Fire Weather Watch 1, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
227 PM PDT Tue Aug 10 2021

.SYNOPSIS...
Upper level ridge of high pressure will build into Western
Washington through the middle and latter portions of the week.
This will send temperatures well above normal again for several
days as a heat wave develops across the area. The ridge of high
pressure will weaken and slide east by late this week which will
allow for onshore flow to develop Thursday and Friday along the
coast and bring relief there. Hot weather will hold on the east
side of the Puget Sound through Saturday. A trough of low pressure
will push into the region by late Saturday and Sunday and bring
much cooler weather with temperatures dropping back to near
normal. There will be increasing rain chances and cooler
temperatures Monday with the trough of low pressure.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
Skies have become mainly clear across Western Washington, except
for some cirrus across the interior and a bit of stubborn coastal
stratus. Temperatures have warmed into the low 70s on the coast
and upper 70s to low 80s inland. While skies remain clear
overnight, heights are rising and a warmer night is expected
tonight. Lows will dip to low 60s in the urban areas and warmer
spots, with 50s in the outlying areas.

Heights continue to rise on Wednesday as the 500mb ridge of high
pressure over the eastern Pacific builds east. By late Wednesday,
heights of around 594dm will be common. 850mb temps will increase
to over 20C across the region as well, combining to spell a much
warmer day on Wednesday. Highs will top out in the mid 80s to low
90s in the interior lowlands and upper 70s to low 80s on the
coast. Overnight lows will experience only minor cooling with most
areas staying in the 60s overnight and even mid 60s in urban
areas.

Thursday the heat will increase with 850 temps of +21 to +23C in
the area. This will likely also be the warmest of the days along
the coast as the wind will start offshore but looks to turn
onshore late in the day. This is the biggest change, to cool high
temps across portions of the Olympic Peninsula and expecting highs
in the mid 80s to near 90 there. Otherwise it will remain on track
elsewhere with highs in the 90s interior areas and upper 90s
showing up south of Seattle, and very hot again in the Cascade
Valleys. This will lead to a very warm night for the lowlands and
urban areas Thursday night. Briefly dipping into the upper 60s for
urban centers and very little relief anywhere except the immediate
Pacific Coast.

Friday the 850mb temps will remain very warm. Some more westerly
component will keep Pacific Coastal areas cooler but interior
areas will be very hot again, with widespread low to mid 90s and
many upper 90s appearing in the Cascade Valleys and from Seattle
south. This will give way to another very warm night especially in
the urban areas and from the Sound to the east, but cooler on the
coast.

Existing heat watch has been upgraded to a heat warning in all
areas except for the Olympic mountains and north coast. With
guidance suggesting a blunting of the heat wave on the north
coast, an advisory for those zones looked more appropriate at this
time. However heat risk values suggest excessive heat warning
warranted for other zones further east through Friday. Important
note - this heat wave is not as hot as the late June one. However,
this doesn't mean we can let our guard down as temperatures in the
90s to near 100 are still significant for our area and potentially
record setting. Impacts will be greatest on our most vulnerable
populations.

Smoke questions - at this time the regional satellite does not
show a significant amount of smoke nearby. As winds shift we will
see some elevated smoke pushing into the area by later this week,
however not expecting increasing smoke at low levels to bring
reduced air quality concerns. Johnson

.LONG TERM /SATURDAY THROUGH TUESDAY/...
By Saturday the ridge will have shifted east as a trough of low
pressure begins to push in off the Pacific. Heights will be much
lower Saturday. However there will be a lingering pool of very
warm 850 mb temps still east of the Sound and so one last
lingering hot day is expected. Temps on the Pacific coast will be
comfortable in the 70s but it will remain in the low to mid 90s in
the lowlands and valleys east of Puget Sound. The Excessive Heat
Warning will continue Saturday east of the Sound where the hottest
temperatures are expected to remain.

The next question is chance of convection as the flow turns more
southerly on Saturday. Looking at the potential over the
Cascades, it is noted that there will be very steep lapse rates,
however a very dry atmosphere. At this time will not carry mention
of thunderstorms in the area but this needs to continue to be
monitored given the pattern recognition in this type of transition
with an approaching trough offshore.

Sunday will see much cooler weather with the approaching trough of
low pressure and lower heights. Clouds will increase and there
will be a chance of showers for the coast and north. This trough
will look to linger into early next week. Some rain chances will
persist along with temperatures near or below normal in spots.
Highs will be more in the 70s early next week with mid 60s along
coastal areas.

Johnson

&&

.AVIATION...Northerly flow aloft and at the surface will continue
into Wednesday. KHQM and KOLM could see a slight wind shift to
become more westerly with a very weak marine layer moving inland.
In general skies are expected to remain in VFR with mostly clear
skies throughout the region. Terminals near the waters will likely
see some breezier conditions through the rest of this afternoon
and again tomorrow afternoon. These terminals could see gusts
around 15 knots. Sustained winds throughout W WA are expected to
be 7-10 knots during the daytime hours and easing slightly during
the overnight.

KSEA...VFR conditions will remain in place with some thin cirrus
passing overhead. Northerly winds 7-10 knots through the remainder
of the day, easing to 5-7 during the overnight before picking back
up Wednesday morning.

&&

.MARINE...Northerly winds over the outer coastal waters as well as
through the Northern Inland waters are expected to reach small
craft advisory level starting tonight and continuing through
Wednesday morning. Due to winds and the northwesterly swell, we
are expecting seas to increase Wednesday to 5-8 feet. Highest seas
are expected to be in the outer coastal waters.
A shift to easterly flow is expected to occur starting on Thursday
due to a thermal trough develops offshore. Seas are also expected
to rise to 8-10 feet during this later part of the week.
Butwin
&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Excessive Heat Warning from noon Wednesday to 7 PM PDT Saturday
     for Bellevue and Vicinity-Cascades of Pierce and Lewis
     Counties-Cascades of Snohomish and King Counties-Cascades
     of Whatcom and Skagit Counties-East Puget Sound Lowlands-
     Seattle and Vicinity-Southwest Interior-Tacoma Area.

     Heat Advisory from noon Wednesday to 8 PM PDT Friday for
     Olympics.

     Excessive Heat Warning from noon Wednesday to 8 PM PDT Friday
     for Bremerton and Vicinity-Everett and Vicinity-Hood Canal
     Area-Lower Chehalis Valley Area-Western Skagit County-
     Western Whatcom County.

     Heat Advisory from noon Wednesday to 8 PM PDT Thursday for North
     Coast.

PZ...Small Craft Advisory from 8 PM this evening to 8 AM PDT
     Wednesday for Coastal Waters From Cape Flattery To James
     Island 10 To 60 Nm-Coastal Waters From James Island To
     Point Grenville 10 To 60 Nm-Coastal Waters From Point
     Grenville To Cape Shoalwater 10 To 60 Nm.

     Small Craft Advisory from 11 PM this evening to 8 AM PDT
     Wednesday for Northern Inland Waters Including The San Juan
     Islands.

&&

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