Kilbourne Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kilbourne Observatory clear sky chart from 2005-11-06 to 2025-02-06.

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	15% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	109558
	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 33%	108727
Transparency	Day	50% 6% 11% 20% 11% 1	113247
	Night	49% 6% 11% 20% 12% 2	113177
Seeing	Day	19% 10% 26% 23% 16% 7%	15517
	Night	19% 8% 27% 30% 14% 2	25262

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	15% 19% 8% 17% 8% 5% 4 3 4 4 12%	4056
	11th to 20th	Day	14% 21% 6% 13% 7% 6% 7% 3 3 3 16%	4060
	21st to end	Day	22% 17% 9% 10% 8% 7% 4 4 4 4 13%	4466
February	1st to 10th	Day	20% 15% 5% 10% 8% 4 3 3 4 4 23%	1755
	11th to 20th	Day	16% 13% 6% 14% 8% 4 4 3 5% 5% 23%	1818
	21st to end	Day	18% 16% 5% 9% 5% 4 4 3 4 6% 27%	1570
March	1st to 10th	Day	21% 16% 6% 9% 5% 4 4 3 5% 5% 22%	3266
	11th to 20th	Day	13% 10% 4 9% 4 5% 4 3 5% 6% 36%	3480
	21st to end	Day	21% 10% 4 8% 4 5% 4 3 4 6% 31%	3815
April	1st to 10th	Day	16% 13% 3 9% 5% 4 5% 3 4 7% 32%	2139
	11th to 20th	Day	18% 10% 3 6% 5% 4 4 3 5% 6% 35%	2402
	21st to end	Day	18% 9% 3 8% 5% 5% 5% 3 4 6% 33%	2470
May	1st to 10th	Day	22% 10% 3 8% 5% 5% 4 4 5% 6% 29%	4082
	11th to 20th	Day	21% 8% 2 7% 4 4 3 3 5% 7% 34%	4081
	21st to end	Day	12% 6% 2 7% 5% 5% 6% 5% 8% 9% 35%	4476
June	1st to 10th	Day	12% 7% 2 7% 6% 5% 5% 4 6% 9% 37%	2470
	11th to 20th	Day	11% 7% 2 6% 5% 5% 5% 5% 6% 9% 38%	2532
	21st to end	Day	11% 5% 2 6% 6% 6% 5% 4 7% 10% 38%	2660
July	1st to 10th	Day	10% 7% 3 7% 6% 5% 5% 4 6% 9% 38%	4386
	11th to 20th	Day	9% 5% 2 5% 4 5% 5% 4 8% 11% 43%	4120
	21st to end	Day	11% 6% 2 6% 4 5% 5% 5% 8% 10% 37%	4466
August	1st to 10th	Day	9% 5% 3 7% 5% 6% 5% 5% 7% 10% 38%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 6% 8% 10% 38%	4044
	21st to end	Day	7% 4 2 6% 5% 4 6% 5% 7% 10% 44%	4472
September	1st to 10th	Day	13% 5% 2 4 4 4 4 3 5% 7% 48%	2100
	11th to 20th	Day	9% 6% 2 4 5% 5% 4 4 6% 9% 46%	2090
	21st to end	Day	19% 7% 2 6% 4 4 3 3 5% 6% 41%	2090
October	1st to 10th	Day	14% 6% 3 6% 3 4 4 4 5% 7% 43%	2033
	11th to 20th	Day	15% 8% 2 7% 4 4 4 4 5% 6% 41%	1900
	21st to end	Day	21% 11% 3 7% 4 4 5% 3 5% 6% 32%	2024
November	1st to 10th	Day	12% 8% 3 6% 5% 4 4 3 5% 6% 45%	1762
	11th to 20th	Day	17% 13% 4 6% 6% 4 4 2 4 6% 33%	1800
	21st to end	Day	19% 14% 6% 9% 5% 3 4 3 4 5% 28%	1800
December	1st to 10th	Day	20% 12% 6% 16% 5% 4 3 2 4 5% 23%	2930
	11th to 20th	Day	23% 16% 7% 10% 5% 4 3 3 3 4 21%	3373
	21st to end	Day	26% 21% 6% 11% 6% 4 4 2 3 4 13%	4466
January	1st to 10th	Night	15% 18% 8% 19% 5% 4 4 2 4 4 16%	5889
	11th to 20th	Night	13% 18% 9% 15% 8% 8% 5% 3 3 4 14%	5900
	21st to end	Night	22% 16% 6% 10% 6% 4 3 2 3 5% 22%	6490
February	1st to 10th	Night	20% 14% 4 10% 6% 5% 4 4 4 4 25%	2536
	11th to 20th	Night	17% 13% 4 9% 7% 5% 5% 3 5% 6% 26%	2247
