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 2026-06-01.

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	15% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	132976
	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 33%	130186
Transparency	Day	50% 6% 11% 21% 11% 1	136621
	Night	50% 5% 10% 20% 12% 2	134611
Seeing	Day	19% 10% 26% 22% 16% 7%	17299
	Night	19% 8% 27% 30% 14% 2	26982

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	17% 19% 7% 15% 7% 5% 4 3 5% 5% 12%	5258
	11th to 20th	Day	13% 19% 6% 14% 8% 7% 6% 3 3 4 17%	5280
	21st to end	Day	19% 15% 7% 12% 8% 7% 4 4 4 5% 14%	5780
February	1st to 10th	Day	18% 16% 5% 11% 7% 4 3 3 4 5% 23%	1890
	11th to 20th	Day	16% 13% 6% 14% 7% 3 4 3 5% 5% 23%	2016
	21st to end	Day	17% 15% 5% 10% 5% 4 4 3 4 7% 28%	1730
March	1st to 10th	Day	17% 13% 7% 12% 5% 4 4 3 4 5% 26%	4786
	11th to 20th	Day	13% 10% 4 8% 4 4 4 3 5% 6% 39%	5090
	21st to end	Day	20% 11% 4 9% 5% 5% 4 3 4 6% 30%	5586
April	1st to 10th	Day	16% 13% 3 9% 5% 4 4 3 4 7% 31%	2365
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 3 5% 6% 35%	2658
	21st to end	Day	17% 9% 3 8% 5% 5% 5% 3 5% 6% 34%	2730
May	1st to 10th	Day	22% 9% 3 8% 5% 5% 5% 4 5% 5% 28%	5992
	11th to 20th	Day	19% 9% 3 7% 5% 4 4 3 5% 8% 33%	5991
	21st to end	Day	17% 7% 2 6% 4 4 5% 5% 7% 8% 34%	6576
June	1st to 10th	Day	12% 7% 2 7% 6% 5% 5% 4 6% 9% 37%	2600
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 4 6% 9% 37%	2665
	21st to end	Day	11% 5% 2 6% 5% 6% 5% 4 7% 10% 38%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	6278
	11th to 20th	Day	11% 6% 2 6% 4 5% 6% 5% 8% 11% 36%	5900
	21st to end	Day	11% 7% 2 7% 4 5% 5% 4 7% 10% 37%	6424
August	1st to 10th	Day	8% 5% 3 7% 5% 6% 5% 5% 6% 10% 39%	4234
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 6% 8% 10% 37%	4174
	21st to end	Day	7% 4 2 6% 5% 4 6% 5% 7% 10% 44%	4613
September	1st to 10th	Day	12% 5% 2 4 4 4 4 3 5% 7% 49%	2210
	11th to 20th	Day	9% 6% 2 4 5% 5% 4 4 6% 9% 48%	2200
	21st to end	Day	18% 7% 2 6% 4 4 3 3 5% 6% 41%	2200
October	1st to 10th	Day	14% 6% 2 6% 3 4 4 3 5% 7% 45%	2140
	11th to 20th	Day	15% 8% 2 6% 4 4 4 4 5% 6% 43%	2000
	21st to end	Day	21% 11% 3 6% 4 4 5% 3 5% 6% 32%	2130
November	1st to 10th	Day	12% 8% 3 6% 5% 4 4 3 5% 6% 44%	1852
	11th to 20th	Day	17% 12% 4 6% 6% 4 4 3 4 6% 34%	1890
	21st to end	Day	19% 14% 7% 9% 5% 3 4 3 4 5% 28%	1890
December	1st to 10th	Day	20% 13% 6% 16% 5% 4 4 2 4 5% 22%	3020
	11th to 20th	Day	23% 16% 7% 10% 5% 4 4 3 3 4 21%	3463
	21st to end	Day	26% 21% 6% 11% 6% 4 4 2 3 4 13%	4565
January	1st to 10th	Night	15% 18% 7% 18% 6% 5% 5% 3 4 4 16%	7635
	11th to 20th	Night	11% 17% 9% 16% 8% 7% 6% 3 3 4 15%	7680
	21st to end	Night	18% 15% 5% 10% 6% 5% 4 3 4 6% 24%	8401
February	1st to 10th	Night	19% 13% 4 10% 6% 5% 4 3 4 4 26%	2730
	11th to 20th	Night	17% 13% 5% 9% 7% 6% 5% 3 5% 6% 25%	2489
