Shaggy Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shaggy Mountain Observatory clear sky chart from 2005-11-06 to 2024-04-03.

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	4 6% 3 6% 6% 4 5% 5% 6% 8% 48%	78854
	Night	4 6% 3 6% 6% 4 5% 5% 6% 8% 47%	81333
Transparency	Day	33% 8% 11% 19% 18% 10%	78579
	Night	33% 9% 12% 20% 17% 9%	81129
Seeing	Day	8% 15% 31% 31% 12% 2	13930
	Night	8% 9% 22% 36% 21% 4	24593

By Month

Percentage Cloud Cover SW (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	3 9% 5% 13% 10% 7% 8% 6% 6% 6% 27%	2858
	11th to 20th	Day	5% 13% 6% 12% 9% 5% 6% 5% 6% 7% 27%	2860
	21st to end	Day	4 11% 5% 9% 8% 5% 7% 6% 5% 8% 32%	3146
February	1st to 10th	Day	5% 9% 5% 8% 9% 5% 7% 5% 5% 7% 35%	1710
	11th to 20th	Day	4 10% 5% 8% 9% 5% 6% 6% 6% 7% 35%	1749
	21st to end	Day	5% 10% 5% 9% 8% 4 6% 5% 6% 8% 33%	1570
March	1st to 10th	Day	3 10% 4 6% 6% 5% 6% 6% 7% 8% 39%	2020
	11th to 20th	Day	4 7% 3 7% 6% 4 6% 6% 7% 10% 40%	2090
	21st to end	Day	6% 10% 4 10% 8% 5% 7% 6% 6% 7% 31%	2299
April	1st to 10th	Day	6% 8% 4 7% 7% 4 7% 5% 5% 7% 41%	2007
	11th to 20th	Day	5% 6% 3 7% 6% 4 6% 5% 7% 7% 43%	2283
	21st to end	Day	4 6% 3 6% 6% 3 5% 5% 6% 8% 48%	2340
May	1st to 10th	Day	5% 6% 3 6% 6% 3 6% 6% 7% 9% 44%	2340
	11th to 20th	Day	4 5% 2 5% 5% 4 5% 5% 8% 10% 47%	2301
	21st to end	Day	5% 5% 3 5% 6% 5% 6% 6% 8% 8% 42%	2530
June	1st to 10th	Day	3 2 2 5% 4 2 5% 6% 6% 10% 56%	2340
	11th to 20th	Day	4 4 1 3 4 3 4 4 5% 6% 63%	2340
	21st to end	Day	1 1 1 3 3 2 3 4 5% 5% 72%	2340
July	1st to 10th	Day	2 2 1 3 3 2 4 5% 6% 8% 64%	2340
	11th to 20th	Day	3 3 2 3 4 3 4 5% 7% 7% 58%	2340
	21st to end	Day	4 2 2 4 4 4 5% 7% 6% 8% 55%	2545
August	1st to 10th	Day	3 3 2 4 4 3 5% 6% 7% 8% 56%	2328
	11th to 20th	Day	3 2 1 4 4 2 4 4 6% 7% 63%	2299
	21st to end	Day	3 3 2 4 4 3 4 4 6% 8% 60%	2566
September	1st to 10th	Day	2 2 1 2 3 2 3 4 5% 5% 70%	2012
	11th to 20th	Day	4 2 1 3 3 3 4 5% 5% 7% 64%	1980
	21st to end	Day	5% 2 1 3 4 2 3 4 4 6% 68%	1980
October	1st to 10th	Day	6% 5% 2 4 4 3 5% 4 6% 6% 54%	1904
	11th to 20th	Day	5% 4 2 4 5% 2 3 4 5% 7% 61%	1800
	21st to end	Day	4 4 2 5% 4 3 5% 5% 5% 8% 56%	1962
November	1st to 10th	Day	7% 5% 2 5% 5% 3 5% 6% 6% 8% 48%	1674
	11th to 20th	Day	6% 7% 3 6% 5% 3 4 5% 5% 8% 47%	1710
	21st to end	Day	3 8% 4 7% 7% 4 5% 7% 6% 8% 42%	1635
December	1st to 10th	Day	5% 8% 4 8% 7% 4 5% 5% 6% 7% 40%	1520
	11th to 20th	Day	5% 9% 4 8% 9% 4 6% 7% 8% 9% 32%	1990
	21st to end	Day	4 10% 5% 8% 8% 5% 6% 5% 8% 9% 32%	3146
January	1st to 10th	Night	4 9% 4 10% 9% 6% 6% 6% 6% 8% 31%	4097
	11th to 20th	Night	4 15% 5% 11% 8% 5% 6% 6% 7% 9% 25%	4110
	21st to end	Night	4 9% 4 8% 8% 5% 8% 7% 6% 10% 30%	4521
February	1st to 10th	Night	4 7% 4 7% 8% 4 7% 6% 7% 9% 37%	2470
	11th to 20th	Night	3 9% 4 8% 6% 4 6% 6% 5% 7% 43%	2314
	21st to end	Night	3 10% 4 7% 6% 4 7% 5% 6% 8% 40%	1884
