Flood watch for snow melt in effect until further notice in Harney County
By Mindy Gould on Wednesday, April 26th, 2023 in Eastern/Southeast Oregon News More Top Stories
Harney County-Harney County is currently in flood watch for snow melt until further notice. It is effecting the Silvies River near Burns. At 12.0 feet, flooding of fields will occur in the Burns area. Water will encroach on some private properties along North Broadway Ave, Foley Road, and Stancliff Road. Water will be close to flowing on to Highway 20 at the Silvies River Bridge. Low spots in the Burns RV Park may be impacted.
Snow melt flooding occurs when the major source of water involved in a flood is caused by melting snow. The northern tier states and mountainous areas of the U.S. are particularly susceptible to snow melt flooding. Unlike rainfall that can reach the soil almost immediately, the snow pack can store the water for an extended amount of time until temperatures rise above freezing and the snow melts. This frozen storage delays the arrival of water to the soil for days, weeks, or even months. Once it begins to melt and does reach the soil, water from snow melt behaves much as it would if it had come from rain instead of snow by either infiltrating into the soil, running off, or both. Flooding can occur when there is more water than the soil can absorb or can be contained in storage capacities in the soil, rivers, lakes and reservoirs.
High soil moisture conditions prior to snow melt can contribute to snow melt flooding. Rainfall during the late fall is particularly important because there is less evapotranspiration and less time for the soil to drain and dry before it freezes. Ground frost or frozen soil is another contributor. Deep, hard ground frost prevents snow melt from infiltrating into the soil. Cold temperatures prior to heavy snowfall and normal or above normal soil moisture contribute to this.
Deep snow cover can worsen snow melt flooding since there is more water stored and available for snow melt. Also, when snow cover is widespread, it usually keeps air temperatures cooler and delays spring warming, which increases the potential for more rapid snow melt.
Rain falling while snow is still on the ground contributes more water for flooding and helps to melt the snow pack, thus rain-on-snow events are watched carefully.
Most often, snow melt is a relatively slow phenomenon. Snow melt rates are usually comparable to light or moderate rainfall.
Important exceptions to this can occur, especially during unusually warm periods with high dew point temperatures, and when nighttime temperatures remain above freezing.
Snow melt rates can be much higher than normal under these conditions, which can increase the risk of snow melt flooding.
