Rain Check data and methodology
Where Rain Check’s climates come from: NOAA’s 1991–2020 U.S. Climate Normals, one weather station per city, and how the clues are measured.
Where the climate comes from
Every chart in Rain Check is drawn from U.S. Climate Normals 1991–2020, published by NOAA’s National Centers for Environmental Information (NCEI). A climate normal is a 30-year average, and the monthly set gives, for each of the twelve months, the average high temperature, the average low, the precipitation and the snowfall at a weather station. Rain Check uses those four averages as published, adding up the twelve months for a year’s totals, and the one exception is the snow rule below. The dataset is cited as Palecki, M. et al. (2021), U.S. Climate Normals 1991–2020, doi:10.25921/wck8-er13. Because they are averages over three decades, the charts describe what a month is typically like, not what any one year did.
How each field is defined
| Field | Definition |
|---|---|
| Distance | Great-circle miles between the guess and the answer, measured from each city’s own point, never from its weather station. |
| State | The city’s state, or DC or Puerto Rico. It reads close when two different states share a Census division. |
| Winter | The 1991–2020 normal average low temperature for January, in °F. |
| Summer | The 1991–2020 normal average high temperature for July, in °F. |
| Precip | The year’s precipitation, rain plus melted snow: the twelve monthly normals added up, in inches. |
| Snow | The year’s snowfall: the twelve monthly normals added up, in inches of snow. |
One weather station per city
Each city uses a single station, so its chart never blends two places. Rain Check picks the nearest airport or weather-service office within 30 kilometers, about 19 miles, that has complete normals: all twelve months of high, low and precipitation, flagged by NOAA as standard or representative rather than provisional or estimated. Most cities use one of those. Thirty-four of the 263 use a cooperative observer station instead, another kind of NOAA station, where no suitable airport station was in reach or a station in the city itself was the better match. Cities that would use the same station are a single entry, named for the largest of them, with the others kept as alternate names the guess box understands: Cambridge is part of Boston’s entry, Bellevue of Seattle’s and St. Paul of Minneapolis’s.
How snow is counted
Snowfall is the hardest normal to get, because most airports carry only provisional snow normals, which NOAA calculates from at least ten years of data. Rain Check accepts those for snow, though never for temperature or precipitation; refusing them would have pushed cities onto stations in other towns. If a station has no usable snow normals at all, its snow counts as zero only where no month’s average low falls below 32°F, as in Phoenix and Honolulu. Anywhere colder, missing snow is missing data rather than no snow, and the station is not used.
Which cities, and where they are
The city list starts from the Census Bureau’s 2024 population estimates for cities and towns. It takes the most populous places and adds enough others that every state, the District of Columbia and Puerto Rico has at least one, and it keeps a place only if a station meeting the rules above sits within 30 kilometers. That leaves 263 entries, each reviewed by hand for anything implausible. Each city’s location is its point in the Census Bureau’s 2024 Gazetteer of places, and every distance is the great-circle distance in miles between two of those points. For seven cities the Census point sits far from downtown, so the location is set by hand instead. San Francisco’s Gazetteer point, for example, falls on the Farallon Islands. Of the 263 entries, 172 can be the city of the day. No two of them are within 40 kilometers of each other, and every state, DC and Puerto Rico has at least one.
Divisions
Regions in the State clue and the region hint are the Census Bureau’s nine divisions: New England, Middle Atlantic, East North Central, West North Central, South Atlantic, East South Central, West South Central, Mountain and Pacific. Alaska and Hawaii are part of the Pacific division. Puerto Rico, which the Census places in no division, is grouped with the South Atlantic.
Updates and fairness
The city chosen for a published puzzle never changes, and the schedule is fixed ahead of time, never repeating a city within 60 days. The figures may be refreshed if NOAA publishes a correction or a new set of normals. If a correction is needed for a city that appears in a future puzzle, the change is made before that day. To report a data problem, email hello@guessday.com with the puzzle number.
Attribution and independence
Climate normals come from NOAA’s National Centers for Environmental Information, and city populations and locations from the U.S. Census Bureau. Both are U.S. government agencies, and their data are works of the United States government. Rain Check is not affiliated with NOAA or the National Weather Service. Nothing on this site is official weather or climate guidance, and no agency logos appear in the game.