{
 "slug": "chicago-il",
 "place": {
  "name": "Chicago",
  "state": "IL",
  "census_name": "Chicago city",
  "census_geoid": "1714000",
  "lat": 41.83705,
  "lon": -87.68494,
  "station_distance_km": 27.1
 },
 "station": {
  "id": "USW00094846",
  "name": "CHICAGO OHARE INTL AP, IL US",
  "lat": 41.995,
  "lon": -87.9336,
  "elevation_m": 200.6,
  "elevation_ft": 658,
  "source_urls": {
   "monthly": "https://www.ncei.noaa.gov/data/normals-monthly/1991-2020/access/USW00094846.csv",
   "annual": "https://www.ncei.noaa.gov/data/normals-annualseasonal/1991-2020/access/USW00094846.csv"
  }
 },
 "period": "1991-2020",
 "units": {
  "temperature": "F",
  "precipitation": "in",
  "snowfall": "in",
  "days": "days",
  "dates": "MM-DD",
  "prob_low_le_32f_pct": "percent"
 },
 "months": [
  {
   "month": 1,
   "name": "January",
   "high_f": 31.6,
   "low_f": 18.8,
   "mean_f": 25.2,
   "precip_in": 1.99,
   "snow_in": 11.3,
   "days_precip_ge_0_01in": 11.0,
   "days_precip_ge_0_10in": 5.2,
   "days_snow_ge_1_0in": 3.6,
   "days_high_ge_90f": 0.0,
   "days_high_le_32f": 16.5,
   "days_low_le_32f": 28.1,
   "prob_low_le_32f_pct": 100.0
  },
  {
   "month": 2,
   "name": "February",
   "high_f": 35.7,
   "low_f": 21.8,
   "mean_f": 28.8,
   "precip_in": 1.97,
   "snow_in": 10.7,
   "days_precip_ge_0_01in": 9.4,
   "days_precip_ge_0_10in": 4.7,
   "days_snow_ge_1_0in": 3.1,
   "days_high_ge_90f": 0.0,
   "days_high_le_32f": 11.2,
   "days_low_le_32f": 24.4,
   "prob_low_le_32f_pct": 100.0
  },
  {
   "month": 3,
   "name": "March",
   "high_f": 47.0,
   "low_f": 31.0,
   "mean_f": 39.0,
   "precip_in": 2.45,
   "snow_in": 5.5,
   "days_precip_ge_0_01in": 10.8,
   "days_precip_ge_0_10in": 5.5,
   "days_snow_ge_1_0in": 1.5,
   "days_high_ge_90f": 0.0,
   "days_high_le_32f": 3.0,
   "days_low_le_32f": 19.9,
   "prob_low_le_32f_pct": 99.8
  },
  {
   "month": 4,
   "name": "April",
   "high_f": 59.0,
   "low_f": 40.3,
   "mean_f": 49.7,
   "precip_in": 3.75,
   "snow_in": 1.3,
   "days_precip_ge_0_01in": 12.3,
   "days_precip_ge_0_10in": 7.1,
   "days_snow_ge_1_0in": 0.4,
   "days_high_ge_90f": 0.0,
   "days_high_le_32f": 0.1,
   "days_low_le_32f": 6.0,
   "prob_low_le_32f_pct": 93.0
  },
  {
   "month": 5,
   "name": "May",
   "high_f": 70.5,
   "low_f": 50.6,
   "mean_f": 60.6,
   "precip_in": 4.49,
   "snow_in": 0.0,
   "days_precip_ge_0_01in": 12.5,
   "days_precip_ge_0_10in": 8.1,
   "days_snow_ge_1_0in": 0.0,
   "days_high_ge_90f": 0.8,
   "days_high_le_32f": 0.0,
   "days_low_le_32f": 0.2,
   "prob_low_le_32f_pct": 10.4
  },
  {
   "month": 6,
   "name": "June",
   "high_f": 80.4,
   "low_f": 60.8,
   "mean_f": 70.6,
   "precip_in": 4.1,
   "snow_in": 0.0,
   "days_precip_ge_0_01in": 11.1,
   "days_precip_ge_0_10in": 6.7,
   "days_snow_ge_1_0in": 0.0,
   "days_high_ge_90f": 4.1,
   "days_high_le_32f": 0.0,
   "days_low_le_32f": 0.0,
   "prob_low_le_32f_pct": 0.0
  },
  {
   "month": 7,
   "name": "July",
   "high_f": 84.5,
   "low_f": 66.4,
   "mean_f": 75.4,
   "precip_in": 3.71,
   "snow_in": 0.0,
   "days_precip_ge_0_01in": 9.7,
   "days_precip_ge_0_10in": 5.8,
   "days_snow_ge_1_0in": 0.0,
   "days_high_ge_90f": 6.5,
   "days_high_le_32f": 0.0,
   "days_low_le_32f": 0.0,
   "prob_low_le_32f_pct": 0.0
