Sulligent
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sulligent clear sky chart from 2005-11-06 to 2025-09-19.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	126131
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 45%	122969
Transparency	Day	38% 6% 11% 22% 18% 5%	129873
	Night	37% 5% 10% 21% 20% 7%	127289
Seeing	Day	16% 10% 23% 24% 19% 8%	16176
	Night	15% 9% 23% 29% 20% 4	25756

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	16% 11% 4 6% 2 2 3 3 3 5% 45%	3617
	11th to 20th	Day	16% 6% 3 7% 3 2 2 2 3 5% 51%	4197
	21st to end	Day	20% 11% 2 6% 3 3 3 3 4 5% 41%	4972
February	1st to 10th	Day	18% 10% 3 6% 4 3 3 3 5% 5% 40%	2000
	11th to 20th	Day	22% 7% 2 6% 4 4 3 3 3 5% 39%	1948
	21st to end	Day	20% 7% 3 6% 4 4 3 3 5% 4 41%	1650
March	1st to 10th	Day	21% 8% 3 7% 4 4 4 4 4 5% 35%	4480
	11th to 20th	Day	13% 6% 3 6% 4 4 4 4 6% 6% 44%	4708
	21st to end	Day	14% 8% 3 7% 4 4 4 3 5% 8% 40%	5967
April	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 5% 8% 46%	2400
	11th to 20th	Day	13% 7% 3 5% 4 3 3 3 5% 6% 48%	2374
	21st to end	Day	10% 6% 2 6% 4 4 5% 3 6% 9% 46%	2400
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	5537
	11th to 20th	Day	14% 8% 3 8% 5% 5% 6% 5% 7% 8% 31%	5861
	21st to end	Day	12% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	6433
June	1st to 10th	Day	9% 6% 2 7% 6% 6% 6% 5% 8% 10% 37%	2600
	11th to 20th	Day	7% 4 2 6% 5% 5% 5% 5% 8% 10% 42%	2781
	21st to end	Day	8% 4 2 5% 4 6% 6% 5% 7% 9% 45%	2800
July	1st to 10th	Day	6% 5% 3 7% 6% 7% 6% 6% 8% 10% 36%	6360
	11th to 20th	Day	7% 4 2 5% 5% 6% 7% 6% 10% 14% 35%	6227
	21st to end	Day	9% 6% 2 7% 6% 7% 7% 6% 9% 12% 29%	5953
August	1st to 10th	Day	3 3 2 4 4 4 4 4 7% 8% 56%	3905
	11th to 20th	Day	5% 5% 2 5% 5% 4 6% 4 6% 10% 47%	3849
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 6% 8% 51%	4312
September	1st to 10th	Day	9% 5% 2 7% 5% 5% 5% 4 6% 8% 45%	2400
	11th to 20th	Day	10% 5% 3 6% 5% 4 4 4 5% 7% 45%	2209
	21st to end	Day	11% 4 2 5% 4 4 4 4 5% 7% 51%	2090
October	1st to 10th	Day	9% 5% 2 5% 3 3 3 3 5% 6% 56%	2090
	11th to 20th	Day	9% 5% 1 5% 3 3 4 3 4 6% 57%	1975
	21st to end	Day	15% 5% 1 4 3 3 4 3 4 5% 54%	2037
November	1st to 10th	Day	11% 6% 1 5% 4 3 4 3 5% 6% 54%	1762
	11th to 20th	Day	14% 5% 3 4 3 3 4 3 4 6% 53%	1800
	21st to end	Day	14% 8% 2 6% 3 3 4 3 5% 6% 45%	1800
December	1st to 10th	Day	18% 9% 2 5% 4 3 4 3 4 5% 43%	2930
	11th to 20th	Day	20% 9% 3 6% 3 4 3 3 4 5% 41%	3373
	21st to end	Day	19% 8% 3 6% 3 4 4 3 4 6% 41%	4334
January	1st to 10th	Night	18% 10% 3 7% 3 3 3 3 3 5% 42%	6348
	11th to 20th	Night	16% 10% 4 7% 3 2 2 2 3 4 48%	5765
	21st to end	Night	21% 10% 2 5% 3 2 3 3 3 4 44%	5984
February	1st to 10th	Night	19% 9% 3 6% 3 3 3 3 4 5% 42%	2400
	11th to 20th	Night	22% 8% 3 6% 4 3 3 3 4 4 41%	2338
	21st to end	Night	19% 8% 2 6% 5% 3 3 3 5% 6% 39%	1980
