Mountain forecast guide

Moderate or heavy 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.

Very strenuous walking conditions with any mobility virtually impossible over exposed ground. A high risk of being blown over and standing may be impossible at times with a risk of being blown off one's feet. Tasks such as using a map, putting on extra clothing or communication become extremely difficult away from shelter.

Winds with consistent gusts above 50 mph.

Difficult and strenuous conditions with a risk of being blown over. There is often a marked increase in winds through cols or on exposed ridges and summits. Distances can take longer to cover and compass bearings become harder to follow accurately.

Severe reduction in visibility due to low cloud, falling snow or blowing snow. Visibility often 50m or less.

Difficult route finding with few or no visual references and risk of disorientation. Distances can become hard to judge. A risk of white-out conditions when heavy falling or blowing snow or fog is combined with deep snow cover.

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.

Covering the whole 5 day period. Describes the main uncertainties or forecasting challenges. For example, if there is uncertainty in the timing of a weather front bringing rain or snow across the area you may want to plan to be off the hill in good time. Or there may be high confidence for certain conditions to persist for a few days giving the user confidence to plan routes further in advance.

A few words to set the scene and give the main emphasis for the day. This is a brief summary and should be used in conjunction with the other parts of the mountain forecast to gain a full picture of the conditions.

Nine weather hazards have been identified as most significant for the mountain environment. The likelihood of each hazard is assessed as either Nil, Low, Medium or High.

The likelihoods are based on predicted severity, extent and timing of each hazard across the forecast area and provide a general guide or overview of what may be encountered. There are often large variations in conditions depending on location, height and time of day so this should always be used in conjunction with the rest of the forecast to get the full details. Note that hazards only affecting a small part of the area or occurring for a short period of the day or at night will often be assigned a lower likelihood.

For the full list of hazards please see the Hazard Criteria table above.

Weather symbols summarise the weather conditions at three hourly intervals for the height stated. This gives an indication of the most likely conditions across most of the area. The symbol will not be representative of the conditions at every location so it must be used in conjunction with the other parts of the mountain forecast to gain a full picture of the expected weather.

The Chance of precipitation section indicates the extent of the forecast area likely to be affected by precipitation at each time. This could be in the form of rain, drizzle, sleet, snow etc.

Winds and temperatures at different heights and freezing level given for three hourly intervals throughout the period.

The table represents typical conditions on exposed ground but please note there are often large variations in conditions in the mountain environment which may not be represented in the table. For example, ridges or high plateau may experience stronger winds than shown or there may be large variations across the forecast area such as during the passage of a low pressure centre.

When significant differences are expected from those shown in the table, either aerially or with height, these are described in the ‘Meteorologist’s View’ section.

Description of precipitation (type, extent, intensity and duration), extent of cloud and sunshine and any other weather elements to consider. The forecast is for the whole 24 hour period but with more detail provided for daylight hours and for 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.

The chance of your efforts being rewarded with a view from the summit. This section includes full details on the extent and persistence of low cloud across the area. Significant aerial or temporal variations are highlighted in the text.

Also known as clarity of air outwith any low cloud, there are a number of ways this is described but can be classified in the following way:

i. Very Hazy - less than 10 km

ii. Hazy - less than 30 km

iii. Good - between 30 and 60 km

iv. Excellent - over 60 km

An opportunity for the Meteorologist to give their view on the weather situation and include any further information not otherwise covered in the forecast. This section highlights any notable detail or variations in temperature and winds not already covered in the data tables such as funnelling effects across ridges or strong downslope gusts. It may also highlight notable changes in the weather or any particularly unseasonable conditions such as extremes in temperature.

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 above which the ground is expected to be frozen. Account is not taken of melting of surfaces in direct sunshine during the day.

Ground conditions are provided by authoritative partners in the Lake District and Snowdonia for October to April.