A report labeled "September 30" needs to say where that day begins and ends. A local calendar day and a UTC day can cover different periods, even when their date labels match.
The Weather API uses UTC days for history. On a paid plan, request Deep and a past date to ask for the summary at your coordinates:
GET /weather?lat=35.2271&lon=-80.8431&deep=true&date=2026-09-30
Parse-Version: 2.0.0
When available, the requested summary appears in deep.history. Its date identifies September 30 in UTC. Label it that way in a report, such as "Weather summary for September 30, 2026, UTC." Relabeling it as the person's local September 30 does not change the period summarized.
The response still has its ordinary current object and station context. current.observed_at is the timestamp of the current station observation. Passing the historical date does not move that reading back to September 30. An application that needs the past day's high should read deep.history.high, rather than taking current.temperature from the same response.
The historical fields carry their units in metric and imperial pairs:
| Historical field | Unit | Paired field | Unit |
|---|---|---|---|
high, low | Celsius | high_f, low_f | Fahrenheit |
precipitation | Millimeters | precipitation_in | Inches |
wind_max | Kilometers per hour | wind_max_mph | Miles per hour |
The temperatures are daily high and low values, precipitation is the day's total, and wind is the maximum sustained wind in the summary. They describe a period rather than a single timestamped observation. A precipitation total is also a different quantity from a forecast's precipitation chance.
History accepts completed past UTC days. The current UTC day is still incomplete, and a future date cannot supply history. A successful paid Deep response can have deep.history: null when the archived summary is unavailable, so a valid-looking date alone does not promise a populated result. Individual measurements can also be null. Without a date, the history key is omitted from ordinary Deep responses, and Free plans return an empty Deep object.
Keep the coordinates, selected date, and returned summary together. If your report specifically needs statistics over local midnight-to-midnight, a UTC daily summary cannot be converted into that period by changing its label or offset. That report needs weather data summarized over the intended local interval.