Area Forecast Discussion
Issued by NWS Sterling, VA

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826
FXUS61 KLWX 191550
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1050 AM EST Thu Jan 19 2017

.SYNOPSIS...
High pressure will settle overhead today before moving off to the
east tonight. A warm front will move into the area Friday and
stall out nearby through Saturday. Low pressure will affect the
area Sunday and Monday. Weak high pressure may approach the area
Tuesday before a cold front approaches Wednesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Surface high pressure will crest overhead today, leading to dry
conditions and light winds. Guidance from yesterday has
considerably underestimated both low and high level moisture, with
plenty of lower cumulus clouds stuck under the subsidence
inversion as well as some high cirrus moving in aloft from the
southwest. Temperatures remain mild, with highs in the 50s area-
wide.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
Low pressure system will then push northeastward out
of the Mississippi Valley and into the Lower Great Lakes late
today and tonight before weakening on Friday. This will send an
area of rain towards the Mid Atlantic states for Friday along the
weakening warm frontal boundary. Current indications are that rain
will begin to overspread the region from southwest to northeast
in the late night/early morning hours, reaching the DC metro area
between 8 AM and 10 AM. The period of rain will continue into the
afternoon, tapering off by late afternoon. Low clouds as well as
areas of fog and drizzle likely to continue into Friday night.
Rainfall amounts on the light side, on average one to two tenths.

Lows tonight in the 30s and 40s with highs on Friday from 45-55F,
coolest northeastern Maryland where rain will be occurring during
peak heating, warmest across the Shenandoah Valley and portions of
eastern WV where rain ends earliest. Friday night lows drop back
to around 40F or so.

Saturday, while mainly dry, will likely see a continuation of low
clouds with little flow, especially east of the Blue Ridge.
Temperatures mild, with highs in the low-mid 50s east of the Blue
Ridge under more clouds to low-mid 60s west where there`s better
chance at some sun.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A potent jetmax in the southern stream of the jet will continue to
develop into a cutoff low Sunday over the Gulf Coast States. The
low will track northeast into the Mid-Atlantic Sunday night and it
will slowly pass by just to our east later Monday through Monday
night.

Warm and moist air from the Gulf of Mexico and Atlantic will
overrun the surface cooler air in place well ahead of the low
Sunday. A soaking rain is likely during this time. Soaking rains
are likely to continue for Sunday night through Monday as the low
approaches from the south. Rain may taper off Monday night or
Tuesday as the low slowly moves off to our north and east and weak
high pressure approaches.

Precipitable waters over one inch are likely Sunday into Monday
due to the moisture from the Gulf of Mexico and Atlantic. This is
unusually high for this time of year. In fact...it is well above
the 90th percentile for this time of year at KIAD. The moisture
combined with the forcing from the low suggests that moderate to
locally heavy rainfall is possible. 00z GEFS members are
indicating around 2-3 inches of rain are possible with this system
Sunday through Monday.

Localized flooding is possible later Sunday and Monday...but
confidence is too low to put in the Hazardous Weather Outlook at
this time since rain will be spaced out over a couple days and our
area will remain on the cool side of the boundary.

A cold front may impact the area during the middle portion of next
week...but unusually warm conditions are possible ahead of the
boundary Wednesday.

&&

.AVIATION /16Z THURSDAY THROUGH MONDAY/...
Scattered to broken strato-cumulus clouds will continue this
morning and into this afternoon, with generally VFR conditions.
Will be some lingering periods of MVFR, especially MRB. In
addition, some high clouds will overspread the region as well.
Winds generally light at around 5 knots. VFR continues into
tonight.

IFR conditions then expected to develop on Friday with period of
rain and lowering ceilings as a warm front crosses the region. Low
clouds and areas of fog likely to persist Friday night, and
possibly into Saturday as well.

Low pressure will impact the terminals Sunday through Monday
night. A soaking rain is likely along with IFR/subIFR conditions.

&&

.MARINE...
Sub-SCA winds from the northwest today will turn light southerly
tonight and into Friday with warm frontal passage. Light flow
continues through Saturday, turning southeast and gradually
increasing Saturday night.

Low pressure will impact the waters Sunday through Monday. Weak
high pressure will approach the waters Tuesday behind the
departing low. A Small Craft Advisory will likely be needed for
the waters during this time. A Gale Warning may be needed for
portions of the waters Sunday night and Monday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...BJL
NEAR TERM...MM/RCM
SHORT TERM...MM
LONG TERM...BJL
AVIATION...BJL/MM/RCM
MARINE...BJL/MM



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