Thread by @NWSSaltLakeCity

1/9 To shed some light on the science, here's a schematic look at the structure of a downslope wind event along the Wasatch Front. For more detail on this graphic and the setup for this impactful event, keep reading... #utwx

2/9 The September 2020 wind storm was a complex meteorological event combining elements of strong synoptic winds associated with deep low pressure system with components of a classic downslope wind event. It was this combination that led to a widespread, long-duration event #utwx

3/9 A pool of cold continental air moved southward from Canada through the Intermountain West with the progression of an upper-level trough. As the system deepened, upper level winds (our 'background' flow) increased, and significant transport of this dense cold air occurred.

4/9 The background flow set the stage for a strong wind event, the downslope component enhanced them to the highly impactful level we experienced. The cold air transported into the region is channeled and trapped by the Wasatch and Uinta Mountains, creating a deepening cold pool.

5/9 Eventually, the depth of the cold pool becomes sufficient so that easterly winds allow the cold air to overtop the Wasatch Front, spilling onto the west side. The dense cold air accelerates as it descends under a stable layer, producing enhanced winds along the Wasatch Front.

6/9 This process can also 'mix' the upper-level flow down to the surface, with the two processes working together to produce winds well in excess of 60 mph up and down the Wasatch Front.

7/9 To get some of the highest wind gusts (US-89 at Park Lane reaching 99 mph), canyons along the Wasatch Front provided the final component, further channeling the dense cold air, and with the stable layer as a 'lid,' forces the flow to accelerate as it reaches the valley floor.

8/9 One of the unique characteristics of a downslope wind storm that was evident during this event is the 'hydraulic jump' and rotor. This was responsible for the light easterly winds on the northwest end of the Salt Lake Valley and chaotic wind directions near the SLC airport.

9/9 There are many more pieces to the puzzle as downslope events are incredibly complex. Many subtle ingredients must come together with the terrain and the 3-D structure of the atmosphere to produce an event like this. We hope you enjoyed some basics! #utwx