Red Buttes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red Buttes Observatory clear sky chart from 2005-11-06 to 2025-04-26.

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 6% 3 7% 5% 5% 5% 4 6% 8% 49%	117698
	Night	2 5% 3 7% 4 4 4 4 6% 8% 54%	119807
Transparency	Day	17% 44% 6% 15% 13% 5%	117441
	Night	16% 42% 8% 17% 14% 4	119654
Seeing	Day	12% 25% 32% 20% 9% 2	16250
	Night	8% 27% 32% 24% 8% 1	26426

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	5% 5% 10% 8% 5% 5% 4 5% 6% 48%	3638
	11th to 20th	Day	5% 4 12% 9% 7% 6% 4 5% 6% 42%	3685
	21st to end	Day	3 3 7% 6% 4 4 3 5% 6% 58%	4510
February	1st to 10th	Day	1 6% 3 10% 7% 5% 5% 4 6% 8% 46%	1800
	11th to 20th	Day	1 6% 3 8% 6% 5% 7% 4 7% 8% 46%	1861
	21st to end	Day	6% 3 7% 5% 4 4 4 6% 8% 52%	1650
March	1st to 10th	Day	1 8% 4 8% 4 4 4 4 5% 7% 51%	4500
	11th to 20th	Day	2 9% 3 8% 5% 5% 5% 4 6% 8% 45%	4996
	21st to end	Day	2 8% 3 8% 6% 5% 5% 5% 6% 9% 41%	5783
April	1st to 10th	Day	3 9% 2 6% 5% 5% 5% 4 7% 8% 45%	2400
	11th to 20th	Day	5% 12% 4 9% 6% 5% 5% 3 6% 8% 37%	2371
	21st to end	Day	6% 11% 4 8% 6% 4 5% 5% 5% 8% 38%	2341
May	1st to 10th	Day	7% 14% 4 10% 6% 5% 5% 4 6% 7% 33%	4174
	11th to 20th	Day	7% 6% 2 6% 6% 6% 7% 6% 7% 7% 39%	4388
	21st to end	Day	5% 6% 2 6% 5% 5% 6% 5% 7% 8% 44%	4825
June	1st to 10th	Day	4 4 2 5% 4 5% 6% 5% 9% 10% 45%	2660
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 7% 8% 50%	2660
	21st to end	Day	3 3 1 5% 5% 4 5% 6% 8% 8% 52%	2660
July	1st to 10th	Day	4 4 2 5% 4 5% 5% 5% 7% 8% 52%	4430
	11th to 20th	Day	2 3 1 5% 5% 5% 7% 5% 7% 9% 49%	4430
	21st to end	Day	4 4 2 6% 5% 5% 6% 5% 7% 9% 49%	4772
August	1st to 10th	Day	4 4 2 6% 5% 6% 6% 5% 9% 10% 43%	4092
	11th to 20th	Day	4 4 2 6% 5% 5% 6% 5% 6% 8% 49%	3827
	21st to end	Day	4 4 2 5% 4 5% 5% 4 6% 8% 54%	4180
September	1st to 10th	Day	4 5% 2 4 4 3 5% 4 4 8% 58%	2280
	11th to 20th	Day	4 4 2 4 3 3 5% 4 5% 7% 59%	2280
	21st to end	Day	5% 5% 2 5% 3 3 4 2 4 6% 62%	2063
October	1st to 10th	Day	4 3 1 4 3 2 2 2 3 4 71%	3170
	11th to 20th	Day	3 5% 2 6% 5% 4 4 4 5% 7% 56%	3150
	21st to end	Day	3 7% 3 5% 3 3 3 3 4 6% 58%	3314
November	1st to 10th	Day	3 4 2 5% 4 4 3 3 5% 8% 58%	1763
	11th to 20th	Day	2 7% 2 5% 3 3 3 3 6% 8% 58%	1795
	21st to end	Day	1 6% 3 7% 5% 4 5% 3 5% 7% 54%	1600
December	1st to 10th	Day	3 2 8% 4 3 4 3 5% 5% 64%	2620
	11th to 20th	Day	1 6% 2 6% 4 3 3 3 5% 9% 59%	3026
	21st to end	Day	1 5% 3 10% 6% 5% 5% 4 6% 7% 47%	4004
January	1st to 10th	Night	6% 4 13% 6% 4 4 3 5% 7% 47%	6327
	11th to 20th	Night	4 4 11% 6% 5% 5% 4 5% 8% 49%	6326
	21st to end	Night	5% 3 9% 5% 4 4 3 4 6% 57%	6468
February	1st to 10th	Night	1 6% 3 9% 5% 4 4 3 6% 8% 52%	2600
	11th to 20th	Night	1 6% 3 8% 6% 5% 5% 4 6% 7% 49%	2425
	21st to end	Night	1 7% 3 7% 4 4 4 3 4 6% 57%	1980
