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Another inversion is building up — along with pollution levels — but it's not expected to stick around for long.

Air-quality officials issued a "red" pollution warning Wednesday for Salt Lake, Davis and Cache counties.

That means people in sensitive groups — the young, the old and those with heart and lung problems — should avoid prolonged exertion outdoors Thursday. It also means that using wood- and coal-burning stoves is prohibited through Thursday in the affected counties.

In Weber County, where the warning for Thursday is "yellow," people are urged to use public transportation and take other steps to pollute less.

The air-quality forecast for Friday is expected to be "green," or good, for all Utah counties.

Late Thursday and Friday morning, a storm system is expected to move in and sweep away the pollution, which has been trapped in the valley basins beneath a layer of warm air. Mike Conger of the National Weather Service office in Salt Lake City said much of the Wasatch Front can expect at least a little snow before the weekend and possibly a little rain during the weekend.

With the waves of mild storminess, said Conger,"we're starting to work the cold air out of the valley" along with the pollution contained in that cold air.

High temperatures in Salt Lake City will remain in the mid-30s for the next week. —

Air quality how-to coming soon

Utah's health and environment agencies are getting ready to roll out tutorials aimed at helping the public learn more about air quality and its impact on health. A package of three videos will be posted later this month on YouTube and on the Choose Clean Air Web pages later this month. The tutorials will cover such topics as how to use the air-quality website, how to develop a recess guidance plan for elementary school students and the links between air pollution and health.