	21st to end	Night	19% 14% 5% 11% 4 5% 4 2 4 5% 27%	2076
March	1st to 10th	Night	20% 13% 4 7% 4 4 4 3 5% 5% 33%	5273
	11th to 20th	Night	13% 8% 3 6% 4 4 4 3 6% 8% 41%	5090
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 6% 36%	5588
April	1st to 10th	Night	18% 10% 2 7% 5% 4 4 4 5% 7% 34%	2273
	11th to 20th	Night	15% 8% 2 7% 5% 4 5% 4 5% 8% 36%	1909
	21st to end	Night	16% 9% 3 8% 4 3 4 4 6% 7% 37%	1890
May	1st to 10th	Night	24% 10% 3 8% 4 5% 4 4 5% 6% 28%	4123
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 9% 37%	4122
	21st to end	Night	14% 7% 2 6% 5% 4 5% 4 6% 9% 39%	4520
June	1st to 10th	Night	9% 6% 2 6% 4 6% 4 4 6% 8% 45%	1800
	11th to 20th	Night	9% 6% 2 5% 5% 5% 4 4 8% 10% 43%	1726
	21st to end	Night	10% 5% 2 4 5% 4 5% 4 7% 9% 45%	1600
July	1st to 10th	Night	11% 6% 2 6% 4 4 5% 4 5% 8% 45%	3679
	11th to 20th	Night	10% 5% 2 7% 5% 5% 5% 5% 7% 9% 42%	4057
	21st to end	Night	9% 6% 3 7% 5% 4 5% 4 6% 8% 43%	4427
August	1st to 10th	Night	9% 6% 2 8% 4 5% 5% 5% 7% 10% 39%	2915
	11th to 20th	Night	10% 8% 3 8% 5% 4 4 3 5% 7% 44%	2875
	21st to end	Night	4 4 1 5% 5% 5% 6% 5% 7% 8% 50%	3281
September	1st to 10th	Night	11% 5% 2 4 3 4 3 3 5% 7% 52%	2170
	11th to 20th	Night	9% 4 2 4 3 3 3 3 5% 7% 57%	2200
	21st to end	Night	15% 6% 2 5% 5% 4 4 4 5% 6% 45%	2200
October	1st to 10th	Night	11% 6% 2 5% 4 4 3 3 6% 6% 51%	2260
	11th to 20th	Night	16% 7% 2 6% 4 3 4 4 5% 6% 43%	2400
	21st to end	Night	20% 8% 3 6% 4 3 4 4 4 6% 37%	2706
November	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 5% 6% 46%	2666
	11th to 20th	Night	17% 12% 3 7% 4 4 4 3 5% 6% 35%	2730
	21st to end	Night	20% 13% 4 8% 5% 4 4 4 5% 6% 27%	2730
December	1st to 10th	Night	18% 12% 6% 10% 5% 5% 6% 4 5% 7% 23%	4380
	11th to 20th	Night	18% 18% 7% 11% 5% 4 4 3 4 5% 21%	4952
	21st to end	Night	24% 21% 6% 10% 5% 4 3 3 4 5% 15%	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	74% 5% 10% 9% 2	5259
	11th to 20th	Day	72% 4 7% 8% 9%	5280
	21st to end	Day	73% 4 7% 11% 4	5780
February	1st to 10th	Day	64% 5% 10% 14% 7%	1890
	11th to 20th	Day	63% 5% 8% 16% 7% 1	2026
	21st to end	Day	57% 5% 12% 18% 6% 2	1730
March	1st to 10th	Day	61% 5% 7% 21% 6%	4786
	11th to 20th	Day	45% 6% 10% 29% 9% 1	5090
	21st to end	Day	55% 6% 10% 21% 8% 1	5586
April	1st to 10th	Day	53% 6% 12% 17% 11% 1	2365
	11th to 20th	Day	49% 5% 12% 19% 13% 2	2658
	21st to end	Day	49% 6% 11% 21% 11% 2	2730
May	1st to 10th	Day	56% 7% 10% 16% 9% 2	6027
	11th to 20th	Day	49% 6% 13% 22% 10% 1	5995
	21st to end	Day	43% 8% 12% 23% 11% 3	6590
June	1st to 10th	Day	42% 8% 10% 24% 15% 1	2600
	11th to 20th	Day	42% 8% 15% 21% 13% 1	2665
	21st to end	Day	38% 9% 14% 21% 15% 3	2800
July	1st to 10th	Day	39% 6% 10% 29% 15% 2	6210
	11th to 20th	Day	40% 6% 15% 24% 14% 1	5831
	21st to end	Day	40% 6% 13% 21% 18% 3	6240
August	1st to 10th	Day	38% 7% 16% 25% 13% 1	4221
