Rainbow Springs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rainbow Springs Observatory clear sky chart from 2005-11-06 to 2025-05-26.

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	8% 5% 2 6% 5% 5% 5% 5% 7% 10% 42%	114445
	Night	9% 6% 2 6% 4 4 5% 4 6% 9% 44%	114830
Transparency	Day	35% 9% 16% 19% 15% 6%	118238
	Night	35% 8% 15% 19% 16% 7%	119176
Seeing	Day	9% 5% 17% 25% 24% 19%	16108
	Night	10% 4 19% 33% 26% 7%	26210

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	10% 5% 2 5% 4 3 4 3 4 7% 53%	4056
	11th to 20th	Day	20% 10% 3 8% 4 3 4 3 3 5% 35%	4060
	21st to end	Day	11% 5% 2 4 3 3 3 3 6% 10% 49%	4741
February	1st to 10th	Day	13% 7% 2 6% 4 5% 4 4 6% 7% 43%	2000
	11th to 20th	Day	10% 5% 2 5% 3 4 4 3 4 6% 53%	1948
	21st to end	Day	10% 6% 1 6% 4 4 4 4 5% 8% 47%	1685
March	1st to 10th	Day	10% 7% 3 6% 5% 4 4 4 6% 9% 43%	4935
	11th to 20th	Day	7% 3 1 4 3 3 3 3 5% 8% 59%	4980
	21st to end	Day	10% 4 2 5% 3 3 3 4 6% 9% 51%	5465
April	1st to 10th	Day	7% 3 2 4 4 3 5% 4 7% 9% 52%	2200
	11th to 20th	Day	8% 5% 3 6% 5% 4 4 4 6% 8% 49%	2176
	21st to end	Day	4 3 1 4 3 4 5% 5% 7% 9% 55%	2470
May	1st to 10th	Day	4 2 1 3 3 4 5% 4 6% 9% 59%	4212
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 8% 10% 39%	4211
	21st to end	Day	5% 3 1 4 4 4 4 4 6% 9% 55%	4541
June	1st to 10th	Day	10% 7% 4 7% 6% 6% 7% 6% 8% 10% 29%	2470
	11th to 20th	Day	6% 5% 2 7% 7% 6% 8% 8% 10% 12% 31%	2470
	21st to end	Day	8% 6% 3 7% 6% 7% 8% 7% 8% 12% 29%	2470
July	1st to 10th	Day	6% 5% 3 8% 7% 6% 8% 7% 11% 15% 22%	4120
	11th to 20th	Day	5% 5% 2 7% 7% 7% 8% 7% 10% 14% 27%	4120
	21st to end	Day	4 5% 2 8% 7% 8% 8% 8% 10% 15% 25%	4466
August	1st to 10th	Day	9% 5% 2 6% 6% 6% 7% 6% 9% 14% 31%	4104
	11th to 20th	Day	6% 5% 2 6% 5% 6% 7% 5% 9% 15% 35%	3793
	21st to end	Day	8% 5% 3 9% 6% 6% 7% 6% 9% 12% 28%	3863
September	1st to 10th	Day	9% 6% 3 9% 8% 7% 8% 7% 8% 11% 23%	2090
	11th to 20th	Day	11% 8% 3 9% 7% 6% 8% 6% 9% 9% 26%	2090
	21st to end	Day	10% 7% 3 8% 6% 5% 7% 4 6% 9% 35%	2090
October	1st to 10th	Day	12% 6% 2 7% 6% 6% 4 4 5% 8% 38%	2090
	11th to 20th	Day	6% 4 2 5% 5% 4 4 3 5% 7% 56%	1929
	21st to end	Day	6% 4 2 6% 4 4 5% 4 5% 10% 50%	2090
November	1st to 10th	Day	7% 6% 2 4 4 4 4 4 6% 7% 51%	1957
	11th to 20th	Day	8% 6% 2 7% 4 5% 5% 4 6% 6% 48%	1984
	21st to end	Day	10% 5% 2 6% 4 4 4 4 5% 9% 47%	1800
December	1st to 10th	Day	5% 4 2 4 4 3 4 3 6% 7% 58%	2930
	11th to 20th	Day	10% 6% 3 6% 4 4 4 3 7% 8% 46%	3373
	21st to end	Day	13% 7% 3 7% 4 3 4 3 5% 7% 44%	4466
January	1st to 10th	Night	9% 5% 2 4 3 3 3 3 5% 8% 56%	5889
	11th to 20th	Night	20% 8% 3 7% 4 5% 4 3 7% 7% 32%	5900
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 8% 41%	6199
February	1st to 10th	Night	12% 6% 2 6% 4 4 3 3 5% 8% 46%	2400
	11th to 20th	Night	11% 7% 2 5% 4 4 4 4 6% 6% 48%	2338
	21st to end	Night	9% 7% 2 6% 5% 3 4 4 6% 8% 47%	1943
