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 2025-04-26.

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% 4 5% 4 6% 7% 39%	113951
	Night	14% 8% 3 7% 4 4 4 4 5% 7% 40%	114690
Transparency	Day	43% 6% 11% 21% 16% 3	117745
	Night	43% 5% 11% 21% 16% 4	119034
Seeing	Day	18% 9% 21% 24% 19% 8%	15423
	Night	17% 8% 21% 31% 20% 3	25550

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% 12% 3 9% 5% 4 4 3 6% 6% 32%	4056
	11th to 20th	Day	15% 10% 4 8% 4 4 4 4 4 6% 37%	4060
	21st to end	Day	21% 10% 3 7% 4 3 3 2 4 6% 36%	4466
February	1st to 10th	Day	19% 9% 4 8% 4 4 4 3 5% 6% 34%	1990
	11th to 20th	Day	22% 10% 3 8% 5% 3 3 2 4 6% 33%	1948
	21st to end	Day	21% 8% 2 5% 4 5% 5% 4 5% 5% 36%	1650
March	1st to 10th	Day	19% 9% 3 6% 5% 5% 4 3 6% 6% 34%	4634
	11th to 20th	Day	11% 6% 3 6% 4 4 4 3 5% 6% 48%	4980
	21st to end	Day	16% 7% 2 6% 4 4 4 3 5% 6% 42%	5465
April	1st to 10th	Day	12% 5% 2 6% 4 5% 6% 5% 7% 8% 42%	2260
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 6% 45%	2392
	21st to end	Day	15% 6% 2 6% 4 4 4 4 5% 7% 41%	2535
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	15% 5% 1 4 4 3 4 3 4 6% 50%	2076
November	1st to 10th	Day	12% 4 2 5% 3 3 3 3 5% 5% 53%	1762
	11th to 20th	Day	12% 7% 2 5% 4 4 3 4 5% 7% 47%	1800
	21st to end	Day	13% 8% 3 7% 4 3 4 4 4 7% 43%	1800
December	1st to 10th	Day	14% 7% 3 7% 5% 5% 4 4 5% 6% 41%	2930
	11th to 20th	Day	17% 13% 4 10% 6% 5% 4 3 5% 5% 28%	3373
	21st to end	Day	13% 14% 4 8% 5% 5% 4 4 6% 7% 30%	4466
January	1st to 10th	Night	17% 11% 4 9% 3 3 3 3 4 5% 38%	5889
	11th to 20th	Night	20% 8% 2 6% 4 3 3 2 4 5% 41%	5900
	21st to end	Night	18% 9% 4 7% 4 4 4 3 4 5% 40%	6490
February	1st to 10th	Night	17% 10% 3 6% 4 4 4 4 5% 6% 36%	2408
	11th to 20th	Night	23% 10% 3 6% 4 4 4 3 4 4 33%	2338
	21st to end	Night	22% 9% 2 6% 4 4 4 3 5% 6% 34%	1980
March	1st to 10th	Night	19% 10% 3 7% 4 4 4 3 5% 6% 35%	5217
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 5% 8% 50%	4980
	21st to end	Night	12% 7% 3 6% 5% 5% 5% 4 5% 7% 41%	5467
April	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 6% 7% 46%	2155
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 47%	1955
	21st to end	Night	13% 5% 2 7% 4 4 5% 4 6% 7% 43%	1761
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%	2517
November	1st to 10th	Night	13% 7% 2 5% 4 3 3 3 4 5% 51%	2536
	11th to 20th	Night	14% 8% 2 5% 3 3 4 3 4 7% 46%	2600
	21st to end	Night	15% 7% 2 5% 4 4 4 3 5% 6% 45%	2600
December	1st to 10th	Night	15% 10% 3 8% 4 4 3 3 5% 5% 39%	4250
	11th to 20th	Night	19% 12% 4 8% 5% 4 4 3 4 6% 32%	4822
	21st to end	Night	16% 12% 3 8% 5% 5% 5% 4 5% 7% 30%	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	52% 4 8% 20% 15% 1	4057
	11th to 20th	Day	50% 4 6% 15% 24% 1	4060
	21st to end	Day	50% 3 7% 23% 15% 2	4466
February	1st to 10th	Day	52% 5% 9% 17% 15% 2	1990
	11th to 20th	Day	56% 4 7% 16% 15% 2	1958
	21st to end	Day	51% 5% 7% 14% 18% 6%	1650
March	1st to 10th	Day	50% 4 6% 14% 17% 8%	4634
	11th to 20th	Day	39% 4 6% 17% 25% 10%	4980
	21st to end	Day	44% 3 8% 30% 13% 1	5465
April	1st to 10th	Day	39% 8% 11% 23% 16% 2	2260
	11th to 20th	Day	40% 6% 9% 17% 23% 4	2392
	21st to end	Day	43% 7% 10% 25% 13% 2	2535
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	26% 4 6% 21% 31% 11%	3480
