Singing Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Singing Mountain Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	4 7% 2 6% 4 4 4 4 6% 7% 52%	105385
	Night	5% 9% 3 6% 4 4 4 3 5% 6% 52%	103071
Transparency	Day	28% 9% 10% 21% 22% 10%	105143
	Night	31% 7% 11% 22% 21% 9%	102902
Seeing	Day	8% 9% 25% 33% 21% 4	15450
	Night	8% 4 22% 43% 21% 1	25626

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	5% 8% 3 11% 6% 5% 6% 5% 7% 6% 39%	2707
	11th to 20th	Day	8% 15% 3 11% 4 4 4 3 6% 6% 37%	2860
	21st to end	Day	5% 11% 3 7% 4 3 3 2 5% 6% 49%	3146
February	1st to 10th	Day	7% 12% 3 8% 5% 4 5% 3 6% 5% 43%	1710
	11th to 20th	Day	6% 13% 4 7% 4 4 3 3 5% 9% 41%	1695
	21st to end	Day	6% 16% 5% 9% 5% 3 4 3 4 5% 40%	1570
March	1st to 10th	Day	4 14% 4 8% 5% 4 4 4 6% 7% 40%	3430
	11th to 20th	Day	3 8% 3 8% 5% 4 5% 5% 6% 7% 44%	3490
	21st to end	Day	6% 15% 5% 11% 6% 5% 4 4 5% 5% 34%	3845
April	1st to 10th	Day	7% 9% 3 6% 4 4 5% 4 5% 7% 47%	2280
	11th to 20th	Day	7% 11% 2 7% 5% 5% 5% 4 5% 6% 43%	2251
	21st to end	Day	5% 8% 3 6% 4 5% 4 4 6% 8% 47%	2280
May	1st to 10th	Day	6% 11% 4 9% 5% 5% 5% 4 5% 6% 40%	4065
	11th to 20th	Day	4 4 2 5% 4 5% 5% 5% 7% 9% 50%	4166
	21st to end	Day	6% 5% 2 4 3 3 4 4 5% 6% 57%	4825
June	1st to 10th	Day	3 3 2 3 3 4 3 4 6% 8% 61%	2660
	11th to 20th	Day	3 3 1 3 2 4 4 3 6% 6% 65%	2660
	21st to end	Day	2 2 1 3 3 3 4 4 6% 8% 64%	2660
July	1st to 10th	Day	2 2 1 3 3 3 3 3 4 6% 70%	4430
	11th to 20th	Day	1 2 1 3 3 3 5% 6% 11% 13% 52%	4156
	21st to end	Day	3 3 1 3 3 4 5% 5% 7% 8% 59%	4454
August	1st to 10th	Day	3 2 1 4 5% 5% 6% 5% 10% 13% 46%	4092
	11th to 20th	Day	3 3 1 4 3 4 5% 5% 7% 10% 55%	3918
	21st to end	Day	2 2 1 4 4 4 4 5% 8% 11% 54%	4180
September	1st to 10th	Day	5% 3 1 4 3 3 5% 3 6% 7% 60%	2280
	11th to 20th	Day	4 3 1 3 3 4 4 4 6% 6% 62%	2273
	21st to end	Day	4 3 1 4 3 3 3 3 4 5% 67%	2001
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 4 76%	3170
	11th to 20th	Day	4 3 1 4 3 4 5% 4 7% 10% 55%	3150
	21st to end	Day	5% 5% 1 4 3 3 3 2 4 6% 64%	3438
November	1st to 10th	Day	4 5% 2 3 2 3 4 3 5% 5% 63%	1908
	11th to 20th	Day	7% 6% 2 5% 2 3 3 3 4 6% 59%	1755
	21st to end	Day	5% 9% 3 6% 4 3 3 2 4 5% 57%	1600
December	1st to 10th	Day	8% 11% 3 6% 3 4 3 2 4 5% 51%	1560
	11th to 20th	Day	7% 11% 4 9% 4 3 4 3 4 7% 43%	1926
	21st to end	Day	5% 12% 4 7% 4 5% 4 4 6% 7% 44%	2794
January	1st to 10th	Night	5% 11% 7% 12% 6% 4 4 4 4 5% 39%	4275
	11th to 20th	Night	7% 21% 5% 7% 4 3 4 2 4 5% 39%	4110
	21st to end	Night	6% 16% 5% 8% 4 3 3 3 4 4 45%	4521
February	1st to 10th	Night	7% 14% 3 8% 4 4 3 2 5% 5% 45%	2470
	11th to 20th	Night	6% 12% 3 8% 5% 4 2 4 5% 6% 44%	2370
	21st to end	Night	6% 14% 5% 8% 4 3 3 3 4 5% 45%	1884
March	1st to 10th	Night	5% 15% 4 7% 4 4 5% 4 4 5% 44%	3440
