Dogstar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dogstar Observatory clear sky chart from 2005-11-06 to 2025-04-26.

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	14% 8% 3 7% 5% 5% 5% 4 5% 7% 37%	114038
	Night	14% 9% 3 6% 4 4 4 4 5% 7% 40%	114592
Transparency	Day	43% 7% 11% 17% 16% 7%	117819
	Night	40% 8% 12% 17% 17% 7%	118950
Seeing	Day	21% 13% 23% 21% 14% 7%	15557
	Night	19% 9% 21% 28% 18% 4	25696

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	13% 10% 4 5% 3 3 3 3 5% 5% 47%	4056
	11th to 20th	Day	11% 9% 4 7% 3 3 3 2 3 3 51%	4060
	21st to end	Day	17% 10% 3 5% 4 3 3 2 5% 5% 43%	4466
February	1st to 10th	Day	15% 10% 4 7% 4 4 3 3 5% 6% 39%	1935
	11th to 20th	Day	18% 12% 3 6% 5% 3 3 3 4 6% 37%	1948
	21st to end	Day	19% 11% 2 7% 4 4 4 3 4 6% 37%	1650
March	1st to 10th	Day	20% 8% 3 6% 4 4 4 3 4 5% 38%	4752
	11th to 20th	Day	13% 8% 2 5% 3 3 3 3 4 6% 50%	4980
	21st to end	Day	18% 8% 3 6% 4 4 4 3 5% 5% 42%	5465
April	1st to 10th	Day	12% 9% 3 6% 5% 4 5% 5% 6% 7% 40%	2200
	11th to 20th	Day	14% 9% 3 7% 4 4 5% 4 5% 6% 40%	2406
	21st to end	Day	15% 8% 3 6% 5% 5% 4 3 5% 7% 40%	2535
May	1st to 10th	Day	16% 11% 3 8% 5% 5% 5% 4 5% 6% 32%	4082
	11th to 20th	Day	19% 10% 4 8% 5% 4 6% 4 5% 6% 28%	4081
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 5% 7% 9% 35%	4476
June	1st to 10th	Day	12% 10% 3 9% 7% 7% 6% 5% 7% 7% 27%	2470
	11th to 20th	Day	8% 7% 3 10% 6% 7% 8% 6% 9% 8% 28%	2470
	21st to end	Day	10% 7% 3 7% 8% 6% 7% 6% 7% 9% 30%	2470
July	1st to 10th	Day	8% 6% 3 10% 8% 6% 7% 6% 8% 10% 29%	4120
	11th to 20th	Day	10% 8% 4 10% 7% 7% 7% 6% 8% 8% 26%	4120
	21st to end	Day	14% 10% 5% 14% 9% 9% 8% 5% 6% 7% 13%	4466
August	1st to 10th	Day	8% 8% 4 9% 7% 7% 7% 6% 8% 9% 26%	4104
	11th to 20th	Day	11% 6% 3 8% 6% 7% 7% 5% 8% 11% 29%	4044
	21st to end	Day	8% 7% 3 9% 6% 6% 6% 5% 7% 7% 36%	4134
September	1st to 10th	Day	11% 9% 4 9% 6% 6% 7% 5% 6% 7% 31%	2090
	11th to 20th	Day	15% 9% 4 10% 6% 6% 5% 4 6% 8% 29%	2090
	21st to end	Day	14% 8% 3 7% 5% 6% 5% 4 5% 6% 36%	2090
October	1st to 10th	Day	11% 6% 2 6% 4 5% 4 3 5% 7% 46%	2090
	11th to 20th	Day	11% 7% 2 5% 3 3 3 3 4 6% 53%	1900
	21st to end	Day	13% 7% 1 4 3 3 3 2 4 6% 53%	2090
November	1st to 10th	Day	11% 6% 2 4 3 4 4 4 5% 5% 53%	1829
	11th to 20th	Day	12% 7% 2 4 3 3 4 3 5% 7% 50%	1800
	21st to end	Day	13% 9% 2 7% 4 3 4 3 5% 6% 45%	1800
December	1st to 10th	Day	19% 7% 2 4 3 3 3 3 4 5% 47%	2930
	11th to 20th	Day	21% 10% 3 5% 4 4 3 3 5% 4 37%	3373
	21st to end	Day	17% 8% 4 7% 4 3 3 3 4 6% 41%	4466
January	1st to 10th	Night	13% 11% 3 5% 3 3 3 2 4 4 49%	5889
	11th to 20th	Night	15% 10% 2 5% 3 3 3 3 4 4 48%	5900
	21st to end	Night	15% 12% 3 6% 3 3 3 3 3 5% 44%	6490
February	1st to 10th	Night	14% 10% 3 6% 4 5% 4 3 5% 6% 39%	2460
	11th to 20th	Night	19% 12% 3 7% 4 4 4 3 4 5% 36%	2338
	21st to end	Night	19% 10% 4 8% 4 3 4 3 5% 6% 34%	1980
