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 2024-08-15.

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% 34%	95368
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 36%	93316
Transparency	Day	48% 6% 11% 21% 12% 2	95132
	Night	48% 6% 10% 21% 13% 2	93157
Seeing	Day	17% 9% 26% 24% 16% 8%	15151
	Night	18% 8% 27% 30% 15% 2	24922

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%	2527
	11th to 20th	Day	15% 16% 6% 13% 6% 6% 9% 4 4 3 16%	2597
	21st to end	Day	26% 18% 10% 11% 5% 4 3 3 3 4 13%	3124
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	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 43%	2457
	11th to 20th	Day	8% 5% 2 7% 5% 6% 6% 4 8% 10% 39%	2357
	21st to end	Day	8% 5% 3 6% 4 5% 5% 5% 7% 9% 43%	2418
September	1st to 10th	Day	12% 6% 2 5% 5% 5% 4 4 5% 6% 47%	2057
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 6% 8% 47%	1980
	21st to end	Day	14% 6% 2 6% 5% 3 3 2 4 6% 48%	1980
October	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 6% 5% 44%	1980
	11th to 20th	Day	14% 8% 2 5% 4 4 4 3 5% 7% 44%	1819
	21st to end	Day	18% 11% 3 8% 4 4 4 3 6% 8% 31%	1824
November	1st to 10th	Day	9% 8% 3 5% 3 4 3 3 5% 7% 49%	1672
	11th to 20th	Day	15% 12% 4 9% 5% 4 3 4 4 6% 35%	1710
	21st to end	Day	18% 12% 4 8% 5% 4 4 3 5% 6% 31%	1710
December	1st to 10th	Day	18% 16% 6% 10% 6% 5% 4 2 5% 5% 23%	1710
	11th to 20th	Day	14% 15% 7% 13% 5% 5% 5% 4 4 5% 25%	2153
	21st to end	Day	22% 20% 9% 11% 6% 5% 4 3 4 4 11%	2805
January	1st to 10th	Night	16% 16% 6% 13% 6% 5% 5% 3 5% 4 21%	4428
	11th to 20th	Night	14% 18% 8% 14% 7% 5% 5% 3 4 5% 17%	4365
	21st to end	Night	26% 18% 7% 9% 5% 4 3 2 4 4 18%	4532
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	6% 4 2 6% 5% 4 6% 5% 7% 10% 46%	1701
	11th to 20th	Night	5% 5% 2 7% 4 4 5% 4 7% 8% 49%	1643
	21st to end	Night	5% 4 2 5% 4 4 5% 4 6% 9% 51%	1934
September	1st to 10th	Night	13% 5% 2 4 3 4 3 3 5% 9% 49%	1885
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 5% 8% 55%	1980
	21st to end	Night	12% 6% 2 5% 4 4 4 3 5% 7% 50%	1980
October	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 6% 51%	1980
	11th to 20th	Night	16% 8% 2 7% 5% 4 4 3 4 6% 41%	2139
	21st to end	Night	19% 8% 2 6% 4 4 4 3 4 6% 39%	2528
November	1st to 10th	Night	12% 8% 2 5% 4 3 4 3 5% 7% 47%	2406
	11th to 20th	Night	15% 9% 3 7% 5% 3 4 3 5% 7% 37%	2470
	21st to end	Night	17% 12% 5% 8% 6% 5% 5% 3 5% 6% 29%	2470
December	1st to 10th	Night	19% 13% 4 9% 6% 4 4 3 5% 6% 26%	2470
	11th to 20th	Night	17% 14% 5% 10% 4 4 4 4 5% 6% 26%	3042
	21st to end	Night	22% 18% 8% 11% 6% 5% 4 3 4 4 16%	4852