March	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 4 7% 44%	4918
	11th to 20th	Night	5% 5% 2 5% 3 3 4 3 6% 9% 56%	4980
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 7% 50%	5467
April	1st to 10th	Night	8% 5% 2 4 4 4 4 4 6% 8% 52%	2200
	11th to 20th	Night	6% 5% 2 5% 4 3 4 4 6% 8% 52%	2173
	21st to end	Night	6% 3 1 4 3 4 4 3 5% 8% 58%	1944
May	1st to 10th	Night	5% 2 1 4 3 4 3 4 6% 9% 59%	2903
	11th to 20th	Night	7% 5% 2 6% 5% 4 4 4 6% 10% 47%	2902
	21st to end	Night	3 3 1 3 3 3 3 3 5% 9% 64%	3130
June	1st to 10th	Night	10% 5% 2 7% 5% 6% 5% 5% 7% 9% 38%	1710
	11th to 20th	Night	6% 6% 2 6% 5% 5% 6% 5% 9% 16% 34%	1710
	21st to end	Night	6% 5% 2 6% 5% 6% 6% 5% 9% 13% 36%	1710
July	1st to 10th	Night	6% 7% 3 9% 8% 7% 8% 7% 9% 13% 23%	2840
	11th to 20th	Night	3 4 2 7% 6% 7% 9% 6% 12% 14% 28%	2840
	21st to end	Night	6% 7% 4 10% 8% 8% 8% 6% 10% 13% 22%	3087
August	1st to 10th	Night	7% 4 3 8% 5% 6% 7% 5% 9% 11% 35%	2825
	11th to 20th	Night	4 4 2 6% 5% 5% 6% 5% 8% 15% 42%	3030
	21st to end	Night	8% 6% 3 8% 6% 6% 7% 6% 9% 11% 29%	3759
September	1st to 10th	Night	7% 8% 3 8% 6% 6% 7% 7% 8% 11% 28%	2090
	11th to 20th	Night	10% 9% 3 9% 6% 6% 6% 5% 7% 10% 30%	2090
	21st to end	Night	10% 5% 2 8% 6% 5% 5% 4 7% 9% 39%	2090
October	1st to 10th	Night	10% 7% 2 7% 5% 4 4 5% 6% 8% 42%	2090
	11th to 20th	Night	5% 5% 2 4 4 4 4 4 6% 7% 57%	2250
	21st to end	Night	8% 6% 2 6% 3 3 4 3 6% 8% 51%	2508
November	1st to 10th	Night	8% 5% 1 5% 3 5% 4 3 5% 8% 52%	2341
	11th to 20th	Night	9% 7% 2 6% 4 5% 4 3 5% 6% 49%	2412
	21st to end	Night	9% 6% 2 6% 4 3 4 3 6% 7% 49%	2600
December	1st to 10th	Night	7% 5% 2 5% 3 3 4 3 4 7% 58%	4250
	11th to 20th	Night	9% 7% 2 6% 4 3 4 3 5% 6% 50%	4822
	21st to end	Night	13% 8% 3 7% 4 5% 4 4 5% 7% 40%	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	30% 5% 9% 14% 27% 15%	4057
	11th to 20th	Day	52% 3 4 14% 16% 10%	4060
	21st to end	Day	31% 5% 12% 25% 18% 10%	4741
February	1st to 10th	Day	39% 6% 10% 14% 20% 11%	2000
	11th to 20th	Day	31% 5% 9% 19% 24% 11%	1958
	21st to end	Day	34% 7% 9% 18% 21% 11%	1685
March	1st to 10th	Day	36% 6% 12% 17% 21% 8%	4935
	11th to 20th	Day	24% 5% 11% 21% 23% 17%	4980
	21st to end	Day	30% 5% 10% 28% 18% 9%	5465
April	1st to 10th	Day	28% 7% 14% 21% 20% 10%	2200
	11th to 20th	Day	34% 6% 10% 18% 23% 9%	2176
	21st to end	Day	22% 8% 14% 25% 23% 9%	2470
May	1st to 10th	Day	18% 9% 19% 31% 18% 5%	4250
	11th to 20th	Day	36% 11% 16% 25% 11% 2	4215
	21st to end	Day	23% 8% 16% 33% 19% 2	4554
June	1st to 10th	Day	44% 13% 19% 18% 6%	2470
	11th to 20th	Day	39% 14% 22% 21% 4	2470
	21st to end	Day	43% 15% 22% 15% 4 1	2470
July	1st to 10th	Day	43% 16% 33% 8% 1	4055
	11th to 20th	Day	40% 18% 35% 6% 1	4051
	21st to end	Day	41% 18% 32% 9% 1	4324
August	1st to 10th	Day	38% 14% 31% 14% 3	4091
	11th to 20th	Day	34% 14% 26% 20% 5%	3831
