The remnants of Tropical Storm Rachel are driving widespread rainfall across Utah, raising significant flash flood concerns for Southern Utah through Monday afternoon. A slow-moving Pacific Northwest low-pressure system is pairing with tropical moisture to bring heavy precipitation, elevated flood risks in slot canyons and dry washes, and dropping temperatures across the state.
Widespread Flood Watch in Effect
A flood watch was in effect from Saturday afternoon through Monday afternoon, Oct. 12, covering a vast portion of the state. According to the National Weather Service, the watch included areas such as Zion National Park, Capitol Reef National Park, Bryce Canyon Country, and the San Rafael Swell. Other affected locations included the Glen Canyon Recreation Area/Lake Powell, the Wasatch Plateau, and the Book Cliffs.
High Risk for Burn Scars and Canyons
The National Weather Service warned that excessive runoff from the heavy rainfall could result in flooding of rivers, creeks, streams, and dry washes. Low-lying and flood-prone locations, including slickrock areas and recent burn scars such as Forsyth, Cottonwood, Silver King, France Canyon, and Monroe Canyon, were specifically identified as high-risk areas for flash flooding.
Tropical Moisture and Low Pressure
The current weather pattern involves a Pacific Northwest low-pressure system acting as the dominant feature through the middle of the week. The National Weather Service Salt Lake City reported on Monday, Oct. 12, that this system is pairing with an abundant amount of moisture from tropical cyclone remnants to maintain well-above-normal precipitation levels across the region. This combination is expected to increase the likelihood of showers and thunderstorms, potentially bringing moderate to heavy rainfall.
Flash Flood Potential by Location
In Southern Utah, the risk of flash flooding due to short-lived moderate to heavy rainfall remains elevated, particularly if cloud cover does not mute convection. According to automated hydrologic observations issued on Monday morning, several areas face significant flash flood potential. Bryce Canyon National Park and Capitol Reef National Park are listed with a 'probable' flash flood potential, while the Glen Canyon National Recreation Area and Zion National Park also face a 'probable' rating. Arches National Park and Canyonlands National Park have a 'possible' rating for flash flooding.
Heavy Rainfall Totals Forecasted
The moisture from the remnants of Tropical Storm Rachel was forecast to bring widespread rainfall totals ranging from 2 to 4 inches. In some areas, highly localized amounts of 6 to 8 inches are possible, particularly in terrain-favored locations across southwestern Utah, the Book Cliffs, and the Bear River Range.
Dropping Temperatures and Snow Levels
As the low-pressure system progresses, temperatures are expected to drop significantly. The National Weather Service reported that snow levels were expected to drop from approximately 9,500 feet on Monday afternoon to between 7,500 and 8,000 feet by Tuesday morning. This drop in temperature and elevation may bring accumulating mountain snow through at least Tuesday, posing a significant risk to travelers on seasonal roads like Guardsman Pass and Bald Mountain Pass if they are unprepared.
Forecasted Drying and Warming Trend
While the wet weather is expected to persist through Tuesday, conditions are forecasted to steadily dry during the latter half of the week. The National Weather Service anticipates a gradual warming trend through the weekend as a ridge builds into the area. However, there remains uncertainty regarding how quickly the low-pressure system will exit the region, which will dictate the speed of the warming and drying trend.
