Skyline Rd
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Skyline Rd clear sky chart from 2005-11-06 to 2026-01-17.

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	5% 6% 2 6% 4 4 4 4 5% 7% 51%	136590
	Night	6% 7% 3 7% 5% 4 5% 4 6% 7% 47%	132434
Transparency	Day	31% 8% 13% 23% 17% 7%	131338
	Night	34% 9% 15% 23% 14% 5%	128685
Seeing	Day	11% 17% 29% 27% 13% 3	15971
	Night	9% 10% 26% 35% 17% 2	25071

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	12% 14% 6% 13% 7% 7% 7% 5% 6% 8% 15%	3719
	11th to 20th	Day	8% 12% 4 7% 5% 5% 5% 4 6% 6% 41%	3688
	21st to end	Day	9% 12% 4 12% 6% 6% 5% 3 4 6% 32%	4206
February	1st to 10th	Day	8% 12% 4 9% 7% 7% 6% 4 7% 8% 28%	1800
	11th to 20th	Day	7% 11% 3 8% 5% 5% 6% 5% 8% 10% 32%	1755
	21st to end	Day	6% 9% 3 10% 6% 7% 5% 5% 7% 9% 33%	1629
March	1st to 10th	Day	5% 9% 3 9% 6% 5% 6% 6% 8% 10% 32%	4554
	11th to 20th	Day	7% 12% 4 9% 5% 5% 5% 4 5% 5% 39%	5000
	21st to end	Day	7% 10% 4 11% 7% 8% 8% 6% 7% 8% 24%	5739
April	1st to 10th	Day	8% 9% 3 8% 6% 8% 5% 5% 7% 10% 31%	2400
	11th to 20th	Day	6% 8% 4 8% 7% 5% 6% 4 6% 8% 38%	2369
	21st to end	Day	5% 6% 2 6% 4 5% 6% 6% 7% 10% 43%	2539
May	1st to 10th	Day	7% 5% 1 5% 3 3 3 3 5% 7% 58%	6320
	11th to 20th	Day	4 4 2 5% 4 4 4 4 4 8% 56%	6277
	21st to end	Day	5% 4 2 5% 4 4 5% 3 6% 9% 53%	6902
June	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 3 7% 8% 47%	2800
	11th to 20th	Day	4 4 2 5% 4 4 5% 4 5% 8% 55%	2800
	21st to end	Day	3 2 1 4 3 3 4 4 5% 6% 66%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 2 3 4 83%	6319
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 3 86%	6320
	21st to end	Day	2 1 1 2 1 2 2 2 3 4 81%	6880
August	1st to 10th	Day	2 2 1 3 2 3 3 3 4 6% 72%	6042
	11th to 20th	Day	2 2 1 3 2 3 3 3 5% 6% 70%	5796
	21st to end	Day	4 4 2 4 3 3 3 3 5% 6% 63%	6014
September	1st to 10th	Day	3 1 1 3 2 2 3 2 5% 6% 74%	2400
	11th to 20th	Day	2 3 1 5% 4 4 4 4 6% 7% 59%	2400
	21st to end	Day	5% 5% 2 6% 4 4 4 3 4 6% 58%	2137
October	1st to 10th	Day	5% 4 2 5% 3 3 3 3 5% 5% 63%	3280
	11th to 20th	Day	5% 3 2 6% 5% 5% 5% 5% 8% 9% 46%	3261
	21st to end	Day	8% 7% 3 9% 7% 5% 5% 5% 6% 8% 38%	3363
November	1st to 10th	Day	8% 10% 3 8% 8% 6% 6% 4 6% 8% 31%	1821
	11th to 20th	Day	7% 13% 4 9% 8% 6% 8% 6% 8% 8% 23%	1680
	21st to end	Day	6% 13% 4 7% 6% 6% 5% 5% 6% 9% 33%	1680
December	1st to 10th	Day	7% 8% 4 8% 5% 4 5% 3 5% 5% 45%	2700
	11th to 20th	Day	10% 15% 6% 12% 8% 7% 7% 6% 6% 7% 16%	3108
	21st to end	Day	9% 14% 5% 12% 8% 6% 6% 6% 7% 7% 21%	4092
January	1st to 10th	Night	14% 14% 7% 14% 7% 6% 7% 5% 6% 6% 14%	6446
	11th to 20th	Night	8% 11% 3 7% 5% 4 4 3 4 7% 44%	6404
	21st to end	Night	9% 12% 4 10% 6% 6% 5% 4 4 5% 35%	6756
February	1st to 10th	Night	7% 11% 4 9% 6% 6% 6% 4 6% 8% 33%	2600
	11th to 20th	Night	7% 11% 4 8% 5% 5% 6% 4 6% 7% 38%	2532
	21st to end	Night	7% 10% 3 8% 6% 5% 4 5% 6% 9% 38%	2000
