Maryville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maryville clear sky chart from 2005-11-06 to 2024-10-25.

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	13% 7% 3 7% 5% 5% 5% 4 6% 8% 38%	100924
	Night	15% 8% 3 7% 4 4 4 4 5% 7% 39%	97848
Transparency	Day	44% 7% 12% 20% 14% 2	100736
	Night	44% 7% 12% 20% 15% 3	97705
Seeing	Day	18% 9% 21% 25% 19% 9%	14822
	Night	17% 7% 20% 31% 21% 3	24837

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	17% 11% 3 8% 5% 5% 4 4 8% 6% 30%	2836
	11th to 20th	Day	17% 11% 3 9% 5% 5% 5% 4 5% 5% 31%	2840
	21st to end	Day	23% 12% 3 7% 4 4 4 2 4 6% 32%	3124
February	1st to 10th	Day	20% 9% 4 8% 4 3 4 3 5% 6% 34%	1890
	11th to 20th	Day	21% 11% 3 8% 5% 3 3 2 4 6% 34%	1848
	21st to end	Day	22% 9% 3 5% 4 5% 5% 4 5% 5% 34%	1570
March	1st to 10th	Day	24% 10% 3 6% 4 4 4 3 5% 6% 32%	3232
	11th to 20th	Day	13% 6% 3 6% 4 4 3 3 5% 5% 47%	3480
	21st to end	Day	18% 8% 3 7% 4 4 4 3 5% 5% 38%	3815
April	1st to 10th	Day	11% 5% 2 6% 4 5% 6% 5% 7% 8% 42%	2147
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 6% 45%	2271
	21st to end	Day	14% 6% 2 6% 4 4 4 4 5% 7% 42%	2470
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 7% 35%	4082
	11th to 20th	Day	17% 7% 3 8% 6% 5% 5% 4 5% 6% 34%	4081
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 39%	4476
June	1st to 10th	Day	10% 6% 2 6% 6% 5% 6% 6% 7% 9% 37%	2470
	11th to 20th	Day	5% 5% 2 6% 5% 6% 7% 6% 8% 10% 41%	2470
	21st to end	Day	8% 5% 2 6% 6% 6% 6% 5% 8% 11% 38%	2470
July	1st to 10th	Day	6% 4 2 6% 5% 6% 7% 6% 10% 14% 35%	4120
	11th to 20th	Day	9% 6% 2 7% 6% 5% 6% 5% 7% 9% 40%	4120
	21st to end	Day	13% 11% 4 11% 8% 6% 7% 5% 8% 8% 19%	4466
August	1st to 10th	Day	7% 4 2 7% 5% 5% 6% 5% 8% 12% 37%	4104
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 6% 8% 10% 39%	3955
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 6% 8% 51%	4180
September	1st to 10th	Day	11% 6% 2 7% 5% 4 5% 4 6% 8% 43%	2100
	11th to 20th	Day	16% 6% 2 7% 5% 4 4 4 5% 8% 41%	2090
	21st to end	Day	15% 5% 2 5% 3 4 4 4 6% 7% 46%	2090
October	1st to 10th	Day	12% 5% 2 5% 3 3 4 3 5% 5% 55%	2090
	11th to 20th	Day	13% 5% 2 5% 3 3 3 3 4 7% 52%	1944
	21st to end	Day	16% 5% 1 4 4 3 4 3 4 6% 50%	2014
November	1st to 10th	Day	12% 4 2 5% 3 3 3 3 5% 5% 54%	1672
	11th to 20th	Day	12% 7% 2 5% 5% 4 3 3 5% 7% 48%	1710
	21st to end	Day	14% 8% 3 6% 4 3 3 4 5% 6% 44%	1710
December	1st to 10th	Day	20% 9% 3 7% 4 4 5% 4 5% 6% 33%	1710
	11th to 20th	Day	15% 13% 3 6% 4 4 4 4 5% 6% 35%	2153
	21st to end	Day	17% 16% 3 7% 4 4 4 3 5% 6% 31%	3124
January	1st to 10th	Night	20% 12% 3 8% 4 4 3 3 4 6% 33%	4109
	11th to 20th	Night	21% 9% 2 7% 5% 3 3 2 4 5% 37%	4120
	21st to end	Night	23% 12% 4 7% 4 3 3 3 3 5% 34%	4532
February	1st to 10th	Night	17% 10% 3 6% 4 4 4 4 6% 6% 36%	2288
	11th to 20th	Night	23% 10% 3 6% 4 4 4 3 4 4 35%	2218
