Young Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Young Road Observatory clear sky chart from 2005-11-06 to 2025-03-12.

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%	109227
	Night	13% 6% 2 5% 4 4 4 4 5% 7% 45%	109778
Transparency	Day	37% 6% 11% 20% 19% 6%	113008
	Night	36% 6% 10% 19% 21% 8%	114136
Seeing	Day	16% 9% 24% 24% 19% 8%	15459
	Night	16% 9% 22% 30% 20% 3	25600

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 3 3 3 4 6% 49%	4056
	11th to 20th	Day	12% 5% 1 4 3 2 2 2 4 6% 58%	4060
	21st to end	Day	20% 7% 2 7% 4 3 3 2 3 4 45%	4466
February	1st to 10th	Day	15% 5% 3 6% 4 4 5% 3 6% 6% 42%	1985
	11th to 20th	Day	21% 6% 2 5% 3 4 3 3 4 5% 43%	1948
	21st to end	Day	18% 7% 2 5% 5% 3 3 3 4 6% 43%	1650
March	1st to 10th	Day	23% 9% 2 6% 4 3 3 3 4 5% 38%	3448
	11th to 20th	Day	11% 4 2 5% 4 3 4 4 4 7% 51%	3491
	21st to end	Day	19% 6% 2 6% 4 4 4 3 4 5% 41%	3815
April	1st to 10th	Day	11% 5% 2 5% 4 5% 4 5% 5% 7% 48%	2090
	11th to 20th	Day	11% 6% 2 5% 5% 4 4 4 5% 6% 49%	2214
	21st to end	Day	10% 3 1 5% 4 4 4 3 6% 8% 52%	2470
May	1st to 10th	Day	10% 7% 3 7% 4 4 4 4 6% 9% 42%	4082
	11th to 20th	Day	17% 7% 3 7% 5% 4 4 3 5% 8% 37%	4081
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 10% 46%	4476
June	1st to 10th	Day	9% 6% 2 7% 6% 6% 6% 5% 8% 11% 34%	2470
	11th to 20th	Day	6% 4 1 5% 5% 6% 5% 6% 8% 10% 43%	2470
	21st to end	Day	4 5% 2 6% 7% 7% 7% 6% 8% 10% 38%	2470
July	1st to 10th	Day	10% 7% 3 8% 6% 7% 8% 5% 8% 10% 29%	4120
	11th to 20th	Day	7% 4 2 7% 6% 7% 6% 5% 10% 12% 34%	4120
	21st to end	Day	10% 7% 3 10% 7% 7% 9% 6% 9% 12% 21%	4466
August	1st to 10th	Day	13% 6% 2 7% 6% 6% 7% 5% 9% 11% 29%	4104
	11th to 20th	Day	9% 5% 2 5% 5% 5% 5% 5% 8% 11% 40%	3995
	21st to end	Day	8% 4 2 6% 4 5% 5% 4 6% 8% 49%	4060
September	1st to 10th	Day	9% 6% 2 7% 6% 5% 5% 5% 6% 8% 40%	2090
	11th to 20th	Day	16% 6% 2 6% 4 5% 4 4 5% 7% 40%	2090
	21st to end	Day	16% 5% 2 5% 4 4 4 4 4 6% 46%	2090
October	1st to 10th	Day	13% 5% 2 5% 3 3 3 3 4 6% 53%	2090
	11th to 20th	Day	12% 4 2 3 3 3 3 3 4 6% 58%	1911
	21st to end	Day	10% 4 2 4 3 4 3 3 4 5% 57%	2090
November	1st to 10th	Day	14% 5% 2 5% 4 3 3 3 4 5% 53%	1890
	11th to 20th	Day	14% 5% 2 4 3 3 2 3 4 7% 53%	1800
	21st to end	Day	12% 5% 2 4 4 3 4 4 4 6% 50%	1800
December	1st to 10th	Day	15% 7% 2 5% 4 3 4 3 4 5% 48%	2930
	11th to 20th	Day	16% 7% 3 5% 4 3 4 3 5% 6% 45%	3373
	21st to end	Day	23% 5% 2 5% 3 3 3 2 5% 6% 43%	4466
January	1st to 10th	Night	14% 5% 2 5% 3 3 3 2 4 5% 54%	5889
	11th to 20th	Night	13% 6% 2 4 4 3 4 3 5% 6% 49%	5900
	21st to end	Night	16% 9% 2 5% 3 3 3 3 4 5% 46%	6490
February	1st to 10th	Night	15% 6% 2 5% 4 4 3 4 5% 6% 46%	2411
	11th to 20th	Night	19% 8% 2 6% 4 3 4 3 4 5% 43%	2338
	21st to end	Night	16% 6% 2 6% 4 4 4 3 4 6% 46%	1980
March	1st to 10th	Night	22% 8% 3 5% 3 4 4 3 5% 6% 37%	3623