	11th to 20th	Night	4 12% 3 7% 5% 4 4 3 5% 6% 47%	3490
	21st to end	Night	8% 19% 4 9% 4 4 4 3 5% 5% 33%	3806
April	1st to 10th	Night	8% 12% 3 6% 5% 4 3 3 4 6% 45%	1900
	11th to 20th	Night	9% 9% 3 8% 4 4 4 4 5% 5% 45%	1877
	21st to end	Night	10% 9% 2 6% 4 3 4 3 4 6% 49%	1900
May	1st to 10th	Night	10% 11% 2 6% 5% 4 4 3 6% 7% 43%	2901
	11th to 20th	Night	6% 5% 2 5% 4 4 5% 5% 6% 8% 50%	2721
	21st to end	Night	8% 4 1 5% 3 3 3 3 4 6% 59%	2762
June	1st to 10th	Night	2 3 2 5% 3 3 3 4 6% 8% 62%	1520
	11th to 20th	Night	4 3 1 4 3 3 3 3 5% 6% 67%	1520
	21st to end	Night	2 2 1 3 3 4 4 4 6% 7% 65%	1520
July	1st to 10th	Night	1 2 1 3 3 4 3 3 4 5% 69%	2540
	11th to 20th	Night	1 2 1 3 4 4 5% 4 9% 12% 55%	2810
	21st to end	Night	2 2 1 5% 4 4 4 4 7% 9% 57%	3109
August	1st to 10th	Night	3 3 2 7% 5% 6% 7% 7% 9% 12% 40%	2847
	11th to 20th	Night	3 3 1 4 3 4 5% 5% 8% 9% 54%	2918
	21st to end	Night	3 3 2 5% 4 5% 6% 5% 7% 9% 52%	3487
September	1st to 10th	Night	3 3 1 4 4 3 4 3 6% 7% 61%	1900
	11th to 20th	Night	5% 3 1 4 4 3 4 3 6% 6% 61%	1903
	21st to end	Night	5% 2 1 4 2 2 2 2 3 5% 69%	2177
October	1st to 10th	Night	4 3 1 2 2 2 2 2 3 5% 75%	3800
	11th to 20th	Night	4 3 1 4 3 4 5% 4 6% 8% 58%	3778
	21st to end	Night	6% 6% 2 4 3 3 3 2 3 4 64%	4120
November	1st to 10th	Night	5% 6% 2 4 3 2 3 3 4 5% 62%	2370
	11th to 20th	Night	7% 6% 2 5% 2 2 2 2 4 5% 62%	2644
	21st to end	Night	7% 10% 3 5% 2 2 3 3 4 6% 56%	2800
December	1st to 10th	Night	9% 11% 3 5% 3 2 2 3 4 5% 52%	2737
	11th to 20th	Night	7% 13% 4 7% 4 4 3 4 5% 8% 41%	3271
	21st to end	Night	5% 13% 4 9% 4 4 4 3 4 7% 44%	4873

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	38% 15% 15% 20% 11% 1	2708
	11th to 20th	Day	44% 10% 18% 18% 9% 1	2860
	21st to end	Day	35% 9% 14% 30% 10% 2	3146
February	1st to 10th	Day	43% 9% 15% 19% 11% 3	1710
	11th to 20th	Day	42% 7% 10% 23% 16% 3	1704
	21st to end	Day	45% 7% 8% 19% 17% 3	1570
March	1st to 10th	Day	36% 14% 10% 21% 16% 4	3430
	11th to 20th	Day	33% 9% 13% 34% 9% 2	3490
	21st to end	Day	44% 15% 8% 20% 12% 1	3845
April	1st to 10th	Day	36% 7% 9% 23% 19% 6%	2280
	11th to 20th	Day	39% 8% 10% 19% 20% 4	2254
	21st to end	Day	34% 9% 9% 24% 22% 3	2280
May	1st to 10th	Day	34% 14% 9% 16% 22% 4	4065
	11th to 20th	Day	24% 13% 8% 28% 23% 4	4169
	21st to end	Day	24% 9% 8% 18% 35% 7%	4825
June	1st to 10th	Day	20% 6% 8% 21% 30% 15%	2660
	11th to 20th	Day	19% 5% 7% 11% 28% 29%	2660
	21st to end	Day	17% 7% 7% 15% 26% 28%	2660
July	1st to 10th	Day	16% 6% 5% 9% 21% 43%	4361
	11th to 20th	Day	17% 9% 12% 26% 25% 12%	4085
	21st to end	Day	20% 8% 11% 19% 19% 22%	4314
August	1st to 10th	Day	24% 11% 20% 20% 14% 11%	4078
	11th to 20th	Day	24% 9% 11% 16% 26% 13%	3957
	21st to end	Day	21% 11% 11% 19% 24% 14%	4179
September	1st to 10th	Day	23% 8% 8% 14% 29% 19%	2280
	11th to 20th	Day	21% 7% 10% 19% 28% 16%	2273
