This is the current Met Office forecast for Sunday:
Rather cloudy with showers, these most frequent around the middle of the day, perhaps merging to more persistent rain for a time. The east of the park is likely to see the best of brighter intervals, with these becoming more prevalent into the evening. Winds remaining strong.
Visibility
Very good out of precipitation, moderate in rain or showers, very poor in any hill fog patches.
Hill Fog
Broken around 500m for a time in more persistent precipitation.
Max wind above 400m
Southwesterly 40mph.
Temperature
Valleys:
Plus 5 becoming 10 Celsius.
600m:
Plus 5 becoming 2 Celsius.
Freezing level:
Above the peaks.
Wind Chill? definitely sub zero!
The race organiser advises that In addition to standard FRA kit, you are strongly advised to wear warm full-length tights and a thermal top and to carry an extra layer.