091
FXUS66 KSEW 240408
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
908 PM PDT Thu May 23 2024

.SYNOPSIS...A weak surface low will cross the Pacific Northwest
Friday into Saturday, bringing cooler temperatures and the return
chance of showers. Sunday looks to dry out some before additional
disturbance pass through next week.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...The brief ridge that cross
the area today is quickly moving off to the east with a shortwave
trough moving back into the region from the northwest. Return
echoes are quickly filling in as they move towards the coast on
KLGX. Cloud cover will continue to fill in through the overnight
as the frontal feature moves into the area. Low temperatures
tonight are expected to drop into the mid to upper 40s.

Heading into Friday, the aforementioned upper-level trough is
expected to pass through Friday into Saturday. The main surface
low will arrive on Friday, with a surface low pressure tracking
southeastward over Washington. This will bring a weakening
occluded front through the region, with onshore westerly flow into
Washington. Moisture is limited with this round of showers, but
the best chance of seeing anything over a tenth of an inch of QPF
is from Snohomish to Skagit County (possible convergence zone late
Friday night). If convection is able to form, amounts may exceed
a quarter of an inch with the heaviest showers. A rumble of
thunder is possible but not likely at this point (given increased
temperatures aloft). Temperatures cool down into the 50s Friday
and Saturday. Winds remain light out of the southwest 5-10 mph.

Upper level ridging Sunday appears to dry out most of the region.
Only caveat is a surface low will pass to the northwest of
Washington well into Canada. This will keep shower chances Sunday
confined to the coast, West Olympics and North Cascades. There is
also a slight warm up to the 60s during the day as well.

.LONG TERM /MONDAY THROUGH THURSDAY/...Agreement is good between
ensemble/deterministic models for troughing to continue through
much of next week. This is as upper level ridging in the
Rockies/Great Plains keeps us influenced by a trough off the coast
of B.C. Canada. This will stop the pattern from progressing for
the first part of the week, with the blockage of the ridge
eastward. Overall, shower chances will continue for much of the
extended forecast with a slow moving cold front passing through
Monday into Tuesday. Monday appears to be the warmest day with
highs potentially topping out in the upper 60s to low 70s
(depending on how much warm air advection is brought in behind the
ridge before the trough). Remainder of the week brings a lot of
mid 60s for high temperatures across western Washington.

Davis/HPR

&&

.AVIATION....Westerly flow aloft turning more northwesterly
through the day Friday with onshore flow at the surface. VFR
conditions are expected to prevail tonight with clouds lowering by
Friday morning with a return to MVFR conditions as the next
frontal system moves into the region. Showers mainly along the
coast 12-20Z with vicinity showers in the interior.

KSEA...VFR conditions tonight with S wind around 5-10 kt. MVFR
conditions return by 14-16Z with showers in the vicinity through
the afternoon.

Davis/33

&&

.MARINE...Generally light winds across the waters tonight as the
next frontal system dives southward into the region. This feature
will cross western Washington on Friday with a brief westerly
push down the Strait of Juan de Fuca. High pressure over the NE
Pacific maintains onshore flow through Saturday with N/NW winds
near Small Craft Advisory criteria over the the Outer Coastal
Waters. The next frontal system will move into B.C. on Sunday with
south flow increasing over the waters.

33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$