Comprix Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Comprix Observatory clear sky chart from 2005-11-06 to 2025-05-26.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 33%	114672
	Night	16% 10% 4 8% 5% 4 4 3 5% 6% 35%	114566
Transparency	Day	50% 3 11% 22% 12% 2	118377
	Night	49% 3 10% 22% 13% 2	118999
Seeing	Day	19% 8% 24% 24% 17% 8%	15669
	Night	19% 7% 25% 32% 15% 2	25671

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	16% 20% 8% 16% 8% 4 4 3 4 4 15%	4056
	11th to 20th	Day	14% 20% 6% 14% 7% 8% 5% 2 3 4 17%	4060
	21st to end	Day	21% 16% 7% 10% 8% 7% 5% 3 4 5% 15%	4466
February	1st to 10th	Day	22% 14% 4 10% 6% 4 4 3 4 4 24%	1800
	11th to 20th	Day	18% 12% 5% 13% 6% 4 4 4 5% 5% 24%	1924
	21st to end	Day	19% 14% 5% 9% 4 4 4 2 4 5% 29%	1650
March	1st to 10th	Day	18% 14% 5% 11% 5% 3 4 3 4 6% 27%	4702
	11th to 20th	Day	13% 8% 3 8% 5% 5% 4 4 5% 6% 40%	4980
	21st to end	Day	21% 9% 3 8% 5% 5% 4 3 4 6% 32%	5465
April	1st to 10th	Day	16% 13% 3 7% 5% 4 5% 3 5% 6% 33%	2240
	11th to 20th	Day	17% 9% 3 7% 4 4 4 4 5% 6% 37%	2527
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	2600
May	1st to 10th	Day	22% 9% 3 7% 5% 5% 4 4 5% 7% 29%	4212
	11th to 20th	Day	22% 7% 3 6% 4 4 4 4 5% 7% 34%	4211
	21st to end	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 10% 35%	4541
June	1st to 10th	Day	12% 6% 3 6% 5% 5% 5% 4 6% 9% 37%	2470
	11th to 20th	Day	12% 5% 2 8% 5% 4 4 5% 7% 9% 39%	2470
	21st to end	Day	11% 5% 2 6% 6% 5% 5% 5% 6% 11% 37%	2577
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 4 6% 9% 39%	4158
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 5% 7% 10% 45%	4120
	21st to end	Day	11% 7% 2 6% 5% 5% 6% 5% 7% 9% 36%	4466
August	1st to 10th	Day	10% 5% 2 7% 5% 5% 5% 5% 7% 10% 39%	4104
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 10% 40%	4044
	21st to end	Day	6% 5% 1 5% 4 6% 6% 4 6% 9% 48%	4453
September	1st to 10th	Day	14% 5% 2 4 4 3 4 3 6% 6% 50%	2091
	11th to 20th	Day	9% 6% 2 5% 4 4 5% 3 5% 7% 48%	2090
	21st to end	Day	19% 7% 2 6% 4 3 4 3 5% 5% 43%	2090
October	1st to 10th	Day	13% 6% 2 6% 4 5% 4 3 5% 8% 45%	2033
	11th to 20th	Day	14% 7% 2 6% 4 5% 4 4 5% 6% 43%	1900
	21st to end	Day	21% 8% 2 8% 4 4 3 3 5% 5% 36%	2041
November	1st to 10th	Day	11% 7% 2 6% 4 4 3 3 5% 6% 48%	1762
	11th to 20th	Day	16% 13% 3 6% 6% 5% 4 3 4 5% 34%	1800
	21st to end	Day	19% 13% 4 8% 5% 4 4 3 4 6% 30%	1800
December	1st to 10th	Day	20% 12% 4 15% 5% 4 4 3 4 4 25%	2930
	11th to 20th	Day	24% 16% 6% 9% 4 3 4 3 5% 5% 21%	3373
	21st to end	Day	25% 19% 6% 10% 5% 5% 4 4 4 4 15%	4466
January	1st to 10th	Night	16% 17% 8% 16% 6% 4 3 3 4 5% 18%	5889
	11th to 20th	Night	13% 17% 7% 15% 8% 6% 5% 3 4 4 17%	5900
	21st to end	Night	22% 13% 7% 9% 6% 4 4 3 3 4 26%	6490
February	1st to 10th	Night	21% 13% 4 9% 6% 4 4 3 4 5% 28%	2600
	11th to 20th	Night	19% 12% 4 10% 6% 5% 5% 3 5% 6% 26%	2358
