You’ve heard the jokes. People think Portlanders are basically moss-covered humans who haven't seen the sun since the Clinton administration. If you look at the data for Portland OR weather monthly, you'll see why the stereotype stuck, but you'll also see where it's dead wrong.
It rains. A lot. But it's not a monsoon. It’s more of a persistent, annoying mist that the locals just ignore while they wait in line for brunch.
Actually, the "Big Dark" is real. From November to March, the sky looks like the inside of a Tupperware container. But then July hits, and suddenly everyone forgets the six months of gloom because the Willamette Valley turns into a Mediterranean paradise. It’s a weird, bipolar climate that catches newcomers off guard every single time.
The Reality of the "Rainy" Season
Let's talk about the damp. Most people think Portland is the rainiest city in the US. It's not. Not even close. Cities like Miami and Atlanta actually get more total inches of rainfall per year. The difference is intensity. In the South, it dumps three inches in an hour and then the sun comes out. In Portland, it drizzles for twelve days straight without a single break in the clouds.
January is the peak of the soggy vibe. You’re looking at an average high of about 47°F ($8.3°C$) and a low of 37°F ($2.8°C$). It’s rarely "cold-cold" like Chicago, but it’s a wet cold that sinks into your bones. It feels heavier. According to the National Weather Service (NWS) Portland office, January averages about 5 inches of rain. That sounds manageable until you realize that rain is spread across 18 or 19 days. It’s constant.
February feels like a long-distance runner hitting a wall. You want spring. You need spring. But the weather says no. Usually, this is when we get our one "snow event." I use quotes because two inches of snow will literally shut down the entire city. The hilly terrain and lack of salt trucks turn the West Hills into a giant ice rink. If you're visiting then, honestly, just stay at your hotel. Nobody knows how to drive in it.
By March, the Portland OR weather monthly stats start to shift, but don't get excited yet. The "Spring Transition" is a lie. You’ll get one day of 65-degree bliss where everyone wears shorts, followed by three days of hail and 40-degree winds. It’s a tease. Total rainfall drops slightly to about 3.9 inches, but the gray stays consistent.
The Secret Season: Why May is the Real Winner
If you want the best of Portland without the crowds or the heatwaves, May is the sleeper hit. The roses start blooming at the International Rose Test Garden in Washington Park. The air smells like damp earth and flowers.
Temperatures in May settle into a sweet spot around 68°F. It's perfect hiking weather. You can hit the Columbia River Gorge trails without sweating through your shirt, and the waterfalls are at their absolute peak because of the mountain snowmelt.
June is a gamble. Locals call it "June Gloom." We often get a "Rose Festival" rainstorm that ruins parades. But when it's good, it’s incredible. The days are insanely long. Because Portland is so far north, the sun doesn't fully set until nearly 9:00 PM in late June. You get these massive, golden-hour evenings that feel like they last forever.
Surviving the Summer Heat Domes
Lately, the Portland OR weather monthly charts have some scary spikes. We used to brag about not needing air conditioning. That’s over. Ever since the 2021 Heat Dome—where temperatures hit a terrifying 116°F—summers have felt different.
July and August are now bone-dry.
- July: Average high is 81°F, but 90-degree streaks are common.
- August: Usually the driest month. We’re talking less than 0.7 inches of rain.
- September: Often the best month of the year. The smoke from wildfires is the only real threat.
The humidity stays low, which is the saving grace. You can sit on a patio at 5:00 PM and it feels crisp, not sticky. But the lack of rain means the grass turns brown and crunchy by mid-August. It’s a stark contrast to the lush green of the winter.
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If you are planning a trip, aim for September. The kids are back in school, the weather is a consistent 75°F, and the "Big Dark" hasn't started its slow crawl across the horizon yet. It’s basically peak Oregon.
The Autumn Slide and the Return of the Gray
October is the pivot point. The first half is usually "Second Summer." Then, usually around the third week, the "Switch" happens.
One day it’s sunny; the next morning, you wake up, the sky is charcoal, and it stays that way until May.
