Cat's Eye Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cat's Eye 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	10% 6% 2 5% 4 4 4 3 5% 7% 49%	132524
	Night	11% 6% 2 5% 3 3 3 3 5% 7% 53%	130973
Transparency	Day	32% 6% 10% 20% 20% 12%	136342
	Night	31% 5% 10% 20% 21% 14%	135219
Seeing	Day	12% 9% 25% 30% 18% 5%	16880
	Night	12% 9% 31% 35% 13% 1	26874

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% 6% 3 5% 2 3 3 3 4 5% 57%	5289
	11th to 20th	Day	11% 7% 2 4 3 2 3 2 4 5% 57%	5310
	21st to end	Day	19% 6% 2 6% 4 3 3 2 4 6% 46%	6446
February	1st to 10th	Day	14% 6% 2 6% 3 3 3 3 5% 5% 51%	2100
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 4 6% 48%	2049
	21st to end	Day	12% 7% 2 4 2 3 3 3 4 6% 54%	1730
March	1st to 10th	Day	10% 6% 2 5% 3 3 3 2 5% 6% 56%	4855
	11th to 20th	Day	11% 7% 2 6% 3 3 3 2 4 5% 55%	5090
	21st to end	Day	10% 6% 2 6% 4 4 4 3 5% 7% 51%	5583
April	1st to 10th	Day	11% 7% 2 6% 5% 4 4 4 5% 7% 45%	2310
	11th to 20th	Day	16% 6% 2 6% 4 3 4 3 5% 6% 45%	2405
	21st to end	Day	11% 7% 2 5% 6% 4 4 3 4 5% 47%	2611
May	1st to 10th	Day	16% 6% 2 6% 4 4 4 4 6% 7% 39%	5992
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 6% 9% 45%	5992
	21st to end	Day	13% 6% 2 7% 4 5% 5% 5% 7% 8% 37%	6577
June	1st to 10th	Day	5% 4 2 5% 5% 4 5% 4 6% 9% 51%	2601
	11th to 20th	Day	5% 5% 2 5% 5% 4 4 4 7% 9% 50%	2600
	21st to end	Day	6% 4 2 5% 6% 5% 6% 5% 7% 9% 45%	2600
July	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 6% 8% 37%	5900
	11th to 20th	Day	4 4 2 5% 4 5% 5% 4 7% 10% 49%	5900
	21st to end	Day	6% 5% 2 5% 4 5% 5% 4 8% 10% 47%	6422
August	1st to 10th	Day	1 1 1 3 3 3 4 3 5% 9% 67%	4047
	11th to 20th	Day	4 2 1 3 3 4 4 4 5% 10% 60%	3846
	21st to end	Day	3 4 2 5% 5% 6% 6% 5% 7% 10% 47%	4231
September	1st to 10th	Day	9% 6% 3 8% 6% 5% 4 3 5% 6% 47%	2200
	11th to 20th	Day	9% 7% 2 7% 5% 5% 5% 4 6% 8% 43%	2200
	21st to end	Day	9% 3 2 5% 4 4 5% 4 7% 7% 50%	2200
October	1st to 10th	Day	5% 4 1 5% 4 4 4 3 5% 7% 58%	2200
	11th to 20th	Day	10% 5% 2 4 4 3 3 3 4 6% 55%	2128
	21st to end	Day	10% 5% 2 4 3 3 3 3 3 5% 60%	2200
November	1st to 10th	Day	13% 6% 2 5% 4 3 3 3 5% 5% 51%	2032
	11th to 20th	Day	8% 5% 2 5% 3 3 5% 3 5% 6% 55%	1890
	21st to end	Day	13% 7% 3 6% 4 3 3 2 3 6% 49%	1890
December	1st to 10th	Day	19% 10% 3 7% 3 2 2 2 4 4 43%	3030
	11th to 20th	Day	11% 9% 3 7% 4 3 4 3 5% 6% 46%	3481
	21st to end	Day	10% 6% 2 5% 3 2 3 2 3 4 61%	4587
January	1st to 10th	Night	11% 5% 2 6% 3 2 3 2 3 5% 58%	7634
	11th to 20th	Night	8% 4 2 3 2 2 2 2 4 6% 65%	7680
	21st to end	Night	24% 7% 2 5% 3 3 3 2 4 5% 43%	7824
February	1st to 10th	Night	12% 7% 2 6% 4 3 2 3 4 4 53%	2520
	11th to 20th	Night	14% 6% 2 5% 3 4 3 3 4 6% 50%	2458
	21st to end	Night	13% 7% 2 5% 4 3 3 3 4 6% 51%	2076
March	1st to 10th	Night	10% 8% 2 5% 3 4 4 3 5% 8% 48%	5225
