Silver Moonlight Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Silver Moonlight Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	11% 6% 2 6% 5% 4 5% 4 7% 9% 39%	126990
	Night	13% 7% 2 6% 4 4 4 3 5% 8% 43%	124597
Transparency	Day	37% 8% 16% 20% 13% 5%	130638
	Night	36% 7% 14% 20% 15% 8%	129012
Seeing	Day	11% 4 13% 25% 33% 14%	16225
	Night	14% 4 15% 29% 30% 8%	26126

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	21% 12% 3 7% 4 3 3 3 4 5% 34%	4086
	11th to 20th	Day	16% 8% 3 6% 3 3 3 3 5% 6% 44%	4080
	21st to end	Day	26% 9% 3 6% 4 4 4 3 6% 6% 30%	4488
February	1st to 10th	Day	20% 8% 3 7% 5% 4 4 4 5% 6% 34%	1915
	11th to 20th	Day	21% 9% 4 7% 4 3 3 3 4 5% 36%	2002
	21st to end	Day	19% 10% 3 6% 3 4 4 3 5% 6% 37%	1815
March	1st to 10th	Day	16% 8% 3 8% 5% 4 4 4 6% 8% 35%	4936
	11th to 20th	Day	14% 7% 3 7% 5% 4 4 3 5% 6% 42%	4980
	21st to end	Day	16% 8% 3 7% 5% 4 4 3 5% 7% 40%	5462
April	1st to 10th	Day	14% 8% 3 7% 4 4 4 3 6% 7% 39%	2200
	11th to 20th	Day	14% 7% 2 7% 5% 4 4 4 6% 7% 39%	2324
	21st to end	Day	9% 7% 2 6% 6% 5% 4 4 6% 8% 42%	2400
May	1st to 10th	Day	16% 9% 4 8% 5% 6% 6% 5% 8% 8% 26%	5405
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 42%	5811
	21st to end	Day	8% 6% 3 7% 5% 6% 7% 7% 10% 12% 28%	6434
June	1st to 10th	Day	4 3 1 5% 4 5% 5% 5% 9% 12% 47%	2600
	11th to 20th	Day	5% 4 1 5% 5% 6% 6% 6% 9% 12% 41%	2600
	21st to end	Day	7% 4 2 5% 5% 5% 6% 6% 10% 13% 36%	2600
July	1st to 10th	Day	6% 5% 2 7% 5% 5% 6% 5% 8% 12% 38%	5900
	11th to 20th	Day	4 5% 3 9% 6% 6% 7% 6% 9% 13% 32%	5900
	21st to end	Day	8% 6% 2 7% 6% 5% 5% 5% 8% 10% 39%	6422
August	1st to 10th	Day	2 2 1 2 2 3 4 4 7% 11% 62%	4234
	11th to 20th	Day	2 2 1 4 4 4 6% 6% 10% 15% 47%	3943
	21st to end	Day	5% 4 2 7% 6% 6% 7% 6% 9% 13% 37%	4217
September	1st to 10th	Day	9% 6% 2 7% 5% 6% 6% 6% 8% 11% 34%	2200
	11th to 20th	Day	12% 6% 2 8% 5% 5% 5% 6% 7% 9% 35%	2200
	21st to end	Day	8% 6% 2 5% 4 4 5% 5% 5% 7% 48%	2200
October	1st to 10th	Day	5% 4 1 5% 4 4 4 4 6% 8% 55%	2075
	11th to 20th	Day	8% 6% 2 5% 3 3 4 3 5% 6% 53%	2000
	21st to end	Day	9% 4 2 5% 4 4 3 3 5% 7% 54%	2200
November	1st to 10th	Day	9% 5% 3 5% 5% 4 5% 4 7% 8% 45%	2058
	11th to 20th	Day	14% 6% 2 5% 4 3 5% 3 5% 5% 47%	2100
	21st to end	Day	16% 6% 3 7% 5% 4 4 4 5% 6% 41%	2100
December	1st to 10th	Day	24% 9% 3 7% 4 3 4 3 4 6% 33%	3035
	11th to 20th	Day	11% 7% 2 6% 4 4 4 4 6% 9% 42%	3481
	21st to end	Day	13% 7% 3 7% 4 4 4 3 5% 6% 44%	4587
January	1st to 10th	Night	21% 8% 3 7% 4 4 4 3 4 6% 35%	5902
	11th to 20th	Night	17% 9% 3 6% 4 3 3 2 4 6% 44%	5900
	21st to end	Night	26% 9% 3 7% 4 3 4 3 5% 7% 29%	6490
February	1st to 10th	Night	19% 9% 2 7% 4 4 3 4 5% 6% 38%	2500
	11th to 20th	Night	19% 9% 4 5% 3 2 3 2 4 6% 42%	2283
	21st to end	Night	19% 9% 3 6% 4 4 4 4 4 6% 38%	1815
