The persistent cold pool exists over the Great Salt Lake Basin, including the Salt Lake Valley, where widespread fog and stratus are present, as illustrated by yesterday afternoons modis imagery. It is sometimes difficult to discern fog and stratus from snow in visible imagery, but the smooth nature of the coverage and the inability to see the Great Salt Lake are dead giveaways.
|Modis Imagery 13 January 2019|
|Source: NWS Aviation Weather Center|
|Sounding source: SPC|
As we have discussed previously, although it looks dark and dreary, the reality is that a deep cold pool of this type, capped by stratus, results in mixing through a deeper layer than when the inversion is based right at the valley floor. As a result, while there is still pollution, the concentration levels along the valley floor are not as bad as in periods when the inversion is lower. Note, for example, how PM2.5 concentrations over the past couple of days have been lower than they were on the 10th and the 11th.
|Source: Utah Division of Air Quality|
Although the persistent cold pool present over the Salt Lake Valley doesn't burn off during the day, the cold pool in the Snyderville Basin is diurnal. It forms at night and burns off during the day.
Compare, for example, the temperature traces (red line) at the Salt Lake City airport and Silver Creek Junction (note scale change). There is practically no diurnal (daily) temperature cycle at the Salt Lake City International airport. Instead, there is a gradual decline in temperature during the period. This reflects the presence of low clouds, which reduce incoming solar radiation received at the ground as well as the overnight cooling. We remain capped by an elevated inversion all day long.
In contrast, there is a huge diurnal cycle at Silver Creek. Temperatures last night and the previous night fell to below zero, but yesterday afternoon, the high was 30ºF. Here, a shallow cold pool forms under clear skies each night, and then burns off during the day.
Residents of the Summit Park area observe some remarkable temperature variations on days like this. Note how it is -8ºF at Kimball Junction, -6ºF along Pinebrook Boulevard near I-80, 9˚F near the top of Pinebrook Road, and 21˚F across I-80 at the Parley's Summit SNOTEL.
My skate ski today, which will be my final ski of the season in Utah, will need to wait until afternoon when temperatures are more tolerable...