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Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
945 PM EDT Mon may 22 2017

a cold front is crossing the region this evening. High pressure
will briefly return overnight before low pressure develops over
eastern Carolina Tuesday and moves northeast off the Delmarva
Tuesday night. Upper-level low pressure will move toward the
area Wednesday through Friday.


Near term /through Tuesday/...
cold front is currently near the Blue Ridge but only slowly
moving eastward. Have slight chance pops til late evening for
anything the front initiates, but at this points odds favor
nothing more tonight.

If the front makes it through the area overnight, it won't be
by much, but drier air should eventually filter in. Before it
does so, some patchy fog may develop, mainly in southeastern
areas. Lows will be in the 50s to lower 60s.


Short term /Tuesday night through Wednesday night/...
tuesday's forecast remains very tricky due to a gap between the
synoptic and mesoscale models handling low pressure development
along the front to our southeast. Previous shift chatted with
wpc, and they think the GFS/European model (ecmwf) could be suffering from
feedback, and think the NAM/wrfs simulations may prove more
accurate unless an unmodeled mesoscale convective vortex pulls the surface low farther
north. With better precipitable water values to our southeast,
think heavy rain threat is limited, but areas from
Charlottesville to St. Marys could have a period of moderate
rain. It is more uncertain how much rain falls in the metros.
The low will be progressive though, with any rain ending for
most areas Tuesday evening.

A closed upper low will be moving south into the mid-west Wednesday
while a sfc low and associated cold front moves eastward across the
Ohio Valley. A brief period of subsidence is expected across the mid-
Atlantic Wednesday leading to mostly dry conditions for most of the
day. Weak instability and lift increase across the southwest by
late afternoon. If current trends hold, widespread rainfall will
occur Wednesday night as a boundary lifts northward into the
area. There may be some weak instability, resulting in a few
rumbles of thunder.

Have not strayed too far from model consensus for temperatures.
Diurnal ranges will be muted due to clouds and precipitation,
with lows in the 50s to lower 60s and highs in the upper 60s to
mid 70s.


Long term /Thursday through Monday/...
a slow-moving low pressure system will allow for the chance for rain
showers and a few thunderstorms to linger across the region Thursday
into Thursday evening.

The chance for rain showers shift to the Mason-Dixon line and
adjacent areas Friday as the storm system finally departs northeast
into New England.

By Friday night and Saturday, weak high pressure will move into the
region. Dry conditions and a gusty breeze should ensue.

Rain showers develop in the region again for Sunday as the next
storm system pivots into the region. Temperatures will be warmer.


Aviation /02z Tuesday through Saturday/...
VFR to high MVFR currently, with lower clouds lingering in spots.
Some patchy fog may develop overnight, most likely affecting mountain
and BWI. No additional precip expected through early Tuesday.

Tuesday forecast remains uncertain with guidance spread in
position of low pressure and moderate rainfall. Continued to
hedge toward a more optimistic solution of MVFR for now except
at cho, but IFR isn't out of the question. A break in
precipitation is expected Tuesday night through most of
Wednesday, although with continued uncertainty of how ceilings
will respond.

Showers and perhaps a storm are possible Wed night-Thu night as
a warm front moves across the terminals. Sub-VFR conditions
possible during this time.

IFR conditions Thursday. Winds southwest around 5 knots Thursday.
MVFR conditions Thursday night. Winds becoming west 5 to 10 knots
Thursday night. VFR conditions Friday into Friday night. Winds
increasing northwest 10 to 15 knots gusts 20 knots Friday,
diminishing to 5 to 10 knots Friday night.


winds remain less than 10 kt. Southerly flow will become
west/northwest overnight with a cold frontal passage. No further
showers expected overnight.

The pressure gradient will tighten Tuesday as low pressure
moves up the coast. Have kept Small Craft Advisory for the mid
Bay and lower Potomac, where the gradient will be the best. The
winds should subside Tuesday night as the low moves away.

Low pressure will be moving west of the area Wednesday night
into Thursday, lifting a warm front into the area. Southerly
flow may reach Small Craft Advisory criteria.

No marine hazards Thursday night. Small craft advisories
possible Friday. No marine hazards Friday night.


Tides/coastal flooding...
anomalies have continued to fall to around 1/2 ft except on the
Potomac. Flooding looks unlikely for the next couple cycles at
least. However, a coastal low Tuesday provides some
uncertainty. Guidance ensembles then diverge substantially
through midweek, although increasing water levels look more
likely by Wednesday night.


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory from 2 PM Tuesday to midnight EDT Tuesday
night for anz533-534-537-543.



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