The New Freedom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The New Freedom Observatory 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	11% 6% 2 6% 5% 4 5% 4 6% 8% 43%	126085
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	122971
Transparency	Day	37% 7% 12% 19% 18% 7%	129860
	Night	36% 6% 11% 18% 20% 9%	127265
Seeing	Day	14% 8% 22% 25% 20% 11%	16181
	Night	13% 7% 23% 31% 22% 4	26167

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	15% 6% 2 5% 3 3 3 2 4 5% 53%	4056
	11th to 20th	Day	13% 6% 2 4 3 2 2 2 4 7% 54%	4060
	21st to end	Day	17% 7% 2 6% 4 4 3 3 5% 7% 44%	4673
February	1st to 10th	Day	14% 8% 3 6% 5% 5% 4 4 5% 6% 41%	2000
	11th to 20th	Day	19% 6% 2 6% 3 2 4 3 5% 6% 43%	1948
	21st to end	Day	15% 7% 2 6% 4 4 3 3 5% 8% 43%	1650
March	1st to 10th	Day	19% 8% 3 7% 4 4 4 3 5% 6% 38%	4742
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 5% 7% 53%	4980
	21st to end	Day	15% 6% 3 6% 4 3 4 3 4 5% 47%	5465
April	1st to 10th	Day	10% 6% 2 6% 5% 4 4 3 5% 6% 48%	2200
	11th to 20th	Day	11% 5% 2 5% 4 4 3 3 5% 7% 52%	2331
	21st to end	Day	7% 4 1 5% 5% 4 4 4 5% 8% 53%	2565
May	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 4 5% 8% 43%	5862
	11th to 20th	Day	14% 6% 3 6% 4 4 5% 5% 7% 10% 36%	5861
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 7% 9% 45%	6433
June	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 6% 8% 11% 32%	2600
	11th to 20th	Day	5% 4 2 6% 6% 5% 6% 5% 8% 13% 40%	2600
	21st to end	Day	6% 5% 2 7% 6% 6% 7% 6% 8% 12% 36%	2600
July	1st to 10th	Day	10% 6% 2 9% 7% 7% 9% 7% 8% 10% 24%	5900
	11th to 20th	Day	3 4 2 6% 6% 6% 7% 6% 10% 13% 37%	5900
	21st to end	Day	6% 5% 3 8% 7% 7% 8% 7% 10% 12% 25%	6424
August	1st to 10th	Day	13% 6% 2 6% 5% 6% 6% 6% 9% 12% 30%	4234
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 4 7% 10% 47%	3913
	21st to end	Day	8% 5% 2 6% 4 5% 5% 5% 8% 11% 42%	4223
September	1st to 10th	Day	10% 6% 2 7% 4 5% 5% 5% 7% 10% 39%	2200
	11th to 20th	Day	13% 5% 2 7% 4 4 5% 5% 7% 8% 40%	2178
	21st to end	Day	12% 6% 2 7% 6% 4 4 3 6% 6% 43%	2090
October	1st to 10th	Day	12% 6% 2 3 4 3 4 3 5% 6% 51%	2090
	11th to 20th	Day	10% 3 1 4 3 3 3 3 5% 7% 58%	1969
	21st to end	Day	10% 5% 1 5% 3 3 3 3 5% 5% 57%	2090
November	1st to 10th	Day	12% 6% 2 4 4 3 4 3 4 6% 52%	1879
	11th to 20th	Day	12% 6% 2 5% 4 3 3 3 5% 6% 53%	1800
	21st to end	Day	14% 6% 2 5% 4 4 4 4 5% 6% 47%	1800
December	1st to 10th	Day	12% 7% 2 5% 4 3 4 2 4 5% 51%	2930
	11th to 20th	Day	16% 6% 3 5% 4 3 4 3 4 5% 48%	3373
	21st to end	Day	19% 8% 2 6% 3 3 3 2 4 5% 44%	4466
January	1st to 10th	Night	14% 5% 2 4 4 4 3 3 5% 5% 53%	5889
	11th to 20th	Night	12% 6% 2 6% 4 5% 5% 4 5% 7% 46%	5900
	21st to end	Night	17% 8% 2 6% 4 3 3 3 4 7% 43%	6278
February	1st to 10th	Night	14% 7% 3 6% 3 4 4 3 6% 5% 45%	2400
	11th to 20th	Night	18% 6% 2 5% 4 3 3 3 4 5% 46%	2338
