SOUTH LAKE TAHOE, Calif. — The unseasonably warm temperatures at Lake Tahoe have prompted officials to issue a flood warning for a rapidly melting snowpack.

The National Weather Service in Reno issued a flood watch for the region that goes into effect at 8 p.m. Thursday, May 18, and lasts through 8 p.m., Monday, May 22, for excessive runoff that may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Creeks and streams may rise out of their banks and low-water crossings may be flooded, the advisory said.

“The current period of unseasonably warmer temperatures will result in excessive snowmelt and runoff from higher mountain areas into lower elevation locations along the Carson River, Walker River basins, and eastern Sierra basins. Creeks, streams, and main stem river areas will continue to run high, fast, and cold after expiration of this watch,” said the advisory. “Through the diurnal melt cycle, peak flow and heights will occur overnight and early morning in many cases.”

The warm temperatures may make it seem like a good idea to jump into area waters to cool off, the water is extremely cold and shock can quickly set in, causing loss of motor function, the service said. There are also likely to be snow bridges present in the backcountry with water flowing beneath. Caution is advised.

The temperatures are expected to peak Friday and Saturday with highs in the mid 70s and slowly dropping into the upper 60s next week.

The service added that thunderstorm chances are increasing with a 15-20% chance on Friday, and jumping up to 30% on Saturday and 40% on Sunday across Mono and Mineral counties. Gusty winds of 40-50 mph, small hail, and localized heavy rainfall will be possible in the vicinity of any thunderstorms.