585  
FXUS61 KLWX 100904  
AFDLWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
404 AM EST MON DEC 10 2018  
   
SYNOPSIS
 
 
LOW PRESSURE WILL PULL AWAY FROM THE CAROLINA COAST TODAY AS  
HIGH PRESSURE BUILDS IN FROM THE OHIO VALLEY. THIS AREA OF HIGH  
PRESSURE WILL RETREAT TO OFFSHORE OF NEW ENGLAND THROUGH THE END  
OF THE WEEK AS A LARGE AREA OF LOW PRESSURE DEVELOPS OVER THE  
TENNESSEE VALLEY AND HEADS TOWARD THE REGION FOR THE WEEKEND.  
 

 
   
NEAR TERM /THROUGH TUESDAY/
 
 
LATEST SURFACE ANALYSIS SHOWS LOW PRESSURE OVER THE ATLANTIC  
JUST EAST OF CAPE HATTERAS, HEADING EASTWARD INTO THE OPEN  
OCEAN. HIGH PRESSURE IS CENTERED OVER THE CENTRAL PLAINS, BUT  
EXTENDS EASTWARD INTO THE SOUTHERN GREAT LAKES, WITH A SECOND  
HIGH PRESSURE CENTERED OVER SOUTHERN QUEBEC AND ONTARIO. ALOFT,  
SEVERAL DEEP TROUGHS/CLOSED LOWS ARE LOCATED ACROSS THE REGION,  
WITH ONE NEAR THE SOUTHERN APPALACHIANS, ANOTHER IN THE CENTRAL  
PLAINS, AND A THIRD JUST NORTH OF MAINE.  
 
THROUGH TODAY, ALL THESE FEATURES WILL PROGRESS IN A GENERAL  
EAST-SOUTHEAST FASHION, ALLOWING INCLEMENT WEATHER TO CONTINUE  
PUSHING AWAY FROM US AND LETTING HIGH PRESSURE BUILD INTO THE  
REGION. CLOUDS WILL BREAK FOR INCREASING SUNSHINE, THOUGH A  
LITTLE PATCHY FOG COULD OCCUR EARLY THIS MORNING BEFORE THE SUN  
COMES OUT, MAINLY IN THE SHENANDOAH VALLEY AND CENTRAL VA. WHERE  
SNOW DID NOT FALL ON SUNDAY, TEMPS SHOULD REBOUND TO AROUND 40,  
BUT IT WILL LIKELY GET STUCK IN THE 30S ACROSS CENTRAL VA  
THANKS TO THE SNOW COVER. THAT SAID, WE EXPECT TEMPS TO REACH  
ABOVE FREEZING NEARLY EVERYWHERE, SO THERE SHOULD BE SOME  
MELTING.  
 
TONIGHT AND TUESDAY, HIGH PRESSURE CONTINUES SLOWLY BUILDING  
EASTWARD INTO THE REGION. THIS SHOULD KEEP IT DRY WITH  
DIMINISHING WINDS AS THE LOW CONTINUES PULLING AWAY. AREAS WITH  
SIGNIFICANT SNOW COVER COULD GET RATHER COLD TONIGHT, WHILE  
OTHER LOCATIONS LIKELY STAY IN THE 20S TONIGHT. TEMPS WILL  
MODERATE A BIT ON TUESDAY WITH A BIT OF WARM ADVECTION ALOFT AND  
MORE SUNSHINE, SO EXPECT TEMPS TO BE A FEW DEGREES ABOVE TODAY'S  
READINGS. THAT SAID, LINGERING SNOW IN CENTRAL VA AND ADJACENT  
AREAS WILL LIKELY KEEP TEMPS DOWN A BIT COMPARED TO LOCATIONS  
FURTHER NORTH THAT ARE SNOW-LESS.  
 

 
   
SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/
 
 
A WEAK SHORTWAVE AND COLD FRONT WILL CROSS THE REGION TUESDAY  
NIGHT. FORCING AND MOISTURE LOOK SO LIMITED THAT IT SEEMS LIKE  
IT WILL BE VERY DIFFICULT TO GET ANY PRECIP WITH IT, BUT SOME  
GUIDANCE HINTS THAT A LITTLE UPSLOPE FLURRY ACTIVITY COULD  
DEVELOP. LOWS WILL BE IN THE 20S FOR THE MOST PART.  
 
