Thermopolis, Wyoming climate: Normal weather by month, frost dates and records
Thermopolis's normal year runs from 12°F January nights to 92°F July afternoons, with 11.9 inches of precipitation and 27 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 9.2°C, January lows of −11°C, July highs of 33°C, 304 mm of precipitation a year.
- NOAA stationThermopolis
- Station IDUSC00488875
- Location43.65°N 108.20°W
- Elevation4,321 ft (1,317 m)
- Population2,748
On October 23, the normal high in Thermopolis is 61°F and the normal low 31°F, and the chance of measurable rain or snow is 14%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Thermopolis.
- Jan 37° 12°
- Feb 42° 16°
- Mar 54° 26°
- Apr 62° 33°
- May 71° 43°
- Jun 83° 51°
- Jul 92° 57°
- Aug 90° 55°
- Sep 80° 46°
- Oct 65° 34°
- Nov 49° 22°
- Dec 38° 12°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Thermopolis each month?
July is the warmest month, with normal highs of 92°F; January the coldest, with normal lows of 12°F. The most precipitation falls in May (2.53 in), the least in January (0.39 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 37°F | 12°F | 24.4°F | 0.39 | 5.4 | 3 | <1 | 30 | 9 h 20 min |
| February | 42°F | 16°F | 28.6°F | 0.44 | 4.9 | 4 | <1 | 27 | 10 h 30 min |
| March | 54°F | 26°F | 39.8°F | 0.85 | 2.3 | 4 | <1 | 25 | 11 h 50 min |
| April | 62°F | 33°F | 47.6°F | 1.63 | 2.2 | 7 | <1 | 13 | 13 h 20 min |
| May | 71°F | 43°F | 57.0°F | 2.53 | 0.2 | 8 | 1 | 2 | 14 h 40 min |
| June | 83°F | 51°F | 66.8°F | 1.31 | 0.0 | 7 | 8 | <1 | 15 h 20 min |
| July | 92°F | 57°F | 74.5°F | 0.76 | 0.0 | 5 | 22 | <1 | 15 h 10 min |
| August | 90°F | 55°F | 72.4°F | 0.50 | 0.0 | 4 | 19 | <1 | 14 h |
| September | 80°F | 46°F | 62.7°F | 1.21 | 0.3 | 5 | 5 | 1 | 12 h 30 min |
| October | 65°F | 34°F | 49.1°F | 1.27 | 2.1 | 5 | <1 | 13 | 11 h 10 min |
| November | 49°F | 22°F | 35.1°F | 0.60 | 5.5 | 4 | <1 | 27 | 9 h 40 min |
| December | 38°F | 12°F | 24.9°F | 0.46 | 4.5 | 3 | <1 | 30 | 9 h |
| Year (annual) | 63°F | 34°F | 48.6°F | 11.95 | 27.4 | 59 | 55 | 168 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 3°C | −11°C | −4.2°C | 10 mm | 14 cm |
| February | 5°C | −9°C | −1.9°C | 11 mm | 12 cm |
| March | 12°C | −4°C | 4.3°C | 22 mm | 6 cm |
| April | 17°C | 1°C | 8.7°C | 41 mm | 6 cm |
| May | 22°C | 6°C | 13.9°C | 64 mm | 1 cm |
| June | 28°C | 10°C | 19.3°C | 33 mm | 0 cm |
| July | 33°C | 14°C | 23.6°C | 19 mm | 0 cm |
| August | 32°C | 13°C | 22.4°C | 13 mm | 0 cm |
| September | 27°C | 8°C | 17.1°C | 31 mm | 1 cm |
| October | 18°C | 1°C | 9.5°C | 32 mm | 5 cm |
| November | 9°C | −6°C | 1.7°C | 15 mm | 14 cm |
| December | 3°C | −11°C | −3.9°C | 12 mm | 11 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00488875; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Thermopolis?
Normal highs sit between 65°F and 85°F in May, June and September. Of those, September has the fewest days with rain (5).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00488875.
When is the last frost in Thermopolis?
In Thermopolis, the last spring frost (32°F) comes after May 5 in half of years and after May 19 in one year in ten; the first autumn frost comes before October 5 in half of years and before September 23 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- May 51 year in 10 after May 19; 9 in 10 after April 23
- First autumn frost, half of years before
- October 51 year in 10 before September 23; 9 in 10 before October 18
NOAA puts the median frost-free season at 152 days, and the season without a hard freeze (28°F) at 173 days.
A hard freeze (28°F) comes after April 23 in half of springs and before October 15 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Thermopolis in zone 4b in ZIP code 82430, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Thermopolis's NOAA station is in zone 5a: the coldest night of a typical year reaches −17°F (30 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Wyoming · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00488875; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Thermopolis?
