SAN FRANCISCO (KRON) — An atmospheric river poised to bring widespread storm conditions beginning Thursday now looks set to begin impacting the area a little earlier than first expected. A flood watch has been issued for the Bay Area beginning Thursday, the National Weather Service said. The flood watch will go into effect from Thursday afternoon and last through Sunday morning, according to the NWS website.

Residents are being warned of flooding caused by excessive rainfall across the entire Bay Area and Central Coast. Rain and winds in the coming forecast will make driving hazardous and present flooding danger beginning Thursday, according to a tweet from Contra Costa Fire. There will also be an increased risk of downed trees, power lines and power outages.

In January, a series of atmospheric rivers brought unprecedented winter storms that wreaked havoc in the Bay Area and across the state. The weather pattern approaching this week also is likely to bring impactful rainfall and potential flooding, the NWS says.

The consensus among most forecasters is that the brunt of the storm will roll in overnight Thursday and into Friday, possibly a little earlier than initially expected. The timing of the storm’s arrival could impact the exact amounts of rainfall we should expect and the areas of greatest impact, according to the NWS.

“It looks like light rain starting in the morning Thursday and heavy rain hitting by early afternoon,” said KRON4 Meteorologist Kyla Grogan.

“March has been an interesting weather month already and as we get in to the second half of this week, that trend continues,” added Grogan. “After a cool system that’s brought us chilly air, rain and even snow at our peaks, we are now looking at the potential for an atmospheric river to set up beginning on Thursday bringing us very heavy rain.” 

Rain totals for Thursday and Friday could approach record levels in some areas, according to a tweet from the NWS. As Grogan explains, rain is only one element of the weather system we’re likely to see this week.

Graphic: Kyla Grogan

“Wind will also be a part of this system that will tap into tropical moisture and bring enhanced rain totals our way,” Grogan said.

Rain and wind, coupled with our already water-soaked ground, could lead to downed trees, powerlines and other hazards.

“Because we have such saturated ground we will also need to be on the lookout for trees that could come down and debris flow, particularly in any of our burn scar areas,” Grogan warned. “Wind is expected too, so this will be a high impact system in every way.”

Graphic: Kyla Grogan

With rain expected to soak the Bay Area, we’re also likely to see snow in the Sierras and other higher elevations. That snow, according to Grogan, could also lead to flood risks

“In addition to rain in the Bay Area, the Sierra will be getting more snow,” said Grogan. “This storm will have a warmer air mass so our Sierra snowpack may see some melting that could contribute to additional flooding concerns there.” 

Graphic: Kyla Grogan

According to KRON4’s Meteorologist John Shrable, the heavy rain and atmospheric river that arrives Thursday is likely to continue into early Saturday. The National Weather Service is encouraging residents to monitor the forecast for late week into the weekend and to consider prepping for the possibility of heavy rain and flooding.