000
FXUS66 KSEW 082309
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
409 PM PDT Wed Jul 8 2020
.SYNOPSIS...A weak ridge is providing a break in significant cloud
cover today, but will collapse ahead of more upper level low
pressure systems that will move into the area through the rest of
the week. Light rain expected with no significant impacts
expected.
&&
.SHORT TERM /TONIGHT THROUGH SATURDAY/...Weak ridging has held off
a thick cloud layer this afternoon and has brought the afternoon
highs up a few degrees across the region. It will be short lived
as the next trough moves onshore tomorrow and will bring light
rain to the area. QPF amounts are still roughly around a tenth of
an inch around the Sound and nearly a quarter of an inch possible
at coastal locations.
Thursday`s trough will shift east and heights will rise in
response to the upper level ridge building over the Desert
Southwest. This summertime synoptic phenomenon is a hallmark of
the North American Monsoon season and advects moisture from
Mexico, the Gulf of California and Gulf of Mexico into the Desert
Southwest states for summertime thunderstorms to take place. The
Pacific Northwest can benefit from this ridge, as it can help
break up the unsettled pattern and allow for some warmer days to
take shape across the region as it expands. This is likely going
to help our temperatures on Friday come back up into the 70s,
under mostly sunny skies. With the center of this ridge set up
over the Southwest, temperatures will easily climb well above the
110 degree point in the near future, a stark contrast to our
summer weather here in the Pacific Northwest.
By Saturday afternoon, the next trough will be just offshore.
Depending on the thickness of the clouds moving in ahead of this
Saturday`s system, the high temperature forecast could fluctuate
by a few degrees. If the timing stays on track for it to move
onshore later in the day or in the evening hours, Saturday will
still likely be a pleasant day in the 70s under partly sunny
skies.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...The trough axis will move
overhead on Sunday before exiting toward the east on Sunday. A
round or two of light rain showers can be expected. Looking into
early next week, the indication is for drier and sunnier weather.
After Sunday, the pattern seems to show signs of improvement as a
ridge develops offshore, raising the geopotential heights over the
area. Highs will climb back up to normal or just slightly above
in the first half of the week, given that this signal persists. It
doesn`t look to be a very dramatic pattern change, but one that
could garner some excitement from those longing for summer to be a
touch drier and more sunny.
Kristell
&&
.AVIATION...Clouds have scattered enough this afternoon to allow for
partly to mostly cloudy skies, with most ceilings at VFR level at
the terminals. These conditions will persist through the evening
hours tonight, with higher level cloud cover beginning to spread
into the region from the west ahead of the next frontal system.
Given continued onshore flow and the aforementioned frontal system
enroute, low clouds will increase in coverage overnight and drop
cigs to MVFR. Showers will also increase in coverage as the clouds
lower and thicken. Pockets of IFR will be possible in the vicinity
of showers through Thursday morning. Shower coverage will then
become more isolated into the afternoon hours where some cig
recovery appears possible. Winds still predominately S/SW thru the
period (W at CLM and HQM) at 5-10kts, with the exception of a brief
shift to N around Puget Sound terminals this evening.
KSEA...VFR cigs at SCT-BKN through the evening, before lowering back
to MVFR overnight as onshore flow and a frontal system work in
tandem. Showers will be possible early Thursday and through much of
the morning, becoming more isolated in the afternoon with cigs
remaining predominately MVFR. Winds S/SW 5-10kts, with a brief shift
to the N possible this evening.
Kovacik
&&
.MARINE...Afternoon surface analysis reveals expansive anticyclone
still the dominant feature across the North Pacific, with a weak
frontal system noted offshore the BC Coast, and a stronger area of
low pressure noted across southern Saskatchewan. With some ridge
influence from the Pacific anticyclone over the Pacific Northwest
today, and low pressure to the east across southern Canada, onshore
flow will predominate into Thursday. In addition to this flow
regime, the weak frontal boundary near the BC coast will also
approach the area. These conditions combined will allow for the
redevelopment of low level cloud cover overnight tonight along with
the increasing threat for rain showers. Rain showers will become
more isolated across the waters Thursday afternoon and evening.
Headlines: Gradients indicate the potential for low-end small craft
winds across the Central and Eastern Strait of Juan de Fuca this
evening through midnight tonight. Have issued a small craft advisory
for these waters to account for this potential with the afternoon
marine forecast package. Another small craft event appears possible
again Thursday evening and likely each evening/overnight period thru
the weekend.
Onshore flow will then continue into next week with a frontal system
pushing across the area just about every other day. No significant
impacts are expected with the passage of these systems. Seas will
remain under 5ft into next week, with wind waves of 2-4ft possible
down the Central & Eastern Strait during small craft episodes.
Kovacik
&&
.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 1 AM PDT Thursday for Central U.S.
Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
Strait Of Juan De Fuca.
&&
$$
www.weather.gov/seattle
NWS SEW Office Area Forecast Discussion
