FXUS66 KSEW 161621

Area Forecast Discussion
National Weather Service Seattle WA
921 AM PDT Thu Aug 16 2018

.SYNOPSIS...A weak trough will approach the WA/OR coast tonight
helping to usher in better onshore flow in the lower levels and
better air quality. Another deck of marine stratus can be expected
Friday morning as the trough moves across the area. Best
rain/thunder chances remain south and east of the local area as
the system moves east. Ridging returns briefly Saturday before a
pattern change suggests persistent troughing through most of next


.SHORT TERM...As of 9am Thursday...a blanket of stratus
encompasses coastal and lowland areas as a result of stronger
onshore flow in the low levels. Some fog and haze will continue
through the morning hours as the stratus slowly retreats back to
the coastline by this afternoon. Given the marine push...air
quality continues to improve across the entire CWA and this trend
will continue through the remainder of the week. Latest glance at
MRMS and regional radar data depict a few light showers south and
east of the CWA but this activity will not affect the local area.

16z water vapor imagery confirms that the upper level ridge axis
has shifted well east of the area and a weak trough lingers just
off the WA/OR coastline. This weak trough will make slow but
noticeable progress to the coastline by this evening. Best jet
dynamics and height falls will remain south of the CWA across
Oregon where thunderstorms will be possible. Do not expect this
activity to move into or develop across western Washington today
or tonight. In fact, for us, the trough will continue to allow
for cleaner marine air to filter into the area.

The trough will slide east across the state through the day on
Friday. This will allow for another push of marine stratus across
most of the area Friday morning into the early afternoon. Best
lift and moisture associated with the trough will remain east of
the CWA across eastern Washington and Idaho so another dry and
seasonal day will be on tap with highs generally mid to upper 70s.
As the trough exits the region Friday night a shortwave ridge
will swiftly pass thru the local area on Saturday. Despite some
marine stratus along coastal locations...should see a pretty nice
day with highs rebounding back to near 80 /minus coastal
locations/. A pattern shift then looks likely into the long term.


.LONG TERM...PREVIOUS DISCUSSION...High pressure will be offshore
with lower pressure over the Pacific Northwest. A couple of hazy
smoky days are not a bad bet and another marine push is likely
around the middle of next week.


.AVIATION...Flow aloft will remain southwesterly today as a
weak upper level trough works onshore. Strengthening onshore flow
has brought marine stratus into much of the interior lowlands,
Puget Sound, and Strait of Juan de Fuca this morning. IFR to LIFR
conditions will linger into mid-morning before stratus lifts and
scatters out during the day. Stronger marine push expected
tonight with stratus and IFR/LIFR conditions returning early
Friday morning for the coast into the interior lowlands and Puget
Sound. Lingering smoke will remain aloft, but should improve at
the surface throughout the day.

KSEA...Marine stratus and LIFR conditions will continue to impact
the terminal the morning hours with improvement expected by mid-
day. Smoke remains aloft. Another marine push expected tonight
with another round of LIFR conditions after 12 UTC Friday. Winds
will remain south/southwest 10 mph or less. CEO


Onshore flow will strengthen later today into Friday before weakening
on Saturday. Gale force winds are possible over parts of the
Strait of Juan de Fuca this evening into tonight. Small craft advisory
strength northwest winds look to be a persistent feature over the
northern and central outer coastal waters into the weekend. CEO


PZ...Gale Warning until 5 AM PDT Friday 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 midnight PDT
     tonight for West Entrance U.S. Waters Strait Of Juan De

     Small Craft Advisory until 6 AM PDT Friday 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.




NWS SEW Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather