Black Cliff
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Cliff clear sky chart from 2005-11-06 to 2025-03-12.

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	2 4 1 4 3 3 3 3 4 6% 66%	113612
	Night	3 4 1 4 3 3 3 3 5% 6% 64%	114168
Transparency	Day	18% 3 8% 18% 27% 27%	113369
	Night	20% 4 9% 19% 27% 22%	114001
Seeing	Day	6% 10% 23% 30% 23% 9%	15522
	Night	5% 6% 20% 40% 26% 3	25319

By Month

Percentage Cloud Cover SW (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	2 4 2 4 4 4 4 3 5% 8% 59%	3660
	11th to 20th	Day	2 4 2 4 2 3 3 2 4 5% 69%	4100
	21st to end	Day	3 9% 2 5% 4 4 4 3 4 7% 55%	4510
February	1st to 10th	Day	3 5% 2 5% 4 3 3 4 6% 8% 56%	1970
	11th to 20th	Day	4 5% 1 5% 4 4 4 4 5% 8% 54%	1950
	21st to end	Day	3 6% 2 5% 3 3 3 3 5% 7% 59%	1650
March	1st to 10th	Day	2 8% 2 7% 5% 4 4 3 5% 7% 53%	3238
	11th to 20th	Day	3 8% 2 7% 4 4 4 3 5% 6% 52%	3489
	21st to end	Day	4 8% 3 7% 4 4 5% 4 6% 8% 46%	3825
April	1st to 10th	Day	3 5% 1 6% 4 4 4 4 5% 6% 59%	2261
	11th to 20th	Day	3 4 2 4 4 3 3 3 5% 5% 63%	2249
	21st to end	Day	4 4 1 3 3 2 3 3 5% 7% 66%	2468
May	1st to 10th	Day	2 3 1 4 3 3 4 3 4 6% 68%	4110
	11th to 20th	Day	2 3 1 3 3 3 4 3 5% 7% 67%	4071
	21st to end	Day	2 3 1 5% 3 4 4 3 4 5% 68%	4477
June	1st to 10th	Day	1 2 1 3 3 3 4 3 5% 6% 68%	2470
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 6% 74%	2622
	21st to end	Day	2 2 2 2 2 2 2 3 5% 78%	2660
July	1st to 10th	Day	2 1 1 2 2 2 2 2 3 4 81%	4420
	11th to 20th	Day	2 3 1 4 3 4 4 3 5% 7% 65%	4221
	21st to end	Day	2 2 1 4 4 4 4 4 6% 8% 62%	4454
August	1st to 10th	Day	2 2 1 3 2 2 2 2 4 5% 73%	4092
	11th to 20th	Day	1 1 2 2 2 2 2 3 4 82%	3906
	21st to end	Day	2 1 1 2 2 2 2 2 3 4 80%	4180
September	1st to 10th	Day	2 2 1 3 3 3 3 3 4 4 74%	2200
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 5% 77%	2090
	21st to end	Day	1 1 1 2 2 2 2 2 3 5% 80%	2090
October	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 76%	3490
	11th to 20th	Day	1 2 1 1 2 2 3 3 4 4 78%	3310
	21st to end	Day	2 3 1 2 2 2 2 2 3 4 78%	3168
November	1st to 10th	Day	3 3 1 3 3 2 3 3 4 7% 67%	1764
	11th to 20th	Day	2 2 1 3 2 2 3 3 4 7% 71%	1800
