Modding:Weather data

Overview

Weather in Stardew Valley is set within the newDayAfterFade() function. For those using SMAPI, this function runs before the AfterNewDayStarted event.

The weather is controlled by the variable weatherForTomorrow, an integer. It takes one of the following arguments (For a description of each weather as the player sees it, look at Weather)

Variable (Weather)	Value
weather_sunny (Sunny)	0
weather_rain (Rain)	1
weather_debris (Windy)	2
weather_lightning (Lightning)	3
weather_festival (Festival)	4
weather_snow (Snow)	5
weather_wedding (Wedding)	6

How Weather Is Set

To determine how it's set, and what debris is set, the following steps are followed:

After it handles day chance code, it checks for force weather (which is in the table at the bottom)
It checks if today is a festival, and if it is, it sets the weather to 4. (weather_festival)
If today is a wedding, it sets the weather to 6. (weather_wedding).
It then updates if it was raining yesterday by checking the isRaining or isLightning flags.
It then clears all the flags, and sets them in the following pattern
1. If it is going to rain or storm, set the rain flag to true
2. If it is going to storm, set the storm flag to true
3. If the weather is (sunny, debris) or (festival || snowy || wedding), clear all the flags
4. and then if it's snowy, set snowy to true
5. It then sets the song based on this
6. Clear the debris weather array and clear the flag
7. if bloom isn't null, clear it's visibility
8. If the wedding is debris, populate the debris array.
If it's not raining, and the chance to rain tomorrow is less than .1, it will try to create a bloom day.
It then calculates the rain chance for tomorrow. It follows the following algorithm
1. Check to see if it's summer.
  1. If not, check to see if it's winter.
    1. If it's not, the rain chance is .183
    2. Else, it's .63
  2. If it is, it uses the following: Check if it's day 1.
    1. If it's not, the chance is .12 + dayOfMonth * 3/1000
    2. If it is, the chance is 0. Which.. is kinda redundant, as the force days take care of this.
Check to see if a random number is less than the odds. If it is, it follows the following algorithm
1. Set weatherForTomorrow to 1. (weather_rain)
2. If:
  1. It's summer, and if a random number is less than .85
  2. Or If it's not winter, and if a random number is less than .25 AND the day of the month is more than 2 and more than 27 days have been played
  3. Set weatherForTomorrow to 3. (weather_lightning)
3. If it is winter
  1. Set weatherForTomorrow to 5. (weather_snow)
Else, if it's over the rain odds.
1. If you've played less than 3 days.
2. Or: if
  1. It's not spring or a random number is greater than or equal to .2 (so 80%) and spring.
  2. And it's not fall or a random number is greater than or equal to .6 (so 40%) and fall.
  3. Or: If there is a wedding today
    1. Set weatherForTomorrow to 0. (weather_sunny) if true
    2. Set weatherForTomorrow to 2. (weather_debris) if false
3. Check if tomorrow is a festival, and set weather to 4 (weather_festival) if true.
4. Again force the 3rd day to be 1. (weather_rain).

At this point, the main function is done setting weather.

TV Channel

The TV checks the weather, but will occasionally set it on certain days. It follows the following chart:

The TV force sets by:

day	season	year	weather
1	spring	any	weather_sunny[1]
1	summer	any	weather_sunny[1]
13	summer	any	weather_lightning[2]
25	summer	any	weather_lightning[2]
1	fall	any	weather_sunny[1]
1	winter	any	weather_sunny[1]

[1] also set (and therefore overriden) by the newDayAfterFade() function
[2] These are set by current_day mod 12, which results in the 13th and 25th.

Description:

It will check the weather, and do the following:

Sunny or Wedding: A 50% chance of one of two strings: "It's going to be clear and sunny all day." or "It's going to be a beautiful, sunny day tommorow!"
Rain: "It's going to rain all day tomorrow"
Debris: Spring: "Partially cloudy with a light breeze. Expect lots of pollen!" Not Fall: "It's going to snow all day. Make sure you bundle up, folks!" and defaults with: "It's going to be cloudy, with gusts of wind throught the day."
Storm: "Looks like a storm is approaching. Thunder and lightning is expected."
Festival: It attempts to read the festival data, will spit out an amusing "Um... that's odd. My information sheet just says 'null'. This is embarrassing..." if it fails to read the data, other wise will read out where it is and when it is.
Snow: A 50% chance of one of two strings: "Expect a few inches of snow tomorrow" or "Bundle up, folks. It's going to snow tomorrow!"

It returns an empty string for all other weathers. (which should be none, but.)

Notes:

The TV will not necessarily be accurate for Summer 13,26 or Spring 2,4. Those are force set within the newDayAfterFade() function.

Weather Icon

Thanks to Entoarox, the logic for this is pretty simple:

This is set by Game1::updateWeatherIcon().

