What CLIMAT Messages Contain—and How to Explore Them
Understanding the nuances of the Earth’s climate system begins at the local level. Behind the sweeping global temperature anomalies reported in the news is a fundamental unit of measurement: the monthly meteorological summary for a single weather station. This summary is transmitted internationally as a standardized report known as a CLIMAT message.
One Station, One Month
A CLIMAT message is a highly structured dispatch that distills an entire month of weather observations from a single land station into a compact statistical summary. Defined by the World Meteorological Organization (WMO) within the Manual on Codes (WMO-No. 306), this format is strictly designed to support global climate monitoring rather than daily weather forecasting.
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 of these messages are governed by strict WMO encoding standards, primarily utilizing modern BUFR (Binary Universal Form for the Representation of meteorological data) templates. Specifically, sequences 3-01-150 and 3-07-073 define the structure for monthly land station values.
Depending on the operational capacity of the reporting station, a complete CLIMAT message may contain:
- Air Temperature: The mean monthly temperature, alongside the absolute maximum and minimum temperatures recorded during that month.
- Precipitation: The total accumulated monthly precipitation and the number of days with precipitation exceeding specific thresholds.
- Vapor Pressure: The mean monthly vapor pressure, indicating atmospheric moisture.
- Atmospheric Pressure: Mean station-level pressure and mean sea-level pressure.
- Sunshine: The total hours of sunshine 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
Once a month concludes, participating weather stations do not hold their summaries. NOAA documentation describes WMO member nations as typically transmitting CLIMAT reports between the second and tenth day of the new month.
Historically, these dispatches were broadcast as dense alphanumeric text via the Global Telecommunication System (GTS), a secure, dedicated network connecting national meteorological agencies. Today, the global meteorological community is actively transitioning to the WMO Information System 2.0 (WIS2). This upgrade replaces legacy, closed-network broadcasting with modern web protocols, making the rapid sharing of BUFR-encoded data more efficient and scalable.
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 plays a critical role in this ecosystem. It publishes the raw CLIMAT messages alongside separate recent and historical quality-controlled products intended for climatological applications. These products make the global station records openly available while keeping their processing stage visible to users.
The WMO Climate Explorer leverages this exact upstream data. Rather than requiring users to parse complex BUFR sequences, the Explorer provides an interactive public interface layered directly on top of the DWD’s historical and recent quality-controlled CLIMAT archive. It allows users to visually navigate the network, select individual stations, and immediately explore the historical and modern observations derived from these monthly messages.
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?
Stations typically transmit their summaries during the first ten days of the new month. The data travels through the WMO’s Global Telecommunication System (GTS), which is currently transitioning to the modern, web-based WMO Information System 2.0 (WIS2).
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 | Raw and recent products receive new monthly reports; historical quality-controlled series are released 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 the message structure, while the WMO GTS overview explains the exchange network and its transition to WIS2. NOAA’s GHCN-Monthly technical documentation describes the typical transmission window. DWD publishes the raw CLIMAT messages and the separate quality-controlled products used by the WMO Climate Explorer.