  },
  {
   "month": 8,
   "name": "August",
   "high_f": 82.5,
   "low_f": 65.1,
   "mean_f": 73.8,
   "precip_in": 4.25,
   "snow_in": 0.0,
   "days_precip_ge_0_01in": 9.4,
   "days_precip_ge_0_10in": 6.5,
   "days_snow_ge_1_0in": 0.0,
   "days_high_ge_90f": 3.7,
   "days_high_le_32f": 0.0,
   "days_low_le_32f": 0.0,
   "prob_low_le_32f_pct": 0.0
  },
  {
   "month": 9,
   "name": "September",
   "high_f": 75.5,
   "low_f": 57.1,
   "mean_f": 66.3,
   "precip_in": 3.19,
   "snow_in": 0.0,
   "days_precip_ge_0_01in": 8.5,
   "days_precip_ge_0_10in": 5.6,
   "days_snow_ge_1_0in": 0.0,
   "days_high_ge_90f": 1.6,
   "days_high_le_32f": 0.0,
   "days_low_le_32f": 0.1,
   "prob_low_le_32f_pct": 0.4
  },
  {
   "month": 10,
   "name": "October",
   "high_f": 62.7,
   "low_f": 45.4,
   "mean_f": 54.0,
   "precip_in": 3.43,
   "snow_in": 0.2,
   "days_precip_ge_0_01in": 10.5,
   "days_precip_ge_0_10in": 6.3,
   "days_snow_ge_1_0in": 0.1,
   "days_high_ge_90f": 0.0,
   "days_high_le_32f": 0.0,
   "days_low_le_32f": 2.7,
   "prob_low_le_32f_pct": 62.0
  },
  {
   "month": 11,
   "name": "November",
   "high_f": 48.4,
   "low_f": 34.1,
   "mean_f": 41.3,
   "precip_in": 2.42,
   "snow_in": 1.8,
   "days_precip_ge_0_01in": 10.0,
   "days_precip_ge_0_10in": 5.3,
   "days_snow_ge_1_0in": 0.5,
   "days_high_ge_90f": 0.0,
   "days_high_le_32f": 2.2,
   "days_low_le_32f": 14.5,
   "prob_low_le_32f_pct": 99.9
  },
  {
   "month": 12,
   "name": "December",
   "high_f": 36.6,
   "low_f": 24.4,
   "mean_f": 30.5,
   "precip_in": 2.11,
   "snow_in": 7.6,
   "days_precip_ge_0_01in": 10.6,
   "days_precip_ge_0_10in": 4.8,
   "days_snow_ge_1_0in": 2.2,
   "days_high_ge_90f": 0.0,
   "days_high_le_32f": 10.4,
   "days_low_le_32f": 25.4,
   "prob_low_le_32f_pct": 100.0
  }
 ],
 "annual": {
  "high_f": 59.5,
  "low_f": 43.0,
  "mean_f": 51.2,
  "precip_in": 37.86,
  "snow_in": 38.4,
  "days_precip_ge_0_01in": 125.8,
  "days_snow_ge_1_0in": 11.4,
  "days_high_ge_90f": 16.7,
  "days_high_le_32f": 43.4,
  "days_low_le_32f": 121.3
 },
 "frost": {
  "semantics": {
   "last_spring": "PRBLST: an N% chance that the last night at or below the threshold comes on or after this date",
   "first_fall": "PRBFST: an N% chance that the first night at or below the threshold has come by this date",
   "season_days": "PRBGSL: length of the season above the threshold, days; P50 is the median"
  },
  "thresholds_f": [
   36,
   32,
   28,
   24,
   20,
   16
  ],
  "probabilities_pct": [
   10,
   20,
   30,
   40,
   50,
   60,
   70,
   80,
   90
  ],
  "table": {
   "36": {
    "status": "computed",
    "freeze_in_most_years": true,
    "last_spring": {
     "10": "05-13",
     "20": "05-08",
     "30": "05-04",
     "40": "05-01",
     "50": "04-29",
     "60": "04-26",
     "70": "04-23",
     "80": "04-20",
     "90": "04-15"
    },
    "first_fall": {
     "10": "10-03",
     "20": "10-08",
     "30": "10-11",
     "40": "10-15",
     "50": "10-18",
     "60": "10-21",
     "70": "10-23",
     "80": "10-26",
     "90": "10-30"
    },
    "season_days": {
     "10": 189.0,
     "20": 183.0,
     "30": 178.0,
     "40": 174.0,
     "50": 170.0,
     "60": 167.0,
     "70": 163.0,
     "80": 158.0,
     "90": 151.0