	21st to end	Night	20% 13% 6% 10% 4 4 3 3 4 5% 28%	1980
March	1st to 10th	Night	20% 12% 4 7% 4 3 4 3 4 5% 35%	5150
	11th to 20th	Night	13% 7% 2 5% 4 4 4 4 6% 7% 42%	4980
	21st to end	Night	20% 9% 3 7% 5% 4 5% 3 4 5% 36%	5467
April	1st to 10th	Night	17% 9% 3 5% 5% 4 4 4 5% 6% 37%	2177
	11th to 20th	Night	15% 8% 2 7% 4 4 5% 4 5% 7% 38%	1822
	21st to end	Night	15% 8% 2 7% 5% 4 4 3 6% 8% 37%	1800
May	1st to 10th	Night	28% 8% 3 7% 5% 3 5% 4 5% 6% 27%	2903
	11th to 20th	Night	18% 7% 2 5% 4 4 4 3 5% 8% 40%	2902
	21st to end	Night	11% 5% 2 6% 4 4 4 5% 6% 8% 45%	3130
June	1st to 10th	Night	9% 5% 3 5% 4 5% 5% 3 6% 8% 46%	1710
	11th to 20th	Night	8% 5% 2 5% 3 5% 6% 4 8% 11% 44%	1710
	21st to end	Night	9% 5% 2 5% 4 4 5% 4 8% 10% 44%	1580
July	1st to 10th	Night	12% 6% 2 6% 4 4 5% 4 5% 7% 46%	2768
	11th to 20th	Night	9% 5% 1 5% 5% 4 4 5% 6% 8% 48%	2840
	21st to end	Night	9% 6% 3 7% 5% 5% 5% 5% 7% 7% 40%	3087
August	1st to 10th	Night	9% 6% 3 7% 5% 5% 5% 4 7% 10% 37%	2825
	11th to 20th	Night	10% 7% 3 7% 5% 5% 4 2 6% 7% 44%	2785
	21st to end	Night	5% 3 2 6% 4 4 5% 4 6% 9% 51%	3186
September	1st to 10th	Night	14% 4 1 4 3 4 4 3 4 6% 53%	2068
	11th to 20th	Night	9% 4 1 5% 3 3 4 4 5% 7% 55%	2090
	21st to end	Night	16% 7% 2 6% 3 3 4 3 4 6% 47%	2090
October	1st to 10th	Night	10% 4 2 5% 4 4 4 4 5% 7% 50%	2146
	11th to 20th	Night	16% 8% 2 5% 3 3 4 3 5% 6% 45%	2280
	21st to end	Night	21% 7% 2 6% 4 3 4 3 5% 5% 39%	2555
November	1st to 10th	Night	15% 6% 2 6% 3 4 3 3 4 6% 48%	2536
	11th to 20th	Night	17% 10% 3 6% 5% 4 4 4 5% 6% 36%	2600
	21st to end	Night	20% 13% 4 7% 5% 4 4 3 5% 5% 30%	2600
December	1st to 10th	Night	19% 12% 5% 9% 5% 4 4 3 6% 6% 27%	4250
	11th to 20th	Night	19% 16% 7% 10% 5% 4 3 3 4 6% 23%	4822
	21st to end	Night	25% 19% 5% 9% 5% 5% 4 3 4 5% 16%	6490

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	75% 2 7% 12% 4	4057
	11th to 20th	Day	74% 2 8% 9% 7% 1	4060
	21st to end	Day	74% 2 10% 8% 6%	4466
February	1st to 10th	Day	63% 3 10% 16% 8%	1800
	11th to 20th	Day	62% 4 8% 17% 8%	1934
	21st to end	Day	58% 2 12% 18% 8% 1	1650
March	1st to 10th	Day	60% 2 7% 23% 7% 1	4702
	11th to 20th	Day	46% 2 9% 30% 11% 1	4980
	21st to end	Day	55% 2 9% 22% 11% 2	5465
April	1st to 10th	Day	53% 3 10% 20% 12% 1	2240
	11th to 20th	Day	48% 4 11% 21% 13% 3	2527
	21st to end	Day	49% 5% 10% 22% 12% 2	2600
May	1st to 10th	Day	56% 3 11% 23% 7% 1	4250
	11th to 20th	Day	50% 4 12% 22% 12% 1	4215
	21st to end	Day	43% 5% 13% 22% 13% 3	4554
June	1st to 10th	Day	43% 5% 11% 25% 15% 2	2470
	11th to 20th	Day	40% 5% 16% 24% 15% 1	2470
	21st to end	Day	40% 5% 16% 21% 15% 3	2577
July	1st to 10th	Day	42% 4 12% 23% 16% 3	4093
	11th to 20th	Day	34% 4 11% 31% 19% 1	4051
	21st to end	Day	43% 4 13% 19% 18% 4	4324
August	1st to 10th	Day	40% 4 15% 29% 11% 1	4091
