A powerful, record-breaking winter storm plastered Colorado, Wyoming and western Nebraska with heavy snow and howling winds Sunday, generating whiteout conditions and bringing travel to a halt. The same storm was responsible for spawning tornadoes in the Texas Panhandle on Saturday, including two in the same place at the same time.

In Denver, conditions became so bad Sunday afternoon that the National Weather Service issued an emergency alert urging residents to stay off roads.

The snowstorm began gently Saturday before gaining strength Saturday night into Sunday. The National Weather Service upgraded a winter storm warning in effect for Denver, Boulder and Fort Collins in Colorado to a blizzard warning on Sunday afternoon as winds raged and snow intensified. Snowfall totals of 14 to 24 inches were expected in northern Colorado through Sunday night, with 20 to 30 inches in southeastern Wyoming, where a blizzard warning was also in effect.

Heavier amounts, topping three feet, were predicted in some of the highest terrain. Through mid-afternoon Sunday, nearly 33 inches had fallen in Aspen Park, Colorado about 30 miles southwest of Denver, with 19.6 inches falling in just four hours. About 35 inches of snow had fallen about 40 miles west of Cheyenne.

Cheyenne itself had received 25.8 inches of snow through noon local time, clinching a record for its biggest two-day snow total. In Cheyenne and throughout southeastern Wyoming, the Weather Service called for very “difficult to impossible travel conditions” with “deep, snow-packed roadways and whiteout conditions.” Snow drifts reached three to four feet.

In Colorado, 10 to 20 inches had fallen around Denver into Sunday afternoon and 15 to 20 inches in Fort Collins. By the time the storm was over, the snow total in Fort Collins was expected to rank among its top 10 most on record according to Becky Bolinger, Colorado’s assistant state climatologist.

Denver International Airport, which reported 19.1 inches Sunday afternoon, shut down all runways as conditions deteriorated. It reported eight consecutive hours of moderate to heavy snow Sunday morning and afternoon, with frequent wind gusts of 30 to 40 mph, and a visibility of one-quarter mile or less. The runways were not expected to reopen until 6 p.m., when snow and wind were forecast to ease some.

About 18 inches of snow had fallen in Boulder through Sunday afternoon, according to Bob Henson, a meteorologist and freelance journalist.

In some areas, the water content of the snow was bringing down trees and power lines.

“We just received a report from a caller in Wellington [about 10 miles north of Fort Collins] who said 10′ diameter trees were snapped in his neighborhood and power lines are laying on the ground,” the Weather Service in Boulder tweeted.

PowerOutage.US reported about 40,000 customers without electricity in northern Colorado Sunday afternoon, focused in the region around Fort Collins and Loveland. The heavy snow also posed a serious avalanche danger for Colorado’s Front Range, according to the Colorado Avalanche Information Center.

Travel has proved challenging across Colorado and Wyoming throughout the storm. At Denver International Airport, about 1,900 flights had been canceled Sunday.

On Saturday evening, as the sun set, officials began shutting stretches of major interstates. The main arteries, Interstates 70 and 25, running east-west and north-south through Colorado, had been closed in various stretches because of low visibility and slippery conditions, snarling travel. Interstate 70 — a major corridor for skiers to get from Denver through the Rocky Mountains — can be notorious for treacherous travel in snow.

In Wyoming, portions of Interstate 25 and the major east-west corridor Interstate 80 also shut down Saturday evening.

Through early afternoon Sunday, I-70 through the Plains and I-25 through northern Colorado to Wyoming were still closed to travelers, along with various portions of interstates and secondary roads across the two states. (Travelers can check out conditions in Colorado at COtrip.org.)

“Avoid any unnecessary travel! Numerous road closures, including some major interstates, across the Front Range and plains,” the Weather Service office serving Denver and Boulder tweeted.

Denver public schools announced they would close Monday due to the extreme weather.

Dangerous blizzard conditions in southeastern Wyoming and western Nebraska

In southeastern Wyoming and western Nebraska, winds were howling as the storm cranked up Sunday. On satellite imagery, the storm resembles a comma, with clouds rotating counterclockwise across nearly the entire central United States. Moisture was being drawn into the system from as far away as the Gulf of Mexico.

Cheyenne recorded 11 straight hours of gusts topping 40 mph amid the heavy snow through Sunday afternoon, meeting the criteria for a blizzard.

Amid the snow and wind, weather radar even indicated a lightning strike southwest of Cheyenne, where thundersnow occurred. The Weather Service office in Cheyenne described the deteriorating conditions as “an incredibly dangerous and impactful” event in its morning forecast discussion.

With 25.8 inches through noon, Cheyenne had not only attained its two-day snowfall record, but also its three-day storm record, surpassing the old mark of 25.6 inches set in 1979.

Scottsbluff, Neb., where rain had changed to a wind-whipped wet snow, also reported frequent gusts topping 35 mph Saturday night into Sunday morning. “Much of the panhandle’s roadways are closed due to weather conditions,” tweeted the Nebraska’s Department of Transportation on Sunday afternoon.

The Cheyenne office noted that conditions had aligned “perfectly” for heavy snow in its vicinity, because of moisture feeds from the Pacific Ocean and the Gulf of Mexico drawn into the area and then forced up the mountain slopes, where the air cooled and dumped copious amounts of snow.

Conditions were forecast to gradually improve in Wyoming and western Nebraska Sunday evening.

Severe thunderstorms and tornadoes in the Texas Panhandle

As the storm intensified Saturday, warm air was drawn from the Gulf of Mexico and clashed with the cold, dry air pouring in from the west, causing severe thunderstorms to erupt in the Texas Panhandle. The Weather Service received nearly 50 reports of severe weather, including 11 tornadoes.

About 3:30 p.m. Central time, two tornadoes spun up simultaneously about 15 to 20 miles south of Amarillo and were captured in a video widely circulated on social media:

Hail larger than ping-pong balls also was reported in the Texas Panhandle.

The tornadoes appeared to avoid population centers.

“Power lines and a cell tower are down,” Amarillo Area Emergency Management Director Chad Orton told USA Today. “One house was damaged, but the family was in the basement … there have been no injuries or fatalities.”

Kerrin Jeromin reported from Denver.