	21st to end	Day	4 4 1 4 4 3 3 4 5% 6% 62%	1800
December	1st to 10th	Day	2 4 1 4 2 3 3 3 4 6% 69%	2950
	11th to 20th	Day	4 6% 2 6% 4 4 4 4 6% 10% 51%	3409
	21st to end	Day	3 5% 1 6% 4 4 4 4 6% 9% 54%	4488
January	1st to 10th	Night	2 4 2 5% 3 3 3 3 4 7% 64%	6221
	11th to 20th	Night	1 3 1 4 3 3 3 3 5% 6% 67%	5880
	21st to end	Night	4 9% 3 5% 3 3 3 3 5% 7% 56%	6468
February	1st to 10th	Night	3 6% 2 5% 3 3 3 3 6% 7% 58%	2426
	11th to 20th	Night	4 6% 2 3 3 4 4 3 5% 8% 58%	2338
	21st to end	Night	4 6% 3 6% 3 4 4 2 5% 7% 57%	1980
March	1st to 10th	Night	3 9% 2 6% 5% 4 4 4 5% 6% 53%	3856
	11th to 20th	Night	5% 8% 3 6% 4 4 4 4 6% 8% 50%	3518
	21st to end	Night	6% 9% 3 6% 3 4 3 3 5% 7% 51%	3828
April	1st to 10th	Night	4 4 2 4 4 3 4 4 5% 6% 60%	1914
	11th to 20th	Night	3 4 2 4 4 3 2 3 4 6% 65%	1879
	21st to end	Night	5% 4 1 4 3 4 4 4 5% 6% 61%	1710
May	1st to 10th	Night	4 4 2 5% 3 3 3 3 5% 6% 63%	2860
	11th to 20th	Night	4 3 2 4 4 3 3 3 6% 8% 60%	2834
	21st to end	Night	4 4 1 5% 4 4 4 3 6% 6% 59%	3110
June	1st to 10th	Night	2 3 1 3 3 3 3 3 4 7% 68%	1710
	11th to 20th	Night	2 4 1 3 2 3 2 2 3 4 74%	1551
	21st to end	Night	2 1 1 2 2 2 3 2 4 5% 75%	1520
July	1st to 10th	Night	2 2 1 2 2 2 2 1 2 3 81%	2540
	11th to 20th	Night	3 3 2 5% 4 4 4 4 6% 8% 58%	2727
	21st to end	Night	4 3 2 6% 5% 4 4 4 7% 7% 53%	3109
August	1st to 10th	Night	2 3 1 3 3 4 4 3 5% 7% 65%	2847
	11th to 20th	Night	1 1 1 2 2 2 2 2 3 5% 80%	2933
	21st to end	Night	2 1 2 1 2 2 2 2 3 82%	3498
September	1st to 10th	Night	2 2 1 3 2 2 3 2 4 5% 73%	1978
	11th to 20th	Night	3 2 1 2 2 2 2 2 4 5% 75%	2090
	21st to end	Night	1 1 2 1 2 2 2 2 4 82%	2090
October	1st to 10th	Night	2 2 1 3 2 2 2 2 3 4 77%	3490
	11th to 20th	Night	3 4 1 3 3 2 3 2 3 5% 72%	3623
	21st to end	Night	3 3 1 2 2 2 3 2 4 5% 74%	4386
November	1st to 10th	Night	3 3 1 3 3 3 2 2 4 8% 69%	2535
	11th to 20th	Night	2 3 1 3 3 2 3 3 4 6% 70%	2600
	21st to end	Night	3 4 1 3 3 3 3 3 5% 6% 65%	2600
December	1st to 10th	Night	3 3 1 3 3 3 3 3 4 6% 68%	4240
	11th to 20th	Night	4 4 1 4 2 3 3 3 5% 11% 59%	4811
	21st to end	Night	2 5% 2 6% 5% 5% 5% 4 7% 11% 49%	6468

