September
September · October · May
75climate match
United States · 1991–2020
Best time to visit
Helena.
September leads for comfortable weather in Helena: typically 29.6°C by day, 15.5°C at night, with 65 mm of rain. Based on measured 1991–2020 NOAA station history.
Best comfortSeptember
Typical high29.6°C
Typical low15.5°C
Rain in September65 mm
September
September · July · August
76climate match
October
October · April · March
79climate match
The weakest month is January, scoring 12 against September’s 75 — days reach only 8.2°C, 16° below the 24°C the score treats as ideal, and nights drop to -5.1°C.
Month by month
The whole year,
without the guesswork.
The bars show the comfort score. Day and night temperatures come from daily observed highs and lows; rain is the historical monthly estimate.
Jan
128.2° / -5.1°
Feb
2210.6° / -3.4°
Mar
4516.1° / 1.6°
Apr
6621.2° / 6.4°
May
7326.4° / 12.8°
Jun
5332.1° / 18.4°
Jul
4435° / 20.9°
Aug
4634° / 20°
Sep
7529.6° / 15.5°
Oct
7522.6° / 8.2°
Nov
4415.1° / 1.2°
Dec
168.9° / -3.7°
| Month | Day | Night | Rain | Wet days | Daylight | Comfort | Coverage |
|---|---|---|---|---|---|---|---|
| January | 8.2°C | -5.1°C | 26 mm | 3 | 9 h 55 | 12 | Strong coverage |
| February | 10.6°C | -3.4°C | 32 mm | 3.6 | 10 h 47 | 22 | Strong coverage |
| March | 16.1°C | 1.6°C | 56 mm | 5.1 | 11 h 51 | 45 | Strong coverage |
| April | 21.2°C | 6.4°C | 83 mm | 6.1 | 13 h 04 | 66 | Strong coverage |
| May | 26.4°C | 12.8°C | 111 mm | 7.8 | 14 h 05 | 73 | Strong coverage |
| June | 32.1°C | 18.4°C | 112 mm | 7 | 14 h 38 | 53 | Strong coverage |
| July | 35°C | 20.9°C | 82 mm | 5.4 | 14 h 26 | 44 | Strong coverage |
| August | 34°C | 20°C | 94 mm | 7 | 13 h 33 | 46 | Strong coverage |
| September | 29.6°C | 15.5°C | 65 mm | 4.6 | 12 h 22 | 75 | Strong coverage |
| October | 22.6°C | 8.2°C | 77 mm | 5.2 | 11 h 11 | 75 | Strong coverage |
| November | 15.1°C | 1.2°C | 41 mm | 3.6 | 10 h 10 | 44 | Strong coverage |
| December | 8.9°C | -3.7°C | 37 mm | 3.8 | 9 h 40 | 16 | Strong coverage |
What has changed
Helena runs +1.1°C
on the 1961–1990 baseline.
Each bar compares the 2011–2025 daytime average for that month against the same month in 1961–1990, measured at the same station. Months where the older record is too thin to compare are left blank.
Jan
+2.1
Feb
+0.6
Mar
+2.0
Apr
+0.4
May
+0.2
Jun
+1.2
Jul
+0.3
Aug
+0.1
Sep
+2.1
Oct
+0.9
Nov
+1.4
Dec
+2.2
| Month | Record high | Record low | Wettest day | Wettest / driest month | Years |
|---|---|---|---|---|---|
| January | 27.8°C23 Jan 1967 | -25.6°C8 Jan 1988 | 68 mm5 Jan 2005 | 97 mm2005 · driest 0 mm in 1986 | 73 |
| February | 33.3°C13 Feb 1962 | -29.4°C10 Feb 2011 | 65 mm21 Feb 1997 | 119 mm2013 · driest 0 mm in 1976 | 73 |
| March | 37.2°C19 Mar 1907 | -18.3°C3 Mar 2014 | 125 mm3 Mar 1988 | 257 mm1973 · driest 0 mm in 1910 | 73 |
| April | 37.2°C13 Apr 1972 | -7.8°C3 Apr 1975 | 181 mm26 Apr 2009 | 253 mm2009 · driest 3 mm in 1996 | 74 |
| May | 40.6°C31 May 1985 | -1.7°C6 May 1944 | 116 mm21 May 2019 | 371 mm2019 · driest 7 mm in 1970 | 75 |
