Solarity Observatory
Clear Sky Chart
History

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

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	13% 6% 2 6% 4 4 4 4 6% 7% 42%	114504
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	114452
Transparency	Day	38% 6% 10% 21% 19% 6%	118302
	Night	37% 5% 9% 21% 21% 7%	118795
Seeing	Day	16% 10% 23% 23% 19% 9%	15332
	Night	15% 8% 22% 29% 21% 4	25125

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	18% 8% 4 6% 3 3 3 2 4 5% 44%	4056
	11th to 20th	Day	14% 6% 5% 7% 3 2 2 2 3 5% 50%	4308
	21st to end	Day	22% 10% 3 5% 3 3 3 3 4 5% 39%	4972
February	1st to 10th	Day	19% 10% 3 6% 3 3 3 3 4 6% 39%	2000
	11th to 20th	Day	22% 8% 3 6% 4 3 3 3 5% 5% 39%	1948
	21st to end	Day	20% 8% 3 6% 4 4 3 3 4 5% 40%	1650
March	1st to 10th	Day	20% 9% 3 7% 5% 4 4 4 5% 4 36%	4480
	11th to 20th	Day	13% 6% 3 6% 4 4 4 3 5% 6% 45%	4703
	21st to end	Day	14% 7% 3 7% 4 4 4 3 5% 7% 42%	5865
April	1st to 10th	Day	11% 5% 3 6% 5% 4 4 4 6% 7% 46%	2400
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 47%	2374
	21st to end	Day	10% 5% 2 6% 4 4 4 4 5% 9% 47%	2400
May	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	4105
	11th to 20th	Day	15% 7% 2 6% 4 5% 4 4 7% 9% 38%	4081
	21st to end	Day	9% 5% 2 6% 6% 5% 5% 4 7% 9% 42%	4476
June	1st to 10th	Day	10% 5% 2 7% 6% 5% 7% 4 8% 10% 36%	2470
	11th to 20th	Day	5% 4 2 5% 5% 5% 6% 5% 8% 10% 45%	2470
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 6% 9% 43%	2610
July	1st to 10th	Day	6% 5% 2 8% 7% 7% 8% 6% 9% 12% 29%	4318
	11th to 20th	Day	8% 5% 2 6% 5% 6% 7% 7% 10% 13% 30%	4120
	21st to end	Day	13% 8% 4 9% 6% 7% 7% 6% 8% 10% 22%	4312
August	1st to 10th	Day	4 3 1 4 4 4 5% 5% 8% 9% 54%	3785
	11th to 20th	Day	5% 4 2 6% 4 5% 5% 5% 7% 10% 47%	3729
	21st to end	Day	7% 4 1 5% 5% 5% 5% 4 6% 8% 50%	4180
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 7% 4 6% 9% 41%	2261
	11th to 20th	Day	12% 7% 2 7% 4 5% 5% 4 6% 7% 42%	2090
	21st to end	Day	11% 5% 2 6% 4 4 3 4 4 6% 51%	2090
October	1st to 10th	Day	9% 4 2 6% 3 4 4 3 4 7% 54%	2090
	11th to 20th	Day	9% 4 1 5% 3 4 3 3 5% 7% 55%	2059
	21st to end	Day	14% 4 1 5% 4 3 3 2 4 6% 53%	1971
November	1st to 10th	Day	12% 5% 2 6% 3 3 4 3 4 5% 53%	1762
	11th to 20th	Day	13% 6% 2 5% 3 3 4 3 4 6% 53%	1800
