A strong storm system is wreaking havoc in the southwestern United States, leading to widespread flooding and forcing evacuations. Flood watches are in effect for Southern California and Arizona as the storm shifts eastward, with the possibility of snowfall in parts of the Four Corners area and the southern Rockies.

In Santa Barbara, California, more than half a foot of rain fell, causing significant damage. An off-ramp from U.S. Route 101 was swamped, and North Salsipuedes Street downtown experienced over six inches of flooding. Storm drains were unable to cope with the heavy rainfall, leading to additional runoff. As a result, emergency services had to wade through knee-deep water to reach flooded residences. Numerous cars were also partially submerged, creating dangerous conditions for motorists.

The National Weather Service described some rain bursts as "extreme." In Santa Barbara, an inch of rain fell within one hour, marking the fourth-wettest hour on record since 1948. Curiously, all ten of the wettest hours on record have occurred in this century, likely attributable to the increasingly warm and wet atmosphere caused by human-induced climate change.

The Oxnard civic center, although not an official Weather Service observation site, reported a remarkable 3.18 inches of rainfall within a single hour on Wednesday night.

Several rainfall records were shattered on Thursday. Camarillo Airport reported 1.19 inches of rain, while Santa Barbara Airport recorded 2.60 inches. The Oxnard National Weather Service office saw an impressive 2.78 inches of rain.

Fierce thunderstorms accompanied by rotating thunderstorms and downpours prompted the issuance of four tornado warnings for Southern California. The Weather Service has cautioned about the possibility of more coastal thunderstorms and offshore waterspouts on Friday. Areas near Oxnard experienced heavy thunder and lightning for several hours.

One of the most notable aspects of this storm system is the exceptional amount of rain it has delivered to low-lying areas. Santa Barbara, which is close to sea level, saw over 6 inches of rainfall, a remarkable occurrence. Typically, mountains are required to focus atmospheric moisture and enhance rainfall rates.

The rainfall is being caused by an upper-level low centered just offshore of the U.S.-Mexico border, west of San Diego and Tijuana. Gradually moving eastward, it is expected to pass over Arizona on Friday night. This low-pressure system, coupled with a tongue of tropical moisture from the equatorial regions, is fueling widespread downpours and a few thunderstorms. Even Phoenix could receive up to 1.5 inches of rain.

As the storm system advances into Arizona, it is predicted to spread over the southern half of the state, potentially causing hazardous travel conditions on Interstates 8, 10, and 17.

By Friday evening, the first wave of downpours will shift eastwards into New Mexico, while a second batch of storms will develop over western Arizona. The presence of the upper-level low and chilly temperatures aloft will allow for the formation of thunderstorms, and there is a marginal risk of severe weather. Although the tornado risk is minimal, thunderstorms in southern Arizona, from Yuma to Tucson, could produce gusty winds and small hail.

As the storm and moisture continue to move eastward into the high terrain of eastern Arizona, significant snowfall of 3 to 7 inches is expected above 8,000 feet, with up to 2 feet possible above 10,000 feet.

Over the weekend, the upper-level low will gradually shift northeastward, merging with a similar disturbance over the central Rockies. This convergence will bring snowfall to Colorado, the Four Corners region, and parts of the central and northern Plains by Sunday.

In addition, there is a possibility of additional rain and thunderstorms, including a few strong-to-severe storms, over West Texas and the southern High Plains.

Residents in the affected areas are advised to stay updated on the evolving weather conditions and take necessary precautions to ensure their safety.