- Rain Oct to Mar: about 74% of the year
- Best window: before October
- Highest value: gutters & downspouts
- Never: pressure wash asphalt shingles
About three quarters of Portland’s yearly rain, roughly 27 of its 37 inches, falls between October and March, according to National Weather Service normals for PDX. Before it arrives, handle five things: clear the gutters and confirm every downspout drains, treat moss while it is still dormant, trim branches back off the roof, check flashing and pipe boots at every roof penetration, and look in the attic for stains or daylight. The work is far cheaper and easier now than once the roof is wet and every roofer in the metro is chasing active leaks.
October brings more than twice as much rain as September at PDX, 3.42 inches versus 1.52, and the National Weather Service notes that nearly 90 percent of Portland’s yearly rain falls between mid-October and mid-May. From there we typically do not get an extended dry stretch again until spring. The gap between now and the first sustained rain is the single best window of the year to deal with your roof, and it is also the window most homeowners let slip by.
Here is our honest take on fall roof prep for homes in Portland, Vancouver, and across Clark County: most of it is straightforward, some of it you can do yourself, and a fair amount of what gets sold as urgent in October is really just work that should have been scheduled during the dry stretch. This checklist is meant to help you sort one from the other.
How much rain is coming?
Here is what a normal wet season looks like at Portland International Airport, based on the National Weather Service’s 1991 to 2020 climate normals.
| Month | Normal rain (PDX) | What it means for your roof |
|---|---|---|
| September | 1.52 in | Last reliable dry window for repairs and moss treatment |
| October | 3.42 in | First real storms; clogged gutters show up fast |
| November | 5.45 in | Peak wind season begins; leaves and needles pile up |
| December | 5.77 in | Wettest month of the year |
| January | 5.03 in | Wind, rain, and the occasional ice storm |
| February & March | 7.65 in combined | Moss grows fastest; small leaks keep getting worse |
Source: National Weather Service Portland, 1991 to 2020 normals at PDX (36.92 inches per year).
The airport is also one of the drier spots in the metro. Downtown Portland averages 44 inches a year, Troutdale about 40, and the West Hills around 60, according to the National Weather Service. If you live near the Gorge or up in the hills, your roof sees noticeably more water than the PDX numbers suggest. Our local pages cover what that means in Portland, Troutdale, and Battle Ground.
How last season compared: from October 1, 2025 through September 22, 2026, PDX recorded 34.80 inches against a normal of 36.38, slightly dry. Troutdale recorded 41.12 inches against a normal of 40.00, slightly wet. A dry year does not mean your roof got off easy. It means the problems a wetter year would have exposed may still be waiting.
Why the dry season beats the wet season for roof work
Four practical reasons.
- Asphalt shingles seal properly in warm weather. Shingles bond using a heat-activated adhesive strip. Installed in 75-degree weather, they seal within days. Installed in 45-degree drizzle, that bond can take weeks and may need hand-sealing. The material performs the same either way once it is set, but the margin for error is thinner in the cold.
- Sealed shingles are what hold up in wind. The Malarkey shingles we install carry a 110 mph standard wind warranty, and up to 130 mph when installed to Malarkey’s enhanced specification. Our storms rarely come close to that: gusts topped 50 mph in Portland during the January 2024 ice storm and reached 80 mph in the Columbia River Gorge. When shingles blow off here, it is usually because they are old, never sealed, or were nailed wrong, not because the wind beat the product.
- You can actually find the problem. A dry roof is easier to inspect. Once everything is soaked and slick, both diagnosis and safe access get harder.
- Schedules are open. After the first big storm, every reputable roofer in the metro is triaging active leaks. If you call in November with a non-emergency, you are behind homeowners with water coming through their ceilings, and rightly so.