	21st to end	Day	15% 6% 2 5% 4 3 4 4 4 7% 45%	1800
December	1st to 10th	Day	19% 9% 2 5% 3 3 3 3 4 5% 43%	2930
	11th to 20th	Day	19% 9% 3 7% 4 4 3 3 3 4 41%	3373
	21st to end	Day	20% 8% 3 6% 4 3 3 3 4 6% 40%	4466
January	1st to 10th	Night	17% 9% 4 7% 3 4 3 3 4 5% 43%	5889
	11th to 20th	Night	17% 8% 3 7% 3 2 3 2 4 4 46%	5647
	21st to end	Night	20% 10% 2 5% 3 3 3 2 4 4 44%	5984
February	1st to 10th	Night	19% 8% 3 6% 3 3 3 3 5% 5% 43%	2400
	11th to 20th	Night	23% 7% 3 6% 3 3 3 2 4 4 41%	2338
	21st to end	Night	20% 6% 2 6% 4 4 4 3 5% 5% 41%	1980
March	1st to 10th	Night	21% 9% 3 8% 4 4 3 3 5% 5% 34%	5373
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 5% 7% 49%	5256
	21st to end	Night	16% 8% 3 7% 5% 4 4 3 3 5% 43%	5105
April	1st to 10th	Night	12% 6% 2 5% 3 4 4 4 6% 8% 47%	2000
	11th to 20th	Night	13% 5% 2 5% 3 4 4 3 5% 6% 50%	1975
	21st to end	Night	10% 6% 2 5% 3 4 3 4 6% 7% 50%	2000
May	1st to 10th	Night	11% 5% 3 7% 5% 5% 4 3 5% 9% 43%	3006
	11th to 20th	Night	15% 7% 3 6% 4 4 4 3 6% 7% 40%	2818
	21st to end	Night	6% 4 1 6% 4 4 5% 5% 8% 12% 45%	3079
June	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 5% 9% 9% 42%	1710
	11th to 20th	Night	4 4 1 4 4 4 4 3 7% 12% 52%	1710
	21st to end	Night	6% 5% 2 7% 5% 5% 5% 4 6% 9% 47%	1554
July	1st to 10th	Night	6% 6% 3 7% 6% 6% 6% 5% 7% 12% 35%	2623
	11th to 20th	Night	8% 6% 2 7% 6% 6% 6% 4 9% 12% 35%	2840
	21st to end	Night	9% 9% 4 10% 8% 6% 7% 5% 8% 9% 25%	3235
August	1st to 10th	Night	2 2 1 3 4 4 5% 4 6% 11% 58%	3144
	11th to 20th	Night	4 3 1 5% 4 4 4 4 7% 10% 54%	3100
	21st to end	Night	5% 4 1 4 3 4 4 3 5% 8% 56%	3476
September	1st to 10th	Night	8% 6% 3 6% 4 4 4 3 5% 8% 48%	1900
	11th to 20th	Night	11% 6% 2 6% 4 4 4 3 6% 8% 45%	2089
	21st to end	Night	7% 5% 2 5% 4 4 3 4 6% 7% 53%	2090
October	1st to 10th	Night	9% 5% 2 3 3 3 3 3 4 4 61%	2090
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 6% 55%	2118
	21st to end	Night	15% 5% 2 4 3 3 2 2 3 5% 56%	2625
November	1st to 10th	Night	11% 5% 1 5% 4 4 3 3 5% 5% 54%	2536
	11th to 20th	Night	13% 6% 1 4 3 3 3 3 4 7% 53%	2600
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 5% 48%	2600
December	1st to 10th	Night	21% 6% 2 3 3 3 3 2 4 6% 47%	4250
	11th to 20th	Night	20% 8% 2 6% 4 3 3 2 4 4 44%	4822
	21st to end	Night	21% 7% 3 6% 4 4 4 3 5% 6% 38%	6490

