SPARQ Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SPARQ Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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	8% 5% 2 4 3 2 3 2 4 6% 61%	135536
	Night	10% 6% 2 6% 3 3 3 3 5% 6% 52%	132282
Transparency	Day	26% 3 8% 20% 24% 19%	130433
	Night	33% 3 8% 19% 21% 16%	128387
Seeing	Day	11% 10% 23% 30% 19% 6%	16732
	Night	12% 5% 15% 32% 29% 6%	25969

By Month

Percentage Cloud Cover SW (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	14% 5% 2 6% 4 3 3 4 6% 8% 45%	3892
	11th to 20th	Day	16% 7% 3 6% 3 3 3 2 4 5% 49%	4100
	21st to end	Day	18% 6% 3 6% 3 3 3 3 4 6% 44%	4510
February	1st to 10th	Day	19% 6% 2 6% 4 4 3 3 4 4 46%	1800
	11th to 20th	Day	14% 7% 3 7% 4 4 4 4 5% 7% 41%	1789
	21st to end	Day	16% 7% 2 4 5% 3 3 3 4 7% 47%	1650
March	1st to 10th	Day	16% 10% 3 8% 4 4 4 3 4 7% 36%	4946
	11th to 20th	Day	14% 5% 2 6% 3 3 4 4 6% 7% 47%	5000
	21st to end	Day	18% 7% 2 6% 4 4 5% 4 6% 9% 35%	5516
April	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 6% 7% 43%	2400
	11th to 20th	Day	9% 5% 3 5% 4 4 4 3 5% 6% 52%	2369
	21st to end	Day	7% 5% 1 4 3 3 3 3 6% 9% 57%	2400
May	1st to 10th	Day	4 2 1 2 1 1 2 2 3 6% 75%	5807
	11th to 20th	Day	3 2 1 3 2 2 2 2 4 5% 75%	5942
	21st to end	Day	2 2 1 3 2 1 2 1 3 5% 78%	6902
June	1st to 10th	Day	6% 5% 2 4 2 2 2 3 5% 8% 60%	2800
	11th to 20th	Day	2 2 1 2 2 2 2 3 4 6% 74%	2800
	21st to end	Day	2 3 1 3 2 2 2 2 3 4 76%	2800
July	1st to 10th	Day	1 3 1 3 1 1 2 1 2 4 81%	6319
	11th to 20th	Day	1 4 3 3 2 1 2 1 3 5% 76%	5889
	21st to end	Day	1 5% 2 3 2 1 2 2 3 4 75%	6402
August	1st to 10th	Day	1 2 2 4 2 2 2 3 4 6% 73%	5777
	11th to 20th	Day	1 2 1 3 2 1 1 1 3 4 80%	5634
	21st to end	Day	1 3 2 6% 2 2 2 2 4 7% 68%	5984
September	1st to 10th	Day	1 3 1 3 2 2 2 2 4 6% 74%	2400
	11th to 20th	Day	4 4 2 5% 3 3 3 3 4 7% 63%	2386
	21st to end	Day	4 3 1 4 2 1 2 2 3 6% 72%	2110
October	1st to 10th	Day	4 3 1 2 2 2 3 2 4 6% 70%	3280
	11th to 20th	Day	8% 4 2 4 2 2 3 2 4 5% 64%	3261
	21st to end	Day	7% 4 1 5% 3 3 4 3 5% 8% 57%	3558
November	1st to 10th	Day	10% 4 1 4 3 4 3 3 5% 7% 55%	2040
	11th to 20th	Day	13% 6% 3 6% 5% 3 4 3 4 7% 47%	1821
	21st to end	Day	12% 5% 1 5% 2 3 5% 3 5% 6% 53%	1600
December	1st to 10th	Day	11% 4 2 4 3 3 3 4 7% 11% 50%	2620
	11th to 20th	Day	27% 8% 2 6% 4 4 4 3 6% 8% 28%	3028
	21st to end	Day	24% 8% 3 7% 4 4 4 3 5% 7% 29%	4004
January	1st to 10th	Night	12% 6% 2 5% 3 4 4 4 8% 9% 42%	6059
	11th to 20th	Night	16% 6% 2 6% 4 3 4 3 5% 8% 44%	5880
	21st to end	Night	19% 7% 3 7% 3 3 3 3 5% 5% 42%	6468
February	1st to 10th	Night	19% 6% 2 5% 3 3 3 3 4 6% 47%	2600
	11th to 20th	Night	14% 8% 3 6% 4 4 3 3 5% 8% 42%	2497
	21st to end	Night	14% 6% 1 3 2 3 4 2 5% 6% 53%	1980
March	1st to 10th	Night	16% 10% 3 8% 4 4 4 3 5% 7% 36%	4945
