The forecaster on duty at the SIDC produces each day (nominal issue time 12:30 UTC) a forecast of the value of the K-index in Belgium, for time periods of 3 hours. The forecast covers the period of three days, starting from the day of the issue of forecast at 12:00 UTC, and the two consecutive days at 00:00 UTC. Note that the three first values reported at 03:00 UTC, 06:00 UTC, and 09:00 UTC correspond to the measured values.
| Select forecasted day: |  |
| Forecast/Issue date | 2026-03-01 | 2026-03-02 | 2026-03-03 |
|---|---|---|---|
| 2026-03-04 00:00-03:00 | 2 | 2 | 1 |
| 2026-03-04 03:00-06:00 | 3 | 2 | 3 |
| 2026-03-04 06:00-09:00 | 2 | 2 | 2 |
| 2026-03-04 09:00-12:00 | 2 | 1 | 2 |
| 2026-03-04 12:00-15:00 | 1 | 1 | |
| 2026-03-04 15:00-18:00 | 2 | 2 | |
| 2026-03-04 18:00-21:00 | 3 | 3 | |
| 2026-03-04 21:00-00:00 | 4 | 4 |
This web page forms part of the European Space Agency's network of space weather services and service development activities, and is supported under ESA contract number 4000134036/21/D/MRP.
For further product-related information or enquiries contact helpdesk. E-mail: helpdesk.swe@esa.int
All publications and presentations using data obtained from this site should acknowledge Solar Influences Data analysis Centre (SIDC) at the Royal Observatory of Belgium (ROB) and The ESA Space Safety Programme.
For further information about space weather in the ESA Space Safety Programme see: www.esa.int/spaceweather
Access the ESA SWE portal here: swe.ssa.esa.int
| Variable | Values required for this product |
|---|---|
| pc | G158 |
| psc | a |
| component | latest | archive |
| Variable | Values required for this product |
|---|---|
| dts_start | YYYY-MM-DDTHH:MM:SSZ |
| dts_end | YYYY-MM-DDTHH:MM:SSZ |
To access the latest data, the "component" variable in the API URL should be set to "latest": component=latest. Available at: https://ssa.sidc.be/prod/API/index.php?component=latest&pc=G158&psc=a
It returns all 3-day K Dourbes forecasts issued by a SIDC Space Weather forecaster for the days of today, today+1day, today+2days. The issue_time is that of today-2days, today-1day and today. The result is returned in JSON format.
To access the archived data, the "component" variable in the API URL should be set to "archive": component=archive. Available at: https://ssa.sidc.be/prod/API/index.php?component=archive&pc=G158&psc=a
It returns a list of the values forecasted for the K-index in Dourbes for the default time range(default is from time of query to time of query+2days). The result is returned in JSON format.
The information in the returned JSON include the end time of the forecast (the day of issue+2 days), the issue time of the forecast, the start time that the K-index value is valid for and the value forecasted.
JSON example|
[ { "data": { "end_time": [datetime], "issue_time": [datetime], "start_time": [datetime], "value": [integer] } } ] |
The 3-day K-Belgium forecast product provides forecasting values of the geomagnetic K-index in Belgium. The measured K-Belgium index is based on data from the two belgian stations located in Dourbes (latitude 50.1 degrees North, longitude 4.6 degrees East) and in Manhay (latitude 50° 17.9 North, longitude 5° 40.9 East). For more information, please see: Verhulst, T. G. W., Bracke, S., Humbled, F., & Stankov, S. M. (2021). Local magnetic activity index nowcast based on concurrent measurements at two observatories in close proximity. Space Weather, 19, e2020SW002709.
The space weather forecaster is monitoring the solar activity, solar wind conditions, including coronal mass ejections and coronal holes to evaluate and forecast potential geomagnetic storms.
The K-index is a proxy for the extent of the disturbance of the geomagnetic field, measured by ground-based monitors. The index ranges from 0 to 9 [0-2: quiet, 3: unsettled, 4: active, 5-9: geomagnetic storm]. The SIDC Space Weather forecaster provides daily their estimation of the geomagnetic activity K-index, covering a period of the day of issue, plus the two following days. The estimated values are the maximum during a time period of three hours and given in 3-hour bins, namely 00:00-03:00 UTC, 03:00-06:00 UTC, ... Such data are useful to all users concerned with geomagnetic activity, particularly for latitudes around 50 degrees.
The product has been provided by the Royal Observatory of Belgium (ROB) since 2004.
The on-duty SIDC space weather forecaster of ROB consults remote solar observations and solar wind in-situ measurements available to determine the space weather activity of the past weeks. Special attention is given to the monitoring of specific geo-effective events such as coronal mass ejections heading towards Earth and recurrent space weather phenomena; for example high speed streams coming from equatorial corona holes. In addition, the forecaster consults the K_Bel index values issued the past days, as provided from the Ionosphere and Space Weather section of the Royal Meteorological Institute of Belgium. Those values are reported hourly while, for historical reasons, ROB is reporting the indices applicable to the end of bin of 3 hours. Based on the K-indices recorded and their so far analysis, the forecaster predicts the local K index for a period of three days.
The product is issued daily, 365 days a year at 12:30 UTC.
Since the forecast is issued at 12:30 UTC, the first three values of the date of issue given by the forecaster, corresponding to the time bins 00:00-03:00 UTC, 03:00-06:00 and 06:00-09:00 UTC, are not a forecast but the values reported for K_Bel. To indicate that, those values are shown as grey in the "Latest" and "Query" tabs. If K-Belgium for 12:00 UTC has also been reported by the time of issue, the observed value is inserted in the time bin 09:00-12:00 UTC, however this value is not greyed out. The user should bare in mind that the forecast reported is the estimation of the index and not the associated confidence interval.
The tab Latest shows the most recent K-index forecast, covering the prediction for the date of issue, plus the following two days. It is also accessible via the API as a JSON file. New data are provided by ROB daily, at 12:30 UTC. Because the forecast is issued on 12:30 UTC, at least the first three values (if no delays in their issuance, then the first four values) reported for the day of issue are observations from Dourbes and not forecasts. To indicate that, those values are being greyed out.
The tab Query displays a list of all the archived forecasts going back to 2002-01-15. The list can be filtered by providing the desired date for which the user wants to retrieve all the forecasts made, in the format YYYY-MM-DD.
For example, entering the date 2021-02-28 and clicking on the "Submit" button will return a list of all of the K-indices forecasted within the specified day. Since the forecasts cover a 3-days period (date of issue + two consecutive days) the forecasts for the day 2021-02-28 returned will be those issued on 26th to 28th Feb 2021. In addition, since on day 2021-02-28 the forecast is issued at 12:30 UTC, at least the first three values reported are observations from Dourbes and not forecasts. To indicate that, they are being greyed out.
All archived forecasts are accessible via the API.