March	1st to 10th	Night	19% 10% 3 6% 3 4 4 3 5% 6% 37%	4919
	11th to 20th	Night	15% 9% 2 6% 4 3 4 3 4 5% 45%	4980
	21st to end	Night	16% 9% 2 6% 3 3 3 3 4 6% 45%	5467
April	1st to 10th	Night	13% 8% 2 6% 4 4 4 4 5% 7% 42%	2200
	11th to 20th	Night	14% 5% 2 6% 5% 3 4 3 3 8% 48%	2023
	21st to end	Night	12% 6% 2 7% 5% 4 4 4 5% 7% 44%	2000
May	1st to 10th	Night	22% 10% 3 7% 4 4 4 3 6% 8% 29%	4490
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 6% 9% 47%	4084
	21st to end	Night	11% 9% 3 7% 4 5% 5% 5% 8% 12% 32%	4443
June	1st to 10th	Night	6% 3 1 4 3 4 3 3 6% 13% 54%	1800
	11th to 20th	Night	5% 4 2 5% 4 3 4 4 8% 12% 50%	1800
	21st to end	Night	5% 4 2 5% 4 5% 6% 5% 9% 13% 41%	1800
July	1st to 10th	Night	5% 5% 2 6% 5% 5% 5% 4 8% 13% 43%	4078
	11th to 20th	Night	2 3 2 6% 5% 6% 6% 5% 8% 14% 45%	4077
	21st to end	Night	5% 4 2 6% 5% 5% 6% 4 7% 11% 45%	4449
August	1st to 10th	Night	1 1 2 2 2 3 3 5% 8% 73%	2926
	11th to 20th	Night	2 2 1 3 3 3 5% 3 7% 14% 56%	3105
	21st to end	Night	4 3 1 4 4 4 5% 5% 8% 14% 49%	3675
September	1st to 10th	Night	7% 5% 2 6% 5% 6% 6% 5% 8% 12% 40%	2200
	11th to 20th	Night	11% 7% 2 7% 5% 4 5% 5% 6% 8% 42%	2200
	21st to end	Night	7% 5% 2 6% 4 4 4 3 5% 9% 51%	2200
October	1st to 10th	Night	5% 4 1 4 4 3 4 4 5% 9% 58%	2302
	11th to 20th	Night	8% 3 1 4 2 3 3 3 5% 7% 60%	2400
	21st to end	Night	9% 4 2 4 3 3 4 3 4 5% 59%	2640
November	1st to 10th	Night	8% 5% 2 5% 4 5% 4 3 5% 7% 52%	2460
	11th to 20th	Night	12% 5% 2 5% 4 4 3 3 5% 6% 50%	2520
	21st to end	Night	13% 6% 2 6% 5% 4 5% 3 5% 6% 44%	2520
December	1st to 10th	Night	25% 9% 4 8% 4 4 3 3 5% 7% 28%	4370
	11th to 20th	Night	12% 8% 3 7% 5% 4 4 4 5% 7% 41%	4946
	21st to end	Night	13% 7% 3 7% 4 4 3 3 4 5% 46%	6633

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	52% 5% 7% 18% 13% 6%	4087
	11th to 20th	Day	40% 7% 9% 19% 17% 9%	4080
	21st to end	Day	54% 4 6% 12% 14% 9%	4488
February	1st to 10th	Day	50% 5% 8% 12% 14% 10%	1915
	11th to 20th	Day	50% 6% 9% 13% 15% 7%	2012
	21st to end	Day	47% 7% 11% 15% 12% 8%	1815
March	1st to 10th	Day	45% 9% 12% 16% 8% 11%	4936
	11th to 20th	Day	41% 8% 10% 13% 16% 13%	4980
	21st to end	Day	42% 7% 11% 18% 18% 4	5464
April	1st to 10th	Day	41% 9% 12% 16% 14% 8%	2200
	11th to 20th	Day	40% 9% 13% 16% 13% 8%	2324
	21st to end	Day	36% 9% 13% 21% 16% 5%	2400
May	1st to 10th	Day	48% 11% 15% 15% 8% 2	5440
	11th to 20th	Day	33% 9% 17% 22% 16% 3	5815
	21st to end	Day	38% 12% 19% 24% 6%	6447
June	1st to 10th	Day	23% 11% 22% 31% 14%	2600
	11th to 20th	Day	27% 11% 21% 28% 12% 1	2600
	21st to end	Day	31% 13% 24% 26% 5%	2600
July	1st to 10th	Day	35% 7% 37% 19% 2	5836
	11th to 20th	Day	40% 9% 33% 16% 2	5831
	21st to end	Day	37% 10% 24% 23% 5%	6240
August	1st to 10th	Day	14% 7% 22% 46% 10%	4220
	11th to 20th	Day	20% 11% 42% 25% 2	3981
	21st to end	Day	35% 13% 21% 22% 8% 1	4216
