textproduct: Salt Lake City

KEY MESSAGES

- A prolonged inversion period will set up this weekend across the northern valleys and persist through at least Wednesday. This will result in an increase in haze, nocturnal fog, and a degradation in air quality.

DISCUSSION

High pressure continues to build over the western US, with early morning satellite imagery showing a broad ridge over the western US. While not terribly amplified quite yet at the 500-mb level, this ridge is expected to strengthen over the west coast through the week, resulting in persistent subsidence and dry conditions over Utah and southwest Wyoming. Looking at the past few soundings from KSLC, we can see a stout subsidence inversion clearly developing and moving downwards through the profile with time. This trend will likely continue, with valley inversions lasting through at least Wednesday.

Despite mountaintops warming through mid-week, valley temperatures will struggle to increase under the inversion, particularly across northern areas. Valley haze will slowly develop, with the Utah Department of Air Quality forecasting Yellow/Moderate air quality conditions through at least Monday along the urban corridor.

In addition to the presence of haze, valley fog chances will increase with this prolonged subsident pattern. Scattered high clouds moving across the area overnight have limited cooling just enough with current dewpoint depressions around 2-4 degrees in the Cache and Bear River Valleys. Still, there remains a chance for patchy freezing fog in these areas before 8AM. Tonight, with clearing skies, fog chances will be a bit higher, with the highest chances in the Cache/Bear River Valleys, near Deer Creek Reservoir in Heber City, and adjacent to the Great Salt Lake in Weber and Davis counties (30-50% chance).

Luckily, there remains hope that a shortwave trough will slide southward along the eastern periphery of the ridge into Utah, potentially mixing out valleys in the Thursday-Friday timeframe. Currently, ensemble guidance is split roughly 65-35, with 65% of members favoring cooler 700-mb temperatures (which could mix out valleys) and the remainder favoring less of a cooldown and therefore lesser chances for mixing. The ridge is expected rebuild heading into the weekend, so let's hope for the majority solution.

REST OF UTAH AND SOUTHWEST WYOMING

Broken high clouds will track from north to south through the day with clearing after that. For southwest Wyoming and northern Utah, broken clouds will transition to scattered clouds by 19Z. Clear conditions are then likely by 00- 03Z. Further south, clouds will build through the morning, with broken high clouds much of the day. Clouds will decrease, scattered clouds after 00Z and clear conditions by 06-09Z. Winds will be light throughout southwest Wyoming and Utah.

SLC WATCHES/WARNINGS/ADVISORIES

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