    }
   },
   "32": {
    "status": "computed",
    "freeze_in_most_years": true,
    "last_spring": {
     "10": "05-01",
     "20": "04-26",
     "30": "04-22",
     "40": "04-19",
     "50": "04-16",
     "60": "04-14",
     "70": "04-11",
     "80": "04-08",
     "90": "04-03"
    },
    "first_fall": {
     "10": "10-15",
     "20": "10-20",
     "30": "10-24",
     "40": "10-26",
     "50": "10-28",
     "60": "10-31",
     "70": "11-03",
     "80": "11-05",
     "90": "11-11"
    },
    "season_days": {
     "10": 213.0,
     "20": 206.0,
     "30": 201.0,
     "40": 197.0,
     "50": 193.0,
     "60": 189.0,
     "70": 185.0,
     "80": 180.0,
     "90": 173.0
    }
   },
   "28": {
    "status": "computed",
    "freeze_in_most_years": true,
    "last_spring": {
     "10": "04-19",
     "20": "04-14",
     "30": "04-10",
     "40": "04-07",
     "50": "04-05",
     "60": "04-02",
     "70": "03-31",
     "80": "03-27",
     "90": "03-21"
    },
    "first_fall": {
     "10": "10-27",
     "20": "11-01",
     "30": "11-02",
     "40": "11-05",
     "50": "11-07",
     "60": "11-10",
     "70": "11-13",
     "80": "11-17",
     "90": "11-22"
    },
    "season_days": {
     "10": 238.0,
     "20": 231.0,
     "30": 225.0,
     "40": 221.0,
     "50": 217.0,
     "60": 212.0,
     "70": 209.0,
     "80": 204.0,
     "90": 198.0
    }
   },
   "24": {
    "status": "computed",
    "freeze_in_most_years": true,
    "last_spring": {
     "10": "04-08",
     "20": "04-03",
     "30": "03-31",
     "40": "03-28",
     "50": "03-24",
     "60": "03-21",
     "70": "03-17",
     "80": "03-13",
     "90": "03-07"
    },
    "first_fall": {
     "10": "11-03",
     "20": "11-07",
     "30": "11-11",
     "40": "11-14",
     "50": "11-17",
     "60": "11-20",
     "70": "11-23",
     "80": "11-27",
     "90": "12-02"
    },
    "season_days": {
     "10": 260.0,
     "20": 253.0,
     "30": 247.0,
     "40": 242.0,
     "50": 238.0,
     "60": 234.0,
     "70": 229.0,
     "80": 224.0,
     "90": 217.0
    }
   },
   "20": {
    "status": "computed",
    "freeze_in_most_years": true,
    "last_spring": {
     "10": "03-29",
     "20": "03-24",
     "30": "03-20",
     "40": "03-16",
     "50": "03-13",
     "60": "03-10",
     "70": "03-06",
     "80": "03-02",
     "90": "02-26"
    },
    "first_fall": {
     "10": "11-10",
     "20": "11-15",
     "30": "11-19",
     "40": "11-23",
     "50": "11-26",
     "60": "11-29",
     "70": "12-02",
     "80": "12-06",
     "90": "12-14"
    },
    "season_days": {
     "10": 281.0,
     "20": 273.0,
     "30": 267.0,
     "40": 262.0,
     "50": 258.0,
     "60": 254.0,
     "70": 249.0,
     "80": 244.0,
     "90": 236.0
    }
   },
   "16": {
    "status": "computed",
    "freeze_in_most_years": true,
    "last_spring": {
     "10": "03-19",
     "20": "03-15",
     "30": "03-11",
     "40": "03-08",
     "50": "03-05",
     "60": "03-02",
     "70": "02-28",
     "80": "02-24",
     "90": "02-17"
    },
    "first_fall": {
     "10": "11-18",
     "20": "11-25",
     "30": "11-28",
     "40": "12-01",
     "50": "12-03",
     "60": "12-07",
     "70": "12-12",
     "80": "12-17",
     "90": "12-23"
    },
    "season_days": {
