Night-time Cloud Cover
Amateur astronomers probably spend as much
time studying meteorology as they do astronomy, especially in the UK. Very detailed
weather statistics and satellite images are available on the Web,
but none cater specifically for the amateur astronomers needs and provide night-time cloud
cover data.
In 1979 and 1981 I logged night-time cloud cover and air temperature for my location in Liverpool, UK, and produced monthly statistics. These were very informative and broadly hold for conditions today. December tends to be very overcast, April and September often produce transparent cloudless night-time skies.
I decided to restart collection of data in 2000 and make it available here. Each year my data will be added on a separate link at left with data updated monthly on the current year spreadsheet. My overall objective is to collect night-time cloud cover statistics for my location using the simple scale shown below. I take the night to be sunset to sunrise as this is the period most useful for astronomical observations other than solar work.
a - The sky is mainly clear
b - The sky is partly cloudy
c - The sky is completely overcast
Naturally the weather does not conform to this simple scale but a combination of letters can be used to describe more accurately what the cloud cover was like. For example a-c means the night was clear then clouded over (a familiar story!). Where it is difficult to assign a coding the letter which best represents conditions will be chosen. I do not have the time or stamina to get up during the early hours to check on the weather so a best estimate is given using other data such as local forecast and satellite images. I chose not to use the formal meteorological cloud cover scale in octas, as this is more suited to recording cloud cover at a given instant, rather than trying to represent the whole night-time period.
I would like to thank Dave Galvin and Gerard Gilligan for their ongoing support for this project. Dave very kindly logs the weather for me whilst I am away from home.
If you would like additional detailed data the West Cheshire College weather site gives half-hourly data for Cheshire (broadly very similar to my location) which include temperature, rainfall dew-point etc. but not cloud cover.
I hope this will be of interest, if you have any comments please let me
know by e-mail to:
robjn <at> blueyonder.co.uk
Latest UK Synoptic Chart
try this 'clear sky clock' from 7Timer