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 2024-02-10.

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	3 4 2 4 4 2 4 4 5% 7% 63%	78973
	Night	3 4 2 4 4 2 4 4 5% 7% 62%	79986
Transparency	Day	20% 4 9% 19% 25% 23%	78690
	Night	22% 4 9% 21% 25% 19%	79791
Seeing	Day	5% 10% 22% 30% 23% 9%	14057
	Night	5% 6% 20% 40% 27% 3	23886

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	3 6% 2 5% 5% 3 4 5% 5% 8% 54%	2546
	11th to 20th	Day	2 5% 3 5% 4 3 4 4 5% 7% 56%	2860
	21st to end	Day	5% 10% 2 4 4 3 4 4 5% 7% 51%	3146
February	1st to 10th	Day	3 6% 2 4 4 2 4 4 5% 9% 56%	1862
	11th to 20th	Day	4 5% 2 4 4 3 4 4 5% 8% 56%	1750
	21st to end	Day	4 6% 3 5% 4 2 4 3 5% 7% 58%	1480
March	1st to 10th	Day	4 6% 3 5% 6% 3 4 4 6% 7% 53%	1800
	11th to 20th	Day	3 6% 2 5% 4 2 4 5% 6% 8% 54%	1967
	21st to end	Day	4 6% 2 4 3 3 4 5% 5% 7% 57%	2178
April	1st to 10th	Day	3 4 2 5% 5% 3 4 4 5% 6% 59%	2142
	11th to 20th	Day	3 3 2 4 4 3 3 4 5% 5% 63%	2129
	21st to end	Day	4 3 1 3 3 2 3 4 4 7% 66%	2338
May	1st to 10th	Day	2 3 1 4 4 3 4 5% 5% 8% 61%	2340
	11th to 20th	Day	2 4 2 3 4 2 4 4 5% 8% 63%	2301
	21st to end	Day	3 4 1 5% 5% 4 5% 5% 5% 7% 58%	2530
June	1st to 10th	Day	1 2 1 3 3 3 4 4 4 6% 69%	2340
	11th to 20th	Day	2 2 1 2 2 1 2 3 4 6% 74%	2484
	21st to end	Day	2 2 2 2 1 3 3 3 5% 78%	2520
July	1st to 10th	Day	3 2 2 4 3 2 4 4 4 6% 68%	2520
	11th to 20th	Day	2 3 1 4 4 3 4 4 5% 7% 63%	2412
	21st to end	Day	4 3 2 5% 5% 3 5% 4 6% 9% 53%	2545
August	1st to 10th	Day	3 2 1 3 3 2 2 4 5% 5% 69%	2328
	11th to 20th	Day	2 2 1 2 3 2 3 4 4 7% 70%	2229
	21st to end	Day	2 2 1 2 3 2 3 4 4 6% 72%	2376
September	1st to 10th	Day	2 2 1 3 3 2 3 3 4 4 74%	2085
	11th to 20th	Day	2 2 1 2 2 1 2 3 3 5% 77%	1980
	21st to end	Day	1 1 1 2 2 1 2 2 3 5% 79%	1980
October	1st to 10th	Day	4 2 1 3 3 2 4 3 4 5% 69%	1980
	11th to 20th	Day	2 2 1 1 2 1 3 4 4 4 76%	1890
	21st to end	Day	2 2 1 2 2 2 2 3 4 5% 75%	1824
November	1st to 10th	Day	3 3 1 3 3 2 3 3 4 8% 68%	1674
	11th to 20th	Day	2 2 1 2 3 2 3 3 4 7% 71%	1710
	21st to end	Day	4 4 1 4 4 2 3 4 5% 6% 63%	1710
December	1st to 10th	Day	3 5% 3 5% 4 3 4 4 4 6% 60%	1710
	11th to 20th	Day	7% 8% 3 7% 5% 4 4 5% 6% 8% 44%	2169
	21st to end	Day	3 5% 2 5% 5% 3 5% 6% 7% 9% 50%	3138
January	1st to 10th	Night	3 6% 2 5% 5% 3 4 4 4 6% 59%	4347
	11th to 20th	Night	2 5% 2 5% 5% 3 4 5% 6% 8% 56%	4110
	21st to end	Night	6% 9% 2 4 4 3 3 4 6% 9% 50%	4521
February	1st to 10th	Night	4 6% 2 5% 3 2 3 3 5% 7% 59%	2298
	11th to 20th	Night	4 6% 3 3 3 3 4 3 4 8% 59%	2098
	21st to end	Night	4 6% 3 6% 4 3 5% 3 5% 7% 54%	1776
March	1st to 10th	Night	4 6% 2 4 5% 3 3 5% 6% 7% 54%	2160
	11th to 20th	Night	4 7% 3 6% 4 3 4 5% 6% 8% 51%	1992
	21st to end	Night	4 5% 3 5% 3 2 3 4 4 6% 60%	2178
