Celestial Exploration Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Celestial Exploration Observatory clear sky chart from 2005-11-06 to 2026-04-17.

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% 6% 2 6% 4 4 4 4 6% 7% 39%	131655
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 42%	130500
Transparency	Day	41% 7% 12% 22% 15% 2	135170
	Night	41% 6% 12% 22% 16% 3	135071
Seeing	Day	21% 14% 28% 22% 11% 4	16719
	Night	19% 10% 31% 30% 10% 1	26088

By Month

Percentage Cloud Cover NE (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	13% 7% 2 6% 4 4 4 4 6% 6% 44%	4661
	11th to 20th	Day	13% 8% 4 9% 5% 5% 4 3 5% 6% 38%	4710
	21st to end	Day	15% 6% 2 7% 4 4 5% 4 6% 6% 40%	5780
February	1st to 10th	Day	15% 7% 3 7% 4 5% 5% 4 6% 7% 39%	1890
	11th to 20th	Day	15% 9% 3 6% 4 5% 5% 3 5% 6% 38%	1981
	21st to end	Day	18% 8% 3 7% 5% 4 4 4 4 6% 37%	1730
March	1st to 10th	Day	21% 6% 2 5% 4 4 4 3 5% 6% 41%	4576
	11th to 20th	Day	13% 7% 3 7% 4 5% 4 4 5% 7% 42%	5086
	21st to end	Day	18% 6% 2 5% 3 3 4 4 5% 7% 42%	5914
April	1st to 10th	Day	18% 7% 2 6% 5% 4 5% 4 5% 7% 37%	2520
	11th to 20th	Day	16% 6% 2 6% 5% 4 4 4 6% 7% 39%	2446
	21st to end	Day	16% 5% 2 7% 5% 4 4 4 6% 8% 39%	2400
May	1st to 10th	Day	27% 7% 2 6% 4 4 4 4 5% 8% 29%	5923
	11th to 20th	Day	24% 8% 3 6% 4 4 3 3 5% 7% 33%	6318
	21st to end	Day	21% 6% 2 5% 4 4 4 4 6% 9% 36%	6949
June	1st to 10th	Day	14% 6% 2 6% 5% 5% 6% 5% 6% 9% 37%	2800
	11th to 20th	Day	15% 5% 2 6% 5% 5% 5% 4 7% 9% 36%	2800
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 42%	2800
July	1st to 10th	Day	8% 6% 2 6% 5% 6% 5% 5% 7% 10% 39%	6360
	11th to 20th	Day	11% 6% 2 8% 5% 5% 6% 5% 8% 11% 33%	6360
	21st to end	Day	12% 6% 3 7% 4 5% 4 4 6% 9% 41%	6883
August	1st to 10th	Day	20% 6% 2 7% 4 4 5% 4 7% 8% 32%	4234
	11th to 20th	Day	14% 5% 2 6% 4 4 6% 4 6% 7% 42%	3886
	21st to end	Day	13% 5% 2 4 3 3 4 4 5% 8% 49%	4312
September	1st to 10th	Day	15% 5% 2 6% 4 6% 4 3 5% 7% 44%	2400
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 5% 7% 52%	2370
	21st to end	Day	19% 7% 2 6% 4 4 5% 3 5% 6% 39%	2195
October	1st to 10th	Day	18% 6% 3 5% 3 3 4 3 5% 6% 43%	2000
	11th to 20th	Day	16% 5% 2 5% 3 4 4 3 5% 7% 46%	2000
	21st to end	Day	19% 6% 2 5% 3 4 4 3 5% 8% 42%	2115
November	1st to 10th	Day	13% 6% 2 4 3 3 3 3 4 6% 51%	1851
