A deep-layer cyclone is expected to transport significant tropical moisture into the Southwest, bringing heavy rain and thunderstorms to portions of Utah and the Four Corners region from Wednesday, October 21, through Friday, October 23, 2026. The National Weather Service has identified a risk of excessive rainfall and severe thunderstorms during this period, driven by an approaching upper-level trough.
Rainfall Forecast for Southern Utah
According to the National Weather Service, the weather pattern will bring varied conditions across different parts of the region. In Saint George, Utah, Wednesday, October 21, is forecast to have a 100 percent chance of precipitation, with showers and possible thunderstorms and a high near 77 degrees Fahrenheit. Rainfall amounts are expected to reach between a quarter and half an inch, though higher amounts are possible during thunderstorms.
Forecasts for Zion National Park and Zion Canyon indicate a similar pattern for Wednesday, October 21, with a 100 percent chance of precipitation and a high near 76 degrees Fahrenheit. The National Weather Service reports that rainfall amounts between a quarter and half an inch are possible, with a breeze from the east between 15 and 20 mph that decreases to 8 to 13 mph in the afternoon.
By Thursday, October 22, the likelihood of precipitation remains high in both locations. In Saint George, the chance of precipitation is 100 percent with a high near 73 degrees Fahrenheit. In Zion National Park, the chance of precipitation is also 100 percent with a high near 74 degrees Fahrenheit. Both areas may experience thunderstorms during this period.
Severe Thunderstorm Risks
The Storm Prediction Center has identified an enhanced risk of severe thunderstorms for portions of Arizona and the nearby Four Corners area on Wednesday, October 21. This scenario is described as climatologically rare and a concerning, well-above-typical risk that could include large hail, damaging winds, and tornadoes.
Forecasters noted that the severe risk could peak during the afternoon and evening of Wednesday, October 21, but may persist through the late-night hours of Wednesday night into early Thursday, October 22, particularly in central and northern Arizona. Localized severe risks may also exist along the coast of central and southern California due to an approaching upper low.
Excessive Rainfall Concerns
The National Weather Service's Weather Prediction Center has issued a slight risk of excessive rainfall over portions of the Southwest and the Four Corners region for Wednesday, October 21, and Wednesday night. This risk extends into Thursday, October 22, and Thursday night.
On Wednesday, October 21, a deep layer cyclone moving toward Point Conception is expected to scoop up moisture from the tropics and fling it into the Southwest. This process is expected to create a broadening zone of Integrated Vapor Transport between 300 and 600 kg/ms.
Forecast models suggest that hourly rain amounts could reach 2.5 inches in scattered spots across parts of Arizona, New Mexico, and the Four Corners due to potential cell training or backbuilding. The National Weather Service warned that urban areas, burn scars, slot/box canyons, and dry washes or arroyos would be the primary areas of concern for heavy rainfall impacts.
Atmospheric Moisture and Instability
The atmospheric conditions driving this weather include high values of precipitable water and significant instability. The National Weather Service reports that precipitable water values could rise into a range of 1 to 1.5 inches, which is considered very high by October standards.
In some areas, moisture levels are expected to be 5 to 6 plus standard deviations above normal. On Thursday, October 22, the Risk of excessive rainfall remains a concern as a deep mid/upper level low and an amplified upper trough move from California into the Great Basin. The National Weather Service noted that the degree of deep-layer instability may support significant local impacts, with hourly rain amounts of 2.5 inches remaining possible.
Weekend Outlook
Weather conditions are expected to stabilize toward the end of the week. For Saint George, the forecast predicts mostly sunny skies with a high near 65 degrees Fahrenheit on Friday, October 24, followed by a sunny Saturday, October 25, with a high near 67 degrees Fahrenheit.
In Zion National Park, the chance of rain decreases to 30 percent on Friday, October 24, with mostly sunny skies and a high near 63 degrees Fahrenheit. Both Saint George and Zion National Park are forecast to have sunny conditions through the following Monday, October 27.
