A tanker truck is tended to by firefighters after sliding off the snowy highway near mile marker 48 on Interstate 90 in Piedmont, S.D., Tuesday afternoon, Dec. 3, 2013. (AP Photo/Rapid City Journal, Chris Huber) (REV-SHARE). A woman walks dogs through the snow-covered limbs in Liberty Park, Tuesday, Dec. 3, 2013, in Salt Lake City, Utah. Tuesday, Dec. 3, 2013. The National Weather Service said up to 16 inches of snow are expected to fall in higher elevations of Utah. Light snow falls as a bighorn sheep ram along a hillside across from Cleghorn Springs State Fish Hatchery on Highway 44 in Rapid City, S.D., on Tuesday morning, Dec. 3, 2013. AP Photo/Rapid City Journal, Chris Huber A storm system will produce rain and snow over the Great Lakes region, with showers from western New York to the south over the lower Mississippi Valley. Low pressure will produce snow over much of the central and southern Rockies. UNR students walk to class on the university campus during the first snow fall of the season on Tuesday, Dec. 3, 2013, in Reno, Nev. (AP) - A wintry storm pushing through the western half of the country is bringing bitterly cold temperatures that prompted safety warnings for residents in the Rockies and threatened crops as far south as California. The jet stream is much farther south than normal, allowing the cold air to push in from the Arctic and drop temperatures by 20 to 40 degrees below normal levels, AccuWeather meteorologist Tom Kines said Tuesday. Areas of Montana and the Dakotas were forecast to reach lows in the minus-20s, while parts of California could see the thermometer drop to the 20s. The icy arctic blast was expected to be followed by another one later in the week, creating an extended period of cold weather that hasn't been seen since the late 1990s, meteorologists said. Officials warned residents to protect themselves against frostbite if they are going to be outside for any length of time. When it gets this cold, you don't need 30, 40 mile-per-hour winds to get that wind chill down to dangerous levels. All it takes is a little breeze," Kines said. The storm hit the northern Rockies on Monday and Tuesday, dumping up to 2 feet of snow in the mountains and in Yellowstone National Park. Snow and ice created hazardous driving conditions throughout the West, and were a factor in a four-vehicle crash in central Montana that killed 21-year-old Chelsea Stanfield of Great Falls. Authorities said Stanfield was driving too fast for the conditions. The weather also closed a stretch of Interstate 90 on Tuesday between Sheridan and Buffalo, Wyo. In eastern Oregon, authorities closed much of Interstate 84 as trucks jackknifed in the snow. Transportation authorities in Utah and Nevada reported dozens of crashes. In the Dakotas, cattle ranchers who lost thousands of animals in an October blizzard were bracing for the latest wintry weather, with wind chills of 40 degrees below zero expected by week's end. Cattle should be able to withstand the harsh conditions better than they did the Oct. 4 blizzard, said Julie Ellingson, executive vice president of the North Dakota Stockmen's Association. "Cattle are a hardy species; they can endure a lot," she said. With that October storm, they didn't have their winter hair coat yet. They've acquired some of that extra hair that will help insulate them better. The cold was expected to keep pushing south and bring near-record low temperatures to parts of California. Citrus famers in the Central Valley checked wind machines and ran water through their fields in anticipation of temperatures at or below freezing Tuesday night, followed by even colder weather on Saturday. However, farmers should not panic, said Bob Blakely of California Citrus Mutual, a trade association. Cold weather can be good for the crops, he said. "Trees and fruits need some of that cold weather to harden off and prepare for late December and January," he said. The system was pushing south, and Texans enjoying balmy 80-degree days should be seeing temperatures in the 40s by Thursday, Kines said. The cold air is expected to linger until next week then move east, where it will bring less-drastic temperature changes, he said. AP writers Ben Neary in Cheyenne, Wyo., Blake Nicholson in Bismarck, N.D., and Scott Sonner in Reno, Nev., contributed to this report.