Monday, March 6, 2017

A Night of Extreme Change

The "Steenburgh Effect" was in full play this weekend as I was out of town skiing in Jackson Hole and of course missed out blogging about the best frontal passage we've had in months.  Nevertheless, I saw what was coming and we ended up getting off the mountain at 1 PM yesterday, and racing home via Evanston, experiencing the full force of the pre-frontal southerlies, but arriving home just ahead of the post-frontal snowmaggedon.

I took a quick gander through the wind reports over northern Utah and it appears that nobody escaped the full force of the winds.  Gusts over 70 mph were reported at all elevations and in many areas that you might think of as being "sheltered."  Here are a few selected peak gusts, all of which were recorded in the pre-frontal environment.

Arrowhead Summit (Sundance): SSW 110 mph (0010 UTC)
Windy Peak (Uinta Mts): SW 97 mph (0100 UTC)
Mt. Baldy (Central Wasatch): SSW 96 mph (0000 UTC)
Big Mountain Pass: SW 96 mph (2220 UTC)
Ogden Peak: S 89 mph (1530 UTC)

Mid-Elevation Hills and Canyons
Eureka (6584 ft): W 95 mph (2240 UTC)
Vernon Hill (5761 ft): SE 90 mph (2230 UTC)
Deer Creek Dam (5429 ft): SSW 83 mph (0110 UTC)
Mayflower Summit/US-40 (6929 ft): S 81 mph (0120 UTC)
S-Turns Big Cottonwood (6235 ft): W 78 mph (2230 UTC)

Salt Lake Valley
SR-201/I-80: WSW 82 (2310 UTC)
Olympus Cove (4960 ft): SW 73 mph (0030 UTC)
Kennecott Tailings Magna (4440 ft): SW 72 mph (0000 UTC)
Draper (5052 ft): W 68 mph (2140 UTC)
University of Utah: S 64 mph (2315 UTC)

The driver of these strong winds was a strong cold front that developed over the Great Basin and moved across northern Utah yesterday afternoon.  The intense surface trough accompanying the front featured strong pre- and post-frontal pressure gradients.

Although the strongest gusts were generally observed ahead of the front, the winds behind the cold front were nothing to laugh about either.  Here at the University of Utah, the peak gust of 64 mph occurred about 90 minutes ahead of the frontal wind shift.  Although there was a temporary drop in the wind speeds following the frontal passage, they picked up again, with a prolonged period of W-NW flow and gusts above 30 knots, as the frontal precipitation band came through.

The lag between the surface based front, as indicated by the pressure trough, and the precipitation band was clearly evident in the analysis for 0200 UTC below.

The combination of heavy snow and strong W-NW flow made for a quick coating of white at our place in the upper Avenues (about 5000 feet) by about 8 PM MST.  It's always hard to take night-time pictures of snow, especially with an old cell phone, but the combination of snow and wind made for about the nastiest weather I've seen in the valley this winter.

I suspect this morning provided a rude awakening for many as temperatures on campus are around 24ºF with NW winds gusting from 15-20 mph over the past couple of hours.  Throw in icy sidewalks and you have conditions best described as "sporting."  After a high on campus yesterday of 59ºF, it is safe to say that it was a night of extreme change.

Also this morning in the post-frontal environment we have some beautiful orographic clouds draped over the mountains, such as these over the Oquirrh Mountains as I walked to the bus at about 7 am.

Thanks to the post-frontal convection, graupel has been falling at times on campus.

Enjoy this taste of winter.


  1. In addition to all the other crazy weather yesterday, saw this picture on twitter: do you think it's a real tornado?

    1. That's a really great photo. Without knowing the time of the photo to do more digging, all I can say is that there is some potential that it was an extreme dust devil or a gustnado. If there was a cell nearby, as suggested by Brek Bolton in the tweet, there is a chance it is a weak tornado associated with a non-rotating updraft. Sometimes those are called "landspouts," but they are tornadoes.

  2. The pre-frontal southerly wind was very gusty due to surface heating and cooling aloft (plus the development of some virga) which resulted in some microburst type of activity. Also, during the post frontal blizzard I saw what I thought to be lightning at first but turned out to be arching electricity from power lines nearby. I had a few really brief outages from it.