Boswell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boswell Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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	10% 7% 3 6% 4 4 4 3 5% 7% 46%	100800
	Night	10% 7% 2 6% 4 3 4 3 5% 7% 50%	98197
Transparency	Day	37% 6% 13% 25% 16% 2	100612
	Night	34% 5% 12% 27% 19% 3	98056
Seeing	Day	14% 10% 30% 29% 14% 3	15755
	Night	12% 9% 34% 33% 11% 1	25600

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	9% 11% 5% 12% 8% 6% 5% 3 4 6% 30%	2847
	11th to 20th	Day	8% 12% 4 9% 4 4 6% 4 5% 6% 38%	2850
	21st to end	Day	7% 11% 6% 14% 5% 4 4 3 4 6% 36%	3135
February	1st to 10th	Day	9% 12% 4 8% 7% 4 4 3 5% 7% 37%	1710
	11th to 20th	Day	8% 9% 3 8% 4 4 4 4 5% 7% 43%	1758
	21st to end	Day	8% 9% 3 6% 4 5% 5% 3 5% 6% 47%	1570
March	1st to 10th	Day	11% 8% 3 5% 4 3 3 3 3 5% 53%	3338
	11th to 20th	Day	11% 8% 2 5% 4 3 3 3 5% 6% 50%	3480
	21st to end	Day	17% 10% 3 8% 4 5% 4 3 5% 7% 33%	3814
April	1st to 10th	Day	15% 6% 3 5% 4 3 3 3 5% 6% 47%	2100
	11th to 20th	Day	14% 8% 2 6% 5% 5% 3 4 5% 7% 42%	2409
	21st to end	Day	20% 6% 3 6% 4 4 3 4 6% 7% 39%	2470
May	1st to 10th	Day	14% 8% 2 6% 5% 4 4 4 6% 8% 40%	4082
	11th to 20th	Day	14% 6% 3 7% 4 3 4 3 5% 6% 45%	4082
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 6% 7% 41%	4477
June	1st to 10th	Day	6% 5% 2 5% 4 4 4 3 7% 9% 52%	2470
	11th to 20th	Day	9% 5% 2 6% 3 3 5% 4 7% 9% 47%	2548
	21st to end	Day	6% 5% 2 5% 5% 5% 5% 4 6% 9% 49%	2470
July	1st to 10th	Day	12% 6% 2 5% 5% 4 4 4 5% 8% 46%	4120
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 3 6% 9% 52%	4120
	21st to end	Day	4 3 1 4 4 4 5% 4 7% 10% 53%	4465
August	1st to 10th	Day	7% 5% 2 5% 4 4 5% 5% 7% 10% 46%	4104
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 8% 44%	4041
	21st to end	Day	5% 4 2 6% 4 4 4 4 6% 8% 53%	4505
September	1st to 10th	Day	13% 4 1 3 3 3 3 3 5% 7% 55%	2137
	11th to 20th	Day	9% 4 2 5% 3 3 3 3 5% 7% 56%	2090
	21st to end	Day	9% 4 2 4 3 3 3 2 5% 6% 58%	2090
October	1st to 10th	Day	13% 6% 2 4 3 3 4 3 3 6% 54%	1986
	11th to 20th	Day	10% 5% 2 5% 3 3 3 2 4 5% 59%	1900
	21st to end	Day	13% 6% 3 5% 4 3 3 2 4 5% 52%	2077
November	1st to 10th	Day	9% 4 1 4 3 3 4 3 4 7% 57%	1673
	11th to 20th	Day	8% 7% 2 6% 4 4 4 3 4 7% 52%	1710
	21st to end	Day	12% 8% 2 5% 4 3 4 4 4 7% 46%	1600
December	1st to 10th	Day	8% 8% 1 6% 4 4 4 4 6% 7% 47%	1520
	11th to 20th	Day	8% 10% 4 8% 5% 4 4 3 5% 8% 42%	1918
	21st to end	Day	14% 12% 4 14% 5% 5% 5% 3 4 5% 28%	3134
January	1st to 10th	Night	7% 11% 4 15% 5% 4 5% 4 5% 6% 35%	4108
	11th to 20th	Night	8% 9% 3 6% 4 5% 7% 4 5% 5% 43%	4120
	21st to end	Night	11% 12% 5% 11% 3 3 3 3 4 5% 39%	4532
February	1st to 10th	Night	11% 11% 4 7% 5% 4 5% 3 6% 5% 39%	2470
	11th to 20th	Night	8% 8% 2 7% 5% 5% 5% 3 6% 8% 43%	2327
	21st to end	Night	9% 8% 2 6% 4 3 3 3 5% 6% 51%	1884