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	20% 4 17% 32% 23% 4	3660
	11th to 20th	Day	18% 3 12% 23% 28% 16%	4100
	21st to end	Day	29% 4 11% 21% 26% 9%	4510
February	1st to 10th	Day	25% 5% 13% 27% 22% 8%	1970
	11th to 20th	Day	26% 5% 9% 26% 26% 8%	1960
	21st to end	Day	24% 4 12% 27% 25% 9%	1650
March	1st to 10th	Day	29% 4 8% 27% 23% 8%	3238
	11th to 20th	Day	28% 4 10% 26% 24% 8%	3489
	21st to end	Day	31% 4 13% 25% 23% 5%	3825
April	1st to 10th	Day	24% 4 10% 21% 27% 15%	2261
	11th to 20th	Day	21% 3 7% 20% 29% 20%	2252
	21st to end	Day	18% 3 8% 20% 38% 13%	2468
May	1st to 10th	Day	17% 3 6% 18% 39% 17%	4110
	11th to 20th	Day	14% 3 8% 15% 35% 25%	4074
	21st to end	Day	17% 3 6% 12% 36% 26%	4477
June	1st to 10th	Day	15% 2 6% 12% 32% 33%	2470
	11th to 20th	Day	11% 3 5% 9% 24% 49%	2622
	21st to end	Day	9% 2 4 5% 21% 58%	2660
July	1st to 10th	Day	10% 1 3 4 8% 74%	4351
	11th to 20th	Day	16% 4 5% 9% 18% 47%	4148
	21st to end	Day	17% 5% 7% 13% 19% 38%	4314
August	1st to 10th	Day	14% 3 4 11% 31% 38%	4078
	11th to 20th	Day	8% 2 4 9% 21% 56%	3945
	21st to end	Day	9% 2 3 7% 22% 56%	4179
September	1st to 10th	Day	14% 3 5% 8% 22% 48%	2200
	11th to 20th	Day	11% 2 4 13% 27% 43%	2090
	21st to end	Day	10% 1 4 10% 36% 38%	2090
October	1st to 10th	Day	11% 3 4 8% 30% 45%	3490
	11th to 20th	Day	11% 2 3 16% 35% 33%	3310
	21st to end	Day	12% 2 3 21% 45% 16%	3168
November	1st to 10th	Day	17% 2 10% 25% 31% 15%	1764
	11th to 20th	Day	14% 2 10% 29% 36% 9%	1800
	21st to end	Day	22% 2 9% 23% 32% 12%	1800
December	1st to 10th	Day	17% 3 7% 23% 33% 16%	2950
	11th to 20th	Day	27% 6% 11% 25% 28% 4	3408
	21st to end	Day	24% 5% 17% 30% 21% 3	4488
January	1st to 10th	Night	20% 3 16% 31% 26% 3	6221
	11th to 20th	Night	18% 4 15% 23% 28% 14%	5880
	21st to end	Night	28% 4 11% 21% 26% 11%	6468
February	1st to 10th	Night	25% 4 12% 28% 24% 7%	2426
	11th to 20th	Night	24% 4 10% 24% 29% 9%	2339
	21st to end	Night	27% 3 10% 25% 26% 9%	1980
March	1st to 10th	Night	29% 4 11% 25% 23% 8%	3856
	11th to 20th	Night	29% 5% 10% 27% 21% 7%	3518
	21st to end	Night	31% 4 10% 23% 26% 6%	3828
April	1st to 10th	Night	23% 5% 9% 27% 24% 12%	1914
	11th to 20th	Night	21% 3 9% 21% 31% 15%	1879
	21st to end	Night	22% 4 7% 18% 37% 12%	1710
May	1st to 10th	Night	20% 3 7% 16% 34% 20%	2860
	11th to 20th	Night	17% 4 11% 16% 32% 20%	2835
	21st to end	Night	21% 4 8% 11% 34% 22%	3110
June	1st to 10th	Night	16% 3 5% 13% 30% 33%	1710
	11th to 20th	Night	15% 1 5% 8% 23% 48%	1551
	21st to end	Night	11% 2 4 7% 19% 58%	1520
July	1st to 10th	Night	11% 2 3 4 6% 74%	2500
	11th to 20th	Night	20% 5% 5% 10% 18% 42%	2678
	21st to end	Night	26% 6% 8% 13% 13% 35%	3011
August	1st to 10th	Night	17% 4 5% 11% 27% 35%	2838
	11th to 20th	Night	9% 3 4 7% 21% 57%	2960
	21st to end	Night	8% 2 4 8% 20% 58%	3498
September	1st to 10th	Night	13% 3 6% 9% 22% 47%	1978
	11th to 20th	Night	13% 2 5% 12% 24% 44%	2090
	21st to end	Night	9% 2 5% 11% 33% 41%	2090
October	1st to 10th	Night	11% 3 4 9% 26% 48%	3490
	11th to 20th	Night	16% 2 3 12% 35% 32%	3623
	21st to end	Night	15% 2 4 17% 42% 21%	4386
November	1st to 10th	Night	16% 2 8% 25% 33% 15%	2535
	11th to 20th	Night	14% 3 7% 25% 40% 11%	2600
	21st to end	Night	19% 3 7% 23% 36% 13%	2600
December	1st to 10th	Night	18% 4 7% 25% 31% 15%	4240
	11th to 20th	Night	20% 5% 12% 29% 30% 4	4811
	21st to end	Night	27% 6% 14% 30% 20% 3	6468

