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 2025-03-12.

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	9% 9% 3 6% 4 4 4 4 6% 7% 43%	112566
	Night	11% 12% 3 7% 4 4 4 4 5% 7% 40%	115069
Transparency	Day	22% 45% 7% 13% 9% 3	112334
	Night	26% 43% 8% 14% 7% 2	114947
Seeing	Day	16% 16% 29% 25% 11% 3	15234
	Night	17% 10% 24% 33% 16% 2	24179

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% 12% 5% 5% 5% 4 4 4 16%	3639
	11th to 20th	Day	13% 9% 3 5% 3 3 4 3 8% 9% 40%	3616
	21st to end	Day	20% 20% 4 6% 3 3 3 3 6% 6% 27%	4004
February	1st to 10th	Day	11% 15% 4 8% 5% 4 5% 4 5% 8% 30%	1660
	11th to 20th	Day	10% 14% 4 9% 5% 5% 4 4 6% 8% 31%	1759
	21st to end	Day	9% 13% 4 9% 5% 7% 5% 5% 7% 7% 29%	1650
March	1st to 10th	Day	10% 14% 4 8% 5% 4 6% 4 6% 7% 33%	3238
	11th to 20th	Day	7% 7% 2 5% 3 3 4 4 5% 8% 51%	3329
	21st to end	Day	12% 12% 3 7% 5% 5% 6% 5% 7% 9% 29%	4130
April	1st to 10th	Day	10% 9% 3 10% 6% 6% 6% 5% 6% 7% 30%	2280
	11th to 20th	Day	8% 8% 2 8% 5% 5% 5% 6% 8% 8% 37%	2261
	21st to end	Day	8% 9% 3 8% 5% 6% 5% 5% 6% 8% 37%	2569
May	1st to 10th	Day	8% 6% 2 5% 5% 4 5% 4 7% 10% 45%	4420
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 7% 11% 44%	4377
	21st to end	Day	13% 9% 3 7% 6% 6% 7% 5% 7% 8% 29%	4813
June	1st to 10th	Day	12% 7% 3 8% 6% 5% 4 4 6% 8% 37%	2769
	11th to 20th	Day	11% 6% 3 7% 6% 5% 5% 5% 8% 9% 36%	2893
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 6% 8% 50%	2979
July	1st to 10th	Day	2 2 1 2 2 2 2 3 4 5% 75%	4521
	11th to 20th	Day	2 2 1 3 2 2 3 2 3 4 75%	4420
	21st to end	Day	2 2 1 2 2 2 4 3 5% 7% 69%	4790
August	1st to 10th	Day	2 2 1 2 2 3 4 4 6% 8% 67%	4401
	11th to 20th	Day	2 2 1 4 3 3 4 4 6% 8% 61%	4282
	21st to end	Day	5% 4 2 5% 3 4 4 4 6% 8% 56%	4186
September	1st to 10th	Day	4 4 2 4 2 3 4 3 4 6% 65%	2280
	11th to 20th	Day	7% 4 2 4 4 4 4 4 6% 8% 52%	2252
	21st to end	Day	8% 6% 2 6% 3 4 4 3 5% 7% 53%	2085
October	1st to 10th	Day	7% 4 2 5% 4 4 4 3 5% 7% 54%	3180
	11th to 20th	Day	12% 9% 3 7% 4 4 4 3 5% 7% 41%	3072
	21st to end	Day	14% 11% 4 9% 4 4 4 3 4 5% 38%	3101
November	1st to 10th	Day	19% 11% 3 6% 5% 5% 5% 4 6% 7% 29%	1709
	11th to 20th	Day	17% 16% 3 8% 5% 4 4 4 5% 5% 30%	1600
	21st to end	Day	15% 18% 5% 10% 6% 4 3 4 5% 8% 22%	1549
December	1st to 10th	Day	12% 11% 4 6% 5% 4 5% 5% 7% 8% 34%	2290
	11th to 20th	Day	16% 27% 5% 9% 4 4 4 3 4 4 18%	2642
	21st to end	Day	15% 21% 8% 12% 6% 5% 6% 3 5% 4 13%	3820
January	1st to 10th	Night	19% 27% 8% 10% 4 3 3 2 3 4 17%	6306
	11th to 20th	Night	13% 10% 3 6% 4 4 5% 3 6% 8% 40%	6282
	21st to end	Night	19% 21% 5% 6% 3 3 3 4 4 5% 27%	6952
February	1st to 10th	Night	13% 16% 5% 9% 5% 4 5% 3 6% 6% 27%	2739
	11th to 20th	Night	10% 15% 4 7% 4 4 4 4 6% 7% 34%	2527
	21st to end	Night	11% 13% 4 9% 6% 4 4 5% 6% 8% 30%	1980
