UKC

Hi, I want to learn a more about identifying the potential risk of avalanche during winter conditions and hoping this was a good place to learn alongside other media’s. 
 

I did a winter skills course a few years ago that touched briefly on physically identifying snowpack condition (windslab mainly) and cornice formations whilst you are on site, but I’m interested in learning how to use forecast information to help judge the risk beforehand. 
 

I’ll focus on Snowdonia because this is my closest stomping ground and there is no official avalanche forecasting available like there is in Scotland and I’ll also focus on PFG as this is on my list at some point this year should conditions allow. 
 

Take this forecast image attached just as an example. Ignore the fact it’s far in advance, imagine this was an accurate forecast a couple of days beforehand. Are my understanding of these points correct and would this forecast indicate safe climbing conditions in the days following the snowfall indicated on day 6/7.

1. Given that PFG is north facing, and the winds are coming from the N/NE/NW - my understanding is that a windslab nor cornice wouldn’t form within the gully itself but instead on the south side of the ridge and the wind direction being fairly consistent would reduce the risk of cross loading? 

2. Given that this would be the first snow to settle in the gully, there would be no bond between snow packs that could fail?

3. If climbed before the snow consolidated, there could be a risk of powder avalanche?

4. Given the continuous frozen temperatures, thaw and a wet slab avalanche would be unlikely? 
 

Thanks,

By "PFG" do you mean Parsley Fern Gully (I)? I wish you would say so if so, thank you 

Apologies, yes I do. 

I've forgotten where you get this forecast. Could you remind us please. Thank you.

Thank you! For clarifying 

This from the Scottish Avalanche service will help you in decision making.

https://beaware.sais.gov.uk/

The forecast is taken from https://www.mountain-forecast.com/peaks/Snowdon/forecasts/1085

I also refer to Met Office, MWIS and the Yr Wyddfa Ground Conditions report

This is very helpful and just what I was after, thank you.

This framework is great. For novices, it helps to identify when "I don't know" is your response to judging conditions and for experienced folk it reduces risk of falling into heuristic traps.

Historic weather forecasts and their corresponding avalanche reports are online. If you want to invest time and effort in this, I would recommend looking at the weather forecast, making up your own avalanche report and then checking it against the real avalanche forecast. Bruce Tremper's "Staying alive in Avalanche Terrain" is the go-to book on the topic.

In reponse to the OP: I'm just someone on an online forum, so checking the resources above and making up your own mind is a good idea, but FWIW I reckon you're thinking along the right lines. In steep and complex terrain the wind can be whip snow around and deposit it in odd places, so just be aware that small areas of slab can be caused by very localised wind currents. Also, full depth avalanches can form where the weak layer is between the full snowpack and the ground (e.g. wet snow on slippy grass).

Something to bare in mind is the temps of the snow and the ground beneath it, there are various ground temp monitoring stations. I believe there is one on trinity face. This should help to identify if the air temp is warm or cold and if the underlying ground temp is warm or cold. This can help in predicting full thickness wet snow pack avalanches. Every year in the clachaig they have a snow safety evening. They may post a video of it somewhere it's interesting to watch. 

Thanks

Taking avalanche advice off random users of a forum isn't ideal, but you've had some good advice to look at the Be Avalanche Aware framework. You can use the basic principals of this to help you try and make sound decisions. The Chris Walker trust has some good collated information you might find helpful: https://chriswalkertrust.co.uk/avalanche-awareness-resources/

Snowpack analysis whilst on the mountain is actually of limited use outside of general interest and confirming what you know. If you're looking at windslab and worrying about it, then you're in the wrong place and should have taken that into account in the planning phase. Use the BAA framework to assess the hazards and work out how to avoid them.

However, to answer your questions:

1: Generally, you are correct that windslab and cornices both build in the lee of the wind. Sometimes this is as simple as the opposite side of the mountain to the prevailing wind direction, sometimes localised topography has a huge effect and can cause accumulations in places you wouldn't expect. A cornice won't form 'in' a gully but around the rim at the top. Windslab can occur anywhere. 

2: Full depth avalanches can occur to ground level and many different layers can build during one snowfall event. E.g snowfall on bare ground overnight could form: 5cm of powder, 10cm of windslab, 1cm of graupul and 10cm of windslab giving hazardous layers even if there was no snow on the mountain the day before. This example is quite extreme, but illustrates that one snowfall event isn't just even snowfall. 

3: Powder avalanches can occur, but theres rarely enough fresh powder in Snowdonia to make this an issue. Windslab is far more prevalent. From a climbing and enjoyment perspective, battling up Parsley Fern Gully when it's full of powder is going to be slow and unpleasant. 

4: Given settled cold conditions, any snow which falls will stay in the state it has formed in. Cold settled conditions where the snow does not change condition will preserve any weak layers in the snow. A wet, thawing, avalanche would only occur if it's thawing, often full depth sliding on the grass which has been lubricated by melt water. 

Your ideal conditions for climbing easy snow gullies come after a cold spell to cool the ground and freeze the turf, a big dump of wet snow, a slight thaw and then a hard freeze. This thaw-freeze cycle will turn powdery or mushy unconsolidated snow into firm neve which is easy and enjoyable to climb, although serious in the event of a slip or fall.