Portland records about 914mm of rain across roughly 144 wet days a year, which is a 39% chance on an average day. December is the wettest month at 138mm (15% of the annual total) and August the driest at 12mm. Local rain type: drizzle. Portland lives up to its rainy reputation — persistent drizzle from October through May is the norm. Locals never carry umbrellas; rain jackets are the uniform.
Chance of rain on an average day: 39%
Rainfall climatology for Portland. The live hour-by-hour answer for today loads at the top of this page from Open-Meteo and refreshes through the day — the figures below describe a typical year, not today.
Last updated: · Live forecast data refreshes hourly.
| Annual rainfall | 914mm |
| Rain days per year | 144 |
| Odds on an average day | 39% |
| Wettest month | December — 138mm over 23 days |
| Driest month | August — 12mm over 2 days |
| Rain type | drizzle |
| Best dry window | July and August are spectacularly dry and sunny — Portland's glorious secret season. |
| Worst rain window | November through January brings persistent grey drizzle with very short days. |
December delivers 1050% more rain than August (138mm vs 12mm). That gap is the difference between planning around showers and ignoring them.
No single month holds more than 15% of the annual total, so rain in Portland is spread through the year — there is no season you can rely on being dry.
Portland rain is mostly persistent drizzle, where a waterproof shell beats an umbrella.
Rain falls on about 23 days in December against 2 in August — the frequency swing matters more for planning than the millimetre totals.
Climate normals. Use them to judge whether today's live forecast at the top of the page is typical or unusual for the season.
| Month | Rainfall | Rain days | Chance on a given day | Highs |
|---|---|---|---|---|
| January | 125mm | 21 | 70% | 8°C |
| February | 93mm | 16 | 53% | 8°C |
| March | 91mm | 15 | 50% | 11°C |
| April | 64mm | 11 | 37% | 15°C |
| May | 56mm | 10 | 33% | 20°C |
| June | 38mm | 6 | 20% | 24°C |
| July | 14mm | 2 | 7% | 27°C |
| August | 12mm | 2 | 7% | 27°C |
| September | 28mm | 5 | 17% | 24°C |
| October | 72mm | 12 | 40% | 20°C |
| November | 116mm | 20 | 67% | 15°C |
| December | 138mm | 23 | 77% | 11°C |
Rain probability is the chance that at least 0.2mm falls at your location — not how long it rains. For Portland we combine the hourly probability curve, expected volume in millimetres, and the city's own rainfall record into a single umbrella verdict.
| Factor | Weight | What it measures |
|---|---|---|
| Hourly probability | 40% | Peak and sustained chance of measurable rain across the next 24 hours. |
| Expected volume | 30% | Total millimetres, which separates a passing shower from a genuine soaking. |
| Timing & duration | 20% | When rain starts, when it eases, and the longest continuous dry window. |
| Local rain type | 10% | Drizzle, brief showers, thunderstorms or monsoon — each needs different gear. |
Live hourly values come from Open-Meteo and refresh through the day. Monthly rainfall figures are climate normals, so they describe a typical year rather than a forecast.
Portland records rain on roughly 144 days a year — about a 39% chance on any given day — totalling around 914mm.
December, with about 138mm over 23 rain days. That is 15% of the entire year's rainfall in a single month.
August is the driest month at 12mm across roughly 2 days. July and August are spectacularly dry and sunny — Portland's glorious secret season.
Portland lives up to its rainy reputation — persistent drizzle from October through May is the norm. Locals never carry umbrellas; rain jackets are the uniform.
No. Probability is the chance that at least 0.2mm of rain falls at your location at some point in the period. Check the expected millimetres alongside it: 40% with 0.4mm is a passing shower, 40% with 12mm is a soaking.