Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 161742 AAA
Area Forecast Discussion
National Weather Service Seattle WA
938 AM PST Thu Feb 16 2017
.SYNOPSIS...A broad upper trough will bring cool and showery
weather to the area today. Weak high pressure aloft will bring
mostly dry weather Friday. A weather system will clip the area
Saturday. Wet weather will return for the first half of next week.
.SHORT TERM...Updated marine section below. A front pushed inland
earlier this morning. Post-frontal showers will prevail today with
easing winds. Snow levels will fall to 4000-5000 feet and the
mountains should pick up a few inches of new snow. There are also
some lingering flooding concerns today. See the hydrology section
below for details. Weak high pressure aloft will build over the area
on Friday for a mostly dry day. A weather system mostly moving
onshore to the south will clip the area with a little rain on
Saturday. Recent models have trended a little more widespread with
the precipitation. Schneider
.LONG TERM...Previous discussion...A longwave trough over the
West will keep the weather pattern active through at least the
middle of next week. There is a chance of showers each period as
the models bring systems into the Pac NW. Temperatures will
continue to trend a few degrees below normal. We may see a break
late next week as a ridge over the NE Pacific shifts closer and
.AVIATION...A front moved inland at daybreak and the air mass will
be moist and showery behind the front. Southwest flow aloft will
continue with low level onshore flow. Conditions will be variable
over Western Washington today due to leftover layers from the
frontal system, leftover low level moisture, and the showers.
KSEA...There will be scattered showers and sunbreaks today with a
vcsh and a southerly breeze. The mvfr cigs this morning will likely
break up by afternoon.
.MARINE...Update...Gradients have come down so fast in the wake of
the front that small craft advisories for seas remain on the coast
and west entrance to the Strait of Juan de Fuca...and for westerlies
15-25kt in the Central Strait of Juan de Fuca. Elsewhere the wind
forecast is mostly southwest 10 to 20 knots for today.
A weak surface low in the offshore waters will move closer to the
coast and dissipate on Friday. Northerly pressure gradients
will develop later Friday then weaken late Friday night. Another
weather system will reach the area Sunday and a deeper but smaller
low is forecast by the gfs to reach the area Monday.
.HYDROLOGY...Rivers flowing off the Olympics and north Cascades
have seen sharp rises from heavy rain the past 24-36 hours. So far
only one river, the Skokomish, is over flood stage. Not all rivers
have crested yet. A couple, like the Dungeness and Nooksack may
crest just under flood stage. Heavy rain has ended this morning
and most rivers will begin to gradually recede over the next day
or two. Otherwise, river flooding is not expected over the next 7
The recent heavy rains have pushed USGS landslide guidance above
the threshold at which landslides typically occur. This means
another cycle of landslides is likely over the next few days. A
special weather statement is in effect to address this threat.
WA...Flood Watch through this evening for Bellevue and Vicinity-
Cascades of Snohomish and King Counties-Cascades of Whatcom
and Skagit Counties-East Puget Sound Lowlands-Everett and
Vicinity-Western Skagit County-Western Whatcom County.
Flood Watch until 10 AM PST this morning for Admiralty Inlet
Area-Central Coast-Eastern Strait of Juan de Fuca-Hood
Canal Area-Lower Chehalis Valley Area-North Coast-Olympics-
Western Strait of Juan De Fuca.
PZ...Small Craft Advisory for rough bar conditions Grays Harbor
bar...small craft advisory for hazardous seas coastal waters
and west entrance to the Strait of Juan de Fuca. Small craft
advisory central Strait of Juan de Fuca.
You can see an illustrated version of this discussion at