The pre-rain checklist
Six items, in the order we would tackle them. The detail on each follows below.
| Task | Why it matters | DIY or pro? |
|---|---|---|
| 1. Clear gutters & downspouts | Blocked water backs up under the shingle edge and saturates the fascia and sheathing. | DIY if single-story and accessible; pro for heights |
| 2. Treat moss | Once rain returns, moss swells and lifts shingle edges, holding moisture all winter. | DIY for light growth; pro for steep or heavy |
| 3. Trim overhanging branches | Limbs abrade granules, drop debris, and shade the roof so it stays damp. | Pro for anything near power lines or large limbs |
| 4. Inspect flashing & penetrations | Most leaks are flashing failures, not shingle failures. Pipe boots fail at 10 to 15 years. | Pro. Requires close-up roof access |
| 5. Check the attic | Daylight means a hole; staining means water has been getting in, possibly for a while. | DIY with a flashlight |
| 6. Check the shingles | Curling, bald patches, and heavy granule loss point to a roof near the end of its life. | DIY from the ground with binoculars |
1. Clear the gutters and check the downspouts
This is the highest-value item on the list and the one most often skipped. Douglas fir needles and big-leaf maple debris pack into gutters and turn to sludge. When water cannot move, it backs up under the shingle edge, saturates the fascia, and eventually finds the sheathing.
Clear the troughs, then run a hose and confirm every downspout actually discharges. A downspout that dumps against the foundation is its own separate problem. If your gutters are sagging, pulling away, or undersized for the roof area feeding them, the dry stretch is the time to address it. More on how drainage protects the whole structure in our guide to gutters and roof drainage.
2. Deal with moss before it rehydrates
Moss in the dry months is dormant, brittle, and gray. It looks harmless. It is not. Once the rain returns it swells, lifts shingle edges, and holds moisture against the roof surface all winter.
The right approach is gentle: brush or blow off loose growth, apply a zinc or copper-based treatment, and let the rain carry it through. What you should never do is pressure wash an asphalt roof. It strips the granules that are the shingle’s actual weather protection and can shorten a roof’s life by years.
One thing to know if you have algae-resistant shingles: they are not moss-proof. Malarkey’s algae warranties, for example, cover only blue-green algae streaking and expressly exclude moss and lichens. In our climate, moss still needs treatment no matter which shingle is on the roof. Our full guide to moss prevention and removal on PNW roofs covers what works and what wrecks shingles, and our write-up on roof maintenance and cleaning covers the rest.
3. Trim back overhanging branches
Limbs that touch or hang over the roof do three bad things: they abrade granules in wind, they drop constant debris, and they shade the roof so it stays damp and grows moss. Aim for several feet of clearance.
This is also windstorm insurance. On December 17, 2025, a windstorm on the heels of an atmospheric river knocked out power to at least 90,000 Clark Public Utilities customers, and a tree came through a townhome in Tualatin. Soil already soaked from the week before is what let so many trees go over. The branch you trim in the dry season is the one that does not come through your roof in December. If one does, our storm damage roof repair guide walks through the first 48 hours and how to document a claim, and our guide to atmospheric river roof damage explains why long soaking storms find weak spots.
4. Inspect flashing and penetrations
Most leaks are not shingle failures. They are flashing failures. Look at every place something interrupts the roof plane: chimney, plumbing vents, skylights, valleys, and wall-to-roof transitions. You are looking for lifted metal, cracked sealant, rusted fasteners, and rubber pipe boots that have split from UV exposure. Pipe boots in particular tend to fail around the 10 to 15 year mark, well before the shingles do, and replacing one is a minor roof repair. See our roof leak repair cost guide for what that runs compared to what the resulting leak costs.
5. Look at your attic, not just your roof
Go up with a flashlight on a bright day. Daylight through the decking means a hole. Dark staining on rafters or sheathing means water has been getting in, possibly for a while. Compressed or damp insulation near the eaves usually points to a ventilation problem rather than a leak.
That last one matters more here than in drier climates. When a house is sealed up through a wet Northwest winter, moisture from showers, cooking, and laundry rises into the attic. Without adequate intake and exhaust, it condenses on the underside of the sheathing and rots the roof from the inside. If your attic feels stuffy or you have seen frost on nails in winter, read up on roof and attic ventilation.
6. Check the shingles themselves
From the ground with binoculars is fine. Curling or cupped edges, bald patches where granules have washed off, cracked or missing tabs, and a heavy accumulation of granules in the gutters all point to a roof nearing the end of its service life. One or two of these signs is a repair conversation. All of them, on a roof past 20 years, is a replacement conversation.
