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 2024-11-25.

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% 5% 4 5% 4 5% 7% 50%	105562
	Night	6% 7% 3 7% 5% 4 5% 4 6% 7% 46%	102603
Transparency	Day	32% 9% 13% 22% 16% 8%	105305
	Night	34% 10% 15% 22% 13% 6%	102449
Seeing	Day	11% 17% 29% 27% 13% 3	14603
	Night	10% 11% 26% 34% 17% 2	23620

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	10% 13% 6% 12% 7% 6% 6% 5% 7% 9% 19%	2539
	11th to 20th	Day	11% 17% 5% 9% 6% 6% 7% 5% 7% 6% 21%	2540
	21st to end	Day	12% 16% 6% 15% 7% 7% 6% 4 4 6% 15%	2926
February	1st to 10th	Day	7% 12% 4 9% 7% 7% 6% 4 7% 8% 29%	1710
	11th to 20th	Day	7% 11% 3 8% 6% 5% 6% 5% 8% 10% 32%	1665
	21st to end	Day	6% 10% 3 9% 6% 7% 5% 5% 7% 9% 33%	1550
March	1st to 10th	Day	4 10% 4 10% 7% 6% 6% 6% 8% 10% 29%	3161
	11th to 20th	Day	4 8% 3 7% 5% 5% 5% 4 6% 6% 49%	3490
	21st to end	Day	6% 10% 4 12% 8% 7% 8% 5% 6% 7% 27%	4000
April	1st to 10th	Day	8% 9% 3 8% 6% 8% 5% 5% 7% 9% 31%	2280
	11th to 20th	Day	6% 9% 4 9% 7% 5% 6% 4 6% 8% 36%	2249
	21st to end	Day	5% 6% 2 6% 4 6% 6% 7% 7% 10% 42%	2411
May	1st to 10th	Day	9% 6% 2 6% 4 4 4 3 6% 6% 51%	4420
	11th to 20th	Day	4 3 1 3 3 3 3 3 4 6% 65%	4377
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 4 7% 9% 45%	4813
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 8% 45%	2660
	11th to 20th	Day	4 4 2 6% 4 4 5% 4 5% 8% 54%	2660
	21st to end	Day	3 2 1 4 3 3 4 3 5% 6% 66%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 3 4 84%	4420
	11th to 20th	Day	1 1 1 2 1 2 2 2 3 3 83%	4420
	21st to end	Day	1 1 1 2 1 2 2 2 3 4 82%	4790
August	1st to 10th	Day	2 2 1 2 2 3 2 2 4 5% 75%	4281
	11th to 20th	Day	1 1 1 3 2 3 4 3 5% 7% 70%	4026
	21st to end	Day	3 3 1 5% 3 3 3 3 4 5% 68%	4197
September	1st to 10th	Day	3 1 3 2 2 3 2 4 5% 76%	2280
	11th to 20th	Day	3 3 1 5% 5% 4 5% 4 6% 7% 58%	2280
	21st to end	Day	5% 5% 2 6% 4 4 4 3 5% 6% 58%	2030
October	1st to 10th	Day	5% 4 2 5% 3 2 3 3 5% 5% 63%	3180
	11th to 20th	Day	5% 3 2 6% 5% 5% 5% 5% 8% 9% 46%	3161
	21st to end	Day	8% 7% 3 9% 7% 5% 5% 5% 6% 8% 38%	3259
November	1st to 10th	Day	8% 10% 3 9% 8% 6% 6% 4 7% 8% 30%	1733
	11th to 20th	Day	7% 13% 4 9% 8% 7% 8% 6% 8% 8% 23%	1600
	21st to end	Day	6% 12% 4 7% 6% 7% 5% 5% 7% 9% 33%	1552
December	1st to 10th	Day	8% 13% 6% 11% 7% 5% 6% 4 6% 5% 30%	1520
	11th to 20th	Day	7% 14% 5% 13% 9% 8% 8% 7% 7% 6% 16%	1928
	21st to end	Day	9% 15% 6% 14% 9% 6% 6% 5% 5% 6% 20%	2794
January	1st to 10th	Night	10% 13% 7% 13% 7% 6% 6% 5% 7% 7% 18%	4406
	11th to 20th	Night	11% 16% 5% 10% 7% 6% 5% 4 5% 7% 24%	4420
	21st to end	Night	12% 15% 6% 13% 8% 8% 6% 5% 5% 6% 17%	4731
February	1st to 10th	Night	7% 10% 4 9% 6% 6% 5% 4 6% 9% 33%	2470
	11th to 20th	Night	7% 10% 3 8% 5% 5% 6% 4 6% 7% 38%	2402
	21st to end	Night	6% 10% 3 8% 6% 5% 4 5% 7% 9% 37%	1903
