Owl Hollow
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Owl Hollow clear sky chart from 2005-11-06 to 2026-03-03.

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	5% 5% 2 5% 4 4 4 4 6% 8% 52%	139843
	Night	5% 6% 2 6% 4 4 4 4 5% 7% 52%	138798
Transparency	Day	28% 6% 10% 24% 23% 9%	134765
	Night	30% 5% 11% 25% 22% 7%	134886
Seeing	Day	8% 8% 24% 32% 21% 7%	17417
	Night	8% 7% 30% 41% 13% 1	27564

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	2 8% 3 8% 4 3 4 2 5% 6% 56%	4720
	11th to 20th	Day	1 3 2 6% 5% 5% 5% 4 6% 8% 55%	4740
	21st to end	Day	1 7% 3 7% 3 3 3 3 5% 6% 58%	5724
February	1st to 10th	Day	3 8% 5% 7% 5% 4 5% 5% 6% 6% 47%	1890
	11th to 20th	Day	2 6% 3 8% 4 5% 5% 4 7% 7% 49%	2040
	21st to end	Day	2 8% 4 6% 4 4 4 3 4 6% 55%	1730
March	1st to 10th	Day	4 7% 3 6% 3 4 4 4 5% 8% 52%	4520
	11th to 20th	Day	5% 7% 3 6% 4 4 4 4 6% 7% 51%	4811
	21st to end	Day	5% 7% 3 7% 5% 5% 5% 5% 6% 9% 44%	5897
April	1st to 10th	Day	7% 7% 2 4 4 4 5% 4 6% 7% 49%	2400
	11th to 20th	Day	11% 9% 3 6% 4 4 4 4 6% 8% 41%	2371
	21st to end	Day	10% 7% 2 6% 4 4 5% 4 7% 8% 43%	2400
May	1st to 10th	Day	9% 8% 2 7% 4 4 5% 4 5% 6% 47%	5900
	11th to 20th	Day	7% 4 2 6% 4 5% 5% 5% 7% 9% 45%	6270
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 6% 8% 45%	6925
June	1st to 10th	Day	6% 3 1 4 3 4 4 4 8% 11% 52%	2800
	11th to 20th	Day	6% 3 1 4 4 4 5% 5% 7% 9% 53%	2800
	21st to end	Day	3 3 1 5% 3 4 5% 5% 8% 9% 54%	2800
July	1st to 10th	Day	5% 3 1 4 4 4 5% 4 7% 9% 55%	6339
	11th to 20th	Day	3 2 1 4 4 5% 5% 6% 9% 11% 48%	6340
	21st to end	Day	4 4 2 6% 5% 5% 5% 4 7% 9% 49%	6903
August	1st to 10th	Day	8% 3 1 4 4 5% 5% 5% 8% 11% 46%	5867
	11th to 20th	Day	2 3 1 4 4 4 5% 4 7% 10% 57%	5366
	21st to end	Day	7% 5% 2 6% 4 4 6% 4 6% 8% 48%	5984
September	1st to 10th	Day	4 4 1 4 2 3 4 3 5% 9% 62%	2400
	11th to 20th	Day	6% 2 1 4 3 3 4 4 6% 7% 60%	2348
	21st to end	Day	7% 4 1 3 2 3 3 2 4 5% 65%	2200
October	1st to 10th	Day	5% 4 1 3 2 2 2 2 3 5% 74%	3366
	11th to 20th	Day	4 5% 2 4 3 3 2 3 5% 6% 63%	3250
	21st to end	Day	7% 6% 2 4 3 3 3 3 5% 7% 59%	3321
November	1st to 10th	Day	3 4 2 5% 3 4 3 4 6% 8% 58%	1853
	11th to 20th	Day	4 6% 1 3 3 4 4 3 5% 8% 58%	1890
	21st to end	Day	3 7% 3 6% 4 3 4 3 4 7% 58%	1780
December	1st to 10th	Day	2 4 2 6% 3 3 3 2 4 6% 64%	2700
	11th to 20th	Day	3 7% 2 5% 3 4 3 3 4 7% 59%	3106
	21st to end	Day	3 8% 3 8% 4 4 4 3 6% 8% 49%	4092
January	1st to 10th	Night	3 8% 4 7% 4 4 4 3 5% 7% 51%	8201
	11th to 20th	Night	1 5% 2 7% 4 4 4 4 5% 7% 56%	8250
	21st to end	Night	2 7% 3 8% 4 3 3 3 4 6% 57%	8533
February	1st to 10th	Night	3 8% 4 7% 5% 4 4 4 5% 7% 49%	2730
	11th to 20th	Night	4 8% 3 8% 5% 4 5% 4 6% 7% 47%	2465
	21st to end	Night	3 8% 3 7% 4 3 3 3 4 5% 57%	2076
March	1st to 10th	Night	4 9% 3 8% 4 3 3 3 4 5% 54%	5398
