Red Rock Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red Rock Ranch clear sky chart from 2005-11-06 to 2025-02-06.

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	12% 5% 2 5% 4 4 4 3 5% 7% 49%	109081
	Night	13% 5% 2 4 3 3 3 3 5% 7% 53%	109414
Transparency	Day	34% 4 9% 22% 19% 11%	112979
	Night	31% 4 11% 21% 20% 14%	113643
Seeing	Day	13% 3 17% 33% 26% 8%	14945
	Night	13% 4 23% 43% 16% 1	25044

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	16% 5% 1 4 2 2 2 2 3 4 58%	4077
	11th to 20th	Day	14% 5% 2 4 3 2 2 3 5% 6% 55%	4310
	21st to end	Day	23% 7% 1 5% 3 2 3 2 4 7% 42%	4994
February	1st to 10th	Day	16% 8% 3 5% 4 2 3 3 4 4 48%	1950
	11th to 20th	Day	17% 6% 2 6% 4 3 3 2 4 6% 47%	1849
	21st to end	Day	14% 6% 2 5% 4 2 2 3 5% 7% 51%	1570
March	1st to 10th	Day	17% 8% 2 6% 3 3 4 3 4 6% 45%	3267
	11th to 20th	Day	23% 9% 3 7% 4 3 4 3 4 5% 36%	3480
	21st to end	Day	14% 6% 2 5% 4 3 3 3 5% 6% 50%	3814
April	1st to 10th	Day	13% 6% 2 6% 3 3 4 3 5% 7% 47%	2090
	11th to 20th	Day	15% 6% 2 5% 3 4 4 3 4 7% 47%	2202
	21st to end	Day	14% 6% 2 5% 4 3 3 3 4 6% 48%	2283
May	1st to 10th	Day	19% 7% 2 7% 4 3 4 3 5% 7% 40%	4082
	11th to 20th	Day	12% 5% 2 6% 5% 4 4 4 6% 7% 45%	4082
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 7% 10% 44%	4477
June	1st to 10th	Day	5% 3 1 3 3 4 5% 4 7% 10% 55%	2470
	11th to 20th	Day	6% 4 2 4 4 5% 5% 4 6% 9% 52%	2470
	21st to end	Day	6% 5% 2 5% 5% 6% 5% 6% 6% 9% 46%	2470
July	1st to 10th	Day	7% 5% 2 5% 4 4 4 3 6% 8% 51%	4120
	11th to 20th	Day	7% 4 1 5% 4 4 5% 4 6% 9% 50%	4120
	21st to end	Day	6% 4 2 6% 5% 5% 5% 5% 6% 10% 46%	4375
August	1st to 10th	Day	1 1 1 2 2 3 2 2 4 8% 74%	3785
	11th to 20th	Day	3 2 1 2 3 4 3 4 6% 9% 63%	3726
	21st to end	Day	5% 3 1 5% 4 4 5% 4 7% 11% 52%	4130
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 4 6% 7% 41%	2090
	11th to 20th	Day	11% 6% 2 7% 4 4 5% 4 6% 8% 42%	2090
	21st to end	Day	8% 4 2 6% 4 5% 4 4 6% 7% 50%	2090
October	1st to 10th	Day	7% 4 2 5% 4 4 4 3 4 6% 58%	2090
	11th to 20th	Day	14% 4 2 6% 3 4 3 3 4 5% 52%	2081
	21st to end	Day	12% 4 2 4 3 2 3 3 4 4 59%	2090
November	1st to 10th	Day	16% 8% 2 5% 4 3 3 3 4 6% 46%	1938
	11th to 20th	Day	15% 5% 2 4 3 4 3 3 4 6% 52%	1800
	21st to end	Day	16% 6% 3 5% 3 4 3 3 4 5% 48%	1800
December	1st to 10th	Day	30% 10% 3 5% 4 3 2 2 3 4 35%	2940
	11th to 20th	Day	17% 7% 3 6% 4 4 3 3 5% 6% 42%	3391
	21st to end	Day	12% 6% 2 4 3 3 3 2 3 4 58%	4488
January	1st to 10th	Night	17% 4 2 4 2 2 2 2 4 6% 55%	5888
	11th to 20th	Night	12% 3 1 2 2 3 3 2 3 6% 62%	5698
	21st to end	Night	27% 5% 2 4 3 3 3 3 4 5% 42%	5984
February	1st to 10th	Night	13% 5% 2 4 2 3 4 3 4 5% 56%	2340
	11th to 20th	Night	18% 6% 2 4 2 2 2 3 3 5% 53%	2218
	21st to end	Night	13% 6% 2 5% 3 3 3 4 5% 5% 50%	1884
March	1st to 10th	Night	14% 8% 2 5% 3 4 4 3 5% 7% 46%	3589
