textproduct: Salt Lake City

KEY MESSAGES

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

- Widespread valley rain is expected with the heaviest amounts north of I-70 through Monday evening.

- Additional freezes may impact the Sanpete and Sevier Valleys, western Uinta Basin, and southwest Utah Tuesday morning.

DISCUSSION

Visible satellite shows clouds increasing from the closed low that is moving onshore the California coast. This is sparking some light showers to our southwest that will soon transition to widespread precipitation over the Great Basin as the low tracks further inland and starts to interact with a broad upper level low spinning across southern Saskatchewan.

As the low approaches, moisture will start to increase with showers developing along southern and central Utah, primarily over the mountains. Model sounds show a stubborn dry surface layer that could lead to some momentum transfer of gusty winds aloft towards the surface. Even still, winds aloft are only around 25-30kts so any gusts should generally remain below advisory criteria. Impressive PWATs will gradually move into the region, maximizing by Sunday morning in the range of 0.55-0.65" which could verify among the 95th-99th percentile for this time of year. So there will be plenty of moisture for the approaching low to work with.

Valley rain and mountain snow really starts to blossom across the entire area after midnight tonight. Precipitation quickly moves through southern Utah with a bulk of the activity dwindling by sunrise across the south. It will be a different story across central and northern Utah/SW Wyoming as the low starts to pivot across the north with a deformation band forming. Most guidance have this band developing from southwest over Dugway and stretching to the northeast across the GSL and Wasatch. Areas that are underneath this band will likely see the great QPF totals. Since there isn't a significantly cooler airmass accompanying the low (H7 temps go from 0C to -5C by Monday morning) snow levels will remain well above valley floors. They will start around 7500-8000 feet before falling to ~6500 feet by Monday morning where they will stay for the remainder of the storm.

There won't be too much of a break in precipitation before a trough (associated with the parent low across southern Canada) moves into the area from the northwest on Monday. Given that a bulk of the moisture will still be in place there will be another blossoming of precipitation across central and northern Utah (and scraping southern Utah) during the day on Monday.

All in all, QPF totals will range from 0.5-1.25 inches (25th-75th percentile) across central and northern valleys and 1.00-2.25 inches for most mountain locations. Valleys across southern Utah will see about a third to a quarter amount of these totals given the shorter duration of precipitation. There is the potential for some valleys that are favored underneath the heaviest portion of the deformation band to verify closer to the 90th-95th percentile which would result in QPF totals close to 2 inches. This would translate to near 2.5 inches of QPF across the mountains. As a result, mountain locations above 8500 feet will see between 6 to 12 inches of snow with up to 18+ inches across the Tushars and upper Cottonwoods. These totals are about 72 hour totals, so compaction, solar loading, and melting due to temperatures near or even above freezing will make it hard for these numbers to be fully realized at any one point. Freezing conditions will return for Tuesday morning for various valley locations across near the Idaho border and across eastern and central Utah from Cedar City up through the western Uinta Basin.

More shortwaves will scrape northern Utah Wednesday and Thursday bringing diurnal showers for areas further north, but totals will be substantially less than the upcoming storm. A warming trend will commence through the week as the coldest air aloft shifts east. A ridge does start to build into the area by the weekend with much greater warming.

REST OF UTAH AND SOUTHWEST WYOMING

Clouds will increase this afternoon as moisture spreads into the area. Winds at the northern terminals should remain on the light side until showers approach the region after midnight, though afternoon convective development could create some vicinity microburst winds over the higher terrain. Rain is expected at all terminals except for snow at EVW. Periods of MVFR are likely, with brief IFR possible during the heaviest precipitation. Southern terminals can expect gusty winds through the afternoon and evening, becoming erratic with showers. VFR cigs are possible at CDC, with a 10 percent chance of reduced visibility there as well.

SLC WATCHES/WARNINGS/ADVISORIES

UT...None. WY...None.