Supernova Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Supernova Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	19% 12% 4 9% 5% 4 4 4 5% 6% 29%	126796
	Night	20% 13% 5% 10% 5% 4 4 3 4 5% 26%	122547
Transparency	Day	54% 6% 12% 19% 9% 1	130287
	Night	58% 6% 11% 16% 8% 1	127143
Seeing	Day	27% 15% 26% 20% 10% 3	15846
	Night	27% 13% 25% 26% 9% 1	24935

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	13% 21% 11% 21% 7% 4 4 2 2 4 12%	3597
	11th to 20th	Day	13% 22% 9% 20% 7% 5% 4 2 3 4 11%	3570
	21st to end	Day	16% 21% 7% 11% 8% 5% 5% 4 4 5% 15%	4264
February	1st to 10th	Day	17% 17% 6% 15% 9% 6% 5% 3 3 4 16%	1800
	11th to 20th	Day	16% 18% 6% 16% 7% 4 3 3 3 6% 18%	1824
	21st to end	Day	21% 16% 7% 13% 6% 4 4 3 4 5% 18%	1650
March	1st to 10th	Day	22% 16% 6% 12% 5% 5% 3 2 3 4 22%	4476
	11th to 20th	Day	15% 17% 5% 8% 4 3 4 3 5% 6% 30%	4952
	21st to end	Day	20% 13% 5% 10% 4 4 3 3 4 5% 30%	5803
April	1st to 10th	Day	20% 15% 3 8% 4 3 3 3 4 6% 30%	2400
	11th to 20th	Day	21% 11% 2 7% 4 4 4 3 5% 5% 34%	2374
	21st to end	Day	22% 12% 3 7% 4 4 4 3 4 5% 31%	2416
May	1st to 10th	Day	33% 10% 3 7% 4 4 4 3 4 5% 24%	6300
	11th to 20th	Day	20% 9% 3 7% 5% 5% 5% 4 5% 6% 31%	6318
	21st to end	Day	23% 9% 3 7% 4 4 4 4 5% 8% 30%	6949
June	1st to 10th	Day	20% 6% 2 8% 5% 4 4 5% 6% 8% 31%	2800
	11th to 20th	Day	20% 6% 2 5% 5% 5% 5% 5% 6% 9% 33%	2800
	21st to end	Day	20% 7% 2 6% 5% 4 5% 5% 6% 8% 33%	2800
July	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 5% 8% 11% 36%	6360
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 4 7% 9% 36%	6360
	21st to end	Day	14% 5% 2 6% 4 4 5% 4 6% 8% 41%	6926
August	1st to 10th	Day	18% 6% 2 6% 4 4 5% 4 6% 8% 36%	4384
	11th to 20th	Day	19% 7% 3 7% 4 4 6% 4 7% 9% 30%	3993
	21st to end	Day	19% 6% 2 5% 4 4 4 4 6% 9% 37%	4312
September	1st to 10th	Day	16% 6% 1 5% 4 4 5% 4 5% 8% 42%	2400
	11th to 20th	Day	16% 6% 2 6% 3 3 3 4 4 7% 46%	2379
	21st to end	Day	18% 6% 3 6% 5% 5% 4 4 5% 8% 36%	2174
October	1st to 10th	Day	22% 8% 2 8% 4 5% 4 3 4 6% 33%	1930
	11th to 20th	Day	23% 9% 2 6% 6% 4 3 3 5% 7% 32%	1900
	21st to end	Day	27% 10% 3 7% 4 4 4 3 5% 6% 25%	1958
November	1st to 10th	Day	17% 14% 4 7% 5% 4 5% 4 5% 6% 30%	1761
	11th to 20th	Day	17% 15% 4 8% 6% 4 5% 3 5% 5% 27%	1720
	21st to end	Day	23% 17% 4 9% 5% 3 4 4 4 6% 20%	1600
December	1st to 10th	Day	22% 24% 10% 14% 5% 4 3 2 3 3 10%	2600
	11th to 20th	Day	20% 20% 9% 14% 5% 4 4 3 3 3 15%	2986
	21st to end	Day	22% 19% 7% 10% 5% 4 4 3 4 5% 17%	3960
January	1st to 10th	Night	17% 21% 10% 21% 5% 4 3 3 3 4 9%	6349
	11th to 20th	Night	12% 19% 10% 22% 8% 5% 4 3 4 3 9%	6315
	21st to end	Night	16% 18% 7% 16% 9% 5% 4 3 4 5% 14%	6675
February	1st to 10th	Night	18% 17% 5% 15% 7% 5% 4 4 4 5% 16%	2600
	11th to 20th	Night	15% 16% 6% 13% 8% 5% 5% 3 5% 5% 18%	2460