	21st to end	Night	20% 14% 5% 10% 4 5% 4 3 4 5% 26%	1884
March	1st to 10th	Night	20% 14% 4 7% 5% 4 4 2 5% 5% 31%	3587
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 5% 7% 41%	3480
	21st to end	Night	19% 9% 3 6% 4 4 4 3 4 6% 38%	3817
April	1st to 10th	Night	17% 10% 2 7% 5% 4 4 4 5% 8% 35%	2057
	11th to 20th	Night	16% 8% 2 7% 5% 4 5% 4 5% 8% 36%	1725
	21st to end	Night	16% 8% 3 8% 5% 3 5% 4 6% 7% 37%	1710
May	1st to 10th	Night	24% 11% 3 7% 4 5% 4 4 5% 6% 28%	2813
	11th to 20th	Night	19% 8% 3 6% 3 4 3 3 4 8% 39%	2812
	21st to end	Night	9% 5% 2 6% 4 5% 4 4 7% 10% 44%	3079
June	1st to 10th	Night	9% 6% 2 6% 5% 6% 4 4 6% 8% 45%	1710
	11th to 20th	Night	8% 6% 2 4 5% 5% 5% 4 8% 10% 44%	1640
	21st to end	Night	10% 5% 2 4 5% 4 5% 4 7% 9% 45%	1520
July	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 5% 8% 46%	2578
	11th to 20th	Night	9% 3 2 5% 3 4 5% 4 6% 9% 49%	2840
	21st to end	Night	9% 6% 3 7% 5% 5% 5% 5% 6% 8% 43%	3087
August	1st to 10th	Night	9% 6% 2 8% 4 5% 5% 5% 7% 10% 38%	2825
	11th to 20th	Night	10% 8% 3 8% 5% 4 3 3 5% 7% 43%	2785
	21st to end	Night	4 4 2 5% 5% 5% 6% 5% 7% 8% 50%	3180
September	1st to 10th	Night	12% 6% 2 4 4 4 3 3 5% 7% 51%	2061
	11th to 20th	Night	9% 4 2 4 3 3 3 3 5% 7% 56%	2090
	21st to end	Night	15% 6% 2 5% 5% 4 4 4 5% 6% 46%	2090
October	1st to 10th	Night	11% 6% 2 5% 4 4 3 3 6% 7% 51%	2147
	11th to 20th	Night	17% 7% 2 6% 4 3 5% 4 5% 6% 42%	2280
	21st to end	Night	21% 8% 3 6% 4 3 4 4 4 6% 37%	2570
November	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 4 6% 45%	2536
	11th to 20th	Night	17% 12% 3 7% 4 4 4 3 5% 6% 35%	2600
	21st to end	Night	20% 13% 4 8% 5% 4 4 4 5% 6% 27%	2600
December	1st to 10th	Night	18% 12% 6% 10% 5% 5% 6% 4 5% 6% 24%	4250
	11th to 20th	Night	19% 18% 8% 11% 5% 4 3 2 4 5% 21%	4822
	21st to end	Night	24% 22% 6% 10% 5% 4 3 3 4 5% 15%	6490

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	75% 7% 6% 10% 2	4057
	11th to 20th	Day	73% 5% 7% 7% 7%	4060
	21st to end	Day	76% 4 7% 8% 5%	4466
February	1st to 10th	Day	64% 5% 10% 13% 7%	1755
	11th to 20th	Day	63% 6% 8% 16% 7% 1	1828
	21st to end	Day	59% 5% 11% 17% 7% 2	1570
March	1st to 10th	Day	63% 6% 9% 17% 4	3266
	11th to 20th	Day	47% 8% 9% 27% 8% 1	3480
	21st to end	Day	53% 7% 11% 21% 7%	3815
April	1st to 10th	Day	53% 6% 12% 17% 11% 1	2139
	11th to 20th	Day	49% 6% 12% 18% 13% 2	2402
	21st to end	Day	51% 6% 10% 19% 11% 2	2470
May	1st to 10th	Day	53% 8% 12% 20% 6% 1	4120
	11th to 20th	Day	48% 7% 14% 22% 9% 1	4085
	21st to end	Day	38% 11% 14% 21% 12% 3	4489
June	1st to 10th	Day	42% 8% 11% 25% 14% 1	2470
	11th to 20th	Day	41% 8% 15% 22% 14% 1	2532
	21st to end	Day	39% 9% 14% 21% 14% 3	2660
July	1st to 10th	Day	42% 7% 12% 22% 15% 3	4318
	11th to 20th	Day	32% 6% 14% 27% 19% 1	4051
	21st to end	Day	39% 7% 14% 19% 17% 3	4324
August	1st to 10th	Day	38% 8% 15% 25% 13% 1	4091
