Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 301050
Area Forecast Discussion
National Weather Service Seattle WA
350 AM PDT SAT JUL 30 2016
.SYNOPSIS...An upper level low pressure trough will track across
British Columbia today through Sunday morning, brushing western
Washington and increasing our cooling onshore flow. A closed upper
low will move across northwest Washington on Monday night and
Tuesday morning, bringing scattered showers and lower
temperatures. Sunny skies and higher temperatures will return by
the middle of next week.
.SHORT TERM...An upper trough will slowly move across B.C.,
brushing western Washington. Upper heights will continue to fall
until Sunday morning. The main sensible impact has been a pickup
in cooling onshore flow since yesterday afternoon, and the
cooling will be felt today in the form of 10-15 degree drops in
high temperatures today over the interior. Marine stratus is not
widespread at the beaches early this morning, but it has filled in
the Chehalis Valley and inland to Shelton. Marine stratus will
easily burn off by late this morning.
For tonight, models agree in increasing the OTH-SEA gradient
enough to send marine stratus surging northward through the
interior lowlands and the Seattle metro area late tonight and
early Sunday morning. The NAM and Hi-Res NMM even suggest some
drizzle early Sunday morning. Once again, stratus will burn off
in the afternoon.
Models are consistent in bringing a closed upper low across
northwest Washington late Monday, but they have slowed down the
feature by about 6-12 hours since this time yesterday. Showers
will hold off for most of the forecast area until Monday night or
even Tuesday morning. Haner
.LONG TERM...The upper low will exit into eastern Washington on
Tuesday afternoon, leading to diminishing shower chances late
Tuesday. However, the clouds, lingering showers and strong onshore
flow will make Tuesday the coolest of the next 7 days. Upper
heights will rise on Tuesday night and Wednesday, with rain-free
weather and a warming trend on Wednesday. For Thursday and Friday,
moderate onshore flow with 575-580 dam heights at 500 mb, as well
as rain-free weather will to classically normal early August
weather in the Pacific Northwest. Haner
.AVIATION...An upper trough over the Pacific Northwest will bring
westerly flow aloft today and tonight. At the surface, onshore
flow will prevail with high pressure offshore and lower pressure
inland. The air mass is stable.
There are areas of low clouds early this morning, mainly over the
Central and Southwest Interior. Low clouds should expand a bit over
the next several hours but with plenty of clear areas as well. Low
clouds should burn off by afternoon, then redevelop and become more
widespread tonight and Sunday morning.
KSEA...Mostly clear today. Patchy stratus could affect the
terminal for a few hours this morning after sunrise. Low clouds
are more likely tonight after midnight. Southerly wind 5-10
.MARINE...Onshore flow will prevail for the next several days with
high pressure offshore and lower pressure. Small craft advisory
westerly winds are likely most evenings in the Central and
Eastern Strait of Juan De Fuca.
For the outer Coastal Waters, there will be some borderline gale
force northwest winds this morning. Otherwise, there will be small
craft advisory northwest winds for the next couple of days with
winds gradually easing overall.
There will also be some 10-13 foot short period northwest swell
over the outer coastal waters this weekend. This will subside to
more normal summertime levels early next week. Schneider
PZ...Small Craft Advisory until 5 AM PDT Sunday for Coastal Waters
From Cape Flattery To James Island Out 10 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
Gale Warning until 6 PM PDT this evening 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.
Small Craft Advisory from noon today to 5 AM PDT Sunday 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 Sunday
for Admiralty Inlet-Northern Inland Waters Including The
San Juan Islands.
Small Craft Advisory from noon today to 3 AM PDT Sunday for West
Entrance U.S. Waters Strait Of Juan De Fuca.
You can see an illustrated version of this discussion at