Waterloo, IA

Iowa · Records since 1895–2026

☀️ 78°F
Currently in Waterloo
As of 1:30 PM CDT

Records for September 11

🔥 Record High

98°F

September 11, 2000

+19° from 79° normal

❄ Record Low

32°F

September 11, 1917

-22° from 54° normal
🌞 Normal high: 79°F 🌑 Normal low: 54°F 1991–2020 normals

All-Time Records — Waterloo

🔥
112°F
Hottest Day Ever
Jul 14, 1936
❄
-34°F
Coldest Day Ever
Jan 16, 2009
🌧
6.00"
Wettest Day Ever
Sep 8, 1941
☃
14.0"
Most Snow in One Day
Nov 30, 1934

First & Last Dates — Waterloo

How early and how late each seasonal turning point has ever arrived, across the full period of record

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Range ever recorded Normal date (1991–2020)
189 days
Longest growing season
2025
110 days
Shortest growing season
1917
154 days
Normal growing season
1991–2020 average

Top 10 Record Highs — September 11

# Temp Date
🏆 98°F September 11, 2000
2 95°F September 11, 1931
3 95°F September 11, 1906
4 94°F September 11, 1895
5 93°F September 11, 1908
6 92°F September 11, 1927
7 91°F September 11, 1978
8 90°F September 11, 2012
9 90°F September 11, 2005
10 90°F September 11, 1998

Top 5 Record Lows — September 11

# Temp Date
🥶 32°F September 11, 1917
2 34°F September 11, 1955
3 35°F September 11, 1992
4 38°F September 11, 1959
5 38°F September 11, 1922
About this data — Records are sourced from the NOAA Threadex dataset via RCC ACIS, a quality-controlled record for long-term climate stations. Threadex adjusts for station relocations and observation-time changes, making records comparable across all years since 1895–2026. Climate normals represent the 1991–2020 average.

Heat Wave Summary — Waterloo

threshold: 92°F (90th percentile of historical Jun–Aug highs)
4.5
Avg heat wave length
days (historical)
98°
Avg peak temp
during heat waves
15
Dangerous nights 2026
Overnights ≥ 70°F
0
Heat waves 2026
so far

Days ≥ 90°F Per Year

1895–2026
12
2026 so far
21
Avg/year 1970–2025
22
Avg/year (last 10 complete)
60
Most in a year (1936)

Average Daily High by Decade

Full year · complete decades only

Longest Heat Waves — Waterloo

# Dates Days Peak Avg High Avg Overnight Low
🏆 Jul 9, 1901 – Jul 27, 1901 19 107°F (Jul 24) 100°F 70°F
2 Jul 3, 1936 – Jul 18, 1936 16 112°F (Jul 13) 104°F 71°F
3 Jun 22, 1934 – Jul 2, 1934 11 107°F (Jun 27) 100°F 69°F
4 Jul 21, 1916 – Jul 31, 1916 11 104°F (Jul 29) 99°F 68°F
5 Jun 22, 1931 – Jul 1, 1931 10 106°F (Jun 28) 103°F 74°F
6 Jul 26, 1955 – Aug 4, 1955 10 103°F (Jul 30) 98°F 74°F
7 May 28, 1934 – Jun 5, 1934 9 108°F (May 31) 100°F 66°F
8 Jul 27, 1988 – Aug 4, 1988 9 105°F (Jul 31) 98°F 68°F
9 Jul 23, 1919 – Jul 31, 1919 9 101°F (Jul 27) 96°F 68°F
10 Jul 14, 1931 – Jul 22, 1931 9 99°F (Jul 17) 97°F 67°F

Heat Waves Per Year

Warm Summer Nights (Jun–Aug)

Nights where the overnight low exceeded the 1991–2020 normal low

47
2026 total
above-normal nights
36.3
Avg / summer
1970–2020
56
Most in a summer
1943

Above-Normal Summer Nights Per Year

Average June–August Low by Decade

Overnight lows · complete decades only

Precipitation

Annual totals and trend across the full period of record · see this year's standing →

Monthly Precipitation — Last 24 Months

Blue = actual · dashed line = monthly normal

Annual Precipitation Per Year (1895–2026)

Blue = above average · tan = below average · gold = 2026 (partial)
Since 1895, annual totals have trended +0.37" per decade, about +4.9" across the record.

Heavy Rain Days Per Year (≥ 1.0")

Compare year-to-year changes in days with heavy rainfall (≥ 1.0")

This Year — 2026

How Waterloo is tracking against normal, year to date

Daily High Temperature vs Normal

Above normal Below normal

126 of 253 days with data were above the 1991–2020 normal high for their date.

Precipitation, Year to Date

30.40"
2026 YTD
Normal: 28.22"
+2.18"
0.62"
September so far
September normal: 3.14"
-2.52"
10
2026 heavy rain days
Days with ≥ 1.0"

Accumulation vs. Normal

Running total since Jan 1 against the normal pace for the same date · Waterloo is 2.18" ahead of the normal pace

Period Review — Aug 11 – Sep 10, 2026

Any window, evaluated against every other year on record — 31 days

Quick picks: Last 7 days Last 30 days Last 90 days This month
Seasons: Spring (Mar–May) Summer (Jun–Aug) Fall (Sep–Nov)
73.0°F
Average temperature
22nd-warmest of 132
+3.8°
vs. average
Normal: 69.2°F (1991–2020)
2.56"
Precipitation
46th-driest of 132
-1.39"
vs. average
Normal: 3.95" · 65% of normal

Average Temperature by Year — Aug 11 – Sep 10

1895–2026 · 2026 highlighted · trend -0.07° per decade (cooling since 1895)

Precipitation by Year — Aug 11 – Sep 10

1895–2026 · 2026 highlighted

Warmest Aug 11 – Sep 10 on Record

# Year Avg Temp
1 1947 78.7°F
2 1936 76.7°F
3 1983 76.2°F
4 1900 75.7°F
5 1937 75.6°F
6 1959 75.4°F
7 1922 75.1°F
8 1913 75.0°F
9 2023 74.5°F
10 1990 74.0°F

Coolest Aug 11 – Sep 10 on Record

# Year Avg Temp
1 1967 62.2°F
2 1992 63.1°F
3 1977 64.2°F
4 1965 64.6°F
5 1986 64.8°F
6 1950 64.9°F
7 1934 65.0°F
8 2017 65.2°F
9 1902 65.7°F
10 1915 65.7°F

Wettest Aug 11 – Sep 10 on Record

# Year Total
1 1965 11.46"
2 2018 10.03"
3 2007 9.88"
4 1936 9.26"
5 1993 9.14"
6 1941 9.06"
7 1964 8.80"
8 1912 8.26"
9 1994 8.13"
10 1902 7.83"

Driest Aug 11 – Sep 10 on Record

# Year Total
1 1930 0.02"
2 2003 0.15"
3 1955 0.37"
4 2000 0.55"
5 1950 0.67"
6 1976 0.68"
7 1933 0.69"
8 1953 0.74"
9 2023 0.81"
10 2013 0.85"
About this data. Pick any start and end date and this becomes the same kind of review as the Month and Fall tabs, just for exactly the window you asked for — the generalized version of the same engine, evaluated across every year on record. Average temperature is the mean of each day's (high + low) / 2; precipitation is the sum of daily totals. A year missing more than about a fifth of the window's days is excluded from the temperature ranking; any missing day excludes a year from the precipitation ranking, since an unreported day is unreported rain. Ranges that cross from December into January aren't supported yet. Normals are the 1991–2020 mean for the same window.
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