Dun Glen
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dun Glen clear sky chart from 2005-11-06 to 2024-11-03.

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	3 6% 2 5% 4 4 4 3 5% 7% 58%	101171
	Night	4 7% 2 6% 4 4 4 4 5% 7% 52%	97978
Transparency	Day	25% 4 8% 18% 22% 23%	100912
	Night	30% 5% 9% 19% 20% 17%	97827
Seeing	Day	6% 8% 22% 32% 24% 9%	14798
	Night	7% 4 15% 40% 27% 6%	24161

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	5% 15% 7% 10% 5% 5% 5% 5% 7% 9% 27%	2539
	11th to 20th	Day	6% 13% 4 12% 7% 5% 5% 5% 6% 9% 28%	2540
	21st to end	Day	6% 13% 5% 10% 7% 7% 6% 6% 7% 11% 23%	2894
February	1st to 10th	Day	4 8% 3 8% 6% 5% 6% 3 7% 10% 41%	1805
	11th to 20th	Day	3 8% 3 8% 6% 5% 5% 4 7% 9% 42%	1850
	21st to end	Day	2 8% 3 7% 5% 5% 5% 4 7% 10% 43%	1570
March	1st to 10th	Day	3 11% 4 12% 7% 6% 6% 5% 7% 9% 31%	3138
	11th to 20th	Day	2 6% 2 5% 4 4 3 3 6% 11% 53%	3241
	21st to end	Day	3 10% 3 9% 7% 6% 6% 5% 7% 8% 36%	4165
April	1st to 10th	Day	5% 9% 3 7% 5% 5% 5% 4 6% 8% 42%	2280
	11th to 20th	Day	5% 8% 2 6% 6% 4 4 4 5% 8% 48%	2249
	21st to end	Day	6% 8% 2 6% 4 4 4 3 5% 8% 50%	2365
May	1st to 10th	Day	4 6% 2 5% 3 3 3 4 5% 8% 57%	4110
	11th to 20th	Day	4 4 2 3 2 2 2 3 4 5% 69%	4154
	21st to end	Day	4 4 1 5% 3 4 4 3 5% 6% 61%	4813
June	1st to 10th	Day	4 5% 1 4 4 4 4 5% 6% 7% 56%	2660
	11th to 20th	Day	3 3 1 3 3 3 3 3 3 6% 69%	2660
	21st to end	Day	2 2 1 2 2 2 2 2 4 4 75%	2660
July	1st to 10th	Day	1 1 1 1 2 1 2 2 3 86%	4420
	11th to 20th	Day	1 2 1 3 2 2 3 3 4 6% 73%	4420
	21st to end	Day	2 2 1 3 2 3 3 3 5% 6% 69%	4790
August	1st to 10th	Day	3 2 1 3 2 2 2 2 4 6% 72%	4177
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 85%	3724
	21st to end	Day	2 2 1 2 2 2 2 2 2 3 82%	4180
September	1st to 10th	Day	1 2 1 1 1 1 2 2 3 4 81%	2280
	11th to 20th	Day	3 2 1 2 3 3 3 3 5% 5% 70%	2161
	21st to end	Day	2 3 1 3 2 2 2 2 4 6% 74%	2090
October	1st to 10th	Day	5% 4 1 4 4 3 3 2 4 4 65%	2071
	11th to 20th	Day	3 4 1 4 3 2 3 3 4 6% 66%	1900
	21st to end	Day	3 3 2 4 3 3 3 4 5% 8% 63%	1895
November	1st to 10th	Day	4 9% 2 7% 4 4 3 4 5% 6% 52%	1692
	11th to 20th	Day	5% 6% 2 5% 3 3 3 5% 6% 10% 52%	1710
	21st to end	Day	4 8% 4 7% 5% 4 4 3 5% 8% 49%	1710
December	1st to 10th	Day	5% 7% 3 7% 7% 5% 5% 3 5% 7% 45%	1536
	11th to 20th	Day	5% 9% 4 10% 7% 7% 6% 5% 9% 10% 28%	1928
	21st to end	Day	5% 10% 4 9% 8% 6% 5% 4 7% 9% 34%	2794
January	1st to 10th	Night	4 12% 5% 11% 6% 6% 5% 5% 7% 9% 32%	4406
	11th to 20th	Night	9% 11% 4 10% 6% 5% 5% 4 7% 7% 30%	4420
	21st to end	Night	6% 12% 4 8% 6% 5% 7% 5% 7% 10% 30%	4762
February	1st to 10th	Night	4 8% 3 8% 4 4 5% 4 6% 7% 46%	2372
