After a 30- to 40-degree plummet between Sunday to Monday afternoons, temperatures continue to slip overnight. And that could mean frost or freeze by morning.Temperatures early Tuesday will be mainly in the 30s across eastern Montana and northern Wyoming. Most of Billings will be in the upper 30s but most of the region could feel a nip on late-season vegetation.Suddenly, temperatures will reverse course and Tuesday afternoon will end up mainly in the 70s. 67 is the average early October high temperature.For the rest of the week, overnight temperatures will range from the mid-30s to low 50s depending on location and day of the week, and highs will range from the mid-60s to around 80. Winds could be brisk Tuesday afternoon, Wednesday and Saturday.The one constant will be continued dry days.