Glass Mountains
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glass Mountains 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	8% 5% 2 5% 3 3 4 3 5% 7% 55%	101123
	Night	8% 5% 2 4 3 3 3 3 5% 7% 57%	98010
Transparency	Day	28% 5% 10% 25% 24% 8%	104894
	Night	25% 5% 10% 24% 26% 9%	102355
Seeing	Day	10% 8% 27% 32% 19% 4	15442
	Night	10% 9% 34% 36% 11% 1	25305

By Month

Percentage Cloud Cover SE (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	8% 6% 2 7% 4 5% 4 4 5% 6% 50%	2847
	11th to 20th	Day	6% 6% 2 4 3 3 4 3 5% 7% 57%	2850
	21st to end	Day	15% 8% 3 4 2 3 2 3 4 5% 51%	3135
February	1st to 10th	Day	9% 10% 3 7% 3 3 3 2 4 5% 51%	1843
	11th to 20th	Day	7% 6% 2 5% 4 3 3 3 3 5% 58%	1849
	21st to end	Day	7% 6% 2 6% 4 3 3 4 4 5% 56%	1570
March	1st to 10th	Day	9% 7% 1 4 2 2 2 2 3 5% 62%	3267
	11th to 20th	Day	8% 6% 2 4 3 4 4 3 4 5% 58%	3480
	21st to end	Day	11% 8% 3 7% 5% 4 4 3 5% 6% 44%	3814
April	1st to 10th	Day	8% 4 2 6% 3 2 3 3 5% 8% 56%	2104
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 5% 7% 48%	2304
	21st to end	Day	14% 5% 2 4 3 3 4 3 5% 5% 52%	2470
May	1st to 10th	Day	18% 7% 2 5% 3 3 4 3 4 6% 45%	4082
	11th to 20th	Day	9% 4 2 5% 3 4 3 4 5% 8% 52%	4082
	21st to end	Day	10% 6% 2 6% 4 4 3 4 5% 6% 51%	4477
June	1st to 10th	Day	5% 4 1 4 3 4 4 3 7% 10% 53%	2470
	11th to 20th	Day	5% 3 2 3 4 4 5% 3 6% 8% 57%	2470
	21st to end	Day	5% 3 1 4 3 4 4 4 6% 8% 58%	2470
July	1st to 10th	Day	8% 5% 3 5% 4 4 4 4 5% 8% 50%	4120
	11th to 20th	Day	3 3 1 5% 3 4 4 4 6% 9% 58%	4120
	21st to end	Day	4 2 1 4 3 4 4 4 6% 9% 60%	4465
August	1st to 10th	Day	7% 3 2 5% 3 4 4 4 6% 9% 54%	4104
	11th to 20th	Day	5% 4 2 4 3 3 4 3 6% 8% 56%	4041
	21st to end	Day	4 4 1 4 3 3 3 3 5% 7% 63%	4187
September	1st to 10th	Day	8% 5% 1 4 3 4 4 3 4 6% 58%	2104
	11th to 20th	Day	10% 4 2 5% 3 4 6% 4 4 6% 52%	2090
	21st to end	Day	7% 3 1 4 3 4 3 3 5% 6% 60%	2090
October	1st to 10th	Day	9% 4 2 3 3 3 4 2 4 6% 61%	2090
	11th to 20th	Day	8% 3 1 3 2 2 2 2 3 3 70%	1914
	21st to end	Day	10% 5% 1 5% 3 2 2 3 3 4 62%	2088
November	1st to 10th	Day	6% 4 2 3 2 3 3 2 4 6% 65%	1700
	11th to 20th	Day	6% 5% 2 3 2 2 3 2 4 6% 66%	1710
	21st to end	Day	9% 5% 2 4 2 3 3 2 4 7% 60%	1710
December	1st to 10th	Day	7% 6% 2 5% 3 3 3 3 4 6% 58%	1710
	11th to 20th	Day	9% 6% 2 4 4 3 4 3 4 5% 56%	2161
	21st to end	Day	7% 9% 3 9% 6% 4 5% 3 5% 6% 43%	3135
January	1st to 10th	Night	9% 8% 3 5% 3 3 4 3 4 6% 54%	4108
	11th to 20th	Night	5% 4 1 4 3 4 4 4 4 6% 60%	4120
	21st to end	Night	16% 7% 2 4 3 2 3 3 3 4 52%	4532
February	1st to 10th	Night	10% 9% 3 6% 3 3 2 3 5% 5% 51%	2352
	11th to 20th	Night	9% 7% 2 5% 3 3 3 3 5% 6% 54%	2218
	21st to end	Night	6% 5% 3 5% 3 3 3 4 4 7% 58%	1884
March	1st to 10th	Night	5% 6% 2 5% 4 3 3 3 5% 6% 60%	3590
