textproduct: Salt Lake City

SYNOPSIS

A significant winter storm will impact northern and central Utah late Thursday into Sunday morning. The potential for unsettled weather continues through the middle of next week.

DISCUSSION

A significant winter storm will impact northern Utah, central Utah, and southwest Wyoming from Friday through Sunday.

Key Messages and Impacts:

- Mountain snow is expected across the northern and central Utah mountains from Thursday evening through Sunday morning, with the heaviest period of snowfall expected Friday night into Saturday morning. Storm total snow accumulations are expected to range from 1 to 3 feet of heavy, wet snow.

- Valley snow will be dependent on elevation and cold pool strength. Accumulations will most likely range from 1-2 inches in the Cache Valley and eastern Box Elder County, 3-8 inches in the Ogden Valley, 7-16 inches in Park City area, trace to 1 inch in the Salt Lake Valley, 1-3 inches near Ogden, and 1-3 inches in the Heber Valley. There is still a 25% chance that snow totals exceed these amounts.

- Snowfall will linger in the mountainous terrain of northern Utah through late Sunday morning before tapering off into early next week. Another system may graze Utah and southwest Wyoming early to mid-week next week, bringing another round of mountain snow.

Satellite imagery this afternoon is already showing a broad veil of cloud cover pushing into northern Utah and southwest Wyoming as moisture begins spreading over the area. This moisture is tied to an incoming inland-penetrating atmospheric river that will bring significant impacts across the northern half of the CWA from late this evening through Sunday morning. While there still exists some uncertainty with precipitation type in lower elevation valley areas of northern Utah, accumulating snowfall is expected early Friday morning before a transition to rainfall arrives as warmer air spreads over the region.

Precipitation (already noted on northern Utah radar) will gradually fill into the northern Utah mountains late this evening and through the overnight period, eventually falling into valley areas early Friday morning. Before any cold pools erode, light snowfall is anticipated for valley areas from the Utah/Idaho border southward through the Wasatch Front. As the overhead airmass warms gradually through Friday morning, snow levels for the lower elevation (and less sheltered) valleys are expected to rise above valley floors, allowing for a transition to rain. Before the transition to rain, snow totals are likely (75% chance) to amount to less than 1 inch in the Salt Lake Valley and Utah Valley, and upwards of 1 to 2 inches in the Ogden area.

For the more sheltered lower elevation valleys (i.e. Cache Valley, eastern Box Elder Co., and Ogden Valley) the snow forecast becomes more complex and a bit more uncertain as the strength of the cold pools will ultimately dictate how much snow is seen in these areas. At the very least, the thought is that valley cold pools will be maintained for longer than the Wasatch Front, allowing for a longer period of snowfall... and thus greater snow accumulation potential. For the Cache, current model guidance supports anywhere from 1 to 3 inches of snow at the valley floor, with upwards of 4 to 6 inches for the higher elevation portions of the valley by mid-morning Friday. Similar amounts can be anticipated for eastern Box Elder Co., with guidance in the Ogden Valley supporting anywhere from 5 to 10 inches (high end amounts favored if the cold pool holds strong).

By at least Friday afternoon snow levels are likely to rise above most valley areas (outside of the Park City area), forcing rain on top of the resulting snowpack. By Friday evening, upper level support for heavier precipitation finally begins to spread across the region, marking the beginning of the heaviest mountain snowfall and valley rain. This period favoring heavy snow is largely expected between 9PM Friday and 9AM Saturday, translating from north to south through the overnight period. Behind the heaviest precipitation, colder air will fill in the wake, allowing for snow levels to drop once again. That said, there is unlikely to be sufficient moisture and forcing in place to see appreciable snowfall in lower elevation valleys in the wake of the heaviest precipitation period... but a few snow showers may still be seen on Saturday morning.

Upslope snowfall lingers across northern and central Utah through Saturday, gradually tapering off through the overnight hours into Sunday. When all is said and done, snowfall amounts in the mountainous terrain across northern and central Utah will range from 1 to 3 feet, with the higher end of the forecast falling in the northern Bear River Mountains and the central Wasatch.

Conditions stabilize temporarily on Sunday in the wake of the atmospheric river, however, we'll find ourselves on the eastern periphery of an upstream ridge with active weather continuing in the PacNW region. As such, there is still a chance (15-25%) that the northern Utah mountains do not stop seeing light snow showers until after our next potential storm system slated for Tuesday/ Wednesday. Given the current guidance and the strength of the aforementioned ridge, it seems unlikely that this Tuesday/ Wednesday system will bring another round of significant mountain snow. More to come on this system in the coming days.

REST OF UTAH AND SOUTHWEST WYOMING

Moisture will increase from the NW this evening, with snow developing across northern Utah valleys from late this evening through the overnight hours, with periods of snow continuing through the morning before mixing with or changing to rain Friday afternoon. Exception will be across SW Wyoming where all snow (>90% chance for all snow) is expected. Two scenarios emerge for Cache Valley and Wasatch Back, as probabilities for rain vs. snow are nearly equal by Friday evening. Better than a 50% chance exists for valley terminals to see MVFR flight categories develop between 04Z-08Z overnight, with ~25% chance for IFR. Mountain obscuration will develop across the northern and central mountains.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory from 11 PM this evening to 11 AM MST Friday for UTZ103-107.

Winter Storm Warning from 11 PM this evening to 5 AM MST Sunday for UTZ108-112-113-117.

Winter Weather Advisory from 5 PM Friday to 5 PM MST Saturday for UTZ109.

Winter Storm Warning from 8 PM this evening to 5 AM MST Sunday for UTZ110-111.

WY...Winter Weather Advisory from 5 PM Friday to 5 PM MST Saturday for WYZ021.