	11th to 20th	Day	25% 3 6% 23% 29% 14%	3210
	21st to end	Day	27% 3 7% 30% 23% 10%	3402
November	1st to 10th	Day	33% 4 10% 20% 28% 5%	1762
	11th to 20th	Day	38% 4 9% 22% 24% 4	1800
	21st to end	Day	41% 5% 9% 21% 20% 4	1800
December	1st to 10th	Day	45% 5% 6% 19% 23% 2	2930
	11th to 20th	Day	59% 2 9% 16% 12% 1	3370
	21st to end	Day	51% 3 14% 23% 9% 1	4466
January	1st to 10th	Night	51% 3 8% 22% 15% 1	5889
	11th to 20th	Night	48% 3 8% 16% 20% 4	5900
	21st to end	Night	49% 3 7% 20% 18% 3	6490
February	1st to 10th	Night	49% 5% 9% 19% 16% 2	2408
	11th to 20th	Night	56% 5% 7% 16% 13% 3	2339
	21st to end	Night	51% 6% 8% 15% 16% 4	1980
March	1st to 10th	Night	50% 4 8% 16% 18% 4	5217
	11th to 20th	Night	33% 4 8% 21% 23% 12%	4980
	21st to end	Night	43% 4 10% 27% 14% 2	5467
April	1st to 10th	Night	39% 6% 12% 22% 18% 3	2155
	11th to 20th	Night	38% 5% 10% 20% 22% 5%	1955
	21st to end	Night	40% 7% 12% 26% 14% 1	1761
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	30% 3 6% 21% 29% 11%	3480
	11th to 20th	Night	26% 3 6% 23% 27% 15%	3706
	21st to end	Night	25% 3 5% 29% 25% 13%	4141
November	1st to 10th	Night	37% 4 7% 21% 24% 7%	2536
	11th to 20th	Night	40% 4 7% 19% 23% 7%	2600
	21st to end	Night	41% 4 8% 23% 20% 4	2600
December	1st to 10th	Night	50% 3 7% 16% 22% 2	4250
	11th to 20th	Night	55% 3 8% 18% 15% 1	4824
	21st to end	Night	52% 4 14% 18% 10% 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	23% 23% 29% 20% 4	300
	11th to 20th	Day	30% 21% 28% 15% 5% 1	300
	21st to end	Day	23% 21% 36% 15% 5%	330
February	1st to 10th	Day	24% 18% 31% 19% 7%	300
	11th to 20th	Day	37% 21% 27% 13% 2	300
	21st to end	Day	34% 20% 31% 14% 2	249
March	1st to 10th	Day	26% 17% 31% 17% 8% 1	363
	11th to 20th	Day	22% 16% 36% 19% 7%	500
	21st to end	Day	26% 13% 33% 21% 7%	550
April	1st to 10th	Day	21% 18% 24% 27% 9% 2	500
	11th to 20th	Day	19% 13% 28% 23% 14% 2	492
	21st to end	Day	19% 12% 27% 25% 13% 4	480
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	21% 7% 17% 31% 21% 3	525
November	1st to 10th	Day	17% 9% 27% 29% 15% 3	300
	11th to 20th	Day	16% 12% 31% 32% 9% 1	300
	21st to end	Day	15% 11% 33% 27% 13% 1	300
December	1st to 10th	Day	25% 18% 33% 19% 5%	300
	11th to 20th	Day	24% 14% 29% 24% 9% 1	300
	21st to end	Day	26% 17% 27% 21% 8% 1	330
January	1st to 10th	Night	24% 13% 28% 30% 4	800
	11th to 20th	Night	25% 14% 31% 26% 5%	800
	21st to end	Night	21% 13% 33% 30% 2	880
February	1st to 10th	Night	22% 11% 31% 32% 4	800
	11th to 20th	Night	28% 15% 32% 22% 2	783
	21st to end	Night	29% 14% 32% 23% 2	660
March	1st to 10th	Night	23% 14% 28% 31% 5%	800
	11th to 20th	Night	23% 11% 33% 27% 6% 1	800
	21st to end	Night	21% 10% 31% 29% 8%	880
April	1st to 10th	Night	17% 10% 31% 32% 9% 1	755
	11th to 20th	Night	17% 9% 31% 29% 14%	593
	21st to end	Night	16% 6% 25% 37% 15% 1	587
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% 20% 38% 18% 2	836
November	1st to 10th	Night	16% 5% 18% 38% 20% 3	780
	11th to 20th	Night	17% 9% 27% 34% 13% 1	800
	21st to end	Night	20% 9% 23% 35% 12%	800
December	1st to 10th	Night	26% 11% 25% 32% 7%	800
	11th to 20th	Night	22% 10% 25% 34% 10%	800
	21st to end	Night	24% 13% 21% 35% 6%	880

Page generated at 2025-04-23 09:25:05. Version ac07

Copyright © 2025 Attilla Danko.