September
September · June · May
79climate match
United States · 1991–2020
Best time to visit
Cornwall.
September leads for comfortable weather in Cornwall: typically 24.2°C by day, 12.6°C at night, with 118 mm of rain. Based on measured 1991–2020 NOAA station history.
Best comfortSeptember
Typical high24.2°C
Typical low12.6°C
Rain in September118 mm
July
July · August · June
68climate match
May
May · October · September
73climate match
The weakest month is January, scoring 5 against September’s 79 — days reach only 2.8°C, 21° below the 24°C the score treats as ideal.
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
52.8° / -6.1°
Feb
54.7° / -5.3°
Mar
119.7° / -1.2°
Apr
4216.6° / 4.1°
May
6922.2° / 9.9°
Jun
7426.7° / 15°
Jul
6129.1° / 17.5°
Aug
6828° / 16.5°
Sep
7924.2° / 12.6°
Oct
4917.8° / 6.1°
Nov
2211.3° / 0.7°
Dec
55.4° / -3.3°
| Month | Day | Night | Rain | Wet days | Daylight | Comfort | Coverage |
|---|---|---|---|---|---|---|---|
| January | 2.8°C | -6.1°C | 77 mm | 8.2 | 9 h 36 | 5 | Strong coverage |
| February | 4.7°C | -5.3°C | 63 mm | 7.3 | 10 h 36 | 5 | Strong coverage |
| March | 9.7°C | -1.2°C | 88 mm | 8.5 | 11 h 49 | 11 | Strong coverage |
| April | 16.6°C | 4.1°C | 95 mm | 9.6 | 13 h 13 | 42 | Strong coverage |
| May | 22.2°C | 9.9°C | 101 mm | 10.1 | 14 h 23 | 69 | Strong coverage |
| June | 26.7°C | 15°C | 114 mm | 9.3 | 15 h 01 | 74 | Strong coverage |
| July | 29.1°C | 17.5°C | 123 mm | 9 | 14 h 46 | 61 | Strong coverage |
| August | 28°C | 16.5°C | 118 mm | 8.3 | 13 h 46 | 68 | Strong coverage |
| September | 24.2°C | 12.6°C | 118 mm | 7.8 | 12 h 24 | 79 | Strong coverage |
| October | 17.8°C | 6.1°C | 104 mm | 8.1 | 11 h 04 | 49 | Strong coverage |
| November | 11.3°C | 0.7°C | 82 mm | 7.1 | 9 h 53 | 22 | Strong coverage |
| December | 5.4°C | -3.3°C | 91 mm | 8.6 | 9 h 19 | 5 | Strong coverage |
What has changed
Cornwall runs +0.1°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
+0.5
Feb
+1.1
Mar
+0.3
Apr
0.0
May
+0.2
Jun
-0.4
Jul
-0.1
Aug
-0.7
Sep
+0.1
Oct
+0.2
Nov
-0.4
Dec
+0.9
| Month | Record high | Record low | Wettest day | Wettest / driest month | Years |
|---|---|---|---|---|---|
| January | 21.1°C26 Jan 1967 | -30.0°C22 Jan 1985 | 94 mm3 Jan 1976 | 235 mm1976 · driest 12 mm in 1980 | 61 |
| February | 26.1°C21 Feb 2018 | -24.4°C18 Feb 1979 | 52 mm1 Feb 2008 | 152 mm2008 · driest 6 mm in 1987 | 61 |
| March | 28.9°C31 Mar 1998 | -20.0°C8 Mar 1989 | 69 mm21 Mar 2000 | 166 mm1977 · driest 12 mm in 1981 | 60 |
| April | 32.8°C17 Apr 2002 | -7.8°C7 Apr 1982 | 63 mm30 Apr 2020 | 222 mm1983 · driest 15 mm in 1989 | 60 |
| May | 35.0°C18 May 2026 | -2.8°C11 May 1966 | 74 mm18 May 2015 | 238 mm2025 · driest 4 mm in 2023 | 61 |
| June | 37.8°C28 Jun 1966 | 2.8°C3 Jun 1986 | 225 mm22 Jun 1972 | 435 mm1972 · driest 21 mm in 1991 | 60 |
| July | 39.4°C4 Jul 1966 | 6.7°C1 Jul 1988 | 178 mm22 Jul 2013 | 392 mm2018 · driest 22 mm in 1968 | 60 |
| August | 36.7°C31 Aug 1973 | 3.3°C29 Aug 1982 | 92 mm2 Aug 2020 | 305 mm2018 · driest 15 mm in 1995 | 59 |
| September | 36.7°C11 Sep 1983 | -1.1°C24 Sep 1974 | 145 mm7 Sep 2011 | 457 mm2011 · driest 9 mm in 1980 | 60 |
| October | 32.2°C2 Oct 2019 | -7.8°C31 Oct 1975 | 94 mm19 Oct 1996 | 229 mm1976 · driest 2 mm in 2024 | 61 |
| November | 27.8°C3 Nov 1982 | -12.8°C30 Nov 1976 | 70 mm28 Nov 1993 | 219 mm2018 · driest 26 mm in 2015 | 61 |
| December | 23.9°C30 Dec 1984 | -20.0°C31 Dec 2017 | 65 mm11 Dec 2008 | 220 mm1972 · driest 13 mm in 1998 | 60 |
| Month | Days 25°C+ | Days 30°C+ | Frost nights | Heavy rain (10 mm+) | Snow days |
|---|---|---|---|---|---|
| January | 0 | 0 | 27 | 3 | 3 |
| February | 0 | 0 | 24 | 2 | 3 |
| March | <1 | 0 | 20 | 3 | 1 |
| April | 3 | <1 | 6 | 3 | <1 |
| May | 10 | 3 | <1 | 4 | 0 |
| June | 21 | 7 | 0 | 4 | 0 |
| July | 29 | 13 | 0 | 4 | 0 |
| August | 27 | 9 | 0 | 4 | 0 |
| September | 14 | 3 | 0 | 4 | 0 |
| October | 3 | <1 | 3 | 3 | 0 |
| November | <1 | 0 | 15 | 3 | <1 |
| December | 0 | 0 | 24 | 3 | 2 |
| Month | Warm & dry days | Wet days | Washouts | Week with 3+ wet days | Daytime mean has ranged |
|---|---|---|---|---|---|
| January | <1% | 27% | 8% | 31% | -0.5–5.9°C |
| February | <1% | 26% | 8% | 30% | 1.6–8.0°C |
| March | 6% | 27% | 9% | 32% | 6.8–13.7°C |
| April | 24% | 31% | 11% | 37% | 14.8–19.4°C |
| May | 51% | 33% | 13% | 42% | 20.0–24.6°C |
| June | 68% | 31% | 12% | 38% | 25.2–28.8°C |
| July | 71% | 29% | 12% | 33% | 27.3–31.6°C |
| August | 74% | 26% | 11% | 25% | 26.5–30.2°C |
| September | 66% | 26% | 11% | 28% | 22.4–26.5°C |
| October | 31% | 24% | 10% | 22% | 16.1–20.4°C |
| November | 6% | 26% | 9% | 28% | 9.0–14.2°C |
| December | <1% | 26% | 10% | 30% | 3.0–8.3°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 5185465
- NOAA station
- USC00364896 · LEBANON 2 W
- Station distance
- 8.5 km from the place centre
- Climate period
- 1991–2020
- Minimum month coverage
- 30 usable years
- Daylight
- Calculated from latitude 40.27°, 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.