	11th to 20th	Night	12% 5% 1 4 2 3 3 4 6% 8% 51%	3498
	21st to end	Night	19% 5% 2 6% 4 4 4 3 5% 6% 42%	3817
April	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 6% 7% 50%	2090
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 8% 52%	1926
	21st to end	Night	8% 5% 2 5% 4 4 4 4 5% 7% 53%	1710
May	1st to 10th	Night	8% 6% 2 6% 4 4 5% 5% 6% 10% 44%	2813
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 6% 8% 42%	2812
	21st to end	Night	6% 4 2 4 4 4 5% 5% 6% 10% 50%	3079
June	1st to 10th	Night	8% 6% 2 6% 5% 5% 6% 5% 8% 12% 35%	1710
	11th to 20th	Night	5% 5% 2 5% 6% 4 5% 5% 8% 11% 44%	1710
	21st to end	Night	7% 4 2 5% 6% 4 6% 7% 9% 11% 39%	1710
July	1st to 10th	Night	12% 6% 3 8% 5% 6% 6% 5% 8% 10% 31%	2840
	11th to 20th	Night	6% 5% 2 7% 6% 5% 7% 6% 10% 14% 31%	2840
	21st to end	Night	10% 9% 4 9% 7% 6% 7% 7% 10% 11% 22%	3087
August	1st to 10th	Night	12% 6% 2 9% 5% 6% 6% 6% 9% 12% 27%	2825
	11th to 20th	Night	11% 5% 2 5% 5% 5% 5% 5% 8% 11% 38%	2816
	21st to end	Night	7% 5% 2 5% 5% 5% 5% 4 6% 8% 47%	3562
September	1st to 10th	Night	9% 6% 2 6% 5% 4 5% 5% 7% 10% 40%	2090
	11th to 20th	Night	14% 7% 2 7% 5% 4 5% 3 6% 7% 40%	2090
	21st to end	Night	14% 4 2 6% 4 3 5% 3 5% 7% 47%	2090
October	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 6% 6% 52%	2090
	11th to 20th	Night	12% 5% 1 4 3 3 3 3 4 4 58%	2266
	21st to end	Night	10% 4 2 4 3 3 4 3 4 5% 59%	2508
November	1st to 10th	Night	12% 6% 2 5% 3 2 3 2 4 6% 54%	2406
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 6% 53%	2600
	21st to end	Night	14% 4 1 5% 4 4 4 4 5% 6% 50%	2600
December	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 3 5% 54%	4250
	11th to 20th	Night	18% 5% 2 5% 4 3 4 3 5% 6% 47%	4822
	21st to end	Night	21% 7% 2 5% 4 4 3 3 4 5% 42%	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	37% 4 4 20% 26% 9%	4057
	11th to 20th	Day	30% 3 4 20% 31% 12%	4060
	21st to end	Day	45% 2 3 18% 22% 10%	4466
February	1st to 10th	Day	42% 4 8% 21% 19% 7%	1985
	11th to 20th	Day	43% 3 6% 18% 22% 7%	1958
	21st to end	Day	43% 5% 7% 15% 22% 9%	1650
March	1st to 10th	Day	50% 5% 6% 14% 15% 11%	3448
	11th to 20th	Day	33% 6% 7% 16% 26% 12%	3491
	21st to end	Day	45% 4 6% 20% 20% 4	3815
April	1st to 10th	Day	35% 5% 9% 21% 22% 7%	2090
	11th to 20th	Day	36% 6% 8% 18% 23% 10%	2214
	21st to end	Day	30% 6% 9% 27% 24% 4	2470
May	1st to 10th	Day	36% 8% 13% 24% 16% 3	4120
	11th to 20th	Day	45% 6% 11% 23% 14% 1	4085
	21st to end	Day	30% 9% 16% 23% 21% 2	4489
June	1st to 10th	Day	39% 10% 17% 21% 11% 2	2470
	11th to 20th	Day	31% 9% 19% 25% 15% 1	2470
	21st to end	Day	35% 11% 17% 20% 12% 4	2470
July	1st to 10th	Day	44% 12% 18% 19% 6% 1	4055
	11th to 20th	Day	37% 13% 25% 20% 4 2	4051
	21st to end	Day	51% 14% 18% 13% 5%	4324
August	1st to 10th	Day	45% 9% 17% 25% 5%	4091
	11th to 20th	Day	34% 9% 18% 23% 14% 2	4034
	21st to end	Day	32% 8% 14% 25% 17% 5%	4060