	11th to 20th	Night	9% 5% 1 4 2 3 2 3 4 6% 61%	3480
	21st to end	Night	8% 6% 2 5% 4 4 4 3 5% 7% 51%	3817
April	1st to 10th	Night	9% 4 1 3 3 3 3 3 5% 8% 59%	2071
	11th to 20th	Night	12% 5% 2 5% 3 4 3 2 5% 7% 53%	1827
	21st to end	Night	13% 4 2 4 3 3 4 3 5% 7% 53%	1710
May	1st to 10th	Night	17% 7% 2 5% 3 2 3 2 5% 5% 49%	2823
	11th to 20th	Night	9% 4 2 5% 4 4 5% 4 7% 9% 48%	2823
	21st to end	Night	7% 4 2 3 3 3 3 3 6% 8% 58%	3090
June	1st to 10th	Night	6% 3 1 3 3 4 3 4 6% 11% 56%	1710
	11th to 20th	Night	5% 3 1 3 3 3 4 4 6% 12% 56%	1710
	21st to end	Night	5% 3 1 3 3 3 4 3 5% 9% 61%	1710
July	1st to 10th	Night	5% 5% 2 4 3 3 4 4 6% 10% 54%	2850
	11th to 20th	Night	3 3 1 4 3 4 4 4 5% 11% 60%	2850
	21st to end	Night	3 2 1 3 2 3 4 3 7% 10% 61%	3098
August	1st to 10th	Night	4 2 1 4 4 3 5% 5% 7% 10% 56%	2836
	11th to 20th	Night	5% 3 1 5% 4 5% 5% 4 7% 10% 51%	2798
	21st to end	Night	3 2 1 3 3 4 4 3 5% 9% 63%	3477
September	1st to 10th	Night	8% 3 1 3 3 3 3 3 4 7% 62%	2075
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 6% 6% 54%	2090
	21st to end	Night	5% 3 2 5% 3 3 4 3 4 6% 61%	2090
October	1st to 10th	Night	8% 4 1 3 3 3 3 2 5% 6% 61%	2090
	11th to 20th	Night	8% 3 1 3 2 2 2 2 4 4 69%	2245
	21st to end	Night	9% 3 1 3 3 2 2 2 3 4 66%	2508
November	1st to 10th	Night	8% 4 1 3 2 2 2 2 4 6% 65%	2450
	11th to 20th	Night	5% 4 1 4 3 3 3 3 3 6% 66%	2470
	21st to end	Night	10% 5% 1 3 2 3 2 2 3 6% 62%	2470
December	1st to 10th	Night	8% 5% 1 4 3 3 2 2 4 8% 60%	2470
	11th to 20th	Night	8% 5% 2 4 4 3 3 3 4 4 60%	3036
	21st to end	Night	11% 8% 2 6% 3 3 4 3 5% 6% 49%	4532

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	34% 6% 9% 24% 24% 3	2848
	11th to 20th	Day	26% 4 16% 22% 24% 7%	2850
	21st to end	Day	37% 3 6% 25% 25% 4	3135
February	1st to 10th	Day	37% 3 11% 22% 21% 6%	1843
	11th to 20th	Day	31% 4 7% 28% 22% 8%	1859
	21st to end	Day	31% 3 7% 24% 24% 11%	1570
March	1st to 10th	Day	27% 3 7% 19% 23% 21%	3267
	11th to 20th	Day	28% 5% 10% 23% 28% 7%	3480
	21st to end	Day	39% 7% 11% 24% 16% 3	3814
April	1st to 10th	Day	28% 4 10% 24% 25% 9%	2104
	11th to 20th	Day	37% 4 10% 23% 18% 9%	2304
	21st to end	Day	33% 5% 11% 26% 21% 4	2470
May	1st to 10th	Day	41% 5% 11% 16% 19% 8%	4120
	11th to 20th	Day	29% 7% 14% 28% 17% 5%	4086
	21st to end	Day	34% 6% 10% 19% 18% 13%	4489
June	1st to 10th	Day	25% 7% 19% 28% 15% 6%	2470
	11th to 20th	Day	24% 6% 13% 26% 23% 8%	2470
	21st to end	Day	21% 7% 14% 25% 24% 9%	2470
July	1st to 10th	Day	31% 6% 11% 26% 21% 6%	4056
	11th to 20th	Day	21% 6% 11% 30% 26% 5%	4051
	21st to end	Day	19% 6% 13% 30% 28% 3	4325
August	1st to 10th	Day	26% 7% 11% 28% 23% 6%	4090
	11th to 20th	Day	24% 6% 14% 30% 22% 3	4080
	21st to end	Day	20% 5% 13% 33% 25% 5%	4186
September	1st to 10th	Day	28% 5% 9% 23% 23% 12%	2104
	11th to 20th	Day	31% 6% 10% 22% 25% 6%	2090
