Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 240105
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
905 PM EDT THU OCT 23 2014

.SYNOPSIS...
LOW PRESSURE WILL MOVE FROM OFF CAPE COD TO THE CANADIAN MARITIMES
BY FRIDAY. HIGH PRESSURE WILL RETURN TO THE MID ATLANTIC TONIGHT
AND REMAIN OVER THE AREA THROUGH THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...

LOPRES OFF ACK THIS EVE. IT/LL CONT TO PULL AWAY OVNGT. AS
XPCTD...THE GRADIENT SLACKENED QUITE A BIT AFT SUNSET...AND MAY
COME CLS TO OUTRIGHT DCPLG BY DAWN. STILL HV STCU TO CONTEND WITH
THO. THERES A PATCH OVER THE WRN SLOPES OF THE APLCNS AND ANTHR FM
HGR-EZF NEWD. CLD DECK LOOKING RATHER THIN ON RAOB...BUT THERE/S
AN INVSN ATOP IT. GDNC BUFR DATA SUGGESTING LTLCHG IN CLDS OVNGT.
WL GNLY SIDE W/ THAT SOLN...ALTHO MAY EASE UP ON INTENSITY
/PERCENTAGE/ TWD DAWN. THAT CLDCVR CHG WL IN TURN AFFECT MIN-T.
ADDED A CONTRIBUTION FM MET/NAM WHICH BROUGHT MIN-T CLOSER TO
LAMP.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
HIGH PRESSURE CONTINUES TO BUILD IN FROM THE WEST FRIDAY. THERE
WILL BE SOME LEFTOVER PRESSURE GRADIENT FROM THE COASTAL
LOW...WHICH WILL BE REACHING THE MARITIMES BY THE END OF THE
DAY...SO NW WINDS WILL GUST TO AROUND 20KT IN THE LATE MORNING AND
AFTERNOON. WITH MORE SUNSHINE...SLIGHTLY HIGHER 1000-500MB
THICKNESS AND A PARTIAL DOWNSLOPE WIND COMPONENT...HIGHS WILL BE A
FEW DEGREES WARMER THAN THURSDAY. MID TO UPPER 60S EXPECTED EAST
OF THE BLUE RIDGE AND IN THE SHENANDOAH VALLEY...AND MID 50S TO
LOW 60S AT HIGHER ELEVATIONS.

HIGH PRESSURE PERSISTS TO THE SOUTH AND WEST FRIDAY NIGHT THROUGH
SATURDAY. WEAK COLD FRONT MOVES THROUGH SATURDAY NIGHT...BUT WILL
HAVE LIMITED MOISTURE. DRY FRONTAL PASSAGE EXPECTED...EXCEPT
POSSIBLY SOME UPSLOPE RAIN OVER THE POTOMAC HIGHLANDS SATURDAY
NIGHT. HIGHS GENERALLY MID TO UPPER 60S FRIDAY...AND UPPER 60S TO
AROUND 70 IN SOME SPOTS SATURDAY. LOWS IN THE 40S FRIDAY NIGHT IN
THE METRO AREAS...AND IN THE MID TO UPPER 30S IN AREAS THAT
RADIATE WELL FRIDAY NIGHT. SATURDAY NIGHT LOWS GENERALLY IN THE 40S.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
MOST OF THE LONG TERM PERIOD WILL FEATURE A RATHER BENIGN
PATTERN...WITH DEEP-LAYER RIDGING ANCHORED ALONG THE EAST COAST FOR
THE FIRST HALF OF NEXT WEEK. THERE ARE A FEW FEATURES OF NOTE...1- A
PRESSURE SURGE/SECONDARY COLD FRONT SUNDAY ACCOMPANIED BY GUSTY
WINDS AND FALLING TEMPERATURES BUT NO PRECIPITATION ON SUNDAY...2- A
COLD FRONT ON WEDNESDAY...AND 3- A POTENTIAL APPROACHING TROUGH
LATER IN THE WEEK.

ALL GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH THE MIDDLE OF NEXT
WEEK...BUT THEN DIVERGES AFTER THAT.

DEEP-LAYER /DRY/ NORTHWESTERLY FLOW WILL PREVENT APPRECIABLE
MOISTURE FROM MOVING OVER THE REGION ON SUNDAY AS AN UPPER-LEVEL
TROUGH SWINGS BY TO THE NORTH OVER NEW ENGLAND. THUS THE REFLECTION
AT THE SURFACE IN THE FORM OF A COLD FRONT WILL NOT BE ACCOMPANIED
BY ANY PRECIPITATION. WINDS WILL INCREASE THROUGH THE DAY AFTER THE
FRONT MOVES THROUGH AND COULD BE GUSTY. THESE GUSTY WINDS WILL USHER
IN A COOLER AIRMASS SUNDAY NIGHT...WITH LOW TEMPERATURES DROPPING TO
FREEZING OVER PORTIONS OF THE WESTERN SLOPES. RIGHT NOW THE AREAS
THAT ARE MOST LIKELY TO FALL TO FREEZING HAVE ALREADY HAD THEIR
GROWING SEASON ENDED BY A FREEZE EARLIER THIS WEEK...BUT IF WINDS
DIE OFF QUICKER THAN CURRENTLY FORECAST DURING THE EVENING MORE
WIDESPREAD FROST/FREEZE CONDITIONS WILL BE POSSIBLE OVER THE
HIGHLANDS.

