San Francisco residents woke up to a tornado warning early Saturday morning as a powerful storm system battered the region with heavy rain and wind.

The National Weather Service issued the warning just before 6 a.m. for northern San Mateo County and parts of downtown San Francisco

According to the NWS, there was a cyclone signature on the radar that had generated enough of a rotation signature to trigger the warning.

The warning ended for San Francisco at 6:07 a.m. as the storm moved northeast of downtown. The warning for the rest of the area expired at 6:20 a.m

The warning led to a flood of social media posts from residents who were woken up by the alarm on their cell phones. It was reported to be the first tornado warning for San Francisco.

There was also a special warning for a possible water release in the San Francisco Bay in the Bay Bridge area, which expired ten minutes after the tornado warning.