Dog-Star Observatory
Clear Sky Chart
History

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

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	15% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	113599
	Night	15% 10% 4 9% 5% 5% 4 3 5% 6% 33%	114693
Transparency	Day	49% 6% 11% 20% 11% 2	117238
	Night	49% 5% 12% 20% 12% 2	119193
Seeing	Day	23% 15% 27% 21% 11% 4	15242
	Night	22% 12% 25% 29% 11% 1	24848

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	12% 17% 6% 18% 4 4 4 3 3 4 24%	3615
	11th to 20th	Day	10% 16% 10% 19% 9% 7% 4 3 4 3 15%	4060
	21st to end	Day	17% 17% 7% 10% 6% 4 3 3 4 5% 23%	4466
February	1st to 10th	Day	15% 16% 5% 10% 7% 5% 4 3 4 6% 24%	1800
	11th to 20th	Day	14% 11% 5% 12% 6% 5% 5% 4 6% 5% 26%	1753
	21st to end	Day	17% 12% 4 11% 5% 4 4 4 4 6% 28%	1628
March	1st to 10th	Day	18% 12% 4 8% 5% 4 4 3 4 6% 34%	4924
	11th to 20th	Day	13% 11% 4 9% 5% 5% 4 3 5% 7% 36%	4980
	21st to end	Day	13% 10% 4 8% 6% 5% 5% 4 5% 5% 36%	5500
April	1st to 10th	Day	17% 11% 3 8% 5% 5% 5% 3 5% 6% 31%	2400
	11th to 20th	Day	16% 11% 3 7% 4 4 4 3 6% 6% 35%	2254
	21st to end	Day	20% 8% 4 7% 5% 5% 4 3 5% 6% 33%	2356
May	1st to 10th	Day	28% 8% 3 7% 5% 4 4 3 5% 6% 29%	4082
	11th to 20th	Day	23% 8% 3 8% 5% 5% 4 3 5% 7% 28%	4324
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 7% 9% 40%	4823
June	1st to 10th	Day	13% 7% 3 6% 6% 6% 5% 4 6% 8% 35%	2660
	11th to 20th	Day	14% 6% 2 7% 5% 6% 5% 4 6% 9% 35%	2660
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 9% 39%	2660
July	1st to 10th	Day	7% 6% 3 8% 6% 5% 5% 5% 7% 9% 37%	4440
	11th to 20th	Day	7% 6% 3 7% 6% 6% 6% 5% 8% 10% 38%	4381
	21st to end	Day	10% 8% 3 8% 6% 5% 5% 5% 6% 7% 37%	4466
August	1st to 10th	Day	18% 7% 3 7% 5% 5% 6% 4 7% 9% 29%	4104
	11th to 20th	Day	13% 6% 3 7% 5% 6% 7% 5% 7% 7% 34%	4012
	21st to end	Day	13% 7% 2 5% 4 4 5% 4 6% 9% 42%	4180
September	1st to 10th	Day	16% 6% 2 6% 5% 3 4 4 4 6% 44%	2280
	11th to 20th	Day	14% 5% 2 4 4 3 4 3 5% 8% 48%	2261
	21st to end	Day	22% 8% 2 6% 4 4 3 3 7% 6% 36%	1991
October	1st to 10th	Day	17% 7% 3 6% 5% 4 4 4 4 7% 39%	1900
	11th to 20th	Day	17% 8% 3 7% 5% 4 4 4 6% 6% 36%	1900
	21st to end	Day	18% 9% 3 6% 4 4 5% 4 5% 6% 37%	2090
November	1st to 10th	Day	11% 7% 3 6% 4 4 5% 4 5% 6% 43%	1846
	11th to 20th	Day	15% 13% 3 7% 6% 5% 6% 4 5% 6% 31%	1653
	21st to end	Day	16% 12% 3 8% 6% 5% 5% 4 6% 6% 28%	1600
December	1st to 10th	Day	15% 13% 6% 16% 6% 5% 4 4 4 5% 20%	2600
	11th to 20th	Day	22% 16% 4 8% 4 3 4 4 4 5% 26%	2990
	21st to end	Day	19% 17% 7% 11% 7% 5% 5% 4 5% 4 17%	3960
January	1st to 10th	Night	12% 13% 6% 21% 7% 5% 4 3 4 6% 21%	6326
	11th to 20th	Night	12% 14% 6% 19% 7% 5% 4 3 5% 7% 19%	5900
	21st to end	Night	17% 13% 5% 11% 6% 6% 6% 3 5% 5% 23%	6490
February	1st to 10th	Night	15% 12% 4 9% 6% 5% 4 4 5% 7% 29%	2600
	11th to 20th	Night	16% 10% 4 9% 6% 5% 7% 4 5% 5% 29%	2533
