Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 192000

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

High pressure will move 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.


High pressure is currently located directly overhead. The low
clouds which lingered much of the morning have now mostly
dissipated, though high clouds continue to stream over the region.
Aloft, the ridge axis remains to our west over West Virginia.
Further west, a closed upper low is over the central Plains, with
the associated surface low near Memphis and a warm front extending
eastward towards Savannah.

The clouds may thin late this afternoon and this evening as the
ridge axis aloft passes overhead, before thickening again
overnight in advance of the approaching system. Warm advection,
albeit rather weak, starts late tonight and continues on Friday as
the closed low opens into a shortwave and lifts northeast across
the region. With this overall being a weakening feature, rainfall
is not expected to be particularly significant on Monday,
generally less than a quarter of an inch. Rain may move through as
several bands as suggested by short-range high resolution
guidance, so went with "periods of rain" given potential for dry
intervals. That all having been said, in general we expect rain to
arrive across metro DC 8-10 AM, with light rain likely occurring
at swearing in, and the rain should mostly depart 2-4 PM. However,
the low clouds, fog and drizzle may persist given light southeast
flow and no frontal passage expected.

Lows tonight will drop into the 30s in many spots given the lack
of low clouds this evening, but may rise late as clouds re-develop
and thicken. With the rain expected on Friday, expect highs to
stay below guidance, mid to upper 40s generally.


Friday night into Saturday night, the region is more or less
between systems, but with the warm front stalling to our south and
nothing to disturb the air mass, low clouds, mist, drizzle and
perhaps fog look likely to remain over the region, at least
through early Saturday. Some insolation may reach the ground
enough to dissipate the drizzle, mist and fog on Saturday
afternoon, but it will be short lived. Warm advection precip with
the next complex low pressure system will start Saturday evening,
with rain likely to overspread much of the region late Saturday

With the clouds, mist, drizzle and patchy fog, lows on Friday
night should not drop much, with readings generally in the 40s.
Highs on Saturday will be dependent on the clouds thinning a bit
with a break in the fog and drizzle. Assuming this occurs, we will
likely rise into the low-mid 50s. Saturday night lows should stay
in the 40s with the clouds and rain arriving late.


A storm system will develop over the Mississippi Valley and
deepen as it moves toward the east-northeast Sunday and Sunday
night. This low will send energy into our region Sunday into
Sunday night, bringing rain to the region.

On Monday, the main low will move to the northeast a little
further. The threat for rain continue Monday into early Monday
evening. Temperatures will remain mild for January but cooler air
quickly lines up on the doorstep of the region to move in Monday
night. Some guidance suggests enough cold air may arrive before
precipitation ends to allow a change to snow, particularly across
higher elevations well northwest of I-95 corridor. Will need to
watch this potential. Other concern Monday is for gusty winds, and
some guidance is hinting at wind advisory gusts as the low passes
just to the east. Will need to look at this harder in coming day
or two.

High pressure will usher in drier air Tuesday and Tuesday night.
Clouds will break for sun, except for clouds and upslope rain
and/or snow showers in the Potomac Highlands possible.

An upper level trough of low pressure will sag from the Great
Lakes region toward the mid-Atlantic Wednesday. A return of mild
air from the south will evolve ahead of the trough with some
sunshine giving way to some clouds.

Temperatures will be seasonable with some sunshine Thursday. An
upper level trough of low pressure will be just to the north but
dry conditions should prevail. There is a chance of upslope rain
or snow showers in the Potomac Highlands.


VFR through late tonight with high pressure overhead sliding to
the east. With the approaching warm front, clouds will thicken and
lower, with intervals of rain starting early-mid morning Friday
and continuing into the afternoon. Visibility and cigs will lower
at least to MVFR, and likely IFR. While rain ends in the
afternoon, low clouds, mist and drizzle with IFR conditions likely
to persist through Friday night into Saturday morning before
improving perhaps to MVFR Saturday afternoon and evening.
Conditions may drop again late Saturday night as rain moves back

Sub-VFR conditions Sunday through Monday with gusty winds
developing Monday. Improving conditions Tuesday.


Winds should remain below SCA through Saturday night. Rain,
drizzle and fog/mist likely to arrive Friday morning and persist
through Saturday morning. Improved conditions seem likely Saturday
afternoon and evening before rain returns late at night.

Approaching system looks to bring increasing winds Sunday and
Monday as it strengthens and moves northeast along the coast. SCA
looks likely with gales possible Monday. Winds begin to diminish


Tidal anomalies have risen considerably today. Some of the
sensitive sites may reach action stage this evening, but we expect
anomalies to start decreasing a bit this evening so we should
avoid any minor coastal flooding. If minor flooding were to
occur, it would most likely occur at Straits Point. Odds of
coastal flooding in DC remain low.




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