The PMF is basically the answer to a math problem. Basically, hydrologists try to figure out the absolute largest amount of water that could ever come shooting down a watershed, based on storm size and ground characteristics. It's supposed to be a more deterministic calculation for how tough to build a dam, let's say, than the probabilistic whatever-year storm size. "The thing I've heard it equated to," says Tina Stannard, a water resources engineer at the engineering firm Freese and Nichols, "is a 1-in-10,000 year event."
For my second career, as a weather anchor, I worked on the Canadian prairie, which is the second-best place to chase severe weather, after Tornado Alley. I was also studying for a certificate in meteorology so I could interpret weather data and make my own forecasts. I didn't want to be looked at as some ditz who didn't know what she was talking about. Around that time, a photographer friend invited me to chase with him in the Alley for a month. I said sure; I wanted to learn everything I could.
The U.S. National Hurricane Center said Selma hit El Salvador's coast in the morning before losing strength over land, weakening to a tropical depression with maximum sustained winds of 35 mph (55 kph). The storm's center was located about 45 miles (75 kilometers) east of San Salvador, and it was heading northeast at 8 mph (13 kph).