Chiefland Astronomy Village
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chiefland Astronomy Village clear sky chart from 2005-11-06 to 2025-09-04.

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	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 42%	125990
	Night	9% 6% 2 6% 4 4 5% 4 6% 9% 45%	122741
Transparency	Day	37% 6% 16% 20% 15% 6%	129750
	Night	37% 5% 15% 20% 16% 7%	127050
Seeing	Day	11% 8% 22% 26% 21% 12%	16421
	Night	11% 6% 21% 32% 23% 7%	26417

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	11% 5% 2 5% 3 2 2 3 4 7% 55%	4056
	11th to 20th	Day	20% 9% 3 8% 4 3 3 3 4 6% 37%	4060
	21st to end	Day	10% 5% 2 5% 3 3 4 3 6% 9% 50%	4805
February	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 5% 6% 45%	2000
	11th to 20th	Day	13% 5% 2 5% 4 3 3 3 5% 5% 53%	1948
	21st to end	Day	11% 6% 2 6% 3 4 3 3 5% 6% 50%	1650
March	1st to 10th	Day	14% 6% 2 6% 3 3 4 3 6% 9% 42%	4935
	11th to 20th	Day	8% 4 2 4 2 3 3 3 6% 8% 57%	4980
	21st to end	Day	11% 5% 2 5% 3 3 4 3 5% 9% 50%	5465
April	1st to 10th	Day	8% 4 2 4 3 4 4 4 7% 9% 51%	2200
	11th to 20th	Day	10% 5% 2 6% 3 4 5% 4 5% 7% 48%	2176
	21st to end	Day	5% 3 1 4 4 5% 4 4 7% 9% 55%	2513
May	1st to 10th	Day	5% 4 2 4 4 5% 6% 5% 7% 10% 49%	5862
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 9% 46%	5861
	21st to end	Day	4 3 2 4 4 4 5% 4 7% 11% 52%	6433
June	1st to 10th	Day	9% 6% 3 7% 6% 6% 7% 6% 9% 12% 30%	2600
	11th to 20th	Day	5% 5% 2 7% 7% 7% 8% 7% 9% 13% 31%	2600
	21st to end	Day	8% 6% 3 7% 7% 6% 8% 6% 9% 11% 29%	2600
July	1st to 10th	Day	6% 5% 3 8% 7% 8% 9% 8% 12% 14% 19%	5900
	11th to 20th	Day	4 4 2 6% 6% 8% 8% 8% 11% 15% 28%	5900
	21st to end	Day	5% 4 2 7% 6% 6% 8% 7% 10% 14% 30%	6424
August	1st to 10th	Day	10% 5% 3 6% 6% 6% 7% 6% 9% 13% 28%	4234
	11th to 20th	Day	6% 5% 2 7% 6% 6% 8% 7% 9% 12% 31%	3851
	21st to end	Day	10% 5% 3 7% 7% 7% 7% 6% 8% 12% 27%	4048
September	1st to 10th	Day	10% 7% 4 11% 8% 7% 7% 6% 8% 10% 22%	2123
	11th to 20th	Day	11% 8% 2 9% 7% 7% 7% 5% 8% 9% 27%	2090
	21st to end	Day	10% 7% 2 8% 6% 5% 5% 4 6% 8% 39%	2090
October	1st to 10th	Day	12% 6% 3 7% 6% 5% 5% 4 6% 7% 39%	2090
	11th to 20th	Day	6% 3 2 5% 4 4 4 3 5% 7% 57%	1952
	21st to end	Day	6% 4 2 5% 4 4 5% 4 5% 7% 52%	2090
November	1st to 10th	Day	8% 6% 1 4 4 4 4 3 6% 8% 51%	1957
	11th to 20th	Day	9% 7% 2 6% 4 5% 4 4 6% 5% 49%	1928
	21st to end	Day	11% 6% 1 6% 5% 3 4 3 5% 7% 49%	1800
December	1st to 10th	Day	6% 4 1 5% 3 4 4 3 5% 8% 57%	2930
	11th to 20th	Day	11% 6% 2 6% 3 3 4 4 6% 8% 47%	3373
	21st to end	Day	15% 7% 3 6% 4 4 3 3 5% 7% 43%	4466
January	1st to 10th	Night	10% 6% 2 4 3 2 3 3 4 7% 56%	5889
	11th to 20th	Night	19% 8% 3 8% 4 4 4 4 5% 7% 33%	5900
	21st to end	Night	15% 7% 2 6% 4 4 4 3 6% 8% 42%	6148
February	1st to 10th	Night	12% 6% 2 7% 5% 4 4 3 4 7% 47%	2400
	11th to 20th	Night	12% 8% 2 5% 4 3 3 4 6% 6% 47%	2338