	11th to 20th	Night	6% 8% 3 6% 4 4 4 3 5% 6% 53%	5179
	21st to end	Night	9% 9% 3 7% 4 5% 5% 3 6% 8% 42%	5058
April	1st to 10th	Night	7% 7% 2 7% 4 4 4 4 5% 7% 50%	2000
	11th to 20th	Night	12% 8% 3 7% 4 3 4 3 4 6% 45%	1977
	21st to end	Night	14% 8% 3 6% 4 4 5% 3 5% 7% 41%	1998
May	1st to 10th	Night	11% 6% 3 7% 4 4 5% 4 6% 7% 43%	4080
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 4 6% 10% 44%	3629
	21st to end	Night	14% 7% 2 6% 4 5% 4 4 5% 7% 42%	3972
June	1st to 10th	Night	7% 4 1 4 3 3 4 5% 7% 10% 52%	1600
	11th to 20th	Night	6% 4 2 3 3 4 4 4 7% 9% 55%	1600
	21st to end	Night	5% 3 2 5% 4 4 5% 5% 8% 7% 52%	1600
July	1st to 10th	Night	4 3 1 5% 4 4 5% 4 6% 8% 55%	3640
	11th to 20th	Night	4 3 2 5% 4 5% 6% 5% 8% 11% 48%	3640
	21st to end	Night	5% 4 2 6% 4 5% 6% 5% 8% 10% 46%	3970
August	1st to 10th	Night	10% 4 1 6% 5% 5% 5% 4 8% 8% 43%	3928
	11th to 20th	Night	3 4 2 6% 5% 5% 6% 4 7% 9% 50%	4483
	21st to end	Night	7% 6% 2 6% 4 4 6% 5% 7% 9% 43%	4993
September	1st to 10th	Night	5% 4 2 5% 3 4 4 3 5% 8% 56%	2000
	11th to 20th	Night	6% 4 1 4 4 3 4 3 5% 7% 58%	2050
	21st to end	Night	7% 3 1 4 3 4 3 3 5% 5% 63%	2200
October	1st to 10th	Night	6% 3 1 4 3 2 2 2 3 5% 69%	3816
	11th to 20th	Night	7% 4 2 5% 3 3 4 3 5% 7% 57%	3898
	21st to end	Night	7% 4 2 5% 3 3 3 3 4 6% 60%	4445
November	1st to 10th	Night	4 5% 2 4 3 4 3 3 5% 7% 59%	2665
	11th to 20th	Night	4 6% 2 5% 3 3 4 3 5% 7% 59%	2730
	21st to end	Night	3 7% 3 5% 4 3 3 3 5% 6% 57%	2835
December	1st to 10th	Night	2 5% 2 5% 4 4 3 3 3 5% 65%	4710
	11th to 20th	Night	2 5% 2 5% 4 4 4 3 5% 7% 58%	5321
	21st to end	Night	4 9% 4 7% 5% 5% 4 4 5% 7% 47%	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	29% 4 8% 33% 21% 5%	4723
	11th to 20th	Day	25% 6% 11% 28% 24% 6%	4740
	21st to end	Day	26% 4 11% 25% 26% 7%	5724
February	1st to 10th	Day	35% 5% 11% 26% 17% 5%	1890
	11th to 20th	Day	32% 5% 11% 26% 21% 4	2050
	21st to end	Day	30% 4 8% 25% 23% 10%	1730
March	1st to 10th	Day	29% 4 8% 19% 32% 8%	4520
	11th to 20th	Day	32% 4 12% 23% 25% 4	4811
	21st to end	Day	33% 7% 14% 31% 12% 2	5897
April	1st to 10th	Day	32% 6% 13% 25% 17% 8%	2400
	11th to 20th	Day	39% 6% 11% 21% 17% 6%	2374
	21st to end	Day	36% 7% 10% 28% 18% 2	2400
May	1st to 10th	Day	36% 7% 10% 27% 17% 4	5900
	11th to 20th	Day	30% 9% 12% 21% 22% 6%	6274
	21st to end	Day	33% 7% 12% 23% 20% 4	6926
June	1st to 10th	Day	24% 8% 19% 25% 17% 7%	2800
	11th to 20th	Day	26% 7% 9% 23% 22% 13%	2800
	21st to end	Day	23% 7% 10% 25% 23% 13%	2800
July	1st to 10th	Day	23% 5% 9% 18% 28% 16%	6271
	11th to 20th	Day	25% 7% 12% 25% 19% 12%	6265
	21st to end	Day	29% 6% 10% 18% 19% 18%	6705
August	1st to 10th	Day	31% 8% 14% 23% 17% 8%	4268
	11th to 20th	Day	25% 6% 11% 20% 23% 14%	3882
	21st to end	Day	24% 4 10% 21% 25% 17%	4311
September	1st to 10th	Day	20% 5% 7% 23% 28% 17%	2400
