Clear Sky Chart

Astronomy-Weather Map
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104F to 113F
95F to 104F
86F to 95F
77F to 86F
68F to 77F
59F to 68F
50F to 59F
41F to 50F
32F to 41F
23F to 32F
14F to 23F
5F to 14F
-3F to 5F
-12F to -3F
-21F to -12F
-30F to -21F
-40F to -31F
< -40F
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Map provided by the Canadian Meteorological Center and is © Crown copyright, product of Environment Canada.
Allan Rahill, of CMC, developed the forecast.

Cursor shows location of the Brentwood Clear Sky Chart.
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Previous ForecastTime
Local Time 18:00 01Z
Cloud Cover
This Forecast Time
Local Time 19:00 02Z
Cloud Cover
Next Forecast Time
Local Time 20:00 03Z
Cloud Cover
What does Z mean?

The times on the maps are in Zulu time. Also casually called GMT or UT. A conversion table to local times is here. But the colored blocks, labelled in local time, will always point to the correct maps in Zulu time on this page.

Why check these maps?

The colored blocks on the clear sky charts show the forecast from these maps for the location of the chart. But the colored bock doesnt show you how nearby very different weather could be. Look at these maps to see if a colored block on the chart corresponds to a tiny clear hole surrounded by clouds or a large clear area. The larger the area of the same color under the cross hair, the higher the accuracy of the forecast. .

Why isnt there a single forecast map for observing conditions?

The observation of fine detail seen in telescopes on planets or the moon requires good seeing but can still be good during poor transparency. Visiblity of galaxies and nebulae in telescopes, or the milky way with the un-aided eye, requires good transparency but isn't much affected by seeing. All astronomical observations require a low percentage of cloud cover or clear skies. Humidity, Wind, and Temperature won't determine if you can observe, but they might affect how comfortable you are or how much your telescope will shake or dew up. Many factors affecting observing means many maps.

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