AUSTIN (KXAN) — As Austin’s record-breaking heat wave continues, you’ve probably heard the terms Heat Advisory and Excessive Heat Warning.

But what do they mean and how are they different?

The National Weather Service issues these heat alerts based on forecast high temperatures and heat indices.

The criteria varies across the country, so while a heat index of 100° would prompt a Heat Advisory in New York City, it wouldn’t in Austin.

Here’s the criteria used by the NWS in the Austin/San Antonio office:

The summer of 2011 saw the most Heat Advisories issued in recent years. An advisory was in place for Travis County on 20 separate days. The summer went on to have a record 90 days at or above 100°.

The first Excessive Heat Warning for Travis County was issued in 2018. Since then, an Excessive Heat Warning has been in effect for Austin on 12 days in total.

As of July 12, a Heat Advisory has been issued for Austin on six days so far this year, while five days have had an Excessive Heat Warning in effect.