The following will always apply: snowing sets 7, sunny 2, wedding 0, festival 1, raining 4, stormy 5
In spring, debris weather is 3, summer will be unset (this defaults to sunny), fall 6, and winter 7 (the same as snowing)
These icons are located in LooseSprite/Cursors.xnb

Rain Totem

The rain totem item is (681), and is controlled by Object::rainTotem (invoked by Object::performUseAction)

It makes sure you aren't in multiplayer and that tomorrow isn't a festival day. If so, it sets the weather for tomorrow to weather_rain and displays the message. Of a note, the item is still used up and every other animation is played even if it's not set if you're in MP or if tomorrow is a festival day.

Breakdown of Weather Chances by Type

Now that we've broken down the flow, here's a (long winded) breakdown of each weather's chances.

Sunny Weather (Weather Variables: 0,4,6)

In Spring, there is first an 18.3% base chance that it rains assuming that it's not overridden. (81.7% chance remaining for other weathers). If it doesn't rain, it has an 80% chance to remain sunny. (except on Spring 3, which will always be rainy.). This means in _Spring_, there is a 66.4% chance of it being sunny.

In Summer, there is a diminishing chance daily of sunny weather, but generally, you have a 86% chance on the second day, to 79.9% chance on the last day. The precise chance is: 1 - [13% + (.3 * day of the month)] per day, and it's a 0% chance on day 1. Bear in mind that Summer 12,13,24 and 26 will be stormy.

In Fall, the odds are precisely the same as Spring. There's no forced weather though.

In Winter, there is a 63% chance of precipitation, so only a 37% chance of sunny weather.

Rainy Weather (1)

In Spring, you have a 18.3% chance of rain. If it rains, there's only a 25% chance of storms, _as long as it is not Year 1_. So the rain odds in Spring is a flat 18.3% in Year 1, and 13.725% in Year 2 and beyond. It will be rainy on Spring 3 Year 1.

In Summer, you have a steadily increasing chance of rain starting at 14% on Summer 2 to a 21.1% chance on Summer 27. However, during Summer, you have a 85% chance to make the rain into storms. So you have a scale of [13% + (.3 * day of the month)] * .85 to determine your chances of rainfall. (See the note about forced weather above.)

In Fall, it's the same as Spring, although Fall Year 1 can be stormy, so it's 13.725%.

In Winter, it does not rain.

Debris Weather (2)

In Spring, you have a 20% chance for this after rain, so approximately 16.6% chance of debris weather.

In Summer and Winter you cannot have debris weather.

In Fall, you have a 60% chance for this after rain, so approximately 49.8% chance of debris weather.

Stormy Weather (3)

In Spring, you have a 4.57% of storms.

In Summer, you have a variable chance of storms. It starts at 11.9% and increases to 17.9% chance.

In Fall, you have a 4.57% of storms.

In Winter, you cannot have stormy weather.

Snowy Weather

In Winter, you have a 63% chance of snow.

No other season has snow.

Weather and Save Files

Your save file is a snapshot of the day at 0600 the next morning. As such, changing WeatherForTommorow in there will not affect the day loaded. If you really need to alter weather in the save file, you'll want to look at the following attributes: isRaining, isDebrisWeather, isLightning, isSnowing. For details of what to set which, look at the next section. This applies to trying to change weather in game, as well.

NB: Changing isDebrisWeather during an active game will not by itself create the array. You will need to call Game1::populateDebrisWeatherArray to get the debris populated. Corrospondingly, if you are removing the debris weather flag, remember to call Game1::debrisWeather::Clear

Detecting Current Weather (in game)

This is a brief overview. While it's generally obvious, I'll lay it out

weather	isRaining	isDebrisWeather	isLightning	isSnowing
Sunny	F	F	F	F
Rainy	T	F	F	F
Storm	T	F	T	F
Debris	F	T	F	F
Snowing	F	F	F	T
Festival	F	F	F	F
Wedding	F	F	F	F

Notes/FAQ

The TV can be fixed by overriding it - or just by using Entoroax's Framework.
You can set snow and debris at any time, the game just won't.

Appendix: Override Table

Day	Season	Year	Forced Weather	Overriden by
1	spring	any	weather_sunny	newday and tv
2	spring	1	weather_sunny	newday
3	spring	1	weather_rain	newday
4	spring	1	weather_sunny	newday
13	spring	any	weather_festival	newday
24	spring	any	weather_festival	newday
1	summer	any	weather_sunny	newday and tv
11	summer	any	weather_festival	newday
13	summer	any	weather_lightning	newday and tv
25	summer	any	weather_lightning	tv
26	summer	any	weather_lightning	newday
28	summer	any	weather_festival	newday
1	fall	any	weather_sunny	newday and tv
16	fall	any	weather_festival	newday
27	fall	any	weather_festival	newday
1	winter	any	weather_festival	newday and tv
8	winter	any	weather_festival	newday
25	winter	any	weather_festival	newday

Contributions

This was originally from canimod.com, written by me with contributions from Pathoschild. It has been rewritten by me for the wiki, with assistance from the modding channel on the stardew valley discord.