April	1st to 10th	Night	4 4 2 3 5% 2 4 5% 5% 6% 60%	1814
	11th to 20th	Night	3 3 2 3 4 2 3 4 4 6% 65%	1779
	21st to end	Night	5% 4 1 3 4 2 4 4 5% 6% 62%	1620
May	1st to 10th	Night	4 4 2 5% 5% 2 4 4 4 7% 60%	1620
	11th to 20th	Night	4 3 2 4 4 2 3 3 6% 7% 63%	1594
	21st to end	Night	5% 4 2 4 5% 3 5% 4 6% 7% 54%	1746
June	1st to 10th	Night	2 3 1 3 3 2 3 4 4 7% 68%	1620
	11th to 20th	Night	2 3 1 3 2 2 2 2 3 5% 74%	1470
	21st to end	Night	2 1 1 2 3 2 3 3 4 5% 75%	1440
July	1st to 10th	Night	3 3 1 3 4 3 4 3 3 4 70%	1440
	11th to 20th	Night	3 4 2 5% 4 3 3 4 5% 7% 61%	1543
	21st to end	Night	4 4 2 5% 5% 4 5% 5% 8% 8% 48%	1773
August	1st to 10th	Night	3 3 2 4 3 3 4 3 5% 6% 63%	1611
	11th to 20th	Night	2 2 1 3 4 1 3 3 4 7% 69%	1668
	21st to end	Night	2 2 1 3 2 2 3 4 4 6% 72%	1980
September	1st to 10th	Night	2 2 1 2 3 1 3 3 4 5% 73%	1873
	11th to 20th	Night	3 2 1 2 2 2 2 3 4 5% 75%	1980
	21st to end	Night	1 1 2 2 1 2 2 2 4 81%	1980
October	1st to 10th	Night	4 2 1 3 3 2 3 3 4 6% 69%	1980
	11th to 20th	Night	2 2 1 2 2 2 3 3 3 6% 74%	2070
	21st to end	Night	2 2 1 2 2 2 2 3 4 6% 76%	2528
November	1st to 10th	Night	3 3 1 3 3 2 2 2 4 7% 69%	2405
	11th to 20th	Night	2 2 1 2 3 2 3 4 4 6% 71%	2470
	21st to end	Night	3 3 2 3 3 2 3 4 5% 7% 65%	2470
December	1st to 10th	Night	5% 5% 2 4 4 3 4 5% 4 7% 59%	2470
	11th to 20th	Night	7% 5% 3 5% 4 3 4 5% 5% 10% 50%	3041
	21st to end	Night	3 5% 3 6% 6% 4 5% 6% 6% 9% 46%	4521

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	24% 5% 14% 36% 19% 2	2546
	11th to 20th	Day	26% 4 17% 32% 17% 4	2860
	21st to end	Day	32% 4 15% 29% 18% 3	3146
February	1st to 10th	Day	26% 5% 13% 27% 23% 7%	1862
	11th to 20th	Day	25% 4 9% 26% 27% 8%	1760
	21st to end	Day	25% 4 13% 26% 24% 7%	1480
March	1st to 10th	Day	29% 4 8% 25% 29% 5%	1800
	11th to 20th	Day	25% 4 9% 30% 23% 9%	1967
	21st to end	Day	26% 4 11% 28% 24% 7%	2178
April	1st to 10th	Day	25% 4 10% 21% 25% 15%	2142
	11th to 20th	Day	21% 3 7% 20% 28% 20%	2132
	21st to end	Day	18% 3 8% 21% 37% 13%	2338
May	1st to 10th	Day	21% 3 7% 17% 35% 18%	2340
	11th to 20th	Day	20% 3 7% 18% 32% 20%	2304
	21st to end	Day	24% 5% 8% 15% 30% 19%	2530
June	1st to 10th	Day	15% 2 6% 12% 31% 34%	2340
	11th to 20th	Day	12% 3 5% 9% 24% 47%	2484
	21st to end	Day	10% 2 4 5% 22% 57%	2520
July	1st to 10th	Day	18% 2 5% 7% 14% 54%	2451
	11th to 20th	Day	19% 4 7% 13% 17% 40%	2339
	21st to end	Day	24% 6% 9% 15% 19% 28%	2404
August	1st to 10th	Day	16% 3 6% 10% 20% 46%	2313
	11th to 20th	Day	13% 3 6% 11% 17% 50%	2229
	21st to end	Day	13% 2 5% 11% 24% 44%	2376
September	1st to 10th	Day	15% 3 6% 8% 20% 49%	2085
	11th to 20th	Day	11% 2 4 12% 26% 44%	1980
	21st to end	Day	10% 1 4 11% 37% 37%	1980
October	1st to 10th	Day	18% 3 6% 13% 31% 28%	1980