	11th to 20th	Night	16% 7% 3 6% 3 3 3 3 5% 6% 46%	5000
	21st to end	Night	16% 10% 3 6% 3 3 3 3 5% 8% 39%	5457
April	1st to 10th	Night	10% 6% 3 6% 5% 3 4 4 4 6% 51%	2000
	11th to 20th	Night	8% 8% 2 6% 4 3 3 3 3 6% 54%	1979
	21st to end	Night	6% 5% 2 4 3 3 3 3 4 7% 60%	2000
May	1st to 10th	Night	4 4 2 4 2 2 2 2 3 5% 71%	4159
	11th to 20th	Night	3 4 2 7% 4 3 3 2 3 5% 63%	3964
	21st to end	Night	2 2 1 3 2 1 2 2 4 4 77%	3972
June	1st to 10th	Night	5% 7% 2 4 3 3 2 3 5% 8% 58%	1600
	11th to 20th	Night	2 3 1 3 3 2 3 2 3 6% 73%	1600
	21st to end	Night	3 4 2 4 2 2 2 2 3 4 71%	1600
July	1st to 10th	Night	1 5% 2 6% 2 2 2 2 3 4 71%	3640
	11th to 20th	Night	1 13% 5% 8% 4 2 2 2 3 5% 56%	4087
	21st to end	Night	1 12% 4 6% 5% 2 3 3 5% 7% 52%	4472
August	1st to 10th	Night	2 3 3 9% 4 3 3 4 5% 6% 58%	4035
	11th to 20th	Night	5% 2 5% 3 2 2 2 3 6% 70%	4208
	21st to end	Night	1 4 3 12% 4 3 2 3 6% 6% 55%	5015
September	1st to 10th	Night	1 3 1 3 3 2 3 2 5% 7% 68%	2000
	11th to 20th	Night	5% 6% 2 6% 3 3 3 2 5% 7% 58%	2010
	21st to end	Night	4 5% 2 5% 2 2 2 2 4 4 67%	2290
October	1st to 10th	Night	3 4 1 3 3 2 2 2 4 6% 70%	3920
	11th to 20th	Night	6% 7% 3 7% 3 2 3 2 5% 5% 57%	3897
	21st to end	Night	9% 4 2 4 3 3 4 3 5% 6% 57%	4253
November	1st to 10th	Night	10% 6% 2 4 3 3 3 3 5% 8% 52%	2476
	11th to 20th	Night	13% 6% 2 5% 3 2 4 3 5% 7% 49%	2731
	21st to end	Night	11% 4 2 5% 3 3 3 2 4 6% 55%	2800
December	1st to 10th	Night	12% 4 2 4 3 4 4 3 7% 10% 48%	4560
	11th to 20th	Night	26% 8% 2 6% 4 4 4 4 8% 9% 25%	5176
	21st to end	Night	30% 8% 2 6% 4 3 3 2 4 4 33%	6952

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	37% 7% 15% 22% 13% 6%	3892
	11th to 20th	Day	40% 4 7% 15% 20% 15%	4100
	21st to end	Day	42% 3 7% 15% 14% 19%	4510
February	1st to 10th	Day	43% 4 7% 19% 20% 8%	1800
	11th to 20th	Day	42% 5% 9% 20% 18% 7%	1798
	21st to end	Day	39% 5% 9% 25% 16% 7%	1650
March	1st to 10th	Day	49% 5% 6% 21% 17% 2	4946
	11th to 20th	Day	36% 5% 14% 27% 10% 8%	5000
	21st to end	Day	45% 8% 14% 22% 10% 1	5516
April	1st to 10th	Day	41% 5% 13% 22% 16% 4	2400
	11th to 20th	Day	33% 5% 13% 23% 19% 6%	2372
	21st to end	Day	25% 5% 14% 30% 22% 4	2400
May	1st to 10th	Day	14% 2 9% 28% 30% 18%	5807
	11th to 20th	Day	14% 2 7% 34% 34% 10%	5945
	21st to end	Day	12% 3 8% 35% 38% 3	6904
June	1st to 10th	Day	24% 5% 11% 29% 26% 6%	2800
	11th to 20th	Day	13% 3 10% 20% 38% 15%	2800
	21st to end	Day	14% 2 4 16% 36% 28%	2800
July	1st to 10th	Day	11% 1 2 8% 24% 54%	6251
	11th to 20th	Day	13% 1 4 5% 19% 58%	5819
	21st to end	Day	14% 1 5% 16% 30% 34%	6217
August	1st to 10th	Day	17% 2 4 11% 28% 37%	4206
	11th to 20th	Day	9% 1 4 13% 42% 31%	4081
	21st to end	Day	17% 2 5% 13% 37% 27%	4311
September	1st to 10th	Day	12% 1 5% 12% 31% 39%	2400
	11th to 20th	Day	21% 3 6% 25% 33% 11%	2386
