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 2024-11-04.

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	3 6% 2 6% 4 5% 5% 4 6% 7% 52%	104796
	Night	4 6% 2 6% 4 5% 5% 4 6% 8% 50%	102977
Transparency	Day	29% 8% 10% 19% 21% 14%	104561
	Night	30% 8% 11% 19% 19% 12%	102801
Seeing	Day	8% 15% 31% 31% 12% 2	14760
	Night	8% 9% 23% 36% 21% 4	25310

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% 4 15% 9% 9% 7% 5% 6% 6% 27%	2858
	11th to 20th	Day	4 14% 5% 14% 7% 6% 6% 4 6% 7% 27%	2860
	21st to end	Day	4 12% 5% 10% 7% 6% 6% 4 5% 8% 32%	3146
February	1st to 10th	Day	5% 10% 5% 9% 7% 6% 7% 4 5% 7% 35%	1710
	11th to 20th	Day	4 12% 4 10% 7% 6% 5% 5% 6% 7% 35%	1749
	21st to end	Day	4 12% 4 10% 7% 6% 5% 4 6% 8% 33%	1570
March	1st to 10th	Day	2 8% 4 8% 6% 8% 7% 5% 8% 8% 36%	3342
	11th to 20th	Day	3 9% 3 8% 5% 5% 5% 4 6% 8% 44%	3490
	21st to end	Day	5% 13% 4 12% 7% 7% 7% 5% 7% 8% 25%	3825
April	1st to 10th	Day	5% 8% 3 8% 6% 6% 6% 5% 6% 6% 41%	2095
	11th to 20th	Day	5% 7% 3 8% 6% 6% 5% 5% 6% 6% 44%	2412
	21st to end	Day	4 6% 3 7% 6% 4 5% 4 6% 8% 47%	2470
May	1st to 10th	Day	6% 8% 3 9% 5% 6% 5% 4 6% 8% 40%	4110
	11th to 20th	Day	3 3 1 4 3 3 4 4 6% 9% 58%	4071
	21st to end	Day	4 5% 2 5% 5% 5% 5% 5% 7% 8% 51%	4477
June	1st to 10th	Day	2 3 1 5% 4 4 4 5% 6% 10% 56%	2470
	11th to 20th	Day	4 4 1 4 3 3 4 3 5% 6% 63%	2470
	21st to end	Day	1 1 1 3 3 3 3 3 5% 5% 72%	2470
July	1st to 10th	Day	1 1 1 2 2 2 3 3 4 5% 76%	4110
	11th to 20th	Day	2 3 1 3 3 4 5% 5% 7% 9% 59%	4110
	21st to end	Day	2 2 1 3 3 3 4 4 5% 7% 67%	4454
August	1st to 10th	Day	2 2 1 3 3 4 4 4 6% 8% 64%	4092
	11th to 20th	Day	2 1 1 3 3 4 4 3 6% 8% 67%	4028
	21st to end	Day	2 2 1 3 2 3 3 3 5% 6% 70%	4500
September	1st to 10th	Day	2 2 1 2 2 3 3 3 5% 5% 70%	2123
	11th to 20th	Day	3 2 1 4 3 3 5% 3 5% 7% 64%	2090
	21st to end	Day	4 2 1 3 3 2 2 3 4 5% 69%	2090
October	1st to 10th	Day	3 3 1 3 2 3 3 2 4 5% 69%	3344
	11th to 20th	Day	6% 4 1 4 3 3 3 3 5% 7% 62%	3150
	21st to end	Day	4 5% 2 5% 4 4 5% 3 4 6% 59%	3408
November	1st to 10th	Day	6% 6% 2 6% 4 4 6% 5% 7% 7% 47%	1701
	11th to 20th	Day	6% 8% 3 6% 4 4 4 4 5% 8% 47%	1710
	21st to end	Day	3 9% 3 9% 6% 5% 5% 5% 6% 7% 41%	1635
December	1st to 10th	Day	5% 9% 3 9% 6% 5% 6% 4 6% 6% 40%	1520
	11th to 20th	Day	4 10% 4 9% 7% 7% 6% 5% 7% 9% 31%	1990
	21st to end	Day	4 10% 4 10% 7% 6% 6% 4 8% 9% 32%	3146
January	1st to 10th	Night	4 10% 3 12% 8% 7% 6% 4 6% 8% 31%	4097
	11th to 20th	Night	4 15% 5% 12% 7% 6% 6% 5% 7% 8% 25%	4110
	21st to end	Night	4 10% 4 9% 7% 7% 8% 6% 6% 10% 30%	4521
February	1st to 10th	Night	4 8% 3 9% 7% 6% 7% 5% 7% 9% 37%	2470
	11th to 20th	Night	3 10% 3 8% 5% 6% 5% 4 5% 7% 42%	2314
	21st to end	Night	3 10% 3 8% 5% 6% 6% 4 7% 8% 40%	1884
March	1st to 10th	Night	2 6% 3 9% 6% 8% 7% 5% 9% 9% 36%	3530
	11th to 20th	Night	2 6% 3 7% 4 4 5% 4 7% 8% 50%	3490
	21st to end	Night	4 9% 3 10% 7% 6% 6% 5% 7% 6% 37%	3828
April	1st to 10th	Night	7% 8% 2 7% 4 4 4 3 5% 7% 49%	2085