THE AIRMASS WILL REBOUND QUICKLY EARLY NEXT WEEK AS HIGH PRESSURE
SETS UP JUST OFF THE SOUTHEAST COAST...SETTING UP A SOUTHWESTERLY
RETURN FLOW. MODELS/ENSEMBLES ARE IN VERY GOOD AGREEMENT REGARDING
THE TIMING OF A COLD FRONT WEDNESDAY AFTERNOON...WHICH MAY BRING
RAIN SHOWERS TO THE AREA. HOWEVER THE BEST UPPER-LEVEL FORCING
PASSES OVER THE WESTERN GREAT LAKES SO AT THE MOMENT PRECIPITATION
WOULD LIKELY BE OF THE MORE SCATTERED VARIETY.

BEYOND THIS TIME IS WHEN THE MODELS DIVERGE...WITH NON-NCEP GUIDANCE
DEPICTING A FLAT SHORTWAVE APPROACHING THE EAST COAST...WHILE THE
GFS/SEVERAL GEFS MEMBERS HAVE A MUCH DEEPER TROUGH AND IMPENDING
CYCLOGENESIS NEAR THE MID-ATLANTIC BY THE END OF NEXT THURSDAY. THE
UNCERTAINTY STEMS FROM SPREAD IN HOW GUIDANCE HANDLES A LARGE
UPPER-LEVEL LOW MOVING OUT OF THE GULF OF ALASKA...WITH THE GFS
SLOWER/DEEPER RESULTING IN WEST COAST RIDGING/DEEPER EAST COAST
TROUGHING...AND THE NON-NCEP GUIDANCE A LITTLE QUICKER BRINGING THE
UPPER LOW CLOSER TO THE NORTHWEST COAST AND FLATTENING OUT THE
DOWNSTREAM FLOW RESULTING IN A LESS AMPLIFIED PATTERN IN OUR NECK OF
THE WOODS. THE MAJORITY OF THE GUIDANCE AND TELECONNECTIONS WOULD
TEND TO FAVOR A LESS AMPLIFIED PATTERN AT THE MOMENT BUT THAT STRAYS
FROM THE PATTERN WE HAVE SEEN OVER THE LAST SEVERAL WEEKS. TIME WILL
BE THE BEST INDICATOR AS TO WHETHER OR NOT THE PATTERN IS READY FOR
A CHANGE OR IF THE MID-ATLANTIC IS IN STORE FOR ANOTHER LARGE AND
SLOW-MOVING AREA OF LOW PRESSURE AND STORMINESS LATE NEXT WEEK.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
VFR THROUGH VALID TAF PD. NW FLOW AROUND 10KT OVNGT...LIGHTER AT KCHO.
VFR CONTINUES FRIDAY WITH NW WINDS 10-15KT...GUSTING TO 20KT LATE
MORNING THROUGH AFTERNOON. VFR FRIDAY NIGHT THROUGH SATURDAY NIGHT
WITH LIGHTER WINDS.

VFR CONDITIONS EXPECTED SUN-MON NIGHT. GUSTY NW FLOW SUN UP TO 25
KTS POSSIBLE...DIMINISHING SUN NIGHT INTO MON AROUND 10 KTS OR LESS.

&&

.MARINE...
WINDS SUBSIDING AS LOPRES PULLS AWAY. MAROBS SUGGEST ALL WINDS AOB
15 KT ATTM...AND HV BEEN SO SINCE JUST AFDK. HV DROPPED SCA FOR
NARROWER WATERWAYS /MID-UPR PTMC/NRN BAY/BALT HARBOR/PAX RIVER/
THUS FAR. AM REAL TEMPTED TO DROP THE REST FOR THE OVNGT HRS.

WNNDS RENEW FRIDAY MORNING W/ DIURNAL MIXING AS GUSTS AROUND 20KT
ARE EXPECTED MID MORNING THROUGH THE AFTERNOON. LIGHTER WINDS FRI
NIGHT THROUGH SAT NIGHT UNDER HIGH PRESSURE.

A PRESSURE SURGE BEHIND A DRY COLD FRONT WILL LIKELY LEAD TO SOLID
SMALL CRAFT ADVISORY CONDITIONS OVER THE WATERS DURING THE DAY ON
SUNDAY INTO SUNDAY EVENING. WINDS/SEAS SUBSIDE MONDAY INTO MONDAY
NIGHT...BEFORE SOUTHERLY CHANNELING BETWEEN OFFSHORE HIGH PRESSURE
AND A COLD FRONT APPROACHING FROM THE OHIO VALLEY COULD RESULT IN
SMALL CRAFT ADVISORY CONDITIONS TUESDAY INTO WEDNESDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 9 AM TO 6 PM EDT FRIDAY FOR ANZ530-
     531-535-536-538>540-542.
     SMALL CRAFT ADVISORY UNTIL 6 PM EDT FRIDAY FOR ANZ532>534-537-
     541-543.

&&

$$
SYNOPSIS...HTS
NEAR TERM...HTS
SHORT TERM...KCS
LONG TERM...DFH
AVIATION...HTS/KCS/DFH
MARINE...HTS/KCS/DFH







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