Weather in Portland in September

Prime time. If you get to pick your dates, September is the one. Highs average 25.8 °C, lows 12.1 °C, and rain falls on 7 days — nothing in the month is working against you.

September ranks 2 of 12 in Portland. Only July scores clearly higher, and the difference is small enough to be settled by price rather than weather.

Rain on 7 days, 2 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: 7 days top 30 °C — hot spells arrive, but they break. Across the twenty years measured, the hottest September day reached 40.1 °C and the coldest night fell to 3.7 °C, and the wettest single day dropped 55 mm — roughly 96% of the month's rain in one day.

This is the volatile part. September rainfall has ranged from 2 mm to 230 mm across the twenty years measured — a 228 mm spread around an average of 57 mm. The average is real but almost no individual September looks like it, so treat the figure as the middle of a wide range rather than a forecast.

Wind is light at 2.6 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 68%.

How September sits in the year

The month is on the way down: 4.1 °C cooler than August, with October dropping another 7.6 °C. The first week and the last are not the same trip. Rain is the thing that moves: October brings 7 days more of it, so the earlier half of a flexible trip is the safer half.

Daylight in September

12.6 hours of daylight, losing 1.6 hours across the month. That is between Portland's extremes of 15.7 and 8.7 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 27.7 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in Portland versus nearby

If Portland is one option among several, the nearby comparison is worth making. Eugene is close enough to be a coin toss — within a degree on temperature, 1 day less rain. Seattle is close enough to be a coin toss — 4.8 °C cooler, 3 days more rain.

So: September is effectively as good as it gets here — 3 points behind July, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Portland

See all twelve months in Portland, or where else to go in September.