Friday, April 8, 2016

Downslope Winds

Strong easterly winds (photo taking looking north) this morning in the Avenues foothills
Easterly downslopes winds are creating blustery conditions along the east bench and on the University of Utah campus this morning.  Observations at about 8 AM showed strong esterly flow from Parley's canyon north with gusts to 31 in the Avenues, 35 on campus, and 39 at the mouth of Parleys (annotated numbers below are current wind gusts in mph).  Winds are stronger along the east bench than in the canyons and most upper-elevation bench locations. 

There is also clear evidence of a rotor near the Salt Lake City International Airport.  Note how the easterlies extend to downtown, but the flow at the airport is westerly, as depicted below.

Source: Whiteman (2000)
Rotors sometimes feature sub-rotors (smaller-scale circulation centers embedded in the larger-scale rotor), strong wind shear, and turbulence.  I've often wondered if the airport is just far enough west that planes on take-off and approach avoid these features or if its a bumpy ride on days like this.

The cause of these downslope winds is easterly to southeasterly 700-mb (10,000 ft) flow being driven by a closed low off the coast of California and an elongated upper level ridge extending northwestward from Texas to the Pac NW.

Peak gusts so far include 47 mph on the Bountiful Bench, 45 mph in Farmington, and 43 mph at the University of Utah.  These winds should slacken in the next few hours.


  1. Good education on downslope winds. Having personally experience this last year in a light airplane they are NOT fun. Flying from Heber Airport where the winds are currently "cslm" it can be a bit of a suprise fllying to Bountiful Airport over the city. as I found out. The only way for a pilot to find out is if SLC International is reporting wind sheer righth but right now winds arew 170 at 4. Any ideas on how to predict this for a pilot? Jim Church

    1. Napoleon learned all too well that all bad things come from the east. Although not all easterly flow events produce downslope winds and rotors, I would have heightened concern whenever the pass or crest-level flow is out of the east.

  2. Noticed these winds upon driving north from SL valley up to Powder mountain (through Ogden canyon). Winds in the next valley (Eden) and atop the peak of the resort were much lighter.

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