Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220800

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EDT Mon Aug 22 2016

High pressure will build eastward from the Ohio Valley today. The
high will gradually shift eastward though the week ahead before a
cold front crosses the area on Friday. High pressure behind that
front will dominate through the weekend.


The primary cold front is offshore this morning, with high
pressure located over the MS Valley. A secondary front/trough axis
is located over northern PA, where light showers have been
diminishing. Precipitation should not be a concern locally today
though, as the high builds toward the Ohio Valley and upper level
troughing exits New England. While highs won`t be that far from
climo in the lower to mid 80s, the drop in humidity (dew points in
upper 50s) will be noticeable.

The center of the high will nearly be over the Mid-Atlantic by
late tonight. This will mean rural sheltered areas will likely
drop into the 50s, while the metros should remain in the mid 60s.
One caveat is that that NAM keeps some clouds across the area
which may hold temperatures up if realized.


Little sensible weather to talk about through the middle of the
week as the surface high inches offshore and ridging builds aloft.
Tuesday`s temperatures will be similar to Monday, while both the
temperature and dew point will tick up on Wednesday as southerly
flow develops -- but still relatively pleasant.

Theta-e ridge will approach the mountains ahead of low pressure
moving through the upper Great Lakes Wednesday afternoon or night,
but dry air aloft supports a dry forecast for now, despite some
light QPF model output.


Reasonably good agreement on long range guidance through the
weekend. High pressure will be sliding east off the coast on
Thursday. This will promote a warm and more humid southerly flow
across our region. Next cold front will cross the region on
Friday. Some advance showers and thunderstorms may affect the area
as early as late Thursday but bulk of activity expected Friday.
Guidance is not robust with this system and not expecting a great
deal of rain at this time. High pressure then slides eastward from
the northern Plains into northern New England on Saturday with
slightly cooler and less humid weather. By Sunday the easterly
flow will begin to bring more moisture back and with some
insolation added in...we may start to see some afternoon diurnal
showers or storms in the higher terrain.


High pressure will dominate the weather through the middle of the
week. A few NW wind gusts near 20 kt are possible after sunrise
this morning. VFR cumulus can be expected during the afternoons.
The NAM indicates a possible deck around FL050 tonight, but will
withhold cig for now. Fog appears unlikely tonight with dry air
remaining in place, but may become a concern Tuesday and Wednesday
nights near MRB/CHO as dew points increase.

Main concern Thursday into this weekend is scattered showers and
thunderstorms possible late Thursday and Friday with the next
cold front.


NW flow has been established behind a cold front. 20+ kt gusts
have mainly been limited to the wider waters. Am hesitant to
cancel the SCA though, as there could still be gusts after sunrise
when mixing increases. Have also extended the SCA until 3 PM for
the Bay south of Drum Pt and Tangier Sound based on latest hi-res
guidance. Elsewhere, solid 15 kt gusts will be possible through
afternoon before easing as high pressure builds.

Flow will become onshore Tuesday and southerly Wednesday as high
pressure moves east. At this time, winds are expected to remain
less than 15 kt.

Next front may bring some stronger SCA level winds late Thursday
into Friday with cold advection behind it Friday night into
Saturday. Odds are not high yet and will leave out of HWO for now.


MARINE...Small Craft Advisory until noon EDT today for ANZ530>533-
     Small Craft Advisory until 3 PM EDT this afternoon for ANZ534-
     Small Craft Advisory until 10 AM EDT this morning for ANZ535-


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