Some Records

A bit calmer and cooler today than 24 hours ago. The storm that rolled through yesterday morning through the afternoon was punchy and quick, but still managed to throw out some significant and noteworthy weather numbers. Strong wind gusts 70+ mph were recorded at many sites across northern Utah as the main energy/front passed over early afternoon. Top of Snowbasin reported a gust of 94 mph and a gust of 77 mph was observed at the Alta Guard House. 

The high winds aided in vigorous mixing and possibly some down slope warming off the mountains, which produced record high temperatures at many locations across the Wasatch Front for the date. 

If we look at soundings from KSLC from the morning and afternoon of 12/17, we can identify the valley was inverted in the morning, with cooler air pooled near the valley surface and warmer air overlying. The late afternoon sounding reveals the temperature inversion and cooler air in the valley had been eroded away in the afternoon by the strong winds. Note the afternoon KSLC sounding was observed well after the record high temps (67 F ~12:50 PM), but the sounding still exhibits how the temperature profile evolved with the storm.

So how did the winds create abnormally warm temps? The winds mixed warmer air from above the valley surface down to the ground. As the air was forced towards the surface, it compressed and warmed at the adiabatic lapse rate (9.8C/km). For example, when the 10C air at 800 mb (~1 km AGL) was mixed down to the valley floor it had the potential to warm to 20C (68F). This is how we observed record temperatures during the early afternoon hours from the storm yesterday. 

Unfortunately, no records or even significant numbers related to snowfall were observed. Only a few inches of wet snow/graupel were reported at Alta. All said and done, Alta observed a total snowfall of 3" with a total liquid of 1.06" over the course of the storm. This probably did not all fall as frozen precipitation as temps were warm enough for rain early on 12/17. Either way, I would say the snow that fell is dense or mostly graupel/rimed snow..