PORTLAND, Ore. (KOIN) — With temperatures rising into the 90s this weekend, a heat advisory is officially in effect for the greater Portland and Vancouver area until Monday night.

The heat advisory follows an excessive heat watch that the National Weather Service issued earlier this week. But what’s the difference between the two? KOIN 6 Chief Meteorologist Natasha Stenbock reports that an excessive heat watch is upgraded to an advisory when there is a higher level of predictability.

KOIN — Weather Alerts

“A heat advisory is not a downgrade from an excessive heat watch,” Stenbock said. “The language is differentiated by timing to the event, forecast certainty, and temperature criteria by region. To simplify, the ‘watch’ graduates to an ‘advisory’ with more forecast certainty.”

The NWS’s next and most severe stage is a heat warning. Heat warnings are issued in response to immediate weather threats that are potentially deadly.

“At this point, the NWS has not issued any heat warning,” Stenbock said. “If our temps were expected to rise into the 100’s then you can bet NWS would issue a warning instead of an advisory.”

The NWS provides the following definitions for each alert:

Excessive Heat Watch: Issued when an excessive heat event is likely in the next 12 to 48 hours. A watch means very hot weather is likely within the next day or two, but forecasters are still not certain whether it will occur or exactly when it will begin. A heat watch is issued to give agencies and persons who need to prepare enough time to do so.

Heat Advisory: Issued when an excessive heat event is imminent. A Heat Advisory is issued within 12 hours of the onset of extremely dangerous heat conditions.  A heat advisory is less serious than a heat warning. An advisory means it will be hot enough to be very uncomfortable, and unless you are cautious it could be dangerous to your health and threaten life or property.

Excessive heat warning: This is the most serious heat alert, issued when conditions pose a threat to life or property. It means that within 12 hours the heat index will be at least 105 F.