textproduct: Salt Lake City

KEY MESSAGES

- Freezing conditions will occur across central and southern valley locations tonight into Wednesday morning.

- A strong cold front will bring accumulating valley snow to northern Utah Thursday afternoon into Thursday night, with snow showers continuing into Friday morning. Snow may impact both the Thursday evening and Friday morning commutes along the Wasatch Front.

- Very cold temperatures in the teens to upper 20s will occur across most valleys of Utah Thursday night into Friday morning and each subsequent overnight period through Sunday morning. Temperatures this cold can freeze sprinkler systems and cause widespread fruit orchard blossom death. Consider re-winterizing sprinkler systems to avoid property damage.

DISCUSSION

Late this evening, showers have largely diminished across the area, with only isolated areas of low-level clouds still lingering as mid-level heights gradually rise. Clearing skies overnight will allow temperatures to drop down to below freezing again across many valleys in central/southern Utah, indicated by the ongoing Freeze Warnings. However, expect a brief respite after tonight as warmer, southwesterly flow develops through the day on Wednesday under shortwave ridging. Isolated showers and thunderstorms may still develop during the afternoon, mainly across northern Utah.

The warmth will not last. A potent trough will quickly dive southward through the PacNW Wednesday night bringing a strong cold front through Utah and southwest Wyoming between mid Thursday morning and late Thursday night. This system, while dynamically strong, moves through fairly quickly and has only modest moisture, likely limiting snow amounts even though snow levels are expected to dip below valley floors. The main threat will be widespread freezing temperatures, which could impact crops, gardens, and unprotected sprinkler systems.

This cold front is likely to enter northwestern Utah by late Thursday morning, moving through the Wasatch Front between 3-6PM and reaching southeastern Utah after 3AM or so. Along and just behind this front, expect a stark transition to northwesterly winds and a period of heavier snow, particularly across northern Utah. In the valleys, while rain will quickly transition to snow, warm antecedent surface temperatures could cause a delay in any accumulating snow...though we will still be watching snow chances in time for the Thursday evening commute. Another area worth watching will be the I-15 corridor between Nephi and Cedar City, as this area tends to do well in northwest flow. In the mountains, could see snowfall rates in excess of 1"/hr, particularly as snow ratios rise behind the front and especially in areas favored in northwest flow such as the Upper Cottonwoods.

Forecast snow amounts are highest across northern Utah where the best moisture and dynamics are maximized. The northern mountains, for example, can expect around 6-12 inches of snow, though models have trended slightly lower in recent runs. Valley snow amounts have also trended a bit lower, with 1-2 inches likely across northern valleys (2-5 inches in the Wasatch Back).

One area of uncertainty that could result in underforecast snow amounts is the potential for lake-effect snow early Friday morning downwind of the Great Salt Lake. The environment looks mostly favorable, with steep low-level lapse rates and a very cold air mass over a warm lake. The main question is how much moisture will linger in the low levels, and if it will be enough to generate lake-effect showers. Northwest to west-northwesterly flow looks to lighten up more by Friday morning, which would favor a more cellular mode, though the lake-land temperature difference will be pretty substantive by that point, which could favor a heavier band setting up. Either way, it'll be interesting to see how showers evolve...if moisture hangs on long enough.

Widespread freezing temperatures are expected by Friday morning across all of Utah and southwest Wyoming except Lower Washington County, lower elevations of Zion NP, and areas near Lake Powell. Some areas could even see low temperatures below freezing through the weekend before temperatures rebound enough.

Although quieter conditions are expected for the weekend, model guidance suggests more active weather returning. The main question is when this happens; some models suggests a closed low moves through the area by late Tuesday, and others suggest high pressure sticks around for a couple more days.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will continue tonight through Wednesday. Mostly clear skies can be expected overnight, with CIGS between 14-17kft MSL developing across northern through west-central Utah along with southwest Wyoming Wednesday afternoon. Meanwhile, southern Utah will see scattered high clouds for Wednesday. Otherwise, increasing southwesterly winds can be expected across most terminals Wednesday afternoon.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Freeze Watch from Thursday evening through Friday morning for UTZ102>106-114>116-118>122-129.

Freeze Warning until 9 AM MDT Wednesday for UTZ114>116-118>122- 130.

WY...None.