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 2024-12-02.

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% 42%	101344
	Night	14% 6% 2 5% 4 4 4 4 5% 7% 45%	98211
Transparency	Day	38% 6% 12% 24% 16% 4	104990
	Night	37% 5% 11% 24% 18% 4	102705
Seeing	Day	19% 10% 26% 25% 14% 6%	15058
	Night	18% 7% 26% 33% 15% 2	24729

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% 6% 2 5% 3 4 4 3 4 5% 47%	2754
	11th to 20th	Day	11% 10% 3 8% 6% 5% 5% 3 4 5% 40%	2840
	21st to end	Day	15% 8% 3 8% 5% 4 4 4 5% 5% 38%	3124
February	1st to 10th	Day	11% 8% 2 7% 5% 5% 4 5% 6% 6% 41%	1710
	11th to 20th	Day	16% 8% 2 6% 4 3 4 4 5% 7% 42%	1667
	21st to end	Day	16% 8% 3 6% 5% 3 4 3 5% 6% 40%	1607
March	1st to 10th	Day	20% 7% 2 6% 4 4 4 4 5% 6% 38%	3435
	11th to 20th	Day	8% 5% 2 6% 4 4 4 4 5% 7% 52%	3480
	21st to end	Day	18% 8% 2 6% 4 4 4 3 5% 6% 39%	3815
April	1st to 10th	Day	10% 6% 2 5% 5% 5% 5% 4 6% 7% 45%	2266
	11th to 20th	Day	13% 6% 2 6% 3 4 4 4 4 5% 49%	2254
	21st to end	Day	16% 6% 2 7% 6% 4 4 3 5% 7% 40%	2298
May	1st to 10th	Day	19% 7% 2 7% 6% 5% 5% 4 6% 8% 30%	4082
	11th to 20th	Day	23% 6% 2 6% 4 5% 4 4 6% 8% 32%	4102
	21st to end	Day	11% 4 2 5% 4 4 5% 5% 6% 10% 42%	4823
June	1st to 10th	Day	11% 5% 2 5% 4 5% 6% 5% 7% 8% 43%	2660
	11th to 20th	Day	10% 5% 3 6% 5% 5% 6% 5% 7% 10% 39%	2660
	21st to end	Day	8% 4 2 5% 5% 6% 5% 5% 8% 10% 43%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 5% 6% 5% 9% 11% 42%	4390
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 9% 12% 37%	4120
	21st to end	Day	11% 6% 3 8% 6% 6% 6% 5% 7% 10% 34%	4466
August	1st to 10th	Day	14% 5% 2 6% 5% 6% 6% 5% 8% 11% 33%	4104
	11th to 20th	Day	9% 4 2 6% 5% 5% 5% 5% 7% 10% 41%	3951
	21st to end	Day	10% 4 2 4 4 4 5% 4 6% 8% 49%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 5% 6% 47%	2280
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 9% 46%	2237
	21st to end	Day	22% 7% 3 6% 4 3 4 4 5% 6% 37%	2005
October	1st to 10th	Day	15% 5% 2 5% 4 3 5% 3 5% 6% 46%	1900
	11th to 20th	Day	15% 4 2 4 4 4 4 3 5% 5% 51%	1900
	21st to end	Day	14% 5% 2 5% 3 3 4 2 4 6% 53%	2090
November	1st to 10th	Day	11% 5% 1 4 4 3 3 2 5% 6% 54%	1949
	11th to 20th	Day	14% 4 2 3 4 3 4 3 5% 6% 50%	1725
	21st to end	Day	14% 4 1 3 3 4 3 4 5% 6% 50%	1600
December	1st to 10th	Day	15% 7% 2 5% 3 5% 4 4 6% 7% 42%	1528
	11th to 20th	Day	15% 5% 2 5% 4 3 3 3 4 5% 51%	1910
	21st to end	Day	20% 6% 2 6% 4 4 4 4 6% 7% 38%	2772
January	1st to 10th	Night	12% 7% 2 4 3 3 3 3 5% 6% 51%	4173
	11th to 20th	Night	16% 8% 2 4 3 3 3 2 5% 5% 49%	4120
	21st to end	Night	18% 7% 3 5% 4 3 3 3 4 5% 44%	4532
February	1st to 10th	Night	13% 8% 2 6% 4 4 4 4 6% 7% 42%	2470
	11th to 20th	Night	18% 7% 2 5% 3 4 4 3 5% 5% 43%	2399
	21st to end	Night	14% 8% 3 5% 4 4 4 3 5% 7% 44%	1845
March	1st to 10th	Night	20% 6% 2 6% 4 4 5% 4 5% 5% 39%	3418
