Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 241829
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
229 PM EDT Sat Sep 24 2016

.SYNOPSIS...
High pressure will build in for tonight and Sunday before moving
off the coast Monday. A cold front will pass through the area
overnight Monday into Tuesday. An upper-level low may impact the
area during the middle portion of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
Cold front is currently crossing central Virginia on its way
southward. Plenty of low clouds have followed the front on its way
south but these should start to break up towards sunset from north
to south as high pressure and drier air nose southward into our
area. Exception will be areas where front is just reaching now, as
these areas currently have a decent cumulus field and guidance
continues to insist on some spotty showers developing during the
rest of the afternoon. After any convective showers dissipate,
upslope clouds look likely to remain and some patchy mist/drizzle
may develop overnight tonight. Further north, clearing skies and
decreasing winds should result in the coolest night of the season
thus far, with 50s widespread and 40s in the colder/northern
locales.

On Sunday, high pressure drifts by to the north and flow becomes
more easterly. Temps will rebound only into the lower 70s in most
areas due to cool air aloft in northern areas and persistent
clouds further south. Some drizzle/mist may linger in central
Virginia during the morning.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
High pressure continues drifting eastward away from us Sunday
night and Monday as the next frontal boundary approaches from the
west. With persistent east/southeast flow the available moisture
will increase and the front may be slow enough and forcing strong
enough to allow for a decent rain across the area Monday night
into early Tuesday. Right now guidance is a bit uncertain on exact
timing but certainly Monday night looks wet...with uncertainty on
just how fast it arrives late Monday and how fast it departs
Tuesday. Lows will be cool again Sunday night (50s to high 40s) with
highs Monday as the front approaches again stuck in the lower 70s.
Monday night will be milder with the front crossing the
area, with lows staying in the 60s for many spots. Clouds
breaking Tuesday will likely allow for 70s to return once again.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Cold front moves away from our region Tuesday night, with some
showers possibly lingering to the eastern part of our CWA. Conditions
become dry overnight Tuesday into Wednesday.

A cutoff upper level low will push south from the Great Lakes
Wednesday into Thursday night or even late Friday. Guidance is in
disagreement on location of this upper level low and this will
affect the forecast in the long term. GFS keeps the upper low
moving over the Mid-Atlantic early on Thursday with the ridge
building behind it on Friday and northerly flow through early
Saturday. This scenario brings showers over our CWA Wednesday
night into Thursday, and then dry into Sunday. On the other hand,
the Euro keeps the upper level low to our west and lingering to
our southwest through early Friday before moving back north. This
scenario allows for southerly or easterly flow advecting moisture
into our region and bringing precipitation chances Wednesday
night into Saturday before finally drying out late Saturday into
Sunday. Temperatures will be affected by the position of the upper
lever low, but for now forecasting near normal.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
MVFR cigs this afternoon have been more persistent than expected
but they are gradually lifting so think VFR returns around 21Z or
thereabouts. Some low clouds may try to get into CHO late today or
tonight but uncertain in this regard so have kept out of TAF for
now. Could also be some patchy mist or drizzle around CHO later
tonight. Generally VFR Sunday-early Monday, then sub-VFR with
approaching front and associated SHRA Monday night into early
Tuesday. Winds generally around 10 knots or less through
Tuesday...starting off northeasterly today...turning southeasterly
Sunday...and southerly Monday...then westerly Tuesday.

VFR conditions expected Tuesday night into Wednesday, then sub-
VFR conditions possible late Wednesday into Friday as upper level
disturbance brings showers into the region.

&&

.MARINE...
SCA gusts may continue for a while tonight given a secondary
boundary pushing southward and cool air advecting over the warm
bay waters so have pushed SCA thru tonight. May not last that long
and perhaps could be taken down before morning. High pressure
likely to bring lighter winds Sunday before southerly channelingahead
of cold front bring another threat of SCA for Monday and then cold
advection brings more potential SCA gusts Tuesday behind
aforementioned front.

Winds diminish Tuesday night into Wednesday night. Possible small
craft advisory conditions late in the week an as upper level
disturbance moves nearby.

&&

.TIDES/COASTAL FLOODING...
High pressure building southward just to the northeast of the area
will result in northeasterly flow through tonight, then easterly to
southeasterly flow late Sunday into early next week. Anomalies have
dropped some this afternoon, but the overall pattern will not allow
much more water to drain out of the Chesapeake Bay/Tidal Potomac
River. Anomalies will likely begin to increase again starting later
tonight. Minor coastal flooding appears possible by the Sunday
night high tide cycle.

&&

.CLIMATE...
Unusually warm weather has persisted over the area for
quite some time. Autumn-like temperatures are finally making an
appearance over the area, and DCA may fall below 60 degrees
early Sunday morning for the first time since June 9th (total of
106 days through September 23rd). The record most consecutive
days at or above 60 degrees in the Washington DC area is 112 set
in 2012.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Sunday for ANZ530>534-
     537>543.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...IMR
AVIATION...IMR/RCM
MARINE...IMR/RCM
TIDES/COASTAL FLOODING...DFH
CLIMATE...DFH



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