March	1st to 10th	Night	19% 13% 4 6% 4 4 4 3 5% 5% 33%	5099
	11th to 20th	Night	13% 7% 2 5% 3 3 4 3 4 7% 47%	4980
	21st to end	Night	15% 8% 3 6% 5% 4 4 4 5% 6% 40%	5467
April	1st to 10th	Night	15% 9% 3 7% 4 4 5% 3 5% 6% 42%	2200
	11th to 20th	Night	12% 9% 3 5% 4 3 4 3 6% 7% 44%	1958
	21st to end	Night	12% 8% 3 7% 5% 4 4 3 4 7% 44%	1761
May	1st to 10th	Night	17% 12% 3 8% 4 4 5% 3 5% 7% 31%	2813
	11th to 20th	Night	19% 10% 3 7% 5% 4 5% 3 5% 7% 31%	2812
	21st to end	Night	8% 7% 3 7% 6% 5% 6% 5% 8% 10% 36%	3079
June	1st to 10th	Night	10% 8% 3 7% 5% 5% 5% 6% 8% 11% 32%	1710
	11th to 20th	Night	6% 6% 2 6% 4 4 7% 5% 8% 11% 39%	1710
	21st to end	Night	9% 6% 2 5% 4 5% 6% 6% 9% 11% 37%	1710
July	1st to 10th	Night	9% 7% 2 8% 6% 6% 7% 6% 8% 12% 29%	2840
	11th to 20th	Night	10% 6% 3 6% 6% 6% 6% 6% 8% 10% 33%	2840
	21st to end	Night	17% 11% 4 10% 7% 7% 6% 5% 7% 8% 20%	3087
August	1st to 10th	Night	8% 6% 3 8% 6% 5% 7% 5% 8% 12% 32%	2825
	11th to 20th	Night	15% 7% 2 8% 5% 5% 5% 4 6% 9% 33%	2785
	21st to end	Night	8% 6% 2 5% 4 4 5% 4 7% 10% 45%	3483
September	1st to 10th	Night	10% 7% 3 8% 5% 6% 6% 5% 8% 8% 35%	2090
	11th to 20th	Night	12% 8% 3 9% 5% 5% 5% 4 6% 9% 34%	2090
	21st to end	Night	13% 8% 2 6% 4 5% 4 4 5% 7% 42%	2090
October	1st to 10th	Night	12% 6% 2 5% 4 4 4 3 5% 7% 48%	2090
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 4 6% 48%	2280
	21st to end	Night	12% 8% 2 4 3 3 4 3 4 5% 52%	2508
November	1st to 10th	Night	12% 7% 2 5% 4 4 3 4 5% 7% 47%	2466
	11th to 20th	Night	13% 10% 3 6% 4 3 3 3 4 6% 47%	2600
	21st to end	Night	14% 9% 2 6% 3 4 4 4 4 6% 45%	2600
December	1st to 10th	Night	18% 10% 3 5% 3 3 3 3 3 5% 45%	4250
	11th to 20th	Night	20% 11% 4 8% 3 3 4 3 3 4 37%	4822
	21st to end	Night	15% 11% 5% 7% 4 4 4 3 4 7% 36%	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	35% 5% 7% 14% 31% 9%	4057
	11th to 20th	Day	34% 6% 6% 11% 29% 14%	4060
	21st to end	Day	40% 4 9% 15% 21% 12%	4466
February	1st to 10th	Day	46% 5% 8% 19% 17% 6%	1935
	11th to 20th	Day	49% 5% 6% 16% 19% 6%	1958
	21st to end	Day	48% 4 8% 12% 20% 8%	1650
March	1st to 10th	Day	46% 4 6% 13% 18% 13%	4752
	11th to 20th	Day	35% 4 6% 15% 21% 20%	4980
	21st to end	Day	44% 4 8% 25% 14% 5%	5465
April	1st to 10th	Day	41% 6% 11% 20% 18% 5%	2200
	11th to 20th	Day	42% 5% 9% 17% 20% 5%	2406
	21st to end	Day	43% 6% 10% 24% 15% 2	2535
May	1st to 10th	Day	47% 10% 11% 19% 12% 2	4120
	11th to 20th	Day	51% 10% 10% 20% 9% 1	4085
	21st to end	Day	40% 11% 15% 19% 15% 1	4489
June	1st to 10th	Day	51% 10% 15% 17% 6% 1	2470
	11th to 20th	Day	45% 11% 17% 15% 10% 1	2470
	21st to end	Day	46% 11% 15% 16% 10% 2	2470
July	1st to 10th	Day	45% 14% 17% 17% 6%	4055
	11th to 20th	Day	50% 15% 19% 11% 4 1	4051
	21st to end	Day	66% 11% 10% 8% 4	4324
August	1st to 10th	Day	47% 13% 16% 20% 3	4091
	11th to 20th	Day	42% 12% 21% 13% 9% 3	4083
