Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 272144
Area Forecast Discussion
National Weather Service Seattle WA
240 PM PDT MON JUN 27 2016
.SYNOPSIS...A weak upper trough was moving through the area
late this afternoon. No significant weather systems will affect the
region Tuesday through Thursday. Cloudier cooler weather with a
chance of showers will arrive for the weekend.
.SHORT TERM...A shortwave will probably trigger a couple of
thunderstorms over the Olympics and Cascades late this afternoon. For
the lowlands conditions are generally warm and sunny. The coast had
marine stratus for much of the day. An increase in onshore flow will
deepen the marine layer along the coast and stratus should be more
widespread later tonight and Tuesday morning. After areas of morning
clouds, ridging will give the region mostly sunny skies Tuesday
afternoon and Wednesday and possibly into Thursday with seasonable
middle of the road temps.
.LONG TERM...Upper heights will fall off and the weather pattern
will change to one of a deep marine layer and a possibly enough
lift for some showers as weak troughs reach the area. Overall, a
large upper trough will gradually develop over the region and by
Sunday or Monday additional shotwaves rotating through the longwave
trough could give some precip. The 12z GFS has the best looking
little closed upper low dropping over the area Sunday afternoon
and evening. The ECMWF seems also to have that idea but holds it
off til Monday. There is a good chance of the Puget Sound Convergence
Zone setting up at least a couple of times over the holiday weekend.
.AVIATION...A upper short wave will move through Western Washington
this evening in southwest flow aloft. Weak high pressure aloft will
move over the area tonight. At the surface, onshore flow will
prevail with high pressure offshore and lower pressure inland.
Onshore flow will increase this evening as the upper short waves
The air mass is dry and stable. Mid level moisture will increase
slightly today and the air mass will become unstable, especially
over the mountains. Areas of stratus along the coast will spread
inland tonight. 13
KSEA...High clouds at times today with westerly wind 5-10 knots.
There is a good chance stratus could reach the terminal after
sunrise Tuesday morning. The wind should become light southerly
early Tuesday morning.
.MARINE...Onshore flow will prevail through Friday with high
pressure offshore and lower pressure inland. Small craft advisory
west winds should occur for the Central and Eastern Strait each
day. There will also be small craft advisory northwest winds over
the coastal waters at times, with the strongest winds generally in
the late afternoon and evening hours.
Onshore flow will increase this evening. This will likely bring gale
force west winds to the Central and Eastern Strait tonight. A gale
warning has been issued. Gale force winds are possible again for the
Strait Tuesday evening and pretty much every evening for the
remainder of the week as moderate to strong onshore flow continues.
PZ...Small Craft Advisory from 5 PM this afternoon to 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 from 5 PM this afternoon to midnight PDT
tonight for Coastal Waters From James Island To Point
Grenville Out 10 Nm-Coastal Waters From Point Grenville To
Cape Shoalwater Out 10 Nm.
Gale Warning from 5 PM this afternoon to 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 from 5 PM this afternoon to 3 AM PDT
Tuesday for Admiralty Inlet-Northern Inland Waters
Including The San Juan Islands.
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.
You can see an illustrated version of this discussion at