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Inversion season is here.
The question is will a relatively small disturbance moving across northern Utah on Friday be enough to break the temperature inversion that has trapped pollutants in valleys?
On Thursday, the Utah Department of Environmental Quality issued a "red air quality alert" for Salt Lake, Davis and Weber counties. In addition, the Bear River District Health Department issued a "red" condition in Cache County.
People with respiratory or heart disease should reduce prolonged exertion outdoors during such alerts and residents are encouraged to drive less. In those counties, burning wood is illegal during red conditions, when federal Environmental Protection Agency pollution standards are surpassed.
A "yellow air quality action" condition was issued for Utah, Tooele and Box Elder counties, indicating that pollution levels are approaching the federal limit.
The forecast calls for a weak storm system to bring showers Friday morning to northern Utah valleys, but it may not be enough to scour out poor air quality, said Eric Schoening, meteorologist for the National Weather Service.
"Most of the [storm] energy will be to the north of us," he said.
There is a 40 percent chance of snow turning to rain Friday, with highs in the mid-30s, according to the forecast for Salt Lake and Tooele valleys. Lows will be in the mid-20s Friday night and Saturday morning.
Saturday will become partly cloudy with highs in the upper 30s. The mercury could hit 40 by Sunday in northern Utah valleys.
On Monday, there's a 50 percent chance of rain with highs around 40, according to the weather service forecast. It's also unclear if that storm system will break the inversion, Schoening said.
Park City and Heber City should see snow flurries Friday morning but no significant accumulation is expected. Saturday will become partly cloudy by afternoon with highs near 40. Lows will be near 20. Air quality in those areas will remain good.
In St. George, Friday's high temperature will be in the mid-50s under partly cloudy skies. The mercury will climb to the upper 50s Saturday and could hit 60 Sunday with partly cloudy conditions.
Although no large storms loom, the mountain snowpack across the state is well above normal, said Brian McInerney, hydrologist for the National Weather Service.
The snowpack in mountains east of Salt Lake Valley is 128 percent of normal. The Uinta Mountains are 160 percent of normal. The mountains of central Utah are 120 to 150 percent of normal. And southern Utah mountains also are about 150 percent of normal.
Air quality alerts
The winter inversion season in Utah runs from November through February. A red alert is issued when pollutants exceed the federal limit. Yellow signifies the limit is being approached. Here's how many red and yellow days were recorded by the Utah Division of Air Quality in the past three years.
2009-10 • 22 red days, 22 yellow days.
2008-09 • 7 red days, 14 yellow days.
2007-08 • 13 red days, 19 yellow days.
Source • Utah Division of Air Quality