	11th to 20th	Day	36% 8% 11% 30% 14% 1	4213
	21st to end	Day	33% 8% 13% 31% 12% 2	4612
September	1st to 10th	Day	34% 7% 12% 23% 21% 4	2210
	11th to 20th	Day	34% 6% 13% 25% 20% 3	2200
	21st to end	Day	43% 6% 10% 20% 20% 1	2200
October	1st to 10th	Day	27% 5% 10% 34% 23% 1	3491
	11th to 20th	Day	36% 4 10% 27% 21% 3	3240
	21st to end	Day	42% 4 11% 24% 18% 2	3419
November	1st to 10th	Day	40% 5% 11% 25% 16% 2	1852
	11th to 20th	Day	52% 4 10% 21% 10% 2	1890
	21st to end	Day	60% 4 10% 17% 9% 1	1890
December	1st to 10th	Day	66% 4 13% 14% 3	3020
	11th to 20th	Day	67% 4 11% 13% 4	3460
	21st to end	Day	76% 5% 6% 8% 4	4565
January	1st to 10th	Night	72% 4 8% 13% 3	7636
	11th to 20th	Night	73% 4 7% 9% 5% 1	7680
	21st to end	Night	63% 3 11% 16% 6% 1	8401
February	1st to 10th	Night	61% 5% 10% 17% 7% 1	2730
	11th to 20th	Night	59% 6% 10% 16% 9% 1	2490
	21st to end	Night	61% 4 10% 15% 8% 2	2076
March	1st to 10th	Night	53% 5% 9% 23% 9% 1	5273
	11th to 20th	Night	40% 5% 11% 32% 10% 1	5090
	21st to end	Night	50% 5% 9% 22% 14% 1	5588
April	1st to 10th	Night	48% 6% 11% 19% 13% 2	2273
	11th to 20th	Night	44% 7% 13% 16% 17% 3	1909
	21st to end	Night	45% 7% 11% 20% 16% 1	1890
May	1st to 10th	Night	55% 7% 10% 15% 10% 3	4150
	11th to 20th	Night	45% 6% 9% 24% 14% 1	4123
	21st to end	Night	40% 8% 13% 26% 11% 2	4528
June	1st to 10th	Night	36% 7% 13% 22% 20% 2	1800
	11th to 20th	Night	34% 8% 15% 25% 15% 3	1726
	21st to end	Night	33% 9% 14% 24% 18% 3	1600
July	1st to 10th	Night	36% 5% 12% 26% 17% 4	3640
	11th to 20th	Night	37% 7% 15% 27% 13% 1	4006
	21st to end	Night	38% 5% 14% 20% 19% 3	4297
August	1st to 10th	Night	38% 8% 15% 26% 12% 1	2904
	11th to 20th	Night	40% 5% 9% 26% 19%	2902
	21st to end	Night	29% 7% 15% 30% 17% 2	3281
September	1st to 10th	Night	32% 6% 11% 25% 20% 6%	2170
	11th to 20th	Night	27% 5% 10% 29% 25% 4	2200
	21st to end	Night	40% 6% 10% 19% 24% 1	2200
October	1st to 10th	Night	25% 4 8% 30% 32% 2	3689
	11th to 20th	Night	32% 5% 10% 28% 22% 5%	3899
	21st to end	Night	36% 4 8% 27% 21% 4	4367
November	1st to 10th	Night	39% 5% 11% 24% 18% 3	2666
	11th to 20th	Night	50% 5% 8% 22% 13% 3	2730
	21st to end	Night	57% 6% 11% 19% 7% 1	2730
December	1st to 10th	Night	61% 4 12% 18% 6%	4380
	11th to 20th	Night	66% 4 13% 12% 5%	4954
	21st to end	Night	73% 4 8% 11% 3	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	29% 15% 35% 15% 6% 1	330
	11th to 20th	Day	24% 21% 41% 10% 4	330
	21st to end	Day	30% 16% 32% 17% 5% 1	363
February	1st to 10th	Day	26% 15% 37% 17% 3 1	330
	11th to 20th	Day	26% 20% 36% 16% 2	330
	21st to end	Day	23% 20% 42% 12% 2	273
March	1st to 10th	Day	22% 17% 35% 21% 5%	419
	11th to 20th	Day	24% 16% 36% 17% 5% 1	540
	21st to end	Day	28% 15% 32% 20% 5%	594
April	1st to 10th	Day	24% 14% 32% 20% 9% 1	540
	11th to 20th	Day	21% 15% 29% 21% 9% 4	532
	21st to end	Day	21% 12% 32% 22% 10% 4	540