	21st to end	Day	24% 5% 10% 23% 28% 10%	2090
October	1st to 10th	Day	16% 3 7% 16% 43% 16%	3480
	11th to 20th	Day	16% 3 6% 24% 34% 16%	3154
	21st to end	Day	21% 3 7% 26% 32% 11%	3415
November	1st to 10th	Day	21% 3 8% 24% 31% 13%	1700
	11th to 20th	Day	22% 4 8% 28% 29% 10%	1710
	21st to end	Day	27% 2 6% 28% 27% 10%	1710
December	1st to 10th	Day	28% 4 10% 30% 22% 5%	1710
	11th to 20th	Day	31% 4 9% 21% 28% 7%	2159
	21st to end	Day	39% 6% 9% 23% 19% 4	3135
January	1st to 10th	Night	32% 5% 10% 28% 20% 5%	4108
	11th to 20th	Night	23% 6% 16% 22% 27% 6%	4120
	21st to end	Night	36% 4 8% 21% 26% 5%	4532
February	1st to 10th	Night	36% 4 8% 24% 21% 7%	2352
	11th to 20th	Night	32% 4 9% 24% 23% 8%	2218
	21st to end	Night	27% 4 8% 21% 25% 15%	1884
March	1st to 10th	Night	25% 5% 7% 19% 23% 21%	3590
	11th to 20th	Night	25% 4 9% 28% 26% 8%	3480
	21st to end	Night	31% 7% 10% 26% 20% 6%	3817
April	1st to 10th	Night	24% 5% 10% 22% 26% 13%	2071
	11th to 20th	Night	31% 5% 11% 25% 18% 10%	1827
	21st to end	Night	31% 6% 10% 26% 23% 4	1710
May	1st to 10th	Night	37% 6% 9% 15% 21% 11%	2850
	11th to 20th	Night	31% 8% 16% 25% 17% 3	2824
	21st to end	Night	23% 6% 13% 23% 22% 13%	3099
June	1st to 10th	Night	22% 8% 18% 31% 17% 5%	1710
	11th to 20th	Night	22% 6% 14% 30% 22% 7%	1710
	21st to end	Night	19% 5% 13% 28% 22% 12%	1710
July	1st to 10th	Night	25% 6% 15% 27% 24% 4	2805
	11th to 20th	Night	18% 5% 11% 28% 32% 6%	2796
	21st to end	Night	18% 5% 15% 30% 30% 3	2999
August	1st to 10th	Night	20% 7% 14% 25% 26% 8%	2826
	11th to 20th	Night	25% 6% 14% 27% 23% 5%	2825
	21st to end	Night	19% 6% 13% 36% 22% 5%	3477
September	1st to 10th	Night	23% 4 9% 25% 27% 11%	2075
	11th to 20th	Night	29% 6% 10% 20% 26% 8%	2090
	21st to end	Night	23% 6% 8% 23% 29% 11%	2090
October	1st to 10th	Night	16% 4 7% 15% 36% 22%	3480
	11th to 20th	Night	14% 3 5% 22% 37% 18%	3731
	21st to end	Night	16% 3 6% 25% 39% 12%	4120
November	1st to 10th	Night	21% 3 10% 21% 30% 15%	2450
	11th to 20th	Night	21% 4 8% 25% 31% 11%	2470
	21st to end	Night	26% 3 7% 23% 29% 12%	2470
December	1st to 10th	Night	25% 4 10% 28% 27% 6%	2470
	11th to 20th	Night	29% 3 7% 26% 28% 8%	3037
	21st to end	Night	34% 6% 9% 22% 22% 7%	4532

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	10% 11% 40% 27% 11% 1	270
	11th to 20th	Day	14% 17% 36% 27% 5%	270
	21st to end	Day	10% 13% 45% 25% 6%	297
February	1st to 10th	Day	14% 15% 40% 25% 5%	270
	11th to 20th	Day	14% 14% 43% 21% 8%	270
	21st to end	Day	12% 19% 43% 22% 3	225
March	1st to 10th	Day	11% 14% 40% 28% 6%	270
	11th to 20th	Day	16% 20% 35% 21% 7%	270
	21st to end	Day	18% 18% 39% 21% 5%	297
April	1st to 10th	Day	14% 17% 43% 20% 7%	284
	11th to 20th	Day	13% 21% 39% 24% 3	502
	21st to end	Day	17% 16% 36% 22% 8% 1	650
