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 2024-11-28.

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	13% 6% 2 5% 4 4 4 4 5% 7% 45%	101210
	Night	15% 5% 2 5% 3 3 3 3 5% 7% 49%	98424
Transparency	Day	37% 5% 10% 21% 18% 9%	105041
	Night	34% 5% 11% 20% 19% 11%	102720
Seeing	Day	14% 7% 21% 29% 22% 6%	14838
	Night	17% 6% 24% 35% 17% 1	24781

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	16% 7% 3 4 3 3 3 2 4 5% 50%	2847
	11th to 20th	Day	18% 5% 2 3 2 2 2 2 4 5% 55%	2850
	21st to end	Day	20% 7% 2 5% 2 3 3 3 5% 8% 42%	3400
February	1st to 10th	Day	21% 6% 2 6% 3 2 3 3 4 5% 45%	1900
	11th to 20th	Day	20% 7% 2 5% 3 3 2 2 4 6% 43%	1849
	21st to end	Day	19% 6% 2 4 3 3 3 3 5% 5% 47%	1570
March	1st to 10th	Day	17% 8% 2 7% 4 4 4 3 4 5% 42%	3397
	11th to 20th	Day	23% 9% 3 8% 5% 5% 4 3 3 4 32%	3480
	21st to end	Day	19% 6% 2 4 3 3 3 3 4 7% 46%	3814
April	1st to 10th	Day	15% 8% 2 7% 5% 3 4 3 5% 5% 43%	2090
	11th to 20th	Day	21% 7% 3 5% 3 3 3 3 4 5% 42%	2066
	21st to end	Day	16% 8% 3 5% 5% 3 3 3 4 5% 43%	2398
May	1st to 10th	Day	25% 9% 3 7% 4 4 4 3 5% 6% 31%	4082
	11th to 20th	Day	14% 7% 3 6% 4 4 4 4 5% 7% 41%	4082
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 10% 39%	4477
June	1st to 10th	Day	7% 5% 1 5% 5% 5% 5% 5% 7% 9% 47%	2470
	11th to 20th	Day	8% 6% 2 6% 4 5% 6% 4 7% 9% 43%	2470
	21st to end	Day	9% 7% 2 6% 6% 6% 6% 5% 7% 9% 36%	2470
July	1st to 10th	Day	8% 5% 2 6% 6% 5% 4 5% 6% 8% 46%	4120
	11th to 20th	Day	6% 4 2 6% 5% 6% 6% 5% 7% 11% 44%	4120
	21st to end	Day	10% 6% 2 6% 6% 5% 5% 5% 8% 10% 36%	4465
August	1st to 10th	Day	1 2 1 3 3 3 3 3 5% 8% 67%	4026
	11th to 20th	Day	4 3 1 4 3 4 4 4 8% 12% 55%	3726
	21st to end	Day	5% 3 1 6% 6% 5% 5% 5% 7% 10% 46%	3998
September	1st to 10th	Day	9% 6% 3 7% 6% 5% 5% 5% 6% 7% 41%	2090
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 8% 39%	2090
	21st to end	Day	9% 4 2 5% 4 4 4 3 5% 8% 51%	2090
October	1st to 10th	Day	6% 4 1 5% 4 4 5% 3 5% 7% 55%	2090
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 5% 51%	1976
	21st to end	Day	12% 4 2 5% 3 3 3 2 3 6% 57%	2090
November	1st to 10th	Day	16% 7% 3 6% 4 4 4 3 5% 6% 43%	1958
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 5% 6% 49%	1880
	21st to end	Day	18% 7% 2 6% 4 3 3 3 4 5% 45%	1773
December	1st to 10th	Day	19% 6% 2 5% 3 4 3 3 5% 6% 44%	1710
	11th to 20th	Day	18% 8% 2 6% 4 3 4 3 4 5% 43%	2161
	21st to end	Day	18% 6% 2 4 3 2 2 2 4 4 53%	3135
January	1st to 10th	Night	20% 5% 2 3 3 3 2 2 4 6% 51%	4108
	11th to 20th	Night	15% 4 1 3 2 2 2 1 3 4 64%	4120
	21st to end	Night	24% 6% 2 6% 3 2 2 3 4 6% 42%	4294
February	1st to 10th	Night	21% 6% 2 4 3 3 3 3 4 5% 46%	2280
	11th to 20th	Night	21% 7% 2 4 3 2 2 2 3 6% 48%	2218
	21st to end	Night	22% 6% 2 4 3 2 3 3 5% 5% 45%	1884
March	1st to 10th	Night	22% 9% 2 5% 4 4 4 3 4 4 39%	3459
