The Weather Channel's Roth said the tornado threat would "almost completely" be gone by Tuesday, but added: "There will be another storm system coming through the Tennessee and Ohio Valley areas. We can't rule out tornadoes but there doesn't look like a severe threat at this point."
In Missouri, where a tornado damaged up to 300 homes in the town of Orrick on Saturday, Gov. Jay Nixon issued an emergency declaration and urged people to stay alert and heed weather warnings.
Denver officials said they were deploying 70 snowplows overnight to prepare for Monday's commute.
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"May snow certainly isn't unheard of here in Colorado, even down in the Denver metro area," said David Barjenbruch, a Boulder-based weather service meteorologist. "If we see the total accumulations that we are anticipating from this storm, we are certainly going to see a top 10 May snow event for the Denver metro area."
The weather service said mountainous areas in south-central Wyoming got up to 2 feet of snow, and the metro areas of Cheyenne and Laramie averaged 6 to 10 inches.
—By Henry Austin of NBC News. The Associated Press contributed to this report.