March	1st to 10th	Night	4 6% 3 7% 6% 6% 6% 6% 9% 11% 37%	5337
	11th to 20th	Night	5% 8% 3 8% 6% 6% 5% 4 6% 7% 42%	5000
	21st to end	Night	8% 8% 3 8% 7% 6% 7% 6% 9% 11% 29%	5236
April	1st to 10th	Night	7% 8% 3 7% 6% 5% 6% 5% 7% 9% 37%	2000
	11th to 20th	Night	5% 7% 2 6% 4 6% 5% 4 6% 9% 45%	1979
	21st to end	Night	6% 6% 2 6% 4 4 4 4 8% 10% 47%	1860
May	1st to 10th	Night	8% 5% 1 4 3 2 3 2 4 5% 63%	3640
	11th to 20th	Night	4 3 1 4 4 4 4 4 6% 8% 59%	3616
	21st to end	Night	5% 4 1 4 3 3 4 4 6% 11% 55%	3972
June	1st to 10th	Night	7% 6% 2 5% 5% 5% 4 5% 6% 8% 49%	1600
	11th to 20th	Night	4 4 2 4 4 3 4 4 5% 8% 59%	1600
	21st to end	Night	2 3 2 4 3 3 3 3 4 4 69%	1600
July	1st to 10th	Night	1 1 2 2 1 2 2 4 4 82%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 2 4 85%	3640
	21st to end	Night	1 1 1 1 1 1 2 3 5% 83%	3970
August	1st to 10th	Night	2 2 1 3 2 3 3 3 5% 7% 69%	3755
	11th to 20th	Night	3 2 1 3 3 3 3 2 4 5% 72%	4052
	21st to end	Night	2 2 1 4 3 3 4 3 4 6% 68%	4983
September	1st to 10th	Night	1 2 1 2 2 2 3 2 4 5% 76%	2000
	11th to 20th	Night	3 2 1 3 5% 3 3 4 6% 8% 62%	2000
	21st to end	Night	4 4 2 4 3 3 3 4 5% 7% 62%	2260
October	1st to 10th	Night	4 3 1 4 3 2 3 3 5% 7% 67%	3920
	11th to 20th	Night	4 4 2 5% 4 4 6% 4 8% 10% 50%	3897
	21st to end	Night	8% 5% 2 6% 5% 5% 6% 5% 7% 9% 42%	4440
November	1st to 10th	Night	9% 8% 3 9% 7% 6% 6% 5% 7% 6% 34%	2697
	11th to 20th	Night	8% 11% 4 9% 6% 6% 6% 6% 6% 8% 30%	2940
	21st to end	Night	6% 10% 3 8% 6% 6% 7% 5% 8% 7% 35%	2940
December	1st to 10th	Night	6% 7% 3 7% 5% 5% 5% 4 5% 6% 48%	4700
	11th to 20th	Night	11% 15% 6% 11% 7% 7% 7% 5% 6% 7% 18%	5316
	21st to end	Night	10% 13% 6% 12% 7% 6% 6% 4 6% 6% 25%	7106

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	60% 14% 15% 9% 2	3719
	11th to 20th	Day	43% 9% 15% 24% 8% 1	3688
	21st to end	Day	47% 11% 12% 18% 10% 2	4206
February	1st to 10th	Day	51% 14% 17% 14% 4 1	1800
	11th to 20th	Day	43% 16% 19% 16% 6% 1	1764
	21st to end	Day	46% 13% 17% 15% 9%	1629
March	1st to 10th	Day	37% 11% 16% 21% 13%	4554
	11th to 20th	Day	44% 8% 11% 27% 9%	5000
	21st to end	Day	50% 14% 16% 15% 5%	5739
April	1st to 10th	Day	44% 11% 18% 18% 8%	2400
	11th to 20th	Day	42% 9% 17% 17% 13% 2	2372
	21st to end	Day	32% 13% 19% 23% 10% 2	2539
May	1st to 10th	Day	25% 7% 11% 32% 23% 2	6320
	11th to 20th	Day	25% 7% 15% 31% 19% 3	6280
	21st to end	Day	26% 10% 23% 32% 9%	6904
June	1st to 10th	Day	33% 8% 16% 27% 14% 2	2800
	11th to 20th	Day	27% 7% 16% 33% 14% 3	2800
	21st to end	Day	18% 5% 14% 35% 21% 7%	2800
July	1st to 10th	Day	8% 2 5% 20% 32% 32%	6251
	11th to 20th	Day	7% 2 3 12% 34% 42%	6245
	21st to end	Day	9% 3 8% 31% 31% 18%	6681
August	1st to 10th	Day	13% 3 6% 20% 34% 23%	4401
	11th to 20th	Day	14% 5% 11% 38% 25% 7%	4195
	21st to end	Day	19% 5% 11% 25% 33% 7%	4329
