Darke Sky Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Darke Sky Ranch clear sky chart from 2005-11-06 to 2025-01-22.

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	14% 9% 4 8% 5% 5% 5% 4 6% 7% 35%	105261
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 35%	104084
Transparency	Day	47% 5% 11% 22% 13% 1	108930
	Night	47% 5% 10% 22% 14% 2	108554
Seeing	Day	17% 9% 26% 24% 16% 8%	15699
	Night	18% 8% 27% 30% 15% 2	25565

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	17% 15% 8% 10% 6% 5% 5% 3 4 5% 22%	2607
	11th to 20th	Day	15% 16% 6% 13% 6% 6% 9% 4 4 3 17%	2680
	21st to end	Day	26% 18% 10% 11% 5% 4 3 3 3 4 13%	3133
February	1st to 10th	Day	18% 14% 6% 11% 6% 4 5% 3 4 5% 23%	1786
	11th to 20th	Day	15% 12% 4 13% 7% 6% 5% 3 5% 6% 25%	1848
	21st to end	Day	17% 13% 4 11% 6% 4 4 2 3 6% 30%	1570
March	1st to 10th	Day	21% 18% 5% 9% 5% 4 3 3 4 5% 23%	3140
	11th to 20th	Day	12% 9% 3 8% 5% 4 4 3 5% 7% 39%	3480
	21st to end	Day	17% 10% 4 9% 5% 5% 4 4 5% 7% 29%	3815
April	1st to 10th	Day	14% 12% 3 9% 6% 4 5% 4 4 7% 32%	2251
	11th to 20th	Day	16% 9% 2 8% 4 4 4 4 5% 6% 37%	2318
	21st to end	Day	18% 8% 3 8% 5% 4 5% 3 5% 8% 32%	2470
May	1st to 10th	Day	20% 10% 3 7% 5% 5% 5% 4 6% 7% 30%	4082
	11th to 20th	Day	20% 8% 2 6% 4 4 4 3 5% 8% 36%	4081
	21st to end	Day	10% 6% 2 8% 6% 5% 6% 5% 9% 10% 35%	4476
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 5% 5% 8% 39%	2551
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 5% 6% 10% 42%	2660
	21st to end	Day	9% 5% 2 6% 6% 5% 5% 5% 8% 10% 40%	2660
July	1st to 10th	Day	11% 6% 3 8% 5% 5% 6% 4 7% 10% 34%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 7% 11% 45%	4394
	21st to end	Day	8% 7% 3 7% 6% 6% 6% 5% 7% 9% 37%	4466
August	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 10% 44%	4104
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 4 7% 10% 43%	4044
	21st to end	Day	7% 4 2 6% 4 4 4 4 7% 10% 47%	4250
September	1st to 10th	Day	11% 6% 2 5% 5% 4 4 4 5% 6% 49%	2171
	11th to 20th	Day	9% 5% 2 6% 4 4 4 3 6% 8% 48%	2090
	21st to end	Day	15% 6% 2 6% 5% 3 3 2 4 6% 46%	2090
October	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 5% 5% 46%	2090
	11th to 20th	Day	14% 8% 2 5% 4 4 4 3 5% 7% 45%	1920
	21st to end	Day	18% 10% 3 8% 5% 3 4 3 6% 8% 32%	1925
November	1st to 10th	Day	9% 8% 3 6% 3 4 3 3 5% 7% 49%	1762
	11th to 20th	Day	15% 12% 4 9% 5% 4 4 4 4 6% 34%	1800
	21st to end	Day	18% 13% 4 9% 5% 4 4 3 5% 5% 31%	1800
December	1st to 10th	Day	16% 12% 4 8% 4 4 3 2 4 5% 37%	2930
	11th to 20th	Day	17% 15% 7% 12% 5% 5% 4 4 4 5% 23%	3373
	21st to end	Day	23% 19% 7% 10% 5% 5% 4 3 4 5% 14%	4004
January	1st to 10th	Night	16% 16% 7% 13% 6% 5% 5% 3 5% 4 21%	4568
	11th to 20th	Night	14% 18% 8% 14% 7% 5% 5% 3 4 5% 17%	4502
	21st to end	Night	26% 18% 7% 8% 5% 4 3 2 4 4 18%	4546
February	1st to 10th	Night	20% 13% 5% 9% 6% 4 4 3 4 6% 27%	2393