	21st to end	Night	13% 6% 3 6% 4 3 4 4 6% 6% 46%	1980
March	1st to 10th	Night	20% 8% 2 5% 3 4 4 3 5% 7% 40%	5108
	11th to 20th	Night	9% 4 2 4 4 4 4 3 6% 8% 52%	4980
	21st to end	Night	13% 6% 2 5% 4 4 4 4 5% 6% 47%	5467
April	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 6% 7% 49%	2200
	11th to 20th	Night	10% 4 1 5% 3 4 4 4 5% 7% 51%	2032
	21st to end	Night	7% 3 2 5% 4 3 5% 4 5% 7% 55%	1831
May	1st to 10th	Night	8% 6% 2 7% 5% 5% 5% 4 7% 10% 40%	4033
	11th to 20th	Night	15% 5% 2 6% 4 4 5% 5% 7% 9% 38%	4032
	21st to end	Night	7% 5% 2 5% 4 4 5% 5% 7% 11% 46%	4421
June	1st to 10th	Night	9% 6% 3 7% 6% 5% 5% 6% 9% 11% 34%	1800
	11th to 20th	Night	4 4 2 6% 5% 5% 5% 5% 9% 12% 43%	1800
	21st to end	Night	5% 5% 2 7% 6% 7% 6% 5% 9% 12% 37%	1800
July	1st to 10th	Night	11% 8% 3 9% 6% 6% 8% 6% 9% 11% 23%	4058
	11th to 20th	Night	3 4 2 6% 6% 7% 8% 7% 10% 14% 34%	4057
	21st to end	Night	7% 7% 4 8% 7% 7% 7% 7% 10% 12% 25%	4427
August	1st to 10th	Night	12% 7% 3 9% 5% 5% 6% 5% 7% 11% 29%	2915
	11th to 20th	Night	6% 4 2 6% 4 5% 5% 4 7% 12% 45%	3131
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 7% 10% 48%	3641
September	1st to 10th	Night	10% 6% 2 7% 6% 5% 5% 5% 7% 10% 38%	2200
	11th to 20th	Night	12% 6% 2 6% 5% 4 6% 4 5% 7% 42%	2179
	21st to end	Night	10% 6% 2 7% 4 5% 4 4 6% 6% 44%	2090
October	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 52%	2090
	11th to 20th	Night	11% 5% 1 3 3 2 2 2 4 6% 60%	2209
	21st to end	Night	10% 4 1 5% 3 3 4 4 4 5% 57%	2508
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	2415
	11th to 20th	Night	14% 6% 2 4 3 3 2 2 4 6% 54%	2600
	21st to end	Night	13% 5% 3 6% 5% 4 3 3 5% 6% 49%	2600
December	1st to 10th	Night	12% 6% 2 4 3 3 3 3 4 5% 56%	4250
	11th to 20th	Night	15% 6% 2 5% 3 4 3 3 4 6% 50%	4822
	21st to end	Night	18% 8% 3 6% 4 3 3 3 4 5% 42%	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	35% 2 4 16% 33% 9%	4057
	11th to 20th	Day	32% 3 4 16% 32% 14%	4060
	21st to end	Day	41% 3 6% 16% 21% 12%	4673
February	1st to 10th	Day	44% 4 9% 16% 19% 9%	2000
	11th to 20th	Day	42% 4 5% 16% 24% 8%	1958
	21st to end	Day	40% 5% 7% 16% 21% 11%	1650
March	1st to 10th	Day	47% 4 7% 13% 21% 9%	4742
	11th to 20th	Day	29% 5% 9% 16% 21% 21%	4980
	21st to end	Day	40% 4 7% 19% 19% 11%	5465
April	1st to 10th	Day	37% 6% 9% 21% 18% 10%	2200
	11th to 20th	Day	32% 4 8% 21% 23% 12%	2331
	21st to end	Day	28% 6% 10% 25% 25% 6%	2565
May	1st to 10th	Day	39% 6% 14% 22% 16% 3	5897
	11th to 20th	Day	41% 7% 18% 22% 11% 1	5865
	21st to end	Day	32% 8% 16% 23% 20% 1	6447
June	1st to 10th	Day	43% 9% 15% 19% 12% 2	2600
	11th to 20th	Day	32% 9% 18% 23% 16% 2	2600
	21st to end	Day	38% 11% 18% 19% 12% 2	2600
July	1st to 10th	Day	48% 14% 18% 16% 3 1	5835
	11th to 20th	Day	32% 14% 29% 23% 3 1	5831
	21st to end	Day	44% 15% 20% 18% 3	6240
August	1st to 10th	Day	43% 11% 19% 24% 4	4221
	11th to 20th	Day	30% 8% 16% 31% 14% 1	3951
