C.O.A.M.N.D.
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the C.O.A.M.N.D. clear sky chart from 2005-11-06 to 2025-09-04.

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	19% 13% 4 10% 6% 5% 5% 3 5% 6% 25%	125837
	Night	17% 14% 5% 11% 6% 5% 4 3 4 5% 25%	122897
Transparency	Day	59% 6% 11% 17% 7% 1	129305
	Night	60% 5% 11% 16% 8% 1	127517
Seeing	Day	28% 20% 28% 16% 6% 1	16477
	Night	26% 18% 27% 22% 7% 1	24807

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	11% 22% 8% 17% 10% 7% 7% 3 3 2 10%	3597
	11th to 20th	Day	7% 16% 7% 22% 15% 10% 3 2 2 2 14%	3570
	21st to end	Day	6% 10% 8% 21% 7% 7% 8% 4 4 4 19%	3960
February	1st to 10th	Day	12% 17% 7% 14% 10% 7% 5% 3 3 4 17%	1645
	11th to 20th	Day	13% 18% 9% 15% 6% 5% 5% 3 4 3 18%	1903
	21st to end	Day	12% 17% 6% 14% 7% 5% 5% 3 4 5% 22%	1650
March	1st to 10th	Day	16% 19% 6% 13% 6% 4 5% 3 3 4 20%	4476
	11th to 20th	Day	14% 19% 5% 10% 5% 5% 4 4 5% 5% 25%	4830
	21st to end	Day	19% 17% 5% 10% 5% 3 4 3 3 4 27%	5712
April	1st to 10th	Day	22% 18% 4 10% 4 3 3 2 3 5% 24%	2400
	11th to 20th	Day	19% 16% 5% 7% 4 4 3 3 4 5% 32%	2497
	21st to end	Day	22% 12% 5% 9% 4 4 4 3 4 6% 28%	2600
May	1st to 10th	Day	25% 12% 4 9% 5% 5% 5% 3 4 5% 23%	5900
	11th to 20th	Day	22% 10% 3 8% 5% 5% 5% 4 5% 7% 25%	6318
	21st to end	Day	22% 9% 3 8% 5% 5% 5% 4 5% 6% 28%	7147
June	1st to 10th	Day	25% 9% 3 7% 5% 5% 5% 3 7% 7% 24%	3000
	11th to 20th	Day	22% 7% 2 6% 4 5% 5% 5% 6% 7% 29%	3000
	21st to end	Day	26% 11% 4 8% 6% 4 4 4 5% 4 25%	3000
July	1st to 10th	Day	21% 9% 3 9% 6% 5% 5% 4 6% 7% 23%	6557
	11th to 20th	Day	18% 9% 3 7% 6% 4 5% 5% 7% 8% 29%	6360
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 6% 8% 37%	6926
August	1st to 10th	Day	21% 7% 3 8% 5% 6% 5% 4 6% 9% 27%	4467
	11th to 20th	Day	21% 9% 3 9% 5% 6% 7% 5% 6% 6% 24%	4175
	21st to end	Day	22% 9% 2 7% 4 4 4 4 5% 6% 33%	4529
September	1st to 10th	Day	21% 8% 3 6% 4 3 5% 4 5% 7% 34%	2307
	11th to 20th	Day	21% 7% 2 4 5% 4 3 3 4 5% 41%	2090
	21st to end	Day	23% 9% 3 6% 3 4 4 4 5% 7% 35%	2090
October	1st to 10th	Day	23% 12% 3 7% 4 4 4 3 4 6% 31%	2090
	11th to 20th	Day	24% 19% 3 7% 4 4 4 3 3 5% 23%	1752
	21st to end	Day	26% 19% 4 9% 4 3 4 3 4 4 20%	1881
November	1st to 10th	Day	20% 20% 5% 8% 4 3 3 2 4 3 26%	1761
	11th to 20th	Day	20% 18% 7% 10% 5% 5% 3 2 4 4 21%	1789
	21st to end	Day	19% 23% 6% 12% 6% 3 3 3 3 3 18%	1457
December	1st to 10th	Day	17% 19% 6% 15% 9% 5% 5% 3 4 3 14%	2280
	11th to 20th	Day	18% 18% 7% 12% 7% 4 3 2 3 4 21%	2618
	21st to end	Day	18% 18% 6% 12% 7% 4 4 3 4 4 20%	3503
January	1st to 10th	Night	12% 18% 9% 18% 11% 6% 4 4 4 3 12%	6349
	11th to 20th	Night	8% 19% 8% 23% 14% 6% 3 2 2 2 13%	6315
	21st to end	Night	6% 11% 8% 17% 8% 8% 7% 5% 6% 5% 20%	6996
February	1st to 10th	Night	11% 17% 6% 14% 10% 6% 5% 3 4 4 21%	2755
