Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 220231 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
931 PM EST SUN DEC 21 2014

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE COAST OVERNIGHT...AHEAD OF A WEAK
COASTAL LOW PRESSURE SYSTEM OVER THE SOUTHERN ATLANTIC. THE LOW
WILL TRACK UP THE MID-ATLANTIC COAST MONDAY INTO TUESDAY. A STRONG
COLD FRONT WILL APPROACH THE AREA WEDNESDAY BEFORE PASSING THROUGH
WEDNESDAY NIGHT. BREEZY CONDITIONS ON THURSDAY...THEN HIGH
PRESSURE WILL BUILD BACK INTO THE REGION TO CLOSE OUT THE WEEK.

&&

.NEAR TERM /THROUGH MONDAY/...
HIGH TEMPS ACROSS AREA WERE ON PAR W/ AVG VALUES FOR THIS...THE
WINTER SOLSTICE. HOWEVER...AFTER ONLY REACHING THE LOW-MID 40S
EARLIER THIS AFTN MOST AREAS ARE BACK BELOW FREEZING...WELL AHEAD
OF ANY INCOMING PRECIP. CLEAR SKIES AND CALM SFC WINDS EASILY
ALLOWING TEMPS TO DROP DOWN TOWARD CURRENT DEWPOINTS VALUES IN THE
LOWS 20S. SLOW AND STEADY DEVELOPMENT OF A COASTAL LOW PRES SYSTEM
OVER THE SRN ATLC STATES IS THE NEXT FEATURE TO MONITOR...AS DENSE
CLOUD COVER AND LIGHT/SCATTERED SHOWERS ARE EXPECTED TO MOVE UP
THE EASTERN SEABOARD OVERNIGHT.

MANY SMALLER-SCALE ELEMENTS ARE COMING TOGETHER OVER A MUCH LARGER
PICTURE AND WILL CONTINUE TO DO SO WELL INTO THE MIDDLE OF THE
CURRENT WEEK. NEARLY TWO-THIRDS OF THE CONUS WILL BE AFFECTED IN
SOME PART OF THESE ELEMENTS OR A LARGER COMBINATION OVER THE NEXT
FEW DAYS. THIS FIRST PIECE IS THE INITIAL GROUPING OF A SHORTWAVE
OVER THE SRN ATLC COAST AND A TROUGH STILL WELL BACK TO THE WEST.
THE TROUGH WILL FORCE THE ATLC MOISTURE UP THE COAST...THIS FIRST
BATCH AFFECTING OUR AREA MONDAY INTO EARLY TUE - W/ THE MORE
MOISTURE-LADEN SYSTEM MOVING THRU THE REGION ON THU.

SUCH A COMPLEX SYSTEM OF WAVES...TROUGHS...SYNOPTIC FEATURES
INTERACTING W/ EACH OTHER OVER A MULTI-DAY PERIOD CAN SHOW VERY
VARIED DEPICTIONS AMONGST THE GUIDANCE SUITE. HOWEVER...MOST
MEMBERS IN BOTH THE ENSEMBLE AND DETERMINISTIC FIELDS ARE IN
FAIRLY GOOD AGREEMENT EARLY ON W/ THE INCOMING PRECIP. THE NAM
STILL THE COLDER MODEL IN TERMS OF TEMPS/DEWPOINTS BUT IS NOW
COMING INTO BETTER AGREEMENT W/ GFS/EURO ON PRECIP TIMING.

THE I-95 CORRIDOR WHICH IS NORMALLY A DIVIDING LINE OF NEAR-
FREEZING TEMPS W/ INCOMING PRECIP IS NO DIFFERENT FOR THIS
INCOMING WAVE MON MORNING. HOWEVER...HI-RES AND NEAR TERM GUIDANCE
DOES NOT HAVE THE FIRST BATCHES OF LIGHT PRECIP ARRIVING UNTIL
POST-DAWN AND ACTUALLY MORE TOWARD MID-LATE MRNG...ESPECIALLY
FURTHER NORTH. TEMPS WILL STILL BE BORDERLINE FREEZING/SUB-
FREEZING ACROSS THE PIEDMONT/FOOTHILLS - WHERE THE FREEZING RAIN
ADZY IS IN EFFECT - BUT THE I-95 CORRIDOR MAY ONLY SEE A BRIEF
ONSET PERIOD OF A FZRA/SLEET MIX...THEN TEMPS WILL RISE EVEN A
COUPLE MORE DEGREES HEADING INTO THE LATE MRNG/EARLY AFTN.

