Chicago, IL 15 day Weather Forecast
The 15 day forecast is calculated with an ensemble forecast that gives the probability of events. The daily temperature and amount of precipitation are shown as a range of 80% likelihood. There is a 10% chance that the actual temperature or amount of precipitation is lower than the probability range, and a 10% chance that it is higher.
In the temperature chart the light shading shows the 80% probability range, and the darker shading shows the 50% probability range. The curve in the middle of the darker area is the median temperature, which is the most probable temperature.