Red River Valley Flooding - March 2009
Major early-spring flooding occurred during the later half of March in the Red River basin and a few other Minnesota watersheds. In the Red River basin, major flooding is still underway as of this writing, and a significant secondary crest is expected. The flooding event was remarkable for its early onset, and for its unparalleled magnitude at some reporting stations. Five components are often cited as contributors to major flooding along the Red River:
- Heavy autumn precipitation. Precipitation totals for the meteorological autumn (September through November) were far above long-term averages in the Red River basin. Precipitation values exceeded historical averages by four or more inches across most of the watershed. Both Fargo and Grand Forks set all-time autumn precipitation records for the three-month period.
- Deeply and solidly frozen soil. Very cold temperatures in arrived in December before a significant snow cover. The cold temperatures, along with a saturated soil profile, resulted in "concrete frost", an impervious layer highly conducive to runoff.
- Heavy winter snowfall. Record-setting snowfall totals were reported in southern sections of the Red River basin in December and in March. These totals, combined with near-average snowfall in January and February, made the snow season of 2008-2009 one of the snowiest ever in this region.
- An unfavorable melt pattern. The middle of March brought a ten-day period of relative warmth to the Red River Valley. For eight of the ten days, temperatures climbed approximately ten degrees above the historical average. The warm weather came in conjunction with ...
- Heavy rain on melting snow. Precipitation totals in some portions of southeastern North Dakota, central Minnesota, and northern Minnesota ranged from two to four inches for the period March 22 through March 25. For historical context, the MONTHLY NORMAL precipitation for that region is approximately one and one quarter inches. In some locations, 24-hour precipitation totals for March 23 and March 24 set all-time records for those dates. In a few cases, 24-hour precipitation totals were the greatest ever recorded for ANY March date. The four-day precipitation total at Fargo, 2.76 inches, is greater than the all-time MONTHLY March precipitation record of 2.62 (set in 1995).