Weather is more than just set dressing to establish mood—it's environmental components can have mechanical implications in the source of both Exploration and Combat. You can pick weather to fit your campaign or roll on the Weather table to determine the weather for a given day, adjusting for the terrain and season as appropriate.
| Weather | |
| d20 | Temperature |
| 1-14 | normal for the season |
| 15-17 | 1d4 × 10 degrees Fahrenheit colder than normal |
| 18-20 | 1d4 × 10 degrees Fahrenheit hotter than normal |
| Wind | |
| d20 | Wind |
| 1-12 | no wind |
| 13-17 | light wind |
| 18-20 | strong wind |
| Precipitation | |
| d20 | Precipitation |
| 1-12 | no precipitation |
| 13-17 | light rain or light snowfall |
| 18-20 | heavy rain or heavy snowfall |
A strong wind imposes disadvantage on ranged weapon attack rolls and Wisdom (Perception) checks that rely on hearing. A strong wind also extinguishes open flames, disperses fog, and makes flying by nonmagical means nearly impossible. A flying creature in a strong wind must land at the end of its turn or fall.
A strong wind in a desert can create a sandstorm that imposes disadvantage on Wisdom (Perception) checks that rely on sight.
At the DM's discretion, strong winds on the order of a hurricane or similar weather effect might also be heavily obscured and considered difficult terrain.
Precipitation has three modes: no precipitation, a clear day; light precipitation, such as a shower or flurry; and heavy precipitation, such as a downpour or whiteout.
Everything within an area of light rain has disadvantage on Strength (Athletics) checks to climb or scale objects and disadvantage on ability checks made to maintain balance or keep one's footing.
Everything within an area of light snowfall is lightly obscured, and creatures in the area have disadvantage on Wisdom (Perception) checks that rely on sight. Creatures in the area also have advantage on Wisdom (Survival) checks made to track creatures.
Everything within an area of heavy rain is lightly obscured, and creatures in the area have disadvantage on Wisdom (Perception) checks that rely on sight. Heavy rain also extinguishes open flames and imposes disadvantage on Wisdom (Perception) checks that rely on hearing, Strength (Athletics) checks to climb or scale objects, on ability checks made to maintain balance or keep one's footing, and on Wisdom (Survival) checks made to track creatures. Creatures gain advantage on Wisdom (Survival) checks to forage for water.
Everything within an area of heavy snowfall is lightly obscured, and creatures in the area have disadvantage on Wisdom (Perception) checks that rely on sight. Additionally, creatures gain advantage on Wisdom (Survival) checks to track creatures, and checks to forage for water automatically succeed. At the DM's discretion, an area of heavy snowfall might also be considered difficult terrain.
There are two basic kinds of fog: light fog and heavy fog. An area covered in light fog—such as a mist-clad mountainside—is considered lightly obscured obscured and creatures in the area have disadvantage on Wisdom (Perception). An area covered in heavy fog—such as a shrouded ghost town—is considered heavily obscured rendering creatures in the area effective blind for the purpose of Wisdom (Perception) checks that rely on sight.
Fog is somewhat irregular compared to ordinary weather patterns, but is most prevalent early in the morning, around dawn, and is more common in autumn than other seasons.
Whenever the temperature is at or below 0 degrees Fahrenheit, a creature exposed to the cold must succeed on a DC 10 Constitution saving throw at the end of each hour or gain one level of exhaustion. Creatures with resistance or immunity to cold damage automatically succeed on the saving throw, as do creatures wearing cold weather gear (thick coats, gloves, and the like) and creatures naturally adapted to cold climates.
When submerged in water that is 40 degrees Fahrenheit or less, a creature can spend a number of minutes equal to its Constitution modifier without issue. After that, at the end of each minute, the creature must make a DC 10 Constitution saving throw or suffer one level of exhaustion.
If a creature has resistance or immunity to cold damage or is naturally adapted to living in frigid waters, they automatically succeed on this saving throw.
When the temperature is at or above 100 degrees Fahrenheit, a creature exposed to the heat and without access to drinkable water must succeed on a Constitution saving throw at the end of each hour or gain one level of exhaustion. The DC is 5 for the first hour and increases by 1 for each additional hour.
Creatures wearing medium or heavy armor, or who are clad in heavy clothing, have disadvantage on the saving throw. Creatures with resistance or immunity to fire damage automatically succeed on the saving throw, as do creatures naturally adapted to hot climates.
Traveling at altitudes of 10,000 feet or higher above sea level is taxing for a creature that needs to breathe, because of the reduced amount of oxygen in the air. Each hour such a creature spends traveling at high altitude counts as 2 hours for the purpose of determining how long that creature can travel.
Breathing creatures can become acclimated to a high altitude by spending 30 days or more at this elevation. Breathing creatures can't become acclimated to elevations above 20,000 feet unless they are native to such environments.