368
FXUS66 KSEW 170305
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
805 PM PDT Sun Jun 16 2024

.SYNOPSIS...An upper level trough over Western Washington will
shift east of the area on Monday. High pressure aloft will
gradually build through the week for a trend toward drier and
warmer conditions. Another upper trough is expected to approach
the region late next weekend for a cooling trend and a returning
chance of showers to portions of the area.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...There are just a few
showers left, with some producing cloud flashes of lightning in
Pierce and Lewis counties. Activity should wane considerably after
sunset. Other than that, no forecast changes have been made this
evening and the previous discussion will follow, including an
update to the aviation and marine sections.

The trough axis will be east of the Cascades on Monday, but
continued weak troughing aloft will keep clouds and a chance of
showers in the forecast. Heights continue to rise on Tuesday with
onshore flow weakening. This will allow much of the area to clear
out by Tuesday afternoon with temperatures bouncing back to near
seasonal levels. Upper ridging centered well offshore continues to
strengthen on Wednesday as 500 millibar heights approach 570 dam
with 850 millibar temps approaching 14 C. With thermal troughing
just to our south and only weak onshore flow, much of the interior
of Western Washington should warm into the mid to upper 70s with
60s along the coast.


.LONG TERM /FRIDAY THROUGH MONDAY/...Low amplitude ridging
continues to build across the area Thursday and Friday for
continued dry and warmer conditions with portions of the interior
from Seattle southward reaching near or above 80 degrees.
Ensembles are in fairly good agreement that the ridge axis will
shift east of the region early in the coming weekend as an upper
trough deepens along the British Columbia coast. This will result
in a cooling trend along with a returning chance for
showers...especially over the Olympic Peninsula and across the
North Interior. 27


&&

.AVIATION...Broad upper low will pass over the Pac NW tonight with a
cool and slightly unstable air mass over western Washington (via
northwesterly flow aloft). Showers continue this evening in the
interior/Rainier region (with a couple of small thunderstorms still
possible until dusk). The showers will continue in the interior
through Monday morning. Drier conditions expected Monday afternoon
as the upper trough departs east. Ceilings are expected to drop to
MVFR overnight, but will improve to VFR by mid to late Monday
afternoon. Surface winds out of the north this evening will taper
overnight, and become southwesterly by Monday. Few gusts to 18 kt
possible in the interior Monday afternoon.

KSEA...Showers still in the vicinity this evening, but will taper
going into tonight. W/NW wind to 10 kt through 06z, becoming S. Low
clouds, light rain and MVFR conditions early Monday. Lower
ceilings possibly persisting through mid to late afternoon.

33/HPR


&&

.MARINE...High pressure over the NE Pacific will maintain onshore
flow over western WA this week. Highest wind and waves will be
through the Strait of Juan de Fuca, mainly during the afternoon and
evening hours. The strongest pushes will be tonight and Monday
afternoon, which may affect small craft. Seas remain at 4 to 6 feet
throughout the week.

33/HPR


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Monday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$