Serenity Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Serenity Hill Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	14% 7% 3 6% 4 4 4 4 5% 7% 41%	130891
	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	130415
Transparency	Day	39% 6% 11% 22% 17% 4	134570
	Night	39% 5% 10% 22% 19% 5%	134799
Seeing	Day	18% 11% 24% 24% 17% 6%	16955
	Night	18% 10% 25% 28% 17% 3	26808

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	18% 11% 4 9% 3 3 3 3 4 5% 36%	4691
	11th to 20th	Day	14% 6% 3 7% 3 3 3 2 4 5% 51%	4968
	21st to end	Day	20% 7% 3 7% 4 3 4 3 5% 5% 39%	6207
February	1st to 10th	Day	19% 11% 3 7% 4 3 4 3 4 5% 38%	2100
	11th to 20th	Day	21% 10% 3 7% 4 3 2 3 3 5% 37%	2048
	21st to end	Day	22% 9% 3 5% 4 4 4 2 4 6% 38%	1730
March	1st to 10th	Day	16% 12% 3 8% 5% 4 4 3 4 5% 36%	4500
	11th to 20th	Day	14% 8% 2 6% 4 4 4 3 4 5% 46%	4686
	21st to end	Day	12% 7% 2 7% 5% 5% 4 3 5% 7% 43%	5967
April	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 5% 6% 46%	2400
	11th to 20th	Day	16% 8% 2 6% 4 3 3 3 5% 7% 44%	2374
	21st to end	Day	14% 7% 2 6% 5% 4 5% 3 6% 8% 40%	2400
May	1st to 10th	Day	20% 8% 3 6% 5% 5% 5% 5% 7% 8% 28%	5720
	11th to 20th	Day	16% 9% 3 9% 6% 5% 5% 4 5% 7% 30%	5861
	21st to end	Day	18% 8% 2 7% 4 4 4 4 5% 8% 37%	6433
June	1st to 10th	Day	9% 7% 3 7% 4 4 6% 4 7% 10% 39%	2734
	11th to 20th	Day	6% 3 2 6% 5% 5% 5% 5% 8% 9% 46%	2800
	21st to end	Day	6% 4 1 6% 5% 6% 7% 6% 8% 11% 42%	2800
July	1st to 10th	Day	7% 4 2 7% 5% 6% 6% 5% 8% 12% 39%	6360
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 5% 9% 13% 35%	6360
	21st to end	Day	12% 7% 3 7% 5% 5% 6% 5% 8% 11% 32%	6387
August	1st to 10th	Day	4 3 1 4 4 5% 5% 4 7% 10% 54%	3905
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 6% 10% 45%	3849
	21st to end	Day	5% 4 2 5% 3 4 4 4 5% 7% 56%	4312
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 6% 8% 43%	2400
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 5% 7% 45%	2233
	21st to end	Day	11% 6% 2 5% 3 3 4 3 4 7% 50%	2200
October	1st to 10th	Day	10% 5% 2 4 2 3 3 4 5% 6% 57%	2200
	11th to 20th	Day	11% 5% 2 4 3 3 3 3 5% 6% 55%	2059
	21st to end	Day	18% 7% 2 5% 3 3 3 2 3 5% 50%	2087
November	1st to 10th	Day	13% 6% 2 5% 2 3 2 3 3 5% 55%	1852
	11th to 20th	Day	16% 6% 2 4 3 3 3 2 5% 6% 50%	1890
	21st to end	Day	16% 8% 2 5% 4 3 4 3 5% 6% 44%	1890
December	1st to 10th	Day	18% 8% 3 5% 4 3 3 3 3 5% 46%	3020
	11th to 20th	Day	22% 9% 3 7% 4 3 3 3 3 5% 38%	3398
	21st to end	Day	19% 10% 4 6% 4 5% 4 4 5% 6% 33%	4070
January	1st to 10th	Night	19% 11% 4 7% 3 3 3 3 4 5% 38%	8232
	11th to 20th	Night	15% 9% 4 7% 3 3 3 2 3 4 48%	8007
	21st to end	Night	21% 9% 3 7% 4 4 3 2 4 4 38%	7968
February	1st to 10th	Night	20% 12% 2 7% 5% 4 3 2 4 5% 35%	2520
	11th to 20th	Night	24% 10% 3 6% 4 3 3 2 4 4 36%	2458
	21st to end	Night	22% 8% 3 6% 4 3 3 3 4 5% 39%	2076
