Anarchist Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anarchist Mountain Observatory clear sky chart from 2005-11-06 to 2026-07-16.

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% 9% 3 6% 4 4 5% 4 6% 7% 44%	142075
	Night	11% 11% 3 7% 4 4 4 4 5% 7% 40%	139278
Transparency	Day	26% 36% 8% 18% 10% 3	141802
	Night	29% 36% 8% 17% 8% 2	139133
Seeing	Day	17% 16% 29% 25% 10% 3	17057
	Night	17% 10% 24% 32% 15% 2	25760

By Month

Percentage Cloud Cover NW (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% 22% 8% 13% 5% 5% 5% 4 4 5% 15%	4723
	11th to 20th	Day	10% 8% 2 5% 3 3 4 3 7% 9% 44%	4716
	21st to end	Day	18% 17% 3 6% 4 4 4 3 6% 6% 29%	5186
February	1st to 10th	Day	11% 15% 4 8% 5% 5% 5% 4 6% 8% 29%	1743
	11th to 20th	Day	9% 14% 4 9% 5% 5% 4 4 6% 8% 32%	1849
	21st to end	Day	9% 12% 4 9% 5% 7% 5% 5% 8% 7% 29%	1730
March	1st to 10th	Day	7% 11% 3 7% 5% 5% 7% 5% 7% 8% 36%	4618
	11th to 20th	Day	7% 9% 3 8% 5% 5% 5% 4 6% 7% 42%	4854
	21st to end	Day	11% 12% 4 9% 5% 6% 6% 5% 7% 8% 27%	6052
April	1st to 10th	Day	9% 9% 3 9% 6% 6% 6% 5% 7% 7% 32%	2520
	11th to 20th	Day	7% 8% 2 7% 5% 5% 5% 6% 8% 8% 39%	2502
	21st to end	Day	7% 8% 3 7% 5% 5% 5% 5% 6% 9% 40%	2839
May	1st to 10th	Day	6% 6% 2 6% 4 3 4 3 5% 9% 52%	8195
	11th to 20th	Day	7% 7% 3 8% 5% 5% 6% 4 7% 10% 38%	8160
	21st to end	Day	9% 8% 3 7% 5% 5% 6% 4 7% 9% 36%	8993
June	1st to 10th	Day	11% 7% 3 7% 5% 5% 4 4 6% 8% 40%	3061
	11th to 20th	Day	10% 6% 3 7% 5% 5% 5% 5% 7% 8% 39%	3198
	21st to end	Day	6% 5% 2 6% 5% 4 5% 4 6% 8% 49%	3293
July	1st to 10th	Day	2 2 1 3 2 2 2 2 4 6% 74%	6606
	11th to 20th	Day	2 2 1 3 2 2 3 2 3 5% 75%	6391
	21st to end	Day	3 3 1 3 3 2 4 3 5% 7% 65%	6874
August	1st to 10th	Day	2 2 1 3 3 3 4 4 6% 8% 66%	4541
	11th to 20th	Day	3 2 1 4 3 3 4 4 6% 8% 61%	4421
	21st to end	Day	5% 4 2 5% 3 4 4 4 6% 8% 56%	4318
September	1st to 10th	Day	4 4 2 4 2 3 4 3 4 6% 65%	2400
	11th to 20th	Day	7% 4 2 4 4 4 4 4 6% 8% 53%	2370
	21st to end	Day	8% 6% 2 6% 3 4 4 3 5% 7% 53%	2195
October	1st to 10th	Day	7% 4 2 5% 4 4 4 3 5% 7% 55%	3280
	11th to 20th	Day	12% 9% 3 7% 4 4 4 3 5% 7% 41%	3169
	21st to end	Day	14% 11% 4 9% 5% 4 4 3 4 5% 38%	3200
November	1st to 10th	Day	19% 10% 3 6% 5% 5% 5% 4 6% 7% 30%	1796
	11th to 20th	Day	17% 16% 4 8% 5% 4 4 3 5% 5% 29%	1680
