Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 191031
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
631 AM EDT Wed Apr 19 2017

.SYNOPSIS...
High pressure centered over northern New England will wedge down
the east coast today. A cold front will cross the area Friday
afternoon. High pressure builds over New England for the
weekend. Low pressure moving in from the west will impact the
Mid Atlantic Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Light rain has broken out over the western DC metro and farther
west over the past three hours. This will further strengthen the
onshore flow and cold air damming. Have limited temperatures to
near normal.

See coastal flood section for minor update.

As of 3am, a 1038mb surface high is centered over the Canadian
Maritimes with a surface ridge extending SW through the central Mid-
Atlantic to Atlanta. Easterly flow is spreading across the CWA with
the entire Balt-Wash metro currently reporting light east winds.
This cold air damming flow will continue through today with low
clouds and light rain/drizzle eventually forming by this afternoon.
Max temps struggle to reach 60F everywhere except valleys west of
the Shenandoah where less marine influence should allow for mid 60s.

Continued onshore flow tonight should allow cloud ceilings to drop
near the surface, resulting in areas of fog. Min temps in the 50s,
near the dewpoint that will steadily rise as marine air is advected
in.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
Low pressure develops over the Great Lakes Thursday. An associated
warm front will lift north across the central Mid-Atlantic in the
morning with a threat for elevated then later surface based
thunderstorms spreading in from the SW. 12 to 14C 850mb temps
overspread the area with MaxT in the (mostly likely) low 80s.

Bulk shear is low through Thursday evening over the area, making the
severe threat minimal. The shear increased Thursday night, but given
diurnal decreases in instability, the severe threat should remain
low.

The cold front reaches the central Appalachians around sunrise
Friday and slowly progresses through the CWA through midday Friday.
Should the cold front be delayed, early afternoon thunderstorms
would be possible over SErn zones (lower southern MD and
nearby waters) before the front shifts SE of the area.

Cold air advection is slow to arrive into the LWX CWA Friday with
max temps again reaching the low 80s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Cold front will sag south of the forecast area Friday night.
This won`t blast through the area...while it should be dry there
will likely still be clouds around. Lows will range from the
mid 40s far west to mid 50s I-95 and east.

Highs Saturday 60-65. High pressure will be centered over the
eastern Great Lakes while the previously mentioned front will
remain south of the Mid Atlantic.

Conditions will deteriorate Saturday night ahead of low pressure
which will form on the frontal boundary. By late night PoPs will
be up to likely. By Sunday morning it should be raining across
the forecast area as the high moves over northern New England
and a CAD wedge forms on the east side of the Appalachians. Have
raised PoPs to categorial. QPF of over one inch will be
possible. It will be a cool day as well, with high temps only
55-60, which is almost ten degrees below normal.

High pressure returns to the area for the first part of next
week. Temperatures will rise into the 60s during the day.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Cold air damming surface pressure ridge persists over the DC metros
through this evening. Conds lower to IFR through the morning hours
as the onshore flow saturates with rain/drizzle developing by this
afternoon and continuing as late as Thursday morning. Tonight may be
more fog than drizzle as noted in the 06Z TAFs.

A warm front lifts over the area Thursday with southerly flow and
scattered thunderstorms over the DC metros and west in the afternoon.

A cold front moves across the DC metros Friday morning with chances
for gusty showers.

If it rains Friday there may be some concern for fog
development. VFR conditions expected Saturday. Ceilings are
expected to degrade Saturday night, continued sub-VFR Sunday.

&&

.MARINE...
Onshore flow from current time into or through tonight under high
pressure ridge. SCA for SEly flow up the tidal Potomac has ended
with gusts generally around 15kt across the area through tonight.

A warm front lifts north through the area Thursday with afternoon/
evening scattered thunderstorms with gusty winds possible.

A cold front crosses the waters midday/early afternoon Friday.
Thunderstorm threat is for southern MD waters in the early
afternoon.

Winds in the 15-20 kt range possible Saturday. A wet Sunday
looks on tap for the waters.

&&

.TIDES/COASTAL FLOODING...
Southeasterly flow over the Bay has caused water levels to rise
a little more than one foot above normal. This will make for
elevated high tides and minor coastal flooding at the most
sensitive sites. A coastal flood advisory is in effect for Anne
Arundel county with a high tide in Annapolis around noon.

Elevated water levels can be expected until Friday morning when
a cold front passes.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory from 10 AM this morning to 2 PM EDT
     this afternoon for MDZ014.
VA...None.
WV...None.
MARINE...None.

&&

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



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