textproduct: Salt Lake City

KEY MESSAGES

- Two storm systems will impact Utah Tuesday through Friday. The first will be relatively warm, bringing valley rain and high elevation mountain snow to much of the area. The second will be much colder, allowing for snowfall to lower elevations in the mountains and a chance for minor accumulations in the northern area valleys.

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

DISCUSSION

For the first time in a while, the eastern Great Basin area will experience a period of active weather that will introduce wetter, cooler weather throughout the week. Two storm systems will push through Utah from now through Friday, with each bringing a shot of moisture and progressively colder temperatures. Already, moisture is streaming into the region overhead as an inland penetrating atmospheric river moves into the southwest. Radar returns are already noted areawide across Utah and southwest Wyoming, however, surface-based observations reveal a significant amount of dry air at the surface. As such, little to no precipitation has been observed outside of higher elevation sites.

As we head through the remainder of today, and especially the overnight hours, storm dynamics will intensify as the upper level trough progresses eastward and introduces a cold frontal boundary into the region. The cold front will be the main focus for heavier valley rain and mountain snow, and will shift the focus of heavy precipitation from north to south through the overnight hours. Given the very warm antecedent temperatures, snow levels will start out at around 9,000ft. With the introduction of the cold front, snow levels will gradually drop through the overnight hours to around 7,500ft in northern Utah, 8,000ft in central Utah, and 8,500ft in southern Utah. As such, any accumulation of snowfall will be limited to elevations above these elevation bands. For the valleys, moderate rainfall, with periods of heavier rain, can be expected throughout the evening and overnight hours. Total rainfall amounts in the valleys (especially those along and west of the I-15 corridor) will range from 0.25-0.4 inches on the low end to upwards of 0.6-1 inch on the higher end. Locally on the Wasatch Front, even higher rainfall totals will be possible as lake induced instability will help to maintain post-frontal rain showers through Wednesday morning. Total amounts in this region may see upwards of 1.1-1.4 inches (25% chance of greater amounts).

A majority of the precipitation from this first system will wrap up by late Wednesday morning, however, lingering instability and moisture will help to maintain at least isolated showers across the region through Wednesday afternoon. A brief lull in showers is anticipated Wednesday night before moisture begins increasing overhead once again through the early morning hours on Thursday as our next storm system begins pushing into Utah.

This trailing storm system will be much colder than the first, allowing for snow levels to drop to valley floors by the time the associated cold frontal boundary makes its way through the area. That said, models are becoming more consistent with holding the deeper moisture availability to the northern half of Utah and southwest Wyoming, meaning that a majority of the precipitation associated with this second storm will be found across the northern half of the CWA. As such, the concern for winter-related impacts will exist primarily across northern Utah and southwest Wyoming. With antecedent temperatures expected to be much warmer than the previous storm, snow levels will be starting around 7,500-8,000ft, and will drop down to valley floors as the more robust cold front pushes through the region from Thursday afternoon through Friday morning. While overall snow-water equivalent numbers will be similar, if not lower, than the first system, colder temperatures will favor higher snow ratios which will allow for similar snow totals in the northern mountains... just lower density. Additionally, with the lower snow levels, the extent of snow related impacts in the mountainous terrain will be more widespread. Current forecast snow amounts (25th to 75th percentile) for the northern Utah mountains will range from 4-8 inches, with locally up to 12 inches in the northern Bear Rivers and western Uintas, and upwards of 18-20 inches in the upper Cottonwood Canyons. Depending on moisture availability after the cold frontal passage, minor snow accumulations in the northern Utah/ southwest Wyoming valleys will also be possible on Friday morning. Current model guidance supports upwards of a half inch of snow on the central Wasatch Front (with up to 1 to 3 inches on the east benches).

As we're left with colder temperatures in the wake of this cold front, freezing temperatures are expected across a majority of Utah (exception of lower elevation valleys in southern Utah) and southwest Wyoming on Friday and Saturday morning. Any early season agricultural efforts are likely to be impacted from this cold. The good news is that this cold does not last long as warm high pressure is expected to reestablish over the region as we head through the weekend and into next week.

REST OF UTAH AND SOUTHWEST WYOMING

Gusty southwest winds will remain in place across southern Utah with gusts to around 35-40 knots. Localized areas of blowing dust cannot be ruled out in that area. Precipitation will become more widespread across the airspace overnight tonight with most areas seeing steady precipitation with MVFR restrictions especially between midnight tonight and 6am Wednesday. Precipitation trends showery and dissipates into the day on Wednesday with gradual improvement to VFR conditions.

SLC WATCHES/WARNINGS/ADVISORIES

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