Nirvana
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nirvana clear sky chart from 2005-11-06 to 2025-08-05.

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	16% 11% 4 9% 5% 5% 4 3 5% 6% 31%	126206
	Night	16% 12% 4 9% 5% 5% 4 3 5% 6% 31%	121838
Transparency	Day	51% 6% 11% 19% 11% 1	129736
	Night	52% 7% 12% 18% 10% 1	126395
Seeing	Day	23% 18% 32% 18% 7% 2	15340
	Night	22% 15% 32% 22% 8% 1	24495

By Month

Percentage Cloud Cover NE (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	12% 15% 5% 14% 8% 6% 6% 4 5% 5% 20%	3597
	11th to 20th	Day	11% 17% 10% 16% 7% 5% 6% 3 4 4 17%	3570
	21st to end	Day	13% 19% 7% 17% 7% 4 3 3 4 4 19%	4353
February	1st to 10th	Day	13% 17% 5% 14% 8% 5% 5% 4 5% 5% 20%	1800
	11th to 20th	Day	12% 17% 6% 11% 6% 6% 3 3 5% 5% 26%	1753
	21st to end	Day	18% 16% 5% 9% 6% 4 5% 4 4 5% 24%	1590
March	1st to 10th	Day	18% 14% 5% 11% 5% 5% 4 3 4 6% 26%	4695
	11th to 20th	Day	10% 14% 5% 10% 6% 5% 5% 4 6% 7% 28%	4980
	21st to end	Day	16% 14% 4 8% 3 3 3 2 3 4 38%	5634
April	1st to 10th	Day	20% 14% 4 7% 5% 5% 4 3 3 5% 30%	2400
	11th to 20th	Day	21% 11% 3 6% 4 3 4 3 4 5% 36%	2374
	21st to end	Day	21% 11% 3 8% 4 4 4 3 4 4 33%	2569
May	1st to 10th	Day	23% 9% 3 8% 4 4 5% 3 5% 5% 31%	6272
	11th to 20th	Day	16% 9% 3 9% 5% 5% 4 4 5% 6% 33%	6318
	21st to end	Day	20% 8% 3 7% 5% 5% 4 3 5% 7% 33%	6949
June	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 4 5% 7% 30%	2800
	11th to 20th	Day	15% 6% 2 6% 5% 5% 6% 5% 6% 9% 36%	2800
	21st to end	Day	19% 7% 3 7% 5% 4 5% 4 6% 6% 34%	2800
July	1st to 10th	Day	14% 7% 2 7% 5% 5% 5% 4 6% 9% 34%	6360
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 9% 42%	6360
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 6% 9% 45%	6926
August	1st to 10th	Day	15% 9% 3 8% 5% 5% 5% 3 6% 7% 34%	4226
	11th to 20th	Day	17% 8% 3 6% 5% 4 4 4 7% 7% 35%	4044
	21st to end	Day	12% 7% 2 6% 4 5% 4 5% 7% 9% 39%	4225
September	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 3 5% 7% 40%	2280
	11th to 20th	Day	12% 6% 2 5% 5% 4 4 3 5% 7% 46%	2280
	21st to end	Day	19% 6% 2 7% 5% 4 4 3 5% 7% 36%	1995
October	1st to 10th	Day	21% 9% 3 8% 5% 3 3 4 5% 6% 33%	1900
	11th to 20th	Day	22% 12% 4 8% 4 5% 4 3 5% 6% 26%	1900
	21st to end	Day	26% 13% 3 8% 5% 5% 5% 3 5% 4 24%	2014
November	1st to 10th	Day	15% 12% 3 8% 5% 5% 5% 3 5% 7% 32%	1696
	11th to 20th	Day	15% 16% 5% 10% 6% 5% 5% 3 4 5% 26%	1600
	21st to end	Day	22% 17% 5% 10% 7% 5% 4 4 3 5% 18%	1600
December	1st to 10th	Day	20% 23% 6% 11% 6% 5% 4 3 5% 5% 14%	2600
	11th to 20th	Day	16% 20% 7% 13% 6% 4 3 3 3 3 23%	2986
	21st to end	Day	21% 19% 6% 13% 5% 3 2 2 3 5% 20%	3960
January	1st to 10th	Night	14% 15% 8% 14% 7% 6% 5% 3 4 5% 19%	6349
	11th to 20th	Night	9% 16% 7% 16% 9% 7% 6% 4 5% 5% 16%	6315
	21st to end	Night	13% 16% 8% 15% 7% 6% 4 3 4 4 20%	6600
February	1st to 10th	Night	12% 16% 5% 11% 7% 5% 5% 4 6% 6% 22%	2600