	11th to 20th	Night	11% 19% 6% 15% 8% 6% 5% 2 4 3 20%	2378
	21st to end	Night	13% 17% 6% 12% 7% 5% 4 2 3 4 26%	1980
March	1st to 10th	Night	18% 18% 5% 12% 6% 4 5% 3 4 5% 22%	5364
	11th to 20th	Night	13% 16% 5% 12% 6% 6% 6% 4 5% 6% 22%	5128
	21st to end	Night	18% 18% 5% 10% 5% 4 4 2 3 4 28%	5205
April	1st to 10th	Night	21% 17% 6% 8% 4 4 4 3 3 4 27%	2000
	11th to 20th	Night	20% 14% 3 8% 4 4 4 3 5% 6% 30%	1851
	21st to end	Night	21% 14% 4 7% 5% 4 4 2 5% 4 30%	1800
May	1st to 10th	Night	24% 11% 3 8% 5% 5% 5% 4 4 6% 26%	4054
	11th to 20th	Night	21% 12% 2 7% 4 4 4 3 4 6% 31%	3603
	21st to end	Night	20% 8% 3 6% 4 4 4 4 5% 7% 36%	3733
June	1st to 10th	Night	24% 9% 3 7% 6% 5% 5% 4 6% 5% 27%	1400
	11th to 20th	Night	19% 8% 2 8% 4 5% 6% 4 5% 6% 35%	1400
	21st to end	Night	23% 10% 3 7% 5% 5% 5% 4 5% 6% 29%	1400
July	1st to 10th	Night	20% 9% 4 9% 5% 4 4 3 6% 8% 29%	3393
	11th to 20th	Night	25% 9% 2 6% 4 4 3 3 4 6% 32%	3600
	21st to end	Night	16% 8% 2 7% 5% 4 5% 4 5% 7% 38%	3926
August	1st to 10th	Night	23% 7% 3 6% 5% 5% 5% 4 5% 8% 31%	2649
	11th to 20th	Night	20% 11% 3 9% 5% 5% 5% 4 4 6% 28%	2872
	21st to end	Night	18% 9% 3 8% 4 4 4 3 5% 7% 36%	3353
September	1st to 10th	Night	21% 7% 2 6% 4 4 4 3 4 6% 39%	1939
	11th to 20th	Night	20% 8% 2 6% 3 3 4 2 4 6% 42%	2090
	21st to end	Night	21% 8% 2 5% 4 4 4 3 5% 6% 39%	2090
October	1st to 10th	Night	22% 10% 3 5% 4 4 5% 3 5% 5% 36%	2090
	11th to 20th	Night	25% 14% 3 7% 5% 4 4 2 4 4 28%	2424
	21st to end	Night	25% 16% 3 8% 4 4 4 3 4 4 25%	2717
November	1st to 10th	Night	21% 17% 5% 9% 5% 4 4 3 4 5% 25%	2537
	11th to 20th	Night	19% 15% 5% 11% 5% 4 4 3 3 4 27%	2609
	21st to end	Night	17% 21% 8% 12% 5% 4 4 2 4 3 19%	2940
December	1st to 10th	Night	15% 17% 9% 21% 10% 6% 4 2 3 3 11%	4910
	11th to 20th	Night	18% 19% 7% 14% 8% 5% 3 2 3 4 18%	5591
	21st to end	Night	18% 19% 6% 11% 4 4 4 2 3 3 25%	7456

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	77% 4 6% 8% 3	3598
	11th to 20th	Day	76% 4 5% 10% 5% 1	3600
	21st to end	Day	65% 6% 6% 11% 12% 1	3960
February	1st to 10th	Day	71% 4 5% 10% 8% 1	1645
	11th to 20th	Day	71% 4 7% 10% 7% 1	1912
	21st to end	Day	64% 5% 7% 16% 6% 2	1650
March	1st to 10th	Day	69% 3 7% 10% 9% 4	4479
	11th to 20th	Day	61% 6% 13% 12% 8%	4830
	21st to end	Day	61% 4 6% 15% 12% 2	5712
April	1st to 10th	Day	64% 4 8% 13% 9% 2	2400
	11th to 20th	Day	55% 5% 8% 20% 11% 2	2497
	21st to end	Day	58% 5% 8% 17% 10% 2	2600
May	1st to 10th	Day	63% 5% 7% 17% 8% 1	5911
	11th to 20th	Day	57% 6% 14% 16% 5% 2	6322
	21st to end	Day	55% 7% 10% 18% 8% 3	7147
June	1st to 10th	Day	57% 7% 9% 20% 6% 1	3000
	11th to 20th	Day	50% 7% 14% 20% 9% 1	3000
	21st to end	Day	62% 5% 11% 15% 7%	3000
July	1st to 10th	Day	57% 7% 13% 17% 6%	6487
	11th to 20th	Day	49% 7% 16% 24% 3	6285
	21st to end	Day	42% 7% 15% 28% 7%	6728
