Area Forecast Discussion
Issued by NWS Sterling, VA

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234
FXUS61 KLWX 231556
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1056 AM EST Mon Jan 23 2017

.SYNOPSIS...
Low pressure over North Carolina will track northeast off the
Delmarva tonight. 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/...
A year ago today we were beginning the dig out from 2-3 feet of
snow from the blizzard. Strong low pressure is impacting the area
today - but the big differences are this one`s path is 150 miles
farther to the west...and temperatures are 20 degrees warmer.

Morning surface analysis showed low pressure centered over
northern NC. A large swatch of precip (rain) is affecting
southwestern VA, which is south of our forecast area. There is a
strong pressure gradient between the low and high pressure over
northern ME. This is causing strong easterly winds across the
area. We are seeing gusts of 30-40 mph across much of the region.
These will remain strong throughout the day.

So far Upper Sherando reports 1.83" of rain. Big Meadows has
received 2.28" in the past 12 hours.

Previous discussion:

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.

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 /16Z MONDAY THROUGH FRIDAY/...
IFR will continue through tonight. Steadier/Heavier rain will
impact all terminals through mid afternoon...before showers
become more scattered. Gusty winds up to 30-40 knots are also
possible 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...
Gale Warning in effect until 6 PM. Expect solid SCA conditions to
continue into Tuesday behind departing low pressure system...with
an SCA 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.

&&

.HYDROLOGY...

We have issued a flood watch along the I-81 corridor from
Rockingham to Berkeley. Only water to show much response at the
moment is Wardensville...but is is still only half way to flood
stage. Area of moderate rainfall is on its way to that area. We
will continue to monitor. The heavy rain should be north of the
watch area by midnight.

&&

.TIDES/COASTAL FLOODING...
Persistent easterly flow has lead to elevated water levels.
Coastal Flood Advisory was issued for Straits Point through the
evening high tide cycle. 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. 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 until 3 AM EST Tuesday for MDZ016-017.
VA...Flood Watch through this evening for VAZ026>031-038>040-507.
     Wind Advisory until 4 PM EST this afternoon for VAZ053-054.
     Coastal Flood Advisory until 3 AM EST Tuesday for VAZ057.
WV...Flood Watch through this evening for WVZ052-053.
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.

&&

$$
UPDATE...WOODY!
PREVIOUS...MSE/HTS



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