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 2024-04-03.

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	14% 8% 4 7% 6% 3 5% 5% 5% 7% 37%	78718
	Night	14% 9% 4 7% 6% 3 4 4 5% 6% 38%	81471
Transparency	Day	46% 7% 13% 22% 11% 1	78418
	Night	47% 6% 12% 22% 12% 1	81291
Seeing	Day	16% 9% 28% 27% 15% 5%	15027
	Night	18% 8% 30% 31% 12% 1	25114

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% 13% 7% 10% 7% 4 5% 4 4 5% 29%	2527
	11th to 20th	Day	11% 12% 5% 11% 7% 4 8% 8% 6% 5% 22%	2530
	21st to end	Day	16% 17% 7% 11% 7% 3 4 3 5% 5% 21%	2819
February	1st to 10th	Day	11% 11% 5% 8% 7% 4 5% 5% 5% 6% 33%	1710
	11th to 20th	Day	11% 10% 4 7% 6% 3 5% 5% 5% 6% 37%	1781
	21st to end	Day	12% 10% 6% 8% 6% 4 5% 5% 6% 6% 33%	1570
March	1st to 10th	Day	13% 10% 4 7% 5% 3 5% 5% 5% 7% 37%	1900
	11th to 20th	Day	11% 10% 4 6% 6% 3 4 5% 5% 8% 39%	1986
	21st to end	Day	19% 10% 5% 6% 6% 3 5% 4 5% 7% 31%	2494
April	1st to 10th	Day	17% 12% 4 6% 6% 4 4 6% 4 6% 31%	2184
	11th to 20th	Day	20% 9% 3 6% 6% 3 5% 5% 4 5% 34%	2134
	21st to end	Day	20% 9% 3 7% 6% 4 4 5% 4 6% 33%	2263
May	1st to 10th	Day	17% 7% 3 7% 5% 4 5% 5% 6% 7% 33%	2429
	11th to 20th	Day	17% 7% 2 5% 6% 3 5% 4 5% 7% 38%	2479
	21st to end	Day	14% 6% 2 6% 6% 3 5% 5% 6% 7% 39%	2725
June	1st to 10th	Day	12% 5% 2 5% 4 3 5% 5% 5% 8% 46%	2520
	11th to 20th	Day	14% 4 3 4 5% 3 5% 4 6% 9% 42%	2520
	21st to end	Day	11% 6% 2 5% 5% 3 5% 5% 5% 10% 43%	2520
July	1st to 10th	Day	7% 4 2 4 4 3 6% 6% 8% 10% 47%	2520
	11th to 20th	Day	8% 4 2 4 4 3 5% 5% 7% 10% 48%	2520
	21st to end	Day	9% 4 2 4 5% 4 5% 5% 6% 9% 49%	2743
August	1st to 10th	Day	7% 5% 2 4 6% 4 5% 7% 7% 9% 44%	2507
	11th to 20th	Day	11% 6% 2 5% 5% 3 5% 6% 5% 8% 43%	2208
	21st to end	Day	12% 5% 2 5% 5% 3 5% 5% 5% 7% 45%	2376
September	1st to 10th	Day	14% 4 3 6% 5% 3 5% 4 5% 7% 45%	2160
	11th to 20th	Day	13% 4 2 4 5% 3 3 5% 5% 8% 48%	2088
	21st to end	Day	14% 6% 3 6% 5% 3 4 5% 6% 7% 41%	1980
October	1st to 10th	Day	15% 7% 3 5% 5% 2 4 4 5% 7% 43%	1854
	11th to 20th	Day	20% 9% 3 6% 6% 3 5% 4 6% 7% 31%	1796
	21st to end	Day	17% 10% 4 7% 5% 3 4 4 4 5% 37%	1782
November	1st to 10th	Day	12% 7% 3 7% 5% 4 5% 4 5% 6% 43%	1672
	11th to 20th	Day	14% 10% 6% 8% 6% 4 5% 4 5% 6% 32%	1680
	21st to end	Day	16% 10% 4 7% 5% 3 4 5% 4 6% 36%	1520
December	1st to 10th	Day	13% 11% 6% 10% 7% 3 5% 5% 5% 7% 30%	1520
	11th to 20th	Day	13% 12% 5% 9% 7% 4 5% 5% 4 7% 27%	1918
	21st to end	Day	20% 18% 8% 11% 8% 3 5% 4 4 5% 17%	2783
January	1st to 10th	Night	13% 14% 9% 9% 6% 3 3 3 3 4 33%	4428
	11th to 20th	Night	12% 12% 7% 12% 8% 4 7% 8% 6% 5% 21%	4440
	21st to end	Night	15% 18% 8% 10% 6% 3 4 4 4 4 24%	4848
February	1st to 10th	Night	11% 12% 5% 9% 6% 4 4 5% 4 5% 35%	2470
	11th to 20th	Night	10% 9% 4 7% 6% 4 5% 5% 5% 5% 40%	2285
	21st to end	Night	16% 10% 4 8% 6% 3 4 4 4 6% 36%	1884