	21st to end	Night	23% 9% 2 6% 4 5% 4 3 5% 6% 32%	1884
March	1st to 10th	Night	23% 9% 3 6% 4 5% 4 3 5% 6% 30%	3619
	11th to 20th	Night	14% 5% 2 5% 3 4 4 3 5% 8% 48%	3480
	21st to end	Night	15% 7% 2 7% 5% 4 5% 3 5% 6% 41%	3817
April	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 7% 47%	2047
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 46%	1856
	21st to end	Night	13% 5% 2 7% 4 4 5% 3 5% 7% 44%	1710
May	1st to 10th	Night	15% 7% 3 8% 4 4 6% 4 6% 8% 34%	2813
	11th to 20th	Night	20% 7% 3 6% 4 4 3 3 5% 8% 36%	2812
	21st to end	Night	8% 6% 2 8% 5% 5% 5% 5% 6% 10% 41%	3079
June	1st to 10th	Night	7% 6% 3 7% 5% 5% 5% 6% 9% 10% 37%	1710
	11th to 20th	Night	3 4 2 5% 4 4 5% 5% 9% 13% 46%	1710
	21st to end	Night	7% 5% 2 7% 5% 5% 6% 5% 7% 12% 40%	1710
July	1st to 10th	Night	9% 6% 2 7% 6% 6% 7% 5% 9% 11% 32%	2840
	11th to 20th	Night	9% 5% 2 6% 4 4 6% 4 8% 10% 42%	2840
	21st to end	Night	12% 10% 5% 10% 7% 6% 6% 5% 8% 9% 22%	3087
August	1st to 10th	Night	7% 6% 2 8% 5% 6% 6% 6% 7% 10% 38%	2825
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 5% 6% 10% 41%	2871
	21st to end	Night	6% 4 2 6% 4 4 5% 5% 8% 11% 47%	3476
September	1st to 10th	Night	10% 6% 2 7% 5% 5% 5% 4 6% 7% 43%	2059
	11th to 20th	Night	12% 6% 3 9% 4 4 6% 4 6% 7% 41%	2090
	21st to end	Night	12% 6% 2 5% 5% 5% 4 4 5% 7% 46%	2090
October	1st to 10th	Night	12% 6% 2 5% 3 3 3 2 5% 6% 54%	2090
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 4 5% 52%	2233
	21st to end	Night	14% 6% 2 5% 3 3 3 3 4 6% 52%	2443
November	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 4 5% 52%	2406
	11th to 20th	Night	14% 8% 2 5% 3 3 4 3 4 7% 47%	2470
	21st to end	Night	15% 7% 2 5% 4 4 4 3 5% 6% 45%	2470
December	1st to 10th	Night	20% 10% 3 7% 5% 4 3 3 5% 6% 34%	2470
	11th to 20th	Night	17% 11% 4 7% 3 3 3 3 4 6% 38%	3042
	21st to end	Night	19% 13% 3 8% 5% 5% 5% 4 6% 7% 26%	4532

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	51% 5% 10% 17% 15% 2	2837
	11th to 20th	Day	55% 5% 9% 13% 16% 1	2840
	21st to end	Day	54% 4 9% 19% 13% 1	3124
February	1st to 10th	Day	53% 5% 8% 16% 15% 2	1890
	11th to 20th	Day	55% 4 7% 17% 15% 2	1858
	21st to end	Day	52% 5% 8% 14% 16% 6%	1570
March	1st to 10th	Day	52% 6% 8% 16% 12% 6%	3232
	11th to 20th	Day	40% 5% 8% 22% 21% 4	3480
	21st to end	Day	48% 5% 9% 26% 11% 2	3815
April	1st to 10th	Day	39% 9% 11% 22% 16% 2	2147
	11th to 20th	Day	41% 6% 9% 17% 24% 4	2271
	21st to end	Day	42% 7% 10% 25% 13% 2	2470
May	1st to 10th	Day	47% 10% 12% 20% 11% 1	4120
	11th to 20th	Day	51% 8% 10% 21% 9% 1	4085
	21st to end	Day	39% 10% 13% 19% 17% 2	4489
June	1st to 10th	Day	43% 12% 14% 19% 11% 2	2470
	11th to 20th	Day	37% 12% 18% 20% 12% 2	2470
	21st to end	Day	39% 12% 16% 17% 13% 3	2470
July	1st to 10th	Day	37% 11% 24% 20% 8%	4055
	11th to 20th	Day	41% 8% 21% 21% 7% 2	4051
	21st to end	Day	62% 9% 13% 11% 5%	4324
August	1st to 10th	Day	40% 7% 17% 26% 8%	4091
