Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 190751
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
351 AM EDT THU MAY 19 2016

.SYNOPSIS...High pressure will build through Friday morning. Low
pressure will approach the area Friday night from the Tennessee
Valley and track to our south Saturday. High pressure will build
overhead early next week...but an upper-level low will remain
close by just off the Mid-Atlantic coast.

&&

.NEAR TERM /THROUGH TONIGHT/...Showers have diminished in coverage
but radar still picking up some light returns over eastern areas.
Guidance indicates drying in the 850-500 mb layer through the
morning with shortwave-trough axis crossing the area around 12z.
After that, height rises and building sfc high pressure will lead
to tranquil conditions through Fri morning. However, some spotty
light showers are possible over the Appalachians where models show
weak upslope flow developing. Otherwise, mostly cloudy to cloudy
as shallow moisture remains trapped beneath a subsidence
inversion. Conditions tonight will be favorable for fog
development due to moist ground, light winds and clear skies.
Model soundings indicate it, but MOS guidance fails to drop
visibilities much anywhere. Have added patchy fog to the fcst.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...Dense high clouds
will start advancing northeastward rather quickly ahead of low
pressure over the TN valley Fri. Combo of height falls, moisture
advection over cool air mass will lead to rain Fri night into Sat.
Models continue to show a faster and weaker trend of upper trough
crossing the area Sat. This leads to an earlier end of the steady
rains Sat with lighter amounts of 1 to 1.5 inches total with
heaviest over the southern portions of the fcst area. At this
time, flooding appears unlikely. Low pressure exits the area Sat
night with mid-levels drying out, but additional shortwave-energy
moving across the area as longwave pattern amplifies will keep the
chance of showers in the fcst.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...The long term forecast will
largely be influenced by a closed upper low. This low will form
Sunday as a shortwave trough rotates into the mean troughing along
the east coast after the departing coastal low on Saturday.
Therefore expect a chance of showers on Sunday, particularly
during the afternoon. Shower chances are a little more uncertain
for Monday and Tuesday, depending on the location of the upper low
and the placement of embedded vorticity maxima. The 00Z
operational guidance doesn`t suggest any additional surface low
development, which would point to light, showery activity focused
on diurnal heating. Wednesday will have the best chance of being
dry as the upper low pulls away far enough to have high pressure
from the west to be the dominant influence.

While temperatures (especially highs) will likely remain below
normal due to the upper low, current layer RH forecasts suggest some
breaks in the clouds will be possible. Thus temperatures should be
closer to the 70F mark than some of our recent unsettled periods.
Will have to watch Monday though, as low level flow will be from the
NE. Assuming the low can move to the east by Wednesday, there is
plenty of warm air available to spread eastward from the Plains.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...Mvfr cigs at KCHO through
12Z. Otherwise, bkn-ovc050 through 21z. Skies clear tonight which
may give to fog development given wet soils and light winds. Model
soundings suggest this but MOS guidance fails to pick up on it.
Rain moves in after 00Z Sat and spreads northeast by 12z Sat.
Mvfr/ifr cigs expected Fri night through Sat. Improving cigs Sat
night.

Widespread aviation impacts are not expected Sunday into Monday,
although scattered showers will be possible at times due to upper
level low pressure (highest chance Sunday). There is a chance sub-
VFR clouds could develop Monday in NE flow.

&&

.MARINE...Winds below 10 kt through Fri night. Winds strengthen
Sat through Sun with small craft advisory conditions likely. Gusts
to 30 kt possible.

A trough axis will pass through on Sunday, and northerly winds may
reach SCA criteria. The pressure gradient should relax enough Sunday
night into Monday to keep NE winds in the 10-15 kt range.

&&

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

&&

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



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