- Nov to Jan: 16 of Portland’s 37 yearly inches
- Wettest month: December
- Top leak points: flashing & clogged gutters
- Free: pre-storm roof check
Portland gets about 16 of its 37 yearly inches of rain in just November, December, and January, according to National Weather Service normals for PDX, and atmospheric rivers are a big reason why. These storms can keep a roof soaked for days with wind pushing rain sideways, which turns loose flashing, lifted shingles, clogged gutters, and worn pipe boots into active leaks. The best protection is fixing those weak spots before the storm, not during it.
Portland homeowners are no strangers to rain, but when forecasters warn of an atmospheric river, it is a different level of storm. These systems bring days of steady rain, wind-driven moisture, and saturated ground that expose roof problems across the metro. Atmospheric river events are when we see the most emergency leaks, ceiling stains, and water intrusion calls all year.
What is an atmospheric river?
An atmospheric river is a long, narrow band of water vapor pulled inland from the Pacific Ocean. The National Weather Service describes an average one as carrying about as much water vapor as the flow at the mouth of the Mississippi River. When one stalls over Portland and the Willamette Valley, it can drop several inches of rain over a few days with little drying time in between.
Many Portland homes have older roofing systems, mature trees overhead, and complex rooflines with dormers, chimneys, and valleys. Those are exactly the details that a multi-day soaking finds.
When atmospheric rivers hit Portland
Our wettest stretch lines up with atmospheric river season. Here is what a normal winter looks like at Portland International Airport, from the National Weather Service’s 1991 to 2020 climate normals.
| Month | Normal rain (PDX) | What we see on roofs |
|---|---|---|
| October | 3.42 in | First storms; gutters clog with leaves and needles |
| November | 5.45 in | Wind-driven rain finds flashing and ridge caps |
| December | 5.77 in | Wettest month; long soaking storms and tree damage |
| January | 5.03 in | Rain plus the occasional ice storm |
Source: National Weather Service Portland, 1991 to 2020 normals at PDX (36.92 inches per year).
And the airport is one of the drier spots in the metro. Downtown Portland averages about 44 inches a year and the West Hills around 60, so homes in the hills and near the Gorge take even more water from the same storm.
A recent example: December 2025
In mid-December 2025, a second atmospheric river in two weeks hit the region. On December 17, the windstorm that came with it knocked out power to at least 90,000 Clark Public Utilities customers, according to The Columbian. KOIN reported gusts around 40 mph near Portland and a tree that crashed through a townhome in Tualatin.
The detail that matters for roofs: the ground was already soaked from the storm the week before, and saturated soil is what let so many trees go over. When one atmospheric river follows another, the second one does more damage with less wind. That is why trimming branches and fixing small leaks between storms is worth doing even mid-season.
How atmospheric rivers damage roofs
1. Days of constant saturation
Unlike short storms, atmospheric rivers keep roofs wet for days. Shingles, underlayment, and flashing stay saturated, and water works its way into even tiny gaps. We see this most in older neighborhoods like Sellwood, Montavilla, and St. Johns, and on roofs nearing the end of their service life.
2. Wind-driven rain gets under shingles
Gusts push rain sideways, forcing water beneath shingles, ridge caps, and the flashing around chimneys, skylights, and vents. Once water gets underneath, leaks often show up inside within hours.
The wind itself is rarely strong enough to beat a good roof. The Malarkey shingles we install carry a 110 mph standard wind warranty, and our storms usually gust well below that. When shingles lift, it is usually because they are old, never sealed properly, or were nailed wrong.
3. Gutters overwhelmed by debris
Portland’s tree canopy is beautiful, but during an atmospheric river it is a liability. Clogged gutters back water up under roof edges, rot fascia and eaves, and cause ceiling leaks. It is one of the most common causes of winter leaks we see. Our guide to gutters and roof drainage covers what to fix.
