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Snowdonia

Confidence

High for a continuation of unsettled conditions. Low for details concerning the rain on Sunday.

Thursday 17 August 2017

Weather hazards

Strong sunlight Medium likelihood Hide 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.

Heavy persistent rain Low 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.

Forecast

Low cloud and patchy rain clearing to leave a day of sunny spells and showers.

Weather at 800m

06:00 09:00 12:00 15:00 18:00 21:00
Fog Cloudy Sunny intervals Light shower day Light shower day Light shower night
60% 20% 30% 50% 60% 60%
Chance of precipitation
1,900 1,900 2,100 2,300 2,000 2,200
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 17 21 SW 21 26 SW 25 34 SW 28 38 SW 32 42 SW 32 42
600m SW 12 15 SW 18 24 SW 20 30 SW 22 30 SW 24 33 SW 23 33
300m SW 6 11 SW 12 21 SW 13 28 SW 13 27 SW 13 30 SW 12 28
Valley W 12 23 SW 21 34 SW 24 42 SW 21 37 SW 21 38 SW 20 36

Temperature (°C) By altitude above mean sea level

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

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

06:00 09:00 12:00 15:00 18:00 21:00
900m 5 5 5 6 4 4
600m 9 8 8 9 8 7
300m 12 12 13 13 12 11
Valley 12 13 14 14 13 12
Sunrise: 06:00   Sunset: 20:40
Moon phase: Third quarter

Weather

Low cloud and patchy rain soon clearing, then becoming dry with sunny periods, especially across the east. Western facing slopes more likely to see some patchy cloud at times. This afternoon scattered showers will arrive, with the odd heavier one possible, these likely to continue into the evening. Winds will freshen late in today.

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

10% initially becoming 40% once rain clears. 80% by mid-morning with cloud associated with showers likely to cover higher peaks.

Visibility

Becoming very good generally once rain clears with distant hills discernible. Reducing in showers to a few kilometres, though only briefly.

Meteorologist's view

Data looks to offer good guidance to expected conditions.

Ground conditions

No adverse ground conditions reported on 17 of Aug

Friday 18 August 2017

Sunrise: 06:02   Sunset: 20:38
Moon phase: Waning crescent

Weather

A day of sunshine and blustery showers. Some of the showers will be heavy, with thunder possible. Winds will be strong, possibly gale force over higher peaks and ridges, and it will feel chilly in those strong winds.

Temperature

  • At 800m Plus 9 C.
  • Valley Plus 7 rising to plus 15 C.
  • Freezing level Well above the summits.

Visibility

Very good in between showers but expect rapid, albeit short lived deteriorations associated with showers.

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

80% with only heavy showers likely to lower cloud onto higher tops.

Maximum wind speed expected

Westerly 45 to 50 mph.

Saturday 19 August 2017

Sunrise: 06:03   Sunset: 20:36
Moon phase: Waning crescent

Another day of sunshine and showers although they will tend to be lighter than on Friday and tend to die away through the afternoon. The strong winds should ease.

Sunday 20 August 2017

Sunrise: 06:05   Sunset: 20:33
Moon phase: Waning crescent

Dry at first but there is an increasing risk of some rain and strong winds through the latter part of the day.

Monday 21 August 2017

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

Considerable uncertainty but at this stage Monday looks likely to see some strong winds and heavy rain, especially at first. Perhaps becoming drier and brighter later.

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