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Office: LWX

FXUS61 KLWX 170754

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
354 AM EDT Tue Jul 17 2018

A cold front will approach the area today before passing
through tonight. High pressure will return for Wednesday and
Thursday before moving offshore Friday. Low pressure may impact
the area during the weekend.


Skies are mainly clear overnight. A light south to southwest
wind exists in a couple spots. Lows will range in the 70s across
the region. Dewpoint temperatures are in the middle to upper 60s
to around 70 in some places. This translates to high humidity
and a sticky airmass in place overnight.

A surface cold front, currently elongated with Lake Erie, will
approach the mountains this morning, and cross the area later
today. Most guidance solutions suggest that the front will be
near the I-95 corridor between 22z and 00Z, suggesting that the
afternoon hours will be the most active. Sufficient instability
will be able to stream north ahead of the front. However, the
slightly earlier timing and better forcing north of the area
should preclude numerous/damaging wind gusts. Nonetheless,
enough low level convergence/lift present for likely PoPs
beginning late morning.

Most convection will be pushing east of the Chesapeake Bay this
evening. We should encounter widespread drier air late this
evening and mainly after midnight into the predawn hours


Lower dewpoint temperatures, thus dry air, will continue to
advect southward Wednesday as high pressure builds from the
Great Lakes. Wednesday's highs will be upper 70s-mid 80s, with
dewpoints around 60F.

High pressure will move overhead on Thursday. Dry weather and
well below normal humidity levels expected Thursday and Thursday
night. Dewpoint temperatures will be in the 50s Thursday.


High pressure over New England will shift off the coast during the
day on Friday, resulting in a southeasterly flow over the area and
dry conditions. The southeasterly winds will help pump in a bit more
moisture off the Atlantic, with dewpoints rising in to the middle
60s by the end of the day. Some showers/thunderstorms will be
possible late Friday and Friday evening along our far western zones
as the eastern periphery of an upper level low over the Great Lakes
approaches from the west. Do think much of the CWA stays dry during
the day on Friday, with any activity waning overnight Friday. Highs
on Friday will top out near or slightly below normal in the mid to
upper 80s, while lows Friday night will range from the middle 60s to
near 70 degrees as clouds will be on the increase.

The upper level low and associated trough will swing further
eastward on Saturday, bringing increased shower and thunderstorm
chances. Current model guidance favors the latter half of Saturday
and into Sunday to carry the highest precipitation chances as moist
warm air advection and veering winds aloft increases, as well as
vorticity maxima passing overhead. Low pressure over the Great Lakes
will stretch a trailing cold front just to our west Saturday night
into Sunday, as a warm front lifts into our area. The ECMWF depicts
a coastal low garnering support from the upper level jet and
traversing the Delmarva during this time period. Details will need
to be ironed out the next few days, but at this time, above normal
rain chances looking more likely this weekend. The upper level
low/trough will park is self overhead on Monday, keeping unsettled
weather across the region. Slightly below normal temperatures
expected during this time period as a result of the increased rain
chances and ample cloud cover.


Showers/thunderstorms will become more numerous today, possibly
beginning as soon as late morning...especially for MRB, and
then gradually cross the terminals. The back edge should push
east late afternoon...perhaps early evening for DCA/BWI/MTN.
While it won't be raining the whole time (probably less than 50%
for the time), flight restrictions as well as gusty winds
possible within any storm. Have opted not to include many
restrictive details in the TAF at this time due to confidence
uncertainties in specifics.

VFR flying conditions will be favored on Friday at all terminals
with high pressure over the New England coastline delivering a light
southeasterly flow and mainly dry conditions. Showers and
thunderstorms are a possibility at MRB late in the day on Friday,
but confidence in this occurrence is low at this time. A better
chance of showers and thunderstorms, and ultimately sub VFR
conditions, will be realized the latter half of Saturday into Sunday
as a trough of low pressure approaches from the west. South
southeasterly winds at 10 knots or less will prevail this


Southerly flow is expected to continue overnight. A Small Craft
Advisory is in effect through early this morning for the mid
Bay/lower Potomac.

Additionally, a longer period Small Craft Advisory is in effect
around mid-afternoon today through late morning Wednesday for
the advancement of a cold front across all waters.

Showers and thunderstorms are expected to impact the waters.
Some storms could be strong, producing gusty winds and the need
for Special Marine Warnings.

High pressure over the New England coastline Thursday and
Friday will promote a light to gentle southeasterly breezes
across the waters, with sub SCA conditions forecast. Gradient
increases on Saturday and Sunday as a warm front lifts northward
through the waters and a trough of low pressure approaches from
the west. As a result, SCA wind gusts will be possible for the
duration of the weekend, as well as increasing chances for
showers and thunderstorms.


Water levels continue to run between one-half and three-quarters of
a foot above astronomical normals. Do not anticipate any minor
flooding concerns over the next several tidal cycles, but Caution
Stage will be plausible at Annapolis and the Baltimore Harbor during
high tide this morning and again this evening.


The high temperature at Ronald Reagan Washington National
Airport (DCA) on Monday was 98 degrees. This now stands as the
warmest temperature observed in 2018 at DCA, besting the high
temperature of 97 degrees observed on July 3rd. The last time
temperatures reached 98 degrees or warmer at DCA was on July
20th 2017 when a high temperature of 98 degrees was also

Weather records for the Washington DC area have been recorded at
what is now Ronald Reagan Washington National Airport since 1941. The
official weather record consists of that data back to 1945, and
observations taken in downtown Washington from 1871 through


MARINE...Small Craft Advisory from 2 PM this afternoon to 11 AM EDT
     Wednesday for ANZ530>543.
     Small Craft Advisory until 9 AM EDT this morning for