September	1st to 10th	Day	39% 8% 14% 17% 17% 5%	2090
	11th to 20th	Day	42% 7% 10% 18% 21% 2	2090
	21st to end	Day	39% 4 10% 21% 19% 6%	2090
October	1st to 10th	Day	28% 4 5% 16% 36% 12%	3480
	11th to 20th	Day	19% 3 4 16% 30% 29%	3151
	21st to end	Day	25% 3 4 22% 32% 14%	3428
November	1st to 10th	Day	35% 4 7% 16% 27% 11%	1890
	11th to 20th	Day	32% 4 6% 21% 26% 10%	1800
	21st to end	Day	35% 5% 8% 19% 27% 7%	1800
December	1st to 10th	Day	38% 3 6% 16% 27% 10%	2930
	11th to 20th	Day	41% 5% 8% 19% 20% 8%	3370
	21st to end	Day	42% 4 7% 23% 22% 2	4466
January	1st to 10th	Night	33% 3 4 19% 31% 8%	5889
	11th to 20th	Night	34% 4 4 19% 29% 10%	5900
	21st to end	Night	41% 3 4 15% 29% 8%	6490
February	1st to 10th	Night	38% 4 9% 20% 21% 8%	2411
	11th to 20th	Night	44% 3 5% 18% 22% 8%	2339
	21st to end	Night	39% 5% 7% 16% 21% 12%	1980
March	1st to 10th	Night	47% 5% 10% 14% 16% 8%	3623
	11th to 20th	Night	30% 5% 8% 15% 28% 14%	3498
	21st to end	Night	42% 5% 6% 19% 17% 11%	3817
April	1st to 10th	Night	33% 6% 10% 19% 23% 9%	2090
	11th to 20th	Night	32% 4 7% 23% 24% 11%	1926
	21st to end	Night	30% 7% 10% 25% 22% 6%	1710
May	1st to 10th	Night	33% 10% 14% 23% 17% 3	2840
	11th to 20th	Night	40% 7% 12% 23% 17% 1	2813
	21st to end	Night	26% 8% 15% 26% 22% 3	3087
June	1st to 10th	Night	36% 11% 19% 20% 12% 2	1710
	11th to 20th	Night	31% 9% 19% 25% 13% 3	1710
	21st to end	Night	33% 12% 20% 19% 12% 4	1710
July	1st to 10th	Night	44% 13% 21% 15% 5% 2	2795
	11th to 20th	Night	37% 15% 23% 20% 4 1	2786
	21st to end	Night	51% 14% 18% 12% 4 1	2988
August	1st to 10th	Night	45% 9% 22% 20% 4	2814
	11th to 20th	Night	36% 11% 21% 20% 11% 1	2843
	21st to end	Night	33% 8% 13% 25% 18% 3	3562
September	1st to 10th	Night	36% 11% 15% 17% 17% 4	2090
	11th to 20th	Night	42% 8% 12% 16% 18% 4	2090
	21st to end	Night	36% 6% 12% 18% 22% 7%	2090
October	1st to 10th	Night	28% 5% 8% 15% 35% 8%	3480
	11th to 20th	Night	19% 2 5% 16% 27% 31%	3765
	21st to end	Night	22% 4 4 20% 31% 18%	4120
November	1st to 10th	Night	33% 4 7% 19% 25% 13%	2406
	11th to 20th	Night	34% 3 6% 18% 26% 13%	2600
	21st to end	Night	34% 5% 7% 19% 26% 9%	2600
December	1st to 10th	Night	35% 4 5% 16% 32% 8%	4250
	11th to 20th	Night	39% 4 12% 16% 22% 7%	4824
	21st to end	Night	44% 4 5% 26% 19% 2	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	26% 19% 38% 14% 3	300
	11th to 20th	Day	27% 17% 34% 16% 6%	300
	21st to end	Day	24% 25% 38% 9% 4	330
February	1st to 10th	Day	21% 20% 37% 19% 4	300
	11th to 20th	Day	38% 16% 31% 14% 1	300
	21st to end	Day	29% 19% 39% 12% 2	249
March	1st to 10th	Day	24% 15% 30% 24% 7%	437
	11th to 20th	Day	22% 15% 38% 18% 6% 1	464
	21st to end	Day	20% 17% 34% 20% 8%	506
April	1st to 10th	Day	21% 15% 30% 23% 10% 1	460
	11th to 20th	Day	15% 14% 34% 23% 13% 2	452
	21st to end	Day	13% 11% 30% 26% 17% 3	460
