Whispering Pines Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whispering Pines Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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	4 5% 2 5% 4 4 4 4 6% 8% 54%	140125
	Night	4 6% 2 5% 3 3 4 3 5% 7% 56%	139222
Transparency	Day	25% 6% 10% 23% 24% 11%	135099
	Night	25% 6% 11% 24% 25% 9%	135256
Seeing	Day	7% 9% 28% 30% 19% 6%	17409
	Night	6% 5% 34% 41% 13% 1	27572

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	1 7% 3 7% 3 3 3 3 5% 8% 59%	4720
	11th to 20th	Day	1 4 2 7% 5% 3 4 3 4 6% 61%	4874
	21st to end	Day	1 4 2 8% 4 4 3 3 5% 6% 61%	5844
February	1st to 10th	Day	2 8% 3 6% 4 3 4 4 5% 7% 55%	1898
	11th to 20th	Day	1 4 2 6% 4 4 4 4 7% 8% 58%	2049
	21st to end	Day	2 7% 3 5% 4 2 2 3 5% 6% 61%	1730
March	1st to 10th	Day	2 9% 3 5% 3 3 3 2 5% 6% 59%	4600
	11th to 20th	Day	4 9% 3 6% 4 4 4 3 6% 7% 50%	5002
	21st to end	Day	4 7% 2 5% 4 4 4 4 6% 8% 52%	5983
April	1st to 10th	Day	6% 8% 2 6% 4 3 4 4 6% 7% 51%	2413
	11th to 20th	Day	7% 8% 3 7% 4 4 5% 3 7% 8% 45%	2371
	21st to end	Day	8% 9% 2 4 4 4 5% 4 7% 8% 45%	2400
May	1st to 10th	Day	10% 7% 2 6% 4 4 5% 4 6% 7% 46%	5757
	11th to 20th	Day	8% 6% 2 5% 4 4 5% 4 7% 8% 47%	6196
	21st to end	Day	7% 5% 2 6% 4 4 6% 5% 7% 9% 46%	6925
June	1st to 10th	Day	5% 4 2 5% 3 4 6% 5% 8% 9% 49%	2800
	11th to 20th	Day	5% 4 2 5% 3 4 4 5% 9% 9% 51%	2800
	21st to end	Day	4 3 2 4 5% 5% 6% 5% 7% 10% 49%	2800
July	1st to 10th	Day	3 2 1 3 3 4 5% 4 7% 9% 57%	6339
	11th to 20th	Day	3 3 1 5% 4 5% 6% 6% 8% 12% 48%	6340
	21st to end	Day	5% 4 2 6% 5% 6% 6% 5% 8% 9% 46%	6813
August	1st to 10th	Day	6% 4 1 6% 5% 6% 6% 6% 9% 11% 39%	5703
	11th to 20th	Day	3 3 1 4 4 5% 6% 5% 7% 9% 53%	5366
	21st to end	Day	6% 4 2 6% 5% 5% 6% 5% 8% 9% 45%	5984
September	1st to 10th	Day	5% 3 1 5% 4 3 5% 3 6% 8% 58%	2400
	11th to 20th	Day	5% 3 2 4 3 3 4 4 6% 7% 58%	2360
	21st to end	Day	5% 3 1 4 3 3 3 2 5% 7% 63%	2200
October	1st to 10th	Day	4 3 1 3 2 2 2 2 3 5% 74%	3341
	11th to 20th	Day	3 4 2 5% 3 3 3 3 4 8% 62%	3250
	21st to end	Day	4 7% 1 3 2 2 2 2 4 5% 67%	3399
November	1st to 10th	Day	2 5% 1 4 3 3 3 3 5% 8% 64%	1853
	11th to 20th	Day	1 6% 2 4 3 3 4 2 4 7% 64%	1890
	21st to end	Day	3 7% 2 5% 3 2 3 3 4 6% 62%	1827
December	1st to 10th	Day	1 6% 3 4 3 3 2 2 4 6% 68%	2700
	11th to 20th	Day	1 4 1 4 3 3 3 2 5% 6% 67%	3106
	21st to end	Day	1 6% 3 6% 4 4 5% 4 5% 7% 54%	4092
January	1st to 10th	Night	1 9% 4 7% 3 3 3 2 5% 7% 56%	8201
	11th to 20th	Night	1 5% 2 7% 4 4 3 3 4 6% 61%	8172
	21st to end	Night	1 5% 2 6% 3 3 3 3 5% 5% 63%	8370
February	1st to 10th	Night	1 7% 3 7% 4 3 3 3 4 8% 57%	2719
	11th to 20th	Night	2 8% 4 6% 5% 4 3 3 6% 7% 53%	2458
	21st to end	Night	2 7% 2 5% 4 3 3 2 3 6% 63%	2076
March	1st to 10th	Night	3 9% 3 5% 3 3 3 3 5% 5% 58%	5494