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	44% 3 5% 26% 19% 3	4057
	11th to 20th	Day	38% 3 5% 25% 27% 3	4308
	21st to end	Day	48% 2 6% 17% 20% 6%	4972
February	1st to 10th	Day	47% 3 7% 19% 20% 4	2000
	11th to 20th	Day	48% 3 6% 18% 18% 6%	1958
	21st to end	Day	47% 4 6% 14% 22% 6%	1650
March	1st to 10th	Day	50% 4 7% 13% 18% 8%	4480
	11th to 20th	Day	38% 4 7% 18% 19% 14%	4703
	21st to end	Day	42% 4 8% 22% 20% 4	5867
April	1st to 10th	Day	36% 5% 11% 22% 18% 7%	2400
	11th to 20th	Day	37% 4 7% 22% 22% 8%	2374
	21st to end	Day	35% 6% 10% 25% 21% 3	2400
May	1st to 10th	Day	38% 6% 13% 26% 15% 2	4141
	11th to 20th	Day	41% 6% 13% 26% 13% 1	4085
	21st to end	Day	36% 8% 12% 27% 15% 1	4489
June	1st to 10th	Day	40% 9% 15% 19% 17% 1	2470
	11th to 20th	Day	31% 8% 15% 26% 17% 2	2470
	21st to end	Day	36% 9% 15% 23% 12% 5%	2610
July	1st to 10th	Day	39% 13% 22% 19% 6% 1	4252
	11th to 20th	Day	38% 13% 23% 20% 5% 1	4051
	21st to end	Day	53% 11% 14% 15% 6%	4174
August	1st to 10th	Day	22% 8% 13% 36% 21% 1	3773
	11th to 20th	Day	30% 8% 16% 28% 16% 3	3765
	21st to end	Day	30% 8% 14% 20% 23% 4	4179
September	1st to 10th	Day	37% 8% 14% 18% 17% 5%	2261
	11th to 20th	Day	39% 8% 11% 17% 20% 4	2090
	21st to end	Day	34% 6% 10% 21% 22% 8%	2090
October	1st to 10th	Day	21% 4 5% 15% 31% 24%	3480
	11th to 20th	Day	19% 3 5% 17% 32% 26%	3403
	21st to end	Day	25% 4 4 22% 35% 11%	3222
November	1st to 10th	Day	34% 4 7% 18% 28% 9%	1762
	11th to 20th	Day	34% 4 6% 18% 28% 10%	1800
	21st to end	Day	38% 5% 7% 19% 24% 7%	1800
December	1st to 10th	Day	44% 3 5% 18% 26% 4	2930
	11th to 20th	Day	49% 3 6% 20% 17% 5%	3370
	21st to end	Day	46% 3 7% 24% 19% 1	4466
January	1st to 10th	Night	45% 3 5% 22% 23% 3	5889
	11th to 20th	Night	42% 3 4 20% 24% 6%	5647
	21st to end	Night	45% 3 4 18% 24% 6%	5984
February	1st to 10th	Night	44% 3 6% 20% 21% 7%	2400
	11th to 20th	Night	47% 3 5% 18% 18% 8%	2339
	21st to end	Night	45% 4 6% 16% 20% 9%	1980
March	1st to 10th	Night	51% 4 6% 14% 17% 8%	5373
	11th to 20th	Night	34% 4 8% 17% 22% 16%	5256
	21st to end	Night	46% 3 6% 22% 18% 6%	5105
April	1st to 10th	Night	35% 4 12% 22% 20% 7%	2000
	11th to 20th	Night	36% 3 7% 21% 22% 11%	1975
	21st to end	Night	32% 6% 11% 26% 22% 5%	2000
May	1st to 10th	Night	37% 7% 13% 21% 20% 2	3035
	11th to 20th	Night	41% 7% 14% 24% 12% 2	2819
	21st to end	Night	29% 8% 14% 28% 17% 2	3087
June	1st to 10th	Night	34% 10% 14% 21% 18% 2	1710
	11th to 20th	Night	25% 7% 17% 28% 20% 4	1710
	21st to end	Night	32% 8% 14% 23% 20% 4	1554
July	1st to 10th	Night	39% 10% 24% 19% 6% 2	2580
	11th to 20th	Night	34% 12% 25% 21% 7% 1	2786
	21st to end	Night	51% 12% 16% 14% 6% 1	3132
August	1st to 10th	Night	18% 7% 15% 37% 21% 2	3132
	11th to 20th	Night	23% 9% 18% 30% 17% 3	3130
	21st to end	Night	25% 7% 15% 22% 24% 6%	3476
September	1st to 10th	Night	34% 7% 16% 20% 17% 6%	1900
	11th to 20th	Night	36% 7% 12% 18% 21% 6%	2089
	21st to end	Night	28% 7% 9% 24% 23% 9%	2090
October	1st to 10th	Night	19% 4 5% 17% 30% 24%	3480
	11th to 20th	Night	20% 2 4 16% 31% 27%	3513
	21st to end	Night	22% 3 4 23% 31% 16%	4324
November	1st to 10th	Night	32% 3 7% 18% 26% 13%	2536
	11th to 20th	Night	32% 3 7% 18% 28% 12%	2600
	21st to end	Night	37% 4 6% 20% 23% 9%	2600
December	1st to 10th	Night	40% 3 6% 22% 26% 4	4250
	11th to 20th	Night	45% 4 6% 18% 23% 4	4824
	21st to end	Night	46% 4 6% 25% 17% 2	6490