| June | 45.0°C25 Jun 1911 | 7.8°C1 Jun 1964 | 138 mm23 Jun 1963 | 245 mm2007 · driest 13 mm in 1944 | 73 |
| July | 45.0°C30 Jul 1986 | 10.0°C14 Jul 1990 | 166 mm19 Jul 1997 | 255 mm1979 · driest 0 mm in 1983 | 71 |
| August | 44.4°C7 Aug 1964 | 8.9°C29 Aug 1988 | 85 mm3 Aug 1995 | 227 mm1989 · driest 0 mm in 1973 | 69 |
| September | 42.2°C4 Sep 2000 | -0.6°C30 Sep 1984 | 222 mm12 Sep 2008 | 257 mm2008 · driest 1 mm in 2000 | 70 |
| October | 36.7°C9 Oct 1979 | -11.1°C31 Oct 1993 | 127 mm3 Oct 1986 | 282 mm2002 · driest 0 mm in 1978 | 69 |
| November | 32.8°C9 Nov 2006 | -15.0°C27 Nov 1975 | 104 mm3 Nov 1974 | 200 mm2024 · driest 0 mm in 1965 | 70 |
| December | 26.7°C27 Dec 2021 | -26.1°C23 Dec 1989 | 48 mm20 Dec 2011 | 93 mm2011 · driest 0 mm in 2017 | 72 |
| Month | Days 25°C+ | Days 30°C+ | Frost nights | Heavy rain (10 mm+) | Snow days |
|---|---|---|---|---|---|
| January | <1 | 0 | 27 | <1 | 1 |
| February | <1 | <1 | 22 | <1 | 2 |
| March | 4 | <1 | 12 | 2 | 1 |
| April | 9 | 2 | 4 | 2 | 0 |
| May | 20 | 9 | <1 | 3 | 0 |
| June | 29 | 22 | 0 | 4 | 0 |
| July | 30 | 28 | 0 | 2 | 0 |
| August | 30 | 26 | 0 | 3 | 0 |
| September | 25 | 16 | 0 | 2 | 0 |
| October | 12 | 4 | 2 | 2 | <1 |
| November | 2 | <1 | 13 | 1 | <1 |
| December | 0 | 0 | 25 | 1 | 2 |
| Month | Warm & dry days | Wet days | Washouts | Week with 3+ wet days | Daytime mean has ranged |
|---|---|---|---|---|---|
| January | 5% | 9% | 2% | 5% | 3.7–11.6°C |
| February | 13% | 13% | 4% | 8% | 5.4–14.5°C |
| March | 31% | 15% | 5% | 11% | 12.1–19.4°C |
| April | 54% | 19% | 8% | 17% | 18.9–23.9°C |
| May | 68% | 25% | 11% | 29% | 23.6–28.5°C |
| June | 77% | 23% | 11% | 22% | 29.3–34.0°C |
| July | 83% | 17% | 8% | 14% | 32.8–37.2°C |
| August | 80% | 19% | 8% | 18% | 31.6–36.4°C |
| September | 79% | 17% | 6% | 13% | 27.2–32.0°C |
| October | 64% | 15% | 6% | 14% | 19.9–25.2°C |
| November | 26% | 12% | 4% | 9% | 11.6–18.3°C |
| December | 4% | 11% | 3% | 6% | 5.3–12.0°C |
A warm and dry day reaches 20°C with under 1 mm of rain; a wet day gets 1 mm or more; a washout gets 10 mm or more. The week column is the share of seven-day stretches in that month, across the station’s whole daily record, that contained three or more wet days — the odds a week-long trip is rained on repeatedly, counted rather than modelled. The last column is the 10th to 90th percentile of that month’s daytime average across individual years: a narrow band means the average is what you will get, a wide one means the average is a midpoint between years that felt quite different.
The evidence behind this page
Nearby, measured,
and named.
- Place identity
- GeoNames 4538544
- NOAA station
- USC00344019 · HELENA 1 SSE
- Station distance
- 1 km from the place centre
- Climate period
- 1991–2020
- Minimum month coverage
- 30 usable years
- Daylight
- Calculated from latitude 36.55°, mid-month, sunrise to sunset including refraction. Not a station measurement.
- Important limit
- Historical climate is not a forecast. Nearby stations can miss mountains, coasts, and local microclimates.