	21st to end	Night	15% 11% 3 11% 5% 6% 4 4 5% 5% 31%	2001
March	1st to 10th	Night	18% 11% 5% 7% 5% 4 3 3 4 5% 33%	4928
	11th to 20th	Night	10% 9% 5% 7% 4 5% 4 3 5% 7% 42%	4980
	21st to end	Night	13% 9% 4 8% 5% 4 4 3 5% 5% 39%	5431
April	1st to 10th	Night	18% 12% 4 9% 5% 4 4 4 4 6% 31%	2000
	11th to 20th	Night	16% 8% 3 6% 5% 4 4 4 5% 6% 38%	1882
	21st to end	Night	17% 6% 3 6% 5% 5% 4 4 5% 8% 37%	1839
May	1st to 10th	Night	27% 9% 3 6% 5% 4 4 3 4 5% 29%	2813
	11th to 20th	Night	26% 10% 3 7% 3 4 4 3 5% 6% 30%	2565
	21st to end	Night	13% 6% 2 7% 5% 5% 5% 4 7% 10% 39%	2732
June	1st to 10th	Night	12% 6% 2 7% 4 4 4 3 6% 9% 44%	1520
	11th to 20th	Night	11% 6% 3 7% 5% 3 5% 5% 7% 9% 40%	1520
	21st to end	Night	11% 6% 1 5% 4 5% 5% 4 8% 11% 42%	1520
July	1st to 10th	Night	8% 6% 3 8% 6% 5% 5% 4 6% 9% 41%	2520
	11th to 20th	Night	6% 5% 3 6% 4 5% 5% 5% 7% 10% 44%	2574
	21st to end	Night	12% 7% 2 7% 5% 5% 5% 4 5% 7% 42%	3087
August	1st to 10th	Night	16% 7% 3 6% 4 4 5% 4 6% 8% 36%	2825
	11th to 20th	Night	14% 8% 3 6% 4 4 5% 4 6% 7% 40%	2785
	21st to end	Night	14% 5% 2 5% 4 4 5% 4 5% 8% 46%	3476
September	1st to 10th	Night	16% 5% 2 4 5% 4 4 3 5% 7% 46%	1900
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 5% 8% 51%	1914
	21st to end	Night	20% 6% 2 6% 4 4 4 3 4 7% 40%	2187
October	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 4 7% 44%	2280
	11th to 20th	Night	15% 8% 2 6% 5% 3 4 3 5% 6% 43%	2280
	21st to end	Night	19% 9% 3 5% 3 4 4 3 5% 6% 39%	2508
November	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 4 6% 50%	2451
	11th to 20th	Night	17% 11% 3 6% 5% 4 4 3 5% 6% 35%	2745
	21st to end	Night	17% 11% 5% 7% 5% 4 5% 4 5% 6% 33%	2800
December	1st to 10th	Night	13% 11% 7% 13% 5% 5% 5% 4 5% 7% 24%	4580
	11th to 20th	Night	20% 12% 5% 10% 5% 5% 4 3 4 6% 27%	5205
	21st to end	Night	19% 14% 5% 11% 6% 5% 5% 3 5% 5% 22%	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	63% 5% 10% 14% 6% 1	3616
	11th to 20th	Day	74% 4 6% 9% 6% 1	4060
	21st to end	Day	63% 4 10% 15% 7%	4466
February	1st to 10th	Day	60% 5% 11% 15% 7% 1	1800
	11th to 20th	Day	57% 6% 9% 20% 7% 1	1762
	21st to end	Day	56% 6% 11% 18% 7% 3	1628
March	1st to 10th	Day	52% 4 12% 20% 10% 2	4924
	11th to 20th	Day	47% 6% 15% 22% 8% 2	4980
	21st to end	Day	49% 5% 11% 19% 15% 2	5500
April	1st to 10th	Day	52% 5% 10% 18% 12% 2	2400
	11th to 20th	Day	47% 6% 10% 18% 15% 3	2254
	21st to end	Day	50% 6% 10% 20% 13% 2	2356
May	1st to 10th	Day	55% 7% 9% 19% 10% 1	4120
	11th to 20th	Day	53% 8% 14% 16% 7% 1	4328
	21st to end	Day	37% 10% 14% 24% 13% 2	4837
June	1st to 10th	Day	44% 8% 12% 22% 14% 1	2660
	11th to 20th	Day	43% 8% 14% 20% 13% 2	2660
	21st to end	Day	39% 7% 14% 26% 13% 1	2660
July	1st to 10th	Day	42% 7% 15% 24% 11% 2	4370
	11th to 20th	Day	40% 6% 14% 24% 15% 1	4306
	21st to end	Day	44% 5% 11% 23% 16% 1	4324
