Millions of residents in the Los Angeles and San Diego areas were issued Flash Flood Warnings on Saturday morning as a powerful low-pressure system drenched Southern California in yet another bout of heavy rainfall. This storm, swirling off the coast of Central California, tapped into tropical moisture as it moved south towards the Los Angeles Basin, resulting in a brief atmospheric river storm and triggering concerns of flash flooding.

The National Weather Service in Los Angeles issued separate Flash Flood Warnings for both the heart of Los Angeles and San Diego, alerting residents of the potential for flash flooding and landslides. In Los Angeles, over 5.5 million people were affected by heavy rains, with rainfall totals already reaching between 0.75 and 1.50 inches before dawn. Rain gauges indicated that the storm was pouring in at rates of 0.5 to 1.0 inches per hour.

Los Angeles' LAX Airport reported significant rainfall, with 0.81 inches recorded in just one hour and a total of 1.68 inches so far. San Diego also faced Flash Flood Warnings, with radar indicating that 0.25 to 0.75 inches of rain had fallen, and an additional half inch to a full inch was likely within an hour.

Additionally, a brief Tornado Warning was issued for Santa Barbara County after Doppler Radar detected rotation in a passing thunderstorm. Fortunately, the storm dissipated without any reports of tornado formation.

Coastal Southern California, including the Los Angeles Basin and San Diego area, is expected to receive 1.5-3 inches of rain, while higher elevations in the foothills and mountains could see totals of 3-6 inches. The rainfall outlook for the Los Angeles area extends through Monday, posing potential risks of flooding and landslides.

The storm arrived at an especially inconvenient time, as traditional outdoor Easter activities were affected. Easter egg hunts in Pasadena, Huntington Beach, and Santa Anita were either canceled or postponed to a later date due to the threat of heavy rain.

Northern California also faced heavy rainfall, with the San Francisco Bay Area receiving about half an inch of rain and gusty winds of up to 40-50 mph. San Joaquin County experienced power outages affecting approximately 15,000 customers.

Although the bulk of the steady rainfall is expected to pass through Southern California on Saturday with the storm's cold front, unstable atmospheric conditions may lead to thunderstorms on Saturday night and Sunday. There is even a low chance of severe weather, including torrential downpours, hail, strong wind gusts, and the potential for a weak tornado or waterspout.

Residents are urged to remain vigilant as rockslides, mudslides, and loosened soils remain a concern. The saturated ground and above-average rainfall in Downtown Los Angeles since the start of the year and the wet month of February have increased the risk of such incidents.

Furthermore, high wind warnings continue over the Santa Lucia Mountains, with gusts expected to reach 45-60 mph.

Higher elevations in the Southern California mountains will also experience heavy snowfall, with 2-6 inches likely above 4,500 feet and 12-24 inches expected above 6,500 feet. Traveling in the mountains is strongly discouraged due to hazardous conditions.

As the low-pressure system moves inland, Arizona will also experience rain and wind, though to a lesser extent compared to Southern California. Flash flood threats are in effect for south-central Arizona, including Phoenix and Tucson.

Strong gusty winds are forecasted for Saturday across the region before gradually subsiding. Wind advisories are in effect for various times into Saturday evening and night, with gusts ranging from 40-50 mph.

In conclusion, Southern California is bracing for the impact of heavy rains, flash flooding, and potential thunderstorms. Residents are urged to take necessary precautions and remain vigilant as the storm makes its way through the region.