safety
Scotland's Avalanche Forecast: How to Read and Use SAIS
How to read the Scottish Avalanche Information Service (SAIS) forecast before any winter hill day — hazard ratings, aspect diagrams, and what each level means in practice.
Quick Summary
- SAIS (Scottish Avalanche Information Service) publishes forecasts for 6 regions from December to April — Cairngorms, Lochaber, Creag Meagaidh, Northern Cairngorms, Southern Cairngorms and Torridon
- The hazard scale runs 1–5 (Low to Very High) — in Scotland, most avalanche fatalities occur at Considerable (3) because walkers underestimate it
- Check SAIS every day before a winter hill day — conditions can change overnight after wind and snowfall
- SAIS is free at sais.gov.uk — bookmark it on your phone before you need it
Scotland has a functioning avalanche problem every winter. In the Cairngorms and Lochaber alone, SAIS observers recorded over 600 avalanche events in the 2024/25 season. Most do not involve people. The ones that do are frequently fatal. Knowing how to read the forecast before any winter hill day — and understanding what the numbers mean in practice — is a non-negotiable winter skill.
Quick Answer: Scotland's avalanche forecast is produced by the Scottish Avalanche Information Service (SAIS) at sais.gov.uk. It covers 6 regions from December to April. The hazard scale runs 1 (Low) to 5 (Very High). Check it the evening before and again the morning of your hill day — pay particular attention to the aspect and elevation diagrams, which tell you which slopes and which heights are dangerous. At Considerable (3), hazards are described as "human-triggered avalanches likely" — this is the level at which most Scottish avalanche accidents occur, partly because the rating is easy to underestimate.
What SAIS covers
SAIS runs six forecast regions, each based around a mountain area with a dedicated observer:
| Region | Key hills |
|---|---|
| Cairngorms | Cairn Gorm, Ben Macdui, Braeriach, Lochnagar |
| Lochaber | Ben Nevis, Aonach Mor, Mamores, Grey Corries |
| Creag Meagaidh | Creag Meagaidh, Monadh Liath |
| Northern Cairngorms | Cairn Gorm funicular area, Northern corries |
| Southern Cairngorms | Glenshee, Mount Keen, Glas Maol |
| Torridon | Liathach, Beinn Eighe, An Teallach |
If you are hillwalking in any of these areas between December and April, you should check the relevant region before going. For areas outside SAIS coverage (e.g. the Southern Uplands or lower hills), the risk is generally lower but not zero after significant snowfall.
The five-point hazard scale
SAIS uses the European Avalanche Hazard Scale, which runs from 1 to 5:
| Level | Description | What it means in practice |
|---|---|---|
| 1 — Low | Generally stable snowpack | Avalanche triggering possible only on very steep slopes with very heavy loads. Rare in Scotland. |
| 2 — Limited | Mostly stable snowpack | Human-triggered avalanches possible on steep slopes (35°+) with specific aspect/elevation problems. Experienced parties can manage. |
| 3 — Considerable | Unstable slabs on steep slopes | Human-triggered avalanches likely on steep slopes. Natural avalanches possible. Most Scottish fatalities occur here. |
| 4 — High | Very unstable snowpack | Natural and human-triggered avalanches certain on many steep slopes. Avalanche runout extends further than expected. |
| 5 — Very High | Extremely unstable snowpack | Widespread natural avalanches even on gentle slopes. Rare in Scotland, but occurs. |
Reading the aspect and elevation diagrams
The hazard number alone tells you little. The forecast also shows:
The aspect rose
A compass rose coloured to show which aspects (compass directions) are dangerous at each hazard level. In Scotland, north and northeast-facing slopes load most heavily because prevailing southwesterly winds deposit snow on them. But after unusual wind events, any aspect can be dangerous.
The elevation diagram
Shows which elevation bands carry the highest risk — typically above 900m or above 700m depending on the snowpack. Below the affected elevation, the risk is typically lower.
How to use them together: If the forecast shows Considerable on N–NE aspects above 800m, and your planned route crosses north-facing slopes at 900m, you have a problem to plan around — either avoid those slopes, or cross them very early before solar heating, or accept the risk.
The avalanche problem type
SAIS also identifies the problem type:
- Wind slab — the most common Scottish problem. A layer of compacted, wind-deposited snow on lee slopes that can release as a slab. Hard to see from above.
- Persistent slab — an old weak layer buried by subsequent snowfall. Can be triggered days or weeks after it forms; very unpredictable.
- Wet slab — warming temperature causes surface melt, lubricating a weak layer. Afternoon problem in spring.
- Loose snow / point release — unconsolidated snow releasing from a point and spreading downward. Lower consequences than slab but a risk on steep slopes.
