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fxus61 klwx 181605 

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1105 am EST Fri Jan 18 2019

a cold front will move through the region today, with a brief
warm up ahead of it. High pressure builds in tonight into early
Saturday. Stronger low pressure will track through the
Tennessee Valley Saturday, before passing through our area
Saturday night into Sunday. Arctic high pressure will build
overhead later Sunday through Monday, ushering in very cold air
into the region. High pressure moves offshore Tuesday.


Near term /through tonight/...
low level moisture has been persistent behind last night's
precipitation, resulting in low clouds and fog. This is very
gradually starting to break up. Expect most areas to lose their
fog in the next hour or so, at least those areas that haven't
yet lost it.

The cold front associated with the aforementioned surface low
pressure system will swing through the area early today. Warmer
temperatures are expected today as a result, as the front is
fairly weak, and has no real push of cold air advection to come
along with it. Accordingly, low-level moisture will be slow to
leave the area, as flow is very weak behind the front. Thus,
clouds will linger today. This will be the difference between
high temps into the upper 40s/low 50s, or high temps barely
reaching 40 again. Temps were nudged down especially in the
north due to this.


Short term /Saturday through Sunday night/...
a strong area of low pressure will approach the region from the
Tennessee Valley on Saturday. Warm advection aloft will
overspread the area late Saturday morning through early Saturday
afternoon allowing precipitation to breakout. Precip looks to
arrive a bit earlier than previously anticipated, but still
should transition fairly quickly from snow to sleet to freezing
rain and then, in the warmer spots, rain. With high pressure
situated to the north, and model guidance indicating a small
wedge of higher pressure holding strong to the west of the Blue
Ridge/east of the Allegheny Front, there is high concern that
cold air will remain locked in at the surface much longer
across portions of West Virginia Panhandle, western/northern
Maryland and the northern Shenandoah Valley. All model guidance
has a strong southerly low-level jet (on the order of 50 kts)
blasting warm air in aloft Saturday evening across the entire
County Warning Area. If cold air remains locked in at the surface for the
aforementioned areas, a prolonged period of freezing rain or
sleet could ensue. Temps were trended down and ice amounts
trended up based on this. Some expansion of the Winter Storm
Watch is possible later today.

The remainder of the area, including the immediate I-95
corridor, will receive a dose of heavy rainfall Saturday night
into early Sunday. Around an inch of rainfall is expected to
fall area-wide. All of that rain falling on top of remnant snow
pack from last weekend's storm could lead to instances of
flooding Saturday night (smaller Stem streams/rivers) through
Sunday night (main-Stem rivers).

Behind the system, pops were trended down rapidly on Sunday as
the system pulls away. Main story will be falling temps,
refreeze (for those areas that get above freezing Saturday
night), and gusty winds, with winds potentially approaching
advisory gusts (46 mph). Sunday night will turn out bitterly
cold with temps falling to the single digits or low teens.


Long term /Monday through Thursday/...
a tight northwest gradient will remain over the area on Monday,
with cold and blustery conditions continuing. Wind chills will
likely remain in the single digits and teens most of the day.
High pressure will build in from the Ohio Valley for Monday
night into Tuesday, allowing winds to gradually relax.
Temperatures will remain well below normal Monday night (lows in
the single digits/teens), with high temperatures returning
closer to average Tuesday as return flow commences.

A low pressure system will pass through the Great Lakes Tuesday
night into Wednesday, which will allow some precipitation to
spread into the area. While ridging aloft may support above-
freezing air, there may be lingering cold air from the Arctic
high. Given the extended range of the forecast and uncertainty
on timing, have only mentioned rain or snow in the forecast, but
freezing rain could also be possible. Model spread increases
thereafter, although a period of rain is likely on Wednesday as
the trailing cold front enters the area. If a wave of low
pressure is able to develop along the front, there could be
additional precipitation that could be wintry. The system will
likely exit on Thursday with below normal temperatures


Aviation /16z Friday through Tuesday/...
IFR to LIFR conditions gradually abating today as low levels
slowly mix out the moisture lingering from the overnight snow.

Once the moisture is finally scoured out later today/this
evening, VFR conditions and light winds are expected through
tonight as weak high pressure build into the area.

Sub-VFR conditions appear likely later Saturday night into
early Sunday morning as a storm system approaches the area then
tracks nearly overhead. Gusty northwesterly winds will be
possible Sunday afternoon through Monday in the wake of the
departing system. Visibility/cigs should improve back to VFR by
late Sunday afternoon.

Strong northwest winds will continue Monday before abating Monday
night as high pressure builds in. VFR conditions are expected.


a cold front will cross the waters today, but the flow behind
it is weak, so no advisories are expected through tonight as
weak high pressure builds in.

A Small Craft Advisory may be needed Saturday and Saturday night in southerly
flow ahead of an area of low pressure. Gale level northwesterly
winds appear likely Sunday morning through Sunday night.

High end Small Craft Advisory or low end Gale Warning conditions
will continue in strong northwest flow on Monday. Winds will
gradually diminish Monday night, with light winds expected Tuesday
as high pressure builds in.


Tides/coastal flooding...
an onshore flow will increase later today through Saturday
night as low pressure passes through the area. Minor tidal
flooding for sensitive areas near high tide is possible during
this time. A strong offshore flow will develop later Sunday and
Monday. Tidal blowout conditions are possible during this time.


Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...dense fog advisory until noon EST today for mdz004-005-503>506.
Winter Storm Watch from Saturday afternoon through Sunday
morning for mdz003-501-502.
Virginia...dense fog advisory until noon EST today for vaz026>031-039-040-
Winter Storm Watch from Saturday afternoon through Sunday
morning for vaz028.
WV...dense fog advisory until noon EST today for wvz053.
Winter Storm Watch from Saturday afternoon through Sunday
morning for wvz050>052-055-501>504.


near term...klw

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