01:17 Making Snowflakes Any Time of the Year The Weather Channel meteorologist Kelly Cass looks at how you can make a snowflake any season of the year.

Another round of stormy weather is set to pound the Pacific Northwest, and that's bad news for an area that has already seen serious impacts from flooding.

Roads in Portland, Oregon, were left impassable by flooding that ejected manhole covers and left drivers stranded on Interstate 5 , while mudslides broke sewer pipes and sent sewage into the streets. Forecasters say the wave of moisture won't be as potent in the coming days, but could still cause additional problems. The latest round of stormy weather on Thursday even spawned a tornado that caused damage in the southwest Washington town of Battle Ground.

The problems created by the heavy rainfall in Oregon led to Gov. Kate Brown's emergency declaration for the 13 hardest-hit counties.

(MORE: How Long This Storm System Will Linger )

In Oregon and Washington, more than 100,000 combined customers lost power at the height of the outages. Here are the latest impacts from these storms.

California

A medical helicopter crashed Thursday night in Central California, and although an official cause has yet to be determined, officials say poor weather conditions were likely a factor.

The SkyLife air ambulance was carrying four people from Porterville Municipal Airport to San Joaquin Community Hospital in Bakersfield when it crashed, Kern County fire officials told the Associated Press. All four people aboard the helicopter were killed.

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The crash, which occurred at about 7 p.m. PST Thursday night, happened while conditions were rapidly deteriorating in the area, according to National Weather Service observations in the area. Overcast skies were accompanied by fog and mist, and visibilities dropped to just 1.25 miles at times.

(MORE: The Dangers of Driving in Fog )

American Ambulance General Manager Todd Valeri told the AP that "weather conditions are always a factor," but the weather hasn't officially been blamed for the crash.

"This was a safe, experienced crew," he added.

Dense fog also made search efforts more difficult; crews couldn't find the crash site for more than two hours, the AP also reported.

In Southern California, Ventura Pier was closed and nearby homes were evacuated when high surf brought large, dangerous waves into the area Friday afternoon, KABC-TV reported. Swimmers and surfers were asked to stay out of the water, the report added.

ABC7 reports that strong waves caused wooden posts to break off of the sides of the pier.

Two surfers had to be rescued from choppy waters in Ventura County. According to County fire Capt. Mike Lindbery, the man and woman were unhurt after being pulled from the water at Mondos Beach. The woman was rescued by a passerby and the man became stuck between breaking waves and onshore rocks before being pulled out by county rescue swimmers.

Oregon

Oregon Gov. Kate Brown issued a State of Emergency for 13 counties across the state after days of severe storms.

The governor says the federal government is making $1 million available to Oregon to help restore roads and bridges damaged by the flooding.

"Heavy rains and wind have required the evacuation of residences, and mudslides and high water have severely damaged or blocked major roadways in these areas of the state,” Brown said. "The emergency declaration ensures state resources, emergency response personnel, and equipment can be activated to respond to communities in need if their local resources are exhausted."

A woman in southeastern Portland was killed early Wednesday morning when a tree fell on her home , KOIN.com reported. The Oregonian identified the woman as 60-year-old Roberta "Bobbi" Elleson.

When he heard the tree crash through the house, Elleson's husband, Dennis, rushed to her side.

"I ran in the bedroom and she was moaning," he told the Oregonian. "I went to her side and told her, 'Hang on. Hang on.'"

A second female was killed Wednesday afternoon in Clatskanie, about 60 miles northwest of Portland, when the car in which she was riding became submerged , according to a separate Oregonian report. Penny Forrest, 72, drowned inside the vehicle, while her husband, 82-year-old Richard Forrest, was rescued, the Oregon State Police said.

In the town of St. Helens, 17 homes were evacuated Wednesday morning due to floodwaters, according to local storm reports. Upwards of 18 inches of rain have fallen in Lee's Camp, the NWS said.

(MORE: Storm Lashes U.K., Ireland with Winds Over 100 mph )

More residents were evacuated in the town of Vernonia as it flooded Wednesday morning, according to NWS reports.

According to Portland’s Bureau of Environmental Services, heavy, sustained rainfalls have overflowed the city’s combined sewer system into the Willamette River Monday. Residents are urged to avoid contact with the river from the Sellwood Bridge to the Columbia River due to increased bacteria in the water.

