textproduct: Salt Lake City

KEY MESSAGES

- High pressure will bring dry, stable, and increasingly mild conditions through Wednesday. Developing inversions may limit warming in prone valleys and bring some decrease in visibility and air quality.

- An unsettled pattern returns Wednesday night onward into at least early next, bringing periods of mountain snow and low elevation rain.

- There is upwards of a 40-60% chance of a period of freezing rain to impact a portion of Utah's West Desert, Castle Country, and US-89 corridor east of Kanab early Thursday morning. Significant travel impacts will be possible.

DISCUSSION

Another day of stout valley inversions are evident across the forecast area as high temperatures "warm" into the mid- to upper-30s across the northern Utah valleys, a warming trend that is relatively slow given the warm airmass in place overhead. Additionally, a valley haze is noted across the Wasatch Front as trapped pollutants continue to accumulate under very stable conditions. This trend is expected to continue through at least the next 24 hours before our next storm system begins to move into the region. The biggest change with Wednesday is that we'll see a notable increase in high level cloud cover across much of the area. This trend is already being observed across southwest Utah.

The aforementioned shield of clouds pushing in from the south are tied to our next weather system which is expected to move into the region from late Wednesday evening through late Friday/ early Saturday. Current model guidance is supportive of sufficient moisture pushing into the southern portion of the forecast area by late Wednesday afternoon/ early Wednesday evening, with valley rain and mountain snow above ~8,500ft in elevation spreading from south to north through the evening and overnight hours. As mentioned above, valley areas have been struggling to warm as strong inversions have been established. There is increasing concern for areas of freezing rain to develop across a portion of Utah's West Desert, Castle County region, and the US-89 corridor east of Kanab as temperatures to drop well below freezing tonight, with cloud cover limiting heating the next day, then temperatures dropping back to freezing (or lower) by the time precipitation is introduced to these areas. With freezing rain, very little accumulation (0.01in or less) can cause significant impacts to travel. At this point in time, the aforementioned areas are the most likely area to see accumulations of freezing rain (50-60% chance), with upwards of a 30-40% chance of seeing a significant (0.1 inches or greater) amount of ice accumulation. Any travelers moving through this area should be aware of the potential. On the Wasatch Front, there is upwards of a 20% chance of seeing freezing rain for a brief period of time, particularly in Utah County. While a low probability event, again, it takes only a little bit of freezing rain to generate a lot of impacts. No headlines have been issued at this time as we would like to see consistency with model guidance, but the big picture potential is still there regardless. Continue to monitor forecasts.

In addition to the freezing rain potential, mountain snowfall is expected for elevations above about 8,000-8,500ft through the duration of the event, with rain expected below this elevation band. Given the generally weak forcing and warm nature of the system about to push through the region, we are not expecting any significant impacts in the mountainous terrain at this time. For the lower elevation mountains (below 8,500ft), snow accumulations are expected to range from a trace to 2 inches while the higher elevation mountains will range from 2 to 8 inches. Rain is expected for most valley areas.

As a whole, the precipitation will wane through the late morning on Friday, with the northern mountains maintaining a chance for upslope snow showers to linger through Saturday morning. A brief stabilization of conditions is expected by Saturday, however, the storm track looks to remain active shortly thereafter. As such, anticipate chances for precipitation to increase once again by Sunday as an ejecting shortwave trough pushes across the Great Basin region. The upstream longwave trough is anticipated to gradually shift inland through the first half of next week, keeping the precipitation train going alongside the introduction of cooler temperatures into the forecast area.

REST OF UTAH AND SOUTHWEST WYOMING

Light and diurnally-driven winds will persist for the valid TAF period, with VFR conditions prevailing. The one exception to this is a low (20%) chance for fog at KLGU between ~11-15z. CIGs will start to drop from southwest to northeast across the area late Wednesday evening.

SLC WATCHES/WARNINGS/ADVISORIES

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