Bowser Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bowser Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	14% 6% 2 5% 4 4 4 3 5% 7% 45%	127554
	Night	16% 6% 2 5% 3 3 3 3 5% 7% 48%	124757
Transparency	Day	37% 5% 10% 21% 18% 10%	131346
	Night	36% 4 10% 19% 18% 12%	129028
Seeing	Day	14% 7% 21% 29% 22% 6%	16362
	Night	17% 6% 24% 35% 16% 1	26399

By Month

Percentage Cloud Cover SE (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	19% 8% 3 4 2 3 3 2 3 5% 48%	4167
	11th to 20th	Day	17% 6% 2 4 3 3 2 2 5% 5% 52%	4170
	21st to end	Day	28% 6% 2 4 2 2 2 2 4 6% 41%	4987
February	1st to 10th	Day	21% 7% 2 6% 3 2 3 3 4 5% 45%	2000
	11th to 20th	Day	20% 7% 3 5% 3 3 2 2 4 7% 43%	1949
	21st to end	Day	20% 6% 2 4 3 3 3 3 5% 5% 47%	1650
March	1st to 10th	Day	15% 6% 2 5% 3 3 3 2 4 6% 51%	4884
	11th to 20th	Day	16% 7% 2 6% 4 3 3 2 3 5% 50%	4980
	21st to end	Day	21% 7% 2 5% 3 2 3 3 4 6% 45%	5462
April	1st to 10th	Day	15% 8% 2 7% 5% 4 4 3 5% 5% 44%	2200
	11th to 20th	Day	20% 7% 3 5% 3 3 4 3 4 5% 42%	2176
	21st to end	Day	16% 8% 3 6% 5% 3 4 3 4 5% 42%	2525
May	1st to 10th	Day	23% 8% 3 6% 4 4 4 3 5% 7% 33%	5862
	11th to 20th	Day	11% 6% 2 6% 4 4 4 4 5% 7% 47%	5862
	21st to end	Day	14% 6% 2 6% 5% 5% 5% 4 6% 9% 36%	6434
June	1st to 10th	Day	6% 5% 1 5% 5% 5% 5% 5% 7% 9% 47%	2600
	11th to 20th	Day	8% 6% 2 6% 4 5% 6% 4 7% 9% 43%	2600
	21st to end	Day	8% 7% 2 6% 6% 6% 6% 5% 8% 10% 36%	2600
July	1st to 10th	Day	12% 8% 3 8% 6% 5% 5% 4 5% 7% 36%	5900
	11th to 20th	Day	7% 4 2 6% 5% 6% 7% 5% 8% 10% 39%	5900
	21st to end	Day	8% 6% 2 6% 5% 6% 5% 5% 8% 10% 40%	6422
August	1st to 10th	Day	1 2 1 3 3 3 3 3 6% 8% 67%	4154
	11th to 20th	Day	4 3 1 4 3 4 4 4 8% 12% 54%	3846
	21st to end	Day	5% 3 1 6% 5% 5% 5% 5% 7% 10% 46%	4124
September	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 5% 6% 7% 42%	2200
	11th to 20th	Day	11% 6% 2 5% 5% 5% 5% 4 7% 8% 41%	2200
	21st to end	Day	9% 4 2 5% 4 4 4 3 5% 8% 51%	2200
October	1st to 10th	Day	6% 4 1 5% 4 4 5% 3 5% 7% 56%	2200
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 4 5% 52%	2080
	21st to end	Day	11% 4 2 5% 3 3 3 3 4 5% 57%	2200
November	1st to 10th	Day	15% 7% 3 6% 4 4 3 3 5% 5% 45%	2058
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 5% 6% 50%	1974
	21st to end	Day	19% 7% 3 7% 4 3 3 3 4 4 44%	1890
December	1st to 10th	Day	30% 7% 3 5% 3 3 2 2 4 5% 36%	3030
	11th to 20th	Day	19% 8% 3 5% 4 3 4 3 4 6% 43%	3481
	21st to end	Day	16% 6% 2 3 3 2 3 2 4 4 57%	4587
January	1st to 10th	Night	21% 6% 2 4 2 2 2 2 3 6% 50%	6018
	11th to 20th	Night	13% 3 1 3 2 2 3 2 4 5% 62%	6030
	21st to end	Night	32% 5% 1 4 3 2 2 3 3 4 40%	6275
February	1st to 10th	Night	21% 6% 2 4 3 3 3 3 4 5% 47%	2400
	11th to 20th	Night	22% 7% 2 4 3 2 2 2 3 6% 47%	2338
	21st to end	Night	22% 6% 2 4 3 2 3 3 4 5% 45%	1980
