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 2024-02-10.

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% 9% 3 6% 5% 3 5% 5% 6% 7% 40%	78220
	Night	13% 12% 4 6% 5% 3 4 4 5% 7% 37%	80674
Transparency	Day	44% 9% 13% 20% 12% 3	77946
	Night	47% 8% 12% 19% 11% 2	80528
Seeing	Day	16% 16% 29% 26% 11% 3	13840
	Night	17% 9% 23% 33% 16% 2	22808

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% 22% 8% 10% 6% 3 4 4 4 5% 15%	2539
	11th to 20th	Day	18% 12% 4 6% 5% 3 5% 5% 6% 6% 29%	2516
	21st to end	Day	28% 26% 5% 7% 4 2 3 3 3 5% 15%	2794
February	1st to 10th	Day	12% 14% 4 7% 6% 3 5% 5% 5% 8% 29%	1569
	11th to 20th	Day	10% 14% 4 8% 6% 4 4 5% 6% 9% 32%	1578
	21st to end	Day	9% 12% 3 8% 6% 5% 5% 6% 8% 7% 30%	1480
March	1st to 10th	Day	11% 12% 4 7% 6% 3 6% 6% 7% 8% 30%	1800
	11th to 20th	Day	11% 9% 4 7% 6% 3 6% 7% 6% 9% 33%	1873
	21st to end	Day	10% 11% 5% 8% 7% 4 6% 5% 7% 9% 28%	2354
April	1st to 10th	Day	10% 8% 3 9% 7% 4 7% 7% 6% 7% 30%	2160
	11th to 20th	Day	8% 8% 3 7% 6% 4 6% 7% 8% 7% 36%	2140
	21st to end	Day	8% 8% 3 7% 6% 4 6% 6% 6% 8% 38%	2433
May	1st to 10th	Day	8% 6% 3 5% 6% 4 6% 5% 7% 9% 43%	2520
	11th to 20th	Day	10% 6% 3 6% 6% 3 5% 6% 7% 8% 40%	2477
	21st to end	Day	12% 7% 3 5% 7% 4 7% 6% 7% 8% 34%	2723
June	1st to 10th	Day	12% 6% 3 7% 6% 4 4 5% 6% 8% 37%	2623
	11th to 20th	Day	11% 6% 3 6% 6% 4 6% 6% 7% 9% 35%	2740
	21st to end	Day	6% 5% 2 5% 5% 3 5% 4 6% 8% 50%	2823
July	1st to 10th	Day	4 3 2 3 4 2 4 5% 6% 8% 59%	2579
	11th to 20th	Day	3 3 2 4 3 2 4 4 4 6% 65%	2520
	21st to end	Day	2 2 1 2 2 1 3 4 5% 6% 71%	2741
August	1st to 10th	Day	3 3 1 3 3 3 3 5% 5% 8% 64%	2507
	11th to 20th	Day	4 2 1 3 3 2 3 3 4 7% 67%	2453
	21st to end	Day	3 4 1 4 4 3 4 5% 6% 9% 57%	2382
September	1st to 10th	Day	4 4 2 3 3 2 4 4 4 6% 65%	2160
	11th to 20th	Day	8% 4 2 4 5% 3 4 4 6% 8% 52%	2134
	21st to end	Day	8% 6% 2 5% 4 3 3 4 5% 7% 52%	1976
October	1st to 10th	Day	9% 5% 2 4 5% 3 5% 4 5% 8% 49%	1800
	11th to 20th	Day	11% 6% 3 6% 4 3 4 5% 5% 8% 43%	1752
	21st to end	Day	19% 9% 3 6% 6% 3 4 4 5% 7% 36%	1782
November	1st to 10th	Day	19% 9% 4 6% 5% 4 6% 5% 6% 7% 29%	1622
	11th to 20th	Day	16% 14% 4 7% 5% 4 5% 4 5% 5% 31%	1520
	21st to end	Day	15% 16% 8% 9% 6% 3 3 4 5% 8% 23%	1472
December	1st to 10th	Day	15% 13% 6% 8% 5% 3 5% 5% 6% 6% 28%	1330
	11th to 20th	Day	17% 23% 6% 9% 5% 3 5% 4 5% 5% 19%	1682
	21st to end	Day	16% 19% 8% 10% 7% 4 4 5% 6% 5% 17%	2666
January	1st to 10th	Night	21% 25% 7% 9% 5% 3 3 3 3 5% 14%	4406
	11th to 20th	Night	19% 14% 4 6% 5% 3 4 3 4 6% 33%	4382
	21st to end	Night	25% 28% 7% 6% 4 2 3 4 3 4 13%	4862
