Marietta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marietta clear sky chart from 2005-11-06 to 2025-10-19.

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% 2 6% 4 4 5% 4 6% 8% 41%	126352
	Night	13% 7% 2 6% 4 4 4 4 5% 7% 44%	123370
Transparency	Day	39% 7% 11% 20% 18% 5%	130138
	Night	38% 6% 10% 20% 21% 6%	127640
Seeing	Day	16% 10% 22% 22% 19% 10%	16113
	Night	16% 8% 23% 29% 21% 4	26086

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% 9% 4 5% 3 3 4 3 4 4 46%	4056
	11th to 20th	Day	11% 8% 3 5% 3 3 4 2 4 5% 52%	4060
	21st to end	Day	22% 10% 3 7% 3 3 3 2 4 6% 37%	4711
February	1st to 10th	Day	16% 8% 3 6% 5% 4 5% 3 5% 7% 39%	2000
	11th to 20th	Day	22% 8% 2 6% 4 2 4 4 5% 5% 39%	1948
	21st to end	Day	20% 7% 2 6% 4 4 3 3 5% 5% 40%	1650
March	1st to 10th	Day	21% 11% 3 7% 4 4 4 3 5% 5% 34%	4572
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 5% 7% 49%	4980
	21st to end	Day	15% 6% 3 7% 5% 4 4 3 4 6% 43%	5465
April	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 6% 6% 45%	2285
	11th to 20th	Day	11% 5% 2 7% 4 4 4 3 6% 6% 48%	2374
	21st to end	Day	10% 5% 2 5% 4 4 4 4 7% 8% 48%	2540
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 9% 35%	5862
	11th to 20th	Day	17% 8% 3 8% 5% 5% 6% 5% 7% 8% 29%	5861
	21st to end	Day	13% 7% 3 6% 4 4 4 4 6% 8% 40%	6433
June	1st to 10th	Day	9% 7% 3 9% 5% 5% 6% 5% 8% 10% 34%	2600
	11th to 20th	Day	6% 3 1 5% 4 6% 6% 6% 10% 11% 43%	2600
	21st to end	Day	6% 5% 2 7% 6% 6% 6% 6% 8% 11% 39%	2600
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 7% 6% 9% 12% 33%	5900
	11th to 20th	Day	6% 4 2 6% 6% 6% 7% 5% 9% 14% 35%	5900
	21st to end	Day	8% 8% 3 9% 7% 8% 7% 6% 9% 11% 24%	6424
August	1st to 10th	Day	6% 5% 2 7% 5% 5% 6% 5% 9% 13% 37%	4234
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 7% 11% 43%	3858
	21st to end	Day	7% 4 2 5% 4 4 4 4 8% 9% 48%	4312
September	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 4 7% 9% 41%	2223
	11th to 20th	Day	13% 7% 3 6% 4 4 5% 5% 5% 8% 42%	2200
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 5% 6% 47%	2200
October	1st to 10th	Day	12% 5% 2 5% 2 3 4 3 4 6% 54%	2200
	11th to 20th	Day	10% 4 1 4 3 3 3 3 5% 6% 57%	2088
	21st to end	Day	13% 6% 2 5% 3 3 3 2 4 5% 55%	2085
November	1st to 10th	Day	13% 7% 2 5% 3 3 3 2 5% 5% 52%	1762
	11th to 20th	Day	14% 5% 2 5% 3 4 3 3 5% 5% 52%	1800
	21st to end	Day	13% 5% 2 6% 4 3 4 4 6% 7% 46%	1800
December	1st to 10th	Day	19% 6% 2 5% 3 3 4 3 4 6% 45%	2930
	11th to 20th	Day	15% 10% 3 8% 5% 4 4 3 4 5% 39%	3373
	21st to end	Day	21% 7% 3 5% 3 3 3 3 5% 6% 39%	4466
January	1st to 10th	Night	16% 7% 2 6% 3 4 3 3 4 6% 46%	5889
	11th to 20th	Night	13% 8% 3 6% 3 4 4 3 4 4 48%	5900
	21st to end	Night	19% 10% 2 5% 3 3 3 2 3 5% 43%	6242
February	1st to 10th	Night	15% 8% 3 5% 4 4 4 3 5% 6% 43%	2400
	11th to 20th	Night	22% 7% 2 6% 4 3 3 3 3 5% 41%	2338