	11th to 20th	Day	22% 5% 9% 20% 28% 15%	2348
	21st to end	Day	22% 4 6% 22% 36% 11%	2200
October	1st to 10th	Day	16% 2 6% 18% 33% 25%	3366
	11th to 20th	Day	23% 3 9% 28% 28% 10%	3250
	21st to end	Day	25% 3 8% 27% 28% 9%	3321
November	1st to 10th	Day	23% 4 12% 26% 25% 10%	1853
	11th to 20th	Day	24% 4 8% 27% 29% 8%	1890
	21st to end	Day	27% 3 9% 25% 27% 8%	1780
December	1st to 10th	Day	21% 3 8% 33% 28% 6%	2700
	11th to 20th	Day	26% 4 8% 32% 27% 5%	3104
	21st to end	Day	33% 4 10% 26% 20% 6%	4092
January	1st to 10th	Night	32% 4 10% 29% 19% 6%	8202
	11th to 20th	Night	27% 5% 11% 24% 25% 8%	8250
	21st to end	Night	29% 4 10% 26% 26% 6%	8533
February	1st to 10th	Night	34% 5% 13% 25% 18% 4	2730
	11th to 20th	Night	35% 6% 11% 25% 19% 4	2465
	21st to end	Night	30% 4 7% 24% 24% 11%	2076
March	1st to 10th	Night	33% 4 6% 18% 31% 9%	5398
	11th to 20th	Night	32% 5% 10% 17% 29% 8%	5179
	21st to end	Night	38% 7% 14% 27% 13% 2	5058
April	1st to 10th	Night	34% 5% 10% 25% 19% 7%	2000
	11th to 20th	Night	39% 5% 11% 23% 18% 4	1977
	21st to end	Night	41% 7% 9% 24% 18% 2	1998
May	1st to 10th	Night	36% 8% 11% 29% 12% 3	4080
	11th to 20th	Night	33% 8% 16% 23% 15% 5%	3630
	21st to end	Night	38% 9% 16% 21% 13% 3	3972
June	1st to 10th	Night	25% 7% 23% 27% 13% 4	1600
	11th to 20th	Night	24% 8% 13% 23% 20% 12%	1600
	21st to end	Night	27% 6% 12% 26% 23% 7%	1600
July	1st to 10th	Night	24% 6% 12% 24% 27% 8%	3600
	11th to 20th	Night	27% 7% 18% 24% 18% 5%	3592
	21st to end	Night	30% 7% 16% 22% 18% 8%	3856
August	1st to 10th	Night	36% 9% 17% 20% 14% 4	2851
	11th to 20th	Night	32% 8% 14% 21% 16% 9%	3243
	21st to end	Night	25% 7% 16% 21% 22% 9%	3597
September	1st to 10th	Night	26% 5% 10% 21% 24% 14%	2000
	11th to 20th	Night	25% 5% 10% 25% 23% 13%	2050
	21st to end	Night	23% 4 8% 24% 30% 11%	2200
October	1st to 10th	Night	19% 4 7% 19% 28% 23%	3816
	11th to 20th	Night	27% 4 10% 26% 25% 8%	3898
	21st to end	Night	27% 2 8% 27% 25% 10%	4445
November	1st to 10th	Night	25% 4 10% 24% 26% 10%	2665
	11th to 20th	Night	25% 4 9% 28% 27% 8%	2730
	21st to end	Night	28% 4 10% 26% 27% 6%	2835
December	1st to 10th	Night	22% 4 9% 33% 26% 6%	4710
	11th to 20th	Night	26% 3 6% 37% 24% 4	5322
	21st to end	Night	35% 5% 8% 26% 22% 4	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	6% 9% 27% 37% 16% 5%	330
	11th to 20th	Day	9% 10% 35% 33% 12% 1	330
	21st to end	Day	4 12% 36% 37% 8% 2	363
February	1st to 10th	Day	6% 12% 38% 38% 5% 2	330
	11th to 20th	Day	7% 8% 34% 41% 9% 2	330
	21st to end	Day	6% 15% 37% 33% 9%	273
March	1st to 10th	Day	5% 10% 31% 34% 16% 4	306
	11th to 20th	Day	11% 13% 28% 32% 14% 2	415
	21st to end	Day	11% 13% 34% 33% 8% 2	550
April	1st to 10th	Day	14% 16% 31% 27% 11% 2	500
	11th to 20th	Day	17% 19% 28% 23% 11% 2	492
	21st to end	Day	16% 15% 25% 26% 14% 4	500
