The Little Colorado River at Winslow, Arizona, surged past flood stage overnight and is forecast to reach a record crest on Tuesday, putting the town's levee and the Ames Acres and Bushman Acres neighbourhoods at risk. The National Weather Service in Flagstaff issued a flash flood warning for Winslow early on Monday, November 2, after the river gauge rose rapidly above moderate flood stage while flooding was already occurring.

This is a major new development on the same river Awaaz Punjab already covered in a flood warning for the Holbrook reach of the Little Colorado. That warning covered rising water upstream; the new warnings cover Winslow itself, downstream, where the river is now forecast to crest above its previous record and where the levee, not just low land, is in the forecast.

What the gauges show

The Flagstaff weather office issued a flood warning at 10:15 p.m. Mountain Standard Time on Sunday, November 1, for the Little Colorado River from Woodruff to Leupp, in effect until 10 a.m. Mountain Standard Time on Tuesday. At 9:15 p.m. on Sunday the gauge at Winslow read 16.96 feet, below the 19-foot flood stage, but the same warning forecast a crest of 29.04 feet at Winslow at 6 a.m. on Tuesday.

By 1 a.m. on Monday the gauge at Winslow had already reached 23.05 feet, well above flood stage, and the weather office issued a flash flood warning at 2:06 a.m. for Coconino and Navajo counties, covering Winslow, Leupp, Birdsprings, Bushman Acres and Homolovi Ruins State Park, until 8 a.m. on Monday. The warning said a river gauge had rapidly risen above moderate flood stage because of upstream heavy rainfall, that further rises to above major flood stage were expected shortly, and that flash flooding was already occurring.

What each river level means for Winslow

The weather service's own impact ladder for the Winslow gauge explains why the numbers matter. At 17 feet, the approaches to the bridge over the river on Navajo Route 71 near Bird Springs flood, and Leupp comes within three feet of flooding problems. At 18 feet, water flowing above that level for about six hours or more may erode the levee and eventually cause leakage or failure.

At 19 feet, the flood stage itself, water overflows the right bank and approaches Ames Acres and Bushman Acres on the left bank in the Winslow area, with erosion likely on the left-bank levee. Downstream, with about an 18-hour lag after the Winslow crest, the approaches to the Navajo Route 71 bridge near Bird Springs flood and evacuations of homes near the intersection of Navajo Route 2 and Navajo Route 71 are conducted.

At 22 feet, there is lowland flooding on the right bank and damage on the left bank to Ames Acres and Bushman Acres if the levee fails. At 25 feet, the weather service says plainly: the levee is overtopped, with major flooding of portions of Winslow including Ames Acres and Bushman Acres.

A record crest, by more than one measure

The Weather Channel, reporting on Monday, described record flooding unfolding along the Little Colorado River near Winslow, and along the Gila River near Solomon in southeastern Arizona. A separate weather analysis by Balanced Weather put the forecast final crest at Winslow at about 25.55 feet on Tuesday, which it said would be more than three feet above the previous record at a gauge with about 25 years of records — and, critically, above the levee level that causes major flooding in Winslow.

Readers should know that crest forecasts were still being updated as the gauge rose rapidly overnight, so different National Weather Service issuances carried different crest numbers. The consistent facts across them are the ones that matter for safety: the river was already at 23.05 feet at 1 a.m., well above the 19-foot flood stage; the forecast crest was above the 25-foot levee-overtopping level; and the warning covered Winslow, Leupp, Birdsprings and Bushman Acres through Tuesday morning.

The wider flood, and what it means for drivers

Winslow sits on Interstate 40 in northern Arizona, one of the main east-west trucking routes across the state, and the Little Colorado River valley is the low ground that route crosses. No Interstate 40 closure at Winslow was reported in the warnings reviewed for this story, but drivers should check Arizona's AZ511 road conditions before crossing the valley, because river flooding can close low roads and washes with little warning, and the weather service's flood watch for northern Arizona, issued at 4:42 a.m. on Monday, said considerable areal flooding was still present across much of northern and central Arizona even as the rain ended.

More than ten rivers, creeks and washes in Arizona and southwestern Colorado had surged past major flood stage, the highest level, the Weather Channel reported, and a few had set new record crests. Flooding of some swollen waterways could last through at least Tuesday, it said, and crews in Arizona were still searching for a man who fell into fast-moving floodwater in Flagstaff, with rooftop rescues reported around Sedona.

What happens next

The flood warning for the Little Colorado from Woodruff to Leupp runs until 10 a.m. Mountain Standard Time on Tuesday, and the forecast crest at Winslow falls on Tuesday morning, with the downstream effect at Leupp and Bird Springs arriving about 18 hours later. The decisions to watch are whether the crest reaches or passes the 25-foot levee-overtopping level, whether evacuations are ordered for Ames Acres and Bushman Acres, and how long the river stays above flood stage after the crest.

Sources: National Weather Service Flagstaff flood warning, November 1, and flash flood warning, November 2 (via FlagScanner and GovOneStop); The Weather Channel via KION, November 2; Balanced Weather, November 2; National Weather Service Flagstaff flood watch, November 2.