Addison Oaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Addison Oaks Observatory clear sky chart from 2005-11-06 to 2025-08-05.

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% 10% 3 8% 5% 5% 5% 4 6% 7% 33%	124991
	Night	13% 10% 4 8% 5% 5% 4 4 5% 7% 35%	123135
Transparency	Day	47% 6% 12% 20% 12% 2	128560
	Night	47% 6% 12% 21% 12% 1	127636
Seeing	Day	17% 12% 30% 23% 13% 5%	16380
	Night	18% 10% 29% 29% 12% 1	26015

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	10% 16% 6% 15% 6% 5% 4 3 5% 6% 25%	3617
	11th to 20th	Day	13% 15% 6% 16% 9% 9% 6% 4 5% 5% 13%	3620
	21st to end	Day	21% 16% 6% 12% 6% 5% 5% 3 4 5% 17%	4403
February	1st to 10th	Day	13% 13% 5% 13% 9% 7% 5% 4 5% 6% 21%	1800
	11th to 20th	Day	13% 14% 5% 12% 8% 6% 4 3 5% 6% 23%	1871
	21st to end	Day	12% 15% 5% 12% 6% 4 5% 4 5% 5% 25%	1650
March	1st to 10th	Day	14% 12% 5% 11% 6% 4 4 3 4 6% 31%	4611
	11th to 20th	Day	11% 12% 4 9% 6% 5% 4 4 5% 7% 32%	4980
	21st to end	Day	17% 14% 4 9% 5% 4 5% 3 5% 6% 28%	5465
April	1st to 10th	Day	16% 12% 3 8% 5% 5% 4 4 5% 7% 30%	2313
	11th to 20th	Day	16% 10% 3 8% 5% 4 5% 3 6% 7% 34%	2552
	21st to end	Day	16% 8% 3 8% 5% 5% 4 3 5% 7% 35%	2600
May	1st to 10th	Day	17% 9% 3 8% 4 4 5% 4 5% 6% 35%	5862
	11th to 20th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 7% 34%	5861
	21st to end	Day	13% 7% 3 7% 4 4 4 3 5% 7% 41%	6433
June	1st to 10th	Day	9% 7% 2 7% 5% 5% 5% 4 7% 9% 40%	2947
	11th to 20th	Day	10% 6% 3 6% 5% 5% 5% 4 6% 9% 41%	3000
	21st to end	Day	9% 5% 3 6% 5% 5% 6% 5% 7% 10% 37%	2928
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 4 8% 11% 39%	6360
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 45%	6360
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 9% 45%	6520
August	1st to 10th	Day	12% 5% 2 6% 4 5% 6% 5% 7% 8% 41%	4156
	11th to 20th	Day	8% 6% 2 7% 5% 5% 5% 5% 8% 9% 41%	4044
	21st to end	Day	8% 6% 2 7% 5% 6% 5% 5% 8% 9% 39%	4516
September	1st to 10th	Day	10% 7% 3 7% 4 4 6% 4 6% 9% 39%	2140
	11th to 20th	Day	10% 4 2 5% 3 4 6% 5% 6% 10% 45%	2090
	21st to end	Day	15% 7% 3 6% 6% 5% 5% 4 7% 9% 35%	2090
October	1st to 10th	Day	12% 8% 3 6% 4 4 5% 4 5% 7% 42%	2024
	11th to 20th	Day	16% 10% 3 8% 5% 5% 5% 3 5% 7% 34%	1900
	21st to end	Day	18% 12% 4 8% 5% 5% 5% 3 6% 7% 29%	1943
November	1st to 10th	Day	11% 9% 4 8% 6% 4 5% 4 6% 8% 37%	1762
	11th to 20th	Day	14% 12% 3 10% 7% 5% 5% 4 6% 6% 30%	1800
	21st to end	Day	16% 14% 5% 9% 6% 5% 5% 3 5% 6% 27%	1639
December	1st to 10th	Day	12% 14% 6% 11% 6% 5% 5% 4 6% 7% 23%	2600
	11th to 20th	Day	17% 20% 5% 9% 5% 4 4 3 6% 6% 21%	2758
	21st to end	Day	24% 21% 6% 11% 5% 4 4 3 4 4 13%	3776
January	1st to 10th	Night	13% 12% 5% 10% 6% 5% 5% 4 5% 6% 29%	6348
	11th to 20th	Night	10% 15% 6% 13% 9% 7% 6% 4 5% 7% 18%	6360
	21st to end	Night	16% 14% 8% 11% 5% 6% 5% 3 4 5% 23%	6540
February	1st to 10th	Night	13% 16% 5% 11% 7% 6% 5% 4 5% 5% 23%	2600
