Mineral Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mineral Ranch Observatory clear sky chart from 2005-11-06 to 2024-12-24.

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	11% 6% 2 6% 5% 5% 5% 4 6% 8% 43%	101433
	Night	12% 6% 2 5% 4 3 4 3 5% 7% 49%	98792
Transparency	Day	37% 6% 12% 21% 16% 8%	105251
	Night	34% 6% 13% 22% 16% 10%	103101
Seeing	Day	11% 6% 22% 30% 23% 8%	14780
	Night	14% 6% 26% 37% 16% 1	24785

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	15% 7% 2 7% 5% 3 3 2 3 4 48%	2847
	11th to 20th	Day	16% 5% 2 4 3 3 3 2 4 6% 54%	2850
	21st to end	Day	21% 7% 3 6% 3 3 4 4 7% 6% 37%	3427
February	1st to 10th	Day	19% 8% 3 7% 4 4 2 2 4 5% 42%	1900
	11th to 20th	Day	18% 8% 2 6% 3 3 4 4 4 5% 43%	1849
	21st to end	Day	17% 7% 2 5% 3 4 4 3 6% 4 46%	1579
March	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 4 7% 7% 33%	3436
	11th to 20th	Day	21% 10% 3 9% 6% 4 5% 3 5% 5% 29%	3480
	21st to end	Day	10% 6% 2 5% 4 4 4 3 6% 7% 49%	3814
April	1st to 10th	Day	11% 6% 3 6% 5% 4 5% 4 6% 6% 43%	2090
	11th to 20th	Day	16% 7% 3 7% 5% 4 4 3 5% 6% 40%	2066
	21st to end	Day	12% 8% 2 6% 5% 4 4 4 5% 5% 45%	2313
May	1st to 10th	Day	14% 7% 3 8% 6% 5% 5% 4 5% 8% 36%	4082
	11th to 20th	Day	9% 6% 2 7% 6% 5% 5% 4 6% 7% 43%	4082
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 4 7% 10% 44%	4477
June	1st to 10th	Day	5% 3 2 5% 5% 5% 6% 5% 7% 10% 47%	2470
	11th to 20th	Day	5% 4 2 6% 5% 6% 5% 6% 7% 9% 45%	2470
	21st to end	Day	7% 5% 2 6% 7% 7% 6% 7% 9% 9% 35%	2470
July	1st to 10th	Day	7% 5% 2 6% 6% 6% 6% 5% 7% 9% 41%	4120
	11th to 20th	Day	5% 6% 3 9% 6% 6% 6% 6% 8% 10% 35%	4120
	21st to end	Day	9% 6% 3 7% 6% 6% 6% 6% 7% 10% 34%	4465
August	1st to 10th	Day	1 1 1 3 3 4 4 3 6% 9% 65%	4019
	11th to 20th	Day	3 2 1 4 3 4 6% 5% 9% 13% 49%	3726
	21st to end	Day	5% 4 2 7% 6% 6% 8% 6% 9% 11% 37%	3928
September	1st to 10th	Day	10% 6% 2 7% 6% 7% 6% 5% 7% 8% 35%	2090
	11th to 20th	Day	10% 6% 3 7% 5% 6% 6% 4 6% 8% 39%	2090
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 6% 8% 46%	2090
October	1st to 10th	Day	5% 5% 1 5% 5% 5% 5% 5% 6% 7% 51%	2090
	11th to 20th	Day	10% 6% 2 4 4 4 4 4 5% 7% 50%	1967
	21st to end	Day	9% 4 2 4 4 3 3 3 4 5% 58%	2090
November	1st to 10th	Day	10% 6% 2 7% 5% 5% 4 3 5% 8% 45%	1958
	11th to 20th	Day	13% 5% 2 5% 4 3 3 3 5% 6% 50%	1965
	21st to end	Day	17% 8% 2 7% 3 4 4 4 5% 6% 41%	1800
December	1st to 10th	Day	18% 8% 2 7% 4 4 3 2 5% 6% 42%	1800
	11th to 20th	Day	16% 9% 3 6% 4 4 4 3 5% 6% 41%	2251
	21st to end	Day	13% 6% 2 7% 4 3 4 3 4 6% 47%	3162
January	1st to 10th	Night	18% 7% 2 6% 3 3 3 3 4 5% 47%	4108
	11th to 20th	Night	15% 4 1 4 2 2 2 2 4 6% 58%	4120
	21st to end	Night	24% 6% 2 6% 4 3 4 2 6% 7% 36%	4267
February	1st to 10th	Night	17% 8% 3 5% 4 4 4 3 4 6% 42%	2280
	11th to 20th	Night	19% 6% 2 5% 2 2 3 2 5% 6% 47%	2218
