Heavy Rain, Rapid Snowmelt Causes Flooding, Mudslides in Parts of Nevada, California
A warmer atmosphere drives more extreme precipitation across all storm types, and warming temperatures convert snowfall to rainfall, which in turn can melt snow pack. Both factors increase the risk of flooding. In 2015, for the first time in 120 years of record keeping, the winter average minimum temperature in the Sierra Nevada was above freezing, a key threshold for maintaining snow pack. 68% of weather stations in California between 2,000' and 5,000' of elevation are recording a lower percentage of precipitation falling as snow during the winter snow season over the last several decades.
Climate conditions in California are polarizing further, amplifying the flood/drought pattern that has repeatedly visited the state over the last century. Overall basin dryness has increased, due to warming temperatures which dry out soils and amplifies drought conditions. This in turn decreases flood risk. However at the same time, as rainfall is concentrated into extreme precipitation events and as increasingly less precipitation falls as snow, flood risk increases. These trends combine to drive weather toward extremes at either end of the drought/flood spectrum.
Coastal flooding in California is also fueled by seal level rise, which combines with high tides and extreme rainfall to drive flooding in low-lying coastal areas, as seen in Bay Area flooding in Redwood city and Kentfield during this event.
Heavy rain and rapid snowmelt in the Sierra Mountains had led to widespread flooding in parts of Nevada and California, triggering mudslides and road washouts.
According to the Elko Sheriff's Department in Nevada, the record rapid snowmelt and subsequent flooding is a "life-threatening" situation. Authorities have warned motorists to refrain from driving on flooded roads.
"Widespread overland flooding from excessive rain and snowmelt is occurring," the National Weather Service reports. "Many dirt roads in the warning area have reported washouts or flooding and structures in Osino are being impacted by the flooding. Additional streams exiting the higher terrain and flowing into valleys are also likely flooding.
The latest in a series of storms for the West rolled in on Tuesday, and since this was a warmer storm, it brought higher snow levels along with heavy rainfall. With grounds already saturated from January's barrage of winter storms, the region is now very prone to flooding, said weather.com meteorologist Chris Dolce.