The arrival of spring in Oregon is not marked by a single date, but rather a progression that sweeps across the state’s diverse landscape. Separated by the towering Cascade Mountains, Western and Eastern Oregon experience two distinctly different transitions from winter to warmer months. This geographic complexity means that when one region is experiencing early blooms, another is still covered in deep snow. Understanding when spring begins requires focusing on the actual climatic shift in each major area.
Calendar vs. Meteorological Spring
The common understanding of the first day of spring aligns with the astronomical calendar, which begins on the vernal equinox, usually around March 20th or 21st. This date marks the moment when day and night are nearly equal in length. Climatologists and meteorologists, however, prefer a definition that better reflects the annual temperature cycle for consistent record-keeping. Meteorological spring encompasses the full months of March, April, and May. This three-month division allows for easier comparison of seasonal statistics and captures the time when temperatures consistently begin to rise. For Oregon, where the shift to warmer weather is gradual and regionally specific, the meteorological definition proves more practical.
The West Side: Willamette Valley and Coastal Timing
West of the Cascade Range, the mild, oceanic climate of the Willamette Valley and the Coast allows meteorological spring to begin quite early. The first signs of the season often appear in late February or early March, characterized by lengthening daylight hours and a noticeable warming trend. Plentiful winter rain fuels an explosion of green, with the first blooms of bulbs, such as daffodils and tulips, appearing in March. Portland and the surrounding valley see average high temperatures rise from the mid-50s in March to the high 60s by May. Precipitation transitions from heavy winter rains to scattered, lighter showers interspersed with sun. This early start supports the wine industry, where “bud break” signals the official start of the growing season in April.
The East Side: High Desert and Mountain Timing
Across the Cascades, the High Desert and mountainous regions experience a much later and more dramatic shift into spring. The Cascade Range effectively blocks the moist, moderating air from the Pacific, resulting in a drier and more temperature-variable climate. Meteorological spring often does not truly take hold in cities like Bend and Redmond until mid-to-late April. While low-lying areas may see the earliest desert wildflowers in March, the transition is slow due to lingering snowpack at higher elevations. Temperatures can fluctuate wildly, with warm, sunny days often followed by nights that still drop below freezing well into May, meaning many mountain passes remain inaccessible due to snow until late May or even June.
Typical Spring Weather Patterns
Once the season is underway, Oregon’s spring is defined by its unpredictability and variability, especially in the western part of the state. It is common to experience rapid shifts from bright sunshine to heavy cloud cover and back again within a single afternoon. The transition from the wet winter to the dry summer is characterized by frequent sun breaks, which offer glimpses of warmth but do not signify the end of precipitation. While the number of rainy days decreases steadily from March through May, cool temperatures and scattered showers are expected well into June. Layered clothing is the standard recommendation, as the day’s weather can feel like “four seasons in one day.”