Interesting report today.

[surf88]

The most notable snowpack related topic we are watching is the crust that encapsulated the mountain earlier in the week. A steep temperature gradient over the past 48 hours has formed rapid faceting beneath the crust. These facets are growing through vapor movement from below the crust and through robbing it of it's own moisture. This is currently doing 2 things we will be watching. First it's developing an increasingly weak layer under the crust and second is weakening the tensile strength of the crust to support load from above. This tensile strength may become so weak there is a remote potential for a human trigger to actually avalanche the crust itself. This could be a problem if it knocks you off your feet in a compromising location. This weakening will also become a concern with another 24 hours of facet growth and the snow coming in tomorrow and Saturday. Snow is expected to come in on light WSW winds and increase while wrapping to the NW through the day. If this occurs I would expect a light density soft slab or unconsolidated snow to be loaded with an increasingly dense slab over it through day light hours. This may place slabs with a higher degree of elastic energy and fracture propagation potential over several potential weak layers. The weak layers to watch should be the light density new snow itself, the interface with the icy crust where it's exposed and not already buried, and the increasing weak facets beneath the crust. To add a little more complexity to this is the variability of our current snow surface. There are a number of areas that already have some new snow sitting on crust that fell and loaded since Monday's sleet/ice pellet event that formed the icy layer. These locations should have slower facet growth due to a more diminished temperature gradient and will offer better adhesion for new snow. So the key element here is the new loading snow on Friday and Saturday depositing over different surface conditions creating for a great degree of spatial variability (aka-different conditions) from location to location. I know this was all a lot to soak in so we will focus in a bit tomorrow as the weather system becomes clearer and facets have another 24 hours to do their thing. The good news is snow is on the way with 3-6 inches (7.5-15cm) forecasted with upwards of .6" (1.5cm) of water. But as last week's weather event taught all of us in the weather business Mother Nature doesn't always comply with what we say she will do. This is what makes it so interesting, compelling, vexing and motivating to figure her out. Another weather item to watch is the dropping temperatures through the day on Saturday sending the summit back deep into the negatives for the overnight.
I thought the crust analysis in this report was pretty interesting.

[RR]

I can't wait for episode 2!

Seriously...it is interesting :eek:

[surfy]

I think what he's trying to say is that avalanche conditions will be high this weekend.

There, I said it with 1500 fewer words.

[PWDR8S]

Vewy vewy intewesting. I suspected these conditions would make it very interesting to follow.

Thanks for posting that. We'll have to remember this layer(s) later in the season. It will be important.

[RR]

Here's todays update...
Tuckerman and Huntington Ravines currently have Low avalanche danger. Natural avalanches are very unlikely and human triggered avalanches are unlikely except in isolated pockets. Normal caution is advised.

Another storm that wasn't. It currently appears that the brunt of the precipitation will fall to our East and North. Although the NWS still has a range of 4-9" (10-22.5cm) for the next 48 hours a close scrutiny of the mountains points to less. Through conversations with the Observatory we should be at the bottom end of the range for each 12 hour forecast period. We expect an inch (2.5cm) for our mountains today with another 1-2" (2.5-5cm) for the overnight into Saturday morning. Snow should begin a bit later today as we are currently in a dry slot between moisture to our south moving northeasterly and a system moving east from upper New York State. I believe snow accumulations today will keep the avalanche danger at Low, however be prepared to move into Moderate if we pick up 2" (5cm) during daylight hours. This is primarily due to the anticipated winds for the day. Winds have already moved from the SW to the W as of 7am and are expected to continue to the NW and increase from 30mph to 70+ (48-112+kph) late this afternoon. Snowfall will therefore be loaded on mostly E to SE aspects with an increasingly dense slab over softer slab from the beginning of the event. This will all depend on the wind speeds and direction when the precipitation initiates and how much we actually receive. We have been watching a facet layer beneath the crust and believed it could be a stability issue for this weather event. I don't feel this is the case any longer. In addition to diminished snowfall expectations field observations in Tuckerman witnessed an incredible amount of spatial variability. There were different things going on with every quick pit, I can't come up with a consistent theme to focus on except variability. Even the crust differs from location to location with a fair amount covered by hard slab from Tuesday and Wednesday morning. With warming temperatures the gradient driving facet growth has slowed down keeping near surface faceting to 1mm-1.5mm in size. As new snow comes in it will cover the Ravine's great surface diversity which will make it challenging to know what it may be attempting to bond with below when seeing the old surface is no longer an option. Did snow fall on a slick crust, a textured wind effected slab, or a smooth hard slab? All of these scenarios will occur with enough snow. So be ready to exercise caution this weekend and consistently re-assess snow stability.

The other main concern besides snow stability for tomorrow will be very high and very gusty winds with a dropping temperatures. We are expecting gusting over 110mph (177+kph) with a high temperature of only -15F (-26C). As tomorrow is a Saturday this is very concerning as more people will consider attempting to go to the summit. Do not consider this a personal challenge to overcome. If the forecast plays out these are truly desperate conditions. High winds are underestimated by many because they have been in 70mph (112kph) winds so what could another 40mph (65kph) matter? Trust me, A LOT! Anyone being out at all should have the best arctic mountain clothing possible. Feet, hands, and face are the locations have we have seen the most frostbitten. So good boots, mittens and the often-neglected face gear is extremely important.

[surfy]

Translation: Too effin miserable to come play on the mountain this weekend.

[DMC]

"A steep temperature gradient over the past 48 hours has formed rapid faceting beneath the crust. These facets are growing through vapor movement from below the crust and through robbing it of it's own moisture. "

I always thought this stuff was cool... Water moving through snow...

I wonder what the temp gradient was?

So what i got out of it is...
Temps are changing and drawing moisture from the snow near the ground to the top of the snow. This makes the snow on the bottom less stable and causing not just facteting but creating large factets underneath a layer of crust from ice/sleet earlier in the week.. Meanwhile more snow is expected to be depoisted on the stuff and thats bad...

[Sledhaulingmedic]

Nice catch!

IIRC, this occurs mostly early season with a new, not-very-deep snow pack, warmer ground, very cold air. The temperature gradient is greater because of the large temp difference across a small snow depth.

(Snow temp@ ground - snow temp at surface)/snpw depth=temp gradient

(Someone correct me if I'm wrong.)

The result it TG metamorphism and a VERY WEAK layer. Nice info D

Edit: "I must spread..."