March	1st to 10th	Night	10% 6% 2 5% 4 3 3 3 4 5% 56%	3517
	11th to 20th	Night	11% 6% 2 4 2 2 3 3 4 6% 57%	3480
	21st to end	Night	18% 8% 2 7% 4 4 4 3 6% 6% 37%	3817
April	1st to 10th	Night	12% 7% 3 6% 4 3 4 4 5% 6% 49%	2079
	11th to 20th	Night	11% 8% 3 6% 4 3 3 4 4 8% 48%	1718
	21st to end	Night	16% 6% 2 6% 4 3 4 3 5% 6% 45%	1710
May	1st to 10th	Night	19% 7% 2 4 3 3 3 3 5% 5% 45%	2823
	11th to 20th	Night	10% 6% 2 6% 3 4 4 2 5% 7% 50%	2823
	21st to end	Night	14% 6% 2 5% 4 3 4 3 5% 7% 45%	3090
June	1st to 10th	Night	5% 4 2 4 5% 4 4 3 7% 8% 55%	1707
	11th to 20th	Night	7% 4 2 4 3 3 4 5% 6% 10% 53%	1575
	21st to end	Night	4 4 1 4 3 3 4 4 6% 10% 58%	1710
July	1st to 10th	Night	8% 6% 2 6% 3 4 3 3 5% 8% 52%	2850
	11th to 20th	Night	4 3 1 4 3 4 3 4 6% 8% 60%	2850
	21st to end	Night	3 2 1 3 2 3 4 4 6% 9% 62%	3098
August	1st to 10th	Night	3 2 1 5% 4 4 4 3 6% 10% 57%	2836
	11th to 20th	Night	12% 5% 2 5% 3 4 3 3 6% 7% 50%	2798
	21st to end	Night	5% 4 1 4 3 4 3 3 5% 9% 58%	3159
September	1st to 10th	Night	8% 4 2 3 3 3 4 2 4 7% 62%	2041
	11th to 20th	Night	7% 4 2 4 3 3 4 3 5% 7% 58%	2090
	21st to end	Night	8% 5% 1 4 3 3 3 3 4 4 62%	2090
October	1st to 10th	Night	13% 4 2 4 3 3 4 4 6% 6% 52%	2175
	11th to 20th	Night	11% 5% 1 4 4 3 2 2 3 5% 59%	2280
	21st to end	Night	13% 5% 2 4 3 3 3 3 4 6% 55%	2517
November	1st to 10th	Night	6% 4 1 5% 3 3 3 3 5% 6% 61%	2412
	11th to 20th	Night	9% 6% 1 5% 4 4 4 3 4 6% 55%	2470
	21st to end	Night	11% 7% 2 4 3 3 3 2 5% 6% 54%	2574
December	1st to 10th	Night	8% 7% 2 6% 5% 3 4 3 5% 7% 50%	2660
	11th to 20th	Night	9% 8% 3 6% 3 3 3 3 5% 6% 53%	3275
	21st to end	Night	17% 12% 4 10% 4 4 3 2 4 5% 35%	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	55% 5% 12% 18% 9% 1	2848
	11th to 20th	Day	47% 5% 16% 20% 11% 1	2850
	21st to end	Day	50% 6% 11% 20% 13%	3135
February	1st to 10th	Day	45% 5% 16% 22% 9% 2	1710
	11th to 20th	Day	40% 5% 13% 24% 15% 3	1767
	21st to end	Day	37% 6% 12% 25% 17% 3	1570
March	1st to 10th	Day	35% 4 9% 27% 21% 4	3338
	11th to 20th	Day	34% 6% 11% 28% 20% 1	3480
	21st to end	Day	49% 7% 21% 17% 5% 1	3814
April	1st to 10th	Day	38% 5% 12% 25% 17% 2	2100
	11th to 20th	Day	42% 5% 13% 24% 14% 3	2409
	21st to end	Day	44% 6% 11% 26% 12% 1	2470
May	1st to 10th	Day	41% 6% 12% 24% 13% 4	4120
	11th to 20th	Day	40% 6% 10% 24% 19% 1	4086
	21st to end	Day	39% 7% 13% 27% 13% 1	4489
June	1st to 10th	Day	27% 8% 16% 33% 13% 2	2470
	11th to 20th	Day	32% 7% 13% 29% 17% 2	2548
	21st to end	Day	30% 8% 14% 29% 14% 5%	2470
July	1st to 10th	Day	36% 6% 12% 27% 18% 1	4056
	11th to 20th	Day	29% 6% 12% 31% 19% 3	4051
	21st to end	Day	23% 8% 14% 28% 22% 4	4325
August	1st to 10th	Day	31% 7% 17% 25% 15% 5%	4090
	11th to 20th	Day	37% 6% 17% 22% 18% 1	4080
	21st to end	Day	28% 6% 15% 25% 20% 6%	4504
