DarkSights Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DarkSights Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	6% 5% 2 5% 3 3 3 3 4 6% 60%	136031
	Night	8% 7% 3 8% 4 4 4 3 4 6% 50%	133442
Transparency	Day	23% 5% 8% 18% 25% 21%	130961
	Night	30% 5% 9% 18% 21% 16%	129497
Seeing	Day	10% 11% 27% 32% 17% 4	16928
	Night	11% 5% 15% 36% 28% 6%	26363

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	13% 7% 2 5% 3 3 4 4 6% 8% 44%	3925
	11th to 20th	Day	10% 7% 3 7% 5% 4 3 2 3 4 52%	4190
	21st to end	Day	16% 8% 3 8% 4 4 3 3 5% 6% 40%	4609
February	1st to 10th	Day	16% 8% 2 6% 4 3 3 3 6% 6% 43%	1801
	11th to 20th	Day	12% 8% 3 6% 4 5% 4 3 6% 8% 41%	1854
	21st to end	Day	13% 7% 2 7% 4 3 3 3 5% 6% 47%	1650
March	1st to 10th	Day	10% 10% 4 11% 6% 5% 5% 5% 6% 6% 32%	4838
	11th to 20th	Day	10% 7% 2 5% 4 4 4 4 5% 7% 48%	5000
	21st to end	Day	10% 7% 3 7% 5% 6% 6% 5% 7% 9% 35%	5590
April	1st to 10th	Day	11% 8% 2 6% 5% 4 4 3 5% 7% 45%	2400
	11th to 20th	Day	8% 6% 3 5% 3 4 4 3 4 6% 55%	2369
	21st to end	Day	4 5% 2 4 3 3 4 3 5% 9% 57%	2400
May	1st to 10th	Day	4 3 1 2 2 2 2 2 3 5% 75%	5588
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 5% 74%	6014
	21st to end	Day	2 3 2 4 2 2 2 2 3 6% 71%	6902
June	1st to 10th	Day	3 5% 2 4 3 3 3 3 6% 7% 62%	2800
	11th to 20th	Day	1 2 1 2 2 2 2 2 5% 6% 74%	2800
	21st to end	Day	2 2 1 3 2 2 2 2 3 5% 75%	2800
July	1st to 10th	Day	1 1 3 2 2 2 2 2 4 82%	6319
	11th to 20th	Day	1 1 1 2 2 2 3 2 3 5% 78%	5974
	21st to end	Day	2 2 5% 3 2 3 2 4 6% 70%	6402
August	1st to 10th	Day	1 2 1 3 2 2 3 2 4 7% 72%	5777
	11th to 20th	Day	2 2 4 2 2 2 2 3 5% 76%	5495
	21st to end	Day	1 2 1 4 3 3 2 3 4 6% 73%	5984
September	1st to 10th	Day	1 2 1 4 2 2 1 2 3 5% 78%	2400
	11th to 20th	Day	2 5% 2 5% 3 3 3 3 4 6% 65%	2400
	21st to end	Day	3 3 1 3 2 2 2 2 4 6% 74%	2129
October	1st to 10th	Day	2 2 1 3 2 2 2 2 4 6% 72%	3280
	11th to 20th	Day	3 3 2 5% 3 3 3 2 4 6% 67%	3261
	21st to end	Day	4 5% 2 4 3 3 4 3 5% 7% 59%	3558
November	1st to 10th	Day	7% 5% 2 5% 2 3 4 4 5% 9% 55%	2000
	11th to 20th	Day	8% 8% 2 7% 5% 4 4 3 4 7% 48%	1890
	21st to end	Day	11% 6% 2 4 2 3 3 3 5% 7% 53%	1732
December	1st to 10th	Day	7% 5% 2 4 3 3 4 4 6% 9% 54%	2700
	11th to 20th	Day	19% 9% 3 7% 5% 5% 5% 4 7% 8% 29%	3108
	21st to end	Day	17% 14% 4 7% 5% 4 5% 4 6% 7% 28%	4092
January	1st to 10th	Night	9% 7% 2 6% 3 3 3 3 6% 9% 48%	6244
	11th to 20th	Night	11% 7% 3 8% 5% 4 4 3 4 5% 46%	6010
	21st to end	Night	14% 11% 4 8% 4 3 3 3 3 5% 41%	6611
February	1st to 10th	Night	16% 9% 2 4 3 3 3 3 5% 5% 48%	2600
	11th to 20th	Night	12% 7% 3 7% 4 4 4 3 4 8% 43%	2431
	21st to end	Night	11% 7% 2 5% 4 3 4 3 5% 7% 51%	1980
March	1st to 10th	Night	13% 13% 5% 10% 5% 4 4 3 4 6% 34%	5053
	11th to 20th	Night	12% 9% 3 8% 4 3 3 3 4 5% 46%	5000
