When it comes to weather, there are certain red flags that can indicate dangerous conditions. But what exactly are these red flags? And how do you know when you’re in the midst of a hazardous weather event? Here’s a quick rundown of the criteria that must be met before a “Red Flag Warning” is issued.
The Basics of Red Flag Warnings
A Red Flag Warning is an alert issued by the National Weather Service (NWS) when conditions are favorable for extreme fire behavior. This includes strong winds, low humidity levels, and high temperatures. These conditions increase the risk of fires rapidly spreading out of control.
When a Red Flag Warning is issued, it means that all outdoor burning should be avoided as dry vegetation and windy conditions create perfect fuel for wildfires to spread quickly. Additionally, any existing fires should be closely monitored and immediately reported if they flare up or spread unexpectedly.
What Criteria Must Be Met?
For a Red Flag Warning to be issued, the NWS must observe either one or both of two criteria:
1) Extremely dry air or
2) Strong winds combined with low relative humidity levels.
Extremely Dry Air - A Red Flag Warning will be issued when Relative Humidity (RH) drops below 25%. Low RH levels create drier vegetation which makes it easier to ignite and spread quickly due to increased fuel availability.
Strong Winds & Low Relative Humidity - A second criterion for issuing a warning is sustained wind speeds greater than 25 mph combined with relative humidity levels below 35%. Wind speeds this high can blow embers from one area to another, causing small fires to rapidly become larger ones. Additionally, wind-driven flames can burn up hillsides with ease—making them especially dangerous in hilly terrain areas such as Los Angeles County's Angeles National Forest.
Red Flag Warnings have been around since the late 1990s but still catch many people off guard when they occur. Whenever you hear about extreme wildfire warnings, remember these two criteria—low relative humidity plus strong winds or extremely dry air—and prepare accordingly! By familiarizing yourself with these key warning signs now, you'll be better prepared if and when they arise in your area!