Area Forecast Discussion
Issued by NWS Sterling, VA

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314
FXUS61 KLWX 042250
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
550 PM EST THU FEB 4 2016

.SYNOPSIS...
A WAVE OF LOW PRESSURE WILL RIDE ALONG A STATIONARY
BOUNDARY PASSING BY WELL TO OUR SOUTH AND EAST THURSDAY NIGHT
INTO FRIDAY. HIGH PRESSURE WILL RETURN FOR SATURDAY. COASTAL LOW
PRESSURE WILL PASS BY WELL TO OUR SOUTH AND EAST SUNDAY. ANOTHER
LOW PRESSURE SYSTEM MAY IMPACT THE AREA EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH FRIDAY/...
BASED ON ADDITIONAL MODEL GUIDANCE COMING IN DURING THE LATE
AFTERNOON...IT APPEARS THE SNOWFALL ACCUMULATIONS WILL BE REACHING
A LITTLE FARTHER TO THE NW. THIS WILL BEGIN TO FALL INTO OUR ONE
INCH DURING RUSH HOUR CRITERIA. UNCERTAINTY INCREASES NEARER TO
I-95. HAVE EXPANDED THE ADVISORY UP TO DC AND BALTIMORE PROPER AT
THIS TIME.

PREVIOUS DISCUSSION...

LOW PRESSURE IS DEVELOPING ACROSS THE
CAROLINAS ALONG A NEARLY STATIONARY COLD FRONT. HIGHER PRESSURE IS
SLOWLY MOVING INTO THE REGION FROM THE WEST TODAY HOWEVER THE PRESSURE
PATTERN WILL BARELY CHANGE INTO TONIGHT.

LOW PRESSURE ACROSS THE CAROLINAS WILL DEEPEN TODAY AND TONIGHT
AHEAD OF A DEEP UPPER LEVEL TROUGH. COLD AIR ADVECTION WILL CONTINUE
TO MOVE INTO THE MID-ATLANTIC REGION FROM THE WEST WITH THE 0 DEG
850MB ISOTHERM CURRENTLY ORIENTED N-S ALONG THE SHENANDOAH VALLEY.
RAIN WILL CONTINUE TO RIDE THE STALLED FRONTAL BOUNDARY AND MOVE
SOUTH TO NORTH ACROSS THE PIEDMONT AND SOUTHERN MD. DUE TO THE
ORIENTATION OF THE FRONT...RAIN SHOULD STAY CONFINED TO THIS AREA
THROUGH THE AFTERNOON AND EVENING.

LOW PRESSURE WILL MOVE OFF THE EAST COAST AT THE OUTER BANKS AND THE
ENTRANCE REGION OF THE UPPER LEVEL JET WILL BE RIGHT OVERHEAD. THIS
WILL ENHANCE LIFT AND MOISTURE FROM THE ATLANTIC. CAA WILL CONTINUE
OVERNIGHT AND THE REGION SHOULD BE BELOW 0 AT 850MB BY 6Z. AT THE
SFC...TEMPS WILL BE DROPPING INTO THE 20S/30S OVERNIGHT. RAIN WILL
BE ONGOING ACROSS THE PIEDMONT/SOUTHERN MD REGION HOWEVER AS THE LOW
DEEPENS LIGHT PRECIPITATION IS EXPECTED TO MOVE FURTHER WEST WHERE
IT WILL BE COLDER. LIGHT SNOW OR FLURRIES ARE POSSIBLE ACROSS THE
REGION AFTER MIDNIGHT TONIGHT. FURTHER EAST...HEAVIER PRECIPITATION
IS EXPECTED CLOSER TO THE COASTAL LOW AND RAIN WILL TRANSITION TO
SNOW BETWEEN 6-10Z. ACCUMULATING SNOW IS EXPECTED WITH 2-3 INCHES
ACROSS SOUTHERN MD TO LESS THAN AN INCH ALONG I-95.

PRECIPITATION SHOULD END ACROSS THE REGION AROUND SUNRISE FRIDAY
MORNING. HIGH PRESSURE WILL PUSH INTO THE REGION CAUSING WINDS TO
INCREASE. NW WINDS 10-20MPH WITH GUSTS UP TO 30MPH.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
HIGH PRESSURE
WILL BE IN CONTROL FRIDAY NIGHT AND INTO SATURDAY AS IT MOVES TO
THE SOUTH OF THE REGION. DRY AND MOSTLY SUNNY CONDTIONS EXPECTED
SATURDAY WITH TEMPS REACHING THE MID 40S. A DEEP TROUGH WILL MOVE
ACROSS THE REGION SUNDAY RESULTING IN CLOUDS TO INCREASE. LOW
PRESSURE IS EXPECTED TO OVER THE ATLANTIC OCEAN LEAVING THE MID-
ATLANTIC DRY. TEMPS ON SUNDAY WILL BE SLIGHTLY WARMER IN THE MID
TO U40S TO L50S.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
COMPUTER MODELS HAVE SOME
AGREEMENT ON A COASTAL LOW FORMING ALONG OR JUST OFFSHORE THE
NORTH AND SOUTH CAROLINA COAST SUNDAY NIGHT.

