Dark Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dark Ridge Observatory clear sky chart from 2005-11-06 to 2026-07-16.

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 3 1 4 3 4 4 4 6% 7% 61%	145242
	Night	2 3 1 3 2 3 3 3 5% 8% 67%	144948
Transparency	Day	19% 6% 8% 16% 26% 25%	140332
	Night	16% 4 8% 17% 28% 27%	140865
Seeing	Day	11% 16% 26% 26% 16% 5%	17004
	Night	7% 16% 27% 29% 18% 3	27179

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	1 4 2 4 2 2 4 3 5% 6% 67%	5318
	11th to 20th	Day	1 1 2 1 1 2 2 3 5% 80%	5340
	21st to end	Day	2 4 1 4 3 3 3 3 6% 8% 63%	5844
February	1st to 10th	Day	1 2 2 3 2 3 3 3 4 6% 71%	2096
	11th to 20th	Day	2 3 2 4 2 3 3 2 5% 7% 68%	2049
	21st to end	Day	1 2 1 3 2 2 3 2 4 6% 75%	1730
March	1st to 10th	Day	1 5% 1 4 3 3 3 2 4 6% 68%	4784
	11th to 20th	Day	3 6% 1 3 2 3 3 3 4 6% 66%	5110
	21st to end	Day	1 2 1 3 3 3 4 3 6% 8% 65%	5848
April	1st to 10th	Day	2 3 1 3 2 2 3 3 4 7% 70%	2520
	11th to 20th	Day	3 3 1 2 2 2 3 2 4 7% 71%	2491
	21st to end	Day	2 3 1 1 2 1 2 2 4 4 78%	2520
May	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 7% 67%	7057
	11th to 20th	Day	2 2 1 2 2 3 4 3 4 5% 71%	7032
	21st to end	Day	1 1 1 2 2 3 3 3 5% 8% 71%	8216
June	1st to 10th	Day	2 2 1 4 3 4 5% 6% 8% 9% 57%	2940
	11th to 20th	Day	2 2 1 3 2 3 4 4 6% 8% 65%	2940
	21st to end	Day	7% 4 1 5% 5% 5% 6% 7% 9% 8% 44%	2916
July	1st to 10th	Day	7% 4 2 7% 6% 7% 8% 6% 8% 10% 36%	6009
	11th to 20th	Day	3 2 1 4 5% 6% 8% 7% 11% 10% 43%	5946
	21st to end	Day	6% 4 2 8% 7% 8% 9% 7% 10% 10% 30%	6299
August	1st to 10th	Day	4 2 2 6% 5% 6% 7% 6% 9% 10% 42%	5348
	11th to 20th	Day	4 3 2 7% 6% 7% 8% 6% 9% 9% 39%	5366
	21st to end	Day	6% 4 2 6% 5% 6% 7% 6% 8% 9% 42%	5984
September	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 45%	2400
	11th to 20th	Day	8% 4 2 6% 4 4 4 4 4 8% 50%	2384
	21st to end	Day	5% 3 1 4 3 3 3 2 5% 7% 63%	2200
October	1st to 10th	Day	4 3 1 3 3 3 3 2 4 5% 69%	3336
	11th to 20th	Day	3 4 1 4 2 2 3 3 4 6% 67%	3250
	21st to end	Day	1 1 1 1 1 1 1 1 2 4 85%	3548
November	1st to 10th	Day	2 2 1 2 2 2 2 2 4 4 77%	2059
	11th to 20th	Day	1 2 1 3 2 2 3 3 6% 7% 72%	1895
	21st to end	Day	3 4 1 2 3 2 3 2 5% 7% 69%	1890
December	1st to 10th	Day	4 5% 2 4 2 2 3 2 4 6% 67%	3030
	11th to 20th	Day	1 2 1 4 2 3 3 2 5% 7% 70%	3243
	21st to end	Day	1 2 1 2 2 2 3 2 5% 6% 76%	4304
January	1st to 10th	Night	1 4 2 5% 3 3 3 3 5% 8% 63%	7605
	11th to 20th	Night	1 1 2 2 2 3 2 3 5% 78%	7650
	21st to end	Night	2 4 2 4 3 3 3 3 5% 8% 63%	8370
February	1st to 10th	Night	2 1 2 2 3 3 3 5% 7% 71%	2520
	11th to 20th	Night	2 2 3 1 3 3 3 5% 7% 71%	2458
	21st to end	Night	1 2 1 1 1 2 2 2 5% 7% 75%	2076
March	1st to 10th	Night	2 1 3 1 2 2 2 4 7% 75%	5314
	11th to 20th	Night	4 9% 2 2 2 2 2 2 3 6% 67%	5110
