What's the elevation of your home? You do know, don't you? Your altitude determines your weather. Summer afternoons often bring clouds to mountain towns like Phoenicia, while places near the river remain clear. But sun is the morning rule in the mountains, just as thick early fog lingers from Newburgh to Saratoga.

Then from November through April, elevation storms enter the picture. They routinely influence our lives. Kingston High gets plain rain when Onteora struggles with ice and Tannersville is closed under a foot of snow. Cars drive by with roofs sagging under eight wet inches when our own neighborhood receives only a dusting.

That's because temperature falls dramatically with altitude. It's the wonderful adiabatic lapse rate, which amounts to about four degrees per thousand feet. Result: The malls of Kingston, just 200 feet above sea level, are typically 12 degrees warmer than Hunter's ski slopes.

Our elevation affects us in lots of other ways, too. Each thousand-foot rise boosts the sun's ultraviolet intensity by four percent. Result: Hunter's skiers get 12 percent more UV, on top of the doubling produced by snow's high (90 percent) UV reflectivity. No wonder snowboarders have burnt Rudolph noses.

Radiation cranks up as well. Each of us gets about 360 millirems of radiation yearly. Three hundred comes from natural sources, the rest mostly from medical X-rays. But every 100 feet higher your home is located brings you an extra millirem a year, from space. People living in Tannersville, up at 2,000 feet, receive 20 more annual millirems than those in friendly Saugerties. That difference alone amounts to 30 times more radiation than you'd get from living right next door to a nuclear power plant. (As we pointed out in 2003, the biggest radiation source by far is radon, leaking out of the ground from your basement. Get that checked, install a vent fan if necessary, and you'll easily remove half your yearly radiation exposure.)

Altitude affects water's boiling point, too. At the Rondout in Kingston - elevation eight feet - water boils at 212 degrees, and coffee is nice and hot. In Woodstock - elevation 550 feet - water boils at 211. It's 208 in Hunter, and 204 atop Hunter Mountain. In some towns in Colorado and New Mexico, water never gets hotter than 186 degrees. On Mount Everest, water boils at 159. Maybe that's why it's not famous for its tea. Where the Concorde used to fly, at 63,000 feet, water boils at body temperature. Exposed eyes and blood simply bubble away. This unpleasant altitude is called the Armstrong Limit.

The elevations around here would seem impressive in low-lying Mississippi, but we'd be flatlanders to folks in the Rockies. It's all relative. We'd never think of the SUNY-New Paltz campus as being at a lofty elevation; yet its main entrance sits at the same 345-foot altitude as Florida's extreme highest point, Britton Hill.

From much of our region you can see Mohonk's Sky Top tower, on a prominent rocky ledge 1,500 feet up. It's bested by the gigantic radio tower at Highland, across the river from Poughkeepsie, whose top is 2,000 feet higher than the Hudson. The river itself is only three feet above sea level.

The highest places you can drive, around here? Heading out of Woodstock, Route 212 hits 1,100 feet in Lake Hill. If you take Route 214 out of Phoenicia, you traverse Stony Clove Notch at 1,840 feet; and, turning right onto Route 23A and left at Tannersville onto 23C, you reach 2,380 feet at Onteora Park. (If anyone knows where one can drive higher on a public road, let me know.) Of course, hikers can easily reach the top of Slide Mountain, at 4,200 feet, and make a nice cup of hot chocolate - or rather, warm chocolate.