838
FXUS66 KPQR 202209
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
309 PM PDT Thu Jun 20 2024

.SYNOPSIS...Well above normal temperatures persist through end
of the work week into the first half of the weekend thanks to
high pressure building overhead - moderate heat risk expected
from Portland to Salem through Saturday. More seasonable
temperatures return on Sunday into early next week. Conditions
will remain mostly dry over the next week aside from areas of
coastal and Cascade foothill drizzle Saturday night into Sunday
morning.


.DISCUSSION...Tonight through Wednesday night...High pressure
continues to build overhead tonight headed into Friday and the
weekend, remaining the dominate weather feature the next several
days. Outside of a 15% chance for a pop-up shower over the
higher elevations south Washington Cascades headed into sunset
hours this evening, confidence is extremely high dry conditions
prevail overhead through Saturday with mostly sunny skies and
hot afternoon inland temperatures. The HeatRisk index will stay
in the moderate category from Portland and the lower elevations
of SW Washington to roughly Salem Friday through Saturday with
high temps in the upper 80s to lower 90s. Very little model
spread is evident in the latest guidance and the NBM 1D Viewer
highlights this well as the 10th-90th percentile only ranges
from 90-95F on Friday and 85-91F on Saturday in the Portland
metro with similar spreads elsewhere. While high temps punching
up into the lower 90s in mid to late June isn`t enough to
warrant a Heat Advisory, those extremely sensitive to heat could
suffer from heat exhaustion or heat stroke if exposed to the
heat for long enough, especially in direct sunlight. Be sure to
stay hydrated and for those who must work outside, plan on
frequent breaks during the afternoon hours. Much cooler at the
coast where low-level onshore flow will keep high temps in the
upper 60s to lower 70s.

Fortunately, those rooting for the return of slightly cooler
temperatures are in luck as the ridge begins to loosen its grip
over the Pacific northwest later Saturday followed by the
passage of a weak upper-level trough to our north Sunday
increasing onshore flow. Confidence is very high for a period of
relatively cooler temperatures across all of northwest OR and
western WA Sunday into early next week, albeit reverting to just
around normal for mid to late June. The NBM and other ensemble
guidance show a little more spread Sunday/Monday compared to the
days prior with highs in either the mid 70s to low 80s inland.
The outcome of these temperatures will be highly dependent on
the degree of morning cloud cover and depth of the marine layer.

Despite the cooler temps, conditions look to remain dry through
early next week across the area. The only exception to that is
at the coast, western slopes of the coast range, and potentially
the Cascade foothills Saturday night/Sunday morning when a
period of drizzle or light rain is possible due to the
aforementioned passing shortwave trough. This feature will
significantly deepen the marine layer to according to NAM/GFS
soundings, which when combined with weak up slope flow is more
than deep enough to produce drizzle given the weak synoptic lift
in place. Nearly every ensemble members from the GEFS/EPS/CMC
shows light QPF amounts in Astoria. The current forecast
expanded the mention of drizzle due to added run to run model
consistency.

Beyond Monday temperatures trend a little warmer on Tuesday as
guidance show another ridge of high pressure amplifying
overhead. However guidance continues to trend towards the
arrival of an upper-level trough of low pressure into the
Pacific Northwest sometime in the Wednesday-Thursday time frame
which would bring any brief warming trend Monday into Tuesday to
a quick end and increase chances for precipitation. That said,
confidence in the exact timing of this feature is only moderate.
-Schuldt/TK

&&

.AVIATION...Surface high pressure remains over the region with
dry conditions. This will maintain VFR with variable high clouds
at times for the interior, but may result in low stratus or fog
development along the coast (30-40% probability). Coast terminals
are expected to see conditions drop into IFR/LIFR conditions
around 07-09Z Friday, then improving back to VFR by 18-20Z Friday.
An exception is KONP, which was LIFR last night and has been
bouncing between MVFR/IFR this morning and afternoon. As a result,
there is low confidence that KONP will return to VFR around
18-20Z Friday, with chances of maintaining MVFR/IFR around 20-40%
around the specified time. Otherwise, northwesterly winds will
pick up along the coast up to 10-15 kt by 18Z Friday, with gusts
up to 20 kt more prominent at KONP.


PDX AND APPROACHES...VFR with mostly clear skies throughout the
TAF period. Northwest winds increasing to around 8-10 kt this
afternoon. Similar winds will return tomorrow afternoon.
-JH

&&

.MARINE...Not much change as high pressure offshore is expected
to persist through the week. Northerly winds around 15-20 kt will
continue today, strongest offshore beyond 10 NM. Expect periods
of winds gusting up to 25 kt through Friday morning. As such, will
maintain the Small Craft Advisory for the outer coastal waters
through Friday morning. Seas around 4 to 6 feet will generally be
wind driven through the week. A weak front is expected to
approach the coastal waters this weekend, weakening the high
pressure. Winds will likely become more onshore and ease to below
15 kt. The front will also bring an increasing westerly swell,
though seas are only likely to build up to 8 ft on Sunday.
-JH/DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 8 AM PDT Friday for PZZ271>273.
&&

$$

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