	11th to 20th	Night	14% 12% 4 9% 6% 5% 4 4 4 6% 31%	2218
	21st to end	Night	19% 13% 5% 10% 4 4 4 2 4 6% 28%	1884
March	1st to 10th	Night	20% 13% 4 6% 4 3 3 3 4 5% 33%	3712
	11th to 20th	Night	11% 8% 3 6% 5% 4 5% 3 5% 7% 44%	3480
	21st to end	Night	18% 10% 3 7% 4 3 3 3 4 6% 38%	3817
April	1st to 10th	Night	14% 9% 3 7% 5% 4 5% 5% 6% 7% 36%	1943
	11th to 20th	Night	16% 8% 3 5% 5% 5% 4 4 5% 8% 38%	1809
	21st to end	Night	17% 7% 3 7% 4 5% 4 4 6% 7% 36%	1710
May	1st to 10th	Night	19% 12% 3 7% 5% 5% 4 4 5% 7% 27%	2813
	11th to 20th	Night	19% 7% 2 6% 4 4 4 3 5% 7% 39%	2812
	21st to end	Night	8% 5% 2 6% 4 5% 4 3 7% 10% 45%	3079
June	1st to 10th	Night	9% 4 2 6% 5% 4 5% 3 6% 8% 48%	1624
	11th to 20th	Night	8% 5% 2 5% 5% 4 4 4 6% 10% 47%	1520
	21st to end	Night	6% 5% 2 5% 4 4 5% 6% 7% 9% 47%	1520
July	1st to 10th	Night	11% 5% 2 6% 5% 5% 5% 3 5% 8% 46%	2530
	11th to 20th	Night	6% 4 2 5% 4 3 4 4 7% 8% 54%	2560
	21st to end	Night	10% 6% 3 6% 4 4 5% 4 6% 10% 41%	3087
August	1st to 10th	Night	10% 6% 3 7% 4 4 5% 4 6% 9% 42%	2825
	11th to 20th	Night	6% 5% 3 7% 4 4 5% 4 7% 8% 48%	2785
	21st to end	Night	4 3 2 6% 4 5% 5% 4 7% 9% 51%	3402
September	1st to 10th	Night	12% 4 2 4 3 4 3 3 5% 8% 51%	1990
	11th to 20th	Night	9% 5% 2 4 3 3 4 4 5% 8% 56%	2090
	21st to end	Night	13% 6% 2 5% 4 4 3 3 5% 6% 48%	2090
October	1st to 10th	Night	10% 5% 2 6% 4 3 4 3 5% 6% 53%	2090
	11th to 20th	Night	15% 8% 2 7% 5% 3 4 3 4 6% 43%	2258
	21st to end	Night	18% 8% 2 6% 4 4 4 3 4 6% 40%	2669
November	1st to 10th	Night	13% 8% 2 5% 4 3 4 3 5% 7% 47%	2536
	11th to 20th	Night	15% 9% 3 8% 5% 3 4 3 5% 7% 37%	2600
	21st to end	Night	17% 12% 5% 8% 6% 5% 5% 3 5% 6% 28%	2600
December	1st to 10th	Night	16% 10% 3 8% 5% 4 4 3 5% 6% 34%	4250
	11th to 20th	Night	18% 17% 6% 11% 4 4 4 3 5% 5% 22%	4822
	21st to end	Night	24% 18% 7% 10% 5% 4 4 3 4 5% 15%	6950

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	64% 5% 6% 15% 9%	2608
	11th to 20th	Day	71% 4 9% 10% 6%	2680
	21st to end	Day	76% 4 6% 10% 3 1	3133
February	1st to 10th	Day	64% 4 10% 13% 9% 1	1786
	11th to 20th	Day	60% 4 9% 18% 8%	1858
	21st to end	Day	58% 4 10% 19% 8% 1	1570
March	1st to 10th	Day	64% 4 8% 17% 7%	3140
	11th to 20th	Day	44% 6% 9% 28% 12% 1	3480
	21st to end	Day	53% 7% 12% 21% 7%	3815
April	1st to 10th	Day	51% 6% 11% 19% 12% 1	2251
	11th to 20th	Day	46% 5% 13% 21% 13% 3	2318
	21st to end	Day	50% 5% 12% 21% 11% 2	2470
May	1st to 10th	Day	52% 6% 11% 22% 8% 1	4120
	11th to 20th	Day	46% 6% 13% 25% 9% 1	4085
	21st to end	Day	40% 8% 14% 22% 14% 1	4489
June	1st to 10th	Day	41% 7% 11% 24% 15% 3	2551
	11th to 20th	Day	36% 8% 13% 24% 18% 1	2660
	21st to end	Day	38% 8% 14% 22% 15% 4	2660
July	1st to 10th	Day	44% 5% 11% 22% 16% 2	4371
	11th to 20th	Day	32% 4 14% 29% 20% 1	4319
	21st to end	Day	42% 5% 13% 20% 16% 4	4324
August	1st to 10th	Day	35% 5% 16% 29% 14% 1	4091