September	1st to 10th	Day	13% 4 10% 31% 28% 14%	2400
	11th to 20th	Day	23% 6% 13% 28% 22% 7%	2400
	21st to end	Day	27% 6% 14% 28% 19% 6%	2137
October	1st to 10th	Day	23% 6% 11% 31% 26% 3	3280
	11th to 20th	Day	31% 10% 19% 23% 16% 1	3261
	21st to end	Day	41% 9% 14% 25% 10% 1	3363
November	1st to 10th	Day	47% 12% 17% 17% 6%	1821
	11th to 20th	Day	53% 17% 14% 12% 4	1680
	21st to end	Day	45% 12% 19% 17% 7% 1	1680
December	1st to 10th	Day	38% 10% 15% 25% 12%	2700
	11th to 20th	Day	60% 14% 15% 9% 2	3108
	21st to end	Day	56% 13% 16% 12% 3	4092
January	1st to 10th	Night	65% 13% 12% 8% 2	6446
	11th to 20th	Night	41% 7% 17% 27% 7%	6404
	21st to end	Night	47% 11% 11% 19% 11%	6756
February	1st to 10th	Night	46% 13% 19% 17% 4 1	2600
	11th to 20th	Night	42% 12% 19% 19% 8%	2534
	21st to end	Night	42% 12% 18% 20% 8% 1	2000
March	1st to 10th	Night	34% 10% 16% 26% 14% 1	5337
	11th to 20th	Night	36% 9% 15% 29% 11%	5000
	21st to end	Night	42% 16% 22% 17% 3	5236
April	1st to 10th	Night	38% 13% 19% 22% 8% 1	2000
	11th to 20th	Night	34% 10% 20% 22% 12% 3	1979
	21st to end	Night	30% 12% 18% 27% 12% 2	1860
May	1st to 10th	Night	24% 5% 9% 29% 32% 1	3637
	11th to 20th	Night	22% 6% 17% 30% 23% 2	3616
	21st to end	Night	22% 9% 27% 32% 10% 1	3972
June	1st to 10th	Night	33% 8% 13% 30% 14% 2	1600
	11th to 20th	Night	23% 6% 17% 35% 17% 3	1600
	21st to end	Night	19% 5% 11% 35% 23% 8%	1600
July	1st to 10th	Night	9% 2 7% 18% 31% 33%	3600
	11th to 20th	Night	7% 2 6% 10% 31% 44%	3592
	21st to end	Night	7% 2 6% 31% 33% 22%	3857
August	1st to 10th	Night	13% 3 6% 17% 37% 24%	2725
	11th to 20th	Night	14% 3 9% 39% 25% 10%	2929
	21st to end	Night	13% 5% 12% 28% 31% 11%	3589
September	1st to 10th	Night	12% 4 11% 31% 27% 15%	2000
	11th to 20th	Night	20% 8% 12% 28% 21% 11%	2000
	21st to end	Night	21% 6% 13% 31% 21% 7%	2260
October	1st to 10th	Night	18% 5% 11% 36% 27% 3	3920
	11th to 20th	Night	27% 9% 21% 26% 15% 2	3897
	21st to end	Night	34% 10% 15% 28% 12% 1	4440
November	1st to 10th	Night	44% 12% 15% 20% 8%	2697
	11th to 20th	Night	47% 14% 16% 18% 5%	2940
	21st to end	Night	42% 12% 19% 21% 6% 1	2940
December	1st to 10th	Night	34% 11% 17% 31% 8%	4700
	11th to 20th	Night	61% 12% 15% 10% 2	5316
	21st to end	Night	53% 14% 15% 13% 5%	7106

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	21% 20% 28% 20% 9% 1	220
	11th to 20th	Day	18% 13% 27% 29% 11% 2	212
	21st to end	Day	14% 17% 28% 26% 13% 1	305
February	1st to 10th	Day	15% 23% 32% 23% 7% 1	400
	11th to 20th	Day	16% 24% 31% 22% 6%	395
	21st to end	Day	19% 22% 30% 23% 6%	404
March	1st to 10th	Day	15% 21% 36% 21% 5% 1	500
	11th to 20th	Day	15% 19% 33% 23% 10% 1	500
	21st to end	Day	20% 22% 31% 22% 6%	550
April	1st to 10th	Day	20% 23% 27% 19% 9% 1	500
	11th to 20th	Day	15% 25% 32% 18% 8% 3	492
	21st to end	Day	11% 23% 33% 21% 11% 2	500
May	1st to 10th	Day	13% 20% 30% 23% 12% 2	503
