Friday, December 13, 2024

A Welcome Storm

The Alta snowstake cam suggests we're getting more action that may have been advertised by the models with perhaps 6-7 inches on the stake earlier this morning before the ski patrol wipe (kudos to my friends at OpenSnow for producing the Alta Snow Stake time laps so I could grab this image). 


And then another inch was added since then (not shown).  

The automated sensors are coming in a bit below that with about a 6" increase in the total snow depth and 6" on the interval board (ignore the spurious 34 reading at 08:00).  

Those numbers are a bit higher than advertised by the HRRR and GFS over the past few runs.  Below are the forecasts for Alta-Collins going back to 0000 UTC 12 December for snowall amounts through 9 AM this morning.  Only one of the HRRR runs went for 6" and the most recent was only an inch.  The GFS was a bit more optimistic overall, but never got above 4.5 inches.  

0Z 12 Dec HRRR: 1.1”
6Z 12 Dec HRRR: 6.0”
12Z 12 Dec HRRR: 3.3”
18Z 12 Dec HRRR: 2.4”
0Z 13 Dec HRRR: 1.0”
6Z 13 Dec HRRR: 1.0”

0Z 12 Dec GFS: 0.0”
6Z 12 Dec GFS: 3.7”
12Z 12 Dec GFS: 2.5”
18Z 12 Dec GFS: 3.4”
0Z 13 Dec GFS: 4.5”
6Z 13 Dec GFS: 4.5”

And a total of say 6-8" is also near the top of the snowiest members of the Utah Snow Ensemble over the runs since 0Z 12 Dec.  The snowiest member I could find from the last three runs of the ensemble was in the forecast below which produced about 7.5" for Alta Collins through 9 AM MST (16Z 13 Dec).  Even that was an outlier.  


Consider yourselves blessed.  Let's hope the snow keeps coming as we need all we can get.

5 comments:

  1. Is this an example of the "blower pow" the models struggle to capture? still snowing nicely in Alta and the sun is poking through

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    1. Looks like something around 25:1. That is on the upper end of what our machine learning models *could* predict. The forecast snow-to-liquid ratios for 1 AM to 9 AM were 13:1 to 19:1 depending on the hour, so the forecast SLRs were low. That's a common occurrence when we're in the 20:1 or higher snow to liquid ratos.

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  2. It's been a while since I have thought about this calculation, but Utah Avy reported 0.2" SWE. Is the density 6" / 0.2" = 30%? That seems wrong. Sorry for the nube question. What am I missing here? I need a refresher...

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    Replies
    1. The Utah Avy report comes out earlier than 9 AM. They reported 5" with .2 water, which would be 25:1 snow-to-liquid ratio or 4% water content.

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    2. I understand now! Thank you for the refresher!

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