Forecast Discussion for SEW NWS Office
000
FXUS66 KSEW 212151
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
251 PM PDT Sun Jul 21 2019

.SYNOPSIS...Dry weather will continue into Monday with
temperatures slightly above normal. A cold front and upper level
trough will bring showers and a chance of thunderstorms in the
Cascades on Tuesday. Strong onshore flow will prevail on Wednesday
then weaken on Thursday. Mild weather will continue into the
weekend.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Temperatures have warmed
into the 80s across parts of western WA this afternoon. We may
see a few low 90s too in the interior, away from the sound. The
coast is cooler and in the mid 60s to 70s with light onshore flow.
There is a thin strip of stratus clouds along the coast which
should expand and push inland tonight, clipping the south sound by
morning.

Monday will be slightly cooler (compared to today) as an upper
level low spins over the NE Pacific. Highs in the interior will
reach the lower 80s with 60s to 70s along the coast in NW onshore
flow. A weak disturbance may trigger showers or t-storms, but most
likely over eastern WA where dynamics are favored (per the NAM
solution).

A cold front and upper trough will then cross the area Tuesday and
Tuesday night for a chance of showers. Thunderstorms are possible
in the Cascades where heating and instability are the greatest.
We`ll be under post-frontal onshore flow through Wednesday with
morning clouds expected. Temperatures will return to normal. 33

.LONG TERM /THURSDAY THROUGH SUNDAY/...Weak, flat ridging will
bring dry weather as we move toward the end of the week. Onshore
flow will prevail through the period. Weak upper level disturbances
may clip the area Saturday or Sunday but there`s little to no
moisture attached. Dry and quiet weather may continue into early
next week across western WA. 33

&&

.AVIATION...Not a cloud in the sky over western Washington TAF sites
this afternoon. Only clouds showing up on vis imagery are some
stratus hugging the northern coast, well north of HQM. Clear skies
will rule thru the evening with marine stratus building a bit
stronger offshore and along the coast tonight. This layer of stratus
will push inland overnight, with confidence not high on exactly how
far inland. Dropped ceilings at HQM and OLM late this evening and
early Mon morning, respectively. Kept remaining sites VFR. Should
see some more cirrus and perhaps some mid level clouds Monday, but
VFR should prevail for all by the afternoon. A stronger marine push
overnight Mon into Tues will likely drop ceilings down sub-VFR from
Sound to coast. Winds generally W/NW under 10kts through sunset
dropping to light and variable overnight and picking back up W/SW
Mon afternoon.

KSEA...Clear skies, some passing cirrus on Monday. MVFR stratus
early Monday is expected to remain south of the terminal across
southern portions of Puget Sound. W/NW wind 5-10 kts through sunset,
becoming light and variable overnight and picking back up W/SW near
10kts Monday afternoon.

Kovacik

&&

.MARINE...Afternoon sfc analysis still argues that weak offshore
flow is in place across western Washington as an expansive area of
high pressure remains in place from the northern Rockies into the
southern Canadian Prairies and into the northern Great Plains while
low pressure resides well offshore the Washington Coast. This has
allowed for calm conditions over the waters today, aside from some
wind waves of generally 1-3 feet. This pattern will become disrupted
late this afternoon and evening as a thermal trough builds north
into Washington from Nevada and the offshore low inches closer
towards the coast. These features will cause the flow to turn back
onshore and help develop a stronger marine layer across the offshore
waters and along the coast, eventually pushing inland some. In
addition, it will cause a westerly push down the Strait of Juan de
Fuca this evening and overnight, keeping a small craft advisory in
place for central and eastern portions 5pm this evening thru 5am
Monday. Winds will come down briefly in the Strait Monday morning
before a stronger westerly push sets in by the afternoon. This will
lead to another round of small craft winds for the central and
eastern Strait and eventually into the Admiralty and Northern Inland
Waters early Tuesday morning.

Onshore flow will continue for much of the week, varying in
intensity. The potential for gale force winds will exist Tuesday
night into Wednesday for the central and eastern Strait.

Kovacik

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Monday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$

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NWS SEW Office Area Forecast Discussion