Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 160433

Area Forecast Discussion
National Weather Service Seattle WA
915 PM PDT Thu Mar 15 2018

.SYNOPSIS...An upper trough and surface low will shift south and
east of the area tonight and Friday. A few showers could still
rotate around the low across southern Washington. Another weak upper
low could produce additional showers this weekend but most areas
will see little if any rain and partial sunshine. Shower chances
will decrease early next week. Rain will develop later Wednesday or
Thursday as moisture associated with a wet system offshore moves
northeast into the area.


.SHORT TERM...Radar indicates shower activity is staying confined
south of the WA/oregon border this evening. The main closed upper
low is aligned with the surface low which is shifting south and
eastward tonight. Models take the system into oregon Friday. Models
hint at some possible light wrap around showers reaching the area
but more than likely the weather will be dry with partial sunshine.

The ECWMF/GFS hold back some upper level energy with lower heights
over the Pacific Northwest this weekend. Moisture will be limited
with very little dynamic lift. However, with some spring sunshine,
diurnal showers this time of year cannot be ruled out during the
afternoon and evening hours. Highs will stay close to average in the
50s. Mercer

.LONG TERM...From previous discussion...The GFS keeps low shower
chances going on Monday with the weakening upper low overhead while
the ECMWF has a very weak shortwave trough moving southward across
the area behind the lead cut off system that it takes well to the
southeast. The end result though is for mostly cloudy conditions
with a chance of showers and temperatures near average for this time
of year. Short wave ridging will give the best chance for a nice day
on Tuesday with temperatures again near normal. Later Wednesday or
more likely Thursday, models agree that a northern stream short wave
trough will help to eject a wet system in the North Pacific
northeastward into the area, and the latter half of next week looks
wet. Today`s extended forecast for next week represents a blend of
model solutions. Albrecht


.AVIATION...An upper level and surface low pressure system will
remain southeast of the area through Friday. Isolated pockets of
IFR cigs/vis possible associated with radiational fog in only the
most prone areas such as along the Snohomish river in the southwest
Interior. Otherwise VFR skies.

KSEA...Clear skies with VFR conditions tonight, with a few high
clouds possible at times. Northerly winds 6 to 8 knots will become
northeasterly 4 to 6 knots late. dtm


.MARINE...Weak surface low pressure will continue shifting
south and east of the region through Friday. Light low level
offshore flow will transition to onshore on Friday and linger
through Saturday. Offshore flow will return late in the weekend as
weak surface low pressure develops over the offshore waters. dtm


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



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