	21st to end	Night	1 1 2 2 2 3 3 5% 7% 74%	5344
April	1st to 10th	Night	2 2 1 2 2 2 3 3 6% 8% 70%	2100
	11th to 20th	Night	3 2 2 2 2 2 2 4 7% 73%	2077
	21st to end	Night	1 2 1 3 2 2 2 2 4 5% 77%	2100
May	1st to 10th	Night	4 4 1 3 2 2 2 3 4 6% 68%	5890
	11th to 20th	Night	2 2 1 2 2 2 2 2 4 6% 75%	5860
	21st to end	Night	2 2 1 2 2 2 3 2 4 5% 76%	5955
June	1st to 10th	Night	3 3 1 3 3 4 5% 5% 6% 8% 59%	1680
	11th to 20th	Night	2 2 2 3 2 3 3 5% 8% 71%	1680
	21st to end	Night	5% 3 1 4 4 5% 6% 6% 6% 10% 49%	1695
July	1st to 10th	Night	9% 6% 1 4 3 3 4 4 7% 9% 49%	4190
	11th to 20th	Night	2 2 1 4 3 4 6% 6% 8% 12% 52%	4145
	21st to end	Night	4 4 2 4 4 4 5% 5% 11% 16% 40%	4570
August	1st to 10th	Night	2 2 1 3 3 4 5% 4 8% 14% 54%	4464
	11th to 20th	Night	3 3 2 4 4 4 4 5% 8% 14% 50%	4483
	21st to end	Night	4 3 1 4 3 4 5% 5% 8% 13% 51%	4993
September	1st to 10th	Night	6% 4 2 5% 3 4 4 3 7% 9% 52%	2000
	11th to 20th	Night	7% 4 1 4 2 3 3 3 5% 8% 60%	2015
	21st to end	Night	6% 3 1 3 2 3 3 3 4 6% 68%	2200
October	1st to 10th	Night	3 2 1 2 2 2 2 2 3 5% 76%	3847
	11th to 20th	Night	3 3 1 3 2 3 3 3 4 5% 69%	3898
	21st to end	Night	2 1 1 2 1 1 1 1 3 5% 82%	4252
November	1st to 10th	Night	3 3 1 2 2 2 1 2 4 5% 75%	2460
	11th to 20th	Night	1 1 1 2 3 2 3 3 5% 7% 73%	2700
	21st to end	Night	2 4 1 4 3 3 3 3 4 6% 68%	2730
December	1st to 10th	Night	2 6% 2 3 2 2 2 2 4 6% 67%	4380
	11th to 20th	Night	1 2 1 3 2 3 3 3 5% 7% 71%	5179
	21st to end	Night	2 2 1 3 2 2 2 2 4 6% 75%	6958

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	18% 4 3 11% 36% 28%	5321
	11th to 20th	Day	8% 2 4 15% 36% 35%	5340
	21st to end	Day	18% 5% 5% 11% 33% 28%	5844
February	1st to 10th	Day	15% 3 6% 16% 28% 33%	2096
	11th to 20th	Day	17% 4 5% 19% 27% 28%	2059
	21st to end	Day	13% 2 4 12% 30% 39%	1730
March	1st to 10th	Day	16% 4 4 9% 19% 48%	4784
	11th to 20th	Day	17% 6% 4 10% 29% 34%	5110
	21st to end	Day	16% 4 6% 14% 31% 28%	5848
April	1st to 10th	Day	15% 4 5% 14% 35% 27%	2520
	11th to 20th	Day	14% 3 4 12% 31% 35%	2494
	21st to end	Day	11% 3 4 15% 35% 33%	2520
May	1st to 10th	Day	16% 5% 7% 16% 22% 33%	7057
	11th to 20th	Day	12% 5% 5% 13% 25% 40%	7035
	21st to end	Day	11% 6% 8% 12% 18% 46%	8217
June	1st to 10th	Day	18% 7% 11% 18% 26% 20%	2940
	11th to 20th	Day	15% 5% 5% 16% 23% 36%	2940
	21st to end	Day	30% 9% 10% 17% 17% 16%	2916
July	1st to 10th	Day	35% 12% 14% 18% 12% 8%	5946
	11th to 20th	Day	25% 14% 18% 21% 18% 4	5877
	21st to end	Day	36% 14% 20% 18% 11% 1	6116
August	1st to 10th	Day	26% 10% 14% 31% 16% 3	3892
	11th to 20th	Day	29% 10% 13% 20% 25% 3	3882
	21st to end	Day	33% 12% 16% 25% 12% 2	4311
September	1st to 10th	Day	32% 8% 12% 18% 19% 11%	2400
	11th to 20th	Day	30% 7% 8% 19% 27% 9%	2384
	21st to end	Day	20% 5% 7% 23% 31% 14%	2200
