FXUS66 KSEW 250217

Area Forecast Discussion
National Weather Service Seattle WA
715 PM PDT Sat Aug 24 2019

.SYNOPSIS...Lingering moisture coupled with northwesterly flow aloft
will keep mid to high level clouds over Western Washington into
Sunday morning. A ridge will build north into the area late Sunday
and continue through Wednesday kicking off a late summer warming
trend bringing daytime highs into the mid to upper 80s and allowing
dry conditions to persist through much of the week. A troughing
pattern returns late in the week bringing a chance for showers.


.SHORT TERM /TONIGHT THROUGH TUESDAY/...Current radar is fairly
clear and satellite imagery some clearing over southern portions of
the CWA. Clouds continue to linger over approx the northern two
thirds of the area but trends show some slow scattering. Low level
onshore flow might prove to limit this however...as moisture from
the exiting system coupled with marine air will allow for stratus
development overnight and into Sunday morning. Skies are expected to
clear Sunday afternoon and thru the remainder of the day as upper
level ridging moves into the area. Monday sees the influence of the
ridge strengthen over the area. Low level flow will still be onshore
as large area of sfc high pressure remains offshore so could have
some stratus near the coast but otherwise sunny skies. Low level
flow then turns offshore on Tuesday as a thermal trough builds north
from California. With upper level ridge influence, this will make
for noticeably warmer temps, into the lower to mid 80s for most.


Discussion...Upper level ridge will remain in place to begin the
extended, as will low level offshore flow. Wednesday will likely be
the warmest day of the week with highs at least mid to upper 80s
across the interior.

By Thursday, the ridge will begin to dampen, with axis shifting
east, opening the region up to more of a SW flow aloft regime.
A few weak shortwave disturbances appear to be embedded in the
larger scale flow, which may help enhance at least some mid and
high level cloud cover, even maybe a shower or two across parts of
the Pacific Northwest. This may keep temps a few degrees cooler
if this were to verify, however, mid level heights still remain
fairly high, so regardless it will continue to be warm with highs
in the 80s for many.

By Friday, a system well offshore the Washington Coast will
amplify. This will help reestablish the ridge to some degree
across the Pacific Northwest, despite some weak perturbations
becoming trapped underneath. By the end of the forecast period on
Saturday, larger scale trough looks to return to the region, with
which some showers may begin to spread into the area along
a sfc cold frontal boundary.



.AVIATION...Northwesterly flow aloft as an upper level trough
departs the Pacific Northwest. Onshore flow at the surface. VFR cigs
in place throughout W WA this evening and will persist into early
tonight before marine stratus push brings cigs down to MVFR late
tonight/early Sunday morning. Cigs expected to lift back into VFR
late morning/early afternoon as upper level ridging begins to exert
influence over the area.

KSEA...VFR cigs with mid and high level clouds this evening before
MVFR cigs with stratus developing at or around 12Z. North to
northeast winds this evening and tonight before becoming
southwesterly after 12Z and into Sunday afternoon. Wind speeds 5-10
knots. SMR


.MARINE...Onshore flow continues tonight and into Monday. Small
Craft Advisory winds currently being observed in portions of the
Central and Eastern Strait...and as such will leave inherited
headlines in place with evening forecast package. As this onshore
flow persists into Sunday...there is the potential for another round
of SCA winds for Sunday evening and Sunday night. Offshore flow is
expected Tuesday and will persist through much of next week. JD/SMR


.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.


PZ...Small Craft Advisory until 5 AM PDT Sunday for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
Strait Of Juan De Fuca.



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