	21st to end	Night	18% 17% 6% 13% 8% 4 3 4 3 5% 18%	1980
March	1st to 10th	Night	22% 12% 7% 12% 7% 4 4 3 3 4 21%	5364
	11th to 20th	Night	20% 16% 4 7% 4 3 3 3 5% 6% 28%	4991
	21st to end	Night	25% 12% 4 10% 4 4 4 3 3 4 26%	5128
April	1st to 10th	Night	24% 13% 3 8% 4 4 3 3 4 6% 28%	2000
	11th to 20th	Night	22% 11% 3 7% 5% 4 4 3 4 5% 33%	1975
	21st to end	Night	21% 9% 2 6% 5% 4 4 3 5% 6% 35%	1982
May	1st to 10th	Night	36% 10% 3 7% 4 3 4 3 4 4 22%	3670
	11th to 20th	Night	17% 12% 4 8% 4 4 4 4 5% 6% 32%	3575
	21st to end	Night	23% 10% 3 7% 4 4 4 3 5% 5% 31%	3926
June	1st to 10th	Night	19% 7% 3 6% 5% 4 4 4 6% 8% 35%	1600
	11th to 20th	Night	19% 5% 2 5% 4 4 5% 4 5% 8% 40%	1600
	21st to end	Night	17% 5% 3 7% 4 5% 4 4 6% 8% 37%	1600
July	1st to 10th	Night	14% 7% 3 7% 6% 5% 5% 4 7% 8% 33%	3600
	11th to 20th	Night	16% 7% 2 6% 4 4 4 4 5% 7% 39%	3600
	21st to end	Night	12% 6% 2 5% 4 4 4 4 6% 8% 46%	3926
August	1st to 10th	Night	21% 9% 2 6% 4 4 4 3 5% 6% 37%	2748
	11th to 20th	Night	19% 8% 3 6% 5% 4 4 3 5% 6% 37%	3021
	21st to end	Night	17% 5% 2 5% 4 4 5% 4 6% 8% 41%	3586
September	1st to 10th	Night	15% 8% 2 6% 3 3 5% 3 6% 6% 42%	2000
	11th to 20th	Night	17% 5% 1 5% 3 4 3 3 4 5% 49%	2020
	21st to end	Night	19% 7% 2 5% 3 4 5% 4 5% 7% 38%	2223
October	1st to 10th	Night	24% 8% 3 8% 5% 5% 4 3 4 6% 31%	2317
	11th to 20th	Night	23% 9% 2 7% 5% 5% 4 3 5% 6% 31%	2280
	21st to end	Night	29% 11% 3 8% 5% 4 4 3 4 5% 23%	2639
November	1st to 10th	Night	19% 12% 3 7% 5% 4 4 3 4 6% 33%	2537
	11th to 20th	Night	21% 14% 4 7% 4 4 4 4 4 6% 29%	2676
	21st to end	Night	20% 18% 5% 8% 5% 5% 4 3 5% 5% 22%	2800
December	1st to 10th	Night	22% 24% 9% 11% 5% 4 4 3 4 4 10%	4580
	11th to 20th	Night	26% 20% 6% 11% 4 4 4 3 4 4 15%	5208
	21st to end	Night	27% 17% 7% 8% 4 3 3 3 3 4 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	76% 7% 6% 9% 2	3598
	11th to 20th	Day	76% 7% 7% 6% 4 1	3600
	21st to end	Day	69% 6% 11% 9% 5% 1	4264
February	1st to 10th	Day	74% 4 8% 11% 3 1	1800
	11th to 20th	Day	70% 5% 8% 13% 3	1833
	21st to end	Day	70% 4 9% 11% 6%	1650
March	1st to 10th	Day	66% 5% 10% 12% 6% 1	4479
	11th to 20th	Day	54% 6% 19% 12% 8% 2	4952
	21st to end	Day	57% 5% 7% 15% 15% 1	5803
April	1st to 10th	Day	57% 4 8% 20% 9% 2	2400
	11th to 20th	Day	51% 5% 10% 21% 12% 1	2374
	21st to end	Day	55% 5% 9% 18% 11% 3	2416
May	1st to 10th	Day	62% 6% 8% 15% 8% 1	6311
	11th to 20th	Day	52% 7% 11% 21% 8% 1	6322
	21st to end	Day	51% 7% 12% 21% 8%	6949
June	1st to 10th	Day	49% 8% 11% 20% 11% 1	2800
	11th to 20th	Day	47% 6% 14% 23% 9% 1	2800
	21st to end	Day	48% 7% 14% 21% 10% 1	2800
July	1st to 10th	Day	39% 8% 15% 25% 13%	6290
	11th to 20th	Day	41% 8% 14% 25% 11% 1	6285
	21st to end	Day	39% 7% 13% 30% 11%	6728
August	1st to 10th	Day	45% 8% 14% 21% 13%	4370
	11th to 20th	Day	46% 9% 17% 22% 6%	4032
