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NOAA GHCNm Guide: Monthly Climate Trends and Downloads

Use the NOAA GHCNm Explorer to locate global stations, compare monthly temperature and precipitation trends, and access source archives.

Open the GHCNm Explorer

Maintained by Climate Explorer · Last reviewed 13 July 2026.

Quick start

1. Open the explorer and choose temperature or precipitation.
2. Filter by country or search for a station, then select its map marker.
3. Set the period and compare monthly values, annual summaries, and trend lines.
4. Use the station-panel controls, or follow the NOAA archive links below.

1. Introduction

The GHCNm Explorer is an interactive dashboard for exploring Global Historical Climatology Network monthly (GHCNm) data. It allows you to visualize long-term, homogenized weather records from thousands of stations worldwide, focusing on monthly temperature averages and precipitation totals. This tool is ideal for analyzing multi-decadal climate trends.

2. Global Navigation (Sidebar)

The sidebar on the left controls the global view of the application and filters the data displayed on the map.

• Select Year Range: Define the temporal window for analysis. The dataset spans back to 1750, though data availability depends on the specific station. You can narrow this range to focus on specific centuries or decades.
• Select Parameter: Choose the meteorological variable to visualize on the map (e.g., Temperature or Precipitation).
• Select Month: Filter the data to a specific month (e.g., January through December) to analyze seasonal trends across the years.

3. Data Explorer (Map View)

The primary interface is the Data Explorer, an interactive map showing available weather stations.

GHCNm explorer global map view with station markers and sidebar filters

• Blue Dots: Represent stations available within your selected filters.
• Layer Control: Use the layer icon in the top left of the map to switch basemaps (e.g., Satellite, OpenFreeMap) and toggle labels.
• Selection: Click any blue dot to select a station. This will open the detailed plot panel.

4. Station Plot Panel

When you click a station on the map, a detailed data panel appears over the map.

GHCNm explorer plot panel showing historical monthly temperature and trend lines

This panel provides specialized visualizations for the selected station based on your active parameter:

• Temperature/Precipitation Charts: Time series plots displaying the monthly values over the station’s history for the selected month.
• Trend Analysis: A linear trend line is overlaid on the charts to highlight long-term warming, cooling, or precipitation shifts. The trend is computed using an Ordinary Least Squares (OLS) linear regression model applied to the active temporal window. The calculated slope (e.g., +0.02 °C/year) and long-term mean are displayed beneath the plot.
• Fullscreen Mode: Use the fullscreen icon in the top right navigation bar to expand the dashboard for easier data analysis.

How to interpret a trend

The fitted line summarizes change over the selected window; it does not by itself explain the cause of that change. Compare like-for-like months, inspect gaps and outliers, and test whether the result changes when the start or end year moves. A station record represents its local observing history and may not represent a whole country or region.

5. Parameter Reference

The following table lists the primary parameters available in the GHCNm Explorer.

Parameter	Definition	Unit
Temperature	Average/Maximum/Minimum Monthly Temperature	°C
Precipitation	Total Monthly Precipitation	mm

6. Direct Data Access

Advanced users can download the full historical raw data directly from the NOAA NCEI repository.

• Base URL (Temperature): https://www.ncei.noaa.gov/data/global-historical-climatology-network-monthly/v4/temperature/archive/
• Base URL (Precipitation): https://www.ncei.noaa.gov/data/ghcnm/v4/precipitation/archive/

For examples of station coverage, anomalies, and long-term interpretation, read Exploring global climate trends with GHCNm.

7. Troubleshooting and data limits

• No marker is available: Widen the year range, change the month or parameter, or clear the country filter.
• The plot has gaps: Monthly records are not complete for every station and year; treat gaps as missing rather than zero.
• The slope changes: Trend estimates depend on the chosen month, parameter, station, and time window.
• You need the original format: Use the NOAA archive links and retain the source documentation with downloaded files.