	21st to end	Day	16% 2 5% 22% 32% 23%	2110
October	1st to 10th	Day	16% 2 4 13% 25% 40%	3280
	11th to 20th	Day	23% 3 6% 22% 26% 20%	3261
	21st to end	Day	26% 4 8% 24% 26% 12%	3558
November	1st to 10th	Day	29% 5% 8% 28% 19% 11%	2040
	11th to 20th	Day	38% 5% 11% 22% 16% 8%	1821
	21st to end	Day	32% 4 11% 20% 19% 13%	1600
December	1st to 10th	Day	28% 4 7% 28% 24% 9%	2620
	11th to 20th	Day	55% 4 8% 17% 14% 3	3028
	21st to end	Day	55% 5% 12% 18% 7% 3	4004
January	1st to 10th	Night	35% 7% 22% 19% 13% 5%	6059
	11th to 20th	Night	39% 5% 8% 18% 17% 13%	5880
	21st to end	Night	44% 4 7% 9% 19% 17%	6468
February	1st to 10th	Night	39% 4 8% 20% 18% 11%	2600
	11th to 20th	Night	41% 4 10% 19% 19% 7%	2499
	21st to end	Night	32% 4 11% 26% 20% 6%	1980
March	1st to 10th	Night	48% 6% 8% 19% 16% 2	4945
	11th to 20th	Night	38% 3 13% 20% 19% 7%	5000
	21st to end	Night	44% 6% 13% 24% 11% 2	5457
April	1st to 10th	Night	35% 6% 13% 22% 20% 4	2000
	11th to 20th	Night	32% 3 12% 26% 17% 10%	1979
	21st to end	Night	24% 4 11% 31% 24% 6%	2000
May	1st to 10th	Night	18% 2 5% 24% 33% 18%	4156
	11th to 20th	Night	23% 2 6% 27% 28% 14%	3965
	21st to end	Night	12% 2 7% 34% 40% 6%	3972
June	1st to 10th	Night	25% 4 10% 23% 30% 8%	1600
	11th to 20th	Night	14% 2 7% 21% 36% 20%	1600
	21st to end	Night	19% 2 5% 13% 32% 30%	1600
July	1st to 10th	Night	18% 1 2 8% 23% 49%	3600
	11th to 20th	Night	34% 1 3 6% 14% 42%	4034
	21st to end	Night	32% 1 4 11% 21% 30%	4345
August	1st to 10th	Night	32% 1 3 12% 25% 26%	2929
	11th to 20th	Night	14% 1 4 10% 38% 33%	3046
	21st to end	Night	23% 1 5% 12% 32% 26%	3608
September	1st to 10th	Night	14% 2 5% 10% 30% 39%	2000
	11th to 20th	Night	25% 2 7% 19% 32% 15%	2010
	21st to end	Night	19% 2 4 20% 28% 26%	2290
October	1st to 10th	Night	17% 2 5% 11% 23% 43%	3920
	11th to 20th	Night	29% 2 6% 22% 20% 20%	3897
	21st to end	Night	27% 4 6% 22% 26% 16%	4253
November	1st to 10th	Night	30% 4 11% 26% 19% 11%	2476
	11th to 20th	Night	34% 4 13% 24% 17% 8%	2731
	21st to end	Night	32% 3 9% 20% 22% 14%	2800
December	1st to 10th	Night	30% 3 7% 26% 23% 12%	4560
	11th to 20th	Night	54% 4 8% 15% 15% 4	5176
	21st to end	Night	56% 5% 10% 17% 10% 3	6952

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	27% 13% 24% 20% 13% 3	310
	11th to 20th	Day	21% 11% 24% 26% 16% 3	400
	21st to end	Day	16% 11% 23% 28% 18% 3	440
February	1st to 10th	Day	22% 13% 20% 23% 19% 4	400
	11th to 20th	Day	19% 17% 27% 24% 12% 1	412
	21st to end	Day	16% 15% 25% 28% 15% 1	414
March	1st to 10th	Day	25% 17% 27% 21% 7% 3	500
	11th to 20th	Day	23% 15% 27% 21% 10% 4	500
	21st to end	Day	18% 19% 30% 23% 9% 2	550
April	1st to 10th	Day	16% 19% 28% 24% 10% 4	500
	11th to 20th	Day	13% 20% 29% 22% 12% 4	492
	21st to end	Day	9% 17% 30% 26% 12% 6%	500
