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Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
925 PM EDT Mon may 29 2017

upper level low pressure will drift east across the north side
of the Great Lakes this week. In the meantime, weak high
pressure will prevail over the mid Atlantic outside of weak
cold frontal passages Tuesday night and Wednesday night. Low
pressure approaches from the west this weekend.


Near term /through Tuesday/...
primary forecast challenge tonight remains timing the return of
marine wedge back into the area. This will occur as easterly onshore
flow continues to be reestablished to the north of a quasi-
stationary surface low across southern/northern VA/NC. While
mid/high clouds are somewhat obscuring the western extent of the
marine layer...advanced GOES microphysical products and
ceilometer data indicate gradual westward motion...with marine
layer beginning to impact portions of the western Chesapeake
Bay coastline...even reaching BWI over the past few minutes.
Low clouds will continue shifting westward overnight banking up
against the Blue Ridge through morning. Some spotty drizzle is
also possible overnight.

Previous discussion...
Tuesday morning will be a struggle to erode marine air mass
once again. That will impede afternoon thunderstorm development.
However, the right rear quad of the upper jet, differential
heating, and another surface boundary supported by a 500 mb
shortwave should provide the catalyst for scattered if not
numerous showers. Guidance generating enough cape west of the
maritime layer to justify including chance thunder.


Short term /Tuesday night through Wednesday night/...
we will have one more front with shortwave support to contend
with...this time late Wednesday. Have not made many changes to
the database in association with this feature (still chance
pops). In keeping with this pattern, have been reserved in use
of thunder. Clouds should be numerous in advance of the front.
One difference though is that this time it appears as though we
will have a decent push of drier air behind the front, to
support clearing skies Wednesday night.

Decent consistency in guidance temps. Have not strayed far from
an ensemble blend.


Long term /Thursday through Monday/...
Thu is looking like a very pleasant day with Canadian high pressure
settling in over the region for the first time in quite awhile.
Plentiful sunshine and highs near or even slightly cooler than
normal for the first day of June. It will be short lived however. By
Saturday morning the next cold front is slowing as it approaches
US from the north early Saturday. It will likely stall over or very
close to US over the weekend, with low pressure riding along west to
east across it and over US Sunday.


Aviation /01z Tuesday through Saturday/...
marine layer spreads inland overnight. MVFR has already returned
to BWI/mtn...and have high confidence marine layer will continue
westward...reaching most sites (though maybe not mrb/cho).
However, questions revolve around timing. Current tafs a bit on
the conservative side...currently have restrictions just for the
morning push...though, it could be sooner.

Erosion Tuesday will be a challenge as well. Restrictions will
into mid morning if not later. Then, afternoon showers and
thunderstorms a good possibility. These flight restrictions
should be brief.

Wouldn't rule out more fog-related restrictions early Wed
morning, followed by another round of possible thunderstorms Wed

VFR likely for rest of week.


flow pattern should be light for most of the week. Bigger
concern would be fog tonight into Tue morning. Lesser chance Tue
night into Wed morning. By late Wednesday, a cold front should
dry airmass out.

There could also be a few thunderstorms each afternoon through
Wednesday, although not likely strong.


Tides/coastal flooding...
water levels remain high and should continue to be above normal for
the next couple of days due to the persistent onshore flow.

Coastal flood advisories are in place for Washington District of Columbia and St.
Marys for the ongoing high tide cycle, which is the lower of
the next two cycles. The advisory for St. Marys continues
through Tuesday. A coastal flood advisory will be issued shortly
for Annapolis and Solomons (i.E., Once they pass current high
tide cycle) it appears likely they will reach minor flood
stage for the morning high tide cycle.

It is also likely that additional advisories will be needed for
high tide cycles through Wednesday for the sensitive locations,
and possibly elsewhere. By Thursday, northwesterly flow as high
pressure builds in should finally allow anomalies to drop.


Lwx watches/warnings/advisories...
District of Columbia...coastal flood advisory until 2 am EDT Tuesday for dcz001.
Maryland...coastal flood advisory until midnight EDT Tuesday night for


near term...mse/hts
short term...heights

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