	11th to 20th	Night	18% 8% 2 7% 4 4 3 3 4 5% 42%	3480
	21st to end	Night	12% 5% 2 4 4 3 4 3 5% 7% 52%	3817
April	1st to 10th	Night	9% 5% 2 4 4 3 4 4 6% 9% 51%	2090
	11th to 20th	Night	15% 5% 1 4 4 3 3 4 5% 6% 49%	1923
	21st to end	Night	15% 5% 2 6% 4 3 3 3 3 6% 52%	1895
May	1st to 10th	Night	17% 5% 2 4 3 3 3 3 5% 7% 48%	2823
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 5% 7% 53%	2823
	21st to end	Night	8% 4 2 5% 3 4 4 3 6% 8% 54%	3090
June	1st to 10th	Night	3 2 2 3 2 2 4 3 4 11% 64%	1710
	11th to 20th	Night	4 2 1 3 4 4 4 4 6% 9% 60%	1710
	21st to end	Night	5% 3 2 4 5% 4 4 4 6% 10% 53%	1710
July	1st to 10th	Night	5% 4 1 4 3 4 3 3 5% 9% 59%	2850
	11th to 20th	Night	3 3 2 5% 4 4 5% 5% 6% 9% 53%	2850
	21st to end	Night	8% 3 1 4 3 4 4 4 7% 10% 51%	3181
August	1st to 10th	Night	1 1 2 2 2 3 2 4 7% 75%	3155
	11th to 20th	Night	3 2 1 3 2 3 4 3 6% 10% 65%	3113
	21st to end	Night	4 3 1 5% 4 4 4 3 7% 9% 56%	3535
September	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 4 7% 8% 45%	2090
	11th to 20th	Night	9% 6% 2 5% 5% 4 4 4 6% 8% 46%	2090
	21st to end	Night	8% 4 2 5% 3 3 3 3 7% 8% 54%	2090
October	1st to 10th	Night	5% 3 2 3 3 2 3 2 4 7% 65%	2090
	11th to 20th	Night	13% 3 2 3 3 3 4 2 4 5% 58%	2090
	21st to end	Night	11% 3 1 3 3 2 2 2 3 4 66%	2496
November	1st to 10th	Night	13% 6% 2 5% 3 2 2 3 5% 6% 54%	2356
	11th to 20th	Night	10% 5% 1 5% 3 3 3 3 5% 6% 57%	2600
	21st to end	Night	15% 4 2 4 4 4 3 3 5% 6% 50%	2600
December	1st to 10th	Night	31% 7% 2 5% 3 2 3 2 3 4 37%	4250
	11th to 20th	Night	19% 6% 2 5% 4 3 3 2 4 5% 47%	4816
	21st to end	Night	13% 5% 1 4 2 2 3 3 4 5% 57%	6490

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	33% 2 3 20% 26% 17%	4078
	11th to 20th	Day	32% 2 4 16% 24% 23%	4310
	21st to end	Day	45% 2 4 13% 23% 13%	4994
February	1st to 10th	Day	41% 3 5% 13% 19% 19%	1950
	11th to 20th	Day	40% 2 5% 16% 21% 15%	1859
	21st to end	Day	34% 3 8% 18% 21% 16%	1570
March	1st to 10th	Day	42% 3 8% 16% 19% 12%	3267
	11th to 20th	Day	51% 3 6% 11% 16% 13%	3480
	21st to end	Day	34% 3 9% 18% 17% 20%	3814
April	1st to 10th	Day	37% 3 8% 18% 18% 15%	2090
	11th to 20th	Day	39% 3 7% 19% 17% 16%	2202
	21st to end	Day	38% 3 7% 20% 19% 14%	2283
May	1st to 10th	Day	45% 4 9% 20% 13% 9%	4120
	11th to 20th	Day	39% 4 8% 24% 17% 9%	4086
	21st to end	Day	34% 5% 9% 34% 16% 2	4489
June	1st to 10th	Day	23% 6% 14% 32% 21% 4	2470
	11th to 20th	Day	27% 4 12% 29% 20% 7%	2470
	21st to end	Day	33% 5% 14% 28% 16% 4	2470
July	1st to 10th	Day	30% 5% 14% 39% 11% 1	4056
	11th to 20th	Day	29% 7% 18% 29% 16% 2	4051
	21st to end	Day	29% 7% 18% 31% 14% 1	4237
August	1st to 10th	Day	11% 4 12% 43% 28% 2	3772
	11th to 20th	Day	17% 5% 20% 43% 13% 2	3762
	21st to end	Day	26% 7% 19% 26% 21% 2	4129
