Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 190944

Area Forecast Discussion
National Weather Service Seattle WA
245 AM PDT Mon Mar 19 2018

.SYNOPSIS...Today will be partly to mostly sunny, with isolated
showers in the mountains. A weak ridge over the region Tuesday
will bring a mostly sunny day. Rain will return Wednesday and
Thursday as a system moves through, with cool showery weather Friday
into the weekend.


.SHORT TERM...Showers have dissipated and radar only shows isolated
showers off the coast. An upper low off the Oregon coast will move
farther away today, so any shower activity should be minimal. Models
show a few showers in the mountains so have kept slight chance pops
there. Skies will be partly to mostly sunny after patchy morning
for. Highs today will be in the low to mid 50s.

Tuesday will also be mostly dry. Skies will be mostly sunny, except
northern sections could see some clouds from a weak system in
southern British Columbia. Have also included some slight chance
pops in the afternoon for the north Cascades, Olympics, and north
coast. Highs Tuesday will be a few degrees warmer than today.

A significant change in the pattern will occur around Wednesday. An
approaching trough will turn the upper flow southerly, and moisture
will advect into the area. Rain will develop on Wednesday, in the
mountains at first, then spreading to all areas by Wednesday night.
Skies will be mostly cloudy, but warm advection will allow highs to
reach the mid to upper 50s. Burke

.LONG TERM...Models have recently backed off on the strength of the
surface gradient over the region as a surface trough moves toward
the coast on Thursday. Now it appears conditions will be no more
than breezy. Rain will continue at times on Thursday.

The upper trough following the frontal system will bring cool
showery weather to the area Friday through Saturday. The snow
level will fall to around 1000 ft, so precipitation could fall as
snow over the higher lowland areas. Despite being past the
equinox on Wednesday, this is a wintry pattern. Highs will be
mostly in the 40s, and snow will fall in the mountains. The
upper trough will move off to the east on Sunday, for decreasing
showers and more sun breaks. Burke


.AVIATION...Light east to northeast flow aloft over western
Washington today as an upper level trough remains over the Oregon
offshore waters. The air mass will continue to dry and stabilize
today with the flow aloft becoming light northerly tonight as the
trough shifts inland and a broad upper ridge centered well offshore
noses into British Columbia. Except for some patchy late night and
morning valley fog, VFR conditions are expected into Tuesday.

KSEA...Expecting VFR conditions through the forecast period today
and tonight. With some easterly flow aloft, may see some
stratocumulus drift off the Cascades later today for some periods of
BKN050-060 mainly during the midday and afternoon hours. Light and
variable wind becoming northerly less than 8 knots late this
afternoon and evening.      27


.MARINE...Light onshore flow through Tuesday. A developing frontal
system will slowly move into the coastal waters Wednesday. The front
will push through the inland waters Wednesday night or early
Thursday. At least small craft strength winds area expected in most
waters. There is a chance of stronger surface low development which
could produce stronger winds over portions of the waters Thursday,
possibly near gale force coast and east entrance to the Strait.
Confidence remains low on the strength of winds late Wednesday and
Thursday, forecasts should be monitored. Weaker fronts will affect
the waters Friday through the weekend. dtm


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




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