Mossy Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mossy Creek Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	12% 8% 3 7% 5% 5% 5% 4 6% 8% 37%	126844
	Night	13% 8% 3 7% 5% 4 5% 4 6% 8% 38%	123870
Transparency	Day	44% 3 11% 23% 16% 3	130581
	Night	44% 3 10% 22% 17% 4	128202
Seeing	Day	17% 8% 19% 24% 20% 11%	16330
	Night	17% 6% 19% 34% 20% 3	26366

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	16% 11% 4 10% 5% 5% 4 4 5% 6% 32%	4056
	11th to 20th	Day	15% 8% 6% 10% 6% 4 3 3 4 5% 35%	4060
	21st to end	Day	17% 13% 3 7% 4 4 3 3 4 6% 36%	4466
February	1st to 10th	Day	18% 10% 4 7% 5% 4 4 3 5% 6% 34%	1940
	11th to 20th	Day	22% 9% 4 9% 4 4 3 3 5% 5% 32%	1948
	21st to end	Day	21% 9% 3 7% 5% 4 3 4 4 6% 35%	1650
March	1st to 10th	Day	17% 9% 3 8% 5% 4 5% 3 5% 5% 35%	4699
	11th to 20th	Day	11% 7% 2 6% 4 3 3 3 5% 7% 48%	4980
	21st to end	Day	15% 8% 3 6% 4 4 4 3 4 6% 43%	5465
April	1st to 10th	Day	13% 6% 2 7% 4 5% 5% 5% 6% 7% 42%	2220
	11th to 20th	Day	14% 7% 2 6% 4 4 4 3 5% 7% 43%	2427
	21st to end	Day	12% 7% 3 7% 5% 5% 4 3 6% 7% 40%	2600
May	1st to 10th	Day	14% 9% 3 9% 6% 5% 5% 4 6% 9% 29%	5862
	11th to 20th	Day	12% 9% 4 10% 7% 6% 7% 5% 7% 7% 27%	5861
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 4 7% 9% 35%	6433
June	1st to 10th	Day	9% 5% 3 7% 7% 6% 6% 5% 7% 9% 37%	2600
	11th to 20th	Day	5% 5% 2 7% 6% 7% 7% 6% 8% 9% 38%	2600
	21st to end	Day	7% 5% 2 6% 5% 6% 6% 5% 9% 11% 38%	2600
July	1st to 10th	Day	5% 4 1 6% 5% 6% 6% 5% 9% 12% 40%	5900
	11th to 20th	Day	9% 6% 3 8% 6% 6% 6% 5% 8% 11% 33%	5900
	21st to end	Day	12% 9% 4 9% 7% 7% 7% 5% 8% 9% 22%	6424
August	1st to 10th	Day	8% 6% 2 9% 6% 6% 6% 6% 8% 10% 34%	4234
	11th to 20th	Day	8% 5% 2 7% 5% 6% 6% 5% 8% 12% 37%	4174
	21st to end	Day	5% 4 2 5% 4 4 6% 4 7% 9% 49%	4297
September	1st to 10th	Day	11% 6% 2 7% 6% 5% 5% 4 5% 8% 43%	2200
	11th to 20th	Day	12% 5% 2 7% 4 5% 5% 3 6% 8% 43%	2200
	21st to end	Day	14% 6% 2 6% 4 4 4 3 6% 7% 44%	2200
October	1st to 10th	Day	10% 6% 2 5% 3 3 3 4 5% 6% 53%	2200
	11th to 20th	Day	12% 5% 2 5% 3 3 4 3 4 7% 53%	2014
	21st to end	Day	15% 6% 3 5% 3 3 4 3 4 6% 48%	2200
November	1st to 10th	Day	10% 6% 2 5% 3 4 3 3 5% 7% 52%	1867
	11th to 20th	Day	12% 8% 2 5% 4 5% 3 3 5% 7% 47%	1890
	21st to end	Day	14% 8% 3 7% 4 3 5% 3 5% 6% 42%	1890
December	1st to 10th	Day	13% 9% 3 7% 4 4 5% 3 4 5% 42%	2948
	11th to 20th	Day	18% 13% 4 9% 5% 4 4 4 5% 5% 27%	3373
	21st to end	Day	13% 11% 4 9% 6% 6% 6% 4 6% 7% 29%	4466
January	1st to 10th	Night	15% 11% 4 11% 4 4 4 3 5% 6% 34%	5889
	11th to 20th	Night	19% 9% 3 6% 4 4 4 3 4 6% 38%	5900
	21st to end	Night	15% 11% 3 7% 4 4 4 3 5% 7% 37%	6490
February	1st to 10th	Night	17% 9% 3 7% 4 4 5% 4 5% 6% 35%	2455
	11th to 20th	Night	22% 10% 3 7% 4 4 4 3 5% 4 33%	2338
	21st to end	Night	20% 10% 3 7% 4 4 3 4 5% 6% 34%	1980