	11th to 20th	Day	37% 8% 11% 29% 14% 1	4083
	21st to end	Day	33% 8% 13% 31% 12% 3	4471
September	1st to 10th	Day	35% 7% 12% 22% 20% 4	2100
	11th to 20th	Day	35% 6% 13% 24% 19% 3	2090
	21st to end	Day	43% 6% 10% 21% 20% 1	2090
October	1st to 10th	Day	27% 5% 11% 34% 23% 1	3384
	11th to 20th	Day	36% 4 9% 27% 21% 3	3140
	21st to end	Day	42% 4 11% 24% 18% 2	3313
November	1st to 10th	Day	39% 5% 11% 25% 17% 2	1762
	11th to 20th	Day	53% 5% 10% 20% 11% 2	1800
	21st to end	Day	59% 4 10% 17% 9% 1	1800
December	1st to 10th	Day	66% 4 13% 14% 3	2930
	11th to 20th	Day	68% 4 11% 13% 4	3370
	21st to end	Day	76% 5% 6% 9% 4	4466
January	1st to 10th	Night	72% 5% 7% 12% 4	5889
	11th to 20th	Night	75% 5% 8% 8% 5% 1	5900
	21st to end	Night	66% 4 11% 12% 6% 2	6490
February	1st to 10th	Night	62% 5% 10% 16% 7% 1	2536
	11th to 20th	Night	58% 6% 10% 16% 9% 1	2248
	21st to end	Night	61% 5% 9% 14% 9% 2	1884
March	1st to 10th	Night	54% 6% 11% 20% 9% 1	3587
	11th to 20th	Night	41% 7% 11% 29% 10% 2	3480
	21st to end	Night	47% 5% 10% 27% 10% 1	3817
April	1st to 10th	Night	46% 7% 12% 19% 13% 2	2057
	11th to 20th	Night	44% 7% 13% 16% 18% 3	1725
	21st to end	Night	45% 7% 12% 19% 15% 2	1710
May	1st to 10th	Night	54% 9% 10% 17% 8% 2	2840
	11th to 20th	Night	44% 7% 11% 26% 11% 1	2813
	21st to end	Night	32% 10% 14% 27% 14% 3	3087
June	1st to 10th	Night	36% 8% 13% 22% 19% 2	1710
	11th to 20th	Night	32% 8% 15% 25% 15% 3	1640
	21st to end	Night	33% 9% 14% 24% 17% 3	1520
July	1st to 10th	Night	37% 5% 12% 23% 17% 6%	2537
	11th to 20th	Night	30% 7% 13% 31% 18% 1	2786
	21st to end	Night	37% 6% 15% 21% 17% 4	2988
August	1st to 10th	Night	39% 8% 16% 25% 12% 1	2814
	11th to 20th	Night	41% 5% 9% 25% 19%	2812
	21st to end	Night	29% 7% 15% 29% 17% 2	3180
September	1st to 10th	Night	33% 7% 11% 24% 19% 6%	2061
	11th to 20th	Night	28% 5% 11% 28% 24% 4	2090
	21st to end	Night	39% 6% 10% 20% 23% 1	2090
October	1st to 10th	Night	25% 4 8% 30% 31% 2	3576
	11th to 20th	Night	32% 5% 10% 28% 21% 5%	3779
	21st to end	Night	36% 4 8% 26% 21% 4	4231
November	1st to 10th	Night	39% 5% 11% 23% 18% 3	2536
	11th to 20th	Night	50% 5% 8% 21% 13% 3	2600
	21st to end	Night	57% 6% 11% 19% 7% 1	2600
December	1st to 10th	Night	61% 4 12% 18% 5%	4250
	11th to 20th	Night	66% 4 13% 12% 5%	4824
	21st to end	Night	73% 4 9% 11% 3	6490

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	29% 16% 34% 15% 5% 1	300
	11th to 20th	Day	24% 19% 43% 10% 4	300
	21st to end	Day	31% 15% 32% 17% 5% 1	330
February	1st to 10th	Day	29% 16% 35% 16% 2 1	285
	11th to 20th	Day	26% 20% 36% 15% 3	270
	21st to end	Day	25% 20% 40% 12% 2	225
March	1st to 10th	Day	23% 17% 34% 21% 6%	351
	11th to 20th	Day	23% 16% 36% 18% 6% 1	460
	21st to end	Day	29% 13% 32% 20% 6%	506
April	1st to 10th	Day	24% 13% 31% 20% 10% 2	460
	11th to 20th	Day	23% 15% 27% 21% 10% 5%	452
	21st to end	Day	21% 13% 33% 22% 9% 2	460