     "10": 299.0,
     "20": 291.0,
     "30": 284.0,
     "40": 280.0,
     "50": 275.0,
     "60": 270.0,
     "70": 266.0,
     "80": 261.0,
     "90": 253.0
    }
   }
  },
  "notes": []
 },
 "derived": {
  "hottest_month": {
   "month": 7,
   "name": "July",
   "value": 75.4
  },
  "coldest_month": {
   "month": 1,
   "name": "January",
   "value": 25.2
  },
  "hottest_month_by_high": {
   "month": 7,
   "name": "July",
   "value": 84.5
  },
  "wettest_month": {
   "month": 5,
   "name": "May",
   "value": 4.49
  },
  "driest_month": {
   "month": 2,
   "name": "February",
   "value": 1.97
  },
  "snowiest_month": {
   "month": 1,
   "name": "January",
   "value": 11.3
  },
  "winter": "cold",
  "summer": "warm",
  "precipitation": "moderate",
  "snow": "heavy",
  "annual_precip_in": 37.86,
  "annual_snow_in": 38.4,
  "annual_range_f": 50.2,
  "mean_daily_range_f": 16.6,
  "months_high_ge_90f": [],
  "months_low_le_32f": [
   1,
   2,
   3,
   12
  ],
  "last_spring_32f_p50": "04-16",
  "first_fall_32f_p50": "10-28",
  "freeze_free_days_p50": 193.0,
  "freeze_free_span_days_p50": 195
 },
 "rules": {
  "hottest_coldest_month": "by monthly mean temperature (MLY-TAVG-NORMAL); ties go to the earlier month",
  "wettest_driest_month": "by monthly precipitation normal (MLY-PRCP-NORMAL); ties go to the earlier month",
  "winter": {
   "basis": "mean temperature of the coldest month, F",
   "bands": [
    [
     null,
     20,
     "very cold"
    ],
    [
     20,
     32,
     "cold"
    ],
    [
     32,
     45,
     "cool"
    ],
    [
     45,
     60,
     "mild"
    ],
    [
     60,
     null,
     "warm"
    ]
   ]
  },
  "summer": {
   "basis": "mean daily high of the hottest month (by high), F",
   "bands": [
    [
     null,
     70,
     "cool"
    ],
    [
     70,
     80,
     "mild"
    ],
    [
     80,
     90,
     "warm"
    ],
    [
     90,
     100,
     "hot"
    ],
    [
     100,
     null,
     "very hot"
    ]
   ]
  },
  "precipitation": {
   "basis": "annual precipitation normal, inches (sum of months if no annual value)",
   "bands": [
    [
     null,
     10,
     "arid"
    ],
    [
     10,
     20,
     "semi-arid"
    ],
    [
     20,
     40,
     "moderate"
    ],
    [
     40,
     60,
     "wet"
    ],
    [
     60,
     null,
     "very wet"
    ]
   ]
  },
  "snow": {
   "basis": "annual snowfall normal, inches; 'no data' when NOAA publishes no snowfall normal",
   "bands": [
    [
     null,
     1,
     "rare or none"
    ],
    [
     1,
     12,
     "light"
    ],
    [
     12,
     36,
     "moderate"
    ],
    [
     36,
     72,
     "heavy"
    ],
    [
     72,
     null,
     "very heavy"
    ]
   ]
  },
  "bands": "lower bound inclusive, upper bound exclusive",
  "frost_free": "true when the 32F last-spring and first-fall P50 dates are -9999 with flag Y (insufficient values) and the 32F growing season P50 is 365 days or the annual number of nights at or below 32F rounds to 0.0",
  "freeze_free_days_p50": "NOAA ANN-TMIN-PRBGSL-T32FP50 (median length of the 32F freeze-free season), as published",
  "freeze_rare": "true when 32F dates are published but the 32F growing season P50 is 365 days: no 32F night in at least half of years; the P50 spring and fall dates then cross and freeze_free_span_days_p50 is null",
