This set of images compares the actual infrared satellite image for midday Saturday 13th September 2008 with forecasts made on the same day and up to 5 days ahead. The forecasts made up to 2-3 days ahead are quite accurate, so that a reasonable estimate of the astronomy prospects for a Saturday night could be made on the Thursday beforehand. While the general trends are still correct in the 5 day forecast, the details for a particular location become much less accurate.

Edit Oct 2009: Since I originally wrote this article, SkippySky has become available. It uses the same US GFS weather model data so the discussion about accuracy is still relevant, but SkippySky is a much more convenient way to access the cloud forecast data, with great maps for all of Australia among other places.

Check out Cloud Forecasts for Astronomers for the story behind some of this and how to generate your own cloud forecast maps using US GFS model data.

Also see Cloud Forecast Accuracy for comparisons of the forecast charts with actual satellite images.

Edit Oct 2009: Since I originally wrote this article, SkippySky has become available. It uses the same US GFS weather model data so the discussion about accuracy is still relevant, but SkippySky is a much more convenient way to access the cloud forecast data, with great maps for all of Australia among other places.

Astronomers want good weather forecasts. In particular, they need to know about cloud. When you're deciding whether to travel two hours to a dark sky site for the weekend, an accurate forecast is invaluable.

Saturday 13th September 2008

1 Day Ahead Forecast

The 'Clear Sky Clock' is available via the web to amateur astronomers across North America, and includes not only cloud forecasts but also estimates for transparency and seeing. For those of us in the rest of the world, there are several other options:

• Updated Oct 2009: SkippySky - The most convenient option now for Australia, New Zealand and Europe.
• Global Forecast System (GFS) Cloud Charts from US NCEP
• 7Timer Astroweather Panel (APanel) Forecasts by Quanzhi
• Astroforecast.org Cloud Forecasts by Jeff Bullard
• Air Force MM5 Model Cloud Top Temperature Charts

Below are a few weather links that may be of some use to other astronomers. I've listed them in the way that I use them ahead of a decision on whether to travel north from Melbourne for a night of astrophotography. I have no formal qualifications in this area (although I am the son of a meteorologist). This may be most relevant for other's in the south-east but the links should be useful in most areas of Australia.

BoM = Australian Bureau of Meteorology
GFS = US Numerical Model
All times quoted are AEST (UT +10)

2-4 Days Ahead

The Aberdeen Astronomical Society (AAS) in Scotland has a dark sky site on Forestry Commission land around 20 miles west of Aberdeen. Just hope the weather co-operates!

Scotland Aberdeen Astronomical Society

Australia Astronomical Society of Victoria

International Dark Sky Association: Everybody should join!

WeatherZone: Is it Cloudy in Victoria now?