September	1st to 10th	Day	30% 5% 10% 29% 19% 6%	2137
	11th to 20th	Day	28% 5% 12% 29% 24% 2	2090
	21st to end	Day	27% 3 9% 32% 26% 2	2090
October	1st to 10th	Day	34% 5% 10% 24% 27% 1	1986
	11th to 20th	Day	29% 4 7% 28% 24% 7%	1900
	21st to end	Day	36% 3 13% 23% 21% 5%	2077
November	1st to 10th	Day	28% 4 14% 27% 22% 3	1673
	11th to 20th	Day	33% 5% 11% 28% 21% 2	1710
	21st to end	Day	38% 4 11% 29% 17% 2	1600
December	1st to 10th	Day	35% 5% 14% 30% 14% 2	1520
	11th to 20th	Day	41% 5% 14% 30% 10%	1915
	21st to end	Day	57% 5% 9% 18% 9% 1	3134
January	1st to 10th	Night	49% 5% 12% 21% 13% 1	4108
	11th to 20th	Night	41% 5% 13% 26% 14%	4120
	21st to end	Night	47% 4 13% 19% 15% 1	4532
February	1st to 10th	Night	44% 6% 13% 20% 14% 3	2470
	11th to 20th	Night	38% 6% 14% 24% 16% 3	2328
	21st to end	Night	35% 4 11% 23% 21% 7%	1884
March	1st to 10th	Night	31% 4 9% 28% 25% 3	3517
	11th to 20th	Night	29% 4 8% 28% 25% 5%	3480
	21st to end	Night	44% 8% 20% 21% 6% 1	3817
April	1st to 10th	Night	36% 5% 9% 27% 19% 3	2079
	11th to 20th	Night	35% 6% 11% 27% 18% 3	1718
	21st to end	Night	38% 6% 10% 26% 17% 1	1710
May	1st to 10th	Night	41% 5% 11% 24% 16% 3	2850
	11th to 20th	Night	33% 6% 11% 28% 21% 1	2824
	21st to end	Night	36% 8% 14% 21% 20% 1	3099
June	1st to 10th	Night	25% 7% 15% 32% 18% 2	1707
	11th to 20th	Night	25% 7% 15% 30% 18% 5%	1575
	21st to end	Night	21% 7% 14% 33% 22% 3	1710
July	1st to 10th	Night	31% 6% 12% 29% 18% 4	2805
	11th to 20th	Night	21% 6% 13% 32% 23% 4	2796
	21st to end	Night	15% 7% 17% 30% 28% 3	2999
August	1st to 10th	Night	22% 6% 17% 29% 21% 5%	2826
	11th to 20th	Night	33% 5% 16% 29% 16% 2	2825
	21st to end	Night	24% 5% 17% 29% 17% 9%	3159
September	1st to 10th	Night	23% 5% 12% 28% 23% 9%	2041
	11th to 20th	Night	25% 5% 11% 31% 24% 4	2090
	21st to end	Night	26% 4 7% 29% 30% 4	2090
October	1st to 10th	Night	31% 5% 10% 24% 26% 3	2175
	11th to 20th	Night	30% 3 8% 26% 26% 8%	2280
	21st to end	Night	32% 4 10% 26% 24% 4	2517
November	1st to 10th	Night	24% 4 13% 28% 26% 6%	2412
	11th to 20th	Night	31% 4 10% 29% 22% 3	2470
	21st to end	Night	32% 3 11% 28% 22% 3	2574
December	1st to 10th	Night	34% 5% 13% 32% 16% 2	2660
	11th to 20th	Night	33% 4 11% 37% 14% 1	3277
	21st to end	Night	52% 5% 9% 24% 8% 1	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	17% 14% 38% 23% 6% 2	270
	11th to 20th	Day	20% 16% 35% 20% 9% 1	270
	21st to end	Day	14% 11% 45% 22% 6%	297
February	1st to 10th	Day	14% 23% 39% 20% 4	270
	11th to 20th	Day	14% 13% 42% 23% 7% 1	270
	21st to end	Day	12% 19% 48% 17% 4	225
March	1st to 10th	Day	17% 14% 42% 20% 6% 1	270
	11th to 20th	Day	29% 10% 33% 21% 6% 1	270
	21st to end	Day	29% 20% 35% 12% 4	297
April	1st to 10th	Day	19% 21% 40% 17% 3	280
	11th to 20th	Day	19% 16% 37% 21% 7%	607
	21st to end	Day	22% 16% 31% 20% 8% 2	650