March	1st to 10th	Night	16% 9% 3 8% 5% 5% 4 3 5% 7% 35%	5153
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 8% 51%	4980
	21st to end	Night	12% 7% 2 6% 5% 5% 5% 4 6% 7% 40%	5467
April	1st to 10th	Night	12% 6% 3 6% 4 5% 4 4 6% 8% 43%	2195
	11th to 20th	Night	14% 7% 3 7% 4 3 4 4 5% 7% 44%	1921
	21st to end	Night	14% 6% 2 6% 5% 5% 5% 4 6% 6% 42%	1800
May	1st to 10th	Night	15% 9% 4 8% 6% 5% 6% 5% 6% 9% 28%	4033
	11th to 20th	Night	17% 10% 4 10% 6% 5% 5% 4 6% 7% 28%	4032
	21st to end	Night	13% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	4421
June	1st to 10th	Night	8% 6% 3 7% 6% 5% 6% 5% 7% 11% 35%	1800
	11th to 20th	Night	4 5% 2 6% 5% 5% 5% 5% 8% 13% 41%	1800
	21st to end	Night	6% 6% 2 7% 6% 6% 7% 5% 7% 10% 39%	1800
July	1st to 10th	Night	9% 6% 3 7% 6% 6% 7% 6% 8% 11% 31%	4058
	11th to 20th	Night	8% 6% 2 7% 4 6% 6% 5% 8% 12% 34%	4057
	21st to end	Night	11% 9% 4 11% 7% 6% 7% 5% 8% 10% 21%	4427
August	1st to 10th	Night	7% 6% 2 8% 6% 5% 6% 5% 7% 10% 37%	2915
	11th to 20th	Night	9% 7% 2 6% 4 5% 6% 4 7% 9% 42%	2875
	21st to end	Night	6% 4 2 5% 4 5% 5% 5% 6% 11% 49%	3573
September	1st to 10th	Night	11% 7% 2 7% 5% 5% 5% 4 5% 6% 44%	2190
	11th to 20th	Night	11% 7% 3 8% 6% 4 5% 3 6% 8% 40%	2200
	21st to end	Night	12% 6% 2 6% 5% 4 4 4 5% 6% 44%	2200
October	1st to 10th	Night	12% 5% 2 6% 4 3 3 3 5% 6% 51%	2200
	11th to 20th	Night	13% 6% 2 4 3 4 3 2 4 6% 52%	2385
	21st to end	Night	14% 6% 2 6% 3 3 3 2 4 5% 50%	2640
November	1st to 10th	Night	13% 5% 2 6% 4 3 4 4 4 6% 49%	2647
	11th to 20th	Night	14% 8% 2 5% 3 4 4 3 5% 6% 46%	2730
	21st to end	Night	14% 7% 3 6% 4 4 3 3 5% 7% 44%	2730
December	1st to 10th	Night	16% 9% 3 8% 5% 4 4 4 6% 7% 35%	4277
	11th to 20th	Night	20% 11% 4 10% 5% 5% 4 3 4 5% 31%	4822
	21st to end	Night	14% 12% 4 8% 5% 4 5% 4 6% 9% 29%	6490

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	53% 3 4 25% 14% 1	4057
	11th to 20th	Day	53% 2 4 17% 23% 1	4060
	21st to end	Day	51% 2 7% 24% 15% 1	4466
February	1st to 10th	Day	52% 3 8% 19% 17% 2	1940
	11th to 20th	Day	55% 3 8% 18% 14% 2	1958
	21st to end	Day	51% 2 7% 16% 18% 5%	1650
March	1st to 10th	Day	51% 2 5% 15% 19% 8%	4699
	11th to 20th	Day	37% 2 5% 19% 29% 8%	4980
	21st to end	Day	45% 2 5% 32% 15% 2	5465
April	1st to 10th	Day	40% 4 10% 24% 19% 3	2220
	11th to 20th	Day	41% 3 7% 20% 23% 6%	2427
	21st to end	Day	43% 3 10% 27% 14% 3	2600
May	1st to 10th	Day	52% 3 13% 21% 10% 1	5897
	11th to 20th	Day	55% 3 14% 19% 7% 1	5865
	21st to end	Day	46% 3 12% 21% 15% 3	6447
June	1st to 10th	Day	43% 5% 15% 23% 13% 2	2600
	11th to 20th	Day	38% 6% 18% 21% 15% 2	2600
	21st to end	Day	37% 7% 16% 23% 14% 3	2600
July	1st to 10th	Day	34% 7% 21% 23% 14% 1	5835
	11th to 20th	Day	43% 6% 24% 20% 5% 2	5831
	21st to end	Day	55% 5% 16% 16% 7%	6240
August	1st to 10th	Day	42% 5% 17% 25% 10% 1	4221
	11th to 20th	Day	38% 5% 18% 25% 12% 2	4213