February	1st to 10th	Night	14% 15% 5% 8% 5% 3 5% 4 6% 7% 26%	2595
	11th to 20th	Night	10% 13% 4 7% 5% 3 5% 5% 6% 8% 34%	2268
	21st to end	Night	10% 12% 5% 8% 8% 3 5% 5% 6% 8% 32%	1776
March	1st to 10th	Night	12% 10% 4 8% 5% 3 5% 5% 7% 9% 32%	2160
	11th to 20th	Night	12% 9% 4 6% 7% 3 5% 5% 7% 8% 35%	2083
	21st to end	Night	10% 9% 4 7% 6% 4 7% 6% 7% 7% 33%	2001
April	1st to 10th	Night	11% 7% 2 6% 5% 3 6% 5% 7% 9% 38%	1800
	11th to 20th	Night	6% 7% 3 7% 6% 3 5% 6% 6% 8% 43%	1771
	21st to end	Night	7% 7% 3 6% 6% 3 5% 6% 7% 8% 42%	1526
May	1st to 10th	Night	7% 6% 2 4 5% 4 5% 6% 5% 8% 48%	1440
	11th to 20th	Night	8% 5% 2 5% 5% 3 6% 6% 6% 10% 43%	1416
	21st to end	Night	9% 7% 3 6% 6% 4 6% 6% 6% 9% 39%	1552
June	1st to 10th	Night	10% 5% 3 5% 5% 2 5% 6% 7% 9% 42%	1332
	11th to 20th	Night	10% 6% 3 4 5% 4 6% 6% 6% 8% 43%	1212
	21st to end	Night	5% 3 1 3 4 3 6% 5% 6% 8% 56%	1131
July	1st to 10th	Night	3 3 2 3 3 2 4 4 6% 7% 63%	1372
	11th to 20th	Night	1 3 2 2 3 2 3 5% 4 8% 68%	1440
	21st to end	Night	2 1 2 2 2 2 3 4 6% 76%	1576
August	1st to 10th	Night	2 2 1 3 3 3 3 4 4 7% 67%	1432
	11th to 20th	Night	1 2 1 2 2 2 3 3 4 8% 71%	1443
	21st to end	Night	5% 2 1 2 3 2 4 5% 6% 8% 63%	1972
September	1st to 10th	Night	3 4 1 3 3 2 3 4 5% 7% 65%	1800
	11th to 20th	Night	7% 4 2 4 3 2 3 3 4 8% 59%	1826
	21st to end	Night	7% 6% 2 4 5% 2 4 4 6% 8% 53%	1980
October	1st to 10th	Night	10% 6% 2 5% 3 2 4 5% 6% 7% 49%	2160
	11th to 20th	Night	11% 7% 3 6% 4 3 5% 5% 6% 8% 43%	2207
	21st to end	Night	17% 8% 2 4 5% 3 4 4 5% 7% 40%	2574
November	1st to 10th	Night	19% 12% 3 5% 5% 3 5% 4 5% 7% 32%	2455
	11th to 20th	Night	19% 14% 3 6% 5% 3 4 4 6% 7% 30%	2660
	21st to end	Night	18% 16% 6% 7% 5% 3 4 5% 5% 6% 24%	2686
December	1st to 10th	Night	15% 15% 6% 10% 6% 2 4 4 5% 6% 27%	2850
	11th to 20th	Night	18% 24% 6% 9% 6% 2 4 4 5% 4 18%	3510
	21st to end	Night	18% 24% 5% 7% 5% 3 3 4 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	70% 8% 7% 11% 4	2539
	11th to 20th	Day	53% 7% 15% 16% 4 5%	2540
	21st to end	Day	72% 6% 9% 9% 4	2794
February	1st to 10th	Day	53% 10% 14% 15% 6% 2	1569
	11th to 20th	Day	51% 10% 16% 16% 7%	1587
	21st to end	Day	52% 11% 13% 15% 9%	1480
March	1st to 10th	Day	50% 12% 15% 14% 8% 2	1800
	11th to 20th	Day	50% 13% 13% 18% 6%	1873
	21st to end	Day	55% 12% 16% 13% 3	2354
April	1st to 10th	Day	54% 10% 14% 16% 6% 1	2160
	11th to 20th	Day	48% 11% 12% 18% 10% 1	2140
	21st to end	Day	45% 11% 12% 19% 10% 2	2433
May	1st to 10th	Day	40% 10% 14% 25% 10% 1	2520
	11th to 20th	Day	45% 11% 14% 21% 7% 1	2480
	21st to end	Day	50% 10% 13% 20% 7% 1	2724