	11th to 20th	Night	11% 8% 2 4 3 3 3 3 4 5% 53%	5090
	21st to end	Night	11% 10% 2 5% 3 2 3 3 4 6% 50%	5588
April	1st to 10th	Night	9% 7% 3 6% 4 4 4 3 5% 6% 49%	2310
	11th to 20th	Night	14% 8% 2 5% 4 3 3 3 4 6% 47%	2159
	21st to end	Night	14% 8% 2 5% 4 4 3 3 4 6% 48%	2006
May	1st to 10th	Night	19% 10% 3 5% 4 3 3 3 4 6% 40%	4143
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 6% 7% 50%	4143
	21st to end	Night	12% 8% 2 6% 4 4 4 4 6% 9% 41%	4542
June	1st to 10th	Night	3 4 2 3 3 2 4 3 7% 10% 60%	1800
	11th to 20th	Night	4 4 1 4 2 3 4 3 5% 8% 61%	1800
	21st to end	Night	5% 4 1 4 3 4 4 4 7% 8% 55%	1800
July	1st to 10th	Night	9% 6% 3 6% 4 4 5% 4 6% 10% 43%	4078
	11th to 20th	Night	3 3 1 5% 3 4 4 4 6% 10% 57%	4077
	21st to end	Night	5% 6% 2 6% 3 4 5% 4 7% 10% 50%	4449
August	1st to 10th	Night	1 1 2 2 2 3 3 4 6% 76%	3107
	11th to 20th	Night	3 2 1 3 2 3 4 4 6% 10% 62%	3213
	21st to end	Night	3 5% 1 5% 3 3 4 4 7% 10% 54%	3661
September	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 3 6% 8% 51%	2200
	11th to 20th	Night	8% 7% 2 6% 4 4 5% 3 6% 8% 48%	2200
	21st to end	Night	7% 5% 2 4 4 3 5% 3 6% 8% 53%	2200
October	1st to 10th	Night	4 4 1 4 3 3 3 3 4 7% 65%	2200
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 4 6% 58%	2250
	21st to end	Night	12% 5% 2 4 2 2 3 2 3 3 62%	2640
November	1st to 10th	Night	11% 6% 2 6% 3 3 2 2 3 5% 57%	2481
	11th to 20th	Night	8% 5% 1 5% 3 3 3 3 5% 6% 59%	2730
	21st to end	Night	14% 6% 2 5% 3 3 4 3 5% 6% 50%	2730
December	1st to 10th	Night	19% 8% 3 5% 3 4 4 3 4 5% 43%	4380
	11th to 20th	Night	15% 10% 2 5% 3 2 3 2 3 5% 48%	4946
	21st to end	Night	12% 7% 2 4 2 2 2 2 3 4 60%	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	29% 4 6% 22% 26% 13%	5290
	11th to 20th	Day	30% 3 4 15% 27% 21%	5310
	21st to end	Day	41% 3 5% 13% 25% 12%	6446
February	1st to 10th	Day	36% 4 7% 12% 21% 19%	2100
	11th to 20th	Day	37% 4 7% 19% 19% 15%	2059
	21st to end	Day	33% 3 6% 17% 24% 17%	1730
March	1st to 10th	Day	30% 4 6% 16% 18% 27%	4855
	11th to 20th	Day	33% 5% 6% 9% 15% 33%	5090
	21st to end	Day	33% 6% 8% 18% 21% 15%	5585
April	1st to 10th	Day	38% 5% 10% 16% 17% 14%	2310
	11th to 20th	Day	40% 5% 8% 15% 20% 12%	2405
	21st to end	Day	39% 6% 7% 20% 18% 11%	2611
May	1st to 10th	Day	40% 8% 10% 17% 18% 7%	6030
	11th to 20th	Day	34% 6% 12% 15% 21% 12%	5996
	21st to end	Day	40% 8% 11% 24% 13% 3	6590
June	1st to 10th	Day	28% 7% 14% 28% 20% 3	2601
	11th to 20th	Day	29% 7% 12% 24% 22% 6%	2600
	21st to end	Day	33% 10% 12% 23% 17% 5%	2600
July	1st to 10th	Day	42% 7% 17% 28% 6%	5836
	11th to 20th	Day	27% 8% 16% 32% 14% 2	5831
	21st to end	Day	28% 8% 18% 26% 19% 1	6240
August	1st to 10th	Day	14% 5% 12% 38% 30% 1	4033
	11th to 20th	Day	19% 6% 22% 38% 12% 2	3882
	21st to end	Day	28% 11% 17% 24% 18% 2	4230
