Heat in Washington, May 12 to 16, 2023

Area Forecast Discussion
National Weather Service Seattle WA
848 AM PDT Fri May 12 2023

.UPDATE...Temperatures have warmed well into the 50s and even low
60s across a number of locations here this morning. Comparing
conditions to yesterday around this time, a noticeable warm up
has been observed. We'll continue to see the amplification of
upper-level ridging today, kick-starting a period of well-above
normal temperatures for today and into the beginning of next week.
No changes have been made to the forecast in this morning's
update. The previous discussion remains below:

&&

.SYNOPSIS...A strong ridge of high pressure aloft will build into
the region and bring a significant warm up to western Washington
over the weekend. Heat-related impacts will become the primary
forecast concern, with temperatures climbing into the 80s and low
90s. An upper level low will then meander into the area on Monday,
bringing the potential for some convection to the area.

&&

.SHORT TERM /TODAY THROUGH SUNDAY/...A strong upper level ridge
will build into the region today, marking the start of a warm up
across western Washington. Afternoon high temperatures look to
climb into the mid 70s to low 80s across the majority of the
interior lowlands. Areas along the coast will remain cooler,
topping out in the upper 60s to low 70s.

High pressure aloft then looks to intensify over British Columbia
and Alberta over the weekend, with most guidance still suggestive
of mid level heights reaching 588-590 dm in its center. Low level
thermal troughing will become more pronounced, causing low level
flow to turn offshore later Saturday into Sunday. Temperatures
will climb well above seasonal norms - and a couple degrees each
day - as a result, with afternoon highs climbing into the 80s
across the majority of the lowlands on Saturday. Afternoon highs
then look to climb back into the 80s and even into the low 90s by
Sunday, especially for areas across the southern interior (like
the Chehalis River Valley). Overnight lows will also become
progressively warmer each night, limiting overnight cooling, and
thus increasing heat-related impacts. Widespread lowland HeatRisk
levels look to reach moderate by Saturday, with a few areas
across western Washington reaching major on Sunday. This level of
heat will affect most individuals who are sensitive to heat,
especially those without effective cooling or hydration. Thus, a
Heat Advisory has been issued for the majority of the lowlands
with this morning's forecast package.

An additional item to note: Those planning to be outdoors either on
or near the water should practice cold water safety as rivers and
lake temperatures will remain in the 40s to mid 50s. Rivers will
run fast due to mountain snow melt and it's important to remember
to wear a life jacket for those who plan to be out on the water.

.LONG TERM /MONDAY THROUGH THURSDAY/...Conditions across western
Washington still look to remain hot on Monday, with guidance
still suggesting high temperatures climbing back into the 80s and
even into the low 90s. However, an upper level low looks to
meander into the region from the south through the day. While
there is still some uncertainty in its track, this feature could
help to create an unstable environment and bring convection to
portions of western Washington during the afternoon and evening
hours on Monday. The progression of this low will need to continue
to be monitored over the weekend, however have kept current
mention of thunderstorms in the forecast for now - and mostly
confined to the Cascades. This upper level low will then linger
across the region Tuesday and Wednesday, helping to cool
temperatures a couple of degrees from Monday's highs. Ensemble
guidance is then suggestive of upper level riding building back
into the region late in the week as the low exits the area. This
will likely keep temperatures above normal as the weekend
approaches. 14/McMillian

&&

.AVIATION...An upper ridge will remain in place over the Pacific
Northwest through at least the weekend with light southwest flow
into Saturday morning. Clear skies through tonight with high clouds
around at times. A brief period of lower cigs/vsbys possible along
the immediate coast early Saturday morning. Light winds this morning
will increase a bit north-northwest into this afternoon and evening.

KSEA...Mainly clear with VFR high clouds at times through the
period. Light N winds this morning increasing a bit from N/NW to 5
to 8 kts this afternoon and evening. JD

&&

.MARINE...Generally calm to light northerly winds over the waters
will continue as high pressure remains offshore. A thermally induced
surface trough will start to move north from the Oregon coast into
WA today through Saturday. Northerly winds will further increase
Saturday afternoon into Saturday evening, however, winds are
expected to remain below Small Craft Advisory criteria. Easterly,
offshore winds increase Sunday for potential SCA winds through the
central and western Strait of Juan de Fuca.

Combined seas 4 to 6 feet will increase to 5 to 7 feet through the
weekend. JD/18

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Heat Advisory from 2 PM Saturday to 8 PM PDT Monday for Bellevue
     and Vicinity-Bremerton and Vicinity-Central Coast-East
     Puget Sound Lowlands-Everett and Vicinity-Hood Canal Area-
     Lower Chehalis Valley Area-North Coast-Seattle and Vicinity-
     Southwest Interior-Tacoma Area-Western Skagit County-
     Western Whatcom County.

PZ...None.
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