March	1st to 10th	Night	20% 11% 3 6% 4 4 3 3 5% 5% 35%	5373
	11th to 20th	Night	12% 7% 2 5% 3 3 4 3 5% 7% 50%	5279
	21st to end	Night	19% 7% 3 7% 4 3 3 2 3 4 43%	4962
April	1st to 10th	Night	12% 6% 2 6% 4 3 4 4 5% 7% 47%	2000
	11th to 20th	Night	12% 5% 2 5% 3 4 3 4 5% 7% 50%	1975
	21st to end	Night	11% 6% 2 5% 4 4 4 2 5% 7% 49%	2000
May	1st to 10th	Night	14% 8% 3 7% 4 3 4 4 6% 8% 40%	4357
	11th to 20th	Night	17% 9% 3 9% 5% 4 4 3 5% 6% 33%	4032
	21st to end	Night	10% 6% 2 6% 4 5% 5% 5% 7% 10% 40%	4421
June	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 5% 8% 9% 45%	1800
	11th to 20th	Night	4 5% 2 5% 4 3 4 4 7% 11% 51%	1611
	21st to end	Night	5% 4 1 4 5% 4 6% 4 7% 10% 49%	1600
July	1st to 10th	Night	5% 5% 2 7% 6% 6% 5% 5% 9% 13% 39%	3618
	11th to 20th	Night	5% 5% 2 6% 4 5% 5% 6% 8% 14% 40%	3739
	21st to end	Night	7% 7% 3 9% 6% 6% 6% 6% 10% 13% 28%	4879
August	1st to 10th	Night	2 2 1 3 3 4 4 4 7% 9% 62%	3244
	11th to 20th	Night	3 3 1 5% 3 4 5% 4 7% 11% 54%	3200
	21st to end	Night	5% 3 2 5% 4 4 5% 4 6% 8% 55%	3586
September	1st to 10th	Night	10% 6% 2 5% 3 4 4 3 5% 9% 48%	2000
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 6% 8% 47%	2125
	21st to end	Night	8% 4 1 4 3 4 4 3 7% 8% 54%	2090
October	1st to 10th	Night	7% 4 2 4 2 2 4 3 4 5% 63%	2090
	11th to 20th	Night	12% 6% 1 5% 3 3 3 2 4 6% 55%	2200
	21st to end	Night	16% 6% 2 4 2 2 3 2 4 5% 55%	2560
November	1st to 10th	Night	11% 5% 1 6% 3 4 3 2 4 5% 54%	2536
	11th to 20th	Night	12% 6% 2 4 3 3 4 3 5% 5% 53%	2600
	21st to end	Night	16% 6% 2 4 4 3 3 3 5% 4 50%	2600
December	1st to 10th	Night	21% 7% 2 3 2 3 3 3 4 6% 47%	4250
	11th to 20th	Night	18% 9% 2 6% 3 3 3 3 4 5% 44%	4822
	21st to end	Night	20% 8% 3 5% 3 3 4 3 6% 6% 38%	6605

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	43% 3 4 28% 19% 3	3618
	11th to 20th	Day	37% 3 5% 25% 27% 4	4197
	21st to end	Day	47% 2 5% 19% 20% 7%	4972
February	1st to 10th	Day	47% 3 7% 19% 19% 4	2000
	11th to 20th	Day	48% 3 6% 18% 19% 6%	1958
	21st to end	Day	47% 3 6% 14% 22% 8%	1650
March	1st to 10th	Day	51% 3 7% 13% 18% 8%	4480
	11th to 20th	Day	40% 4 7% 18% 20% 12%	4708
	21st to end	Day	43% 4 8% 22% 18% 4	5969
April	1st to 10th	Day	37% 5% 10% 22% 19% 7%	2400
	11th to 20th	Day	37% 3 7% 23% 22% 7%	2374
	21st to end	Day	35% 4 10% 25% 22% 3	2400
May	1st to 10th	Day	45% 6% 12% 25% 10% 2	5572
	11th to 20th	Day	48% 8% 15% 20% 9% 1	5865
	21st to end	Day	42% 6% 12% 24% 14% 2	6447
June	1st to 10th	Day	39% 8% 14% 21% 16% 2	2600
	11th to 20th	Day	33% 8% 13% 24% 18% 2	2781
	21st to end	Day	33% 8% 17% 22% 16% 4	2800
July	1st to 10th	Day	37% 11% 18% 23% 10% 1	6291
	11th to 20th	Day	32% 13% 28% 22% 4 1	6152
	21st to end	Day	42% 12% 23% 18% 4	5782
August	1st to 10th	Day	23% 8% 13% 33% 22% 1	3893
	11th to 20th	Day	31% 7% 16% 29% 14% 2	3885
	21st to end	Day	29% 8% 14% 23% 22% 4	4311