March	1st to 10th	Night	15% 8% 4 6% 5% 3 4 4 6% 6% 39%	2280
	11th to 20th	Night	13% 7% 3 5% 7% 3 5% 4 5% 8% 41%	2209
	21st to end	Night	19% 9% 4 6% 5% 3 5% 4 4 6% 36%	2104
April	1st to 10th	Night	21% 8% 4 6% 6% 3 4 4 4 5% 35%	1820
	11th to 20th	Night	21% 7% 3 5% 4 3 4 4 5% 6% 37%	1775
	21st to end	Night	18% 7% 4 6% 5% 2 4 5% 5% 7% 38%	1697
May	1st to 10th	Night	19% 6% 3 6% 6% 3 5% 5% 5% 7% 34%	1529
	11th to 20th	Night	17% 7% 3 5% 5% 3 6% 4 5% 7% 39%	1416
	21st to end	Night	12% 4 2 5% 6% 3 5% 6% 6% 9% 41%	1551
June	1st to 10th	Night	10% 5% 2 5% 4 3 5% 6% 6% 8% 48%	1440
	11th to 20th	Night	11% 6% 2 5% 5% 2 5% 5% 5% 9% 44%	1440
	21st to end	Night	8% 4 2 4 4 3 4 5% 5% 9% 51%	1440
July	1st to 10th	Night	7% 5% 1 3 3 2 3 5% 6% 10% 55%	1440
	11th to 20th	Night	7% 3 2 5% 5% 3 5% 6% 5% 7% 52%	1440
	21st to end	Night	6% 3 1 4 4 3 4 5% 5% 8% 56%	1575
August	1st to 10th	Night	7% 4 2 4 4 3 5% 6% 5% 10% 50%	1432
	11th to 20th	Night	8% 6% 2 4 5% 2 5% 3 7% 8% 50%	1688
	21st to end	Night	10% 4 2 4 4 3 3 4 5% 7% 52%	1980
September	1st to 10th	Night	11% 5% 2 4 4 3 4 4 6% 7% 51%	1800
	11th to 20th	Night	13% 5% 2 4 4 2 4 4 4 5% 53%	1853
	21st to end	Night	12% 5% 2 5% 5% 2 4 5% 5% 7% 47%	1980
October	1st to 10th	Night	13% 6% 2 6% 4 2 4 4 5% 6% 47%	2102
	11th to 20th	Night	17% 8% 3 5% 5% 4 4 5% 5% 6% 38%	2164
	21st to end	Night	19% 9% 2 6% 5% 3 5% 5% 4 6% 35%	2574
November	1st to 10th	Night	13% 8% 3 4 5% 2 4 4 5% 7% 45%	2406
	11th to 20th	Night	15% 10% 4 8% 6% 3 5% 5% 4 5% 34%	2498
	21st to end	Night	15% 9% 4 6% 6% 3 4 4 4 6% 38%	2660
December	1st to 10th	Night	13% 13% 5% 8% 6% 3 5% 5% 4 7% 31%	2660
	11th to 20th	Night	13% 14% 6% 9% 7% 4 5% 4 4 5% 29%	3279
	21st to end	Night	23% 17% 6% 9% 6% 3 3 4 4 5% 21%	4884

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	59% 6% 14% 15% 6%	2528
	11th to 20th	Day	60% 9% 11% 15% 5%	2530
	21st to end	Day	66% 6% 10% 14% 4	2819
February	1st to 10th	Day	51% 6% 13% 20% 9% 1	1710
	11th to 20th	Day	46% 7% 12% 23% 10% 2	1790
	21st to end	Day	52% 7% 11% 18% 10% 2	1570
March	1st to 10th	Day	47% 7% 14% 21% 10% 2	1900
	11th to 20th	Day	43% 8% 13% 21% 13% 1	1986
	21st to end	Day	53% 6% 12% 21% 6% 1	2494
April	1st to 10th	Day	53% 7% 12% 17% 11% 1	2184
	11th to 20th	Day	51% 7% 8% 21% 11% 2	2134
	21st to end	Day	52% 7% 11% 18% 10% 2	2263
May	1st to 10th	Day	48% 8% 14% 21% 8% 1	2429
	11th to 20th	Day	43% 8% 13% 23% 11% 2	2483
	21st to end	Day	42% 8% 13% 23% 13% 2	2725
June	1st to 10th	Day	36% 7% 14% 27% 15% 1	2520
	11th to 20th	Day	37% 9% 13% 26% 15% 1	2520
	21st to end	Day	36% 9% 15% 26% 13% 2	2520
July	1st to 10th	Day	29% 9% 16% 30% 13% 2	2451
	11th to 20th	Day	30% 9% 16% 28% 15% 2	2445
	21st to end	Day	30% 9% 16% 27% 16% 3	2591
August	1st to 10th	Day	32% 9% 18% 28% 11% 1	2492
	11th to 20th	Day	37% 8% 14% 28% 12% 1	2208