	11th to 20th	Night	5% 9% 2 5% 3 3 4 3 5% 6% 54%	5211
	21st to end	Night	6% 9% 3 6% 3 3 4 4 5% 7% 50%	5217
April	1st to 10th	Night	5% 9% 3 5% 4 4 3 3 5% 7% 55%	2010
	11th to 20th	Night	9% 9% 3 5% 3 3 3 3 5% 6% 50%	1977
	21st to end	Night	11% 9% 2 5% 3 4 4 3 5% 7% 48%	2000
May	1st to 10th	Night	12% 8% 2 6% 4 3 4 3 5% 7% 45%	4221
	11th to 20th	Night	8% 7% 2 6% 4 4 4 3 6% 9% 48%	3715
	21st to end	Night	9% 5% 2 5% 3 3 4 3 5% 7% 53%	3972
June	1st to 10th	Night	5% 4 1 4 4 3 3 3 8% 11% 54%	1600
	11th to 20th	Night	5% 3 1 4 3 3 4 4 7% 7% 61%	1600
	21st to end	Night	3 4 1 5% 4 4 5% 4 8% 9% 53%	1600
July	1st to 10th	Night	3 3 2 4 4 5% 4 4 7% 8% 54%	3640
	11th to 20th	Night	4 4 2 5% 4 5% 5% 4 8% 11% 49%	3640
	21st to end	Night	4 3 2 5% 4 5% 6% 5% 8% 10% 47%	4055
August	1st to 10th	Night	6% 5% 2 6% 4 4 5% 4 7% 10% 46%	4108
	11th to 20th	Night	4 4 2 5% 5% 5% 5% 5% 8% 10% 48%	4483
	21st to end	Night	7% 5% 2 5% 4 5% 5% 5% 7% 10% 44%	4993
September	1st to 10th	Night	6% 4 2 5% 3 3 4 4 6% 9% 55%	2000
	11th to 20th	Night	5% 3 1 4 3 3 4 4 5% 7% 60%	2040
	21st to end	Night	6% 3 2 5% 3 3 3 2 4 6% 63%	2200
October	1st to 10th	Night	4 4 1 4 2 2 3 2 4 6% 67%	3844
	11th to 20th	Night	6% 4 1 5% 3 3 4 4 6% 7% 57%	3898
	21st to end	Night	3 6% 3 4 2 2 3 2 4 5% 66%	4366
November	1st to 10th	Night	2 3 2 4 3 3 3 2 5% 7% 67%	2665
	11th to 20th	Night	2 5% 2 5% 3 3 3 3 3 6% 66%	2730
	21st to end	Night	3 7% 3 5% 4 3 3 2 5% 7% 60%	2788
December	1st to 10th	Night	1 3 2 4 2 2 2 2 4 5% 72%	4710
	11th to 20th	Night	1 5% 2 4 3 3 3 3 5% 7% 65%	5321
	21st to end	Night	3 8% 3 6% 4 4 4 3 5% 7% 54%	7128

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	24% 3 7% 30% 26% 9%	4723
	11th to 20th	Day	22% 4 11% 25% 29% 10%	4874
	21st to end	Day	24% 4 8% 27% 26% 12%	5844
February	1st to 10th	Day	27% 4 11% 28% 20% 9%	1898
	11th to 20th	Day	23% 6% 10% 28% 26% 8%	2059
	21st to end	Day	24% 5% 6% 21% 28% 16%	1730
March	1st to 10th	Day	23% 4 8% 16% 29% 20%	4600
	11th to 20th	Day	29% 6% 9% 22% 26% 7%	5002
	21st to end	Day	26% 7% 11% 34% 19% 3	5983
April	1st to 10th	Day	29% 6% 12% 23% 21% 9%	2413
	11th to 20th	Day	33% 7% 10% 21% 19% 9%	2374
	21st to end	Day	32% 9% 11% 25% 20% 3	2400
May	1st to 10th	Day	33% 7% 11% 26% 18% 6%	5757
	11th to 20th	Day	30% 8% 11% 20% 21% 10%	6200
	21st to end	Day	29% 10% 12% 23% 19% 6%	6926
June	1st to 10th	Day	27% 9% 15% 23% 17% 9%	2800
	11th to 20th	Day	25% 8% 12% 17% 23% 15%	2800
	21st to end	Day	26% 8% 12% 19% 23% 13%	2800
July	1st to 10th	Day	19% 7% 9% 16% 27% 21%	6271
	11th to 20th	Day	24% 8% 14% 23% 19% 11%	6265
	21st to end	Day	31% 9% 13% 16% 17% 15%	6617
August	1st to 10th	Day	35% 11% 15% 21% 13% 5%	4154
	11th to 20th	Day	26% 8% 14% 17% 22% 13%	3882
	21st to end	Day	26% 8% 13% 19% 25% 10%	4311
September	1st to 10th	Day	24% 5% 8% 23% 25% 16%	2400
