How Heat Advisories Work

As the heat continues to build for our Tuesday, the National Weather Service has issued a Heat Advisory for southern Wisconsin, but nothing for northern Illinois, despite similar weather conditions. So what gives?

From NWS Chicago

Each weather service office has slightly different criteria for what is needed to issue a Heat Advisory. This can explain why some areas get an advisory and some don't. The picture to the right shows how NWS Chicago issues advisories. You might notice there are even different standards for Cook County and the rest of northeast Illinois! From the weather service...

"For areas besides Cook County if there is a 4th consecutive day of a max heat index of 100°F+ then an advisory will be issued, and if a 4th consecutive day with a max heat index of 105°F+ then a warning will be issued."

NWS Quad Cities, which covers some of our western counties, lists these guidelines for heat-related advisories:

• Local Heat Advisory Criteria:  Heat Index at/above 100ºF
• Local Excessive Heat Warning Criteria: Heat Index at/above 105ºF and a minimum heat index at/above 75ºF for a 48-hour period; OR 4 consecutive days of Heat Advisory criteria

NWS Milwaukee lists its criteria for a Heat Advisory as a heat index of 100° or more during the day or a heat index of 95-99° for four consecutive days or more.

As you can see, the business of heat can be a tricky one, but when the weather is this hot, you don't need an advisory to know you need to stay safe! -BA