Guide to mountain forecasts

Moderate or heavy dry falling snow (either continuous or in the form of frequent showers) with winds speeds of 30 mph or more and a reasonably extensive snow cover.

Near zero visibility and total disorientation likely.

Heavy snow falling during the day with over 15 cm (6 inches) of average depth of fresh snow expected.

Significantly reduced visibility, potential danger with losing footing if paths are obscured. Navigation more difficult. Progress likely to be affected to a considerable degree. Marked increased risk of white–out conditions. Marked increased risk of hypothermia if snow is wet

Winds with consistent gusts above 70 mph.

Risk of losing one’s footing in gusts. Danger increased on exposed ridges. NB When gusts of over 90 mph expected, winds will be ‘Hurricane force’ with likelihood of being blown over.

Winds with consistent gusts above 50 mph.

Considerable buffeting.

Cloud bases at or below 600 metres (500 metres for Peak District) for two hours or more.

Please note that on some high level plateaux, especially the Cairngorms, as well as on Ben Nevis, considerably higher cloud bases can be as hazardous.

Significantly reduced visibility resulting in major navigation difficulties, especially where there is extensive snow cover with the risk of white–out conditions. White–out conditions are defined as when one’s field of view becomes totally featureless due to a combination of mist or fog and deep snow cover, with or without falling snow.

Lightning strikes.

Lightning strikes are likely to cause danger, especially on exposed tops and ridges

When cooling is greatly increased by strong winds, normally exceeding 35 mph. mean wind speed. If driving rain or sleet is also forecast winds may be lower than 35 mph.   

Please note that other factors such as mist, sunshine, precipitation and snow cover will either mitigate or enhance cooling.

Considerable risk of hypothermia and frostbite, unless adequately equipped and protected. NB: Even though winds in valleys or glens may be light, sudden and very marked increases can occur at higher levels.

Persistent, heavy, rain (or sleet), lasting at least 3 hours, or over 40 mm expected in 24 hours, starting from dusk of the previous day.

Risk of major discomfort unless adequately equipped and protected. Reduced visibility possible. Watercourses likely to become rapidly in spate and marked increased risk of very boggy terrain. Marked increased risk of hypothermia, especially if combined with strong winds, unless adequately protected.

Exposure to moderate or high levels of UV

During snow conditions, significant glare off the snow pack.

Please note: The Strong Sunlight hazard used in the Mountain Area Forecasts is based on both the UV level corrected for altitude and weather conditions in each mountain area. In winter, where there is extensive snow cover and strong sunlight, this also takes into account the risk of glare off the snow pack. For this reason, the UV index on the Mountain Area Forecasts may differ from those on our standard forecasts.

Risk of sunburn — seek shade during midday hours, cover up and wear high protection factor sun screen.

High levels of reflected light which may be unpleasant and potentially lead to snow blindness — wear appropriate eye protection.

A brief summary of conditions over the area in question (including all the Scottish Highlands for the Scottish areas, and all of Wales for the Welsh areas). As suggested, this is a summary and should be used in conjunction with the other parts of the Mountain forecast in order to understand the expected weather.

The level of risk of several hazards is provided. This is assessed as either Nil, Low, Medium or High and shown using a traffic light system. Where a risk is identified, additional information is provided. These are described for Day 1 of the forecast only.

For detail on the criteria and impacts of the various hazards see the mountain hazards key.

A weather symbol is provided to give a summary of the weather conditions for each three hour period. This gives an indication of the most likely conditions across the majority of the area. You should remember that this symbol will not be representative of the conditions at every location in the area and at all times through the period. This should be used in conjunction with the other parts of the Mountain forecast in order to understand the expected weather.

The Probability of Precipitation section indicates the percentage likelihood of precipitation falling in the area during the period. This could be in the form of rain, drizzle, sleet, snow etc. More detail will be contained in the detailed forecast section.

The forecasts are for all levels, but will emphasise weather above 600 metres for the Scottish areas, 500 metres for the Lake District and Snowdonia, and 400 metres for the Peak District, Yorkshire Dales and Brecon Beacons. Please note that if precipitation, especially heavy snow, is forecast, the visibility will be markedly reduced.

Also known as Clarity of Air, this can be classified in the following ways:

1. Very Hazy — less than 10 km
2. Hazy — less than 30 km
3. Good — between 30 and 60 km
4. Excellent — over 60 km

Indicates whether low cloud will cover the ground within a region and is classified in the following ways:

1. Persistent — covering ground over 90% of the time
2. Periods — between 50 and 90% of the time
3. Occasional — between 20 and 50% of the time
4. Occasional Patches — less than 20% of the time

Winds speeds cited are the highest expected, these normally occurring on exposed peaks or ridges, though it should be noted that winds in mountains are very turbulent. Any changes during the course of the day will be emphasised, as will any differences in speeds over the forecast area.

Freezing Level is defined as the level above which snow is expected to settle, or the level above which the ground is expected to be frozen. Account is not taken of melting of surfaces in direct sunshine during the day. In most situations, except in mid–winter, this is to be expected during the middle part of the day. In late spring or early summer it is common to find the snow cover frozen, even when other surfaces are not. Please note that the freezing level may not appear to tie in with the temperature at 900 metres.

When severe weather warnings have been issued for the area this will be indicated at the bottom of the forecast.

A brief text summary for days three to five.

Currently ground conditions are only available for a limited number of areas where we are able to guarantee reliable information from authoritative partners. This information is generally only available during the winter season, but may be available at other times of year during severe weather:

Lake District — October to April
Snowdonia — October to April

There is a printable view which contains the whole forecast (grouped conventionally). This can be added to favourites or bookmarked and is recommended for use on hand–held devices for speed of download