Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 230859
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EST Mon Jan 23 2017

.SYNOPSIS...
Low pressure will impact the area through today before moving away
Tuesday. A cold front will pass through the area Wednesday night.
An upper-level trough will build overhead for the end of the week
into the weekend.
&&

.NEAR TERM /THROUGH TONIGHT/...
Large dynamic system poised to impact the Mid-Atlantic region
through Tuesday...as surface low treks to our south across the
Carolinas and then northeastward along the coast. Light rain
already occurring over parts of the area...though
steadier/heaviest rain pivots into the area from the south near
and shortly after daybreak. Guidance in reasonable agreement with
shifting the heaviest rain across the area from 7 AM through 2
PM...with dry slot working into much of the area for the
afternoon. Greatest rain totals expected along the eastern slopes
of the Blue Ridge...as upslope enhances precipitation efficiency
there (could see > 2 inches). Generally 1-2 inches expected
elsewhere. Not entirely out of the question to see a rumble of
thunder in some convective elements across S MD this afternoon as
weak mid-level instability develops due to cold temperatures aloft
as upper low passes by. However, chances remain too low to add at
the moment.

Also have strong winds to deal with. Winds have already picked up
across the area with gusts already 20-30 kts. Winds will further
intensify later through the morning and into the afternoon as sfc
low nudges closer to the area. Wind Advisory looks in good shape to
account for wind gusts in excess of 40 kts.

Lastly, some wintry precipitation could develop late this afternoon
through tonight across the higher terrain of W MD, WV, and VA as the
column continues to cool. Some uncertainty remains as to when this
occurs...and the type of wintry precipitation. Could be a period of
sleet/freezing rain as low levels cool slightly faster than mid-
levels. Increased snow totals a bit to account for greater faster
cooling of the column...though...any accumulations will initially be
hampered by warm ground temperatures. Generally 1-2 inches at the
higher elevations with less than an inch elsewhere...though a few
isolated spots at higher elevations could pick up a bit more.
&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Tuesday remains a transition day...as center of surface low
continues its eastward progression off the Jersey coast and high
pressure across the gulf states gradually builds northward toward
the area. A few lingering light showers remain possible through
midday mainly from DC and to the N/NE. Additionally, upslope
snow/rain showers could continue into mid-afternoon before
moisture becomes too shallow and upslope winds turn to southerly
as high pressure nudges up into the area. While rain will shift
out of the area by midday...breezy W/NW winds gusting up to 25 kts
remain...with relatively warm conditions on the drying flow.

Heights crest over the area through midday Wednesday...with
unseasonably warm temperatures (e.g., highs near 60F). Cold front
crosses the region late Wednesday into Thursday...and, with limited
moisture east of the mountains, expect most areas to remain dry.
Upslope flow will allow for some rain/snow showers to develop by
late Wednesday night.
&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
A sharp shortwave axis will cross the forecast area Thursday
morning, which will carve out a deeper 500mb trough axis and pave
the way for a series of disturbances into the weekend. The bulk of
the moisture will be squeezed out by the Appalachians, but a
northwest flow/cold advection pattern will be maintained areawide.
In terms of temperatures, that means we`ll be much closer to normal.
(Thursday will be the transition day; the temperature trace may not
be truly diurnal, but its still quite far out to deviate from the
norm.) Any precipitation would be snow, and it could be significant.
However, it seems as though this would be a case of a couple of
inches each day/night. It`s already mentioned in the Hazardous
Weather Outlook, so will leave it there.
&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
IFR...to at times sub-IFR...will continue through tonight as low
pressure system impacts the area. Steadier/Heavier rain will impact
all terminals near daybreak through mid afternoon...before showers
become more scattered in nature. Gusty winds up to 30-40 knots are
also possible through the day today.

MVFR may linger at a few sites (mainly BWI/MTN) for a few hours
Tuesday morning...before showers move out of the area and all sites
become VFR by afternoon. However, breezy conditions will continue
with NW wind gusts 20-25 kts...before subsiding Tuesday night. High
pressure briefly nudges into the area late Tuesday into Wednesday
with dry weather and VFR prevailing. Weak front moves through late
Wednesday...though at the moment it appears showers should avoid
terminals.

Mainly VFR conditions should prevail Thursday-Friday in northwest
flow. MRB has the best chance at receiving impacts from cold air
stratocumulus and potential MVFR/scattered snow showers; low
confidence in that outcome though.  Winds (from the northwest) will
be gusty.
&&

.MARINE...
Solid gale force winds expected through early evening...as surface
low impacts the area. Gale Warning in effect until 6 PM to account
for this. While winds subside below gale force later this
evening...expect solid SCA conditions to continue into Tuesday
behind departing low pressure system...with a SCA now in effect
from 6 PM tonight to 6 PM Tuesday.

Winds slacken late Tuesday as influence from low wanes. Mostly dry
cold front crosses the waters late Wednesday into Thursday...with
gusty winds possibly to SCA criteria behind it Thursday afternoon.

Northwest flow on the waters Thursday/Friday as cold(er) air invades
area. Small Craft Advisories appear likely. Wouldn`t completely rule
out gales.
&&

.TIDES/COASTAL FLOODING...
Persistent easterly flow has lead to elevated water levels at a few
tidal sites. Coastal Flood Advisory was issued for Straits Point for
this morning and this evenings high tide cycles. Elsewhere...action
stage is expected at Annapolis and Solomons...though further
increase in anomalies could lead to tidal levels near minor stage.
DC/Alexandria also forecast to reach minor stage late this
afternoon. Will wait for next forecast cycle to decide if any
advisories are needed as confidence is too low currently. Developing
westerly flow should allow for some decrease in anamolies by later
Tuesday.
&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Wind Advisory until 4 PM EST this afternoon for DCZ001.
MD...Wind Advisory until 4 PM EST this afternoon for MDZ004>006-011-
     013-014-016>018-503>508.
     Coastal Flood Advisory from 8 AM this morning to 3 AM EST
     Tuesday for MDZ017.
VA...Wind Advisory until 10 AM EST this morning for VAZ507-508.
     Wind Advisory until 4 PM EST this afternoon for VAZ053-054.
WV...None.
MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EST
     Tuesday for ANZ530>543.
     Gale Warning until 6 PM EST this evening for ANZ530>543.

&&

$$
SYNOPSIS...MSE
NEAR TERM...MSE
SHORT TERM...MSE
LONG TERM...HTS
AVIATION...MSE/HTS
MARINE...MSE/HTS
TIDES/COASTAL FLOODING...MSE



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