Colbeck Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colbeck Observatory clear sky chart from 2005-11-06 to 2025-07-21.

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	14% 12% 5% 10% 6% 5% 5% 4 5% 6% 28%	120984
	Night	13% 12% 5% 12% 6% 5% 5% 4 5% 6% 28%	118002
Transparency	Day	55% 6% 10% 18% 10% 1	124603
	Night	55% 5% 11% 18% 10% 1	122545
Seeing	Day	20% 15% 30% 21% 11% 4	15846
	Night	19% 14% 31% 25% 10% 1	24689

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	10% 14% 9% 20% 10% 5% 4 3 4 4 18%	3487
	11th to 20th	Day	8% 20% 10% 24% 10% 11% 5% 2 2 2 6%	4023
	21st to end	Day	13% 17% 8% 23% 8% 6% 5% 3 3 4 10%	4466
February	1st to 10th	Day	12% 18% 7% 17% 12% 7% 5% 3 3 3 12%	1800
	11th to 20th	Day	12% 14% 7% 18% 11% 6% 4 3 6% 5% 14%	1753
	21st to end	Day	14% 17% 7% 12% 9% 5% 5% 3 5% 4 17%	1575
March	1st to 10th	Day	15% 13% 4 13% 7% 5% 4 3 4 5% 26%	4882
	11th to 20th	Day	10% 13% 8% 11% 6% 5% 5% 4 5% 7% 26%	4980
	21st to end	Day	16% 15% 7% 10% 5% 4 4 3 4 5% 28%	5465
April	1st to 10th	Day	15% 17% 4 10% 5% 5% 4 3 5% 6% 26%	2324
	11th to 20th	Day	17% 12% 4 6% 4 4 4 3 5% 6% 34%	2516
	21st to end	Day	19% 12% 4 7% 4 4 4 4 5% 6% 31%	2600
May	1st to 10th	Day	17% 10% 3 8% 5% 4 4 3 5% 6% 35%	5888
	11th to 20th	Day	16% 10% 3 8% 5% 5% 5% 4 5% 7% 33%	6170
	21st to end	Day	19% 8% 3 6% 4 4 4 3 5% 6% 37%	6949
June	1st to 10th	Day	14% 8% 3 7% 4 5% 4 5% 7% 7% 36%	2800
	11th to 20th	Day	11% 7% 2 6% 5% 4 5% 5% 7% 8% 39%	2976
	21st to end	Day	16% 6% 2 6% 5% 5% 4 4 7% 8% 37%	3000
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 6% 5% 8% 8% 35%	4910
	11th to 20th	Day	10% 6% 2 6% 5% 4 6% 4 7% 8% 41%	4588
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 7% 9% 39%	4466
August	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 5% 6% 8% 34%	4104
	11th to 20th	Day	13% 8% 3 8% 5% 6% 6% 5% 7% 10% 29%	4044
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 5% 7% 8% 40%	4422
September	1st to 10th	Day	14% 7% 3 8% 5% 5% 4 4 6% 8% 37%	2280
	11th to 20th	Day	12% 8% 2 6% 4 5% 4 4 6% 8% 41%	2109
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 4 8% 8% 31%	2086
October	1st to 10th	Day	17% 11% 3 8% 5% 5% 5% 4 5% 6% 31%	1900
	11th to 20th	Day	21% 14% 4 9% 5% 5% 4 4 4 6% 24%	1900
	21st to end	Day	24% 18% 4 8% 5% 4 4 3 5% 6% 18%	2080
November	1st to 10th	Day	15% 17% 4 8% 6% 4 5% 4 4 6% 26%	1695
	11th to 20th	Day	14% 17% 6% 10% 7% 6% 5% 3 5% 7% 21%	1600
	21st to end	Day	15% 21% 7% 13% 6% 5% 4 4 5% 5% 15%	1600
December	1st to 10th	Day	14% 26% 11% 15% 5% 4 4 3 3 5% 10%	2600
	11th to 20th	Day	18% 22% 8% 14% 7% 4 3 3 4 4 14%	2986
	21st to end	Day	21% 21% 9% 16% 7% 5% 4 2 4 3 9%	3960
January	1st to 10th	Night	12% 13% 8% 22% 9% 5% 4 3 4 5% 15%	6349
	11th to 20th	Night	10% 13% 8% 22% 14% 10% 6% 3 3 3 8%	5859
	21st to end	Night	12% 14% 8% 20% 9% 6% 7% 4 5% 5% 12%	6490
February	1st to 10th	Night	12% 17% 7% 13% 10% 6% 5% 4 5% 5% 16%	2600
