What CLIMAT Messages Contain—and How to Explore Them
Many global climate products begin with observations made at individual stations. A CLIMAT message packages one station’s monthly summary for international exchange: useful evidence, but not yet a regional average, climate anomaly or long-term trend.
One Station, One Month
A CLIMAT message is a structured report that distils a calendar month of observations from a land station into a compact statistical summary. The World Meteorological Organization (WMO) defines the code structure in its Manual on Codes (WMO-No. 306). The report supports climate monitoring, research and archiving; it is not a daily forecast product.
While a daily weather forecast requires high-frequency data to predict incoming storms, climatology relies on detecting subtle, long-term shifts. By summarizing the available daily observations for each calendar month into averages, totals and selected extremes, CLIMAT messages can be compared across time. Detecting a climate trend still requires quality control, treatment of station changes and an explicitly defined comparison method.
What a Message Contains
The contents are governed by WMO encoding standards, including BUFR (Binary Universal Form for the Representation of meteorological data). WMO’s current CLIMAT conversion template uses sequences 3-01-150 and 3-07-073 for monthly land-station reports.
Depending on the operational capacity of the reporting station, a complete CLIMAT message may contain:
- Air temperature: monthly mean temperature, absolute maximum and minimum temperature, and means of daily maxima and minima.
- Precipitation: monthly accumulation and counts of days meeting defined precipitation thresholds.
- Vapour pressure: a monthly atmospheric-moisture measure.
- Atmospheric pressure: monthly station-level and sea-level pressure fields.
- Sunshine: total bright-sunshine duration for the month.
Crucially, the message also includes completeness indicators—such as the number of missing daily observations—that help users judge that month’s summary. Fields may be left empty when a station does not report a particular variable.
The Global Transmission Network
After a reporting month ends, participating national services prepare and exchange CLIMAT summaries. Arrival is not simultaneous: a recent archive can contain different latest months for different stations and variables.
The Global Telecommunication System (GTS) has historically carried operational meteorological messages between services. WMO is transitioning international exchange to the WMO Information System 2.0 (WIS2), whose current technical framework uses web standards and publish-subscribe messaging. The transition changes transport and discovery; it does not turn a monthly CLIMAT summary into real-time data.
From Encoded Transmissions to Public Insight
While raw BUFR messages are essential for machine-to-machine exchange, they are exceptionally difficult for the public to read. This is where national meteorological agencies step in to act as global aggregators.
The Deutscher Wetterdienst (DWD) Climate Data Center publishes raw CLIMAT messages alongside separate parameter-level recent and historical products for climatological applications. The recent directories extend available station series, while historical products are published separately as versioned files.
The WMO Climate Explorer parses the DWD historical and recent CLIMAT parameter files into a public station interface. It lets readers discover stations and inspect monthly observations without decoding BUFR. The WMO Climate task guide separately documents station verification, field meanings, like-month comparisons and CSV export.
What the Explorer Does Not Calculate
The Explorer displays monthly station observations. Its Dashboard cards summarize the loaded series, including months from different seasons; those card averages are not climatological normals. A stored date such as 2026-07-01 labels the July 2026 monthly record rather than an observation made only on 1 July.
To calculate an anomaly, a user must subtract a documented reference for the same variable, calendar month and matching station. A trend requires further checks for gaps, station changes, observing practices and suitability of the statistical method. Neither calculation is produced automatically by the WMO Climate Explorer.
Limitations of Interpretation
When exploring this data, it is vital to remember the scale of observation. A single station’s monthly summary is invaluable for local climate monitoring—it can describe that station’s conditions and, when compared with an appropriate reference period, indicate how unusual the month was. However, one station is merely a single point in a massive global network. No single station’s record, regardless of how extreme, can establish a global climate change trend on its own. Large-scale climate assessments combine many station series using quality control, treatment of station changes and spatial analysis; CLIMAT messages are one source of observations for that work.
Frequently Asked Questions
What does a CLIMAT message contain?
A CLIMAT message contains a statistical summary of the previous month’s weather for a single land station. Common reported variables include mean air temperature, total precipitation, vapor pressure, and total sunshine hours, though availability depends on the station’s capabilities.
How are these monthly observations transmitted?
National meteorological services exchange coded monthly reports through WMO information systems. GTS has historically carried these messages, while WMO is transitioning exchange to WIS2. Stations and variables can appear in recent archives at different times.
How can I explore this global climate data?
You can interactively explore these monthly observations using the WMO Climate Explorer, which visualizes the quality-controlled global CLIMAT archive maintained by the Deutscher Wetterdienst (DWD) Climate Data Center.
Data Annex
| Metadata Category | Dataset Details |
|---|---|
| Upstream Data Owner | Deutscher Wetterdienst (DWD) Climate Data Center |
| Temporal Resolution | Monthly statistical summaries compiled from daily observations |
| Update Frequency | Each record summarizes one month; recent parameter files are refreshed as reports are processed, while historical series are issued separately in versioned updates |
| Coverage | Global land stations transmitting WMO CLIMAT messages |
| Important Limitations | Monthly data preserve selected extremes but not the complete day-by-day sequence. Station availability fluctuates due to international reporting capacities. |
| Variable | Description |
|---|---|
| Air Temperature | Mean monthly temperature, absolute max/min, and mean daily max/min |
| Precipitation | Total accumulated monthly precipitation, and days with ≥1mm |
| Sunshine | Total monthly sunshine duration |
| Atmospheric Pressure | Mean sea-level pressure |
| Vapor Pressure | Mean monthly vapor pressure |
Data Sources
The WMO CLIMAT template documents fields and BUFR sequences. WMO’s Manual on Codes overview describes coded international exchange, while its GTS overview and WIS2 manual overview document the exchange systems. DWD publishes the raw CLIMAT messages and the separate quality-controlled products used by the Explorer.