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 2024-08-30.

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	16% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	95966
	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 34%	93037
Transparency	Day	50% 7% 11% 20% 11% 1	95737
	Night	49% 6% 11% 20% 12% 2	92871
Seeing	Day	19% 10% 26% 23% 16% 7%	14979
	Night	19% 8% 27% 30% 14% 2	24627

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% 19% 8% 13% 5% 5% 4 3 4 5% 15%	2836
	11th to 20th	Day	16% 22% 6% 11% 5% 7% 8% 3 3 4 15%	2840
	21st to end	Day	27% 20% 10% 10% 6% 6% 3 2 3 3 10%	3124
February	1st to 10th	Day	19% 16% 5% 11% 8% 4 3 3 4 4 24%	1710
	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	8% 4 3 7% 5% 5% 5% 4 7% 11% 40%	2457
	11th to 20th	Day	10% 6% 2 7% 6% 5% 6% 6% 7% 10% 36%	2433
	21st to end	Day	8% 5% 2 6% 4 4 6% 4 7% 10% 44%	2660
September	1st to 10th	Day	13% 5% 2 4 4 4 5% 4 5% 7% 46%	1990
	11th to 20th	Day	10% 6% 2 5% 5% 5% 4 4 6% 9% 45%	1980
	21st to end	Day	17% 7% 2 5% 4 4 4 3 5% 7% 43%	1980
October	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 6% 7% 41%	1926
	11th to 20th	Day	16% 8% 2 7% 4 4 4 4 5% 6% 40%	1800
	21st to end	Day	21% 11% 3 7% 4 4 5% 3 5% 6% 31%	1918
November	1st to 10th	Day	11% 8% 3 6% 5% 4 4 3 4 6% 45%	1672
	11th to 20th	Day	17% 13% 4 6% 6% 3 4 2 4 6% 35%	1710
	21st to end	Day	19% 13% 6% 9% 5% 3 4 3 4 6% 29%	1710
December	1st to 10th	Day	20% 17% 7% 10% 6% 4 4 3 4 5% 18%	1710
	11th to 20th	Day	19% 16% 6% 10% 6% 5% 5% 3 4 5% 22%	2153
	21st to end	Day	25% 22% 7% 10% 6% 4 4 3 3 5% 10%	3124
January	1st to 10th	Night	17% 19% 8% 14% 5% 5% 4 3 4 4 18%	4109
	11th to 20th	Night	15% 18% 7% 15% 6% 5% 6% 4 3 4 15%	4120
	21st to end	Night	27% 20% 7% 12% 6% 4 3 2 2 4 14%	4532
February	1st to 10th	Night	21% 14% 4 10% 6% 4 4 4 4 4 26%	2470
	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	6% 4 2 6% 4 5% 5% 6% 7% 10% 43%	1701
	11th to 20th	Night	9% 6% 2 7% 5% 5% 4 4 5% 8% 45%	1688
	21st to end	Night	6% 4 1 4 4 4 5% 5% 7% 8% 52%	1901
September	1st to 10th	Night	13% 6% 2 4 4 4 3 3 5% 7% 50%	1952
	11th to 20th	Night	10% 4 2 4 3 3 3 3 5% 7% 56%	1980
	21st to end	Night	13% 6% 2 5% 5% 4 4 4 5% 6% 48%	1980
October	1st to 10th	Night	11% 6% 2 5% 4 4 3 3 6% 7% 49%	2034
	11th to 20th	Night	18% 7% 2 7% 4 3 5% 4 5% 6% 40%	2160
	21st to end	Night	22% 9% 3 7% 4 3 4 4 4 5% 35%	2434
November	1st to 10th	Night	14% 7% 2 6% 3 4 4 3 5% 6% 45%	2406
	11th to 20th	Night	16% 12% 4 7% 4 4 4 3 5% 6% 35%	2470
	21st to end	Night	20% 12% 4 8% 4 4 4 4 5% 7% 28%	2470
December	1st to 10th	Night	21% 15% 7% 10% 5% 4 4 3 4 5% 22%	2470
	11th to 20th	Night	17% 15% 7% 10% 5% 4 4 3 5% 5% 25%	3042
	21st to end	Night	24% 21% 7% 10% 5% 4 3 3 3 5% 15%	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	70% 8% 8% 12% 3	2837
	11th to 20th	Day	74% 5% 9% 9% 3	2840
	21st to end	Day	81% 4 6% 6% 2	3124
February	1st to 10th	Day	64% 5% 10% 13% 7%	1710
	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	36% 9% 14% 26% 14% 1	2444
	11th to 20th	Day	38% 9% 14% 26% 11% 1	2433
	21st to end	Day	34% 9% 14% 24% 15% 4	2660
September	1st to 10th	Day	36% 7% 12% 22% 18% 4	1990