October	1st to 10th	Day	17% 4 7% 11% 30% 31%	3336
	11th to 20th	Day	18% 5% 8% 16% 28% 24%	3250
	21st to end	Day	7% 1 3 13% 41% 34%	3548
November	1st to 10th	Day	12% 2 3 21% 33% 28%	2059
	11th to 20th	Day	13% 2 6% 19% 32% 27%	1895
	21st to end	Day	16% 3 7% 18% 29% 28%	1890
December	1st to 10th	Day	19% 4 4 17% 31% 25%	3030
	11th to 20th	Day	15% 3 6% 13% 36% 28%	3241
	21st to end	Day	11% 3 5% 13% 37% 32%	4304
January	1st to 10th	Night	19% 4 4 13% 38% 21%	7605
	11th to 20th	Night	10% 2 4 13% 32% 38%	7650
	21st to end	Night	19% 5% 5% 12% 31% 28%	8370
February	1st to 10th	Night	14% 3 5% 16% 28% 34%	2520
	11th to 20th	Night	14% 3 7% 16% 31% 29%	2458
	21st to end	Night	10% 2 6% 14% 30% 37%	2076
March	1st to 10th	Night	10% 3 4 9% 27% 48%	5314
	11th to 20th	Night	19% 4 3 8% 32% 33%	5110
	21st to end	Night	10% 3 6% 15% 37% 28%	5344
April	1st to 10th	Night	12% 3 5% 14% 38% 27%	2100
	11th to 20th	Night	12% 2 7% 14% 30% 35%	2077
	21st to end	Night	11% 2 4 17% 34% 32%	2100
May	1st to 10th	Night	16% 5% 7% 16% 22% 34%	5888
	11th to 20th	Night	12% 3 5% 14% 30% 36%	5861
	21st to end	Night	12% 3 5% 11% 20% 48%	5957
June	1st to 10th	Night	20% 6% 10% 18% 23% 22%	1680
	11th to 20th	Night	13% 3 6% 18% 22% 39%	1680
	21st to end	Night	26% 8% 15% 18% 15% 17%	1695
July	1st to 10th	Night	29% 8% 17% 28% 14% 5%	4145
	11th to 20th	Night	19% 10% 21% 29% 18% 3	4091
	21st to end	Night	26% 10% 27% 24% 11% 1	4440
August	1st to 10th	Night	20% 7% 17% 33% 19% 3	3244
	11th to 20th	Night	19% 7% 15% 28% 29% 2	3243
	21st to end	Night	25% 10% 22% 26% 16% 2	3597
September	1st to 10th	Night	27% 6% 15% 19% 20% 12%	2000
	11th to 20th	Night	24% 5% 13% 21% 27% 11%	2015
	21st to end	Night	20% 3 10% 22% 31% 14%	2200
October	1st to 10th	Night	13% 3 6% 12% 32% 35%	3847
	11th to 20th	Night	17% 6% 7% 13% 30% 28%	3898
	21st to end	Night	9% 2 3 14% 37% 36%	4252
November	1st to 10th	Night	13% 3 4 17% 33% 31%	2460
	11th to 20th	Night	12% 3 4 18% 33% 30%	2700
	21st to end	Night	19% 3 6% 17% 31% 24%	2730
December	1st to 10th	Night	18% 3 5% 18% 32% 23%	4380
	11th to 20th	Night	14% 2 5% 15% 31% 34%	5180
	21st to end	Night	12% 3 3 16% 33% 33%	6958

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% 27% 35% 18% 5% 1	330
	11th to 20th	Day	14% 23% 34% 19% 8% 2	330
	21st to end	Day	10% 26% 30% 22% 10% 1	363
February	1st to 10th	Day	12% 28% 30% 21% 6% 3	330
	11th to 20th	Day	22% 25% 33% 13% 5% 1	330
	21st to end	Day	23% 29% 27% 15% 4 1	273
March	1st to 10th	Day	22% 27% 34% 12% 5%	410
	11th to 20th	Day	22% 25% 33% 13% 5% 2	540
	21st to end	Day	19% 31% 31% 13% 5% 2	594
April	1st to 10th	Day	14% 31% 35% 15% 4 1	540
	11th to 20th	Day	17% 31% 36% 13% 3 1	532
	21st to end	Day	16% 30% 35% 16% 4	540
May	1st to 10th	Day	10% 27% 40% 19% 4 1	543