	11th to 20th	Night	24% 9% 3 7% 4 4 4 3 4 5% 32%	3480
	21st to end	Night	19% 7% 2 5% 4 3 3 3 4 5% 44%	3817
April	1st to 10th	Night	15% 7% 2 6% 4 3 3 3 5% 7% 45%	2090
	11th to 20th	Night	21% 7% 2 4 4 3 3 3 4 6% 44%	2063
	21st to end	Night	21% 5% 2 5% 4 3 3 2 4 4 45%	1774
May	1st to 10th	Night	28% 7% 2 5% 3 3 3 3 4 5% 36%	2823
	11th to 20th	Night	16% 5% 2 5% 4 3 4 3 5% 7% 47%	2823
	21st to end	Night	15% 6% 2 5% 3 4 3 3 6% 9% 43%	3090
June	1st to 10th	Night	7% 4 1 3 3 3 4 3 5% 9% 58%	1710
	11th to 20th	Night	5% 4 2 3 3 4 4 4 6% 9% 56%	1710
	21st to end	Night	7% 5% 2 5% 4 4 4 5% 7% 9% 48%	1710
July	1st to 10th	Night	6% 4 2 4 3 4 4 4 7% 11% 51%	2850
	11th to 20th	Night	4 4 1 5% 5% 5% 6% 4 7% 10% 49%	2850
	21st to end	Night	12% 6% 3 6% 4 4 4 4 6% 10% 41%	3098
August	1st to 10th	Night	1 2 1 2 2 2 3 3 4 7% 73%	2895
	11th to 20th	Night	3 2 1 3 3 3 4 4 7% 13% 56%	3113
	21st to end	Night	6% 3 1 4 3 3 4 4 7% 10% 55%	3659
September	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 5% 8% 48%	2090
	11th to 20th	Night	10% 7% 2 6% 4 5% 5% 3 5% 8% 45%	2090
	21st to end	Night	9% 5% 1 5% 4 4 4 3 6% 8% 51%	2090
October	1st to 10th	Night	7% 4 1 3 4 3 4 3 5% 7% 59%	2090
	11th to 20th	Night	15% 4 1 5% 3 2 3 2 4 6% 54%	2183
	21st to end	Night	15% 4 2 3 2 2 2 2 3 4 61%	2508
November	1st to 10th	Night	15% 6% 2 5% 3 3 3 2 4 5% 51%	2340
	11th to 20th	Night	12% 5% 1 5% 3 3 4 2 4 6% 54%	2515
	21st to end	Night	19% 5% 2 5% 3 3 2 3 4 6% 48%	2562
December	1st to 10th	Night	17% 7% 2 4 3 3 3 3 4 6% 49%	2470
	11th to 20th	Night	20% 7% 2 5% 3 3 3 2 3 5% 45%	3036
	21st to end	Night	20% 6% 2 3 2 2 2 2 3 5% 52%	4532

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	38% 3 4 15% 26% 15%	2848
	11th to 20th	Day	34% 2 6% 17% 24% 18%	2850
	21st to end	Day	42% 3 4 12% 29% 9%	3400
February	1st to 10th	Day	43% 4 5% 12% 20% 15%	1900
	11th to 20th	Day	42% 3 7% 16% 19% 13%	1859
	21st to end	Day	40% 4 7% 16% 18% 15%	1570
March	1st to 10th	Day	45% 5% 6% 17% 18% 9%	3397
	11th to 20th	Day	55% 6% 6% 8% 17% 9%	3480
	21st to end	Day	38% 5% 9% 17% 20% 12%	3814
April	1st to 10th	Day	43% 4 7% 16% 17% 12%	2090
	11th to 20th	Day	44% 4 7% 16% 17% 12%	2066
	21st to end	Day	43% 4 7% 19% 17% 10%	2398
May	1st to 10th	Day	53% 6% 9% 14% 13% 5%	4120
	11th to 20th	Day	40% 7% 9% 18% 19% 7%	4086
	21st to end	Day	36% 7% 13% 31% 11% 1	4489
June	1st to 10th	Day	30% 8% 13% 26% 20% 3	2470
	11th to 20th	Day	34% 7% 12% 24% 19% 4	2470
	21st to end	Day	40% 8% 12% 24% 13% 3	2470
July	1st to 10th	Day	35% 5% 16% 36% 7% 1	4056
	11th to 20th	Day	33% 6% 19% 27% 14% 1	4051
	21st to end	Day	40% 6% 18% 27% 8%	4325
August	1st to 10th	Day	15% 5% 11% 44% 24% 1	4012
	11th to 20th	Day	21% 6% 24% 35% 11% 2	3762
	21st to end	Day	31% 7% 19% 24% 17% 2	3997