	21st to end	Day	29% 4 15% 37% 13% 2	4297
September	1st to 10th	Day	40% 5% 11% 21% 17% 6%	2200
	11th to 20th	Day	40% 5% 10% 25% 18% 3	2200
	21st to end	Day	39% 4 11% 22% 18% 6%	2200
October	1st to 10th	Day	28% 3 6% 22% 31% 10%	3590
	11th to 20th	Day	25% 2 6% 26% 29% 12%	3254
	21st to end	Day	30% 1 6% 31% 23% 9%	3538
November	1st to 10th	Day	33% 3 8% 23% 28% 5%	1867
	11th to 20th	Day	38% 2 7% 25% 24% 4	1890
	21st to end	Day	42% 3 7% 25% 20% 3	1890
December	1st to 10th	Day	44% 3 6% 21% 24% 1	2948
	11th to 20th	Day	58% 2 8% 19% 12% 2	3370
	21st to end	Day	53% 2 11% 24% 10% 1	4466
January	1st to 10th	Night	52% 2 6% 22% 16% 1	5889
	11th to 20th	Night	48% 2 4 19% 22% 4	5900
	21st to end	Night	49% 2 5% 23% 19% 2	6490
February	1st to 10th	Night	49% 4 8% 21% 17% 2	2455
	11th to 20th	Night	55% 2 7% 18% 14% 4	2339
	21st to end	Night	51% 3 7% 19% 16% 4	1980
March	1st to 10th	Night	51% 1 5% 20% 17% 5%	5153
	11th to 20th	Night	32% 2 7% 22% 26% 11%	4980
	21st to end	Night	44% 2 9% 29% 15% 2	5467
April	1st to 10th	Night	39% 3 12% 24% 19% 4	2195
	11th to 20th	Night	40% 3 7% 21% 22% 6%	1921
	21st to end	Night	42% 4 10% 27% 15% 2	1800
May	1st to 10th	Night	54% 3 14% 20% 8% 1	4060
	11th to 20th	Night	56% 3 13% 20% 8%	4033
	21st to end	Night	47% 3 12% 23% 14% 1	4429
June	1st to 10th	Night	40% 7% 17% 21% 14% 1	1800
	11th to 20th	Night	32% 9% 20% 22% 15% 2	1800
	21st to end	Night	39% 7% 14% 22% 14% 5%	1800
July	1st to 10th	Night	44% 7% 19% 20% 10% 1	4015
	11th to 20th	Night	41% 5% 26% 19% 6% 2	4006
	21st to end	Night	55% 7% 16% 16% 6%	4297
August	1st to 10th	Night	41% 5% 18% 27% 8% 1	2904
	11th to 20th	Night	38% 5% 17% 28% 12% 1	2902
	21st to end	Night	29% 5% 14% 37% 13% 2	3573
September	1st to 10th	Night	41% 4 13% 19% 17% 6%	2190
	11th to 20th	Night	42% 4 12% 21% 19% 2	2200
	21st to end	Night	41% 4 8% 22% 20% 5%	2200
October	1st to 10th	Night	35% 3 6% 20% 28% 9%	3590
	11th to 20th	Night	24% 2 5% 25% 29% 15%	3884
	21st to end	Night	27% 2 4 29% 28% 10%	4252
November	1st to 10th	Night	38% 3 6% 23% 23% 7%	2647
	11th to 20th	Night	39% 3 5% 23% 24% 6%	2730
	21st to end	Night	41% 3 6% 27% 19% 3	2730
December	1st to 10th	Night	48% 3 6% 21% 21% 1	4277
	11th to 20th	Night	56% 2 6% 21% 13% 2	4824
	21st to end	Night	53% 2 12% 20% 12% 1	6490

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	25% 18% 32% 21% 4 1	300
	11th to 20th	Day	26% 21% 29% 16% 7% 1	300
	21st to end	Day	23% 18% 34% 19% 6%	330
February	1st to 10th	Day	22% 17% 31% 23% 7%	300
	11th to 20th	Day	36% 19% 29% 12% 4	300
	21st to end	Day	33% 20% 28% 15% 4	249
March	1st to 10th	Day	25% 14% 29% 21% 10% 1	389
	11th to 20th	Day	23% 15% 29% 26% 6% 1	500
	21st to end	Day	24% 13% 26% 27% 9%	550
April	1st to 10th	Day	20% 13% 25% 26% 15% 1	500
	11th to 20th	Day	18% 13% 23% 26% 17% 3	492
	21st to end	Day	19% 9% 25% 27% 15% 6%	500
