-- Discussion containing changed information from previous version are highlighted. --
266
FXUS66 KPQR 210952
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
252 AM PDT Fri Jun 21 2024

.SYNOPSIS...
-- Changed Discussion --
High pressure will maintain above normal temperatures for
inland areas through Saturday. Moderate heat risk expected from
Portland to Salem. More seasonable temperatures return Sunday into
early next week as onshore flow strengthens and chances for morning
cloud cover increase. Conditions will remain mostly dry through
Tuesday aside from areas of drizzle Saturday night into Sunday
morning for the coast, west slopes of the Coast Range, and Cascade
foothills. Precipitation chances increase across northwest OR and
southwest WA Wednesday into Thursday as an upper level trough moves
inland, which will also bring relatively cooler temperatures.
-- End Changed Discussion --

&&

.DISCUSSION...
-- Changed Discussion --
Friday through Thursday night...High pressure
continues to build overhead Friday, which will remain the dominate
weather feature over the next couple of days. With little change to
the weather pattern and 850 mb temps today, expect high temps very
similar to what was observed yesterday (upper 80s to lower 90s across
the interior lowlands, mid 60s to lower 70s at the coast). Still
expecting temps to be a few degrees cooler on Saturday as onshore
flow strengthens slightly and 850 mb temps decrease, but still rather
hot with highs well into the 80s. As such, HeatRisk remains in the
moderate category from Portland to Salem and for the Columbia River
Gorge and Upper Hood River Valley. While high temps in the lower 90s
in mid to late June isn`t hot 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.

Conditions begin to change Saturday night into Sunday morning as
low-level onshore flow strengthens and a weak upper level shortwave
deepens the marine layer to 1-1.5 km according to NAM/GFS soundings.
This will help spread cloud cover inland Sunday morning, which should
limit high temps to the 70s despite afternoon sunshine. Cannot
completely rule out highs in the lower 80s if morning cloud cover
scatters out fast enough (5-15% chance over the Willamette Valley and
Portland metro according to the NBM). Although conditions should
remain dry over the interior lowlands, it still appears areas of
drizzle will impact the coast, western slopes of the Coast Range,
Willapa Hills, and south WA/north OR Cascade foothills Saturday night
into Sunday morning due to the deepening marine layer, moist westerly
upslope flow at low levels, and lift associated with the upper level
shortwave. NBM PoPs seem a bit too low in the aforementioned areas
given the pattern in place and the latest ensemble guidance for QPF.
Therefore decided to increase PoPs a bit in these areas by nudging
towards CONSShort, ensuring there is a mention of drizzle in the
forecast.

Dry and seasonable on Monday before temps trend a bit warmer again on
Tuesday. This is in response to another ridge of high pressure
amplifying overhead. However, this ridge looks to be transient as the
next upper level trough will be approaching from the northeast
Pacific. This trough will bring the return of cooler temps and precip
chances late in the week. However, confidence is low in regards to
the exact timing and exact rain amounts as there is currently a large
degree of model spread for QPF. Nevertheless, the NBM is showing a
10-40% chance for 24-hr rain amounts in excess of 0.25" from 5pm
Wednesday through 5pm Thursday (highest chance in the mountains,
lowest chance in the Willamette Valley). -TK
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
VFR prevailing except along the coast where IFR/LIFR
cigs persist. Surface high pressure offshore will maintain onshore
flow, but with a subsidence the coastal stratus not expected to
make it past the coastal mountains. The coastal stratus is
expected to dissipate around 16-19Z Fri in the KAST-KTMK area. But
towards KONP, IFR conditions likely (50-80% chance) last through
20Z Fri. Chances for IFR decrease to around 30-50% chance after
20Z Fri. 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 nearly clear skies throughout the
TAF period. Northwest winds increasing to around 8-10 kt this
afternoon and evening. /mh
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
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 early this morning. As such, will maintain the Small
Craft Advisory for the outer coastal waters through 8 AM Friday.
Seas around 4 to 6 feet will generally be wind driven through the
week.

A weak front is expected to approach the coastal waters
Saturday, 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. High pressure gradually rebuilds early next
week. /mh
-- End Changed Discussion --

&&

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

&&

$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland