{
  "schemaVersion": 1,
  "slug": "snow-day-probability-calculator",
  "category": "weather",
  "kind": "implementation",
  "independentValidation": false,
  "implementationHash": "982e7269a2a609722ae2e809ce435cb422ab298926affd3f827547000dc7be16",
  "provenance": "Generated from the calculation contract used by the published page. Publication is not external validation.",
  "sourceFiles": [
    "data/calculators/snow-day-probability-calculator.json",
    "src/engine.js"
  ],
  "runtimeSource": "/sources/engine.txt",
  "runtimeHash": "5c888d8898afbdee36267bb9977829e1e2ac568f6677c8ee87469c139864645c",
  "scope": "The compute function records implemented equations, constants, lookup tables and custom rules. Inputs record defaults and allowed values; outputs record precision and units. Defaults are examples, not recommendations. General background references are not evidence for this specific algorithm.",
  "publishedFormula": {
    "formula": "P = clamp(0, 98, min(55, 5.5s) + C(T) + W(w) + 15i + d + t)",
    "vars": [
      [
        "s",
        "Expected snowfall (in)"
      ],
      [
        "T",
        "Temperature (°F)"
      ],
      [
        "w",
        "Wind chill (°F)"
      ],
      [
        "i",
        "Ice flag (0 or 15)"
      ],
      [
        "d",
        "District adjustment"
      ],
      [
        "t",
        "Timing adjustment"
      ],
      [
        "C",
        "Temperature score (piecewise, see note)"
      ],
      [
        "W",
        "Wind-chill score (piecewise, see note)"
      ],
      [
        "P",
        "Probability of a snow day (%)"
      ]
    ],
    "note": "Adds heuristic points for snowfall, temperature, wind chill, ice, district type and timing. The score is uncalibrated and is not a probability."
  },
  "externalEvidence": {
    "reviewedAt": "2026-10-12",
    "sources": [
      {
        "name": "NWS — Snowfall and snow-to-liquid variability",
        "url": "https://www.weather.gov/arx/why_snowratios"
      }
    ],
    "referenceRole": "context",
    "implementationHash": "982e7269a2a609722ae2e809ce435cb422ab298926affd3f827547000dc7be16",
    "basis": "P = clamp(0, 98, min(55, 5.5s) + C(T) + W(w) + 15i + d + t)",
    "limitations": "The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions."
  },
  "contract": {
    "compute": "const snowScore = Math.min(55, snowfall*5.5); const coldScore = temperature <= 0 ? 12 : temperature <= 10 ? 8 : temperature <= 20 ? 4 : 0; const windScore = windChill <= -15 ? 10 : windChill <= 0 ? 6 : windChill <= 15 ? 3 : 0; const iceScore = ice === 'yes' ? 15 : 0; const districtAdj = rural === 'rural' ? 6 : rural === 'urban' ? -5 : 0; const timingAdj = timing === 'overnight' ? 8 : timing === 'morning' ? 3 : -12; const total = Math.max(0, Math.min(98, snowScore + coldScore + windScore + iceScore + districtAdj + timingAdj)); return { heuristicScore: Math.round(total) };",
    "inputs": [
      {
        "name": "snowfall",
        "type": "number",
        "default": 6,
        "min": 0,
        "max": 40,
        "step": 0.5,
        "slider": true
      },
      {
        "name": "temperature",
        "type": "number",
        "default": 20,
        "min": -40,
        "max": 50,
        "step": 1,
        "slider": true
      },
      {
        "name": "windChill",
        "type": "number",
        "default": 5,
        "min": -60,
        "max": 50,
        "step": 1,
        "slider": true
      },
      {
        "name": "ice",
        "type": "select",
        "default": "no",
        "options": [
          {
            "value": "no"
          },
          {
            "value": "yes"
          }
        ]
      },
      {
        "name": "rural",
        "type": "select",
        "default": "suburban",
        "options": [
          {
            "value": "urban"
          },
          {
            "value": "suburban"
          },
          {
            "value": "rural"
          }
        ]
      },
      {
        "name": "timing",
        "type": "select",
        "default": "overnight",
        "options": [
          {
            "value": "overnight"
          },
          {
            "value": "morning"
          },
          {
            "value": "afternoon"
          }
        ]
      }
    ],
    "outputs": [
      {
        "name": "heuristicScore",
        "precision": 0,
        "unit": "points"
      }
    ],
    "interpret": null
  }
}