	11th to 20th	Night	13% 13% 5% 12% 5% 5% 5% 4 5% 5% 28%	2533
	21st to end	Night	12% 15% 5% 8% 6% 5% 5% 4 6% 7% 27%	2038
March	1st to 10th	Night	18% 14% 4 10% 6% 4 4 3 3 4 29%	5144
	11th to 20th	Night	10% 12% 4 9% 6% 5% 6% 5% 7% 9% 27%	4979
	21st to end	Night	17% 11% 4 8% 5% 4 4 3 5% 6% 32%	5297
April	1st to 10th	Night	19% 12% 3 8% 5% 4 4 3 5% 5% 32%	2000
	11th to 20th	Night	18% 9% 3 6% 5% 4 4 3 4 6% 37%	1975
	21st to end	Night	19% 10% 2 8% 5% 5% 4 4 5% 5% 33%	1849
May	1st to 10th	Night	23% 9% 3 6% 4 5% 5% 4 5% 6% 30%	3653
	11th to 20th	Night	15% 7% 3 6% 4 4 3 3 5% 7% 42%	3575
	21st to end	Night	18% 9% 3 6% 4 4 5% 4 5% 7% 35%	3926
June	1st to 10th	Night	15% 7% 3 6% 5% 5% 4 5% 6% 8% 35%	1600
	11th to 20th	Night	12% 7% 3 6% 5% 3 3 4 5% 7% 44%	1600
	21st to end	Night	18% 7% 2 6% 4 5% 4 4 6% 7% 37%	1600
July	1st to 10th	Night	12% 7% 3 6% 6% 5% 6% 4 6% 7% 37%	3600
	11th to 20th	Night	13% 6% 2 6% 4 3 3 3 5% 6% 49%	3600
	21st to end	Night	8% 5% 2 6% 4 4 4 4 5% 7% 50%	3926
August	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 6% 8% 45%	2788
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 5% 7% 43%	2785
	21st to end	Night	13% 5% 2 6% 4 4 4 4 7% 8% 44%	3398
September	1st to 10th	Night	11% 6% 1 6% 5% 4 4 3 6% 8% 47%	1900
	11th to 20th	Night	13% 5% 2 5% 3 3 4 4 4 6% 51%	1900
	21st to end	Night	17% 7% 2 5% 4 3 4 3 6% 5% 43%	2182
October	1st to 10th	Night	19% 9% 3 6% 3 4 5% 3 5% 5% 38%	2280
	11th to 20th	Night	20% 10% 3 9% 6% 4 4 4 4 5% 30%	2280
	21st to end	Night	21% 13% 4 8% 5% 5% 4 3 4 7% 26%	2584
November	1st to 10th	Night	15% 13% 4 7% 4 4 4 3 5% 6% 34%	2598
	11th to 20th	Night	17% 13% 5% 9% 5% 4 4 4 5% 5% 29%	2800
	21st to end	Night	19% 17% 5% 9% 6% 5% 4 3 5% 6% 21%	2800
December	1st to 10th	Night	19% 19% 6% 12% 6% 4 5% 4 5% 6% 15%	4580
	11th to 20th	Night	20% 18% 6% 12% 5% 3 3 2 3 5% 22%	5208
	21st to end	Night	24% 19% 5% 12% 6% 4 3 2 3 4 18%	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	62% 8% 9% 14% 7% 1	3598
	11th to 20th	Day	68% 6% 9% 8% 7% 1	3600
	21st to end	Day	69% 5% 6% 10% 8% 2	4353
February	1st to 10th	Day	63% 6% 9% 15% 6% 1	1800
	11th to 20th	Day	59% 6% 10% 15% 10% 1	1762
	21st to end	Day	61% 5% 10% 12% 10% 1	1590
March	1st to 10th	Day	59% 5% 10% 10% 15% 2	4698
	11th to 20th	Day	53% 7% 15% 15% 9% 2	4980
	21st to end	Day	50% 4 7% 19% 17% 3	5634
April	1st to 10th	Day	56% 4 7% 17% 12% 3	2400
	11th to 20th	Day	51% 5% 8% 20% 16% 1	2374
	21st to end	Day	55% 5% 7% 15% 15% 3	2569
May	1st to 10th	Day	52% 7% 9% 19% 10% 4	6283
	11th to 20th	Day	49% 8% 11% 16% 16% 1	6322
	21st to end	Day	49% 7% 11% 20% 12% 2	6949
June	1st to 10th	Day	53% 7% 10% 18% 12% 1	2800
	11th to 20th	Day	43% 7% 13% 22% 13% 2	2800
	21st to end	Day	48% 7% 12% 20% 12% 1	2800
July	1st to 10th	Day	44% 7% 13% 24% 11%	6290
	11th to 20th	Day	36% 8% 13% 27% 15%	6285
