“The strength of the sun’s UV rays reaching the ground depends on a number of factors, such as:

• Time of day: UV rays are strongest in the middle of the day, between 10 am and 4 pm.
• Season of the year: UV rays are stronger during spring and summer months. This is less of a factor near the equator.
• Distance from the equator (latitude): UV exposure goes down as you get further from the equator.
• Altitude: More UV rays reach the ground at higher elevations.
• Cloud cover: The effect of clouds can vary, but it’s important to know that UV rays can get through to the ground, even on a cloudy day.
• Reflection off surfaces: UV rays can bounce off surfaces like water, sand, snow, or pavement, leading to an increase in UV exposure.”

American Cancer Society (https://www.cancer.org/cancer/risk-prevention/sun-and-uv/uv-protection.html)