	21st to end	Day	36% 8% 13% 25% 17% 1	2376
September	1st to 10th	Day	38% 7% 12% 25% 17% 1	2160
	11th to 20th	Day	34% 7% 16% 31% 11% 1	2088
	21st to end	Day	41% 7% 13% 29% 10%	1980
October	1st to 10th	Day	40% 7% 12% 28% 12%	1854
	11th to 20th	Day	51% 7% 13% 20% 9% 1	1796
	21st to end	Day	49% 7% 13% 20% 10%	1782
November	1st to 10th	Day	41% 6% 14% 23% 14% 2	1672
	11th to 20th	Day	54% 6% 13% 19% 8% 1	1680
	21st to end	Day	50% 6% 14% 22% 7%	1520
December	1st to 10th	Day	55% 6% 14% 18% 6% 1	1520
	11th to 20th	Day	56% 5% 15% 16% 6% 2	1915
	21st to end	Day	71% 7% 8% 10% 4	2783
January	1st to 10th	Night	57% 5% 9% 20% 8% 1	4428
	11th to 20th	Night	63% 7% 10% 13% 7%	4440
	21st to end	Night	64% 5% 9% 16% 5%	4848
February	1st to 10th	Night	52% 6% 10% 21% 10% 1	2470
	11th to 20th	Night	46% 6% 11% 24% 10% 2	2286
	21st to end	Night	51% 5% 12% 19% 11% 2	1884
March	1st to 10th	Night	45% 6% 14% 22% 10% 3	2280
	11th to 20th	Night	41% 6% 13% 23% 15% 2	2209
	21st to end	Night	50% 5% 9% 22% 11% 2	2104
April	1st to 10th	Night	51% 5% 9% 17% 16% 2	1820
	11th to 20th	Night	48% 5% 9% 20% 15% 3	1775
	21st to end	Night	44% 8% 12% 21% 14% 1	1697
May	1st to 10th	Night	47% 8% 13% 18% 12% 1	1529
	11th to 20th	Night	44% 7% 12% 23% 12% 2	1417
	21st to end	Night	39% 8% 14% 22% 15% 1	1552
June	1st to 10th	Night	34% 7% 14% 27% 17% 1	1440
	11th to 20th	Night	36% 7% 11% 26% 19% 1	1440
	21st to end	Night	30% 8% 16% 29% 13% 3	1440
July	1st to 10th	Night	25% 6% 15% 32% 19% 3	1400
	11th to 20th	Night	28% 8% 15% 28% 18% 3	1392
	21st to end	Night	24% 8% 18% 30% 15% 5%	1487
August	1st to 10th	Night	28% 9% 17% 29% 15% 2	1423
	11th to 20th	Night	31% 8% 15% 30% 16% 1	1688
	21st to end	Night	30% 7% 14% 27% 20% 3	1980
September	1st to 10th	Night	31% 7% 12% 25% 23% 1	1800
	11th to 20th	Night	32% 7% 12% 34% 15% 1	1853
	21st to end	Night	35% 6% 12% 31% 14% 1	1980
October	1st to 10th	Night	37% 6% 10% 30% 16% 2	2102
	11th to 20th	Night	45% 7% 14% 20% 13% 1	2164
	21st to end	Night	50% 7% 11% 20% 11%	2574
November	1st to 10th	Night	39% 6% 12% 26% 15% 2	2406
	11th to 20th	Night	52% 7% 13% 17% 11% 1	2498
	21st to end	Night	48% 5% 16% 24% 7% 1	2660
December	1st to 10th	Night	54% 6% 13% 20% 6% 1	2660
	11th to 20th	Night	59% 6% 11% 17% 7% 1	3281
	21st to end	Night	66% 6% 9% 14% 4	4884

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	16% 9% 32% 30% 10% 2	270
	11th to 20th	Day	21% 10% 33% 28% 7% 1	270
	21st to end	Day	19% 8% 31% 32% 9%	297
February	1st to 10th	Day	11% 13% 43% 24% 7% 1	270
	11th to 20th	Day	15% 16% 40% 19% 9% 1	270
	21st to end	Day	16% 14% 44% 24% 2	225
March	1st to 10th	Day	21% 12% 39% 19% 9% 1	270
	11th to 20th	Day	20% 15% 33% 21% 8% 3	270
	21st to end	Day	27% 9% 28% 25% 10% 1	492
April	1st to 10th	Day	24% 11% 32% 25% 7%	428
	11th to 20th	Day	25% 13% 30% 18% 12% 3	412