	21st to end	Day	41% 8% 13% 30% 7% 1	4312
September	1st to 10th	Day	39% 7% 13% 29% 11% 1	2400
	11th to 20th	Day	38% 5% 11% 29% 16% 1	2379
	21st to end	Day	46% 7% 12% 24% 11% 1	2174
October	1st to 10th	Day	46% 7% 12% 27% 8% 1	3190
	11th to 20th	Day	46% 5% 15% 23% 11%	3140
	21st to end	Day	46% 7% 16% 23% 8%	3209
November	1st to 10th	Day	54% 6% 11% 19% 9% 1	1761
	11th to 20th	Day	59% 5% 10% 16% 9% 2	1720
	21st to end	Day	64% 6% 15% 12% 3	1600
December	1st to 10th	Day	80% 5% 6% 6% 1	2600
	11th to 20th	Day	72% 6% 9% 10% 3	2986
	21st to end	Day	69% 6% 8% 12% 5%	3960
January	1st to 10th	Night	80% 6% 7% 6% 2	6349
	11th to 20th	Night	76% 8% 8% 5% 3	6360
	21st to end	Night	72% 5% 8% 6% 7% 1	6675
February	1st to 10th	Night	70% 6% 9% 12% 4	2600
	11th to 20th	Night	68% 6% 9% 13% 4	2462
	21st to end	Night	68% 5% 10% 11% 5%	1980
March	1st to 10th	Night	65% 6% 10% 13% 6% 1	5374
	11th to 20th	Night	55% 6% 17% 13% 6% 2	4992
	21st to end	Night	62% 4 6% 19% 8% 1	5128
April	1st to 10th	Night	59% 4 11% 17% 8% 1	2000
	11th to 20th	Night	54% 6% 9% 18% 12% 1	1975
	21st to end	Night	49% 5% 11% 18% 13% 3	1982
May	1st to 10th	Night	65% 6% 7% 13% 8% 1	3676
	11th to 20th	Night	51% 7% 13% 20% 9% 1	3576
	21st to end	Night	54% 7% 9% 18% 11% 1	3927
June	1st to 10th	Night	47% 6% 12% 23% 12% 1	1600
	11th to 20th	Night	43% 6% 14% 23% 13% 1	1600
	21st to end	Night	43% 10% 11% 25% 12% 1	1600
July	1st to 10th	Night	45% 8% 14% 20% 13% 1	3560
	11th to 20th	Night	43% 7% 13% 22% 15%	3552
	21st to end	Night	35% 6% 13% 33% 13% 1	3809
August	1st to 10th	Night	46% 8% 13% 24% 9%	2738
	11th to 20th	Night	46% 7% 14% 25% 8%	3048
	21st to end	Night	39% 7% 15% 29% 9%	3586
September	1st to 10th	Night	40% 7% 12% 28% 11% 1	2000
	11th to 20th	Night	37% 5% 11% 29% 17%	2020
	21st to end	Night	44% 7% 12% 25% 11% 1	2223
October	1st to 10th	Night	52% 7% 11% 21% 9% 1	3837
	11th to 20th	Night	45% 6% 15% 19% 13% 1	3779
	21st to end	Night	53% 6% 11% 23% 6%	4338
November	1st to 10th	Night	53% 5% 11% 18% 10% 2	2537
	11th to 20th	Night	56% 6% 11% 18% 8% 1	2676
	21st to end	Night	63% 6% 14% 14% 3	2800
December	1st to 10th	Night	77% 6% 9% 7% 1	4580
	11th to 20th	Night	71% 6% 8% 10% 4	5208
	21st to end	Night	69% 5% 8% 10% 7% 1	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	37% 15% 27% 17% 5% 1	200
	11th to 20th	Day	39% 23% 30% 7% 2 1	200
	21st to end	Day	30% 24% 30% 13% 3	287
February	1st to 10th	Day	41% 24% 27% 7% 1	300
	11th to 20th	Day	36% 30% 26% 8% 1	371
	21st to end	Day	38% 18% 29% 12% 2	414
March	1st to 10th	Day	34% 19% 27% 17% 3	500
	11th to 20th	Day	32% 22% 28% 14% 3	500
	21st to end	Day	36% 20% 25% 13% 4 2	550
April	1st to 10th	Day	36% 21% 23% 14% 5% 1	500
	11th to 20th	Day	36% 21% 21% 12% 8% 3	492
	21st to end	Day	34% 19% 23% 16% 6% 2	500