	21st to end	Night	18% 8% 3 5% 3 4 3 3 5% 5% 45%	1873
March	1st to 10th	Night	22% 9% 2 6% 4 4 4 3 5% 6% 33%	3419
	11th to 20th	Night	24% 10% 3 9% 4 4 4 2 4 5% 30%	3480
	21st to end	Night	14% 6% 2 4 3 3 3 3 4 6% 52%	3817
April	1st to 10th	Night	12% 6% 2 6% 5% 5% 6% 4 6% 8% 41%	2090
	11th to 20th	Night	15% 7% 3 6% 3 3 4 3 5% 7% 43%	2063
	21st to end	Night	16% 8% 3 7% 5% 4 4 3 5% 6% 40%	1859
May	1st to 10th	Night	17% 10% 3 6% 4 4 4 4 6% 7% 34%	2823
	11th to 20th	Night	13% 8% 2 5% 3 4 4 3 5% 9% 44%	2823
	21st to end	Night	8% 6% 2 6% 5% 5% 5% 4 6% 9% 44%	3090
June	1st to 10th	Night	5% 4 1 4 3 3 3 3 7% 10% 58%	1710
	11th to 20th	Night	4 3 1 4 4 4 4 4 6% 9% 59%	1710
	21st to end	Night	5% 4 2 5% 4 4 5% 5% 8% 11% 49%	1710
July	1st to 10th	Night	5% 4 2 5% 4 4 4 3 7% 9% 54%	2850
	11th to 20th	Night	4 5% 2 6% 4 4 5% 4 7% 10% 47%	2850
	21st to end	Night	6% 4 3 6% 4 5% 5% 4 6% 11% 45%	3098
August	1st to 10th	Night	1 2 1 1 2 3 4 7% 79%	2915
	11th to 20th	Night	3 2 1 3 3 4 4 3 7% 12% 58%	3113
	21st to end	Night	3 3 1 4 3 4 4 3 6% 13% 58%	3730
September	1st to 10th	Night	7% 5% 2 6% 5% 4 4 4 7% 8% 48%	2090
	11th to 20th	Night	9% 6% 2 5% 4 4 4 4 5% 9% 49%	2090
	21st to end	Night	6% 5% 2 6% 4 3 4 3 5% 7% 56%	2090
October	1st to 10th	Night	4 3 1 3 3 3 3 3 6% 6% 65%	2090
	11th to 20th	Night	9% 4 1 4 3 3 3 3 4 6% 60%	2194
	21st to end	Night	10% 4 1 4 2 2 2 2 4 5% 65%	2508
November	1st to 10th	Night	10% 5% 2 5% 4 3 4 2 5% 8% 51%	2340
	11th to 20th	Night	13% 5% 2 4 3 3 3 3 3 5% 55%	2430
	21st to end	Night	14% 7% 2 5% 4 4 4 3 5% 6% 46%	2600
December	1st to 10th	Night	18% 7% 3 6% 4 3 3 2 4 6% 45%	2600
	11th to 20th	Night	18% 8% 3 6% 5% 3 3 3 5% 6% 41%	3166
	21st to end	Night	14% 7% 2 5% 3 3 3 3 5% 7% 47%	4578

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	41% 3 5% 12% 23% 16%	2848
	11th to 20th	Day	34% 4 5% 20% 24% 15%	2850
	21st to end	Day	46% 4 5% 14% 23% 8%	3427
February	1st to 10th	Day	47% 4 6% 11% 19% 14%	1900
	11th to 20th	Day	43% 4 8% 16% 17% 12%	1859
	21st to end	Day	41% 5% 8% 17% 17% 12%	1579
March	1st to 10th	Day	47% 6% 10% 17% 14% 6%	3436
	11th to 20th	Day	57% 5% 7% 9% 14% 7%	3480
	21st to end	Day	33% 5% 12% 20% 16% 14%	3814
April	1st to 10th	Day	40% 6% 10% 15% 17% 12%	2090
	11th to 20th	Day	44% 5% 8% 17% 14% 12%	2066
	21st to end	Day	40% 6% 8% 19% 17% 11%	2313
May	1st to 10th	Day	45% 6% 14% 18% 10% 6%	4120
	11th to 20th	Day	39% 7% 9% 19% 18% 8%	4086
	21st to end	Day	32% 7% 11% 38% 11% 1	4489
June	1st to 10th	Day	28% 9% 15% 27% 19% 2	2470
	11th to 20th	Day	32% 8% 11% 26% 20% 4	2470
	21st to end	Day	39% 11% 14% 25% 10% 2	2470
July	1st to 10th	Day	35% 8% 19% 32% 6%	4056
	11th to 20th	Day	40% 10% 19% 21% 10% 1	4051
	21st to end	Day	40% 10% 19% 25% 5%	4325
August	1st to 10th	Day	15% 6% 14% 46% 18% 1	4005
	11th to 20th	Day	22% 10% 28% 32% 7% 1	3762
