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 2024-01-14.

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	6% 6% 3 6% 6% 3 5% 5% 6% 7% 47%	74772
	Night	6% 7% 3 6% 6% 4 5% 5% 6% 8% 44%	75011
Transparency	Day	35% 9% 14% 22% 15% 5%	74475
	Night	36% 10% 15% 21% 13% 4	74829
Seeing	Day	11% 17% 30% 27% 13% 3	13438
	Night	10% 10% 26% 34% 17% 2	22576

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	11% 14% 5% 11% 8% 5% 7% 6% 6% 8% 20%	1519
	11th to 20th	Day	7% 11% 5% 11% 10% 5% 9% 7% 7% 7% 21%	1464
	21st to end	Day	8% 12% 5% 10% 7% 5% 6% 6% 6% 9% 26%	1660
February	1st to 10th	Day	8% 11% 4 7% 8% 5% 7% 6% 6% 8% 30%	1620
	11th to 20th	Day	7% 9% 3 6% 7% 3 6% 7% 8% 10% 33%	1575
	21st to end	Day	6% 9% 4 8% 7% 5% 6% 6% 8% 8% 33%	1461
March	1st to 10th	Day	7% 11% 4 8% 9% 4 7% 7% 7% 9% 27%	1810
	11th to 20th	Day	6% 9% 5% 8% 9% 5% 8% 7% 7% 8% 28%	1980
	21st to end	Day	7% 9% 4 9% 9% 5% 9% 8% 7% 9% 25%	2276
April	1st to 10th	Day	8% 8% 3 7% 7% 6% 7% 6% 7% 10% 31%	2160
	11th to 20th	Day	7% 8% 4 8% 8% 4 6% 5% 6% 8% 36%	2129
	21st to end	Day	4 6% 2 5% 5% 4 6% 8% 7% 10% 43%	2283
May	1st to 10th	Day	5% 4 2 6% 6% 4 5% 5% 7% 7% 50%	2520
	11th to 20th	Day	8% 5% 3 5% 6% 4 5% 6% 6% 8% 43%	2477
	21st to end	Day	8% 5% 3 5% 5% 3 6% 4 6% 8% 46%	2723
June	1st to 10th	Day	8% 5% 3 6% 6% 3 5% 5% 7% 9% 45%	2520
	11th to 20th	Day	4 4 2 5% 5% 3 5% 5% 5% 8% 54%	2520
	21st to end	Day	3 2 1 3 3 2 4 4 4 7% 66%	2520
July	1st to 10th	Day	1 1 1 2 2 1 2 4 4 6% 75%	2520
	11th to 20th	Day	2 2 1 2 2 2 2 3 3 4 75%	2520
	21st to end	Day	1 1 1 1 2 1 1 2 3 3 85%	2741
August	1st to 10th	Day	1 1 1 1 2 2 3 3 3 6% 77%	2440
	11th to 20th	Day	1 1 1 2 2 2 2 3 3 5% 77%	2298
	21st to end	Day	2 2 1 3 3 2 3 3 4 6% 72%	2393
September	1st to 10th	Day	3 1 2 2 1 2 2 4 6% 76%	2160
	11th to 20th	Day	3 3 1 4 5% 3 5% 4 6% 7% 58%	2160
	21st to end	Day	5% 5% 2 5% 4 3 4 4 4 7% 56%	1924
October	1st to 10th	Day	8% 5% 3 6% 5% 2 3 5% 6% 6% 52%	1800
	11th to 20th	Day	7% 4 2 6% 5% 3 4 5% 7% 9% 47%	1800
	21st to end	Day	9% 7% 3 6% 7% 4 5% 6% 6% 7% 40%	1872
November	1st to 10th	Day	9% 9% 4 7% 9% 5% 6% 6% 7% 9% 30%	1645
	11th to 20th	Day	7% 11% 6% 8% 8% 5% 9% 8% 8% 8% 23%	1520
	21st to end	Day	7% 10% 5% 7% 6% 5% 6% 6% 7% 9% 33%	1520
December	1st to 10th	Day	8% 11% 7% 10% 8% 4 6% 5% 6% 6% 30%	1520
	11th to 20th	Day	8% 13% 6% 11% 10% 6% 8% 9% 7% 7% 16%	1928
	21st to end	Day	9% 15% 6% 12% 10% 5% 6% 7% 5% 6% 20%	2794
January	1st to 10th	Night	10% 11% 6% 12% 9% 4 7% 7% 7% 9% 19%	2646
	11th to 20th	Night	7% 11% 5% 10% 10% 6% 7% 7% 6% 9% 23%	2574
	21st to end	Night	9% 10% 4 9% 7% 5% 8% 7% 7% 8% 27%	2693
February	1st to 10th	Night	7% 9% 4 8% 7% 4 6% 6% 6% 9% 33%	2340
