Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 162155
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
255 PM PDT Sun Apr 16 2017

.SYNOPSIS...A low pressure system off the Oregon coast will move
northeast overnight, and will be over eastern Washington by
daybreak. Expect the threat of precipitation to increase Monday
afternoon ahead of a warm front that will move across the area
Monday night. The cold front will follow on Tuesday morning.
Another low pressure system will impact the region on Wednesday.

&&

.SHORT TERM...
Temps this afternoon ended up being warmer than forecast, marking
today as the warmest day so far this year for many locations. A
number of lowland places from the Puget Sound Region south and
westward as well as the Cascade foothills and the coast climbed
into the mid 60s this afternoon. At 2 PM PDT, it was 64 degrees at
Sea-Tac International. The mild weather was brought to you by high
pressure aloft combined with low level offshore flow. Enjoy it while
it lasts because the weather will return to, more or less, what it
has typically been thus far this season...starting tonight.

A low pressure system currently off the southwest OR coast will
continue moving northeast and will be over eastern WA by daybreak
Monday. This system will bring a threat of light precipitation to
the area overnight. The best chance of precip will likely be over
the central Cascades. There is a possibility that Monday morning
could be dry for much of the CWA in between systems.

Expect a stronger and colder low pressure system to park itself
offshore onshore on Monday. Look for the threat of precip to
increase Monday afternoon ahead of a warm front. This front will
move north across the CWA late Monday night. Look for the cold front
to follow on Tuesday morning. The air mass will destabilize Tuesday
afternoon due to relatively strong cooling aloft. There is a chance
that there could be isolated thunderstorms Tuesday afternoon;
however, it was still a little too early to put them in the
forecast. Would prefer to wait and see if this trend continues.

It looks like there will be a dry period Tuesday night before the
next round of precip arrives. The models appeared to be moving in
the direction of the ECMWF solution, which has been the slowest
with the Wednesday system. Expect a gradually increasing chance of
precip from west to east during the day Wednesday. There is a chance
that the Cascades could stay dry on this day. The cold or occluded
front is anticipated to move across the region Wednesday night.

.LONG TERM...
An upper level trough of low pressure will move across the Pacific
Northwest on Thursday for cool and showery conditions. Dry and
warmer weather will return on Friday. There is a chance that temps
on Friday will be warmer than what they were today, with some
lowland sites possibly climbing into the lower 70s. In other words,
the current forecast for Friday might end up being on the cool
side. At any rate, Friday looks like a nice day if you don`t enjoy
clouds and getting wet.

Beyond Friday, confidence in the forecast was low due to disagree-
ment between the medium range model solutions. Specifically, the
models differed on the timing and strength of the system due to
affect the region this weekend.

&&

.AVIATION...A weak upper trough will move through the area
tonight. A somewhat stronger frontal system will reach the area
later Monday. The flow aloft will be mainly southwest through
Monday. At the surface, offshore flow will switch to onshore
tonight as a weak surface trough moves through the area. The air
mass is stable with high level moisture. Ceilings will lower
tonight as moisture increases from the south. Mid clouds should
increase this evening then low clouds Monday morning.

KSEA...High clouds will give way to mid clouds this evening then
MVFR low clouds will develop after midnight as some rain moves up
from the south. MVFR low clouds are possible Monday morning.
Easterly wind 10-15 knots will will become south after midnight
tonight. Schneider

&&

.MARINE...Offshore flow will ease and turn onshore tonight as a
trough moves up from the south. A series of frontal systems will
move through the waters Monday through Wednesday night with small
craft advisory winds for the Coastal Waters and entrances to the
Strait at times during this period. High pressure will move over
the area Thursday night and Friday. Schneider

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 11 AM Monday to 5 AM PDT Tuesday 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 until 6 PM PDT this evening for Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from noon to 6 PM PDT Monday for East
     Entrance U.S. Waters Strait Of Juan De Fuca-West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 3 PM PDT this afternoon for Central
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 PM PDT this afternoon for Puget Sound
     and Hood Canal.

&&

$$

www.weather.gov/seattle

An illustrated version of this forecast discussion can be seen at
www.weather.gov/seattle/gafd/latest_webafd.html



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