ONE DISAGREEMENT IS THAT THE GFS MODEL KEEPS THE COASTAL LOW AN
OPEN AREA OF LOW PRESSURE AND PUSHES IT FASTER OUT TO SEA SUNDAY
NIGHT AND MONDAY THAN THE EUROPEAN MODEL...WHICH CLOSES OFF THE LOW
AND INTENSIFIES IT BEFORE PUSHING IT OUT TO SEA.

NONETHELESS...THIS COASTAL LOW WILL JUST SPREAD ADDITIONAL CLOUDS
INTO OUR REGION SUNDAY WITH NO EXPECTED PRECIPITATION.

A MUCH LARGER AREA OF LOW PRESSURE IN THE UPPER LEVELS IS EXPECTED TO
DROP SOUTHEASTWARD FROM THE UPPER MIDWEST AND GREAT LAKES INTO THE
OHIO VALLEY AND MID-ATLANTIC REGION MONDAY. A NEW SURFACE LOW
PRESSURE SYSTEM COULD FORM OVER SOUTHWEST VIRGINIA ON THE SOUTHEAST
FLANK OF THIS BROAD LOW AROUND MIDDAY MONDAY AND MONDAY AFTERNOON.
THIS NEWLY FORMED LOW COULD HAVE A MORE DIRECT IMPACT TO OUR
REGION...BRINGING A CHANCE FOR RAIN AND SNOW SHOWERS MONDAY BEFORE
BECOMING MORE OF A LIGHT TO MODERATE SNOW THREAT MONDAY NIGHT WITH
COLDER AIR TO SUPPORT THE NEW LOW.

ONE SIMILARITY WITH THE EUROPEAN MODEL AND THE GFS MODEL WITH THIS
NEW LOW IS BOTH CLOSE OFF THE NEW LOW NEAR THE MID-ATLANTIC COAST
TUESDAY BEFORE PIVOTING IT NORTHWARD TOWARD NEW ENGLAND TUESDAY
NIGHT.

THE DIFFERENCE IN THE POSITION OF THIS CLOSED LOW WILL DETERMINE
WHETHER THE MID-ATLANTIC REGION GETS HIT HARD WITH ANOTHER SNOWSTORM
OR GETS A FEW RAIN AND SNOW SHOWERS WITH LITTLE TO NO ACCUMULATION.
RIGHT NOW...THE EUROPEAN MODEL CLOSES THE LOW NEAR THE MOUTH OF THE
CHESAPEAKE BAY AND MAKES IT A STRONGER LOW. THE GFS MODEL CLOSES THE
LOW NEAR THE MOUTH OF THE DELAWARE BAY...FARTHER NORTH...AND IS NOT
AS STRONG WITH THIS SYSTEM. FOR THE TIME BEING...WE HAVE A CHANCE OF
RAIN OR SNOW IN OUR REGION TUESDAY AND TUESDAY NIGHT.

THE MAIN UPPER LEVEL SUPPORT BEHIND THE COASTAL LOW WILL SLOWLY
PIVOT FROM THE OHIO VALLEY...ACROSS THE REGION...AND OFFSHORE
WEDNESDAY AND WEDNESDAY NIGHT. SOME UPSLOPE SNOW SHOWERS MAY EXIST
IN THE POTOMAC HIGHLANDS WITH COLDER AIR ALOFT PUNCHING INTO THE
REGION. ELSEWHERE...COLDER AND DRIER AIR WILL FILTER INTO THE REGION
AS HIGH PRESSURE BUILDS IN FROM THE WEST.

HIGH PRESSURE SHOULD DOMINATE THURSDAY WITH CHILLY AND DRY AIR. ANY
UPPER LEVEL DISTURBANCES MOVING OVERHEAD THURSDAY WILL BE QUICK AND
MAY NOT PRODUCE ANY PRECIPITATION...JUST ADDITIONAL CLOUDS.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS EXPECTED TODAY
AND TONIGHT. -SN IS EXPECTED ALONG AND EAST OF I-95 AFTER 6Z AND
MAY RESULT IN REDUCED VSBYS HOWEVER CONFIDENCE IS LOW IN THE
COVERAGE OF SNOW SHOWERS AT THIS TIME. -SN QUICKLY MOVES OUT BY
12Z FRIDAY AND VFR CONDITIONS ARE EXPECTED. NW WINDS WILL INCREASE
EARLY FRIDAY MORNING. GUSTS AROUND 25KT ARE EXPECTED HOWEVER GUSTS
UP TO 35KTS POSSIBLE FRIDAY MORNING.

