Dear Tom,

The nation's highest and lowest temperatures on Oct. 31 were at Chandler, Ariz., and Alamosa, Colo., respectively — about 450 miles apart. Are there any records for the closest proximity between a day's highest and lowest temperatures?

Rob Davis, Lake Bluff

Dear Rob,

Your question is posed quite often, so let's revisit the issue. Because temperatures usually decline by 5.4 degrees for every 1,000 feet of vertical ascent, elevation is the key to an answer. Locations near each other, but at greatly different elevations, are the likely candidates, and a documentation of the nation's daily temperature extremes since 1995 bears out the proposition. The results indicate that Truckee (elevation 5,840 feet) and Death Valley (190 feet below sea level), both in California and 264 miles apart, occasionally register the nation's lowest and highest temperatures, respectively, on the same day.