	11th to 20th	Night	7% 8% 3 6% 6% 4 6% 6% 6% 8% 40%	2272
	21st to end	Night	6% 9% 4 7% 6% 3 5% 6% 7% 9% 37%	1794
March	1st to 10th	Night	7% 9% 4 7% 7% 4 5% 7% 7% 9% 33%	2147
	11th to 20th	Night	6% 8% 4 6% 8% 5% 6% 6% 7% 10% 34%	1980
	21st to end	Night	5% 8% 4 7% 9% 5% 7% 6% 7% 8% 33%	2080
April	1st to 10th	Night	7% 8% 3 7% 7% 3 6% 6% 7% 9% 36%	1800
	11th to 20th	Night	5% 6% 3 6% 5% 4 7% 6% 6% 10% 42%	1779
	21st to end	Night	6% 5% 2 5% 5% 3 4 5% 8% 10% 46%	1676
May	1st to 10th	Night	4 4 2 5% 5% 3 4 6% 8% 7% 53%	1440
	11th to 20th	Night	7% 4 2 3 5% 3 6% 5% 8% 9% 48%	1416
	21st to end	Night	3 5% 2 5% 4 3 6% 6% 7% 11% 48%	1552
June	1st to 10th	Night	7% 6% 2 5% 6% 3 5% 6% 6% 8% 47%	1440
	11th to 20th	Night	4 4 2 4 4 2 4 4 5% 8% 58%	1440
	21st to end	Night	2 3 2 3 4 1 4 4 4 4 69%	1440
July	1st to 10th	Night	2 1 2 2 1 2 2 5% 5% 77%	1440
	11th to 20th	Night	1 1 1 1 1 1 2 3 3 6% 79%	1440
	21st to end	Night	1 1 1 1 1 1 2 2 4 85%	1576
August	1st to 10th	Night	2 1 1 2 2 1 3 3 4 5% 77%	1496
	11th to 20th	Night	1 1 2 3 1 3 3 2 5% 78%	1602
	21st to end	Night	1 1 2 2 2 3 3 4 5% 77%	1962
September	1st to 10th	Night	1 1 1 2 2 1 2 3 4 4 79%	1800
	11th to 20th	Night	4 2 1 3 5% 3 3 5% 7% 7% 61%	1800
	21st to end	Night	4 4 2 4 4 3 3 4 4 8% 60%	2033
October	1st to 10th	Night	7% 4 2 6% 5% 2 3 4 5% 5% 57%	2160
	11th to 20th	Night	5% 4 3 6% 6% 3 5% 5% 5% 8% 51%	2160
	21st to end	Night	8% 6% 2 5% 6% 3 5% 5% 6% 8% 46%	2482
November	1st to 10th	Night	9% 8% 3 8% 7% 4 7% 6% 7% 6% 35%	2433
	11th to 20th	Night	8% 10% 4 8% 6% 4 7% 7% 6% 9% 31%	2660
	21st to end	Night	5% 8% 4 8% 7% 4 7% 7% 8% 8% 35%	2660
December	1st to 10th	Night	9% 10% 5% 8% 7% 4 6% 6% 6% 7% 31%	2660
	11th to 20th	Night	9% 14% 5% 10% 8% 6% 8% 7% 6% 8% 20%	3276
	21st to end	Night	8% 12% 7% 12% 9% 5% 6% 6% 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	60% 15% 14% 9% 2	1519
	11th to 20th	Day	59% 10% 16% 11% 4 1	1464
	21st to end	Day	53% 11% 17% 12% 6%	1660
February	1st to 10th	Day	50% 14% 18% 14% 4 1	1620
	11th to 20th	Day	41% 16% 19% 17% 6% 1	1584
	21st to end	Day	47% 13% 17% 14% 9%	1461
March	1st to 10th	Day	48% 12% 17% 16% 7%	1810
	11th to 20th	Day	51% 11% 15% 19% 4	1980
	21st to end	Day	53% 14% 15% 15% 3	2276
April	1st to 10th	Day	45% 11% 17% 18% 8%	2160
	11th to 20th	Day	45% 9% 17% 14% 12% 2	2132
	21st to end	Day	32% 13% 20% 22% 10% 2	2283
May	1st to 10th	Day	31% 9% 15% 30% 15%	2520
	11th to 20th	Day	37% 9% 15% 25% 13% 1	2480
	21st to end	Day	35% 9% 19% 28% 9%	2724
June	1st to 10th	Day	35% 9% 16% 26% 12% 1	2520
	11th to 20th	Day	28% 8% 17% 32% 12% 2	2520
	21st to end	Day	19% 5% 14% 34% 22% 6%	2520
July	1st to 10th	Day	11% 4 12% 27% 30% 15%	2451
