Cottonwood Creek Bridge · Photo: Robstutz · CC BY-SA 4.0Ismay sits near the bottom of U.S. towns for winter warmth
July afternoons average 88°. Precipitation is light here, less than falls on 93% of U.S. towns. January has warmed most since 1901–2000, part of a 1.0° rise. Seedlings are safe outdoors from about May 21, with the first autumn frost due around September 20.
A year in Ismay at a glance
Each month’s typical high and low, and what it brings.
What stands out about Ismay’s climate
Compared with towns across the U.S., with Ismay’s place in Montana beside it.
What a year in Ismay feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 121 frost-free days a year
In half of years the last 32° night comes by May 21 and the first by September 20. Frost and day counts come from NOAA’s station at Plevna, MT, 14 miles from the town’s center, 230 ft higher.
The 2023 USDA map puts Ismay’s center in zone 4a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −27°. 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 34 inches of snow a winter
Snow, measured at Plevna, MT, is heaviest from January through March, about 6 inches a month. Precipitation (rain plus melted snow) adds up to 15 inches a year; May is the wettest month and January the driest. Rain or snow falls on about 96 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Ismay
94% 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 Plevna, MT.
Living with Ismay’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
121 frost-free days in zone 4a. The last frost comes by May 21 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Sep 20.
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 Ismay from natural hazards, river flooding is the largest share (39%); heat waves, cold waves, winter storms and ice storms together are 34%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Ismay and similar climates
TownRatings has no climate map of the towns around Ismay yet.
Climates most like Ismay’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 |
|---|---|---|---|---|
| Ismay, MT | 7° | 88° | 15" | 34" |
| Sheridan, WY | 11° | 89° | 15" | 33" |
| Pierre, SD | 9° | 88° | 19" | 37" |
| Gypsum, CO | 11° | 86° | 14" | 39" |
| Alliance, NE | 13° | 88° | 17" | 45" |
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 Ismay averaged 1.0° warmer than the 1900s. The biggest change is in January (+3.8°).
A smaller shift than in 78% 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 Ismay compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Ismay’s place among Montana’s.
Ismay weather by month
Highs, lows and precipitation from NOAA’s grid at Ismay’s center; snow, wet days and snow on the ground from Plevna, MT. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 30° | 7° | 0.4" | 5.9" | 7 | 25 | 8° – 32° |
| February | 34° | 11° | 0.4" | 5.6" | 7 | 18 | 2° – 35° |
| March | 46° | 21° | 0.6" | 5.4" | 7 | 11 | 19° – 46° |
| April | 57° | 30° | 1.6" | 4.8" | 8 | 2 | 38° – 49° |
| May | 68° | 41° | 2.8" | 1.3" | 12 | 0 | 49° – 61° |
| June | 78° | 51° | 2.5" | 0.0" | 12 | 0 | 59° – 69° |
| July | 88° | 57° | 2.0" | 0.0" | 9 | 0 | 63° – 78° |
| August | 87° | 54° | 1.2" | 0.0" | 7 | 0 | 65° – 76° |
| September | 76° | 44° | 1.4" | 0.1" | 7 | 0 | 54° – 67° |
| October | 59° | 32° | 1.1" | 2.0" | 8 | 2 | 37° – 50° |
| November | 44° | 19° | 0.5" | 4.1" | 6 | 8 | 19° – 40° |
| December | 32° | 10° | 0.4" | 5.0" | 6 | 17 | 9° – 30° |
| Year | 58° | 31° | 14.7" | 34.2" | 96 | 82 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 2° to 35°. June is the most reliable, staying within 10°.
Where Ismay’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 Ismay’s center.
- Snow: Plevna, MT.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Plevna, MT, 14 miles from the town’s center, 230 ft higher; 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 Ismay’s climate
What is the weather like in Ismay?
A typical July afternoon reaches 88°, a January night drops to 7°, and about 34 inches of snow falls in a normal winter. Colder January nights than 97% of U.S. towns; hotter July afternoons than 65% of U.S. towns.
How cold does it get in Ismay in winter?
January nights average 7°. About 188 nights a year reach 32° or below and 31 reach 0° or below. In the coldest January of the last 30 years the month averaged 8°.
How much snow does Ismay get?
About 34 inches in a normal winter at Plevna, MT, heaviest from January through March, about 6 inches a month, with snow on the ground about 82 days a year.
How hot does it get in Ismay?
July, with a typical high of 88° and a low of 57°. About 30 days a year reach 90° and 3 reach 100° (Plevna, MT).
When is the first and last frost in Ismay?
In half of years the last spring frost (32°) comes by May 21 and the first fall frost by September 20, about 121 frost-free days, at Plevna, MT.
What growing zone is Ismay in?
Zone 4a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −27°.
What is the best time of year to visit Ismay?
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 Ismay getting warmer?
Yes: 1991–2020 averaged 1.0° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 78% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Ismay.
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.