May	1st to 10th	Day	17% 11% 30% 21% 15% 6%	503
	11th to 20th	Day	17% 7% 21% 22% 24% 10%	527
	21st to end	Day	15% 7% 15% 25% 19% 18%	573
June	1st to 10th	Day	11% 4 16% 26% 27% 16%	530
	11th to 20th	Day	6% 4 17% 27% 29% 18%	530
	21st to end	Day	9% 3 15% 24% 30% 18%	530
July	1st to 10th	Day	12% 2 10% 21% 30% 25%	525
	11th to 20th	Day	12% 3 8% 24% 29% 25%	524
	21st to end	Day	14% 2 7% 26% 29% 22%	576
August	1st to 10th	Day	16% 4 11% 21% 27% 21%	526
	11th to 20th	Day	13% 2 9% 26% 31% 19%	519
	21st to end	Day	13% 2 5% 20% 31% 30%	583
September	1st to 10th	Day	12% 3 9% 23% 32% 20%	530
	11th to 20th	Day	14% 4 9% 19% 32% 22%	530
	21st to end	Day	18% 5% 12% 27% 29% 10%	530
October	1st to 10th	Day	14% 3 14% 30% 25% 13%	530
	11th to 20th	Day	13% 8% 21% 28% 25% 5%	530
	21st to end	Day	20% 7% 19% 28% 22% 3	583
November	1st to 10th	Day	17% 7% 26% 28% 17% 5%	345
	11th to 20th	Day	14% 14% 32% 25% 15% 1	330
	21st to end	Day	17% 12% 25% 29% 15% 2	330
December	1st to 10th	Day	23% 17% 27% 23% 9%	306
	11th to 20th	Day	25% 9% 28% 27% 9% 1	300
	21st to end	Day	25% 11% 27% 27% 10% 1	330
January	1st to 10th	Night	22% 14% 24% 34% 5%	800
	11th to 20th	Night	27% 11% 28% 30% 5%	800
	21st to end	Night	21% 10% 33% 34% 2	880
February	1st to 10th	Night	22% 9% 28% 37% 4	800
	11th to 20th	Night	28% 12% 33% 26% 2	783
	21st to end	Night	24% 11% 33% 29% 3	660
March	1st to 10th	Night	22% 10% 27% 36% 5%	800
	11th to 20th	Night	19% 8% 33% 31% 8% 1	800
	21st to end	Night	19% 8% 27% 36% 9%	880
April	1st to 10th	Night	17% 9% 29% 33% 12% 1	795
	11th to 20th	Night	16% 7% 26% 36% 14%	593
	21st to end	Night	17% 4 20% 45% 14% 1	600
May	1st to 10th	Night	16% 6% 20% 38% 19% 2	600
	11th to 20th	Night	16% 5% 16% 35% 25% 4	591
	21st to end	Night	10% 4 12% 30% 38% 6%	650
June	1st to 10th	Night	11% 2 11% 36% 36% 5%	600
	11th to 20th	Night	5% 2 12% 36% 37% 9%	600
	21st to end	Night	10% 2 10% 32% 38% 9%	600
July	1st to 10th	Night	12% 2 6% 28% 42% 10%	585
	11th to 20th	Night	10% 2 4 24% 47% 13%	582
	21st to end	Night	10% 3 5% 27% 43% 11%	657
August	1st to 10th	Night	12% 3 5% 25% 46% 9%	597
	11th to 20th	Night	12% 2 4 30% 44% 7%	594
	21st to end	Night	12% 2 5% 25% 46% 11%	660
September	1st to 10th	Night	13% 3 8% 30% 38% 8%	790
	11th to 20th	Night	15% 3 8% 30% 38% 7%	800
	21st to end	Night	16% 3 12% 36% 31% 3	800
October	1st to 10th	Night	14% 4 15% 33% 29% 6%	800
	11th to 20th	Night	15% 5% 18% 41% 20% 2	800
	21st to end	Night	18% 5% 19% 38% 19% 2	880
November	1st to 10th	Night	16% 5% 16% 42% 19% 2	820
	11th to 20th	Night	17% 8% 22% 42% 11% 1	840
	21st to end	Night	18% 7% 23% 40% 12%	840
December	1st to 10th	Night	25% 7% 25% 36% 7%	809
	11th to 20th	Night	25% 8% 23% 36% 8%	800
	21st to end	Night	24% 9% 22% 39% 6%	880

Page generated at 2025-11-30 01:00:50. Version ac07

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