A UV index reading of 8 to 10 means very high risk of harm from unprotected sun exposure.
Take extra precautions because unprotected skin and eyes will be damaged and can burn quickly.
Minimize sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun protective clothing,
a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen
every 2 hours, even on cloudy days, and after swimming or sweating.
Bright surfaces, such as sand, water, and snow, will increase UV exposure.
On the ground:
Wind felt on face; leaves rustle; ordinary vanes moved by wind.
On the sea:
Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break.
Power systems: Voltage corrections may be required,
false alarms triggered on some protection devices.
Spacecraft operations: Surface charging may occur on satellite components,
drag may increase on low-Earth-orbit satellites, and corrections may be needed for orientation problems.
Other systems: Intermittent satellite navigation and low-frequency radio navigation
problems may occur, HF radio may be intermittent,
and aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic latitude.).
A UV index reading of 6 to 7 means high risk of harm from unprotected sun exposure.
Protection against skin and eye damage is needed.
Reduce time in the sun between 10 a.m. and 4 p.m. If outdoors,
seek shade and wear sun protective clothing, a wide-brimmed hat, and UV-blocking sunglasses.
Generously apply broad spectrum SPF 30+ sunscreen every 2 hours,
even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow,
will increase UV exposure.
On the ground:
Leaves and small twigs in constant motion; wind extends light flag.
On the sea:
Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.
Power systems: Weak power grid fluctuations can occur.
Spacecraft operations: Minor impact on satellite operations possible.
Other systems: Migratory animals are affected at this and higher levels;
aurora is commonly visible at high latitudes (northern Michigan and Maine).
On the ground:
Direction of wind shown by smoke drift, but not by wind vanes.
On the sea:
Ripples with the appearance of scales are formed, but without foam crests.