Two forecasts for astronomical observing are given below. The first is centered on Bare Hill in Wonder Lake State Park. The Second is centered on the eastern part of Fahnestock State Park. A big "Thank you!" to Atilla Danko of cleardarksky.com and the Canadian Meteorological Center for providing these specifically for us here in Kent. Instructions on how to read the forecasts are found following the charts.
Reading a Clear Sky Chart
In the body of chart, each row of colored blocks is the forecast for something important about observing conditions. For example, the first row tells how much of the sky is forecast to be covered by clouds. Each column in the body of the chart is the forecast for a specific hour of a specific day. The date, the days of the week and the hours of the day covered by the forecast are all listed just below the title for the chart. The hours of the day run from 0 (midnight) through 12 (noon) to 23 (11:00 pm). The vertical red lines mark the boundary between days.
The body of the chart is divided into two sections. The top section tells about sky conditions. The bottom section tells about conditions on the ground. The sky conditions are the heart of the forecast. The ground conditions section tells more about whether you and your equipment will be comfortable than about how well you’ll be able to see.
Sky Conditions
The best viewing occurs when the cloud cover, transparency, seeing and darkness rows are all blue, the darker the better. You can read about what each means, below.
| The Cloud Cover row tells how much of the sky is covered by clouds. (more)
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| |
Overcast |
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40% covered |
| |
90% covered |
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30% covered |
| |
80% covered |
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20% covered |
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70% covered |
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10% covered |
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60% covered |
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Clear |
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50% covered |
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| The Transparency row tells how transparent the air is from the ground all the way to space. Water vapor and dust make the air less transparent. A white block in this row means that there is no forecast for transparency because there is too much cloud cover. (more)
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| |
Poor |
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Above average |
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Below Average |
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Transparent |
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Average |
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| The Seeing row tells how well you will be able to see fine details at high magnification. When seeing is excellent the atmosphere is calm and its temperature decreases smoothly with altitude. When seeing is poor, the atmosphere is turbulent or the temperature gradient is not uniform. (more)
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Bad |
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Good |
| |
Poor |
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Excellent |
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Average |
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| The Darkness row tells how dark the sky would be if there were no light pollution. The numbers tell the magnitude of the dimmest star visible when looking straight up. White is daytime bright, dark blue is moonless midnight. (more)
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-4 |
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+4.0 |
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-3 |
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+4.5 |
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-2 |
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+5.0 |
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-1 |
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+5.2 |
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0 |
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+5.4 |
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+1.0 |
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+5.6 |
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+2.0 |
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+5.8 |
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+3.0 |
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+6.0 |
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+3.5 |
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Ground Conditions
| The Wind row forecasts the wind speed at tree-top level. (more)
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>45mph |
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12 to 16 mph |
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29 to 45 mph |
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6 to 11 mph |
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17 to 28 mph |
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0 to 5 mph |
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| The Humidity row forecasts the relative humidity. (more)
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<25% |
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60% to 65% |
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25% to 30% |
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65% to 70% |
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30% to 35% |
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70% to 75% |
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35% to 40% |
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75% to 80% |
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40% to 45% |
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80% to 85% |
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45% to 50% |
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85% to 90% |
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50% to 55% |
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90% to 95% |
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55% to 60% |
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95% to 100% |
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| The Temperature row forecasts the ground level temperature. (more)
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<-40F |
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41F to 50F |
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-40F to -31F |
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50F to 59F |
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-30F to -21F |
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59F to 68F |
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-21F to -12F |
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68F to 77F |
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-12F to -3F |
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77F to 86F |
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-3F to 5F |
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86F to 95F |
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5F to 14F |
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95F to 104F |
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14F to 23F |
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104F to 113F |
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23F to 32F |
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>113F |
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32F to 41F |
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