Ryan Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ryan Observing Site clear sky chart from 2005-11-06 to 2026-03-03.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 43%	131009
	Night	14% 6% 2 5% 4 4 4 4 5% 7% 46%	130137
Transparency	Day	38% 6% 11% 23% 17% 5%	134611
	Night	37% 5% 11% 23% 19% 5%	134606
Seeing	Day	19% 11% 26% 25% 14% 5%	16620
	Night	17% 8% 26% 33% 15% 2	26389

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	13% 5% 2 6% 4 4 4 3 4 5% 49%	5122
	11th to 20th	Day	11% 8% 2 6% 4 4 4 3 3 4 52%	5280
	21st to end	Day	12% 6% 2 8% 4 4 4 4 5% 5% 45%	5780
February	1st to 10th	Day	11% 8% 2 7% 4 5% 4 4 6% 6% 43%	1890
	11th to 20th	Day	16% 8% 2 6% 4 3 3 4 5% 7% 41%	1848
	21st to end	Day	15% 8% 3 6% 5% 3 4 3 5% 6% 41%	1771
March	1st to 10th	Day	16% 6% 2 5% 4 4 5% 4 5% 6% 43%	4957
	11th to 20th	Day	10% 5% 2 6% 4 4 3 3 5% 6% 52%	4980
	21st to end	Day	15% 7% 2 6% 4 4 5% 4 5% 7% 42%	5465
April	1st to 10th	Day	11% 6% 2 5% 5% 5% 5% 4 6% 7% 45%	2385
	11th to 20th	Day	13% 6% 2 6% 3 4 3 4 4 5% 49%	2374
	21st to end	Day	16% 6% 2 7% 6% 4 4 3 5% 7% 41%	2419
May	1st to 10th	Day	16% 6% 2 7% 6% 5% 5% 4 7% 9% 32%	5862
	11th to 20th	Day	22% 6% 2 5% 4 5% 4 4 7% 9% 32%	5896
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 6% 9% 39%	6934
June	1st to 10th	Day	10% 5% 2 5% 4 5% 5% 5% 7% 8% 43%	2800
	11th to 20th	Day	11% 4 3 6% 5% 5% 6% 5% 7% 10% 39%	2800
	21st to end	Day	8% 4 2 5% 5% 6% 5% 5% 7% 10% 44%	2800
July	1st to 10th	Day	7% 4 2 6% 5% 5% 6% 4 8% 11% 43%	6296
	11th to 20th	Day	8% 6% 2 7% 6% 6% 6% 6% 10% 12% 30%	5900
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 11% 39%	6424
August	1st to 10th	Day	14% 5% 2 6% 5% 6% 6% 5% 8% 11% 34%	4234
	11th to 20th	Day	9% 4 2 6% 5% 5% 5% 5% 8% 10% 40%	4078
	21st to end	Day	10% 4 2 4 4 4 5% 4 6% 8% 49%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 4 3 5% 6% 48%	2400
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 9% 46%	2355
	21st to end	Day	23% 7% 3 6% 4 3 4 4 5% 6% 36%	2110
October	1st to 10th	Day	15% 5% 2 5% 4 3 4 3 4 6% 48%	2000
	11th to 20th	Day	15% 4 2 4 4 4 4 4 5% 5% 51%	2000
	21st to end	Day	14% 5% 1 5% 3 3 4 3 4 6% 53%	2200
November	1st to 10th	Day	10% 5% 1 4 4 4 3 2 5% 7% 54%	2048
	11th to 20th	Day	14% 4 2 3 4 4 4 3 5% 6% 51%	1811
	21st to end	Day	14% 4 2 4 3 5% 3 4 5% 6% 50%	1680
December	1st to 10th	Day	11% 5% 2 4 3 4 4 4 5% 7% 52%	2680
	11th to 20th	Day	17% 6% 2 5% 3 3 3 3 4 6% 48%	3070
	21st to end	Day	18% 7% 2 6% 4 4 4 4 6% 7% 40%	4048
January	1st to 10th	Night	10% 6% 2 5% 4 4 5% 4 5% 6% 51%	7753
	11th to 20th	Night	13% 7% 2 4 2 3 3 2 4 5% 55%	7680
	21st to end	Night	13% 6% 2 5% 3 3 3 3 4 5% 52%	8401
February	1st to 10th	Night	12% 7% 2 6% 4 4 5% 4 6% 7% 43%	2730
	11th to 20th	Night	18% 7% 2 5% 3 4 4 3 5% 5% 43%	2657
	21st to end	Night	13% 8% 3 5% 4 4 4 3 5% 6% 45%	2033
