How to · 3 min read · updated

How to find the weather on a past date

The night you were born, the night you met, the night the power went out. The weather that night is on record, usually to the hour.

The short answer

Look up the nearest weather station's hourly reports in NOAA's public records, which The Sky That Night searches back to 1940; for places with no station nearby, NASA has hourly estimates for any spot from 2001 on. The moon phase and sunrise for any night can be calculated exactly, no records needed.

Where the records live

The main source is NOAA's hourly station archive (its name is GHCNh, the Global Historical Climatology Network hourly). It's public domain, and each station's file holds its reports of temperature, cloud and wind through the day, usually every hour. You want the station nearest the place, at the hour closest to the moment.

When no station within 40 km reported that night, the fallback is NASA POWER, which estimates hourly weather for any point on the map from 2001 on. It's a regional estimate rather than an observation, so label it that way. The Sky That Night does: the plate names the station it used, or says it's a regional estimate.

The gotchas

  • Recent nights aren't in yet. NOAA publishes station files in batches, and they trail real time by about two months. Last week's weather isn't in the archive yet.
  • Clocks change. Use the local time at that place on that date, daylight saving included. On the night the clocks spring forward, 2:00 AM never happened; it becomes 3:00 AM.
  • The station isn't the house. An airport 16 km away can have a different evening from the backyard. Note the station's name and distance.
  • Our lookup starts in 1940. Earlier dates get a polite no.
  • Some nights have no weather at all. If no station within 40 km reported and the date is before 2001, there's no estimate to fall back on. That happens most in rural places.

The moon and sun are pure maths

You don't need a record for the moon. Its phase, and the sunrise and sunset, can be calculated for any place and date with standard astronomy formulas. The Sky That Night does that itself, and its numbers are checked against NASA JPL's Horizons system.

Turn it into a poster

On The Sky That Night you type the place, the date and time, and what happened. It finds the weather and the moon, writes a one-line caption in the mood you pick (sappy, honest or petty), and paints the scene on top. The numbers print on a plate underneath with where they came from, and they aren't editable: the painting is art, the numbers are the record.

Posters come in 12 x 16 and 18 x 24 in, framed or unframed, in three looks: riso, midnight and sunwash.

Questions people ask

How far back do hourly weather records go?

Many stations have hourly reports for decades. The Sky That Night searches back to January 1, 1940.

Why can't I find the weather from last week?

NOAA's station files trail real time by about two months. Try again later, or settle for the regional estimate if there is one.

Is the weather on the poster real?

Yes. The temperature, cloud and wind come from the station report (or the NASA estimate, which the poster says), and the moon is calculated. Only the painting and the caption are made up.

What if there's no weather station near the place?

If no station within 40 km reported, it uses NASA's hourly estimate for that spot and labels it as an estimate. That estimate only goes back to 2001, so an earlier night in a place with no station nearby can't be looked up.