September	1st to 10th	Day	41% 7% 10% 17% 17% 8%	2090
	11th to 20th	Day	39% 9% 11% 19% 17% 5%	2090
	21st to end	Day	31% 7% 10% 21% 18% 13%	2090
October	1st to 10th	Day	17% 4 6% 12% 24% 36%	3480
	11th to 20th	Day	26% 3 8% 19% 24% 21%	3268
	21st to end	Day	28% 4 5% 19% 29% 16%	3428
November	1st to 10th	Day	42% 4 7% 17% 17% 12%	1958
	11th to 20th	Day	36% 4 9% 16% 20% 15%	1880
	21st to end	Day	43% 4 6% 15% 19% 13%	1773
December	1st to 10th	Day	41% 4 7% 20% 19% 8%	1710
	11th to 20th	Day	43% 5% 6% 10% 21% 14%	2159
	21st to end	Day	36% 3 5% 17% 25% 13%	3135
January	1st to 10th	Night	36% 3 5% 14% 21% 20%	4108
	11th to 20th	Night	27% 2 4 17% 29% 20%	4120
	21st to end	Night	45% 3 4 12% 25% 11%	4294
February	1st to 10th	Night	41% 4 6% 12% 19% 18%	2280
	11th to 20th	Night	41% 2 6% 16% 19% 15%	2218
	21st to end	Night	41% 5% 5% 17% 18% 15%	1884
March	1st to 10th	Night	47% 4 7% 16% 16% 9%	3459
	11th to 20th	Night	53% 6% 8% 11% 12% 10%	3480
	21st to end	Night	41% 5% 9% 14% 20% 10%	3817
April	1st to 10th	Night	37% 5% 10% 18% 16% 14%	2090
	11th to 20th	Night	42% 5% 9% 12% 16% 16%	2063
	21st to end	Night	42% 4 9% 19% 16% 10%	1774
May	1st to 10th	Night	49% 5% 10% 16% 14% 6%	2850
	11th to 20th	Night	36% 6% 11% 21% 19% 7%	2824
	21st to end	Night	36% 7% 15% 30% 12% 1	3099
June	1st to 10th	Night	24% 6% 16% 30% 22% 2	1710
	11th to 20th	Night	22% 7% 15% 31% 20% 5%	1710
	21st to end	Night	30% 8% 17% 28% 14% 3	1710
July	1st to 10th	Night	26% 7% 24% 37% 5% 1	2805
	11th to 20th	Night	28% 8% 21% 28% 14% 1	2796
	21st to end	Night	38% 6% 24% 25% 7%	2999
August	1st to 10th	Night	11% 4 17% 47% 20%	2885
	11th to 20th	Night	20% 6% 32% 33% 7% 1	3143
	21st to end	Night	24% 11% 23% 27% 14% 2	3659
September	1st to 10th	Night	33% 7% 16% 21% 15% 7%	2090
	11th to 20th	Night	35% 8% 15% 22% 15% 5%	2090
	21st to end	Night	29% 7% 16% 20% 17% 12%	2090
October	1st to 10th	Night	17% 4 7% 15% 20% 37%	3480
	11th to 20th	Night	22% 3 9% 17% 29% 20%	3617
	21st to end	Night	26% 3 7% 19% 29% 16%	4120
November	1st to 10th	Night	36% 4 8% 18% 20% 14%	2340
	11th to 20th	Night	32% 5% 9% 17% 21% 17%	2515
	21st to end	Night	39% 3 7% 17% 19% 14%	2562
December	1st to 10th	Night	37% 4 7% 20% 20% 12%	2470
	11th to 20th	Night	43% 3 5% 11% 19% 18%	3037
	21st to end	Night	36% 4 5% 14% 28% 13%	4532

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% 21% 4 1	270
	11th to 20th	Day	25% 16% 26% 24% 7% 1	270
	21st to end	Day	19% 15% 33% 25% 7%	297
February	1st to 10th	Day	32% 14% 28% 17% 9%	270
	11th to 20th	Day	29% 17% 31% 18% 5% 1	270
	21st to end	Day	25% 20% 40% 14% 1	225
March	1st to 10th	Day	24% 15% 41% 17% 3	270
	11th to 20th	Day	17% 21% 39% 18% 5%	270
	21st to end	Day	22% 18% 35% 21% 5%	297
April	1st to 10th	Day	21% 17% 37% 23% 3	270
	11th to 20th	Day	21% 14% 37% 22% 6%	264
	21st to end	Day	18% 11% 38% 27% 6%	578