What to do with the forecast
Before you go
- Check SAIS the evening before — get the overview and understand the problem type
- Check again the morning of your walk — overnight wind can transform conditions
- Cross-reference with the MWIS mountain weather forecast for your region — high winds + fresh snow overnight means dramatically elevated risk the next day
- Adjust your route to avoid the forecast problem aspects and elevations, or choose a lower-altitude objective
On the hill
The forecast is a starting point, not a guarantee. Conditions can vary significantly from the forecast, and the observer covers a wide area. On the hill, watch for:
- Recent avalanche activity — debris on slopes indicates instability. Do not cross the slope above fresh debris.
- Cracking or "whumpfing" — sounds and cracks radiating from your footsteps indicate an unstable slab. Leave the slope immediately and gently.
- Wind loading — plumes of snow streaming from ridges, cornices building, hollow-sounding snow underfoot on a lee slope
- Rapid temperature rise — warming above 0°C after snow can trigger wet avalanches on sun-facing slopes within hours
SAIS vs MWIS: which to check?
Both. They give different information:
- SAIS (sais.gov.uk) — avalanche hazard, snowpack conditions, aspect and elevation diagrams. Updated once daily from December to April. Check this for winter hill days.
- MWIS (Mountain Weather Information Service, mwis.org.uk) — mountain weather forecast (wind, temperature, cloud, precipitation) for hillwalkers. Updated daily, year-round. Check this for any hill day.
For a winter day, you need both. A Considerable avalanche forecast becomes Very High if MWIS is forecasting 60mph winds and heavy snow overnight.
Where to learn more
The avalanche forecast is a tool for informed decision-making — it is not a substitute for avalanche education. Mountaineering Scotland runs avalanche awareness courses and the Glenmore Lodge runs snow and avalanche courses from around £120. If you plan to spend regular winter days in the Scottish hills above 600m, this training is worth doing before you need it.
Try it yourself
Our free Naismith Calculator
helps plan your winter day — add 10 minutes per 100m of height on snow-covered ground to Naismith's standard formula for accurate timing.
No sign-up required.Frequently Asked Questions
What is the SAIS avalanche forecast?
SAIS — the Scottish Avalanche Information Service — is the publicly funded body that produces daily avalanche hazard forecasts for six mountain regions in Scotland from December to April. Forecasts are produced by field observers who physically check snowpack conditions each day. The service is free at sais.gov.uk and is the primary avalanche safety resource for Scottish hillwalkers.
What time is the SAIS forecast updated?
The forecast is typically updated in the morning (around 7–8am) for the coming day. If you are planning an early start, check the evening before for the broad outlook, then check again on the morning of your walk for the updated forecast.
Is there an avalanche risk on all Scottish Munros in winter?
No. Avalanche risk is specific to slopes above about 30-35° gradient that hold significant snow loading. Lower-angle Munros with rounded tops and gentle ridges carry minimal risk even when the regional forecast is Considerable. The risk is highest in corried mountains with north and northeast-facing hollows: Ben Nevis, Aonach Mor, Cairn Gorm, Beinn Eighe, Liathach, Creag Meagaidh. Flatter plateau hills (e.g. Ben Hope, Ben Klibreck) carry lower risk but are not immune.
What does Considerable (Level 3) mean in practice?
Considerable means human-triggered avalanches are likely on steep slopes. This is the most dangerous rating in practice because it sounds manageable — but it is the level at which the majority of Scottish avalanche accidents occur. Route choice is critical: avoid lee slopes, avoid steep (30°+) snow-covered ground, do not travel beneath loaded slopes, and be ready to turn back if conditions on the hill look worse than the forecast suggested.
Do I need avalanche safety equipment for Scottish hills?
For any serious winter hillwalking on avalanche-prone terrain, yes: an avalanche transceiver (beacon), probe and shovel are standard kit. Without all three, a buried companion has a very low chance of survival. A transceiver alone is insufficient — you need to probe to locate the body precisely, and shovel to dig quickly. The window for survival is roughly 15 minutes. Carry the kit and know how to use it — practice transceiver searches before you need them in an emergency.
Where can I learn more about Scottish avalanche safety?
Mountaineering Scotland runs avalanche awareness events and the Glenmore Lodge offers snow and avalanche courses at glenmorelodge.org.uk. The SAIS website also has an extensive archive of forecast reports and avalanche incident summaries that are worth reading before your first winter season in the hills.
Related articles
- Winter Hillwalking in Scotland: The Beginner's Guide — ice axe, crampons, and getting started safely
- How to Read the Mountain Weather Forecast — using MWIS and Met Office for hill days
- How to Start Hillwalking in Scotland — the broader beginner guide
- Munros section — individual hill pages with SAIS region links and winter notes
This article is for informational purposes only. Avalanche safety requires practical training and qualified instruction — the information here is not a substitute. Never enter avalanche terrain without appropriate training, equipment and experience. OutdoorSCOT is not liable for any incidents arising from the use of this information.
Sources
- SAIS avalanche forecast — Scottish Avalanche Information Service
- Avalanche awareness — Mountaineering Scotland
- European Avalanche Hazard Scale — European Avalanche Warning Services
- MWIS mountain forecasts — Mountain Weather Information Service