Beaver Meadow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beaver Meadow Observatory clear sky chart from 2005-11-05 to 2009-12-29.

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% 12% 6% 7% 6% 5% 5% 24%	16439
	Night	17% 12% 7% 9% 7% 5% 5% 23%	16495
Cloud Cover	Day	19% 11% 6% 7% 6% 5% 24%	16452
	Night	18% 12% 7% 8% 7% 5% 5% 24%	16512
Transparency	Day	7% 14% 18% 11%	11888
	Night	7% 14% 17% 9%	11844
Seeing	Day	12% 30% 22% 14% 5%	912
	Night	22% 30% 22% 7%	4645

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	16% 22% 10% 15% 9% 5% 6%	1049
	Night	20% 21% 13% 13% 9% 6%	1650
February	Day	18% 17% 11% 12% 13% 5% 8%	1001
	Night	13% 18% 11% 15% 13% 5% 6% 6%	1406
March	Day	18% 14% 10% 8% 5% 21%	1338
	Night	15% 10% 9% 12% 6% 5% 5% 22%	1341
April	Day	19% 11% 6% 34%	1452
	Night	21% 10% 5% 5% 5% 33%	1155
May	Day	16% 7% 6% 5% 5% 7% 34%	1688
	Night	13% 5% 6% 6% 8% 37%	1021
June	Day	18% 6% 5% 6% 5% 5% 5% 8% 30%	1663
	Night	16% 6% 6% 5% 5% 6% 7% 33%	956
July	Day	16% 6% 6% 6% 8% 6% 6% 8% 25%	1685
	Night	11% 6% 5% 5% 6% 6% 7% 7% 37%	1004
August	Day	17% 6% 5% 6% 5% 5% 6% 8% 32%	1567
	Night	13% 6% 5% 6% 5% 6% 7% 37%	1146
September	Day	22% 8% 6% 5% 6% 30%	1357
	Night	21% 6% 5% 41%	1247
October	Day	26% 15% 7% 21%	1223
	Night	24% 11% 6% 5% 6% 24%	1471
November	Day	18% 19% 7% 7% 5% 19%	1199
	Night	19% 16% 5% 7% 5% 6% 21%	1972
December	Day	19% 21% 14% 15% 6% 5%	1217
	Night	18% 19% 13% 14% 9% 5% 6%	2126

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	17% 20% 11% 15% 9% 5% 7%	1047
	Night	21% 19% 13% 13% 10% 6%	1651
February	Day	18% 15% 12% 13% 11% 6% 10%	999
	Night	14% 16% 11% 14% 13% 5% 6% 7%	1397
March	Day	18% 12% 10% 9% 5% 22%	1361
	Night	16% 9% 9% 11% 6% 6% 22%	1363
April	Day	19% 11% 6% 5% 34%	1451
	Night	21% 11% 5% 5% 5% 33%	1155
May	Day	17% 7% 5% 5% 5% 5% 7% 35%	1682
	Night	13% 6% 6% 6% 7% 38%	1015
June	Day	19% 7% 5% 5% 5% 5% 8% 31%	1672
	Night	16% 6% 6% 6% 5% 6% 6% 34%	958
July	Day	17% 5% 6% 5% 7% 6% 7% 8% 26%	1685
	Night	11% 5% 5% 6% 6% 5% 9% 37%	1005
August	Day	17% 7% 5% 5% 5% 5% 6% 7% 32%	1562
	Night	13% 5% 5% 6% 6% 6% 6% 38%	1148
September	Day	23% 7% 5% 5% 7% 30%	1356
	Night	21% 5% 5% 41%	1248
October	Day	26% 14% 6% 22%	1223
	Night	25% 11% 6% 5% 6% 25%	1471
November	Day	18% 20% 7% 6% 5% 5% 20%	1197
	Night	20% 15% 5% 8% 5% 6% 23%	1971
December	Day	19% 20% 16% 13% 7% 6%	1217
	Night	18% 18% 13% 14% 9% 5% 6%	2130

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	7% 14%	623
	Night	6% 9% 5%	954
February	Day	8% 13% 8%	587
	Night	8% 14% 8%	825
March	Day	6% 16% 22% 7%	856
	Night	7% 16% 17% 9%	908
April	Day	6% 16% 19% 23%	1012
	Night	5% 14% 22% 19%	796
May	Day	6% 14% 23% 17%	1304
	Night	7% 17% 24% 17%	828
June	Day	9% 17% 24% 11%	1274
	Night	8% 21% 23% 10%	738
July	Day	10% 18% 20% 9%	1070
	Night	8% 20% 26% 10%	671
August	Day	7% 11% 21% 15%	1389
	Night	7% 13% 24% 17%	994
September	Day	5% 12% 21% 13%	1098
	Night	5% 11% 29% 17%	1026
October	Day	6% 11% 15% 8%	1008
	Night	7% 13% 17% 10%	1229
November	Day	6% 16% 11% 9%	872
	Night	7% 17% 14% 6%	1464
December	Day	6% 9% 6%	795
	Night	7% 11% 5%	1411

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	38% 33% 6%	406
February	Day	14% 42% 21% 7%	14
	Night	36% 33% 10%	374
March	Day	21% 32% 19% 10%	107
	Night	29% 33% 17%	445
April	Day	18% 32% 18% 11%	104
	Night	20% 31% 27% 6%	385
May	Day	11% 36% 22% 9% 7%	114
	Night	10% 32% 32% 13%	271
June	Day	7% 37% 25% 17%	105
	Night	7% 38% 37% 7%	216
July	Day	8% 33% 24% 18% 5%	103
	Night	36% 40% 11%	242
August	Day	7% 23% 25% 15% 12%	117
	Night	7% 29% 30% 18%	372
September	Day	11% 19% 16% 22% 11%	107
	Night	9% 19% 31% 20%	432
October	Day	13% 27% 22% 10%	110
	Night	16% 27% 23% 8%	449
November	Day	12% 29% 22% 22%	31
	Night	24% 32% 17% 6%	513
December	Night	38% 28% 10%	540

Page generated at 2009-12-30 05:20:55. Version ab11