Tuesday, October 26, 2021

Storm Update

It was quite a night last night with many sites in the Salt Lake Valley recording over an inch of rain.  Amounts were greatest in the Olympus cove area where just over 1.5 inches fell.  Even the airport recorded 1.21 inches.  And it's still raining.

Meanwhile in the mountains we're up to about 8 inches of dense snow based on the Alta-Collins and the Snowbird snow stakes, the latter below.  

Source: Snowbird.  Downloaded 7:38 AM 26 Oct 2021.

Observations from Alta-Collins show that precipitation began between 1600 and 1700 MDT yesterday with temperatures near 40˚F.  About 0.18" or so fell at temperatures above 34˚F.  Temperatures reached 34˚F at 2000 MDT afterwhich snow fell at this elevation (it wasn't long after that it was falling to the Town of Alta.  I guestimate that the snow 8" of snow contains about an inch of water, for an 8:1 snow-to-liquid ratio or a 12.5% water content.  Total precipitation 1.22".  

The GFS-derived forecast from yesterday is doing pretty well through 7 AM this morning.  The forecast presented in yesterday's post called for a total of 1.29" of total precipitation and 11" of snow through 7 AM.  The former is just .07" higher than observed and the latter 3" too high.  The main shortcoming of the GFS was that it was a bit drier before temperatures fell and a bit wetter after.  Hence the 3" snowfall overforecast.  Still, that's a pretty good forecast.   

We are now transitioning to the unstable, post-frontal regime.  The latest radar image shows precipitation over the eastern Tooele Valley, Salt Lake Valley, Central Wasatch, and Bountiful-Area Wasatch.  There's also a weak lake-band over the Great Salt Lake.

It is likely that snow will continue in the Cottonwoods for the next hour or two and snowfall should transition to lower density.  After that, periods of snow.  I'll go for another 3-6" at Alta Collins from 7-5 PM, although I confess it's a bit more of a crap shoot for this period than the frontal period and we could do better if the instability or the lake goes off (the latter is less likely in the afternoon).  That's some waffling to keep a friend of mine happy.  

Suspect the skiing will be good later today.  Stay safe out there. 

1 comment:

  1. This storm in general was very impressive in terms of its large scale and how much precipitation fell over such a large area. It exceeded forecast amounts by quite a bit in much of CA I think, and even areas downwind of major mountain barriers (such as western parts of NV) had impressive rain totals. I heard that at least some 24 hour rainfall records were broken in places but not sure about any October records etc.