	21st to end	Night	19% 7% 2 7% 4 3 4 3 4 6% 41%	1980
March	1st to 10th	Night	20% 10% 3 7% 4 4 4 4 5% 6% 34%	5266
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 8% 51%	4980
	21st to end	Night	14% 6% 2 6% 5% 4 4 3 5% 6% 45%	5467
April	1st to 10th	Night	12% 5% 2 5% 4 4 5% 4 6% 7% 47%	2130
	11th to 20th	Night	13% 6% 2 4 3 4 4 3 6% 7% 50%	1975
	21st to end	Night	9% 5% 2 5% 4 4 3 4 6% 8% 50%	1860
May	1st to 10th	Night	10% 8% 3 8% 6% 5% 5% 4 6% 9% 37%	4033
	11th to 20th	Night	18% 8% 3 8% 5% 5% 5% 5% 7% 8% 30%	4032
	21st to end	Night	11% 6% 2 6% 4 4 4 4 7% 10% 42%	4421
June	1st to 10th	Night	6% 5% 2 7% 5% 6% 5% 6% 9% 12% 37%	1800
	11th to 20th	Night	4 4 2 5% 5% 5% 5% 5% 8% 12% 44%	1800
	21st to end	Night	6% 4 2 6% 4 5% 5% 5% 9% 11% 43%	1800
July	1st to 10th	Night	6% 7% 3 9% 7% 5% 6% 6% 8% 10% 33%	4058
	11th to 20th	Night	4 4 2 7% 5% 6% 7% 5% 9% 13% 36%	4057
	21st to end	Night	9% 8% 4 9% 6% 6% 7% 5% 8% 10% 28%	4427
August	1st to 10th	Night	7% 4 2 6% 5% 6% 5% 6% 8% 13% 38%	2915
	11th to 20th	Night	7% 6% 3 6% 5% 4 4 3 6% 8% 48%	3186
	21st to end	Night	8% 5% 2 5% 4 4 5% 3 6% 8% 50%	3586
September	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 4 7% 10% 41%	2155
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 6% 7% 45%	2200
	21st to end	Night	12% 6% 2 5% 4 4 5% 3 5% 6% 49%	2200
October	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 6% 55%	2200
	11th to 20th	Night	10% 4 2 5% 4 3 3 2 3 5% 60%	2267
	21st to end	Night	12% 5% 2 4 3 3 3 3 4 5% 57%	2508
November	1st to 10th	Night	13% 6% 2 4 4 3 3 3 4 5% 55%	2536
	11th to 20th	Night	12% 6% 2 5% 3 3 3 2 4 6% 53%	2600
	21st to end	Night	14% 6% 2 4 4 4 4 4 5% 6% 47%	2600
December	1st to 10th	Night	15% 7% 2 5% 3 3 3 3 4 5% 50%	4250
	11th to 20th	Night	17% 8% 2 5% 4 4 4 3 4 5% 45%	4822
	21st to end	Night	20% 7% 2 6% 4 4 4 3 4 6% 39%	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	42% 3 5% 22% 22% 5%	4057
	11th to 20th	Day	36% 2 6% 22% 28% 6%	4060
	21st to end	Day	49% 3 4 16% 21% 6%	4711
February	1st to 10th	Day	45% 4 8% 19% 20% 4	2000
	11th to 20th	Day	47% 4 6% 18% 19% 6%	1958
	21st to end	Day	46% 4 8% 15% 20% 8%	1650
March	1st to 10th	Day	52% 3 7% 11% 18% 7%	4572
	11th to 20th	Day	35% 5% 6% 15% 24% 16%	4980
	21st to end	Day	43% 4 7% 22% 20% 4	5465
April	1st to 10th	Day	37% 6% 10% 23% 18% 6%	2285
	11th to 20th	Day	36% 5% 7% 20% 24% 7%	2374
	21st to end	Day	33% 6% 11% 27% 20% 2	2540
May	1st to 10th	Day	43% 8% 14% 20% 14% 1	5897
	11th to 20th	Day	49% 9% 15% 19% 8% 1	5865
	21st to end	Day	40% 7% 10% 24% 17% 2	6447
June	1st to 10th	Day	41% 9% 16% 22% 10% 2	2600
	11th to 20th	Day	29% 10% 20% 27% 13% 1	2600
	21st to end	Day	35% 9% 17% 24% 12% 3	2600
July	1st to 10th	Day	37% 13% 20% 23% 7% 1	5835
	11th to 20th	Day	34% 13% 29% 19% 4 1	5831
	21st to end	Day	48% 13% 17% 18% 4	6240
August	1st to 10th	Day	34% 10% 14% 32% 10%	4221
	11th to 20th	Day	33% 9% 15% 26% 14% 2	3894
