Rainbow Park Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rainbow Park Observatory clear sky chart from 2005-11-06 to 2026-10-14.

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	2 3 1 3 3 3 4 4 6% 8% 63%	156846
	Night	4 4 2 5% 4 4 4 4 6% 7% 58%	152506
Transparency	Day	17% 5% 9% 22% 27% 19%	151842
	Night	22% 6% 9% 20% 26% 17%	148517
Seeing	Day	5% 7% 20% 30% 26% 10%	17600
	Night	6% 5% 25% 42% 20% 2	27717

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	2 6% 3 5% 3 2 4 4 6% 7% 60%	5318
	11th to 20th	Day	1 2 1 3 2 2 2 2 4 5% 77%	5340
	21st to end	Day	4 4 2 4 3 4 4 3 4 5% 62%	5844
February	1st to 10th	Day	3 6% 2 4 3 2 2 3 6% 6% 64%	1890
	11th to 20th	Day	4 5% 2 5% 4 4 3 3 5% 7% 59%	2032
	21st to end	Day	3 5% 1 3 4 2 3 2 4 7% 66%	1730
March	1st to 10th	Day	2 3 1 3 3 3 3 3 4 6% 68%	4974
	11th to 20th	Day	6% 4 1 4 4 4 5% 4 4 7% 58%	5110
	21st to end	Day	2 4 1 4 3 3 3 4 5% 8% 62%	5711
April	1st to 10th	Day	3 3 1 4 3 3 3 3 5% 7% 67%	2520
	11th to 20th	Day	2 4 1 5% 3 3 4 3 4 5% 66%	2491
	21st to end	Day	2 3 1 3 2 3 3 4 5% 6% 70%	2520
May	1st to 10th	Day	3 3 1 4 3 3 5% 4 5% 8% 61%	7057
	11th to 20th	Day	2 2 1 3 3 3 3 3 6% 7% 68%	7365
	21st to end	Day	1 2 1 2 2 2 3 3 5% 6% 73%	8823
June	1st to 10th	Day	2 2 1 2 3 3 4 4 6% 9% 63%	2940
	11th to 20th	Day	2 1 2 2 3 3 3 5% 6% 73%	2940
	21st to end	Day	4 3 1 4 3 4 4 4 6% 8% 60%	2940
July	1st to 10th	Day	2 2 1 3 3 3 4 4 6% 8% 65%	7770
	11th to 20th	Day	1 2 1 3 3 4 6% 6% 10% 13% 51%	7650
	21st to end	Day	2 3 1 5% 4 5% 6% 6% 10% 12% 47%	8304
August	1st to 10th	Day	1 1 1 3 3 4 5% 5% 9% 12% 58%	7461
	11th to 20th	Day	2 1 1 3 3 3 5% 4 7% 11% 60%	7003
	21st to end	Day	2 2 1 4 4 5% 6% 5% 9% 13% 49%	7751
September	1st to 10th	Day	4 4 2 4 3 4 5% 4 6% 7% 57%	2520
	11th to 20th	Day	5% 3 1 4 3 3 5% 3 6% 7% 60%	2520
	21st to end	Day	4 3 1 3 3 2 4 3 4 6% 68%	2251
October	1st to 10th	Day	3 1 1 2 2 2 2 2 4 4 76%	3370
	11th to 20th	Day	3 2 1 4 3 3 3 3 4 5% 68%	3280
	21st to end	Day	2 2 1 2 1 1 1 2 3 5% 80%	3548
November	1st to 10th	Day	2 2 1 2 2 3 3 3 3 5% 74%	2059
	11th to 20th	Day	2 2 1 2 2 2 4 3 4 6% 72%	1908
	21st to end	Day	4 4 2 3 3 3 3 2 4 6% 67%	1890
December	1st to 10th	Day	2 3 1 2 2 2 2 2 2 4 79%	2700
	11th to 20th	Day	3 2 1 4 3 3 3 3 4 7% 68%	3106
	21st to end	Day	3 3 1 3 2 2 3 3 4 6% 68%	4210
January	1st to 10th	Night	2 7% 3 5% 4 4 5% 4 5% 6% 54%	7605
	11th to 20th	Night	2 3 1 2 2 2 2 2 3 4 77%	7650
	21st to end	Night	4 6% 2 4 3 3 3 3 5% 7% 61%	8370
February	1st to 10th	Night	2 5% 2 3 3 2 2 2 4 7% 67%	2730
	11th to 20th	Night	5% 5% 2 5% 3 3 3 3 4 6% 59%	2473
	21st to end	Night	3 5% 2 4 2 2 3 3 4 5% 69%	2076
March	1st to 10th	Night	4 4 2 4 3 3 3 2 4 5% 66%	5121
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 4 6% 55%	5110
