(CNN) -- Here we go again.
On the heels of a January and February filled with vicious, snarling storms, the first March wave of arctic air pushing eastward has prompted National Weather Service warnings, watches, and advisories for more than 90 million people.
Snow is threatening to add to the already record-high accumulations in cities across the Midwest, Southeast and Northeast. The winter-weary Washington area is awaiting a dangerous tenth of an inch of ice, topped by 8 to 12 inches of snow.
The precipitation means more misery for travelers, and the airlines that carry them. As of 4:30 p.m. ET Sunday, flightaware.com reported close to 1,800 canceled flights and some 4,400 flight delays within, into or out of the United States. Inclement weather around the Dallas Fort Worth airport was causing the greatest inconveniences.
This storm is a coast-to-coast event. It started as a low pressure system dumping rain on California, then proceeded east in two prongs. As the northern prong of the system has cascaded across the country, it's delivered dangerous, even deadly, weather to places unfazed by typical winters.
Conditions are expected to deteriorate throughout the day Sunday as the massive storm continues to move east.
In Denver, a series of three accidents involving 104 vehicles on Saturday shut down a stretch of Interstate 25, the city's main north-south artery, for hours, Denver police said. At least one person died and 20 more were injured in those accidents, police spokesman Sonny Jackson said.
In Minnesota, Carleton College said three of its students died in a car wreck blamed on icy conditions.
A tower-mounted camera from CNN affiliate WXYZ showed that between Detroit and Windsor, Ontario, the Detroit River froze over.
Government agencies are trying to prevent traffic debacles such as those that gridlocked Atlanta and Raleigh, North Carolina, earlier this winter. The Missouri Department of Transportation issued a "No Travel" advisory Saturday night, warning, "Once the storm hits your area, avoid travel unless it is a dire emergency."
Despite 213 Missouri DOT trucks working the streets all night around Kansas City, Missouri, ramps to and from Interstate 70 were "dicey with ice," KCTV reporter Jamie Oberg told HLN's "Weekend Express."
The National Weather Service prediced that Sunday's high temperature will be the coldest ever recorded in Kansas City in March, staying in single digits.
The string of winter storms has left many jurisdictions around the country low on road clearing supplies. In New Albany, Indiana, where salt is now in short supply, the city has shifted to a product called "IMIX," which combines natural sand and calcium chloride, CNN affiliate WAVE reported.
The snow won't let up in some areas until Tuesday, and meteorologists predict accumulations could reach a foot or more in the mountains of West Virginia and Virginia.
To the south, the threats are different, with a slight risk of severe thunderstorms bearing damaging winds, a few isolated tornadoes, and possibly large hail.
CNN weather producers Judson Jones and Matt Daniel and CNN's AnneClaire Stapleton contributed to this report