May	1st to 10th	Day	14% 11% 41% 26% 8% 1	653
	11th to 20th	Day	15% 9% 27% 31% 16% 2	675
	21st to end	Day	12% 8% 32% 30% 15% 3	734
June	1st to 10th	Day	7% 5% 21% 39% 22% 5%	680
	11th to 20th	Day	5% 5% 29% 38% 20% 3	680
	21st to end	Day	4 3 26% 43% 20% 5%	680
July	1st to 10th	Day	6% 2 13% 36% 32% 10%	671
	11th to 20th	Day	3 1 12% 43% 33% 7%	668
	21st to end	Day	5% 1 8% 39% 37% 10%	739
August	1st to 10th	Day	6% 1 13% 43% 32% 5%	676
	11th to 20th	Day	7% 2 14% 38% 34% 6%	665
	21st to end	Day	4 1 11% 37% 36% 10%	546
September	1st to 10th	Day	8% 1 11% 33% 37% 11%	314
	11th to 20th	Day	6% 1 21% 39% 29% 5%	300
	21st to end	Day	8% 4 21% 37% 22% 8%	300
October	1st to 10th	Day	9% 3 31% 29% 22% 6%	300
	11th to 20th	Day	7% 9% 37% 31% 13% 3	300
	21st to end	Day	18% 11% 33% 22% 13% 3	330
November	1st to 10th	Day	10% 10% 34% 33% 12% 2	279
	11th to 20th	Day	9% 14% 34% 26% 15% 2	270
	21st to end	Day	16% 14% 32% 26% 10% 3	270
December	1st to 10th	Day	9% 9% 42% 28% 11% 1	270
	11th to 20th	Day	11% 15% 33% 30% 10% 1	270
	21st to end	Day	16% 20% 35% 23% 6%	297
January	1st to 10th	Night	8% 10% 40% 35% 7%	950
	11th to 20th	Night	11% 12% 38% 33% 6%	950
	21st to end	Night	11% 10% 40% 33% 6%	1045
February	1st to 10th	Night	13% 12% 41% 29% 4	832
	11th to 20th	Night	13% 14% 40% 29% 4	744
	21st to end	Night	10% 15% 43% 29% 3	628
March	1st to 10th	Night	8% 14% 39% 36% 4	681
	11th to 20th	Night	16% 12% 36% 31% 6%	570
	21st to end	Night	15% 14% 41% 25% 5%	627
April	1st to 10th	Night	11% 15% 42% 26% 7%	570
	11th to 20th	Night	14% 15% 44% 23% 3	563
	21st to end	Night	16% 13% 37% 27% 6% 1	570
May	1st to 10th	Night	13% 11% 42% 28% 6%	570
	11th to 20th	Night	11% 6% 34% 34% 13% 1	561
	21st to end	Night	8% 8% 34% 36% 12% 1	617
June	1st to 10th	Night	8% 5% 29% 39% 18% 1	570
	11th to 20th	Night	5% 4 36% 45% 10%	570
	21st to end	Night	5% 3 33% 47% 12%	570
July	1st to 10th	Night	5% 1 19% 48% 25% 2	555
	11th to 20th	Night	3 1 17% 52% 25% 2	552
	21st to end	Night	5% 1 11% 53% 29% 1	624
August	1st to 10th	Night	4 1 16% 52% 26% 1	567
	11th to 20th	Night	6% 1 15% 53% 23% 1	564
	21st to end	Night	3 1 15% 46% 32% 3	627
September	1st to 10th	Night	9% 2 17% 46% 25% 2	570
	11th to 20th	Night	13% 2 25% 40% 19% 2	570
	21st to end	Night	6% 4 28% 42% 18% 1	570
October	1st to 10th	Night	10% 4 29% 37% 19% 1	570
	11th to 20th	Night	10% 8% 39% 36% 7%	725
	21st to end	Night	11% 9% 36% 30% 13%	836
November	1st to 10th	Night	10% 7% 37% 35% 10% 1	942
	11th to 20th	Night	8% 10% 40% 33% 8%	950
	21st to end	Night	11% 12% 33% 35% 9%	950
December	1st to 10th	Night	10% 10% 37% 34% 8%	950
	11th to 20th	Night	14% 11% 40% 31% 5%	950
	21st to end	Night	12% 13% 38% 32% 5%	1045

Page generated at 2024-11-01 21:47:33. Version ac07

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