September	1st to 10th	Day	36% 7% 13% 20% 19% 5%	2400
	11th to 20th	Day	38% 6% 11% 18% 22% 5%	2209
	21st to end	Day	33% 5% 9% 23% 21% 9%	2090
October	1st to 10th	Day	19% 4 6% 15% 29% 28%	3480
	11th to 20th	Day	18% 3 4 17% 33% 25%	3254
	21st to end	Day	25% 2 5% 21% 35% 12%	3339
November	1st to 10th	Day	32% 4 7% 20% 28% 9%	1762
	11th to 20th	Day	34% 4 6% 19% 27% 11%	1800
	21st to end	Day	39% 4 6% 20% 23% 7%	1800
December	1st to 10th	Day	44% 4 5% 21% 24% 3	2930
	11th to 20th	Day	48% 3 6% 19% 18% 6%	3370
	21st to end	Day	44% 4 7% 23% 20% 1	4334
January	1st to 10th	Night	46% 3 4 21% 24% 2	6348
	11th to 20th	Night	43% 2 4 19% 25% 7%	5765
	21st to end	Night	46% 3 3 18% 24% 7%	5984
February	1st to 10th	Night	45% 3 6% 20% 19% 7%	2400
	11th to 20th	Night	48% 3 5% 17% 19% 8%	2339
	21st to end	Night	46% 4 5% 17% 19% 9%	1980
March	1st to 10th	Night	51% 3 6% 14% 17% 9%	5373
	11th to 20th	Night	34% 5% 7% 18% 20% 17%	5279
	21st to end	Night	46% 3 5% 22% 18% 6%	4962
April	1st to 10th	Night	37% 4 10% 22% 19% 7%	2000
	11th to 20th	Night	34% 4 7% 22% 23% 10%	1975
	21st to end	Night	35% 5% 9% 24% 22% 5%	2000
May	1st to 10th	Night	41% 6% 14% 21% 16% 2	4387
	11th to 20th	Night	49% 6% 12% 22% 9% 2	4033
	21st to end	Night	37% 8% 13% 23% 17% 2	4429
June	1st to 10th	Night	33% 9% 12% 22% 20% 3	1800
	11th to 20th	Night	26% 7% 16% 27% 20% 4	1611
	21st to end	Night	29% 9% 18% 21% 20% 4	1600
July	1st to 10th	Night	33% 11% 22% 23% 9% 2	3580
	11th to 20th	Night	30% 12% 28% 24% 5% 1	3694
	21st to end	Night	41% 14% 23% 17% 4 1	4737
August	1st to 10th	Night	17% 7% 13% 37% 24% 2	3232
	11th to 20th	Night	23% 8% 20% 29% 17% 2	3230
	21st to end	Night	26% 8% 15% 21% 24% 6%	3586
September	1st to 10th	Night	33% 7% 15% 21% 18% 6%	2000
	11th to 20th	Night	34% 6% 12% 20% 21% 6%	2125
	21st to end	Night	28% 5% 9% 26% 23% 9%	2090
October	1st to 10th	Night	17% 4 6% 17% 29% 28%	3480
	11th to 20th	Night	20% 2 4 15% 31% 27%	3647
	21st to end	Night	23% 2 4 24% 29% 18%	4208
November	1st to 10th	Night	32% 4 7% 19% 25% 13%	2536
	11th to 20th	Night	32% 3 6% 18% 29% 12%	2600
	21st to end	Night	38% 3 6% 21% 23% 9%	2600
December	1st to 10th	Night	41% 3 5% 22% 26% 3	4250
	11th to 20th	Night	44% 4 6% 19% 23% 4	4824
	21st to end	Night	45% 4 6% 24% 19% 2	6605

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	28% 23% 33% 14% 2	300
	11th to 20th	Day	31% 18% 33% 14% 4	300
	21st to end	Day	25% 25% 33% 13% 3	330
February	1st to 10th	Day	28% 21% 33% 14% 4	300
	11th to 20th	Day	40% 19% 30% 11% 1	300
	21st to end	Day	33% 22% 33% 11% 1	249
March	1st to 10th	Day	29% 21% 33% 12% 5%	300
	11th to 20th	Day	26% 24% 31% 16% 3	326
	21st to end	Day	23% 17% 36% 17% 6%	550
April	1st to 10th	Day	22% 17% 33% 19% 8% 1	500
	11th to 20th	Day	20% 16% 30% 22% 9% 2	492
	21st to end	Day	15% 14% 31% 26% 13% 1	500