DESPITE THE FRONT'S PASSAGE, THERE IS MINIMAL COLD AIR BEHIND  
IT, WITH TEMPERATURES EXPECTED TO REBOUND BACK INTO THE LOW 40S  
ON WEDNESDAY WITH SOME SUNSHINE.  
 
WEDNESDAY NIGHT, MOST GUIDANCE IS DRY, BUT THE EC HAS NOW FOR  
TWO RUNS IN A ROW DEPICTED A WEAK DISTURBANCE COMING IN FROM THE  
WEST WITH THE POTENTIAL FOR A FEW SNOW SHOWERS. WILL NEED TO  
WATCH IT, BUT FOR NOW HAVE KEPT MOST AREAS DRY. LOWS LIKELY IN  
THE 20S AGAIN.  
 

 
   
LONG TERM /THURSDAY THROUGH SUNDAY/
 
 
BY THURSDAY, AN AMPLIFIED TROUGH AXIS WILL BE IN THE PLAINS,  
APPROACHING THE MISSISSIPPI RIVER VALLEY. DOWNSTREAM RIDGING  
WILL RESIDE ACROSS THE SOUTHEASTERN UNITED STATES. HOWEVER,  
SHORTWAVE ENERGY WILL BE CROSSING THE GREAT LAKES HEADED TOWARD  
NORTHERN NEW ENGLAND. HOWEVER, THE ECMWF IS MUCH MORE AMPLIFIED  
THAN THE GFS OR GDPS. GIVEN THE PRESENCE OF AN UPPER LEVEL  
JETLET, THAT PROVIDES ENOUGH LIFT FOR A POCKET OF PRECIPITATION.  
THERMALLY, THE THE LOWER LAYERS OF THE ATMOSPHERE WOULD BE COLD  
ENOUGH FOR SNOW AT THAT TIME, BUT ITS NOT CLEAR THAT THE MID  
LEVEL IS. FURTHER, BOUNDARY LAYER TEMPERATURES SHOULD BE  
RISING...UNLESS THERE IS SUFFICIENT WET BULB COOLING TO OFFSET  
THE DIURNAL TREND. AM NOT CONFIDENT THAT THERE WILL BE. AT THE  
SAME TIME, FEEL SOME CREDENCE FOR THE ECMWF OUTPUT WARRANTED.  
RESULT WILL BE A 20% POP FOR THE DATABASE, WHICH WON'T BE  
REFLECTED IN TEXT FORECASTS. AM GOING WITH A RAIN/SNOW MIX FOR  
WEATHER TYPE.  
 
THE MAIN BATCH OF PRECIPITATION WILL ARRIVE WITH THE TROUGH  
AXIS, PRIMARILY FRIDAY-FRIDAY NIGHT. ONSET LIKELY TO BE PRE-DAWN  
FRIDAY, AGAIN MAKING PRECIP TYPE A QUESTION. OTHERWISE, WE'RE  
LOOKING AT A PERIOD OF RAIN, WITH PLENTY OF MOISTURE TO WORK  
WITH...ESPECIALLY FOR MID-DECEMBER. OPERATIONAL AND ENSEMBLE  
FORECASTS CONTINUE TO SUPPORT FORECAST SOLUTIONS SUGGESTING AN  
INCH OR MORE OF RAINFALL.  
 
IT REMAINS TO BE SEEN HOW QUICKLY THIS PRECIPITATION WILL EXIT  
AS A CUT-OFF LOW WILL DEVELOP AT THE BASE OF THE TROUGH. THERE  
IS AT LEAST SOME CONSISTENCY THAT LOW PRESSURE WILL LINGER INTO  
THE WEEKEND. THAT MAKES EITHER THE POP AND/OR TEMPERATURE  
FORECASTS LOWER CONFIDENCE.  
 

 
   
AVIATION /09Z MONDAY THROUGH FRIDAY/
 
 
PATCHY FOG MAY AFFECT MRB AND CHO EARLY THIS MORNING THANKS TO  
LIGHT WINDS AND RADIATIONAL COOLING UNDER CLEARING SKIES.  
OTHERWISE, EXPECT VFR TO PREVAIL THROUGH WEDNESDAY NIGHT AT ALL  
TERMINALS AS HIGH PRESSURE DOMINATES. WINDS WILL GENERALLY BE  
BELOW 20 KNOTS THROUGH WEDNESDAY NIGHT.  
 