	21st to end	Day	33% 8% 13% 35% 11%	6728
August	1st to 10th	Day	48% 6% 14% 21% 11%	4212
	11th to 20th	Day	45% 7% 15% 25% 7% 1	4083
	21st to end	Day	38% 7% 15% 30% 9% 1	4225
September	1st to 10th	Day	42% 7% 12% 28% 11%	2280
	11th to 20th	Day	37% 7% 12% 29% 15%	2280
	21st to end	Day	47% 7% 14% 22% 11%	1995
October	1st to 10th	Day	46% 6% 11% 29% 8%	3160
	11th to 20th	Day	49% 5% 13% 21% 11% 1	3140
	21st to end	Day	55% 7% 14% 18% 6%	3304
November	1st to 10th	Day	50% 8% 15% 20% 7% 1	1696
	11th to 20th	Day	59% 6% 11% 14% 9% 1	1600
	21st to end	Day	68% 7% 9% 9% 7% 1	1600
December	1st to 10th	Day	72% 5% 12% 8% 2	2600
	11th to 20th	Day	66% 5% 9% 13% 7%	2986
	21st to end	Day	68% 5% 7% 13% 7%	3960
January	1st to 10th	Night	66% 6% 10% 12% 6%	6349
	11th to 20th	Night	66% 9% 10% 9% 6%	6360
	21st to end	Night	68% 5% 7% 7% 12% 1	6600
February	1st to 10th	Night	60% 6% 12% 15% 7% 1	2600
	11th to 20th	Night	57% 5% 11% 18% 8% 1	2535
	21st to end	Night	54% 7% 10% 19% 10% 1	2038
March	1st to 10th	Night	58% 4 8% 14% 11% 5%	5154
	11th to 20th	Night	49% 9% 17% 16% 7% 2	4980
	21st to end	Night	50% 6% 8% 19% 13% 2	5297
April	1st to 10th	Night	53% 6% 8% 19% 12% 2	2000
	11th to 20th	Night	48% 5% 8% 22% 15% 1	1975
	21st to end	Night	50% 7% 8% 16% 16% 3	1849
May	1st to 10th	Night	52% 7% 10% 19% 9% 4	3659
	11th to 20th	Night	39% 8% 15% 21% 15% 2	3576
	21st to end	Night	47% 7% 13% 18% 14% 1	3927
June	1st to 10th	Night	44% 8% 13% 22% 12% 1	1600
	11th to 20th	Night	37% 6% 13% 25% 17% 1	1600
	21st to end	Night	44% 7% 15% 21% 12% 1	1600
July	1st to 10th	Night	42% 7% 15% 20% 15% 1	3560
	11th to 20th	Night	35% 6% 12% 32% 14%	3552
	21st to end	Night	32% 7% 13% 35% 13%	3809
August	1st to 10th	Night	36% 7% 15% 27% 13% 2	2778
	11th to 20th	Night	39% 7% 16% 28% 9% 1	2812
	21st to end	Night	34% 9% 15% 30% 11% 1	3398
September	1st to 10th	Night	35% 7% 15% 28% 14% 1	1900
	11th to 20th	Night	33% 7% 14% 34% 12% 1	1900
	21st to end	Night	41% 7% 11% 29% 10% 1	2182
October	1st to 10th	Night	40% 6% 11% 27% 16%	3800
	11th to 20th	Night	44% 7% 16% 21% 11%	3779
	21st to end	Night	50% 7% 17% 20% 7%	4244
November	1st to 10th	Night	49% 7% 14% 21% 9% 1	2598
	11th to 20th	Night	55% 7% 12% 17% 9% 1	2800
	21st to end	Night	63% 7% 11% 15% 4	2800
December	1st to 10th	Night	68% 8% 13% 9% 2	4580
	11th to 20th	Night	66% 4 8% 12% 8% 1	5208
	21st to end	Night	71% 4 6% 11% 8%	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	21% 24% 39% 13% 3 1	200
	11th to 20th	Day	28% 20% 37% 13% 4	200
	21st to end	Day	24% 26% 35% 10% 3	307
February	1st to 10th	Day	31% 30% 28% 9% 2	300
	11th to 20th	Day	30% 29% 35% 5%	300
	21st to end	Day	35% 22% 33% 10% 1	354
March	1st to 10th	Day	26% 24% 33% 14% 3	500
	11th to 20th	Day	27% 21% 33% 14% 3 1	500
	21st to end	Day	33% 21% 29% 13% 4	550
April	1st to 10th	Day	29% 25% 30% 10% 5%	500
	11th to 20th	Day	34% 22% 22% 15% 6% 1	492
