Portland weather by month — averages, rainfall & climate trends
A green, rain-loving city in the Willamette Valley, Portland captures the Pacific Northwest in miniature — soft, drizzly winters, glorious dry summers, and forests kept lush by the long wet season. Average temperatures and rainfall by month, a climate graph, today's conditions versus the long-term average, and how the climate has shifted since 1940 — all on one page for Portland, United States.
Today vs average
+1.7°Cwarmer than usual
How it’s changed
Right now
What it's doing today vs the historical average for this date.
Right now
21.1°
31°16°36°21°
38°21°36°20°33°19°30°16°31°16°On this date — July 20
About average
- Record high: 39.2° · 1946
- Record low: 9.1° · 1950
- One year ago: 26.8°
Every July 20 in history — coldest to hottest
Dots show daily highs (top) and lows (bottom) for each July 20 on record (n = 87). Outlined dots are today's forecast.
Area we sample
Each city's history comes from one ERA5 grid cell — about 28 km across, shown by the dashed box. Near mountains or coasts, conditions can vary across the cell.
Location & data
Historical weather for Portland is sampled from the ECMWF ERA5 reanalysis at 45.52°N, 122.68°W, with daily records since 1940.
- Coordinates
- 45.52°N, 122.68°W
- Time zone
- America/Los Angeles
- Period
- 1940–2026
- Data source
- ERA5 (ECMWF)
Last 30 days
15 of the last 31 days were warmer than the historical average for that date. Average difference: +0.4°C.
Each bar is one day, from morning low to afternoon high. Warm-colored bars are days whose mean ran above average; cool bars ran below. The dot inside the bar is the daily mean. The shaded band is the typical 10–90% range expected for that date. Average = the day's mean temperature averaged across every year of record (1940–2026) for that calendar date.
This date over the years
One dot per year — the mean temperature on this calendar date. Dots are warmer or cooler than the long-term average (dashed line); the shaded band is the typical 10–90% range, and the highlighted dot is today's forecast. Based on ERA5 reanalysis — modelled estimates, not station readings.
Weather by month
Average temperatures and rainfall for each month — what a typical year looks like, from the full record.Climate overview
Portland has a warm-summer Mediterranean climate (Köppen Csb), the classic Pacific Northwest pattern of wet, mild winters and warm, dry summers. Lying about 100 km inland in the Willamette Valley, it is sheltered by the Oregon Coast Range to the west and backed by the Cascades to the east. Through the cooler half of the year it sits in the path of the stormy westerly flow off the Pacific; in summer the North Pacific High pushes the storm track north, bringing long, dry, sunny spells.
Thunderstorms and tornadoes are rare. The city's most dramatic recent event was the late-June 2021 heat dome, when an extraordinary regional heat wave drove temperatures to an all-time high; 2018, too, brought more 90-degree days than ever before. Winter occasionally turns disruptive when cold air and Pacific moisture combine to produce ice and snow.
The warmest month is August, with a daily mean around 20.1°C and typical afternoon highs of 28.5°C. At the other extreme, January averages 4.8°C, with typical overnight lows of 2.4°C. Around 20 days a year dip below freezing.
In total, Portland averages about 1298 mm of precipitation a year; December is usually the wettest month (201 mm) and July the driest (14 mm).
Comparing the record's first decade with its most recent one, Portland now averages 1.5°C warmer than it did in the 1940s. Days above 30°C have grown noticeably more frequent — from around 30 a year in the first decade to about 50 in the last.
Climate graph (climograph)
August is the warmest month, January the coolest — a yearly swing of 15°C. Wettest month: December (~201 mm). Whole year averages ~1298 mm of rain.
Bars = average monthly rainfall (right axis). Lines = average daily high and low (left axis). Average = each month's value averaged across every year of record (1940–2026).
Monthly wind
Average daily peak wind at 10 m, by month.
Monthly solar energy
Average daily incoming solar energy in megajoules per square metre — a measured proxy for how sunny the month is.