	11th to 20th	Night	12% 12% 7% 16% 9% 6% 5% 4 5% 6% 18%	2533
	21st to end	Night	12% 13% 5% 14% 8% 5% 5% 4 6% 7% 22%	2053
March	1st to 10th	Night	12% 11% 5% 11% 6% 6% 6% 4 6% 6% 28%	4957
	11th to 20th	Night	7% 10% 5% 12% 6% 5% 5% 5% 6% 8% 32%	4979
	21st to end	Night	18% 10% 4 10% 4 4 4 3 5% 5% 32%	5467
April	1st to 10th	Night	17% 14% 4 10% 5% 4 4 3 4 6% 28%	2075
	11th to 20th	Night	15% 11% 4 7% 5% 5% 4 3 5% 5% 36%	1850
	21st to end	Night	14% 11% 3 9% 6% 5% 5% 4 6% 5% 33%	1800
May	1st to 10th	Night	16% 10% 3 7% 5% 4 4 3 4 7% 38%	4053
	11th to 20th	Night	13% 9% 3 7% 4 5% 4 4 5% 6% 41%	3723
	21st to end	Night	16% 8% 2 6% 3 3 3 3 5% 6% 45%	3926
June	1st to 10th	Night	12% 6% 2 7% 5% 4 5% 4 5% 8% 42%	1600
	11th to 20th	Night	9% 6% 2 7% 4 5% 6% 4 7% 9% 41%	1417
	21st to end	Night	13% 6% 2 6% 5% 4 3 3 5% 8% 44%	1400
July	1st to 10th	Night	6% 6% 2 6% 5% 4 4 4 6% 7% 50%	2280
	11th to 20th	Night	10% 7% 2 5% 4 4 3 4 5% 6% 51%	2586
	21st to end	Night	6% 7% 2 6% 4 4 5% 4 6% 7% 48%	3087
August	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 6% 47%	2825
	11th to 20th	Night	12% 8% 2 6% 4 4 4 4 5% 7% 45%	2785
	21st to end	Night	11% 6% 3 7% 5% 4 4 3 4 7% 47%	3188
September	1st to 10th	Night	9% 6% 2 8% 3 4 5% 4 5% 7% 47%	1900
	11th to 20th	Night	11% 5% 2 5% 4 4 3 3 6% 6% 51%	2066
	21st to end	Night	15% 9% 2 7% 4 4 4 3 5% 8% 38%	2092
October	1st to 10th	Night	16% 8% 3 7% 5% 5% 4 3 4 6% 37%	2280
	11th to 20th	Night	18% 12% 4 9% 5% 5% 5% 3 4 6% 29%	2280
	21st to end	Night	18% 13% 4 9% 5% 5% 5% 4 6% 6% 23%	2517
November	1st to 10th	Night	15% 13% 3 9% 6% 4 4 4 5% 7% 29%	2601
	11th to 20th	Night	14% 16% 5% 9% 6% 5% 5% 4 6% 7% 23%	2800
	21st to end	Night	17% 16% 7% 11% 6% 5% 4 4 6% 7% 18%	2800
December	1st to 10th	Night	13% 21% 9% 17% 7% 6% 5% 3 4 5% 11%	4580
	11th to 20th	Night	12% 21% 9% 18% 8% 4 4 3 4 4 14%	5208
	21st to end	Night	19% 20% 9% 17% 6% 5% 4 3 4 4 8%	6996

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% 4 7% 10% 7% 1	3488
	11th to 20th	Day	87% 3 4 4 2 1	4057
	21st to end	Day	79% 4 7% 7% 3	4466
February	1st to 10th	Day	76% 4 6% 11% 3 1	1800
	11th to 20th	Day	71% 4 7% 12% 5% 1	1762
	21st to end	Day	68% 5% 8% 12% 6% 1	1575
March	1st to 10th	Day	61% 5% 12% 12% 10% 1	4885
	11th to 20th	Day	57% 4 12% 19% 6% 3	4980
	21st to end	Day	59% 4 9% 18% 9% 2	5465
April	1st to 10th	Day	59% 4 8% 19% 9% 1	2324
	11th to 20th	Day	50% 6% 9% 20% 14% 1	2516
	21st to end	Day	53% 6% 10% 18% 11% 2	2600
May	1st to 10th	Day	49% 5% 11% 18% 10% 6%	5897
	11th to 20th	Day	49% 8% 9% 16% 16% 1	6174
	21st to end	Day	47% 6% 10% 20% 14% 4	6949
June	1st to 10th	Day	45% 7% 11% 22% 15% 1	2800
	11th to 20th	Day	40% 8% 12% 24% 15% 1	2976
	21st to end	Day	42% 7% 13% 24% 13% 1	3000
July	1st to 10th	Day	43% 8% 13% 20% 15% 1	4836
	11th to 20th	Day	37% 7% 11% 32% 12% 1	4511
	21st to end	Day	39% 8% 12% 22% 18% 1	4324