March	1st to 10th	Night	1 10% 4 7% 4 4 4 3 5% 6% 51%	5374
	11th to 20th	Night	1 7% 4 7% 4 4 4 3 5% 7% 54%	5000
	21st to end	Night	4 10% 3 8% 5% 4 4 4 5% 8% 45%	5178
April	1st to 10th	Night	3 7% 2 6% 5% 4 4 3 7% 7% 51%	2000
	11th to 20th	Night	5% 10% 3 7% 5% 4 4 3 6% 7% 47%	1977
	21st to end	Night	7% 10% 3 7% 4 3 3 3 6% 6% 48%	1955
May	1st to 10th	Night	5% 9% 3 7% 5% 4 5% 4 5% 7% 46%	2777
	11th to 20th	Night	7% 5% 2 7% 4 5% 6% 4 7% 9% 45%	2517
	21st to end	Night	5% 5% 2 4 4 4 5% 4 7% 7% 53%	2762
June	1st to 10th	Night	3 2 1 3 3 4 4 5% 7% 11% 54%	1520
	11th to 20th	Night	4 3 1 4 3 3 5% 4 6% 8% 60%	1520
	21st to end	Night	3 3 2 4 3 4 3 3 5% 9% 60%	1520
July	1st to 10th	Night	3 3 2 4 4 4 4 4 6% 8% 58%	2540
	11th to 20th	Night	2 2 1 3 3 5% 5% 6% 8% 10% 55%	2540
	21st to end	Night	2 2 1 5% 4 4 5% 5% 7% 9% 58%	2787
August	1st to 10th	Night	3 3 1 5% 4 5% 5% 5% 8% 11% 50%	2847
	11th to 20th	Night	2 4 2 6% 4 4 5% 5% 8% 10% 50%	3012
	21st to end	Night	3 3 2 4 3 3 4 4 7% 9% 58%	3487
September	1st to 10th	Night	5% 4 2 4 3 3 4 3 5% 8% 59%	1900
	11th to 20th	Night	3 4 1 4 3 3 5% 3 4 6% 64%	1900
	21st to end	Night	5% 3 1 4 3 3 4 3 5% 6% 63%	2113
October	1st to 10th	Night	3 3 1 3 2 2 2 3 4 5% 73%	3800
	11th to 20th	Night	4 3 2 5% 3 4 4 3 6% 8% 57%	3778
	21st to end	Night	3 6% 2 4 2 3 3 3 4 7% 63%	4213
November	1st to 10th	Night	3 5% 2 4 3 3 4 3 5% 8% 60%	2535
	11th to 20th	Night	2 6% 2 5% 4 3 4 3 4 7% 60%	2604
	21st to end	Night	1 6% 3 6% 4 3 4 3 7% 8% 56%	2800
December	1st to 10th	Night	3 2 5% 4 4 4 3 4 5% 67%	4570
	11th to 20th	Night	1 4 3 5% 4 4 4 3 5% 9% 58%	5181
	21st to end	Night	1 8% 4 9% 5% 5% 5% 4 6% 8% 46%	6974

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	26% 34% 9% 13% 16% 2	3639
	11th to 20th	Day	29% 35% 10% 11% 12% 4	3685
	21st to end	Day	17% 30% 11% 18% 19% 5%	4510
February	1st to 10th	Day	12% 62% 8% 8% 7% 3	1800
	11th to 20th	Day	9% 63% 5% 14% 7% 2	1870
	21st to end	Day	10% 63% 3 12% 11% 2	1650
March	1st to 10th	Day	22% 31% 4 21% 17% 5%	4500
	11th to 20th	Day	25% 31% 9% 19% 14% 1	4996
	21st to end	Day	24% 33% 12% 24% 5% 1	5783
April	1st to 10th	Day	12% 64% 5% 13% 6% 1	2400
	11th to 20th	Day	17% 65% 3 8% 7% 2	2374
	21st to end	Day	18% 65% 3 10% 4	2341
May	1st to 10th	Day	29% 45% 4 9% 10% 4	4174
	11th to 20th	Day	20% 45% 7% 17% 10% 1	4392
	21st to end	Day	18% 43% 5% 16% 14% 3	4825
June	1st to 10th	Day	9% 67% 6% 9% 7% 2	2660
	11th to 20th	Day	11% 66% 4 9% 7% 2	2660
	21st to end	Day	11% 65% 4 10% 8% 2	2660
July	1st to 10th	Day	13% 37% 6% 9% 20% 14%	4361
	11th to 20th	Day	18% 39% 6% 13% 13% 11%	4355
	21st to end	Day	16% 37% 6% 10% 16% 15%	4621
August	1st to 10th	Day	19% 42% 8% 16% 9% 6%	4078
	11th to 20th	Day	18% 41% 8% 10% 18% 6%	3865
	21st to end	Day	15% 39% 7% 11% 17% 11%	4179
