Adirondack Astronomy Retreat
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Adirondack Astronomy Retreat clear sky chart from 2005-11-05 to 2008-11-27.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	18% 8% 5% 5% 6% 5% 5% 6% 31%	12256
	Night	19% 8% 5% 5% 5% 5% 5% 6% 31%	12137
Cloud Cover	Day	16% 8% 5% 6% 5% 6% 5% 5% 7% 29%	12272
	Night	17% 8% 5% 6% 5% 6% 5% 6% 29%	12162
Transparency	Day	13% 18% 22% 10%	8163
	Night	13% 18% 24% 9%	8072
Seeing	Day	59% 11% 12% 6%	827
	Night	62% 13% 10%	3744

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	15% 8% 5% 8% 6% 7% 5% 5% 5% 27%	740
	Night	18% 10% 6% 8% 6% 5% 5% 6% 24%	1300
February	Day	9% 11% 9% 9% 7% 6% 6% 6% 25%	772
	Night	11% 11% 7% 8% 6% 9% 5% 6% 5% 26%	1019
March	Day	13% 8% 7% 6% 5% 5% 35%	983
	Night	15% 7% 8% 6% 6% 6% 5% 33%	1013
April	Day	22% 9% 5% 6% 32%	1100
	Night	23% 6% 6% 5% 6% 5% 5% 31%	877
May	Day	22% 5% 5% 5% 7% 33%	1285
	Night	21% 5% 5% 6% 37%	763
June	Day	22% 5% 9% 7% 6% 8% 26%	1251
	Night	21% 5% 6% 5% 5% 8% 32%	718
July	Day	15% 5% 6% 8% 5% 6% 8% 31%	1301
	Night	15% 5% 7% 9% 10% 35%	740
August	Day	12% 5% 5% 5% 7% 6% 7% 36%	1184
	Night	11% 5% 6% 5% 6% 6% 44%	849
September	Day	18% 6% 5% 6% 42%	1033
	Night	18% 5% 6% 44%	944
October	Day	21% 7% 6% 7% 32%	899
	Night	23% 7% 5% 5% 34%	1135
November	Day	21% 12% 6% 6% 5% 5% 25%	964
	Night	23% 9% 5% 6% 6% 6% 25%	1482
December	Day	19% 22% 10% 5% 17%	744
	Night	23% 15% 7% 5% 5% 21%	1297

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	15% 8% 5% 9% 6% 8% 5% 6% 24%	739
	Night	17% 9% 7% 8% 6% 6% 6% 6% 22%	1301
February	Day	8% 11% 10% 9% 8% 5% 5% 7% 23%	770
	Night	10% 11% 6% 11% 6% 9% 6% 6% 6% 23%	1010
March	Day	12% 8% 7% 7% 5% 6% 5% 32%	1004
	Night	13% 8% 7% 8% 6% 7% 6% 30%	1037
April	Day	20% 8% 5% 7% 5% 5% 31%	1099
	Night	21% 7% 7% 6% 5% 5% 6% 29%	877
May	Day	20% 6% 5% 6% 7% 32%	1284
	Night	19% 7% 5% 5% 7% 35%	763
June	Day	19% 5% 5% 5% 8% 7% 6% 9% 24%	1260
	Night	20% 6% 5% 8% 7% 31%	720
July	Day	13% 5% 6% 5% 8% 7% 6% 8% 29%	1301
	Night	13% 6% 7% 9% 11% 33%	741
August	Day	9% 7% 6% 6% 5% 6% 7% 8% 33%	1178
	Night	10% 5% 5% 8% 5% 5% 5% 43%	851
September	Day	17% 6% 6% 7% 39%	1032
	Night	15% 6% 5% 6% 43%	945
October	Day	19% 8% 5% 7% 6% 31%	899
	Night	20% 8% 5% 6% 5% 33%	1135
November	Day	19% 10% 5% 8% 5% 6% 5% 5% 5% 23%	962
	Night	22% 9% 6% 7% 6% 6% 5% 23%	1481
December	Day	18% 20% 12% 7% 5% 6% 6% 15%	744
	Night	20% 16% 6% 6% 5% 5% 5% 6% 19%	1301

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	16% 20% 22% 8%	437
	Night	21% 17% 20% 10%	749
February	Day	15% 21% 18% 7%	474
	Night	15% 19% 20% 8%	624
March	Day	11% 20% 22% 13%	636
	Night	11% 20% 27% 9%	654
April	Day	12% 10% 26% 12% 11%	639
	Night	12% 12% 23% 19% 6%	516
May	Day	10% 21% 23% 15%	828
	Night	10% 15% 29% 15%	498
June	Day	20% 24% 17% 7%	780
	Night	16% 27% 29% 5%	455
July	Day	15% 22% 19% 10%	697
	Night	21% 21% 29% 7%	427
August	Day	13% 16% 23% 9%	1027
	Night	10% 17% 28% 13%	723
September	Day	10% 14% 31% 10%	856
	Night	8% 16% 37% 8%	774
October	Day	12% 12% 21% 12%	736
	Night	11% 15% 18% 12%	914
November	Day	14% 19% 21%	645
	Night	12% 15% 17% 6%	1013
December	Day	15% 17% 17%	408
	Night	16% 20% 16%	725

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	73% 13% 5%	371
February	Day	68% 11% 11%	44
	Night	73% 9% 8%	318
March	Day	74% 6% 9%	93
	Night	76% 8% 6%	371
April	Day	73% 8% 5% 6%	90
	Night	72% 9% 8%	338
May	Day	70% 9% 8% 5%	93
	Night	70% 12% 8%	204
June	Day	70% 14% 5% 5%	84
	Night	66% 10% 13%	169
July	Day	65% 6% 16% 7%	81
	Night	62% 9% 17%	162
August	Day	41% 14% 15% 13% 5%	90
	Night	38% 17% 21% 11%	283
September	Day	42% 9% 14% 10% 6%	88
	Night	40% 17% 20% 8%	350
October	Day	38% 14% 21% 7%	91
	Night	44% 17% 16% 5%	367
November	Day	49% 16% 15%	73
	Night	60% 19% 7%	442
December	Night	74% 8% 5%	369

Page generated at 2008-11-27 13:47:48. Version ab11