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Published March 25, 2011, 02:33 PM

Flood Forecast from NWS

Most risk factors have increased as heavy snow has continued and snowmelt is now delayed into April.

The following is the full flood forecast issued by the National Weather Service

This outlook is based on conditions as of 3/23/10.

Most risk factors have increased as heavy snow has continued and snowmelt

is now delayed into April.

In general, the risk of major to record scale flooding has increased across the headwaters areas, and the central and southern Red River Basin, from Hillsboro and Halstad to points south.

Accordingly, risk has increased along the entire mainstem Red River as well. Risk has increased throughout the mid to upper Sheyenne sub-basin and the Devils Lake basin, while several of the tributaries in the far northern basin have seen risks decrease slightly.

These changes are mostly due to the significant snow events on March 5-6 and on March 22-23, both of which mainly impacted the southern two-thirds of the basin. Otherwise, the northernmost third of the basin received only minimal new snowfall.

Key points for the Red River Basin, from south to north:

- All points along the Red River now have a better than 98 percent risk of major flooding.

- Wahpeton and Fargo, now have a more than 40-45 percent risk of exceeding 2009 flood levels. [in 2009 Fargo hit a flood of record at 40.84 ft, Wahpeton hit 3rd place at 17.5 ft]

- The flood risk at Halstad is back up to a 25 percent risk of exceeding 2009 levels.

- Grand Forks flood risk levels have increased by a foot or more due to a reduced margin of error for timing on Red River and Red Lake River crests, and increased Red River flows.

- Continuing north, Oslo now has a better than 60 percent risk for record flooding, while both Drayton and Pembina have had their flood risks increased only slightly.

On North Dakota Tributaries:

- The ND Wild Rice at Abercrombie has a 30-35 percent risk of 2009 scale flooding.

- The risk levels along the Sheyenne River from Valley City into Lisbon have increased by as much as a foot or more, to about a 25 percent risk of meeting or exceeding 2009 levels. Past Lisbon into Kindred, West Fargo, and Harwood the flood risks will likely meet or exceed 2009 levels (60-80 percent chance).

- Enderlin and Mapleton on the Maple River now have a 50 percent risk of 2009 levels.

- Risk along the Goose River into Hillboro has jumped roughly a foot, as recent snowfall has more than exceeded recent melt and runoff.

- Otherwise, risk along the Forest, Park, and Pembina Rivers has dropped just slightly.

On Minnesota Tributaries:

- Risk along the Buffalo River has stayed steady, as recent snowfall has nearly equaled previous runoff.

- Risk along the MN Wild Rice at Hendrum is now nearly 50 percent of meeting or exceeding 1997’s record [33.85 ft].

- Risk along the Sand Hill and Marsh Rivers is now around 30-40 percent of 2009 levels.

- Risk along the Red Lake River has remained steady with Crookston having a 35 percent chance of meeting or exceeding 2009 levels.

- Risks along the Snake and Two Rivers sub-basins have dropped by half a foot, while risk along the Roseau River has increased by about half a foot.

Key points for the Devils Lake Basin: This outlook still indicates that Devils Lake and Stump Lake will certainly rise (more than 90 percent probability) to a new record height in excess of a 1454.1 ft elevation, which is two feet above their previous record set last summer. These lakes

could rise (30 percent probability) to a height in excess of a 1455.1 feet, or three feet above their previous record. Overall risk factors have been increased slightly for this update, largely due to above normal snowfall through March. [Creel Bay gauge at 1451.79 on 3/24/11]

What has occurred since Mar 3rd:

Total precipitation amounts have varied from one half inch in north central portions of the Red River Basin to about an inch in portions of the Devils Lake Basin and the Minnesota Lakes country. Nearly two inches of moisture have been added across the central and southern Red River basin and portions of the upper Sheyenne.

A mid-March thaw period did initiate snowmelt processes over much of the area and produced localized runoff in select headwaters areas. A recent snowfall and rapid cool down has replenished the snowpack in those areas and slowed large-scale runoff considerably.

In the central and southern portions of the basin, ditches and streams have begun to carry melt-waters to the larger rivers. Most rivers are rising very slowly in response.

What will be occurring over the next few days:

Cold temperatures through the weekend will prevent large scale runoff, and areas of open water over fields and ditches will become ice affected. Slush and frozen ice may constrict flow in culverts and low bridges.

Larger streams and tributaries will continue to show open flows in places, and could rise slightly due to localized runoff from ditches and smaller streams.

The mainstem Red River from Wahpeton into Fargo will likely begin to see edge-water developing as it rises slowly in response to initial runoff.

What is likely to happen through the first week of April:

Through next week, temperatures will rise slowly and begin the thaw-freeze cycle once again. By late week, some local runoff could pick up into local streams. Temperatures throughout the first week of April look to remain slightly below seasonal normals, but should allow the gentle freeze-thaw cycle to continue.

Precipitation through the first week of April will be minimal, with light rain/snow chances beginning next Thursday, March 31st, and continuing through April 3rd.

A more significant warm-up and heavier precipitation events are both possible early in the second week of April.

The later into April the snowmelt is delayed, the increased risk we have for heavier rains and a more rapid thaw cycle to commence.

Normal high temperatures climb rapidly from the mid 40s early in April to the mid 50s by mid month.

The overall CPC climate outlook for April calls for cooler and wetter conditions, while this active storm pattern is expected to persist well into May.

This should be the last probabilistic outlook of this spring preparation period. Rivers will steadily transition to deterministic forecast products as they began to flow more freely.

Seven day deterministic forecasts will be issued at least once per day when river forecast locations are showing open water and are expected to be in flood during that period.

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