Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 190250
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
950 PM EST TUE NOV 18 2014

.SYNOPSIS...
SURFACE HIGH PRESSURE CENTERED OVER EASTERN TEXAS WILL BUILD SHIFT
EAST ACROSS THE DEEP SOUTH THROUGH WEDNESDAY. A WARM FRONT WILL LIFT
NORTH OVER THE AREA LATE WEDNESDAY...WITH A DRY COLD FRONT PASSING
FROM THE WEST LATE THURSDAY. HIGH PRESSURE WILL CROSS THE AREA
FRIDAY NIGHT. THE HIGH WILL MOVE OFF THE COAST SATURDAY AND A WARM
FRONT WILL CROSS THE AREA SUNDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 02Z...SURFACE HIGH PRESSURE WILL CONTINUE TO NOSE
NORTHEASTWARD FROM THE CENTRAL GULF COAST TONIGHT WHILE A DEEP LOW
PRESSURE SYSTEM MOVES AWAY FROM LABRADOR. THE PRESSURE GRADIENT IS
EXPECTED TO SIGNIFICANTLY RELAX AFTER 06Z...ALTHOUGH A LOT OF THE
GUSTS HAVE ALREADY DIMINISHED AT THIS HOUR. MEANWHILE A WEAK WAVE
OF LOW PRESSURE IS APPROACHING FROM THE OHIO VALLEY...MOST NOTED
BY THE INCREASING CLOUDS APPROACHING THE CENTRAL APPALACHIANS.
SNOW SHOWER/FLURRY ACTIVITY HAS BEEN OBSERVED UPSTREAM WITH THIS
WAVE AND IT IS REASONABLE TO EXPECT SOME OF THIS MOISTURE TO BE
REALIZED ON THE WESTERN FACING SLOPES. THINK THE CHANCE OF
MEASURABLE SNOW IS IFFY...BUT SOME LOCATIONS MAY SQUEEZE OUT
SEVERAL TENTHS. AFTER THE MAIN WAVE PASSES AROUND 07-08Z...CARRIED
A MENTION OF FLURRIES THROUGH 12Z.

THE MAIN STORY CONTINUES TO BE THE COLD THOUGH WITH THE DEEP UPPER
TROUGH OVERHEAD...AND THERMAL PROFILES HAVE BOTTOMED OUT FOR THIS
EVENT. FROM THE 00Z SOUNDING DATA...850 MB TEMPERATURE OF -15.9C
TIES FOR THE 5TH LOWEST TEMPERATURE AT THAT LEVEL IN THE MONTH OF
NOVEMBER (CORRECTION - MONTH OMITTED IN PREVIOUS AFD) FROM DCA/IAD
SOUNDINGS DATING TO 1948. HOWEVER...THIS IS THE EARLIEST DATE FOR
A READING THAT LOW...AS ALL OF THE TOP 5 OCCURRED ON 11/25 OR
LATER. SO EXPECTING A VERY COLD NIGHT WITH RECORD LOWS THREATENED
(SEE CLIMATE SECTION BELOW). TEMPERATURES HAVE ALREADY STARTED
PLUMMETING THIS EVENING OWING TO A RELATIVELY QUICK SLACKENING OF
THE WINDS AND CLEAR SKIES. DEW POINTS ARE CURRENTLY IN THE LOWER
SINGLE DIGITS. THE ONLY THINGS THAT WILL HOLD BACK A COMPLETE
FREEFALL ARE A LITTLE BIT OF A BREEZE AND SOME ENCROACHING CLOUDS
FROM THE AFOREMENTIONED WAVE. THE LOW TEMPERATURE FORECAST STILL
NEEDED TO BE LOWERED BY SEVERAL DEGREES HOWEVER...AND WOULDNT BE
SURPRISED IF SOME LOCATIONS DROPPED LOWER...PARTICULARLY ANY WIND
SHELTERED AREAS TOWARD CENTRAL VA AND THE SOUTHERN SHENANDOAH
VALLEY. LOCATIONS OUTSIDE OF URBAN AND COASTAL AREAS CAN EXPECT
MID TEENS OR LOWER. WIND CHILLS (ASSUMING THE WIND DOESNT
COMPLETELY DECOUPLE) WILL BE IN THE LOWER TEENS TO SINGLE DIGITS
IN THE LOWLANDS...AND THE ADVISORY STILL LOOKS GOOD ABOVE 3000FT
FOR READINGS OF -5 TO -15.

