Wednesday, March 27, 2024
The Goods on Graupel
Monday, March 25, 2024
Just What the Doctor Ordered
The Saturday night frontal passage seemed to provide just what the doctor ordered for transitioning from spring skiing back to proper powder skiing. I found good skiing yesterday with just a hint of bottom feeding at mid elevations if you kept the slope angles reasonable.
Storm totals per the Alta-Collins site are now over two feet. Elsewhere, a healthy lake band developed overnight, but raged over the western Salt Lake and Utah Valleys.
It has since broken up some but scattered lake-effect snowshowers continue this morning, albeit a bit farther west than central Wasatch skiers would like.
The unsettled post-frontal weather will continue through Tuesday evening. Although not in the lake-effect now, expect periods of snow showers throughout this period in the Cottonwoods and perhaps even a thunderstorm or two in the afternoons. For the period from 6 AM MDT this morning through 6 PM 12 AM MDT Wednesday March 27, the GFS produces .79" of water and 14.7" of snow at Alta. The HRRR was less excited (.44"/7.6"). Regardless, it will come in fits and starts, which is my new phrase for the week. It's great skiing for late March. Hopefully the sun will not do too much damage when it appears at times.
Enjoy.
Sunday, March 24, 2024
Storm Update
Pretty good delivery of the white in the upper Cottonwoods yesterday afternoon and last night. As of 6 AM, Alta-Collins is already at 13 inches with 1.32" of water. That's a mean water content of 10%, although I suspect it's right side up. We need some high density snow to bury the coral reef anyway. All in all this is good news.
Radar early this morning showed a fairly active northwesterly flow pattern.
Expect periods of snow in the northwesterly flow to continue today. The HRRR really lights it up with .66" of water and 11.1" of snow at Alta from 7 AM to 5 PM MDT today. The GFS is not as excited puts out .19" of water and 3.6" of snow. A big reason for this discrepancy is the HRRR really gets things going in the northwesterly flow, including some lake effect, as illustrated by the forecast radar image for 2000 UTC (2 PM) this afternoon.
And for the 6-h period ending at 0000 UTC (6 PM MDT) the HRRR is generating 7.5" of snow for Alta and even higher amounts along the Alpine ridge to the west in the Lone Peak area.
A real question is how much to buy into the HRRR forecast? I'm inclined to expect another 4-8" at Alta-Collins for 7 AM this morning through 5 PM this afternoon, which sits between the GFS and HRRR. I'd put the odds of going above that higher than below. How bout we throw in the chance of a T-storm too? Welcome to spring.
Saturday, March 23, 2024
Winter to Return
After about a week of splendid spring weather, winter will be returning to the Wasatch Range today with the arrival of a cold front this evening.
Although there will be some periods of high-elevation snow and low elevation rain ahead of the front, the main action will be associated with the frontal passage which will bring a few hours of steady snowfall overnight.
The cold-front is very apparent in the latest HRRR run with an abrupt drop in the wet-bulb zero height at between 7 and 8 PM.
We base the wet-bulb zero level estimate on the model forecast from the airport (if we used data from Alta we would not be able to estimate snow level most of the winter since there's no data below ground), so expect that drop to be more like from 8-9 PM in Little Cottonwood. Snow levels are usually a bit below the wet-bulb zero, so expect them to be in the area of 7000-7500 feet today, possibly higher in the afternoon with heating, and then drop to near bench levels after the frontal passage.
The HRRR is calling for about 0.85" of water and 8.6" of snow at Alta Collins through 9 AM Sunday. A bit less than half of this is high density snow that falls in fits and starts ahead of the front, including this afternoon, and the remainder is with the frontal passage. Densities will be decreasing behind the front.
The HRRR then shuts things down late tonight through tomorrow afternoon when things begin to pick up again.
The GFS is less enthused about the pre-frontal precipitation today but is in rough agreement on the frontal passage. It's also a bit more active during the day tomorrow. Through 9 AM Sunday it's at .55" of water and 7.6" of snow.
So, expect some fits and starts of wet snow at upper elevations today and then steady snow with the frontal passage this evening and tonight. I'm inclined to go close to the model water numbers on this with 0.5 to 1" of water and 6-10 inches of snow at upper elevations through 9 AM tomorrow.
Given the warmth of the past week, I'm not overly optimistic that the frozen coral reef will be buried by tomorrow morning. Things will need to go above those numbers probably to prevent a lot of bottom feeding. If that doesn't happen, the better skiing tomorrow morning will probably be in lower angle terrain where the snow surface is currently fairly smooth.
That said, behind the front, unstable northwesterly flow looks to predominate through at least Tuesday and possibly Tuesday night. The GFS time-height section shows this well.
Wednesday, March 20, 2024
Beautiful Spring Weather
If you look carefully, you can see a couple of clouds in the Mt. Baldy web cam from Alta Ski Area this morning.
Source: Alta Ski Area |
Those are not enough, however, to mar the incredible run of beautiful weather we have had since the demise of the easterlies on Saturday.
Indeed, that run will continue today with clear skies and temperatures into the upper 60s in the valley. If we can't have powder, this is a pretty good alternative.
A weak short-wave trough will come through tomorrow and bring in a few more clouds and maybe a spritz of a shower or upper-elevation snow shower for the mountains tomorrow. Significant weather will hold off until the weekend when a cold front is expected to push across northern Utah on Saturday. Current forecasts suggest that the front will arrive in the afternoon. Below is the ECMWF forecast valid 2100 UTC 23 March (3 PM MDT Saturday) with the front approaching Salt Lake City.
Sunday, March 17, 2024
Sastrugi
Along with graupel, sastrugi is one of my favorite weather-related words and I saw plenty of it ski touring yesterday.
Sastrugi is defined by avalanche.org as "heavily wind eroded snow with wavy textures." Sometimes it looks rough or pockety. In the photo below, it appears there is avalanche debris on this slope, but in reality it is all sastrugi.
In some areas, the sastrugi was dense wind board and generally supportive of a skier.
In others, it was actually somewhat soft and didn't ski to bad on the descent. Each turn was a mystery!
Although I like sastrugi as a word, it's not my favorite snow surface to ski. We can blame the sastrugi in this case on the multiday easterly wind event that has been affecting the Wasatch Range and Front since Thursday. Observations from Alta's Mt. Baldy show the winds veering (turning clockwise) from southwesterly just prior to 1200 MCT 12 March (Tuesday) to north by 0000 MDT 14 March and then locking in with easterly flow with gusts reaching over 50 mph on the 15th (Friday) when most of the damage was done.
The large-scale setup for these winds was something that meteorologists call anticyclonic wave breaking in which a high-amplitude ridge develops in the high latitudes and leads to the formation of a closed low downstream and to the south. Below is the GFS analysis for 1200 UTC 15 March during the period of stronger easterly flow on Mt. Baldy. Note the ridge off the Pacific Northwest coast and the deep closed low centered along the CA-MX border, resulting in strong easterly 700-mb (crest-level) flow over the Wasatch.