March	1st to 10th	Night	19% 7% 2 5% 4 4 3 3 4 4 45%	4973
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 3 5% 48%	4980
	21st to end	Night	23% 9% 2 4 3 3 3 2 4 5% 42%	5467
April	1st to 10th	Night	15% 6% 2 6% 4 3 3 3 5% 7% 45%	2200
	11th to 20th	Night	21% 7% 2 4 3 3 3 3 4 6% 45%	2173
	21st to end	Night	21% 6% 2 5% 4 3 3 2 4 5% 44%	1867
May	1st to 10th	Night	27% 8% 2 6% 4 3 3 3 5% 5% 34%	4053
	11th to 20th	Night	12% 4 2 4 4 4 4 4 6% 9% 47%	4053
	21st to end	Night	16% 7% 2 7% 4 4 4 4 6% 10% 36%	4443
June	1st to 10th	Night	7% 4 2 3 4 3 4 3 5% 9% 57%	1800
	11th to 20th	Night	6% 4 2 3 3 4 4 4 6% 9% 56%	1800
	21st to end	Night	7% 5% 2 5% 4 4 4 5% 7% 9% 48%	1800
July	1st to 10th	Night	10% 7% 3 7% 4 5% 5% 4 6% 10% 40%	4078
	11th to 20th	Night	6% 4 2 5% 4 5% 6% 5% 8% 12% 45%	4077
	21st to end	Night	10% 6% 2 6% 4 4 4 4 7% 9% 44%	4449
August	1st to 10th	Night	1 1 1 2 2 2 3 3 4 7% 73%	2987
	11th to 20th	Night	3 2 1 3 3 3 4 4 8% 13% 56%	3213
	21st to end	Night	6% 3 1 4 3 3 4 4 7% 10% 55%	3775
September	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 5% 8% 48%	2200
	11th to 20th	Night	9% 6% 2 6% 5% 5% 4 4 5% 8% 46%	2200
	21st to end	Night	9% 4 2 6% 4 4 4 3 6% 9% 51%	2200
October	1st to 10th	Night	6% 4 1 4 4 4 4 3 5% 7% 59%	2200
	11th to 20th	Night	14% 4 1 4 3 2 3 2 4 5% 56%	2298
	21st to end	Night	15% 4 2 3 2 2 2 2 3 4 62%	2640
November	1st to 10th	Night	15% 6% 2 5% 3 3 3 2 4 5% 53%	2460
	11th to 20th	Night	13% 5% 1 4 3 3 4 2 4 6% 55%	2641
	21st to end	Night	19% 5% 2 5% 4 3 3 3 4 6% 47%	2730
December	1st to 10th	Night	27% 9% 3 6% 3 3 3 2 3 5% 36%	4380
	11th to 20th	Night	23% 7% 2 4 3 3 2 2 3 4 46%	4946
	21st to end	Night	19% 6% 2 3 2 2 2 2 3 4 55%	6633

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	41% 3 4 18% 23% 11%	4168
	11th to 20th	Day	36% 2 5% 17% 22% 20%	4170
	21st to end	Day	47% 2 3 11% 25% 12%	4987
February	1st to 10th	Day	43% 4 5% 12% 20% 16%	2000
	11th to 20th	Day	42% 4 7% 17% 18% 12%	1959
	21st to end	Day	40% 4 7% 15% 19% 15%	1650
March	1st to 10th	Day	36% 3 5% 20% 15% 21%	4884
	11th to 20th	Day	39% 4 4 8% 17% 28%	4980
	21st to end	Day	42% 4 7% 19% 19% 10%	5464
April	1st to 10th	Day	43% 4 7% 16% 17% 13%	2200
	11th to 20th	Day	44% 4 7% 16% 17% 12%	2176
	21st to end	Day	44% 4 8% 18% 17% 10%	2525
May	1st to 10th	Day	50% 6% 8% 18% 14% 4	5900
	11th to 20th	Day	36% 5% 11% 20% 20% 8%	5866
	21st to end	Day	41% 6% 11% 28% 13% 1	6447
June	1st to 10th	Day	30% 8% 13% 28% 19% 3	2600
	11th to 20th	Day	34% 7% 12% 24% 19% 4	2600
	21st to end	Day	40% 7% 13% 24% 13% 3	2600
July	1st to 10th	Day	47% 5% 16% 27% 5% 1	5836
	11th to 20th	Day	37% 5% 19% 28% 11% 1	5831
	21st to end	Day	37% 5% 17% 25% 13% 3	6240
August	1st to 10th	Day	15% 5% 11% 44% 24% 1	4140
	11th to 20th	Day	21% 6% 24% 35% 11% 2	3882
	21st to end	Day	30% 7% 20% 24% 17% 2	4123
