Weather
Illinois is occasionally known to have tornadoes from time to time. The National Weather Service issues two types of alerts during periods of severe storms. The first alert is a Tornado Watch. A Tornado Watch means conditions are favorable for the formation of a tornado. The second alert is a Tornado Warning. A Tornado Warning is issued when a tornado funnel cloud has been spotted or a tornado is found by weather radar. Emergency sirens are activated during a Tornado Warning. Upon hearing the sirens or being notified by TV or radio you should seek shelter. For more information on tornados please read the NOAA Tornado Guide.
Great Lakes Naval Station Average Temperatures and Precipitation
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
| High | 30° | 35° | 46° | 58° | 70° | 79° | 84° | 81° | 74° | 62° | 47° | 34° |
| Low | 14° | 19° | 29° | 38° | 48° | 57° | 63° | 62° | 54° | 42° | 32° | 20° |
| Average | 22° | 27° | 37° | 48° | 59° | 68° | 73° | 72° | 64° | 52° | 39° | 27° |
| Precip. (in) | 1.8 | 1.6 | 2.7 | 3.7 | 3.4 | 3.6 | 3.5 | 4.6 | 3.3 | 2.7 | 3.0 | 2.4 |
| Snow (in) | 11.3 | 8.3 | 6.0 | 1.6 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.3 | 1.8 | 8.7 |