585
FXUS66 KPQR 172117
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
217 PM PDT Wed Jul 17 2024

.SYNOPSIS...An exiting upper level trough will bring a 15-20%
chance of thunderstorms over the south WA Cascades, Columbia
River Gorge, Upper Hood River Valley, and north Oregon Cascades
through this afternoon. This evening onward, high pressure will
re-build and return quieter weather. We`ll still see above-
average temperatures through the weekend, with mostly sunny
skies and morning clouds along the coast. Early next week, a
cooling trend will likely bring temperatures close to normal.

&&

.SHORT TERM...Today through Friday night...Water vapor satellite
imagery as of 2 PM PDT Wednesday depicts the upper level trough
gradually exiting our area. Instability from this upper trough
will be conducive for convection this afternoon, leading to a
15-20% chance of thunderstorms for the south WA Cascades,
Columbia River Gorge, Upper Hood River Valley, and north Oregon
Cascades. The Red Flag Warnings in these areas were extended
through 5 PM PDT Wednesday to cover the potential for fire
starts due to lightning and critically dry fuels. So far today,
radar imagery has detected several lightning strikes in Hood
River County and areas along the Skamania/Klickitat/Yakima
County border. Note that any thunderstorms that develop this
afternoon have the potential for producing outflow winds with
gusts up to 40 mph, which could result in erratic fire spread.

The upper level trough will be far removed from our area by this
evening, which should end the threat for thunderstorms. High
pressure will begin to re-build, returning quieter weather.
Tonight, most locations will be clear except along the coast
where moistening conditions will return a marine layer. Expect
high temperatures tomorrow (Thursday) and Friday in the upper
80s to low 90s for interior lowland valleys. NBM probabilities
for temperatures above 90 in the Willamette Valley are around
45-65% on Thursday and 75-85% on Friday.

Humidities for interior locations tomorrow are forecast to be
above critical thresholds, around 30-35%, however further drying
may bring humidities down to 25-30% on Friday. We maintain onshore
flow, with westerly winds shifting north/northwest on Friday
when high pressure re-builds in the NE Pacific. Fortunately,
Winds are not expected to be impactful, but the strongest winds
will be in the Columbia River Gorge and Upper Hood River Valley
where winds could gust to 20-25 mph.     -Alviz

&&

.LONG TERM...Saturday through Tuesday Night...500 mb WPC Cluster
analysis maintains good agreement among ensemble guidance as it
shows an the upper level ridge anchored over the Great Basin,
amplifying through the weekend, before a low coming in from the NE
Pacific cause the high to weaken an push the ridge axis eastward
towards the start of the upcoming week. This will likely result in
temperatures warming on Saturday, before a slight cooling trend for
the start of next week. Daytime highs on Saturday look to remain a
few degrees above normal, with the Willamette Valley in the low to
mid 90s, low 70s to low 80s for the Coast and mid 80s to mid 90s for
the Cascades. For the start of next week, temperatures look to cool
closer towards seasonal normals. This cooling trend can also be seen
in the Climate Prediction Center (CPC) 6-10 day outlook, which does
show portions of NW Oregon and SW Washington having temperatures
near normal. /42

&&

.AVIATION...VFR with decreasing clouds across all but the central
Oregon Coast this afternoon as an upper level disturbance tracks
north of the region. Any associated shower or thunderstorm
activity will remain confined to the northern Oregon and south
Washington Cascades through early evening. Patchy marine stratus
is resulting in intermittent MVFR cigs below FL020 from KONP south
along the coast. Expect marine stratus to fill in this evening and
return to all coastal terminals with MVFR/IFR cigs after 03z Thu.
Strengthened onshore flow may support further inland intrusion of
the marine layer tonight, with guidance indicating around a 40
percent chance for MVFR cigs at KEUG after 09z Thu and around a 30
percent chance at Portland area terminals after 12z.

PDX AND APPROACHES...VFR through this evening with decreasing mid
and high clouds as a system departs to the north. Onshore flow may
bring stratus back into the terminal towards daybreak Thursday,
with a 30 percent chance for MVFR cigs after 12z Thu. /CB

&&

.MARINE...Showers and thunderstorms have diminished across the
coastal waters this afternoon as an upper level disturbance
continues to push north of the region. Weak surface low pressure
will linger off the Washington coast tonight and maintain 10-15 kt
southerly breezes across the waters into this evening. Expect
mostly light winds Thursday and Friday in the absence of strongly
defined pressure gradient. Moderate to strong northerly breezes
will then return this weekend as stronger high pressure builds
offshore. Seas will generally remain at or below 5 ft through the
period in the presence of a few minor mid and long period background
swells out of the west and south respectively. /CB

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

www.weather.gov/portland

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