March	1st to 10th	Night	19% 11% 3 7% 4 4 4 3 5% 6% 35%	5398
	11th to 20th	Night	12% 7% 2 6% 3 3 3 3 5% 6% 49%	5317
	21st to end	Night	16% 7% 2 7% 4 4 4 3 4 6% 42%	4962
April	1st to 10th	Night	14% 6% 3 5% 4 4 4 4 5% 6% 47%	2000
	11th to 20th	Night	16% 7% 2 5% 3 3 3 3 5% 7% 47%	1975
	21st to end	Night	12% 7% 2 6% 4 4 4 3 5% 8% 43%	2000
May	1st to 10th	Night	17% 10% 3 8% 4 5% 4 3 5% 7% 34%	4174
	11th to 20th	Night	15% 10% 3 8% 6% 5% 5% 4 5% 7% 33%	4032
	21st to end	Night	15% 7% 3 7% 5% 4 5% 4 6% 8% 36%	4421
June	1st to 10th	Night	9% 6% 2 7% 4 4 4 4 7% 9% 44%	1660
	11th to 20th	Night	4 3 1 4 4 3 4 5% 7% 10% 54%	1600
	21st to end	Night	3 3 1 4 4 4 5% 5% 6% 12% 52%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 5% 6% 5% 8% 10% 40%	3618
	11th to 20th	Night	5% 4 2 5% 4 4 5% 5% 9% 15% 42%	3617
	21st to end	Night	8% 6% 3 7% 5% 5% 5% 5% 7% 14% 34%	4463
August	1st to 10th	Night	3 3 1 4 3 4 4 3 5% 8% 62%	3244
	11th to 20th	Night	4 3 1 4 3 4 5% 5% 7% 11% 52%	3200
	21st to end	Night	5% 3 1 4 3 3 4 3 6% 8% 58%	3586
September	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 7% 7% 50%	2000
	11th to 20th	Night	10% 6% 1 5% 4 4 4 4 5% 7% 50%	2145
	21st to end	Night	9% 5% 2 6% 3 4 4 3 5% 6% 53%	2200
October	1st to 10th	Night	10% 4 1 3 2 3 3 2 4 6% 63%	2200
	11th to 20th	Night	13% 5% 1 5% 3 3 3 2 5% 5% 55%	2337
	21st to end	Night	17% 7% 2 4 2 3 4 3 4 5% 49%	2750
November	1st to 10th	Night	13% 5% 2 4 3 4 3 3 4 5% 53%	2666
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 6% 7% 51%	2730
	21st to end	Night	17% 8% 2 5% 3 3 3 3 4 6% 46%	2730
December	1st to 10th	Night	20% 9% 2 5% 3 3 3 2 4 5% 43%	4380
	11th to 20th	Night	23% 8% 3 5% 3 3 3 2 4 4 43%	4999
	21st to end	Night	21% 11% 4 7% 5% 5% 5% 3 4 5% 30%	7150

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	50% 4 11% 23% 11% 1	4692
	11th to 20th	Day	37% 4 7% 23% 29% 1	4968
	21st to end	Day	46% 4 7% 20% 18% 5%	6207
February	1st to 10th	Day	49% 4 8% 20% 15% 3	2100
	11th to 20th	Day	51% 4 7% 20% 15% 4	2058
	21st to end	Day	48% 4 7% 17% 16% 7%	1730
March	1st to 10th	Day	51% 5% 5% 15% 15% 9%	4500
	11th to 20th	Day	39% 6% 7% 20% 19% 9%	4686
	21st to end	Day	40% 6% 10% 24% 19% 1	5969
April	1st to 10th	Day	40% 5% 9% 23% 20% 4	2400
	11th to 20th	Day	40% 5% 9% 21% 20% 6%	2374
	21st to end	Day	40% 7% 11% 23% 17% 2	2400
May	1st to 10th	Day	49% 9% 12% 19% 10% 1	5756
	11th to 20th	Day	50% 9% 14% 17% 10% 1	5865
	21st to end	Day	44% 8% 9% 21% 15% 3	6447
June	1st to 10th	Day	38% 8% 14% 20% 17% 2	2734
	11th to 20th	Day	30% 8% 18% 24% 17% 3	2800
	21st to end	Day	32% 10% 16% 23% 15% 4	2800
July	1st to 10th	Day	35% 10% 17% 26% 11% 1	6291
	11th to 20th	Day	35% 9% 21% 27% 5% 1	6285
	21st to end	Day	43% 9% 22% 20% 5%	6203
August	1st to 10th	Day	23% 8% 15% 31% 20% 2	3893
	11th to 20th	Day	33% 8% 15% 26% 17% 3	3885
