Storm System Will Create Risk of Flash Flooding in Southern California and Beyond

Posted: December 21, 2023 1:32 pm

Officials in California are warning that a large portion of the state could be in for some rocky conditions in the coming days as heavy rain creates the risk of flash flooding. The threat will eventually spread into parts of Arizona. Here is the latest on this developing weather situation.

Pacific Storm Slams Into Southern California

A moisture-packed storm is currently moving across California and headed into the Desert Southwest, prompting local authorities to warn about the possibility of dangerous flash fooding, debris flows, and mudslides. The storm that originated in the depths of the Pacific Ocean is expected to bring up to a month’s worth of rainfall through the end of the week, potentially eclipsing the rainfall totals delivered last August when Hurricane Hilary swept through the region.

This same weather maker has dumped significant amounts of rain to the northern and central portions of California this week despite the core of the storm remaining offshore. However, forecasters are predicting that the center of the storm will move to the south before pushing inland and drenching Southern California.

The heavy rain has already moved into parts of Southern California with the moisture expected to linger through Thursday. The worst of the rain will move out of the central portions of California, including the resort city of Santa Barbara, by late Thursday. Los Angeles will bear the brunt of the rain during the day Thursday and into early Friday. Heading farther south and east, San Diego and Palm Springs will get blasted late Thursday and into Friday morning.

How much rain can you expect by the time the system exits the region? The low-lying areas along the coast in Los Angeles and down into San Diego are forecast to see a general 1 to 4 inches of rain. It will be even wetter in the higher terrains. The mountains in Santa Barbara, Ventura, and Los Angeles counties are forecast to see a whopping 6 to 8 inches of rain.

Potential Impacts of the Steady Stream of Moisture

The resulting water will pool in low-lying areas on roads, creating ponding and potentially causing debris to block storm drains. This will raise the risk of urban flooding in some of the region’s largest metropolitan areas. Because so many of the area lakes and reservoirs are already nearing full capacity, the water will collect in streams and rivers.

The dry streambeds known as arroyos will quickly become overwhelmed with the torrential rain, turning them into torrents of water that can create flooding concerns in an instant. Authorities have put some residents on alert to be prepared to evacuate, if necessary.

Areas that have experienced recent wildfires will also be in danger of seeing landslides, mudslides, and road washouts. Debris flows are also a good possibility in these areas with new burn scars.

All of these issues will combine to create traffic delays throughout the region. The Thursday evening and Friday morning commutes will are most likely to be impacted.

Chances of Snow With This Storm System?

The storm coming in from the Pacific is accompanied by warm temperatures. This will translate to higher than normal freezing levels, limiting the amount of snow that falls over the next few days. The mountain passes in Southern California will dodge the snow with the wintry precipitation only forecast to fall in the highest elevations of the Sierra Nevada.

Instead, the top terrains of Southern California are forecast to see heavy rain, strong winds, and widespread fog. It will be wise to check the road conditions if you are headed up in this area over the next several hours.

The back end of the storm will create the chance of snow in the mountain communities of Arizona and New Mexico. The leftover moisture from this system will also create the risk of significant snow for parts of the Rocky Mountains in Colorado and Wyoming and down into the High Plains. This chance of snowfall will happen at the tail end of the week and into the weekend.

There is also the threat of severe thunderstorms that may kick up as the storm continues to push onshore. Isolated hail events may ignite in Southern California along with the chance of waterspouts.

Arizona and New Mexico Will Also See Moisture

By the end of the week, the storm will bring its surge of moisture into Arizona and western New Mexico. This rain will be a welcome sight for a part of the Southwest that has been dealing with drought conditions. While much of Southern California padded its annual precipitation readings with Hilary last summer, this part of the Southwest did not get in on the moisture machine.

For instance, Hilary brought nearly 3 inches of rain to downtown Los Angeles. San Diego picked up 1.84 inches of rain from this tropical weather event. The normally bone dry Palm Springs area saw 3.23 inches of rain from Hilary. Although forecasters do not anticipate the current weather maker to rival these totals, it will still be the most significant rain event that the region has seen since that time.

Phoenix is expected to pick up about a half of an inch of rain on Friday with locally heavier amounts possible. The rain will linger in the evening and overnight hours, pairing with the chance of thunderstorms. Light rain will stick around on Saturday in the Valley of the Sun before drier conditions arrive just in time for Christmas Eve festivities. The cloud cover will keep temperatures in the low 60s for a high with overnight lows falling into the mid 50s.

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