May	1st to 10th	Day	12% 14% 32% 21% 15% 5%	463
	11th to 20th	Day	15% 5% 22% 30% 19% 9%	487
	21st to end	Day	13% 5% 18% 28% 24% 12%	529
June	1st to 10th	Day	11% 4 18% 29% 28% 9%	490
	11th to 20th	Day	6% 5% 18% 27% 24% 21%	490
	21st to end	Day	5% 4 19% 32% 24% 15%	490
July	1st to 10th	Day	7% 2 11% 26% 31% 23%	485
	11th to 20th	Day	9% 2 8% 25% 38% 19%	484
	21st to end	Day	6% 1 10% 30% 34% 19%	532
August	1st to 10th	Day	14% 3 15% 24% 26% 18%	486
	11th to 20th	Day	11% 4 9% 26% 34% 17%	479
	21st to end	Day	11% 4 12% 24% 32% 17%	539
September	1st to 10th	Day	10% 3 15% 27% 33% 12%	490
	11th to 20th	Day	18% 3 12% 23% 33% 9%	490
	21st to end	Day	17% 4 17% 26% 26% 9%	490
October	1st to 10th	Day	17% 3 25% 30% 16% 9%	490
	11th to 20th	Day	12% 10% 24% 27% 21% 6%	490
	21st to end	Day	15% 9% 24% 28% 20% 4	539
November	1st to 10th	Day	21% 9% 24% 29% 15% 3	428
	11th to 20th	Day	16% 16% 38% 24% 5% 2	300
	21st to end	Day	13% 16% 35% 23% 11% 2	300
December	1st to 10th	Day	28% 18% 32% 17% 4 1	300
	11th to 20th	Day	26% 13% 35% 20% 5% 1	300
	21st to end	Day	32% 17% 26% 16% 6% 2	330
January	1st to 10th	Night	22% 20% 31% 23% 5%	800
	11th to 20th	Night	22% 17% 29% 23% 9%	800
	21st to end	Night	22% 17% 33% 26% 3	880
February	1st to 10th	Night	19% 13% 31% 32% 5%	800
	11th to 20th	Night	24% 16% 32% 25% 3	783
	21st to end	Night	21% 16% 33% 28% 3	660
March	1st to 10th	Night	17% 16% 32% 29% 5%	800
	11th to 20th	Night	17% 14% 33% 26% 10% 1	767
	21st to end	Night	18% 14% 30% 29% 9%	836
April	1st to 10th	Night	16% 14% 31% 27% 11%	760
	11th to 20th	Night	15% 12% 28% 29% 15% 1	654
	21st to end	Night	12% 7% 28% 34% 19% 1	570
May	1st to 10th	Night	10% 9% 26% 35% 20% 1	570
	11th to 20th	Night	11% 6% 22% 34% 25% 3	561
	21st to end	Night	12% 2 12% 35% 33% 5%	617
June	1st to 10th	Night	11% 3 15% 35% 31% 5%	570
	11th to 20th	Night	7% 3 15% 30% 35% 11%	570
	21st to end	Night	8% 2 12% 37% 33% 8%	570
July	1st to 10th	Night	10% 2 8% 28% 39% 13%	555
	11th to 20th	Night	9% 1 5% 30% 43% 12%	552
	21st to end	Night	6% 3 9% 31% 43% 8%	624
August	1st to 10th	Night	10% 2 9% 29% 40% 9%	567
	11th to 20th	Night	13% 3 6% 31% 41% 7%	564
	21st to end	Night	13% 4 7% 30% 36% 10%	674
September	1st to 10th	Night	11% 3 10% 30% 38% 8%	760
	11th to 20th	Night	17% 4 12% 26% 36% 5%	760
	21st to end	Night	16% 4 14% 30% 33% 3	760
October	1st to 10th	Night	14% 3 18% 33% 26% 6%	760
	11th to 20th	Night	14% 6% 23% 31% 23% 3	760
	21st to end	Night	12% 9% 21% 31% 24% 2	836
November	1st to 10th	Night	15% 7% 21% 34% 20% 2	780
	11th to 20th	Night	17% 10% 29% 30% 14% 1	800
	21st to end	Night	16% 11% 26% 31% 14% 2	800
December	1st to 10th	Night	19% 17% 25% 31% 8% 1	800
	11th to 20th	Night	20% 12% 28% 28% 11% 1	800
	21st to end	Night	29% 12% 24% 28% 6%	880

Page generated at 2025-03-09 08:08:45. Version ac07

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