September	1st to 10th	Day	37% 15% 17% 18% 11% 3	2200
	11th to 20th	Day	41% 12% 14% 19% 14% 1	2200
	21st to end	Day	33% 9% 14% 21% 16% 8%	2200
October	1st to 10th	Day	20% 5% 9% 16% 19% 30%	3374
	11th to 20th	Day	22% 5% 8% 24% 31% 11%	3240
	21st to end	Day	23% 5% 8% 21% 33% 10%	3538
November	1st to 10th	Day	33% 8% 12% 21% 20% 6%	2058
	11th to 20th	Day	36% 6% 11% 17% 18% 11%	2100
	21st to end	Day	42% 8% 11% 17% 15% 9%	2100
December	1st to 10th	Day	52% 6% 10% 18% 12% 3	3035
	11th to 20th	Day	37% 7% 11% 19% 16% 9%	3479
	21st to end	Day	39% 7% 8% 16% 19% 11%	4587
January	1st to 10th	Night	48% 7% 8% 14% 14% 9%	5902
	11th to 20th	Night	42% 5% 7% 15% 22% 9%	5900
	21st to end	Night	55% 4 7% 11% 14% 9%	6490
February	1st to 10th	Night	46% 6% 9% 10% 16% 13%	2500
	11th to 20th	Night	43% 5% 9% 16% 17% 11%	2283
	21st to end	Night	46% 6% 9% 13% 17% 8%	1815
March	1st to 10th	Night	45% 8% 10% 16% 12% 10%	4919
	11th to 20th	Night	40% 7% 8% 13% 15% 16%	4980
	21st to end	Night	39% 6% 11% 16% 21% 7%	5467
April	1st to 10th	Night	40% 6% 12% 19% 15% 9%	2200
	11th to 20th	Night	36% 6% 13% 18% 14% 12%	2023
	21st to end	Night	37% 7% 13% 22% 15% 6%	2000
May	1st to 10th	Night	49% 9% 14% 16% 9% 3	4520
	11th to 20th	Night	31% 7% 14% 29% 14% 5%	4085
	21st to end	Night	38% 10% 20% 24% 6% 1	4452
June	1st to 10th	Night	23% 7% 20% 33% 17%	1800
	11th to 20th	Night	25% 7% 18% 33% 16% 2	1800
	21st to end	Night	29% 12% 25% 25% 9%	1800
July	1st to 10th	Night	32% 6% 37% 23% 2	4035
	11th to 20th	Night	29% 7% 38% 22% 3	4026
	21st to end	Night	33% 10% 25% 27% 6%	4320
August	1st to 10th	Night	10% 6% 19% 52% 13%	2916
	11th to 20th	Night	18% 6% 39% 32% 4	3133
	21st to end	Night	25% 14% 25% 25% 10% 1	3675
September	1st to 10th	Night	35% 11% 21% 19% 11% 4	2200
	11th to 20th	Night	40% 9% 14% 21% 15% 2	2200
	21st to end	Night	31% 7% 15% 22% 17% 7%	2200
October	1st to 10th	Night	19% 6% 9% 17% 20% 30%	3770
	11th to 20th	Night	17% 4 8% 25% 32% 14%	3899
	21st to end	Night	19% 4 7% 19% 35% 15%	4252
November	1st to 10th	Night	30% 7% 13% 21% 20% 9%	2460
	11th to 20th	Night	33% 5% 13% 18% 19% 11%	2520
	21st to end	Night	40% 6% 12% 19% 16% 7%	2520
December	1st to 10th	Night	56% 5% 9% 16% 9% 4	4370
	11th to 20th	Night	40% 6% 10% 16% 14% 13%	4947
	21st to end	Night	39% 6% 7% 16% 24% 8%	6633

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% 8% 30% 29% 10% 2	303
	11th to 20th	Day	18% 9% 26% 34% 13% 1	300
	21st to end	Day	21% 9% 31% 29% 10%	330
February	1st to 10th	Day	27% 5% 25% 32% 10% 1	300
	11th to 20th	Day	26% 7% 25% 32% 9% 1	300
	21st to end	Day	19% 8% 30% 36% 6%	249
March	1st to 10th	Day	18% 7% 32% 35% 9%	300
	11th to 20th	Day	21% 6% 30% 34% 7% 2	300
	21st to end	Day	15% 7% 26% 42% 10%	330
April	1st to 10th	Day	17% 10% 29% 33% 10%	300
	11th to 20th	Day	18% 8% 26% 28% 18% 2	442
