How to read GraySky climate data

Averages describe a period, not a prediction

Monthly temperatures are calculated from available NOAA GHCN-Daily station observations using the baseline displayed on each city page, usually 1991–2020. A station may cover only part of that baseline. The available station history is shown separately. An average January is not a forecast for next January.

The station name and distance tell you where observations were taken. Airports, coasts, valleys and city centres can experience different conditions.

Precipitation and snowfall are different measurements

Precipitation totals include liquid rain and the water equivalent of snow and other frozen precipitation. Snowfall depth is a separate quantity; it should not be added to a precipitation total. The past-year section is dated separately from the climate baseline. Rain estimates can combine station observations and radar; snow uses reporting stations.

Sunshine and humidity use a weather reconstruction

ERA5 combines observations with a physical model of the atmosphere. Our sunshine percentage is estimated from cloud cover, rather than measured sunshine duration. It is useful for comparing months, but should not be interpreted as a precise count of sunny hours. Humidity is also derived from ERA5. The current payload does not supply a separate ERA5 averaging period, so we do not assign the station's baseline to it.

Water temperatures are omitted from city climate pages when the data cannot identify the sampled water body. A nearby model grid cell is not sufficient evidence for the temperature of a named lake or beach.

Records mean the available station history

A record high or wettest day refers to the station and date range displayed on the page. It is not necessarily the official all-time record for the city. Data gaps, station changes and a longer record at another station can produce different values.

Comparisons and visiting advice

Month comparisons use one location's available data with consistent units. “Best time to visit” summarizes typical temperature comfort; it does not account for your activities, crowds, travel prices or future extreme weather. Country percentiles compare the reporting locations in our dataset, not equal areas of the country.

Explore seasonal temperature differences across 30 cities.

Primary sources

NOAA GHCN-Daily observations · NOAA climate normals methodology · ECMWF ERA5.

GraySky computes these summaries from source data; the city tables are not an official NOAA publication. To report a discrepancy, include the city, metric and source in a message through support.