Heat advisory, flash flooding potential in Utah's Pioneer Day forecast

SALT LAKE CITY — Pioneer Day will be hot for many Utahns, but some may also deal with flash flooding this year.

The National Weather Service has issued a heat advisory for a large portion of Utah's northern half, where temperatures could top out at 100-104 degrees along the Wasatch Front, West Desert, northern Utah and parts of central Utah on Wednesday.

However, the agency also advises that scattered monsoonal thunderstorms may produce flash flooding across southern Utah and other parts of central Utah on both Tuesday and Wednesday.

A high-pressure system set up west of Utah is the reason behind these differing forecasts, KSL meteorologist Matt Johnson explains. Its core is parked above Nevada, pushing winds from the northwest into the northern half, which also means smoke from Western fires will continue to make its way into the region.

The way it's set up will likely prevent any moisture from reaching the region aside from some possible mountain showers or clouds over the next two days, he said.

This could also push temperatures close to all-time Pioneer Day records in some parts of the state. Salt Lake City's Pioneer Day heat record of 105 degrees set in 1931 is one of the records that could be tested.

The weather service notes in that heat advisory that anyone planning outdoor activities for the state holiday should drink plenty of fluids and wear lightweight and loose-fitting clothing, especially in the afternoon hours. It also advises that people save any strenuous activities for either the early morning or evening.

In general the agency recommends that people stay in an air-conditioned room and out of the sun, if possible.

Gov. Spencer Cox referenced the heat when he urged residents and visitors to recreate safely for the upcoming Pioneer Day holiday during a press briefing on Friday. That was before a fourth person died this month from heat-related illness while hiking in temperatures above 100 degrees.

"We've seen some tragedies in southern Utah because of the extreme heat," he said. "People who are hiking: Make sure you are well-hydrated, wear lots of sunscreen and you dress appropriately for the weather conditions."

Meanwhile, Johnson said moisture will still be able to circulate in the southern half, which is why scattered showers and thunderstorms are in that region's forecast. Some of these can produce a good deal of rain in a short amount of time. Central, in Washington County, received 0.54 inches of rain in about 30 minutes from a storm on Monday.

Flash flooding is possible in some of Utah's recreation gems on Tuesday, but the risk is elevated to probable on Wednesday at Bryce Canyon and Zion national parks, as well as Grand Staircase-Escalante National Monument, according to the National Weather Service. The agency advises outdoor recreators to be careful around slot canyons and dry washes in particular.

Weather service meteorologists add that "deep moisture" is expected to increase across the region and spread north as the high-pressure shifts east. Storm potential may linger into the weekend in northern Utah, which hasn't received much rain at all this month.

"We'll clear the smoke and bring in some thunderstorm chances and then it's dry and cool for your weekend," Johnson said, noting that "cool" means high temperatures may only top out in the low 90s on Saturday.

Full seven-day forecasts for areas across Utah can be found online, at the KSL Weather Center.

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