September	1st to 10th	Day	11% 60% 3 9% 12% 4	2280
	11th to 20th	Day	8% 60% 3 10% 14% 4	2280
	21st to end	Day	10% 60% 3 7% 15% 5%	2063
October	1st to 10th	Day	8% 36% 2 9% 24% 20%	3170
	11th to 20th	Day	17% 38% 4 22% 15% 4	3150
	21st to end	Day	18% 37% 4 24% 16% 2	3314
November	1st to 10th	Day	10% 57% 5% 15% 11% 2	1763
	11th to 20th	Day	9% 57% 3 16% 13% 3	1795
	21st to end	Day	15% 58% 4 12% 9% 2	1600
December	1st to 10th	Day	11% 37% 6% 28% 16% 2	2620
	11th to 20th	Day	15% 32% 13% 28% 12% 1	3024
	21st to end	Day	23% 31% 9% 19% 14% 4	4004
January	1st to 10th	Night	28% 30% 9% 17% 12% 4	6327
	11th to 20th	Night	23% 31% 14% 11% 17% 4	6326
	21st to end	Night	20% 29% 12% 18% 17% 4	6468
February	1st to 10th	Night	11% 63% 9% 9% 6% 2	2600
	11th to 20th	Night	10% 62% 5% 13% 7% 2	2426
	21st to end	Night	9% 62% 4 10% 12% 3	1980
March	1st to 10th	Night	22% 31% 5% 19% 16% 7%	5374
	11th to 20th	Night	21% 29% 8% 19% 22% 2	5000
	21st to end	Night	26% 32% 12% 24% 5%	5178
April	1st to 10th	Night	11% 64% 6% 12% 7% 1	2000
	11th to 20th	Night	14% 63% 4 11% 7% 1	1977
	21st to end	Night	15% 65% 4 11% 5%	1955
May	1st to 10th	Night	21% 44% 3 14% 15% 3	2777
	11th to 20th	Night	19% 44% 9% 20% 6% 3	2518
	21st to end	Night	15% 42% 8% 18% 16%	2762
June	1st to 10th	Night	5% 66% 9% 10% 8% 2	1520
	11th to 20th	Night	8% 66% 5% 11% 7% 3	1520
	21st to end	Night	9% 63% 3 12% 9% 3	1520
July	1st to 10th	Night	15% 37% 5% 14% 18% 11%	2500
	11th to 20th	Night	13% 38% 8% 19% 15% 7%	2492
	21st to end	Night	13% 36% 6% 17% 16% 12%	2700
August	1st to 10th	Night	16% 40% 13% 15% 13% 3	2838
	11th to 20th	Night	19% 41% 12% 13% 10% 6%	3040
	21st to end	Night	14% 38% 10% 12% 21% 6%	3487
September	1st to 10th	Night	8% 60% 4 12% 11% 5%	1900
	11th to 20th	Night	7% 60% 4 12% 13% 5%	1900
	21st to end	Night	10% 60% 3 9% 13% 5%	2113
October	1st to 10th	Night	7% 36% 2 12% 27% 15%	3800
	11th to 20th	Night	14% 39% 6% 19% 19% 3	3778
	21st to end	Night	14% 37% 6% 25% 16% 3	4213
November	1st to 10th	Night	11% 56% 5% 14% 11% 2	2535
	11th to 20th	Night	9% 58% 4 14% 12% 3	2604
	21st to end	Night	13% 59% 5% 14% 8% 2	2800
December	1st to 10th	Night	10% 37% 8% 30% 14% 2	4570
	11th to 20th	Night	15% 33% 9% 31% 11% 1	5182
	21st to end	Night	24% 31% 7% 21% 13% 3	6974

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	17% 32% 29% 15% 6% 2	300
	11th to 20th	Day	15% 43% 29% 12% 1	300
	21st to end	Day	10% 42% 34% 11% 3	330
February	1st to 10th	Day	21% 50% 23% 5% 1	300
	11th to 20th	Day	18% 41% 32% 9% 1	300
	21st to end	Day	23% 39% 29% 8% 1	249
March	1st to 10th	Day	13% 41% 32% 12% 3	300
	11th to 20th	Day	16% 30% 37% 14% 2	496
	21st to end	Day	18% 34% 33% 13% 2	550
April	1st to 10th	Day	19% 35% 35% 10% 2	500
	11th to 20th	Day	22% 38% 27% 9% 3	492
	21st to end	Day	17% 32% 32% 14% 4 1	481
