Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 200415

Area Forecast Discussion
National Weather Service Seattle WA
815 PM PST Sat Jan 19 2019

.UPDATE...Updated aviation/marine sections below.

659 PM UPDATE: Showers continue to diminish across the region
this evening. However, there have been a couple flare-ups in the
past 90 minutes with one cell near Lynden/Everson dropping hail
between 0.5-0.75" in diameter. At this point cells are generally
weakening and the threat of additional thunderstorm activity
appears to be rapidly dissipating. As mentioned by the previous
shift, the next system will just glance the southern portions of
the forecast area Sunday. -Wolcott-


.SYNOPSIS...Moist onshore flow will continue to produce a few
showers across Western Washington through tonight. Showers will
decrease overnight as the air mass begins to stabilize. The next
low pressure system will mainly track into CA/Oregon Sunday, with
spotty light rain possible over southern Washington. The low will
quickly shift southeast with mainly dry weather Monday. Another
system will track further north with light rain over Western
Washington on Tuesday. After a weak system brushes the area late
Tuesday, a strong ridge of high pressure will maintain mostly dry
weather into next weekend.


.SHORT TERM...Radar indicates some decent shower activity picking
up over parts of Western Washington this afternoon. Most of the
instability is aloft with broken low/mid clouds across the area.
The flow will begin to back tonight ahead of the next system
heading mainly to our south. This will bring more stable air with
decreasing showers. Light rain will develop along the Oregon coast
later tonight with a weak frontal band lifting north into
southern Washington by Sunday morning. Models are in good
agreement that the bulk of moisture will be in the mid/upper
levels with not much lift. A few spots south of Puget Sound could
get a few hundredths, otherwise dry or trace amounts with
sprinkles across greater Puget Sound and the coast.

Global models including both the GFS and ECMWF show a progressive
split flow pattern early next week. A break is expected between
systems Sunday night and Monday. There will be some northerly
surface gradient Monday morning, but some patchy fog should still
be anticipated in prone valleys.

Clouds will gradually increase Monday night with the next system
further north, reaching Western Washington on Tuesday with light
widespread rainfall. It will be breezy in spots, especially north.
Temperatures will remain relatively mild, above average for

.LONG TERM...A trailing wave behind the Tuesday system will bring
some additional light rainfall to the area Tuesday night. Once
again, the progressive pattern should allow light rain to quickly
taper off by Wednesday afternoon.

Global models remain in fairly good agreement in showing a
strengthening ridge building over the Pacific Northwest Thursday
into next weekend. The chance for any precipitation looks minimal
and certainly not significant. The air mass will remain mild with
above average temperatures continuing. Patchy fog will be
possible some mornings when higher clouds manage to clear. Partial
afternoon or filtered sunshine may allow some spots to reach the
low 50s for highs. Milder metro areas will may not fall to
freezing, although colder outlying spots could have some frost.


.AVIATION...Light southerly surface flow will transition to north
or northeast overnight. Winds will remain generally light at 8 kts
or less at most TAF sites. Showers continue to decrease late this
evening and CIGS are generally VFR over the area. However, a fog-
prone locations will likely see conditions deteriorate through the
overnight hours into IFR or even LIFR at KOLM.

KSEA...VFR conditions are expected to persist into at least late
morning Sunday. Winds will remain southerly under 8 kts through
tonight before becoming northerly by 12z early Sunday morning.
North winds may increase to 8-12 kts by Sunday afternoon.


.MARINE...While winds there have fallen out of SCA
criteria...swells continue to exceed SCA for hazardous seas
thresholds.As a result, SCA`s remain in effect for the coastal
waters through much of Sunday. High pressure will then build over
the waters making for much quieter conditions for late Sunday and
Monday. Another frontal system will affect area waters on
Tuesday...albeit weaker than the most recent system.


.HYDROLOGY...The Skokomish was just over flood stage at Potlatch
this morning, but it will continue to fall through tonight. The
Skokomish will rise Tuesday and Wednesday a bit, but flooding
seems rather unlikely with those two fronts. Elsewhere, river
flooding is not expected in the next 7 days.


WA...Coastal Flood Advisory from 10 AM to 2 PM PST Sunday for Central

PZ...Small Craft Advisory for hazardous seas until 4 PM PST Sunday
     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 for rough bar until 10 AM PST Sunday for
     Grays Harbor Bar.

     Small Craft Advisory for hazardous seas until 10 AM PST Sunday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.


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