WEDNESDAY...A SFC HIGH RIDGE WILL SHIFT OFF THE CAROLINA COAST
DURING THE DAY WITH AFTERNOON SWLY FLOW. THIS CONTINENTAL AIR IS
DRY AND WILL HAVE LITTLE SENSIBLE EFFECT OTHER THAN MID-LEVEL
CLOUDS. TEMPS SLOWLY RISE IN THE MORNING DUE TO LACK OF MIXING AND
POSSIBLE CLOUDS. MAX TEMPS GENERALLY MID 30S...UPR 20S FOR RIDGES
AND AROUND 30 FOR NERN MD WHERE THE SWLY FLOW REACHES LAST.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
LOW PRESSURE IS EXPECTED TO BE ACROSS THE NRN GREAT LAKES WITH A
COLD FRONT MOVING THROUGH THE OHIO VALLEY WEDNESDAY NIGHT. HIGH
PRESSURE WILL BE MOVING OFF THE SE COAST DURING THIS TIME. WINDS
WILL BE OUT OF THE SOUTH WED EVENING AHEAD OF THE ADVANCING COLD
FRONT. CLOUDS WILL INCREASE FROM WEST TO EAST AS THE COLD FRONT
NEARS. SNOW SHOWERS ARE POSSIBLE ALONG THE WESTERN SLOPES OF THE
ALLEGHENY FRONT LATE WEDNESDAY NIGHT AND THURSDAY. FURTHER
EAST...LITTLE MOISTURE WILL LEAD TO A DRY FRONTAL PASSAGE BY
THURSDAY AFTERNOON. WINDS WILL BECOME WESTERLY THURSDAY. THIS WILL
LEAD TO ANOTHER ROUND OF COLD AIR ADVECTION BY THURSDAY EVENING.
MOSTLY SUNNY CONDITIONS EAST OF THE BLUE RIDGE WILL ALLOW TEMPS TO
RISE INTO THE MID TO UPPER 40S.

HIGH PRESSURE MOVES INTO THE REGION THURSDAY NIGHT. FCST MIN TEMPS
WILL BE IN THE 20S.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
A BUILDING RIDGE OF HIGH PRESSURE EXPECTED FRIDAY AND FRIDAY NIGHT.
TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH FRIDAY NIGHT.

THE HIGH WILL SHIFT TO THE COAST AND THEN OFFSHORE SATURDAY AND
SATURDAY NIGHT. WINDS WILL SHIFT TO THE SOUTH AHEAD OF A STORM
SYSTEM AND COLD FRONT MOVING ACROSS THE WESTERN OHIO VALLEY.
TEMPERATURES WILL MODIFY SATURDAY NIGHT THROUGH MONDAY. DRY
CONDITIONS SATURDAY WITH A SLIGHT CHANCE OF SOME WARM-FRONTAL
PERIODS OF LIGHT SNOW...MIXING WITH RAIN SHOWERS...SATURDAY NIGHT
FROM THE POTOMAC HIGHLANDS TOWARD THE WASHINGTON D.C. AREA.
SOME LIGHT RAIN WILL MOVE IN AS TEMPERATURES MODIFY SUNDAY AND
SUNDAY NIGHT. THERE IS A CHANCE OF A FEW LINGERING RAIN SHOWERS
MONDAY INTO MONDAY NIGHT BUT THE HIGHER PROBABILITIES OF RAIN WOULD
BE SUNDAY AND SUNDAY NIGHT.

A TRAILING COLD FRONT WILL GRADUALLY MOVE EAST MONDAY NIGHT INTO
TUESDAY. ALTHOUGH MOST RAIN ACTIVITY SHOULD BE OFFSHORE TUESDAY...WE
CAN`T RULE OUT A FEW LINGER RAIN SHOWERS ALONG AND ON THE COLD SIDE
OF THE TRAILING FRONT.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD AS HIGH PRESSURE
BUILDS ALONG THE GULF COAST TONIGHT AND TOWARD THE SOUTHEASTERN
STATES WEDNESDAY. WIND GUSTS WILL BEGIN TO RELAX THIS EVENING...BUT
GRADIENT FROM STRONG LOW PRESSURE OVER LABRADOR WILL PREVENT WINDS
FROM DIMINISHING COMPLETELY. THE WINDS WILL SHIFT TO SOUTHERLY
BETWEEN 16-19Z WEDNESDAY AND BEGIN INCREASING TOWARD EVENING AS A
LOW PRESSURE SYSTEM SWINGS INTO THE GREAT LAKES. MID LEVEL CLOUDS
WILL ALSO INCREASE WEDNESDAY AFTERNOON.

VFR CONDITIONS EXPECTED WEDNESDAY NIGHT THROUGH THURSDAY NIGHT. A
COLD FRONT WILL CROSS THE REGION CAUSING S WINDS TO BECOME WEST BY
THURSDAY EVENING. LACK OF MOISTURE WILL ONLY ALLOW A MID-HIGH LEVEL
CLOUD DECK TO MOVE ACROSS THE TERMINALS.

