United States · 1991–2020

Best time to visit
Leyden.

September leads for comfortable weather in Leyden: typically 23.9°C by day, 10.4°C at night, with 95 mm of rain. Based on measured 1991–2020 NOAA station history.

Best comfortSeptember

Typical high23.9°C

Typical low10.4°C

Rain in September95 mm

Comfort

September

September · August · June

79climate match

Beach

July

July · August · June

68climate match

Outdoors

May

May · September · October

74climate match

The weakest month is January, scoring 5 against September’s 79 — days reach only -2.1°C, 26° 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

5-2.1° / -11.5°

Feb

50.2° / -9.8°

Mar

57° / -3.8°

Apr

3214.4° / 2.1°

May

6321.1° / 8.7°

Jun

7226.6° / 14.2°

Jul

6828.5° / 16.3°

Aug

7327.7° / 15.2°

Sep

7923.9° / 10.4°

Oct

4616.5° / 4°

Nov

97.9° / -2.1°

Dec

50.9° / -7.8°

Monthly climate evidence for Leyden — daylight is calculated from latitude, everything else is measured
Month	Day	Night	Rain	Wet days	Daylight	Comfort	Coverage
January	-2.1°C	-11.5°C	43 mm	7	9 h 21	5	Strong coverage
February	0.2°C	-9.8°C	41 mm	6.2	10 h 28	5	Strong coverage
March	7°C	-3.8°C	52 mm	7	11 h 48	5	Strong coverage
April	14.4°C	2.1°C	91 mm	9.2	13 h 19	32	Strong coverage
May	21.1°C	8.7°C	104 mm	10.3	14 h 36	63	Strong coverage
June	26.6°C	14.2°C	125 mm	9.5	15 h 18	72	Strong coverage
July	28.5°C	16.3°C	106 mm	8.1	15 h 02	68	Strong coverage
August	27.7°C	15.2°C	108 mm	7.3	13 h 55	73	Strong coverage
September	23.9°C	10.4°C	95 mm	7.4	12 h 26	79	Strong coverage
October	16.5°C	4°C	76 mm	7.5	10 h 58	46	Strong coverage
November	7.9°C	-2.1°C	60 mm	6.5	9 h 41	9	Strong coverage
December	0.9°C	-7.8°C	49 mm	7.1	9 h 03	5	Strong coverage

Records at AFTON - JANESVILLE WWTP, 1987–2026
Month	Record high	Record low	Wettest day	Wettest / driest month	Years
January	15.6°C7 Jan 2008	-34.4°C31 Jan 2019	46 mm5 Jan 2004	104 mm2005 · driest 5 mm in 2025	39
February	23.3°C28 Feb 2024	-35.0°C3 Feb 1996	42 mm9 Feb 2001	106 mm2008 · driest 3 mm in 1995	39
March	28.3°C22 Mar 2012	-24.4°C1 Mar 2015	68 mm25 Mar 2009	147 mm2009 · driest 13 mm in 1999	39
April	31.7°C19 Apr 2002	-9.4°C8 Apr 2018	92 mm18 Apr 2026	268 mm2026 · driest 31 mm in 2015	39
May	35.6°C28 May 2018	-2.8°C4 May 2005	71 mm13 May 2014	188 mm2004 · driest 12 mm in 2026	39
June	38.3°C20 Jun 1988	2.2°C1 Jun 1993	85 mm4 Jun 2025	272 mm2024 · driest 13 mm in 1992	39
July	39.4°C7 Jul 2012	7.2°C2 Jul 2001	103 mm29 Jul 2016	283 mm2017 · driest 34 mm in 1988	39
August	38.9°C1 Aug 1988	6.1°C16 Aug 1992	107 mm5 Aug 2007	442 mm2007 · driest 16 mm in 1996	39
September	35.6°C2 Sep 2000	-2.2°C23 Sep 1995	75 mm12 Sep 2022	295 mm2019 · driest 6 mm in 2004	39
October	31.7°C4 Oct 2025	-10.0°C29 Oct 1988	71 mm24 Oct 2001	191 mm2001 · driest 8 mm in 2005	39
November	24.4°C2 Nov 2016	-20.0°C29 Nov 1995	68 mm5 Nov 2022	151 mm2015 · driest 8 mm in 2007	38
December	19.4°C6 Dec 2001	-31.7°C26 Dec 2000	42 mm14 Dec 2015	124 mm2015 · driest 8 mm in 2017	39

Typical days per month at AFTON - JANESVILLE WWTP, 1991–2020
Month	Days 25°C+	Days 30°C+	Frost nights	Heavy rain (10 mm+)	Snow days
January	0	0	29	1	7
February	0	0	27	1	5
March	<1	0	24	2	3
April	2	<1	10	3	<1
May	9	2	<1	4	0
June	21	8	0	4	0
July	27	11	0	3	0
August	25	8	0	4	0
September	14	4	<1	3	0
October	3	<1	7	3	<1
November	0	0	21	2	1
December	0	0	28	2	5

How often, not how much — every day in AFTON - JANESVILLE WWTP’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	0%	22%	4%	21%	-4.4–1.2°C
February	<1%	21%	4%	19%	-4.3–4.2°C
March	4%	23%	6%	25%	4.0–10.4°C
April	16%	31%	10%	39%	11.5–17.3°C
May	43%	31%	11%	37%	18.8–24.1°C
June	67%	30%	13%	36%	25.2–28.7°C
July	74%	26%	11%	28%	26.7–30.6°C
August	75%	24%	12%	25%	25.9–29.6°C
September	62%	24%	9%	28%	21.8–26.3°C
October	25%	24%	8%	27%	13.6–19.5°C
November	4%	22%	7%	19%	3.4–11.7°C
December	0%	23%	5%	21%	-2.7–4.2°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.

1988Each stripe is one year’s mean temperature against the 36-year average. Warmest: 2012. Coolest: 2014.2025

The evidence behind this page

Nearby, measured,
and named.

Place identity: GeoNames 5259867
NOAA station: USC00470045 · AFTON - JANESVILLE WWTP
Station distance: 11.7 km from the place centre
Climate period: 1991–2020
Minimum month coverage: 28 usable years
Daylight: Calculated from latitude 42.73°, 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 AFTON - JANESVILLE WWTP is what differs

Janesville→Footville→Hanover→Afton→Anderson→Fellows (historical)→

Or put two places side by side: Leyden vs Janesville

Best time to visitLeyden.

September

July

May

The whole year,without the guesswork.

Nearby, measured,and named.

Best time to visit
Leyden.

The whole year,
without the guesswork.

Nearby, measured,
and named.