Carson City braced for possible flash flooding Thursday night, but for the second day this week a thunderstorm stayed just outside the danger area.
Thunderstorms and sudden downpours over the same area that burned during the Waterfall fire could easily send mud, water and rocks into homes and affect the city's water supply, officials said.
The area still has a slight chance - less than 10 percent - to experience such a disastrous storm today and Saturday, said meteorologist Jane Hollingsworth, with the National Weather Service in Reno.
"If we saw a thunderstorm developing over the burn area and it looked fairly strong, we're looking at a storm and flash-flood warning," Hollingsworth said.
The city stacked sandbags and built berms along west-side canyons in preparation Thursday afternoon.
Last week's fire left behind unstable soils, burning off the vegetation that usually held it in place. A one-hour moderate to heavy downpour would be enough to cause flooding, said Casey Shannon, a U.S. Forest Service hydrologist assessing the burn area.
"Homeowners directly below the stream channels could have flows into their houses," Shannon said. "We're recommending no one be in the canyons in the event of rains."
Residents living between Kings Canyon and Ash Canyon roads were notified of landslides and mudslide possibilities Thursday.
City workers placed sandbags at Carson Middle School, the west end of Ash Canyon Road, Mountain Street Trailhead and Kings Canyon Road near the creek crossing. City crews were expected to cut berms into hills to create diversions for water to flow away from homes and into streams.
Heavy rains could also cause the city to shut off a major water treatment plant in the area. Streams would be turned to mud, filled with the silty ash and soils as it washed downhill. The city's Quill treatment plant in Kings Canyon isn't designed to treat that type of water, said Utilities Manager Tom Hoffert.
The plant, usually producing 3 million gallons a day, could be shut down for 8 to 12 hours and minimize the city's water supplies. City water consumers use about 20 million gallons a day.
"I'm concerned, very concerned," Hoffert said. "This threat could always be there. We just need to be prepared the best we can to minimize impacts to our water supply and impacts to the community."
A storm Wednesday narrowly missed the Carson City area, but produced 1/2 to 3/4 inches of rain over an hour's time in Silver Springs and more than 1 inch of rain in 30 minutes near Pyramid Lake and Whiskey Springs. A report of 1/2 to 3/4-inch hail in Palomino Valley was also reported.
Northern Nevada is starting to see monsoonal moisture conditions typical for this time of year, Hollingsworth said. The thunderstorm patterns are expected to persist through July and into August.
Contact Jill Lufrano at firstname.lastname@example.org or 881-1217.