	21st to end	Day	34% 10% 18% 26% 12% 1	4223
September	1st to 10th	Day	38% 9% 16% 18% 15% 3	2200
	11th to 20th	Day	39% 8% 10% 19% 19% 4	2178
	21st to end	Day	40% 6% 9% 20% 18% 6%	2090
October	1st to 10th	Day	33% 4 7% 13% 27% 16%	3480
	11th to 20th	Day	16% 2 5% 17% 26% 34%	3248
	21st to end	Day	20% 3 5% 17% 39% 16%	3428
November	1st to 10th	Day	35% 4 7% 14% 25% 15%	1879
	11th to 20th	Day	33% 3 6% 17% 25% 16%	1800
	21st to end	Day	37% 4 8% 17% 23% 10%	1800
December	1st to 10th	Day	36% 3 7% 16% 27% 10%	2930
	11th to 20th	Day	39% 3 6% 22% 22% 7%	3370
	21st to end	Day	44% 4 5% 19% 24% 3	4466
January	1st to 10th	Night	33% 4 5% 16% 33% 9%	5889
	11th to 20th	Night	38% 4 5% 17% 26% 10%	5900
	21st to end	Night	42% 3 6% 15% 25% 9%	6278
February	1st to 10th	Night	40% 4 7% 18% 21% 11%	2400
	11th to 20th	Night	41% 4 6% 16% 21% 12%	2339
	21st to end	Night	38% 5% 8% 15% 18% 15%	1980
March	1st to 10th	Night	45% 3 9% 15% 16% 12%	5108
	11th to 20th	Night	30% 5% 9% 13% 24% 19%	4980
	21st to end	Night	38% 4 7% 17% 20% 14%	5467
April	1st to 10th	Night	35% 5% 10% 18% 19% 13%	2200
	11th to 20th	Night	32% 4 7% 21% 24% 12%	2032
	21st to end	Night	28% 6% 11% 24% 23% 9%	1831
May	1st to 10th	Night	36% 8% 16% 22% 15% 3	4060
	11th to 20th	Night	39% 9% 18% 23% 10% 2	4033
	21st to end	Night	30% 7% 16% 25% 19% 2	4429
June	1st to 10th	Night	41% 10% 16% 19% 13% 1	1800
	11th to 20th	Night	31% 11% 18% 26% 14% 2	1800
	21st to end	Night	37% 11% 21% 16% 12% 3	1800
July	1st to 10th	Night	49% 15% 20% 12% 3 1	4015
	11th to 20th	Night	35% 15% 30% 17% 3	4006
	21st to end	Night	47% 16% 20% 15% 2	4297
August	1st to 10th	Night	46% 11% 20% 21% 3	2904
	11th to 20th	Night	30% 9% 19% 28% 12% 1	3159
	21st to end	Night	29% 8% 20% 31% 11% 1	3641
September	1st to 10th	Night	39% 10% 17% 17% 13% 4	2200
	11th to 20th	Night	40% 9% 12% 16% 19% 4	2179
	21st to end	Night	38% 7% 13% 15% 21% 6%	2090
October	1st to 10th	Night	34% 5% 8% 13% 24% 17%	3480
	11th to 20th	Night	17% 3 4 12% 30% 35%	3669
	21st to end	Night	20% 3 4 19% 34% 20%	4120
November	1st to 10th	Night	33% 4 8% 14% 26% 15%	2415
	11th to 20th	Night	33% 3 6% 15% 28% 15%	2600
	21st to end	Night	37% 4 7% 18% 23% 12%	2600
December	1st to 10th	Night	32% 3 7% 20% 29% 9%	4250
	11th to 20th	Night	37% 4 9% 18% 24% 8%	4824
	21st to end	Night	45% 3 5% 20% 25% 3	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	19% 19% 47% 12% 2	300
	11th to 20th	Day	17% 21% 37% 16% 7% 2	300
	21st to end	Day	23% 21% 41% 11% 4	330
February	1st to 10th	Day	19% 21% 40% 15% 6%	300
	11th to 20th	Day	30% 17% 34% 18% 1	300
	21st to end	Day	20% 18% 44% 14% 3	249
March	1st to 10th	Day	17% 21% 31% 24% 7% 1	406
	11th to 20th	Day	16% 14% 37% 24% 9% 1	500
	21st to end	Day	19% 14% 35% 24% 8%	550
April	1st to 10th	Day	17% 18% 27% 25% 12% 2	500
	11th to 20th	Day	13% 12% 30% 27% 15% 3	492