	21st to end	Day	29% 8% 15% 24% 21% 3	4311
September	1st to 10th	Day	37% 9% 15% 17% 18% 4	2223
	11th to 20th	Day	39% 8% 10% 21% 20% 2	2200
	21st to end	Day	36% 6% 11% 18% 22% 6%	2200
October	1st to 10th	Day	26% 3 6% 13% 39% 13%	3590
	11th to 20th	Day	20% 3 5% 16% 31% 26%	3393
	21st to end	Day	27% 3 5% 22% 31% 12%	3411
November	1st to 10th	Day	35% 3 7% 15% 30% 10%	1762
	11th to 20th	Day	35% 3 7% 18% 28% 10%	1800
	21st to end	Day	38% 5% 7% 19% 26% 6%	1800
December	1st to 10th	Day	41% 4 4 19% 27% 6%	2930
	11th to 20th	Day	48% 3 7% 18% 19% 5%	3370
	21st to end	Day	45% 4 8% 25% 16% 2	4466
January	1st to 10th	Night	39% 4 5% 20% 27% 5%	5889
	11th to 20th	Night	40% 2 5% 20% 26% 7%	5900
	21st to end	Night	45% 2 4 15% 28% 6%	6242
February	1st to 10th	Night	41% 4 8% 19% 19% 8%	2400
	11th to 20th	Night	47% 3 6% 17% 20% 7%	2339
	21st to end	Night	45% 4 6% 17% 18% 10%	1980
March	1st to 10th	Night	50% 4 7% 14% 19% 6%	5266
	11th to 20th	Night	31% 5% 8% 15% 26% 17%	4980
	21st to end	Night	40% 4 6% 22% 20% 8%	5467
April	1st to 10th	Night	36% 5% 9% 20% 23% 7%	2130
	11th to 20th	Night	33% 4 8% 20% 25% 10%	1975
	21st to end	Night	32% 5% 11% 27% 20% 5%	1860
May	1st to 10th	Night	41% 9% 15% 20% 12% 2	4060
	11th to 20th	Night	49% 7% 15% 20% 8% 1	4033
	21st to end	Night	36% 7% 14% 24% 17% 2	4429
June	1st to 10th	Night	35% 13% 17% 20% 14% 2	1800
	11th to 20th	Night	29% 10% 21% 24% 14% 2	1800
	21st to end	Night	30% 11% 19% 20% 15% 4	1800
July	1st to 10th	Night	42% 10% 17% 24% 6% 1	4015
	11th to 20th	Night	35% 14% 26% 19% 5% 1	4006
	21st to end	Night	48% 12% 19% 17% 4 1	4297
August	1st to 10th	Night	35% 9% 17% 31% 9% 1	2904
	11th to 20th	Night	33% 8% 14% 28% 16% 1	3216
	21st to end	Night	31% 8% 12% 20% 26% 3	3586
September	1st to 10th	Night	36% 10% 14% 18% 17% 5%	2155
	11th to 20th	Night	37% 9% 11% 22% 19% 3	2200
	21st to end	Night	35% 7% 11% 19% 20% 8%	2200
October	1st to 10th	Night	25% 3 8% 13% 37% 13%	3590
	11th to 20th	Night	18% 3 3 17% 34% 25%	3701
	21st to end	Night	23% 2 4 23% 31% 17%	4120
November	1st to 10th	Night	33% 4 8% 17% 27% 12%	2536
	11th to 20th	Night	33% 3 5% 18% 29% 12%	2600
	21st to end	Night	37% 4 6% 19% 26% 7%	2600
December	1st to 10th	Night	38% 4 5% 19% 27% 7%	4250
	11th to 20th	Night	42% 4 9% 15% 24% 6%	4824
	21st to end	Night	46% 4 6% 26% 17% 2	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	26% 26% 36% 10% 3	300
	11th to 20th	Day	29% 20% 30% 15% 5% 1	300
	21st to end	Day	24% 24% 36% 12% 3 1	330
February	1st to 10th	Day	19% 22% 39% 16% 4	300
	11th to 20th	Day	40% 19% 26% 14% 1	300
	21st to end	Day	28% 21% 36% 12% 3	249
March	1st to 10th	Day	26% 20% 31% 18% 6%	340
	11th to 20th	Day	23% 18% 32% 21% 6% 1	500
	21st to end	Day	19% 19% 32% 22% 5% 1	550
April	1st to 10th	Day	19% 15% 31% 22% 12% 1	500
	11th to 20th	Day	12% 16% 35% 22% 13% 2	492
	21st to end	Day	17% 8% 26% 28% 18% 3	500
