487
FXUS66 KPQR 031747
AFDPQR

Area Forecast Discussion...Updated Aviation
National Weather Service Portland OR
1047 AM PDT Thu Jul 3 2025

.SYNOPSIS...Onshore flow through at least the next 24 hours. A
series of short wave troughs aloft will move over the area today
and Friday increasing mixing and enhancing moisture in the area.
Slight chance (20%) of rain early Friday morning over the Lane
and Linn County Cascades. Could see isolated thunderstorms over
the ridges. Warming and drying through next week.

&&

.SHORT TERM...Now through Friday...The onshore flow remains in
place ushering in moderate temperatures and moist air. Stratus
is present along the coast and the northern Willamette Valley
this morning, but will burn off as the sun rises and daytime
heating kicks in. Overall, not expecting a significant change
from yesterday so have maintained a persistence forecast for
today. Increased onshore flow through the day within the
Columbia River Gorge will make for gusty winds within the Upper
Hood River Valley. Have increased wind speeds slightly towards
the 75th percentile of the NBM to account for the wind direction
effects.

Overnight into Friday conditions become a bit more complicated
as a shortwave trough pushes inland from the Northeast Pacific.
This shortwave will generally be non-impactful to most areas,
but could see convective activity over the Lane and Linn County
Cascades. This shortwave will bring in trailing monsoonal
moisture from a low pressure system anchored over southeast
Oregon and northern California. Given the location of the low,
the showers will clip the Cascades after midnight tonight into
Friday morning. Cannot rule out bleed over thunderstorms over
the Cascades though confidence is low. The HRRR is the main high
resolution model to show the lightning while others are keeping
conditions too dry for initiation. Overall there is around a
10% chance for isolated thunderstorms overnight into Friday.

  -Muessle


.LONG TERM...Friday Night through Wednesday...Friday night is
curtains up for what will be steady week of warmer temperatures
and dry conditions. Skies will clear Friday night as high
pressure begins to develop with an upper level low positioned
over the northern California coast. This means that we will see
a gradual shift to north-northeasterly flow over the weekend.
Temperatures will rise a few degrees each day through Sunday.

As the low continues to spin over northern California, warmer
air will wrap around it and move into the region creating a
thermal trough. Heights will rise with the increased warming as
850 mb temperatures build to around 20 degrees C on Monday.
On Monday, temperatures will be warmest within the Willamette
Valley with highs ranging from near 80 degrees F to the lower
90s (10th to 90th percentile). Based on the NBM ensembles, the
25th to 75th percentile range for minimum humidity (specifically
within the Willamette Valley), is 20-30%.

Transitioning into Tuesday and Wednesday, temperatures will
rise once again with highs exceeding seasonable normals by 10
degrees or so. The thermal trough will also intensify as a low
aloft and high pressure at the surface build and the axis shifts
over the coast. Humidity too will fall even further with the
10th percentile (low end of the ensemble) showing humidity
around 15-25%. There is a slight westerly component to the
surface wind so have trended towards the mean RH. Would not be
surprised if highs were well above normal on both days, but will
greatly depend on the pace of an incoming zonal flow pattern
shift.
  -Muessle


&&

.AVIATION...Marine MVFR stratus continues to affect the area,
though primarily in southern terminals (KSLE, KEUG, KONP). This
marine stratus continues to dissipate, with all terminals
anticipated to be clear sky VFR by 22z Thu. Additionally, by 20z
Thu, winds will begin to increase throughout the area, with
broadly north-northwesterly gusts up to 15-18 kts possible at all
terminals (20-25 kts at the coast). Diurnal winds ease overnight,
dropping below 6 kts.

PDX AND APPROACHES...Generally VFR conditions through the period,
though a 25-30% chance of MVFR marine stratus developing again
tonight around 15z Thu. Wind gusts up to 15-18 kts possible
beginning around 20z Thu, dropping below 6 kts again over Thursday
night. /JLiu

&&

.MARINE...Persistent surface high pressure offshore will result in
continued northerly to northwesterly winds across the waters.
Diurnal gusts will reach 10-15 kt north of Cape Falcon and 15-20
kt from Cape Falcon to Florence each afternoon, easing to around
10 kt overnight. A locally tightened pressure gradient across the
inner waters south of Cape Falcon may see occasional gusts above
20 kt this afternoon into this evening, but given marginal wind
speeds, have opted to hold off issuance of any marine hazards for
small craft. Seas will continue at 3-6 ft through the weekend,
before strengthening surface high pressure sees winds and seas
build Sunday into next week. -Picard

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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