May	1st to 10th	Day	26% 10% 30% 20% 10% 4	463
	11th to 20th	Day	24% 7% 22% 25% 15% 6%	487
	21st to end	Day	14% 6% 22% 24% 23% 10%	529
June	1st to 10th	Day	13% 6% 20% 32% 22% 7%	490
	11th to 20th	Day	15% 6% 21% 28% 23% 7%	552
	21st to end	Day	14% 6% 25% 28% 20% 7%	680
July	1st to 10th	Day	12% 3 15% 27% 23% 19%	644
	11th to 20th	Day	13% 2 18% 25% 25% 17%	484
	21st to end	Day	11% 2 17% 24% 30% 15%	532
August	1st to 10th	Day	11% 3 13% 24% 31% 17%	486
	11th to 20th	Day	14% 4 16% 28% 24% 14%	479
	21st to end	Day	9% 4 14% 24% 32% 16%	539
September	1st to 10th	Day	13% 3 15% 26% 29% 14%	490
	11th to 20th	Day	10% 3 13% 25% 33% 17%	490
	21st to end	Day	23% 8% 18% 26% 17% 10%	490
October	1st to 10th	Day	12% 7% 22% 30% 21% 9%	490
	11th to 20th	Day	15% 14% 30% 23% 14% 4	490
	21st to end	Day	25% 11% 33% 21% 9% 1	473
November	1st to 10th	Day	15% 12% 34% 24% 11% 5%	300
	11th to 20th	Day	24% 15% 31% 18% 11% 1	300
	21st to end	Day	28% 13% 38% 16% 4	300
December	1st to 10th	Day	25% 14% 37% 17% 5% 2	300
	11th to 20th	Day	24% 16% 40% 17% 3	300
	21st to end	Day	33% 14% 30% 20% 3	330
January	1st to 10th	Night	24% 15% 37% 22% 3	800
	11th to 20th	Night	28% 14% 35% 19% 4 1	800
	21st to end	Night	26% 13% 34% 25% 3	880
February	1st to 10th	Night	27% 10% 34% 25% 3	781
	11th to 20th	Night	24% 13% 36% 25% 3	743
	21st to end	Night	27% 12% 40% 20% 2	628
March	1st to 10th	Night	24% 12% 32% 27% 6%	760
	11th to 20th	Night	21% 11% 35% 27% 6% 1	760
	21st to end	Night	23% 11% 34% 25% 7%	836
April	1st to 10th	Night	21% 11% 36% 26% 6%	727
	11th to 20th	Night	19% 10% 35% 24% 10% 1	563
	21st to end	Night	20% 7% 39% 25% 8% 1	570
May	1st to 10th	Night	23% 6% 29% 31% 11% 1	570
	11th to 20th	Night	21% 6% 25% 34% 13% 1	561
	21st to end	Night	11% 3 20% 39% 25% 2	617
June	1st to 10th	Night	9% 3 24% 42% 21% 1	570
	11th to 20th	Night	11% 2 18% 45% 22% 2	570
	21st to end	Night	10% 1 21% 42% 24% 2	570
July	1st to 10th	Night	12% 3 12% 39% 29% 6%	555
	11th to 20th	Night	8% 3 14% 37% 33% 5%	552
	21st to end	Night	8% 4 11% 42% 33% 2	624
August	1st to 10th	Night	7% 2 11% 44% 31% 5%	567
	11th to 20th	Night	11% 2 11% 41% 30% 5%	564
	21st to end	Night	7% 1 12% 38% 34% 7%	627
September	1st to 10th	Night	14% 2 14% 35% 30% 5%	731
	11th to 20th	Night	12% 3 12% 36% 34% 4	760
	21st to end	Night	17% 5% 21% 32% 23% 3	760
October	1st to 10th	Night	13% 4 23% 35% 21% 4	760
	11th to 20th	Night	19% 7% 30% 31% 13% 1	760
	21st to end	Night	24% 11% 28% 28% 9%	836
November	1st to 10th	Night	19% 7% 27% 32% 14% 1	780
	11th to 20th	Night	23% 12% 30% 27% 7% 1	800
	21st to end	Night	25% 10% 30% 28% 6%	800
December	1st to 10th	Night	27% 10% 33% 25% 5%	800
	11th to 20th	Night	26% 10% 35% 25% 5%	800
	21st to end	Night	32% 11% 31% 23% 4	880

Page generated at 2025-02-03 03:05:53. Version ac07

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