	21st to end	Day	21% 11% 27% 25% 13% 3	420
May	1st to 10th	Day	18% 11% 34% 24% 11% 2	512
	11th to 20th	Day	20% 10% 27% 26% 12% 5%	625
	21st to end	Day	17% 7% 26% 26% 17% 7%	679
June	1st to 10th	Day	10% 7% 28% 33% 18% 5%	630
	11th to 20th	Day	17% 5% 27% 30% 16% 6%	630
	21st to end	Day	12% 8% 25% 31% 17% 6%	630
July	1st to 10th	Day	7% 3 18% 29% 28% 14%	621
	11th to 20th	Day	9% 6% 22% 30% 23% 9%	618
	21st to end	Day	9% 4 23% 34% 22% 8%	684
August	1st to 10th	Day	9% 4 20% 32% 24% 11%	626
	11th to 20th	Day	13% 5% 16% 24% 28% 15%	495
	21st to end	Day	12% 5% 20% 32% 20% 11%	495
September	1st to 10th	Day	16% 7% 19% 29% 21% 8%	450
	11th to 20th	Day	14% 3 19% 34% 21% 8%	450
	21st to end	Day	17% 10% 26% 22% 19% 6%	450
October	1st to 10th	Day	19% 9% 25% 24% 19% 5%	324
	11th to 20th	Day	20% 16% 32% 24% 8% 1	270
	21st to end	Day	24% 12% 35% 21% 8% 1	297
November	1st to 10th	Day	14% 14% 34% 25% 11% 2	270
	11th to 20th	Day	14% 19% 37% 20% 8% 1	270
	21st to end	Day	21% 13% 38% 21% 6%	270
December	1st to 10th	Day	16% 16% 39% 22% 7% 1	270
	11th to 20th	Day	20% 16% 36% 21% 7% 1	270
	21st to end	Day	26% 13% 39% 18% 4	297
January	1st to 10th	Night	17% 12% 35% 27% 8% 1	950
	11th to 20th	Night	20% 11% 35% 28% 6% 1	950
	21st to end	Night	20% 9% 32% 30% 8%	1045
February	1st to 10th	Night	17% 10% 37% 27% 8%	950
	11th to 20th	Night	15% 12% 39% 25% 8%	810
	21st to end	Night	22% 10% 35% 28% 5%	628
March	1st to 10th	Night	19% 9% 32% 29% 10% 1	760
	11th to 20th	Night	17% 9% 35% 31% 8% 1	689
	21st to end	Night	21% 7% 29% 33% 9% 1	627
April	1st to 10th	Night	24% 9% 34% 27% 5%	546
	11th to 20th	Night	23% 9% 29% 31% 7% 1	533
	21st to end	Night	20% 9% 29% 33% 8% 1	540
May	1st to 10th	Night	20% 7% 32% 33% 7% 1	540
	11th to 20th	Night	19% 7% 30% 34% 9% 1	531
	21st to end	Night	14% 5% 24% 37% 19% 1	584
June	1st to 10th	Night	11% 6% 23% 42% 16% 1	540
	11th to 20th	Night	15% 3 28% 40% 13% 1	540
	21st to end	Night	10% 4 22% 46% 17% 1	540
July	1st to 10th	Night	8% 2 18% 42% 27% 2	525
	11th to 20th	Night	9% 3 20% 42% 24% 2	522
	21st to end	Night	7% 2 17% 47% 24% 2	591
August	1st to 10th	Night	8% 3 15% 47% 25% 2	537
	11th to 20th	Night	10% 4 16% 37% 29% 4	534
	21st to end	Night	12% 2 18% 42% 24% 2	594
September	1st to 10th	Night	12% 4 23% 37% 20% 5%	540
	11th to 20th	Night	15% 3 23% 31% 23% 4	593
	21st to end	Night	13% 9% 24% 32% 19% 2	720
October	1st to 10th	Night	16% 7% 26% 30% 20% 1	720
	11th to 20th	Night	21% 11% 32% 27% 8%	720
	21st to end	Night	25% 10% 29% 28% 9% 1	792
November	1st to 10th	Night	17% 8% 36% 27% 10% 1	740
	11th to 20th	Night	20% 14% 38% 22% 5%	788
	21st to end	Night	20% 12% 36% 25% 7%	950
December	1st to 10th	Night	20% 11% 40% 22% 7%	950
	11th to 20th	Night	23% 11% 34% 24% 7% 1	950
	21st to end	Night	28% 12% 31% 25% 4	1045

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