	21st to end	Day	27% 6% 11% 29% 24% 2	4311
September	1st to 10th	Day	36% 9% 12% 22% 16% 4	2400
	11th to 20th	Day	37% 7% 11% 21% 22% 3	2233
	21st to end	Day	34% 5% 10% 23% 23% 6%	2200
October	1st to 10th	Day	19% 4 6% 15% 43% 13%	3590
	11th to 20th	Day	21% 3 7% 24% 29% 16%	3325
	21st to end	Day	30% 3 5% 23% 32% 7%	3351
November	1st to 10th	Day	33% 4 7% 22% 28% 5%	1852
	11th to 20th	Day	36% 4 7% 21% 24% 7%	1890
	21st to end	Day	41% 3 7% 22% 22% 4	1890
December	1st to 10th	Day	43% 3 5% 28% 18% 2	3020
	11th to 20th	Day	50% 4 7% 21% 14% 4	3395
	21st to end	Day	50% 6% 10% 24% 9% 1	4070
January	1st to 10th	Night	49% 3 12% 21% 13% 1	8233
	11th to 20th	Night	41% 4 5% 18% 28% 4	8007
	21st to end	Night	50% 4 7% 19% 15% 5%	7968
February	1st to 10th	Night	53% 4 10% 16% 16% 2	2520
	11th to 20th	Night	52% 4 7% 17% 15% 4	2459
	21st to end	Night	48% 4 7% 17% 18% 6%	2076
March	1st to 10th	Night	49% 5% 7% 15% 17% 7%	5398
	11th to 20th	Night	36% 5% 7% 20% 18% 15%	5317
	21st to end	Night	42% 5% 8% 22% 20% 3	4962
April	1st to 10th	Night	37% 6% 12% 22% 19% 4	2000
	11th to 20th	Night	37% 4 8% 20% 23% 8%	1975
	21st to end	Night	39% 6% 13% 23% 18% 2	2000
May	1st to 10th	Night	49% 7% 11% 20% 11% 1	4203
	11th to 20th	Night	49% 9% 14% 17% 11% 1	4033
	21st to end	Night	42% 10% 12% 22% 13% 1	4429
June	1st to 10th	Night	35% 8% 13% 23% 19% 2	1660
	11th to 20th	Night	23% 8% 15% 33% 18% 4	1600
	21st to end	Night	24% 10% 20% 25% 18% 4	1600
July	1st to 10th	Night	35% 8% 17% 27% 12% 1	3580
	11th to 20th	Night	28% 9% 24% 32% 5% 2	3572
	21st to end	Night	38% 8% 25% 22% 6%	4334
August	1st to 10th	Night	19% 7% 11% 37% 24% 1	3232
	11th to 20th	Night	23% 8% 21% 29% 17% 2	3230
	21st to end	Night	23% 6% 13% 28% 27% 4	3586
September	1st to 10th	Night	30% 9% 13% 25% 18% 6%	2000
	11th to 20th	Night	33% 6% 12% 20% 26% 3	2145
	21st to end	Night	31% 6% 9% 23% 24% 7%	2200
October	1st to 10th	Night	18% 4 5% 18% 41% 14%	3590
	11th to 20th	Night	20% 3 5% 19% 35% 20%	3797
	21st to end	Night	27% 3 6% 25% 26% 12%	4436
November	1st to 10th	Night	33% 5% 8% 21% 26% 7%	2666
	11th to 20th	Night	32% 5% 8% 21% 26% 8%	2730
	21st to end	Night	40% 4 7% 22% 22% 5%	2730
December	1st to 10th	Night	44% 3 7% 20% 23% 2	4380
	11th to 20th	Night	46% 3 5% 22% 21% 3	5001
	21st to end	Night	54% 6% 9% 21% 8% 2	7150

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% 25% 33% 12% 4	330
	11th to 20th	Day	31% 25% 35% 7% 2 1	330
	21st to end	Day	26% 29% 35% 9% 2	363
February	1st to 10th	Day	28% 25% 34% 11% 2 1	330
	11th to 20th	Day	37% 25% 30% 6% 2	330
	21st to end	Day	39% 22% 28% 9% 2	273
March	1st to 10th	Day	30% 22% 31% 12% 4	306
	11th to 20th	Day	30% 23% 32% 13% 2 1	335
	21st to end	Day	27% 19% 33% 16% 5%	550
April	1st to 10th	Day	26% 18% 30% 19% 7% 1	500
	11th to 20th	Day	24% 17% 31% 20% 8% 1	492
	21st to end	Day	22% 14% 32% 22% 8% 2	500