	11th to 20th	Day	13% 2 4 16% 35% 30%	1890
	21st to end	Day	13% 2 5% 24% 37% 19%	1824
November	1st to 10th	Day	17% 2 10% 26% 31% 14%	1674
	11th to 20th	Day	15% 2 10% 29% 35% 9%	1710
	21st to end	Day	22% 2 9% 23% 32% 11%	1710
December	1st to 10th	Day	25% 5% 11% 25% 27% 8%	1710
	11th to 20th	Day	35% 7% 12% 24% 18% 5%	2168
	21st to end	Day	26% 6% 17% 24% 23% 4	3138
January	1st to 10th	Night	25% 3 14% 33% 23% 2	4347
	11th to 20th	Night	24% 5% 21% 29% 17% 4	4110
	21st to end	Night	31% 5% 14% 28% 18% 4	4521
February	1st to 10th	Night	25% 4 11% 29% 24% 6%	2298
	11th to 20th	Night	24% 3 9% 23% 31% 10%	2099
	21st to end	Night	29% 3 10% 25% 25% 7%	1776
March	1st to 10th	Night	28% 4 10% 26% 26% 6%	2160
	11th to 20th	Night	30% 4 9% 27% 22% 10%	1992
	21st to end	Night	26% 3 12% 30% 24% 7%	2178
April	1st to 10th	Night	23% 5% 9% 27% 23% 13%	1814
	11th to 20th	Night	21% 3 9% 21% 31% 16%	1779
	21st to end	Night	22% 4 7% 18% 36% 12%	1620
May	1st to 10th	Night	23% 3 8% 17% 33% 16%	1620
	11th to 20th	Night	20% 4 7% 17% 31% 21%	1595
	21st to end	Night	27% 3 9% 16% 33% 13%	1746
June	1st to 10th	Night	16% 3 4 13% 30% 34%	1620
	11th to 20th	Night	16% 1 5% 8% 23% 47%	1470
	21st to end	Night	11% 2 4 7% 19% 58%	1440
July	1st to 10th	Night	20% 2 4 7% 11% 56%	1400
	11th to 20th	Night	22% 4 6% 11% 15% 42%	1494
	21st to end	Night	29% 7% 10% 14% 13% 27%	1674
August	1st to 10th	Night	20% 4 7% 9% 19% 41%	1602
	11th to 20th	Night	15% 4 6% 10% 17% 48%	1668
	21st to end	Night	13% 2 6% 10% 24% 44%	1980
September	1st to 10th	Night	14% 3 6% 9% 21% 48%	1873
	11th to 20th	Night	13% 2 5% 12% 24% 44%	1980
	21st to end	Night	9% 2 5% 12% 33% 39%	1980
October	1st to 10th	Night	17% 3 5% 15% 30% 29%	1980
	11th to 20th	Night	13% 3 4 17% 34% 30%	2070
	21st to end	Night	12% 2 5% 20% 40% 20%	2528
November	1st to 10th	Night	16% 2 8% 25% 33% 16%	2405
	11th to 20th	Night	14% 3 7% 24% 39% 12%	2470
	21st to end	Night	19% 3 7% 23% 36% 12%	2470
December	1st to 10th	Night	25% 5% 11% 25% 26% 8%	2470
	11th to 20th	Night	29% 6% 12% 27% 21% 5%	3041
	21st to end	Night	32% 7% 13% 24% 21% 4	4521

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% 7% 23% 35% 17% 3	184
	11th to 20th	Day	8% 7% 23% 37% 21% 4	270
	21st to end	Day	6% 10% 18% 30% 29% 8%	297
February	1st to 10th	Day	8% 14% 24% 29% 19% 6%	428
	11th to 20th	Day	6% 13% 24% 36% 16% 5%	415
	21st to end	Day	7% 12% 31% 31% 15% 4	346
March	1st to 10th	Day	11% 14% 25% 29% 19% 3	420
	11th to 20th	Day	9% 14% 26% 30% 18% 3	420
	21st to end	Day	10% 21% 34% 22% 11% 2	462
April	1st to 10th	Day	10% 16% 25% 25% 18% 5%	420
	11th to 20th	Day	7% 23% 29% 27% 11% 3	412
	21st to end	Day	7% 21% 25% 23% 16% 7%	420
May	1st to 10th	Day	7% 14% 32% 26% 16% 5%	423
	11th to 20th	Day	6% 13% 23% 30% 21% 7%	448