	11th to 20th	Day	13% 4 7% 19% 34% 23%	2445
	21st to end	Day	7% 2 4 22% 42% 23%	2589
August	1st to 10th	Day	11% 4 10% 28% 34% 14%	2423
	11th to 20th	Day	11% 4 9% 27% 37% 12%	2298
	21st to end	Day	14% 4 10% 33% 32% 8%	2393
September	1st to 10th	Day	12% 4 10% 32% 28% 15%	2160
	11th to 20th	Day	25% 6% 13% 26% 23% 7%	2160
	21st to end	Day	28% 7% 15% 25% 19% 6%	1924
October	1st to 10th	Day	32% 8% 13% 25% 17% 4	1800
	11th to 20th	Day	32% 11% 18% 21% 16% 2	1800
	21st to end	Day	41% 11% 15% 23% 10% 1	1872
November	1st to 10th	Day	47% 12% 16% 18% 7%	1645
	11th to 20th	Day	52% 18% 14% 12% 4	1520
	21st to end	Day	45% 13% 18% 16% 7% 1	1520
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	61% 13% 15% 9% 3	2646
	11th to 20th	Night	55% 11% 16% 13% 5% 1	2574
	21st to end	Night	50% 12% 18% 16% 4	2693
February	1st to 10th	Night	46% 13% 20% 17% 3	2340
	11th to 20th	Night	40% 12% 20% 19% 8%	2274
	21st to end	Night	42% 11% 18% 20% 8% 1	1794
March	1st to 10th	Night	44% 11% 17% 20% 6% 1	2147
	11th to 20th	Night	42% 12% 18% 21% 6% 1	1980
	21st to end	Night	44% 14% 19% 16% 6%	2080
April	1st to 10th	Night	40% 12% 18% 20% 8% 1	1800
	11th to 20th	Night	36% 10% 20% 21% 11% 3	1779
	21st to end	Night	31% 12% 18% 25% 11% 2	1676
May	1st to 10th	Night	26% 9% 18% 33% 13% 2	1440
	11th to 20th	Night	30% 8% 20% 26% 14% 2	1416
	21st to end	Night	29% 11% 24% 25% 9% 2	1552
June	1st to 10th	Night	34% 9% 14% 29% 12% 2	1440
	11th to 20th	Night	24% 7% 18% 36% 13% 2	1440
	21st to end	Night	19% 5% 10% 34% 23% 8%	1440
July	1st to 10th	Night	11% 4 12% 24% 28% 21%	1400
	11th to 20th	Night	9% 4 10% 18% 31% 28%	1392
	21st to end	Night	7% 2 5% 16% 40% 30%	1488
August	1st to 10th	Night	11% 3 10% 25% 35% 16%	1488
	11th to 20th	Night	12% 3 9% 26% 35% 15%	1602
	21st to end	Night	10% 4 10% 28% 37% 10%	1962
September	1st to 10th	Night	10% 4 11% 31% 27% 17%	1800
	11th to 20th	Night	20% 8% 12% 26% 21% 13%	1800
	21st to end	Night	22% 7% 13% 29% 21% 7%	2033
October	1st to 10th	Night	28% 7% 11% 28% 22% 4	2160
	11th to 20th	Night	31% 10% 15% 23% 17% 4	2160
	21st to end	Night	35% 10% 14% 22% 18% 1	2482
November	1st to 10th	Night	44% 12% 14% 21% 9%	2433
	11th to 20th	Night	47% 14% 16% 18% 4	2660
	21st to end	Night	41% 12% 18% 22% 6% 1	2660
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	19% 14% 31% 24% 10% 1	166
	21st to end	Day	16% 19% 27% 25% 12% 1	252
February	1st to 10th	Day	16% 23% 31% 23% 6%	340
	11th to 20th	Day	17% 25% 30% 21% 6%	335
	21st to end	Day	19% 23% 29% 22% 7%	338
March	1st to 10th	Day	15% 22% 37% 19% 6% 1	420
	11th to 20th	Day	14% 20% 33% 23% 9%	420
	21st to end	Day	21% 21% 29% 22% 6%	462
April	1st to 10th	Day	22% 23% 26% 19% 9% 1	420
