390 

FXUS66 KPQR 302210

AFDPQR



Area Forecast Discussion

National Weather Service Portland OR

210 PM PST Tue Dec 30 2025



.SYNOPSIS...High pressure remains anchored over the region 

through Wednesday. Cool and dry conditions lead a favorable 

environment for frost and fog development during the overnight

and morning hours through Thursday morning. A pattern shift is 

in store beginning Thursday with relatively warmer air and

precipitation returning, continuing into early next week.



&&



.DISCUSSION...Tuesday Afternoon through Monday...Visible 

satellite imagery Tuesday afternoon depicts mostly clear skies 

across NW Oregon and SW Washington except for a few lingering 

areas of stratus in interior valleys. Upper level high pressure 

remains over the region today with the axis over western OR/WA, 

and a thermally induced trough remains at the surface. This has 

caused a tightening of pressure gradients over the Cascades, 

leading to gusty east winds through Cascade valleys, especially 

the western Columbia River Gorge. Gusts up to 25-35 mph are 

expected in the western Portland metro area with up to 35-45 mph

possible around Troutdale through this afternoon. Local gusts 

up to 50-55 mph have been observed at the typical windiest 

locations such as Corbett, Crown Point, and Three Corner Rock. 

The upper level ridge axis begins moving east of the Cascades 

later this afternoon and through Wednesday, allowing the thermal

trough and subsequent surface pressure gradients to weaken. 

Breezy east winds will subside slightly this evening, though 

gusts up to 35-40 mph are still possible east of Troutdale. 

Winds continue subsiding through the day Wednesday.



Cold temperatures are expected again tonight into Wednesday

morning and again Wednesday night into Thursday morning due to 

mostly clear skies with temperatures in the upper 20s to low 30s

across inland valleys, mid to upper 30s along the coast, and 

low 20s to low 30s in the Cascades. Coldest temperatures will be

tonight into Wednesday morning. Additionally, fog and low 

stratus once again have the potential to form during the same

time periods, mainly along the I-5 corridor from the southern 

Willamette Valley north through Cowlitz County. Both fog and 

frost are less likely in the Portland metro area, especially on 

the east side, due to the increased east winds from the Gorge.



Another area of concern is stagnant air under this ridging. A

strong inversion remains in place through Wednesday afternoon

with stable air in place near the surface. This will allow for

an increase in air quality concerns, especially for locations

outside of the windier eastern Portland metro area. If you are

susceptible to air quality concerns, be sure to monitor air

quality through Air Now.



A pattern change is on the way for Thursday, with wet conditions

returning and continuing into early next week. Ensemble 

guidance indicates a longwave trough deepening over the eastern 

Pacific on Thursday as a separate closed low approaches 

central/southern California from the west. Some uncertainty 

remains in the specifics of the pattern on Thursday into

Saturday, but the general consensus amongst the GFS, Euro, and 

Canadian ensembles is on Thursday, the low approaching 

California will continue moving east with a secondary weak 

shortwave moving north along the main longwave trough into the 

PacNW. This shortwave will carry enough moisture from the closed

low to bring precipitation chances spreading north into NW 

Oregon and SW Washington sometime on Thursday, though 

uncertainty remains on whether the rain will start earlier in 

the day on Thursday or late Thursday night into Friday morning. 

Then the longwave trough slowly moves east through the eastern 

Pacific on Friday into Saturday, with rain continuing in the 

region. Additionally, warmer air will accompany the rain 

beginning Thursday with 850 mb temperatures remaining above 0 

deg C through Saturday, and snow levels will rise to above

4500-5500 feet, meaning snow is only likely over the high 

Cascades. Ensembles indicate a frontal system will move inland 

from the west sometime on Saturday accompanied by a stronger 

wave along the longwave trough. This could bring a period of 

breezy winds along the frontal passage, but strong winds are not

expected. NBM indicates around a 50% chance along the coast of 

gusts above 40 mph with a 10-25% chance for inland areas. 



The specifics of the weather pattern become much more uncertain

in ensemble guidance Sunday into Monday, but in general, upper 

level troughing remains, bringing continued rainy conditions.

None of the rain Thursday into Monday is expected to be

impactful or cause flooding concerns and instead will be more of

a typical winter rain for the PacNW. Looking at NBM's potential

72 hour rain totals from 4 AM Friday through 4 AM Monday, the

mean scenario (or most likely scenario) suggests around 0.75-1

inch for interior lowlands and 0.75-2 inches for the coast and

Cascades. The high end scenario (10% chance of exceeding these

values) indicates around 1.25-1.75 inches for the interior 

lowlands, 1.3-3 inches for the Cascades, and 2-4 inches for the 

Coast. For the low end scenario (90% chance of exceeding these

values), NBM indicates 0.25-0.4 inches for the interior 

lowlands and 0.4-0.9 inches for the Cascades and coast. -03



&&



.AVIATION...An upper level ridge of high pressure over the region

will maintain predominately VFR conditions through the period. A

few areas of low stratus remain in far southeast parts of the 

southern Willamette Valley as well as along the lower Columbia 

River near KKLS where a surface inversion is keeping the colder 

air, along with some near surface moisture, trapped. A strong 

offshore pressure gradient will maintain breezy east winds through

the Columbia River Gorge resulting in gusts up to 30-35 kt at 

KTTD. Given the persistent, strong easterly flow, there is the 

potential for LLWS for KPDX and KHIO through the TAF period as 

well.



Temperatures again fall into the upper 20s to lower 30s across 

the Willamette Valley tonight, resulting in widespread areas of 

frost, with lower confidence of patchy dense fog developing.

Highest chances for fog and freezing fog development will again 

be in the southern Willamette Valley, including KEUG. 



KPDX AND APPROACHES...VFR conditions expected to persist through

the TAF period. Easterly winds around 8-12 kt expected through 

this evening. Strong east winds from the Columbia River Gorge are

not expected to impact the terminal directly. However, given the 

persistent strong, easterly flow, there is the potential for LLWS 

through tonight. /DH



&&



.MARINE...High pressure remains over the region through the middle

of the week. Stronger high pressure inland will maintain offshore

winds across the coastal waters through tonight, before becoming

more southerly on Wednesday. Winds expected to remain around 10 

kt or less, while seas persist around 6 to 7 ft through Wed night.

Southeasterly winds increase on Thursday to around 15 kt as a low

pressure system begins to develop well offshore from the northern

California coast. This low pressure system is expected to

strengthen offshore late in the week, although there remains 

considerable uncertainty regarding the strength and position of

the low into the weekend. That said, there is around a 60-70%

chance of Gale force wind gusts occurring across the waters

sometime late Friday into Saturday. These stronger winds, combined

with a developing fresh southerly swell will likely push seas into

the lower to mid teens by Saturday, with a 10-15% chance of

exceeding 20 ft. /DH



&&



.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.

WA...None.

PZ...None.



&&



$$



www.weather.gov/portland



Interact with us via social media:

www.facebook.com/NWSPortland

x.com/NWSPortland