	11th to 20th	Day	11% 21% 37% 20% 8% 3	568
	21st to end	Day	6% 17% 41% 25% 10% 1	742
June	1st to 10th	Day	4 6% 32% 36% 19% 3	780
	11th to 20th	Day	3 7% 30% 38% 18% 3	780
	21st to end	Day	9% 4 19% 33% 27% 7%	756
July	1st to 10th	Day	7% 2 10% 38% 31% 13%	566
	11th to 20th	Day	4 1 6% 38% 35% 15%	545
	21st to end	Day	3 2 7% 29% 41% 17%	575
August	1st to 10th	Day	4 3 5% 30% 38% 20%	527
	11th to 20th	Day	9% 3 8% 33% 35% 12%	517
	21st to end	Day	9% 3 7% 35% 32% 14%	583
September	1st to 10th	Day	11% 4 14% 40% 24% 8%	530
	11th to 20th	Day	5% 3 20% 40% 25% 7%	514
	21st to end	Day	6% 6% 27% 31% 24% 5%	330
October	1st to 10th	Day	13% 8% 24% 33% 16% 5%	330
	11th to 20th	Day	11% 14% 31% 24% 16% 4	330
	21st to end	Day	12% 15% 29% 27% 12% 6%	363
November	1st to 10th	Day	13% 22% 33% 17% 13% 2	330
	11th to 20th	Day	9% 20% 30% 22% 15% 4	330
	21st to end	Day	14% 27% 29% 16% 12% 1	330
December	1st to 10th	Day	15% 22% 31% 24% 7% 1	330
	11th to 20th	Day	13% 22% 32% 25% 6% 2	330
	21st to end	Day	16% 28% 32% 17% 6% 1	363
January	1st to 10th	Night	9% 20% 33% 24% 10% 3	840
	11th to 20th	Night	6% 24% 31% 27% 9% 3	840
	21st to end	Night	6% 26% 32% 25% 10% 1	924
February	1st to 10th	Night	5% 23% 38% 23% 8% 3	840
	11th to 20th	Night	10% 24% 39% 22% 4 1	824
	21st to end	Night	11% 31% 38% 16% 4 1	692
March	1st to 10th	Night	11% 28% 32% 22% 6% 1	840
	11th to 20th	Night	12% 20% 32% 25% 10%	840
	21st to end	Night	8% 25% 37% 22% 7%	813
April	1st to 10th	Night	7% 23% 41% 23% 4	630
	11th to 20th	Night	9% 23% 38% 25% 5%	623
	21st to end	Night	6% 26% 35% 26% 7%	630
May	1st to 10th	Night	6% 18% 43% 29% 4 1	630
	11th to 20th	Night	7% 14% 32% 33% 12% 2	621
	21st to end	Night	5% 12% 36% 33% 13% 1	683
June	1st to 10th	Night	3 4 27% 45% 19% 1	630
	11th to 20th	Night	3 5% 30% 40% 20% 1	630
	21st to end	Night	6% 3 18% 38% 31% 3	630
July	1st to 10th	Night	7% 2 7% 38% 43% 3	615
	11th to 20th	Night	4 2 4 32% 50% 9%	597
	21st to end	Night	5% 2 3 24% 54% 11%	657
August	1st to 10th	Night	6% 1 3 29% 49% 13%	597
	11th to 20th	Night	4 2 5% 31% 45% 14%	594
	21st to end	Night	5% 2 3 28% 52% 10%	660
September	1st to 10th	Night	7% 4 6% 36% 39% 8%	600
	11th to 20th	Night	9% 2 8% 45% 33% 4	600
	21st to end	Night	7% 3 16% 44% 27% 3	600
October	1st to 10th	Night	8% 7% 22% 39% 21% 4	753
	11th to 20th	Night	8% 10% 27% 36% 16% 3	800
	21st to end	Night	8% 13% 27% 30% 16% 7%	880
November	1st to 10th	Night	7% 14% 30% 30% 14% 5%	820
	11th to 20th	Night	3 17% 30% 34% 13% 3	1020
	21st to end	Night	9% 21% 30% 26% 12% 3	1050
December	1st to 10th	Night	10% 20% 30% 29% 9% 2	1050
	11th to 20th	Night	7% 26% 32% 26% 9% 1	1050
	21st to end	Night	11% 26% 31% 25% 6% 2	1076

Page generated at 2026-07-13 01:14:51. Version ac07

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