	21st to end	Day	42% 12% 12% 22% 10% 1	4134
September	1st to 10th	Day	48% 9% 11% 16% 13% 3	2090
	11th to 20th	Day	52% 6% 11% 16% 14% 2	2090
	21st to end	Day	46% 7% 12% 15% 14% 5%	2090
October	1st to 10th	Day	28% 6% 7% 17% 30% 12%	3480
	11th to 20th	Day	22% 3 6% 18% 21% 30%	3140
	21st to end	Day	26% 4 7% 23% 22% 17%	3428
November	1st to 10th	Day	32% 4 9% 17% 27% 11%	1829
	11th to 20th	Day	34% 3 7% 20% 26% 10%	1800
	21st to end	Day	38% 4 7% 19% 25% 7%	1800
December	1st to 10th	Day	39% 4 6% 16% 23% 12%	2930
	11th to 20th	Day	47% 4 7% 14% 19% 8%	3370
	21st to end	Day	41% 4 13% 24% 16% 3	4466
January	1st to 10th	Night	35% 4 9% 13% 26% 12%	5889
	11th to 20th	Night	38% 5% 5% 13% 26% 15%	5900
	21st to end	Night	39% 6% 8% 11% 24% 12%	6490
February	1st to 10th	Night	43% 4 11% 17% 19% 5%	2460
	11th to 20th	Night	49% 6% 6% 16% 18% 5%	2339
	21st to end	Night	49% 6% 8% 15% 17% 5%	1980
March	1st to 10th	Night	48% 6% 10% 12% 17% 7%	5099
	11th to 20th	Night	34% 6% 8% 19% 17% 16%	4980
	21st to end	Night	44% 5% 12% 21% 13% 6%	5467
April	1st to 10th	Night	40% 6% 12% 20% 19% 3	2200
	11th to 20th	Night	36% 6% 11% 21% 20% 4	1958
	21st to end	Night	38% 8% 13% 25% 14% 1	1761
May	1st to 10th	Night	45% 12% 13% 21% 8% 1	2840
	11th to 20th	Night	46% 11% 16% 18% 8%	2813
	21st to end	Night	33% 15% 19% 25% 9%	3087
June	1st to 10th	Night	41% 14% 18% 19% 7% 1	1710
	11th to 20th	Night	33% 12% 25% 22% 7% 1	1710
	21st to end	Night	35% 14% 18% 20% 11% 3	1710
July	1st to 10th	Night	42% 16% 20% 17% 5%	2795
	11th to 20th	Night	39% 19% 25% 13% 3 1	2786
	21st to end	Night	58% 13% 15% 10% 3 1	2988
August	1st to 10th	Night	39% 15% 26% 16% 4	2814
	11th to 20th	Night	43% 13% 21% 13% 9% 1	2812
	21st to end	Night	31% 10% 21% 28% 9% 1	3483
September	1st to 10th	Night	41% 12% 15% 17% 12% 2	2090
	11th to 20th	Night	46% 9% 12% 18% 14% 1	2090
	21st to end	Night	40% 8% 13% 19% 15% 4	2090
October	1st to 10th	Night	29% 8% 10% 17% 28% 9%	3480
	11th to 20th	Night	25% 4 8% 16% 20% 27%	3779
	21st to end	Night	29% 5% 7% 22% 20% 17%	4120
November	1st to 10th	Night	34% 5% 10% 20% 22% 9%	2466
	11th to 20th	Night	37% 5% 7% 16% 25% 11%	2600
	21st to end	Night	39% 4 7% 21% 22% 7%	2600
December	1st to 10th	Night	41% 4 7% 15% 22% 11%	4250
	11th to 20th	Night	46% 5% 8% 14% 19% 7%	4824
	21st to end	Night	45% 4 13% 18% 18% 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	36% 22% 29% 11% 1	300
	11th to 20th	Day	39% 23% 21% 14% 2	300
	21st to end	Day	33% 29% 26% 9% 2	330
February	1st to 10th	Day	32% 24% 32% 9% 2	300
	11th to 20th	Day	48% 24% 21% 7%	300
	21st to end	Day	44% 28% 21% 6% 1	249
March	1st to 10th	Day	35% 16% 29% 13% 7%	416
	11th to 20th	Day	30% 23% 28% 14% 4 1	500
	21st to end	Day	29% 24% 26% 15% 5% 1	550
April	1st to 10th	Day	27% 19% 24% 20% 8% 1	500
	11th to 20th	Day	22% 24% 21% 22% 10% 2	492
	21st to end	Day	22% 14% 28% 21% 12% 4	480
