Auroraville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Auroraville 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	13% 8% 3 7% 4 4 5% 4 5% 7% 39%	126385
	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 39%	122596
Transparency	Day	43% 7% 12% 25% 13% 1	129857
	Night	45% 6% 11% 23% 14% 2	127197
Seeing	Day	16% 9% 28% 26% 15% 5%	17134
	Night	17% 8% 30% 31% 12% 1	26938

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	8% 10% 5% 14% 7% 5% 5% 3 5% 5% 33%	3617
	11th to 20th	Day	8% 11% 6% 10% 5% 5% 8% 5% 7% 5% 29%	3620
	21st to end	Day	12% 14% 6% 11% 5% 4 3 3 4 5% 33%	4046
February	1st to 10th	Day	11% 12% 4 9% 6% 5% 5% 4 6% 6% 32%	1800
	11th to 20th	Day	11% 11% 3 8% 5% 5% 5% 4 4 6% 37%	1878
	21st to end	Day	12% 11% 5% 8% 6% 5% 4 4 6% 6% 33%	1650
March	1st to 10th	Day	14% 7% 2 5% 3 3 4 4 5% 6% 47%	4480
	11th to 20th	Day	11% 7% 3 7% 4 4 4 4 5% 8% 44%	4741
	21st to end	Day	25% 10% 4 8% 4 4 4 3 3 5% 30%	5939
April	1st to 10th	Day	17% 13% 3 7% 5% 5% 4 5% 5% 6% 32%	2400
	11th to 20th	Day	20% 10% 3 7% 5% 4 4 4 5% 6% 34%	2374
	21st to end	Day	20% 9% 3 8% 5% 4 4 4 5% 6% 33%	2515
May	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 6% 7% 44%	6091
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 6% 7% 43%	6319
	21st to end	Day	16% 7% 2 6% 4 4 5% 4 6% 7% 39%	6935
June	1st to 10th	Day	12% 5% 2 6% 4 5% 4 4 5% 7% 45%	2800
	11th to 20th	Day	15% 6% 3 5% 5% 5% 5% 4 6% 9% 40%	2800
	21st to end	Day	12% 6% 2 7% 4 4 5% 4 6% 9% 41%	2800
July	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 9% 40%	6360
	11th to 20th	Day	7% 4 1 5% 4 4 5% 4 7% 10% 51%	6360
	21st to end	Day	9% 6% 3 6% 5% 5% 5% 4 6% 8% 44%	6924
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 8% 43%	4563
	11th to 20th	Day	12% 5% 1 5% 3 4 5% 4 6% 8% 45%	3988
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 4 5% 8% 42%	4312
September	1st to 10th	Day	13% 5% 3 7% 4 4 4 3 5% 7% 46%	2316
	11th to 20th	Day	12% 4 2 5% 4 4 4 4 5% 8% 49%	2204
	21st to end	Day	14% 6% 3 6% 4 5% 4 4 6% 7% 42%	2090
October	1st to 10th	Day	14% 7% 3 6% 4 3 4 3 5% 7% 45%	1957
	11th to 20th	Day	19% 10% 3 7% 4 5% 4 3 6% 7% 33%	1895
	21st to end	Day	17% 10% 3 7% 4 3 4 4 4 5% 38%	1881
November	1st to 10th	Day	13% 8% 2 7% 4 5% 5% 3 5% 6% 43%	1762
	11th to 20th	Day	13% 12% 4 9% 5% 5% 5% 3 6% 6% 31%	1768
	21st to end	Day	15% 11% 3 9% 5% 4 4 3 4 6% 36%	1600
December	1st to 10th	Day	9% 11% 6% 9% 6% 5% 5% 4 6% 7% 31%	2610
	11th to 20th	Day	12% 16% 5% 11% 5% 5% 4 3 4 6% 29%	3008
	21st to end	Day	20% 20% 7% 11% 5% 3 4 3 4 5% 17%	3982
January	1st to 10th	Night	9% 13% 7% 11% 6% 4 3 2 4 4 37%	6348
	11th to 20th	Night	10% 13% 6% 12% 6% 5% 7% 5% 5% 5% 26%	6360
	21st to end	Night	10% 16% 7% 10% 5% 4 4 3 4 5% 32%	6932
February	1st to 10th	Night	11% 13% 5% 9% 6% 5% 4 4 4 5% 35%	2600
	11th to 20th	Night	10% 10% 4 9% 6% 4 5% 4 4 5% 40%	2408