	21st to end	Day	15% 19% 6% 10% 6% 4 3 4 5% 8% 22%	1626
December	1st to 10th	Day	12% 12% 4 7% 5% 4 5% 5% 7% 8% 33%	2360
	11th to 20th	Day	16% 26% 5% 9% 4 5% 4 3 5% 4 18%	2712
	21st to end	Day	15% 21% 8% 12% 6% 5% 6% 3 5% 4 14%	3904
January	1st to 10th	Night	18% 26% 8% 11% 4 3 3 3 4 4 16%	8172
	11th to 20th	Night	11% 9% 3 5% 4 4 6% 4 6% 7% 41%	8182
	21st to end	Night	17% 19% 5% 7% 3 3 4 4 4 5% 29%	8994
February	1st to 10th	Night	13% 16% 5% 9% 5% 5% 5% 3 6% 7% 26%	2876
	11th to 20th	Night	10% 14% 4 8% 4 4 4 4 6% 8% 34%	2657
	21st to end	Night	11% 13% 4 10% 6% 4 4 5% 6% 8% 30%	2076
March	1st to 10th	Night	6% 9% 3 9% 5% 6% 5% 4 7% 9% 37%	5496
	11th to 20th	Night	9% 11% 3 7% 4 4 4 3 6% 7% 43%	5362
	21st to end	Night	13% 13% 4 10% 6% 5% 6% 5% 6% 7% 25%	5164
April	1st to 10th	Night	10% 8% 2 7% 5% 4 5% 4 7% 9% 39%	2100
	11th to 20th	Night	6% 7% 2 8% 5% 5% 4 4 7% 8% 43%	2069
	21st to end	Night	7% 7% 2 6% 5% 4 4 5% 7% 9% 43%	1779
May	1st to 10th	Night	4 5% 2 5% 4 4 4 4 5% 9% 55%	4724
	11th to 20th	Night	5% 6% 2 6% 4 5% 5% 4 6% 10% 47%	4700
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 7% 10% 42%	5178
June	1st to 10th	Night	10% 6% 2 5% 5% 3 5% 4 8% 9% 43%	1554
	11th to 20th	Night	8% 6% 2 5% 5% 6% 6% 5% 6% 7% 45%	1413
	21st to end	Night	6% 4 2 4 4 4 5% 3 6% 8% 54%	1320
July	1st to 10th	Night	2 2 1 2 1 2 2 2 5% 6% 74%	3550
	11th to 20th	Night	1 2 1 2 2 2 3 2 4 6% 76%	3680
	21st to end	Night	3 2 1 4 3 3 3 3 4 7% 68%	3969
August	1st to 10th	Night	2 3 1 4 2 4 4 3 5% 7% 65%	2609
	11th to 20th	Night	2 2 1 4 2 3 4 4 6% 10% 62%	2625
	21st to end	Night	6% 3 1 4 3 3 4 4 6% 7% 58%	3600
September	1st to 10th	Night	3 4 1 3 2 3 3 4 5% 7% 66%	2000
	11th to 20th	Night	7% 4 2 5% 3 3 3 3 5% 8% 59%	2030
	21st to end	Night	6% 6% 2 5% 4 4 4 3 5% 8% 53%	2201
October	1st to 10th	Night	6% 5% 2 5% 3 4 6% 4 6% 7% 54%	3920
	11th to 20th	Night	14% 8% 3 7% 3 3 4 4 5% 7% 42%	3985
	21st to end	Night	15% 8% 3 6% 4 4 4 3 5% 6% 43%	4600
November	1st to 10th	Night	18% 13% 3 6% 4 4 5% 3 5% 7% 31%	2721
	11th to 20th	Night	20% 15% 3 7% 5% 4 4 3 6% 6% 28%	2940
	21st to end	Night	17% 19% 6% 8% 5% 4 4 4 5% 5% 23%	2970
December	1st to 10th	Night	10% 12% 4 8% 4 3 6% 4 7% 8% 34%	5040
	11th to 20th	Night	19% 23% 6% 10% 5% 4 4 3 4 4 18%	5700
	21st to end	Night	19% 24% 5% 9% 4 4 4 4 5% 7% 15%	7322

