Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 190350
Area Forecast Discussion
National Weather Service Seattle WA
850 PM PDT SAT JUN 18 2016
.SYNOPSIS...An upper level low is bringing showers and isolated
thunderstorms to the region. The air mass will dry on Sunday with
warm sunny weather in store for Monday. A weak upper low and a push
of marine air will bring clouds and cooler temperatures back into
Western Washington Tuesday. The weather is likely to be cool and
unsettled Thursday and Friday as another upper level trough arrives.
.SHORT TERM...The most vigorous cells have moved into the Cascades
though there is still a band of showers just north of the King-
Snohomish line. Scattered showers persist, but models agree there
will be drying from the south after midnight as the parent upper low
On Sunday, morning clouds and a shower or two should give way to
mostly sunny skies in the afternoon. Highs will be in the upper
60s to mid 70s. The low level flow will turn northerly and skies
should be mostly clear Sunday night. Monday will be sunny and
warmer. However, the flow will not turn offshore and an ocean breeze
in the afternoon will probably keep the coast from getting above 70.
Highs in the warm areas from Seattle south and on the east side
should reach 80.
There will be a decent marine push Monday evening and marine layer
clouds will push well into the area through Tuesday morning. After
a weak upper low or residual trough kicks through, the afternoon
ought to see some sunshine as a weak upper ridge builds later in the
day. Highs Tuesday will be mainly in the 70s. Burke
.LONG TERM...Previous discussion...A weak upper ridge moves east of
the Cascades Tuesday night but Wednesday still looks like a nice
day for the moment--the 12z global models were all dry. There is a
chance for showers starting Thursday and into next weekend, the
details vary--the 12z GFS has precip Thursday and Friday while the
ECMWF has a quicker open trough with some precip in the north
Thursday evening and then a more significant system for next weekend.
.AVIATION...A 5630 meter upper low remains over the Washington
coastal waters this evening, with light westerly flow aloft over
Western Washington. The air mass is moist and unstable, but
thunderstorm activity appears to be decreasing. The upper low will
gradually weaken tonight and Sunday as it sits offshore, with
westerly flow aloft becoming more southerly on Sunday. The air
mass will stabilize late this evening, and the mid and upper
levels will dry.
Ceilings are mainly 045-070 at 8 pm with scattered showers.
Thunderstorm activity has been moving from the Western Washington
interior lowlands into the west slopes of the Cascades during the
past couple hours. There are certainly isolated low conditions
associated with the remaining storms, mainly over the eastern
parts of Snohomish and King Counties. Low level moisture will
remain tonight as the mid and upper atmosphere dries, probably
leading to a layer of stratocumulus with bases around 025 late
tonight and Sunday morning. Morning cloud cover should give way to
mostly sunny skies in the afternoon.
KSEA...Southwest wind 10-16 kt gusting 22 kt, becoming south 4-10
kt around midnight, then northerly 6-12 kt Sunday afternoon. There
will probably be a few more showers this evening, but
thunderstorms appear to be moving into the Cascades at this time.
MVFR ceilings -- probably with bases 025 -- are likely around
.MARINE...High pressure building weakly into Western Washington
from the southwest will produce small craft advisory winds over
most coastal waters zones, the Central and Eastern Strait of Juan
de Fuca, and Puget Sound this evening.
Northerly flow will develop Sunday and turn briefly offshore
Monday, as a thermally induced trough extends northward along the
Pacific Northwest coast. Onshore flow will return Monday night or
Tuesday and continue through Thursday. McDonnal
PZ...Small Craft Advisory until 2 AM PDT 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.
Small Craft Advisory until midnight PDT tonight for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
Strait Of Juan De Fuca-Puget Sound and Hood Canal.
You can see an illustrated version of this discussion at