	11th to 20th	Night	4 6% 2 5% 5% 5% 6% 4 7% 7% 49%	1713
	21st to end	Night	6% 6% 2 6% 4 4 5% 4 6% 6% 50%	1710
May	1st to 10th	Night	4 7% 2 7% 5% 6% 6% 5% 7% 8% 44%	2860
	11th to 20th	Night	3 3 1 4 4 3 4 4 5% 7% 61%	2834
	21st to end	Night	5% 5% 2 5% 4 3 4 4 6% 9% 54%	3110
June	1st to 10th	Night	3 5% 1 4 4 4 4 4 5% 7% 57%	1710
	11th to 20th	Night	3 3 2 3 2 3 4 3 5% 6% 66%	1710
	21st to end	Night	1 2 1 3 3 3 5% 3 6% 8% 66%	1710
July	1st to 10th	Night	1 1 1 3 3 3 3 3 4 5% 73%	2860
	11th to 20th	Night	2 3 1 5% 4 5% 5% 5% 7% 9% 56%	2860
	21st to end	Night	2 3 1 5% 3 4 4 4 6% 7% 60%	3109
August	1st to 10th	Night	2 1 1 4 3 4 3 4 7% 9% 62%	2847
	11th to 20th	Night	2 2 1 4 3 4 4 4 6% 6% 64%	2811
	21st to end	Night	3 2 1 2 2 2 3 3 4 6% 71%	3167
September	1st to 10th	Night	3 3 1 4 2 3 3 3 4 6% 68%	2054
	11th to 20th	Night	3 3 1 4 3 3 3 3 4 7% 66%	2090
	21st to end	Night	5% 2 1 3 3 3 2 3 3 5% 71%	2090
October	1st to 10th	Night	3 2 1 3 2 2 3 3 3 5% 73%	3630
	11th to 20th	Night	5% 3 1 3 3 3 4 3 5% 7% 62%	3778
	21st to end	Night	6% 4 1 4 3 3 3 3 5% 7% 60%	4145
November	1st to 10th	Night	6% 7% 2 6% 4 4 4 4 6% 8% 49%	2450
	11th to 20th	Night	5% 5% 2 5% 4 4 6% 4 7% 9% 50%	2470
	21st to end	Night	5% 8% 2 6% 5% 4 5% 4 5% 9% 47%	2519
December	1st to 10th	Night	4 7% 3 8% 5% 6% 4 3 5% 9% 44%	2660
	11th to 20th	Night	6% 10% 3 8% 6% 5% 5% 5% 6% 9% 36%	3230
	21st to end	Night	5% 10% 4 10% 7% 7% 6% 6% 8% 8% 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	36% 15% 14% 23% 11% 1	3342
	11th to 20th	Day	33% 9% 15% 31% 10% 1	3490
	21st to end	Day	50% 12% 16% 14% 6% 1	3825
April	1st to 10th	Day	40% 9% 12% 19% 15% 5%	2095
	11th to 20th	Day	37% 8% 13% 22% 17% 3	2415
	21st to end	Day	33% 7% 13% 25% 20% 2	2470
May	1st to 10th	Day	34% 9% 12% 22% 19% 5%	4110
	11th to 20th	Day	20% 6% 9% 28% 32% 4	4074
	21st to end	Day	25% 8% 12% 26% 25% 4	4477
June	1st to 10th	Day	22% 7% 10% 22% 29% 10%	2470
	11th to 20th	Day	21% 5% 7% 18% 29% 20%	2470
	21st to end	Day	13% 4 5% 12% 30% 36%	2470
July	1st to 10th	Day	10% 4 4 7% 15% 60%	4046
	11th to 20th	Day	17% 5% 6% 12% 26% 35%	4041
	21st to end	Day	15% 5% 7% 9% 26% 38%	4314
August	1st to 10th	Day	16% 5% 6% 17% 29% 28%	4078
	11th to 20th	Day	15% 4 8% 13% 33% 27%	4067
	21st to end	Day	15% 3 7% 14% 29% 32%	4499
September	1st to 10th	Day	15% 4 6% 16% 28% 30%	2123
	11th to 20th	Day	18% 7% 8% 18% 27% 22%	2090
	21st to end	Day	18% 5% 6% 19% 33% 19%	2090
October	1st to 10th	Day	19% 4 5% 12% 37% 22%	3344
	11th to 20th	Day	23% 4 7% 28% 29% 9%	3150
	21st to end	Day	25% 7% 11% 30% 23% 4	3408
November	1st to 10th	Day	35% 8% 14% 23% 18% 3	1701
	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	38% 11% 14% 22% 13% 1	3530
	11th to 20th	Night	28% 10% 14% 31% 15% 2	3490
	21st to end	Night	41% 13% 13% 20% 12% 2	3828
April	1st to 10th	Night	34% 7% 14% 23% 16% 7%	2085
	11th to 20th	Night	31% 9% 11% 24% 21% 4	1713
	21st to end	Night	31% 9% 14% 23% 21% 2	1710
May	1st to 10th	Night	30% 11% 11% 22% 23% 3	2860