March	1st to 10th	Night	4 8% 4 8% 8% 5% 6% 5% 6% 8% 37%	2158
	11th to 20th	Night	3 6% 3 5% 5% 4 5% 7% 7% 9% 46%	2090
	21st to end	Night	5% 7% 3 7% 6% 4 6% 7% 8% 8% 39%	2299
April	1st to 10th	Night	7% 8% 3 6% 5% 3 4 4 5% 7% 48%	1998
	11th to 20th	Night	4 5% 3 4 6% 4 6% 6% 7% 8% 48%	1622
	21st to end	Night	6% 5% 3 5% 5% 3 5% 5% 6% 7% 51%	1620
May	1st to 10th	Night	6% 6% 2 5% 5% 4 6% 6% 6% 7% 46%	1620
	11th to 20th	Night	5% 4 2 4 5% 2 5% 5% 5% 9% 54%	1594
	21st to end	Night	6% 5% 2 4 6% 3 4 5% 7% 10% 48%	1746
June	1st to 10th	Night	3 5% 1 4 4 3 4 5% 5% 7% 59%	1620
	11th to 20th	Night	3 3 2 3 3 2 4 4 5% 6% 66%	1620
	21st to end	Night	1 3 1 3 3 2 4 4 6% 8% 65%	1620
July	1st to 10th	Night	2 2 1 5% 5% 3 5% 5% 6% 8% 58%	1620
	11th to 20th	Night	3 4 2 5% 5% 3 5% 5% 5% 8% 54%	1620
	21st to end	Night	3 4 2 5% 4 3 5% 5% 6% 10% 53%	1773
August	1st to 10th	Night	3 2 1 5% 5% 3 5% 4 7% 9% 56%	1611
	11th to 20th	Night	2 2 2 4 4 3 5% 5% 7% 7% 59%	1602
	21st to end	Night	1 3 2 3 4 3 5% 6% 6% 8% 60%	1790
September	1st to 10th	Night	3 2 1 4 3 2 3 4 4 6% 68%	1945
	11th to 20th	Night	3 3 1 3 3 2 3 4 4 7% 66%	1980
	21st to end	Night	5% 2 2 3 3 2 3 3 3 5% 69%	1980
October	1st to 10th	Night	5% 4 2 5% 3 2 4 4 4 7% 59%	2055
	11th to 20th	Night	4 3 2 3 4 2 3 4 4 7% 63%	2160
	21st to end	Night	4 4 2 4 4 3 3 4 5% 7% 60%	2389
November	1st to 10th	Night	6% 6% 2 5% 5% 3 4 5% 6% 8% 50%	2405
	11th to 20th	Night	5% 5% 2 4 4 3 6% 4 7% 9% 50%	2470
	21st to end	Night	5% 7% 3 5% 6% 3 5% 5% 5% 10% 47%	2519
December	1st to 10th	Night	4 7% 4 7% 6% 4 5% 5% 5% 9% 45%	2660
	11th to 20th	Night	6% 9% 4 7% 7% 4 5% 6% 6% 9% 37%	3230
	21st to end	Night	5% 9% 4 9% 8% 5% 7% 7% 8% 9% 30%	4521

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% 14% 11% 15% 6%	2859
	11th to 20th	Day	52% 14% 16% 13% 4 1	2860
	21st to end	Day	48% 12% 18% 14% 7% 1	3146
February	1st to 10th	Day	48% 10% 15% 16% 10% 1	1710
	11th to 20th	Day	46% 10% 13% 20% 10% 1	1758
	21st to end	Day	46% 9% 15% 19% 10% 1	1570
March	1st to 10th	Day	39% 12% 14% 23% 11% 2	2020
	11th to 20th	Day	37% 9% 16% 24% 12% 2	2090
	21st to end	Day	48% 11% 15% 16% 8% 2	2299
April	1st to 10th	Day	41% 9% 12% 18% 15% 5%	2007
	11th to 20th	Day	39% 8% 12% 22% 16% 3	2286
	21st to end	Day	33% 7% 12% 25% 21% 2	2340
May	1st to 10th	Day	33% 9% 10% 23% 21% 4	2340
	11th to 20th	Day	29% 9% 11% 24% 22% 6%	2304
	21st to end	Day	32% 10% 14% 23% 17% 4	2530
June	1st to 10th	Day	22% 7% 10% 21% 30% 10%	2340
	11th to 20th	Day	22% 5% 7% 18% 28% 20%	2340
	21st to end	Day	14% 4 5% 13% 30% 35%	2340
July	1st to 10th	Day	17% 5% 7% 13% 24% 34%	2276
	11th to 20th	Day	20% 5% 9% 13% 23% 30%	2271
	21st to end	Day	22% 7% 10% 13% 21% 26%	2404
August	1st to 10th	Day	22% 6% 8% 16% 21% 26%	2313
	11th to 20th	Day	18% 6% 7% 12% 29% 28%	2299
	21st to end	Day	21% 5% 7% 17% 30% 20%	2566
