Widespread precipitation is expected to bring an elevated and prolonged threat of flash flooding across southern and central Utah through Thursday, according to a National Weather Service forecast discussion. A marginal risk for severe thunderstorms is also in place across southern and western Utah for Thursday.
The National Weather Service Salt Lake City reported that a Flood Watch remains in effect through Thursday evening for specific areas including UTZ117, UTZ120, UTZ121, and UTZ123 through UTZ131. While convection is currently in a relative lull, showers and thunderstorms are expected to continue over southern Utah overnight. By early afternoon Thursday, convection is expected to become more intense over southern Utah, with moisture and instability spreading northward into northern portions of the area as the trough moves.
The storm system is expected to bring colder air to the region, resulting in Friday afternoon highs that are 5-10 degrees below seasonal normals. This cooling will also bring snow levels down to approximately 9,000 feet. Accumulating snowfall is likely in the high terrain across northern and central Utah on Friday, with 1-4 inches expected above 9,000 feet, though locally higher amounts may occur in favored locations.
The weather pattern is driven by the approach of a broad closed low toward the California coast, which has allowed deep tropical moisture to move into the forecast area. Satellite-derived precipitable water values are primarily in the 0.6 to 0.7 inch range, which is above the 90th percentile for this time of year. One earlier storm produced golf ball-sized hail, though flash flooding has been identified as the primary threat.
Drier conditions are expected to follow starting Friday as the northern piece of the trough ejects out of the area. However, the southern branch of the low may bring a few showers to at least southeast Utah from Saturday into Sunday. While weak ridging is expected to move over Utah and southwest Wyoming to start the upcoming work week, the storm track is expected to remain active due to the lack of a blocking ridge off the coast.