VFR CONDITIONS FRIDAY AND FRIDAY NIGHT. WINDS COULD GUST OVER 20
KNOTS LATE FRIDAY MORNING INTO MIDDAY AS HIGH PRESSURE BUILDS IN
FROM THE WEST. WINDS WILL BECOME LIGHT AND VARIABLE LATE FRIDAY AND
FRIDAY NIGHT.

VFR CONDITIONS SATURDAY INTO SATURDAY NIGHT. WINDS WILL BECOME
SOUTHERLY AT 5 TO 10 KNOTS.

&&

.MARINE...
NW TO W WINDS HAVE BEEN SLOWLY DIMINISHING THIS EVENING AND WILL
CONTINUE TO DO SO TOWARD DAWN. A SMALL CRAFT ADVISORY REMAINS IN
EFFECT FOR OCCASIONAL GUSTS ABOVE 18 KT. THE NORTHERN TIDAL
POTOMAC WILL DROP OFF AT 3AM...WITH ALL HEADLINES DOWN BY 9AM
OVER THE WATERS WHILE HIGH PRESSURE GAINS GREATER CONTROL FROM THE
SOUTH. AS THE HIGH MOVES OFF THE COAST WEDNESDAY
AFTERNOON...RETURN SOUTHERLY FLOW WILL DEVELOP...LEADING TO
CHANNELING BY THE EVENING.

SOUTHERLY FLOW WILL INCREASE AHEAD OF A COLD FRONT WED NIGHT AND A
SCA IS IN EFFECT THROUGH WED NIGHT. THE COLD FRONT WILL CROSS THE
WATERS BY THURS AFTERNOON AND A WESTERLY PRESSURE SURGE WILL CAUSE
WINDS TO INCREASE ACROSS THE WATERS THURSDAY NIGHT.

SMALL CRAFT ADVISORIES ARE POSSIBLE FRIDAY. WINDS COULD GUST OVER 20
KNOTS FROM THE WEST TO NORTHWEST DUE TO BUILDING HIGH PRESSURE.

SMALL CRAFT ADVISORIES ARE POSSIBLE AGAIN LATER SATURDAY AFTERNOON
AS HIGH PRESSURE SHIFTS TO THE EAST COAST AND WINDS BECOME SOUTHERLY.

&&

.CLIMATE...
A RARE FEAT MAY BE ACCOMPLISHED TONIGHT AT BOTH DULLES AIRPORT AND
BWI. TWO RECORD DAILY MINIMUM TEMPERATURES COULD BE BROKEN IN ONE
NIGHT. TEMPERATURES ARE FALLING QUICKLY THIS EVENING...AND ARE
ALREADY VERY CLOSE TO THEIR RECORDS FOR THE 18TH. AFTER THE CLOCK
HITS MIDNIGHT AND A NEW DAY IS BORN...TEMPERATURES WILL CONTINUE
FALLING...BREAKING THEIR RECORDS FOR THE 19TH.

BELOW IS A TABLE OF RECORD COLD TEMPERATURES FOR TONIGHT...TOMORROW
AND TOMORROW NIGHT.

SITE   11/18 LOW MAX  11/19 MIN  11/19 LOW MAX
DCA      30 (1924)    18 (1891)    33 (1880)
BWI      31 (1959)    20 (1936)    35 (1880)
IAD      39 (2008)    20 (1990)    38 (2008)

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...WIND CHILL ADVISORY UNTIL 7 AM EST WEDNESDAY FOR VAZ503-504.
WV...WIND CHILL ADVISORY UNTIL 7 AM EST WEDNESDAY FOR WVZ501-505-
     506.
MARINE...SMALL CRAFT ADVISORY UNTIL 9 AM EST WEDNESDAY FOR ANZ530>534-
     537-539>541-543.
     SMALL CRAFT ADVISORY FROM 3 PM WEDNESDAY TO 6 AM EST THURSDAY
     FOR ANZ530>534-537>543.
     SMALL CRAFT ADVISORY UNTIL 6 AM EST WEDNESDAY FOR ANZ536-538-
     542.
     SMALL CRAFT ADVISORY UNTIL 3 AM EST WEDNESDAY FOR ANZ535.

&&

$$
SYNOPSIS...BAJ
NEAR TERM...BAJ/ADS
SHORT TERM...HAS
LONG TERM...KLW
AVIATION...ADS/HAS/KLW
MARINE...ADS/HAS/KLW
CLIMATE...DFH






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