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 2005-11-05 to 2024-10-14.

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% 44%	101585
	Night	11% 12% 3 7% 4 4 4 3 5% 7% 40%	97029
Transparency	Day	20% 50% 6% 12% 9% 3	101353
	Night	23% 50% 6% 11% 7% 2	96907
Seeing	Day	16% 16% 29% 26% 11% 3	14855
	Night	16% 10% 23% 33% 16% 2	23557

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	18% 24% 7% 12% 5% 3 4 3 4 5% 15%	2539
	11th to 20th	Day	18% 13% 4 7% 5% 4 5% 4 6% 6% 29%	2516
	21st to end	Day	28% 26% 5% 7% 4 3 2 2 4 5% 15%	2794
February	1st to 10th	Day	12% 15% 4 8% 5% 5% 5% 4 5% 8% 29%	1577
	11th to 20th	Day	9% 15% 4 9% 5% 5% 4 4 6% 8% 31%	1668
	21st to end	Day	9% 13% 4 9% 5% 7% 5% 5% 7% 7% 30%	1570
March	1st to 10th	Day	10% 15% 4 8% 5% 4 5% 4 6% 7% 32%	3138
	11th to 20th	Day	7% 7% 3 5% 3 3 4 4 5% 8% 51%	3318
	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	8% 5% 2 6% 4 4 4 4 5% 8% 50%	1900
	11th to 20th	Day	11% 7% 3 7% 4 4 4 4 5% 8% 44%	1783
	21st to end	Day	18% 9% 3 7% 5% 4 4 3 5% 7% 36%	1782
November	1st to 10th	Day	18% 11% 3 6% 5% 5% 5% 4 6% 7% 29%	1622
	11th to 20th	Day	16% 15% 3 8% 5% 4 5% 3 5% 5% 31%	1520
	21st to end	Day	15% 18% 6% 9% 6% 4 3 4 5% 8% 23%	1472
December	1st to 10th	Day	15% 15% 5% 8% 5% 4 5% 3 7% 6% 27%	1330
	11th to 20th	Day	16% 24% 5% 10% 4 5% 4 3 5% 5% 19%	1682
	21st to end	Day	15% 20% 8% 11% 6% 5% 5% 3 6% 5% 17%	2666
January	1st to 10th	Night	21% 26% 7% 10% 4 4 3 3 4 5% 14%	4406
	11th to 20th	Night	19% 15% 4 7% 4 3 3 2 4 6% 33%	4382
	21st to end	Night	25% 29% 7% 7% 3 3 3 3 4 4 13%	4862
February	1st to 10th	Night	14% 17% 5% 9% 5% 4 5% 3 6% 6% 26%	2603
	11th to 20th	Night	10% 14% 4 8% 4 4 4 4 6% 8% 34%	2398
	21st to end	Night	10% 13% 4 9% 6% 4 4 5% 6% 7% 31%	1884
March	1st to 10th	Night	7% 12% 4 9% 5% 5% 5% 4 7% 9% 32%	3736
	11th to 20th	Night	9% 8% 2 5% 4 3 3 3 5% 7% 51%	3658
	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	10% 6% 2 5% 3 4 4 4 5% 7% 50%	2280
	11th to 20th	Night	11% 7% 3 7% 3 4 4 4 6% 8% 43%	2254
	21st to end	Night	17% 8% 2 5% 4 4 4 4 5% 7% 40%	2574
November	1st to 10th	Night	19% 13% 3 5% 4 4 4 3 5% 7% 32%	2455
	11th to 20th	Night	19% 15% 2 6% 5% 4 4 3 6% 7% 29%	2660
	21st to end	Night	17% 19% 5% 8% 5% 4 4 4 6% 5% 24%	2686
December	1st to 10th	Night	15% 17% 5% 10% 5% 3 5% 3 5% 6% 27%	2850
	11th to 20th	Night	17% 26% 6% 10% 5% 3 4 3 5% 4 18%	3510
	21st to end	Night	18% 26% 5% 8% 4 4 3 3 5% 8% 17%	5018

