An overview of forecast resolution, range, update times, issuance times, and lead times.
Spire Weather owns and operates every stage of the forecast value chain, from satellites and ground stations to the data assimilation process and global forecast model.
Resolution¶
Spire Weather offers 1/8th-degree horizontal global resolution, which is about 14 km (8.6 miles) at the equator and about 12 km in mid-latitudes. One grid cell is approximately:
35,583 acres
14,400 hectares
144 km²
12 km × 12 km
Forecast Ranges and Refresh Rates¶
Forecasts from the past 3 days are always available via the APIs. Additional historical forecasts can be made available upon request.
Spire Optimized Point Forecast¶
Spire’s Optimized Point Forecast is updated every hour.
Spire Global Forecast¶
24-hour forecasts are issued 4 times per day at 00:00, 06:00, 12:00, and 18:00 UTC. This forecast data has hourly granularity (1-hour intervals between lead times).
15-day forecasts are issued 2 times per day at 00:00 and 12:00 UTC:
First 48 hours: 1-hour intervals between lead times
First 5 days: 3-hour intervals between lead times
Full 15 days: 6-hour intervals between lead times
All forecast values are consistent; the only difference is how the model run is sliced into different lead times. The 2-day forecast for 12 UTC contains the same values whether you query with 1-hour, 3-hour, or 6-hour intervals.
These slices are selected with the time_bundle parameter:
| Range | Step | time_bundle | Records (00/12 UTC run) |
|---|---|---|---|
| 48 hours | 1 hour | hourly | 49 |
| 5 days | 3 hours | 3_hourly | 41 |
| 7 days | 6 hours | 6_hourly | 29 |
| 10 days | 6 hours | 6_hourly_extended (alias 6_hourly_10day) | 41 |
| 15 days | 6 hours | 6_hourly_15day | 61 |
The 06 and 18 UTC runs cover 24 hours, so for those issuances hourly returns 25 records and 6_hourly returns 5. Which time bundles your key can use depends on your subscription. See the Operational Reference.
Forecast Dissemination Schedule¶
Forecast updates occur over a range of time, and data is made available in the API on a rolling basis: the first lead times of a run appear about an hour after the issuance time (see the Operational Reference), and the last lead times follow over the next hours. Nominally, all lead times of a run are complete by:
| Issuance Time | Typically Complete By |
|---|---|
| 12:00 UTC | 19:00 UTC |
| 06:00 UTC | 13:00 UTC |
| 00:00 UTC | 07:00 UTC |
| 18:00 UTC (previous day) | 01:00 UTC |
This is not a guarantee; dissemination may be slightly delayed if upstream data partners are delayed.
Terminology¶
“Update time,” “issuance time,” and “lead time” refer to different things:
| Term | Description |
|---|---|
| Update time | When a forecast completes updating, typically around 7 hours after issuance |
| Issuance time | When the forecast run started (00:00, 06:00, 12:00, or 18:00 UTC) |
| Lead time | The valid time of the forecast; the length between issuance time and when the prediction occurs |
Example¶
For a short-range forecast with issuance time 06:00 UTC:
f000 (0h lead time): 06:00 UTC — the “earth state” of the global model at that time
f001 (+1h): 07:00 UTC — first forecasted state
f002 (+2h): 08:00 UTC — second forecasted state
And so on.