March	1st to 10th	Night	16% 5% 2 5% 4 3 4 3 4 5% 49%	4941
	11th to 20th	Night	9% 5% 2 4 3 4 4 3 6% 7% 53%	4980
	21st to end	Night	11% 7% 2 6% 3 4 4 4 5% 7% 48%	5467
April	1st to 10th	Night	14% 7% 2 5% 5% 4 5% 3 6% 6% 44%	2014
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 8% 48%	1975
	21st to end	Night	15% 5% 2 4 4 4 4 4 5% 7% 45%	1998
May	1st to 10th	Night	19% 7% 3 7% 5% 4 4 4 6% 9% 33%	4033
	11th to 20th	Night	25% 6% 2 5% 3 4 4 4 6% 8% 34%	3996
	21st to end	Night	16% 5% 2 6% 4 5% 5% 4 7% 8% 38%	3920
June	1st to 10th	Night	11% 4 2 6% 5% 3 4 4 7% 9% 46%	1600
	11th to 20th	Night	12% 5% 3 5% 5% 5% 5% 4 5% 8% 44%	1600
	21st to end	Night	9% 4 1 4 4 5% 5% 4 7% 10% 45%	1600
July	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 5% 8% 11% 41%	3643
	11th to 20th	Night	9% 8% 3 8% 5% 6% 7% 6% 8% 11% 30%	4057
	21st to end	Night	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 41%	4427
August	1st to 10th	Night	16% 5% 2 7% 4 5% 5% 4 7% 9% 35%	2915
	11th to 20th	Night	10% 6% 3 7% 5% 6% 5% 4 7% 7% 40%	2936
	21st to end	Night	13% 5% 2 5% 3 3 3 3 5% 7% 50%	3586
September	1st to 10th	Night	14% 5% 2 5% 3 4 4 3 6% 8% 47%	2000
	11th to 20th	Night	13% 5% 2 5% 3 3 3 4 5% 7% 48%	2041
	21st to end	Night	25% 5% 2 5% 4 4 3 3 4 6% 40%	2289
October	1st to 10th	Night	18% 5% 2 6% 3 3 3 3 4 5% 48%	2400
	11th to 20th	Night	14% 5% 2 5% 4 3 3 3 4 6% 52%	2400
	21st to end	Night	14% 4 1 4 3 3 3 3 5% 5% 54%	2640
November	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 6% 54%	2466
	11th to 20th	Night	14% 5% 2 4 4 4 4 2 5% 6% 50%	2804
	21st to end	Night	13% 4 1 4 4 4 4 4 5% 6% 50%	2940
December	1st to 10th	Night	9% 4 2 4 4 3 4 3 5% 6% 56%	4720
	11th to 20th	Night	18% 7% 2 5% 3 3 4 4 5% 6% 45%	5345
	21st to end	Night	16% 6% 2 5% 4 4 4 4 5% 8% 43%	7150

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	38% 4 8% 23% 19% 7%	5123
	11th to 20th	Day	36% 4 5% 20% 21% 15%	5280
	21st to end	Day	40% 5% 7% 28% 17% 4	5780
February	1st to 10th	Day	41% 4 11% 25% 16% 3	1890
	11th to 20th	Day	42% 5% 8% 21% 20% 4	1857
	21st to end	Day	44% 5% 12% 19% 16% 5%	1771
March	1st to 10th	Day	41% 5% 9% 19% 17% 10%	4957
	11th to 20th	Day	32% 4 7% 27% 22% 8%	4980
	21st to end	Day	42% 5% 10% 17% 18% 8%	5465
April	1st to 10th	Day	38% 5% 11% 20% 18% 8%	2385
	11th to 20th	Day	36% 4 11% 21% 22% 6%	2374
	21st to end	Day	43% 5% 10% 23% 15% 5%	2419
May	1st to 10th	Day	45% 9% 15% 18% 11% 3	5897
	11th to 20th	Day	48% 7% 11% 22% 11% 1	5900
	21st to end	Day	39% 8% 14% 20% 17% 2	6949
June	1st to 10th	Day	35% 9% 13% 24% 18% 1	2800
	11th to 20th	Day	39% 7% 15% 23% 14% 2	2800
	21st to end	Day	32% 9% 15% 25% 17% 2	2800
July	1st to 10th	Day	33% 11% 19% 20% 14% 4	6227
	11th to 20th	Day	41% 12% 18% 22% 7% 1	5831
	21st to end	Day	37% 8% 11% 24% 19% 1	6240
August	1st to 10th	Day	42% 8% 17% 25% 7%	4221
	11th to 20th	Day	36% 8% 14% 27% 14% 1	4117
