So it mayīe possible to observe during a white transparency forecast, but the real transparency is usually yucky. Large globulars and planets can be observed in poorĪ forecast color of white formally means that CMC didn't compute the transparency forecast because the cloud cover was over 30%. However, open clustersĪnd planetary nebulae are quite observable in below average transparency. It is somewhat independant of the cloud cover forecast in that there can be isolated clouds in a transparent air mass, and poor transparency can occurĪbove average transparency is necessary for good observation of low contrast objects like galaxies and nebulae. It's calculated from the total amount of water vapor in theĪir. The total transparency of the atmosphere from ground to space. Here 'transparency' means just what astronomers mean The line, labeled Transparency, forecasts the transparency of the air. It's always wise to click on a colored block for the hour you want to observe and see if your location is close to a cloud edge.ĬMC's text page explaining this forecast is Is 76% and the mostly-cloudy accuracy is 89%. When the forecast is predicting more than 36 hours into the future, the mostly-clear accuracy Mostly-clear forecasts (cloud75%) have been When the forecast is clear, the sky may still be hazy, if the transparency forecast is poor.Īccuracy averaged over North America for a 30 day period: when the forecast is predicting less than 12 hours into the future, This forecast may miss low cloud and afternoon thunderstorms. Lighter shades of blue are increasing cloudiness and white is overcast. The colors are picked from what color the sky is likely to be, with The line, labeled Cloud Cover forecasts total cloud cover. (Local time for Maple Valley Observatory is -7.0 hours from GMT.) A digit 1 on top of a 3 means 13:00 or 1pm. The two numbers at the top of a column is the time. The colors of the blocks are the colors from CMC's forecast maps for that hour. Summary: In the rows labeled 'sky conditions', find a column of blue blocks. Summarizes CMC's forecast images just for Maple Valley ObservatoryĪnd the surroundings out to about 10 miles. So, I (Attilla Danko) wrote a script to generate the images like the one above It can be a chore to find the one map that tells you if you can observe tonight. CMC's numerical weather forecasts are unique because they are specifically designed for astronomers.īut they have 1180 forecast maps. The data comes from a forecast model developed by Allan Rahill of theĬanadian Meteorological Centre. It's a prediction of when Maple Valley Observatory, WA, will have good weather for astronomical observing. At a glance, it shows when it will be cloudy or clear for the

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