	21st to end	Night	11% 6% 2 6% 3 3 4 4 4 5% 51%	1980
March	1st to 10th	Night	15% 8% 3 7% 4 4 4 3 5% 6% 42%	4918
	11th to 20th	Night	7% 6% 2 4 3 3 3 3 5% 9% 55%	4980
	21st to end	Night	11% 6% 2 5% 4 4 4 4 5% 7% 50%	5467
April	1st to 10th	Night	9% 5% 2 5% 4 3 5% 3 5% 7% 51%	2200
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 6% 8% 51%	2173
	21st to end	Night	6% 4 1 4 3 3 3 3 6% 8% 59%	1900
May	1st to 10th	Night	5% 3 1 5% 3 3 5% 3 7% 9% 55%	4033
	11th to 20th	Night	9% 5% 2 5% 4 4 3 3 5% 9% 51%	4032
	21st to end	Night	3 3 1 4 3 3 4 3 6% 10% 60%	4421
June	1st to 10th	Night	10% 6% 3 7% 4 5% 5% 4 9% 10% 38%	1800
	11th to 20th	Night	5% 4 2 5% 5% 4 7% 6% 10% 14% 38%	1800
	21st to end	Night	6% 4 1 7% 5% 5% 6% 7% 9% 13% 37%	1800
July	1st to 10th	Night	6% 6% 3 11% 7% 8% 9% 7% 10% 14% 20%	4058
	11th to 20th	Night	3 4 2 6% 5% 6% 6% 6% 10% 14% 39%	4057
	21st to end	Night	4 5% 3 9% 6% 6% 7% 7% 11% 13% 29%	4427
August	1st to 10th	Night	8% 4 2 7% 6% 6% 7% 7% 9% 12% 33%	2915
	11th to 20th	Night	4 4 2 5% 4 4 5% 5% 9% 16% 44%	3192
	21st to end	Night	7% 6% 3 9% 7% 6% 6% 6% 9% 11% 29%	3815
September	1st to 10th	Night	8% 7% 3 10% 5% 6% 7% 6% 8% 12% 29%	2124
	11th to 20th	Night	12% 7% 3 8% 6% 6% 6% 5% 8% 10% 29%	2090
	21st to end	Night	11% 6% 2 7% 4 4 5% 4 6% 9% 42%	2090
October	1st to 10th	Night	11% 6% 3 7% 5% 4 4 4 6% 7% 43%	2090
	11th to 20th	Night	7% 4 2 5% 3 4 3 4 6% 8% 56%	2225
	21st to end	Night	7% 5% 2 5% 4 4 4 4 5% 7% 52%	2508
November	1st to 10th	Night	8% 4 2 5% 4 4 4 3 5% 8% 53%	2341
	11th to 20th	Night	9% 6% 2 6% 4 3 4 3 5% 7% 51%	2468
	21st to end	Night	10% 5% 2 6% 5% 3 4 4 5% 7% 48%	2600
December	1st to 10th	Night	10% 5% 2 4 3 3 4 3 4 7% 56%	4250
	11th to 20th	Night	12% 8% 3 6% 3 3 4 3 5% 6% 47%	4822
	21st to end	Night	14% 8% 3 7% 4 4 4 4 5% 6% 41%	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	32% 2 7% 15% 28% 16%	4057
	11th to 20th	Day	51% 1 4 13% 19% 11%	4060
	21st to end	Day	33% 1 12% 26% 17% 11%	4805
February	1st to 10th	Day	41% 2 8% 15% 21% 12%	2000
	11th to 20th	Day	35% 2 9% 19% 25% 11%	1958
	21st to end	Day	35% 2 10% 18% 23% 12%	1650
March	1st to 10th	Day	41% 2 10% 17% 21% 9%	4935
	11th to 20th	Day	27% 2 12% 20% 23% 17%	4980
	21st to end	Day	34% 2 8% 26% 21% 9%	5465
April	1st to 10th	Day	29% 4 14% 21% 20% 11%	2200
	11th to 20th	Day	35% 3 9% 20% 22% 10%	2176
	21st to end	Day	25% 4 12% 26% 24% 9%	2513
May	1st to 10th	Day	30% 5% 20% 28% 13% 4	5897
	11th to 20th	Day	37% 3 14% 32% 13% 2	5865
	21st to end	Day	26% 4 19% 33% 16% 2	6447
June	1st to 10th	Day	45% 6% 19% 22% 7% 1	2600
	11th to 20th	Day	41% 9% 22% 22% 6%	2600
	21st to end	Day	45% 9% 23% 17% 5% 1	2600
July	1st to 10th	Day	47% 16% 30% 6% 1	5835
	11th to 20th	Day	37% 14% 36% 11% 1	5831
	21st to end	Day	39% 14% 27% 19% 2	6240
August	1st to 10th	Day	43% 9% 28% 16% 4	4221
	11th to 20th	Day	39% 10% 26% 18% 7%	3887