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	53% 24% 6% 13% 3	4723
	11th to 20th	Day	25% 22% 17% 26% 8% 2	4740
	21st to end	Day	45% 23% 10% 14% 8%	5187
February	1st to 10th	Day	24% 61% 3 6% 6% 1	1743
	11th to 20th	Day	25% 59% 5% 7% 4	1858
	21st to end	Day	19% 62% 7% 7% 6%	1730
March	1st to 10th	Day	33% 32% 6% 14% 14% 1	4618
	11th to 20th	Day	29% 31% 10% 26% 5%	4854
	21st to end	Day	40% 33% 8% 12% 7%	6052
April	1st to 10th	Day	18% 61% 9% 9% 3	2520
	11th to 20th	Day	16% 61% 6% 12% 4 1	2502
	21st to end	Day	16% 61% 6% 9% 7% 1	2839
May	1st to 10th	Day	23% 26% 4 29% 16% 1	8195
	11th to 20th	Day	32% 25% 12% 22% 8%	8163
	21st to end	Day	32% 26% 13% 23% 5%	8994
June	1st to 10th	Day	15% 61% 5% 11% 6% 1	3061
	11th to 20th	Day	14% 61% 5% 11% 8% 1	3198
	21st to end	Day	15% 59% 5% 13% 7% 1	3293
July	1st to 10th	Day	9% 25% 7% 19% 24% 16%	6537
	11th to 20th	Day	9% 25% 5% 23% 19% 18%	6316
	21st to end	Day	16% 25% 8% 26% 18% 7%	6681
August	1st to 10th	Day	11% 36% 3 19% 25% 7%	4524
	11th to 20th	Day	16% 36% 13% 27% 6% 2	4463
	21st to end	Day	20% 36% 10% 18% 13% 3	4317
September	1st to 10th	Day	11% 58% 7% 13% 10% 2	2400
	11th to 20th	Day	14% 60% 5% 11% 8% 1	2370
	21st to end	Day	15% 59% 8% 12% 6% 1	2195
October	1st to 10th	Day	21% 36% 13% 26% 4	3280
	11th to 20th	Day	33% 37% 4 20% 6%	3169
	21st to end	Day	35% 36% 7% 15% 8%	3200
November	1st to 10th	Day	24% 55% 8% 9% 3	1796
	11th to 20th	Day	27% 56% 6% 6% 3 1	1680
	21st to end	Day	28% 55% 6% 6% 4 1	1626
December	1st to 10th	Day	31% 37% 19% 12% 2	2360
	11th to 20th	Day	50% 32% 7% 7% 4	2714
	21st to end	Day	54% 29% 7% 7% 2	3904
January	1st to 10th	Night	57% 22% 8% 11% 2	8172
	11th to 20th	Night	27% 23% 12% 24% 10% 3	8220
	21st to end	Night	44% 23% 10% 15% 8%	8994
February	1st to 10th	Night	26% 60% 3 6% 4 1	2876
	11th to 20th	Night	24% 59% 5% 8% 4 1	2659
	21st to end	Night	19% 61% 6% 9% 5%	2076
March	1st to 10th	Night	27% 34% 6% 20% 12% 1	5496
	11th to 20th	Night	28% 29% 10% 23% 10%	5363
	21st to end	Night	45% 33% 6% 11% 5%	5164
April	1st to 10th	Night	17% 60% 7% 11% 3 1	2100
	11th to 20th	Night	16% 61% 6% 11% 5% 1	2069
	21st to end	Night	14% 61% 4 13% 8% 1	1779
May	1st to 10th	Night	21% 23% 5% 29% 21% 1	4721
	11th to 20th	Night	26% 24% 12% 29% 8% 2	4700
	21st to end	Night	27% 25% 14% 28% 5%	5182
June	1st to 10th	Night	13% 60% 6% 13% 8%	1554
	11th to 20th	Night	14% 60% 4 11% 10% 1	1413
	21st to end	Night	14% 58% 5% 15% 7% 1	1320
July	1st to 10th	Night	10% 24% 7% 17% 26% 14%	3510
	11th to 20th	Night	9% 25% 8% 20% 19% 19%	3632
	21st to end	Night	17% 25% 4 30% 17% 7%	3857
August	1st to 10th	Night	14% 36% 2 18% 27% 4	2601
	11th to 20th	Night	15% 36% 13% 25% 10% 1	2649
	21st to end	Night	21% 35% 10% 21% 11% 2	3600
September	1st to 10th	Night	10% 58% 7% 13% 11% 1	2000
	11th to 20th	Night	13% 59% 5% 14% 9%	2030
	21st to end	Night	16% 58% 6% 14% 5%	2201
October	1st to 10th	Night	21% 36% 11% 23% 8%	3920
	11th to 20th	Night	30% 36% 6% 18% 9%	3985
	21st to end	Night	30% 36% 9% 21% 5%	4600
November	1st to 10th	Night	25% 56% 8% 8% 3	2721
	11th to 20th	Night	25% 57% 7% 6% 4 2	2940
	21st to end	Night	27% 56% 6% 6% 4 1	2970
December	1st to 10th	Night	26% 37% 15% 20% 2	5040
	11th to 20th	Night	50% 33% 7% 7% 2	5697
	21st to end	Night	49% 28% 9% 10% 4	7322

