDUCTIONS, WITH HIGHEST CHANCES AT DCA/BWI/MTN. HIGH  
PRESSURE WILL THEN BUILD IN FOR SATURDAY.  
 
MAINLY VFR CONDITIONS EXPECTED EARLY SUNDAY INTO TUESDAY.  
HOWEVER PERIODS OF SUB-VFR CONDITIONS ARE POSSIBLE AT TIMES AS  
SHOWERS COULD MOVE THROUGH THE TERMINALS.  
 

 
   
MARINE
 
 
SCA IS IN EFFECT THROUGH THE REST OF THE AFTERNOON FOR ALL  
WATERS WITH GUSTY NORTHWEST WINDS FOLLOWING THE FRONTAL PASSAGE  
THIS MORNING. WINDS WILL GRADUALLY LESSEN THIS EVENING AND  
TONIGHT, BUT WILL LIKELY REMAIN GUSTY ENOUGH OVER MUCH OF THE  
CHESAPEAKE BAY AND LOWER TIDAL POTOMAC TO KEEP SCA GOING UNTIL  
MIDNIGHT. WINDS WILL THEN DROP BELOW SCA CRITERIA LATER TONIGHT  
AND REMAIN THAT WAY THROUGH FRIDAY AS HIGH PRESSURE MOVES  
OVERHEAD.  
 
LOW PRESSURE WILL THEN DEVELOP AND MOVE OUT TO SEA LATER  
FRIDAY. GUSTY WINDS WILL DEVELOP BEHIND THE FRONT FRIDAY NIGHT  
INTO SATURDAY. SCA GOES INTO EFFECT FRIDAY NIGHT AND MAY NEED TO  
BE EXTENDED INTO SATURDAY.  
 
WINDS ARE EXPECTED TO STAY BELOW SMALL CRAFT ADVISORY THRESHOLD  
SUNDAY INTO TUESDAY. WINDS COULD INCREASE TUESDAY NIGHT.  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR ANZ531>534-  
537-539>541-543.  
SMALL CRAFT ADVISORY FROM 8 PM FRIDAY TO 6 AM EST SATURDAY FOR  
ANZ530>534-537-539>541-543.  
SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ530-  
535-536-538-542.  
 

 
 

 
SYNOPSIS...MM  
NEAR TERM...MM  
SHORT TERM...MM  
LONG TERM...IMR  
AVIATION...MM/IMR  
MARINE...MM/IMR  
 
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