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% 7% 15% 9%	2528
	11th to 20th	Day	72% 4 9% 9% 5%	2597
	21st to end	Day	76% 4 6% 10% 3	3124
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	33% 8% 14% 29% 14% 2	2444
	11th to 20th	Day	37% 8% 13% 28% 13% 1	2357
	21st to end	Day	33% 8% 12% 24% 17% 5%	2418
September	1st to 10th	Day	36% 6% 12% 23% 20% 3	2057
	11th to 20th	Day	34% 6% 11% 25% 21% 2	1980
	21st to end	Day	38% 3 10% 25% 22% 1	1980
October	1st to 10th	Day	39% 6% 10% 25% 18% 2	1980
	11th to 20th	Day	39% 5% 9% 25% 19% 2	1819
	21st to end	Day	52% 4 11% 20% 11% 2	1824
November	1st to 10th	Day	35% 4 11% 28% 19% 3	1672
	11th to 20th	Day	51% 4 10% 21% 12% 3	1710
	21st to end	Day	53% 5% 10% 21% 10% 1	1710
December	1st to 10th	Day	64% 4 10% 15% 6% 1	1710
	11th to 20th	Day	61% 5% 8% 18% 7%	2150
	21st to end	Day	76% 5% 6% 7% 5%	2805
January	1st to 10th	Night	64% 6% 9% 13% 7%	4428
	11th to 20th	Night	70% 6% 7% 13% 4	4365
	21st to end	Night	70% 4 7% 13% 5%	4532
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	31% 8% 14% 28% 17% 2	1690
	11th to 20th	Night	31% 8% 12% 28% 19% 1	1643
	21st to end	Night	28% 8% 15% 21% 23% 5%	1934
September	1st to 10th	Night	34% 5% 13% 24% 18% 6%	1885
	11th to 20th	Night	28% 5% 11% 28% 26% 2	1980
	21st to end	Night	34% 6% 10% 23% 25% 3	1980
October	1st to 10th	Night	33% 4 11% 26% 23% 2	1980
	11th to 20th	Night	44% 5% 7% 24% 19% 1	2139
	21st to end	Night	47% 5% 8% 23% 15% 3	2528
November	1st to 10th	Night	38% 4 10% 23% 21% 3	2406
	11th to 20th	Night	45% 5% 9% 22% 16% 3	2470
	21st to end	Night	56% 5% 10% 20% 9% 1	2470
December	1st to 10th	Night	59% 5% 10% 17% 8% 1	2470
	11th to 20th	Night	57% 7% 9% 20% 7% 1	3044
	21st to end	Night	71% 5% 8% 11% 4	4852

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% 18% 33% 20% 6%	270
	11th to 20th	Day	26% 16% 36% 19% 3	270
	21st to end	Day	32% 14% 30% 19% 4 1	297
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 17% 27% 30% 13%	456
	21st to end	Day	10% 4 12% 26% 32% 17%	495
September	1st to 10th	Day	12% 3 13% 27% 28% 17%	450
	11th to 20th	Day	10% 2 14% 26% 31% 18%	450
	21st to end	Day	16% 9% 20% 24% 21% 10%	450
October	1st to 10th	Day	11% 6% 24% 30% 18% 11%	450
	11th to 20th	Day	17% 14% 28% 25% 13% 2	450
	21st to end	Day	26% 13% 35% 20% 6% 1	339
November	1st to 10th	Day	14% 14% 31% 26% 10% 5%	270
	11th to 20th	Day	23% 17% 27% 18% 12% 3	270
	21st to end	Day	26% 11% 39% 21% 4	270
December	1st to 10th	Day	20% 18% 36% 18% 8% 1	270
	11th to 20th	Day	21% 14% 40% 18% 6%	270
	21st to end	Day	31% 19% 29% 18% 4	297
January	1st to 10th	Night	22% 16% 34% 22% 5% 1	950
	11th to 20th	Night	28% 14% 35% 20% 4	901
	21st to end	Night	24% 11% 37% 24% 4	836
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%	549
	21st to end	Night	6% 2 12% 35% 39% 6%	594
September	1st to 10th	Night	13% 6% 13% 31% 33% 5%	625
	11th to 20th	Night	10% 2 13% 33% 37% 5%	720
	21st to end	Night	14% 4 21% 33% 25% 3	720
October	1st to 10th	Night	12% 4 26% 32% 22% 5%	720
	11th to 20th	Night	20% 9% 28% 30% 12% 1	720
	21st to end	Night	24% 10% 31% 27% 8%	792
November	1st to 10th	Night	16% 8% 32% 27% 16% 1	740
	11th to 20th	Night	20% 14% 31% 27% 7% 1	760
	21st to end	Night	23% 12% 28% 29% 7% 1	760
December	1st to 10th	Night	25% 11% 33% 24% 5% 1	760
	11th to 20th	Night	25% 9% 35% 26% 5% 1	760
	21st to end	Night	29% 12% 32% 23% 4	1026

Page generated at 2024-08-12 09:52:51. Version ac07

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