Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 151906
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
306 PM EDT Sat Jul 15 2017

.SYNOPSIS...
Weak high pressure over the midwest will control the weather
through Sunday. An upper level trough will affect the weather
Monday. Another cold front may approach the region by the end of
the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure still west of the mountains. A cumulus field has
developed in response to a rather weak 500 mb trough axis. Any
instability is capped though, aside from perhaps the Chesapeake
Bay. Earlier showers well east over the Delmarva though. The
rest of the afternoon will be dry, as will the evening hours.
Cold advection will continue for several more hours, although
the maximum effect has already been realized, with dewpoints in
the lower-mid 60s. Low temperatures overnight will be in that
range, although a bit higher downtown DC/Baltimore.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Flow will slowly become southerly again Sunday, which will
permit a pinch of moisture/instability return. Given terrain
circulations and isentropic lift, there is an outside chance
that a shower or thunderstorm could develop by the end of the
day Sunday. Elevated instability (decent mid level lapse rates)
will continue into Sunday night as warm advection ensues, and
have kept a slight chance of showers/thunderstorms through the
night.

Monday`s forecast guidance reflects a considerable amount of
spread. However, heights will be dropping as another trough axis
shifts across the Mid-Atlantic. That much is consistent. Therefore
believe it reasonable that there will be at least a chance of
showers/thunderstorms in a marginally unstable atmosphere.
However, activity may be scattered in nature as shear weak and
insolation questionable, and thus have backed off on the upper
end of PoPs slightly.

Temperatures near climo through the period.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...

Main feature across the United States for the upcoming week will be
a large upper level ridge that will shift from the inter-mountain
west and into the central US.

A lingering upper level trough will still be overhead on Tuesday
with chances for some scattered showers and thunderstorms. This will
gradually diminish into Wednesday as the western upper ridge builds
into the plains states and a second ridge builds westward over the
Atlantic. There may still be a few showers/thunderstorms into
Wednesday.

By the end of the week, a more westerly flow will develop as the
ridge builds to our south/west with large scale troughing over
Canada. This will likely keep the area in an active pattern along
the gradient.

Temperatures during the week will trend back up above normal, but
nothing unusual for mid Summer, with highs back up into the 90s.
&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
VFR through the valid TAF period, with diurnal clouds and
northwest winds. Any fog would be valley based. Do not
anticipate impact at any terminal. If there were, CHO would be
the first candidate.

Southwest flow will gradually develop during Sunday. There may
be a stray shower or thunderstorm late Sunday-Sunday night, but
confidence low and coverage would be slim anyways.

A better chance at thunderstorms will arrive on Monday as an
upper level disturbance crosses the area. Flight restrictions
possible in vicinity of any thunderstorms.

Predominantly VFR expected Tuesday and Wednesday,, although there
will be chances for scattered showers/thunderstorms.

&&

.MARINE...
Winds beginning to relax across the waters. Have cancelled a
portion of the Small Craft. Obs in the remainder suggesting
15-20 kt gusts, which should end before the 5pm expiration.

Light winds tonight and Sunday with high pressure, then return
southerly flow will begin Sunday night into Monday. Will have to
keep an eye on channeling potential, but otherwise confidence
is low on SCA conditions being reached.

Sub-SCA conditions expected Tuesday and Wednesday. A few
showers/thunderstorms are possible.

&&

.TIDES/COASTAL FLOODING...
Southerly flow developing across the region as high pressure
shifts offshore will start to build anomalies Sunday, with minor
flooding at high tide possible at our most vulnerable sites
(most likely Straits Point) by Sunday PM. This would likely
continue into Monday. This could become a bit more widespread by
Monday night-Tuesday morning.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ534-
     536-537-543.

&&

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



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