August	1st to 10th	Day	51% 8% 17% 18% 5%	4453
	11th to 20th	Day	56% 10% 15% 14% 4	4214
	21st to end	Day	50% 6% 15% 18% 11% 1	4529
September	1st to 10th	Day	47% 7% 15% 21% 10%	2307
	11th to 20th	Day	45% 4 12% 27% 11%	2090
	21st to end	Day	49% 5% 13% 23% 9%	2090
October	1st to 10th	Day	56% 4 12% 22% 6%	3480
	11th to 20th	Day	60% 4 12% 20% 4	2890
	21st to end	Day	57% 5% 14% 16% 7%	3081
November	1st to 10th	Day	63% 5% 10% 16% 6%	1761
	11th to 20th	Day	67% 4 9% 13% 6% 1	1789
	21st to end	Day	72% 5% 8% 12% 3	1457
December	1st to 10th	Day	74% 5% 8% 8% 6%	2280
	11th to 20th	Day	67% 4 6% 14% 9%	2618
	21st to end	Day	67% 4 5% 10% 10% 3	3503
January	1st to 10th	Night	75% 4 9% 9% 3	6349
	11th to 20th	Night	77% 5% 6% 9% 3	6360
	21st to end	Night	61% 6% 8% 12% 11% 1	6996
February	1st to 10th	Night	66% 4 8% 12% 9% 1	2755
	11th to 20th	Night	68% 6% 6% 13% 7% 1	2380
	21st to end	Night	61% 4 8% 15% 11% 1	1980
March	1st to 10th	Night	65% 4 8% 12% 10% 1	5374
	11th to 20th	Night	61% 6% 14% 11% 7% 1	5129
	21st to end	Night	60% 3 6% 16% 13% 1	5205
April	1st to 10th	Night	60% 4 7% 14% 13% 2	2000
	11th to 20th	Night	54% 6% 8% 20% 11% 1	1851
	21st to end	Night	57% 6% 7% 16% 11% 2	1800
May	1st to 10th	Night	57% 7% 9% 17% 10% 1	4060
	11th to 20th	Night	53% 7% 13% 20% 7%	3604
	21st to end	Night	47% 7% 14% 19% 12% 2	3734
June	1st to 10th	Night	57% 5% 12% 20% 7%	1400
	11th to 20th	Night	47% 8% 11% 21% 11% 2	1400
	21st to end	Night	55% 7% 14% 17% 8%	1400
July	1st to 10th	Night	52% 7% 19% 18% 5%	3353
	11th to 20th	Night	51% 6% 18% 21% 4	3552
	21st to end	Night	43% 7% 19% 23% 7%	3809
August	1st to 10th	Night	51% 6% 16% 23% 4	2639
	11th to 20th	Night	53% 10% 16% 17% 4 1	2899
	21st to end	Night	46% 7% 15% 20% 11% 2	3353
September	1st to 10th	Night	45% 6% 13% 25% 9% 1	1939
	11th to 20th	Night	44% 5% 17% 26% 8% 1	2090
	21st to end	Night	46% 6% 12% 23% 12%	2090
October	1st to 10th	Night	48% 4 11% 27% 9%	3480
	11th to 20th	Night	57% 4 10% 23% 6%	4025
	21st to end	Night	53% 5% 17% 17% 8%	4467
November	1st to 10th	Night	60% 6% 12% 17% 5%	2537
	11th to 20th	Night	60% 7% 10% 14% 9% 1	2609
	21st to end	Night	70% 5% 9% 12% 4	2940
December	1st to 10th	Night	75% 7% 8% 9% 2	4910
	11th to 20th	Night	72% 4 4 14% 6%	5592
	21st to end	Night	64% 3 6% 13% 12% 1	7456

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	28% 31% 34% 7% 2 1	200
	11th to 20th	Day	29% 27% 32% 9% 3	200
	21st to end	Day	20% 31% 35% 10% 3 1	220
February	1st to 10th	Day	37% 25% 26% 9% 2	245
	11th to 20th	Day	29% 27% 32% 10% 2	473
	21st to end	Day	30% 26% 29% 12% 3	414
March	1st to 10th	Day	29% 27% 29% 12% 3	500
	11th to 20th	Day	30% 25% 27% 13% 5% 1	500
	21st to end	Day	32% 25% 24% 11% 6% 2	550
April	1st to 10th	Day	38% 20% 24% 12% 5% 1	500
	11th to 20th	Day	32% 26% 25% 13% 3 1	492
	21st to end	Day	34% 20% 30% 11% 4 1	500