August	1st to 10th	Day	46% 7% 12% 23% 12% 1	4091
	11th to 20th	Day	48% 8% 13% 22% 8%	4083
	21st to end	Day	39% 7% 12% 30% 11% 1	4422
September	1st to 10th	Day	44% 6% 13% 24% 10% 2	2280
	11th to 20th	Day	39% 6% 12% 28% 14% 1	2109
	21st to end	Day	48% 8% 13% 22% 8% 1	2086
October	1st to 10th	Day	47% 7% 11% 22% 12% 1	3160
	11th to 20th	Day	49% 5% 11% 20% 15%	3140
	21st to end	Day	60% 5% 12% 18% 6%	3406
November	1st to 10th	Day	58% 6% 12% 16% 8% 1	1695
	11th to 20th	Day	63% 6% 11% 13% 7% 1	1600
	21st to end	Day	70% 6% 10% 12% 2	1600
December	1st to 10th	Day	77% 5% 10% 6% 1	2600
	11th to 20th	Day	74% 4 8% 9% 5%	2986
	21st to end	Day	80% 5% 4 5% 5%	3960
January	1st to 10th	Night	70% 6% 9% 9% 5% 1	6349
	11th to 20th	Night	82% 4 5% 6% 3	5900
	21st to end	Night	72% 5% 9% 8% 5% 1	6490
February	1st to 10th	Night	67% 5% 10% 14% 3 1	2600
	11th to 20th	Night	65% 5% 10% 14% 6%	2535
	21st to end	Night	60% 4 13% 14% 8% 1	2053
March	1st to 10th	Night	53% 7% 11% 16% 11% 1	4967
	11th to 20th	Night	48% 6% 16% 19% 9% 2	4980
	21st to end	Night	53% 4 9% 18% 14% 2	5467
April	1st to 10th	Night	57% 5% 8% 17% 12% 1	2075
	11th to 20th	Night	49% 5% 8% 21% 15% 2	1850
	21st to end	Night	52% 5% 10% 16% 16% 2	1800
May	1st to 10th	Night	47% 6% 10% 16% 13% 8%	4060
	11th to 20th	Night	42% 9% 11% 21% 15% 2	3724
	21st to end	Night	39% 6% 13% 24% 16% 2	3927
June	1st to 10th	Night	39% 4 12% 25% 18% 2	1600
	11th to 20th	Night	38% 6% 13% 25% 17% 1	1417
	21st to end	Night	39% 6% 11% 27% 15% 1	1400
July	1st to 10th	Night	33% 5% 14% 24% 19% 4	2245
	11th to 20th	Night	33% 5% 11% 34% 17% 1	2541
	21st to end	Night	34% 8% 13% 29% 15% 2	2988
August	1st to 10th	Night	37% 6% 12% 27% 16% 2	2814
	11th to 20th	Night	38% 6% 14% 28% 13% 1	2812
	21st to end	Night	37% 6% 12% 31% 14% 1	3188
September	1st to 10th	Night	35% 8% 13% 29% 14% 2	1900
	11th to 20th	Night	32% 5% 13% 30% 20% 1	2066
	21st to end	Night	45% 6% 13% 25% 11%	2092
October	1st to 10th	Night	39% 5% 9% 25% 21% 1	3800
	11th to 20th	Night	48% 5% 12% 21% 14% 1	3779
	21st to end	Night	48% 6% 15% 23% 8%	4141
November	1st to 10th	Night	53% 6% 12% 19% 9% 1	2601
	11th to 20th	Night	58% 6% 12% 16% 6% 2	2800
	21st to end	Night	64% 6% 13% 12% 3 1	2800
December	1st to 10th	Night	75% 6% 11% 7% 2	4580
	11th to 20th	Night	75% 4 7% 10% 4	5208
	21st to end	Night	79% 5% 5% 8% 3	6996

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	20% 25% 36% 16% 4	200
	11th to 20th	Day	21% 26% 35% 13% 4 1	299
	21st to end	Day	21% 26% 35% 15% 3	330
February	1st to 10th	Day	25% 28% 34% 10% 3	300
	11th to 20th	Day	24% 26% 39% 9% 1	300
	21st to end	Day	31% 27% 31% 10%	249
March	1st to 10th	Day	22% 19% 39% 14% 6%	474
	11th to 20th	Day	22% 19% 37% 16% 5% 1	500
	21st to end	Day	27% 15% 33% 17% 6% 1	550
April	1st to 10th	Day	26% 18% 34% 16% 6%	500
	11th to 20th	Day	29% 18% 24% 17% 9% 3	492