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% 40% 4 8% 4	2539
	11th to 20th	Day	34% 39% 10% 11% 2 5%	2540
	21st to end	Day	52% 40% 3 3 1	2794
February	1st to 10th	Day	21% 67% 3 5% 3 1	1577
	11th to 20th	Day	21% 65% 4 6% 3	1677
	21st to end	Day	14% 68% 5% 7% 6%	1570
March	1st to 10th	Day	30% 46% 4 10% 10% 1	3138
	11th to 20th	Day	13% 44% 13% 27% 3	3318
	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	15% 61% 8% 12% 4	1900
	11th to 20th	Day	18% 64% 4 10% 3	1783
	21st to end	Day	20% 63% 3 10% 3	1782
November	1st to 10th	Day	22% 61% 7% 7% 3	1622
	11th to 20th	Day	23% 61% 6% 6% 3 1	1520
	21st to end	Day	23% 61% 5% 6% 4 1	1472
December	1st to 10th	Day	25% 60% 7% 5% 3	1330
	11th to 20th	Day	36% 51% 6% 4 2	1684
	21st to end	Day	43% 41% 6% 7% 3	2666
January	1st to 10th	Night	46% 39% 5% 7% 2	4406
	11th to 20th	Night	30% 40% 7% 12% 6% 5%	4420
	21st to end	Night	53% 41% 3 3 1	4862
February	1st to 10th	Night	23% 66% 3 4 3 1	2603
	11th to 20th	Night	20% 65% 4 6% 3 1	2400
	21st to end	Night	15% 67% 5% 9% 5%	1884
March	1st to 10th	Night	23% 49% 5% 12% 11%	3736
	11th to 20th	Night	13% 42% 12% 26% 6%	3659
	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	14% 61% 7% 12% 5%	2280
	11th to 20th	Night	17% 63% 5% 10% 4	2254
	21st to end	Night	18% 63% 4 12% 3	2574
November	1st to 10th	Night	22% 61% 7% 7% 3	2455
	11th to 20th	Night	20% 62% 6% 6% 4 2	2660
	21st to end	Night	23% 61% 5% 5% 4 1	2686
December	1st to 10th	Night	25% 60% 5% 9% 1	2850
	11th to 20th	Night	37% 53% 4 3 3	3507
	21st to end	Night	40% 40% 8% 8% 5%	5018

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	25% 15% 22% 27% 7% 3	180
	11th to 20th	Day	27% 11% 25% 25% 10% 3	180
	21st to end	Day	27% 13% 26% 25% 7% 2	198
February	1st to 10th	Day	17% 19% 39% 21% 3 1	237
	11th to 20th	Day	21% 18% 33% 21% 7%	367
	21st to end	Day	15% 16% 35% 26% 8%	382
March	1st to 10th	Day	23% 23% 29% 16% 9% 1	460
	11th to 20th	Day	18% 20% 26% 21% 13% 2	460
	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	16% 18% 26% 25% 12% 2	415
	21st to end	Day	23% 14% 32% 20% 10% 1	297
November	1st to 10th	Day	23% 18% 25% 26% 8%	246
	11th to 20th	Day	24% 20% 23% 18% 14%	180
	21st to end	Day	21% 13% 28% 22% 13% 3	180
December	1st to 10th	Day	24% 6% 25% 26% 15% 4	180
	11th to 20th	Day	22% 17% 27% 25% 7% 2	180
	21st to end	Day	19% 14% 24% 32% 9% 2	198
January	1st to 10th	Night	28% 13% 22% 26% 9% 2	760
	11th to 20th	Night	23% 10% 23% 31% 11% 2	760
	21st to end	Night	20% 9% 24% 32% 13% 1	836
February	1st to 10th	Night	21% 11% 27% 30% 10% 2	760
	11th to 20th	Night	16% 8% 29% 33% 13% 1	744
	21st to end	Night	17% 8% 24% 33% 15% 2	628
March	1st to 10th	Night	17% 12% 23% 31% 16% 2	760
	11th to 20th	Night	14% 11% 26% 31% 16% 1	760
	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	17% 11% 21% 32% 16% 2	734
	21st to end	Night	22% 10% 22% 32% 12% 3	792
November	1st to 10th	Night	26% 11% 27% 29% 7% 1	740
	11th to 20th	Night	25% 13% 22% 26% 13% 1	760
	21st to end	Night	25% 10% 24% 27% 12% 3	786
December	1st to 10th	Night	20% 10% 24% 34% 11% 1	950
	11th to 20th	Night	26% 12% 23% 32% 7% 1	950
	21st to end	Night	25% 12% 27% 29% 6%	927

Page generated at 2024-10-11 07:49:56. Version ac07

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