	21st to end	Night	15% 11% 4 9% 4 4 4 3 4 6% 36%	1980
March	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 5% 6% 46%	5373
	11th to 20th	Night	10% 8% 2 6% 6% 5% 5% 4 5% 7% 42%	5261
	21st to end	Night	23% 10% 4 9% 5% 4 4 3 4 5% 31%	4976
April	1st to 10th	Night	20% 10% 3 7% 5% 4 4 3 4 5% 36%	2000
	11th to 20th	Night	21% 8% 3 7% 3 4 4 3 5% 5% 37%	1975
	21st to end	Night	17% 8% 3 7% 4 3 4 3 5% 7% 39%	1885
May	1st to 10th	Night	15% 7% 3 7% 4 4 4 3 5% 6% 42%	3799
	11th to 20th	Night	10% 6% 2 6% 5% 4 5% 4 6% 8% 45%	3596
	21st to end	Night	18% 8% 2 6% 4 5% 4 4 5% 6% 37%	3942
June	1st to 10th	Night	10% 6% 2 6% 4 4 4 5% 6% 7% 47%	1600
	11th to 20th	Night	11% 6% 2 7% 4 4 4 4 6% 8% 43%	1600
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 48%	1600
July	1st to 10th	Night	12% 5% 2 5% 3 4 4 4 7% 9% 45%	3618
	11th to 20th	Night	9% 4 2 4 3 3 4 4 6% 8% 54%	3617
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 7% 51%	3947
August	1st to 10th	Night	11% 4 2 5% 4 3 4 4 4 8% 49%	2597
	11th to 20th	Night	11% 7% 3 6% 5% 4 5% 3 6% 7% 43%	3058
	21st to end	Night	10% 5% 2 6% 4 4 4 3 6% 8% 49%	3586
September	1st to 10th	Night	10% 5% 2 4 3 3 3 3 6% 7% 53%	1930
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 5% 5% 53%	1956
	21st to end	Night	11% 5% 2 6% 5% 3 4 4 5% 7% 49%	2090
October	1st to 10th	Night	12% 6% 2 7% 3 4 4 3 5% 6% 48%	2219
	11th to 20th	Night	16% 8% 3 6% 4 5% 4 4 5% 6% 40%	2285
	21st to end	Night	19% 9% 2 7% 5% 4 5% 4 4 6% 35%	2717
November	1st to 10th	Night	14% 8% 3 5% 4 4 4 3 5% 6% 45%	2536
	11th to 20th	Night	15% 11% 4 9% 5% 5% 4 4 4 5% 34%	2630
	21st to end	Night	15% 11% 3 8% 5% 4 4 4 5% 6% 36%	2800
December	1st to 10th	Night	9% 11% 4 8% 5% 4 4 4 5% 8% 38%	4580
	11th to 20th	Night	14% 17% 7% 11% 6% 4 3 3 4 4 27%	5199
	21st to end	Night	22% 17% 6% 11% 5% 4 3 3 4 5% 20%	6996

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	55% 6% 13% 19% 8%	3618
	11th to 20th	Day	52% 7% 9% 15% 15% 1	3620
	21st to end	Day	54% 5% 10% 19% 11%	4046
February	1st to 10th	Day	51% 6% 12% 20% 10% 1	1800
	11th to 20th	Day	46% 7% 12% 23% 10% 2	1887
	21st to end	Day	52% 7% 11% 18% 10% 2	1650
March	1st to 10th	Day	38% 4 13% 25% 14% 5%	4480
	11th to 20th	Day	37% 6% 14% 27% 15% 1	4741
	21st to end	Day	58% 5% 8% 17% 11% 1	5941
April	1st to 10th	Day	52% 6% 12% 19% 10% 1	2400
	11th to 20th	Day	50% 7% 9% 21% 12% 2	2374
	21st to end	Day	51% 7% 11% 19% 10% 2	2515
May	1st to 10th	Day	38% 7% 12% 25% 16% 2	6126
	11th to 20th	Day	38% 8% 11% 27% 16% 1	6323
	21st to end	Day	42% 6% 9% 26% 15% 1	6949
June	1st to 10th	Day	38% 7% 13% 26% 16% 1	2800
	11th to 20th	Day	39% 9% 13% 25% 14% 1	2800
	21st to end	Day	38% 8% 15% 25% 13% 2	2800
July	1st to 10th	Day	37% 8% 14% 32% 8% 1	6291
	11th to 20th	Day	28% 8% 14% 34% 15% 1	6285
	21st to end	Day	36% 8% 13% 24% 17% 2	6728
August	1st to 10th	Day	37% 7% 16% 27% 12% 1	4548