September	1st to 10th	Day	41% 7% 10% 18% 17% 8%	2200
	11th to 20th	Day	37% 9% 12% 20% 17% 5%	2200
	21st to end	Day	31% 7% 10% 22% 18% 13%	2200
October	1st to 10th	Day	17% 4 6% 12% 25% 36%	3590
	11th to 20th	Day	25% 3 8% 19% 24% 20%	3372
	21st to end	Day	28% 4 5% 19% 29% 16%	3538
November	1st to 10th	Day	41% 4 7% 17% 19% 13%	2058
	11th to 20th	Day	36% 4 9% 16% 20% 15%	1974
	21st to end	Day	44% 4 6% 14% 19% 12%	1890
December	1st to 10th	Day	53% 3 4 17% 14% 9%	3030
	11th to 20th	Day	43% 4 7% 12% 20% 13%	3479
	21st to end	Day	33% 3 4 18% 26% 16%	4587
January	1st to 10th	Night	38% 2 5% 18% 21% 15%	6018
	11th to 20th	Night	27% 2 4 18% 28% 20%	6030
	21st to end	Night	49% 2 3 11% 20% 15%	6275
February	1st to 10th	Night	40% 4 6% 12% 20% 18%	2400
	11th to 20th	Night	42% 2 6% 17% 18% 14%	2338
	21st to end	Night	42% 4 5% 16% 18% 15%	1980
March	1st to 10th	Night	42% 4 6% 17% 15% 17%	4973
	11th to 20th	Night	39% 4 7% 11% 13% 26%	4980
	21st to end	Night	45% 4 7% 17% 18% 10%	5467
April	1st to 10th	Night	38% 5% 10% 18% 16% 14%	2200
	11th to 20th	Night	41% 5% 9% 13% 16% 16%	2173
	21st to end	Night	44% 4 9% 18% 16% 10%	1867
May	1st to 10th	Night	51% 5% 8% 17% 14% 6%	4080
	11th to 20th	Night	33% 5% 12% 21% 20% 9%	4054
	21st to end	Night	43% 6% 14% 28% 9% 1	4452
June	1st to 10th	Night	25% 6% 16% 30% 21% 2	1800
	11th to 20th	Night	24% 6% 15% 31% 20% 5%	1800
	21st to end	Night	30% 8% 18% 28% 14% 3	1800
July	1st to 10th	Night	40% 7% 23% 26% 4 1	4035
	11th to 20th	Night	30% 6% 24% 29% 10%	4026
	21st to end	Night	35% 6% 21% 23% 12% 3	4320
August	1st to 10th	Night	11% 4 17% 47% 20%	2977
	11th to 20th	Night	20% 6% 32% 33% 7% 1	3243
	21st to end	Night	24% 11% 23% 27% 14% 2	3775
September	1st to 10th	Night	33% 7% 16% 20% 16% 7%	2200
	11th to 20th	Night	35% 8% 15% 23% 14% 5%	2200
	21st to end	Night	29% 7% 16% 21% 16% 12%	2200
October	1st to 10th	Night	17% 5% 7% 15% 20% 36%	3590
	11th to 20th	Night	22% 3 9% 18% 29% 20%	3732
	21st to end	Night	26% 3 7% 19% 29% 17%	4252
November	1st to 10th	Night	35% 4 8% 18% 22% 14%	2460
	11th to 20th	Night	31% 5% 9% 17% 21% 17%	2641
	21st to end	Night	40% 3 8% 17% 18% 14%	2730
December	1st to 10th	Night	53% 3 5% 15% 13% 11%	4380
	11th to 20th	Night	44% 3 7% 9% 21% 17%	4947
	21st to end	Night	35% 3 4 14% 28% 17%	6633

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	23% 12% 38% 20% 6% 1	330
	11th to 20th	Day	23% 15% 29% 25% 7% 1	330
	21st to end	Day	22% 13% 34% 25% 6%	363
February	1st to 10th	Day	32% 13% 27% 19% 9%	300
	11th to 20th	Day	29% 17% 31% 18% 4 1	300
	21st to end	Day	26% 18% 39% 15% 2	249
March	1st to 10th	Day	22% 15% 42% 18% 3	300
	11th to 20th	Day	16% 20% 40% 19% 5%	300
	21st to end	Day	22% 16% 35% 21% 5%	330
April	1st to 10th	Day	20% 16% 36% 25% 3	300
	11th to 20th	Day	20% 14% 36% 22% 8%	294
