Up above, down below

Posted Friday, January 11th, 2019 by Mike Wessler

It’s one of those days where it’s just impossible to convince yourself to drive home at the end of the day, knowing that you’re about to trade a view like this:

Salt Lake Valley from Hidden Peak, courtesy of Snowbird
Salt Lake Valley from Hidden Peak, courtesy of Snowbird

For one a little more like this:

U of U William Browning Building West View
U of U William Browning Building West View

While we have been under a strong surface inversion for the majority of the past few days here in the Salt Lake valley, since yesterday evening, the inversion has deepened. as well as become quite moist. The dense fog and low-level cloud make that quite evident. Though the air quality is becoming steadily worse as pollutants accumulate, the deepening of the inversion has likely slowed the process some. For those interested in the air quality, the ‘official’ measurements show us sitting solidly in Unhealthy for Sensitive (~36 µg/m3) for the majority of the past 24 hours.

Utah Department of Environmental Quality Air Quality PM 2.5 Concentration for Salt Lake (Hawthorne)
Utah Department of Environmental Quality Air Quality PM 2.5 Concentration for Salt Lake (Hawthorne)

So when will it end? When’s the next snow? Well, models hint at a very weak inverted trough to impact our regional weather by the end of the weekend into Monday. The low-level easterly flow models hint will be associated with this passage may help weaken the valley inversions by the advection of colder air aloft – weakening the vertical temperature gradient and allowing for a little mixing. Additionally, drier air from the east may help clear some of the fog and low cloud, though where exactly is not clear – the northern end of the Wasatch seems favored.

Tuesday afternoon GFS forecast 500 mb Heights and Vorticity. Note that the stubborn ridging over the Intermountain West has given way to more zonal flow ahead of the broad trough to our west.
Tuesday afternoon GFS forecast 500 mb Heights and Vorticity. Note that the stubborn ridging over the Intermountain West has given way to more zonal flow ahead of the broad trough to our west.

By Tuesday we finally see more zonal flow, and the weakening of the ridge may finally release the valleys from the inversion’s grasp. Instability and weak synoptic forcing for lift and precipitation will be present across the region, but it’s hard to say how much snow to expect at this point – anything from flurries to feet is possible by the end of next week. Stay tuned and we’ll let you know as we know.

Significant uncertainty exists in the ensemble forecasts due to the broad, weak nature of the trough. We'll wait before diving in to this one.
Significant uncertainty exists in the ensemble forecasts due to the broad, weak nature of the trough. We’ll wait before diving in to this one.

-Mike

 

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