Portland month by month — what to expect
Typical conditions for each month, averaged across the full record (since 1940). Daylight is the time from sunrise to sunset. Record high/low are the most extreme values in the ERA5 dataset (modelled since 1940), so they can differ from official weather-station readings.
| Month | Avg high | Avg low | Rain | Daylight | Record high | Record low |
|---|---|---|---|---|---|---|
| January | 8.4° | 2.4° | 185 mm | 8.9 h | 17.4° (2024) | -21.1° (1950) |
| February | 10.9° | 3.3° | 147 mm | 10.1 h | 21.3° (1968) | -17.5° (1989) |
| March | 13.7° | 4.4° | 152 mm | 11.6 h | 26.2° (2025) | -11.3° (1971) |
| April | 16.8° | 6.1° | 110 mm | 13.3 h | 31.8° (2023) | -3.0° (1968) |
| May | 20.7° | 8.9° | 74 mm | 14.7 h | 38.4° (1983) | -2.3° (1954) |
| June | 24.0° | 11.5° | 48 mm | 15.5 h | 48.0° (2021) | 3.9° (1976) |
| July | 28.4° | 13.5° | 14 mm | 15.2 h | 42.8° (2009) | 5.5° (1962) |
| August | 28.5° | 13.9° | 21 mm | 13.9 h | 42.0° (2023) | 7.0° (1980) |
| September | 25.3° | 11.8° | 50 mm | 12.3 h | 41.8° (1988) | 1.2° (1972) |
| October | 18.3° | 8.2° | 112 mm | 10.7 h | 32.6° (1988) | -3.9° (1971) |
| November | 11.7° | 5.1° | 185 mm | 9.2 h | 21.8° (2010) | -12.1° (1955) |
| December | 8.4° | 3.0° | 201 mm | 8.5 h | 17.8° (1993) | -19.1° (1972) |
How it has changed
Year-by-year signals from 1940 to today.Climate stripes
Annual mean shifted from 1940–1949 to 2016–2025 by +1.5°C.
Each vertical stripe is one year. Color encodes how much that year's annual mean differed from the long-term average. Average = each year's annual mean compared to the average of all years (1940–2026). cooler ← → warmer
Annual mean temperature
Long-term trend: +0.19°C per decade.
One point per year — the temperature averaged across the whole year. The dashed line is the least-squares long-term trend. Based on ERA5 reanalysis — modelled estimates, not station readings.
Seasonal warming
Jun–Aug is warming fastest: +0.25°C per decade.
Each faint line is one three-month period's average per year; the bold dashed line is its long-term trend. Different parts of the year often warm at different rates. Based on ERA5 reanalysis — modelled estimates, not station readings.
Hot days vs frost days
Days ≥ 30°C per year: 30.4 early in the record → 49.1 recently. Frost days: 34 → 20.
Thin lines are raw yearly counts; thick lines are the smoothed trend that removes year-to-year noise. The hot-day threshold is auto-picked per city so the line actually moves. Average = a centered 5-year rolling average to smooth weather noise.
Yearly hot & cold extremes
All-time high in 2021, all-time low in 1950: 48.0°C / -21.1°C.
One point per year — the single hottest and coldest day recorded that year.
Annual rainfall
~1298 mm/year on average. Last decade ran −2% vs that average. Long-term trend: −11 mm per decade.
One bar per year of total rainfall. Dashed line is the long-term average. Average = the average annual rainfall across every year of record (1940–2026).
Day-by-day grid
Each tiny square is one calendar day across the full record — ~30,000 days per city. Use the mode switch above the chart: Anomaly colors each day by how far it ran from the historical average for that date (red = warmer, blue = cooler), Daily mean temp shows the absolute mean temperature for the day (useful to see seasons and heatwaves), and Precipitation shows daily rainfall (useful to spot wet/dry seasons and droughts). Average = the long-term average for that calendar date (1940–2026).