LAS VEGAS (KLAS) — As Tropical Storm Hilary moves into the U.S., the Las Vegas Valley is expecting rainfall, thunderstorms, and possible flooding Sunday into the workweek.

Residents, while preparing for the storm, are also asking how the record-setting storm could affect Lake Mead water levels as the highest rain totals and flash flooding are possible in mountainous regions of southern Nevada.

When wet winter storms struck the Las Vegas Valley in January, National Weather Service officials tempered expectations.

“Rain in the Las Vegas Valley does help with Lake Mead’s water levels,” said National Weather Service officials from the Las Vegas office. “However, it is more like a drop in the bucket compared to the contribution from the snowpack in the Upper Colorado River Basin.” The record snowpack this year eased drought restrictions for Nevada and other Southwest states.

In January, Lake Mead saw a 2-foot rise in water levels moving from 1,044.96 feet on Jan. 1 to 1,046.96 feet on Jan. 31. In that same time frame, southern Nevada received above-average rainfall.

Forecasters say Hilary is expected to bring 1 to 3 inches of rain, with 3 to 5 inches possible where the heaviest rain is expected in mountainous regions. A flood watch has been issued for southern Nevada until Monday afternoon.

Hilary is expected to remain a tropical storm into central Nevada early Monday before dissipating.

It’s yet to be determined if the storm’s rainfall totals will be comparable to January’s. However, Bureau of Reclamation Public Affairs Specialist Doug Hendrix said that while the early-2023 storms did affect Lake Mead’s water levels, the accumulation was not enough to dent historic lows at the lake.

“While the amount of precipitation received in the lower basin and from tributary inflows helps, rainfall from recent winter storms, alone, isn’t enough to offset the decades-long reservoir declines,” Hendrix said.

Clark County Manager Kevin Schiller has declared a State of Emergency for Clark County, where Lake Mead is located. Officials have also advised residents in the area to prepare for flash flooding.

Much of Nevada is under a high wind warning until 5 a.m. local time Monday, as well as a flash flood warning until 5 p.m. Monday.

As of Sunday afternoon, Tropical Storm Hilary had made landfall along Mexico’s Baja California coast.

The Associated Press contributed to this report.