	21st to end	Night	14% 13% 4 8% 4 4 4 3 4 7% 36%	5385
April	1st to 10th	Night	9% 8% 3 6% 5% 3 4 3 6% 7% 46%	2000
	11th to 20th	Night	7% 7% 3 6% 4 3 3 3 5% 6% 52%	1979
	21st to end	Night	4 5% 2 4 4 4 3 4 6% 9% 56%	2000
May	1st to 10th	Night	4 5% 2 5% 3 2 2 2 4 5% 67%	4388
	11th to 20th	Night	2 6% 3 9% 6% 4 4 3 4 5% 55%	3873
	21st to end	Night	2 6% 5% 11% 4 3 3 2 3 5% 57%	3972
June	1st to 10th	Night	4 5% 2 6% 4 4 3 4 6% 7% 56%	1600
	11th to 20th	Night	1 2 2 5% 4 2 2 3 3 6% 69%	1600
	21st to end	Night	1 4 3 6% 4 3 3 2 3 5% 67%	1600
July	1st to 10th	Night	2 1 6% 5% 3 3 3 3 4 69%	3640
	11th to 20th	Night	1 2 1 10% 9% 5% 6% 4 4 5% 54%	3998
	21st to end	Night	1 10% 9% 20% 6% 4 3 2 4 5% 37%	4472
August	1st to 10th	Night	2 3 2 12% 8% 7% 6% 4 4 6% 46%	4035
	11th to 20th	Night	4 3 12% 6% 4 3 3 4 4 56%	4367
	21st to end	Night	1 4 2 10% 6% 5% 5% 3 4 5% 54%	5015
September	1st to 10th	Night	1 5% 2 6% 4 3 2 2 3 6% 66%	2000
	11th to 20th	Night	3 7% 3 9% 5% 3 3 2 5% 6% 53%	2000
	21st to end	Night	2 4 1 5% 4 2 3 2 3 6% 68%	2267
October	1st to 10th	Night	2 3 1 4 3 2 2 2 4 6% 71%	3920
	11th to 20th	Night	3 7% 5% 9% 4 3 3 2 3 5% 54%	3897
	21st to end	Night	5% 6% 2 5% 3 3 4 3 5% 5% 59%	4253
November	1st to 10th	Night	7% 6% 2 4 3 3 4 3 6% 8% 54%	2518
	11th to 20th	Night	10% 7% 3 5% 4 3 3 3 5% 9% 48%	2730
	21st to end	Night	9% 5% 2 5% 4 3 3 3 5% 8% 54%	2882
December	1st to 10th	Night	7% 5% 1 5% 3 3 4 3 4 7% 58%	4700
	11th to 20th	Night	19% 13% 3 7% 4 3 5% 4 8% 9% 27%	5316
	21st to end	Night	18% 11% 4 9% 5% 5% 5% 4 5% 6% 29%	7106

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	34% 8% 18% 21% 14% 5%	3925
	11th to 20th	Day	35% 6% 7% 14% 23% 15%	4190
	21st to end	Day	43% 7% 7% 11% 17% 15%	4609
February	1st to 10th	Day	39% 6% 8% 19% 19% 8%	1801
	11th to 20th	Day	39% 7% 10% 18% 20% 6%	1863
	21st to end	Day	37% 7% 8% 23% 18% 6%	1650
March	1st to 10th	Day	44% 10% 8% 16% 19% 2	4838
	11th to 20th	Day	32% 6% 15% 27% 12% 8%	5000
	21st to end	Day	36% 13% 16% 23% 11% 1	5590
April	1st to 10th	Day	36% 8% 13% 20% 19% 4	2400
	11th to 20th	Day	29% 5% 14% 23% 22% 6%	2372
	21st to end	Day	22% 6% 14% 28% 25% 4	2400
May	1st to 10th	Day	13% 3 8% 27% 31% 19%	5588
	11th to 20th	Day	11% 2 7% 30% 39% 11%	6017
	21st to end	Day	11% 4 10% 28% 41% 6%	6904
June	1st to 10th	Day	20% 5% 11% 25% 29% 11%	2800
	11th to 20th	Day	10% 4 8% 21% 36% 23%	2800
	21st to end	Day	11% 2 4 13% 30% 40%	2800
July	1st to 10th	Day	6% 1 2 7% 22% 63%	6251
	11th to 20th	Day	8% 1 2 5% 11% 71%	5902
	21st to end	Day	13% 1 3 17% 26% 40%	6217
August	1st to 10th	Day	13% 2 2 9% 27% 46%	4206
	11th to 20th	Day	7% 1 3 11% 38% 40%	3977
	21st to end	Day	11% 2 5% 11% 34% 38%	4311
September	1st to 10th	Day	9% 1 5% 11% 30% 44%	2400
	11th to 20th	Day	17% 3 8% 21% 33% 18%	2400
	21st to end	Day	11% 2 7% 21% 33% 25%	2129