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	30% 22% 31% 13% 4	300
	11th to 20th	Day	29% 20% 31% 14% 6%	300
	21st to end	Day	25% 24% 36% 12% 3 1	330
February	1st to 10th	Day	26% 20% 33% 15% 5%	300
	11th to 20th	Day	37% 20% 28% 13% 2 1	300
	21st to end	Day	31% 23% 35% 9% 2	249
March	1st to 10th	Day	26% 23% 34% 11% 4 1	300
	11th to 20th	Day	25% 21% 32% 15% 6% 1	379
	21st to end	Day	22% 17% 35% 19% 8%	550
April	1st to 10th	Day	19% 19% 28% 23% 10% 2	500
	11th to 20th	Day	18% 15% 29% 24% 12% 2	492
	21st to end	Day	14% 13% 29% 29% 15% 1	500
May	1st to 10th	Day	15% 11% 29% 26% 13% 6%	503
	11th to 20th	Day	9% 8% 27% 28% 18% 10%	487
	21st to end	Day	10% 6% 22% 29% 19% 15%	529
June	1st to 10th	Day	13% 3 19% 27% 26% 12%	490
	11th to 20th	Day	8% 3 16% 28% 26% 21%	490
	21st to end	Day	9% 3 16% 27% 29% 15%	630
July	1st to 10th	Day	7% 1 10% 28% 31% 22%	604
	11th to 20th	Day	8% 1 9% 22% 29% 31%	484
	21st to end	Day	8% 3 10% 20% 36% 24%	532
August	1st to 10th	Day	9% 3 11% 23% 29% 25%	486
	11th to 20th	Day	9% 1 11% 30% 32% 17%	479
	21st to end	Day	12% 2 9% 22% 33% 21%	539
September	1st to 10th	Day	9% 4 12% 30% 33% 13%	490
	11th to 20th	Day	12% 4 12% 25% 31% 15%	490
	21st to end	Day	14% 4 15% 24% 32% 10%	490
October	1st to 10th	Day	12% 3 22% 30% 25% 7%	490
	11th to 20th	Day	10% 10% 27% 36% 16% 1	459
	21st to end	Day	18% 12% 23% 29% 16% 2	330
November	1st to 10th	Day	21% 8% 31% 25% 11% 4	300
	11th to 20th	Day	15% 18% 38% 21% 7% 1	300
	21st to end	Day	16% 19% 33% 24% 6% 2	300
December	1st to 10th	Day	30% 17% 31% 18% 4 1	300
	11th to 20th	Day	24% 20% 32% 16% 7% 1	300
	21st to end	Day	32% 15% 29% 17% 5% 1	330
January	1st to 10th	Night	23% 14% 34% 24% 5%	800
	11th to 20th	Night	25% 15% 27% 26% 7%	800
	21st to end	Night	22% 14% 34% 28% 3	880
February	1st to 10th	Night	23% 12% 30% 30% 5%	800
	11th to 20th	Night	28% 14% 30% 25% 3	783
	21st to end	Night	25% 15% 34% 24% 2	660
March	1st to 10th	Night	20% 17% 29% 29% 5%	800
	11th to 20th	Night	18% 14% 33% 26% 8% 1	800
	21st to end	Night	19% 12% 31% 27% 10%	725
April	1st to 10th	Night	15% 14% 31% 28% 12% 1	600
	11th to 20th	Night	15% 10% 32% 27% 14% 2	593
	21st to end	Night	13% 9% 28% 34% 16% 1	600
May	1st to 10th	Night	12% 5% 27% 33% 22% 3	600
	11th to 20th	Night	12% 4 23% 31% 26% 4	563
	21st to end	Night	8% 2 14% 35% 35% 7%	617
June	1st to 10th	Night	9% 2 11% 35% 36% 7%	570
	11th to 20th	Night	5% 1 11% 26% 44% 13%	570
	21st to end	Night	8% 1 8% 28% 44% 11%	570
July	1st to 10th	Night	6% 1 6% 26% 46% 14%	555
	11th to 20th	Night	7% 1 5% 24% 43% 21%	552
	21st to end	Night	8% 1 8% 25% 43% 16%	624
August	1st to 10th	Night	5% 1 3 27% 49% 16%	567
	11th to 20th	Night	7% 1 7% 31% 44% 10%	564
	21st to end	Night	13% 2 6% 26% 43% 11%	627
September	1st to 10th	Night	8% 2 13% 30% 39% 8%	570
	11th to 20th	Night	13% 3 12% 28% 38% 6%	759
	21st to end	Night	9% 2 15% 31% 37% 5%	760
October	1st to 10th	Night	10% 4 18% 33% 29% 6%	760
	11th to 20th	Night	13% 7% 23% 35% 21% 2	760
	21st to end	Night	17% 7% 19% 35% 21% 2	836
November	1st to 10th	Night	13% 8% 21% 34% 21% 3	780
	11th to 20th	Night	14% 10% 29% 32% 13% 2	800
	21st to end	Night	18% 9% 29% 31% 12% 1	800
December	1st to 10th	Night	22% 13% 25% 30% 10%	800
	11th to 20th	Night	24% 12% 27% 27% 10%	800
	21st to end	Night	26% 12% 29% 27% 7%	880

Page generated at 2025-05-08 08:33:57. Version ac07

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