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Snowdonia

Confidence

High confidence in deterioration of conditions through Sunday, but moderate for the extent of cloud, rain, and timing. Also Moderate confidence for another dull start Monday, but clearing through the day. High confidence for warm day Tuesday, with a change to fresher conditions Wednesday.

Sunday 20 August 2017

Weather hazards

Poor visibility Medium likelihood Hide detail

Poor visibility presents challenging route finding conditions. Visibility could be significantly less than 50 metres in all directions with few or no visual references, especially on featureless moors or plateaux. Distances become hard to judge and cliff or cornice edges can be difficult to recognise. These conditions require good navigational skills. There is a risk of white-out conditions when mist or fog is combined with extensive snow cover.

Heavy persistent rain Medium likelihood Show detail

Prolonged exposure to heavy rain can result in drenched clothing and a risk of hypothermia if not wearing good quality waterproofs. Terrain may turn increasingly boggy underfoot, while mountain streams will rapidly rise into spate and may become impassable. There may also be a risk of flooding in valleys or glens. If there is snow cover, a heightened avalanche hazard is possible and avalanche reports should be consulted where available.

Strong sunlight Low likelihood Show detail

Harmful UV levels from sunlight increase with altitude giving a greater risk of sunburn and eye damage, even on some overcast days. On breezy days, the cooling effect of wind on exposed skin may disguise any feeling of sunburn until it is too late. If there is snow cover, glare increases the effect of UV rays especially on the eyes. It is advisable to wear sun block, protective clothing such as a long-sleeved top and hat and have good quality eye protection.

Forecast

A bright, often sunny morning. Turning dull with rain later and low cloud on hills.

Weather at 800m

06:00 09:00 12:00 15:00 18:00 21:00
Sunny intervals Sunny intervals Cloudy Heavy rain Heavy rain Light rain
10% 10% 10% 60% 80% 60%
Chance of precipitation
1,700 1,800 2,000 2,300 3,200 3,400
Freezing level (m)
The level above which snow is expected to settle or the ground is expected to be frozen

Wind speed and direction (mph) By altitude above mean sea level

06:00 09:00 12:00 15:00 18:00 21:00
900m W 14 16 SW 13 16 SW 10 15 S 14 18 SE 17 22 SE 19 24
600m SW 9 11 SW 10 14 S 10 16 S 11 15 SE 11 16 SE 14 20
300m SW 3 7 SW 5 11 S 6 14 S 6 13 SE 5 13 SE 8 19
Valley SW 6 12 SW 11 19 SW 13 20 SW 9 16 SE 8 12 E 8 12

Temperature (°C) By altitude above mean sea level

06:00 09:00 12:00 15:00 18:00 21:00
900m 7 7 9 9 9 10
600m 9 10 11 12 11 12
300m 11 13 14 15 13 13
Valley 11 15 16 16 14 14

Feels like temperature (°C) By altitude above mean sea level

06:00 09:00 12:00 15:00 18:00 21:00
900m 3 4 6 6 6 6
600m 6 7 9 10 9 9
300m 10 12 13 14 13 12
Valley 11 14 15 15 14 13
Sunrise: 06:05   Sunset: 20:33
Moon phase: Waning crescent

Weather

A dry morning, with some sunny spells. High level cloud will increase during the early afternoon and make the sunshine more hazy, then lower and thicken with rain arriving later in the afternoon. This perhaps becoming heavy at times, especially during the evening, before gradually easing after dusk.

Chance of cloud-free mountain/hill tops at 800m

70% during the early morning, with some patchy cloud above 600m. This then increasing to 90% , but becoming less than 10% by evening with cloud descending onto hills above 400,

Visibility

Generally good to very good during the morning, with distant peaks visible, if a little hazy. However this reducing to moderate through the afternoon and becoming poor to very poor as cloud and rain descends upon to the tops, with views of even nearby hills becoming very limited.

Meteorologist's view

Despite good morning conditions, with some brighter spells and light winds, these conditions are likely to deteriorate through the afternoon and evening. This will lead to some wet and difficult descents, with poor visibility developing.

Ground conditions

No adverse ground conditions reported on 20 of Aug

Monday 21 August 2017

Sunrise: 06:07   Sunset: 20:31
Moon phase: New

Weather

A dull and cloudy start with drizzle likely during the morning, and hills obscured above 400 metres. Conditions may improve during the afternoon, especially across eastern parts, with cloud gradually lifting and breaking. However patchy cloud will still linger to many hills above 600m. It will also feel rather humid.

Temperature

  • At 800m 12 Celsius
  • Valley 16 Celsius
  • Freezing level Well above the summits.

Visibility

Very limited views expected during the morning, with even some lower hills obscured by cloud, along with some occasional drizzle. Some moderately distant hills could become visible during the afternoon, mainly in the east.

Chance of cloud-free mountain/hill tops at 800m

Less than 10% at first, rising to 30% during the afternoon, and 60% in the east.

Maximum wind speed expected

Southeasterly 15-20mph, becoming southwesterly 10-15mph during the evening.

Tuesday 22 August 2017

Sunrise: 06:08   Sunset: 20:29
Moon phase: New

Early low cloud will obscure many hills tops. However this will lift and break to give sunny intervals for most. Patches of fog may remain on peaks with a few spots of drizzle. Feeling warm and humid.

Wednesday 23 August 2017

Sunrise: 06:10   Sunset: 20:27
Moon phase: New

A fresher day, with cloud breaking, to sunny spells and a few showery outbreaks of rain. Cloud may cover hills above 600 metres at times. Turning rather breezy at height.

Thursday 24 August 2017

Sunrise: 06:12   Sunset: 20:25
Moon phase: New

A mixed day, with some sunny spells, but also scattered showers with some cloud covering the hills above 600 metres. It will be another breezy day, with blustery southwesterly winds across the tops.

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