May	1st to 10th	Day	21% 25% 31% 15% 7% 1	596
	11th to 20th	Day	16% 19% 33% 21% 9% 2	675
	21st to end	Day	12% 20% 29% 25% 11% 2	734
June	1st to 10th	Day	6% 16% 30% 29% 16% 3	680
	11th to 20th	Day	9% 18% 40% 24% 8% 2	680
	21st to end	Day	4 16% 36% 26% 16% 2	680
July	1st to 10th	Day	6% 6% 28% 34% 23% 4	671
	11th to 20th	Day	4 7% 31% 34% 21% 3	668
	21st to end	Day	6% 6% 27% 34% 24% 4	721
August	1st to 10th	Day	9% 7% 41% 31% 9% 2	487
	11th to 20th	Day	7% 8% 35% 35% 12% 4	477
	21st to end	Day	7% 10% 37% 29% 13% 3	539
September	1st to 10th	Day	9% 14% 31% 30% 13% 3	490
	11th to 20th	Day	4 18% 41% 22% 12% 2	490
	21st to end	Day	7% 20% 33% 20% 15% 5%	304
October	1st to 10th	Day	9% 21% 30% 23% 12% 5%	300
	11th to 20th	Day	16% 28% 30% 17% 6% 3	300
	21st to end	Day	12% 37% 35% 12% 3 1	330
November	1st to 10th	Day	14% 34% 32% 13% 6% 1	300
	11th to 20th	Day	16% 41% 34% 8% 2	300
	21st to end	Day	12% 42% 32% 11% 2	300
December	1st to 10th	Day	18% 42% 30% 6% 4	300
	11th to 20th	Day	17% 51% 24% 8%	300
	21st to end	Day	20% 44% 25% 8% 2 1	330
January	1st to 10th	Night	10% 41% 31% 13% 5% 1	1000
	11th to 20th	Night	8% 52% 26% 11% 4	999
	21st to end	Night	5% 46% 32% 13% 4	880
February	1st to 10th	Night	10% 47% 32% 8% 4	800
	11th to 20th	Night	7% 42% 34% 16% 1	784
	21st to end	Night	10% 45% 34% 10% 1	660
March	1st to 10th	Night	7% 35% 39% 16% 3	800
	11th to 20th	Night	8% 27% 38% 22% 5%	800
	21st to end	Night	10% 28% 39% 17% 4 1	750
April	1st to 10th	Night	10% 27% 40% 21% 3	600
	11th to 20th	Night	12% 25% 40% 19% 4	593
	21st to end	Night	13% 20% 34% 25% 7% 1	587
May	1st to 10th	Night	12% 19% 35% 25% 9% 1	570
	11th to 20th	Night	12% 12% 32% 31% 12% 1	561
	21st to end	Night	7% 14% 33% 29% 16% 1	617
June	1st to 10th	Night	4 11% 31% 37% 16% 2	570
	11th to 20th	Night	6% 12% 39% 35% 9%	570
	21st to end	Night	5% 7% 30% 42% 16% 1	570
July	1st to 10th	Night	4 3 24% 47% 22% 1	555
	11th to 20th	Night	3 1 22% 49% 22% 2	552
	21st to end	Night	4 2 20% 47% 26% 2	624
August	1st to 10th	Night	4 3 22% 50% 20% 1	567
	11th to 20th	Night	4 3 22% 50% 19% 2	564
	21st to end	Night	4 3 24% 42% 25% 2	627
September	1st to 10th	Night	8% 5% 24% 43% 17% 3	570
	11th to 20th	Night	4 7% 28% 42% 16% 2	570
	21st to end	Night	6% 11% 31% 36% 15% 1	598
October	1st to 10th	Night	7% 19% 33% 28% 12% 1	760
	11th to 20th	Night	9% 25% 33% 23% 9% 1	760
	21st to end	Night	10% 25% 42% 16% 5% 1	893
November	1st to 10th	Night	8% 31% 39% 16% 5% 1	975
	11th to 20th	Night	11% 40% 35% 12% 1	1000
	21st to end	Night	6% 38% 40% 14% 2	1000
December	1st to 10th	Night	11% 43% 31% 12% 3	1000
	11th to 20th	Night	8% 48% 31% 11% 2	1000
	21st to end	Night	12% 47% 28% 10% 4	1100

Page generated at 2025-04-23 07:25:04. Version ac07

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