120
FXUS66 KPQR 060449 AAA
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
949 PM PDT Tue Aug 5 2025

Updated Aviation...

.SYNOPSIS...Broad troughing will bring continued below-normal
temperatures through Thursday with clouds and chances for a
widespread wetting rain spreading from west to east starting
Tuesday night and continuing through early Thursday. As the
latter part of this week approaching, high pressure will build
over the region and result in a warming and drying trend Thursday
through the weekend and potentially hazardous heat by early
next week.

&&

.SHORT TERM...Tonight through Thursday Night...A weak surface
low offshore of Vancouver Island will occlude and fill as moves
eastward tonight. A pair of surface fronts extending southward
from this surface low will bring periods of rain to the coast
this early this evening and into tonight, with the fronts
pushing further inland by Wednesday morning. CAM guidance has a
start time for precipitation along the coast around midnight
tonight and a start time for the Willamette Valley around 3 AM
Wednesday with an initial period of steadier stratiform rain.
Precipitation will take on a more showery pattern Wednesday
morning. Model soundings are showing some weak instability, with
the NAM and Canadian showing around 100 J/kg of CAPE, so this
is not a favorable system for thunder, but can`t rule out the
probability of a few rumbles. Currently, there is a 5%-10%
probability for thunderstorms along the southern Washington
Cascades starting Wednesday afternoon through Wednesday night.
Lingering post-frontal showers may continue into Thursday
morning before seasonably cool and dry weather returns Thursday
afternoon into Thursday night.

Abundant moisture associated with this system, as evidenced by
precipitable water values approaching 1.5 inches. If this were
to occur, this would tie or possibly break the daily record for
precipitable water for Aug 6th, when looking at the upper air
sounding for KSLE. For reference, the normal amount of
precipitable water around this time of year is around 0.80
inches. Precipitable water can be described as the amount of
water vapor contained within the entire column of the atmosphere
above one given location. Now, this doesn`t mean that you can
get more precipitation than what is in the column as the
atmosphere is not a static environment and a multitude of
factors/systems can add or remove precipitable water.

Storm total precipitations across the region are as follows:

Willapa Hills, Mount St. Helens and Washington Cascades:
0.50-1.10 inches

Coast and Coast Range:
0.10-1.00 inches

Willamette Valley:
0.01-0.40 inches

Oregon Cascades:
0.01-0.75 inches

The higher accumulations are expected for areas north of Salem,
OR and if a thunderstorm develops, that would also result in an
increase in overall precipitation totals. Overall, slightly
cooler and wetter weather is in the forecast over the next 24-36
hours. /42-Picard

.LONG TERM...Friday through Monday...While near seasonal to
slightly cooler temperatures were a nice reprieve a pattern
shift towards the end of the week will see high pressure
returning. Near seasonal daytime highs on Friday will continue
to rise as early next week approaches. Mid to upper 90s across
inland areas by Sunday and Monday are expected. Models are also
showing that some areas could see daytime highs reach into the
triple digits. For Sunday, there is a 20% probability of 100
degree daytime high in Portland, 45% probability for Salem and
Corvallis and 55% probability for Eugene and Cottage Grove.
Monday the probabilities for 100 are: 50% probability of 100
degree daytime high in Portland, 75% probability for Salem and
Corvallis and 80% probability for Eugene and Cottage Grove.
Tuesday, while being 8 days in the future, models are showing a
50% probability for daytime highs reaching 100 degrees as well.

Through the same time period, dewpoint temperatures in the upper
50s to low 60s will also make conditions feel noticeably
humid/sticky. In addition, overnight lows in the mid to upper
60s are most likely in the Central Willamette Valley,
Portland/Vancouver Metro, Lower Columbia and Cowlitz Valleys,
and through the Columbia River Gorge Sunday and Monday nights,
resulting in areas of Major HeatRisk for the aforementioned
areas.

A lack of sufficient overnight cooling can raise the cumulative
heat stress and elevate the risk for heat illness. Therefore,
residents of the aforementioned areas without access to
adequate cooling should begin to plan for this period of
hazardous heat. /42-Picard

&&

.AVIATION...Radar and surface observations show light rain
spreading into northern coastal areas, bringing MVFR cigs to KAST
as approaching frontal boundary begins to move onshore. MVFR cigs
are also present at KONP, though expect rain to hold off along the
centraL OR Coast until 10-12z. VFR conditions prevail farther
inland, with high clouds starting to stream overhead in advance of
the front. Guidance suggests light rain will begin to move into
the Portland area terminals 10-13z Wed, bringing a gradual
downward trend to MVFR conditions. Expect light rain to make as
far south as KSLE by 14-17z, but KEUG will have a better chance to
stay dry through the period. MVFR cigs and rain showers will
linger through much of the day as an upper level trough crosses
the region, but expect improving conditions after 00z Thu as
showers taper off in the wake of the front.

PDX AND APPROACHES...Currently VFR at the terminal, but expect
cigs to gradually lower overnight ahead of an advancing front,
with light rain showers and MVFR cigs moving into the terminal
10-12z Wed. Winds will also increase to around 8 kt out of the
south with the arrival of the front. MVFR and rain showers
persist through much of the period, improving back to MVFR 03-06z
Thu as showers diminish. /CB

&&

.MARINE...Satellite imagery shows the frontal system sitting over
the northern and central waters with increasing southerly winds.
Buoys have yet to respond, but area observations are showing gusts
to around 20 kt. The peak wind speeds will be with the initial
onset of the front, but will continually see 10 to 15 kt winds
with areas of gusts to 20 kt - especially closer to shore. Cannot
rule out an isolated gusts to 25 kt or two, but not expected to be
widespread or frequent. Seas will be generally unaffected with
this system and remain northwesterly at 4-6 ft. These conditions
will persist through Wednesday.

High pressure develops in the later half of the week causing a
wind reversal and elevated speeds starting Thursday evening.
-Muessle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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