Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
1001 PM EDT Friday Aug 1 2014
a coastal front will remain nearly stationary along the middle-
Atlantic coast through the weekend. A trough is expected to move
through Monday. Weak high pressure builds in Tuesday.
Near term /through Saturday/...
under a larger and very broad trough...lots of smaller waves from
the northern plains to the Great Lakes to the southern Atlantic coast are
spinning about the periphery of the larger wave. This has been
creating pockets of localized shower/thunderstorm activity across the East
Coast states...and will continue to do so into the weekend. As the
main upper trough axis approaches from the west...sections of dry
middle-level air are being pushed in between the smaller upper vorts
and shortwaves. One such pocket of dry air was over the region
earlier...on the fringe of a wave that brought showers to Delaware-Maryland-Virginia
earlier in the day. Another similar scenario is setting up...W/
the dry air batch pushing up against another embedded wave to our
south. The interactions between the two are causing areas of light
to moderate showers to move up the I-95 corridor of southern Virginia and
toward the District of Columbia/balt metropolitan areas late this evening.
Earlier this aftn/eve...subtle near surface boundaries kicked-off a
handful of small/heavy rain showers that were short-lived but
packed some tropical moisture. The airmass we're under...a type of
modified tropical environment - will be west/ US into the weekend.
Isolated and sometimes scattered showers...higher humidities than
in the past few days - and moderated temperatures.
Overnight...temperatures will drop only into the u60s/l70s - l-m60s
across the western zones where some drier dewpoints have mixed-in.
Skies will remain generally overcast and a batch of light rain
will continue to pivot across the lower/eastern fringe of the area.
I-95 will roughly be the boundary between rain/no-rain for the
late night and into the early morning hours. Precipitation stretching much
further west and north will dissipate quickly west/ little-to-no
sustaining force to maintain it...which is typical west/ a tropical-
type airmass. The more solid precipitation activity will be across lower
southern Maryland and to the east of the District of Columbia/balt metropolitan into the middle-morning hours
Scattered and isolated showers will continue into the daytime hours
on Sat as well...but mainly a moderate or lower chance - more like
a 30-40 percent across the central sections of the area and higher
chances closer to the Bay West/ proximity to a stalled coastal front
and waves of low pressure - and Bay/land breeze boundaries. Some
Wedged-in cooler air from high pressure off the New England
coast will remain over the area into Sat...keeping conditions
moderated where it isn't raining - along and west of I-95 mainly.
Maximum temperatures Saturday will remain quite cool for this time of year...
ranging from the 60s in the mountains to near 80 in Washington
Short term /Saturday night through Sunday/...
an upper-level trough will build overhead Saturday night and
Sunday while the coastal front is expected to shift northwest
into our area during on Sunday. More showers and thunderstorms
are possible during this time...especially Sunday where higher
dewpoints and warmer temperatures will lead to more instability.
Maximum temperatures Sunday will be a bit warmer with some breaks of
sunshine...ranging from the 70s in the mountains to the middle 80s
near Washington and Baltimore.
Long term /Sunday night through Friday/...
lower mean heights will persist over the East Coast over much of
next week. At the surface...a front will move slowly offshore early
in the week. This will not only bring an end to shower and
thunderstorm chances...but should also act to steer tropical cyclone
Bertha well offshore. /For the latest on Bertha...please refer to
Near to below normal temperatures are anticipated given the pattern
of weak troughing aloft and high pressure moving over the area at
the surface during the middle part of next week.
Ridging builds in aloft as high pressure moves offshore...resulting
in warmer and more humid conditions during the second half of next
week. An approaching trough will break down the ridge and result in
a chance of showers and thunderstorms by the end of next week.
Aviation /02z Saturday through Wednesday/...
relatively warm and moist air remains in place...and heading into
the overnight hours - that means lowering ceilings. Shower activity
limited to areas largely south and east of the District of Columbia/balt areas. Low
clouds expected to develop quickly into the overnight hours. Periods
of IFR or lower possible across the shen valley and into near-kcho west/
mainly MVFR for the I-95 regions.
More showers are possible Saturday night...but there is a better
chance for showers and thunderstorms Sunday. There is also a
higher degree of certainty that low clouds will develop Saturday
night into Sunday morning.
Light/variable winds Sun night become northeasterly Monday less than 10
kts. Light/variable winds again Monday night into Tuesday...then westerly
around 10 kts Wednesday. Generally VFR...except sub-VFR possible in
showers/isolated thunderstorms Sun night-Monday night.
a coastal front will remain along the middle-Atlantic coast through
Saturday night. The pressure gradient will strengthen a bit
tonight as weak low pressure rides along the front. Wind gusts
will approach Small Craft Advisory criteria along the Bay and lower tidal Potomac
River. However...wind gusts have been capped around 15 knots for
now since the low will be weak. Winds will remain below Small Craft Advisory
criteria Saturday through Saturday night.
Showers and thunderstorms are likely Sunday...but the gradient
winds should remain below Small Craft Advisory criteria.
Sub Small Craft Advisory conditions are expected into the middle
of next week with weak flow over the area. Showers and possible
thunderstorms will diminish as a front departs the coast early in
District of Columbia...none.