	11th to 20th	Day	38% 4 11% 31% 16% 1	4083
	21st to end	Day	32% 4 14% 32% 14% 3	4452
September	1st to 10th	Day	34% 5% 10% 24% 23% 4	2091
	11th to 20th	Day	35% 4 10% 27% 21% 3	2090
	21st to end	Day	44% 4 8% 23% 21% 1	2090
October	1st to 10th	Day	27% 3 9% 34% 27% 1	3384
	11th to 20th	Day	35% 2 10% 28% 22% 3	3140
	21st to end	Day	39% 2 11% 27% 19% 2	3343
November	1st to 10th	Day	37% 4 9% 28% 18% 3	1762
	11th to 20th	Day	53% 3 8% 21% 12% 3	1800
	21st to end	Day	56% 3 11% 20% 10% 1	1800
December	1st to 10th	Day	64% 2 12% 18% 4	2930
	11th to 20th	Day	67% 2 11% 15% 5%	3370
	21st to end	Day	74% 2 9% 11% 4	4466
January	1st to 10th	Night	70% 2 9% 16% 4	5889
	11th to 20th	Night	72% 2 8% 11% 6% 1	5900
	21st to end	Night	65% 2 11% 15% 6% 2	6490
February	1st to 10th	Night	60% 4 10% 18% 8% 1	2600
	11th to 20th	Night	59% 3 10% 18% 10% 1	2359
	21st to end	Night	60% 2 10% 17% 9% 2	1980
March	1st to 10th	Night	53% 2 6% 27% 10% 2	5150
	11th to 20th	Night	41% 2 10% 34% 11% 1	4980
	21st to end	Night	52% 3 6% 24% 14% 2	5467
April	1st to 10th	Night	47% 4 11% 22% 14% 2	2177
	11th to 20th	Night	45% 3 11% 19% 18% 4	1822
	21st to end	Night	45% 4 10% 24% 15% 2	1800
May	1st to 10th	Night	57% 4 9% 20% 7% 2	2930
	11th to 20th	Night	44% 5% 12% 27% 10% 1	2903
	21st to end	Night	35% 5% 13% 30% 13% 3	3138
June	1st to 10th	Night	35% 6% 12% 24% 19% 3	1710
	11th to 20th	Night	32% 6% 15% 25% 17% 3	1710
	21st to end	Night	33% 7% 15% 24% 18% 3	1580
July	1st to 10th	Night	39% 3 11% 23% 18% 5%	2723
	11th to 20th	Night	34% 4 12% 31% 18% 1	2786
	21st to end	Night	41% 4 13% 21% 15% 5%	2988
August	1st to 10th	Night	42% 4 15% 26% 12% 1	2814
	11th to 20th	Night	40% 4 9% 27% 20% 1	2812
	21st to end	Night	29% 4 15% 30% 19% 3	3186
September	1st to 10th	Night	33% 4 12% 23% 21% 6%	2068
	11th to 20th	Night	29% 4 10% 27% 27% 4	2090
	21st to end	Night	40% 3 10% 21% 25% 1	2090
October	1st to 10th	Night	27% 3 6% 30% 31% 3	3575
	11th to 20th	Night	31% 2 10% 29% 24% 4	3779
	21st to end	Night	34% 3 8% 26% 26% 4	4203
November	1st to 10th	Night	38% 3 11% 26% 19% 3	2536
	11th to 20th	Night	49% 3 8% 23% 15% 2	2600
	21st to end	Night	56% 2 12% 20% 9% 1	2600
December	1st to 10th	Night	59% 2 12% 21% 5%	4250
	11th to 20th	Night	64% 2 12% 16% 5%	4824
	21st to end	Night	72% 2 9% 14% 3	6490

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	27% 16% 33% 18% 5% 2	300
	11th to 20th	Day	25% 19% 38% 14% 4	300
	21st to end	Day	29% 14% 35% 15% 6%	330
February	1st to 10th	Day	29% 14% 35% 16% 5%	300
	11th to 20th	Day	28% 19% 35% 14% 3 1	300
	21st to end	Day	24% 18% 40% 16% 2	249
March	1st to 10th	Day	22% 16% 33% 22% 6%	392
	11th to 20th	Day	25% 13% 32% 22% 7% 2	500
	21st to end	Day	29% 12% 32% 21% 6%	550
April	1st to 10th	Day	24% 12% 31% 21% 10% 2	500
	11th to 20th	Day	22% 14% 28% 22% 9% 5%	492
	21st to end	Day	20% 10% 32% 24% 12% 2	500
