Roy, UT Weather

Key Messages

- Widespread precipitation returns Wednesday morning across southern Utah, with coverage expanding northward through Friday. Many areas will see precipitation accumulations between 0.5-2" through this period, with local totals in excess of 3" possible.

- The heavy rain will bring a threat of flash flooding to southern and central Utah, and there is a Slight Risk of Excessive Rainfall across southern Utah Wednesday and across southern through east-central Utah Thursday.

- A few strong to severe thunderstorms may be capable of producing gusty winds and hail across southern Utah on Wednesday and statewide on Thursday, with a 2% chance of a tornado. A Marginal Risk for severe thunderstorms is in place on Wednesday across far southern Utah, southern through west-central Utah on Thursday.

- The late week storm will also bring accumulating snowfall to the high terrain across northern and central Utah on Friday, with 2-6" possible mainly above 9000 feet. Locally higher amounts are possible in favored locations.

Discussion

The large-scale pattern this evening consists of a closed low spinning off the central California coast while Utah remains under a southerly flow ahead of it. An upper jet rounding the base of the low and punching through Arizona this evening is helping to spread tropical moisture northward. Across Utah, PWATs currently range from 0.6-0.9 inches, which is already close to the 99th percentile of climatology. Increased moisture advection will only push these values higher over the next couple of days.

As the jet arrives over Utah, increasing upper diffluence may lead to some isolated shower activity tonight, mainly over northwest Utah. As the deeper moisture arrives after 10z, expect precipitation activity to start increasing across southern Utah. This precipitation will become more widespread across southern and central Utah through the day Wednesday. Models indicate a brief decrease in precipitation Wednesday night before increasing again areawide for Thursday. Areas of moderate to heavy precipitation is expected Wednesday and Thursday, and will be aided in part by potentially strong to severe convection as suggested by hi-res models. If instability does not become inhibited too much by cloud cover, there will be plenty of shear (40-55+ kt of 0-6km shear) and low-level helicity to work with across southern Utah on Wednesday and across a significant portion of the forecast area on Thursday for a few of the stronger storms to produce strong winds, hail, and even an outside chance of a tornado. There is currently a Marginal Risk for Severe Storms across southern Utah on Wednesday and across southern through weest-central Utah on Thursday. Additionally, with the heavy rain, there is also a Slight Risk of Excessive Rainfall across southern Utah on Wednesday and across southern through east-central Utah on Thursday. Also on Thursday, a Marginal Risk for Excessive Rainfall extends through the remainder of Utah. A Flood Watch is in effect across southern through east-central Utah Wednesday through Thursday as a result. Latest NBM continues to indicate widespread 1 to greater than 2.5 inches of QPF across southern through east-central Utah Wednesday through Thursday, with 75th percentile amounts exceeding 3 inches near Brian Head and Boulder Mountain.

On Friday, the upper low is expected to lift across northern Utah while a trailing wave rotating around the low swings across the desert southwest. The track of the low across northern Utah will keep precipitation confined more to the north on Friday, while cooler air arrives into the area (H7 temperatures down to around -3C Friday through Saturday night). This will bring snow levels as low as 7000-7500 feet, with accumulating snow of around 2-6 inches forecast above around 9000 feet, mainly across the Wasatch and Uinta Mountains.

The trailing wave swinging around Arizona now looks to redevelop into a closed low which will then linger over the area. As such, there is now increasing likelihood for cool and unsettled weather to remain in place through the weekend. Thereafter, high pressure looks to build into the area early next week.

Aviation

KSLC...The SLC terminal will see VFR conditions through the overnight hours. Winds are expected to remain southerly tonight and through the day tomorrow, becoming occasionally gusty during the afternoon. There is a 30 percent chance that showers will impact the terminal during the late afternoon and early evening, with the most likely impact being gusty and erratic winds.

REST OF UTAH AND SOUTHWEST WYOMING...The airspace will see VFR conditions through the evening with increasing clouds over southern Utah overnight. Showers and thunderstorms will increase in coverage over southern Utah throughout the morning, spreading into some northern portions of the airspace during the afternoon. Any storms that develop will have the potential of producing gusty and erratic winds, lightning, and brief mountain obscurations.

Slc Watches

UT...Flood Watch from 6 AM MDT Wednesday through Thursday evening for UTZ117-123>131.

Flood Watch from Wednesday afternoon through Thursday evening for UTZ120-121.

WY...None.