May	1st to 10th	Day	18% 11% 27% 27% 13% 3	503
	11th to 20th	Day	12% 7% 31% 26% 16% 8%	527
	21st to end	Day	11% 5% 27% 29% 18% 9%	573
June	1st to 10th	Day	11% 6% 19% 30% 23% 11%	530
	11th to 20th	Day	7% 4 17% 32% 27% 14%	711
	21st to end	Day	9% 3 14% 28% 31% 15%	730
July	1st to 10th	Day	6% 3 11% 33% 32% 16%	721
	11th to 20th	Day	8% 2 8% 25% 33% 23%	663
	21st to end	Day	8% 2 7% 27% 36% 21%	576
August	1st to 10th	Day	6% 3 12% 25% 35% 19%	526
	11th to 20th	Day	8% 2 12% 30% 30% 18%	519
	21st to end	Day	14% 3 11% 23% 30% 20%	583
September	1st to 10th	Day	9% 4 11% 35% 32% 10%	530
	11th to 20th	Day	9% 4 13% 27% 32% 16%	522
	21st to end	Day	14% 4 15% 30% 29% 9%	490
October	1st to 10th	Day	10% 4 22% 34% 22% 7%	490
	11th to 20th	Day	11% 10% 32% 31% 14% 1	375
	21st to end	Day	21% 11% 27% 28% 13% 2	330
November	1st to 10th	Day	18% 10% 30% 26% 13% 2	300
	11th to 20th	Day	15% 16% 38% 23% 6% 1	300
	21st to end	Day	18% 20% 34% 17% 10% 2	300
December	1st to 10th	Day	31% 18% 29% 19% 2 1	300
	11th to 20th	Day	22% 23% 32% 16% 6%	300
	21st to end	Day	29% 18% 33% 15% 5%	330
January	1st to 10th	Night	24% 18% 33% 21% 5%	1000
	11th to 20th	Night	23% 18% 29% 23% 7%	928
	21st to end	Night	23% 14% 36% 25% 2	880
February	1st to 10th	Night	26% 13% 31% 26% 5%	800
	11th to 20th	Night	27% 17% 30% 24% 2	783
	21st to end	Night	23% 20% 33% 22% 2	660
March	1st to 10th	Night	21% 15% 31% 27% 5%	800
	11th to 20th	Night	18% 15% 33% 26% 7% 1	771
	21st to end	Night	20% 10% 36% 24% 10%	660
April	1st to 10th	Night	17% 14% 32% 26% 11% 1	600
	11th to 20th	Night	15% 10% 34% 29% 10% 2	593
	21st to end	Night	13% 10% 32% 31% 14% 1	600
May	1st to 10th	Night	12% 7% 29% 30% 21% 2	600
	11th to 20th	Night	13% 5% 23% 34% 20% 4	591
	21st to end	Night	7% 3 19% 34% 31% 5%	650
June	1st to 10th	Night	7% 3 15% 38% 31% 7%	600
	11th to 20th	Night	6% 2 11% 33% 40% 9%	600
	21st to end	Night	5% 3 10% 30% 41% 11%	600
July	1st to 10th	Night	5% 2 6% 29% 45% 13%	585
	11th to 20th	Night	6% 1 7% 27% 41% 18%	582
	21st to end	Night	6% 2 8% 25% 43% 15%	657
August	1st to 10th	Night	5% 1 5% 28% 47% 14%	597
	11th to 20th	Night	6% 1 8% 33% 40% 12%	594
	21st to end	Night	9% 2 9% 29% 40% 11%	660
September	1st to 10th	Night	11% 3 12% 35% 35% 5%	600
	11th to 20th	Night	11% 4 12% 30% 37% 6%	739
	21st to end	Night	9% 3 16% 32% 36% 4	760
October	1st to 10th	Night	9% 3 20% 33% 30% 5%	760
	11th to 20th	Night	15% 6% 23% 37% 18% 1	760
	21st to end	Night	19% 6% 20% 33% 20% 2	836
November	1st to 10th	Night	13% 9% 22% 36% 17% 3	780
	11th to 20th	Night	13% 12% 30% 32% 13% 1	800
	21st to end	Night	19% 10% 29% 29% 11% 2	800
December	1st to 10th	Night	24% 12% 29% 28% 8%	800
	11th to 20th	Night	23% 13% 30% 26% 8%	800
	21st to end	Night	25% 14% 30% 26% 5%	930

Page generated at 2025-09-16 00:49:13. Version ac07

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