May	1st to 10th	Day	26% 9% 27% 20% 14% 3	503
	11th to 20th	Day	21% 6% 25% 23% 18% 7%	527
	21st to end	Day	13% 6% 21% 27% 22% 10%	549
June	1st to 10th	Day	14% 4 20% 31% 21% 10%	490
	11th to 20th	Day	14% 4 17% 28% 27% 10%	490
	21st to end	Day	12% 5% 23% 28% 22% 9%	597
July	1st to 10th	Day	15% 4 10% 23% 24% 24%	510
	11th to 20th	Day	10% 3 16% 25% 29% 17%	484
	21st to end	Day	12% 2 10% 28% 30% 17%	532
August	1st to 10th	Day	11% 3 12% 22% 34% 19%	486
	11th to 20th	Day	14% 3 16% 29% 24% 15%	479
	21st to end	Day	8% 1 10% 28% 32% 21%	539
September	1st to 10th	Day	14% 3 12% 25% 29% 18%	490
	11th to 20th	Day	10% 2 9% 23% 36% 19%	490
	21st to end	Day	22% 7% 14% 27% 22% 10%	490
October	1st to 10th	Day	12% 5% 22% 30% 20% 11%	490
	11th to 20th	Day	14% 10% 29% 28% 15% 4	490
	21st to end	Day	22% 9% 31% 26% 12% 1	490
November	1st to 10th	Day	14% 10% 31% 28% 13% 4	300
	11th to 20th	Day	22% 18% 26% 20% 12% 2	300
	21st to end	Day	27% 10% 35% 23% 4 1	300
December	1st to 10th	Day	27% 13% 33% 19% 6% 2	300
	11th to 20th	Day	25% 13% 39% 17% 6%	300
	21st to end	Day	32% 13% 29% 21% 5%	330
January	1st to 10th	Night	24% 13% 33% 26% 5%	800
	11th to 20th	Night	28% 12% 33% 23% 4	800
	21st to end	Night	25% 11% 33% 28% 3	880
February	1st to 10th	Night	28% 9% 30% 30% 3	800
	11th to 20th	Night	25% 11% 35% 26% 3	783
	21st to end	Night	25% 12% 37% 25% 2	660
March	1st to 10th	Night	21% 10% 33% 30% 6%	800
	11th to 20th	Night	20% 11% 35% 27% 7%	800
	21st to end	Night	25% 9% 31% 27% 7% 1	880
April	1st to 10th	Night	21% 10% 35% 27% 7%	777
	11th to 20th	Night	17% 7% 35% 28% 12% 1	593
	21st to end	Night	17% 6% 38% 30% 8% 1	600
May	1st to 10th	Night	20% 8% 29% 30% 14%	600
	11th to 20th	Night	20% 4 21% 37% 17% 1	591
	21st to end	Night	9% 4 17% 39% 28% 3	634
June	1st to 10th	Night	10% 4 19% 43% 23% 1	570
	11th to 20th	Night	11% 2 17% 42% 26% 2	570
	21st to end	Night	10% 3 17% 43% 25% 2	570
July	1st to 10th	Night	11% 3 10% 41% 29% 7%	555
	11th to 20th	Night	7% 2 10% 39% 36% 6%	552
	21st to end	Night	10% 2 9% 40% 36% 2	624
August	1st to 10th	Night	7% 1 9% 42% 36% 4	567
	11th to 20th	Night	11% 2 9% 41% 34% 4	564
	21st to end	Night	8% 1 9% 37% 37% 7%	627
September	1st to 10th	Night	16% 2 12% 33% 32% 5%	738
	11th to 20th	Night	10% 2 11% 37% 35% 6%	760
	21st to end	Night	19% 3 18% 34% 24% 2	760
October	1st to 10th	Night	11% 3 21% 38% 24% 3	760
	11th to 20th	Night	19% 6% 27% 33% 14% 1	760
	21st to end	Night	24% 7% 27% 32% 10%	836
November	1st to 10th	Night	19% 5% 26% 33% 16% 1	780
	11th to 20th	Night	21% 10% 29% 30% 10% 1	800
	21st to end	Night	26% 9% 26% 31% 7% 1	800
December	1st to 10th	Night	28% 8% 30% 29% 5%	800
	11th to 20th	Night	25% 9% 32% 29% 5% 1	800
	21st to end	Night	32% 10% 27% 28% 3	880

Page generated at 2025-05-23 09:21:02. Version ac07

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