Hillsboro, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

703
FXUS66 KPQR 100356 AAB
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
856 PM PDT Sat Aug 9 2025

Updated Marine Discussion

.SYNOPSIS...Expect abnormally hot conditions Sunday through
Tuesday thanks to a strong high pressure building over the
eastern Pacific - highest temperatures on Sunday/Monday. Extreme
Heat Warnings and Heat Advisories are now in effect through
Tuesday. Fortunately, conditions return closer to normal on
Wednesday with a cooling trend into the end of the work week.

&&

.SHORT TERM...Now through Monday Night...Not much has changed
in regards to the forecast this weekend as hot temperatures are
slated to begin on Sunday lasting into early next week. A ridge
of high pressure continues to strengthen offshore tonight
allowing 850 mb temps soar into the 21-23 C range for Sunday and
Monday which is well above the 90th percentile of early August
KSLE sounding climatology. This corresponds to peak temperatures
Sunday/Monday spiking well into the 90s to near 100 in the
interior valleys, with chances for the first triple digit
readings of the season ranging from 15-25% in the Cowlitz Valley
to 30-50% across the Portland/Vancouver Metro (highest on
Monday), to about 70-90% in the central/south Willamette Valley
(also highest on chances on Monday). This, along with overnight
lows running in the upper 60s to perhaps 70 degrees in some
urban areas, will drive NWS HeatRisk into the major category
across a wide swath of the area. We`ll also have to keep an eye
on a shortwave/mid-level low feature embedded in the eastern
periphery of the ridge that could provide a minor boost in
onshore flow on Monday. This is reflected in a slightly larger
range of temperature outcomes in the NBM, although most of the
guidance continues to suggest any sensible weather impacts
associated with this feature would be minimal. That said, a
slightly stronger shortwave feature could be the difference
between highs in the mid to upper 90s vs the low triple digits
from the Portland/Vancouver Metro to parts of southwest
Washington, producing a small but non trivial difference in
terms of HeatRisk impacts in some locations on Monday. While
there have been no changes to the placement of existing heat
headlines with this forecast package, the length was extended
into Tuesday evening. -Schuldt/CB


.LONG TERM...Tuesday through Friday...Tuesday represents the
start of the transition out of this coming stretch of hot
weather as the ridge begins to retrograde westward into the
Pacific, opening the door to a welcome cooling trend across the
Pacific northwest. However, it now appears the strongest push of
onshore flow holds off until Tuesday evening as deterministic
and ensemble guidance have slightly delayed the arrival of an
incoming upper level trough. At least, temperature guidance
still is lower than Sunday and Monday but highs reside mostly
in the mid-90s across in the interior valleys on Tuesday
afternoon, with a lingering 20-30% chance to reach 100 degrees
in the Portland metro and closer to a 50-60% chance in Eugene.

Confidence is high the western Oregon and southwest Washington
area should transition fully back into a cooler onshore flow
regime by Wednesday, with temps closer to or even slightly
below seasonal norms in the upper 70s to low 80s through the
end of the week. There is no precipitation in the forecast for
the next seven days, with the exception of a slight chance along
the south Washington coast late in the week as onshore flow
returns. -Schuldt/CB

&&

.AVIATION...VFR conditions will dominate the airspace with mostly
north-northwest winds. Increased subsidence from building high
pressure will result in a shallow marine layer tonight and Sunday
which will confine the marine clouds to the immediate coast.
There is a 25-45% probability of IFR/LIFR conditions developing
along the coast through at least 15Z Sunday, afterwards conditions
along the coast are expected to improve towards VFR and remain
through at least 03Z Monday.

Northerly gusts up to 20 kt inland and 30 kt along the coast will
persist through around 06Z Sunday, with winds subsiding towards
5-10 kt afterwards. Northerly wind gusts return around 16Z Sunday
with gusts up to 20 kt expected within the Willamette Valley and
up to 30 kt along the coast, these gusts will likely persist
though at least 06Z Monday.

PDX AND APPROACHES...VFR for the next 24 hours. North/northwesterly
winds under 10 kt through 06Z Sunday, then increasing to 10-15 kt
with gusts up to 20 kt starting around 17Z Sunday through 06Z
Monday. /42

&&

.MARINE...High pressure across the waters will maintain
northerly winds across the waters through at least Thursday next
week. Pressure gradients will tighten this weekend as high
pressure builds over the NE Pacific, leading to increased winds.
The winds will be strongest in the afternoon and evenings and
will be hazardous to small crafts from this afternoon through at
least Monday. The wind gusts will relax in the mornings,
especially closer to shore. Seas will be mostly wind-driven and
around 3-5 ft at 10-11 sec today. A fresh NW swell builds seas
to 6 to 7 ft at 10-11 sec Sunday, and 9 to 10 ft on Monday. Have
extended the small craft advisory through Monday evening to
account for the steep seas. There is a 60-80% chance of wave
heights exceeding 8 ft by Monday, with the highest chances over
the outer waters. Marine zone 251 (Cape Shoalwater to Cape
Falcon out to 10 nm) is not currently in the small craft
advisory due to slightly weaker surface pressure gradients to
the north. This marine zone is still susceptible to steep seas
on Monday due to stronger winds to the northwest, and will
monitor the swell forecast for this area over the next 12-24
hours to see if the seas will be considered hazardous to small
craft. -TJ

High pressure over the waters will also result in the formation
of dense fog within the inner waters tonight through at least
Sunday morning. Therefore have issued a dense fog advisory as
visibilities could drop below 1 NM or less. /42

&&

.FIRE WEATHER...On Sunday we continue to watch for the
potential of enhanced fire weather concerns as the orientation
of a thermal trough along the west slopes of the Cascades yields
breezy north winds in the Willamette Valley. Currently we do
not anticipate widespread critical fire weather conditions being
met, but the combination of minimum RH values in the low 20s
and north winds gusting to 15-20 mph does raise the possibility
that conditions will flirt with Red Flag criteria in the central
and south Willamette Valley for a time on Sunday afternoon.
Lighter winds will help to limit fire weather concerns on
Monday. -Schuldt/CB

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Heat Advisory from noon Sunday to 10 PM PDT Tuesday for ORZ104-
     105-108.

     Extreme Heat Warning from noon Sunday to 10 PM PDT Tuesday for
     ORZ109>125.

WA...Heat Advisory from noon Sunday to 10 PM PDT Tuesday for WAZ202-
     204-208.

     Extreme Heat Warning from noon Sunday to 10 PM PDT Tuesday for
     WAZ205>207-209-210.

PZ...Dense Fog Advisory until 11 AM PDT Sunday for PZZ210-251>253.

     Small Craft Advisory until 5 PM PDT Monday for PZZ252-253-
     271>273.
&&

$$

www.weather.gov/portland

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