SALT LAKE CITY — Storms set to hit Utah on Tuesday could result in two completely different issues for communities across the state before a cold front ultimately cools down Utah's temperatures this week.
The National Weather Service on Monday issued a flash flood watch for a large section of Utah, from the Wasatch Mountains in Salt Lake County to the state's southern border. It also issued a red flag warning for a chunk of the northwest section of the state due to the threat that lightning could spark new wildfires.
Both the flash flood watch and red flag warning issued Monday were originally set to go into effect at noon Tuesday and remain in effect through Tuesday evening; however, the weather service Tuesday morning extended its flash flood watch through Wednesday evening.
Meteorologists with the National Weather Service tweeted that there are "appreciable amounts of atmospheric moisture, sufficient wind shear and widespread instability" ahead of an incoming cold front set to arrive in the state later Tuesday. With those factors in place, the weather service's Storm Prediction Center on Monday issued a "marginal risk" for severe thunderstorms across most of Utah Tuesday; then, Tuesday morning, it elevated portions of Utah — from the southern part of the Wasatch Mountains to parts of southern Utah — to "slight" risk for severe thunderstorms.
The weather service issued the watch because those thunderstorms are "capable of producing torrential rainfall," which can then result in flash flooding. Slot canyons, slick rock areas, small streams, normally dry washes and recent burn scars are considered most at risk for flash flooding.
The weather service tweeted Tuesday that flash flooding is probable or expected across the state's national parks and other outdoor recreation areas both Tuesday and Wednesday.
*UPDATED* The Flash Flood Watch in effect Noon-Weds Night is expanded to include Zion National Park, Washington, Summit, and Duchesne Counties. The threat will largely be limited to flood prone areas such as burn scars, dry washes, slot canyons, and steep-sided roadways #utwxpic.twitter.com/yu5E9UhzEe— NWS Salt Lake City (@NWSSaltLakeCity) August 17, 2021
At the same time, the weather service issued a red flag warning for the northern Wasatch Front, west-central Utah and the West Desert. The warning issued Monday states that storms Tuesday are expected to provide lightning "after an extended dry period" in addition to gusty winds, microbursts and low relative humidity. The warning expires at 9 p.m. Tuesday.
The relative humidity is expected to be as low as 10% in some areas, while wind gusts are forecast to reach as high as 35 mph.
Cold front cools Utah down, bring more moisture
The cold front from the Pacific Northwest is expected to arrive in Utah late Tuesday night and sweep across the state Wednesday, according to KSL meteorologist Kevin Eubank. The cold front will bring in a trough that's expected to drop temperatures down about 20 degrees and also clear out wildfire smoke that returned to Utah over the weekend.
"This front then slides through the state by Wednesday, with storms to the north and storms to the south and a very active couple of days Wednesday, Thursday and even into Friday across the eastern areas," he said.
The National Weather Service's one-week outlook indicates that almost all of Utah will receive rain within the next week and most of eastern, as well as parts of central and southern Utah, are in position to receive more than a half-inch.
When we mentioned a pattern change, we really meant it! Here is the precipitation forecast through next Monday morning. That's a good bit of rain for Utah!— NWS Salt Lake City (@NWSSaltLakeCity) August 16, 2021
More details this afternoon! #utwxpic.twitter.com/4vHUAuldmO
That's good news considering over 98% of Utah remains in at least an "extreme" drought, with at least half still in an "exceptional" drought, according to the U.S. Drought Monitor.
"This is a really good statewide storm," Eubank said. "We'll wait and see how these totals hold but the bottom line is (there's) plenty of moisture coming in, really starting Tuesday night and running all the way through Thursday night."
Meanwhile, high temperatures across Utah will be unlike anything seen for most of this summer. Logan's forecast high drops from the mid-90s Tuesday to the low-to-mid 70s Wednesday through Friday.
Highs in the Wasatch Front will fall from the mid-to-upper-90s Tuesday to low to mid-70s Wednesday and Thursday before returning to the low to mid-80s to close out the week. St. George's cool down won't be as noticeable. High temperatures there will remain in the low 90s Thursday before returning to near 100 degrees to end the week.
Full forecasts for areas across Utah can be found at the KSL Weather Center.