	11th to 20th	Day	35% 5% 12% 32% 16%	4083
	21st to end	Day	32% 5% 13% 31% 16% 3	4249
September	1st to 10th	Day	35% 5% 12% 23% 22% 4	2171
	11th to 20th	Day	33% 6% 11% 25% 22% 3	2090
	21st to end	Day	41% 3 10% 24% 21% 1	2090
October	1st to 10th	Day	26% 3 10% 32% 28% 1	3480
	11th to 20th	Day	32% 3 10% 29% 26% 1	3173
	21st to end	Day	41% 3 10% 24% 21% 2	3149
November	1st to 10th	Day	36% 4 11% 28% 19% 3	1762
	11th to 20th	Day	52% 4 10% 20% 12% 3	1800
	21st to end	Day	54% 5% 10% 20% 9% 1	1800
December	1st to 10th	Day	52% 2 12% 24% 9%	2930
	11th to 20th	Day	65% 4 10% 16% 6%	3370
	21st to end	Day	74% 4 8% 11% 4	4004
January	1st to 10th	Night	65% 6% 9% 13% 7%	4568
	11th to 20th	Night	69% 5% 7% 13% 5%	4502
	21st to end	Night	70% 4 7% 13% 5%	4546
February	1st to 10th	Night	60% 4 10% 16% 8% 1	2393
	11th to 20th	Night	54% 3 10% 19% 13% 1	2219
	21st to end	Night	59% 4 10% 16% 9% 2	1884
March	1st to 10th	Night	52% 5% 8% 24% 10% 1	3712
	11th to 20th	Night	39% 6% 12% 28% 14% 2	3480
	21st to end	Night	48% 5% 10% 28% 9% 1	3817
April	1st to 10th	Night	45% 7% 12% 22% 13% 1	1943
	11th to 20th	Night	44% 6% 11% 18% 17% 4	1809
	21st to end	Night	46% 6% 12% 22% 12% 3	1710
May	1st to 10th	Night	54% 7% 9% 20% 8% 2	2840
	11th to 20th	Night	42% 8% 13% 27% 9% 1	2813
	21st to end	Night	31% 9% 15% 27% 15% 4	3087
June	1st to 10th	Night	33% 7% 11% 25% 23% 2	1624
	11th to 20th	Night	32% 7% 14% 25% 18% 4	1520
	21st to end	Night	31% 9% 16% 24% 17% 4	1520
July	1st to 10th	Night	38% 5% 10% 26% 16% 5%	2490
	11th to 20th	Night	27% 4 13% 32% 22% 1	2512
	21st to end	Night	38% 5% 15% 21% 19% 3	2988
August	1st to 10th	Night	39% 6% 13% 27% 13% 1	2814
	11th to 20th	Night	34% 5% 11% 31% 19% 1	2812
	21st to end	Night	29% 6% 14% 28% 21% 3	3402
September	1st to 10th	Night	33% 5% 13% 25% 19% 6%	1990
	11th to 20th	Night	27% 5% 10% 27% 27% 3	2090
	21st to end	Night	37% 5% 9% 23% 24% 2	2090
October	1st to 10th	Night	23% 3 7% 32% 33% 2	3480
	11th to 20th	Night	32% 3 9% 27% 28% 1	3744
	21st to end	Night	34% 3 7% 28% 24% 4	4395
November	1st to 10th	Night	38% 4 10% 24% 21% 2	2536
	11th to 20th	Night	46% 5% 8% 22% 15% 3	2600
	21st to end	Night	57% 5% 9% 20% 9% 1	2600
December	1st to 10th	Night	52% 3 11% 24% 9% 1	4250
	11th to 20th	Night	64% 4 10% 15% 7% 1	4824
	21st to end	Night	73% 4 9% 12% 3	6950

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	22% 19% 33% 20% 6%	300
	11th to 20th	Day	24% 19% 35% 18% 3	300
	21st to end	Day	32% 15% 30% 19% 4 1	300
February	1st to 10th	Day	29% 17% 33% 15% 6%	270
	11th to 20th	Day	25% 19% 33% 16% 6%	270
	21st to end	Day	25% 14% 44% 15% 3	225
March	1st to 10th	Day	27% 18% 33% 18% 4	277
	11th to 20th	Day	25% 13% 34% 20% 7% 1	460
	21st to end	Day	30% 12% 33% 18% 7%	506
April	1st to 10th	Day	20% 17% 32% 20% 9% 2	460
	11th to 20th	Day	20% 15% 28% 22% 10% 4	452
	21st to end	Day	23% 11% 33% 22% 9% 2	460
