Foggy

Freezing fog and fog flurries SLC 1/29/2026

A bit icy across northern portions of the Salt Lake Valley this morning, as low-level moisture from yesterdays storm and a trailing stable airmass have created areas of freezing fog and fog flurries. Most fog and associated flurry activity is focused across valley locations near the GSL. Roads conditions are a bit icy with a dusting of snow/ice, so nothing too significant. Fog will likely dissipate or retreat over the GSL as the day progresses. May get additional valley fog development near the GSL again Thursday night into Friday morning. 

The mechanisms responsible for the freezing fog and the attendant fog flurries are somewhat interesting - at least to me -, and don't occur all that often. Typically, snow flakes like to form in a saturated layer of the atmosphere where the temperature is less than -10 C and even more so when the temp is between -12 to -17 C - blue highlighted portion of the red temperature trace in the sounding below. This layer is called the dendritic growth zone and is needed for efficient snowflake formation. However, this morning the sounding from KSLC reveals the saturated layer did not quite have temperatures within the dendritic growth zone. So how did we get flurries to form in the fog? 

KSLC 12Z 1/29/2026 sounding with overlays

I'm not an expert in cloud microphysics, but I will attempt to provide an explanation for the flurry development in the fog.  A mix of different types of ice crystal formation in the lower level of the atmosphere were most likely responsible for the fog flurry formation. Ice crystals developed via a combination heterogenous nucleation and ice multiplication in the colder, super-cooled (< -10 C) saturated layer (highlighted in blue). These ice crystals that formed it the colder layer aloft precipitated down into the underlying 'warmer' layer (-2 to -10 C) saturated layer (highlighted in green), where the falling crystals collided with supercooled water droplets/or other ice crystals to produce larger ice crystals and small snowflakes via a combination of riming and aggregation. This was in effect a seeder-feeder type of process (image below). If not for the colder saturated layer aloft that produced falling ice crystals, the fog would have just remained freezing fog rather than also precipitating snow.

Seeder feeder mechanism

Going Forward

The punchy shortwave trough that moved across northern Utah yesterday was an interesting change up but not anything to write home about. A few brief periods of moderate snow showers impacted the Wasatch Front, with some valley locations picking up a dusting+. The higher resorts in the canyons managed to squeeze out 1-3" in accumulations, mainly thanks to enhancement from orographic lift. 

The short-term forecast doesn't look great. Ridging builds back over the western U.S. and Utah going through the end of the workweek and into the weekend. Temperatures will moderate each day and haze will likely develop at times. Highs potentially peak into the 50s by Saturday or Sunday. Models have trended on bringing a weak shortwave trough over the top of the ridge early next week. The trough looks to graze Utah, but the potential for any precipitation as of now looks very low. The good news is the energy and associated cooler temps may help keep things marginally fresh in the valleys and reduce the strength of any haze/inversion conditions.

ECMWF ENS 12Z 1/29/2026 - Left: 500 mb heights 2/5/2026; Right: 5-day 500 mb height anomalies 2/1-2/5/2026

For the long-term, other than that weak trough early week, conditions look to stabilize again by mid next workweek, with a strong ridge forming over the interior west. This could be one of the stronger ridges this winter, with model ensembles putting a ridge with 500 mb heights > 5800 m over Utah by 2/3-2/5/2026. This ridge combined with a Rex Block set-up (high pressure over low pressure) will likely keep Utah dry going through mid-ish February. If we want to rub the crystal forecasting ball hard, ensembles have the pattern shifting and the next opportunity for active weather coming mid February, but that is very much TBD...