	21st to end	Day	46% 9% 23% 18% 3	4048
September	1st to 10th	Day	53% 9% 20% 12% 6%	2123
	11th to 20th	Day	51% 7% 19% 15% 7% 1	2090
	21st to end	Day	44% 5% 13% 19% 14% 5%	2090
October	1st to 10th	Day	53% 6% 10% 13% 12% 7%	3480
	11th to 20th	Day	21% 3 6% 19% 37% 14%	3218
	21st to end	Day	23% 3 7% 25% 32% 9%	3428
November	1st to 10th	Day	31% 3 11% 22% 20% 13%	1957
	11th to 20th	Day	37% 3 8% 19% 23% 11%	1928
	21st to end	Day	35% 2 9% 21% 24% 8%	1800
December	1st to 10th	Day	27% 3 14% 21% 24% 12%	2930
	11th to 20th	Day	35% 3 9% 24% 20% 9%	3370
	21st to end	Day	42% 3 8% 20% 22% 5%	4466
January	1st to 10th	Night	30% 1 7% 16% 32% 15%	5889
	11th to 20th	Night	52% 2 5% 17% 18% 6%	5900
	21st to end	Night	42% 2 10% 18% 17% 10%	6148
February	1st to 10th	Night	40% 2 9% 17% 20% 12%	2400
	11th to 20th	Night	38% 3 7% 19% 21% 11%	2339
	21st to end	Night	36% 4 9% 18% 23% 10%	1980
March	1st to 10th	Night	44% 2 9% 16% 18% 10%	4918
	11th to 20th	Night	28% 2 12% 20% 20% 18%	4980
	21st to end	Night	36% 2 9% 24% 20% 10%	5467
April	1st to 10th	Night	34% 4 13% 22% 18% 10%	2200
	11th to 20th	Night	31% 3 9% 25% 22% 10%	2173
	21st to end	Night	25% 3 12% 31% 21% 8%	1900
May	1st to 10th	Night	27% 4 20% 33% 13% 4	4060
	11th to 20th	Night	33% 2 17% 30% 17% 2	4033
	21st to end	Night	22% 4 17% 39% 17% 1	4429
June	1st to 10th	Night	39% 6% 22% 26% 7% 1	1800
	11th to 20th	Night	34% 9% 31% 23% 4	1800
	21st to end	Night	35% 11% 26% 22% 5% 1	1800
July	1st to 10th	Night	51% 16% 26% 6% 1	4015
	11th to 20th	Night	33% 14% 39% 12% 1	4006
	21st to end	Night	42% 13% 27% 17% 2	4297
August	1st to 10th	Night	40% 10% 35% 12% 3	2904
	11th to 20th	Night	27% 10% 32% 24% 6%	3222
	21st to end	Night	45% 11% 25% 15% 3	3815
September	1st to 10th	Night	47% 11% 23% 13% 4 1	2124
	11th to 20th	Night	49% 8% 20% 17% 5% 1	2090
	21st to end	Night	38% 6% 17% 21% 14% 4	2090
October	1st to 10th	Night	53% 6% 11% 13% 11% 7%	3480
	11th to 20th	Night	22% 3 7% 22% 35% 11%	3698
	21st to end	Night	25% 3 6% 22% 35% 9%	4120
November	1st to 10th	Night	31% 3 9% 23% 21% 13%	2341
	11th to 20th	Night	34% 2 8% 21% 22% 13%	2468
	21st to end	Night	36% 3 10% 19% 22% 11%	2600
December	1st to 10th	Night	30% 2 10% 23% 19% 15%	4250
	11th to 20th	Night	38% 4 9% 20% 19% 10%	4824
	21st to end	Night	44% 3 9% 21% 18% 5%	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	11% 19% 50% 15% 5%	300
	11th to 20th	Day	15% 15% 43% 17% 7% 2	300
	21st to end	Day	18% 25% 42% 12% 2	330
February	1st to 10th	Day	15% 15% 39% 20% 10% 1	300
	11th to 20th	Day	16% 20% 38% 19% 5% 1	300
	21st to end	Day	11% 17% 46% 19% 6%	249
March	1st to 10th	Day	15% 19% 33% 24% 8% 1	500
	11th to 20th	Day	15% 14% 33% 23% 13% 1	500
	21st to end	Day	12% 15% 33% 27% 12% 1	550
April	1st to 10th	Day	12% 15% 32% 26% 13% 1	500
	11th to 20th	Day	12% 11% 32% 28% 15% 2	492
	21st to end	Day	5% 7% 27% 34% 20% 6%	500