May	1st to 10th	Day	24% 10% 30% 24% 9% 3	463
	11th to 20th	Day	22% 7% 27% 24% 13% 8%	487
	21st to end	Day	11% 5% 27% 27% 16% 13%	529
June	1st to 10th	Day	12% 6% 25% 30% 18% 8%	571
	11th to 20th	Day	11% 6% 23% 31% 21% 8%	680
	21st to end	Day	11% 6% 26% 30% 18% 9%	680
July	1st to 10th	Day	12% 3 16% 24% 26% 18%	671
	11th to 20th	Day	8% 3 20% 28% 27% 15%	648
	21st to end	Day	11% 3 14% 28% 27% 18%	532
August	1st to 10th	Day	10% 5% 11% 23% 33% 18%	486
	11th to 20th	Day	11% 3 18% 27% 29% 12%	479
	21st to end	Day	9% 4 11% 25% 33% 18%	539
September	1st to 10th	Day	11% 4 13% 28% 28% 16%	490
	11th to 20th	Day	9% 2 13% 26% 32% 18%	490
	21st to end	Day	19% 9% 20% 23% 20% 9%	490
October	1st to 10th	Day	10% 6% 23% 31% 18% 11%	490
	11th to 20th	Day	16% 14% 28% 24% 13% 5%	490
	21st to end	Day	24% 13% 35% 20% 7% 1	374
November	1st to 10th	Day	14% 14% 33% 25% 10% 5%	300
	11th to 20th	Day	23% 17% 28% 19% 11% 3	300
	21st to end	Day	26% 11% 39% 20% 3	300
December	1st to 10th	Day	19% 19% 36% 18% 7% 1	300
	11th to 20th	Day	24% 15% 39% 17% 6%	300
	21st to end	Day	31% 18% 29% 18% 4	330
January	1st to 10th	Night	21% 17% 35% 21% 5% 1	1000
	11th to 20th	Night	27% 14% 36% 19% 4	948
	21st to end	Night	24% 11% 37% 24% 4	841
February	1st to 10th	Night	26% 10% 34% 27% 3	760
	11th to 20th	Night	21% 15% 36% 26% 3	743
	21st to end	Night	26% 11% 36% 23% 3	628
March	1st to 10th	Night	22% 11% 32% 29% 6% 1	760
	11th to 20th	Night	18% 15% 33% 28% 6% 1	760
	21st to end	Night	26% 10% 30% 27% 7%	836
April	1st to 10th	Night	20% 11% 33% 28% 7% 1	613
	11th to 20th	Night	19% 10% 31% 27% 10% 1	563
	21st to end	Night	19% 6% 40% 23% 10% 1	570
May	1st to 10th	Night	22% 6% 31% 30% 10% 1	570
	11th to 20th	Night	20% 4 24% 33% 17% 1	561
	21st to end	Night	8% 3 24% 37% 26% 3	617
June	1st to 10th	Night	11% 1 23% 41% 24% 1	570
	11th to 20th	Night	10% 2 19% 42% 25% 1	570
	21st to end	Night	8% 2 24% 38% 27% 2	570
July	1st to 10th	Night	11% 2 14% 34% 33% 6%	555
	11th to 20th	Night	8% 2 13% 40% 30% 7%	552
	21st to end	Night	11% 3 9% 41% 34% 2	624
August	1st to 10th	Night	8% 1 11% 40% 36% 4	567
	11th to 20th	Night	7% 1 11% 43% 33% 5%	564
	21st to end	Night	6% 2 11% 35% 40% 6%	627
September	1st to 10th	Night	12% 6% 13% 32% 32% 4	660
	11th to 20th	Night	9% 2 13% 34% 37% 4	760
	21st to end	Night	16% 4 21% 33% 24% 3	760
October	1st to 10th	Night	12% 4 26% 32% 22% 5%	760
	11th to 20th	Night	19% 9% 28% 30% 13% 1	760
	21st to end	Night	23% 10% 31% 27% 9%	836
November	1st to 10th	Night	16% 9% 32% 27% 15% 1	780
	11th to 20th	Night	20% 14% 32% 27% 7% 1	800
	21st to end	Night	23% 13% 29% 28% 7% 1	800
December	1st to 10th	Night	25% 12% 34% 24% 5% 1	800
	11th to 20th	Night	26% 10% 34% 25% 5% 1	800
	21st to end	Night	30% 12% 32% 23% 4	1080

Page generated at 2025-01-19 03:06:45. Version ac07

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