What is the resolution, range, and refresh rate of Spire forecasts?

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.

As a result, Spire Weather is able to offer 1/8th-degree horizontal global resolution, which is about 12 km or 7.4 miles. This means that 1 grid cell is approximately:

  • 12 km x 12 km
  • 144 km^2
  • 14400 hectares

Forecast Ranges and Refresh Rates

Forecasts from the past 3 days are always available via the APIs, and additional historical forecasts can be made available upon request.

Short-range forecasts are 24 hour forecasts with 1-hour intervals between lead times.

They are updated 4 times per day.

Forecast updates occur over a range of time, and should be complete by:

  • 01:00 UTC for the previous day's 18:00 issuance time
  • 07:00 UTC for the 00:00 issuance time
  • 13:00 UTC for the 06:00 issuance time
  • 19:00 UTC  for the 12:00 issuance time

Medium-range forecasts are 7 day forecasts with 6-hour intervals between lead times.

They are updated 2 times per day.

Forecast updates occur over a range of time, and should be complete by:

  • 07:00 UTC for the 00:00 issuance time
  • 19:00 UTC for the 12:00 issuance time

Daily Forecasts

Weekly Forecasts

 

It's worth emphasizing that "update time", "issuance time", and "lead time" all refer to separate things.

The update time is when a forecast completes updating, around 7 hours after the issuance time.

Issuance times always correspond to 00:00, 06:00, 12:00, or 18:00 (UTC).

Lead times refer to the valid time components of the forecast itself. In other words, lead times represent the length between the issuance time and the occurrence of the predictions.

 

For a short-range forecast with an issuance time of 06:00 UTC, the first lead time is 06:00 UTC, which is the "earth state" of the global forecast model at that time.

The +1h lead time is 07:00 UTC and represents the "first forecasted state".

The +2h lead time is 08:00 UTC and represents the second forecasted state.

The +3h lead time is 09:00 UTC and represents the third forecasted state -- and so on.

 

For more information on the general weather forecast process, please see here.

For information on downloading multiple forecast files via the API, please see here.