Tropical Storm Hilary could dump over year's-worth of rainfall in parts of Desert Southwest

Monsoonal rains of 1.70 i nches in 2022 triggered flash flooding, and debris flows across Death Valley National Park. The National Weather Service identified the flooding as a 1,000-year event.

All modes of tropical weather impacts from Tropical Storm Hilary are expected across California and the Desert Southwest, but the FOX Forecast Center is closely monitoring rainfall rates that could be historic for places that usually don’t see much.

As the moisture shield from Hilary makes its way into the Southwest on Saturday, some communities could see 100-300% of their yearly rainfall in just a three-day period.

Forecast models show areas around Death Valley, the Anz-Borrego Desert and El Centro, California, could see some of the heaviest rainfall when compared to yearly averages.

Mountainous regions of California are expected to see the most rain, but precipitation at higher elevations is not unusual. When it falls on places that are below sea level, it is.


Expected rainfall.
(FOX Weather)


The expected rainfall totals of between 3 and 5 inches are anywhere from 60-275% of some communities’ expected annual rainfall totals.

During an average year, some places only see 2-5 inches of rain, but not in only a few days.

Due to the heavy rainfall threat, the region has been placed under the highest threat zone for flash flooding.

Forecast rainfall
(FOX Weather)


Additionally, Flood Watches are in place for about 26 million residents across four states, with the heaviest rainfall expected between Sunday afternoon through Monday evening.

National Weather Service meteorologists warned excessive runoff may lead to flooding of rivers, streams and other low-lying areas.

Outdoor recreation is not advised until water levels subside and the threat of flash flooding diminishes.


Flash flood threat
(FOX Weather)


Desert communities don’t fair well in heavy rainfall

Even though Death Valley National Park averages just 2.20 inches of rainfall yearly, the area is subject to historic flash floods.

In August 2022, monsoonal moisture dropped a record 1.70 inches of rainfall in just 24 hours.

The downpour was enough to enter the history books as the rainiest day at Furnace Creek and was considered a 1,000-year event.

Park rangers reported hundreds of miles of roads were washed away, and visitors were stranded until rescue crews arrived.

Despite the historic nature of the event, there were no fatalities in the sudden rush of water.