Photo: Sociotard · CC BY 3.0Hardly any U.S. towns collect less precipitation than Firth: 11 inches a year
Midsummer highs settle at about 87°. Its January nights bite harder than in 86% of U.S. towns. The latest 30-year average runs 1.5° warmer than 1901–2000’s, with March up the most. Seedlings are safe outdoors from about May 5, with the first autumn frost due around October 3.
A year in Firth at a glance
Each month’s typical high and low, and what it brings.
What stands out about Firth’s climate
Compared with towns across the U.S., with Firth’s place in Idaho beside it.
What a year in Firth feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 149 frost-free days a year
In half of years the last 32° night comes by May 5 and the first by October 3. Frost and day counts come from NOAA’s station at Blackfoot Fire Dept, ID, 11 miles from the town’s center, at about the same height.
The 2023 USDA map puts Firth’s center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −11°. 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 snow a winter
Snow, measured at Blackfoot Fire Dept, ID, falls mostly in January. Precipitation (rain plus melted snow) adds up to 11 inches a year; May is the wettest month and July the driest. Rain or snow falls on about 74 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Firth
93% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through May.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Blackfoot Fire Dept, ID.
Living with Firth’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
149 frost-free days in zone 5b. The last frost comes by May 5 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 3.
Months with highs of 62–84° and lows of 40° or more: June and September. 4.7 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Firth from natural hazards, river flooding is the largest share (33%); heat waves, cold waves, winter storms and ice storms together are 35%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Firth and similar climates
TownRatings has no climate map of the towns around Firth yet.
Climates most like Firth’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 |
|---|---|---|---|---|
| Firth, ID | 14° | 87° | 11" | 15" |
| Santa Fe, NM | 18° | 86° | 13" | 20" |
| Powell, WY | 11° | 87° | 7" | 11" |
| Ephraim, UT | 14° | 89° | 12" | 20" |
| Show Low, AZ | 19° | 86° | 15" | 19" |
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 Firth averaged 1.5° warmer than the 1900s. The biggest change is in March (+3.5°).
A bigger 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 Firth compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Firth’s place among Idaho’s.
Firth weather by month
Highs, lows and precipitation from NOAA’s grid at Firth’s center; snow, wet days and snow on the ground from Blackfoot Fire Dept, ID. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 31° | 14° | 0.9" | 6.0" | 8 | 14° – 31° |
| February | 36° | 17° | 0.7" | 2.2" | 7 | 17° – 37° |
| March | 48° | 27° | 1.0" | 0.3" | 7 | 30° – 43° |
| April | 58° | 32° | 1.2" | 0.7" | 9 | 40° – 50° |
| May | 68° | 40° | 1.7" | 0.0" | 8 | 48° – 59° |
| June | 77° | 47° | 1.1" | 0.0" | 6 | 56° – 68° |
| July | 87° | 52° | 0.5" | 0.0" | 3 | 59° – 75° |
| August | 86° | 51° | 0.7" | 0.0" | 3 | 62° – 72° |
| September | 75° | 42° | 1.0" | 0.0" | 4 | 55° – 63° |
| October | 60° | 32° | 1.0" | 0.8" | 6 | 37° – 54° |
| November | 44° | 23° | 0.7" | 1.4" | 5 | 25° – 40° |
| December | 32° | 15° | 0.9" | 3.3" | 8 | 17° – 30° |
| Year | 58° | 33° | 11.3" | 14.7" | 74 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 17° to 37°. September is the most reliable, staying within 8°.
Where Firth’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 Firth’s center.
- Snow: Blackfoot Fire Dept, ID.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Blackfoot Fire Dept, ID, 11 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 Firth’s climate
What is the weather like in Firth?
A typical July afternoon reaches 87°, a January night drops to 14°, and about 15 inches of snow falls in a normal winter. Colder January nights than 86% of U.S. towns; hotter July afternoons than 62% of U.S. towns.
How cold does it get in Firth in winter?
January nights average 14°. About 162 nights a year reach 32° or below and 7 reach 0° or below. In the coldest January of the last 30 years the month averaged 14°.
How much snow does Firth get?
About 15 inches in a normal winter at Blackfoot Fire Dept, ID, most of it in January.
How hot does it get in Firth?
July, with a typical high of 87° and a low of 52°. About 26 days a year reach 90° (Blackfoot Fire Dept, ID).
When is the first and last frost in Firth?
In half of years the last spring frost (32°) comes by May 5 and the first fall frost by October 3, about 149 frost-free days, at Blackfoot Fire Dept, ID.
What growing zone is Firth in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −11°.
What is the best time of year to visit Firth?
By one simple rule (highs of 62–84° and lows of 40° or more), June and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Firth getting warmer?
Yes: 1991–2020 averaged 1.5° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 56% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Firth.
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.