	21st to end	Night	3 3 1 3 3 3 3 3 5% 7% 66%	5499
April	1st to 10th	Night	4 4 1 4 3 3 3 3 5% 7% 63%	2100
	11th to 20th	Night	4 5% 2 5% 4 3 4 3 4 5% 61%	2077
	21st to end	Night	5% 3 1 4 3 3 3 3 4 6% 65%	2100
May	1st to 10th	Night	6% 5% 2 6% 4 4 4 4 5% 7% 53%	5890
	11th to 20th	Night	4 4 1 5% 4 3 3 3 5% 7% 63%	5522
	21st to end	Night	2 3 1 5% 4 4 4 3 5% 7% 62%	5366
June	1st to 10th	Night	3 3 1 4 4 4 4 4 6% 10% 56%	1680
	11th to 20th	Night	2 3 1 3 3 3 3 3 5% 7% 67%	1680
	21st to end	Night	4 4 3 5% 4 4 5% 4 8% 10% 49%	1680
July	1st to 10th	Night	1 2 1 5% 4 5% 6% 5% 7% 9% 54%	5212
	11th to 20th	Night	2 4 2 8% 6% 7% 8% 6% 11% 13% 34%	5340
	21st to end	Night	3 5% 2 8% 7% 8% 9% 7% 11% 12% 27%	5805
August	1st to 10th	Night	1 3 2 8% 7% 8% 8% 6% 9% 10% 39%	5357
	11th to 20th	Night	3 4 2 8% 6% 7% 8% 6% 10% 11% 35%	5853
	21st to end	Night	3 4 2 9% 8% 9% 8% 7% 12% 12% 27%	6465
September	1st to 10th	Night	5% 4 2 5% 5% 5% 5% 5% 7% 10% 48%	2100
	11th to 20th	Night	5% 4 2 3 4 4 5% 4 5% 7% 58%	2100
	21st to end	Night	5% 3 1 4 3 3 4 3 4 5% 64%	2362
October	1st to 10th	Night	4 2 1 3 2 2 2 2 3 4 74%	4040
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 4 6% 59%	3934
	21st to end	Night	2 2 1 2 1 2 2 1 3 5% 80%	4252
November	1st to 10th	Night	3 2 1 3 2 1 2 2 3 5% 76%	2460
	11th to 20th	Night	3 2 1 2 2 2 2 2 4 6% 74%	2688
	21st to end	Night	5% 5% 1 3 2 3 2 3 3 5% 66%	2730
December	1st to 10th	Night	3 3 1 2 2 1 2 2 3 6% 76%	4706
	11th to 20th	Night	3 2 1 2 2 2 3 3 5% 8% 68%	5321
	21st to end	Night	3 4 1 4 3 3 3 2 4 5% 68%	7052

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	21% 5% 10% 35% 26% 3	5321
	11th to 20th	Day	11% 4 9% 25% 35% 16%	5340
	21st to end	Day	23% 4 6% 19% 35% 12%	5844
February	1st to 10th	Day	20% 5% 10% 25% 28% 12%	1890
	11th to 20th	Day	23% 5% 8% 25% 28% 11%	2042
	21st to end	Day	20% 3 6% 19% 31% 21%	1730
March	1st to 10th	Day	16% 5% 4 14% 35% 26%	4974
	11th to 20th	Day	19% 10% 8% 19% 26% 19%	5110
	21st to end	Day	18% 5% 6% 21% 37% 13%	5711
April	1st to 10th	Day	17% 4 6% 17% 35% 21%	2520
	11th to 20th	Day	19% 4 7% 15% 29% 25%	2494
	21st to end	Day	15% 4 7% 18% 34% 22%	2520
May	1st to 10th	Day	17% 4 9% 20% 28% 21%	7057
	11th to 20th	Day	13% 5% 6% 14% 28% 34%	7368
	21st to end	Day	11% 3 6% 14% 21% 45%	8824
June	1st to 10th	Day	14% 6% 9% 20% 25% 27%	2940
	11th to 20th	Day	11% 4 5% 12% 22% 46%	2940
	21st to end	Day	20% 5% 9% 19% 20% 28%	2940
July	1st to 10th	Day	16% 6% 8% 12% 20% 38%	7707
	11th to 20th	Day	16% 8% 18% 29% 19% 9%	7581
	21st to end	Day	23% 9% 17% 29% 17% 5%	8120
August	1st to 10th	Day	15% 7% 15% 28% 24% 10%	5912
	11th to 20th	Day	15% 7% 14% 26% 25% 12%	5519
	21st to end	Day	22% 8% 18% 29% 18% 4	6078
September	1st to 10th	Day	23% 8% 11% 21% 24% 14%	2520
	11th to 20th	Day	21% 7% 11% 16% 26% 20%	2520