May	1st to 10th	Day	23% 15% 28% 21% 9% 3	503
	11th to 20th	Day	16% 10% 30% 25% 12% 6%	527
	21st to end	Day	12% 10% 27% 26% 17% 9%	573
June	1st to 10th	Day	12% 6% 21% 29% 21% 11%	664
	11th to 20th	Day	6% 3 19% 34% 25% 12%	730
	21st to end	Day	7% 4 20% 34% 24% 11%	730
July	1st to 10th	Day	8% 3 15% 32% 30% 12%	721
	11th to 20th	Day	8% 4 11% 31% 35% 12%	718
	21st to end	Day	9% 1 13% 30% 32% 15%	637
August	1st to 10th	Day	10% 2 14% 33% 29% 12%	526
	11th to 20th	Day	9% 3 15% 31% 32% 9%	519
	21st to end	Day	11% 3 13% 23% 34% 16%	583
September	1st to 10th	Day	12% 4 12% 35% 29% 9%	530
	11th to 20th	Day	12% 3 12% 29% 31% 13%	530
	21st to end	Day	16% 6% 20% 27% 23% 8%	530
October	1st to 10th	Day	12% 4 22% 30% 24% 7%	530
	11th to 20th	Day	11% 13% 33% 28% 13% 3	389
	21st to end	Day	27% 12% 33% 20% 6% 1	363
November	1st to 10th	Day	23% 12% 31% 25% 8% 1	330
	11th to 20th	Day	18% 21% 34% 23% 4	330
	21st to end	Day	26% 18% 28% 17% 10% 2	330
December	1st to 10th	Day	29% 21% 31% 15% 4 1	330
	11th to 20th	Day	29% 18% 30% 16% 6%	330
	21st to end	Day	28% 23% 35% 12% 2	363
January	1st to 10th	Night	26% 17% 31% 23% 3	1050
	11th to 20th	Night	27% 20% 31% 19% 3	1050
	21st to end	Night	23% 16% 39% 20% 1	1004
February	1st to 10th	Night	28% 14% 34% 20% 3	840
	11th to 20th	Night	30% 18% 30% 19% 2	823
	21st to end	Night	30% 18% 31% 18% 2	692
March	1st to 10th	Night	23% 16% 33% 25% 3	809
	11th to 20th	Night	23% 16% 36% 20% 4 1	790
	21st to end	Night	20% 15% 33% 24% 7%	660
April	1st to 10th	Night	19% 13% 36% 24% 8% 1	600
	11th to 20th	Night	20% 11% 32% 27% 8% 1	593
	21st to end	Night	15% 10% 36% 28% 10% 1	600
May	1st to 10th	Night	17% 7% 33% 28% 13% 2	600
	11th to 20th	Night	13% 6% 28% 31% 19% 2	591
	21st to end	Night	9% 3 23% 34% 25% 6%	650
June	1st to 10th	Night	11% 3 16% 35% 30% 5%	600
	11th to 20th	Night	6% 3 12% 38% 38% 4	600
	21st to end	Night	5% 1 12% 36% 38% 7%	600
July	1st to 10th	Night	11% 2 10% 29% 38% 11%	585
	11th to 20th	Night	7% 2 9% 27% 44% 10%	582
	21st to end	Night	7% 2 9% 32% 42% 9%	657
August	1st to 10th	Night	6% 1 7% 30% 46% 10%	597
	11th to 20th	Night	6% 1 10% 40% 38% 5%	594
	21st to end	Night	9% 2 8% 34% 38% 8%	660
September	1st to 10th	Night	9% 3 11% 37% 36% 5%	600
	11th to 20th	Night	13% 2 12% 31% 36% 6%	745
	21st to end	Night	12% 3 15% 35% 30% 4	800
October	1st to 10th	Night	11% 5% 17% 34% 28% 6%	800
	11th to 20th	Night	15% 8% 23% 33% 19% 1	800
	21st to end	Night	20% 9% 27% 29% 14% 1	880
November	1st to 10th	Night	15% 9% 24% 34% 15% 2	820
	11th to 20th	Night	15% 12% 33% 30% 10% 1	840
	21st to end	Night	23% 12% 30% 25% 10%	840
December	1st to 10th	Night	26% 13% 29% 25% 6%	840
	11th to 20th	Night	25% 12% 31% 26% 6%	861
	21st to end	Night	28% 16% 29% 23% 4	1155

Page generated at 2026-02-28 00:40:21. Version ac07

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