In a normal year in Thermopolis, 55 days a year reach 90°F (4 of them 100°F or more), 168 nights fall to 32°F or colder and 59 days bring measurable precipitation.
- Days at 90°F or more
- 55a normal year
- Days at 100°F or more
- 4a normal year
- Nights at 32°F or colder
- 168a normal year
- Days that stay below freezing
- 30high of 32°F or less
- Days with 0.01 inch of precipitation
- 59a normal year
- Days with 1 inch of snow or more
- 11a normal year
The highest temperature in this station's record (since 1899) is 109°F, on July 12, 2026; the lowest is −42°F, on February 9, 1933.
The wettest calendar year on that record is 1998, with 17.40 in; the snowiest season is 1997–98, with 79.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00488875; records: ACIS (NOAA Regional Climate Centers), station USC00488875. Records use complete months only; a month missing more than three days is left out.
How sunny is Thermopolis?
Over a year 80% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Thermopolis, 4.6 kWh per square metre a day. July is the sunniest month (87%) and December the cloudiest (71%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 77% | 2.1 |
| February | 77% | 3.1 |
| March | 76% | 4.3 |
| April | 75% | 5.5 |
| May | 76% | 6.4 |
| June | 84% | 7.5 |
| July | 87% | 7.3 |
| August | 86% | 6.4 |
| September | 85% | 5.1 |
| October | 78% | 3.4 |
| November | 76% | 2.3 |
| December | 71% | 1.7 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Thermopolis need?
A normal year in Thermopolis brings 6,690 heating degree days, 25% more than the median U.S. place (5,373), and 737 cooling degree days, 19% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,780 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,259 | 0 |
| February | 1,019 | 0 |
| March | 781 | 0 |
| April | 521 | 1 |
| May | 268 | 18 |
| June | 62 | 115 |
| July | 5 | 298 |
| August | 13 | 242 |
| September | 130 | 61 |
| October | 494 | 3 |
| November | 896 | 0 |
| December | 1,243 | 0 |
| Year (annual) | 6,690 | 737 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00488875. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Thermopolis been warmer than normal lately?
2025 averaged 50.5°F, 1.9°F above the 1991-2020 normal of 48.6°F. 3 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 50.1°F | +1.5°F | 9.20 | 28.1 |
| 2022 | 47.8°F | −0.8°F | 10.88 | 49.9 |
| 2023 | 48.2°F | −0.4°F | 15.69 | 49.5 |
| 2024 | 50.6°F | +2.0°F | 10.51 | 20.0 |
| 2025 | 50.5°F | +1.9°F | 13.45 | 31.1 |
Source: observed years: ACIS, station USC00488875. A year counts only with all twelve months complete.
How does Thermopolis's climate compare?
Thermopolis is warmer than 65 of the other 70 places with their own NOAA record in Wyoming, and wetter than 31. Across the 7,247 U.S. stations with normals, its annual mean of 48.6°F is warmer than 34%.
In the Köppen classification computed from these normals, Thermopolis is BSk: cold semi-arid steppe. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Thermopolis share this climate record?
3 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Lucerne, WY466 people · 5 mi N
- East Thermopolis, WY232 people · 0 mi SE
- Kirby, WY75 people · 11 mi N
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Thermopolis's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Thermopolis. This page uses Thermopolis; the other differs by site and elevation:
| Station | From this station | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Thermopolis (9 mi NE) USC00488884 | 8 mi NE | 4,282 ft | 42.6°F | 0°F | 88°F | 12.6 | 51 | May 24 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Thermopolis's climate
What is the coldest month in Thermopolis?
January, with a normal high of 37°F and a normal low of 12°F. The warmest is July (92°F by day, 57°F at night).
Does it snow in Thermopolis?
Yes: 27 inches in a normal year, falling on 13 days with 0.1 inch or more, the most in November (5.5 inches).
What is the rainiest month in Thermopolis?
May, with 2.53 in of precipitation in a normal year; the driest is January with 0.39 in.
What plant hardiness zone is Thermopolis in?
The USDA's 2023 map puts Thermopolis in zone 4b in ZIP code 82430, the nearest ZIP area. By the same method at Thermopolis's NOAA station, the coldest night of a typical year reaches −17°F (30 years, 1991-2020): zone 5a.
How late can frost come in Thermopolis?
In half of years the last 32°F night comes after May 5; in one year in ten it comes after May 19. Waiting until May 19 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Wyoming climateThe statewide normals and every place in the state
- Boysen Dam, WY17 miles from this station, 46.4°F a year
- Black Mountain, WY24 miles from this station, 46.8°F a year
- Thermopolis (21 mi WNW), WY25 miles from this station, 44.6°F a year
- Worland, WY25 miles from this station, 44.6°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made