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afdsew

Area forecast discussion
National Weather Service Seattle Washington
845 PM PDT sun Oct 23 2017

Synopsis...high pressure building over the region will provide dry
weather tonight and Tuesday. Residual moisture will produce some
morning fog or low clouds late tonight and Tuesday morning. A weak
front will move through the area Wednesday with some light rain. Dry
weather will return Thursday and should prevail through the weekend.
Areas of fog will develop late in the week.

&&

Short term...current infrared satellite imagery coupled with observations
indicate that lingering mid level clouds from this afternoon have
mostly cleared out over much of the area...although some still
remain along the northern tier of the olympic peninsula...over
portions of Whatcom and Skagit counties as well as along the
Cascades. Temp-dewpoint spreads ranging on average 3-6 degrees
f...so still some time yet before cooling brings some locations
closer to the potential for fog development. That said...overnight
timing in inherited forecast looks good. Once said fog Burns off by
late morning Tuesday...looks like another sunny day with high
temperatures area-wide generally in the mid 60s...although some
locations may be a bit below that in the lower 60s while other still
a bit above in the upper 60s. All in all...still above expected
normals.

Current GFS solution remains consistent with previous runs regarding
Wednesday as a wholly unimpressive system moves quickly through the
area...deteriorating as it GOES. European model (ecmwf) solutions continue to remain
consistent with themselves as well...showing the system to be wetter
all the while deteriorating in a fashion similar to the GFS.
Inherited forecast does a fairly decent job of seeking a middle
ground between the two solutions. Temperatures will slip a bit down
into the mid to upper 50s with some interior lowland
locations...including the Seattle Metro area getting up to around
60. In the wake of this system...conditions look to clear once more
for Thursday with temperatures rebounding to the upper 50s to low
60s. Smr

Long term...from previous discussion...skies will remain mostly
clear through the weekend as strong upper ridge moves slowly through
the region. Some clouds are possible Sunday and/or Monday as the
tail of a weak upper trough moves by far to the northeast. The
weather will remain dry, however. Have introduced fog each day
Friday through Sunday. The fog could get fairly extensive at night,
and last into the afternoon in some places. Generally temperatures
will be slightly above average, in the low 60s, except in places
where the fog lingers, where it will stay cool all day. Burke

&&

Hydrology...river flooding is unlikely for the next seven days.

&&

Aviation...a strong upper level ridge will remain over the pacnw
through Tuesday. The air mass continues to dry and should be
mostly cloudy free after midnight. Infrared imagery shows clouds
dissipating rapidly over the northwest part of West Washington at 03z. The rest of
the area is clear.

The downside of tonight's clearing is that the resulting good
radiational cooling conditions will probably allow a bit more fog
and stratus to form late tonight and Tuesday morning for spotty
IFR conditions. Light surface winds and a well developed surface
based inversion may prolong the Tuesday morning burn-off over S
Puget Sound and the SW interior.

Ksea...clear skies tonight and Tuesday. There is a small chance
that some low level stratus could form Tuesday morning, 12z-17z
but confidence is not high. I will keep a few006 group in the ksea
taf after 12z to address the possibility. Surface winds will be
northerly up to 7 kt. Kam

&&

Marine...a surface ridge centered over the Pacific
northwest will maintain weak north to NE offshore flow through
Tuesday evening. A weak cold front will move south across the
area on Wednesday. Ahead of the front early Wednesday, west flow in
the central Strait could reach Small Craft Advisory levels. Northwest flow behind the
front Wednesday afternoon could reach Small Craft Advisory levels over the outer
waters.

Northerly offshore flow will prevail Thursday and Friday as a
surface ridge builds over southern British Columbia and a
thermally induced surface trough forms along the Oregon coast. Kam

&&

Sew watches/warnings/advisories...
Washington...none.
Pz...Small Craft Advisory for hazardous seas until 11 PM PDT this
evening for coastal waters from Cape Flattery to James
Island 10 to 60 nm-coastal waters from Cape Flattery to
James Island out 10 nm-coastal waters from James Island to
Point Grenville 10 to 60 nm-coastal waters from James
Island to Point Grenville out 10 nm-coastal waters from
Point Grenville to Cape Shoalwater 10 to 60 nm-coastal
waters from Point Grenville to Cape Shoalwater out 10 nm.

Small Craft Advisory for rough bar until 11 PM PDT this evening
for Grays Harbor bar.

&&

$$

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