	21st to end	Day	21% 5% 7% 17% 39% 12%	2001
October	1st to 10th	Day	15% 4 5% 16% 38% 23%	3170
	11th to 20th	Day	21% 8% 7% 30% 28% 5%	3150
	21st to end	Day	21% 6% 7% 31% 31% 4	3438
November	1st to 10th	Day	22% 7% 9% 26% 32% 4	1908
	11th to 20th	Day	27% 5% 9% 31% 23% 4	1755
	21st to end	Day	32% 5% 9% 28% 23% 4	1600
December	1st to 10th	Day	38% 6% 16% 24% 14% 3	1560
	11th to 20th	Day	42% 7% 8% 26% 16% 1	1924
	21st to end	Day	38% 9% 12% 17% 21% 3	2794
January	1st to 10th	Night	44% 10% 11% 21% 13% 1	4275
	11th to 20th	Night	46% 9% 17% 19% 9% 1	4110
	21st to end	Night	41% 8% 14% 24% 11% 2	4521
February	1st to 10th	Night	41% 7% 14% 21% 15% 2	2470
	11th to 20th	Night	40% 7% 11% 24% 16% 2	2371
	21st to end	Night	41% 5% 8% 24% 18% 3	1884
March	1st to 10th	Night	38% 11% 7% 22% 19% 3	3440
	11th to 20th	Night	34% 9% 12% 30% 12% 2	3490
	21st to end	Night	47% 11% 9% 19% 12% 1	3806
April	1st to 10th	Night	39% 7% 8% 19% 20% 6%	1900
	11th to 20th	Night	39% 8% 8% 18% 21% 6%	1877
	21st to end	Night	35% 6% 9% 23% 24% 3	1900
May	1st to 10th	Night	34% 10% 9% 21% 22% 4	2901
	11th to 20th	Night	26% 9% 10% 31% 20% 3	2722
	21st to end	Night	24% 8% 7% 17% 34% 11%	2762
June	1st to 10th	Night	19% 7% 9% 18% 29% 18%	1520
	11th to 20th	Night	18% 5% 8% 14% 21% 34%	1520
	21st to end	Night	16% 5% 8% 17% 24% 30%	1520
July	1st to 10th	Night	16% 6% 8% 9% 17% 44%	2500
	11th to 20th	Night	17% 8% 12% 31% 15% 17%	2758
	21st to end	Night	20% 8% 15% 19% 18% 20%	3011
August	1st to 10th	Night	30% 11% 21% 14% 12% 11%	2838
	11th to 20th	Night	24% 8% 19% 14% 17% 19%	2945
	21st to end	Night	26% 9% 12% 16% 22% 15%	3487
September	1st to 10th	Night	21% 7% 9% 16% 24% 22%	1900
	11th to 20th	Night	22% 7% 11% 15% 27% 18%	1903
	21st to end	Night	20% 4 5% 18% 38% 15%	2177
October	1st to 10th	Night	14% 4 5% 16% 41% 21%	3800
	11th to 20th	Night	21% 8% 8% 29% 26% 7%	3778
	21st to end	Night	24% 5% 7% 31% 30% 5%	4120
November	1st to 10th	Night	24% 6% 10% 27% 29% 5%	2370
	11th to 20th	Night	26% 4 9% 31% 25% 4	2644
	21st to end	Night	31% 5% 8% 26% 27% 4	2800
December	1st to 10th	Night	35% 5% 15% 25% 18% 2	2737
	11th to 20th	Night	41% 7% 10% 22% 19% 1	3272
	21st to end	Night	40% 7% 10% 17% 23% 2	4873

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	15% 6% 24% 33% 18% 4	270
	11th to 20th	Day	10% 11% 29% 35% 14% 1	270
	21st to end	Day	9% 5% 24% 45% 15% 2	297
February	1st to 10th	Day	11% 12% 32% 34% 9% 1	270
	11th to 20th	Day	13% 13% 31% 31% 10% 1	270
	21st to end	Day	12% 15% 32% 32% 8% 1	225
March	1st to 10th	Day	14% 17% 26% 30% 11% 2	446
	11th to 20th	Day	9% 16% 28% 31% 15% 2	460
	21st to end	Day	17% 20% 33% 23% 7% 1	506
April	1st to 10th	Day	13% 16% 31% 26% 12% 2	460
	11th to 20th	Day	15% 19% 34% 21% 9% 1	452
	21st to end	Day	11% 19% 34% 22% 13%	460
