The southern half and portions of central Utah were under a Flash Flood Watch through Thursday night as thunderstorms and occasionally heavy rain showers moved into the region.

The National Weather Service warned that when those water-laden clouds let loose, slot canyons, forest slopes recently denuded by wildfires, normally dry washes and mountain creeks, streams and rivers could suddenly gush with muddy, rocky runoff.

So, be prepared. "Predicting rain doesn't count," investment giant Warren Buffett once mused. "Building arks does." Perhaps more to the point, actor Denzel Washington added: "You pray for the rain, you got to deal with the mud, too."

A precursor occurred late Wednesday afternoon when heavy rainfall left several inches of floodwater in dozens of homes in Salem. Most of the water came from the overwhelmed Highland and Salem canals, and briefly covered some nearby roads in several inches of water, police said.

By Wednesday night most of the water had receded, leaving homeowners to cope with cleanup, aided by city public works personnel.

Anyway, forecasters say you can blame it all on monsoonal moisture out of the southwest that has settled over much of Utah and southwestern Wyoming as the work week draws to a close.

Along the Wasatch Front high temperatures Thursday were forecast to reach the mid-90s, and building storm clouds afflicted denizens of the Salt Lake and Tooele valleys with rising humidity in addition to the heat.

However, Friday was to be sunny and clear, so mid-90s then should be more like the usual "hot by dry" Utahns are used to in mid-summer.

That's not the case in southern Utah, where thunderstorms and rain are expected to cycle through the redrocks and high deserts through the coming weekend. Friday's highs in St. George will be in the upper-90s, up a few degrees from Thursday's muggy mid-90s heat.

Stormy weather always is a friend to the Utah Division of Air Quality. The agency, which has shamed the state's populous urban valleys with "orange," or unhealthy-for-sensitive-groups grades most of this week, predicted "yellow" conditions through the end of the week: that translates to moderately degraded particulate and ozone pollution for most of the state, and even "green," or healthy air quality for Washington and Carbon counties by Saturday.

The Intermountain Allergy & Asthma website reported mold at "high" levels and other allergens "low," or inconsequential Thursday on its pollen index.

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

remims@sltrib.com

Twitter: @remims

Steve Griffin | The Salt Lake Tribune A kiddie train makes its way through at Liberty Park in Salt Lake City Thursday July 20, 2017.