Seneca is drier than 93% of U.S. towns: 15 inches of precipitation a year
July afternoons average 83°. Its January nights bite harder than in 81% of U.S. towns. Compared with 1901–2000, the average now sits 1.3° higher. Central heating does most of its work from October to May, in months below 50° on average.
A year in Seneca at a glance
Each month’s typical high and low, and what it brings.
What stands out about Seneca’s climate
Compared with towns across the U.S., with Seneca’s place in Oregon beside it.
What a year in Seneca feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
A freeze is possible in every month
About 252 nights a year fall to 32° or below, and 18 to 0° or below. Frost and day counts come from NOAA’s station at Seneca, OR, 0.2 miles from the town’s center, at about the same height.
The 2023 USDA map puts Seneca’s center in zone 5a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −15°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 15 inches of rain a year
December is the wettest month and August the driest.
Rain + melted snow by month
Inches of water
Heating and cooling a home in Seneca
Nearly all of the work is heating: a normal year has almost no cooling days. Months averaging under 55° run from September through June.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Seneca, OR.
Living with Seneca’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
Zone 5a, and frost can come in any month. The longest frost-free stretch in half of years is about 24 days.
Months with highs of 62–84° and lows of 40° or more: July and August. 0.8 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Seneca from natural hazards, river flooding is the largest share (66%); heat waves, cold waves, winter storms and ice storms together are 3%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Seneca and similar climates
TownRatings has no climate map of the towns around Seneca yet.
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Seneca averaged 1.3° warmer than the 1900s. The biggest change is in January (+3.7°).
A smaller shift than in 55% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Seneca compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Seneca’s place among Oregon’s.
Seneca weather by month
Highs, lows and precipitation from NOAA’s grid at Seneca’s center. 1991–2020 normals.
| Month | High | Low | Rain + melt | 30-yr range |
|---|---|---|---|---|
| January | 37° | 16° | 1.8" | 19° – 33° |
| February | 41° | 19° | 1.3" | 23° – 38° |
| March | 47° | 23° | 1.5" | 31° – 41° |
| April | 53° | 27° | 1.4" | 35° – 46° |
| May | 62° | 34° | 2.0" | 43° – 53° |
| June | 71° | 39° | 1.2" | 50° – 61° |
| July | 83° | 43° | 0.5" | 52° – 68° |
| August | 82° | 41° | 0.4" | 57° – 65° |
| September | 73° | 34° | 0.6" | 50° – 58° |
| October | 59° | 27° | 1.2" | 37° – 49° |
| November | 44° | 22° | 1.6" | 25° – 38° |
| December | 36° | 16° | 2.0" | 20° – 30° |
| Year | 57° | 28° | 15.4" |
How much a month can swing
A normal is an average. July swings the most: from 1991 to 2020 its average ranged from 52° to 68°. September is the most reliable, staying within 8°.
Where Seneca’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Seneca’s center.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Seneca, OR, 0.2 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Seneca’s climate
What is the weather like in Seneca?
A typical July afternoon reaches 83°, a January night drops to 16°. Colder January nights than 81% of U.S. towns; cooler July afternoons than 74% of U.S. towns.
How cold does it get in Seneca in winter?
December nights average 16°. About 252 nights a year reach 32° or below and 18 reach 0° or below. In the coldest December of the last 30 years the month averaged 20°.
How hot does it get in Seneca?
July, with a typical high of 83° and a low of 43°. About 13 days a year reach 90° (Seneca, OR).
When is the first and last frost in Seneca?
There is no reliable frost-free season: at Seneca, OR, every month has nights at 32° or below, about 252 a year. In half of years the longest stretch without a freeze is about 24 days.
What growing zone is Seneca in?
Zone 5a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −15°.
What is the best time of year to visit Seneca?
By one simple rule (highs of 62–84° and lows of 40° or more), July and August. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Seneca getting warmer?
Yes: 1991–2020 averaged 1.3° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 55% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Seneca.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.