	11th to 20th	Day	16% 17% 29% 23% 12% 3	528
	21st to end	Day	11% 16% 29% 27% 14% 3	573
June	1st to 10th	Day	9% 20% 27% 27% 12% 5%	530
	11th to 20th	Day	12% 23% 31% 24% 8% 2	530
	21st to end	Day	5% 13% 32% 30% 16% 3	530
July	1st to 10th	Day	3 10% 33% 36% 16% 2	526
	11th to 20th	Day	2 13% 31% 31% 18% 5%	524
	21st to end	Day	2 8% 29% 35% 20% 6%	575
August	1st to 10th	Day	2 8% 28% 32% 22% 8%	527
	11th to 20th	Day	2 8% 26% 33% 23% 8%	517
	21st to end	Day	4 10% 30% 32% 18% 7%	583
September	1st to 10th	Day	4 9% 26% 32% 24% 6%	530
	11th to 20th	Day	5% 10% 27% 35% 20% 2	530
	21st to end	Day	8% 15% 27% 30% 17% 2	530
October	1st to 10th	Day	11% 14% 27% 27% 19% 2	530
	11th to 20th	Day	12% 16% 25% 28% 16% 3	530
	21st to end	Day	14% 20% 29% 22% 12% 3	463
November	1st to 10th	Day	18% 16% 25% 29% 11% 1	312
	11th to 20th	Day	18% 17% 29% 25% 9% 1	220
	21st to end	Day	16% 14% 24% 31% 13% 1	220
December	1st to 10th	Day	14% 17% 23% 27% 15% 5%	220
	11th to 20th	Day	15% 22% 34% 23% 5% 1	220
	21st to end	Day	15% 24% 25% 27% 9%	242
January	1st to 10th	Night	17% 15% 25% 29% 13% 1	840
	11th to 20th	Night	14% 12% 27% 31% 14% 2	824
	21st to end	Night	15% 10% 24% 32% 17% 2	880
February	1st to 10th	Night	11% 17% 26% 31% 14% 1	800
	11th to 20th	Night	15% 15% 25% 29% 15% 1	784
	21st to end	Night	15% 15% 28% 31% 10% 1	660
March	1st to 10th	Night	11% 16% 27% 32% 14% 1	800
	11th to 20th	Night	9% 12% 29% 35% 15% 1	800
	21st to end	Night	11% 17% 29% 31% 10% 1	880
April	1st to 10th	Night	12% 15% 28% 30% 14% 1	800
	11th to 20th	Night	10% 15% 33% 25% 15% 3	791
	21st to end	Night	8% 12% 32% 32% 15% 1	660
May	1st to 10th	Night	7% 12% 32% 31% 16% 1	400
	11th to 20th	Night	6% 9% 28% 35% 20% 3	394
	21st to end	Night	6% 6% 27% 43% 16% 2	433
June	1st to 10th	Night	9% 12% 26% 39% 14% 1	400
	11th to 20th	Night	4 12% 38% 35% 11% 1	400
	21st to end	Night	5% 4 29% 46% 16% 1	400
July	1st to 10th	Night	1 3 28% 50% 17% 1	390
	11th to 20th	Night	1 2 33% 50% 13% 2	388
	21st to end	Night	1 2 25% 50% 20% 2	438
August	1st to 10th	Night	1 2 22% 49% 24% 3	470
	11th to 20th	Night	3 2 15% 40% 32% 8%	594
	21st to end	Night	2 4 26% 42% 22% 4	861
September	1st to 10th	Night	2 6% 20% 42% 28% 4	800
	11th to 20th	Night	4 3 21% 38% 28% 5%	800
	21st to end	Night	5% 7% 22% 36% 26% 4	800
October	1st to 10th	Night	9% 4 25% 37% 23% 3	800
	11th to 20th	Night	7% 9% 24% 34% 23% 4	800
	21st to end	Night	12% 10% 26% 33% 16% 3	880
November	1st to 10th	Night	12% 10% 26% 36% 14% 1	820
	11th to 20th	Night	14% 15% 27% 30% 12% 1	840
	21st to end	Night	10% 11% 25% 35% 17% 2	840
December	1st to 10th	Night	13% 11% 26% 31% 18% 2	840
	11th to 20th	Night	15% 12% 28% 31% 13% 1	840
	21st to end	Night	14% 16% 31% 29% 9% 1	924

Page generated at 2026-01-13 22:14:24. Version ac07

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