	21st to end	Day	32% 6% 16% 30% 15% 2	4312
September	1st to 10th	Day	37% 5% 13% 19% 21% 5%	2400
	11th to 20th	Day	36% 4 8% 28% 20% 3	2355
	21st to end	Day	48% 5% 9% 19% 16% 2	2110
October	1st to 10th	Day	35% 4 7% 20% 29% 5%	3260
	11th to 20th	Day	25% 4 7% 27% 27% 11%	3240
	21st to end	Day	22% 3 9% 30% 26% 11%	3538
November	1st to 10th	Day	31% 3 9% 26% 26% 5%	2048
	11th to 20th	Day	34% 4 10% 23% 22% 7%	1811
	21st to end	Day	35% 4 10% 27% 22% 3	1680
December	1st to 10th	Day	32% 5% 10% 27% 19% 6%	2680
	11th to 20th	Day	39% 3 13% 27% 13% 5%	3066
	21st to end	Day	43% 6% 13% 21% 15% 1	4048
January	1st to 10th	Night	33% 5% 9% 25% 23% 5%	7754
	11th to 20th	Night	33% 3 6% 21% 25% 12%	7680
	21st to end	Night	35% 3 7% 29% 21% 5%	8401
February	1st to 10th	Night	41% 4 11% 25% 17% 2	2730
	11th to 20th	Night	43% 3 8% 22% 18% 7%	2659
	21st to end	Night	40% 5% 11% 21% 17% 7%	2033
March	1st to 10th	Night	38% 4 7% 23% 19% 9%	4941
	11th to 20th	Night	30% 4 9% 23% 26% 7%	4980
	21st to end	Night	36% 5% 11% 21% 21% 6%	5467
April	1st to 10th	Night	40% 5% 9% 19% 21% 5%	2014
	11th to 20th	Night	35% 5% 12% 23% 21% 5%	1975
	21st to end	Night	37% 5% 11% 27% 15% 5%	1998
May	1st to 10th	Night	48% 8% 14% 18% 8% 4	4060
	11th to 20th	Night	48% 7% 11% 22% 11% 1	3997
	21st to end	Night	42% 8% 15% 24% 10% 2	3927
June	1st to 10th	Night	34% 7% 14% 27% 16% 2	1600
	11th to 20th	Night	38% 7% 15% 24% 14% 2	1600
	21st to end	Night	33% 7% 16% 22% 19% 3	1600
July	1st to 10th	Night	37% 12% 18% 16% 15% 2	3605
	11th to 20th	Night	47% 12% 17% 17% 7% 1	4006
	21st to end	Night	36% 9% 16% 24% 15%	4297
August	1st to 10th	Night	44% 7% 17% 24% 7% 1	2904
	11th to 20th	Night	41% 9% 11% 25% 14% 1	2963
	21st to end	Night	34% 5% 14% 30% 15% 1	3586
September	1st to 10th	Night	36% 5% 11% 23% 18% 6%	2000
	11th to 20th	Night	35% 5% 9% 29% 20% 2	2041
	21st to end	Night	47% 5% 9% 19% 17% 3	2289
October	1st to 10th	Night	40% 4 8% 20% 21% 6%	3920
	11th to 20th	Night	23% 4 9% 23% 31% 9%	3899
	21st to end	Night	21% 3 8% 32% 27% 8%	4252
November	1st to 10th	Night	34% 3 8% 24% 25% 7%	2466
	11th to 20th	Night	36% 4 7% 24% 23% 7%	2804
	21st to end	Night	34% 4 10% 25% 22% 5%	2940
December	1st to 10th	Night	29% 4 11% 29% 23% 3	4720
	11th to 20th	Night	41% 4 12% 19% 18% 6%	5348
	21st to end	Night	39% 7% 13% 22% 17% 1	7150

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	27% 22% 29% 18% 4	305
	11th to 20th	Day	27% 25% 30% 16% 3	330
	21st to end	Day	24% 22% 37% 14% 2 1	363
February	1st to 10th	Day	22% 26% 33% 16% 2	330
	11th to 20th	Day	34% 23% 34% 8% 1	335
	21st to end	Day	26% 16% 35% 20% 3	446
March	1st to 10th	Day	24% 18% 31% 22% 5%	508
	11th to 20th	Day	24% 21% 27% 20% 7% 1	500
	21st to end	Day	24% 17% 35% 17% 6% 1	550
April	1st to 10th	Day	24% 22% 26% 18% 9% 1	500
	11th to 20th	Day	20% 16% 27% 22% 11% 4	492
	21st to end	Day	24% 10% 33% 20% 11% 2	500