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 6% 6% 52%	3480
	21st to end	Night	13% 7% 2 5% 3 4 3 3 4 6% 50%	3817
April	1st to 10th	Night	13% 7% 2 5% 5% 4 5% 3 6% 6% 44%	1914
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 8% 49%	1875
	21st to end	Night	16% 6% 2 4 4 4 4 4 5% 7% 45%	1898
May	1st to 10th	Night	21% 7% 3 6% 5% 4 4 4 6% 9% 32%	2813
	11th to 20th	Night	25% 6% 2 6% 3 4 4 4 5% 6% 34%	2790
	21st to end	Night	12% 4 2 5% 4 4 4 4 7% 9% 45%	2732
June	1st to 10th	Night	11% 4 2 5% 5% 3 4 4 8% 9% 46%	1520
	11th to 20th	Night	11% 5% 2 5% 5% 5% 5% 4 6% 8% 44%	1520
	21st to end	Night	10% 4 1 4 4 5% 5% 4 7% 10% 45%	1520
July	1st to 10th	Night	8% 4 2 5% 4 5% 6% 5% 9% 11% 42%	2551
	11th to 20th	Night	7% 6% 2 7% 4 5% 6% 5% 7% 11% 40%	2840
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	3087
August	1st to 10th	Night	16% 5% 2 7% 4 5% 6% 4 7% 9% 35%	2825
	11th to 20th	Night	10% 6% 3 7% 5% 5% 5% 4 7% 7% 41%	2844
	21st to end	Night	13% 5% 2 5% 3 3 3 3 5% 7% 51%	3476
September	1st to 10th	Night	14% 5% 2 5% 3 4 4 3 6% 8% 46%	1900
	11th to 20th	Night	13% 5% 2 5% 4 3 3 4 6% 7% 48%	1939
	21st to end	Night	24% 5% 2 5% 4 3 2 3 4 5% 41%	2174
October	1st to 10th	Night	19% 5% 2 6% 3 3 3 3 5% 5% 47%	2280
	11th to 20th	Night	14% 5% 1 5% 4 3 3 3 4 6% 53%	2280
	21st to end	Night	14% 4 1 4 3 3 3 3 5% 5% 54%	2508
November	1st to 10th	Night	10% 7% 2 5% 3 3 3 3 4 6% 54%	2346
	11th to 20th	Night	14% 5% 2 4 4 4 4 2 5% 6% 50%	2670
	21st to end	Night	14% 4 1 4 4 3 4 4 5% 6% 51%	2800
December	1st to 10th	Night	14% 6% 2 7% 5% 4 4 4 5% 6% 43%	2686
	11th to 20th	Night	15% 6% 2 5% 3 4 4 4 5% 6% 47%	3285
	21st to end	Night	17% 5% 2 5% 4 4 5% 4 5% 7% 42%	4884

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	39% 4 7% 30% 15% 5%	2755
	11th to 20th	Day	44% 5% 7% 18% 17% 8%	2840
	21st to end	Day	46% 5% 9% 22% 15% 3	3124
February	1st to 10th	Day	43% 4 11% 24% 15% 3	1710
	11th to 20th	Day	41% 5% 9% 22% 20% 4	1676
	21st to end	Day	45% 4 12% 17% 17% 5%	1607
March	1st to 10th	Day	47% 4 9% 20% 14% 6%	3435
	11th to 20th	Day	31% 4 7% 27% 24% 6%	3480
	21st to end	Day	45% 5% 9% 20% 16% 4	3815
April	1st to 10th	Day	36% 5% 11% 20% 19% 8%	2266
	11th to 20th	Day	36% 4 11% 21% 22% 7%	2254
	21st to end	Day	43% 5% 10% 22% 14% 5%	2298
May	1st to 10th	Day	49% 8% 11% 20% 10% 2	4120
	11th to 20th	Day	49% 7% 11% 21% 10% 1	4106
	21st to end	Day	34% 8% 15% 21% 18% 3	4837
June	1st to 10th	Day	35% 8% 13% 24% 17% 2	2660
	11th to 20th	Day	38% 7% 15% 24% 14% 2	2660
	21st to end	Day	33% 9% 15% 25% 16% 2	2660
July	1st to 10th	Day	33% 10% 21% 20% 11% 5%	4321
	11th to 20th	Day	36% 9% 17% 27% 9% 1	4051
	21st to end	Day	44% 8% 10% 23% 15% 1	4324
August	1st to 10th	Day	42% 8% 18% 25% 7%	4091
	11th to 20th	Day	35% 8% 14% 27% 15% 1	3990
	21st to end	Day	33% 6% 16% 30% 14% 2	4180
