textproduct: Salt Lake City

KEY MESSAGES

- Precipitation becomes more widespread overnight with snow levels dropping to ~6500 feet behind a cold front that arrives Saturday morning, bringing a line of heavier precipitation.

- Accumulating snow is expected in all mountain areas, especially above 8000 feet, and a Winter Weather Advisory is in effect across the southern mountains.

- Two colder storms arrive next week with the potential for some valley snowfall.

DISCUSSION

A negatively-tilted trough is making its way across the western CONUS this evening. This trough is the result of phasing between a southern stream system ejecting across the desert southwest and a larger system over the PacNW coast. Southerly flow ahead of the trough axis (which currently extends from the Washington coast through western Arizona) remains in place over Utah this evening, which has drawn moisture northward into the forecast area. Showers have already developed, and will continue to increase in coverage overnight. These showers occurring in the warm sector will maintain snow levels mainly above 8 kft through much of the night.

A cold front is expected to move into western Utah before 12z and reach the I-15 corridor between 15-17z. Widespread precipitation near the cold front is then expected to quickly decrease behind it, clearing out in many valleys through the late morning and early afternoon timeframe. The exception will be the mountains and immediate upslope areas where a brief period of favorable orographics will maintain precipitation, especially along northwest aspects. Additionally, some enhancement off the GSL may allow additional showers along the central Wasatch Front and adjacent mountains into the afternoon. Snow levels will quickly lower with the passage of the cold front, with H7 temperatures falling to -4 to -5C towards the end of the precipitation event. This would suggest snow levels down to 6.5-7 kft, although the greatest (and any real impactful) accumulation can be expected above 8-9 kft. Most valleys are expected to see between 0.25-0.7 inches of precipitation with this storm, with between 0.4 to 1.25 inches in the mountains. Locally higher amounts are possible especially near Brian Head and in the upper Cottonwoods. Snow amounts are generally expected to be in the 4-8 inch range (especially above 8-9 kft) with higher amounts in the upper Cottonwoods and near Brian Head.

An upper ridge shifting into the area Saturday night through Sunday will bring a period of drier and stable conditions. The ridge will shift east for Monday, bringing increased southerly flow ahead of the next approaching storm system. This progressive pattern will keep any strong inversions at bay.

The next storm looks to arrive over Utah late Monday night or Tuesday, impacting the area into Wednesday morning. Latest model trends suggest another quick-hitting progressive trough which will bring another round of widespread precipitation to the area. However, this storm looks to be associated with a somewhat cooler airmass. LREF means of H7 temperatures for portions of northern Utah dip as low as -8C, which suggest snow levels down to at least 5 kft.

As this trough exits the area, it will be followed quickly by yet another storm system. While cluster analysis of global ensembles show high confidence in a storm for the second half of next week, there remain some differences regarding its timing and evolution. This storm may arrive as early as Wednesday night but may hold off until later Thursday. Additionally, some members are suggesting that this will end up being another progressive trough while others maintain a closed low solution which would bring an extended period of precipitation to the area. Latest cluster analysis shows an approximately 55%/45% split, favoring the closed low solution slightly.

AVIATION

KSLC...Decreasing CIGS are expected overnight as rain begins to overspread the airspace. Rain showers are expected to impact the terminal after 10z, with potential to create MVFR CIGS/VIS at times before showers become more spotty after 18z. In addition to CIG/VIS reductions, expect terrain obscuration throughout the day Saturday. Southerly winds prevail at the terminal until a cold front brings a switch to northwesterly winds after 18z.

REST OF UTAH AND SOUTHWEST WYOMING...Widespread rain showers will continue spreading northward overnight, resulting in decreasing CIGS across the entire region. While VFR conditions prevail overall for most terminals, there is a 30-50% chance for MVFR CIGS/VIS to develop at times under heavier rainfall. At higher elevation terminals such as KEVW, MVFR and potentially brief IFR conditions are likely as snow mixes in with rain. Winds remain southerly across the region overnight into Saturday morning, before a cold front pushes through the region, switching winds to prevailing northerly late Saturday morning into the early afternoon.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory until 11 AM MST Saturday for UTZ125.

WY...None.