May	1st to 10th	Day	23% 14% 27% 22% 10% 3	503
	11th to 20th	Day	23% 8% 27% 25% 13% 4	527
	21st to end	Day	20% 6% 25% 27% 15% 7%	573
June	1st to 10th	Day	13% 6% 26% 28% 19% 7%	530
	11th to 20th	Day	15% 6% 23% 32% 16% 8%	530
	21st to end	Day	11% 4 23% 34% 22% 7%	530
July	1st to 10th	Day	12% 3 15% 32% 28% 10%	525
	11th to 20th	Day	6% 2 16% 32% 29% 15%	524
	21st to end	Day	13% 1 16% 33% 26% 11%	576
August	1st to 10th	Day	13% 3 19% 27% 25% 12%	526
	11th to 20th	Day	13% 3 17% 29% 25% 13%	519
	21st to end	Day	10% 2 18% 33% 23% 14%	583
September	1st to 10th	Day	16% 4 18% 29% 19% 13%	530
	11th to 20th	Day	17% 3 18% 26% 24% 12%	530
	21st to end	Day	29% 7% 19% 27% 14% 4	530
October	1st to 10th	Day	20% 4 20% 31% 17% 7%	530
	11th to 20th	Day	15% 13% 26% 26% 15% 4	530
	21st to end	Day	18% 13% 30% 25% 12% 3	583
November	1st to 10th	Day	16% 10% 33% 26% 12% 3	529
	11th to 20th	Day	20% 11% 30% 28% 9% 2	351
	21st to end	Day	20% 16% 36% 22% 5%	220
December	1st to 10th	Day	22% 15% 36% 21% 5%	220
	11th to 20th	Day	24% 11% 38% 19% 7% 1	220
	21st to end	Day	28% 14% 35% 18% 6%	242
January	1st to 10th	Night	18% 14% 38% 26% 4	840
	11th to 20th	Night	19% 12% 32% 31% 5%	840
	21st to end	Night	18% 10% 38% 31% 2	924
February	1st to 10th	Night	17% 10% 38% 31% 4	840
	11th to 20th	Night	26% 15% 35% 22% 2	823
	21st to end	Night	19% 14% 37% 27% 3	692
March	1st to 10th	Night	18% 15% 35% 28% 4	809
	11th to 20th	Night	20% 14% 34% 26% 6% 1	800
	21st to end	Night	19% 12% 37% 25% 6% 1	880
April	1st to 10th	Night	20% 14% 33% 27% 6%	800
	11th to 20th	Night	16% 11% 33% 29% 10% 1	791
	21st to end	Night	19% 8% 29% 34% 9% 1	798
May	1st to 10th	Night	22% 6% 23% 31% 17% 1	600
	11th to 20th	Night	20% 4 25% 33% 17% 1	581
	21st to end	Night	18% 2 17% 39% 22% 2	433
June	1st to 10th	Night	11% 1 19% 43% 25% 2	400
	11th to 20th	Night	15% 2 14% 44% 24% 2	400
	21st to end	Night	10% 1 14% 46% 26% 3	400
July	1st to 10th	Night	11% 2 11% 42% 30% 4	409
	11th to 20th	Night	6% 2 6% 38% 42% 6%	582
	21st to end	Night	10% 1 10% 38% 36% 5%	657
August	1st to 10th	Night	13% 2 8% 41% 32% 4	597
	11th to 20th	Night	14% 2 9% 37% 34% 4	629
	21st to end	Night	14% 3 10% 36% 33% 5%	880
September	1st to 10th	Night	18% 2 11% 35% 30% 5%	800
	11th to 20th	Night	14% 3 12% 36% 30% 5%	800
	21st to end	Night	27% 3 16% 31% 21% 2	800
October	1st to 10th	Night	21% 5% 17% 32% 22% 4	800
	11th to 20th	Night	17% 7% 26% 33% 17% 2	800
	21st to end	Night	17% 7% 27% 36% 12% 2	880
November	1st to 10th	Night	15% 7% 28% 36% 13% 2	820
	11th to 20th	Night	17% 9% 31% 34% 8% 1	840
	21st to end	Night	15% 8% 34% 32% 10% 1	840
December	1st to 10th	Night	19% 8% 35% 30% 8%	840
	11th to 20th	Night	18% 7% 33% 36% 5%	840
	21st to end	Night	20% 9% 29% 38% 4	924

Page generated at 2026-02-28 01:40:25. Version ac07

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