May	1st to 10th	Day	13% 11% 30% 26% 14% 5%	503
	11th to 20th	Day	15% 4 24% 28% 17% 11%	527
	21st to end	Day	15% 6% 17% 26% 24% 12%	573
June	1st to 10th	Day	13% 4 15% 26% 29% 13%	530
	11th to 20th	Day	6% 4 14% 26% 25% 24%	530
	21st to end	Day	8% 5% 12% 26% 30% 19%	530
July	1st to 10th	Day	8% 2 8% 24% 33% 26%	525
	11th to 20th	Day	8% 2 9% 18% 32% 32%	524
	21st to end	Day	8% 1 9% 21% 38% 24%	576
August	1st to 10th	Day	13% 3 14% 21% 27% 22%	526
	11th to 20th	Day	11% 4 9% 23% 32% 21%	519
	21st to end	Day	14% 2 11% 24% 27% 22%	583
September	1st to 10th	Day	10% 3 14% 27% 29% 17%	530
	11th to 20th	Day	17% 3 12% 22% 34% 12%	530
	21st to end	Day	15% 4 18% 24% 30% 10%	530
October	1st to 10th	Day	16% 3 21% 32% 21% 8%	530
	11th to 20th	Day	11% 10% 24% 25% 25% 5%	522
	21st to end	Day	17% 8% 22% 28% 20% 4	534
November	1st to 10th	Day	20% 11% 30% 20% 15% 4	300
	11th to 20th	Day	17% 18% 35% 20% 8% 2	300
	21st to end	Day	10% 19% 38% 22% 10% 1	300
December	1st to 10th	Day	24% 24% 31% 16% 3 1	300
	11th to 20th	Day	23% 18% 32% 20% 6%	300
	21st to end	Day	31% 14% 34% 16% 5% 1	330
January	1st to 10th	Night	24% 19% 31% 21% 5% 1	800
	11th to 20th	Night	21% 16% 33% 23% 7%	800
	21st to end	Night	20% 16% 36% 24% 3	880
February	1st to 10th	Night	20% 13% 32% 31% 5%	800
	11th to 20th	Night	26% 15% 33% 23% 2	783
	21st to end	Night	22% 18% 35% 23% 3	660
March	1st to 10th	Night	19% 14% 35% 28% 5%	800
	11th to 20th	Night	17% 14% 34% 25% 10% 1	800
	21st to end	Night	17% 14% 30% 31% 8%	880
April	1st to 10th	Night	14% 12% 33% 28% 12% 1	730
	11th to 20th	Night	17% 11% 28% 32% 12% 1	593
	21st to end	Night	12% 7% 24% 38% 17% 2	600
May	1st to 10th	Night	10% 8% 26% 33% 23% 1	600
	11th to 20th	Night	13% 4 23% 32% 24% 3	591
	21st to end	Night	11% 2 15% 33% 31% 7%	650
June	1st to 10th	Night	9% 1 13% 37% 35% 6%	600
	11th to 20th	Night	4 2 13% 29% 39% 13%	600
	21st to end	Night	7% 2 8% 33% 42% 9%	600
July	1st to 10th	Night	8% 3 8% 24% 44% 14%	585
	11th to 20th	Night	6% 2 7% 18% 51% 16%	582
	21st to end	Night	7% 1 8% 25% 47% 11%	657
August	1st to 10th	Night	10% 2 7% 29% 43% 10%	597
	11th to 20th	Night	11% 2 9% 25% 43% 9%	594
	21st to end	Night	14% 2 9% 27% 38% 10%	660
September	1st to 10th	Night	10% 1 11% 28% 39% 11%	755
	11th to 20th	Night	17% 2 11% 28% 39% 5%	800
	21st to end	Night	15% 2 13% 34% 33% 3	800
October	1st to 10th	Night	10% 6% 20% 33% 24% 7%	800
	11th to 20th	Night	12% 6% 24% 33% 22% 3	793
	21st to end	Night	14% 8% 22% 35% 19% 3	836
November	1st to 10th	Night	15% 7% 22% 34% 21% 2	780
	11th to 20th	Night	16% 11% 30% 28% 14% 2	800
	21st to end	Night	19% 11% 27% 30% 13%	800
December	1st to 10th	Night	20% 14% 31% 28% 7% 1	800
	11th to 20th	Night	24% 10% 30% 27% 9% 1	800
	21st to end	Night	28% 12% 27% 27% 6%	880

Page generated at 2025-10-16 01:50:29. Version ac07

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