United States · 1991–2020

Best time to visit
Alton.

September leads for comfortable weather in Alton: typically 28.2°C by day, 11°C at night, with 60 mm of rain. Based on measured 1991–2020 NOAA station history.

Best comfortSeptember

Typical high28.2°C

Typical low11°C

Rain in September60 mm

Comfort

September

September · May · October

74climate match

Beach

August

August · June · September

64climate match

Outdoors

October

October · April · September

82climate match

The weakest month is January, scoring 5 against September’s 74 — days reach only 5.2°C, 19° below the 24°C the score treats as ideal, and nights drop to -10°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

55.2° / -10°

Feb

68° / -7.9°

Mar

3013.7° / -3°

Apr

5519.1° / 2.3°

May

7324.6° / 8.9°

Jun

6730° / 14.4°

Jul

4433.7° / 18°

Aug

5632.7° / 16.9°

Sep

7428.2° / 11°

Oct

6921.4° / 3.9°

Nov

2612.3° / -3.7°

Dec

56.9° / -8.1°

Monthly climate evidence for Alton — daylight is calculated from latitude, everything else is measured
Month	Day	Night	Rain	Wet days	Daylight	Comfort	Coverage
January	5.2°C	-10°C	18 mm	2.7	9 h 40	5	Good coverage
February	8°C	-7.9°C	19 mm	3.1	10 h 39	6	Good coverage
March	13.7°C	-3°C	47 mm	4.8	11 h 49	30	Good coverage
April	19.1°C	2.3°C	57 mm	6.2	13 h 11	55	Good coverage
May	24.6°C	8.9°C	98 mm	8.7	14 h 19	73	Good coverage
June	30°C	14.4°C	92 mm	8.1	14 h 56	67	Good coverage
July	33.7°C	18°C	128 mm	8.9	14 h 42	44	Good coverage
August	32.7°C	16.9°C	87 mm	7.5	13 h 43	56	Good coverage
September	28.2°C	11°C	60 mm	4.6	12 h 24	74	Good coverage
October	21.4°C	3.9°C	46 mm	4.5	11 h 05	69	Good coverage
November	12.3°C	-3.7°C	39 mm	4	9 h 57	26	Good coverage
December	6.9°C	-8.1°C	17 mm	2.4	9 h 24	5	Good coverage

Records at ALTON 1 W, 1902–2007
Month	Record high	Record low	Wettest day	Wettest / driest month	Years
January	26.7°C11 Jan 1990	-31.7°C12 Jan 1912	37 mm26 Jan 1962	60 mm1932 · driest 0 mm in 1971	103
February	30.6°C29 Feb 1972	-33.9°C13 Feb 1905	110 mm26 Feb 1912	126 mm1912 · driest 0 mm in 1946	103
March	37.2°C21 Mar 1907	-27.2°C3 Mar 1960	81 mm23 Mar 1987	231 mm1973 · driest 0 mm in 1920	102
April	41.1°C23 Apr 1989	-13.3°C3 Apr 1936	89 mm14 Apr 1987	150 mm1944 · driest 1 mm in 1989	101
May	40.6°C23 May 1939	-7.2°C1 May 1909	156 mm22 May 1961	387 mm1961 · driest 0 mm in 1966	101
June	45.6°C26 Jun 1936	0.6°C6 Jun 1998	84 mm23 Jun 1993	289 mm1949 · driest 7 mm in 1918	102
July	49.4°C24 Jul 1936	5.0°C14 Jul 1990	106 mm5 Jul 1993	490 mm1993 · driest 0 mm in 1935	101
August	46.7°C12 Aug 1936	0.6°C26 Aug 1910	124 mm14 Aug 1912	287 mm1950 · driest 0 mm in 1913	102
September	44.4°C3 Sep 1947	-7.8°C30 Sep 1984	120 mm12 Sep 1961	235 mm1963 · driest 0 mm in 1956	104
October	39.4°C5 Oct 1947	-14.4°C27 Oct 1997	86 mm10 Oct 1949	111 mm1986 · driest 0 mm in 1952	103
November	31.1°C9 Nov 2006	-24.4°C22 Nov 1929	85 mm16 Nov 1996	125 mm1996 · driest 0 mm in 1949	102
December	27.8°C23 Dec 1964	-35.0°C23 Dec 1989	32 mm16 Dec 1984	66 mm1913 · driest 0 mm in 1964	101

Typical days per month at ALTON 1 W, 1991–2020
Month	Days 25°C+	Days 30°C+	Frost nights	Heavy rain (10 mm+)	Snow days
January	0	0	31	<1	2
February	<1	0	26	<1	2
March	3	<1	23	2	1
April	8	2	10	2	<1
May	15	6	2	3	0
June	25	16	0	3	0
July	30	24	0	4	0
August	29	22	0	2	0
September	21	13	<1	2	0
October	9	4	8	1	<1
November	1	<1	23	1	<1
December	<1	0	30	<1	2

How often, not how much — every day in ALTON 1 W’s record sorted by what it was actually like, rather than averaged
Month	Warm & dry days	Wet days	Washouts	Week with 3+ wet days	Daytime mean has ranged
January	2%	8%	1%	3%	0.2–9.7°C
February	7%	10%	2%	6%	3.2–12.8°C
March	25%	13%	4%	9%	8.8–17.9°C
April	48%	20%	7%	19%	17.0–22.8°C
May	64%	25%	10%	29%	22.0–27.7°C
June	72%	26%	11%	28%	27.1–34.0°C
July	79%	21%	9%	20%	31.0–37.0°C
August	80%	20%	8%	16%	30.7–36.2°C
September	79%	17%	7%	13%	25.5–31.6°C
October	61%	12%	4%	8%	19.0–25.3°C
November	18%	10%	3%	6%	9.8–16.5°C
December	2%	8%	2%	3%	2.7–10.1°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.

1903Each stripe is one year’s mean temperature against the 92-year average. Warmest: 1934. Coolest: 1993.2006

The evidence behind this page

Nearby, measured,
and named.

Place identity: GeoNames 4267536
NOAA station: USC00140201 · ALTON 1 W
Station distance: 2.1 km from the place centre
Climate period: 1991–2020
Minimum month coverage: 16 usable years
Daylight: Calculated from latitude 39.47°, 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.

These places read the same station, so their numbers are identical — distance from ALTON 1 W is what differs

Osborne→Woodston→Bloomington→Covert→Laton→

Or put two places side by side: Alton vs Osborne

Best time to visitAlton.