Parts of the country are bracing for severe winter storms this week, with snow likely to cause dangerous blizzard conditions in some areas.

Winter conditions are severe in several parts of the US, but the National Weather Service (NWS) has issued winter storm warnings for six states in particular. Parts of North Dakota, Oregon, Alaska, Idaho, Washington and California are all included in the series of warnings issued by the government agency on Tuesday.

The news comes as two powerful weather systems are set to collide and join forces this week as an ‘atmospheric river’ and a ‘bomb cyclone’ meet in the northwest. The atmospheric river (water vapor in the air) will dump rain and snow, while the bomb cyclone (a rapid drop in pressure) will increase the storm’s intensity. Meanwhile, other parts of the country will experience their own winter storms.

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NWS forecasters issued several “urgent” warnings Tuesday that whiteouts are possible in some areas in Oregon and California as a result of the storms.

Whiteouts refer to a dangerous drop in visibility – which can be reduced to near zero under certain conditions – caused by snowstorms or by previously fallen snow being blown around by the wind.

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“Whiteout conditions are possible and will make travel treacherous and potentially life-threatening,” the NWS warned in a briefing covering Siskiyou County (including Interstate 5 and Highway 97 near Weed), Etna Summit and Scott Mountain Pass in California.

Snow will accumulate “between 6 and 7 inches, with up to 2 feet over higher mountains. Wind gusts (will) reach 75 miles per hour over higher exposed terrain.” Tuesday’s commute is likely to be particularly dangerous, while strong winds could topple trees and power lines.

Similar warnings were also issued for the south-central Cascades and Diamond Lake in Oregon – and Crater Lake in California. Portions of highways 62, 138 and 230 will also be affected. Commuting through these areas on Tuesday morning is likely to be particularly risky. In addition to the whiteout conditions, “roads, and especially bridges and overpasses, are likely to become slippery and dangerous.”

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Across the rest of the state, numerous other advisories and several winter storm warnings were in effect, and residents were advised to monitor their local weather forecasts.

Meanwhile, winter storm warnings were also in effect for a series of North Dakota counties, including Benson, Burke, Cavalier, Ramsey, Towner, Bottineau, McHenry, Pierce, Renville, Rolette and Ward.

Alaska’s weather warning warned residents of snow accumulations of up to 10 inches, with winds up to 45 mph and visibility of just half a mile in blowing snow. The weather warning covered the Noatak Valley and the Lower Kobuk Valley and remained in force until 3pm on Wednesday.

The winter storm warning in Idaho covered the Big Lost Highlands/Copper Basin, the Sawtooth/Stanley Basin and the Sun Valley region. Residents were warned to prepare for snow and gusty winds Wednesday through Friday.

Washington is under a storm warning in effect Tuesday through Wednesday, with heavy snow and high winds affecting the Cascades and parts of the northern, central and eastern parts of the state.

In California, a winter storm warning remains in effect Tuesday afternoon through Wednesday afternoon for portions of southern Trinity, east of Forest Glen and Hyampom and above about 11,500 feet, including portions of Highway 36. Additional warnings cover most regions in the U.S. north of the state.

The NWS advised residents to avoid all unnecessary travel, adding: “If you must travel, keep an extra flashlight, food and water in your vehicle in case of an emergency.”