	11th to 20th	Day	23% 6% 9% 19% 27% 17%	2360
	21st to end	Day	21% 5% 7% 21% 34% 13%	2200
October	1st to 10th	Day	15% 3 6% 15% 37% 24%	3341
	11th to 20th	Day	21% 4 8% 24% 34% 9%	3250
	21st to end	Day	20% 2 6% 21% 38% 13%	3399
November	1st to 10th	Day	19% 3 9% 24% 29% 16%	1853
	11th to 20th	Day	20% 4 6% 25% 34% 11%	1890
	21st to end	Day	23% 3 8% 22% 28% 14%	1827
December	1st to 10th	Day	19% 4 7% 31% 30% 10%	2700
	11th to 20th	Day	18% 3 8% 28% 31% 12%	3104
	21st to end	Day	25% 5% 9% 26% 25% 10%	4092
January	1st to 10th	Night	27% 4 6% 29% 28% 6%	8202
	11th to 20th	Night	23% 5% 10% 24% 25% 14%	8172
	21st to end	Night	23% 4 10% 23% 28% 13%	8370
February	1st to 10th	Night	26% 4 9% 26% 25% 9%	2719
	11th to 20th	Night	29% 5% 11% 26% 21% 8%	2458
	21st to end	Night	24% 3 6% 26% 27% 15%	2076
March	1st to 10th	Night	26% 5% 6% 15% 34% 13%	5494
	11th to 20th	Night	29% 5% 10% 16% 28% 13%	5211
	21st to end	Night	30% 6% 10% 33% 18% 2	5217
April	1st to 10th	Night	29% 6% 10% 23% 23% 9%	2010
	11th to 20th	Night	33% 6% 10% 25% 19% 6%	1977
	21st to end	Night	35% 6% 11% 26% 18% 4	2000
May	1st to 10th	Night	35% 8% 13% 28% 9% 6%	4218
	11th to 20th	Night	31% 9% 13% 23% 17% 8%	3716
	21st to end	Night	28% 8% 18% 26% 15% 5%	3972
June	1st to 10th	Night	22% 8% 20% 28% 15% 7%	1600
	11th to 20th	Night	21% 6% 14% 23% 22% 14%	1600
	21st to end	Night	24% 9% 11% 24% 23% 10%	1600
July	1st to 10th	Night	24% 8% 12% 18% 30% 8%	3600
	11th to 20th	Night	26% 8% 20% 26% 16% 4	3592
	21st to end	Night	27% 9% 17% 18% 19% 9%	3940
August	1st to 10th	Night	37% 9% 17% 22% 12% 3	2981
	11th to 20th	Night	29% 9% 18% 20% 17% 7%	3243
	21st to end	Night	24% 9% 17% 26% 20% 4	3597
September	1st to 10th	Night	25% 6% 11% 22% 25% 11%	2000
	11th to 20th	Night	22% 5% 11% 23% 25% 14%	2040
	21st to end	Night	22% 4 9% 23% 31% 11%	2200
October	1st to 10th	Night	18% 5% 8% 19% 32% 18%	3844
	11th to 20th	Night	23% 6% 10% 26% 26% 9%	3898
	21st to end	Night	21% 3 5% 25% 31% 14%	4366
November	1st to 10th	Night	18% 3 9% 24% 30% 15%	2665
	11th to 20th	Night	20% 3 7% 27% 31% 12%	2730
	21st to end	Night	25% 4 8% 23% 29% 10%	2788
December	1st to 10th	Night	16% 3 8% 33% 32% 8%	4710
	11th to 20th	Night	19% 3 6% 28% 35% 8%	5322
	21st to end	Night	29% 4 9% 23% 25% 10%	7128

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	5% 7% 31% 38% 16% 3	330
	11th to 20th	Day	7% 9% 32% 38% 14% 1	330
	21st to end	Day	4 10% 38% 34% 12% 2	363
February	1st to 10th	Day	3 12% 46% 30% 7% 2	330
	11th to 20th	Day	2 10% 46% 30% 11% 1	330
	21st to end	Day	3 15% 41% 30% 9% 2	273
March	1st to 10th	Day	4 10% 37% 29% 15% 4	330
	11th to 20th	Day	9% 17% 35% 26% 11% 3	484
	21st to end	Day	12% 20% 32% 25% 9% 1	594
April	1st to 10th	Day	12% 16% 35% 24% 9% 2	505
	11th to 20th	Day	11% 24% 34% 21% 9% 2	492
	21st to end	Day	15% 16% 31% 25% 12% 1	500