May	1st to 10th	Day	13% 19% 33% 24% 11% 1	463
	11th to 20th	Day	9% 9% 28% 30% 20% 4	544
	21st to end	Day	7% 13% 25% 34% 19% 3	734
June	1st to 10th	Day	4 7% 26% 35% 25% 3	680
	11th to 20th	Day	5% 8% 28% 37% 20% 2	680
	21st to end	Day	2 6% 24% 41% 24% 2	680
July	1st to 10th	Day	1 3 16% 42% 34% 5%	671
	11th to 20th	Day	3 1 11% 41% 35% 9%	515
	21st to end	Day	5% 3 12% 37% 35% 8%	531
August	1st to 10th	Day	4 4 18% 37% 30% 7%	487
	11th to 20th	Day	3 3 17% 39% 31% 7%	477
	21st to end	Day	4 1 16% 41% 31% 7%	539
September	1st to 10th	Day	5% 3 20% 34% 29% 8%	490
	11th to 20th	Day	5% 6% 27% 38% 21% 3	490
	21st to end	Day	5% 10% 20% 28% 29% 7%	401
October	1st to 10th	Day	7% 9% 21% 26% 26% 11%	300
	11th to 20th	Day	4 10% 24% 32% 25% 5%	300
	21st to end	Day	8% 8% 25% 32% 24% 4	330
November	1st to 10th	Day	6% 13% 27% 32% 20% 3	300
	11th to 20th	Day	6% 6% 29% 36% 19% 4	300
	21st to end	Day	12% 5% 27% 33% 19% 4	300
December	1st to 10th	Day	8% 11% 29% 32% 16% 5%	285
	11th to 20th	Day	11% 3 29% 36% 18% 3	270
	21st to end	Day	13% 9% 30% 34% 11% 2	297
January	1st to 10th	Night	11% 5% 22% 43% 18% 1	860
	11th to 20th	Night	11% 4 24% 43% 16% 1	760
	21st to end	Night	13% 4 22% 46% 14% 2	836
February	1st to 10th	Night	12% 4 29% 43% 11% 1	760
	11th to 20th	Night	10% 5% 31% 40% 13%	744
	21st to end	Night	14% 5% 32% 42% 7%	628
March	1st to 10th	Night	11% 6% 31% 40% 11% 1	760
	11th to 20th	Night	6% 4 27% 44% 18% 1	760
	21st to end	Night	13% 8% 27% 41% 11%	826
April	1st to 10th	Night	10% 7% 34% 41% 9%	570
	11th to 20th	Night	12% 8% 28% 38% 12% 2	563
	21st to end	Night	11% 6% 29% 37% 16% 1	570
May	1st to 10th	Night	11% 8% 27% 42% 12%	570
	11th to 20th	Night	8% 4 22% 43% 20% 2	561
	21st to end	Night	7% 8% 25% 37% 21% 2	617
June	1st to 10th	Night	2 3 21% 45% 27% 1	570
	11th to 20th	Night	4 5% 21% 49% 21% 1	570
	21st to end	Night	2 2 16% 48% 31% 1	570
July	1st to 10th	Night	3 1 10% 47% 37% 2	555
	11th to 20th	Night	3 6% 43% 45% 3	552
	21st to end	Night	4 1 6% 42% 45% 2	624
August	1st to 10th	Night	5% 1 10% 41% 41% 2	567
	11th to 20th	Night	3 2 10% 46% 37% 2	564
	21st to end	Night	4 1 11% 45% 37% 2	627
September	1st to 10th	Night	4 2 12% 46% 36% 1	570
	11th to 20th	Night	4 2 14% 46% 32% 1	573
	21st to end	Night	6% 2 17% 40% 31% 4	760
October	1st to 10th	Night	7% 4 18% 45% 24% 1	760
	11th to 20th	Night	6% 2 22% 44% 24% 2	760
	21st to end	Night	10% 4 20% 41% 22% 3	836
November	1st to 10th	Night	5% 4 23% 47% 21% 1	810
	11th to 20th	Night	9% 4 24% 43% 18% 2	1000
	21st to end	Night	9% 6% 23% 43% 18% 2	1000
December	1st to 10th	Night	12% 4 22% 45% 16% 1	978
	11th to 20th	Night	14% 5% 26% 39% 16% 1	950
	21st to end	Night	13% 6% 26% 43% 11% 1	1045

Page generated at 2024-12-03 04:45:15. Version ac07

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