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	15% 8% 22% 33% 18% 3	205
	11th to 20th	Day	8% 8% 25% 35% 20% 4	300
	21st to end	Day	5% 10% 19% 32% 27% 7%	330
February	1st to 10th	Day	10% 14% 24% 27% 19% 5%	470
	11th to 20th	Day	7% 14% 24% 34% 17% 4	495
	21st to end	Day	6% 13% 30% 32% 15% 4	414
March	1st to 10th	Day	12% 14% 26% 27% 19% 3	500
	11th to 20th	Day	9% 14% 27% 29% 17% 4	465
	21st to end	Day	10% 22% 33% 23% 11% 2	506
April	1st to 10th	Day	10% 17% 24% 25% 18% 6%	460
	11th to 20th	Day	6% 22% 29% 27% 12% 4	452
	21st to end	Day	7% 20% 25% 24% 16% 7%	460
May	1st to 10th	Day	7% 14% 34% 25% 16% 4	463
	11th to 20th	Day	5% 12% 23% 29% 22% 8%	488
	21st to end	Day	6% 12% 23% 29% 21% 9%	529
June	1st to 10th	Day	2 10% 23% 27% 25% 13%	490
	11th to 20th	Day	4 13% 25% 26% 22% 8%	490
	21st to end	Day	3 6% 22% 30% 29% 9%	490
July	1st to 10th	Day	2 3 21% 36% 25% 12%	486
	11th to 20th	Day	2 3 17% 36% 28% 15%	484
	21st to end	Day	4 2 13% 39% 27% 15%	531
August	1st to 10th	Day	3 4 19% 37% 24% 13%	487
	11th to 20th	Day	2 4 20% 30% 28% 16%	477
	21st to end	Day	3 5% 19% 27% 30% 16%	539
September	1st to 10th	Day	3 5% 16% 28% 30% 18%	490
	11th to 20th	Day	3 9% 25% 25% 26% 11%	490
	21st to end	Day	2 8% 18% 27% 35% 11%	490
October	1st to 10th	Day	3 9% 24% 25% 24% 14%	490
	11th to 20th	Day	5% 8% 18% 26% 29% 13%	395
	21st to end	Day	5% 8% 18% 30% 26% 13%	330
November	1st to 10th	Day	6% 7% 21% 27% 24% 15%	300
	11th to 20th	Day	4 9% 19% 34% 21% 13%	300
	21st to end	Day	6% 7% 19% 32% 25% 11%	300
December	1st to 10th	Day	6% 7% 23% 31% 24% 9%	300
	11th to 20th	Day	7% 3 22% 36% 26% 6%	300
	21st to end	Day	9% 9% 24% 37% 17% 5%	326
January	1st to 10th	Night	8% 6% 22% 37% 22% 5%	800
	11th to 20th	Night	5% 4 23% 44% 22% 2	800
	21st to end	Night	9% 4 25% 40% 20% 3	880
February	1st to 10th	Night	7% 8% 26% 38% 19% 2	800
	11th to 20th	Night	7% 8% 23% 43% 17% 2	784
	21st to end	Night	7% 7% 27% 42% 15% 2	660
March	1st to 10th	Night	7% 10% 25% 41% 17% 1	800
	11th to 20th	Night	6% 10% 23% 37% 22% 2	766
	21st to end	Night	7% 13% 28% 37% 14% 1	836
April	1st to 10th	Night	6% 13% 26% 36% 18% 1	760
	11th to 20th	Night	5% 13% 28% 37% 16% 2	751
	21st to end	Night	7% 10% 29% 35% 17% 2	570
May	1st to 10th	Night	7% 11% 30% 37% 15% 1	570
	11th to 20th	Night	5% 6% 23% 36% 27% 2	561
	21st to end	Night	7% 10% 21% 36% 25% 1	617
June	1st to 10th	Night	4 5% 22% 42% 24% 2	570
	11th to 20th	Night	3 6% 23% 42% 26%	411
	21st to end	Night	2 1 12% 49% 34% 2	380
July	1st to 10th	Night	3 8% 45% 42% 2	370
	11th to 20th	Night	5% 1 9% 43% 39% 2	476
	21st to end	Night	4 1 9% 41% 43% 2	624
August	1st to 10th	Night	4 1 14% 47% 32% 1	567
	11th to 20th	Night	2 1 11% 43% 41% 2	634
	21st to end	Night	3 1 10% 38% 44% 4	836
September	1st to 10th	Night	2 3 11% 34% 45% 4	760
	11th to 20th	Night	3 4 15% 39% 36% 4	760
	21st to end	Night	1 3 15% 37% 36% 7%	760
October	1st to 10th	Night	5% 5% 18% 37% 33% 3	760
	11th to 20th	Night	4 3 16% 43% 31% 3	760
	21st to end	Night	3 6% 17% 37% 32% 4	836
November	1st to 10th	Night	5% 4 16% 38% 32% 4	780
	11th to 20th	Night	3 5% 19% 43% 26% 4	800
	21st to end	Night	5% 6% 20% 40% 25% 4	800
December	1st to 10th	Night	6% 4 20% 45% 21% 4	800
	11th to 20th	Night	9% 3 23% 43% 21% 1	800
	21st to end	Night	7% 6% 25% 43% 18% 1	880

Page generated at 2025-03-09 05:08:44. Version ac07

Copyright © 2025 Attilla Danko.