September	1st to 10th	Day	38% 7% 9% 19% 18% 9%	2200
	11th to 20th	Day	37% 7% 12% 19% 19% 5%	2200
	21st to end	Day	30% 7% 10% 20% 19% 13%	2200
October	1st to 10th	Day	16% 4 7% 12% 27% 35%	3590
	11th to 20th	Day	24% 4 6% 19% 24% 22%	3446
	21st to end	Day	23% 5% 6% 17% 37% 13%	3538
November	1st to 10th	Day	36% 4 8% 17% 23% 13%	2032
	11th to 20th	Day	30% 5% 8% 17% 21% 19%	1890
	21st to end	Day	38% 4 5% 17% 22% 14%	1890
December	1st to 10th	Day	46% 3 6% 16% 19% 10%	3030
	11th to 20th	Day	38% 6% 8% 10% 23% 14%	3479
	21st to end	Day	28% 3 4 15% 27% 21%	4587
January	1st to 10th	Night	30% 3 6% 18% 28% 15%	7635
	11th to 20th	Night	22% 2 4 16% 30% 26%	7680
	21st to end	Night	45% 3 4 9% 23% 16%	7824
February	1st to 10th	Night	34% 3 8% 11% 23% 20%	2520
	11th to 20th	Night	35% 4 7% 19% 20% 16%	2458
	21st to end	Night	36% 4 6% 12% 23% 19%	2076
March	1st to 10th	Night	32% 5% 7% 18% 20% 17%	5225
	11th to 20th	Night	33% 6% 5% 11% 16% 29%	5090
	21st to end	Night	34% 5% 8% 18% 19% 15%	5588
April	1st to 10th	Night	35% 5% 10% 18% 15% 17%	2310
	11th to 20th	Night	39% 5% 9% 14% 18% 15%	2159
	21st to end	Night	38% 6% 10% 17% 19% 10%	2006
May	1st to 10th	Night	44% 6% 9% 17% 13% 10%	4170
	11th to 20th	Night	31% 7% 13% 17% 18% 14%	4144
	21st to end	Night	38% 7% 14% 26% 11% 4	4551
June	1st to 10th	Night	19% 9% 16% 34% 20% 3	1800
	11th to 20th	Night	21% 6% 16% 29% 22% 6%	1800
	21st to end	Night	25% 7% 17% 29% 18% 4	1800
July	1st to 10th	Night	35% 9% 22% 29% 5%	4035
	11th to 20th	Night	21% 8% 21% 34% 15% 1	4026
	21st to end	Night	27% 8% 22% 26% 14% 3	4320
August	1st to 10th	Night	10% 5% 14% 42% 28% 1	3097
	11th to 20th	Night	16% 7% 28% 35% 11% 2	3243
	21st to end	Night	24% 11% 20% 24% 19% 2	3661
September	1st to 10th	Night	31% 7% 13% 23% 18% 9%	2200
	11th to 20th	Night	33% 8% 15% 22% 16% 6%	2200
	21st to end	Night	28% 7% 12% 22% 18% 14%	2200
October	1st to 10th	Night	13% 3 9% 15% 23% 37%	3590
	11th to 20th	Night	22% 3 9% 17% 29% 20%	3658
	21st to end	Night	24% 4 5% 19% 34% 15%	4252
November	1st to 10th	Night	31% 4 7% 19% 24% 15%	2481
	11th to 20th	Night	27% 4 8% 21% 22% 19%	2730
	21st to end	Night	36% 4 8% 16% 20% 16%	2730
December	1st to 10th	Night	43% 4 7% 15% 17% 12%	4380
	11th to 20th	Night	40% 4 5% 12% 20% 19%	4947
	21st to end	Night	30% 3 4 16% 29% 18%	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	18% 15% 42% 20% 5% 1	330
	11th to 20th	Day	21% 15% 36% 21% 6% 1	330
	21st to end	Day	16% 19% 40% 20% 4	363
February	1st to 10th	Day	23% 13% 35% 22% 7%	330
	11th to 20th	Day	21% 17% 39% 20% 2	330
	21st to end	Day	19% 19% 42% 16% 3	273
March	1st to 10th	Day	19% 20% 41% 18% 2	330
	11th to 20th	Day	18% 20% 36% 19% 6%	330
	21st to end	Day	15% 18% 41% 20% 4 1	363
April	1st to 10th	Day	16% 21% 40% 20% 3	330
	11th to 20th	Day	19% 21% 39% 17% 4	443
