The combination of an unusually deep late-season snowpack and surging warmth this weekend will set into motion rising water on the Red River of the North.
An end of cold, snowy pattern is coming quickly to the northern Plains and the Upper Midwest. However, the sudden shift to more seasonable temperatures will lead to problems.
Much of the existing snow cover will wither away this weekend into early next week. As this happens, water locked up in the snow (the equivalent of 2 to 6 inches and in some cases more) will be released.
Hope is for the meltdown to be gradual enough to limit the flooding to manageable levels.
If heavy rain avoids the area, then there is still a chance that flooding could stop short of record levels. However, even with this scenario, there would still be major problems.
Temperatures are forecast to climb into the 60s and 70s during the day but remain above freezing at night in most areas. The milder conditions at night will thwart a natural slowing of the thaw which normally takes place at night earlier in the spring.
Levees would have to hold back water for possibly a couple of weeks with some unprotected areas being under water for a longer period of time.
Significant rises on Red River will begin this weekend.
As of April 23, the Red River is officially projected by National Weather Service hydrologists to reach major to near-record stages later in April into early May, due to melting snow and minor rainfall events.
Spring flooding is not uncommon for the river which flows across a vast plain. There are not steep hillsides to contain the river. During a flooding event, when left unchecked, the river can stretch for hundreds of square miles beyond its banks.
The river also flows from south to north from a warmer climate to a colder climate, which can amplify flooding in certain situations, such as from ice jams or heavy rain in one part combined with heavy snow in another.
According to the Associated Press, preparations have been under way to protect the cities of Fargo, N.D., and Moorehead, Minn., to a river level of 41 feet. Flooding would begin at 38 feet in the two cities, affecting many homes and businesses, if left unprotected by additional sandbagging efforts.
Normally, with late-season snowstorms, a thaw occurs in between. This allows the ground to warm up and absorb some of the melting snow.
However, this season the weather has remained very cold between the storms, so the ground has not thawed as it normally would at this point in April.
The frozen ground increases the runoff potential into the river system.
Record flooding occurred in Fargo during 2009, when waters reached a level of 40.84 feet on March 28. The 2009 flood was the fourth highest on record at Grand Forks, N.D., with a level of 49.33 feet on April 1.
The most recent flood on the Red River occurred in during the middle of April in 2011. At Grand Forks, waters crested at 49.33 feet. During this flood, the forth highest crest on record occurred at Fargo with a state of 38.81 feet.
The record crest at Grand Forks was 54.35 feet during the April 22, 1997, flood. The 1997 flood brought the second highest crest on record at Fargo with 38.72 feet on April 18.
Other recent significant floods occurred along the Red River in March 2010, April 2006, April 2001, April 1999 and April 1996.