The Weather Vein can be used to forecast the weather for several days ahead. TIP: It only requires power when you are using it; disable it (via the fusebox) after you take a look to save fuel.
Weeks last 5 days. At the end of each week, you'll get a weekly faction report.
Seasons are 20 days.
The game starts in Spring, which is the rainiest. Temperatures range from 11℃ to 21℃ outside and characters will generally be "cold" inside without heaters. Dust storms are rare and thunderstorms are extremely rare, if they can even happen. There is often a good amount of wind.
Summer starts on Day 21. At any time, the temperature can randomly jump up dramatically, at which point your shelter will heat up quickly. Days can get as hot as 44℃, but nights can dip down into the teens and require micromanagement of heaters/coolers. Any characters walking around outside (but not on expeditions) in temperatures of 26℃ or higher will suffer heat strokes. You will need fans to control the temperature (keep in mind that large rooms are easier to cool). The chance of dust storms seems to be higher and thunderstorms are rare but possible. It's still windy, but not as often. You will likely encounter your first instance of black rain.
Autumn is much like spring, but hotter on average: it rains more often than summer and for longer periods of time, and the temperatures are typically similar to spring, although there is a chance for a random extremely hot day (mid-30s C; unknown if this is a bug or not) and it can often be in the upper 20s C. There is a good amount of wind. Dust storms can still happen.
Temperatures outside can jump down to -20℃. You will need lots of heating devices (keep in mind that smaller rooms are easier to heat), and these require a large amount of electricity.
<0℃ - Freezing: characters take damage
0 - 14℃ - Cold: -20 mood modifier
14 - 22℃ - Neither hot nor cold
23-25℃ - Hot: -10 mood modifier
>25℃ - Sweltering: -20 mood modifier, characters move slowly, take damage, and gain "heatstroke," which requires the character to be in 22*C or less temperatures to cure
Harmless. Survivors on the surface (but not on expeditions) will reduce their shower needs.
Harmless to plants, this will cause any survivor on the surface (but not on expeditions) to slowly gain radiation. It will also reduce their shower needs. Radiation gradually goes away over time or can be cured with medicine. Be sure your water purifier is working during these rains.
Any survivor on the surface (but not on expeditions) will rapidly gain radiation. These also cause surface structures with durability to lose durability more quickly.
Lightning strikes can happen and damage your shelter severely: they can cause many items to burst into flames. It can be difficult to control the flames quickly enough before they spread, leading to widespread damage. Lightning rods do very little to mitigate this (will be changed in next patch), but they can help charge batteries.