	11th to 20th	Day	36% 6% 14% 24% 17% 3	1980
	21st to end	Day	41% 6% 10% 22% 20% 1	1980
October	1st to 10th	Day	41% 8% 11% 23% 17% 1	1926
	11th to 20th	Day	44% 6% 11% 23% 15% 2	1800
	21st to end	Day	54% 6% 12% 19% 8% 1	1918
November	1st to 10th	Day	39% 5% 11% 25% 16% 2	1672
	11th to 20th	Day	52% 4 10% 21% 11% 2	1710
	21st to end	Day	58% 4 11% 17% 10% 1	1710
December	1st to 10th	Day	68% 5% 10% 14% 3	1710
	11th to 20th	Day	63% 6% 10% 16% 5%	2150
	21st to end	Day	77% 7% 7% 6% 3	3124
January	1st to 10th	Night	69% 6% 7% 12% 5%	4109
	11th to 20th	Night	73% 6% 9% 10% 2	4120
	21st to end	Night	75% 4 6% 10% 3 1	4532
February	1st to 10th	Night	62% 5% 10% 16% 7% 1	2470
	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	31% 10% 17% 26% 15% 1	1690
	11th to 20th	Night	36% 8% 13% 25% 17% 1	1688
	21st to end	Night	27% 9% 16% 25% 20% 4	1901
September	1st to 10th	Night	34% 7% 12% 24% 18% 6%	1952
	11th to 20th	Night	29% 5% 11% 28% 24% 3	1980
	21st to end	Night	37% 6% 11% 20% 24% 2	1980
October	1st to 10th	Night	34% 6% 12% 25% 20% 2	2034
	11th to 20th	Night	44% 7% 8% 25% 15% 1	2160
	21st to end	Night	50% 5% 9% 21% 12% 2	2434
November	1st to 10th	Night	39% 5% 12% 23% 18% 3	2406
	11th to 20th	Night	50% 5% 8% 21% 13% 2	2470
	21st to end	Night	56% 6% 11% 19% 7% 1	2470
December	1st to 10th	Night	65% 4 9% 16% 6%	2470
	11th to 20th	Night	60% 6% 12% 17% 5%	3044
	21st to end	Night	73% 5% 9% 10% 3	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	29% 15% 33% 16% 6% 1	270
	11th to 20th	Day	25% 17% 42% 11% 4	270
	21st to end	Day	33% 13% 31% 17% 6% 1	297
February	1st to 10th	Day	29% 17% 35% 16% 3 1	270
	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% 17%	532
September	1st to 10th	Day	14% 3 16% 25% 28% 14%	450
	11th to 20th	Day	10% 3 13% 25% 32% 17%	450
	21st to end	Day	20% 8% 19% 26% 18% 10%	450
October	1st to 10th	Day	13% 8% 22% 28% 20% 9%	450
	11th to 20th	Day	15% 15% 31% 24% 13% 2	450
	21st to end	Day	27% 12% 32% 21% 8%	433
November	1st to 10th	Day	14% 13% 33% 25% 11% 5%	270
	11th to 20th	Day	23% 16% 30% 18% 12% 1	270
	21st to end	Day	27% 14% 37% 18% 4	270
December	1st to 10th	Day	25% 15% 35% 17% 6% 2	270
	11th to 20th	Day	23% 16% 40% 18% 3	270
	21st to end	Day	34% 15% 29% 19% 4	297
January	1st to 10th	Night	24% 14% 36% 22% 3	760
	11th to 20th	Night	29% 14% 34% 19% 4 1	760
	21st to end	Night	26% 12% 33% 25% 3	836
February	1st to 10th	Night	27% 10% 34% 26% 3	760
	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% 2 12% 38% 33% 7%	624
September	1st to 10th	Night	15% 2 14% 33% 31% 5%	692
	11th to 20th	Night	12% 3 12% 34% 34% 5%	720
	21st to end	Night	14% 5% 21% 32% 24% 3	720
October	1st to 10th	Night	13% 4 23% 35% 21% 4	720
	11th to 20th	Night	20% 7% 30% 30% 12% 1	720
	21st to end	Night	25% 12% 27% 27% 9%	792
November	1st to 10th	Night	19% 7% 26% 32% 15% 1	740
	11th to 20th	Night	22% 12% 30% 27% 8% 1	760
	21st to end	Night	24% 10% 30% 29% 6%	760
December	1st to 10th	Night	27% 11% 32% 25% 5%	760
	11th to 20th	Night	25% 10% 35% 25% 5%	760
	21st to end	Night	31% 12% 31% 23% 4	836

Page generated at 2024-08-27 09:49:43. Version ac07

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