How many days a year does it rain in London

London, the vibrant capital of England, is often associated with rainy weather—but how much does it actually rain? Understanding the average rainfall helps travelers pack appropriately and residents plan their days. This article explores London’s precipitation patterns, comparing them to the rest of the UK, breaking down rainfall by month, and revealing whether the city deserves its wet reputation.

Defining a “Rainy Day”: meteorological standards in the UK

To accurately determine the number of rainy days in London, it is essential to adhere to the standard definitions employed in meteorology within the United Kingdom. The Met Office, the national weather service for the UK, provides a clear and objective criterion for classifying a day as having rainfall. A day is officially considered a “rainy day” when a minimum of 1 millimeter (mm) of rainfall has been recorded.

The Met Office also makes a distinction between “rain” and “showers”. Rain typically refers to more prolonged periods of continuous wet weather often associated with the passage of weather fronts, which are boundaries between air masses with different properties.

These frontal systems can bring grey, overcast skies and persistent rainfall that can last for hours. In contrast, showers are generally more intermittent and localized, frequently originating from individual clouds that can be observed in the sky. Showers tend to be hit-and-miss, meaning one area might experience heavy downpours while a neighboring area remains dry.

While both rain and showers contribute to the total number of rainy days if the 1mm threshold is met, recognizing this distinction offers a more nuanced understanding of London’s typical weather patterns. It’s possible that London experiences a higher frequency of days with showers, characterized by on-and-off precipitation with intervals of drier and brighter weather, as opposed to solely enduring prolonged periods of continuous rain. This difference has practical implications for residents and visitors when planning daily activities.

Furthermore, it’s important to acknowledge that “precipitation” encompasses all forms of water falling from the atmosphere to the ground, including not only liquid rain but also sleet, snow, and hail. While the primary focus of the user’s query is on rain, from a meteorological perspective, days experiencing other forms of precipitation that meet or exceed the 1mm threshold would also be classified as “rainy days.”

Average number of rainy days in London: a long-term perspective

According to Met Office climate data compiled over a 30-year period, London experiences an average of 106.5 days of rainfall per year where 1mm or more of rain was recorded. This figure signifies that, on average, measurable rainfall occurs on approximately 29% of the days in a year in London. This provides a general benchmark for understanding how frequently London encounters rainfall, suggesting that the city experiences measurable precipitation for roughly one-third of the year. A 30-year average is a standard climatological period used to smooth out any significant year-to-year fluctuations and offer a more representative long-term picture of the climate. The 29% figure further contextualizes the number of rainy days in relation to the total number of days in a calendar year.

The same Met Office source also indicates that the average rainfall across Britain as a whole amounts to 156.2 days per year (based on data from 1981 to 2010). This comparison highlights that London, on average, experiences a lower frequency of rainy days compared to the entirety of the UK. This difference is likely attributable to London’s geographical location in the southeast of England, a region that generally tends to be drier than the western and northern parts of the country, which are more exposed to Atlantic weather systems. Comparing London’s rainfall frequency to the national average provides a broader geographical context and underscores the regional variations in precipitation patterns across the UK, which are often influenced by factors such as proximity to the Atlantic Ocean and the topographical features of different areas.

More localized data from Heathrow, a specific climate observation station within Greater London, for the period spanning 1991 to 2020, reveals an average of 111.66 days of rainfall meeting or exceeding the 1mm threshold per year. This figure is slightly higher than the 106.5 days mentioned earlier, which might represent a broader geographical area of London or a slightly different historical averaging period.

This minor discrepancy suggests that there can be variations in rainfall frequency even within the London region itself, depending on the precise location and the specific timeframe under analysis. Utilizing data from a particular weather station like Heathrow offers a more focused and localized perspective on rainfall frequency within a specific part of London. The slight difference in averages reinforces the idea that rainfall patterns can vary even within a relatively compact urban area.

Monthly distribution of rainy days: seasonal variations  

More specific data for Heathrow, located in West London, for the period 1991-2020 , offers a more localized view of the monthly distribution of rainy days within the London area. While the overall trends are similar to the UK average, there are some notable differences in the specific monthly figures: January averages 11.53 rainy days, February 9.50, March 8.47, April 8.80, May 8.00, June 8.33, July 7.90, August 8.43, September 7.90, October 10.80, November 11.23, and December 10.77 rainy days. This Heathrow-specific data confirms the general trend of fewer rainy days during the summer months (May to September) and a higher frequency during the winter months (October to March). The months with the lowest average number of rainy days appear to be May, July, and September, while January and November tend to have the highest. This more granular view of a specific location within London provides a more accurate picture of the monthly rainfall frequency experienced in at least one part of the city. The slight variations observed when compared to the overall UK average highlight the importance of considering localized data when available to gain a more precise understanding of regional climate patterns.  

To provide a clear and concise overview of the monthly distribution of rainy days in London, the following table summarizes the average number of days with rainfall of 1mm or more per month at Heathrow based on data from 1991-2020 :   

Presenting this monthly data in a tabular format allows for easy visualization and quick identification of the months with the highest and lowest frequency of rainy days in this part of London. Including the annual total provides a summary of the overall rainfall frequency experienced at Heathrow during the specified period.

Geographical variations in rainfall within London: a local perspective

While the overall average number of rainy days provides a general understanding of London’s rainfall frequency, it’s important to recognize that a large and geographically diverse city like London can experience variations in rainfall patterns across its different areas. Factors such as local topography and urban environmental effects can contribute to these differences. Snippets and provide valuable rainfall data for several distinct weather stations located throughout London, including Kew Gardens in the southwest, Hampstead in the north, Northolt in the northwest, and Greenwich in the southeast.

A comparison of the average annual precipitation (measured in millimeters) recorded at these different stations for the period 1991-2020 (where data is consistently available) reveals some interesting geographical variations within London. Hampstead, situated at a higher elevation compared to other parts of the city, recorded the highest average annual rainfall at 722.1 mm. Northolt experienced an average of 663.3 mm, while Kew Gardens reported 627.5 mm. Greenwich, located closer to the River Thames and at a lower elevation, registered the lowest average annual precipitation among these stations, with 562.9 mm.

This data strongly suggests that local topography plays a significant role in influencing precipitation levels across London. Higher elevations, such as Hampstead, often intercept more orographic rainfall, which occurs when air masses are forced to rise by hills or mountains, leading to cooling, condensation, and subsequent precipitation. Conversely, areas at lower elevations or in more sheltered locations might experience less rainfall. The proximity to large bodies of water like the River Thames could also influence local weather patterns in Greenwich, potentially contributing to its lower recorded rainfall.

London compared to other major UK cities

To gain a broader understanding of London’s rainfall frequency, it is informative to compare it with other major cities across the United Kingdom. This provides a relative perspective and helps to contextualize the common perception of London’s weather. Snippet presents a table comparing rainfall amounts (in mm) and the number of days with rainfall exceeding 1 mm for various UK cities. According to this data, Glasgow experiences approximately 170 rainy days per year, Cardiff around 149 days, and Manchester about 152 days, while London is listed with 109 rainy days. This comparison indicates that London generally experiences a notably lower number of rainy days annually compared to cities like Glasgow, Cardiff, and Manchester, which are often perceived as having particularly wet climates. This data challenges the common notion of London being excessively rainy in comparison to other major urban centers in the UK. It suggests that other cities, particularly those located in the western parts of the country, tend to have a higher frequency of rainfall.   

   This table offers a direct comparison, allowing for easy understanding of the differences in rainfall frequency between these major UK cities. The range provided for London reflects the slight variations found across different sources and averaging periods.