September	1st to 10th	Day	40% 6% 12% 20% 15% 7%	2090
	11th to 20th	Day	38% 6% 10% 23% 18% 5%	2090
	21st to end	Day	32% 4 10% 24% 17% 12%	2090
October	1st to 10th	Day	18% 2 5% 14% 22% 38%	3480
	11th to 20th	Day	31% 4 7% 16% 20% 24%	3437
	21st to end	Day	26% 3 5% 15% 36% 15%	3428
November	1st to 10th	Day	40% 3 7% 20% 18% 12%	1938
	11th to 20th	Day	35% 2 7% 19% 20% 17%	1800
	21st to end	Day	40% 2 5% 20% 19% 15%	1800
December	1st to 10th	Day	57% 2 5% 11% 16% 10%	2940
	11th to 20th	Day	43% 3 7% 15% 17% 15%	3389
	21st to end	Day	31% 3 4 16% 29% 17%	4488
January	1st to 10th	Night	32% 3 5% 18% 24% 19%	5888
	11th to 20th	Night	27% 1 4 18% 24% 25%	5698
	21st to end	Night	46% 2 4 12% 21% 15%	5984
February	1st to 10th	Night	32% 2 7% 16% 19% 23%	2340
	11th to 20th	Night	36% 2 6% 18% 20% 18%	2218
	21st to end	Night	35% 4 6% 16% 21% 18%	1884
March	1st to 10th	Night	40% 3 9% 18% 17% 14%	3589
	11th to 20th	Night	46% 4 8% 15% 13% 14%	3480
	21st to end	Night	31% 4 12% 19% 18% 15%	3817
April	1st to 10th	Night	30% 4 12% 19% 19% 16%	2090
	11th to 20th	Night	36% 4 11% 17% 16% 18%	1923
	21st to end	Night	37% 3 9% 20% 17% 14%	1895
May	1st to 10th	Night	36% 4 11% 21% 16% 11%	2850
	11th to 20th	Night	32% 4 12% 21% 20% 11%	2824
	21st to end	Night	28% 5% 15% 31% 18% 4	3099
June	1st to 10th	Night	18% 4 17% 35% 24% 3	1710
	11th to 20th	Night	20% 4 12% 31% 26% 7%	1710
	21st to end	Night	26% 7% 19% 28% 17% 4	1710
July	1st to 10th	Night	22% 6% 22% 40% 9% 1	2805
	11th to 20th	Night	26% 8% 20% 27% 17% 1	2796
	21st to end	Night	25% 8% 22% 33% 11% 1	3080
August	1st to 10th	Night	10% 4 14% 46% 25% 2	3144
	11th to 20th	Night	16% 5% 28% 40% 9% 2	3143
	21st to end	Night	23% 8% 22% 28% 17% 2	3535
September	1st to 10th	Night	34% 7% 16% 20% 16% 7%	2090
	11th to 20th	Night	34% 6% 16% 21% 19% 4	2090
	21st to end	Night	26% 5% 12% 25% 19% 13%	2090
October	1st to 10th	Night	16% 3 7% 18% 19% 36%	3480
	11th to 20th	Night	23% 3 10% 15% 23% 26%	3460
	21st to end	Night	21% 2 8% 18% 34% 17%	4108
November	1st to 10th	Night	33% 3 6% 20% 24% 15%	2356
	11th to 20th	Night	29% 3 9% 20% 21% 17%	2600
	21st to end	Night	35% 3 8% 19% 18% 16%	2600
December	1st to 10th	Night	52% 3 6% 14% 13% 13%	4250
	11th to 20th	Night	41% 3 6% 15% 19% 17%	4817
	21st to end	Night	30% 3 5% 16% 26% 20%	6490

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	20% 8% 26% 33% 13% 1	300
	11th to 20th	Day	20% 6% 23% 37% 12% 1	300
	21st to end	Day	20% 5% 30% 33% 11%	330
February	1st to 10th	Day	25% 5% 23% 26% 19% 3	285
	11th to 20th	Day	22% 6% 34% 27% 9% 2	270
	21st to end	Day	23% 6% 36% 26% 9%	225
March	1st to 10th	Day	21% 6% 34% 30% 9%	270
	11th to 20th	Day	16% 5% 36% 32% 10%	270
	21st to end	Day	15% 8% 37% 32% 7% 1	297
April	1st to 10th	Day	19% 5% 37% 31% 9%	270
	11th to 20th	Day	13% 8% 38% 32% 9% 1	400