June	1st to 10th	Day	48% 11% 10% 17% 10% 4	2623
	11th to 20th	Day	46% 12% 12% 20% 8% 1	2740
	21st to end	Day	33% 9% 15% 24% 17% 2	2823
July	1st to 10th	Day	26% 9% 12% 25% 21% 7%	2510
	11th to 20th	Day	24% 5% 10% 24% 27% 10%	2445
	21st to end	Day	16% 5% 10% 25% 33% 11%	2589
August	1st to 10th	Day	20% 8% 11% 28% 23% 10%	2490
	11th to 20th	Day	20% 6% 12% 30% 27% 6%	2453
	21st to end	Day	26% 9% 13% 31% 19% 2	2382
September	1st to 10th	Day	23% 7% 14% 31% 21% 4	2160
	11th to 20th	Day	32% 10% 10% 25% 19% 4	2134
	21st to end	Day	34% 9% 15% 25% 15% 2	1976
October	1st to 10th	Day	35% 10% 14% 29% 12%	1800
	11th to 20th	Day	41% 10% 16% 22% 11%	1752
	21st to end	Day	48% 10% 12% 23% 7%	1782
November	1st to 10th	Day	55% 9% 13% 15% 7%	1622
	11th to 20th	Day	56% 9% 13% 15% 5% 1	1520
	21st to end	Day	59% 8% 13% 13% 6% 1	1472
December	1st to 10th	Day	54% 9% 16% 16% 5%	1330
	11th to 20th	Day	65% 9% 11% 9% 5%	1684
	21st to end	Day	66% 9% 9% 11% 5%	2666
January	1st to 10th	Night	72% 7% 8% 10% 3	4406
	11th to 20th	Night	50% 8% 12% 17% 8% 6%	4420
	21st to end	Night	74% 5% 9% 8% 3	4862
February	1st to 10th	Night	55% 10% 13% 14% 6% 2	2595
	11th to 20th	Night	49% 8% 17% 19% 7%	2270
	21st to end	Night	51% 9% 15% 16% 10%	1776
March	1st to 10th	Night	47% 11% 16% 16% 9% 1	2160
	11th to 20th	Night	48% 9% 14% 21% 7%	2084
	21st to end	Night	49% 11% 16% 18% 6%	2001
April	1st to 10th	Night	42% 12% 16% 21% 8% 1	1800
	11th to 20th	Night	41% 10% 13% 22% 12% 1	1771
	21st to end	Night	41% 9% 11% 25% 13% 1	1526
May	1st to 10th	Night	35% 9% 14% 27% 15% 1	1440
	11th to 20th	Night	36% 11% 16% 25% 10% 1	1416
	21st to end	Night	42% 9% 15% 26% 8% 1	1552
June	1st to 10th	Night	39% 10% 11% 25% 12% 3	1332
	11th to 20th	Night	37% 11% 13% 27% 12% 1	1212
	21st to end	Night	26% 9% 14% 30% 17% 3	1131
July	1st to 10th	Night	22% 7% 12% 28% 22% 8%	1332
	11th to 20th	Night	18% 7% 12% 26% 27% 9%	1392
	21st to end	Night	11% 5% 7% 30% 36% 11%	1488
August	1st to 10th	Night	19% 6% 10% 26% 30% 9%	1424
	11th to 20th	Night	15% 5% 11% 34% 31% 4	1443
	21st to end	Night	20% 7% 12% 35% 22% 4	1972
September	1st to 10th	Night	20% 7% 14% 30% 25% 4	1800
	11th to 20th	Night	26% 8% 11% 26% 24% 5%	1826
	21st to end	Night	31% 8% 15% 30% 14% 3	1980
October	1st to 10th	Night	35% 9% 14% 27% 14% 1	2160
	11th to 20th	Night	42% 8% 13% 24% 12% 1	2207
	21st to end	Night	44% 9% 13% 25% 8%	2574
November	1st to 10th	Night	54% 10% 13% 13% 8% 1	2455
	11th to 20th	Night	55% 9% 14% 14% 6% 2	2660
	21st to end	Night	61% 7% 12% 12% 6% 1	2686
December	1st to 10th	Night	55% 7% 15% 18% 4	2850
	11th to 20th	Night	68% 11% 8% 8% 5%	3507