	11th to 20th	Night	13% 12% 5% 11% 6% 5% 5% 4 6% 6% 28%	2411
	21st to end	Night	17% 12% 3 9% 6% 4 4 4 6% 6% 29%	1980
March	1st to 10th	Night	14% 11% 3 10% 5% 5% 4 3 5% 7% 35%	5240
	11th to 20th	Night	9% 8% 3 8% 5% 5% 5% 4 6% 8% 41%	4980
	21st to end	Night	14% 9% 3 9% 5% 4 4 4 4 6% 38%	5467
April	1st to 10th	Night	16% 11% 2 8% 4 5% 4 3 6% 6% 34%	2105
	11th to 20th	Night	18% 7% 2 7% 5% 4 3 4 6% 7% 38%	1797
	21st to end	Night	15% 8% 3 6% 4 5% 4 4 6% 7% 39%	1800
May	1st to 10th	Night	20% 9% 3 7% 4 4 4 4 5% 7% 33%	4033
	11th to 20th	Night	16% 8% 3 7% 4 4 4 3 4 6% 40%	4032
	21st to end	Night	13% 5% 2 6% 4 4 3 3 5% 7% 46%	4421
June	1st to 10th	Night	9% 6% 3 6% 4 4 4 4 5% 9% 46%	1444
	11th to 20th	Night	9% 6% 3 5% 4 4 5% 4 6% 10% 44%	1400
	21st to end	Night	8% 7% 3 5% 4 4 4 3 5% 8% 49%	1465
July	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 7% 10% 47%	3618
	11th to 20th	Night	7% 4 2 5% 4 4 5% 4 6% 9% 50%	3617
	21st to end	Night	6% 5% 2 6% 4 4 6% 4 6% 8% 48%	4330
August	1st to 10th	Night	10% 6% 3 6% 4 4 4 4 6% 8% 47%	2861
	11th to 20th	Night	8% 6% 2 6% 4 4 4 4 6% 7% 48%	2785
	21st to end	Night	8% 5% 2 7% 4 4 4 4 5% 8% 48%	3124
September	1st to 10th	Night	9% 6% 3 7% 3 5% 5% 3 6% 6% 48%	2018
	11th to 20th	Night	9% 4 2 5% 3 3 4 3 6% 7% 54%	2090
	21st to end	Night	15% 5% 2 8% 4 3 4 4 5% 7% 43%	2090
October	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 7% 46%	2154
	11th to 20th	Night	18% 9% 3 6% 4 4 6% 4 5% 6% 36%	2280
	21st to end	Night	19% 9% 3 8% 5% 5% 5% 4 5% 6% 32%	2650
November	1st to 10th	Night	13% 8% 2 6% 4 4 4 4 5% 7% 43%	2536
	11th to 20th	Night	15% 10% 3 9% 5% 5% 5% 5% 7% 6% 30%	2600
	21st to end	Night	17% 13% 4 8% 5% 5% 5% 4 5% 7% 27%	2757
December	1st to 10th	Night	12% 13% 5% 13% 7% 5% 5% 4 6% 7% 24%	4580
	11th to 20th	Night	14% 17% 6% 12% 7% 5% 5% 4 5% 5% 20%	5440
	21st to end	Night	22% 22% 7% 10% 5% 4 4 3 4 4 16%	7182

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	59% 6% 11% 16% 7% 1	3618
	11th to 20th	Day	71% 6% 10% 6% 6% 1	3620
	21st to end	Day	70% 5% 12% 8% 5% 1	4403
February	1st to 10th	Day	63% 6% 8% 14% 7%	1800
	11th to 20th	Day	61% 4 10% 16% 8% 1	1880
	21st to end	Day	58% 6% 12% 15% 7% 2	1650
March	1st to 10th	Day	54% 5% 13% 17% 8% 2	4611
	11th to 20th	Day	48% 6% 15% 21% 8% 2	4980
	21st to end	Day	57% 5% 12% 15% 10% 2	5465
April	1st to 10th	Day	52% 6% 12% 19% 11% 1	2313
	11th to 20th	Day	48% 6% 11% 20% 13% 2	2552
	21st to end	Day	48% 6% 13% 18% 13% 2	2600
May	1st to 10th	Day	48% 6% 11% 19% 12% 4	5897
	11th to 20th	Day	46% 8% 11% 21% 12% 2	5865
	21st to end	Day	41% 6% 10% 20% 19% 4	6447
June	1st to 10th	Day	38% 7% 12% 25% 15% 2	2947
	11th to 20th	Day	38% 7% 14% 24% 15% 2	3000
	21st to end	Day	39% 9% 12% 22% 16% 2	2928
July	1st to 10th	Day	37% 8% 14% 24% 16% 2	6291
	11th to 20th	Day	31% 7% 14% 29% 17% 1	6285
	21st to end	Day	33% 8% 14% 22% 23% 1	6334
