Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 250759

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EDT Sun Aug 25 2019

Strong high pressure will build north of the region today. Low
pressure likely will develop off the Carolina coast early in the
week and move out to sea by Tuesday. A cold front will cross
the region on Wednesday.


High pressure ridging southward to the east of the Appalachian
Mountains will promote dry conditions today. A shower or two can`t
be ruled out over southern Maryland or along the Chesapeake Bay
coastline and adjacent areas later this afternoon and early evening.
Temperatures will reach the middle to maybe upper 70s today before
dropping into the middle to upper 50s tonight.


High pressure will move out to the northeast Monday and Monday
night. A persistent wind from the east or northeast will usher in
additional low-level moisture during this period. Dewpoint
temperatures, or the indication of the amount of moisture in the
air, will gradually rise out of the 50s into the 60s during the day.
With this increased moisture and departing high pressure, additional
showers are expected to develop not just in the eastern zones but
parts of the Virginia Piedmont, along the Blue Ridge, and in the
Potomac Highlands Monday afternoon and evening. Temperatures will
reach the middle 70s then fall only into the middle 60s Monday

About the time that showers Monday evening begin to wind down or
dissipate, we could have a tropical system lingering off the East
Coast near the Virginia and North Carolina shoreline. This system is
expected to push onward toward the northeast over the open Atlantic
Tuesday and Tuesday and not have any path toward the Delmarva
Beaches since there will be an upper level trough approaching from
the Ohio Valley. Although we don`t anticipate a direct impact with
this system Tuesday into Tuesday night, it could have an effect on
our coastal waters of the Chesapeake Bay and Tidal Potomac in terms
of coastal flooding. Also, showers and perhaps a diurnal
thunderstorm or two could evolve in parts of our region. The east to
southeast component to the wind expected Tuesday could mean that any
modest convection could evolve due to upslope along the Blue Ridge
and Potomac Highlands. Temperatures Tuesday should approach 80
degrees in most places.


A trough axis crossing the Great Lakes Wednesday will push a cold
front across the Mid Atlantic. The atmosphere will be sufficiently
moist prior to the frontal passage, with respectable instability and
modest shear--certainly enough to justify a shower/thunderstorm
forecast at high chance to maybe likely levels. That said, it is
unlikely that it will be an all day rainfall; rather the
precipitation/fropa seems to be focused on the timeframe of peak
diurnal heating, although the lingering upper trough/jet suggests it
may not move through quickly. Will be keeping chance PoPs east of
the Blue Ridge into Wednesday night.

For the rest of the week, continental high pressure building toward
the east coast will be the primary weather feature. Consequently
temperatures will remain rather mild for late August (highs in the
lower-mid 80s, lows mid 50s-mid 60s).


VFR conditions expected with high pressure to the north then to the
northeast by Tuesday. Any showers should be isolated Monday and
Tuesday with low confidence as to which terminals may or may not
encounter one of these showers. Winds northeast around 10 knots
through Monday night. Winds becoming southeasterly around 10 knots
Tuesday into Tuesday night.

Flight restrictions may linger into Wednesday due to low clouds and
perhaps vsby as a result of east flow. Ceilings will gradually lift
through the day, but an approaching cold front will support a chance
of showers/thunderstorms by afternoon/evening. While exact
convective impact uncertain, odds suggest it wouldn`t be widespread
or of long duration. But, the lingering moisture could result in
restrictions Wednesday night.

Thursday should fare better as high pressure builds. VFR likely.


A Small Craft Advisory remains in effect through this afternoon
for much of the Chesapeake Bay and Tidal Potomac. An extention
to this Small Craft Advisory has been issued for tonight into
early Monday morning. Depending on the gradient between the high
to the north and the developing tropical system along the East
Coast, additional Small Craft Advisories may be needed through
the day Monday into Monday night.

The pressure gradient likely won`t be strong enough to support Small
Craft conditions Wednesday or Thursday. But, a frontal passage late
Wednesday will support showers/thunderstorms so local marine
warnings possible.


MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Monday
     for ANZ530-531-536-538-539.
     Small Craft Advisory until 6 AM EDT Monday for ANZ532-533-
     Small Craft Advisory until 6 AM EDT Monday for ANZ534-537-543.


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