	21st to end	Day	43% 13% 23% 19% 2	3863
September	1st to 10th	Day	48% 18% 18% 11% 5%	2090
	11th to 20th	Day	48% 13% 20% 13% 5%	2090
	21st to end	Day	43% 10% 14% 19% 11% 4	2090
October	1st to 10th	Day	54% 8% 12% 12% 8% 6%	3480
	11th to 20th	Day	22% 5% 7% 21% 34% 11%	3182
	21st to end	Day	23% 6% 8% 24% 31% 8%	3428
November	1st to 10th	Day	30% 7% 13% 21% 17% 13%	1957
	11th to 20th	Day	35% 5% 9% 18% 21% 11%	1984
	21st to end	Day	34% 5% 10% 21% 23% 8%	1800
December	1st to 10th	Day	26% 5% 15% 22% 22% 10%	2930
	11th to 20th	Day	35% 5% 11% 22% 18% 10%	3370
	21st to end	Day	39% 5% 10% 21% 20% 5%	4466
January	1st to 10th	Night	27% 4 8% 16% 31% 15%	5889
	11th to 20th	Night	50% 5% 7% 16% 17% 5%	5900
	21st to end	Night	39% 6% 10% 19% 17% 9%	6199
February	1st to 10th	Night	37% 6% 10% 17% 18% 13%	2400
	11th to 20th	Night	34% 6% 11% 18% 20% 11%	2339
	21st to end	Night	34% 7% 11% 18% 21% 10%	1943
March	1st to 10th	Night	41% 6% 9% 16% 18% 10%	4918
	11th to 20th	Night	24% 6% 14% 19% 20% 17%	4980
	21st to end	Night	32% 5% 10% 25% 19% 9%	5467
April	1st to 10th	Night	29% 8% 14% 22% 18% 8%	2200
	11th to 20th	Night	28% 6% 11% 26% 20% 9%	2173
	21st to end	Night	23% 7% 15% 28% 20% 8%	1944
May	1st to 10th	Night	18% 11% 22% 29% 15% 4	2930
	11th to 20th	Night	30% 10% 21% 26% 12% 2	2903
	21st to end	Night	17% 6% 15% 39% 21% 1	3138
June	1st to 10th	Night	39% 10% 22% 23% 5%	1710
	11th to 20th	Night	35% 13% 29% 20% 3	1710
	21st to end	Night	36% 14% 26% 19% 5% 1	1710
July	1st to 10th	Night	47% 17% 27% 8% 1	2795
	11th to 20th	Night	39% 19% 35% 6% 1	2786
	21st to end	Night	49% 15% 26% 8% 1	2988
August	1st to 10th	Night	38% 13% 33% 12% 3	2814
	11th to 20th	Night	28% 13% 32% 22% 5%	3058
	21st to end	Night	44% 14% 24% 15% 2	3759
September	1st to 10th	Night	44% 15% 23% 12% 5%	2090
	11th to 20th	Night	46% 14% 20% 15% 4 1	2090
	21st to end	Night	38% 11% 18% 18% 13% 3	2090
October	1st to 10th	Night	52% 10% 12% 13% 8% 5%	3480
	11th to 20th	Night	22% 4 8% 20% 37% 8%	3736
	21st to end	Night	25% 5% 8% 21% 34% 7%	4120
November	1st to 10th	Night	29% 5% 13% 22% 18% 12%	2341
	11th to 20th	Night	35% 5% 9% 19% 19% 12%	2412
	21st to end	Night	34% 5% 9% 21% 21% 10%	2600
December	1st to 10th	Night	27% 4 13% 23% 18% 14%	4250
	11th to 20th	Night	34% 6% 11% 21% 17% 10%	4824
	21st to end	Night	43% 6% 11% 19% 16% 5%	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	10% 7% 42% 28% 10% 3	300
	11th to 20th	Day	9% 12% 35% 28% 13% 4	300
	21st to end	Day	14% 14% 39% 25% 7%	330
February	1st to 10th	Day	10% 11% 28% 32% 18% 1	300
	11th to 20th	Day	12% 9% 31% 33% 12% 4	300
	21st to end	Day	9% 8% 32% 30% 19% 3	284
March	1st to 10th	Day	8% 8% 33% 35% 14% 1	500
	11th to 20th	Day	11% 8% 30% 31% 18% 3	500
	21st to end	Day	9% 8% 26% 33% 22% 3	550
April	1st to 10th	Day	9% 10% 25% 30% 24% 2	500
	11th to 20th	Day	8% 9% 25% 29% 26% 3	492
