United States · 1991–2020

Best time to visit
Lemont.

September leads for comfortable weather in Lemont: typically 24.7°C by day, 13.3°C at night, with 83 mm of rain. Based on measured 1991–2020 NOAA station history.

Best comfortSeptember

Typical high24.7°C

Typical low13.3°C

Rain in September83 mm

Comfort

September

September · June · August

84climate match

Beach

July

July · August · June

74climate match

Outdoors

October

October · May · September

69climate match

The weakest month is January, scoring 5 against September’s 84 — days reach only -0.2°C, 24° 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

5-0.2° / -8.6°

Feb

52.1° / -6.9°

Mar

118.9° / -1.3°

Apr

3916.1° / 4.5°

May

6622.2° / 10.5°

Jun

7027° / 15.7°

Jul

6329° / 18.2°

Aug

6727.9° / 17.3°

Sep

8424.7° / 13.3°

Oct

4917.3° / 6.4°

Nov

199.6° / 0.3°

Dec

52.4° / -5.6°

Monthly climate evidence for Lemont — daylight is calculated from latitude, everything else is measured, sea temperature from the nearest open water 38 km away
Month	Day	Night	Rain	Wet days	Sea	Daylight	Comfort	Coverage
January	-0.2°C	-8.6°C	56 mm	7.5	3.3°C	9 h 28	5	Good coverage
February	2.1°C	-6.9°C	51 mm	6.8	2.0°C	10 h 32	5	Good coverage
March	8.9°C	-1.3°C	71 mm	8.1	2.0°C	11 h 48	11	Good coverage
April	16.1°C	4.5°C	109 mm	9.5	3.8°C	13 h 16	39	Good coverage
May	22.2°C	10.5°C	127 mm	11.1	7.1°C	14 h 30	66	Good coverage
June	27°C	15.7°C	124 mm	9.7	14.1°C	15 h 11	70	Good coverage
July	29°C	18.2°C	107 mm	8	20.9°C	14 h 55	63	Good coverage
August	27.9°C	17.3°C	115 mm	8.6	22.5°C	13 h 51	67	Good coverage
September	24.7°C	13.3°C	83 mm	6.9	20.1°C	12 h 25	84	Good coverage
October	17.3°C	6.4°C	94 mm	8.4	14.5°C	11 h 01	49	Good coverage
November	9.6°C	0.3°C	61 mm	7	9.2°C	9 h 46	19	Good coverage
December	2.4°C	-5.6°C	58 mm	7.8	5.6°C	9 h 10	5	Good coverage

Records at ROMEOVILLE WFO, 1997–2026
Month	Record high	Record low	Wettest day	Wettest / driest month	Years
January	18.3°C7 Jan 2008	-31.1°C16 Jan 2009	49 mm8 Jan 2026	127 mm2005 · driest 9 mm in 2003	29
February	22.8°C25 Feb 2000	-25.6°C11 Feb 2014	55 mm28 Feb 2017	131 mm2018 · driest 3 mm in 2026	29
March	29.4°C21 Mar 2012	-25.0°C4 Mar 2002	57 mm8 Mar 2009	166 mm2009 · driest 20 mm in 2015	29
April	31.7°C18 Apr 2002	-8.3°C7 Apr 2018	72 mm25 Apr 2007	200 mm2013 · driest 36 mm in 2021	29
May	36.1°C15 May 2025	-3.3°C3 May 2005	69 mm11 May 2002	257 mm2019 · driest 29 mm in 2007	29
June	37.2°C28 Jun 2012	3.9°C1 Jun 2003	118 mm9 Jun 2011	234 mm2014 · driest 30 mm in 2023	29
July	38.9°C24 Jul 2005	8.9°C2 Jul 2001	125 mm27 Jul 2003	316 mm2003 · driest 18 mm in 2013	29
August	36.1°C1 Aug 2006	8.3°C31 Aug 2009	88 mm12 Aug 2016	248 mm2007 · driest 17 mm in 2020	28
September	34.4°C13 Sep 2005	2.2°C24 Sep 2012	113 mm27 Sep 2019	290 mm2019 · driest 10 mm in 2017	29
October	31.7°C4 Oct 2005	-4.4°C21 Oct 2018	102 mm14 Oct 2017	213 mm2017 · driest 9 mm in 2005	29
November	25.0°C8 Nov 2020	-14.4°C22 Nov 2015	40 mm2 Nov 2003	157 mm2003 · driest 23 mm in 2008	29
December	21.7°C3 Dec 2012	-24.4°C18 Dec 2016	55 mm28 Dec 2015	149 mm2015 · driest 12 mm in 2017	29

Typical days per month at ROMEOVILLE WFO, 1991–2020
Month	Days 25°C+	Days 30°C+	Frost nights	Heavy rain (10 mm+)	Snow days
January	0	0	28	2	8
February	0	0	25	2	6
March	<1	0	20	2	3
April	3	<1	5	4	<1
May	11	3	<1	4	0
June	22	8	0	4	0
July	28	14	0	4	0
August	26	9	0	4	0
September	15	4	0	2	0
October	4	<1	3	3	<1
November	0	0	15	2	2
December	0	0	26	2	6

How often, not how much — every day in ROMEOVILLE WFO’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%	24%	6%	24%	-2.8–2.7°C
February	<1%	23%	5%	21%	-3.0–6.1°C
March	6%	28%	8%	37%	6.9–12.8°C
April	20%	33%	11%	41%	14.2–18.3°C
May	45%	34%	13%	41%	20.2–24.6°C
June	67%	31%	13%	37%	25.5–28.7°C
July	74%	26%	12%	27%	27.0–30.6°C
August	73%	27%	12%	28%	26.4–29.4°C
September	68%	22%	8%	28%	22.8–26.9°C
October	26%	27%	9%	30%	15.5–19.8°C
November	5%	23%	6%	24%	6.0–12.8°C
December	<1%	25%	6%	25%	-1.0–6.0°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.

1998Each stripe is one year’s mean temperature against the 28-year average. Warmest: 2012. Coolest: 2014.2025

The evidence behind this page

Nearby, measured,
and named.

Place identity: GeoNames 4899581
NOAA station: USC00117457 · ROMEOVILLE WFO
Station distance: 10.4 km from the place centre
Climate period: 1991–2020
Minimum month coverage: 23 usable years
Daylight: Calculated from latitude 41.67°, mid-month, sunrise to sunset including refraction. Not a station measurement.
Sea temperature: NOAA OISST v2.1 1991–2020 monthly climatology, nearest open water 38 km from the place centre. A sheltered bay can run warmer than the open sea it is measured from.
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 ROMEOVILLE WFO is what differs

Bolingbrook→Plainfield→Romeoville→Lockport→Homer Glen→Crest Hill→

Or put two places side by side: Lemont vs Bolingbrook

Best time to visitLemont.