What if the checklist turns up something bigger?
Sometimes fall prep reveals that the roof is not going to make it through another winter. That is not a fun discovery, but finding it now is far better than finding it in January.
Most full replacements on a typical local home land between $14,000 and $20,000, and our cost guide covers the full range from about $12,000 to $30,000 and up. The price is driven by square footage, roof pitch and complexity, the condition of the decking underneath, and the material you choose. We break the numbers down honestly in our roof replacement cost guide for Vancouver and Portland, and you can see how we approach the work on our roof replacement page.
If the timing is difficult, say so. A roof that needs replacing does not wait for a convenient quarter, and we would rather talk through financing options than watch a homeowner nurse a failing roof through a wet winter because nobody brought up the subject.
Get ahead of the rain
October normally brings more than twice September’s rain. Spend part of a day on your roof, or have someone do it for you. Whether it turns into a gutter cleaning, a pipe boot replacement, or a bigger conversation, knowing where you stand before the rain starts is worth far more than the hour it takes. We will tell you what we actually see, including when the answer is that your roof is fine and you should spend your money elsewhere.
Request a free estimate WA (360) 952-3998 · OR (503) 523-3449 · customercare@jobinroofing.comFrequently asked questions
What should I check on my roof before winter?
Gutters and downspouts first, then moss, overhanging branches, flashing and roof penetrations, and the attic. From the ground, check the shingles themselves for curling, bald patches, and granule loss. The gutters are the highest-value item and the one most often skipped.
When does the rainy season start in Portland?
Usually in October. National Weather Service normals put October rain at PDX at 3.42 inches, more than double September’s 1.52, and about three quarters of Portland’s yearly rain falls from October through March. December is the wettest month.
Is it too late in the year to replace a roof?
No. We install year-round in this climate, and a properly installed roof performs the same whether it went on in August or February. Warm, dry weather simply makes scheduling more predictable and helps shingles seal faster. If your roof needs replacing, the season should not be the deciding factor.
Can Pacific Northwest wind blow shingles off a newer roof?
It can, but usually because of installation, not the wind itself. Malarkey shingles carry a 110 mph standard wind warranty, and our storms typically gust well below that. Shingles that blow off are usually old, never sealed properly, or were nailed wrong.
How often should a Pacific Northwest roof be inspected?
Once a year is reasonable for most homes, and late summer or early fall is the ideal time. Add a check after any major windstorm. Homes with heavy tree cover benefit from twice-yearly attention, mostly because of debris and moss.
Can I clean the moss off myself?
Light surface moss on a low-slope, accessible roof, yes, using a soft brush and a zinc-based treatment. Steep pitches, second stories, tile, and heavy growth are worth hiring out. Roof falls are serious, and there is no version of this job that is worth an injury.
Do algae-resistant shingles stop moss?
No. Algae-resistant shingles are made to prevent blue-green algae streaks. Malarkey’s algae warranty, for example, expressly excludes moss and lichens. In the Northwest, moss still needs regular treatment.
Should I pressure wash my roof?
No. Pressure washing an asphalt roof strips the granules that are the shingle’s actual weather protection and can shorten the roof’s life by years. Gentle brushing plus a zinc or copper-based treatment is the correct approach.
Will my homeowners insurance cover storm damage this winter?
Sudden storm damage is generally covered in both Oregon and Washington. Gradual deterioration and deferred maintenance generally are not, which is another argument for documenting your roof’s condition now with a few photos.
What does a professional inspection actually include?
A real inspection means someone gets on the roof, examines flashing and penetrations up close, checks the attic, and gives you photos of what they found along with a plain explanation of what needs attention now versus what can wait. If a contractor will not show you photos of the problem they are describing, that is worth questioning.
Sources: National Weather Service Portland, Climate of Portland and precipitation normals (1991 to 2020); NWS daily climate reports for PDX and Troutdale, September 22, 2026; Malarkey Vista AR specifications; The Columbian and KOIN coverage of the December 17, 2025 windstorm; OPB coverage of the January 2024 ice storm.