	21st to end	Day	26% 15% 31% 18% 7% 2	500
May	1st to 10th	Day	22% 13% 30% 22% 11% 2	503
	11th to 20th	Day	18% 11% 30% 24% 11% 5%	527
	21st to end	Day	17% 10% 27% 27% 14% 5%	573
June	1st to 10th	Day	15% 14% 30% 27% 12% 2	530
	11th to 20th	Day	14% 9% 32% 29% 12% 3	706
	21st to end	Day	16% 10% 32% 29% 11% 2	730
July	1st to 10th	Day	11% 9% 27% 28% 20% 5%	721
	11th to 20th	Day	15% 8% 25% 30% 16% 7%	562
	21st to end	Day	11% 4 27% 35% 16% 6%	532
August	1st to 10th	Day	14% 7% 23% 25% 22% 9%	486
	11th to 20th	Day	14% 4 23% 27% 19% 13%	479
	21st to end	Day	14% 7% 27% 25% 18% 9%	539
September	1st to 10th	Day	14% 10% 27% 23% 16% 10%	490
	11th to 20th	Day	12% 6% 21% 25% 23% 12%	490
	21st to end	Day	15% 13% 27% 23% 16% 6%	490
October	1st to 10th	Day	22% 16% 25% 20% 13% 5%	490
	11th to 20th	Day	23% 20% 33% 17% 5% 2	490
	21st to end	Day	32% 16% 28% 19% 5%	529
November	1st to 10th	Day	27% 22% 31% 15% 5% 1	265
	11th to 20th	Day	26% 20% 38% 10% 5% 2	200
	21st to end	Day	24% 22% 39% 14% 2	200
December	1st to 10th	Day	27% 32% 28% 13% 2	200
	11th to 20th	Day	28% 32% 27% 12% 2 1	200
	21st to end	Day	29% 25% 31% 11% 3 1	220
January	1st to 10th	Night	20% 22% 36% 17% 5% 1	800
	11th to 20th	Night	26% 19% 32% 19% 3 1	800
	21st to end	Night	16% 17% 38% 23% 6%	880
February	1st to 10th	Night	21% 23% 37% 19% 2	800
	11th to 20th	Night	20% 19% 37% 20% 3	783
	21st to end	Night	20% 22% 37% 19% 3	660
March	1st to 10th	Night	17% 18% 41% 20% 5%	800
	11th to 20th	Night	18% 20% 39% 18% 5% 1	800
	21st to end	Night	21% 13% 35% 22% 8% 1	880
April	1st to 10th	Night	24% 16% 36% 21% 4	800
	11th to 20th	Night	22% 15% 31% 21% 9% 1	666
	21st to end	Night	22% 11% 31% 27% 9%	600
May	1st to 10th	Night	19% 9% 28% 32% 11% 2	600
	11th to 20th	Night	17% 8% 32% 30% 13% 1	464
	21st to end	Night	12% 8% 27% 37% 15%	433
June	1st to 10th	Night	14% 7% 34% 34% 12%	400
	11th to 20th	Night	11% 8% 31% 38% 13%	400
	21st to end	Night	13% 8% 29% 34% 15%	400
July	1st to 10th	Night	7% 3 20% 49% 19% 1	390
	11th to 20th	Night	10% 4 28% 36% 21% 1	417
	21st to end	Night	9% 4 24% 41% 20% 2	624
August	1st to 10th	Night	11% 3 20% 37% 27% 2	567
	11th to 20th	Night	9% 3 20% 37% 27% 4	564
	21st to end	Night	14% 5% 25% 28% 26% 2	665
September	1st to 10th	Night	11% 7% 24% 32% 19% 6%	760
	11th to 20th	Night	12% 7% 21% 32% 22% 6%	760
	21st to end	Night	19% 9% 23% 29% 16% 4	760
October	1st to 10th	Night	19% 9% 28% 27% 13% 3	760
	11th to 20th	Night	23% 16% 28% 24% 8% 1	760
	21st to end	Night	24% 17% 33% 22% 4	836
November	1st to 10th	Night	22% 17% 31% 23% 7% 1	780
	11th to 20th	Night	21% 21% 32% 19% 6% 1	800
	21st to end	Night	25% 18% 34% 19% 3	800
December	1st to 10th	Night	25% 21% 34% 16% 3 1	800
	11th to 20th	Night	20% 23% 39% 15% 3	800
	21st to end	Night	28% 20% 32% 17% 2	880

Page generated at 2025-07-18 01:10:02. Version ac07

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