Weather warnings may have been issued

Brecon Beacons

Confidence

High for unsettled theme throughout, and for a very mixed day on Friday, with cloud obscuring hills. Also high for a dry start Saturday, but confidence is low regarding timing and extent of rainfall later in the day. Confidence then remains very low with the details and timings thereafter.

Friday 18 August 2017

Weather hazards

Gales Medium likelihood Hide detail

Progress will be impeded by very strong winds. Walking will be difficult and strenuous at times with a potential for one to be blown over in gusts. There can be a marked increase in winds through cols or on exposed ridges and summits. Distances often take longer to cover with compass bearings becoming more difficult to follow accurately.

Poor visibility Low likelihood Show 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.

Thunderstorms Low likelihood Show detail

Lightning is a significant mountain hazard which can result in serious injury or death. Mountain terrain often leaves one highly exposed to lightning strikes. Hail may give unpleasant conditions with torrential rain and localised flash flooding also possible, mainly in Summer months.

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

Windy with sunny spells and showers, some of these heavy.

Weather at 600m

06:00 09:00 12:00 15:00 18:00 21:00
Light shower day Heavy shower day Heavy shower day Heavy shower day Light shower day Light shower night
50% 60% 60% 50% 30% 30%
Chance of precipitation
1,800 1,700 1,700 1,800 2,100 2,100
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
600m W 16 21 W 19 24 SW 23 33 W 27 39 W 31 43 W 28 39
300m SW 9 19 W 13 25 SW 15 32 SW 16 36 W 18 39 W 16 34
Valley W 10 22 W 12 26 W 14 32 W 16 36 W 16 37 W 15 33

Temperature (°C) By altitude above mean sea level

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

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

06:00 09:00 12:00 15:00 18:00 21:00
600m 5 6 6 6 5 6
300m 9 10 11 10 9 9
Valley 10 12 12 11 10 10
Sunrise: 06:02   Sunset: 20:32
Moon phase: Waning crescent

Weather

A bright and breezy start to the day is expected, although scattered showers will soon spread east, perhaps heavy at times. The odd rumble of thunder is also possible. Winds are likely to strengthen further later this afternoon and evening as an area of more organised showers crosses Wales, though these may well stay north of the park.

Chance of cloud-free mountain/hill tops at 600m

90% during the morning, with cloud obscuring some hills above 800m during showers. Decreasing to 70% during the evening, with some ragged cloud descending to around 600m. This then gradually clearing around and after dusk, with 90% chance of cloud free mountain tops by midnight.

Visibility

Good visibility at first, with distant hills visible, and only becoming hazy during showers. This reducing to moderate to poor, during the afternoon with only nearby peaks visible. Some very poor visibility possible across highest summits.

Meteorologist's view

A very mixed day, with showers and rain interspersed with some drier, brighter intervals, leading to the potential for conditions to change rapidly. Winds likely 10-20mph stronger than indicated in the table above especially across exposed ridges and summits, so some care will be needed across any exposed sections at height.

Recent rainfall

  • Location: Neuadd Rain (Near Pontsticill)
  • Altitude: 353m
  • Measurement date: 03:00 on Fri 18 Aug 2017
  • Last 24 hours: 5mm
  • Last 48 hours: 19.2mm
  • Last 72 hours: 19.2mm

Rainfall data provided by the Environment Agency. The Met Office is not responsible for content provided by third parties and may remove this data without warning.

Saturday 19 August 2017

Sunrise: 06:04   Sunset: 20:30
Moon phase: Waning crescent

Weather

Becoming mainly dry overnight and breezy. Sunny spells will develop through the morning along with some scattered showers. However the showers should be lighter than those of Friday and will tend to die away through the afternoon. The evening should be fine with some clear spells.

Temperature

  • At 600m Plus 9 Celsius.
  • Valley Plus 7 Celsius becoming Plus 17 Celsius.
  • Freezing level Above the summits.

Visibility

Good to very good during the morning, with distant hills visible. Some minimal reduction likely during showers, but very poor when in amongst the cloud.

Chance of cloud-free mountain/hill tops at 600m

80%, with some hills above 800m obscured. Increasing to 100% by midday.

Maximum wind speed expected

Westerly 25 to 30 mph.

Sunday 20 August 2017

Sunrise: 06:06   Sunset: 20:28
Moon phase: Waning crescent

A cloudy and humid start, with hills above 500m obscured, and outbreaks of drizzle likely. Winds strengthening ahead of a band of rain, turning heavy and persistent for a time.

Monday 21 August 2017

Sunrise: 06:07   Sunset: 20:26
Moon phase: New

Monday is likely to be dry but warm and humid with low cloud likely to plague some south-west facing slopes. Rain may return from the north-west later.

Tuesday 22 August 2017

Sunrise: 06:09   Sunset: 20:24
Moon phase: New

Early cloud will break to sunny spells, and scattered showers. It is also likely to be feeling much fresher once again.

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