225
FXUS66 KSEW 170921
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
221 AM PDT Mon Jun 17 2024

.SYNOPSIS...Light shower activity will linger today as an upper
level trough shifts eastward. High pressure aloft will gradually
build through the week, allowing conditions to dry out and warm
up. A pattern change is on track for the end of the week as a
trough brings wetter and cooler conditions to western Washington.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...Light shower and virga
activity will continue to push southward throughout the day today
as moisture wraps around an exiting trough to the east. Combined
with onshore flow, cloudy skies will stick around today and limit
temperatures to the low to mid 60s for most areas. Instability
will be lacking, so thunderstorms are unlikely to form this
afternoon. Shower activity will taper off over the Cascades
through the evening and early morning hours as drier air moves
inland.

High pressure will build into the region on Tuesday and Wednesday,
allowing conditions to warm up and dry out. Clearing skies and a
transition to more zonal flow aloft will allow temperatures to
return to near-normal on Tuesday. Thermal troughing to the south
and weak onshore flow will allow most inland lowland areas to
reach the mid to upper 70s on Wednesday, while coastal areas peak
a bit cooler near the 70 degree mark.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Warming will continue
through the end of the week as low amplitude ridging continues to
build across the region on Thursday and Friday. Most lowland areas
apart from the coast will reach 80 degrees on Thursday, and
temperatures are on track to peak on Friday. Temperatures Friday
are slated to reach the mid 80s, roughly 10 to 15 degrees above
normal. This may be the warmest day of the year so far for inland
areas. However, the current forecast is still several degrees
below daily records, and ensembles maintain a low (10% or less)
chance of reaching record temperatures. The latest HeatRisk shows
a moderate risk of localized urban heat stress that may impact
vulnerable populations for the Seattle, Tacoma, and Olympia metro
areas and will continue to be monitored.

Ensembles are in good agreement over a pattern change by the
weekend, with cooler and wetter weather on tap. Temperatures are
favored to return to near-normal by Sunday, with a return of
cloudy skies and a chance (20% to 30%) of light precipitation for
most areas.

Lindeman

&&

.AVIATION...Northerly flow aloft today as an upper level low
continues eastward over the Rockies. Air mass remains moist and
unstable enough to allow the chance for showers over portions of W
WA again today, however the bulk of any activity will focus on the
Cascade crest. Surface winds light and variable in the morning
hours, becoming southerly by afternoon with speeds 5-10 kts.

VFR conditions in place over much of the area as of this writing,
except for some scattered patches of MVFR along the coast. Inherited
forecast has cigs dropping around 12Z to more widespread MVFR
conditions with spots that favor lower cigs potentially getting down
into IFR conditions. Conditions return to VFR by this afternoon and
remain that way into tonight.

KSEA...A band of showers resultant of wrap around moisture from the
exiting upper low may produce occasional rainfall at the terminal
this morning with most activity wrapping up between 12-15Z. While
showers may return during the afternoon, not enough confidence for
TAF inclusion. As mentioned above, cigs dropping to MVFR around 12Z
and remaining that way for much of the morning. VFR conditions
expected to return by 20Z. Light and variable winds this morning
becoming southerly 5-10 kts by noon today.

18

&&

.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. Speeds this afternoon and evening look to exceed SCA
criteria, so new headline will go out with morning forecast
package.

Seas 6 to 8 ft this morning for the outer coastal waters while
remainder of coastal zones remain at 4 to 6 feet. Outer waters will
ease gradually this morning and afternoon, subsiding to 4 to 6 ft by
this evening. Seas expected to remain there for much of the week.

18

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 2 PM this afternoon to 2 AM PDT
     Tuesday for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

&&

$$