	11th to 20th	Day	35% 7% 12% 35% 11%	4027
	21st to end	Day	38% 7% 13% 27% 14% 1	4311
September	1st to 10th	Day	36% 7% 12% 26% 17% 1	2316
	11th to 20th	Day	33% 7% 16% 31% 12% 1	2204
	21st to end	Day	40% 6% 12% 29% 12%	2090
October	1st to 10th	Day	24% 4 7% 39% 25% 1	3256
	11th to 20th	Day	41% 5% 9% 28% 17% 1	3123
	21st to end	Day	42% 5% 13% 28% 12% 1	3081
November	1st to 10th	Day	42% 6% 14% 23% 14% 2	1762
	11th to 20th	Day	54% 6% 13% 19% 8% 1	1768
	21st to end	Day	51% 6% 14% 22% 6%	1600
December	1st to 10th	Day	52% 7% 16% 20% 5%	2610
	11th to 20th	Day	57% 5% 10% 18% 8% 1	3005
	21st to end	Day	70% 6% 7% 11% 6%	3982
January	1st to 10th	Night	52% 4 8% 24% 11% 1	6348
	11th to 20th	Night	59% 6% 9% 11% 15% 1	6360
	21st to end	Night	56% 5% 11% 16% 11%	6932
February	1st to 10th	Night	52% 6% 11% 20% 10% 1	2600
	11th to 20th	Night	46% 6% 11% 25% 11% 2	2409
	21st to end	Night	51% 5% 12% 19% 11% 2	1980
March	1st to 10th	Night	40% 5% 14% 25% 12% 4	5373
	11th to 20th	Night	38% 6% 16% 24% 13% 3	5261
	21st to end	Night	56% 5% 8% 18% 12% 1	4976
April	1st to 10th	Night	50% 5% 9% 18% 17% 1	2000
	11th to 20th	Night	48% 5% 9% 21% 15% 3	1975
	21st to end	Night	44% 7% 12% 22% 14% 1	1885
May	1st to 10th	Night	41% 7% 12% 18% 20% 2	3826
	11th to 20th	Night	34% 9% 14% 22% 18% 2	3597
	21st to end	Night	46% 7% 9% 23% 13% 2	3950
June	1st to 10th	Night	34% 7% 14% 27% 17% 1	1600
	11th to 20th	Night	37% 7% 11% 26% 18% 1	1600
	21st to end	Night	33% 8% 15% 27% 14% 3	1600
July	1st to 10th	Night	34% 6% 14% 32% 10% 3	3580
	11th to 20th	Night	28% 7% 15% 33% 17% 2	3572
	21st to end	Night	30% 8% 15% 24% 21% 2	3832
August	1st to 10th	Night	33% 7% 14% 26% 19% 1	2588
	11th to 20th	Night	38% 7% 12% 28% 14%	3085
	21st to end	Night	32% 6% 14% 25% 20% 2	3586
September	1st to 10th	Night	30% 7% 12% 27% 23% 1	1930
	11th to 20th	Night	32% 7% 11% 34% 15% 1	1956
	21st to end	Night	35% 6% 12% 31% 16% 1	2090
October	1st to 10th	Night	27% 4 6% 36% 24% 2	3700
	11th to 20th	Night	33% 4 11% 32% 17% 2	3796
	21st to end	Night	45% 5% 9% 24% 16%	4467
November	1st to 10th	Night	40% 6% 12% 26% 15% 2	2536
	11th to 20th	Night	52% 6% 12% 17% 11% 1	2630
	21st to end	Night	49% 5% 15% 23% 7% 1	2800
December	1st to 10th	Night	45% 6% 18% 22% 6% 3	4580
	11th to 20th	Night	62% 4 9% 14% 10% 1	5201
	21st to end	Night	67% 5% 8% 14% 6%	6996

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	14% 9% 34% 30% 10% 2	300
	11th to 20th	Day	20% 10% 36% 27% 6% 1	300
	21st to end	Day	18% 10% 33% 30% 8%	330
February	1st to 10th	Day	13% 13% 44% 23% 7% 1	300
	11th to 20th	Day	15% 15% 42% 19% 8% 1	300
	21st to end	Day	16% 14% 44% 23% 2	249
March	1st to 10th	Day	20% 12% 41% 19% 8% 1	300
	11th to 20th	Day	21% 15% 35% 19% 8% 3	300
	21st to end	Day	27% 10% 28% 24% 9% 1	535
April	1st to 10th	Day	24% 13% 32% 24% 7%	500
	11th to 20th	Day	26% 14% 29% 18% 11% 2	492
	21st to end	Day	22% 12% 28% 24% 11% 2	500