September	1st to 10th	Day	38% 5% 13% 19% 21% 5%	2280
	11th to 20th	Day	36% 4 8% 28% 20% 3	2237
	21st to end	Day	47% 5% 9% 20% 17% 3	2005
October	1st to 10th	Day	36% 4 6% 19% 29% 5%	3160
	11th to 20th	Day	24% 4 8% 27% 27% 11%	3140
	21st to end	Day	21% 3 9% 30% 26% 11%	3428
November	1st to 10th	Day	32% 3 8% 26% 25% 5%	1949
	11th to 20th	Day	35% 4 10% 22% 22% 7%	1725
	21st to end	Day	34% 4 10% 27% 23% 3	1600
December	1st to 10th	Day	41% 5% 12% 26% 12% 4	1528
	11th to 20th	Day	37% 2 8% 32% 14% 6%	1906
	21st to end	Day	43% 7% 11% 26% 11% 1	2772
January	1st to 10th	Night	34% 4 8% 27% 23% 5%	4173
	11th to 20th	Night	38% 3 9% 22% 22% 7%	4120
	21st to end	Night	44% 4 8% 24% 19% 2	4532
February	1st to 10th	Night	42% 4 11% 25% 16% 2	2470
	11th to 20th	Night	42% 3 8% 22% 18% 7%	2401
	21st to end	Night	41% 5% 10% 22% 16% 6%	1845
March	1st to 10th	Night	45% 6% 8% 24% 15% 3	3418
	11th to 20th	Night	31% 4 8% 24% 28% 5%	3480
	21st to end	Night	37% 4 10% 23% 20% 5%	3817
April	1st to 10th	Night	39% 5% 10% 19% 21% 5%	1914
	11th to 20th	Night	34% 4 12% 23% 21% 6%	1875
	21st to end	Night	38% 5% 11% 27% 14% 5%	1898
May	1st to 10th	Night	49% 8% 11% 19% 10% 3	2840
	11th to 20th	Night	49% 8% 11% 22% 10% 1	2791
	21st to end	Night	33% 8% 17% 26% 13% 3	2739
June	1st to 10th	Night	33% 7% 14% 28% 15% 2	1520
	11th to 20th	Night	37% 7% 16% 25% 14% 2	1520
	21st to end	Night	33% 7% 17% 22% 18% 3	1520
July	1st to 10th	Night	34% 12% 22% 15% 14% 3	2511
	11th to 20th	Night	37% 10% 19% 24% 10% 1	2786
	21st to end	Night	41% 8% 16% 21% 13% 1	2988
August	1st to 10th	Night	44% 7% 17% 24% 7% 1	2814
	11th to 20th	Night	41% 8% 11% 25% 15% 1	2871
	21st to end	Night	34% 5% 14% 30% 15% 1	3476
September	1st to 10th	Night	38% 5% 11% 22% 18% 6%	1900
	11th to 20th	Night	35% 5% 9% 29% 20% 3	1939
	21st to end	Night	46% 5% 9% 20% 17% 3	2174
October	1st to 10th	Night	40% 4 9% 20% 21% 6%	3800
	11th to 20th	Night	23% 4 9% 23% 32% 9%	3779
	21st to end	Night	21% 3 8% 33% 27% 8%	4120
November	1st to 10th	Night	33% 3 9% 24% 24% 7%	2346
	11th to 20th	Night	36% 4 6% 24% 23% 7%	2670
	21st to end	Night	34% 3 10% 25% 23% 5%	2800
December	1st to 10th	Night	41% 5% 10% 25% 15% 4	2686
	11th to 20th	Night	38% 4 10% 23% 20% 5%	3288
	21st to end	Night	40% 7% 13% 24% 15% 2	4884

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% 21% 31% 18% 4	249
	11th to 20th	Day	29% 21% 30% 17% 3	270
	21st to end	Day	24% 22% 38% 13% 3 1	297
February	1st to 10th	Day	24% 24% 33% 16% 3	270
	11th to 20th	Day	33% 21% 36% 9% 1	274
	21st to end	Day	28% 15% 34% 20% 3	382
March	1st to 10th	Day	24% 18% 31% 22% 5%	460
	11th to 20th	Day	23% 21% 27% 20% 7% 2	460
	21st to end	Day	25% 16% 35% 17% 6% 1	506
April	1st to 10th	Day	22% 22% 26% 19% 9% 2	460
	11th to 20th	Day	20% 15% 27% 23% 11% 4	452