	21st to end	Day	17% 5% 7% 20% 30% 21%	2251
October	1st to 10th	Day	12% 4 5% 13% 31% 34%	3370
	11th to 20th	Day	16% 4 5% 16% 34% 26%	3280
	21st to end	Day	10% 2 5% 20% 41% 23%	3548
November	1st to 10th	Day	13% 3 6% 21% 40% 17%	2059
	11th to 20th	Day	13% 5% 8% 24% 38% 12%	1908
	21st to end	Day	21% 3 6% 26% 31% 13%	1890
December	1st to 10th	Day	13% 2 5% 33% 34% 13%	2700
	11th to 20th	Day	17% 5% 8% 35% 29% 5%	3104
	21st to end	Day	16% 4 10% 29% 33% 9%	4210
January	1st to 10th	Night	28% 6% 10% 28% 23% 5%	7605
	11th to 20th	Night	13% 4 6% 26% 39% 13%	7650
	21st to end	Night	23% 5% 6% 18% 36% 12%	8370
February	1st to 10th	Night	19% 3 9% 24% 32% 13%	2730
	11th to 20th	Night	26% 5% 8% 22% 27% 13%	2473
	21st to end	Night	18% 4 6% 16% 35% 21%	2076
March	1st to 10th	Night	20% 4 4 13% 36% 23%	5121
	11th to 20th	Night	26% 8% 7% 15% 28% 16%	5110
	21st to end	Night	15% 5% 8% 21% 36% 15%	5499
April	1st to 10th	Night	20% 3 7% 15% 32% 23%	2100
	11th to 20th	Night	23% 5% 5% 13% 25% 28%	2077
	21st to end	Night	18% 6% 9% 14% 31% 22%	2100
May	1st to 10th	Night	26% 5% 11% 17% 22% 19%	5888
	11th to 20th	Night	18% 6% 8% 12% 26% 30%	5523
	21st to end	Night	17% 5% 7% 11% 15% 44%	5367
June	1st to 10th	Night	19% 9% 13% 16% 18% 26%	1680
	11th to 20th	Night	15% 5% 7% 10% 20% 42%	1680
	21st to end	Night	25% 9% 13% 12% 14% 26%	1680
July	1st to 10th	Night	23% 8% 9% 14% 15% 31%	5167
	11th to 20th	Night	31% 11% 23% 21% 9% 6%	5286
	21st to end	Night	38% 11% 19% 21% 9% 2	5677
August	1st to 10th	Night	32% 11% 14% 23% 14% 5%	4230
	11th to 20th	Night	34% 10% 15% 18% 13% 10%	4613
	21st to end	Night	37% 12% 21% 18% 9% 3	5069
September	1st to 10th	Night	28% 8% 14% 18% 19% 13%	2100
	11th to 20th	Night	24% 6% 12% 16% 21% 21%	2100
	21st to end	Night	20% 4 8% 16% 27% 25%	2362
October	1st to 10th	Night	14% 4 5% 11% 31% 35%	4040
	11th to 20th	Night	25% 4 5% 11% 26% 29%	3934
	21st to end	Night	10% 2 3 21% 41% 23%	4252
November	1st to 10th	Night	12% 3 4 19% 42% 19%	2460
	11th to 20th	Night	14% 3 6% 19% 40% 17%	2688
	21st to end	Night	22% 4 6% 20% 33% 16%	2730
December	1st to 10th	Night	12% 3 6% 34% 32% 14%	4706
	11th to 20th	Night	15% 4 7% 31% 35% 8%	5322
	21st to end	Night	19% 4 7% 30% 33% 7%	7052

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	5% 5% 29% 45% 15% 1	330
	11th to 20th	Day	6% 9% 26% 35% 20% 3	330
	21st to end	Day	2 8% 35% 34% 17% 4	363
February	1st to 10th	Day	5% 8% 35% 33% 18% 2	330
	11th to 20th	Day	9% 9% 34% 38% 8% 1	330
	21st to end	Day	7% 12% 39% 30% 11%	273
March	1st to 10th	Day	7% 17% 30% 31% 14% 2	498
	11th to 20th	Day	10% 15% 29% 30% 13% 3	540
	21st to end	Day	9% 18% 33% 24% 14% 3	594
April	1st to 10th	Day	7% 16% 31% 29% 14% 4	540
	11th to 20th	Day	7% 17% 35% 28% 12% 1	532
	21st to end	Day	6% 16% 34% 28% 13% 3	540
