Coming soon to the app stores
About
Weather Then puts today’s forecast next to the long local climate record — so you can see how a day, month, or season compares with what has actually been observed nearby.
Geographic coverage
Because we use U.S.-based NOAA GHCN weather stations, historical Then, Trends, and Climate data is currently limited to U.S. locations only and may expand globally in the future. Current conditions and forecasts may still work outside the U.S., but nearby historical records will not be available.
Data sources
Forecasts and historical station records come from different systems. We credit each below.
Forecasts
Current conditions and short-range forecasts are provided by Open-Meteo, which combines open weather model output from national and international meteorological services. We present that data in the app; we do not alter the underlying model fields beyond ordinary unit conversion and display.
Historical observations
Daily highs, lows, precipitation, snowfall, and related climate statistics use NOAA’s Global Historical Climatology Network–Daily (GHCN-Daily) archive from the National Centers for Environmental Information (NCEI). In this app we use the U.S. station network from that archive — quality-controlled station observations, not reanalysis grids.
Menne, M.J., I. Durre, B. Korzeniewski, S. McNeill, K. Thomas, X. Yin, S. Anthony, R. Ray, R.S. Vose, B.E. Gleason, and T.G. Houston, 2012: Global Historical Climatology Network - Daily (GHCN-Daily), Version 3. NOAA National Climatic Data Center. doi:10.7289/V5D21VHZ.
Menne, M.J., I. Durre, R.S. Vose, B.E. Gleason, and T.G. Houston, 2012: An overview of the Global Historical Climatology Network-Daily Database. Journal of Atmospheric and Oceanic Technology, 29, 897–910, doi:10.1175/JTECH-D-11-00103.1.
NOAA and NCEI make no warranty as to the accuracy, reliability, or completeness of the data. Users assume responsibility for determining fitness for a particular purpose.
How we pick a station
Historical weather is measured at observing stations — airports, coop sites, and other fixed points — not at every street address. When you choose a place, we find the nearest NOAA GHCN station with a usable daily record.
Where it helps, we may also stitch in one or more nearby predecessor stations that operated earlier in the same neighborhood. That builds a longer continuous series when the current station is relatively new. On overlapping years, the primary (closest active) station wins.
Each Then, Trends, and Climate view shows which station(s) were used and how far they are from your pin. If the nearest good record is across town or at the airport, that distance is intentional: we would rather show a real thermometer a few miles away than invent weather for your exact coordinates.
Why history isn’t always up to the minute
GHCN-Daily is an archive. Stations report on different schedules, values pass quality checks, and NCEI updates the public files after that work. Fresh days often appear about one to two days after the observation — sometimes longer for cooperative or infrequently reporting sites.
Forecasts update much more often. So “today” on the Home screen can look ahead of the latest day available in the historical series. Trends and Climate use whatever history has landed for your station so far.
How we calculate averages
Averages (typical highs, lows, precip, and similar “normal” style summaries) only include years with enough data for the period you’re looking at. We require at least 85% of the expected days in that window to have observations before a year enters the average.
That keeps a sparse or gappy year from pulling a climatology around. Absolute records — hottest day, wettest month, earliest freeze, and so on — still consider every available observation. A single extreme day counts even if that year would not qualify for an average.
A note on what this app is
Weather Then is a comparison tool built on public observational and forecast data. It is not a substitute for official warnings, NWS products, or emergency information. Station moves, instrument changes, and local microclimates mean any nearby record is an approximation of your backyard — a carefully chosen one, but still an approximation.