textproduct: Salt Lake City

KEY MESSAGES

- Freezes will impact central through southwest Utah valleys and eastern Box Elder County tonight. Freezes are expected again Friday night in the Sanpete Valley and eastern Box Elder County.

- An active pattern will bring the threat of 6+ inches of snow to the higher terrain of Utah Saturday night into Monday.

- Additional freezes may impact the Sanpete and Sevier Valleys and southwest Utah Sunday night and Monday night.

DISCUSSION

A drier northwesterly flow aloft is in place over Utah this evening. Clouds from earlier today have mostly cleared out, and with a cool airmass in place, excellent radiative cooling will bring another round of freezing temperatures to the central through southwest Utah valleys, along with eastern Box Elder County.

A shortwave disturbance rotating around a nearly stationary closed low over southern Saskatchewan will dive south towards the ID/UT border before turning east on Friday. With the upper support remaining north of the forecast area, very little if any precipitation will make it into Utah. However, a shallow cold front will push into northern Utah Friday afternoon and evening. As clouds thin out behind it, freezing temperatures look like a good possibility again across eastern Box Elder County while central/southern valleys trend a bit warmer, although the Sanpete Valley will likely continue to see freezing temperatures.

On Saturday, a slightly warmer southwesterly flow aloft will overspread the area ahead of a shortwave trough moving into the central CA coast. Isolated convection may develop over the spine of Utah Saturday afternoon, otherwise precipitation will wait until Saturday night to fill in. An anomalous moisture plume associated with this trough is expected to bring widespread precipitation to the forecast area Saturday night through Sunday. Behind it, another shortwave trough rotating around the Saskatchewan low will carve south along the West Coast before crossing the Great Basin on Monday. This trough is also expected to bring fairly widespread precipitation to the area for Monday, with very little break between the two system.

While some details still remain to be worked out, the evolution of the large-scale pattern seems to be coming together through early next week. Still, there remains quite a bit of variability in the QPF, although the largest precipitation amounts are still expected to be focused over the northern half of Utah. The 25th percentile of precipitation amounts range from 0.3-0.6 inches in the northern valleys and 0.4 to 1.25 inches across the northern mountains, while the 75th percentile amounts are double that. However, with the airmass being a bit milder, snow levels will remain between 7500-8000 ft with the first storm, falling to between 6500-7000 ft with the second. The high snow levels, combined with snow densities that should generally be higher than 10%, should help moderate snow accumulations a bit. Most mountains are currently expected to see around 6-10 inches of snow along the higher ridgelines, with higher amounts in the upper Cottonwoods, although they are likely very overdone there in the NBM (currently 18-33 inches for the 25th-75th percentile range).

Beyond Monday, model spread increases. However, upstream energy will persist, allowing for the potential for unsettled weather to continue through the end of the week.

REST OF UTAH AND SOUTHWEST WYOMING

The airspace will see VFR conditions through the overnight hours with some scattered clouds, most numerous near the Utah/Idaho border. Winds will be generally light and terrain driven across the area tonight.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Freeze Warning until 9 AM MDT Friday for UTZ103-114>116-118>120- 122.

Freeze Warning from 10 PM Friday to 9 AM MDT Saturday for UTZ103- 118.

WY...None.