March	1st to 10th	Night	7% 11% 4 9% 5% 6% 5% 4 7% 9% 33%	3856
	11th to 20th	Night	9% 8% 2 5% 4 3 3 3 5% 7% 51%	3675
	21st to end	Night	12% 13% 4 9% 6% 5% 5% 5% 6% 7% 29%	3522
April	1st to 10th	Night	11% 8% 2 7% 5% 5% 5% 4 7% 9% 38%	1900
	11th to 20th	Night	6% 7% 3 8% 5% 5% 4 5% 6% 8% 43%	1870
	21st to end	Night	7% 8% 3 7% 5% 4 4 5% 7% 8% 42%	1610
May	1st to 10th	Night	6% 7% 3 6% 5% 4 4 4 5% 8% 48%	2540
	11th to 20th	Night	5% 4 1 5% 4 4 4 4 6% 10% 52%	2516
	21st to end	Night	9% 7% 3 7% 5% 5% 6% 5% 6% 9% 39%	2762
June	1st to 10th	Night	10% 6% 2 6% 5% 3 5% 4 7% 8% 43%	1406
	11th to 20th	Night	9% 6% 3 5% 5% 6% 7% 5% 6% 7% 42%	1279
	21st to end	Night	5% 4 1 4 4 4 5% 3 6% 8% 56%	1194
July	1st to 10th	Night	2 2 1 2 1 2 2 2 4 5% 77%	2430
	11th to 20th	Night	1 2 1 2 1 2 2 3 4 5% 78%	2540
	21st to end	Night	2 2 1 4 2 2 3 3 4 6% 71%	2762
August	1st to 10th	Night	2 3 1 4 2 4 3 3 5% 7% 65%	2529
	11th to 20th	Night	2 2 1 3 2 3 4 4 6% 10% 63%	2544
	21st to end	Night	6% 3 1 4 3 3 4 4 6% 6% 58%	3490
September	1st to 10th	Night	3 4 1 3 2 2 3 4 5% 7% 66%	1900
	11th to 20th	Night	7% 4 2 5% 2 3 3 3 5% 8% 59%	1928
	21st to end	Night	6% 6% 2 5% 4 4 4 3 5% 8% 53%	2091
October	1st to 10th	Night	6% 5% 2 5% 3 4 6% 5% 6% 7% 54%	3800
	11th to 20th	Night	14% 8% 3 7% 3 3 4 4 5% 7% 42%	3862
	21st to end	Night	15% 8% 2 6% 4 4 4 3 5% 6% 43%	4457
November	1st to 10th	Night	19% 13% 3 5% 4 4 5% 3 5% 7% 31%	2588
	11th to 20th	Night	19% 15% 3 7% 5% 4 4 3 6% 6% 28%	2800
	21st to end	Night	17% 19% 5% 8% 5% 4 4 4 5% 5% 23%	2828
December	1st to 10th	Night	10% 12% 4 8% 4 3 6% 4 7% 8% 34%	4890
	11th to 20th	Night	20% 23% 6% 10% 5% 4 4 3 4 4 17%	5550
	21st to end	Night	19% 24% 5% 9% 4 4 4 4 5% 7% 14%	7164

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	48% 30% 5% 14% 3	3639
	11th to 20th	Day	26% 28% 19% 19% 5% 3	3640
	21st to end	Day	42% 29% 9% 12% 8%	4004
February	1st to 10th	Day	22% 64% 3 6% 5% 1	1660
	11th to 20th	Day	23% 62% 5% 7% 4	1768
	21st to end	Day	17% 65% 6% 7% 5%	1650
March	1st to 10th	Day	30% 45% 4 10% 10% 1	3238
	11th to 20th	Day	13% 43% 13% 27% 3	3329
	21st to end	Day	31% 47% 7% 8% 7%	4130
April	1st to 10th	Day	17% 67% 7% 7% 3	2280
	11th to 20th	Day	14% 68% 4 10% 3 1	2261
	21st to end	Day	16% 67% 5% 6% 6%	2569
May	1st to 10th	Day	17% 47% 6% 16% 14% 1	4420
	11th to 20th	Day	18% 44% 11% 19% 8%	4380
	21st to end	Day	28% 47% 9% 13% 3	4814
June	1st to 10th	Day	14% 67% 5% 9% 4 1	2769
	11th to 20th	Day	13% 68% 5% 9% 4	2893
	21st to end	Day	12% 65% 4 11% 7% 1	2979
July	1st to 10th	Day	6% 36% 3 10% 24% 20%	4452
	11th to 20th	Day	7% 36% 2 6% 23% 26%	4345
	21st to end	Day	12% 35% 6% 17% 20% 10%	4639
August	1st to 10th	Day	10% 37% 2 18% 26% 7%	4384
	11th to 20th	Day	15% 38% 13% 27% 6% 2	4324
	21st to end	Day	20% 37% 10% 17% 13% 3	4185
