When it comes to rain and snow, we want it and we need it. But too much too fast can quickly turn dangerous, causing mudslides and flooding.
Fresno’s flood control system is designed to handle up to 3 inches of rain in 48 hours.
Metropolitan flood control district general manager Alan Hofmann says, “We’ve looked through 100 years of records for what is the largest 48 hour storm event and that’s what we set our criteria on and try to keep that available.”
He says the time it takes to move water to storage basins can also be critical during intense rainfall. “The system is designed to handle what we call a 2-year event. That’s the probability of 50% of it happening each year. That’s only about a half inch of rainfall in an hour.”
California’s heaviest rains are most often caused by atmospheric rivers.
Also known as the Pineapple Express, an atmospheric river is weather pattern where a highly concentrated stream moisture pours over the area.
Now, meteorologists have new tool to describe their intensity.
A scale of 5 categories from 1: primarily beneficial — because we do want and need rain — to 5: primarily hazardous.
The atmospheric river affecting us this week may reach category 2 intensity over Fresno… Which is luckily toward the more beneficial side of the scale.