August	1st to 10th	Day	50% 7% 15% 20% 9%	4091
	11th to 20th	Day	46% 5% 10% 27% 10% 1	4051
	21st to end	Day	39% 5% 11% 28% 15% 2	4180
September	1st to 10th	Day	41% 6% 10% 23% 18% 3	2280
	11th to 20th	Day	34% 6% 11% 27% 19% 2	2261
	21st to end	Day	47% 6% 12% 18% 16% 1	1991
October	1st to 10th	Day	41% 4 7% 26% 18% 3	3160
	11th to 20th	Day	44% 4 8% 24% 16% 4	3140
	21st to end	Day	32% 4 14% 31% 18% 1	3428
November	1st to 10th	Day	39% 6% 14% 21% 17% 3	1846
	11th to 20th	Day	53% 6% 10% 20% 10% 2	1653
	21st to end	Day	54% 7% 12% 20% 7%	1600
December	1st to 10th	Day	66% 5% 11% 13% 5% 1	2600
	11th to 20th	Day	60% 4 12% 19% 5%	2986
	21st to end	Day	69% 5% 10% 10% 5% 1	3960
January	1st to 10th	Night	64% 5% 9% 15% 6% 1	6326
	11th to 20th	Night	64% 5% 12% 10% 7% 2	5900
	21st to end	Night	63% 4 9% 16% 8% 1	6490
February	1st to 10th	Night	54% 6% 12% 21% 7% 1	2600
	11th to 20th	Night	53% 6% 10% 19% 11% 1	2535
	21st to end	Night	54% 6% 8% 19% 10% 1	2001
March	1st to 10th	Night	54% 4 11% 19% 10% 2	4928
	11th to 20th	Night	40% 7% 16% 26% 8% 4	4980
	21st to end	Night	47% 4 8% 19% 19% 2	5431
April	1st to 10th	Night	53% 5% 10% 18% 13% 1	2000
	11th to 20th	Night	44% 7% 11% 20% 15% 2	1882
	21st to end	Night	44% 6% 11% 22% 14% 3	1839
May	1st to 10th	Night	55% 7% 8% 17% 10% 2	2840
	11th to 20th	Night	52% 9% 14% 15% 9% 1	2566
	21st to end	Night	37% 9% 17% 21% 12% 4	2739
June	1st to 10th	Night	38% 7% 13% 25% 15% 2	1520
	11th to 20th	Night	37% 9% 14% 23% 14% 2	1520
	21st to end	Night	35% 8% 14% 27% 15%	1520
July	1st to 10th	Night	41% 6% 13% 20% 16% 3	2480
	11th to 20th	Night	35% 6% 15% 26% 16% 1	2526
	21st to end	Night	41% 6% 13% 18% 21% 2	2988
August	1st to 10th	Night	46% 7% 15% 23% 9%	2814
	11th to 20th	Night	43% 4 11% 27% 13% 1	2812
	21st to end	Night	37% 5% 12% 32% 13% 2	3476
September	1st to 10th	Night	38% 7% 11% 23% 18% 3	1900
	11th to 20th	Night	31% 6% 11% 30% 20% 2	1914
	21st to end	Night	44% 6% 11% 22% 17% 1	2187
October	1st to 10th	Night	39% 4 10% 26% 21% 1	3800
	11th to 20th	Night	35% 4 10% 26% 20% 5%	3779
	21st to end	Night	34% 3 13% 28% 20% 2	4120
November	1st to 10th	Night	35% 5% 14% 25% 18% 3	2451
	11th to 20th	Night	48% 5% 10% 21% 13% 3	2745
	21st to end	Night	51% 5% 13% 22% 8% 1	2800
December	1st to 10th	Night	59% 5% 13% 18% 4	4580
	11th to 20th	Night	59% 4 14% 17% 6%	5208
	21st to end	Night	62% 6% 10% 15% 7%	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	30% 28% 27% 10% 5% 1	203
	11th to 20th	Day	38% 21% 29% 10% 1	300
	21st to end	Day	27% 25% 35% 9% 3 1	330
February	1st to 10th	Day	31% 23% 31% 12% 3	300
	11th to 20th	Day	38% 25% 31% 6% 1	300
	21st to end	Day	34% 21% 28% 16% 1	392
March	1st to 10th	Day	31% 20% 28% 18% 4	500
	11th to 20th	Day	30% 22% 28% 15% 4 1	500
	21st to end	Day	29% 21% 30% 14% 4 2	550
April	1st to 10th	Day	30% 21% 26% 18% 4 1	500
	11th to 20th	Day	23% 22% 24% 18% 9% 4	452