	11th to 20th	Night	19% 7% 8% 28% 30% 7%	2835
	21st to end	Night	24% 7% 12% 26% 28% 3	3110
June	1st to 10th	Night	24% 7% 9% 22% 28% 10%	1710
	11th to 20th	Night	18% 5% 8% 17% 31% 21%	1710
	21st to end	Night	16% 4 5% 10% 27% 38%	1710
July	1st to 10th	Night	14% 3 3 8% 10% 61%	2815
	11th to 20th	Night	22% 6% 4 10% 24% 35%	2806
	21st to end	Night	22% 3 7% 10% 22% 36%	3011
August	1st to 10th	Night	17% 4 7% 13% 28% 31%	2838
	11th to 20th	Night	18% 3 9% 12% 30% 27%	2838
	21st to end	Night	15% 4 6% 10% 25% 40%	3167
September	1st to 10th	Night	18% 3 6% 15% 25% 33%	2054
	11th to 20th	Night	18% 5% 7% 17% 27% 25%	2090
	21st to end	Night	18% 3 5% 15% 33% 25%	2090
October	1st to 10th	Night	16% 4 6% 13% 33% 29%	3630
	11th to 20th	Night	21% 6% 6% 26% 28% 12%	3778
	21st to end	Night	23% 6% 6% 28% 30% 6%	4145
November	1st to 10th	Night	31% 8% 10% 24% 21% 5%	2450
	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% 28% 24% 10% 1	460
	11th to 20th	Day	15% 26% 31% 21% 6%	452
	21st to end	Day	12% 25% 28% 25% 8% 1	460
May	1st to 10th	Day	10% 23% 37% 20% 8% 1	463
	11th to 20th	Day	11% 16% 31% 29% 10% 3	488
	21st to end	Day	9% 16% 30% 29% 13% 3	529
June	1st to 10th	Day	3 13% 32% 37% 10% 4	490
	11th to 20th	Day	7% 16% 37% 27% 12% 1	490
	21st to end	Day	2 13% 33% 42% 9% 2	490
July	1st to 10th	Day	1 6% 33% 45% 13% 2	486
	11th to 20th	Day	3 6% 32% 42% 14% 3	484
	21st to end	Day	2 2 28% 47% 18% 3	531
August	1st to 10th	Day	4 7% 29% 44% 14% 2	487
	11th to 20th	Day	3 8% 28% 40% 17% 4	477
	21st to end	Day	4 7% 29% 38% 18% 3	539
September	1st to 10th	Day	3 9% 26% 39% 18% 6%	490
	11th to 20th	Day	6% 11% 30% 34% 16% 3	490
	21st to end	Day	6% 12% 25% 35% 19% 3	490
October	1st to 10th	Day	6% 15% 29% 28% 19% 4	409
	11th to 20th	Day	6% 13% 31% 25% 21% 3	300
	21st to end	Day	8% 15% 32% 30% 14% 1	330
November	1st to 10th	Day	15% 15% 26% 26% 15% 3	279
	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	755
	11th to 20th	Night	7% 14% 29% 36% 12% 2	563
	21st to end	Night	9% 11% 25% 35% 17% 3	570
May	1st to 10th	Night	8% 10% 29% 36% 16% 2	570
	11th to 20th	Night	7% 6% 20% 37% 26% 4	561
	21st to end	Night	8% 7% 24% 32% 24% 5%	617
June	1st to 10th	Night	6% 8% 18% 41% 25% 2	570
	11th to 20th	Night	5% 11% 23% 38% 21% 2	570
	21st to end	Night	3 4 22% 39% 27% 4	570
July	1st to 10th	Night	2 4 19% 38% 34% 3	555
	11th to 20th	Night	4 2 18% 44% 31% 2	552
	21st to end	Night	5% 2 12% 34% 45% 2	624
August	1st to 10th	Night	4 2 18% 41% 33% 2	567
	11th to 20th	Night	3 2 19% 43% 29% 4	564
	21st to end	Night	3 4 18% 40% 32% 4	627
September	1st to 10th	Night	5% 4 15% 38% 32% 5%	724
	11th to 20th	Night	4 5% 18% 38% 27% 7%	760
	21st to end	Night	6% 6% 15% 34% 29% 10%	760
October	1st to 10th	Night	6% 7% 21% 36% 26% 4	760
	11th to 20th	Night	6% 5% 21% 36% 25% 7%	760
	21st to end	Night	7% 9% 24% 33% 22% 5%	836
November	1st to 10th	Night	11% 10% 19% 34% 21% 5%	754
	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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