August	1st to 10th	Day	38% 8% 13% 24% 16% 1	4143
	11th to 20th	Day	36% 9% 12% 31% 11% 1	4083
	21st to end	Day	39% 8% 13% 27% 13% 1	4515
September	1st to 10th	Day	38% 9% 14% 24% 13% 2	2140
	11th to 20th	Day	33% 7% 11% 33% 15% 1	2090
	21st to end	Day	45% 6% 14% 23% 12% 1	2090
October	1st to 10th	Day	31% 5% 11% 31% 20% 2	3362
	11th to 20th	Day	39% 5% 12% 25% 18%	3140
	21st to end	Day	45% 6% 14% 22% 12% 1	3180
November	1st to 10th	Day	44% 7% 13% 24% 11% 1	1762
	11th to 20th	Day	53% 6% 13% 18% 9% 1	1800
	21st to end	Day	57% 5% 12% 18% 6% 1	1639
December	1st to 10th	Day	59% 5% 17% 15% 4	2600
	11th to 20th	Day	64% 5% 11% 12% 7%	2754
	21st to end	Day	73% 5% 9% 7% 5%	3776
January	1st to 10th	Night	54% 6% 11% 20% 7% 2	6348
	11th to 20th	Night	63% 6% 12% 12% 6% 1	6360
	21st to end	Night	63% 5% 11% 14% 7%	6540
February	1st to 10th	Night	62% 7% 10% 14% 7% 1	2600
	11th to 20th	Night	56% 6% 12% 17% 9% 1	2413
	21st to end	Night	54% 5% 13% 18% 9% 1	1980
March	1st to 10th	Night	48% 5% 14% 21% 10% 1	5240
	11th to 20th	Night	40% 6% 15% 24% 14% 1	4980
	21st to end	Night	47% 5% 12% 20% 15% 2	5467
April	1st to 10th	Night	49% 5% 11% 21% 12% 2	2105
	11th to 20th	Night	44% 7% 12% 18% 18% 2	1797
	21st to end	Night	43% 6% 12% 20% 17% 3	1800
May	1st to 10th	Night	50% 6% 10% 16% 14% 5%	4060
	11th to 20th	Night	43% 8% 10% 25% 12% 2	4033
	21st to end	Night	37% 7% 12% 23% 17% 5%	4429
June	1st to 10th	Night	35% 6% 10% 28% 19% 2	1444
	11th to 20th	Night	35% 8% 14% 25% 18% 2	1400
	21st to end	Night	32% 7% 12% 26% 22% 1	1465
July	1st to 10th	Night	30% 6% 15% 28% 17% 4	3580
	11th to 20th	Night	30% 7% 14% 30% 17% 2	3572
	21st to end	Night	31% 8% 15% 22% 23% 2	4203
August	1st to 10th	Night	33% 7% 14% 28% 17% 1	2850
	11th to 20th	Night	33% 7% 12% 34% 12% 2	2812
	21st to end	Night	33% 8% 13% 32% 14% 1	3124
September	1st to 10th	Night	34% 7% 13% 27% 17% 2	2018
	11th to 20th	Night	29% 6% 13% 31% 21% 2	2090
	21st to end	Night	40% 5% 12% 30% 12% 1	2090
October	1st to 10th	Night	26% 5% 10% 31% 27% 1	3596
	11th to 20th	Night	42% 5% 12% 24% 17% 1	3779
	21st to end	Night	42% 4 12% 28% 13% 1	4363
November	1st to 10th	Night	40% 7% 12% 25% 15% 1	2536
	11th to 20th	Night	51% 6% 14% 20% 9% 1	2600
	21st to end	Night	56% 6% 13% 18% 6%	2757
December	1st to 10th	Night	58% 6% 17% 16% 3	4580
	11th to 20th	Night	63% 6% 12% 13% 6% 1	5443
	21st to end	Night	71% 5% 10% 8% 6%	7182

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	18% 21% 38% 16% 6%	300
	11th to 20th	Day	23% 18% 43% 11% 4 1	300
	21st to end	Day	28% 14% 37% 17% 4 1	330
February	1st to 10th	Day	24% 21% 39% 13% 3 1	300
	11th to 20th	Day	24% 20% 38% 16% 2	300
	21st to end	Day	22% 23% 41% 12% 2	249
March	1st to 10th	Day	25% 21% 34% 16% 3 1	353
	11th to 20th	Day	22% 15% 32% 24% 6% 1	500
	21st to end	Day	27% 13% 33% 20% 4 1	550
April	1st to 10th	Day	19% 17% 34% 20% 8% 1	500
	11th to 20th	Day	25% 18% 29% 15% 8% 5%	492