	11th to 20th	Night	3 7% 3 8% 5% 5% 5% 4 6% 8% 45%	2218
	21st to end	Night	2 9% 3 8% 5% 5% 5% 6% 8% 8% 41%	1884
March	1st to 10th	Night	3 12% 6% 11% 6% 5% 5% 4 5% 8% 35%	3736
	11th to 20th	Night	4 7% 2 6% 5% 5% 3 4 5% 8% 52%	3721
	21st to end	Night	5% 10% 3 8% 6% 5% 6% 5% 8% 9% 34%	3488
April	1st to 10th	Night	5% 8% 3 7% 6% 5% 5% 5% 6% 8% 43%	1900
	11th to 20th	Night	5% 7% 3 5% 4 4 4 3 5% 7% 52%	1879
	21st to end	Night	7% 7% 2 5% 4 4 4 2 5% 6% 54%	1812
May	1st to 10th	Night	6% 7% 2 5% 3 2 3 3 4 5% 59%	2860
	11th to 20th	Night	4 3 1 3 3 2 3 2 4 6% 68%	2743
	21st to end	Night	4 5% 2 4 4 3 4 3 5% 7% 60%	2762
June	1st to 10th	Night	6% 5% 2 4 4 4 4 3 6% 7% 56%	1520
	11th to 20th	Night	3 3 1 4 3 3 4 2 4 5% 68%	1520
	21st to end	Night	2 2 1 2 3 3 3 3 4 6% 71%	1520
July	1st to 10th	Night	1 1 2 2 2 2 2 4 3 82%	2540
	11th to 20th	Night	3 4 1 4 3 3 3 3 4 6% 65%	2540
	21st to end	Night	3 3 1 5% 3 4 4 4 6% 8% 60%	2761
August	1st to 10th	Night	3 3 1 4 3 3 3 3 4 6% 65%	2743
	11th to 20th	Night	2 3 1 3 1 2 2 2 3 4 78%	3126
	21st to end	Night	3 2 1 2 2 1 1 2 2 3 80%	3498
September	1st to 10th	Night	3 3 1 3 2 2 2 2 3 4 75%	1900
	11th to 20th	Night	4 3 1 3 3 3 3 3 4 5% 69%	2019
	21st to end	Night	3 2 1 2 2 3 2 2 3 5% 75%	2090
October	1st to 10th	Night	5% 4 2 4 3 3 4 2 3 3 68%	2106
	11th to 20th	Night	3 4 2 4 3 2 4 3 5% 4 67%	2280
	21st to end	Night	5% 2 1 4 2 3 3 3 4 8% 65%	2702
November	1st to 10th	Night	5% 7% 2 5% 4 4 4 4 7% 7% 49%	2431
	11th to 20th	Night	4 6% 2 7% 4 3 4 4 6% 8% 52%	2470
	21st to end	Night	5% 7% 3 6% 5% 5% 5% 4 5% 7% 51%	2470
December	1st to 10th	Night	6% 8% 3 7% 5% 4 5% 4 6% 8% 43%	2641
	11th to 20th	Night	6% 11% 4 10% 6% 5% 5% 5% 8% 10% 31%	3276
	21st to end	Night	6% 10% 4 10% 7% 7% 6% 5% 8% 8% 29%	4862

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	49% 8% 15% 23% 4	2539
	11th to 20th	Day	50% 10% 17% 14% 7% 2	2540
	21st to end	Day	53% 8% 12% 18% 7% 2	2894
February	1st to 10th	Day	37% 6% 14% 27% 13% 3	1805
	11th to 20th	Day	37% 7% 13% 23% 17% 3	1860
	21st to end	Day	33% 7% 16% 25% 15% 4	1570
March	1st to 10th	Day	44% 6% 13% 18% 17% 2	3138
	11th to 20th	Day	25% 4 13% 40% 16% 2	3241
	21st to end	Day	40% 9% 14% 22% 14% 2	4165
April	1st to 10th	Day	39% 5% 10% 24% 16% 6%	2280
	11th to 20th	Day	33% 5% 11% 23% 21% 7%	2252
	21st to end	Day	31% 5% 10% 29% 22% 3	2365
May	1st to 10th	Day	23% 6% 8% 31% 25% 7%	4110
	11th to 20th	Day	19% 3 5% 17% 45% 12%	4157
	21st to end	Day	23% 5% 6% 22% 39% 6%	4814
June	1st to 10th	Day	25% 5% 8% 19% 30% 13%	2660
	11th to 20th	Day	18% 3 5% 16% 32% 27%	2660
	21st to end	Day	14% 2 3 10% 30% 41%	2660
July	1st to 10th	Day	6% 1 2 5% 13% 73%	4351
	11th to 20th	Day	11% 2 4 6% 15% 62%	4345