	21st to end	Day	12% 6% 22% 41% 18% 2	500
May	1st to 10th	Day	14% 6% 20% 43% 16% 1	503
	11th to 20th	Day	10% 2 15% 41% 28% 3	700
	21st to end	Day	5% 3 12% 41% 36% 3	789
June	1st to 10th	Day	6% 2 4 29% 49% 10%	730
	11th to 20th	Day	8% 1 4 24% 52% 11%	730
	21st to end	Day	8% 1 5% 17% 48% 21%	730
July	1st to 10th	Day	8% 2 2 13% 46% 30%	721
	11th to 20th	Day	5% 1 2 7% 52% 34%	718
	21st to end	Day	6% 1 2 8% 52% 30%	794
August	1st to 10th	Day	3 2 7% 46% 42%	726
	11th to 20th	Day	3 1 1 5% 43% 47%	577
	21st to end	Day	10% 1 3 10% 35% 41%	527
September	1st to 10th	Day	12% 2 5% 12% 40% 30%	330
	11th to 20th	Day	9% 1 2 16% 45% 28%	330
	21st to end	Day	8% 1 4 12% 57% 18%	330
October	1st to 10th	Day	4 4 5% 26% 48% 12%	330
	11th to 20th	Day	9% 2 7% 27% 41% 14%	330
	21st to end	Day	14% 5% 13% 28% 35% 5%	363
November	1st to 10th	Day	12% 4 15% 31% 32% 6%	330
	11th to 20th	Day	14% 5% 15% 32% 28% 5%	330
	21st to end	Day	18% 6% 24% 31% 18% 2	330
December	1st to 10th	Day	18% 9% 19% 34% 17% 3	330
	11th to 20th	Day	21% 8% 20% 31% 18% 3	330
	21st to end	Day	18% 5% 24% 28% 22% 3	363
January	1st to 10th	Night	21% 8% 24% 32% 14% 1	1006
	11th to 20th	Night	20% 7% 26% 35% 12% 1	1000
	21st to end	Night	21% 7% 25% 36% 11%	1100
February	1st to 10th	Night	22% 8% 22% 34% 13%	900
	11th to 20th	Night	24% 6% 24% 32% 12% 1	729
	21st to end	Night	24% 7% 27% 34% 8%	495
March	1st to 10th	Night	20% 6% 26% 33% 15% 1	600
	11th to 20th	Night	17% 7% 21% 39% 15% 1	600
	21st to end	Night	14% 4 21% 41% 17% 2	660
April	1st to 10th	Night	16% 3 25% 40% 17%	600
	11th to 20th	Night	16% 5% 25% 34% 19%	593
	21st to end	Night	14% 4 23% 38% 20% 1	600
May	1st to 10th	Night	13% 7% 20% 42% 19%	600
	11th to 20th	Night	10% 2 16% 46% 24% 3	591
	21st to end	Night	6% 3 12% 37% 40% 3	650
June	1st to 10th	Night	5% 1 3 28% 56% 7%	600
	11th to 20th	Night	6% 1 3 26% 54% 10%	600
	21st to end	Night	7% 4 18% 49% 22%	600
July	1st to 10th	Night	6% 2 4 12% 49% 28%	585
	11th to 20th	Night	3 1 1 7% 53% 36%	582
	21st to end	Night	5% 1 2 8% 59% 25%	657
August	1st to 10th	Night	1 1 5% 59% 34%	597
	11th to 20th	Night	5% 1 7% 53% 34%	594
	21st to end	Night	6% 1 3 10% 48% 32%	660
September	1st to 10th	Night	9% 2 3 13% 48% 26%	600
	11th to 20th	Night	16% 1 4 15% 49% 16%	600
	21st to end	Night	11% 1 4 18% 53% 13%	600
October	1st to 10th	Night	6% 2 5% 25% 50% 12%	702
	11th to 20th	Night	10% 2 10% 32% 40% 8%	800
	21st to end	Night	10% 4 14% 30% 35% 6%	880
November	1st to 10th	Night	11% 4 12% 31% 36% 7%	820
	11th to 20th	Night	15% 3 15% 32% 32% 2	840
	21st to end	Night	15% 5% 21% 37% 19% 3	840
December	1st to 10th	Night	22% 6% 18% 29% 21% 3	1040
	11th to 20th	Night	19% 8% 19% 36% 17% 1	1050
	21st to end	Night	20% 7% 23% 32% 16% 2	1155

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