	11th to 20th	Day	16% 7% 1 5% 4 4 4 4 6% 6% 45%	1890
	21st to end	Day	18% 7% 2 5% 4 2 4 3 6% 8% 40%	1721
December	1st to 10th	Day	17% 7% 3 6% 4 4 4 4 5% 6% 41%	2680
	11th to 20th	Day	22% 9% 2 4 3 4 3 3 5% 6% 40%	3066
	21st to end	Day	19% 7% 3 7% 5% 5% 5% 4 5% 7% 34%	4048
January	1st to 10th	Night	13% 8% 2 7% 4 4 4 3 5% 7% 43%	8234
	11th to 20th	Night	13% 8% 3 8% 5% 4 4 3 5% 7% 40%	8159
	21st to end	Night	16% 8% 2 5% 4 4 3 3 4 7% 44%	8401
February	1st to 10th	Night	15% 9% 3 6% 4 4 5% 4 5% 6% 40%	2730
	11th to 20th	Night	18% 7% 3 6% 4 5% 4 4 5% 5% 39%	2523
	21st to end	Night	17% 9% 2 5% 4 3 4 4 5% 5% 41%	2076
March	1st to 10th	Night	19% 8% 2 6% 3 3 4 3 4 5% 42%	5484
	11th to 20th	Night	13% 8% 3 5% 3 3 4 3 4 5% 49%	5089
	21st to end	Night	17% 8% 3 7% 4 4 4 3 4 5% 42%	5260
April	1st to 10th	Night	19% 6% 2 6% 6% 4 4 4 5% 7% 37%	2100
	11th to 20th	Night	16% 7% 2 7% 4 4 4 3 5% 8% 41%	2036
	21st to end	Night	20% 5% 2 4 2 3 4 3 6% 6% 45%	2000
May	1st to 10th	Night	29% 8% 2 6% 4 4 5% 4 5% 7% 28%	4045
	11th to 20th	Night	24% 8% 3 7% 5% 3 3 3 5% 6% 33%	3575
	21st to end	Night	22% 6% 2 6% 4 3 4 3 6% 8% 37%	3926
June	1st to 10th	Night	16% 6% 1 5% 5% 3 4 3 5% 8% 42%	1600
	11th to 20th	Night	14% 5% 2 6% 4 4 5% 4 8% 8% 41%	1600
	21st to end	Night	12% 5% 1 5% 5% 4 5% 5% 6% 9% 44%	1600
July	1st to 10th	Night	12% 7% 2 7% 5% 5% 5% 4 6% 10% 37%	3600
	11th to 20th	Night	15% 7% 3 8% 5% 5% 6% 4 7% 9% 32%	3600
	21st to end	Night	13% 5% 2 5% 3 4 4 4 7% 8% 44%	3965
August	1st to 10th	Night	21% 6% 3 7% 5% 4 5% 4 6% 7% 33%	2915
	11th to 20th	Night	15% 6% 2 7% 4 5% 4 4 5% 6% 41%	3130
	21st to end	Night	13% 4 2 5% 3 3 4 3 5% 8% 48%	3586
September	1st to 10th	Night	15% 6% 2 5% 5% 4 4 3 4 6% 47%	2000
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 5% 53%	2029
	21st to end	Night	18% 6% 2 6% 3 3 4 3 5% 6% 42%	2201
October	1st to 10th	Night	20% 6% 2 5% 3 3 3 3 4 6% 45%	2400
	11th to 20th	Night	16% 6% 1 4 3 3 4 3 4 6% 49%	2400
	21st to end	Night	20% 6% 2 4 3 3 3 4 4 6% 47%	2723
November	1st to 10th	Night	13% 5% 2 4 3 4 3 4 5% 5% 52%	2667
	11th to 20th	Night	16% 8% 2 5% 4 4 4 3 4 6% 46%	2730
	21st to end	Night	15% 6% 1 6% 4 4 4 4 6% 7% 43%	2898
December	1st to 10th	Night	14% 8% 3 6% 4 4 4 3 4 6% 44%	4720
	11th to 20th	Night	24% 7% 2 5% 4 3 4 3 4 5% 40%	5348
	21st to end	Night	21% 10% 3 6% 4 3 4 3 4 5% 37%	7150