May	1st to 10th	Day	27% 10% 31% 19% 10% 3	543
	11th to 20th	Day	23% 8% 24% 26% 14% 6%	567
	21st to end	Day	17% 7% 23% 23% 21% 9%	617
June	1st to 10th	Day	13% 6% 21% 32% 22% 7%	530
	11th to 20th	Day	15% 6% 21% 29% 23% 7%	595
	21st to end	Day	13% 6% 25% 27% 22% 8%	730
July	1st to 10th	Day	12% 3 15% 28% 25% 18%	692
	11th to 20th	Day	14% 2 18% 24% 26% 16%	524
	21st to end	Day	12% 2 17% 23% 30% 16%	576
August	1st to 10th	Day	10% 3 13% 25% 31% 17%	526
	11th to 20th	Day	13% 4 16% 28% 25% 14%	519
	21st to end	Day	9% 4 15% 25% 32% 16%	583
September	1st to 10th	Day	12% 4 15% 26% 28% 14%	530
	11th to 20th	Day	9% 3 12% 25% 33% 19%	530
	21st to end	Day	22% 7% 17% 25% 18% 11%	530
October	1st to 10th	Day	12% 7% 21% 29% 21% 10%	530
	11th to 20th	Day	14% 13% 30% 25% 14% 4	530
	21st to end	Day	25% 11% 34% 22% 8% 1	513
November	1st to 10th	Day	16% 12% 34% 24% 10% 4	330
	11th to 20th	Day	24% 17% 31% 17% 10% 1	330
	21st to end	Day	28% 14% 38% 16% 4	330
December	1st to 10th	Day	24% 15% 38% 16% 5% 2	330
	11th to 20th	Day	25% 17% 39% 17% 3	330
	21st to end	Day	34% 13% 30% 20% 3	363
January	1st to 10th	Night	24% 15% 36% 22% 3	840
	11th to 20th	Night	27% 15% 35% 18% 3	840
	21st to end	Night	25% 13% 35% 24% 3	924
February	1st to 10th	Night	25% 11% 34% 28% 3	840
	11th to 20th	Night	24% 13% 36% 25% 2	823
	21st to end	Night	25% 12% 40% 20% 2	692
March	1st to 10th	Night	25% 12% 32% 25% 6%	840
	11th to 20th	Night	21% 11% 35% 25% 6% 1	840
	21st to end	Night	23% 11% 34% 25% 6%	924
April	1st to 10th	Night	22% 12% 35% 25% 6%	803
	11th to 20th	Night	18% 10% 36% 25% 9% 1	623
	21st to end	Night	20% 7% 38% 26% 8% 1	630
May	1st to 10th	Night	23% 6% 29% 31% 10%	630
	11th to 20th	Night	21% 7% 26% 34% 12% 1	621
	21st to end	Night	13% 3 21% 39% 23% 2	683
June	1st to 10th	Night	10% 3 23% 42% 21% 1	600
	11th to 20th	Night	12% 2 17% 45% 22% 2	600
	21st to end	Night	10% 1 20% 42% 25% 2	600
July	1st to 10th	Night	11% 3 11% 39% 30% 6%	585
	11th to 20th	Night	8% 4 14% 37% 33% 5%	582
	21st to end	Night	9% 4 11% 41% 34% 2	657
August	1st to 10th	Night	7% 2 12% 44% 31% 5%	597
	11th to 20th	Night	11% 2 10% 40% 32% 4	594
	21st to end	Night	7% 2 12% 39% 33% 7%	660
September	1st to 10th	Night	14% 2 15% 35% 30% 5%	770
	11th to 20th	Night	11% 3 11% 36% 34% 5%	800
	21st to end	Night	17% 5% 20% 32% 23% 3	800
October	1st to 10th	Night	13% 4 23% 35% 22% 4	800
	11th to 20th	Night	19% 7% 30% 32% 13% 1	800
	21st to end	Night	23% 11% 29% 28% 9%	880
November	1st to 10th	Night	18% 7% 28% 31% 14% 1	820
	11th to 20th	Night	22% 13% 30% 27% 7% 1	840
	21st to end	Night	25% 10% 30% 28% 6%	840
December	1st to 10th	Night	27% 10% 34% 24% 5%	840
	11th to 20th	Night	25% 10% 35% 25% 4	840
	21st to end	Night	32% 11% 31% 22% 3	924

Page generated at 2026-05-29 01:53:31. Version ac07

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