Horel Research Team: Late June Flash Flooding Hits S. Utah

On Friday, June 21st, 2024, a plume of tropical moisture moved its way

west into S. Utah. With Precipitable Water values exceeding over an inch in

most of southern and eastern Utah, the stage was set for major convective

activity to form. The storms that would result would bring large hail, damaging

winds, and most consequentially, flash flooding. These storms are the focus of

a case study I am performing for my REALM project.

At around 12:30pm, a thunderstorm formed WSW of Page, AZ. By 1:00pm,

the thunderstorm was traveling in an ENE direction and was rapidly intensifying

into a supercell, with even some mild rotation detected on radar velocity returns.

Soon after, the storm crossed the AZ-UT border, and was heading directly

towards Lake Powell.

By 1:18pm MDT, the supercell began to move over Lake Powell, and would affect this area for the next 30 minutes. During this time, Blue Pool Wash, a local slot canyon that intersects US-89, would become flooding, citing a Local Storm Report (LSR) from the National Weather Service Salt Lake City forecast office. There would be golf ball sized hail with this cell, which would batter a multi-million dollar resort, as well as many boaters on the lake. Also from NWS LSR's, this cell would go on to capsize a boat in a channel between Warm Creek and Padre bays.

Below are a couple of videos showing the power of this supercell. The first shows the torrential rains and flash flooding in the Lake, while the other shows the hail hitting boaters.

Credit to Youtube channels 'malcolm' and 'Bryce Vellinga' respectively.

You can see alternate angles of the cell hitting Lake Powell here and here.

Over the next few hours, this supercell would track along the path of the San Juan River in southern Utah, this would cause the river to become overflowing with flood waters as captured here.

By 4:00pm MDT, the cell would move over the Mexican Hat area. The intense local rains would cause flash flooding on US-163, a well-maintained highway, near mile marker 28, as flood waters flowed downstream from the nearby hills up north. This would cause a large chunk of the asphalt to be washed out. This would force UDOT to close the highway in both directions while repairs had to be made. The aftermath of the flooding in Mexican Hat can be seen below, photo courtesy of the Utah Department of Public Safety.

At around 4:45pm, as the supercell to the south moved eastward into Colorado, a complex of thunderstorms was forming to the west of Moab. These storms would organize and continue to slowly head east towards the town, a popular recreation area (See the radar timeline at the bottom of this post).

By 5:30pm, the storm would make it's way into the Moab area. The results were astonishing, with Moab receiving anywhere from 0.9-1.0+ inches of rain in just 10 minutes!

For reference, that is over 2 times the average June monthly rainfall in Moab. This short but extremely intense rainfall would cause widespread flash flooding all over Moab, as well as the in the local creeks and slot canyons.

Photo Credit: Pete Outdoors; Youtube

Hours after the storms passed over Moab, rescues had to be performed by Grand County Search and Rescue in Grandstaff Canyon, a slot canyon just a few miles from Moab. Initially only three hikers were found stranded, trapped by the floodwaters, but soon another large group was found, increasing the total to 20 hikers having to be rescued. The rescues had to be performed past 11:00pm, due to having to wait for the flooding to recede enough for it to be safe for the rescue teams to reach them. There was a large risk for the hikers developing hypothermia due to being cold and wet, but everyone was rescued safely and treated, no injuries resulted.

Photo Credit: Grand County SAR

Moab and the surrounding areas were left with considerable damages. Many areas were left with water damage or buried in mud and debris. The damage resulting from this storm could take years to fix, citing city officials. This, along with later flooding events in the coming days, would bring up calls for improvements in infrastructure and preparation for future flash flooding events.

Tragically, while on an ATV excursion in the Steel Bender Trail, just a few miles SE of Moab, Ray and Maranda Ankofski of Texas were riding when they came upon flash flooding resulting from the storms. According to the Grand County Sheriff's Office, they were believed to have attempted to cross the floodwaters when their ATV got swept away. The ATV would be located about 3/4 of a mile from where they suspected they got caught before stopping. Later, articles of clothing containing Ray's ID were found hanging on a branch. Eventually the search sadly evolved into a "body recovery" effort, with the couple now believed to be deceased.

As of 7/8/2024, they have not been found.

You can read more about their story here, as well as here.

The events that took place on June 21st highlight the continuing need for improvements on the forecasting of flash floods, as well as communication to the general public, especially in the mountain west, where these situations evolve particularly quickly.

Below is a radar timeline I put together in Python. The first half will show the development and movement of the supercell over Lake Powell, indicated by the blue dot, and over US-163 at mile marker 28, indicated by the orange dot.

Now, here is the timeline from the development of the storms to the west of Moab, and their eventual path over the town. Moab is the black dot, Grandstaff Canyon is the purple dot, and the Steel bender Trail where the couple was washed away is the red dot.