May	1st to 10th	Day	15% 14% 32% 23% 13% 3	638
	11th to 20th	Day	14% 9% 26% 31% 16% 4	725
	21st to end	Day	9% 12% 26% 29% 18% 6%	789
June	1st to 10th	Day	7% 6% 23% 30% 24% 9%	730
	11th to 20th	Day	6% 9% 25% 32% 22% 5%	730
	21st to end	Day	5% 5% 26% 34% 24% 6%	730
July	1st to 10th	Day	6% 3 17% 31% 33% 10%	721
	11th to 20th	Day	5% 2 13% 32% 37% 10%	718
	21st to end	Day	8% 2 15% 27% 35% 13%	754
August	1st to 10th	Day	9% 3 21% 30% 26% 11%	527
	11th to 20th	Day	4 3 20% 33% 27% 13%	517
	21st to end	Day	6% 3 22% 34% 26% 9%	583
September	1st to 10th	Day	7% 3 22% 32% 23% 12%	530
	11th to 20th	Day	4 5% 26% 30% 24% 10%	490
	21st to end	Day	6% 5% 20% 28% 26% 15%	330
October	1st to 10th	Day	8% 10% 19% 26% 23% 13%	330
	11th to 20th	Day	2 10% 28% 32% 18% 9%	330
	21st to end	Day	8% 9% 29% 32% 17% 5%	363
November	1st to 10th	Day	4 12% 30% 32% 18% 5%	330
	11th to 20th	Day	5% 8% 30% 36% 17% 4	330
	21st to end	Day	5% 7% 36% 36% 13% 3	330
December	1st to 10th	Day	4 9% 37% 32% 14% 4	330
	11th to 20th	Day	5% 8% 41% 35% 10% 1	330
	21st to end	Day	5% 9% 39% 35% 10% 2	363
January	1st to 10th	Night	4 5% 40% 39% 11% 2	1050
	11th to 20th	Night	4 6% 40% 40% 8% 1	1024
	21st to end	Night	3 3 39% 45% 9% 1	924
February	1st to 10th	Night	4 5% 46% 39% 5% 1	840
	11th to 20th	Night	5% 7% 45% 36% 7%	824
	21st to end	Night	5% 5% 50% 36% 4	692
March	1st to 10th	Night	5% 6% 43% 38% 7% 1	840
	11th to 20th	Night	9% 6% 38% 38% 8% 1	840
	21st to end	Night	8% 8% 41% 37% 7%	751
April	1st to 10th	Night	9% 8% 46% 32% 6%	603
	11th to 20th	Night	13% 11% 35% 33% 7% 1	593
	21st to end	Night	15% 9% 33% 34% 8%	600
May	1st to 10th	Night	12% 8% 32% 38% 10% 1	600
	11th to 20th	Night	16% 4 26% 40% 13% 1	591
	21st to end	Night	11% 5% 32% 38% 14% 1	650
June	1st to 10th	Night	6% 4 23% 46% 20% 2	600
	11th to 20th	Night	6% 3 29% 47% 15% 1	600
	21st to end	Night	4 3 25% 45% 22% 1	600
July	1st to 10th	Night	6% 2 20% 44% 26% 3	585
	11th to 20th	Night	3 1 19% 41% 32% 3	582
	21st to end	Night	6% 3 13% 43% 33% 2	657
August	1st to 10th	Night	8% 2 15% 45% 28% 2	597
	11th to 20th	Night	6% 2 18% 49% 22% 2	594
	21st to end	Night	6% 2 20% 47% 22% 3	660
September	1st to 10th	Night	7% 3 19% 45% 23% 3	600
	11th to 20th	Night	6% 3 24% 44% 21% 2	600
	21st to end	Night	7% 3 25% 44% 19% 2	600
October	1st to 10th	Night	9% 4 28% 41% 16% 2	750
	11th to 20th	Night	4 5% 32% 42% 16% 2	800
	21st to end	Night	7% 4 31% 40% 15% 2	945
November	1st to 10th	Night	3 6% 35% 42% 14% 1	1025
	11th to 20th	Night	4 6% 37% 43% 10% 1	1050
	21st to end	Night	7% 7% 34% 39% 12% 1	1050
December	1st to 10th	Night	3 4 39% 43% 10%	1050
	11th to 20th	Night	5% 4 42% 37% 11% 1	1050
	21st to end	Night	5% 6% 43% 38% 7% 1	1155

Page generated at 2026-03-30 00:18:44. Version ac07

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