September	1st to 10th	Day	15% 5% 6% 16% 27% 30%	2012
	11th to 20th	Day	18% 7% 8% 18% 25% 23%	1980
	21st to end	Day	19% 6% 6% 19% 33% 18%	1980
October	1st to 10th	Day	29% 7% 9% 19% 27% 9%	1904
	11th to 20th	Day	25% 5% 8% 30% 27% 6%	1800
	21st to end	Day	25% 8% 15% 28% 21% 2	1962
November	1st to 10th	Day	34% 8% 14% 23% 19% 3	1674
	11th to 20th	Day	34% 8% 12% 29% 15% 1	1710
	21st to end	Day	38% 10% 13% 24% 14% 2	1635
December	1st to 10th	Day	42% 10% 18% 19% 9% 2	1520
	11th to 20th	Day	48% 11% 12% 20% 9%	1988
	21st to end	Day	44% 10% 17% 15% 13% 1	3146
January	1st to 10th	Night	45% 12% 15% 19% 8% 1	4097
	11th to 20th	Night	51% 15% 14% 14% 6% 1	4110
	21st to end	Night	41% 15% 19% 16% 8% 1	4521
February	1st to 10th	Night	41% 11% 18% 21% 8% 1	2470
	11th to 20th	Night	39% 8% 15% 21% 16% 1	2315
	21st to end	Night	39% 10% 12% 24% 13% 2	1884
March	1st to 10th	Night	43% 9% 13% 22% 12% 1	2158
	11th to 20th	Night	32% 10% 15% 26% 15% 3	2090
	21st to end	Night	39% 12% 14% 23% 10% 3	2299
April	1st to 10th	Night	36% 6% 13% 22% 16% 7%	1998
	11th to 20th	Night	31% 9% 11% 24% 21% 3	1622
	21st to end	Night	31% 8% 13% 23% 22% 2	1620
May	1st to 10th	Night	33% 10% 10% 21% 22% 3	1620
	11th to 20th	Night	26% 9% 10% 26% 22% 8%	1595
	21st to end	Night	29% 9% 15% 25% 18% 4	1746
June	1st to 10th	Night	24% 6% 9% 22% 28% 11%	1620
	11th to 20th	Night	19% 5% 8% 18% 29% 21%	1620
	21st to end	Night	16% 4 5% 10% 27% 37%	1620
July	1st to 10th	Night	22% 5% 6% 15% 17% 35%	1575
	11th to 20th	Night	26% 6% 6% 13% 19% 30%	1566
	21st to end	Night	25% 5% 11% 14% 17% 27%	1674
August	1st to 10th	Night	22% 6% 11% 15% 19% 27%	1602
	11th to 20th	Night	21% 5% 8% 12% 26% 28%	1602
	21st to end	Night	19% 7% 8% 14% 26% 26%	1790
September	1st to 10th	Night	17% 3 6% 15% 25% 33%	1945
	11th to 20th	Night	18% 5% 8% 17% 26% 26%	1980
	21st to end	Night	19% 4 6% 15% 33% 24%	1980
October	1st to 10th	Night	25% 6% 10% 22% 29% 9%	2055
	11th to 20th	Night	22% 6% 8% 26% 30% 9%	2160
	21st to end	Night	23% 8% 10% 26% 27% 5%	2389
November	1st to 10th	Night	31% 8% 10% 24% 21% 6%	2405
	11th to 20th	Night	29% 10% 13% 29% 17% 3	2470
	21st to end	Night	34% 8% 10% 29% 15% 3	2519
December	1st to 10th	Night	36% 10% 16% 24% 11% 3	2660
	11th to 20th	Night	43% 10% 15% 21% 11%	3231
	21st to end	Night	47% 10% 16% 15% 11% 1	4521

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	14% 20% 30% 21% 13% 1	270
	11th to 20th	Day	9% 19% 34% 25% 12% 1	270
	21st to end	Day	8% 16% 32% 31% 11% 1	297
February	1st to 10th	Day	11% 26% 30% 24% 8%	270
	11th to 20th	Day	11% 20% 37% 22% 8% 1	354
	21st to end	Day	11% 23% 39% 21% 4 1	382
March	1st to 10th	Day	11% 23% 36% 23% 7%	460
	11th to 20th	Day	10% 18% 41% 23% 7%	460
	21st to end	Day	17% 25% 34% 21% 4	506
April	1st to 10th	Day	14% 23% 29% 24% 9% 1	429
	11th to 20th	Day	16% 27% 31% 20% 6%	412