	11th to 20th	Day	38% 8% 20% 21% 12% 1	3994
	21st to end	Day	32% 7% 14% 34% 11% 2	4179
September	1st to 10th	Day	40% 9% 12% 16% 17% 5%	2100
	11th to 20th	Day	44% 8% 11% 18% 17% 3	2090
	21st to end	Day	39% 7% 13% 19% 18% 5%	2090
October	1st to 10th	Day	32% 7% 10% 22% 23% 6%	2090
	11th to 20th	Day	33% 5% 9% 23% 24% 7%	1944
	21st to end	Day	35% 4 7% 24% 24% 5%	2014
November	1st to 10th	Day	33% 5% 9% 20% 28% 5%	1672
	11th to 20th	Day	37% 4 9% 22% 24% 5%	1710
	21st to end	Day	41% 5% 8% 21% 21% 4	1710
December	1st to 10th	Day	52% 8% 7% 19% 11% 2	1710
	11th to 20th	Day	50% 3 11% 17% 17% 2	2150
	21st to end	Day	53% 4 10% 23% 9% 1	3124
January	1st to 10th	Night	54% 4 9% 17% 14% 1	4109
	11th to 20th	Night	49% 4 11% 14% 18% 3	4120
	21st to end	Night	56% 4 9% 15% 15% 1	4532
February	1st to 10th	Night	49% 5% 9% 18% 16% 2	2288
	11th to 20th	Night	55% 5% 7% 16% 14% 4	2219
	21st to end	Night	53% 7% 8% 13% 15% 4	1884
March	1st to 10th	Night	53% 6% 11% 13% 14% 3	3619
	11th to 20th	Night	36% 5% 9% 24% 18% 8%	3480
	21st to end	Night	44% 5% 9% 24% 15% 2	3817
April	1st to 10th	Night	38% 6% 12% 22% 19% 3	2047
	11th to 20th	Night	39% 6% 10% 19% 21% 5%	1856
	21st to end	Night	39% 7% 11% 27% 14% 1	1710
May	1st to 10th	Night	45% 10% 13% 21% 10% 1	2840
	11th to 20th	Night	45% 9% 16% 20% 11%	2813
	21st to end	Night	36% 10% 17% 22% 14% 1	3087
June	1st to 10th	Night	38% 11% 17% 21% 11% 1	1710
	11th to 20th	Night	27% 12% 22% 25% 12% 1	1710
	21st to end	Night	38% 10% 15% 21% 12% 4	1710
July	1st to 10th	Night	42% 10% 20% 20% 8%	2795
	11th to 20th	Night	35% 8% 24% 25% 6% 2	2786
	21st to end	Night	57% 10% 16% 12% 5%	2988
August	1st to 10th	Night	39% 7% 17% 27% 10%	2814
	11th to 20th	Night	39% 7% 19% 24% 12%	2898
	21st to end	Night	32% 7% 13% 35% 12% 1	3476
September	1st to 10th	Night	40% 9% 14% 17% 16% 4	2059
	11th to 20th	Night	41% 10% 13% 17% 20% 1	2090
	21st to end	Night	38% 7% 12% 20% 19% 5%	2090
October	1st to 10th	Night	32% 5% 9% 20% 26% 7%	2090
	11th to 20th	Night	36% 5% 9% 22% 22% 7%	2233
	21st to end	Night	34% 4 8% 21% 25% 8%	2443
November	1st to 10th	Night	37% 5% 7% 20% 25% 7%	2406
	11th to 20th	Night	39% 4 7% 19% 23% 7%	2470
	21st to end	Night	41% 5% 8% 23% 20% 4	2470
December	1st to 10th	Night	54% 6% 10% 16% 12% 3	2470
	11th to 20th	Night	49% 4 9% 17% 19% 2	3044
	21st to end	Night	56% 6% 10% 17% 10% 1	4532

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% 24% 28% 21% 4	270
	11th to 20th	Day	31% 22% 25% 16% 4 1	270
	21st to end	Day	23% 21% 37% 14% 5%	297
February	1st to 10th	Day	26% 18% 29% 19% 7%	270
	11th to 20th	Day	37% 20% 27% 14% 2	270
	21st to end	Day	37% 20% 30% 12% 1	225
March	1st to 10th	Day	26% 15% 32% 17% 9% 1	330
	11th to 20th	Day	22% 16% 37% 19% 7%	460
	21st to end	Day	26% 13% 33% 20% 8%	506
April	1st to 10th	Day	21% 18% 22% 28% 10% 2	460
	11th to 20th	Day	20% 12% 28% 23% 14% 3	452
