ポートランドの月別の天気

Portland forum threads describe January as genuinely variable from year to year - some winters bring mostly light drizzle and intermittent showers, others bring ice and snow, and a few bring stretches of clear, sunny cold instead. Typical daytime temperatures were cited around 35-45F, and posters were clear that Portland's reputation for constant heavy rain is somewhat overstated: one poster's data from a past January counted 23 days with measurable precipitation but only 4 of those with more than half an inch, meaning most rainy days here are genuinely light. The consistent theme across threads: expect cloudy, cool and often damp conditions as the baseline, but don't rule out the occasional bright, dry cold spell.

Regulars sum up this month with a local saying rather than a forecast: if you don't like the weather, wait five minutes - a morning can start rainy and cold and end sunny and warm, sometimes needing a rain jacket, a fleece and short sleeves all within the same day. Our row backs the mild, changeable average, 20.8C over 10.3C nights, with 50.2mm of rain across 8.3 days. Regulars are consistent that genuinely settled, predictable weather doesn't really arrive until early July, so layering isn't just advice for this month specifically - it's the baseline strategy through the whole spring stretch. The record: humidity 70 percent, 10.8 hours of sun, an 11.9 kph wind and one of the cleanest air readings in this project, AQI 34.

Portland's forum treats June as the real transition month — some years the dry season has already started, other years a genuine rain system still comes through mid-month. Regulars' consistent advice: pack a rain jacket regardless, but expect at most a quarter inch on a wet day, not an all-day washout.

The local joke here is a date: summer begins on the 5th of July, because it can stay cool and showery right up to the 4th and then simply stops raining until late September. Our row is the joke in numbers - 4.5mm across 1.2 days, which is as close to a dry month as this collection holds outside the deserts. July is also the warmest, 27.6C over 15C, with the occasional run at the upper thirties. Twelve degrees between day and night and only 57 percent humidity mean the evenings are genuinely cool, and 13.1 hours of sun sit inside 15.3 of daylight. The record: a dew point of 11.5C, a 12.3 kph wind and AQI 29, among the cleanest air we hold for a large city.

Nobody on this board will predict an August here, and the variable they mean is not rain but smoke. Fires in central Oregon, eastern Washington or British Columbia can send it down the Cascades and through the Gorge into the city, and whether it arrives depends entirely on which way the wind is sitting that week; the standing advice is to have a plan B. Our AQI of 34 is a thirty-year normal and cannot see a smoke week, which is exactly why the board's warning is worth more than the column. The weather otherwise is the best of the year: 28.1C over 15.8C, 7.7mm of rain across 1.4 days, 11.8 hours of sun. The record: humidity 57 percent and an 11.6 kph wind.

September is the month long-time Oregonians name as the best of the year: sunny, dry, neither too hot nor too cold, with the least rain of the year falling between July and September. It is also when people schedule outdoor weddings, for the odds. The one risk is smoke - wildfire smoke is likelier in September than in July, unpredictable when it comes, easing later in the month, and less of a problem at the coast than inland. Our row is the dry half of that picture: 46.4mm across 5.4 days. The record: 23.9C days, 13.5C nights, humidity 67 percent and 9.8 hours of sun.

Portland forum regulars describe December's reputation as somewhat overstated: “you're as likely (or more) to have dry sunny (cold) weather as to have snow,” and Pacific Northwest rain itself “tends to be very light and intermittent,” with overcast skies doing more to the mood than actual heavy rainfall does. Snow and ice shutting the city down is real but rare — “about once every two to four years,” with no way to predict which year. The standard advice is a warm jacket and a spare pair of socks for a wet puddle rather than anything more extreme. Breweries, walkable neighborhoods like Hawthorne and The Pearl, and the Nutcracker at Oregon Ballet Theater are the go-to plans regardless of what the sky does. Our record: 8.6°C days, 2.9°C nights, 204.8mm of rain across 19.4 days and 4.1cm of snow — genuinely the wettest stretch of the year, more rain than the “light and intermittent” framing suggests.