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 near-westerly flow aloft is in place across Utah this evening as a low-amplitude trough currently moving east along the Montana/Canadian border squashes down the already low- amplitude ridge. A weak surface cold front associated with this trough is currently making its way into far northern Utah at this time. This front will continue to slowly sag farther south into northern Utah overnight before weakening and stalling just south of I-80. An area of high-based showers developed late this afternoon across west-central Utah through Utah County and into the Uinta Basin/Mountains. While a few showers will linger through late tonight aided by increasing low-level convergence, they should generally wind down over the next few hours. Some showers will redevelop across northern Utah Tuesday near and north of the stalled boundary.

Breezy conditions are expected across southern Utah Tuesday afternoon south of the stalled boundary as attention quickly turns to the next trough, which will approach Utah Tuesday afternoon/evening. Accompanied by an upper jet and associated atmospheric river which will punch into southern Utah by late Tuesday afternoon, expect precipitation to become more widespread over the area Tuesday evening. Given deep moisture associated with atmospheric rivers, there is a potential for significant precipitation across the area with this storm. The ECMWF Extreme Forecast Index shows a signal for climatologically anomalous precipitation especially along and near the spine of Utah. From Tuesday evening through Wednesday afternoon, the latest NBM has a 60-80% chance of at least 1 inch of precipitation in the northern Utah mountains. While amounts are expected to be less elsewhere, there is still a 40-55% chance of at least 0.75 inches for the rest of the mountains along with the Wasatch Front.

As the airmass trends cooler, snow levels will lower to around 7500-8000 ft by late Tuesday night into Wednesday. This will bring accumulating snow to the higher elevations, although anything significant (>6 inches) will likely be confined to areas above 9000 ft. As such, impacts due to snow are expected to be fairly limited. Otherwise, temperatures will trend closer to climatological normals by Wednesday.

A relative and brief lull in precipitation is expected Wednesday night under a transient shortwave ridge behind the departing trough and the next one upstream. This next trough is still progged to push a stronger cold front into the area, beginning across northern Utah Thursday morning and through the rest of the area Thursday afternoon and evening. Expect a potential for stronger winds both ahead of and behind this cold front. A much colder airmass will bring H7 temperatures to at least -10C across northern Utah Thursday night into Friday morning (LREF mean of -11C at SLC). This would be cold enough for snow down to the valley floors, but this would be towards the tail end of the heavier precipitation associated with the frontal band, which most deterministic models have tapering off across most areas by 06Z Friday. Still, a moist airmass and steep midlevel lapse rates will allow for favorable orographics across northern Utah mountains through at least Friday morning. Additionally, can not rule out the lake-effect potential, given that the GSL has had a chance to warm up as of late. However, it is still a bit too early to have a good handle on those smaller-scale details. Currently, we are looking at potentially significant snowfall amounts for the northern mountains (60-80% chance of at least 8 inches except greater than 90% chance in the upper Cottonwoods). Most other mountains have a less than 50% chance of even 4 inches and any valley accumulations are expected to be minor (<1 inch) at this time.

Behind the strong cold front, temperatures will cool even more with afternoon maxes on Friday expected to run 8-15 degrees below normal. Furthermore, overnight mins Friday morning and Saturday morning are expected to be near 32F or less, including most valleys except for the lower valleys of far southern Utah. This would have an impact on any early season agriculture. However, as high pressure builds in for the weekend, temperatures will then trend warmer again through early next week.

REST OF UTAH AND SOUTHWEST WYOMING

The airspace will see VFR conditions through the night with some high clouds. Isolated high based showers will continue over portions of northern Utah through the overnight hours, with a few showers capable of producing gusty and erratic wind gusts in excess of 40 mph. Showers will become more widespread by Tuesday afternoon, resulting in areas of mountain obscurations and IFR conditions over the higher terrain.

SLC WATCHES/WARNINGS/ADVISORIES

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