May	1st to 10th	Day	16% 11% 24% 28% 16% 4	703
	11th to 20th	Day	17% 8% 23% 27% 19% 6%	725
	21st to end	Day	11% 7% 24% 30% 20% 7%	789
June	1st to 10th	Day	7% 5% 18% 34% 25% 11%	730
	11th to 20th	Day	7% 5% 27% 32% 24% 5%	730
	21st to end	Day	6% 4 22% 35% 26% 7%	730
July	1st to 10th	Day	9% 2 12% 32% 36% 9%	721
	11th to 20th	Day	3 2 14% 34% 33% 13%	718
	21st to end	Day	5% 1 14% 30% 38% 12%	794
August	1st to 10th	Day	7% 2 14% 35% 33% 9%	584
	11th to 20th	Day	3 4 18% 35% 26% 15%	517
	21st to end	Day	5% 2 18% 33% 30% 11%	583
September	1st to 10th	Day	6% 3 17% 35% 27% 12%	530
	11th to 20th	Day	6% 3 20% 29% 31% 12%	478
	21st to end	Day	10% 2 18% 26% 24% 19%	330
October	1st to 10th	Day	10% 6% 22% 23% 23% 16%	330
	11th to 20th	Day	5% 9% 30% 33% 13% 10%	330
	21st to end	Day	9% 9% 27% 32% 18% 5%	363
November	1st to 10th	Day	7% 10% 28% 34% 15% 7%	330
	11th to 20th	Day	6% 9% 30% 37% 15% 3	330
	21st to end	Day	8% 9% 25% 40% 15% 3	330
December	1st to 10th	Day	6% 14% 30% 32% 15% 3	330
	11th to 20th	Day	8% 12% 38% 36% 8%	330
	21st to end	Day	9% 13% 31% 36% 10% 2	363
January	1st to 10th	Night	6% 9% 33% 39% 11% 2	1050
	11th to 20th	Night	7% 10% 40% 34% 8% 1	1050
	21st to end	Night	7% 5% 42% 37% 7% 1	983
February	1st to 10th	Night	6% 9% 43% 35% 7%	840
	11th to 20th	Night	7% 9% 40% 39% 5%	824
	21st to end	Night	5% 12% 43% 36% 4	692
March	1st to 10th	Night	6% 8% 34% 43% 8%	808
	11th to 20th	Night	9% 8% 32% 40% 11%	800
	21st to end	Night	11% 8% 40% 34% 6% 1	695
April	1st to 10th	Night	11% 11% 37% 35% 6%	600
	11th to 20th	Night	16% 9% 34% 34% 6% 1	593
	21st to end	Night	18% 10% 30% 32% 11%	600
May	1st to 10th	Night	15% 10% 26% 35% 13% 1	600
	11th to 20th	Night	18% 4 26% 36% 13% 2	591
	21st to end	Night	12% 4 30% 38% 15% 1	650
June	1st to 10th	Night	8% 4 21% 43% 23% 1	600
	11th to 20th	Night	8% 3 27% 49% 13%	600
	21st to end	Night	5% 4 23% 50% 18%	600
July	1st to 10th	Night	7% 3 15% 47% 28% 1	585
	11th to 20th	Night	4 1 14% 51% 29% 2	582
	21st to end	Night	6% 2 11% 49% 31% 1	657
August	1st to 10th	Night	8% 2 14% 47% 27% 2	597
	11th to 20th	Night	4 2 14% 53% 26% 1	594
	21st to end	Night	4 3 14% 51% 27% 1	660
September	1st to 10th	Night	7% 4 18% 46% 24% 2	600
	11th to 20th	Night	9% 4 20% 44% 22% 3	600
	21st to end	Night	8% 3 24% 43% 20% 2	600
October	1st to 10th	Night	12% 7% 23% 38% 20% 1	735
	11th to 20th	Night	9% 5% 29% 40% 16% 1	800
	21st to end	Night	10% 8% 28% 42% 11% 1	998
November	1st to 10th	Night	6% 6% 33% 42% 11% 1	1025
	11th to 20th	Night	7% 9% 31% 45% 7% 1	1050
	21st to end	Night	7% 7% 34% 41% 10% 1	1050
December	1st to 10th	Night	6% 9% 38% 40% 7%	1050
	11th to 20th	Night	7% 8% 37% 40% 7% 1	1050
	21st to end	Night	7% 11% 34% 40% 7% 1	1155

Page generated at 2026-02-27 23:40:25. Version ac07

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