	21st to end	Day	36% 11% 18% 23% 12% 1	3927
September	1st to 10th	Day	43% 10% 13% 15% 14% 4	2090
	11th to 20th	Day	40% 9% 14% 19% 14% 4	2090
	21st to end	Day	34% 7% 13% 18% 18% 11%	2090
October	1st to 10th	Day	22% 4 7% 13% 20% 34%	3480
	11th to 20th	Day	25% 5% 10% 18% 21% 20%	3246
	21st to end	Day	25% 4 7% 18% 28% 16%	3428
November	1st to 10th	Day	38% 5% 9% 18% 19% 11%	1958
	11th to 20th	Day	36% 4 10% 17% 19% 15%	1965
	21st to end	Day	44% 4 7% 17% 17% 12%	1800
December	1st to 10th	Day	45% 3 8% 17% 18% 8%	1800
	11th to 20th	Day	44% 5% 7% 12% 18% 15%	2249
	21st to end	Day	38% 4 6% 19% 20% 12%	3162
January	1st to 10th	Night	39% 4 7% 13% 16% 21%	4108
	11th to 20th	Night	30% 3 6% 20% 22% 20%	4120
	21st to end	Night	47% 3 6% 12% 21% 10%	4267
February	1st to 10th	Night	44% 3 9% 11% 16% 17%	2280
	11th to 20th	Night	40% 3 8% 18% 17% 13%	2218
	21st to end	Night	41% 4 8% 19% 17% 11%	1873
March	1st to 10th	Night	50% 6% 10% 15% 13% 6%	3419
	11th to 20th	Night	58% 4 9% 12% 9% 8%	3480
	21st to end	Night	33% 5% 13% 16% 20% 12%	3817
April	1st to 10th	Night	41% 6% 12% 18% 13% 10%	2090
	11th to 20th	Night	41% 5% 10% 16% 14% 15%	2063
	21st to end	Night	44% 5% 10% 17% 15% 9%	1859
May	1st to 10th	Night	49% 6% 12% 17% 11% 6%	2850
	11th to 20th	Night	38% 6% 13% 19% 17% 6%	2824
	21st to end	Night	36% 7% 16% 34% 7%	3099
June	1st to 10th	Night	22% 6% 20% 32% 18% 2	1710
	11th to 20th	Night	24% 6% 13% 33% 21% 3	1710
	21st to end	Night	27% 10% 20% 31% 11% 1	1710
July	1st to 10th	Night	25% 8% 27% 36% 4	2805
	11th to 20th	Night	30% 10% 26% 24% 10%	2796
	21st to end	Night	34% 9% 25% 27% 5%	2999
August	1st to 10th	Night	8% 4 18% 53% 17%	2905
	11th to 20th	Night	18% 7% 37% 34% 4	3143
	21st to end	Night	19% 11% 29% 31% 9% 1	3730
September	1st to 10th	Night	32% 9% 22% 21% 12% 4	2090
	11th to 20th	Night	32% 7% 17% 25% 16% 3	2090
	21st to end	Night	27% 6% 15% 26% 18% 9%	2090
October	1st to 10th	Night	14% 4 9% 19% 21% 34%	3480
	11th to 20th	Night	20% 4 10% 20% 27% 18%	3641
	21st to end	Night	20% 3 8% 24% 31% 15%	4120
November	1st to 10th	Night	32% 6% 11% 19% 21% 10%	2340
	11th to 20th	Night	33% 5% 12% 17% 19% 15%	2430
	21st to end	Night	39% 4 10% 19% 17% 12%	2600
December	1st to 10th	Night	43% 4 9% 18% 17% 10%	2600
	11th to 20th	Night	44% 4 6% 14% 15% 16%	3167
	21st to end	Night	38% 5% 7% 16% 22% 12%	4578

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	19% 10% 38% 24% 7% 2	270
	11th to 20th	Day	20% 8% 34% 26% 10% 1	270
	21st to end	Day	22% 10% 34% 23% 9% 2	297
February	1st to 10th	Day	24% 13% 28% 26% 9% 1	270
	11th to 20th	Day	21% 12% 37% 21% 7%	270
	21st to end	Day	23% 13% 40% 20% 5%	225
March	1st to 10th	Day	19% 11% 40% 24% 7%	270
	11th to 20th	Day	17% 13% 42% 23% 5%	270
	21st to end	Day	15% 13% 43% 24% 5%	297
April	1st to 10th	Day	14% 14% 39% 25% 8%	270
	11th to 20th	Day	19% 13% 33% 24% 9% 1	264
