Layered Plot with Dual-Axis

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "data": {"url": "data/seattle-weather.csv"},
  "layer": [
    {
      "mark": "bar",
      "encoding": {
        "x": {
          "timeUnit": "month",
          "field": "date",
          "type": "ordinal"
        },
        "y": {
          "aggregate": "mean",
          "field": "precipitation",
          "type": "quantitative",
          "axis": {
            "grid": false
          }
        }
      }
    },
    {
      "mark": "line",
      "encoding": {
        "x": {
          "timeUnit": "month",
          "field": "date",
          "type": "ordinal"
        },
        "y": {
          "aggregate": "mean",
          "field": "temp_max",
          "type": "quantitative",
          "axis": {
            "grid": false
          },
          "scale": {"zero": false}
        },
        "color": {"value": "firebrick"}
      }
    }
  ],
  "resolve": {"scale": {"y": "independent"}}
}