	21st to end	Day	6% 13% 23% 29% 20% 8%	485
June	1st to 10th	Day	2 11% 23% 27% 25% 11%	450
	11th to 20th	Day	4 14% 26% 25% 23% 9%	450
	21st to end	Day	3 7% 21% 29% 31% 10%	450
July	1st to 10th	Day	3 2 21% 36% 26% 13%	446
	11th to 20th	Day	2 3 18% 35% 28% 14%	444
	21st to end	Day	4 1 12% 41% 27% 15%	487
August	1st to 10th	Day	3 4 20% 36% 24% 13%	447
	11th to 20th	Day	2 3 17% 31% 30% 18%	437
	21st to end	Day	3 3 19% 29% 31% 15%	495
September	1st to 10th	Day	4 6% 15% 29% 29% 17%	450
	11th to 20th	Day	2 8% 25% 25% 27% 12%	450
	21st to end	Day	2 9% 18% 26% 35% 11%	450
October	1st to 10th	Day	3 10% 25% 26% 22% 14%	450
	11th to 20th	Day	4 8% 17% 27% 30% 14%	360
	21st to end	Day	5% 7% 19% 30% 27% 12%	297
November	1st to 10th	Day	6% 6% 20% 28% 24% 15%	270
	11th to 20th	Day	3 9% 17% 34% 23% 14%	270
	21st to end	Day	6% 7% 18% 30% 27% 12%	270
December	1st to 10th	Day	7% 8% 23% 30% 24% 8%	270
	11th to 20th	Day	7% 3 22% 37% 26% 6%	270
	21st to end	Day	9% 7% 24% 37% 17% 5%	294
January	1st to 10th	Night	8% 5% 21% 37% 23% 5%	760
	11th to 20th	Night	5% 3 22% 45% 22% 3	760
	21st to end	Night	9% 4 23% 40% 21% 4	836
February	1st to 10th	Night	6% 7% 25% 39% 20% 3	758
	11th to 20th	Night	8% 7% 22% 43% 18% 2	704
	21st to end	Night	7% 7% 27% 42% 14% 2	592
March	1st to 10th	Night	6% 10% 24% 41% 18% 1	720
	11th to 20th	Night	7% 9% 22% 38% 22% 2	720
	21st to end	Night	6% 13% 28% 37% 14% 1	792
April	1st to 10th	Night	6% 13% 25% 36% 18% 1	720
	11th to 20th	Night	4 13% 29% 36% 16% 2	711
	21st to end	Night	8% 10% 29% 35% 16% 2	540
May	1st to 10th	Night	6% 10% 29% 38% 16% 1	540
	11th to 20th	Night	5% 6% 23% 36% 27% 2	531
	21st to end	Night	7% 10% 22% 35% 26% 1	584
June	1st to 10th	Night	4 6% 23% 41% 24% 2	540
	11th to 20th	Night	4 6% 23% 41% 26% 1	390
	21st to end	Night	1 1 13% 47% 36% 2	360
July	1st to 10th	Night	3 7% 45% 43% 2	350
	11th to 20th	Night	4 1 10% 44% 39% 2	450
	21st to end	Night	4 1 9% 42% 43% 2	591
August	1st to 10th	Night	4 1 14% 47% 32% 1	537
	11th to 20th	Night	2 1 9% 43% 43% 2	600
	21st to end	Night	3 1 9% 39% 45% 4	792
September	1st to 10th	Night	2 3 12% 33% 45% 4	720
	11th to 20th	Night	3 3 14% 39% 38% 4	720
	21st to end	Night	2 3 15% 35% 38% 8%	720
October	1st to 10th	Night	5% 5% 18% 38% 31% 3	720
	11th to 20th	Night	3 3 15% 43% 33% 3	720
	21st to end	Night	3 6% 17% 37% 33% 5%	792
November	1st to 10th	Night	5% 4 15% 39% 33% 4	740
	11th to 20th	Night	3 4 18% 44% 27% 4	760
	21st to end	Night	5% 6% 20% 40% 26% 4	760
December	1st to 10th	Night	7% 4 20% 45% 20% 4	760
	11th to 20th	Night	10% 3 22% 43% 21% 1	760
	21st to end	Night	7% 6% 25% 43% 18% 1	836

Page generated at 2024-02-07 03:11:57. Version ac07

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