The most dangerous weather in the U.S. this week is occurring in the valleys of northern Utah, where clear skies, light winds, and a strong temperature inversion have combined to create a dangerous 6-day long air pollution episode. (A temperature inversion occurs when air temperature increases with altitude, acting as a stable lid preventing atmospheric mixing; inversions are common in mountain valleys when high pressure dominates.) It’s been unusually cold during most of January in Northeast Utah, with Salt Lake City on track to have its 3rd coldest January on record. The cold weather has caused people to use their wood burning stoves more than usual, resulting in high emissions of smoke. More than 100 Utah doctors delivered a petition to state lawmakers on Wednesday, demanding that authorities immediately lower highway speed limits, curb industrial activity and make mass transit free for the rest of winter. “We’re in a public-health emergency for much of the winter,” said Brian Moench, an anesthesiologist and president of Utah Physicians for a Healthy Environment. He estimated that poor air quality contributes to 1,000 to 2,000 premature deaths each year along Utah’s Wasatch Front.

via Dr. Jeff Masters’ WunderBlog : U.S. deep freeze continues; dangerous air pollution episode in Utah | Weather Underground.