March	1st to 10th	Night	4 7% 3 8% 6% 5% 6% 6% 9% 11% 35%	3710
	11th to 20th	Night	4 6% 2 6% 6% 4 4 4 5% 7% 53%	3490
	21st to end	Night	7% 8% 3 8% 7% 6% 7% 6% 8% 10% 31%	3653
April	1st to 10th	Night	7% 8% 3 7% 6% 5% 6% 5% 7% 9% 36%	1900
	11th to 20th	Night	5% 7% 2 6% 5% 6% 6% 4 6% 9% 43%	1879
	21st to end	Night	6% 6% 2 6% 4 4 4 5% 8% 10% 45%	1768
May	1st to 10th	Night	9% 6% 2 5% 4 3 3 3 5% 5% 55%	2540
	11th to 20th	Night	4 3 1 3 3 3 3 3 5% 7% 66%	2516
	21st to end	Night	3 5% 1 4 4 4 5% 4 7% 11% 52%	2762
June	1st to 10th	Night	7% 6% 2 6% 6% 5% 4 5% 6% 8% 46%	1520
	11th to 20th	Night	4 5% 2 4 4 3 4 4 5% 8% 59%	1520
	21st to end	Night	2 3 2 4 3 3 3 3 4 4 69%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 3 3 86%	2540
	11th to 20th	Night	1 2 1 1 1 1 2 2 3 4 83%	2540
	21st to end	Night	1 1 1 1 1 1 1 2 3 86%	2761
August	1st to 10th	Night	2 2 1 3 1 2 2 2 4 5% 75%	2649
	11th to 20th	Night	1 1 1 3 2 3 3 2 4 5% 74%	2812
	21st to end	Night	1 2 1 3 2 3 3 2 4 5% 74%	3480
September	1st to 10th	Night	1 1 1 2 2 2 3 2 4 5% 78%	1900
	11th to 20th	Night	3 2 1 4 5% 3 4 4 7% 8% 61%	1900
	21st to end	Night	4 4 2 5% 3 3 3 3 5% 7% 61%	2147
October	1st to 10th	Night	4 3 1 4 3 2 3 3 5% 7% 67%	3800
	11th to 20th	Night	4 3 2 5% 4 4 6% 4 8% 10% 50%	3777
	21st to end	Night	8% 5% 2 7% 5% 5% 6% 5% 7% 8% 41%	4302
November	1st to 10th	Night	8% 8% 3 9% 7% 6% 6% 5% 6% 6% 35%	2565
	11th to 20th	Night	8% 11% 4 9% 6% 6% 6% 6% 6% 8% 30%	2800
	21st to end	Night	5% 10% 3 9% 6% 6% 7% 5% 8% 7% 34%	2722
December	1st to 10th	Night	9% 12% 4 9% 7% 6% 5% 5% 6% 6% 31%	2660
	11th to 20th	Night	9% 15% 5% 11% 7% 7% 7% 6% 6% 7% 20%	3276
	21st to end	Night	8% 13% 6% 13% 7% 6% 6% 4 6% 7% 23%	4862

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	55% 16% 17% 11% 2	2539
	11th to 20th	Day	60% 12% 15% 11% 2	2540
	21st to end	Day	61% 14% 14% 7% 3	2926
February	1st to 10th	Day	50% 15% 17% 14% 3 1	1710
	11th to 20th	Day	42% 16% 19% 16% 6% 1	1674
	21st to end	Day	47% 13% 17% 14% 8%	1550
March	1st to 10th	Day	39% 13% 17% 24% 8%	3161
	11th to 20th	Day	34% 8% 14% 34% 10%	3490
	21st to end	Day	48% 15% 15% 16% 6%	4000
April	1st to 10th	Day	45% 11% 18% 18% 8%	2280
	11th to 20th	Day	44% 9% 17% 15% 13% 2	2252
	21st to end	Day	33% 14% 20% 21% 10% 2	2411
May	1st to 10th	Day	31% 9% 13% 28% 18%	4420
	11th to 20th	Day	21% 5% 11% 33% 26% 4	4380
	21st to end	Day	33% 13% 23% 25% 6%	4814
June	1st to 10th	Day	35% 9% 16% 26% 13% 2	2660
	11th to 20th	Day	28% 8% 16% 33% 12% 3	2660
	21st to end	Day	18% 5% 13% 35% 21% 7%	2660
July	1st to 10th	Day	7% 3 7% 16% 23% 44%	4351
	11th to 20th	Day	8% 2 4 11% 25% 48%	4345
	21st to end	Day	8% 3 7% 20% 36% 26%	4639
August	1st to 10th	Day	13% 3 6% 20% 34% 24%	4265
	11th to 20th	Day	14% 5% 11% 38% 25% 7%	4065
	21st to end	Day	19% 5% 11% 25% 33% 6%	4196
September	1st to 10th	Day	12% 4 9% 32% 29% 14%	2280
