Scientific Forecaster Discussion
fxus61 klwx 282317
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
717 PM EDT sun may 28 2017
weak low pressure will move across the area this evening and
move out to sea Monday. Upper level low pressure will drift east
across the north side of the Great Lakes Monday through Friday.
In the meantime, weak high pressure will prevail over the mid-
Atlantic outside of weak trough passages Tuesday night and
Wednesday night. Low pressure approaches from the west this
Near term /overnight/...
The southern Virginia low is picked up in the 12z GFS and drifts east
across the Virginia part of the Chesapeake Bay this evening. Moisture
on southeast flow should be cutoff by this low, limiting
evening rainfall over the balt-wash Metro. Overnight the wind
shifts west with some upslope rain is expected on the western
slopes of the Allegheny Front, but not at an excessive rate.
Mid 60s min temps tonight which are near dewpoints. Should
clearing occur behind the low to our south, fog would be
expected. However, the jet overhead increases overnight, so at
least high clouds should remain and limit fog potential.
Short term /Monday morning through Tuesday night/...
weak trough moves east across the area in the morning with
advance showers ending by noon for the western shore of the Bay.
14 to 15c 850mb temps mix down in light westerly flow making
for Max temps low to mid 80s. The lack of rain and clouds will
make for a marked difference from today!
Weak surface high pressure lingers over the area as the parent
upper low drifts east across the north side of the Great Lakes.
A few shortwaves look to round the low and disrupt the tranquil
weather. The first looks to be Tuesday night so low chance pops
for showers were added then. Otherwise slightly above normal
Long term /Wednesday through Sunday/...
a weak front across the region could spawn a couple of showers or a
thunderstorm in parts of the region Wednesday into Wednesday evening.
Weak high pressure will build in Wednesday night through Thursday
night. Dry conditions and seasonable temperatures expected.
The high moves east Friday to allow for a leeside trough of low
pressure to form east of the Potomac Highlands Friday night. There
is a chance for rain showers along this trough both Friday and
Friday night. Temperatures will be near normal.
There is a better chance for rain showers and perhaps a few
thunderstorms Saturday into Saturday night as a disturbance moves
into the region to accompany the trough of low pressure.
By Sunday, a cold front should work into the region and bring an
additional threat for showers and thunderstorms.
Aviation /23z Sunday through Friday/...
MVFR cigs/vsbys across the District of Columbia metros with rain tapering off
(except for kmrb and west) this evening as low pressure passes
to the south. Fog will develop in any areas that clear.
Weak trough crosses from the west late tonight with light west
winds and VFR Monday into Tuesday. A weak trough crosses late
Tuesday with chances for rain then.
VFR conditions at the terminals, except where pop-up showers or
a thunderstorm develop Wednesday and Wednesday night. MVFR or
IFR conditions in rainfall. Winds west-southwest 10 knots
Wednesday becoming northwest 5 to 10 knots Wednesday night. VFR
conditions Thursday and Thursday night. Winds northwest 5 to 10
knots Thursday, becoming light and variable Thursday night.
light sely flow with low pressure over southern Virginia. This low
crosses the Virginia portion of the Bay this evening with rain ending
as it passes. Weak trough crosses from the west Monday morning
with light westerly flow Monday into Tuesday.
No marine hazards expected Wednesday through Thursday night. Winds
southwest 10 knots Wednesday becoming northwest 10 knots Wednesday
night. Winds northwest 5 to 10 knots Thursday then light and
variable Thursday night.
Flash Flood Watch has been dropped. Rain over our area is
stratiform. Across southern PA the rainfall looks heavier. If
any of this drops into Maryland it looks to be progressive enough to
not pose a problem.
water levels running within a few inches of a foot this
afternoon. Light onshore flow should keep the departure similar
through tonight, if not rising slightly. Since we've just passed
the new moon, there is a decent spread in the semi-diurnal
cycle...with the daytime cycle preferred. Current guidance
indicates that we'll hit minor flood during this cycle for the
next couple of days. However, departures a bit greater at Piney
Point, such that each cycle should hit minor. It'll be a similar
story at SW DC, and perhaps Alexandria as well.
Have made some advisory adjustments, based on the above
guidance and thinking. Included the next two cycles for the
upper Potomac, the next three cycles (through Monday night) for
St Marys (ultimately, the threat there will last longer), and
the second cycle (monday morning) in Calvert/Anne Arundel. No
additional forecasted flooding at this time. Will need to
monitor Dahlgren and Baltimore, both of which will come close to
minor on Monday.
Ensembles suggest a gradual decrease in water level by midweek.
District of Columbia...coastal flood advisory until 2 PM EDT Monday for dcz001.
Maryland...coastal flood advisory from 3 am to 1 PM EDT Monday for mdz014-
Coastal flood advisory until 10 PM EDT Monday for mdz017.
Virginia...coastal flood advisory until 2 PM EDT Monday for vaz054.