About the Data

Every temperature, precipitation, rain-day and snowfall figure on MonthSky is a NOAA NCEI U.S. Climate Normals 1991–2020 value, or a sum, difference, mean or Celsius conversion of those values. The data version is 1991-2020 v1.0.1, file date 2023-04-04. The sitemap lastmod stays on 2026-10-21 until the station or the NOAA revision changes.

All numbers come from the NOAA NCEI U.S. Climate Normals 1991–2020 monthly station files. Average high is MLY-TMAX-NORMAL, average low is MLY-TMIN-NORMAL, and precipitation is MLY-PRCP-NORMAL, in degrees Fahrenheit and inches as published.

Which station a city uses: the station must be inside the Census place boundary or within 15 miles of the downtown reference, and it must have numeric average high, average low and precipitation for all 12 months. Each value needs a measurement flag that is blank or X and a completeness flag of S or R, and at least 24 of the 36 values must be S. S is NCEI's standard class (24 or more years of data). R is the representative class (10 or more years, with missing months filled in from nearby stations). Flags P and E do not count. A station inside the boundary wins over one outside it. Among qualifying stations, we pick the one with the most S flags; if two tie, the closer one. If no station inside the boundary qualifies, we pick, the same way, a station whose published name contains the city name. If no station reaches 24 S flags, a name-matched station within 15 miles can still be used when every month is S or R, and the page notes that those normals are the representative class.

The downtown reference is the representative point of the largest polygon in the Census Bureau's 2024 cartographic boundary for the place, so a small offshore piece doesn't shift it. Distance is the great-circle distance from that point to the station, rounded to a tenth of a mile; it's the distance meant wherever a page says downtown. Elevation is the station elevation in meters times 3.280839895, rounded half up to the nearest foot.

Average temperature is MLY-TAVG-NORMAL when that field has completeness flag S in all 12 months. Otherwise the page uses the mean of the published high and low and says so. Rain days are MLY-PRCP-AVGNDS-GE001HI, and snowfall is MLY-SNOW-NORMAL. Those columns appear only when all 12 months have a numeric value with completeness flag S, R or P. A month's description mentions snow only when its snow normal is above 0.1 inch.

Month-to-month differences are simple subtractions of the published normals. The best-weather rule, stated on each city page, keeps a month when its average high is 65–85°F (inclusive) and its precipitation is below the mean of the 12 monthly precipitation normals. That mean is rounded half up to hundredths of an inch, and the comparison uses the rounded value shown. Celsius = (°F − 32) × 5/9, shown to one decimal.

These are climate averages, not a forecast.

These pages are built automatically from public NOAA data.