Climate averages 1991–2020
Flagstaff weather
in September.
A warm, moderately wet month: the 4th warmest and the 10th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a warm month in Flagstaff: daytime highs average 23.3°C and nights cool to about 12.4°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 57 mm of rain on roughly 9 days, which makes September a moderately wet month (the 10th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 26 min on an average September day.
The nearest other city in this atlas is Surprise (185 km away). In September its highs average 36.6°C, 13.3°C warmer than Flagstaff, with 20 mm of rain.
Among the 498 cities listed in the United States, Flagstaff ranks joint 389th of 498 for the warmest September highs and 177th of 498 for the driest September (rainfall, lowest first). The mean September high of those 498 cities is 26.9°C; Flagstaff is 3.6°C cooler than that mean.
From September to October, average highs fall by 5.7°C to 17.7°C, and monthly rainfall falls from 57 mm to 33 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Flagstaff climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 5.7°C-3.8°C | -3.8°C | 47 | 6.3 | 10.110 h |
| February | 7.0°C-3.0°C | -3.0°C | 50 | 6.9 | 10.911 h |
| March | 10.7°C-0.3°C | -0.3°C | 49 | 7.3 | 11.912 h |
| April | 15.0°C2.8°C | 2.8°C | 31 | 5.6 | 13.113 h |
| May | 20.5°C7.7°C | 7.7°C | 32 | 5.7 | 14.014 h |
| June | 26.8°C13.2°C | 13.2°C | 11 | 3.0 | 14.514 h |
| July | 27.9°C15.9°C | 15.9°C | 115 | 14.7 | 14.314 h |
| August | 26.2°C15.2°C | 15.2°C | 126 | 16.3 | 13.513 h |
| September, selected | 23.3°C12.4°C | 12.4°C | 57 | 8.8 | 12.412 h |
| October | 17.7°C6.9°C | 6.9°C | 33 | 5.2 | 11.311 h |
| November | 11.2°C1.0°C | 1.0°C | 32 | 4.1 | 10.410 h |
| December | 5.7°C-3.6°C | -3.6°C | 41 | 5.8 | 9.810 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Surprise in SeptemberUnited States · 185 kmHigh 36.6°C · Low 23.4°C · 20 mm rain
- Peoria (Arizona), United States in SeptemberUnited States · 188 kmHigh 36.6°C · Low 23.4°C · 22 mm rain
- Scottsdale in SeptemberUnited States · 189 kmHigh 36.5°C · Low 23.1°C · 24 mm rain
- Glendale (Arizona), United States in SeptemberUnited States · 191 kmHigh 36.8°C · Low 23.5°C · 22 mm rain
- Mesa in SeptemberUnited States · 198 kmHigh 36.6°C · Low 22.8°C · 26 mm rain
- Phoenix in SeptemberUnited States · 198 kmHigh 36.9°C · Low 23.4°C · 24 mm rain
- Tempe in SeptemberUnited States · 200 kmHigh 36.8°C · Low 23.2°C · 24 mm rain
- Avondale in SeptemberUnited States · 206 kmHigh 37.4°C · Low 23.9°C · 22 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Flagstaff) is explained once on the Flagstaff year overview and on the Sources, method and limits page.