September	1st to 10th	Day	11% 61% 6% 12% 8% 1	2280
	11th to 20th	Day	13% 63% 5% 10% 7% 1	2252
	21st to end	Day	14% 62% 7% 10% 6% 1	2085
October	1st to 10th	Day	21% 37% 12% 26% 4	3180
	11th to 20th	Day	33% 38% 4 19% 5%	3072
	21st to end	Day	34% 36% 7% 15% 8%	3101
November	1st to 10th	Day	24% 58% 8% 8% 2	1709
	11th to 20th	Day	25% 58% 6% 6% 3 1	1600
	21st to end	Day	26% 58% 6% 6% 4 1	1549
December	1st to 10th	Day	30% 37% 19% 12% 2	2290
	11th to 20th	Day	49% 33% 7% 7% 4	2644
	21st to end	Day	54% 30% 7% 7% 2	3820
January	1st to 10th	Night	53% 28% 6% 12% 2	6306
	11th to 20th	Night	27% 29% 14% 17% 10% 4	6320
	21st to end	Night	44% 29% 9% 12% 6%	6952
February	1st to 10th	Night	24% 63% 3 5% 4 1	2739
	11th to 20th	Night	22% 62% 5% 7% 3 1	2529
	21st to end	Night	17% 64% 6% 9% 5%	1980
March	1st to 10th	Night	23% 48% 5% 13% 11%	3856
	11th to 20th	Night	13% 42% 12% 26% 6%	3676
	21st to end	Night	32% 47% 7% 10% 4	3522
April	1st to 10th	Night	15% 67% 6% 8% 3 1	1900
	11th to 20th	Night	15% 67% 4 8% 5% 1	1870
	21st to end	Night	13% 67% 4 9% 7%	1610
May	1st to 10th	Night	19% 43% 6% 15% 16%	2540
	11th to 20th	Night	13% 43% 10% 24% 7% 3	2516
	21st to end	Night	18% 46% 12% 19% 4	2762
June	1st to 10th	Night	12% 66% 5% 12% 5%	1406
	11th to 20th	Night	14% 66% 4 9% 6% 1	1279
	21st to end	Night	11% 64% 4 14% 7% 1	1194
July	1st to 10th	Night	5% 36% 2 11% 28% 19%	2390
	11th to 20th	Night	6% 36% 3 6% 22% 26%	2492
	21st to end	Night	13% 35% 4 19% 20% 10%	2674
August	1st to 10th	Night	13% 37% 2 17% 28% 4	2521
	11th to 20th	Night	14% 37% 13% 25% 9% 1	2568
	21st to end	Night	21% 36% 10% 21% 11% 1	3490
September	1st to 10th	Night	9% 61% 6% 13% 9% 1	1900
	11th to 20th	Night	12% 62% 5% 12% 8% 1	1928
	21st to end	Night	15% 61% 6% 12% 5%	2091
October	1st to 10th	Night	21% 37% 11% 22% 8%	3800
	11th to 20th	Night	30% 37% 6% 18% 9%	3862
	21st to end	Night	29% 37% 8% 21% 5%	4457
November	1st to 10th	Night	23% 58% 8% 8% 3	2588
	11th to 20th	Night	23% 59% 6% 6% 4 2	2800
	21st to end	Night	25% 58% 6% 5% 4 1	2828
December	1st to 10th	Night	24% 38% 15% 20% 2	4890
	11th to 20th	Night	50% 34% 8% 6% 2	5547
	21st to end	Night	49% 28% 9% 10% 4	7164

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	26% 14% 24% 27% 7% 3	200
	11th to 20th	Day	26% 13% 26% 24% 11% 3	200
	21st to end	Day	25% 12% 29% 25% 7% 2	220
February	1st to 10th	Day	15% 19% 40% 21% 5% 1	260
	11th to 20th	Day	21% 17% 34% 21% 7%	398
	21st to end	Day	16% 17% 35% 25% 7%	414
March	1st to 10th	Day	23% 22% 29% 17% 9% 1	500
	11th to 20th	Day	18% 20% 26% 21% 12% 2	465
	21st to end	Day	22% 21% 26% 19% 10% 2	506
April	1st to 10th	Day	23% 19% 30% 20% 7% 1	460
	11th to 20th	Day	18% 26% 27% 17% 8% 4	452
	21st to end	Day	15% 25% 26% 22% 7% 4	460
May	1st to 10th	Day	15% 22% 28% 24% 10% 2	463
	11th to 20th	Day	20% 12% 28% 26% 10% 4	488