	21st to end	Day	16% 19% 42% 19% 5%	631
May	1st to 10th	Day	15% 14% 41% 26% 4	753
	11th to 20th	Day	17% 12% 35% 26% 10% 1	775
	21st to end	Day	14% 10% 32% 32% 12% 1	844
June	1st to 10th	Day	5% 3 25% 43% 21% 3	731
	11th to 20th	Day	7% 2 21% 50% 16% 2	730
	21st to end	Day	6% 2 15% 41% 30% 6%	730
July	1st to 10th	Day	7% 4 13% 38% 29% 9%	721
	11th to 20th	Day	4 1 8% 43% 37% 7%	718
	21st to end	Day	4 1 6% 41% 37% 10%	794
August	1st to 10th	Day	2 4 41% 41% 12%	617
	11th to 20th	Day	7% 3 5% 34% 38% 14%	517
	21st to end	Day	4 2 7% 28% 42% 16%	541
September	1st to 10th	Day	11% 1 8% 29% 36% 15%	330
	11th to 20th	Day	5% 2 6% 33% 39% 15%	330
	21st to end	Day	11% 1 6% 33% 36% 12%	330
October	1st to 10th	Day	5% 2 15% 38% 32% 9%	330
	11th to 20th	Day	9% 5% 26% 35% 21% 4	330
	21st to end	Day	16% 15% 28% 24% 14% 2	363
November	1st to 10th	Day	20% 8% 28% 31% 11% 3	330
	11th to 20th	Day	16% 12% 28% 28% 11% 5%	330
	21st to end	Day	19% 18% 34% 19% 7% 2	330
December	1st to 10th	Day	17% 11% 36% 27% 8% 2	330
	11th to 20th	Day	16% 17% 36% 22% 7% 2	330
	21st to end	Day	15% 13% 36% 27% 9%	363
January	1st to 10th	Night	15% 11% 37% 29% 6%	1050
	11th to 20th	Night	15% 13% 38% 29% 5%	1050
	21st to end	Night	18% 13% 37% 27% 6%	950
February	1st to 10th	Night	18% 13% 37% 26% 5%	840
	11th to 20th	Night	18% 16% 40% 24% 3	824
	21st to end	Night	18% 16% 47% 19% 1	692
March	1st to 10th	Night	18% 17% 40% 24% 2	727
	11th to 20th	Night	17% 12% 40% 27% 4	630
	21st to end	Night	12% 14% 47% 24% 3	693
April	1st to 10th	Night	10% 15% 51% 22% 3	630
	11th to 20th	Night	18% 16% 43% 22% 2	623
	21st to end	Night	15% 13% 49% 18% 5%	630
May	1st to 10th	Night	14% 13% 45% 25% 3	630
	11th to 20th	Night	12% 9% 40% 31% 8% 1	621
	21st to end	Night	13% 7% 36% 34% 10%	683
June	1st to 10th	Night	3 2 30% 47% 17% 1	600
	11th to 20th	Night	5% 2 35% 46% 11%	600
	21st to end	Night	5% 4 18% 52% 21% 2	600
July	1st to 10th	Night	7% 2 12% 51% 25% 2	585
	11th to 20th	Night	3 1 12% 57% 26% 2	582
	21st to end	Night	3 1 10% 57% 26% 2	657
August	1st to 10th	Night	1 6% 60% 30% 3	597
	11th to 20th	Night	5% 1 7% 53% 31% 3	594
	21st to end	Night	4 1 9% 46% 35% 4	660
September	1st to 10th	Night	9% 1 11% 42% 34% 4	600
	11th to 20th	Night	11% 1 8% 45% 33% 2	600
	21st to end	Night	9% 1 14% 48% 27% 2	600
October	1st to 10th	Night	5% 2 16% 47% 29% 2	600
	11th to 20th	Night	11% 4 24% 43% 16% 2	650
	21st to end	Night	15% 9% 29% 30% 16% 1	880
November	1st to 10th	Night	13% 8% 26% 39% 14% 1	841
	11th to 20th	Night	10% 8% 33% 35% 13% 1	1050
	21st to end	Night	16% 11% 33% 30% 9% 1	1050
December	1st to 10th	Night	15% 10% 34% 34% 7%	1050
	11th to 20th	Night	19% 10% 34% 30% 6%	1050
	21st to end	Night	15% 11% 36% 31% 6%	1155

Page generated at 2026-05-29 00:53:27. Version ac07

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