	21st to end	Day	23% 13% 28% 23% 10% 3	500
May	1st to 10th	Day	22% 13% 29% 22% 10% 3	503
	11th to 20th	Day	20% 11% 28% 21% 13% 6%	527
	21st to end	Day	14% 8% 25% 27% 18% 8%	573
June	1st to 10th	Day	11% 10% 33% 27% 14% 4	717
	11th to 20th	Day	11% 7% 34% 29% 17% 3	730
	21st to end	Day	11% 8% 30% 30% 16% 5%	730
July	1st to 10th	Day	8% 6% 22% 31% 21% 12%	721
	11th to 20th	Day	10% 7% 25% 31% 19% 8%	718
	21st to end	Day	7% 6% 24% 30% 23% 10%	620
August	1st to 10th	Day	10% 4 21% 24% 27% 13%	502
	11th to 20th	Day	12% 3 19% 28% 24% 14%	479
	21st to end	Day	11% 5% 20% 31% 21% 12%	539
September	1st to 10th	Day	12% 5% 26% 23% 21% 13%	490
	11th to 20th	Day	9% 4 20% 23% 28% 16%	490
	21st to end	Day	17% 10% 26% 21% 19% 7%	490
October	1st to 10th	Day	18% 10% 27% 22% 15% 9%	490
	11th to 20th	Day	20% 14% 31% 24% 8% 2	490
	21st to end	Day	26% 14% 35% 20% 5% 1	392
November	1st to 10th	Day	15% 22% 34% 20% 8% 1	300
	11th to 20th	Day	22% 20% 34% 16% 7% 1	300
	21st to end	Day	22% 18% 37% 19% 4	219
December	1st to 10th	Day	22% 20% 38% 15% 6% 1	200
	11th to 20th	Day	28% 21% 36% 12% 4 1	200
	21st to end	Day	27% 21% 34% 15% 3	286
January	1st to 10th	Night	21% 15% 38% 22% 5% 1	1000
	11th to 20th	Night	24% 14% 34% 23% 4 1	1000
	21st to end	Night	19% 14% 34% 27% 6%	904
February	1st to 10th	Night	21% 14% 38% 24% 2	800
	11th to 20th	Night	20% 16% 35% 25% 4	783
	21st to end	Night	24% 16% 39% 20% 2	660
March	1st to 10th	Night	20% 13% 36% 25% 6%	800
	11th to 20th	Night	16% 16% 38% 24% 6% 1	800
	21st to end	Night	22% 13% 31% 27% 7%	880
April	1st to 10th	Night	22% 15% 33% 26% 4 1	705
	11th to 20th	Night	22% 10% 32% 26% 8% 2	593
	21st to end	Night	19% 10% 31% 32% 9%	600
May	1st to 10th	Night	18% 9% 29% 34% 9% 1	600
	11th to 20th	Night	21% 6% 26% 31% 15% 1	591
	21st to end	Night	11% 3 24% 41% 19% 2	650
June	1st to 10th	Night	12% 5% 26% 42% 14%	435
	11th to 20th	Night	11% 5% 23% 50% 11% 1	400
	21st to end	Night	10% 3 23% 46% 17%	465
July	1st to 10th	Night	7% 3 19% 41% 27% 3	585
	11th to 20th	Night	10% 3 18% 40% 25% 4	582
	21st to end	Night	7% 3 18% 47% 23% 2	657
August	1st to 10th	Night	8% 2 18% 37% 31% 3	579
	11th to 20th	Night	8% 1 19% 38% 29% 4	564
	21st to end	Night	11% 3 18% 33% 32% 3	627
September	1st to 10th	Night	12% 6% 19% 33% 25% 5%	689
	11th to 20th	Night	10% 4 17% 34% 29% 6%	760
	21st to end	Night	17% 6% 22% 30% 20% 5%	760
October	1st to 10th	Night	17% 8% 26% 30% 18% 3	760
	11th to 20th	Night	22% 12% 28% 28% 9% 2	760
	21st to end	Night	23% 12% 33% 27% 5%	836
November	1st to 10th	Night	19% 11% 30% 26% 13% 1	780
	11th to 20th	Night	21% 15% 33% 24% 7% 1	800
	21st to end	Night	24% 15% 34% 22% 5%	800
December	1st to 10th	Night	23% 14% 36% 22% 5% 1	800
	11th to 20th	Night	23% 14% 37% 22% 3	910
	21st to end	Night	30% 12% 33% 22% 3	1100

Page generated at 2025-08-02 01:32:24. Version ac07

Copyright © 2025 Attilla Danko.