May	1st to 10th	Day	32% 17% 35% 12% 2 2	503
	11th to 20th	Day	28% 15% 31% 19% 6%	527
	21st to end	Day	25% 22% 29% 17% 6% 1	654
June	1st to 10th	Day	28% 16% 32% 16% 6% 1	730
	11th to 20th	Day	24% 18% 26% 23% 9%	730
	21st to end	Day	30% 15% 28% 18% 9% 1	730
July	1st to 10th	Day	23% 16% 33% 21% 8%	618
	11th to 20th	Day	23% 17% 35% 18% 6% 1	524
	21st to end	Day	23% 16% 34% 20% 6% 1	576
August	1st to 10th	Day	22% 14% 31% 20% 10% 2	526
	11th to 20th	Day	23% 9% 31% 25% 11% 2	519
	21st to end	Day	24% 16% 26% 21% 9% 5%	583
September	1st to 10th	Day	23% 17% 26% 21% 11% 3	502
	11th to 20th	Day	23% 13% 29% 21% 11% 3	490
	21st to end	Day	25% 16% 27% 16% 12% 4	490
October	1st to 10th	Day	26% 19% 24% 18% 11% 2	490
	11th to 20th	Day	35% 20% 22% 14% 7% 1	390
	21st to end	Day	39% 23% 21% 14% 3	429
November	1st to 10th	Day	35% 20% 24% 16% 4 1	395
	11th to 20th	Day	29% 26% 24% 15% 6% 1	400
	21st to end	Day	32% 30% 27% 9% 2	257
December	1st to 10th	Day	31% 22% 28% 16% 3 1	200
	11th to 20th	Day	38% 28% 24% 10% 1 1	200
	21st to end	Day	37% 22% 24% 13% 3 1	220
January	1st to 10th	Night	26% 25% 32% 14% 2	800
	11th to 20th	Night	26% 23% 30% 16% 4	800
	21st to end	Night	19% 22% 36% 19% 4 1	880
February	1st to 10th	Night	21% 28% 32% 15% 4	800
	11th to 20th	Night	26% 25% 31% 14% 3 1	783
	21st to end	Night	26% 21% 31% 18% 4	660
March	1st to 10th	Night	25% 20% 34% 18% 3	800
	11th to 20th	Night	24% 23% 31% 17% 5% 1	800
	21st to end	Night	24% 21% 27% 22% 7%	880
April	1st to 10th	Night	31% 20% 26% 18% 5%	800
	11th to 20th	Night	28% 16% 28% 22% 6%	667
	21st to end	Night	32% 15% 27% 19% 6% 1	600
May	1st to 10th	Night	27% 14% 30% 22% 7%	600
	11th to 20th	Night	25% 10% 28% 28% 8% 1	409
	21st to end	Night	24% 9% 27% 31% 8%	433
June	1st to 10th	Night	28% 8% 29% 26% 8%	400
	11th to 20th	Night	19% 10% 25% 31% 15%	400
	21st to end	Night	26% 11% 24% 29% 10%	400
July	1st to 10th	Night	17% 11% 30% 29% 12%	390
	11th to 20th	Night	22% 9% 20% 37% 12%	388
	21st to end	Night	19% 7% 23% 38% 13%	438
August	1st to 10th	Night	19% 5% 20% 36% 19%	435
	11th to 20th	Night	20% 8% 23% 32% 15% 1	592
	21st to end	Night	19% 10% 24% 31% 14% 3	738
September	1st to 10th	Night	21% 9% 26% 29% 13% 2	773
	11th to 20th	Night	23% 9% 24% 29% 14% 2	760
	21st to end	Night	26% 10% 23% 27% 12% 2	760
October	1st to 10th	Night	24% 15% 23% 28% 10% 1	760
	11th to 20th	Night	30% 17% 24% 20% 8% 1	760
	21st to end	Night	34% 20% 23% 16% 6%	836
November	1st to 10th	Night	30% 19% 27% 19% 5%	780
	11th to 20th	Night	27% 21% 26% 18% 7% 1	805
	21st to end	Night	29% 24% 26% 16% 4 1	900
December	1st to 10th	Night	30% 21% 30% 13% 5% 1	900
	11th to 20th	Night	31% 24% 22% 18% 5%	900
	21st to end	Night	31% 25% 25% 15% 4	980

Page generated at 2025-09-01 01:51:02. Version ac07

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