Twenty-One Ranchhouse · Photo: Jon Roanhaus · CC BY-SA 4.0Precipitation in Sweetwater trails that of 91% of U.S. towns: 18 inches a year
Peak summer warmth arrives in July, with afternoons near 90°. From frosty January to warm July, readings climb 62°. In July, afternoons here are warmer than in 76% of U.S. towns. Plan time outside for May, June and September, when highs sit at 72–80°.
A year in Sweetwater at a glance
Each month’s typical high and low, and what it brings.
What stands out about Sweetwater’s climate
Compared with towns across the U.S., with Sweetwater’s place in Idaho beside it.
What a year in Sweetwater feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 200 frost-free days a year
In half of years the last 32° night comes by April 6 and the first by October 26. Frost and day counts come from NOAA’s station at Lewiston Nez Perce Co Airport, 10 miles from the town’s center, at about the same height.
The 2023 USDA map puts Sweetwater’s center in zone 7b: the coldest night of a typical winter, averaged over 1991–2020, reaches about 7°. 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 13 inches of snow a winter
Snow, measured at Lewiston Nez Perce Co Airport, falls mostly in February and December. Precipitation (rain plus melted snow) adds up to 18 inches a year; May is the wettest month and August the driest. Rain or snow falls on about 106 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Sweetwater
85% of the work is heating. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Lewiston Nez Perce Co Airport.
Living with Sweetwater’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
200 frost-free days in zone 7b. The last frost comes by Apr 6 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 26.
Months with highs of 62–84° and lows of 40° or more: May, June and September.
Parks & trails →Of the yearly building losses FEMA expects in Sweetwater from natural hazards, river flooding is the largest share (78%); heat waves, cold waves, winter storms and ice storms together are 3%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Sweetwater and similar climates
TownRatings has no climate map of the towns around Sweetwater yet.
Climates most like Sweetwater’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Sweetwater, ID | 28° | 90° | 18" | 13" |
| Yreka, CA | 29° | 91° | 20" | 12" |
| Prescott, AZ | 26° | 90° | 15" | 10" |
| Clovis, NM | 24° | 91° | 17" | 13" |
| Plainview, TX | 26° | 92° | 19" | 8.2" |
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 Sweetwater averaged 1.3° warmer than the 1900s. The biggest change is in January (+3.7°).
A smaller shift than in 56% 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 Sweetwater compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Sweetwater’s place among Idaho’s.
Sweetwater weather by month
Highs, lows and precipitation from NOAA’s grid at Sweetwater’s center; snow, wet days and snow on the ground from Lewiston Nez Perce Co Airport. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 41° | 28° | 1.5" | 2.7" | 11 | 3 | 25° – 40° |
| February | 46° | 29° | 1.3" | 3.8" | 10 | 3 | 29° – 45° |
| March | 55° | 33° | 2.0" | 0.8" | 12 | 1 | 38° – 50° |
| April | 62° | 38° | 2.0" | 0.0" | 11 | 0 | 45° – 56° |
| May | 72° | 45° | 2.3" | 0.0" | 11 | 0 | 53° – 63° |
| June | 78° | 50° | 1.8" | 0.0" | 9 | 0 | 60° – 71° |
| July | 90° | 56° | 0.6" | 0.0" | 4 | 0 | 63° – 77° |
| August | 90° | 55° | 0.5" | 0.0" | 3 | 0 | 67° – 75° |
| September | 80° | 47° | 0.8" | 0.0" | 5 | 0 | 60° – 68° |
| October | 63° | 39° | 1.5" | 0.0" | 9 | 0 | 46° – 58° |
| November | 48° | 33° | 1.9" | 1.3" | 11 | 1 | 33° – 46° |
| December | 39° | 28° | 1.7" | 4.1" | 11 | 3 | 27° – 38° |
| Year | 64° | 40° | 17.9" | 12.7" | 106 | 11 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 29° to 45°. August is the most reliable, staying within 7°.
Where Sweetwater’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 Sweetwater’s center.
- Snow: Lewiston Nez Perce Co Airport.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Lewiston Nez Perce Co Airport, 10 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 Sweetwater’s climate
What is the weather like in Sweetwater?
A typical July afternoon reaches 90°, a January night drops to 28°, and about 13 inches of snow falls in a normal winter. Milder January nights than 70% of U.S. towns; hotter July afternoons than 76% of U.S. towns.
How cold does it get in Sweetwater in winter?
December nights average 28°. About 80 nights a year reach 32° or below. In the coldest December of the last 30 years the month averaged 27°.
How much snow does Sweetwater get?
About 13 inches in a normal winter at Lewiston Nez Perce Co Airport, most of it in February and December, with snow on the ground about 11 days a year.
How hot does it get in Sweetwater?
July, with a typical high of 90° and a low of 56°. About 44 days a year reach 90° and 9 reach 100° (Lewiston Nez Perce Co Airport).
When is the first and last frost in Sweetwater?
In half of years the last spring frost (32°) comes by April 6 and the first fall frost by October 26, about 200 frost-free days, at Lewiston Nez Perce Co Airport.
What growing zone is Sweetwater in?
Zone 7b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 7°.
What is the best time of year to visit Sweetwater?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Sweetwater getting warmer?
Yes: 1991–2020 averaged 1.3° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 56% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Sweetwater.
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.