SAN DIEGO (FOX 5/KUSI) — A powerful storm pounded San Diego over the last few days with heavy rain, strong winds, snow, hail and thunderstorms that prompted the National Weather Service to issue a rare tornado warning.

The deadly system fueled by an atmospheric river, described as one of the wettest in the region’s history, caused widespread flooding and mudslides across California, as nearly an entire year’s worth of rain was dumped in some parts of the state in a matter of days.

While it was less catastrophic in San Diego County, the storm’s impact was still sizable, with roads turning into rivers and dramatic cloud formations that had residents speculating on social media whether a tornado was imminent.

Some of the heaviest rainfall was dumped on the county overnight Monday into Tuesday, with parts of the county breaking records for the amount of precipitation received in a single day. By Wednesday, NWS says most of the county had received between two and four inches of rainfall.

Hail was also reported in the county overnight on Monday and Tuesday, including in Chula Vista, Pacific Beach and downtown San Diego.

Flooding caused by the rainfall led to at least one death, a migrant who got swept away in the swollen Tijuana River Channel while attempting to cross the U.S.-Mexico border, and several swift water rescues in other water ways. Dozens of trees were also downed in the storm.

On Tuesday, NWS issued multiple severe weather advisories, including a Flash Flood Warning for possibly “life threatening” flood conditions in North County and a brief Tornado Warning for a stretch of South Bay and East County. Both warnings were canceled around 1 p.m.

NWS did not confirm any spiraling taking place while the Tornado Warning was in place, although many residents in the impacted area took to social media to speculate about a possible twister with images of what forecasters said were likely wall clouds — a type of protruding formation that develops in thunderstorms and can, in some cases, create tornados.

Up in the mountains, inches of snow fell in low-elevation areas overnight into Wednesday, as the tail end of the storm moved through the region and gave way to a second low-pressure system. More snow is expected Thursday, prompting NWS to issue a Winter Storm Warning for the area.

Outside the mountains, showers are expected to continue until the end of the week from the low-pressure system following the historic atmospheric river.