	21st to end	Day	16% 15% 27% 26% 13% 3	529
June	1st to 10th	Day	17% 15% 31% 27% 9% 2	599
	11th to 20th	Day	17% 15% 29% 27% 11% 2	723
	21st to end	Day	9% 15% 30% 29% 15% 2	809
July	1st to 10th	Day	7% 14% 31% 35% 11% 2	548
	11th to 20th	Day	6% 17% 32% 30% 13% 2	484
	21st to end	Day	6% 11% 31% 33% 14% 4	531
August	1st to 10th	Day	5% 10% 31% 34% 14% 6%	487
	11th to 20th	Day	6% 9% 30% 31% 18% 7%	477
	21st to end	Day	11% 14% 27% 29% 13% 5%	539
September	1st to 10th	Day	10% 15% 28% 29% 13% 5%	490
	11th to 20th	Day	16% 14% 26% 27% 14% 3	490
	21st to end	Day	19% 15% 29% 23% 12% 2	490
October	1st to 10th	Day	16% 17% 30% 22% 14% 1	490
	11th to 20th	Day	18% 18% 26% 24% 11% 2	439
	21st to end	Day	24% 13% 34% 20% 9% 1	330
November	1st to 10th	Day	25% 17% 26% 24% 7%	273
	11th to 20th	Day	26% 22% 23% 17% 13%	200
	21st to end	Day	21% 12% 30% 21% 14% 3	200
December	1st to 10th	Day	23% 6% 24% 27% 16% 5%	200
	11th to 20th	Day	24% 17% 27% 24% 7% 2	200
	21st to end	Day	22% 14% 23% 30% 9% 2	220
January	1st to 10th	Night	28% 13% 23% 26% 9% 2	800
	11th to 20th	Night	23% 10% 24% 31% 10% 2	800
	21st to end	Night	19% 9% 26% 32% 13% 1	880
February	1st to 10th	Night	21% 12% 27% 30% 10% 2	800
	11th to 20th	Night	17% 8% 30% 32% 12% 1	784
	21st to end	Night	18% 9% 24% 32% 15% 2	660
March	1st to 10th	Night	17% 12% 24% 32% 15% 2	800
	11th to 20th	Night	15% 11% 26% 31% 16% 1	766
	21st to end	Night	16% 13% 27% 30% 13% 1	836
April	1st to 10th	Night	15% 9% 21% 35% 18% 1	760
	11th to 20th	Night	11% 12% 28% 34% 14% 2	742
	21st to end	Night	11% 11% 29% 34% 14% 1	470
May	1st to 10th	Night	11% 9% 27% 37% 15% 1	380
	11th to 20th	Night	11% 7% 22% 33% 23% 3	374
	21st to end	Night	13% 8% 22% 35% 21% 2	411
June	1st to 10th	Night	14% 9% 24% 37% 15% 1	380
	11th to 20th	Night	15% 7% 30% 32% 15% 1	380
	21st to end	Night	7% 8% 26% 35% 23% 2	380
July	1st to 10th	Night	6% 6% 22% 41% 25% 2	370
	11th to 20th	Night	4 8% 23% 43% 22% 1	368
	21st to end	Night	4 6% 19% 44% 26% 2	416
August	1st to 10th	Night	3 7% 16% 39% 31% 3	378
	11th to 20th	Night	3 3 19% 39% 32% 3	397
	21st to end	Night	7% 6% 19% 41% 25% 2	828
September	1st to 10th	Night	5% 6% 21% 38% 26% 4	760
	11th to 20th	Night	10% 7% 17% 33% 30% 4	760
	21st to end	Night	13% 7% 20% 35% 21% 3	760
October	1st to 10th	Night	18% 9% 18% 31% 22% 2	760
	11th to 20th	Night	18% 11% 22% 31% 16% 2	760
	21st to end	Night	23% 10% 23% 31% 11% 3	836
November	1st to 10th	Night	26% 11% 28% 29% 6% 1	780
	11th to 20th	Night	26% 13% 22% 25% 13% 1	800
	21st to end	Night	25% 10% 24% 26% 12% 3	828
December	1st to 10th	Night	19% 10% 25% 34% 11% 1	1000
	11th to 20th	Night	27% 12% 23% 31% 7% 1	1000
	21st to end	Night	26% 12% 28% 28% 6%	975

Page generated at 2025-03-09 05:08:45. Version ac07

Copyright © 2025 Attilla Danko.