Portland has a **warm-summer Mediterranean climate (Köppen Csb)**, though it is often described more generally as a mild maritime Pacific Northwest climate.
| Season | Typical Conditions | |---|---| | Winter | Cool, cloudy, and wet; daytime highs often in the 40s to low 50s °F (about 7-11 °C) | | Spring | Variable, with rain, bright intervals, and gradually warming temperatures | | Summer | Warm and dry; many days in the 70s and 80s °F (about 21-31 °C), with occasional hotter periods | | Autumn | Mild at first, then increasingly rainy and cooler |
Key climate characteristics:
- **Rainfall:** Most precipitation falls from late autumn through spring. Summers are relatively dry. - **Snowfall:** Snow is infrequent in many winters but can occur, and occasional ice storms can significantly disrupt travel. - **Humidity:** Humidity is often moderate to high in the wet season, though summer air can feel relatively comfortable compared with hotter inland regions. - **Heat:** Extreme heat has become a growing concern, especially after the 2021 Pacific Northwest heat wave. - **Best time to visit:** Many visitors prefer **late spring through early autumn**, especially **June to September**, for drier weather and outdoor activities. - **Natural hazards:** Winter ice storms, river flooding in low-lying areas, wildfire smoke during some late summers, landslide risk on steep wet slopes, and regional earthquake risk.
Average annual precipitation is widely reported at roughly the low-40-inch range, though exact normals depend on station and climate period. Temperatures are moderated by proximity to the Pacific Ocean, but local heat islands and valley geography can make summer conditions warmer than the coastal strip.