Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220801
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
401 AM EDT SUN MAY 22 2016

.SYNOPSIS...
A low pressure near Cape Hatteras today will head northeast
through Monday. High pressure will slide southeastward from the
Ohio Valley on Monday into the southeast on Tuesday and then move
off the coast Wednesday, where it will remain for the rest of the
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Upper level low is currently taking shape in north-central PA per
water vapor and radar. Locally, low level moisture and weak lift is
producing drizzle with pockets of steadier rain. This is reducing
visibility some, but fog/mist is not expected to be dense outside of
the mountaintops (due low clouds).

The suite of hi-res models paint the gloomy picture in store for
today as the upper low drifts south to VA. Expect rain over PA to
likewise move southward, eventually encompassing roughly the
northern two-thirds of the area. Have changed forecast wording to
periods of rain (where POPs categorical) through early afternoon.
Didn`t go with 100 POPs yet due to some placement uncertainties, but
a fairly widespread area will likely see a period of steady rain.

Slightly drier air will begin to wrap into the low this afternoon.
Simulated reflectivity suggest precip will become more showery by
this time. In addition, some weak instability may build generally
west of I-81, so can`t rule out a few thunderstorms there. Expect
another day where temperatures struggle to reach 60, especially the
eastern half of the area where rain is expected to persist longest.

By tonight, the upper low will be drifting to SE VA, and combined
with the diurnal trend, precip should diminish in coverage,
eventually becoming focuses in the Fredericksburg-S MD vicinity. Low
clouds and light fog will develop again, and can`t rule out some
drizzle. Close to persistence for lows...upper 40s to mid 50s.


&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The upper low will be pivoting near the Outer Banks and offshore on
Monday as it spawns a surface low pressure. This will keep a
moisture feed into the area and would thus expect mostly cloudy
skies to continue. Models insist on higher cloud bases though and
perhaps even a few glimpses of sun. This deeper mixing is giving
highs in the upper 60s to perhaps lower 70s, but I`m a little
skeptical it gets that warm. Also with this heating, there should be
some instability building by afternoon, so showers will likely
develop with perhaps a few thunderstorms, especially the further
west you go.

By Monday night, the low will be moving toward Cape Cod, so expect
showers to diminish, with any lingering activity east of the Blue
Ridge. Unfortunately, there will still be enough moisture wrapping
around the low to keep a small chance of showers east of I-95
through midday Tuesday, perhaps extending into the afternoon (along
with an isolated rumble of thunder). However, with diminishing cloud
cover, it looks like a majority of the area will make it into the
70s. Ridging at the surface and aloft arrives in earnest Tuesday
night with lows in the 50s to near 60.


&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Generally warmer and more humid through the long term as a much
more summer-like pattern develops. Ridge axis will remain to our
west on Wednesday with a northwest flow aloft likely suppressing
any convection despite increased instability. By Thursday the
ridge axis is passing and a weak shortwave is approaching.
Combined with the still increasing warmth and
moisture...thunderstorm chances over the higher terrain to the
west will increase. Some may try to reach the lower elevations to
the east before dissipating. Another ridge axis approaches Friday
but by this point instability may be great enough thanks to
continued increase in warmth and humidity that convection may
develop along the terrain to the west regardless. Saturday a ridge
of high pressure aloft looks to develop directly overhead...but
the excessive warmth and moisture may still overcome any
suppressive effects and cause spotty showers and thunderstorms to
develop over the mountains and potentially advect east before
dissipating. By this point highs in the lower elevations may reach
90 for the first time this year...notably later than normal by
several days. Lows will be sultry with 70s possible in the urban
centers.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
Currently a mixture of MVFR, IFR, and localized LIFR across the area
early this morning, with light rain and drizzle at times. Have some
gradual improvement after daybreak, but this will likely be minimal,
especially northern parts of the area, as light rain become more
widespread. Tough to time in any breaks except perhaps CHO. Precip
may become more showery by late afternoon, and this may be the best
chance for a solid push of MVFR. However, expect low clouds and fog
to redevelop tonight. Have limited this to MVFR for now though.
Winds light and generally N or NW.

Monday will remain cloudy, but models insist on higher cloud bases,
perhaps VFR at times. Showers will redevelop quickly by midday
though and there could be a thunderstorm. As precip diminishes
Monday night, there is a chance of lower clouds and perhaps fog,
especially eastern areas. Conditions will improve Tuesday as high
pressure builds with light NW winds.

VFR later next week.


&&

.MARINE...
Northerly winds persisted up to 20 kt quite a bit into the night,
but looks like they are falling below SCA criteria now, so will let
it expire. With a second area of low pressure developing offshore,
winds will remain northerly through Monday night or so, but at this
time, magnitudes appear to be less than 15 kt. High pressure will
begin building Tuesday with winds become NW then W.

Light winds overall thru late next week.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...RCM
NEAR TERM...ADS
SHORT TERM...ADS
LONG TERM...RCM
AVIATION...ADS/RCM
MARINE...ADS/RCM



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