Corn Cycle Information

[Hindfoot]

There seems to be a lot of uncertainty about just what needs to happen to create good corn snow. An uncertain number of freeze/thaw cycles must occur to produce it. There also is a lot of uncertainty in trying to second guess what may be happening as far as corn production by following the NOAA predicted highs and lows for a specific location/elevation. My experience suggests that the night time low air temperatures may not need to go below or even down to freezing to cause the soft snow to freeze up. Perhaps what little heat is in the soft snow gets radiated away to the night sky on clear nights when the air temp is still in the mid 30s or above, so the snow can still freeze. I see this happen at home, where I monitor the nightly lows and up in local high terrain where the pack consistently freezes on nights with actual or predicted lows in the mid 30's or even higher.

Trying to second guess what the snow condition may be, at BC sites where I have to drive at least 3 hours to find out, becomes fairly important so as not to commit to 6 or more hours of driving to get there and find nothing but early morning mush instead of frozen snow with potential to thaw to corn during the day. Can anyone shed some light on any ways to more accurately predict what might be going on someplace where there is no one around to report. One of these sites does have a remote weather sensor, so in those spots data is available on min/max temperatures, but this does not tell me if the snowpack is freezing up at night if I don't know just what conditions it takes to do this. Someone out there must know lots about this.

[MattB]

I usually find that a week of warm sunny days and nights below freezing do the trick, but I don't have it down to an exact science based on that much info yet. But it seems like it usually works well as long as I ski a sunny aspect.

[purplesage]

I don't know much about the exact science of it either but I tend to agree with MattB overall. The temp needs to get down to or slightly below freezing to form the kernels. Also I think some skiers refer to conditions being "corn" snow when they actually are just some of the many other types of spring snow. True corn is a distinct thing that has a particular look, sound and feel as you ski it. I believe it takes quite a bit of experience to predict exactly where and when it will form, and how long it will last. That's why we often skin up early and wait for the perfect moment to shred.

[airinwrite]

If it's clear and calm, the snow will refreeze with temps as warm as 38-40 overnight. If there is cloud cover it needs to be around freezing or lower. Of course if it's cloudy it might not soften, same with wind on a sunny day. Depending on aspect it may take as little as a couple days(southerly) or up to a couple of weeks(northerly) to develop nice corn. Latitude will make a big difference too. I think, no proof, that drier climes make for better corn.

[Hindfoot]

Thanks for the replies, both of you. The situation that has me looking for more information is the current one over much of northern CA and southern OR, where we have been getting clear nights down to only 34-37 degrees and very warm days in the upper 50s and 60s. There seems to be some temperature inversion with temps almost as high, or even higher at upper elevations of 7-8K. Critical to corn formation is whether or not freezing of the snow is happening at these above freezing lows. I know it can happen, but don't know enough about this phenomenon to predict if it might be happening. Or, is the skimpy snowpack just melting away all night as well as all day?

[Hindfoot]

If it's clear and calm, the snow will refreeze with temps as warm as 38-40 overnight. If there is cloud cover it needs to be around freezing or lower. Of course if it's cloudy it might not soften, same with wind on a sunny day. Depending on aspect it may take as little as a couple days(southerly) or up to a couple of weeks(northerly) to develop nice corn. Latitude will make a big difference too. I think, no proof, that drier climes make for better corn.

Yes, thanks Aaron, for giving information supporting my hypothesis as well as more on corn development. Makes sense that on still, clear nights the air right on the snowpack would be coldest, remaining and becoming colder as heat radiates to the night sky. Slope angle may matter also, with steeper slopes causing coldest air on the pack to flow downhill and be replaced by even colder air from higher elevations flowing down??

[freeheelwilly]

I think, no proof, that drier climes make for better corn.

Really? I always have heard the opposite. My buddy in Utah says the corn is not as good because the snow is so dry. Or are you saying something else?

[Matt J]

Really? I always have heard the opposite. My buddy in Utah says the corn is not as good because the snow is so dry. Or are you saying something else?

I doubt humidity has a ton to do with it. There's probably some correlation between how extreme day time highs reach and night time lows and general atmospheric humidity. But, Colorado gets excellent corn and it's nearly as dry as Utah. Utah is lower and gets chinook wind and I think the Wasatch just simply melts out faster. High altitude and the accompanying lower night time temps is probably a bigger factor than relative humidity. Dry snow would just mean lower water content and mixed with lower altitude probably just means a smaller window that there's really "corn." Pow to slush to mtn. biking.

[freeheelwilly]

I don't think his point was atmospheric humidity but rather the snow's moisture content. It sorta made sense to me intuitively but that doesn't mean much. I only remember it because it was probably the first time in recorded history that a skier from Utah admitted that maybe there was some small period of time somewhere on the planet that the snow was better than Utah's.

[MattB]

I suspect that however it fell (low water cold smoke or mashed potatoes) once it's corn the snow moisture levels are about the same.
It also seems likely that Utah's low altitude and warm spring winds just shorten their season and/or keep things too warm at night for it to form like it does here.

I went for a little road spin at lunch today and got a look at some classic corn lines here which are looking pretty good. I think I'm going to have to check them out sooner rather than later.

[airinwrite]

I meant relative humidity. Once you get spring consolidation, water content of the snow when it fell doesn't matter. It might just be that areas that are drier have more clear days/nights and that's what seems to promote corn formation.

Where I live in WA it's dry and the corn is fantastic, probably the cool clear nights. I think in UT the snow quickly transitions to summer snow, a lot different than corn.

[MattB]

That makes more sense than snow moisture content to me.

[Matt J]

Maybe that's something we can all agree on... corn, yum.

Utah's it's own topic. It's a special place and I've had special days there, but that's true of a few other places too. I wouldn't be opposed to skiing New York or at least the east coast sometime. Tremblant maybe. It's just not exactly bucket list material. I found NYC to be worth a trip though.

[KenR]

There seems to be a lot of uncertainty about just what needs to happen to create good corn snow. An uncertain number of freeze/thaw cycles must occur to produce it. There also is a lot of uncertainty in trying to second guess what may be happening as far as corn production by following the NOAA predicted highs and lows for a specific location/elevation.

This is a great question.
But in general the answers are tricky, and getting the (accurate) data you'd need to implement the answers is not so easy (depends on your region?).
And defining what we mean by "good corn snow" is not so simple.

I hope someone can offer some (approximate) numerical formulas which are useful for some regions in some "simple" situations (e.g. clear night sky).

Ken

[aqua toque]

What about latitude -- in terms of solar angle?

If nothing else, it factors into the length of the daily corn window.