textproduct: Salt Lake City

KEY MESSAGES

- Two storm systems will impact Utah Tuesday through Friday, though uncertainty in snow amounts is still high with each one. The first will be relatively warm, bringing valley rain and mountain snow to much of the area.

- A colder, likely stronger system will bring widespread mountain snow and even a chance for light valley snow by Friday morning, particularly across northern Utah/southwest Wyoming.

- Early season agriculture will likely be impacted by freezing temperatures and frost on Friday and Saturday mornings.

DISCUSSION

A plume of moisture can be seen on satellite imagery early this afternoon, bringing moisture into the southwestern US that will ultimately produce widespread precipitation across Utah and southwest Wyoming. Increasing mid- to high- level clouds can also be seen out the window, with a few high-based showers possible across portions of the West Desert this afternoon as a weak boundary sags across the northern third of the state.

As moisture continues to increase from the aforementioned atmospheric river, a strengthening shortwave trough will push across southern Utah late Tuesday night, with the heaviest precipitation expected Tuesday evening and overnight along and just behind a surface cold front. Forecast confidence is still low regarding snow amounts and QPF, though trends have overall increased with models trending toward better jet support and a stronger cold front. A few factors contribute to this snowfall uncertainty: snow ratio, post- frontal wind direction, and the timing of the heaviest precipitation. Lower snow ratios, caused by warmer temperatures, snow compaction, or even the presence of graupel, combined with a quicker passage of the trough would result in snow amounts verifying at the lower end. Forecast snow amounts range between 2-5" on the lower end and 4-8" on the higher end across higher terrain. The Upper Cottonwoods in particular have higher forecast amounts and uncertainty, with low and high amounts around 5-9" and 10-15" respectively. There is even a low chance of even higher amounts if the flow direction is just right and the system moves more slowly through the area.

Wednesday will feature a brief lull, though some mountainous areas may see light snowfall continuing through the day and overnight ahead of the next system.

The next storm system will be colder, though will also have a similar degree of uncertainty with respect to snow amounts. Moisture will be more limited, though with much cooler air moving in behind the cold front, expect higher snow ratios and snow falling into the mid to lower elevations. A period of heavier precipitation is possible along and just behind the front, though drier air will quickly follow, perhaps limiting precipitation on Friday to just the mountains with orographic lift. This will also likely limit valley snow chances along the Wasatch Front, especially considering antecedent warm conditions. Currently, the NBM suggests a 20% chance of reaching 1 inch of snow here at KSLC, though this could be a little bit high considering the warm ground.

Most valleys (all but Lower Washington County and Lake Powell) are likely to see near to below freezing temperatures both Friday and Saturday mornings behind this system, posing a risk to early season agriculture. However, this will not last long as temperatures are likely to rebound later in the weekend as high pressure returns to the area.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will prevail through the TAF period across Utah and southwest Wyoming under increasingly cloudy skies. Breezy west to southwest winds are expected to subside after sunset, however, southwest Wyoming and the Cedar City area may continue to see gusty west to southwest winds through the overnight period. High-based rain showers will build into the northern area around 12Z, introducing local mountain obscuration as CIGs drop to around 7kft or less.

SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...Red Flag Warning until 9 PM MDT this evening for WYZ277.