4. Small issues become active leaks
Loose flashing, lifted shingles, or worn sealant might not leak in a light rain. An atmospheric river turns those small problems into water in the house, fast. A cracked rubber pipe boot is one of the most common examples, and one of the cheapest to fix ahead of time. See our roof leak repair cost guide for what small repairs typically run.
Signs to watch for during or after a storm
- Brown or yellow stains on ceilings
- Dripping or wet insulation in the attic
- Bubbling paint or soft drywall
- A musty smell that was not there before
- Shingles, ridge caps, or granules in the yard
If you notice any of these, your roof likely needs attention. Here is what to do if you discover an active leak.
How to prepare before the next storm
- Clean gutters and downspoutsEspecially after leaf drop. Run a hose and confirm every downspout carries water away from the house.
- Trim branches off the roofLimbs over the roof drop debris and become projectiles in wind, and soaked ground makes whole trees more likely to fall.
- Get flashing and pipe boots checkedThese are the most common leak points in a long soaking rain.
- Check attic ventilationGood airflow keeps moisture from building up and condensing during weeks of wet weather. More on roof and attic ventilation.
- Take a few photos of your roof nowIf a storm does damage it, before photos make an insurance claim much easier.
Our fall roof maintenance checklist walks through each of these in detail.
What to do if your roof leaks during a storm
- Protect what is insideMove belongings, set out buckets, and lay down tarps or towels.
- Stay off the roofWet roofs are dangerous in any weather. Do not climb up during a storm.
- Document everythingTake photos and video of the leak, the ceiling, and any visible roof damage from the ground.
- Call a licensed rooferWe can tarp an open roof to stop the water, then schedule the permanent repair. See our emergency roof repair page.
Fast response prevents mold and structural damage. If wind or a fallen tree caused the damage, our storm damage roof repair guide covers the first 48 hours and how to document a claim.
Why homeowners call Jobin Roofing
We serve Portland and Clark County with detailed inspections, storm damage experience, and honest recommendations, including telling you when a repair will do and a replacement is not needed. We are a Malarkey Emerald Premium Contractor, licensed in Oregon (CCB #221810) and Washington (#JOBINRL824MZ). Our local pages cover roofing in Portland, Troutdale, and Battle Ground.
Don’t wait for the next atmospheric river
November through January brings most of Portland’s heaviest rain. A pre-storm inspection finds the weak spots while they are still small and cheap to fix. We will show you photos of what we find and tell you honestly what can wait.
Request a free estimate WA (360) 952-3998 · OR (503) 523-3449 · customercare@jobinroofing.comFrequently asked questions
What is an atmospheric river?
A long, narrow band of water vapor carried inland from the Pacific Ocean. When one stalls over the Portland area, it can bring several inches of rain over a few days, often with gusty wind.
When is atmospheric river season in Portland?
Mostly late fall through winter. November, December, and January bring about 16 of Portland’s 37 yearly inches of rain at PDX, according to National Weather Service normals, and December is the wettest month.
Why does my roof only leak in heavy storms?
Small weak spots like loose flashing, a cracked pipe boot, or a lifted shingle can stay dry in light rain. Days of steady, wind-driven rain push water through those same gaps. A leak that only shows up in big storms is usually a small, fixable problem.
Should I get on my roof during a storm?
No. Wet roofs are slippery and dangerous. Protect what is inside, take photos from the ground, and call a roofer who can tarp the roof safely.
Will insurance cover atmospheric river roof damage?
Sudden damage from wind or a fallen tree is generally covered in Oregon and Washington. Leaks from gradual wear or deferred maintenance generally are not. Photos of your roof before the storm season help either way.
How do I prepare my roof for an atmospheric river?
Clean gutters and downspouts, trim branches back off the roof, have flashing and pipe boots checked, and make sure the attic is well ventilated. Doing it before November is easiest.
Sources: National Weather Service Portland, Climate of Portland and precipitation normals (1991 to 2020); The Columbian and KOIN coverage of the December 17, 2025 windstorm; Malarkey Vista AR specifications.