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	38% 6% 12% 27% 16% 1	4662
	11th to 20th	Day	44% 5% 11% 20% 15% 5%	4740
	21st to end	Day	42% 7% 14% 22% 15% 1	5780
February	1st to 10th	Day	44% 7% 13% 23% 12% 2	1890
	11th to 20th	Day	46% 6% 10% 23% 13% 2	1990
	21st to end	Day	48% 5% 11% 23% 11% 3	1730
March	1st to 10th	Day	43% 6% 10% 23% 12% 6%	4579
	11th to 20th	Day	38% 8% 13% 27% 10% 4	5086
	21st to end	Day	40% 6% 12% 15% 22% 5%	5914
April	1st to 10th	Day	46% 6% 9% 21% 14% 5%	2520
	11th to 20th	Day	41% 7% 13% 21% 15% 3	2446
	21st to end	Day	42% 7% 11% 21% 16% 4	2400
May	1st to 10th	Day	52% 9% 13% 17% 9% 1	5933
	11th to 20th	Day	51% 7% 9% 21% 11% 1	6322
	21st to end	Day	43% 7% 12% 24% 13% 1	6949
June	1st to 10th	Day	41% 8% 14% 22% 14% 1	2800
	11th to 20th	Day	42% 9% 15% 21% 10% 2	2800
	21st to end	Day	37% 9% 14% 24% 14% 1	2800
July	1st to 10th	Day	39% 10% 13% 21% 15% 1	6290
	11th to 20th	Day	40% 11% 17% 21% 9% 1	6285
	21st to end	Day	38% 7% 11% 21% 21% 1	6685
August	1st to 10th	Day	47% 9% 13% 21% 9%	4221
	11th to 20th	Day	37% 8% 14% 28% 12% 1	3923
	21st to end	Day	33% 7% 12% 30% 17% 2	4312
September	1st to 10th	Day	39% 7% 10% 22% 19% 2	2400
	11th to 20th	Day	31% 6% 12% 24% 25% 3	2370
	21st to end	Day	47% 5% 10% 18% 18% 2	2195
October	1st to 10th	Day	37% 5% 9% 21% 23% 5%	3260
	11th to 20th	Day	28% 5% 11% 28% 24% 4	3240
	21st to end	Day	27% 4 14% 25% 26% 4	3392
November	1st to 10th	Day	34% 5% 14% 24% 20% 3	1851
	11th to 20th	Day	38% 6% 10% 26% 17% 3	1890
	21st to end	Day	39% 7% 14% 28% 10% 2	1721
December	1st to 10th	Day	43% 5% 15% 25% 10% 1	2680
	11th to 20th	Day	45% 4 16% 24% 10% 1	3066
	21st to end	Day	45% 8% 13% 20% 13% 1	4048
January	1st to 10th	Night	39% 6% 14% 23% 15% 3	8234
	11th to 20th	Night	42% 5% 12% 20% 15% 5%	8204
	21st to end	Night	39% 4 10% 24% 20% 3	8401
February	1st to 10th	Night	44% 6% 13% 24% 11% 2	2730
	11th to 20th	Night	46% 5% 10% 20% 15% 3	2525
	21st to end	Night	43% 5% 10% 23% 17% 3	2076
March	1st to 10th	Night	43% 5% 10% 22% 12% 7%	5494
	11th to 20th	Night	35% 6% 16% 26% 13% 4	5090
	21st to end	Night	44% 5% 7% 16% 23% 4	5260
April	1st to 10th	Night	44% 7% 11% 20% 14% 4	2100
	11th to 20th	Night	41% 7% 12% 19% 19% 2	2036
	21st to end	Night	38% 5% 12% 22% 19% 5%	2000
May	1st to 10th	Night	53% 8% 11% 16% 10% 2	4051
	11th to 20th	Night	51% 9% 12% 14% 12% 2	3576
	21st to end	Night	44% 9% 12% 23% 11% 2	3927
June	1st to 10th	Night	40% 7% 12% 21% 19% 1	1600
	11th to 20th	Night	37% 10% 16% 23% 13% 1	1600
	21st to end	Night	34% 10% 14% 27% 15% 1	1600
July	1st to 10th	Night	42% 10% 14% 18% 15% 2	3560
	11th to 20th	Night	45% 11% 14% 20% 10% 1	3552
	21st to end	Night	34% 9% 14% 22% 20% 1	3848
August	1st to 10th	Night	48% 9% 16% 16% 10% 1	2904
	11th to 20th	Night	41% 7% 13% 23% 14% 1	3159
	21st to end	Night	32% 7% 12% 30% 18% 1	3586
September	1st to 10th	Night	39% 6% 11% 22% 20% 2	2000
	11th to 20th	Night	32% 7% 10% 22% 26% 3	2029
	21st to end	Night	42% 5% 10% 21% 20% 1	2201
October	1st to 10th	Night	41% 6% 10% 21% 20% 2	3920
	11th to 20th	Night	27% 5% 9% 29% 26% 4	3899
	21st to end	Night	28% 4 13% 31% 22% 2	4396
November	1st to 10th	Night	33% 6% 13% 24% 21% 4	2667
	11th to 20th	Night	40% 4 11% 23% 18% 4	2730
	21st to end	Night	39% 6% 13% 26% 14% 2	2898
December	1st to 10th	Night	41% 5% 14% 30% 10% 1	4720
	11th to 20th	Night	45% 5% 12% 23% 13% 2	5348
	21st to end	Night	47% 5% 11% 20% 15% 2	7150

