textproduct: Salt Lake City

SYNOPSIS

A more noteworthy surge of moisture and atmospheric support for precipitation will track through the northern CWA overnight into Saturday, bringing a period that will favor heavy mountain snow through Saturday morning. Forcing wanes by late Saturday morning, with upslope snow continuing through early Sunday. Potential for unsettled weather continues into the middle of next week, though likelihood of another significant system is fleeting.

DISCUSSION

Our winter storm continues through the next 24-36 hours, with the period of heaviest snowfall expected in the northern and central mountains expected Friday evening through Saturday morning.

Key Messages and Impacts:

- Heavy mountain snowfall is expected across the northern and central Utah mountains from this afternoon through Saturday morning, with peak snow rates exceeding 1-2 inches per hour through this period. Snowfall rates relax by mid-morning Saturday, however, upslope showers will continue through Sunday morning.

- A majority of valley areas will see a transition of predominant precipitation type to rain as warm advection spreads over the region and raises snow levels above 6,500-7,000ft.

- High pressure noses back into the region following the storm system, with temperatures warming back to near to above-normal levels. That said, moisture will attempt to sag into northern Utah, bringing potential for mountain snow.

As of 3:20PM, the second surge of moisture is already noted across northern Utah, allowing for mountain snow and valley rain to continue after the brief dry period experienced through the day. Though little precipitation was seen through the late morning to early afternoon hours, overhead warm advection was quietly spreading across the region and allowed valley areas to warm sufficiently such that rain will become the dominant precipitation type as the moisture spreads back over the region. Based on UDOT cameras, this thought seems to be verifying for the lower elevation valleys. The exception to this will be in the Park City area where snowfall will be favored throughout a majority of the overnight moisture push. That said, as moisture begins peaking so will the overhead temperatures. Currently, NBM mean snow levels rise to upwards of 7,000-7,200ft during the early morning hours on Saturday which would allow for rain to become the prevailing precipitation type in the Park City area. With precipitation rate driven cooling, would anticipate snow levels max out around 6,800ft, giving the high elevation valleys of the Wasatch Back an opportunity to remain entirely snow. Bottom line, for this high elevation region of the Wasatch Back, anticipate a rain/ snow mix by the early morning hours.

In the mountainous terrain, this moisture surge and more ample upper dynamic support is likely to provide northern and central Utah mountains with a period of heavy snowfall with peak snow rates exceeding 1 to 2 inches per hour (greater than 0.15 to 0.2 inches SWE per hour). These snow rates are expected to be maintained through much of the overnight hours while the best dynamics move through the region, allowing a majority of the storm total snowfall to occur. As mentioned above, snow levels will rise gradually through the overnight which means that the warmer airmass will also help to favor low snow ratios. Wet, heavy snow will be the result in the mountains and will likely reduce overall snowfall observations due to compaction of the snowpack. Regardless, by the end of the peak moisture surge, anticipate a total of 1 to 2 feet of snowfall alongside upwards of 2 to 2.5 inches of SWE in the high terrain. Snowfall amounts in the mountains are expected to decrease notably south of the I-70 corridor with little impacts expected.

Colder air filters into the region through Saturday morning following the peak moisture surge, allowing for high elevation snow ratios to increase again. With moist northwesterly flow remaining in place over the region on Saturday, would anticipate upslope snow showers to continue while valley areas will tend to be shadowed by upstream terrain. If we're going to overperform with snowfall amounts during this storm, this will be the period to do such. Upslope snowfall is expected to continue into Sunday morning for the northern Utah mountains, with light snow showers potentially bleeding over into adjacent valley areas... though impacts will be quite limited.

Through the remainder of Sunday and area of high pressure will nose back into Utah and help to stabilize conditions. A moisture stream will continue to be aimed at the PacNW region during this period, allowing shortwave energy to attempt to break down the northern periphery of the ridge/ surface high pressure. As such, northern Utah mountains will maintain low probability (20-30% chance) for light snow showers continuing Sunday and Monday. There is generally high confidence that this area of high pressure will maintain dominance through the upcoming week with the caveat of the potential for shortwave energy to erode the northern periphery of the ridge. Though NBM guidance shows upwards of a 40-60% chance of precipitation in the northern mountains on Wednesday/ Thursday, ensemble cluster analysis supports only about 20-25% of solutions with a less amplified ridge on the eastern periphery (favoring a deeper/ stronger storm system). Biggest takeaway here is that light precipitation may become favored in the northern Utah mountains, but there is little support for another significant storm system through the next week.

REST OF UTAH AND SOUTHWEST WYOMING

The northern airspace will remain primarily in MVFR/IFR conditions as moisture pushes in this afternoon/evening with valley rain and mountain snow along with mountain obscuration. Snow levels will gradually rise from 5k feet to 7k feet through the evening. Winds will be light and variable across most terminals with stronger winds developing overnight across the far northeastern airspace. Southern airspace will remain dry with VFR conditions prevailing.

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SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Storm Warning until 5 AM MST Sunday for UTZ108-110>113- 117.

Winter Weather Advisory until 5 PM MST Saturday for UTZ109.

WY...Winter Weather Advisory until 5 PM MST Saturday for WYZ021.