Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 242349
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
300 PM PST Tue Jan 24 2017

.SYNOPSIS...A ridge of high pressure will dominate the Pacific
Northwest through Saturday. An approaching weak trough will
dissipate offshore Wednesday but may produce a few light showers
around the area. Otherwise, dry conditions are expected with partial
afternoon sunshine and highs near to slightly above average. The
next front will reach the area Sunday with a chance of rain.

.SHORT TERM...Low level moisture remains in place this afternoon
with just partial scattering apparent on visible satellite imagery,
and also out the office window. Any cloud breaks will be brief as
models show deeper moisture and saturation above 850 mb by
Wednesday. Fog will also form around the area but probably not as
widespread as this morning with more solid stratus limiting
radiational cooling. Lows will still be chilly, down into the 30s and
upper 20s to around freezing in colder valleys. Some freezing fog
could develop again around parts of the south sound and southwest
interior.

Models show a skinny weak upper ridge over the area tonight,
weakening on Wednesday. An approaching trough as associated frontal
band will split and mostly dissipate as it encounters the ridge
Wednesday and Wednesday night. However, models are in better
agreement in showing just enough weak lift under diffluent flow to
squeeze a few light showers around the area. Precipitation will be
tough to measure but a few hundredths could be possible in some
spots, especially south and west of Puget Sound.

Any threat of spotty light rain or showers will probably be confined
to the mountains and coast early Thursday. Models now show a
stronger upper ridge building during the day so an overall drying
trend is expected. Expect residual moisture to remain trapped in
this pattern with some fog and low clouds around Thursday night and
Friday morning. Partial afternoon sun is possible a high
temperatures will begin to warm a bit to near or slightly above
average. Some spots could reach close to 50.

.LONG TERM...Dry weather continues Saturday with a repeat of some
morning clouds or fog with partial afternoon sun. Highs will again
reach close to 50 in warmer spots inland from the water.

Most global models still show a progressive front moving  through
the area Sunday as the ridge is suppressed. The system will likely
be east of the area by early next week with a short period of dry
weather. Additional systems in split westerly flow are possible next
week. Mercer

&&

.AVIATION...An upper level ridge is centered just offshore with nly
flow aloft over WA. There is weak surface high pressure that extends
from Western Oregon to British Columbia and low level winds and
gradients are light. Areas of low clouds persist and there are other
layers as well--generally the low clouds have been north of Seattle
today, a layer around 4000ft has been above that for many areas and
extended into the Cascades. A mid level deck of clouds from the
remnant of a weak weather system also came in--and a few patches of
light rain fell from that system midday.

Tonight and Wednesday should see mostly cloudy skies--with some
areas of low clouds increasing again overnight, and patches of fog
forming overnight and persisting through the morning hours
Wednesday.


KSEA...Low level winds are light and variable or calm and the air is
moist so low stratus should develop overnight and persist through
Wednesday morning.

&&

.MARINE...Weak high pressure is over the area. As fronts approach
the coast there will be increasing southeast winds there at times
into the weekend, but weather systems will not affect the inland
waters much for the next few days. Stronger systems are likely to
reach the area next week.


&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html



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