New Naming System for Heat Alerts Rolled Out by the NWS

There is a change coming in how the National Weather Service (NWS) categorizes heat alerts. Here is what you need to know about this change.

NWS Announces Change in How to Defines Heat Alerts

The NWS is remaining some of its most commonly used heat alerts ahead of the summer season. The renaming will go into effect on March 4. Under the new system, alerts that once used the verbiage "excessive heat" will now use the wording "extreme heat." As such, an Excessive Heat Watch or Warning will go by the designation of an Extreme Heat Watch or Warning.

The verbiage for a Heat Advisory will not change under the renaming rules.

It is challenging to define how various alerts are issued. This is because the criteria for heat alerts vary depending on location. The local NWS office sets the parameters for their area when deciding to issue an alert. However, the constant is that all NWS offices use air temperatures as well as heat index values to determine when to issue an alert.

The reason for the discrepancies within agencies is that each region of the U.S. offers a different climate. As such, residents become accustomed to the weather in their particular region. For example, a person visiting Florida from Montana will deal with the heat and the humidity differently than a resident.

As a general rule, NWS offices located farther north issue heat alerts when the weather is not as toasty as it might be in the south. This is because the residents are not used to dealing with this type of heat, meaning that they will have more challenges when hot weather invades. The alerts are designed to serve as a warning to residents to be aware of the potential of dangerous weather and that extra precautions should be taken.

Conversely, areas farther to the south experience extreme heat and humid conditions more frequently. Thus, the NWS will require a higher threshold to be met before issuing, advisories, watches, or warnings. If this type of discretion was not used, some areas of the South would be under varying levels of heat alerts nearly every day throughout the summer. This would mute the impacts of any advisory as residents would not take it seriously.

Looking at a few specific examples, a Heat Advisory is typically not issued in Florida until the heat index is forecast to hit at least 108 degrees for two hours or longer. However, in Maine, an expected heat index of just 95 degrees would prompt the issue of a Heat Advisory.