Tuesday, February 21, 2017

The Valley Doth Blow as Hard as the Mountains

Here's an interesting non-alternative fact about our current wind storm.  Peak gusts over the past 24-hour period ending at around 8:30 AM are quite similar in the valleys and on the mountain ridges.

Three sites have reported gusts in excess of 70 mph, two upper-elevation sites near Snowbasin (83 and 73 mph) and one in the western Uintas (77 mph) and these are the highest gusts so far in northern Utah.  So, technically one can find a couple of mountain sites that have the highest gusts in the region.

However, if we move a bit closer to the Salt Lake Valley, we see that peak gusts in the valleys are comparable to those in the mountains.  Here's a selection from MesoWest:

SR-201/I-80 Junction: 69 mph
Park City Ridgeline: 69 mph
Mount Baldy: 68 mph
Stockton Bar: 68 mph
Great Salt Lake Marina: 67 mph
Mid-elevation Mt. Timpanogos: 66 mph
Sandy: 66 mph

So, what gives?  Why is the wind blowing so hard in the valleys, especially overnight?

The peak gust in the Salt Lake Valley occurred at 1200 UTC (0500 MST) this morning at the intersection of SR-201 and I-80, but really at that site it blew quite hard all night long, picking up at around 0200 UTC (7 PM MST) yesterday evening.

Source: MesoWest
The valley winds are being driven by a strong pressure gradient between high pressure centered in the Four Corners area and low pressure over the Pacific Northwest.  The sea-level pressure gradient from southeast to northwest Utah is around 12 mb and concentrated in particular near the Salt Lake Valley. 

This pattern favors pressure-driven channeling within the lower-elevation valleys, so much so that winds are comparable to those experienced on the highest peaks.

The big blow is not over yet.  Hold on to your hats today as a cold front approaches from the northwest and is expected to arrive in the Salt Lake Valley around 7-9 PM tonight, when our flirtation with spring thankfully ends.  

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