	21st to end	Night	64% 7% 10% 12% 6% 1	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% 20% 39% 21% 3	235
	11th to 20th	Day	22% 17% 34% 21% 6%	337
	21st to end	Day	13% 17% 34% 28% 8%	346
March	1st to 10th	Day	23% 24% 28% 15% 9% 1	420
	11th to 20th	Day	20% 20% 28% 20% 12% 1	420
	21st to end	Day	23% 21% 27% 18% 10% 2	462
April	1st to 10th	Day	23% 19% 30% 20% 7% 1	420
	11th to 20th	Day	19% 27% 26% 16% 8% 4	412
	21st to end	Day	15% 25% 27% 22% 8% 4	420
May	1st to 10th	Day	15% 22% 28% 24% 9% 2	423
	11th to 20th	Day	20% 12% 28% 26% 10% 4	448
	21st to end	Day	17% 14% 26% 26% 13% 4	485
June	1st to 10th	Day	16% 15% 30% 27% 9% 2	553
	11th to 20th	Day	16% 15% 29% 28% 10% 2	670
	21st to end	Day	8% 14% 30% 30% 16% 3	753
July	1st to 10th	Day	7% 14% 30% 36% 11% 2	505
	11th to 20th	Day	7% 18% 31% 30% 12% 2	444
	21st to end	Day	4 11% 31% 34% 15% 4	487
August	1st to 10th	Day	5% 10% 30% 35% 15% 5%	447
	11th to 20th	Day	6% 9% 30% 30% 18% 6%	437
	21st to end	Day	9% 15% 28% 29% 14% 5%	495
September	1st to 10th	Day	10% 16% 29% 28% 12% 4	450
	11th to 20th	Day	15% 13% 26% 28% 15% 3	450
	21st to end	Day	18% 16% 28% 23% 12% 2	450
October	1st to 10th	Day	15% 18% 28% 23% 15% 2	450
	11th to 20th	Day	17% 19% 26% 25% 11% 2	402
	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% 29% 10% 2	758
	11th to 20th	Night	17% 8% 29% 33% 12% 1	704
	21st to end	Night	17% 8% 24% 34% 15% 2	592
March	1st to 10th	Night	17% 12% 23% 31% 15% 2	720
	11th to 20th	Night	15% 11% 27% 31% 15% 1	720
	21st to end	Night	16% 13% 28% 29% 13% 2	792
April	1st to 10th	Night	14% 9% 22% 35% 18% 1	720
	11th to 20th	Night	12% 11% 28% 33% 14% 2	703
	21st to end	Night	11% 11% 30% 35% 13% 1	446
May	1st to 10th	Night	12% 9% 27% 37% 15% 1	360
	11th to 20th	Night	12% 6% 22% 33% 24% 3	354
	21st to end	Night	13% 7% 22% 35% 21% 2	389
June	1st to 10th	Night	14% 9% 24% 37% 16% 1	360
	11th to 20th	Night	15% 6% 29% 34% 16% 1	360
	21st to end	Night	6% 8% 24% 36% 24% 2	360
July	1st to 10th	Night	6% 5% 21% 41% 26% 2	350
	11th to 20th	Night	4 8% 22% 43% 22% 1	348
	21st to end	Night	3 6% 19% 44% 27% 2	394
August	1st to 10th	Night	4 6% 16% 38% 33% 4	358
	11th to 20th	Night	3 3 19% 39% 33% 3	375
	21st to end	Night	7% 6% 18% 41% 26% 2	784
September	1st to 10th	Night	6% 6% 21% 37% 26% 4	720
	11th to 20th	Night	9% 6% 16% 33% 31% 5%	720
	21st to end	Night	13% 7% 18% 36% 22% 3	720
October	1st to 10th	Night	18% 7% 18% 32% 23% 2	720
	11th to 20th	Night	17% 11% 21% 32% 16% 2	720
	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

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