	21st to end	Day	29% 22% 31% 11% 5% 1	500
May	1st to 10th	Day	27% 16% 33% 16% 5% 3	503
	11th to 20th	Day	21% 17% 35% 18% 6% 2	527
	21st to end	Day	21% 15% 34% 18% 9% 3	573
June	1st to 10th	Day	22% 16% 37% 18% 7%	530
	11th to 20th	Day	15% 19% 35% 21% 9% 2	530
	21st to end	Day	21% 15% 35% 19% 9% 2	530
July	1st to 10th	Day	13% 11% 34% 30% 10% 2	525
	11th to 20th	Day	15% 13% 33% 24% 14% 2	524
	21st to end	Day	14% 10% 37% 27% 9% 3	576
August	1st to 10th	Day	14% 8% 33% 28% 12% 4	502
	11th to 20th	Day	13% 9% 29% 29% 14% 5%	479
	21st to end	Day	14% 12% 32% 26% 10% 6%	539
September	1st to 10th	Day	16% 14% 32% 21% 13% 5%	490
	11th to 20th	Day	12% 11% 26% 23% 18% 10%	490
	21st to end	Day	20% 16% 27% 21% 11% 5%	490
October	1st to 10th	Day	26% 16% 26% 18% 10% 3	490
	11th to 20th	Day	28% 22% 30% 15% 4 1	490
	21st to end	Day	31% 19% 31% 15% 4	499
November	1st to 10th	Day	28% 19% 33% 15% 5%	330
	11th to 20th	Day	28% 25% 30% 13% 4 1	200
	21st to end	Day	30% 27% 31% 9% 2 1	200
December	1st to 10th	Day	32% 22% 35% 9% 3 1	200
	11th to 20th	Day	38% 24% 27% 10% 2 1	200
	21st to end	Day	34% 22% 29% 11% 4	220
January	1st to 10th	Night	27% 21% 33% 14% 4	800
	11th to 20th	Night	27% 20% 31% 17% 5% 1	800
	21st to end	Night	20% 19% 36% 19% 5%	880
February	1st to 10th	Night	22% 22% 37% 17% 2	800
	11th to 20th	Night	20% 24% 40% 13% 3	783
	21st to end	Night	22% 23% 36% 17% 2	660
March	1st to 10th	Night	23% 22% 34% 18% 2	800
	11th to 20th	Night	24% 21% 32% 19% 3 1	800
	21st to end	Night	23% 17% 34% 18% 7% 1	880
April	1st to 10th	Night	27% 18% 34% 18% 4	800
	11th to 20th	Night	24% 22% 30% 18% 7%	791
	21st to end	Night	24% 14% 30% 23% 8%	649
May	1st to 10th	Night	24% 9% 27% 30% 9% 1	433
	11th to 20th	Night	17% 11% 35% 29% 7%	394
	21st to end	Night	14% 10% 36% 28% 12%	433
June	1st to 10th	Night	16% 11% 36% 30% 9%	400
	11th to 20th	Night	15% 12% 33% 31% 9% 1	400
	21st to end	Night	21% 9% 29% 30% 12%	400
July	1st to 10th	Night	7% 8% 36% 36% 13% 1	390
	11th to 20th	Night	12% 6% 29% 39% 14%	388
	21st to end	Night	10% 5% 31% 42% 12%	438
August	1st to 10th	Night	10% 6% 25% 38% 19% 1	532
	11th to 20th	Night	11% 4 24% 37% 21% 2	564
	21st to end	Night	13% 8% 31% 27% 18% 2	784
September	1st to 10th	Night	12% 7% 35% 28% 16% 2	760
	11th to 20th	Night	14% 7% 25% 28% 21% 4	760
	21st to end	Night	21% 11% 23% 25% 18% 2	760
October	1st to 10th	Night	23% 13% 29% 22% 12% 2	760
	11th to 20th	Night	27% 15% 31% 19% 8% 1	760
	21st to end	Night	29% 17% 30% 19% 5%	836
November	1st to 10th	Night	24% 18% 29% 23% 6% 1	780
	11th to 20th	Night	26% 18% 33% 15% 8% 1	800
	21st to end	Night	30% 20% 27% 19% 4	800
December	1st to 10th	Night	30% 18% 34% 15% 3	800
	11th to 20th	Night	27% 20% 34% 17% 2 1	800
	21st to end	Night	34% 16% 33% 14% 3	880

Page generated at 2025-08-02 01:32:26. Version ac07

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