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% 14% 25% 25% 6% 3	220
	11th to 20th	Day	24% 12% 27% 25% 10% 2	220
	21st to end	Day	26% 11% 30% 24% 7% 2	242
February	1st to 10th	Day	17% 18% 39% 21% 5% 1	283
	11th to 20th	Day	21% 16% 34% 22% 7%	428
	21st to end	Day	17% 17% 36% 23% 7%	446
March	1st to 10th	Day	23% 21% 30% 16% 9% 1	540
	11th to 20th	Day	21% 21% 26% 19% 11% 1	540
	21st to end	Day	23% 22% 27% 19% 9% 2	594
April	1st to 10th	Day	22% 19% 29% 21% 8% 1	540
	11th to 20th	Day	20% 24% 27% 18% 7% 3	532
	21st to end	Day	16% 24% 26% 24% 8% 4	540
May	1st to 10th	Day	15% 22% 31% 22% 9% 2	543
	11th to 20th	Day	20% 14% 29% 25% 9% 3	568
	21st to end	Day	17% 16% 28% 24% 12% 3	617
June	1st to 10th	Day	17% 16% 32% 26% 8% 1	691
	11th to 20th	Day	18% 15% 30% 26% 10% 2	828
	21st to end	Day	10% 15% 30% 29% 14% 2	923
July	1st to 10th	Day	8% 15% 32% 33% 10% 2	634
	11th to 20th	Day	8% 19% 33% 28% 11% 2	545
	21st to end	Day	6% 11% 31% 32% 14% 5%	575
August	1st to 10th	Day	5% 10% 32% 33% 14% 6%	527
	11th to 20th	Day	7% 9% 32% 29% 17% 6%	517
	21st to end	Day	11% 14% 27% 30% 13% 6%	583
September	1st to 10th	Day	9% 14% 27% 30% 14% 6%	530
	11th to 20th	Day	15% 13% 27% 28% 14% 3	530
	21st to end	Day	19% 15% 30% 22% 12% 2	530
October	1st to 10th	Day	15% 18% 31% 22% 13% 1	530
	11th to 20th	Day	19% 18% 26% 24% 11% 2	476
	21st to end	Day	25% 13% 33% 20% 8% 1	363
November	1st to 10th	Day	26% 16% 28% 24% 7%	300
	11th to 20th	Day	28% 20% 22% 18% 12%	220
	21st to end	Day	22% 13% 30% 20% 12% 3	220
December	1st to 10th	Day	24% 6% 26% 25% 14% 5%	220
	11th to 20th	Day	25% 17% 27% 22% 6% 2	220
	21st to end	Day	24% 13% 24% 29% 8% 2	242
January	1st to 10th	Night	29% 13% 24% 25% 9% 1	840
	11th to 20th	Night	23% 10% 25% 30% 10% 1	840
	21st to end	Night	19% 9% 26% 32% 12% 1	924
February	1st to 10th	Night	20% 12% 28% 29% 9% 2	840
	11th to 20th	Night	17% 9% 30% 32% 12% 1	824
	21st to end	Night	18% 10% 25% 31% 14% 2	692
March	1st to 10th	Night	16% 12% 25% 31% 14% 2	840
	11th to 20th	Night	16% 13% 27% 29% 14% 1	840
	21st to end	Night	17% 14% 29% 27% 12% 1	924
April	1st to 10th	Night	15% 10% 23% 35% 16% 1	840
	11th to 20th	Night	11% 14% 28% 33% 12% 2	821
	21st to end	Night	11% 12% 30% 34% 13% 1	519
May	1st to 10th	Night	11% 10% 28% 36% 14% 1	420
	11th to 20th	Night	12% 9% 23% 32% 21% 3	414
	21st to end	Night	14% 8% 24% 33% 20% 2	455
June	1st to 10th	Night	14% 9% 26% 36% 14% 1	420
	11th to 20th	Night	15% 8% 32% 31% 14%	420
	21st to end	Night	9% 9% 26% 34% 21% 1	420
July	1st to 10th	Night	7% 8% 22% 39% 22% 1	410
	11th to 20th	Night	4 9% 26% 41% 20% 1	398
	21st to end	Night	4 6% 19% 43% 26% 2	438
August	1st to 10th	Night	4 7% 17% 39% 31% 3	398
	11th to 20th	Night	4 3 21% 38% 31% 3	418
	21st to end	Night	8% 6% 18% 41% 24% 2	872
September	1st to 10th	Night	5% 6% 21% 38% 27% 3	800
	11th to 20th	Night	10% 7% 18% 33% 29% 4	800
	21st to end	Night	14% 8% 21% 34% 20% 3	800
October	1st to 10th	Night	17% 9% 20% 31% 21% 2	800
	11th to 20th	Night	18% 11% 23% 31% 15% 2	800
	21st to end	Night	23% 10% 23% 31% 10% 2	880
November	1st to 10th	Night	26% 11% 28% 27% 6% 1	820
	11th to 20th	Night	27% 13% 22% 24% 12% 1	840
	21st to end	Night	24% 10% 25% 26% 11% 3	870
December	1st to 10th	Night	19% 10% 25% 34% 11% 1	1050
	11th to 20th	Night	27% 12% 24% 30% 6% 1	1050
	21st to end	Night	26% 12% 28% 27% 6%	1023

Page generated at 2026-07-13 00:14:49. Version ac07

Copyright © 2026 Attilla Danko.