May	1st to 10th	Day	11% 16% 31% 27% 12% 3	503
	11th to 20th	Day	10% 14% 29% 27% 15% 4	528
	21st to end	Day	10% 12% 26% 29% 17% 6%	573
June	1st to 10th	Day	8% 11% 27% 31% 16% 7%	530
	11th to 20th	Day	5% 12% 30% 36% 14% 4	530
	21st to end	Day	2 5% 27% 36% 23% 6%	530
July	1st to 10th	Day	5% 4 22% 42% 21% 5%	526
	11th to 20th	Day	2 1 18% 43% 28% 8%	524
	21st to end	Day	1 2 13% 47% 29% 9%	575
August	1st to 10th	Day	3 4 20% 42% 23% 8%	527
	11th to 20th	Day	3 4 20% 38% 26% 9%	517
	21st to end	Day	4 2 19% 38% 28% 9%	583
September	1st to 10th	Day	2 4 21% 38% 25% 9%	530
	11th to 20th	Day	6% 8% 22% 34% 21% 9%	530
	21st to end	Day	6% 8% 22% 33% 24% 8%	530
October	1st to 10th	Day	7% 9% 23% 26% 24% 11%	530
	11th to 20th	Day	9% 8% 19% 28% 25% 12%	530
	21st to end	Day	12% 9% 18% 30% 24% 7%	583
November	1st to 10th	Day	12% 9% 18% 26% 27% 8%	516
	11th to 20th	Day	13% 9% 17% 28% 22% 12%	299
	21st to end	Day	13% 9% 24% 25% 21% 9%	200
December	1st to 10th	Day	17% 17% 13% 23% 20% 12%	200
	11th to 20th	Day	25% 12% 20% 20% 16% 9%	200
	21st to end	Day	21% 15% 22% 24% 14% 4	220
January	1st to 10th	Night	20% 6% 17% 30% 23% 4	800
	11th to 20th	Night	20% 6% 15% 34% 21% 5%	800
	21st to end	Night	19% 5% 15% 32% 24% 4	880
February	1st to 10th	Night	21% 6% 15% 34% 22% 2	800
	11th to 20th	Night	17% 8% 19% 32% 21% 4	784
	21st to end	Night	16% 9% 20% 35% 18% 2	660
March	1st to 10th	Night	22% 10% 20% 27% 19% 3	800
	11th to 20th	Night	19% 7% 18% 32% 21% 3	800
	21st to end	Night	18% 8% 26% 30% 16% 3	880
April	1st to 10th	Night	12% 9% 26% 31% 20% 3	800
	11th to 20th	Night	12% 12% 22% 28% 21% 5%	791
	21st to end	Night	9% 11% 26% 26% 23% 6%	800
May	1st to 10th	Night	9% 7% 21% 31% 27% 4	633
	11th to 20th	Night	5% 4 22% 31% 34% 4	547
	21st to end	Night	6% 8% 21% 32% 29% 4	433
June	1st to 10th	Night	7% 6% 20% 35% 30% 2	400
	11th to 20th	Night	4 5% 19% 44% 26% 2	400
	21st to end	Night	4 2 15% 39% 37% 3	400
July	1st to 10th	Night	3 1 10% 37% 44% 5%	390
	11th to 20th	Night	4 1 4 31% 48% 13%	570
	21st to end	Night	5% 1 4 33% 48% 10%	657
August	1st to 10th	Night	5% 1 10% 31% 42% 11%	597
	11th to 20th	Night	2 1 8% 36% 44% 9%	659
	21st to end	Night	4 1 7% 33% 47% 8%	880
September	1st to 10th	Night	3 1 9% 31% 47% 9%	800
	11th to 20th	Night	7% 3 10% 35% 37% 9%	800
	21st to end	Night	6% 3 12% 32% 36% 11%	800
October	1st to 10th	Night	7% 4 14% 32% 34% 9%	800
	11th to 20th	Night	9% 3 13% 30% 37% 8%	800
	21st to end	Night	11% 4 11% 30% 33% 11%	880
November	1st to 10th	Night	12% 4 14% 28% 33% 9%	820
	11th to 20th	Night	14% 3 14% 35% 29% 5%	828
	21st to end	Night	12% 6% 16% 35% 26% 5%	800
December	1st to 10th	Night	21% 6% 12% 32% 23% 6%	800
	11th to 20th	Night	27% 6% 14% 30% 20% 3	800
	21st to end	Night	25% 7% 19% 32% 16% 2	880

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