	21st to end	Day	12% 6% 37% 36% 8%	463
May	1st to 10th	Day	18% 6% 30% 36% 9% 1	653
	11th to 20th	Day	16% 4 28% 37% 13% 1	675
	21st to end	Day	12% 4 23% 44% 15% 1	734
June	1st to 10th	Day	5% 1 14% 46% 29% 5%	680
	11th to 20th	Day	6% 1 13% 47% 28% 5%	680
	21st to end	Day	7% 1 8% 36% 38% 9%	680
July	1st to 10th	Day	11% 2 4 31% 41% 12%	671
	11th to 20th	Day	5% 1 3 30% 50% 11%	668
	21st to end	Day	4 1 3 31% 48% 13%	685
August	1st to 10th	Day	2 2 29% 49% 17%	487
	11th to 20th	Day	4 1 2 29% 44% 19%	477
	21st to end	Day	6% 3 2 27% 36% 27%	515
September	1st to 10th	Day	12% 2 1 20% 41% 25%	300
	11th to 20th	Day	6% 2 2 16% 44% 30%	300
	21st to end	Day	8% 1 3 19% 46% 22%	300
October	1st to 10th	Day	8% 1 7% 30% 37% 17%	300
	11th to 20th	Day	14% 1 7% 36% 34% 8%	300
	21st to end	Day	16% 5% 19% 29% 25% 6%	330
November	1st to 10th	Day	20% 2 15% 35% 21% 6%	300
	11th to 20th	Day	20% 5% 17% 28% 24% 6%	300
	21st to end	Day	22% 5% 25% 33% 12% 3	300
December	1st to 10th	Day	24% 2 18% 33% 19% 4	300
	11th to 20th	Day	21% 4 23% 33% 18% 1	300
	21st to end	Day	16% 2 25% 34% 19% 3	330
January	1st to 10th	Night	18% 4 23% 41% 13% 1	1000
	11th to 20th	Night	18% 4 26% 43% 8%	915
	21st to end	Night	19% 6% 25% 42% 8%	880
February	1st to 10th	Night	17% 7% 29% 38% 9% 1	780
	11th to 20th	Night	21% 5% 32% 35% 7%	744
	21st to end	Night	17% 6% 36% 39% 3	628
March	1st to 10th	Night	19% 7% 36% 32% 5%	680
	11th to 20th	Night	14% 6% 39% 38% 4	570
	21st to end	Night	12% 8% 43% 33% 4	627
April	1st to 10th	Night	11% 6% 47% 32% 4	570
	11th to 20th	Night	16% 7% 45% 29% 3	563
	21st to end	Night	15% 7% 42% 30% 4 1	570
May	1st to 10th	Night	11% 6% 45% 35% 2	570
	11th to 20th	Night	13% 4 38% 37% 7%	561
	21st to end	Night	9% 3 37% 44% 7%	617
June	1st to 10th	Night	3 1 26% 53% 16%	570
	11th to 20th	Night	3 1 32% 52% 11%	570
	21st to end	Night	5% 3 16% 55% 20% 1	570
July	1st to 10th	Night	8% 2 8% 56% 24% 2	555
	11th to 20th	Night	3 1 10% 58% 27% 2	552
	21st to end	Night	4 2 8% 59% 26% 1	624
August	1st to 10th	Night	2 1 7% 56% 34% 1	567
	11th to 20th	Night	4 2 6% 58% 27% 3	564
	21st to end	Night	5% 2 7% 46% 37% 3	627
September	1st to 10th	Night	9% 1 5% 47% 34% 4	570
	11th to 20th	Night	11% 1 4 42% 37% 4	570
	21st to end	Night	8% 1 8% 44% 34% 4	570
October	1st to 10th	Night	6% 1 11% 50% 31% 2	570
	11th to 20th	Night	14% 2 15% 48% 20% 1	570
	21st to end	Night	13% 3 20% 40% 23% 2	824
November	1st to 10th	Night	14% 2 17% 41% 24% 2	796
	11th to 20th	Night	13% 3 19% 44% 21% 1	1000
	21st to end	Night	17% 3 21% 42% 15% 1	1000
December	1st to 10th	Night	21% 4 17% 42% 17% 1	1000
	11th to 20th	Night	23% 4 20% 40% 13%	1000
	21st to end	Night	16% 4 22% 46% 11% 1	1100

Page generated at 2025-02-03 02:05:56. Version ac07

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