	21st to end	Day	13% 14% 40% 27% 6%	493
May	1st to 10th	Day	11% 14% 42% 25% 7%	653
	11th to 20th	Day	11% 8% 37% 31% 12% 2	675
	21st to end	Day	10% 6% 32% 36% 16% 1	734
June	1st to 10th	Day	6% 2 17% 38% 31% 6%	680
	11th to 20th	Day	6% 1 18% 46% 24% 6%	680
	21st to end	Day	8% 3 12% 34% 32% 11%	680
July	1st to 10th	Day	6% 3 11% 33% 35% 12%	671
	11th to 20th	Day	4 1 6% 33% 44% 13%	668
	21st to end	Day	4 2 6% 36% 38% 14%	739
August	1st to 10th	Day	3 7% 33% 39% 18%	630
	11th to 20th	Day	4 1 6% 36% 36% 18%	477
	21st to end	Day	5% 2 7% 24% 33% 28%	391
September	1st to 10th	Day	11% 1 6% 24% 35% 22%	300
	11th to 20th	Day	8% 5% 16% 41% 30%	300
	21st to end	Day	7% 8% 25% 37% 22%	300
October	1st to 10th	Day	5% 1 11% 31% 38% 14%	300
	11th to 20th	Day	11% 2 11% 36% 29% 11%	300
	21st to end	Day	14% 8% 22% 30% 20% 7%	330
November	1st to 10th	Day	14% 4 19% 32% 26% 4	300
	11th to 20th	Day	19% 5% 21% 30% 21% 4	300
	21st to end	Day	22% 11% 29% 22% 13% 3	300
December	1st to 10th	Day	18% 7% 31% 26% 13% 5%	300
	11th to 20th	Day	19% 10% 28% 29% 13% 1	300
	21st to end	Day	19% 8% 29% 31% 11% 2	306
January	1st to 10th	Night	21% 7% 30% 33% 9% 1	950
	11th to 20th	Night	22% 8% 29% 34% 7%	950
	21st to end	Night	21% 9% 31% 33% 6%	884
February	1st to 10th	Night	23% 12% 31% 29% 5%	760
	11th to 20th	Night	25% 9% 34% 28% 5%	744
	21st to end	Night	24% 11% 42% 21% 3	617
March	1st to 10th	Night	23% 9% 37% 27% 4	570
	11th to 20th	Night	22% 10% 36% 28% 4	570
	21st to end	Night	14% 10% 46% 27% 3	627
April	1st to 10th	Night	14% 8% 49% 25% 4	570
	11th to 20th	Night	20% 8% 39% 27% 6%	563
	21st to end	Night	18% 11% 41% 26% 5%	570
May	1st to 10th	Night	14% 7% 49% 27% 3	570
	11th to 20th	Night	12% 5% 38% 35% 9%	561
	21st to end	Night	9% 5% 36% 40% 10%	617
June	1st to 10th	Night	5% 3 20% 54% 17% 1	570
	11th to 20th	Night	5% 1 23% 56% 14%	570
	21st to end	Night	8% 1 16% 49% 25% 2	570
July	1st to 10th	Night	5% 2 13% 49% 29% 2	555
	11th to 20th	Night	3 1 9% 51% 34% 2	552
	21st to end	Night	3 1 7% 53% 33% 2	624
August	1st to 10th	Night	1 7% 53% 35% 4	567
	11th to 20th	Night	4 1 7% 49% 36% 3	564
	21st to end	Night	5% 1 6% 39% 46% 3	627
September	1st to 10th	Night	9% 1 5% 39% 41% 5%	570
	11th to 20th	Night	11% 1 7% 34% 43% 4	570
	21st to end	Night	7% 1 12% 37% 39% 4	570
October	1st to 10th	Night	4 1 11% 46% 34% 4	570
	11th to 20th	Night	10% 3 22% 46% 17% 2	674
	21st to end	Night	10% 6% 26% 37% 19% 2	836
November	1st to 10th	Night	12% 4 23% 42% 18% 2	780
	11th to 20th	Night	15% 5% 24% 37% 17% 1	830
	21st to end	Night	18% 7% 28% 33% 14% 1	1000
December	1st to 10th	Night	21% 7% 24% 34% 13% 1	1000
	11th to 20th	Night	23% 9% 27% 33% 8%	1000
	21st to end	Night	21% 8% 26% 36% 9% 1	1063

Page generated at 2024-12-21 03:13:48. Version ac07

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