Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 102231

Area Forecast Discussion
National Weather Service Seattle WA
231 PM PST Sat Mar 10 2018

.SYNOPSIS...High pressure at the surface and aloft over Eastern
Washington will give offshore flow through Monday night. The
offshore flow will give dry conditions and warming temperatures to
the region. High temperatures will peak on Monday in the 60s and
lower 70s. A front on Tuesday will bring rain back to the area. A
cool upper level trough will move by to the south of the area
Wednesday through the end of the week giving partly to mostly
cloudy skies and a chance of showers at times.


.SHORT TERM...Conditions are quite nice across the region today
with only a few high clouds. Temperatures have risen into the 50s
with a couple of reports of lower 60s. A weak short wave trough
extending from northeastern California northwestward into a low
near 50N 140W will lift northeast across the area late tonight
into Sunday morning. But with the subsidence and offshore flow
over the area, expect no more than some mid and high clouds by the
time it passes across the area later tonight into early Sunday

With only a few high clouds and dry air in place, tonight will
see more strong radiational cooling and lows will drop into the
30s at most areas. But conditions will quickly warm on Sunday
with highs reaching into the upper 50s to mid 60s across the area
under strong sunshine.

Easterly flow will peak early Monday with the high pressure east
of the Cascades and low pressure approaching from the southwest.
Cross-Cascade easterly pressure gradients will peak at around 9 mb
Monday morning. Good sunshine on Monday and offshore flow will
allow temperatures to warm well into the 60s, and areas exposed to
easterly flow will crack the 70 degree mark. The record for
Seattle on Monday is 68, Olympia 67. It appears that a couple of
records will fall.

The ECMWF has slowed the forward progress of the negatively tilted
frontal system that will move through the region on Tuesday. This
delays the increase in cloud cover and the POPS in the interior
Monday night.

Tuesday will see clouds, rain, and temperatures closer to where we
would normally see them - in the 50s.  Albrecht

.LONG TERM...After the rainy day on Tuesday, the forecast becomes
more uncertain as an upper level low drops in to the southwestern
US. The GFS continues to be the more optimistic of the solutions
in taking the upper low far enough to the south that rain chances
would be minimal and low level flow would be offshore. The ECMWF
solution is farther north with the track of the upper low and
disturbances traveling around it and results in shower chances,
especially over the southern half of the forecast area. Later in
the period, short wave troughs (each model handling the flow
differently) move in from the northwest bringing cooler weather
and a chance of showers. With the uncertainty in the details, the
forecast will represent a model mean that results in a partly
to mostly cloudy forecast with 20-40 percent POPS and seasonal
temperatures. Albrecht


.AVIATION...After the sunshine today, a weak disturbance over
Western Oregon will bring some mid and high clouds to the area
tonight and Sunday morning, followed by more sunshine.

KSEA...Mostly clear skies will give way to some mid and high clouds
tonight and Sunday morning, then back to sunshine. Light north
or northeast breeze.


.MARINE...Offshore flow will continue through Monday. Weak fronts
will affect mainly the coastal waters Tuesday through the end of
the week.


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


PZ...Small Craft Advisory until 11 AM PDT Monday for West Entrance
     U.S. Waters Strait Of Juan De Fuca.


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