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February 23, 2007

Rainfall will extend flood risk from melting snow

WEST LAFAYETTE, Ind. - Expected rainfall this weekend could compound the problem of melting snow and could lead to flooding, according to the Indiana State Climate Office.

"Temperatures will stay above freezing enough hours to melt existing snow by this weekend," said Indiana state climatologist Dev Niyogi. "This can increase river levels and, if we get significant rainfall in the forecast for this weekend, some flooding can be expected."

It is difficult to know how many inches of water the melting snow will contribute, said Niyogi, who also is an assistant professor of earth and atmospheric science and agronomy at Purdue University.

"In blizzard conditions, winds pile up snow into drifts of various depths, and it is tough to accurately measure the snow depth over a broad range," he said. "In addition, the water content of snow varies depending on the air temperature at the time of the snow. In general, colder temperatures yield lower water equivalents."

The climate office estimates that the water equivalent of the Feb. 14 snowfall in Indianapolis ranged from 0.17 inch to 1.23 inches depending on the area, said Ken Scheeringa, associate state climatologist. In Lafayette the water equivalent ranged from 0.39 inch to 1.5 inches, in Bloomington it ranged from zero to 0.87 inch and in South Bend 0.33 inch. The team used measurements available through the Community Collaborative Rain, Hail and Snow Network, known as CoCoRaHS.

"In addition to this snow melt, there is the possibility of 1 to 2 inches of rain on Saturday (Feb. 24)," Scheeringa said. "This weather one-two punch of melting snow and rain could lead to flooding."

Scheeringa encourages people to be aware of the forecast but to understand that it covers a wide area and may not exactly represent conditions at their specific location.

Residents who live near a creek or a river are in the areas most at risk from flooding and should have plans to protect themselves and their property, but everyone should monitor their local weather conditions and make necessary preparations, he said.

"Nighttime temperatures will fall below freezing over the next week, which will lead to a pattern of freeze, thaw, refreeze," Scheeringa said. "Property owners should watch for sidewalks that are wet during the day because they may be slippery at night when the water freezes. Residents also should watch for snow melting and running onto areas that used to be dry. There is the potential for a road that was clear one evening to be icy the next."

Writer: Elizabeth Gardner, (765) 494-2081,

Sources: Dev Niyogi, (765) 494-6574,

Ken Scheeringa, (765) 494-8105,

Purdue News Service: (765) 494-2096;


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