	21st to end	Day	18% 11% 39% 27% 5%	625
May	1st to 10th	Day	19% 12% 36% 25% 7%	703
	11th to 20th	Day	16% 10% 28% 35% 10% 1	725
	21st to end	Day	17% 6% 24% 37% 15% 1	789
June	1st to 10th	Day	8% 3 17% 41% 26% 5%	730
	11th to 20th	Day	10% 1 15% 45% 26% 3	730
	21st to end	Day	10% 2 13% 36% 29% 11%	730
July	1st to 10th	Day	10% 2 9% 33% 36% 10%	721
	11th to 20th	Day	6% 1 8% 28% 47% 10%	718
	21st to end	Day	6% 1 5% 33% 44% 11%	794
August	1st to 10th	Day	3 1 5% 29% 45% 17%	685
	11th to 20th	Day	6% 3 37% 39% 15%	517
	21st to end	Day	4 1 7% 22% 44% 22%	473
September	1st to 10th	Day	12% 1 7% 26% 38% 16%	330
	11th to 20th	Day	7% 1 5% 25% 44% 18%	330
	21st to end	Day	9% 1 11% 24% 37% 18%	330
October	1st to 10th	Day	6% 2 13% 32% 34% 13%	330
	11th to 20th	Day	11% 5% 19% 35% 25% 6%	330
	21st to end	Day	17% 12% 23% 23% 20% 6%	363
November	1st to 10th	Day	18% 10% 23% 30% 15% 5%	330
	11th to 20th	Day	17% 8% 27% 29% 16% 3	330
	21st to end	Day	24% 14% 30% 20% 10% 3	330
December	1st to 10th	Day	22% 8% 33% 26% 7% 3	330
	11th to 20th	Day	22% 15% 26% 25% 11% 2	330
	21st to end	Day	22% 7% 36% 23% 9% 1	363
January	1st to 10th	Night	22% 8% 28% 33% 9%	1050
	11th to 20th	Night	21% 9% 34% 30% 7%	1050
	21st to end	Night	25% 8% 26% 33% 7%	992
February	1st to 10th	Night	26% 10% 29% 29% 6%	800
	11th to 20th	Night	27% 13% 31% 24% 4	784
	21st to end	Night	26% 13% 36% 24% 2	660
March	1st to 10th	Night	23% 13% 34% 27% 3	630
	11th to 20th	Night	21% 11% 36% 28% 5%	600
	21st to end	Night	21% 10% 39% 27% 3	660
April	1st to 10th	Night	17% 10% 41% 29% 3	600
	11th to 20th	Night	22% 11% 36% 26% 5%	593
	21st to end	Night	22% 9% 37% 25% 7% 1	600
May	1st to 10th	Night	20% 8% 39% 29% 4	600
	11th to 20th	Night	16% 6% 35% 35% 8%	591
	21st to end	Night	15% 6% 34% 35% 11%	650
June	1st to 10th	Night	8% 2 24% 46% 20% 1	600
	11th to 20th	Night	7% 2 30% 46% 16% 1	600
	21st to end	Night	8% 1 18% 43% 28% 2	600
July	1st to 10th	Night	9% 2 12% 45% 28% 3	585
	11th to 20th	Night	4 2 12% 48% 32% 2	582
	21st to end	Night	7% 1 9% 46% 34% 3	657
August	1st to 10th	Night	1 1 7% 50% 37% 5%	597
	11th to 20th	Night	4 1 8% 48% 35% 4	594
	21st to end	Night	6% 1 6% 37% 45% 5%	660
September	1st to 10th	Night	10% 1 8% 39% 38% 4	600
	11th to 20th	Night	11% 1 8% 36% 41% 3	600
	21st to end	Night	9% 2 13% 34% 39% 3	600
October	1st to 10th	Night	7% 2 10% 46% 32% 4	600
	11th to 20th	Night	15% 2 18% 40% 22% 2	698
	21st to end	Night	16% 6% 21% 36% 18% 3	880
November	1st to 10th	Night	16% 6% 18% 38% 21% 1	820
	11th to 20th	Night	15% 6% 23% 39% 16% 2	961
	21st to end	Night	21% 9% 25% 32% 13% 1	1050
December	1st to 10th	Night	22% 8% 24% 33% 12% 1	1050
	11th to 20th	Night	27% 7% 24% 32% 10%	1050
	21st to end	Night	23% 7% 27% 34% 9%	1155

Page generated at 2026-01-29 00:21:47. Version ac07

Copyright © 2026 Attilla Danko.