May	1st to 10th	Day	19% 12% 35% 26% 7%	653
	11th to 20th	Day	17% 10% 28% 34% 10% 1	675
	21st to end	Day	17% 6% 24% 37% 15% 1	734
June	1st to 10th	Day	8% 3 17% 40% 27% 5%	680
	11th to 20th	Day	9% 1 14% 45% 27% 3	680
	21st to end	Day	10% 1 13% 36% 30% 10%	680
July	1st to 10th	Day	9% 2 9% 33% 37% 11%	671
	11th to 20th	Day	5% 1 7% 29% 48% 10%	668
	21st to end	Day	6% 1 5% 33% 44% 11%	739
August	1st to 10th	Day	3 1 5% 30% 45% 16%	637
	11th to 20th	Day	6% 3 38% 40% 13%	477
	21st to end	Day	4 1 7% 23% 44% 20%	435
September	1st to 10th	Day	10% 1 8% 26% 39% 15%	300
	11th to 20th	Day	8% 1 5% 25% 44% 17%	300
	21st to end	Day	10% 1 11% 24% 37% 17%	300
October	1st to 10th	Day	6% 2 14% 33% 34% 10%	300
	11th to 20th	Day	11% 5% 19% 36% 24% 4	300
	21st to end	Day	18% 12% 23% 22% 18% 6%	330
November	1st to 10th	Day	19% 10% 23% 30% 13% 4	300
	11th to 20th	Day	18% 9% 28% 27% 15% 3	300
	21st to end	Day	24% 14% 29% 19% 10% 3	291
December	1st to 10th	Day	20% 9% 32% 28% 8% 4	270
	11th to 20th	Day	22% 17% 28% 26% 8%	270
	21st to end	Day	23% 8% 39% 23% 5% 1	297
January	1st to 10th	Night	21% 7% 28% 33% 9%	950
	11th to 20th	Night	22% 9% 31% 30% 8%	950
	21st to end	Night	23% 9% 26% 33% 8%	898
February	1st to 10th	Night	26% 10% 29% 28% 6%	760
	11th to 20th	Night	26% 13% 31% 25% 4	744
	21st to end	Night	25% 13% 37% 23% 2	628
March	1st to 10th	Night	24% 12% 34% 27% 3	599
	11th to 20th	Night	22% 10% 35% 28% 5%	570
	21st to end	Night	20% 10% 40% 26% 4	627
April	1st to 10th	Night	16% 10% 41% 29% 3	570
	11th to 20th	Night	23% 12% 35% 26% 5%	563
	21st to end	Night	22% 9% 37% 25% 7% 1	570
May	1st to 10th	Night	20% 8% 38% 29% 4	570
	11th to 20th	Night	17% 6% 35% 35% 8%	561
	21st to end	Night	15% 6% 33% 35% 11%	617
June	1st to 10th	Night	7% 2 22% 46% 21% 1	570
	11th to 20th	Night	6% 2 30% 46% 16% 1	570
	21st to end	Night	8% 1 18% 43% 27% 2	570
July	1st to 10th	Night	8% 2 12% 46% 28% 4	555
	11th to 20th	Night	4 1 11% 48% 33% 3	552
	21st to end	Night	7% 1 9% 47% 33% 3	624
August	1st to 10th	Night	1 1 7% 50% 36% 5%	567
	11th to 20th	Night	4 1 8% 49% 35% 3	564
	21st to end	Night	7% 1 6% 38% 44% 4	627
September	1st to 10th	Night	11% 1 8% 38% 38% 4	570
	11th to 20th	Night	12% 1 8% 36% 40% 3	570
	21st to end	Night	9% 2 14% 33% 39% 4	570
October	1st to 10th	Night	7% 2 10% 46% 30% 4	570
	11th to 20th	Night	15% 2 19% 40% 21% 2	663
	21st to end	Night	16% 6% 21% 35% 19% 3	836
November	1st to 10th	Night	16% 6% 18% 37% 21% 1	780
	11th to 20th	Night	15% 6% 23% 38% 16% 2	915
	21st to end	Night	21% 8% 25% 32% 13% 1	986
December	1st to 10th	Night	21% 8% 24% 33% 13% 1	950
	11th to 20th	Night	27% 8% 25% 31% 9%	950
	21st to end	Night	22% 7% 28% 34% 9%	1045

Page generated at 2024-11-24 23:22:21. Version ac07

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