"It's really important that folks minimize their contact with this water," a BEC spokeswoman said at a press conference. "It's extremely polluted . There are oil cans, gas cans, dog poop, industrial pollution -- who knows what else. It's really dirty."

State Route 22 was closed for several days after a semi truck crashed into a sinkhole just after midnight Monday, prompting transportation officials to close down the highway, KATU.com reported.

The sinkhole was created when the heavy rainfall eroded the soil on which the road rested, Oregon DOT Incident Response Coordinator Dustin Ross told KATU.com.

Crews managed to pull the semi out of the sinkhole by around 2:30 a.m., the report added, but the highway will stay closed until crews can rebuild the road and drivers should use Highway 18 as an alternate route.

In southeastern Portland, at least 100 families were evacuated from an apartment complex due to rising waters, KATU.com said in a separate report.

In Eagle Creek and Estacade, firefighters went door to door Monday night asking residents to be prepared to evacuate if the Clackamas River continues to rise.

"It's scary because you can't see it, from the house, you don't know where it is," Danee Rardin told KATU.com. "I drove home from work on Highway 30 and that was a trek, that was scary, actually. I don't know, we'll see. I won't sleep tonight."

Travel in Portland was also disrupted as MAX lines and bus routes experienced delays due to the flooding , reports KATU-TV. The city's streetcar was stopped by the Portland Bureau of Transportation in the Southwest Waterfront.

Multiple roads were also closed in Clackamas County, including in Lake Oswego where several cars were stranded in high water. Residents were evacuated from one neighborhood and the American Red Cross opened a shelter at Clackamas Park Friends Church in Milwaukie.

A section of road along Kane Drive near Mount Hood Community College was washed out by flooding, leaving a gaping hole, according to the Gresham Police Department.

OregonLive.com reports that the Oregon Zoo had to be shut down due to flooding on the visitor pathways. It was closed Monday and Tuesday due to the weather conditions.

Washington

Although mudslide danger is expected to remain high through the weekend, Washington's busiest roadway has partially reopened after a huge mudslide stranded thousands of drivers for hours on Thursday.

The landslide that started Wednesday along Interstate 5 closed all lanes as they were covered in rocks and mud that were several feet deep.

"It was crazy and I was scared," Diane Smith of Lacey, Washington, told the AP. She was stranded on I-5 about 26 miles north of Portland, Oregon, by the mudslide for three hours on Thursday before driving a steep, windy road to go around the mudslide, the report also said.

Thursday evening, crews were able to reopen one lane, and officials believe all lanes will be opened by Sunday evening, the AP added.

Damage was reported in Battle Ground, Washington, from a confirmed tornado late Thursday morning. Photos from social media in the town showed numerous downed trees.

The NWS said it was an EF1 tornado with maximum winds of 104 mph, the storm survey revealed.

Multiple structures were damaged by the tornado , including several homes and two commercial buildings - Real Deal Home Decor and IQ Food Market, according to a news release from the City of Battle Ground. There was a report of the smell of natural gas near the Tukes Mountain area as reporters and crews passed by.

(MORE: The Most Stunning Weather Images from the Northwest Storms )

Real Deal Home Decor owner Kathy Corcoran told KOIN 6 News a tree smashed through one window and two others were blown out by winds. The store was emptied as the roof began to buckle and water poured inside of the building.

Seven people from a western Washington homeless camp were swept into the Puyallup River Wednesday morning, according to the AP. Authorities were notified of the incident at about 6:30 a.m. local time, and all were rescued by 8 a.m., the report added.

Washington Gov. Jay Inslee declared a state of emergency on Wednesday after severe weather led to landslides, major power outages and widespread flooding across the state.

"There are people in need across Southwest Washington and the rest of the state and we’re here to provide whatever assistance the local communities require. We’re in this together," said Inslee.

A mudslide in Burien destroyed one home, damaged another, and caused five other homes to be evacuated Tuesday night, KIRO-TV reported.

A second major mudslide was reported on Highway 2 west of Leavenworth, burying the roadway under 10 feet of mud and debris , according to the Seattle Times. It will be days before the mess is cleaned up, and detour routes have been opened, the report added.

Sea-Tac Airport reported 5.96 inches of rain through the first nine days of the month, making it the wettest start to a December on record.

Parts of Spokane, hit hard by high winds in November , have reported flooded roadways, as well as downed trees and power lines, from these storms.

The Federal Highway Administration has said it will be giving Washinngton state $1 million in emergency relief funds.