Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 251334
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
934 AM EDT Fri May 25 2018

.SYNOPSIS...
Surface high pressure will move offshore this afternoon. Weak
disturbances will cross the area over the weekend into early
next week. A cold front will push through the area on Tuesday. A
low pressure system may approach from the south during the
middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure will continue to move offshore of the Virginia and
North Carolina Coast the remainder of the day. A southerly flow
will continue, as well, leading to increasing warmth and
moisture. High temperatures will reach the 80s with perhaps a
few spots pushing 90. It will also be a little more humid as dew
points increase into the 60s. A little better deep layer
moisture return along the Appalachians may result in some
isolated showers by mid- afternoon, but a cap with limited
forcing will likely limit intensity and duration.

While any showers over the mountains will likely diminish with
sunset, there could be a cluster of decaying showers/thunderstorms
which approaches from the Ohio Valley overnight. Even if the
showers hold together, the trajectory around the ridge may make
them more likely to move toward Pennsylvania than our CWA.
Elsewhere, it will remain dry and a bit more muggy, as lows only
drop into the 60s to lower 70s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
The weekend will likely be unsettled with potential for
thunderstorms with heavy rain, but will not be a complete
washout. Moisture will increase further, with dew points pushing
into the 70s and high temperatures remaining in the 80s.
Precipitable water values will also increase to around 1.75".
Combined, moderate instability will likely develop by the
afternoon hours as a subtle disturbance approaches from the
southwest. Given deep layer shear generally less than 25 kt,
storms aren`t expected to be especially organized or widespread
at any one moment, but many areas will see a storm at some point
during the afternoon or evening. The main threat will be
locally heavy rain as storm motions may be around 20 mph or
less. While storms should generally trend downward after sunset,
there will be potential for additional vorticity maxima to
cross overnight with the threat for a few showers or perhaps a
storm.

The set-up doesn`t change much for Sunday, although the ridge
may be suppressed a little as a trough moves across the Great
Lakes. This system may send a back door cold front to the
south, although current projections keep it north of the area.
Coverage of thunderstorms will likely become numerous again
during peak heating, though some models show an early start due
to forcing from the northern system. Locally heavy rain will
again be the biggest threat. Given antecedent conditions which
are still wet, the could be potential for isolated flooding
issues either day. Don`t have a handle at the moment if one day
will be favored over the other, nor any particular area, given
the expected disorganized nature of the thunderstorms.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Southerly flow will continue across our region Monday and into
Tuesday with tropical moisture being advected into our region. A
weak boundary will be lingering to our north on Monday and move
across on Tuesday. The boundary and in addition to diurnal
heating will allow for showers and thunderstorms to develop in
the afternoon/evening hours both days.

A high pressure system will be centered over the Northeast U.S. on
Wednesday and move offshore on Thursday. Flow will become easterly
on Wednesday and then turning more southerly on Thursday. At the
same time a low pressure system will be to our southwest centered
over the Gulf Coast states. Some guidance bring this low into the
Mid-Atlantic and other keeps it tracking east over the Southeast
U.S. This could mean the difference between a dry or wetter second
half of the work week as it could bring additional tropical moisture
to our region...therefore additional showers and thunderstorms.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
VFR through tonight as high pressure continues to move
offshore. Will withhold mentioning any fog for tonight since
cloud cover should begin increasing. Southerly flow will remain
10 kt or less.

A warm and humid airmass combined with weak disturbances will
lead to the potential of showers and thunderstorms Saturday and
Sunday, favored during the afternoon and early evening. Impacts
will likely be brief, with heavy rain the main threat. Fog could
occur overnight in locations that receive rain if skies clear.

Warm and moist air Monday into Wednesday will allow
for additional showers and thunderstorms mainly in the
afternoon/evening hours which brings the possibility of sub-VFR
periods.

&&

.MARINE...
High pressure will move offshore this afternoon, with southerly
winds developing. Winds should stay in the 10-15 kt range
during the day. Have issued a Small Craft Advisory for tonight
for the wider waters of the midday where increasing
southwesterly flow aloft will have enough fetch to mix down.
Winds may also be marginal on Saturday, but am uncertain enough
not to continue the advisory for now. The larger threat may come
from thunderstorms during the afternoon and evening. Sub-SCA
conditions are expected on Sunday too, though showers and
thunderstorms will become likely again during the afternoon and
evening.

Winds are expected to remain below small craft advisory
criteria Monday into Wednesday, therefore not anticipating an
advisory for this period.

&&

.TIDES/COASTAL FLOODING...
Water levels remain slightly elevated at Washington DC, though
trends in the anomalies suggest minor flooding will be a low
threat. It will be close for the next several cycles though. No
coastal flooding issues are expected elsewhere.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 6 PM this evening to 8 AM EDT
     Saturday for ANZ533-534-543.

&&

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


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