	11th to 20th	Day	24% 6% 14% 27% 22% 7%	2280
	21st to end	Day	27% 6% 15% 28% 18% 6%	2030
October	1st to 10th	Day	23% 6% 10% 31% 27% 3	3180
	11th to 20th	Day	31% 10% 19% 23% 16% 1	3161
	21st to end	Day	41% 9% 14% 25% 10% 1	3259
November	1st to 10th	Day	47% 12% 17% 18% 7%	1733
	11th to 20th	Day	53% 18% 13% 12% 4	1600
	21st to end	Day	45% 13% 17% 17% 7% 1	1552
December	1st to 10th	Day	52% 12% 13% 16% 6%	1520
	11th to 20th	Day	57% 16% 16% 8% 2	1928
	21st to end	Day	60% 14% 14% 10% 2	2794
January	1st to 10th	Night	60% 12% 16% 9% 3	4406
	11th to 20th	Night	57% 10% 18% 11% 3	4420
	21st to end	Night	59% 15% 13% 9% 2	4731
February	1st to 10th	Night	46% 13% 20% 17% 3	2470
	11th to 20th	Night	41% 12% 20% 19% 8%	2404
	21st to end	Night	42% 12% 18% 19% 8% 1	1903
March	1st to 10th	Night	35% 11% 17% 27% 10% 1	3710
	11th to 20th	Night	27% 9% 16% 35% 11%	3490
	21st to end	Night	42% 17% 19% 18% 4	3653
April	1st to 10th	Night	39% 13% 19% 20% 8% 1	1900
	11th to 20th	Night	35% 10% 20% 21% 11% 3	1879
	21st to end	Night	31% 12% 19% 25% 11% 2	1768
May	1st to 10th	Night	30% 7% 12% 30% 19% 1	2540
	11th to 20th	Night	18% 5% 13% 30% 32% 3	2516
	21st to end	Night	22% 12% 33% 27% 5% 1	2762
June	1st to 10th	Night	35% 9% 13% 29% 12% 2	1520
	11th to 20th	Night	23% 6% 17% 35% 15% 3	1520
	21st to end	Night	19% 5% 10% 35% 24% 8%	1520
July	1st to 10th	Night	6% 2 7% 15% 27% 43%	2500
	11th to 20th	Night	9% 2 6% 12% 22% 49%	2492
	21st to end	Night	6% 2 6% 19% 36% 32%	2674
August	1st to 10th	Night	13% 3 6% 16% 38% 24%	2641
	11th to 20th	Night	14% 3 9% 40% 25% 9%	2839
	21st to end	Night	13% 5% 13% 28% 31% 11%	3480
September	1st to 10th	Night	10% 4 11% 31% 28% 16%	1900
	11th to 20th	Night	20% 8% 12% 28% 20% 12%	1900
	21st to end	Night	22% 6% 13% 31% 21% 7%	2147
October	1st to 10th	Night	18% 5% 11% 36% 28% 3	3800
	11th to 20th	Night	27% 9% 21% 26% 15% 2	3777
	21st to end	Night	35% 10% 14% 28% 12% 1	4302
November	1st to 10th	Night	44% 12% 14% 21% 9%	2565
	11th to 20th	Night	47% 14% 16% 18% 5%	2800
	21st to end	Night	42% 12% 18% 21% 6% 1	2722
December	1st to 10th	Night	50% 13% 17% 16% 4	2660
	11th to 20th	Night	57% 13% 17% 11% 2	3276
	21st to end	Night	53% 15% 14% 13% 4	4862

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	22% 20% 28% 18% 9% 2	180
	11th to 20th	Day	20% 16% 28% 26% 9% 1	180
	21st to end	Day	15% 19% 28% 26% 12% 1	278
February	1st to 10th	Day	15% 23% 31% 23% 7% 1	370
	11th to 20th	Day	16% 26% 30% 21% 6%	365
	21st to end	Day	18% 23% 29% 23% 6%	373
March	1st to 10th	Day	15% 22% 37% 20% 6% 1	460
	11th to 20th	Day	13% 20% 33% 24% 10% 1	460
	21st to end	Day	20% 22% 31% 22% 6%	506
April	1st to 10th	Day	21% 24% 27% 18% 8% 1	460
	11th to 20th	Day	16% 25% 32% 17% 7% 3	452
	21st to end	Day	12% 24% 33% 21% 9% 2	460
May	1st to 10th	Day	13% 21% 30% 22% 11% 2	463