	21st to end	Day	10% 10% 24% 32% 20% 4	500
May	1st to 10th	Day	8% 10% 28% 30% 17% 7%	503
	11th to 20th	Day	11% 4 24% 28% 20% 13%	527
	21st to end	Day	12% 4 16% 31% 23% 14%	573
June	1st to 10th	Day	12% 3 14% 30% 26% 14%	530
	11th to 20th	Day	8% 2 14% 25% 27% 24%	530
	21st to end	Day	7% 2 13% 28% 30% 21%	530
July	1st to 10th	Day	6% 3 7% 22% 36% 26%	525
	11th to 20th	Day	6% 1 5% 18% 34% 35%	524
	21st to end	Day	5% 1 8% 23% 37% 26%	576
August	1st to 10th	Day	15% 2 8% 22% 31% 21%	526
	11th to 20th	Day	8% 3 7% 20% 39% 24%	519
	21st to end	Day	13% 2 9% 24% 32% 19%	583
September	1st to 10th	Day	13% 2 12% 26% 31% 16%	530
	11th to 20th	Day	15% 3 11% 31% 28% 12%	522
	21st to end	Day	14% 3 14% 27% 29% 13%	490
October	1st to 10th	Day	18% 2 24% 28% 19% 9%	490
	11th to 20th	Day	10% 8% 21% 32% 22% 7%	490
	21st to end	Day	10% 8% 27% 30% 22% 3	539
November	1st to 10th	Day	20% 6% 22% 32% 16% 3	417
	11th to 20th	Day	15% 10% 41% 23% 10% 2	300
	21st to end	Day	13% 16% 32% 26% 12% 1	300
December	1st to 10th	Day	21% 17% 38% 16% 7% 1	300
	11th to 20th	Day	23% 17% 34% 16% 9% 1	300
	21st to end	Day	26% 14% 28% 24% 7% 1	330
January	1st to 10th	Night	19% 15% 34% 26% 5% 1	800
	11th to 20th	Night	16% 13% 31% 28% 11%	800
	21st to end	Night	19% 12% 37% 27% 4	880
February	1st to 10th	Night	18% 11% 32% 32% 7%	800
	11th to 20th	Night	22% 13% 33% 29% 3	783
	21st to end	Night	16% 13% 38% 29% 4	660
March	1st to 10th	Night	15% 12% 34% 33% 7%	800
	11th to 20th	Night	14% 13% 32% 29% 11% 1	800
	21st to end	Night	13% 13% 33% 31% 10%	880
April	1st to 10th	Night	13% 11% 31% 31% 13%	800
	11th to 20th	Night	13% 7% 30% 34% 15% 1	650
	21st to end	Night	7% 6% 25% 41% 20% 1	600
May	1st to 10th	Night	7% 7% 25% 38% 21% 2	600
	11th to 20th	Night	8% 4 23% 35% 24% 5%	591
	21st to end	Night	10% 3 12% 39% 31% 5%	650
June	1st to 10th	Night	11% 2 14% 36% 33% 4	600
	11th to 20th	Night	4 2 11% 34% 39% 9%	600
	21st to end	Night	7% 2 10% 33% 40% 9%	600
July	1st to 10th	Night	8% 2 8% 28% 40% 16%	585
	11th to 20th	Night	7% 1 5% 21% 49% 17%	582
	21st to end	Night	8% 1 6% 27% 46% 12%	657
August	1st to 10th	Night	10% 1 9% 26% 41% 12%	597
	11th to 20th	Night	10% 1 7% 25% 47% 11%	594
	21st to end	Night	12% 2 10% 26% 38% 12%	689
September	1st to 10th	Night	11% 2 9% 30% 40% 8%	800
	11th to 20th	Night	13% 2 10% 32% 37% 5%	793
	21st to end	Night	13% 2 14% 31% 37% 3	760
October	1st to 10th	Night	13% 3 19% 34% 26% 5%	760
	11th to 20th	Night	14% 5% 21% 32% 25% 3	760
	21st to end	Night	11% 5% 23% 33% 26% 2	836
November	1st to 10th	Night	15% 6% 21% 36% 21% 1	780
	11th to 20th	Night	16% 9% 26% 34% 14% 1	800
	21st to end	Night	16% 9% 29% 29% 16% 1	800
December	1st to 10th	Night	15% 9% 32% 30% 14% 1	800
	11th to 20th	Night	18% 8% 30% 31% 12% 1	800
	21st to end	Night	25% 10% 25% 32% 8%	880

Page generated at 2025-09-16 01:49:13. Version ac07

Copyright © 2025 Attilla Danko.