May	1st to 10th	Day	20% 20% 28% 17% 10% 5%	463
	11th to 20th	Day	22% 10% 24% 23% 13% 7%	487
	21st to end	Day	14% 10% 22% 27% 16% 12%	529
June	1st to 10th	Day	17% 7% 22% 28% 17% 11%	490
	11th to 20th	Day	9% 6% 22% 25% 25% 13%	490
	21st to end	Day	14% 7% 27% 21% 18% 13%	490
July	1st to 10th	Day	11% 4 15% 29% 24% 16%	485
	11th to 20th	Day	12% 4 14% 27% 23% 20%	484
	21st to end	Day	11% 5% 14% 26% 26% 19%	532
August	1st to 10th	Day	17% 6% 18% 23% 19% 17%	486
	11th to 20th	Day	13% 5% 17% 25% 27% 12%	479
	21st to end	Day	14% 4 13% 24% 26% 19%	539
September	1st to 10th	Day	10% 6% 16% 28% 27% 13%	490
	11th to 20th	Day	15% 6% 18% 27% 24% 11%	490
	21st to end	Day	18% 8% 19% 28% 22% 6%	490
October	1st to 10th	Day	18% 8% 21% 27% 18% 9%	490
	11th to 20th	Day	14% 14% 26% 27% 16% 3	490
	21st to end	Day	19% 13% 24% 29% 13% 3	539
November	1st to 10th	Day	18% 14% 28% 26% 12% 2	367
	11th to 20th	Day	24% 19% 31% 22% 5%	300
	21st to end	Day	21% 19% 34% 19% 5% 1	300
December	1st to 10th	Day	36% 20% 27% 13% 3	300
	11th to 20th	Day	30% 17% 30% 18% 4 1	300
	21st to end	Day	31% 17% 35% 13% 4	330
January	1st to 10th	Night	29% 13% 30% 23% 5%	800
	11th to 20th	Night	27% 16% 31% 20% 6%	800
	21st to end	Night	22% 16% 36% 23% 3	880
February	1st to 10th	Night	22% 13% 31% 30% 4	800
	11th to 20th	Night	31% 15% 32% 20% 1	783
	21st to end	Night	31% 18% 29% 19% 3	660
March	1st to 10th	Night	25% 15% 30% 25% 5%	800
	11th to 20th	Night	26% 15% 26% 24% 8% 1	800
	21st to end	Night	24% 14% 29% 24% 9%	880
April	1st to 10th	Night	25% 16% 25% 24% 9% 1	800
	11th to 20th	Night	20% 12% 25% 29% 12% 2	641
	21st to end	Night	16% 10% 21% 35% 16% 1	587
May	1st to 10th	Night	16% 10% 23% 31% 18% 2	570
	11th to 20th	Night	15% 8% 18% 32% 22% 4	561
	21st to end	Night	14% 3 13% 30% 32% 7%	617
June	1st to 10th	Night	12% 4 14% 34% 31% 6%	570
	11th to 20th	Night	9% 1 14% 30% 34% 12%	570
	21st to end	Night	11% 3 9% 32% 38% 7%	570
July	1st to 10th	Night	12% 2 9% 24% 45% 9%	555
	11th to 20th	Night	10% 2 7% 25% 42% 13%	552
	21st to end	Night	9% 3 6% 23% 45% 12%	624
August	1st to 10th	Night	13% 2 9% 27% 39% 10%	567
	11th to 20th	Night	12% 4 9% 29% 38% 9%	564
	21st to end	Night	13% 2 8% 25% 39% 13%	649
September	1st to 10th	Night	12% 4 10% 29% 37% 9%	760
	11th to 20th	Night	16% 4 13% 28% 30% 8%	760
	21st to end	Night	17% 5% 13% 34% 27% 4	760
October	1st to 10th	Night	16% 7% 18% 25% 26% 8%	760
	11th to 20th	Night	16% 9% 24% 31% 18% 3	760
	21st to end	Night	17% 10% 18% 37% 15% 3	836
November	1st to 10th	Night	16% 7% 21% 35% 18% 4	780
	11th to 20th	Night	20% 11% 23% 33% 11% 3	800
	21st to end	Night	22% 12% 21% 31% 14% 1	800
December	1st to 10th	Night	28% 11% 25% 29% 8%	800
	11th to 20th	Night	24% 12% 26% 30% 8% 1	800
	21st to end	Night	28% 12% 25% 30% 5%	880

Page generated at 2025-04-23 09:25:02. Version ac07

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