May	1st to 10th	Day	7% 10% 25% 29% 20% 9%	503
	11th to 20th	Day	10% 4 18% 35% 21% 12%	527
	21st to end	Day	9% 4 13% 28% 29% 17%	573
June	1st to 10th	Day	11% 3 16% 27% 25% 17%	530
	11th to 20th	Day	7% 3 13% 25% 30% 21%	530
	21st to end	Day	5% 2 7% 27% 30% 29%	530
July	1st to 10th	Day	7% 3 6% 20% 29% 34%	525
	11th to 20th	Day	6% 2 2 22% 32% 36%	524
	21st to end	Day	8% 2 6% 20% 35% 29%	576
August	1st to 10th	Day	11% 2 8% 21% 32% 26%	526
	11th to 20th	Day	8% 3 4 15% 35% 34%	519
	21st to end	Day	10% 2 6% 25% 34% 24%	583
September	1st to 10th	Day	14% 3 8% 23% 31% 22%	502
	11th to 20th	Day	11% 3 10% 30% 31% 15%	490
	21st to end	Day	11% 4 9% 28% 32% 16%	490
October	1st to 10th	Day	14% 6% 22% 33% 18% 7%	490
	11th to 20th	Day	4 5% 22% 35% 25% 8%	490
	21st to end	Day	8% 5% 26% 39% 21% 2	539
November	1st to 10th	Day	11% 7% 25% 34% 20% 3	495
	11th to 20th	Day	16% 8% 31% 29% 13% 2	428
	21st to end	Day	11% 10% 40% 27% 10% 2	300
December	1st to 10th	Day	8% 18% 38% 24% 10% 2	300
	11th to 20th	Day	15% 15% 37% 24% 9%	300
	21st to end	Day	13% 11% 37% 28% 10% 1	330
January	1st to 10th	Night	17% 12% 32% 30% 9%	800
	11th to 20th	Night	14% 12% 25% 35% 14% 1	800
	21st to end	Night	19% 12% 33% 28% 7%	880
February	1st to 10th	Night	15% 10% 29% 35% 11%	800
	11th to 20th	Night	16% 10% 32% 32% 9% 1	783
	21st to end	Night	13% 11% 32% 38% 6%	660
March	1st to 10th	Night	13% 12% 34% 34% 8%	800
	11th to 20th	Night	12% 11% 28% 35% 14% 1	800
	21st to end	Night	10% 10% 33% 35% 12%	880
April	1st to 10th	Night	11% 9% 30% 35% 14% 1	800
	11th to 20th	Night	9% 8% 34% 37% 12%	791
	21st to end	Night	7% 5% 26% 40% 20% 2	660
May	1st to 10th	Night	6% 3 22% 42% 24% 3	600
	11th to 20th	Night	6% 4 18% 38% 30% 4	591
	21st to end	Night	6% 2 11% 38% 36% 8%	650
June	1st to 10th	Night	12% 3 10% 35% 33% 8%	600
	11th to 20th	Night	6% 2 6% 27% 39% 21%	600
	21st to end	Night	8% 2 5% 20% 44% 21%	600
July	1st to 10th	Night	6% 3 4 18% 43% 27%	585
	11th to 20th	Night	5% 2 2 11% 48% 32%	582
	21st to end	Night	4 1 3 14% 54% 24%	657
August	1st to 10th	Night	8% 1 3 15% 48% 24%	597
	11th to 20th	Night	6% 2 4 13% 48% 27%	594
	21st to end	Night	9% 3 7% 23% 40% 18%	798
September	1st to 10th	Night	9% 3 8% 24% 38% 17%	773
	11th to 20th	Night	15% 3 9% 29% 32% 10%	760
	21st to end	Night	13% 2 12% 29% 36% 7%	760
October	1st to 10th	Night	14% 4 20% 36% 23% 3	760
	11th to 20th	Night	8% 6% 18% 39% 28% 2	760
	21st to end	Night	9% 3 24% 41% 22% 1	836
November	1st to 10th	Night	10% 6% 27% 37% 18% 3	780
	11th to 20th	Night	11% 8% 27% 37% 16% 1	800
	21st to end	Night	12% 7% 31% 38% 13% 1	800
December	1st to 10th	Night	14% 7% 25% 34% 19% 2	800
	11th to 20th	Night	14% 10% 28% 34% 13% 1	800
	21st to end	Night	16% 9% 29% 33% 13% 1	880

Page generated at 2025-09-01 01:51:04. Version ac07

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