About Meteorological Days
What is a Meteorological Day?
A meteorological day runs from 09:00 UTC to 09:00 UTC (the following day), rather than the midnight-to-midnight boundary used for calendar days.
In UK local time, this translates to:
- Summer (BST): 10:00 to 10:00 the next day
- Winter (GMT): 09:00 to 09:00 the next day
Why Do We Use Meteorological Days?
- International Standard: The World Meteorological Organization (WMO) and UK Met Office use 09:00 UTC as the standard daily boundary for weather observations.
- Accurate Daily Totals: Rainfall, sunshine hours, and temperature extremes align better with natural weather patterns when measured from morning to morning.
- Data Consistency: Allows direct comparison with official Met Office data and other weather stations worldwide.
Example
When you see "1 October 2025" in daily data:
During summer (BST), this represents:
- Start: 1 October 2025 at 10:00 BST
- End: 2 October 2025 at 09:59:59 BST
This is a full 24-hour period aligned with the international weather recording standard.
Calendar Day vs Meteorological Day
Calendar Day
Period: 00:00 to 23:59
Used for general civil purposes.
Meteorological Day
Period: 09:00 UTC to 09:00 UTC
Used for weather data.
Which Data Uses Meteorological Days?
The following pages on this website display data based on meteorological days:
- Daily Data - Complete daily summaries
- Recent Data - "Today" and "Yesterday" summaries
- Summaries/Records - Daily weather records
- Data Explorer Tables - Daily summary mode
- Data Explorer Graphs - Daily summary charts
- Data Explorer Query Builder - Custom queries by met day