  "freeze_free_span_days_p50": "days from the 32F P50 last-spring date to the 32F P50 first-fall date (next year if the fall date is earlier in the calendar); differs from the NOAA median season length because a median of lengths is not the span between median dates"
 },
 "flags": {
  "frost_free": false,
  "freeze_rare": false,
  "frost_data_missing": false,
  "year_round_frost_risk": false,
  "snow_normal_absent": false,
  "incomplete_months": []
 },
 "quality": {
  "high_f": {
   "column": "MLY-TMAX-NORMAL",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 30,
   "missing_months": 0
  },
  "low_f": {
   "column": "MLY-TMIN-NORMAL",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 27,
   "missing_months": 0
  },
  "mean_f": {
   "column": "MLY-TAVG-NORMAL",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 27,
   "missing_months": 0
  },
  "precip_in": {
   "column": "MLY-PRCP-NORMAL",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 29,
   "missing_months": 0
  },
  "snow_in": {
   "column": "MLY-SNOW-NORMAL",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 25,
   "missing_months": 0
  },
  "days_precip_ge_0_01in": {
   "column": "MLY-PRCP-AVGNDS-GE001HI",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 30,
   "missing_months": 0
  },
  "days_precip_ge_0_10in": {
   "column": "MLY-PRCP-AVGNDS-GE010HI",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 30,
   "missing_months": 0
  },
  "days_snow_ge_1_0in": {
   "column": "MLY-SNOW-AVGNDS-GE010TI",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 28,
   "missing_months": 0
  },
  "days_high_ge_90f": {
   "column": "MLY-TMAX-AVGNDS-GRTH090",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 30,
   "missing_months": 0
  },
  "days_high_le_32f": {
   "column": "MLY-TMAX-AVGNDS-LSTH032",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 30,
   "missing_months": 0
  },
  "days_low_le_32f": {
   "column": "MLY-TMIN-AVGNDS-LSTH032",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 27,
   "missing_months": 0
  },
  "prob_low_le_32f_pct": {
   "column": "MLY-TMIN-PRBOCC-LSTH032",
   "absent": false,
   "comp_flags": [
    "S"
   ],
   "meas_flags": [],
   "years_min": 27,
   "missing_months": 0
  }
 },
 "citation": {
  "monthly": "Palecki, Michael; Durre, Imke; Applequist, Scott; Arguez, Anthony; Lawrimore, Jay (2021). U.S. Climate Normals 2020: U.S. Monthly Climate Normals (1991-2020). Station USW00094846 (CHICAGO OHARE INTL AP, IL US). NOAA National Centers for Environmental Information. Dataset. https://doi.org/10.25921/wck8-er13. Accessed 2026-10-09.",
  "annual": "Palecki, Michael; Durre, Imke; Applequist, Scott; Arguez, Anthony; Lawrimore, Jay (2021). U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020). Station USW00094846 (CHICAGO OHARE INTL AP, IL US). NOAA National Centers for Environmental Information. Dataset. https://doi.org/10.25921/4ek7-fk11. Accessed 2026-10-09.",
  "metadata_records": [
   "https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C01620",
   "https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C01619"
  ]
 },
 "retrieved": {
  "monthly": "2026-10-09",
  "annual": "2026-10-09"
 }
}