	21st to end	Day	4 4 18% 32% 30% 12%	500
May	1st to 10th	Day	4 4 19% 30% 28% 15%	503
	11th to 20th	Day	8% 3 13% 27% 29% 19%	527
	21st to end	Day	8% 3 8% 20% 33% 29%	549
June	1st to 10th	Day	12% 3 7% 23% 26% 29%	490
	11th to 20th	Day	8% 3 7% 20% 30% 33%	490
	21st to end	Day	5% 1 4 17% 28% 45%	490
July	1st to 10th	Day	5% 2 3 11% 25% 53%	485
	11th to 20th	Day	6% 1 2 7% 29% 55%	484
	21st to end	Day	7% 2 6% 12% 26% 48%	532
August	1st to 10th	Day	9% 2 4 16% 24% 45%	486
	11th to 20th	Day	8% 1 4 9% 27% 51%	479
	21st to end	Day	10% 2 4 15% 30% 38%	539
September	1st to 10th	Day	12% 2 5% 15% 29% 37%	490
	11th to 20th	Day	10% 3 6% 20% 36% 25%	490
	21st to end	Day	10% 2 7% 20% 35% 26%	490
October	1st to 10th	Day	13% 4 14% 36% 22% 11%	490
	11th to 20th	Day	4 4 17% 33% 32% 10%	490
	21st to end	Day	6% 4 16% 38% 29% 6%	539
November	1st to 10th	Day	10% 4 21% 33% 26% 6%	495
	11th to 20th	Day	13% 6% 22% 35% 21% 5%	484
	21st to end	Day	9% 6% 31% 34% 15% 4	300
December	1st to 10th	Day	7% 6% 34% 27% 19% 6%	300
	11th to 20th	Day	13% 10% 30% 29% 15% 2	300
	21st to end	Day	11% 5% 30% 37% 14% 3	330
January	1st to 10th	Night	14% 8% 32% 34% 12% 1	800
	11th to 20th	Night	12% 7% 26% 40% 13% 1	800
	21st to end	Night	18% 9% 33% 33% 8%	880
February	1st to 10th	Night	15% 6% 29% 36% 14% 1	800
	11th to 20th	Night	12% 7% 31% 37% 11% 1	783
	21st to end	Night	12% 6% 31% 43% 8%	660
March	1st to 10th	Night	9% 8% 31% 39% 13%	800
	11th to 20th	Night	9% 8% 28% 40% 15% 1	800
	21st to end	Night	9% 6% 31% 39% 15%	880
April	1st to 10th	Night	10% 4 30% 41% 15% 1	800
	11th to 20th	Night	7% 5% 30% 43% 14% 1	791
	21st to end	Night	7% 3 24% 43% 22% 1	730
May	1st to 10th	Night	5% 4 13% 49% 27% 2	600
	11th to 20th	Night	6% 3 14% 41% 32% 4	591
	21st to end	Night	7% 1 8% 35% 41% 8%	634
June	1st to 10th	Night	11% 2 7% 31% 41% 8%	570
	11th to 20th	Night	6% 2 6% 23% 41% 21%	570
	21st to end	Night	7% 2 5% 16% 45% 25%	570
July	1st to 10th	Night	6% 1 3 14% 43% 33%	555
	11th to 20th	Night	4 1 1 10% 48% 35%	552
	21st to end	Night	6% 1 3 11% 55% 24%	624
August	1st to 10th	Night	7% 1 4 11% 51% 26%	567
	11th to 20th	Night	8% 1 2 8% 48% 33%	564
	21st to end	Night	13% 2 5% 18% 44% 18%	793
September	1st to 10th	Night	10% 2 6% 21% 43% 18%	760
	11th to 20th	Night	12% 3 7% 29% 38% 11%	760
	21st to end	Night	11% 2 9% 30% 40% 8%	760
October	1st to 10th	Night	13% 2 14% 39% 28% 3	760
	11th to 20th	Night	7% 3 16% 41% 31% 3	760
	21st to end	Night	10% 4 17% 42% 26% 2	836
November	1st to 10th	Night	10% 3 23% 38% 24% 2	780
	11th to 20th	Night	11% 5% 24% 40% 19% 2	800
	21st to end	Night	11% 5% 29% 39% 16% 1	800
December	1st to 10th	Night	11% 5% 24% 37% 21% 2	800
	11th to 20th	Night	12% 6% 25% 42% 16% 1	800
	21st to end	Night	13% 6% 26% 37% 16% 1	880

Page generated at 2025-05-23 09:21:00. Version ac07

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