May	1st to 10th	Day	34% 15% 29% 13% 7% 3	503
	11th to 20th	Day	24% 13% 31% 20% 10% 2	527
	21st to end	Day	19% 13% 27% 25% 12% 3	573
June	1st to 10th	Day	21% 16% 27% 25% 9% 2	530
	11th to 20th	Day	22% 13% 25% 25% 12% 2	530
	21st to end	Day	22% 12% 33% 22% 9% 3	530
July	1st to 10th	Day	16% 7% 28% 28% 15% 5%	525
	11th to 20th	Day	14% 7% 28% 30% 18% 4	524
	21st to end	Day	15% 8% 34% 28% 12% 3	576
August	1st to 10th	Day	14% 10% 19% 29% 19% 8%	526
	11th to 20th	Day	18% 8% 21% 27% 19% 7%	519
	21st to end	Day	17% 11% 24% 27% 15% 6%	583
September	1st to 10th	Day	18% 9% 22% 24% 17% 9%	530
	11th to 20th	Day	15% 8% 23% 21% 21% 12%	530
	21st to end	Day	20% 10% 27% 25% 14% 4	530
October	1st to 10th	Day	26% 10% 24% 20% 15% 5%	502
	11th to 20th	Day	28% 16% 24% 20% 11% 1	490
	21st to end	Day	35% 13% 26% 19% 7%	469
November	1st to 10th	Day	29% 17% 20% 25% 9%	395
	11th to 20th	Day	33% 19% 24% 20% 4 1	320
	21st to end	Day	40% 16% 27% 15% 3	200
December	1st to 10th	Day	38% 17% 35% 8% 2 2	200
	11th to 20th	Day	36% 24% 27% 12% 2	200
	21st to end	Day	37% 21% 26% 14% 1	220
January	1st to 10th	Night	33% 23% 25% 17% 2	800
	11th to 20th	Night	33% 19% 28% 17% 4	800
	21st to end	Night	24% 20% 32% 21% 3	880
February	1st to 10th	Night	31% 19% 29% 19% 1	800
	11th to 20th	Night	30% 20% 32% 15% 3	783
	21st to end	Night	31% 18% 31% 17% 3	660
March	1st to 10th	Night	29% 18% 29% 23% 2	800
	11th to 20th	Night	31% 17% 28% 20% 3	800
	21st to end	Night	29% 16% 28% 20% 6% 1	880
April	1st to 10th	Night	30% 15% 29% 22% 3	800
	11th to 20th	Night	28% 16% 28% 21% 7%	791
	21st to end	Night	27% 13% 27% 26% 7%	782
May	1st to 10th	Night	31% 8% 24% 28% 9%	437
	11th to 20th	Night	21% 9% 29% 33% 8% 1	394
	21st to end	Night	18% 5% 23% 41% 13%	433
June	1st to 10th	Night	19% 5% 23% 42% 10% 1	400
	11th to 20th	Night	22% 5% 21% 38% 15%	400
	21st to end	Night	17% 5% 23% 42% 12% 1	400
July	1st to 10th	Night	14% 3 17% 46% 18% 1	390
	11th to 20th	Night	14% 3 13% 50% 19% 2	388
	21st to end	Night	14% 4 16% 48% 17% 1	438
August	1st to 10th	Night	17% 5% 16% 39% 23% 1	495
	11th to 20th	Night	18% 4 14% 35% 25% 3	675
	21st to end	Night	18% 5% 16% 38% 22% 1	880
September	1st to 10th	Night	17% 6% 20% 35% 20% 2	800
	11th to 20th	Night	19% 6% 15% 31% 26% 3	800
	21st to end	Night	20% 8% 21% 33% 16% 2	800
October	1st to 10th	Night	28% 8% 21% 25% 18% 1	773
	11th to 20th	Night	28% 10% 23% 30% 8% 1	760
	21st to end	Night	34% 12% 25% 25% 3	836
November	1st to 10th	Night	26% 12% 26% 28% 8%	780
	11th to 20th	Night	30% 15% 26% 23% 7% 1	800
	21st to end	Night	33% 14% 28% 20% 6%	800
December	1st to 10th	Night	37% 17% 26% 18% 3	800
	11th to 20th	Night	36% 17% 26% 17% 3	800
	21st to end	Night	34% 21% 25% 18% 2	880

Page generated at 2025-10-01 01:39:04. Version ac07

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