THE SHEN VLY AND BLUE RIDGE WILL LIKELY BE ON THE WRN/NRN
PERIPHERY OF THE PRECIP BUT WILL BE MOST PRONE TO HOLDING ONTO THE
SUB-FREEZING CONDITIONS WELL INTO THE MRNG HRS AND EVEN THRU THE
AFTN POTENTIALLY. THE AMOUNTS AND POTENTIAL FOR PRECIP WILL BE THE
MAIN QUESTION BUT THERE IS GOOD CONFIDENCE THAT THESE AREAS WILL
HAVE TROUBLE SEEING TEMPS ABOVE FREEZING FOR VERY LONG TMRW.
LINGERING POCKETS OF DRIZZLE AND LIGHT/SCATTERED RAIN WILL BE THE
REASON FOR AN EXPANSION/EXTENSION OF THE ADZY FOR ALL/MOST OF THE
SHEN VLY/POTOMAC HIGHLANDS/BLUE RIDGE.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
LIGHT PRECIPITATION WILL CONTINUE MONDAY NIGHT INTO TUESDAY MORNING.
THE BIG QUESTION WILL BE HOW LONG THE CAD WEDGE WILL REMAIN IN
PLACE. THERE IS STILL POTENTIAL FOR TEMPERATURES TO REMAIN AT OR
BELOW FREEZING MAINLY WEST OF THE BLUE RIDGE LEAVING THE POTENTIAL
FOR LIGHT FREEZING RAIN TO CONTINUE. TO THE EAST OF THE BLUE RIDGE
AND ACROSS THE METRO AREAS...WARMER AIR WILL LIKELY WIN OUT KEEPING
PRECIPITATION IN THE FORM OF RAIN. A BRIEF RESPITE FROM THE
PRECIPITATION IS POSSIBLE TUESDAY AFTERNOON/EVENING BEFORE THE NEXT
ROUND OF RAINFALL MOVES IN FROM THE WEST LATER TUESDAY NIGHT.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
STRONG COLD FRONT CROSSING THE MID ATLANTIC REGION WEDNESDAY INTO
THURSDAY. LIQUID PRECIPITATION SHOULD ACCOMPANY THE FRONT EXCEPT
ALONG THE ALLEGHENY  FRONT WHERE ARRIVAL OF COLDER AIR WILL CAUSE THE
RAIN TO CHANGE OVER TO SNOW BEFORE PRECIPITATION ENDS THURSDAY.

PASSAGE OF SHORTWAVE WILL SUPPORT DEVELOPMENT OF A COASTAL LOW LATE
SATURDAY AND SUNDAY. PRECIPITATION MAY START AS A WINTRY MIX AT
HIGHER ELEVATIONS.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
VFR CONDITIONS INTO THE OVERNIGHT...W/ MID CLOUD DECKS INCREASING
TOWARD THE PREDAWN MON. PRECIPITATION WILL OVERSPREAD THE
TERMINALS MONDAY MORNING - MOST LIKELY POST-DAWN - FROM SOUTHWEST
TO NORTHEAST. FREEZING RAIN IS EXPECTED ACROSS KCHO AND POSSIBLY
KMRB AND KIAD FOR A RELATIVELY BRIEF PERIOD...W/ TEMPS HOVER NEAR
FREEZING DURING THE MID-MRNG HRS. FREEZING RAIN MAY MIX WITH
SLEET AND SNOW AT THE ONSET. RAIN IS EXPECTED ACROSS THE REST OF
THE TERMINALS. RAIN MAY MIX WITH SLEET AT THE ONSET. CIGS/VSBYS
WILL DETERIORATE TO MVFR LEVELS MONDAY WITH POSSIBLE IFR LEVELS.

SUB VFR CIGS AND VSBYS EXPECTED MONDAY NIGHT INTO TUESDAY. LIGHT
FREEZING RAIN WILL BE POSSIBLE WEST OF THE BLUE RIDGE WITH RAIN TO
THE EAST. A PRECIPITATION RESPITE MAY OCCUR TUESDAY AFTERNOON BEFORE
RAIN MOVES BACK IN LATER TUESDAY NIGHT. A STRONG COLD FRONT WILL
APPROACH THE TERMINALS WEDNESDAY BEFORE PASSING THROUGH
WEDNESDAY NIGHT. MORE RAIN AND SUBVFR CONDITIONS ARE EXPECTED.

&&

.MARINE...
HIGH PRESSURE WILL REMAIN OVER THE WATERS TONIGHT. LOW PRESSURE
WILL TRACK UP THE MID-ATLANTIC COAST MONDAY. A SMALL CRAFT
ADVISORY IS IN EFFECT FOR THE MIDDLE PORTIONS OF THE BAY AND LOWER
TIDAL POTOMAC RIVER.

WINDS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA MONDAY NIGHT THROUGH
TUESDAY NIGHT. A STRONG COLD FRONT WILL APPROACH THE WATERS
WEDNESDAY BEFORE PASSING THROUGH WEDNESDAY NIGHT. A SMALL CRAFT
ADVISORY WILL LIKELY BE NEEDED FOR THE WATERS WEDNESDAY AND
THURSDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...FREEZING RAIN ADVISORY FROM 6 AM TO NOON EST MONDAY FOR VAZ025-
     026-029-036>040-050-051-501>504-507-508.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 AM TO 6 PM EST MONDAY FOR ANZ534-
     537-543.

&&

$$
UPDATE...GMS
PREV DISCUSSION...BJL/KRW/CEM






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