	21st to end	Day	25% 10% 34% 19% 10% 2	460
May	1st to 10th	Day	24% 13% 27% 22% 11% 4	463
	11th to 20th	Day	23% 8% 27% 26% 13% 5%	487
	21st to end	Day	19% 5% 26% 28% 16% 7%	529
June	1st to 10th	Day	14% 6% 25% 28% 20% 7%	490
	11th to 20th	Day	14% 6% 24% 32% 16% 9%	490
	21st to end	Day	11% 5% 24% 34% 20% 6%	490
July	1st to 10th	Day	12% 3 15% 31% 29% 10%	485
	11th to 20th	Day	5% 3 16% 33% 30% 13%	484
	21st to end	Day	13% 1 17% 33% 25% 11%	532
August	1st to 10th	Day	12% 3 20% 27% 26% 13%	486
	11th to 20th	Day	13% 3 17% 29% 25% 13%	479
	21st to end	Day	10% 1 17% 33% 23% 15%	539
September	1st to 10th	Day	17% 4 15% 29% 20% 14%	490
	11th to 20th	Day	17% 3 18% 26% 23% 13%	490
	21st to end	Day	29% 6% 20% 26% 14% 5%	490
October	1st to 10th	Day	21% 4 21% 30% 18% 6%	490
	11th to 20th	Day	14% 13% 26% 28% 16% 4	490
	21st to end	Day	17% 11% 31% 26% 12% 3	539
November	1st to 10th	Day	17% 9% 32% 27% 12% 3	490
	11th to 20th	Day	20% 11% 29% 29% 10% 2	325
	21st to end	Day	19% 16% 38% 23% 5%	200
December	1st to 10th	Day	20% 14% 39% 21% 5% 1	182
	11th to 20th	Day	26% 9% 37% 19% 7% 1	180
	21st to end	Day	27% 11% 36% 20% 6%	198
January	1st to 10th	Night	19% 13% 37% 26% 4	760
	11th to 20th	Night	20% 10% 32% 32% 6%	760
	21st to end	Night	19% 10% 37% 31% 3	836
February	1st to 10th	Night	18% 8% 39% 31% 4	760
	11th to 20th	Night	26% 15% 36% 21% 2	743
	21st to end	Night	20% 13% 37% 27% 3	628
March	1st to 10th	Night	18% 14% 35% 29% 5%	760
	11th to 20th	Night	20% 14% 34% 26% 6% 1	760
	21st to end	Night	19% 12% 36% 26% 6% 1	836
April	1st to 10th	Night	19% 14% 33% 27% 7%	760
	11th to 20th	Night	16% 10% 33% 29% 11% 1	751
	21st to end	Night	20% 8% 30% 33% 9% 1	758
May	1st to 10th	Night	23% 5% 23% 31% 17% 1	570
	11th to 20th	Night	19% 4 25% 33% 17% 1	552
	21st to end	Night	18% 1 16% 39% 23% 2	411
June	1st to 10th	Night	11% 1 17% 44% 25% 2	380
	11th to 20th	Night	14% 2 13% 44% 25% 2	380
	21st to end	Night	10% 1 14% 48% 25% 2	380
July	1st to 10th	Night	12% 2 11% 40% 30% 4	388
	11th to 20th	Night	6% 2 6% 38% 42% 6%	552
	21st to end	Night	11% 1 11% 38% 35% 5%	624
August	1st to 10th	Night	13% 1 8% 42% 32% 4	567
	11th to 20th	Night	14% 2 9% 39% 32% 4	597
	21st to end	Night	14% 2 9% 36% 33% 5%	836
September	1st to 10th	Night	18% 2 10% 35% 30% 5%	760
	11th to 20th	Night	14% 3 12% 35% 30% 5%	760
	21st to end	Night	27% 3 15% 31% 21% 3	760
October	1st to 10th	Night	21% 4 17% 33% 21% 4	760
	11th to 20th	Night	16% 6% 26% 33% 17% 2	760
	21st to end	Night	17% 6% 27% 36% 12% 2	836
November	1st to 10th	Night	15% 6% 28% 35% 13% 2	780
	11th to 20th	Night	18% 8% 30% 35% 8% 1	800
	21st to end	Night	16% 8% 33% 31% 11% 1	800
December	1st to 10th	Night	19% 8% 35% 29% 8% 1	768
	11th to 20th	Night	17% 6% 34% 36% 6%	760
	21st to end	Night	20% 8% 29% 39% 4	836

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