	11th to 20th	Day	16% 15% 29% 23% 13% 3	488
	21st to end	Day	11% 16% 30% 27% 14% 3	529
June	1st to 10th	Day	9% 21% 28% 27% 12% 4	490
	11th to 20th	Day	11% 24% 30% 24% 9% 2	490
	21st to end	Day	5% 13% 33% 31% 15% 3	490
July	1st to 10th	Day	3 9% 35% 37% 15% 2	486
	11th to 20th	Day	2 13% 32% 31% 17% 4	484
	21st to end	Day	2 9% 29% 36% 20% 5%	531
August	1st to 10th	Day	2 8% 28% 33% 22% 8%	487
	11th to 20th	Day	1 8% 26% 34% 23% 8%	477
	21st to end	Day	4 10% 31% 31% 18% 6%	539
September	1st to 10th	Day	4 10% 27% 32% 23% 5%	490
	11th to 20th	Day	6% 11% 28% 34% 19% 2	490
	21st to end	Day	8% 15% 28% 29% 17% 2	490
October	1st to 10th	Day	11% 14% 27% 27% 19% 2	490
	11th to 20th	Day	10% 16% 24% 29% 17% 4	490
	21st to end	Day	14% 21% 29% 22% 12% 3	425
November	1st to 10th	Day	18% 17% 24% 28% 12% 1	284
	11th to 20th	Day	19% 18% 30% 25% 8% 2	200
	21st to end	Day	16% 15% 27% 29% 12% 1	188
December	1st to 10th	Day	13% 18% 24% 27% 13% 4	180
	11th to 20th	Day	13% 23% 35% 23% 4 1	180
	21st to end	Day	14% 25% 25% 26% 10% 1	198
January	1st to 10th	Night	17% 16% 25% 28% 14% 1	760
	11th to 20th	Night	15% 13% 27% 30% 14% 2	760
	21st to end	Night	15% 10% 23% 33% 17% 2	836
February	1st to 10th	Night	12% 17% 26% 30% 14% 1	760
	11th to 20th	Night	15% 15% 25% 29% 15% 1	744
	21st to end	Night	14% 15% 28% 31% 11% 1	628
March	1st to 10th	Night	11% 16% 28% 31% 14% 1	760
	11th to 20th	Night	9% 12% 28% 35% 16% 1	760
	21st to end	Night	11% 17% 29% 31% 10% 2	836
April	1st to 10th	Night	13% 15% 28% 30% 13% 1	760
	11th to 20th	Night	10% 15% 33% 24% 15% 3	751
	21st to end	Night	8% 12% 32% 32% 14% 1	628
May	1st to 10th	Night	7% 12% 33% 30% 16% 1	380
	11th to 20th	Night	6% 9% 27% 34% 20% 3	374
	21st to end	Night	6% 6% 27% 43% 16% 2	411
June	1st to 10th	Night	9% 11% 26% 38% 14% 1	380
	11th to 20th	Night	4 12% 37% 35% 11% 1	380
	21st to end	Night	5% 4 29% 45% 16% 1	380
July	1st to 10th	Night	1 3 28% 50% 17% 1	370
	11th to 20th	Night	1 2 32% 50% 13% 2	368
	21st to end	Night	1 2 26% 49% 20% 2	416
August	1st to 10th	Night	1 2 22% 48% 24% 3	446
	11th to 20th	Night	2 2 15% 41% 33% 8%	564
	21st to end	Night	1 4 28% 40% 22% 4	818
September	1st to 10th	Night	1 6% 21% 41% 27% 4	760
	11th to 20th	Night	4 3 21% 37% 29% 6%	760
	21st to end	Night	5% 7% 22% 35% 26% 4	760
October	1st to 10th	Night	9% 4 24% 37% 23% 3	760
	11th to 20th	Night	7% 8% 23% 34% 24% 4	760
	21st to end	Night	12% 10% 26% 32% 17% 3	836
November	1st to 10th	Night	12% 9% 26% 36% 15% 1	780
	11th to 20th	Night	14% 15% 27% 30% 13% 1	800
	21st to end	Night	10% 11% 26% 35% 17% 2	778
December	1st to 10th	Night	14% 11% 26% 31% 16% 2	760
	11th to 20th	Night	15% 12% 27% 31% 13% 1	760
	21st to end	Night	14% 17% 31% 28% 9% 1	836

Page generated at 2024-11-22 05:02:24. Version ac07

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