GHCNm User Guide

Comprehensive user guide for the GHCNm Explorer, detailing how to navigate the map, filter data, and visualize monthly climate trends.

Access the Application: Return to Explorer

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.

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/