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What are delta layers?

Delta layers highlight how a weather forecast has changed between two model runs. They build on the same wl:* weather layers but use special variable names to describe the comparison you want to visualize. Use delta layers when you need to:
  • Track how the latest forecast differs from the previous run
  • Compare the current run against yesterday’s day-ahead forecast
  • Spot sudden changes in temperature, wind speed, or other weather variables

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Variable naming convention

Delta layers rely on the variable field to describe the comparison target:
Delta typeVariable format exampleMeaning
StandardWindSpeedRaw forecast value (not a delta)
Previous runDeltaPrevRun:WindSpeedDifference between current run and previous run
Day-ahead runDeltaDayAhead:WindSpeedDifference between current run and day-ahead run
⚠️ The part after the colon must be a valid base variable name (WindSpeed, Temperature, etc.).

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Creating a delta layer

Delta layers use the same SDK call as regular weather layers. Simply change the variable value to one of the delta formats. 
# Difference vs the previous forecast run
wind_delta_prev_run = client.layers.create_layer(
    name="WindSpeed Δ vs previous run",
    type="wl:RasterLayer",
    weather_model_id="ECMWF_IFS",
    variable="DeltaPrevRun:WindSpeed",
    altitude=100,
    run_hour=12,
    run_day="2025-01-15",
    deckgl_props={
        "opacity": 0.8,
    }
)

# Difference vs the day-ahead run
temperature_delta_day_ahead = client.layers.create_layer(
    name="Temperature Δ vs day-ahead",
    type="wl:RasterLayer",
    weather_model_id="ECMWF_IFS",
    variable="DeltaDayAhead:Temperature",
    altitude=2,
    run_hour=12,
    run_day="2025-01-15",
    deckgl_props={
        "opacity": 0.75
    }
)

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Supported layer types

Delta variables use the wl:RasterLayer, regardless of which weather variable is used for the comparison.

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Best practices

  • Pick the right comparison: Use DeltaPrevRun for short-term monitoring and DeltaDayAhead for day-ahead bidding or re-forecast analysis.
  • Label clearly: Include the delta type in the layer name to clarify the context when many different layers are used.
  • Combine with base layers: Pair delta layers with the original forecast layer to provide full context, for example with two map components side by side.

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Next steps

Weather Integration

Learn how weather models and variables work.

Layers

See how weather layers fit into the broader layer system.