May	1st to 10th	Day	6% 13% 30% 31% 18% 3	543
	11th to 20th	Day	5% 11% 26% 28% 21% 9%	568
	21st to end	Day	4 9% 24% 38% 21% 5%	771
June	1st to 10th	Day	2 4 16% 35% 35% 8%	780
	11th to 20th	Day	2 4 17% 37% 31% 8%	780
	21st to end	Day	5% 4 13% 32% 37% 9%	780
July	1st to 10th	Day	2 2 8% 27% 43% 17%	609
	11th to 20th	Day	3 1 4 18% 39% 35%	564
	21st to end	Day	3 2 3 17% 39% 36%	619
August	1st to 10th	Day	3 2 5% 19% 47% 25%	567
	11th to 20th	Day	3 2 6% 22% 39% 27%	557
	21st to end	Day	4 3 5% 24% 40% 25%	627
September	1st to 10th	Day	4 2 8% 25% 38% 22%	570
	11th to 20th	Day	4 2 14% 34% 34% 13%	570
	21st to end	Day	7% 5% 15% 24% 35% 15%	420
October	1st to 10th	Day	5% 4 18% 24% 36% 13%	360
	11th to 20th	Day	8% 6% 20% 31% 27% 9%	339
	21st to end	Day	7% 7% 14% 34% 31% 7%	363
November	1st to 10th	Day	5% 10% 18% 37% 25% 4	330
	11th to 20th	Day	3 5% 21% 38% 24% 9%	330
	21st to end	Day	8% 6% 28% 35% 19% 3	330
December	1st to 10th	Day	6% 5% 29% 39% 18% 3	330
	11th to 20th	Day	5% 8% 23% 41% 19% 4	330
	21st to end	Day	9% 8% 28% 41% 12% 2	363
January	1st to 10th	Night	5% 3 31% 44% 14% 1	840
	11th to 20th	Night	8% 5% 34% 38% 14% 1	840
	21st to end	Night	7% 6% 34% 41% 13% 1	924
February	1st to 10th	Night	5% 6% 35% 42% 11% 1	840
	11th to 20th	Night	7% 9% 39% 38% 6%	824
	21st to end	Night	5% 8% 46% 36% 4	692
March	1st to 10th	Night	6% 7% 37% 40% 10%	840
	11th to 20th	Night	7% 7% 32% 42% 11%	840
	21st to end	Night	7% 10% 32% 42% 9%	877
April	1st to 10th	Night	5% 12% 37% 37% 8%	630
	11th to 20th	Night	5% 13% 39% 35% 7%	623
	21st to end	Night	7% 9% 35% 42% 7% 1	630
May	1st to 10th	Night	5% 8% 32% 45% 10% 1	630
	11th to 20th	Night	7% 6% 26% 43% 17% 1	621
	21st to end	Night	3 4 32% 47% 14%	683
June	1st to 10th	Night	3 4 19% 51% 21% 1	630
	11th to 20th	Night	2 5% 24% 47% 22%	630
	21st to end	Night	5% 3 17% 49% 27%	630
July	1st to 10th	Night	3 3 9% 46% 37% 3	615
	11th to 20th	Night	3 3 6% 33% 50% 4	612
	21st to end	Night	4 2 4 30% 51% 8%	690
August	1st to 10th	Night	4 2 6% 28% 52% 8%	627
	11th to 20th	Night	5% 3 6% 40% 42% 4	624
	21st to end	Night	4 2 3 37% 48% 5%	693
September	1st to 10th	Night	5% 2 7% 45% 39% 2	630
	11th to 20th	Night	5% 2 8% 49% 33% 2	630
	21st to end	Night	6% 4 12% 49% 27% 1	744
October	1st to 10th	Night	6% 4 18% 47% 23% 2	840
	11th to 20th	Night	6% 3 22% 49% 19% 2	812
	21st to end	Night	5% 4 23% 45% 20% 3	880
November	1st to 10th	Night	4 2 23% 50% 20% 1	820
	11th to 20th	Night	4 4 26% 48% 17% 2	1008
	21st to end	Night	8% 7% 26% 38% 20% 2	1050
December	1st to 10th	Night	6% 4 32% 44% 13% 1	1050
	11th to 20th	Night	8% 6% 30% 44% 11% 1	1050
	21st to end	Night	8% 6% 34% 42% 10%	1118

Page generated at 2026-10-11 03:06:29. Version ac07

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