May	1st to 10th	Day	18% 10% 33% 26% 10% 2	602
	11th to 20th	Day	19% 10% 27% 26% 13% 5%	725
	21st to end	Day	18% 7% 25% 27% 15% 6%	789
June	1st to 10th	Day	11% 8% 28% 31% 17% 5%	730
	11th to 20th	Day	18% 6% 28% 28% 14% 5%	730
	21st to end	Day	13% 8% 27% 30% 16% 5%	730
July	1st to 10th	Day	9% 3 19% 29% 27% 13%	721
	11th to 20th	Day	9% 6% 23% 31% 22% 9%	718
	21st to end	Day	9% 3 23% 34% 22% 9%	794
August	1st to 10th	Day	9% 5% 21% 31% 24% 11%	726
	11th to 20th	Day	13% 5% 17% 26% 26% 14%	581
	21st to end	Day	11% 6% 20% 31% 21% 10%	583
September	1st to 10th	Day	14% 7% 21% 28% 21% 9%	502
	11th to 20th	Day	13% 3 18% 34% 23% 9%	490
	21st to end	Day	17% 9% 25% 24% 19% 6%	490
October	1st to 10th	Day	17% 9% 27% 24% 18% 5%	357
	11th to 20th	Day	18% 15% 34% 23% 9% 1	300
	21st to end	Day	23% 12% 36% 22% 7% 1	330
November	1st to 10th	Day	16% 13% 34% 25% 10% 2	300
	11th to 20th	Day	15% 19% 37% 20% 8% 1	300
	21st to end	Day	22% 13% 39% 21% 6%	300
December	1st to 10th	Day	15% 16% 39% 22% 7% 1	300
	11th to 20th	Day	20% 16% 37% 20% 7% 1	300
	21st to end	Day	27% 13% 36% 19% 4 1	330
January	1st to 10th	Night	17% 12% 35% 28% 8% 1	1000
	11th to 20th	Night	20% 11% 35% 28% 6% 1	1000
	21st to end	Night	20% 9% 33% 29% 8%	1100
February	1st to 10th	Night	18% 10% 37% 27% 7%	1000
	11th to 20th	Night	15% 12% 40% 25% 8%	853
	21st to end	Night	21% 10% 36% 28% 5%	660
March	1st to 10th	Night	19% 9% 33% 29% 9% 1	800
	11th to 20th	Night	16% 10% 36% 30% 7% 1	725
	21st to end	Night	22% 7% 29% 33% 9% 1	660
April	1st to 10th	Night	24% 9% 34% 27% 6%	600
	11th to 20th	Night	23% 9% 31% 30% 7% 1	593
	21st to end	Night	20% 9% 30% 34% 7% 1	600
May	1st to 10th	Night	19% 8% 32% 33% 7% 1	600
	11th to 20th	Night	18% 7% 31% 35% 9% 1	591
	21st to end	Night	15% 6% 24% 37% 18% 1	650
June	1st to 10th	Night	11% 7% 24% 43% 15% 1	600
	11th to 20th	Night	15% 4 29% 39% 12% 1	600
	21st to end	Night	12% 4 24% 44% 16% 1	600
July	1st to 10th	Night	8% 2 18% 43% 26% 2	585
	11th to 20th	Night	10% 3 19% 42% 24% 2	582
	21st to end	Night	7% 2 17% 49% 24% 2	657
August	1st to 10th	Night	8% 3 16% 47% 25% 2	597
	11th to 20th	Night	11% 4 16% 38% 27% 4	594
	21st to end	Night	12% 3 17% 43% 24% 2	660
September	1st to 10th	Night	11% 3 23% 37% 20% 5%	579
	11th to 20th	Night	15% 3 23% 32% 24% 4	626
	21st to end	Night	13% 8% 24% 33% 20% 2	760
October	1st to 10th	Night	15% 8% 26% 31% 19% 1	760
	11th to 20th	Night	20% 11% 33% 28% 8%	760
	21st to end	Night	25% 10% 29% 28% 8% 1	836
November	1st to 10th	Night	18% 8% 36% 26% 10% 1	780
	11th to 20th	Night	21% 14% 38% 22% 5%	830
	21st to end	Night	20% 12% 36% 25% 7%	1000
December	1st to 10th	Night	20% 12% 40% 22% 7%	1000
	11th to 20th	Night	23% 11% 34% 24% 7% 1	1000
	21st to end	Night	28% 12% 30% 26% 4	1100

Page generated at 2025-09-01 00:51:04. Version ac07

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