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	25% 28% 27% 18% 1	220
	11th to 20th	Day	31% 27% 28% 12% 2	231
	21st to end	Day	24% 26% 32% 12% 5% 1	363
February	1st to 10th	Day	22% 25% 37% 12% 3 1	330
	11th to 20th	Day	28% 19% 39% 13% 1	469
	21st to end	Day	28% 20% 30% 19% 2	446
March	1st to 10th	Day	25% 21% 31% 20% 4	540
	11th to 20th	Day	25% 20% 33% 18% 3 1	540
	21st to end	Day	27% 23% 30% 14% 6% 1	594
April	1st to 10th	Day	25% 23% 30% 15% 6% 1	540
	11th to 20th	Day	24% 22% 28% 17% 7% 3	516
	21st to end	Day	27% 16% 30% 19% 6% 2	500
May	1st to 10th	Day	30% 18% 26% 17% 7% 2	503
	11th to 20th	Day	22% 15% 29% 23% 10% 2	527
	21st to end	Day	21% 9% 24% 24% 19% 4	573
June	1st to 10th	Day	16% 14% 27% 24% 16% 3	530
	11th to 20th	Day	18% 11% 25% 25% 16% 4	530
	21st to end	Day	15% 9% 29% 29% 14% 4	530
July	1st to 10th	Day	10% 6% 23% 31% 22% 8%	525
	11th to 20th	Day	9% 5% 23% 31% 25% 7%	524
	21st to end	Day	14% 6% 27% 32% 16% 5%	576
August	1st to 10th	Day	12% 7% 22% 31% 21% 8%	526
	11th to 20th	Day	15% 5% 18% 34% 20% 8%	519
	21st to end	Day	13% 5% 26% 28% 18% 10%	583
September	1st to 10th	Day	17% 8% 22% 26% 19% 8%	530
	11th to 20th	Day	14% 4 23% 28% 19% 12%	530
	21st to end	Day	22% 10% 22% 27% 15% 5%	530
October	1st to 10th	Day	24% 7% 23% 24% 14% 8%	530
	11th to 20th	Day	19% 14% 30% 22% 12% 2	530
	21st to end	Day	21% 14% 34% 19% 10% 2	536
November	1st to 10th	Day	17% 14% 30% 25% 11% 3	425
	11th to 20th	Day	22% 20% 29% 24% 5% 1	430
	21st to end	Day	27% 18% 33% 16% 5% 1	261
December	1st to 10th	Day	26% 23% 32% 13% 5% 1	220
	11th to 20th	Day	33% 22% 24% 16% 5%	220
	21st to end	Day	25% 19% 30% 18% 6% 1	242
January	1st to 10th	Night	19% 16% 41% 21% 3	840
	11th to 20th	Night	24% 15% 35% 24% 3	840
	21st to end	Night	17% 16% 43% 23% 1	924
February	1st to 10th	Night	20% 13% 39% 26% 2	840
	11th to 20th	Night	23% 16% 41% 18% 1	823
	21st to end	Night	21% 17% 39% 21% 2	692
March	1st to 10th	Night	22% 14% 35% 26% 3	840
	11th to 20th	Night	21% 16% 37% 21% 5%	840
	21st to end	Night	21% 12% 40% 22% 5%	924
April	1st to 10th	Night	21% 16% 37% 21% 5%	840
	11th to 20th	Night	19% 12% 37% 25% 6%	816
	21st to end	Night	22% 10% 33% 28% 7%	800
May	1st to 10th	Night	25% 10% 30% 28% 6%	604
	11th to 20th	Night	20% 8% 35% 30% 8%	394
	21st to end	Night	17% 6% 22% 40% 14% 1	433
June	1st to 10th	Night	18% 4 27% 35% 15% 1	400
	11th to 20th	Night	15% 5% 26% 41% 14%	400
	21st to end	Night	14% 3 21% 48% 14%	400
July	1st to 10th	Night	13% 4 17% 45% 20% 1	390
	11th to 20th	Night	9% 5% 21% 44% 21% 2	388
	21st to end	Night	11% 4 21% 42% 21% 1	452
August	1st to 10th	Night	12% 3 13% 45% 25% 2	597
	11th to 20th	Night	13% 3 17% 37% 28% 2	747
	21st to end	Night	14% 4 16% 41% 24% 1	880
September	1st to 10th	Night	17% 4 21% 37% 19% 2	800
	11th to 20th	Night	13% 4 15% 41% 23% 4	800
	21st to end	Night	21% 4 22% 34% 18% 1	800
October	1st to 10th	Night	20% 7% 24% 27% 19% 3	800
	11th to 20th	Night	18% 8% 29% 34% 11%	800
	21st to end	Night	23% 7% 33% 29% 9%	880
November	1st to 10th	Night	16% 7% 34% 31% 11% 1	820
	11th to 20th	Night	21% 14% 31% 27% 7% 1	840
	21st to end	Night	18% 13% 36% 26% 6%	840
December	1st to 10th	Night	23% 12% 35% 25% 5% 1	840
	11th to 20th	Night	22% 12% 35% 27% 4	840
	21st to end	Night	22% 13% 37% 26% 2	924

Page generated at 2026-04-14 02:44:23. Version ac07

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