VFR CONDITIONS EXPECTED FRIDAY NIGHT THROUGH SUNDAY.

VFR CONDITIONS SUNDAY NIGHT. WINDS NORTHEAST AROUND 5 KNOTS.
MVFR TO IFR CONDITIONS MONDAY WITH LIGHT RAIN AND LIGHT SNOW. WINDS
BECOMING SOUTHEAST 5 KNOTS GUSTS 10 TO 15 KNOTS.

&&

.MARINE...
N WINDS CONTINUE ON THE WATERS BEHIND A COLD FRONT THAT
MOVED THROUGH THIS MORNING. SCA CONDITIONS WILL CONTINUE ON THE
WATERS TODAY WITH GUSTS AROUND 20 KTS EXPECTED. A COASTAL LOW WILL
APPROACH THE WATERS TONIGHT AND RAIN IS EXPECTED TODAY AND
TONIGHT. COLDER AIR WILL MOVE INTO THE REGION AFTER MIDNIGHT AND
RAIN IS MAY CHANGE TO SNOW REDUCING VSBYS. WINDS WILL INCREASE ON
THE WATERS AS THE COASTAL LOW MOVES FURTHER OFF THE COAST EARLY
FRIDAY MORNING. GALE CONDITIONS ARE POSSIBLE NEAR THE MOUTH OF THE
CHESAPEAKE BAY AND LOWER TIDAL POTOMAC. AT THIS TIME...CONFIDENCE
IS LOW AS THE STRONGEST WINDS MAY BE SOUTH OF SMITH ISLAND.

HIGH PRESSURE WILL MOVE OVER THE WATERS FRIDAY AND INTO THE WEEKEND.
SCA CONDITIONS WILL CONTINUE FRIDAY BEFORE WINDS DIMINISH FRIDAY
NIGHT ON THE MAIN CHANNEL OF THE BAY.

NO MARINE HAZARDS SUNDAY NIGHT AND MONDAY.

&&

.HYDROLOGY...
STARTING TO WIND DOWN FROM OUR SNOWMELT FLOOD...WHICH
TURNED OUT TO BE NOT AS SIGNIFICANT AS FORECAST BECAUSE WE DID
NOT SEE AS MUCH RAIN IN THE POTOMAC HEADWATERS AS EXPECTED...AND
WE DID NOT ENTIRELY LOSE THE SNOWPACK IN SOME AREAS WHERE IT WAS
EXPECTED TO HAPPEN.

MINOR FLOODING IS STILL ONGOING ON THE MONOCACY...MAINSTEM
SHENANDOAH...AND MAINSTEM POTOMAC BETWEEN HARPERS FERRY AND GREAT
FALLS. FLOODING WILL CONTINUE ON THE MONOCACY THROUGH TONIGHT...AND
ON THE SHENANDOAH AND POTOMAC THROUGH FRIDAY.

THE LIGHT PRECIPITATION EXPECTED TONIGHT WILL NOT HAVE ANY EFFECT ON
STREAMS.

&&

.TIDES/COASTAL FLOODING...
FRESHWATER INUNDATION OF THE POTOMAC TIDAL
ZONE IN WASHINGTON DC IS OCCURRING...AND MINOR FLOODING IS LIKELY
WITH THE TIDE CYCLE THIS AFTERNOON. COASTAL FLOOD ADVISORY IS IN
EFFECT.

COASTAL FLOOD WATCH REMAINS IN EFFECT FOR THE FOLLOWING TWO TIDE
CYCLES...HOWEVER...WITH NORTHWEST WINDS...THE RIVER MAY BE ABLE TO
HANDLE MORE FRESHWATER THAN USUAL. WE WILL BE MONITORING THIS TIME
PERIOD CLOSELY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EST
     FRIDAY FOR DCZ001.
     COASTAL FLOOD ADVISORY UNTIL 7 PM EST THIS EVENING FOR DCZ001.
MD...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EST
     FRIDAY FOR MDZ006-011-013-014-016>018-507-508.
VA...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EST
     FRIDAY FOR VAZ054-057.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EST FRIDAY FOR ANZ535-536.
     SMALL CRAFT ADVISORY UNTIL 10 PM EST FRIDAY FOR ANZ530>534-
     537>543.

&&

$$
SYNOPSIS...HAS
NEAR TERM...ADS/HAS
SHORT TERM...HAS
LONG TERM...KLW
AVIATION...HAS/KLW
MARINE...HAS/KLW
HYDROLOGY...JE
TIDES/COASTAL FLOODING...JE



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