The good is that with all the snow over the past 3 days, the total snow depth at Alta-Collins has eclipsed 100" (250 cm).
STEENBURGH WINTER IS HERE!!!
For the first time since the 2010/11 ski season, we have over 100 inches of snow at Alta-Collins before February 10. Steenburgh winter is that magical period where we have such a snowpack before February 10, when the sun begins to have a much stronger influence on snow conditions in the Wasatch range. Enjoy the deep snow and the low angle sun while they last.
Now, getting to the bad: Forecasts for Friday night. From 4 PM Friday to 8 AM Saturday, Alta-Collins got 15", including 13" from 5 PM Friday to 5 AM Saturday with 0.55" of water.
Such accumulations were much greater than forecast. I did not put numbers on the snowfall for this blog, but expected only a modest refresh of a few inches. The National Weather Service Little Cottonwood Forecast issued on Friday afternoon called for a 70% chance of 2-5" (with 0.15-0.35" of water) from 5 PM Friday to 5 AM Saturday and a 30% chance of 1-2" (0.05-0.14" of water). As noted by commenters in the previous post, the "bros at the bird" beat us this time. It's hard to say how much of the snow removal, traffic mess, and avalanche closures yesterday in the Cottonwoods were related to the underforecast, but I suspect it was a contributor.
BTW, the NCAR Ensemble handled the event pretty well.
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| NCAR Ensemble Forecast initialized 0000 UTC 20 January 2017 |
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| NCAR Ensemble Forecast initialized 0000 UTC 21 January 2017 |
The ugly? There isn't one. We have a 100" base on January 22nd, with snow in the forecast. Avalanche conditions could be better, but after the past few down years, we shouldn't complain. Just be careful out there.
What's the significance of February 10th? Also in an effort to expand Steenburgh winter I nominate any Cottonwoods snowstake to qualify. We could have had over a week more of Steenburgh winter with Brighton being over 100" for about 10 days ;-)
ReplyDeleteAn avy professional friend once told me that February 10th was the start of spring in the Wasatch because that is when the sun angle becomes high enough that south aspects get baked pretty quickly on a sunny day. It is obviously a highly stringent view of the end of winter and obviously there is good skiing after that date. This is an overidealization, but it is roughly the end of the "low angle" sun season and the beginning of the transition to the higher angle sun.
DeleteJim
I've always thought of a lot of snow on a bare surface as the path to stable continental snowpacks. However, my current feeling is that the typical later season stability in the Wasatch is also a function of the higher angle sun mitigating near surface facets formation on the north side of the compass. So even though steenburgh winter is great my favorite part of the ski season is February to march because of the stability, thinner crowds, and snow that still holds up well on the north side of the compass on sunny days.
DeleteThat being said Steenburgh winter is glorious! I wish I could have such a namesake.
Seeing that the event was going to involve moist northwest flow of pretty decent strength ahead of time, I'm surprised that the NWS forecasted such low totals, not only for the Cottonwoods, but for the valley with the event starting before sunrise with cold surfaces. Valley roads were a disaster in many areas for much of the day and a winter storm warning was never issued, even with bench areas getting 12-18 inches of snow. NWS deserves some flak for this one.
ReplyDeleteAdam:
DeleteThe flow was neither forecast nor did it feature NWflow until the trough passage at about 15 UTC Saturday morning. The heavy snow that was poorly forecast was prior to that.
Check the AMB (Alta-Mount Baldy) observations on MesoWest for confirmation.
Jim
I'll give you that the bulk of the snow in the Cottonwoods was pre-trough passage, but the bulk of the snow in the valley was with the trough passage and NW flow between 4 AM and noon (11Z-19Z). The radar echoes clearly show the trough passage early in this period and then move NW for the rest of it. The valley forecast, which is much more important than the Cottonwoods forecast in terms of impact on people's lives, is where I have more of a gripe.
DeleteJim, big fan here. I am a big weather nerd, very amateur but a weather nerd none the less. It appears that utah is going to ridge up with high pressure over the coming days. The few high pressure times we've seen this year have still been relatively cool in the mountains with near or below 0 temperatures at my house in kamas. What is the difference between the ridges this year with still cold temps and the ridges that we've seen in the past few winters that brought record warmth and crazy high temperatures across the board.
ReplyDeleteRidge amplitude and position matter and make a big difference for crest level temperatures and often valley temperatures.
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