October	1st to 10th	Day	13% 2 5% 11% 28% 41%	3280
	11th to 20th	Day	18% 3 8% 21% 29% 21%	3261
	21st to end	Day	21% 4 7% 20% 33% 15%	3558
November	1st to 10th	Day	26% 6% 11% 23% 22% 11%	2000
	11th to 20th	Day	33% 7% 11% 22% 21% 6%	1890
	21st to end	Day	30% 5% 11% 19% 26% 9%	1732
December	1st to 10th	Day	25% 5% 8% 28% 28% 6%	2700
	11th to 20th	Day	50% 7% 10% 15% 14% 4	3108
	21st to end	Day	51% 9% 12% 17% 10% 2	4092
January	1st to 10th	Night	32% 10% 18% 21% 15% 4	6244
	11th to 20th	Night	39% 8% 9% 12% 21% 11%	6010
	21st to end	Night	45% 6% 7% 10% 18% 13%	6611
February	1st to 10th	Night	39% 5% 9% 18% 19% 11%	2600
	11th to 20th	Night	38% 6% 11% 18% 19% 7%	2433
	21st to end	Night	32% 7% 12% 26% 18% 6%	1980
March	1st to 10th	Night	44% 11% 8% 19% 15% 3	5053
	11th to 20th	Night	34% 7% 14% 23% 14% 8%	5000
	21st to end	Night	40% 13% 15% 19% 11% 3	5385
April	1st to 10th	Night	32% 8% 15% 21% 18% 5%	2000
	11th to 20th	Night	29% 7% 12% 25% 18% 9%	1979
	21st to end	Night	22% 6% 13% 29% 24% 6%	2000
May	1st to 10th	Night	16% 6% 9% 24% 29% 16%	4385
	11th to 20th	Night	16% 3 13% 25% 30% 13%	3873
	21st to end	Night	17% 4 12% 26% 35% 6%	3972
June	1st to 10th	Night	22% 5% 10% 24% 27% 12%	1600
	11th to 20th	Night	13% 3 7% 16% 34% 26%	1600
	21st to end	Night	11% 3 5% 15% 31% 36%	1600
July	1st to 10th	Night	10% 1 1 9% 21% 57%	3600
	11th to 20th	Night	16% 1 2 6% 24% 50%	3947
	21st to end	Night	34% 1 6% 11% 23% 25%	4345
August	1st to 10th	Night	29% 3 2 12% 27% 28%	2929
	11th to 20th	Night	13% 1 4 11% 39% 32%	3154
	21st to end	Night	23% 2 4 12% 29% 31%	3608
September	1st to 10th	Night	16% 2 4 10% 23% 45%	2000
	11th to 20th	Night	23% 3 7% 21% 27% 19%	2000
	21st to end	Night	14% 2 7% 19% 30% 28%	2267
October	1st to 10th	Night	14% 2 6% 12% 22% 45%	3920
	11th to 20th	Night	28% 3 7% 19% 21% 22%	3897
	21st to end	Night	24% 3 6% 21% 27% 20%	4253
November	1st to 10th	Night	26% 6% 11% 25% 18% 14%	2518
	11th to 20th	Night	33% 5% 12% 22% 21% 8%	2730
	21st to end	Night	29% 5% 10% 21% 22% 12%	2882
December	1st to 10th	Night	26% 4 9% 26% 25% 11%	4700
	11th to 20th	Night	52% 7% 9% 14% 15% 3	5316
	21st to end	Night	52% 10% 13% 14% 9% 3	7106

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	24% 14% 29% 21% 11% 1	309
	11th to 20th	Day	17% 10% 23% 32% 16% 2	430
	21st to end	Day	19% 7% 26% 30% 16% 2	473
February	1st to 10th	Day	22% 13% 20% 27% 15% 2	401
	11th to 20th	Day	20% 17% 26% 23% 12% 1	445
	21st to end	Day	13% 15% 30% 30% 11% 1	414
March	1st to 10th	Day	21% 19% 28% 20% 10% 2	500
	11th to 20th	Day	22% 17% 23% 21% 14% 2	500
	21st to end	Day	16% 19% 33% 21% 10% 1	550
April	1st to 10th	Day	17% 18% 30% 21% 11% 3	500
	11th to 20th	Day	13% 20% 31% 23% 9% 3	492
	21st to end	Day	9% 20% 30% 26% 10% 5%	500
May	1st to 10th	Day	10% 17% 33% 28% 12% 1	503