	21st to end	Day	19% 12% 27% 25% 13% 3	460
May	1st to 10th	Day	17% 12% 28% 23% 15% 5%	463
	11th to 20th	Day	14% 7% 24% 23% 23% 9%	487
	21st to end	Day	16% 5% 18% 25% 20% 16%	529
June	1st to 10th	Day	14% 5% 17% 30% 22% 11%	490
	11th to 20th	Day	8% 3 12% 29% 31% 16%	490
	21st to end	Day	11% 4 16% 29% 26% 15%	490
July	1st to 10th	Day	11% 3 12% 23% 30% 22%	485
	11th to 20th	Day	13% 2 9% 29% 27% 20%	484
	21st to end	Day	11% 3 8% 28% 31% 19%	532
August	1st to 10th	Day	16% 4 10% 23% 30% 17%	486
	11th to 20th	Day	11% 3 11% 28% 33% 13%	479
	21st to end	Day	14% 1 8% 22% 32% 23%	539
September	1st to 10th	Day	10% 4 10% 26% 35% 15%	490
	11th to 20th	Day	17% 3 8% 24% 30% 18%	490
	21st to end	Day	16% 5% 14% 27% 31% 7%	490
October	1st to 10th	Day	14% 6% 17% 27% 26% 10%	490
	11th to 20th	Day	14% 10% 21% 30% 21% 4	490
	21st to end	Day	22% 7% 17% 31% 20% 3	501
November	1st to 10th	Day	18% 9% 26% 30% 15% 3	270
	11th to 20th	Day	15% 13% 33% 31% 8% 1	270
	21st to end	Day	15% 9% 33% 29% 13% 1	270
December	1st to 10th	Day	27% 16% 30% 20% 5%	270
	11th to 20th	Day	24% 13% 29% 24% 10% 1	270
	21st to end	Day	26% 16% 29% 21% 7% 1	297
January	1st to 10th	Night	24% 13% 27% 30% 4	760
	11th to 20th	Night	25% 14% 30% 26% 5%	760
	21st to end	Night	22% 13% 32% 30% 2	836
February	1st to 10th	Night	22% 11% 31% 32% 4	760
	11th to 20th	Night	28% 15% 32% 23% 2	743
	21st to end	Night	30% 14% 31% 22% 2	628
March	1st to 10th	Night	23% 13% 28% 31% 5%	760
	11th to 20th	Night	23% 11% 33% 26% 6% 1	760
	21st to end	Night	22% 10% 31% 28% 9%	836
April	1st to 10th	Night	17% 10% 30% 33% 9% 1	717
	11th to 20th	Night	17% 10% 31% 28% 15%	563
	21st to end	Night	15% 6% 26% 38% 14% 1	570
May	1st to 10th	Night	15% 5% 23% 35% 18% 3	570
	11th to 20th	Night	16% 5% 19% 33% 25% 4	561
	21st to end	Night	8% 3 13% 32% 39% 4	617
June	1st to 10th	Night	10% 2 13% 36% 35% 4	570
	11th to 20th	Night	4 3 11% 35% 37% 10%	570
	21st to end	Night	8% 2 11% 33% 39% 6%	570
July	1st to 10th	Night	10% 3 7% 26% 46% 10%	555
	11th to 20th	Night	9% 3 5% 28% 45% 11%	552
	21st to end	Night	9% 2 6% 29% 42% 11%	624
August	1st to 10th	Night	10% 2 6% 26% 47% 9%	567
	11th to 20th	Night	11% 3 6% 31% 43% 6%	564
	21st to end	Night	11% 2 6% 24% 45% 13%	627
September	1st to 10th	Night	11% 4 7% 29% 41% 9%	729
	11th to 20th	Night	15% 4 8% 29% 38% 6%	760
	21st to end	Night	14% 3 13% 34% 33% 3	760
October	1st to 10th	Night	14% 4 16% 26% 32% 8%	760
	11th to 20th	Night	18% 5% 20% 35% 20% 2	760
	21st to end	Night	17% 5% 21% 37% 18% 2	812
November	1st to 10th	Night	17% 5% 18% 36% 21% 3	740
	11th to 20th	Night	16% 9% 27% 34% 13% 1	760
	21st to end	Night	20% 9% 23% 36% 13%	760
December	1st to 10th	Night	26% 10% 24% 32% 7%	760
	11th to 20th	Night	22% 10% 24% 34% 10%	760
	21st to end	Night	25% 13% 21% 35% 6%	836

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