Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 281020
Area Forecast Discussion
National Weather Service Seattle WA
320 AM PDT TUE JUN 28 2016
.SYNOPSIS...High pressure aloft will bring fair weather to Western
Washington today through Thursday. Weak onshore flow will result
in some night and morning cloudiness, but the days should be
mostly sunny a little warmer than normal. An upper trough will
bring cooler, cloudier weather and a chance of showers this
.SHORT TERM...A small upper shortwave moved across Western
Washington late Monday, putting a minor dent in the large scale
upper ridge over the western United States. The shortwave produced
isolated thunderstorms along the Cascades crest and turned the low
level flow onshore. As a result, the coastal marine stratus has
been pushing inland overnight. As of 3 am, it had move down the
Strait of Juan de Fuca and across Whidbey Island and through the
Chehalis Gap into the southern Puget Sound region and the south
interior. Elsewhere, skies were clear for now. Temperatures were
in the 50s at 3 am.
The marine stratus will continue to increase over the Western
Washington interior lowlands for the next few hours, with cloudy
skies over most of the greater Seattle metropolitan area by around
7 am. It should burn off to the coast during the late morning
though, for sunny skies midday through afternoon. It will be a
little cooler today with highs in the 70s to lower 80s inland and
in the mid 60s to lower 70s at the coast and parts of the north
Onshore flow will continue tonight, so marine stratus should
quickly return to the coast in the evening and push into parts of
the interior lowlands again later tonight and Wednesday morning.
Wednesday should be a near repeat of today, though, with the
stratus burning back to the coast for mostly sunny weather.
Temperatures will be similar too.
A weak upper trough will moving onto the British Columbia coast
Wednesday night and Thursday will extend south into Western
Washington. The 500 mb heights will only fall to around 5820
meters, and it won`t have much effect on our weather aside from
high temperatures dropping around 1 to 4 degrees in the interior.
.LONG TERM...For the extended period Friday through Independence
Day the models disagree on details, but they do agree that an
upper trough will begin moving over the region Friday for a trend
toward somewhat cloudier and cooler weather. By Saturday there is
a chance of showers across the forecast area, which will continue
through Monday. McDonnal
.AVIATION...An upper level ridge will remain centered over Idaho
with southwest flow aloft over Washington today and tonight. At
the surface, onshore flow will continue. The air mass is dry and
stable except for marine stratus over western areas. Stratus will
continue to spread inland early this morning until most marine
areas and adjacent land areas have IFR or low end MVFR ceilings.
The ceilings will lift later this morning and the stratus should
evaporate back to the coast in the afternoon.
KSEA...Southerly wind 4-8 kt his morning will become northerly in
the afternoon. Several hours of IFR ceilings below 1k ft are likely
this morning. Should completely clear out after 18z. CHB
.MARINE...Onshore flow will prevail through Friday with high
pressure offshore and lower pressure inland. At least small craft
advisory strength west winds will occur each day in the central and
eastern Strait with gale force westerlies also possible.
For tonight have issued a gale warning for the central and east
strait, along with advisories for the coast, Admiralty Inlet, and the
northern inland waters.
PZ...Small Craft Advisory until 11 AM PDT Tuesday for Coastal Waters
From Cape Flattery To James Island 10 To 60 Nm-Coastal
Waters From James Island To Point Grenville 10 To 60 Nm-
Coastal Waters From Point Grenville To Cape Shoalwater 10
To 60 Nm.
Small Craft Advisory until midnight PDT tonight for Coastal
Waters From James Island To Point Grenville Out 10 Nm-
Coastal Waters From Point Grenville To Cape Shoalwater Out
Gale Watch from Tuesday evening through late Tuesday night for
Central U.S. Waters Strait Of Juan De Fuca-East Entrance
U.S. Waters Strait Of Juan De Fuca.
Gale Warning until 3 AM PDT Tuesday for Central U.S. Waters
Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
Juan De Fuca.
Small Craft Advisory until 3 AM PDT Tuesday for Admiralty Inlet-
Northern Inland Waters Including The San Juan Islands.
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