	21st to end	Day	29% 16% 32% 15% 7% 2	460
May	1st to 10th	Day	31% 17% 27% 13% 10% 3	463
	11th to 20th	Day	25% 16% 25% 18% 12% 4	487
	21st to end	Day	20% 9% 26% 23% 16% 5%	529
June	1st to 10th	Day	18% 14% 26% 26% 12% 4	490
	11th to 20th	Day	19% 10% 26% 27% 14% 4	490
	21st to end	Day	16% 11% 29% 27% 13% 3	490
July	1st to 10th	Day	15% 7% 24% 27% 17% 10%	485
	11th to 20th	Day	10% 6% 28% 30% 20% 6%	484
	21st to end	Day	15% 7% 29% 28% 16% 5%	532
August	1st to 10th	Day	15% 6% 24% 26% 22% 8%	486
	11th to 20th	Day	15% 5% 24% 25% 20% 10%	479
	21st to end	Day	14% 8% 24% 27% 15% 12%	539
September	1st to 10th	Day	19% 8% 19% 28% 18% 8%	490
	11th to 20th	Day	17% 4 20% 27% 23% 9%	490
	21st to end	Day	29% 10% 21% 21% 14% 5%	490
October	1st to 10th	Day	24% 10% 19% 24% 19% 4	490
	11th to 20th	Day	22% 15% 28% 22% 11% 2	490
	21st to end	Day	24% 14% 31% 23% 7% 1	539
November	1st to 10th	Day	18% 16% 30% 23% 11% 2	439
	11th to 20th	Day	26% 21% 29% 17% 7% 1	253
	21st to end	Day	27% 21% 35% 14% 3 1	200
December	1st to 10th	Day	31% 25% 31% 10% 4 1	200
	11th to 20th	Day	31% 21% 31% 16% 2	200
	21st to end	Day	29% 21% 29% 16% 5%	220
January	1st to 10th	Night	26% 20% 33% 18% 4	800
	11th to 20th	Night	28% 17% 30% 22% 3	800
	21st to end	Night	23% 21% 32% 22% 2	880
February	1st to 10th	Night	27% 18% 28% 25% 2	800
	11th to 20th	Night	30% 22% 31% 17% 1	783
	21st to end	Night	28% 18% 32% 20% 2	660
March	1st to 10th	Night	25% 18% 32% 23% 3	800
	11th to 20th	Night	26% 18% 29% 22% 5%	800
	21st to end	Night	25% 15% 33% 21% 6% 1	880
April	1st to 10th	Night	28% 17% 30% 22% 5%	800
	11th to 20th	Night	22% 13% 31% 26% 7% 1	754
	21st to end	Night	23% 12% 28% 30% 7%	699
May	1st to 10th	Night	25% 9% 24% 31% 11% 1	570
	11th to 20th	Night	20% 8% 29% 33% 10%	418
	21st to end	Night	14% 6% 20% 38% 20% 1	411
June	1st to 10th	Night	13% 7% 22% 39% 19% 1	380
	11th to 20th	Night	13% 6% 23% 39% 18%	380
	21st to end	Night	11% 6% 21% 44% 17%	380
July	1st to 10th	Night	12% 6% 18% 41% 22% 3	370
	11th to 20th	Night	6% 3 18% 41% 30% 2	396
	21st to end	Night	12% 3 17% 45% 22% 1	624
August	1st to 10th	Night	10% 1 15% 43% 29% 2	567
	11th to 20th	Night	15% 4 13% 37% 27% 4	564
	21st to end	Night	14% 3 17% 34% 29% 3	836
September	1st to 10th	Night	18% 4 17% 34% 24% 3	760
	11th to 20th	Night	14% 4 17% 32% 28% 5%	760
	21st to end	Night	23% 8% 18% 29% 19% 3	760
October	1st to 10th	Night	22% 7% 20% 28% 20% 3	760
	11th to 20th	Night	20% 13% 24% 31% 11% 1	760
	21st to end	Night	24% 13% 23% 32% 7% 1	836
November	1st to 10th	Night	16% 11% 27% 34% 11% 1	780
	11th to 20th	Night	26% 17% 23% 25% 8% 1	800
	21st to end	Night	24% 17% 28% 26% 5% 1	800
December	1st to 10th	Night	29% 17% 29% 20% 5%	800
	11th to 20th	Night	27% 16% 28% 26% 4	800
	21st to end	Night	26% 16% 28% 28% 3	880

Page generated at 2025-04-08 09:17:28. Version ac07

Copyright © 2025 Attilla Danko.