	11th to 20th	Day	17% 26% 30% 17% 7% 3	412
	21st to end	Day	12% 24% 33% 21% 10% 1	420
May	1st to 10th	Day	12% 21% 30% 24% 12% 2	423
	11th to 20th	Day	17% 16% 28% 24% 13% 3	448
	21st to end	Day	10% 16% 30% 27% 14% 3	485
June	1st to 10th	Day	9% 20% 29% 26% 12% 4	450
	11th to 20th	Day	11% 24% 31% 24% 8% 2	450
	21st to end	Day	5% 13% 33% 31% 15% 3	450
July	1st to 10th	Day	2 9% 36% 37% 14% 1	446
	11th to 20th	Day	2 13% 32% 32% 17% 3	444
	21st to end	Day	1 8% 30% 36% 20% 4	487
August	1st to 10th	Day	2 8% 29% 33% 21% 8%	447
	11th to 20th	Day	1 8% 25% 35% 24% 7%	437
	21st to end	Day	4 10% 32% 31% 18% 5%	495
September	1st to 10th	Day	4 11% 27% 32% 22% 4	450
	11th to 20th	Day	6% 10% 28% 36% 19% 2	450
	21st to end	Day	9% 15% 28% 29% 17% 2	450
October	1st to 10th	Day	12% 14% 27% 27% 18% 1	450
	11th to 20th	Day	11% 17% 24% 27% 17% 4	450
	21st to end	Day	14% 21% 28% 20% 13% 3	387
November	1st to 10th	Day	17% 17% 25% 30% 10% 1	256
	11th to 20th	Day	15% 18% 31% 26% 8% 2	180
	21st to end	Day	17% 16% 27% 29% 11% 1	180
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	14% 12% 27% 31% 14% 2	736
	21st to end	Night	15% 9% 23% 33% 18% 2	792
February	1st to 10th	Night	11% 17% 26% 31% 14% 1	720
	11th to 20th	Night	14% 15% 25% 29% 16% 1	704
	21st to end	Night	15% 14% 29% 30% 11% 1	592
March	1st to 10th	Night	12% 16% 27% 31% 14% 1	720
	11th to 20th	Night	9% 12% 28% 35% 15% 1	720
	21st to end	Night	11% 17% 29% 30% 10% 2	792
April	1st to 10th	Night	13% 14% 27% 31% 13% 1	720
	11th to 20th	Night	10% 15% 32% 24% 16% 3	711
	21st to end	Night	9% 12% 32% 31% 15% 1	596
May	1st to 10th	Night	7% 11% 33% 31% 16% 1	360
	11th to 20th	Night	6% 9% 27% 35% 21% 3	354
	21st to end	Night	6% 6% 27% 42% 16% 2	389
June	1st to 10th	Night	9% 11% 27% 39% 14% 1	360
	11th to 20th	Night	4 13% 36% 36% 11% 1	360
	21st to end	Night	5% 4 29% 44% 16% 1	360
July	1st to 10th	Night	1 3 28% 51% 17% 1	350
	11th to 20th	Night	1 3 33% 49% 13% 2	348
	21st to end	Night	1 2 27% 48% 20% 2	394
August	1st to 10th	Night	1 2 22% 47% 25% 3	422
	11th to 20th	Night	2 2 14% 39% 34% 9%	534
	21st to end	Night	2 4 28% 40% 22% 5%	774
September	1st to 10th	Night	2 6% 21% 41% 27% 4	720
	11th to 20th	Night	4 3 20% 36% 30% 6%	720
	21st to end	Night	6% 7% 22% 35% 26% 4	720
October	1st to 10th	Night	10% 4 24% 36% 23% 3	720
	11th to 20th	Night	7% 9% 23% 33% 25% 4	720
	21st to end	Night	12% 11% 26% 31% 17% 3	792
November	1st to 10th	Night	12% 10% 26% 36% 15% 1	740
	11th to 20th	Night	14% 15% 27% 30% 13% 1	760
	21st to end	Night	9% 11% 26% 35% 17% 3	760
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

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