May	1st to 10th	Day	17% 12% 37% 24% 8% 1	653
	11th to 20th	Day	18% 10% 30% 27% 12% 2	675
	21st to end	Day	18% 8% 31% 30% 10% 3	734
June	1st to 10th	Day	5% 6% 23% 38% 21% 7%	680
	11th to 20th	Day	8% 6% 33% 32% 17% 4	680
	21st to end	Day	7% 6% 34% 36% 14% 2	680
July	1st to 10th	Day	9% 4 19% 35% 27% 7%	671
	11th to 20th	Day	5% 4 19% 42% 23% 7%	668
	21st to end	Day	7% 2 17% 38% 31% 5%	739
August	1st to 10th	Day	8% 4 18% 41% 24% 5%	676
	11th to 20th	Day	8% 6% 20% 42% 21% 3	665
	21st to end	Day	10% 3 20% 34% 25% 6%	734
September	1st to 10th	Day	15% 4 23% 36% 18% 4	347
	11th to 20th	Day	7% 5% 26% 38% 18% 6%	300
	21st to end	Day	12% 9% 30% 31% 13% 4	300
October	1st to 10th	Day	21% 7% 24% 30% 14% 4	300
	11th to 20th	Day	9% 17% 42% 22% 9% 2	300
	21st to end	Day	17% 18% 35% 20% 9% 2	330
November	1st to 10th	Day	17% 14% 35% 24% 7% 2	270
	11th to 20th	Day	13% 14% 44% 20% 8%	270
	21st to end	Day	23% 13% 31% 24% 7% 1	270
December	1st to 10th	Day	10% 12% 43% 26% 8% 1	270
	11th to 20th	Day	18% 11% 37% 27% 7%	270
	21st to end	Day	19% 18% 41% 21% 1	297
January	1st to 10th	Night	13% 12% 37% 32% 6% 1	950
	11th to 20th	Night	13% 13% 38% 29% 7%	950
	21st to end	Night	13% 10% 40% 30% 7%	1045
February	1st to 10th	Night	15% 10% 43% 27% 4	950
	11th to 20th	Night	12% 12% 41% 32% 4	853
	21st to end	Night	14% 13% 42% 26% 5%	628
March	1st to 10th	Night	12% 15% 40% 26% 6% 1	634
	11th to 20th	Night	18% 13% 36% 26% 5%	570
	21st to end	Night	21% 11% 39% 24% 5%	627
April	1st to 10th	Night	15% 15% 42% 25% 4	570
	11th to 20th	Night	16% 15% 38% 28% 4	563
	21st to end	Night	18% 10% 37% 27% 7% 1	570
May	1st to 10th	Night	18% 9% 36% 29% 8%	570
	11th to 20th	Night	14% 9% 34% 33% 9% 1	561
	21st to end	Night	14% 8% 32% 32% 13% 1	617
June	1st to 10th	Night	7% 4 25% 46% 18% 1	570
	11th to 20th	Night	7% 5% 31% 43% 13%	570
	21st to end	Night	3 6% 33% 45% 13%	570
July	1st to 10th	Night	8% 2 16% 44% 28% 1	555
	11th to 20th	Night	4 1 21% 48% 25% 1	552
	21st to end	Night	3 1 17% 53% 26% 1	624
August	1st to 10th	Night	4 2 17% 53% 22% 1	567
	11th to 20th	Night	7% 3 20% 48% 21% 1	564
	21st to end	Night	8% 2 22% 41% 24% 2	627
September	1st to 10th	Night	10% 2 26% 40% 20% 1	570
	11th to 20th	Night	9% 3 30% 40% 18% 1	570
	21st to end	Night	10% 6% 32% 37% 15% 1	570
October	1st to 10th	Night	15% 8% 31% 32% 13% 2	655
	11th to 20th	Night	13% 11% 39% 30% 7%	760
	21st to end	Night	17% 12% 32% 29% 9% 1	845
November	1st to 10th	Night	8% 10% 36% 36% 9%	928
	11th to 20th	Night	11% 12% 41% 29% 7%	950
	21st to end	Night	14% 11% 39% 28% 8% 1	950
December	1st to 10th	Night	12% 11% 41% 29% 6%	950
	11th to 20th	Night	15% 11% 35% 32% 7%	950
	21st to end	Night	20% 11% 36% 28% 5%	1045

Page generated at 2024-10-29 10:20:47. Version ac07

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