Forecasters saw it coming — a large, wet mass of air making its way to Colorado.

But on Sept. 9, a Monday, it was hard to believe the big storm would bring anything but cool drizzle to Colorado. By Wednesday, the air mass was rapidly becoming a statewide deluge that within hours would sweep away roads, people and homes along the Front Range. What had started as a meteorological oddity had become something deadly, something historic.

Fort Collins, a city accustomed to flash floods, went about its normal business in a Wednesday morning drizzle. Residents might have been blissfully unaware, but local forecasters had already flagged the storm sitting over Larimer County as something unusual, containing almost unbelievable amounts of water. If the storm hit the Front Range, it would be bigger than the worst Colorado floods, covering more ground than the Big Thompson Flood of 1976 and the floods of 1965.

On Wednesday morning, a storm that big was just hard to believe.

Twelve hours later, the unbelievable happened: Walls of water washed through Colorado’s foothills, disintegrating bridges and roads, marooning mountain residents and killing at least four people.

“This is worse than Big Thompson, and I never thought I’d say that,” said Erick Nielsson, the emergency manager for Larimer County. Nielsson was an EMT in 1976 when the Big Thompson River flood killed 143 people in Larimer County.

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