Potosi CR

[CheapCigarMan]

9patrickmurphy posted a Conditions Report asking why snow conditions were soft at higher elevations this year.

I’d be interested in hearing answers from the experts as well.

[Tim A]

Cool air sinks, so perhaps when the layer of colder air is shallow, the snow conditions are firmer near valley floors? I’ve encountered this a few times and always assumed it was warmer up higher where the snow was softer, contrary to conventional wisdom.

[cottonmountaineering]

after reading the conditions report, what is to be confused about? they ascended the summer route in the daylight hours during late may, the snow was soft. the end

[CheapCigarMan]

after reading the conditions report, what is to be confused about? they ascended the summer route in the daylight hours during late may, the snow was soft. the end

Our memories deceive us and they’re also short sighted.
But I went back and looked because this year seems different.
Last year April 30th I did Aetna’s Grand couloir, May 7th Moonshine couloir, May 14th Traitor couloir, and May 28th Niagara’s couloir. All with firm consolidated snow in the couloirs. Not my experience this year.

[John Landers]

after reading the conditions report, what is to be confused about? they ascended the summer route in the daylight hours during late may, the snow was soft. the end

Our memories deceive us and they’re also short sighted.
But I went back and looked because this year seems different.
Last year May 7th I did Moonshine couloir, May 14th Traitor couloir, and May 28th Niagara’s couloir. All with firm consolidated snow in the couloirs. Not my experience this year.

May has been rather wet this year, how cloudy have the nights been in the mountains this year vs. last year?

[9patrickmurphy]

after reading the conditions report, what is to be confused about? they ascended the summer route in the daylight hours during late may, the snow was soft. the end

You didn’t read my question. I asked “…a bit confused as to why the snow was way softer up higher, even where no sun had hit and early in the morning. Would appreciate insight here as well.” Of course snow softens in the sun, but we were also finding soft snow above 13,000ft where there was no sun and before 7am. For reference, the snow up to that point had been super firm.

I think Tim’s response of cool air sinking makes sense to me, but then how would I be able to predict this when looking at the forecasts? Looking at NOAA for an area it will show 26°F at 12,000ft so I usually assume colder higher up. Should I actually assume it might be warmer?

Thanks for keeping this conversation going, Brian.

[Scott P]

Without being there, I'd guess that it was because the snow down lower had been avalanched more recently, while the snow up high had not. Snow is harder after it has slid.

The happened to us on Mount Ervin two weeks ago. We climbed the south couloir. Up high the snow became really soft even before sun hit. When we desceded the snow became hard again even though it was warmer and the sun had already hit the snow.

[HikerGuy]

Without being there, I'd guess that it was because the snow down lower had been avalanched more recently, while the snow up high had not. Snow is harder after it has slid.

I think this is the answer too. Snow slides down couloir, firms up. Higher up where the slab released you have normal uncompacted snow.

[k_fergie]

Another guess is that snow that is shallower and near darker rocks tends to be much more faceted and unconsolidated going into spring. Then, during the melt/freeze (particularly the beginning of spring, or N facing later to mature), it can be much less supportable than a solid F to P hard slab that is moving into the melt/freeze. I didn't read much into the referenced CR, but I have observed very unsupportable snow at higher elevations than supportable snow lower down due to similar phenomenon.

[Jorts]

I think Tim’s response of cool air sinking makes sense to me, but then how would I be able to predict this when looking at the forecasts? Looking at NOAA for an area it will show 26°F at 12,000ft so I usually assume colder higher up. Should I actually assume it might be warmer?

Calm overnight conditions often lead to inversions. The cold, denser air travels down the mountain into the valleys as the land cools in the valley floors and there is less in the way of pressure differences caused by radiant heating. And cloud cover with continued calm conditions can preserve inversions longer into the following day. One way to think about it is if you were standing in a cold fog on black asphalt, as the sun rises, the asphalt absorbs that energy and the air near the surface rapidly warms - "burning it off".

This is a comprehensive resource from NOAA talking about inversions (they list 6 different causes!).
https://www.weather.gov/source/zhu/ZHU_ ... rsion.html

[Boggy B]

May is always a crapshoot.
After the dust in April we got a brief freeze/thaw cycle and the dust layer firmed up nicely for early AM missions.
Then it snowed in early May, and the weather has been mostly unsettled since. This isn't atypical.

With exceptions, I don't try to snow climb until mid June, or whenever skiers start complaining about runnels and suncups, but (due to the April setup as far as I can tell) conditions have actually been better than usual for May this season. In general, aspects that are getting lots of sun (E-S-W) or where the May snow has shed or burned off have been decent after clear nights.

The inversion effect is interesting. Twice in the last week I've returned to valley bottoms in the trees (shaded) in late morning and found the slushy snow and tracks I made before dawn frozen solid.

[nyker]

might just need another storm system to come in an "clean out the air" reversing the inversion.
Any meteorologists here?