The systems that make weather feel naturally varied over time: random variation, seasonal cycles, climate-aware probability, and the temperature system that derives values from all of it.
| System | Where | Purpose |
|---|---|---|
| Random Weather Variation | Random Weather Variation category | Periodic random weather changes per season-weighted probability |
| Seasons | Season category | 0–4 float (Spring → Winter) driving probability maps + temperature ranges |
| Climate Presets | Random Weather Variation category | One-shot real-world climate data → probabilities + temperature |
| Temperature | Temperature category | Calculated from weather state + season + biases + interior |
| Temperature Volumes | Blueprints/Weather_Effects/ actor |
Per-region temperature offsets |
When to use this skill
- Setting up weather that changes by itself periodically.
- Making weather change with seasons.
- Picking a real-world climate (tropical, alpine, desert) for a region.
- Reading temperature in F or C from gameplay code.
- Adding local hot zones (near fire) or cold zones.
- Displaying current temperature on screen.
- Driving materials based on the season.
Random Weather Variation
Periodically picks a new weather preset based on season and probability maps. Category: Random Weather Variation.
Timing modes
Random Weather Variation mode |
Trigger |
|---|---|
| Random Interval | Random Weather Change Interval (min/max seconds) — system holds a preset for a random time then picks a new one |
| Daily | Once per in-game day at the time set by Random Weather Change Hour |
| Hourly | Each in-game hour |
Transition Length — fraction of the interval between changes devoted to transitioning old → new.
Probability maps
The Weather Type Probabilities maps hold weather presets and their relative probabilities. Values are relative:
{ Rain: 5, Partly Cloudy: 1, Clear: 1 }
→ Rain is 5x as likely as either of the others
Which map is used depends on the current season (see below). Different probability maps per season is how spring rains differ from summer heat.
Begin Play behavior
Begin Play Weather is Random |
Behavior at play start |
|---|---|
| True | A random weather is selected on play start |
| False | Starts with whatever weather the level editor was displaying; changes after the first interval |
Climate Presets
Same category — apply a climate preset to populate the probability maps with real-world climate data, and set temperature ranges in the Temperature category accordingly. Fastest way to get believable weather for "tropical jungle", "alpine", "desert", etc.
Returning to random after a manual change
Change Weather (see udw-setup-and-state) switches to a static preset. To go back:
UDW.ChangeToRandomWeatherVariation()
Seasons
Category: Season. The Season variable is a float 0–4:
| Value | Meaning |
|---|---|
| 0 | Mid Spring |
| 1 | Mid Summer |
| 2 | Mid Fall |
| 3 | Mid Winter |
| 4 | Wraps back to Spring |
Whole values = middle of a season (where its data is applied purely). In-between values = transition. 0.5 = half Spring + half Summer.
Where Season comes from
Season Mode setting |
Behavior |
|---|---|
| Derived from date | Uses UDS's date (Simulation category, increments per day). See uds-simulation. |
| Uncontrolled | Season variable is uncontrolled — set yourself via SetSeason(value) |
When deriving from date:
| Setting | Effect |
|---|---|
Season Day Offset |
Shifts what date corresponds to what season value |
Meteorological Seasons |
Whether the seasons (at offset 0) represent meteorological or astronomical |
Sampling season in materials
| Material node | Output |
|---|---|
Sample UDW Season |
0–1 per season (four values, total = 1) |
Season Color Blend |
Blends 4 color inputs based on current season |
Use for season-driven material effects (autumn foliage colors, winter rock tinting).
Temperature
Category: Temperature. Sample via:
UDW.GetCurrentTemperature(unit, sampleLocation)
// unit: Fahrenheit or Celsius
// sampleLocation: Global, or per-location (volumes + interior)
How temperature is calculated
Treated as a product of weather, not a driver of it:
1. Start at 0
2. Add every Temperature Bias value in the Temperature category
(biases reflect factors like Time of Day and weather state)
3. Map the resulting -1..1 value into the Min/Max range for current season
4. Add a slowly-changing random value, scaled by Randomize Temperature
5. If sampleLocation != Global:
- Sample Temperature Volumes in the level
- Apply Interior Temperature based on Player Occlusion of the sample point
(Player Occlusion is on UDS — see uds-modifiers-configs-state)
Temperature and Weather Override Volumes
Weather Override Volumes apply their own temperature ranges while the player is inside. Configurable per-WOV or disablable. See udw-spatial-weather.
Temperature Volumes
Actor class Temperature Volume at Blueprints/Weather_Effects/. Place to create local temperature effects.
Example: place around a fire with a positive Temperature Offset — temperature sampled inside the volume reads higher.
Show temperature on-screen
UDW Thermometer widget in the widget designer palette under Ultra Dynamic Sky Widgets. Samples and displays current temperature. Drop into a UMG widget.
Runtime / Blueprint scripting summary
| Action | API |
|---|---|
| Change weather to a preset | ChangeWeather(preset, transitionLength) |
| Change to manual state | ChangeWeather(null, transitionLength) |
| Switch from manual back to random | ChangeToRandomWeatherVariation() |
| Set season manually | SetSeason(value) (when Season Mode isn't deriving from date) |
| Sample temperature | GetCurrentTemperature(unit, sampleLocation) |
| Sample season in materials | Sample UDW Season MF, Season Color Blend MF |
Gotchas
- Random Weather Variation doesn't fire — mode is set to something other than Random Interval / Daily / Hourly. Pick a timing mode.
- Begin Play weather isn't random —
Begin Play Weather is Randomis false. Set it true. - Random weather always picks the same preset — probability map has a strong bias toward one entry; or there's only one entry in the map. Verify the map for the current season.
SetSeasonhas no effect —Season Modeis set to derive from date, which overrides manual season. Switch Season Mode to "Uncontrolled" first.- Temperature reads always the same despite weather changing —
Temperature Biasvalues aren't configured for the weather you care about. Add bias entries for that weather/time-of-day. GetCurrentTemperature(local)reads same as Global — sample location is set to Global, or there are no Temperature Volumes / Player Occlusion isn't computing occlusion at that location. Seeuds-modifiers-configs-state.- Climate preset overwrote a custom probability map — applying a climate preset is destructive to the maps. Save a config asset first (see
uds-modifiers-configs-state) before experimenting.
References & source material
Docs (Ultra Dynamic Weather 9.5):
- Random Weather Variation
- Seasons
- Sampling Temperature (incl. how temperature is calculated, Temperature Volumes, on-screen display)
Plugin asset paths:
Blueprints/Weather_Effects/Weather_Presets/— preset assets weighted by the probability mapsBlueprints/Weather_Effects/— Temperature Volume actor class- Widget designer palette → Ultra Dynamic Sky Widgets → UDW Thermometer
Related skills: udw-setup-and-state, uds-simulation (date drives season when Season Mode set to derive), udw-spatial-weather (WOVs override temperature ranges locally), uds-modifiers-configs-state (Player Occlusion drives Interior Temperature), udw-material-and-screen-effects (Freezing Breath uses calculated temperature).