Late-season snow, cold significantly raise flood risk in Red River Valley

FARGO — Recent heavy snowfalls and persistently frigid weather are combining to ratchet up the spring flood risk in the Red River Valley, with Fargo now very likely facing a major flood, according to the latest flood outlook.

“With our active weather pattern and below normal temperatures persisting, the flood-risk probabilities have increased further with this outlook,” Amanda Lee, a National Weather Service hydrologist, said Thursday, March 23.

The Red River at Fargo now has a 95% chance of reaching 29.5 feet — just under the 30-foot threshold for major flooding — and a 50% chance of cresting at 34.2 feet, according to the weather service outlook released Thursday.

Fargo faces a 25% chance of fighting a 36.4-foot crest, a 10% chance of seeing 37.8 feet and a 5% likelihood of 38.6 feet. The record crest was 40.84 feet in 2009.

Those probabilities indicate "well above normal spring flood risk" for Fargo, Lee said.

Fargo is much better protected than it was during the 2009 flood, which required millions of sandbags. Fargo and Moorhead are well along in providing permanent protections that would allow a 37-foot river without the need for any temporary protections.

Most areas of the cities have floodwalls or levees with protection well above that 37-foot level, which should be the highest river levels during extreme floods once the metro area's flood protection project starts operating in 2027.

Also, many properties in low-lying, flood-prone areas have been removed and no longer have to be protected.

Harwood, downstream from Fargo on the Red River at the confluence with the Sheyenne River, also faces a good chance of moderate to major flooding, Lee said.

Moderate to major flooding is expected along the Red River and tributaries in southeastern North Dakota, while minor to moderate flooding is expected for some Minnesota tributaries, she said.

Downstream, flooding probabilities for Grand Forks range from a 95% chance of a 41-foot crest, 75% chance of 42.9 feet, 50% likelihood of 44.4 feet, and 10% chance of 49.2 feet.

Upstream, flooding probabilities for Wahpeton vary from a 95% chance of 11.9 feet, 75% chance of 13.1 feet, and 10% chance of 16.4 feet.

Throughout the Red River Valley, below-normal temperatures have delayed the spring thaw, increasing the chances for major flooding.

The timing of the thaw and any additional snow or rain will be the most decisive factors contributing to the spring flood risk, according to the weather service flood outlook.

Before freeze-up, soil moisture was below normal and stream flows were near normal. Fall precipitation was below normal across the Red River Basin. Conditions were driest across the lower Sheyenne River Basin and southern Red River Valley, running 3 to 4 inches below normal.

"So we do have some room for infiltration of water from snow melt, but just how much remains to be seen," Lee said, noting that much of the valley is at least abnormally dry or in moderate drought.

"Those drought conditions are expected to ease as we move into the spring," she said. "Our winter so far has probably made up for a good chunk of that dry fall."

Snowfall is above normal for most areas, especially in the Devils Lake and Sheyenne basins — where totals are running about 30 to 40 inches above normal.

In southeastern North Dakota, snowfall has been shallower and more variable. The snowpack in most areas of the basin contains 4 to 6 inches or more of moisture except for the far north, where the moisture held by the snow is about 2 inches.

Frost depths run from 24 inches in Fargo to 36 inches in Grand Forks. The snow depth as of Thursday was 23 inches in Fargo and 20 inches in Grand Forks.

The water content of the snow was estimated at 3.9 inches in Fargo and 5.2 inches in Grand Forks, according to weather service modeling.

Temperatures in Fargo likely will continue to remain below normal, but will gradually increase and eventually melting will occur even with below-normal temperatures, Lee said.

Forecasters don't see any "definitive" signs of significant snow in the next seven days, she said, although there is a chance of snow next Wednesday.

At Wahpeton, essentially where the Red River begins, no river rise is expected in the next week or so, Lee said. Streams in that area likely won't "really start moving" until the second week of April, she added.

Thursday's outlook is likely the weather service's last spring outlook. Once water starts moving, the weather service will issue seven-day river forecasts.

Michael Vosburg/The Forum