A rare West Coast cyclone, Hilary, is forecast to bring heavy rain, possible flash flooding, windy conditions and much cooler weather to the Las Vegas region this weekend.
“Hilary’s rainfall impacts within the southwestern United States are expected to peak this weekend through Monday,” the National Hurricane Center said. “Flash, urban, and stream flooding are possible with the potential for significant impacts.”
Projections for rainfall amounts varied with the hurricane center saying isolated amounts in the mountains west of Las Vegas could reach 10 inches with 5 to 8 inches possible between Saturday and Monday.
“We don’t expect anything that extreme (five to eight inches),” National Weather Service meteorologist Chris Outler said. “The official forecast for the valley is one to two inches, possibly a little more by the weekend.”
The weather service issued a flood advisory for much of the Las Vegas area and southern Nye County beginning Saturday morning through Monday afternoon. He said excess runoff from the storm could cause flash flooding in many areas.
The cone track on Friday morning indicated the storm was heading north off the coast of Baja California as a Category 4 storm (140 mph winds) and toward Southern California.
Hilary could make landfall near San Diego late Sunday afternoon as a tropical storm before heading well north across the Mojave Desert and entering Nevada west of Las Vegas on its way toward central Nevada.
The hurricane center says there is a chance Hilary could still be a tropical storm or tropical depression by the time it reaches the United States. No tropical storm has made landfall in southern California since 1939.
The area potentially affected by the heavy rains could extend from Bakersfield, California, to Yuma, Arizona, as well as parts of southern Nevada.
According to some projections, up to 3 inches of rain per hour could fall from Palm Springs south to the US-Mexico border. San Diego could also receive heavy rain.
Farther north, Death Valley National Park has issued warnings for heavy rain and flash flooding beginning Saturday for several days. The park experienced several major storms this past August, but the effects of Hilary could be worse.
several variables
The storm’s impact is within a day of Las Vegas, and many variables will influence the magnitude of the impact, said weather service meteorologist Morgan Stessman.
“A lot will depend on the terrain,” Stessman said. “Most likely, one to two and a half inches of rain will fall in the valley between Saturday and Monday,” Stessman said, adding that the Spring Mountains and Sheep Range could receive between two to four inches.
The other important factor is the track of the storm. If it moves further west, Las Vegas and the region will likely feel less of a hit. However, if you move further east, the impact could be greater. A forecast track released Friday morning shows the centerline moving just west of the Las Vegas area as it moves north toward Reno.
According to Stessman, Death Valley, which suffered severe flooding a year ago, could receive two inches or more, depending on the terrain. Flash flooding could easily happen with that much rain. The recent York fire south and west of Searchlight could also spell a flash flood situation as well.
The first few showers in the Las Vegas area will not be related to Hilary, but to monsoonal moisture that could fall Friday night. The chance of showers or thunderstorms is 30 percent, according to the weather service. Winds can reach gusts to 18 mph.
A few brief showers fell in southwest Las Vegas during the Friday morning drive, while light showers, thunder and some lightning struck the central valley.
The heaviest rains begin on Saturday
A 70 percent chance of rain is forecast for Saturday. The maximum temperature will be around 90 °F, well below average due to abundant cloudiness. Winds could pick up again with gusts of up to 20 mph.
The chances of rain on Saturday night are 90 percent and on Sunday the same percentage.
A high of about 70° is forecast for Sunday, which could break the record low for August 20. In 1957, the maximum was only 78°.
According to the weather service, rain is possible for much of the week. The daily maximums will remain below 100° and the nightly minimums will be above 70°.
Rare storm in southern California
The possibility of Hilary making landfall in southern California increased Thursday. If it did happen, it would be a very rare event – it only happens a few times in recorded history, according to AccuWeather.
Southern California has seen notable tropical cyclones, such as the unnamed 1858 hurricane that hit San Diego. In addition, the El Niño of 1938-1939 brought four tropical cyclones with significant rainfall to the region. Hurricane Kathleen in 1976 and Hurricanes Linda and Nora in 1997 also left their mark with torrential rains and high winds.
