5.3 How common is icy weather
Evidence of the actual frequency of ice is not readily available to the public. However,the PWSCG (Public Weather Service Customer Group), which holds the MET Office to account on behalf of the public recognises that the frequency of gritter deployment is a ’proxy’.
The documented references to the PWSCG recognition of the proxy status of gritting deployment for ice forecasting are set out at the foot of this section.
Local authority gritting statistics are therefore an objective guide to the number of times icy weather occurs.
Roads are treated by local authorities whenever they receive a weather forecast that either icy weather or snow is predicted. These forecasts are provided by a number of forecasters of which the MET Office is one. These forecasts are not part of the Public Weather Service (PWS).
Using this proxy approach, a survey was carried out of the gritting frequency of 12 local authorities in England for the winter months. The survey used responses to Freedom of Information requests and covered a wide geographical spread and both urban and predominantly rural authorities. Leeds City Council was the most northerly Council surveyed The chart below shows the results for the last 10 years.
The average number of times a week that gritting takes place is 2.7 times per week. There will be some error in sampling gritting frequency in this way to predict the occurrence of ice and the returns for later years contain more samples than those for earlier years. However it is submitted that, even with an occurrence of ice of once per week on average (instead of the actual average local authority survey level of 2.7 times per week) this would be recognised as significant by the cycling population.
A survey of English local authorities across the country showed that, on average, ice occured every 2-3 days from Nov to March in the last 10 years
Think twICE
Documented references to the PWSCG recognition of the of gritting deployment as a proxy for ice forecasting
1 PWSCG initial discussion.
27 January 2016 Minutes of PWSCG:-
‘WW invited DH to provide an update to the Group about a recent engagement with a member of the public who had raised concerns around the hazard which ice presents to cyclists…….The Group welcomed this engagement and there was some discussion about the value of sharing gritting service information with the public as a proxy for ice forecasts’
2 Extract of PWSCG email of 16 February 2017 to KF Daniels detailing MET Office implementation of the publication of gritting service information :-
‘ the Met Office have added a page entitled “Winter Weather and Cycling” http://www.metoffice.gov.uk/barometer/get-ready-for-winter/travel-advice to the Get Ready for Winter pages. …………. It also provides a link to local council gritting information.’
Icy conditions on untreated roads and cycle paths are therefore a common occurrence especially for commuters as ice tends to be most common in the mornings
The MET Office web site provides a link to the Sustrans site which states that ‘The average temperature in the UK during winter is a little less than 4 C’. This temperature will be an air temperature. The MET Office web site also explains that ‘even when air temperatures are as high as four or five degrees Celsius, ground temperatures often dip below freezing so that ice is possible’. Therefore it is not a surprise that icy conditions will occur approximately three times a week
The source data from Local Authority Freedom of Information requests is set out on the table below
The following table shows the adjustment factors made top certain FoI returns to normalise each to a Nov-March base. Actual data was provided by Derbyshire County Council for October and April which are part of their planned gritting season. For these months there were 19 additional days on which gritters were deployed for the three year period over which gritting information was provided. This equates to 7.6 % of the total and so the corrective factor of 0.9 applied to the figures of selected local authorities is reasonable