textproduct: Salt Lake City

KEY MESSAGES

- A cool spring system will continue to move through the area and bring periods of valley rain and accumulating mountain snow through Tuesday. The highest chance of impactful accumulations is noted in the southern and central mountains, with the highest rates expected Sunday and Monday night.

- A colder system is expected to impact the area roughly Thursday into early Saturday. It is anticipated to bring additional mountain snow accumulations, and potential for low elevation snow following passage of an associated cold front.

- There is approximately a 50-70% chance of freezing temperatures along Utah's urban corridor Thursday night and Friday night, and a greater than 80% chance of freezing temperatures elsewhere (excluding lower Washington County/lower Zion).

DISCUSSION

Evening satellite mid level water vapor loop shows the core of a broad Pacific trough shifting eastward into Nevada. Surface observations show an associated cold frontal boundary continuing to gradually advance southeastward through Utah, with scattered showers noted both ahead and behind the front. Gusty southwesterly winds ahead of the front will continue to decrease, and further taper off and shift northwesterly in the hours following frontal passage.

In terms of the forecast with this system, things largely remain on track. The cooler air will result in snow levels gradually dropping down to around 6000-6500 feet by Monday morning, and bring below normal temperatures back into the region. Periods of valley rain and mountain snow showers will persist through Tuesday as the trough tracks east, with timing and location of higher precipitation rates associated with when/where exactly shortwave impulses embedded within the broader (and somewhat messy) circulation of the trough pivot. Models have continued trending to a slightly more southerly track, with forcing and water/snow amounts accordingly favoring southern to central Utah. Given the slow movement of the trough, further locally higher amounts will be possible in any deformation axis near the systems core, though pinpointing where such an axis sets up is a bit nebulous.

Currently, favored timing for these higher rate periods in southern to central Utah seem to be Sunday night, and especially Monday night into Tuesday morning. For northern mountains, latest forecast now only carries a broad 2-6" of snow. Even for favored areas such as the Upper Cottonwoods the probability of exceeding 6" has dropped dramatically to around 20-30%, though suspect any more convectively enhanced showers during the day could result in briefly higher rates. Across the southern and central mountains, forecast totals have trended upward, with now a general 3-8" of snow accumulation. These amounts are locally higher especially in areas of the Tushars, Brian Head area mountains, and to a lesser extent the Manti-La Sal Skyline. In these locations, there is around a 40-60% chance of accumulations in excess of 12", especially in the Tushars. While longer duration and sporadic in nature, the potential for higher rate periods along with the overall trends seems worthy of Winter Weather Advisory headlines. In terms of impacts, this is furthered given the later seasonal aspect to the system, and the infrequency of snow across the southern half of Utah this season. Given the snow levels, anticipate most travel impacts to largely be confined to higher mountain and seasonal routes that are open (especially above 7500 feet or so), and especially during those higher rate periods.

After a brief lull, models continue to remain in good agreement in an even colder system sweeping through the region roughly in the Thursday to Saturday time frame. Timing currently favors late Thursday for the initial frontal passage with this system. To give an idea of just how cold the associated airmass is progged, 700 mb temps ahead of the front are forecast around 1C to 3C, falling quickly to around -8C to -12C following frontal passage. In turn, the pressure gradient along the baroclinic zone could be quite sharp, bringing a gusty frontal passage along with a broader forced band of precip. Within the broader post-frontal cyclonic flow, showery precipitation would likely continue into late Friday and taper off overnight into the weekend. As currently forecast, not only would this system bring another round of accumulating mountain snow, but also favorable odds for snow levels below valley floors, and non-zero chances of light valley snow accumulations. In fact, current NBM guidance carries a greater than 70% chance for 0.1" or more snow for northern valleys, and even around a 30-50% chance of 1" or more. Granted, the warm ground temperatures would likely do a number on melting anything off that doesn't come in with heavy rates.

Aside from the snow potential, the very cold temperatures behind the front would pose a threat to early season agriculture with freezing potential. As of now, there is approximately a 50-70% chance of freezing temperatures along Utah's urban corridor Thursday night and Friday night, and a greater than 80% chance of freezing temperatures elsewhere (excluding lower Washington County/lower Zion).

REST OF UTAH AND SOUTHWEST WYOMING

Southwesterly winds will continue to weaken into the evening, particularly across the northern third of UT and SW-WY where a diffuse cold front has already pushed through. Weak showers will likely continue across mostly western and northern UT through the evening, gradually diminishing between 08-11z. With these showers, there is a 40-50% chance of MVFR VIS/CIGs as well as periods of variable winds. Weak, isolated showers may even linger into the early morning across the southern third of UT. Scattered showers and thunderstorms will redevelop Monday afternoon, largely south of I-80.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory until 3 PM MDT Tuesday for UTZ117-125.

WY...None.