Understanding Rainfall Rates

Destructive rainfall isn’t just about frequency.  Did you know that 2” of rain in the Southeast means something different than 2” of rain in the Southwest, and it all has to do with timing.

Rainfall rates measure the intensity of rain within a certain period of time which is different from rainfall totals, the overall amount of rain expected to fall during a storm.

“When we are talking about rainfall rates of high intensity we are looking at those time scales under one hour,” said David Gomberg, National Weather Service Los Angeles/Oxnard.

These rates are calculated by using rain gauges and Doppler Radar.  “Typically on the order of hourly rainfall estimates and also instantaneous rainfall estimates we kind of use a combination of both of those with the rain gauges that kind of give us an overall picture of rain rates,” Gomberg said.

This information is crucial to know to determine if there is a threat for flooding, especially in areas like the southwest where the ground does not immediately absorb runoff.  This can also lead to mud and debris flow in recent burn scar areas.  The higher the rate is in a shorter time span will likely lead to extremely dangerous and destructive events.

Always remember, when a Flash Flood Warning is issued for your community, that means you need to take action as you might have only minutes to get to a safer location.