CONFLICTING GUIDANCE SOLUTIONS ON THURSDAY LEAD TO A LOWER  
CONFIDENCE FLIGHT RESTRICTION FORECAST. THERE IS A SMALL  
POTENTIAL THAT MVFR/IFR CONDITIONS MAY OVERSPREAD THE TERMINALS  
WITH UPPER LEVEL ENERGY. THE MORE LIKELY TIME PERIOD FOR FLIGHT  
RESTRICTIONS WILL COME ON FRIDAY IN RAIN. WILL NEED TO WATCH  
ONSET TIMING, BUT AT THIS TIME IT APPEARS MORE LIKELY THAN NOT  
ANY COLD AIR WILL EXIT THE TERMINALS PRIOR TO THE ARRIVAL OF  
RAIN.  
 

 
   
MARINE
 
 
SCA FOR THE MIDDLE BAY/LOWER POTOMAC INTO THIS AFTERNOON,  
DWINDLING AFTER THAT AS THE SYSTEM NEAR THE CAROLINA COAST PULLS  
AWAY OUT TO SEA AND HIGH PRESSURE BUILDS IN. SMALL CHANCE SOME  
SCA LEVEL GUSTS LINGER INTO THE EVENING BUT OVERALL EXPECT SUB-  
SCA STARTING TONIGHT AND CONTINUING THROUGH WEDNESDAY NIGHT AS  
HIGH PRESSURE DOMINATES.  
 
THE PRESSURE GRADIENT WILL INCREASE ON FRIDAY AS LOW PRESSURE  
STRENGTHENS NEAR THE WATERS. SMALL CRAFT ADVISORY CONDITIONS  
POSSIBLE.  
 

 
   
CLIMATE
 
 
RAINFALL TOTALS CONTINUE TO CREEP UPWARD, WITH BALTIMORE  
SETTING THE ANNUAL RECORD ALREADY. HERE ARE THE CURRENT RANKINGS  
FOR WETTEST YEAR ON RECORD (THROUGH DECEMBER 9TH):  
 
WASHINGTON DC AREA (DCA)  
1. 61.33 INCHES (1889)  
2. 60.83 INCHES (2003)  
3. 60.78 INCHES (2018)  
4. 60.09 INCHES (1878)  
 
WEATHER RECORDS FOR THE WASHINGTON DC AREA HAVE BEEN KEPT AT  
WHAT IS NOW RONALD REAGAN WASHINGTON NATIONAL AIRPORT (DCA)  
SINCE 1945. PRECIPITATION RECORDS OBSERVED DOWNTOWN EXTEND THE  
PERIOD OF RECORD BACK TO 1871.  
 
BALTIMORE MD AREA (BWI)  
1. 65.67 INCHES (2018)  
2. 62.66 INCHES (2003)  
 
WEATHER RECORDS FOR THE BALTIMORE MD AREA HAVE BEEN KEPT AT  
WHAT IS NOW BALTIMORE-WASHINGTON INTERNATIONAL THURGOOD MARSHALL  
AIRPORT (BWI) SINCE 1950. PRECIPITATION RECORDS OBSERVED  
DOWNTOWN EXTEND THE PERIOD OF RECORD BACK TO 1871.  
 
DULLES VA AREA (IAD)  
1. 65.67 INCHES (2003)  
2. 61.30 INCHES (2018)  
3. 59.05 INCHES (1972)  
 
WEATHER RECORDS HAVE BEEN KEPT AT WHAT IS NOW WASHINGTON DULLES  
INTERNATIONAL AIRPORT (IAD) SINCE 1960.  
 
NOTE: ALL CLIMATE DATA ARE CONSIDERED PRELIMINARY UNTIL  
REVIEWED BY THE NATIONAL CENTERS FOR ENVIRONMENTAL INFORMATION  
(NCEI).  
 

 
   
LWX WATCHES/WARNINGS/ADVISORIES
 
 
DC...NONE.  
MD...NONE.  
VA...NONE.  
WV...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR ANZ532-  
533-540>542.  
SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ534-  
537-543.  
SMALL CRAFT ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR  
ANZ536.  
 

 
 

 
SYNOPSIS...RCM  
NEAR TERM...RCM  
SHORT TERM...RCM  
LONG TERM...HTS  
AVIATION...RCM/HTS  
MARINE...RCM/HTS  
CLIMATE...LWX  
 
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