	21st to end	Day	12% 26% 28% 24% 9% 1	420
May	1st to 10th	Day	9% 20% 39% 22% 9% 1	423
	11th to 20th	Day	11% 15% 31% 29% 10% 4	448
	21st to end	Day	8% 15% 31% 29% 14% 4	485
June	1st to 10th	Day	3 14% 32% 36% 11% 4	450
	11th to 20th	Day	7% 15% 37% 27% 13% 1	450
	21st to end	Day	2 12% 32% 42% 10% 2	450
July	1st to 10th	Day	1 6% 31% 46% 14% 2	446
	11th to 20th	Day	3 6% 34% 41% 13% 3	444
	21st to end	Day	2 2 27% 47% 18% 3	487
August	1st to 10th	Day	4 7% 29% 44% 13% 2	447
	11th to 20th	Day	3 6% 26% 43% 18% 4	437
	21st to end	Day	3 5% 28% 41% 19% 4	495
September	1st to 10th	Day	4 9% 27% 37% 18% 6%	450
	11th to 20th	Day	6% 10% 29% 35% 17% 3	450
	21st to end	Day	6% 13% 23% 35% 20% 3	450
October	1st to 10th	Day	6% 16% 29% 26% 17% 5%	374
	11th to 20th	Day	5% 14% 30% 25% 22% 4	270
	21st to end	Day	8% 14% 32% 31% 15% 1	297
November	1st to 10th	Day	15% 15% 25% 27% 15% 3	270
	11th to 20th	Day	9% 16% 29% 29% 12% 5%	270
	21st to end	Day	12% 14% 23% 27% 20% 3	270
December	1st to 10th	Day	10% 14% 30% 31% 13% 3	270
	11th to 20th	Day	8% 14% 33% 35% 9% 1	270
	21st to end	Day	18% 14% 31% 30% 7%	297
January	1st to 10th	Night	12% 11% 22% 33% 18% 4	760
	11th to 20th	Night	9% 12% 23% 34% 18% 5%	760
	21st to end	Night	10% 11% 21% 34% 19% 4	836
February	1st to 10th	Night	9% 11% 29% 35% 14% 3	760
	11th to 20th	Night	9% 9% 29% 35% 15% 3	744
	21st to end	Night	10% 12% 28% 36% 14% 2	628
March	1st to 10th	Night	9% 13% 29% 35% 11% 3	760
	11th to 20th	Night	7% 10% 26% 35% 19% 3	760
	21st to end	Night	8% 15% 29% 35% 10% 3	836
April	1st to 10th	Night	12% 15% 25% 33% 13% 2	724
	11th to 20th	Night	7% 14% 28% 37% 12% 2	533
	21st to end	Night	9% 11% 24% 35% 18% 3	540
May	1st to 10th	Night	7% 10% 28% 36% 17% 2	540
	11th to 20th	Night	7% 6% 20% 35% 27% 5%	531
	21st to end	Night	8% 7% 23% 32% 25% 5%	584
June	1st to 10th	Night	6% 8% 18% 40% 26% 2	540
	11th to 20th	Night	5% 11% 21% 39% 22% 2	540
	21st to end	Night	3 4 21% 39% 29% 4	540
July	1st to 10th	Night	2 4 18% 38% 35% 3	525
	11th to 20th	Night	4 2 18% 43% 30% 2	522
	21st to end	Night	5% 2 12% 32% 47% 2	591
August	1st to 10th	Night	4 2 18% 40% 34% 2	537
	11th to 20th	Night	3 1 16% 45% 31% 4	534
	21st to end	Night	3 4 16% 41% 33% 4	594
September	1st to 10th	Night	5% 5% 15% 38% 32% 6%	685
	11th to 20th	Night	4 5% 16% 38% 29% 8%	720
	21st to end	Night	6% 6% 15% 33% 29% 11%	720
October	1st to 10th	Night	6% 7% 21% 36% 25% 5%	720
	11th to 20th	Night	6% 5% 20% 35% 26% 7%	720
	21st to end	Night	7% 9% 24% 33% 22% 5%	792
November	1st to 10th	Night	11% 10% 18% 34% 22% 5%	740
	11th to 20th	Night	8% 8% 26% 37% 16% 5%	760
	21st to end	Night	10% 7% 24% 34% 19% 5%	809
December	1st to 10th	Night	9% 10% 24% 37% 18% 2	950
	11th to 20th	Night	14% 9% 26% 36% 13% 2	922
	21st to end	Night	15% 15% 25% 32% 12% 1	836

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