Heavy rainfall Tuesday contributed to a flash flood warning today, which will last until 6 p.m., according to the National Weather Service.
All of western Colorado is on the lookout for flash floods.
"The air masses are moist, creating storms that will produce the heavy rainfall that is prone to flash flooding," said Paul Frisbie, forecaster with the National Weather Service in Grand Junction. "Yesterday's rain makes the soil moist, so if we have more rain it's more prone to wash off so it makes the environment more susceptible to flash floods."
Moffat County Undersheriff Jerry Hoberg said the department is on alert, but can take no action until flooding actually happens.
"We've just got to be aware that it's there and if it comes, we've got to watch ourselves in the low areas," he said. "There's not a lot that's proactive, other than informing the public, that you can do."
Several factors contribute to flash flooding. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and duration is how long the rain lasts. Topography, soil conditions, and ground cover also play an important role.
But, Frisbie said, people don't necessarily have to be in an area that's experiencing heavy rainfall to get flash floods.
Runoff from distant rainfalls contributes to flooding in lower areas as well.
"A flash flood can occur many miles away from heavy rainfall," he said.
Frisbie warns people who are traveling through dry washes or whose homes are located in low-lying areas or near drainage ditches.
That is why so large an area is under the warning.
"Only a small percentage of the warning area will experience flash flooding," Frisbie said. "We don't have the skill to pinpoint in advance where that will occur."
The National Weather Service is predicting late afternoon thunderstorms again in Northwest Colorado, something Hoberg says officials will keep an eye on.
"It's kind of a wait and see situation," he said. "It's so unpredictable."
Flash floods are the number one weather-related killer in the United States.
"This primarily affects travelers," Frisbie said. "Don't drive across flooded roadways or if you're hiking, don't hike in dry washes."
According to the National Weather Service, flash floods can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels and can also trigger catastrophic mud slides.
Most flash flooding is caused by slow-moving thunderstorms or thunderstorms repeatedly moving over the same area.
The National Weather Service offers several tips for people living in areas under a flash flood warning:
Listen for distant thunder. Runoff from a faraway thunderstorm could be headed your way. Look out for water rising rapidly
Know your flood risk and elevation above flood stage. Do your local streams or rivers flood easily? If so, be prepared to move to a place of safety. Know your evacuation routes.