Casper, WY weather in September
In September, Casper sees highs around 76°F and lows around 42°F: mild, with some rain. There are about 7 days with rain or snow. Snowfall averages about 1.5 in. Good for outdoor plans.
- Normal high
- 76°F
- Normal low
- 42°F
- Wet days
- 7
- 0.9 in total
- Snowfall
- 1.5 in
- normal snowfall
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 82°F | 68°F |
| Normal low | 47°F | 37°F |
| Chance of a wet day | 20% | 25% |
| Sunrise / sunset | 6:30 am / 7:40 pm | 7:01 am / 6:48 pm |
| Daylight | 13.2 h | 11.8 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Mountain Time).
A typical September day
- 6 am47°Fdew point 36°F
- 9 am61°Fdew point 37°F
- Noon70°Fdew point 35°F
- 3 pm73°Fdew point 32°F
- 6 pm65°Fdew point 34°F
- 9 pm55°Fdew point 36°F
NOAA hourly normals (local standard time) from Casper Natrona Co Airport (8 mi away); average wind 10 mph; clear or few clouds in 76% of daytime hours, mostly cloudy or overcast in 18%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F14 of 30
- Hot dayshigh 90°F or more2 of 30
- Muggy daysdaily mean dew point 65°F or more0 of 30
- Wet daysat least 0.01 in of rain or melted snow7 of 30
- Notable rainat least 0.10 in3 of 30
- Freezing nightslow 32°F or below3 of 30
- Snow on the groundsnow depth 1 in or more0 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain and snow in September
Normal precipitation is 0.9 in; a dry September brings about 0.4 in and a wet one about 1.4 in (25th and 75th percentiles). Days with half an inch or more are rare. Normal snowfall is 1.5 in.
How September varies from year to year
- Warmest September, 1991-20202015: average high 82°F
- Coolest September1999: average high 70°F
- Wettest September1995: 2.6 in
- Driest September2011: 0.1 in
- Highest reading98°F (September 5, 2020)
- Lowest reading24°F (September 9, 2020)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
September compared with August and October
| August | September | October | |
|---|---|---|---|
| Normal high | 87°F | 76°F | 60°F |
| Normal low | 51°F | 42°F | 31°F |
| Wet days | 6 | 7 | 8 |
| Comfortable days | 4 | 14 | 12 |
| Daylight | 13.9 h | 12.5 h | 11.0 h |
Highs change by -11°F from August and -16°F into October.
Nearby alternatives in September
- Warmer: Greeley, CO188 mi · high 82°F · 6 wet days
- Cooler: Keystone, SD162 mi · high 69°F · 7 wet days
How Casper ranks in September
- Normal high270th warmest of 378 cities; 1st of 4 in Wyoming
- Wet days143rd driest of 378
- Comfortable days116th most of 342
What to pack for Casper in September
- Layers – afternoons near 76°F but nights near 42°F
Frost in September
The first fall frost typically comes around Sep 22; in 1 year in 10 it comes before Sep 5. All frost dates for Casper.
Heating and cooling
September has 214 heating degree days and 31 cooling degree days (base 65°F), 3% of the year's total heating and cooling demand.
Questions
How hot is Casper in September?
The normal high is 76°F and the normal low is 42°F. From 1991 to 2020 the hottest September reading was 98°F (most recently on September 5, 2020).
Does it rain a lot in Casper in September?
About 7 days in September have at least 0.01 in of precipitation, and the normal total is 1.0 in. The wettest September in 1991-2020 was in 1995 (2.6 in); the driest was in 2011 (0.1 in).
Does it snow in Casper in September?
Yes. Normal snowfall in September is 1.5 in.
Is September a good time to visit Casper?
September ranks 3rd of 12 months on our comfort score for Casper (67 out of 100). It has about 14 comfortable days and about 2 days at 90°F or hotter. The best month is May.
Where the numbers come from
- Temperature, rain, snowfall, snow depth, frost dates, humidity and wind by hour and cloud cover: Casper Natrona Co Airport (USW00024089), 7.9 mi WNW of the city center, 5,338 ft (233 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Natrona County International Airport (725690-24089), 8.4 mi WNW of the city center, 5,319 ft (214 ft higher than the city). Hourly observations, 1991-2020.