	11th to 20th	Day	10% 13% 33% 30% 12% 2	528
	21st to end	Day	8% 14% 31% 31% 13% 3	573
June	1st to 10th	Day	6% 12% 34% 32% 14% 3	530
	11th to 20th	Day	2 13% 33% 38% 12% 2	530
	21st to end	Day	3 8% 30% 39% 17% 3	530
July	1st to 10th	Day	2 5% 29% 43% 17% 2	526
	11th to 20th	Day	2 25% 48% 21% 3	524
	21st to end	Day	2 2 26% 45% 19% 6%	575
August	1st to 10th	Day	3 7% 28% 40% 17% 5%	527
	11th to 20th	Day	2 4 29% 39% 19% 7%	517
	21st to end	Day	1 3 23% 44% 22% 7%	583
September	1st to 10th	Day	3 5% 22% 42% 22% 7%	530
	11th to 20th	Day	6% 11% 25% 35% 17% 6%	530
	21st to end	Day	5% 8% 25% 32% 24% 7%	530
October	1st to 10th	Day	5% 8% 27% 30% 22% 8%	530
	11th to 20th	Day	7% 10% 20% 31% 24% 7%	530
	21st to end	Day	7% 11% 24% 30% 23% 5%	583
November	1st to 10th	Day	9% 11% 22% 25% 27% 7%	476
	11th to 20th	Day	10% 12% 17% 35% 21% 6%	330
	21st to end	Day	13% 8% 26% 29% 23% 2	247
December	1st to 10th	Day	13% 13% 22% 25% 21% 5%	220
	11th to 20th	Day	19% 12% 20% 22% 23% 4	220
	21st to end	Day	27% 12% 26% 21% 13% 2	242
January	1st to 10th	Night	19% 7% 13% 33% 21% 6%	840
	11th to 20th	Night	14% 5% 14% 36% 27% 5%	840
	21st to end	Night	18% 4 13% 38% 23% 5%	924
February	1st to 10th	Night	20% 7% 13% 35% 22% 4	800
	11th to 20th	Night	14% 8% 18% 36% 19% 5%	784
	21st to end	Night	13% 10% 17% 37% 20% 3	660
March	1st to 10th	Night	19% 10% 17% 30% 21% 3	800
	11th to 20th	Night	18% 9% 16% 32% 22% 4	800
	21st to end	Night	15% 10% 20% 35% 18% 2	880
April	1st to 10th	Night	12% 8% 20% 37% 20% 3	800
	11th to 20th	Night	12% 9% 22% 33% 20% 4	791
	21st to end	Night	7% 7% 22% 37% 22% 5%	800
May	1st to 10th	Night	7% 6% 20% 41% 23% 4	732
	11th to 20th	Night	8% 3 14% 42% 29% 4	508
	21st to end	Night	8% 7% 21% 38% 24% 3	433
June	1st to 10th	Night	6% 4 18% 45% 26% 2	400
	11th to 20th	Night	2 3 17% 54% 24% 2	400
	21st to end	Night	3 4 14% 41% 37% 2	400
July	1st to 10th	Night	2 3 10% 42% 40% 3	390
	11th to 20th	Night	2 8% 43% 39% 8%	535
	21st to end	Night	3 1 10% 36% 41% 8%	657
August	1st to 10th	Night	4 4 14% 33% 35% 9%	597
	11th to 20th	Night	2 2 12% 41% 36% 6%	728
	21st to end	Night	2 1 11% 40% 39% 8%	880
September	1st to 10th	Night	3 2 10% 36% 40% 10%	800
	11th to 20th	Night	6% 5% 12% 36% 35% 7%	800
	21st to end	Night	4 3 12% 32% 39% 10%	800
October	1st to 10th	Night	6% 3 10% 37% 35% 9%	800
	11th to 20th	Night	8% 4 11% 33% 35% 9%	800
	21st to end	Night	8% 5% 11% 34% 31% 12%	880
November	1st to 10th	Night	8% 4 15% 31% 32% 10%	820
	11th to 20th	Night	14% 3 12% 36% 28% 7%	840
	21st to end	Night	13% 4 14% 37% 26% 6%	840
December	1st to 10th	Night	15% 6% 13% 36% 25% 6%	840
	11th to 20th	Night	22% 6% 13% 34% 22% 4	840
	21st to end	Night	22% 8% 20% 31% 18% 2	924

Page generated at 2026-01-28 22:21:46. Version ac07

Copyright © 2026 Attilla Danko.