Summer and Fall 2009 and Possible Spring 2010 Flood Impacts

As our damp Northern Plains autumn turns to thoughts of an El Nino affected winter, local forecasters’ thoughts also turn to spring and the prospects for flooding.

The record flooding of spring 2009 is still a fairly fresh memory, and though those flood waters have largely receded, top soil conditions across the Red River Basin have been slow to dry out. Summer season precipitation generally decreased after the March-April floods, but unseasonably cool weather and excessive cloud cover during the summer months of June, July and August helped keep the soils moist. Rainfall through the late fall of 2009 has helped maintain this overly-wet ground water condition and helped to keep our river base flows quite high. This excess water remains a threat which could affect our next spring flood, however, expected warmer and somewhat drier conditions this winter could act to reduce that overall flood threat.

Fall soil conditions are quite wet. The very brief respite from above average precipitation this summer was not long enough to allow the river system to fully drain the excess moisture, neither in surface storage areas nor in the soil profile.

Over the summer and fall month, the majority of the significant rainfall has occurred on the North Dakota side of the Red River Valley, with relatively small portions of the Minnesota side affected. Ground conditions in the southern counties of eastern North Dakota (Barnes, Cass, Ransom, Sargent and Richland) and parts of west central Minnesota (Wilkin, Clay, Otter Tail and Becker) are very wet. Soils in many parts of these counties are saturated and surface storage areas are full. Runoff rates from rains in the last week of October were extremely high, contributing greatly to the late season flooding that occurred on the Wild Rice at Abercrombie and Red River in Fargo.

According to the USGS office in Bismarck, this is the highest peak on the Red in Fargo so late in the year (see: Red River Flow in Fargo at Highest Level Ever Recorded for November ).

Soil conditions in the middle counties of eastern North Dakota (Nelson, Grand Forks, Griggs, Steele, and Traill) and northwest Minnesota (Norman, Polk) are a bit better off, but still very wet, with little room for additional water in the soils and surface storage areas. Ground conditions in the northern counties (Cavalier, Pembina, and Walsh) and northwest Minnesota (Kittson, Marshall) are even a bit better off due to lesser rains during the late summer and autumn. Despite the wet October, the overall conditions during the summer and early fall of 2009 have been considerably drier than 2008. Yet due to the wet conditions, timing and amounts of the fall rain, topsoil and subsoil conditions are very similar to those found in the fall of 2008.

Multisensor Precipitation Estimates of Rain

Percent of normal precipitation (mid June 2009 - mid November 2009) across eastern North Dakota and western Minnesota.  The far southern, and extreme northern Red River Basin has been the wettest, as well as parts of the Devils Lake Basin. Data based on RADAR and observed rainfall reports.

Fargo Cumulative Precipitation comparison 2008 vs 2009

Above is a graph comparing the cumulative Fargo rainfall from June 1 through October 31 for water years 2008, 2009, and seasonal normal. . The red line represents the cumulative precipitation from June 1 through October 31 2008, while the blue line represents the cumulative precipitation from June 1 through October 31 2009. The green line represents normal for the same period.


Grand Forks Cumulative Precipitation Comparison 2008 vs 2009

Above is a graph comparing the cumulative Grand Forks rainfall from June 1 through October 31 for water years 2008, 2009, and seasonal normal. The green line represents the cumulative precipitation from June 1 through October 31 2008, while the blue line represents the cumulative precipitation from June 1 through October 31 2009. The red line represents normal for the same period.

Last fall the freeze-up took place early and quickly, from November 8th through 10th, 2008. This led to the saturated top soils becoming a “hard, concrete frost”. These conditions prevailed throughout the winter and into the spring of 2009. The freeze-up has not occurred yet this fall, and the forecasts are not suggesting this will happen until after mid-November.

Winter Outlook points to warmer and drier conditions. This winter season looks like it will be a bit different than last year’s. During the summer of 2009, an El Niño developed and has continued throughout the fall. During typical El Niño winters, temperatures for our region are 2 to 4 degrees above normal, and snowfall tends to be 75% to 80% of normal. While there are other large scale climate signals that can decrease the affect of the El Niño, the winter of 2009/2010 is expected to be warmer and drier than last year. Classic El Niño winters feature less frequent arctic air intrusions, and fewer snow storms. Examples of recent El Niño winters include 2006/2007, 2002/2003, 1997/1998, 1994/1995 and 1991/1992. Below is a table with the average snowfall for Fargo and the University of North Dakota/NWS Climate station and El Niño average snowfall.

 

Station

Season

Snowfall 

 

 

 

 

6 Season

1971-2000

 

1987/1988

1991/1992

1994/1995

1997/98

2002/2003

2006/2007

average

Normal

Fargo

44.5

27.5

50.3

41.1

33.4

38.3

39.1

48.7

Grand Forks

31.6

33.4

37.9

45.3

34.1

47.3

38.3

44.5

Overall, there tends to be slightly less snow during El Niño winter. Typically, the snows do not build up as much as the warmer temperatures often melt the snow between storms. This prevents the snow from accumulating to average depths. Winter season temperatures tend to be warmer across the Northern Plains during an El Nino. Below is a table of the same 6 seasons, except the December through February average temperatures are compared to normal.

 

Station

Season

Average 

Temperature 

 

 

 

6 Season

1971-2000

 

1987/1988

1991/1992

1994/1995

1997/98

2002/2003

2006/2007

average

Normal

Fargo

11.9

19.9

14.6

20.9

12.5

15.0

15.8

11.2

Grand Forks

11.9

18.1

13.2

19.5

11.3

12.4

14.4

10.5

 
Spring 2010 Flood Threat could be somewhat reduced.  Although it is way too soon to provide a reliable spring flood outlook the prospects for an El Nino affected winter could help to mitigate the effects of our otherwise wet soil conditions and high river base flows.
 
Below is a table of crests on the Red River at Fargo and East Grand Forks (the following spring) for the El Nino years, as listed above.
 

Station

Spring Crest

 

 

 

 

 

 

1988

1992

1995

1998

2003

2007

Fargo

15.1

15.8

28.4

28.9

22.6

21.9

Grand Forks

21.2

23.3

39.7

39.8

18.1

36.6

 

Caveats: The larger unknowns at this time include the potential for significant rains near the time of the spring snow-melt, or any late-season, wet and heavy snowfalls that could complicate the spring 2010 snow-melt scenario. Another significant variable is the eventual strength and duration of the El Niño. Should this El Niño weaken rapidly as it did in 2006/2007, the threat for significant spring precipitation would increase. Should the El Niño continue into the spring of 2010, temperatures would likely remain above normal and precipitation below normal. Your NWS will monitor the El Niño and update the impact assessment mid-winter.

In summary, given the persistent wet conditions across the basin this fall, there is certainly a potential for a significant flood in the spring of 2010. However, we are now in an El Niño pattern which does tend to favor warmer and slightly drier winters in our region, and which should help to reduce the threat for significant snowmelt flooding next spring. The NWS will be closely monitoring the winter weather conditions as we prepare our spring flood outlooks later this year.  Keep in mind that a wet fall is only one factor considered for the eventual snowmelt runoff and spring river conditions.

See the following link for a discussion of the other factors which affect flooding on the Red River of the North and its tributaries:

 
North Dakota Geological Survey: "More on Flooding" - Red River Flood Factors
 

See these links to compare recent Red River of the North flows with historic averages and extremes:

USGS Flood Duration Hydrograph for Fargo, ND

 USGS Flood Duration Hydrograph for Grand Forks, ND

USGS Flood Hydrograph for Drayton, ND



Return to News Archive

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.