Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 131547

Area Forecast Discussion
National Weather Service Seattle WA
847 AM PDT Tue Mar 13 2018

.SYNOPSIS...A slow moving front will spread rain inland today
into the evening hours. A cool upper level low will remain off
the coast Wednesday then move south toward southern Oregon and
northern California later Thursday into Friday. Unsettled weather
will continue into the weekend.


.SHORT TERM...Clouds and rain will increase across Western
Washington today as a slow moving front drags inland. There`s a
batch of precip over the interior this morning but the bulk of the
activity is currently along the coast. Easterly winds really
messed up the temperature forecast. Temps were fairly mild this
morning where the east winds kept lows in the lower 60s, like
SeaTac. Most areas are in the 50s and we shouldn`t see much
movement this afternoon. Regarding the winds, a tight east-west
pressure gradient is also giving gusty gap winds at places like
Enumclaw, North Bend and Snoqualmie. These areas where gusting
into the 30-40s MPH with a low 50s in Enumclaw. Models show the
gradient easing and winds decreasing by 18z this morning.

The air mass will remain cool and unstable through Wednesday as a
an upper level low wobbles overhead. Temperatures will be trending
closer to normal with scattered showers. Showers will decrease in
coverage by Thursday as the low center shifts south toward
northern California. 33

.LONG TERM...Previous discussion...Inconsistency in the model
solutions continuing into the extended portion of the forecast on
the 00z run. The ECMWF has the upper level low stalling along the
Oregon coast on Friday with showers pinning around the low moving
up into at least the southern portion of the area. The GFS is
staying with the idea that the upper level low will move into
northern California on Friday. The GFS solution would result in a
fairly dry day for western Washington. Will keep a chance of
showers in the forecast. Confidence in the Saturday through Monday
forecast low. Models having a hard time getting a handle on where
the next upper level low goes off the coast and how long it takes
for the low over southern Oregon/northern california to
dissipate. None of the Saturday through Monday time frame is dry
on both models so for now the broadbrush chance of showers
forecast will continue. Highs will continue to be near normal,
upper 40s to mid 50s. Felton


.AVIATION...Moderate to strong southerly flow aloft over
Western Washington today as a frontal boundary over the central
Oregon coast this morning lifts northeastward across the area this
afternoon. Air mass will become increasingly moist this morning as
precipitation spreads across the region with areas of MVFR ceilings.
The air mass becomes somewhat unstable this afternoon and evening as
a broad upper level trough shifts onshore. At the surface, moderate
east winds early this morning will shift to southerly as onshore
flow develops in the wake of the front.

KSEA...A cold front continues to edge toward the area and rain will
fall at times this afternoon then turning to scattered showers.
The easterlies will give out and there will be a few periods of
breezy southerlies at times.


.MARINE...A low pressure system will move north well off the coast
today, then move back south Wednesday and Thursday. Earlier it
appeared gales might be associated with this low in the coastal
waters, but it seems the strongest winds will be well offshore. The
gale warnings have been dropped in favor of high end small craft
advisories. The west entrance and central strait will have small
craft advisory winds at times. There probably will higher swells
reaching the coast later today and tonight.

Onshore flow will follow a front tonight and Wednesday. Offshore
flow is likely to develop Thursday as the low moves back south.
Winds will be fairly light Friday and Saturday as the low moves well
away from the region and gradients become light.


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


PZ...Small Craft Advisory until 5 AM PDT Wednesday 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-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory for rough bar from 2 PM this afternoon to 5
     AM PDT Wednesday for Grays Harbor Bar.

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


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