- Country: US
- State: IL
- Latitude: 41.856
- Longitude: -87.609
High Temperatures
On August 21 in NORTHERLY ISLAND the average high temperature is 80.2 °F (26.8 °C). The lowest recored high temperature was 71.4 °F (21.9 °C) in 2024 and the highest recored high temperature was 89.6 °F (32.0 °C) in 2013. The high temperature is usually* between 76.5 °F (24.7 °C) and 83.9 °F (28.8 °C). About a quarter of the time, the high temperature is less than 76.5 °F (24.7 °C), and another quarter of the time, the high temperature is greater than and 83.9 °F (28.8 °C). About 95% of the time, the high temperature has been between 69.6 °F (20.9 °C) and 90.8 °F (32.7 °C).
Low Temperatures
On August 21 in NORTHERLY ISLAND the average low temperature is 67.1 °F (19.5 °C). The lowest recored low temperature was 61.0 °F (16.1 °C) in 2015 and the lowest recored low temperature was 73.0 °F (22.8 °C) in 2021. The low temperature is usually* between 64.4 °F (18.0 °C) and 69.8 °F (21.0 °C). About a quarter of the time, the low temperature is less than 64.4 °F (18.0 °C), and another quarter of the time, the low temperature is greater than and 69.8 °F (21.0 °C). About 95% of the time, the low temperature has been between 59.2 °F (15.1 °C) and 75.0 °F (23.9 °C).
Frost
On August 21 in NORTHERLY ISLAND expect the temperatures to drop below freezing for a risk of frost about 0.0% of the time.
Data Source(s)
The data used to compute the average high/low temperatures for this location were taken from the following stations:
- NORTHERLY ISLAND — Integrated Surface Dataset (ISD) station ID: 998499 — from year 2012 to 2025