Record-breaking heat, parched forests and high desert rangelands and approaching thunderstorms triggered wildfire danger and heat warnings for Utah heading toward the weekend.

The National Weather Service put much of the state — from Logan south through Salt Lake City, Provo, Manti and Cedar City through St. George to the New Mexico and Arizona borders, as well as west to Wendover and east to Duchesne — under a "Red Flag" wildfire warning from noon Thursday through 10 p.m. Friday.

That same time period applied to "Excessive Heat" warnings for southwestern Utah and Lake Powell.

Salt Lake City, setting a record Wednesday with a 105 reading, was forecast to be within a degree of a 2007, 103-degree mark for Thursday — and should tie a 103-degree record on Friday set in 2002.

Sunny skies on Thursday were to turn partly cloudy by evening ahead of thunderstorms. Clearing skies were expected Friday morning ahead of the blazing daytime conditions.

Sizzling conditions in Utah's Dixie continue heading into the weekend with temperatures Thursday and Friday at 111 degrees in St. George. That's mighty hot, but should fall 2-4 degrees shy of records.

Once more, the state's populous, urban valleys will be locked within dirty air. The Utah Division of Air Quality gave "orange," a grade deemed unhealthy for sensitive groups, to Salt Lake, Davis, Utah, Weber, Box Elder and Tooele counties through the end of this week. The remainder of the state was "yellow," or at moderate levels for particulate and ozone pollution.

The Intermountain Allergy & Asthma website added a "high" mold rating to the mix, while chenopods were at "moderate" levels on its pollen index as of Thursday.

For more extensive forecast information visit the Tribune's weather page at http://www.sltrib.com/news/weather/.

remims@sltrib.com

Twitter: @remims