November is statistically the wettest month. We average over 6 inches of rain. This isn't the romantic "cuddle by the fire" rain. It’s the "my windshield wipers are on high and I still can't see the car in front of me" rain. The wind picks up too. The Columbia River Gorge acts like a giant wind tunnel, blasting the city with gusts that can knock over patio furniture.
December is dark. Short days. The sun sets at 4:30 PM. It’s the month where everyone in Portland doubles their intake of Vitamin D supplements. If you’re checking the Portland OR weather monthly data for a winter visit, focus on the "Cloud Cover" stats. We average about 80% cloud cover in December.
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A Month-by-Month Snapshot of Averages
To give you a better sense of the rhythm, here is how the temperature and precipitation usually shake out throughout a standard year in the Rose City.
January: High 47°F | Low 37°F | 5.0" Rain
February: High 51°F | Low 37°F | 3.8" Rain
March: High 57°F | Low 41°F | 3.9" Rain
April: High 62°F | Low 44°F | 2.9" Rain
May: High 69°F | Low 49°F | 2.5" Rain
June: High 74°F | Low 54°F | 1.6" Rain
July: High 81°F | Low 58°F | 0.5" Rain
August: High 82°F | Low 59°F | 0.7" Rain
September: High 77°F | Low 54°F | 1.5" Rain
October: High 64°F | Low 47°F | 3.2" Rain
November: High 53°F | Low 41°F | 6.0" Rain
December: High 46°F | Low 36°F | 5.8" Rain
Why the Microclimates Matter
Portland isn't a monolith.
The weather at PDX airport (where the official stats come from) is often different than the weather in the West Hills or out in Gresham. If you live in the West Hills, you might get three inches of snow while the Pearl District just gets rain.
The "Gorge Effect" is the biggest wild card. Cold air from the east side of the Cascade Mountains gets sucked through the Columbia River Gorge. This creates a "cold pool" in East Portland and Troutdale. While downtown might be a chilly 35 degrees, Gresham could be experiencing freezing rain that turns the trees into glass. It's a localized nightmare that weather apps often fail to predict accurately.
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How to Actually Dress for This
Don't buy an umbrella.
Seriously. If you carry an umbrella in Portland, everyone knows you’re from out of town. The wind usually just flips them inside out anyway. The move is a high-quality raincoat with a hood.
Layering is the only way to survive. You need a base layer that wicks moisture, a fleece or light down jacket, and a waterproof shell. This setup works for about 9 months of the year. In the summer, keep a light hoodie in the car. Even when it hits 90 during the day, the temperature can drop 20 or 30 degrees the second the sun goes behind the West Hills.
Actionable Advice for Your Visit
- Check the smoke maps: If you're coming in August or September, check AirNow.gov. Wildfire smoke has become a regular (and depressing) part of the late summer cycle.
- Rent a car with decent tires in winter: If there is even a hint of "wintry mix" in the forecast, the city becomes a parking lot.
- Book the coast for July: If the valley is hitting 100 degrees, drive 90 minutes west to Cannon Beach. It’ll be 65 degrees and foggy. It’s the ultimate "Portland escape" when the heat gets weird.
- Embrace the "Big Dark": If you're here in November, do what we do. Go to a cozy brewery, find a fire pit, and accept that you're going to be a little damp for a while.
The Portland OR weather monthly cycle is less of a predictable calendar and more of a mood ring. It’s moody, gorgeous, occasionally frustrating, but never boring. Just remember: the green you see everywhere is paid for in gray. It's a fair trade once you see the mountains come out on a clear day.
Next Steps for Your Trip Planning:
- Download the 'KGW Weather' or 'KOIN 6' apps: Local meteorologists like Matt Zaffino or Mark Nelsen understand the "Gorge Effect" and microclimates far better than the default Apple or Google weather apps.
- Pack in "Three Layers": Ensure you have a moisture-wicking base, an insulating mid-layer (fleece/wool), and a breathable waterproof outer shell.
- Monitor the NWAC (Northwest Avalanche Center): If you plan on headed to Mt. Hood for skiing or snowshoeing during the winter months, this is the only source you should trust for mountain safety.
- Reserve outdoor dining for "After July 5th": Traditionally, the weather reliably clears up for the summer after the Independence Day holiday; booking outdoor events before then is a gamble with the rain.