The storms that hit the Bay Area in the last 48 hours could have done a lot more damage to the East Bay than they did. What limited the damage was the fact that the storm passed over us faster than expected, giving the wind less time to topple things and the rain less time to accumulate and flood, experts told The Oaklandside.
But the storms are far from over. Heavy wind and rain are expected to return Saturday and continue well into next week. We reached out to atmospheric scientists to learn about the storms and what to expect next.
The Bay Area was on the edge of the storm
According to Alison Bridger, a professor of atmospheric science at San Jose State University, the more-powerful-than-usual storm on Wednesday and Thursday resulted from a nasty combination of unusual weather systems. Mainly, a cold front and a low-pressure front that were much stronger than usual. Cold fronts are the leading edge of a mass of cold air. They’re like a giant moving wall that pushes into warmer air, which has low-pressure, eventually raising the warmer air higher up into the atmosphere. This creates heavy wind, rain, and sometimes thunderstorms.
Bridger told The Oaklandside that while it was important for people to prepare for a strong storm, it was always likely that the Bay Area was only going to be touched by its edge, where wind and rain levels were lower. Had the center of the storm passed over the Bay Area, the effects would have been more destructive.
“[Getting hit by] the center was never going to happen. That was well forecast. The thing that was most difficult to forecast was the amount of rain and how fast the cold front moved through. It rained a lot for a couple of hours, more than expected,” she said.
Bridger said the Bay Area is less likely to suffer from devastating rains due to its location. Most storms typically make landfall further north. “When big weather systems come to us, they come close but usually move eastward and then wash ashore north of California into Oregon, Alaska, and British Columbia. We are on the margins of [those big systems.]”
Climate experts say changes to the jetstreams that move air in the atmosphere are the main reason we are experiencing stronger storms right now.
Jetstreams are bands of air currents that move across the globe eastward, in a zig-zag motion, and carry storms from the ocean onto the land, usually eight to 10 kilometers above the ground. Normally, the jetstream over Northern California moves air and water moisture from north to south, but right now, it’s reoriented in a more direct west-to-east direction, putting the Bay Area in the storm’s crosshairs for hours at a time.
The cold weather the Bay Area usually gets from the Northwest this time of year is also likely to be warmer than usual because it is coming directly from the Ocean. This will lead to warmer storms and more rain.
A ‘bomb cyclone’ is not a cyclone. But it is likely a consequence of global warming
Dan McEvoy, an associate research professor of climatology at the Desert Research Institute, said he believes that the media, particularly TV news, did not do a good job explaining what a bomb cyclone actually is, and this led to some unnecessarily hysterical reactions.
“That terminology leads to some ideas of a more powerful storm system,” he said.
A bomb cyclone, McEvoy explained, only refers to how quickly the cold, low pressure strengthens within a storm’s center. When mentioned on TV without context, McEvoy and Bridger both said, it could have led viewers to believe the storm had the power of a cyclone, which it never did.
“There were a lot of satellite images of this really big storm that [can be misinterpreted],” McEvoy told us.
Focusing on the potential consequences of a bomb cyclone can be difficult enough to deal with without this misunderstanding, particularly in regions with poor maintenance and infrastructure. For example, McEvoy said that this storm system hit the mountainous regions of Santa Cruz as well as coastal areas especially hard. “What really matters is the impact related to the flooding, the rain, the winds, and of course, the mountain snowfall,” he said.
The role that global warming plays in causing higher levels of rain also needs to be better understood, experts said.
According to Bridger, there is no doubt atmospheric moisture is increasing as the planet warms, producing storms with more rain. If the most recent storm had occurred 30 years ago, she said, it probably would not have produced the levels of rainfall we saw this week.
What’s next? And what about the drought?
According to the Global Forecast System, the Bay Area should expect at least two more weeks of rainstorms due to the jetstream’s orientation, as noted above.
McEvoy told The Oaklandside that there will be a break in heavy rain until Saturday when the next storm will make landfall. The Saturday night storm probably won’t be as bad as Wednesday night and Thursday morning. On Monday, we should expect another atmospheric river storm that could be very strong.
San Jose State’s Bridger said people should carefully prepare for this continued rainfall for the next few days. While she suspects many people are already sick of the rain and want it to stop, she advised patience and said it’s important to contextualize the situation and remember last January produced nearly zero rain.
“In the space of two years, we have had two very extreme years of weather. Very dry and very wet. We have had about 50% of the normal amount of rain,” she said. “We need rain in the reservoirs and the groundwater. And we don’t know if this will be enough to break the drought.”
The Shasta reservoir is still low, at about 34% of its capacity, while Lake Oroville is at 39%.
Bridger added that the current pattern of the rains, with big storms for half a day suspended by a half day of inactivity, is less likely to cause flooding. Cities can absorb the rain, let it drain away, and then get ready to receive more.