	21st to end	Day	14% 4 4 8% 24% 47%	4639
August	1st to 10th	Day	14% 2 2 6% 18% 57%	4161
	11th to 20th	Day	7% 1 3 5% 20% 65%	3760
	21st to end	Day	9% 2 2 8% 30% 49%	4179
September	1st to 10th	Day	9% 2 2 8% 28% 52%	2280
	11th to 20th	Day	16% 3 5% 13% 30% 33%	2161
	21st to end	Day	14% 2 5% 17% 31% 31%	2090
October	1st to 10th	Day	23% 3 6% 17% 28% 23%	2071
	11th to 20th	Day	20% 4 6% 22% 32% 17%	1900
	21st to end	Day	20% 3 9% 31% 25% 12%	1895
November	1st to 10th	Day	33% 5% 9% 23% 22% 8%	1692
	11th to 20th	Day	28% 5% 13% 28% 23% 3	1710
	21st to end	Day	34% 4 11% 26% 21% 4	1710
December	1st to 10th	Day	38% 6% 13% 24% 15% 4	1536
	11th to 20th	Day	45% 9% 15% 18% 12% 1	1928
	21st to end	Day	44% 7% 17% 21% 11%	2794
January	1st to 10th	Night	43% 10% 16% 23% 7% 1	4406
	11th to 20th	Night	50% 7% 16% 13% 10% 3	4420
	21st to end	Night	46% 8% 11% 23% 9% 2	4762
February	1st to 10th	Night	35% 6% 13% 27% 16% 3	2372
	11th to 20th	Night	35% 5% 12% 26% 18% 4	2219
	21st to end	Night	35% 7% 14% 23% 16% 5%	1884
March	1st to 10th	Night	45% 6% 12% 19% 13% 6%	3736
	11th to 20th	Night	30% 5% 9% 32% 22% 3	3721
	21st to end	Night	40% 9% 15% 25% 10% 2	3488
April	1st to 10th	Night	37% 6% 10% 25% 16% 5%	1900
	11th to 20th	Night	31% 5% 10% 27% 20% 8%	1879
	21st to end	Night	32% 4 10% 26% 23% 4	1812
May	1st to 10th	Night	26% 4 5% 29% 28% 9%	2860
	11th to 20th	Night	17% 4 6% 15% 45% 14%	2744
	21st to end	Night	24% 6% 7% 21% 37% 6%	2762
June	1st to 10th	Night	27% 5% 6% 24% 26% 12%	1520
	11th to 20th	Night	19% 3 5% 16% 35% 21%	1520
	21st to end	Night	13% 3 5% 11% 28% 39%	1520
July	1st to 10th	Night	9% 2 3 4 13% 69%	2500
	11th to 20th	Night	19% 3 3 5% 13% 57%	2492
	21st to end	Night	19% 6% 4 9% 21% 41%	2674
August	1st to 10th	Night	19% 3 3 7% 17% 51%	2735
	11th to 20th	Night	12% 2 3 5% 19% 60%	3156
	21st to end	Night	12% 2 2 7% 27% 51%	3498
September	1st to 10th	Night	15% 2 2 6% 25% 50%	1900
	11th to 20th	Night	18% 3 4 12% 27% 36%	2019
	21st to end	Night	14% 2 4 15% 29% 36%	2090
October	1st to 10th	Night	22% 3 5% 17% 26% 27%	2106
	11th to 20th	Night	20% 4 5% 20% 31% 21%	2280
	21st to end	Night	18% 3 8% 28% 29% 13%	2702
November	1st to 10th	Night	31% 6% 11% 21% 22% 10%	2431
	11th to 20th	Night	29% 4 12% 24% 27% 4	2470
	21st to end	Night	32% 4 9% 24% 24% 6%	2470
December	1st to 10th	Night	37% 6% 13% 23% 16% 5%	2641
	11th to 20th	Night	45% 7% 13% 21% 11% 4	3276
	21st to end	Night	47% 7% 15% 18% 12% 1	4862

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	9% 9% 26% 26% 26% 5%	180
	11th to 20th	Day	6% 4 25% 28% 27% 10%	180
	21st to end	Day	10% 3 19% 29% 27% 11%	259
February	1st to 10th	Day	7% 5% 22% 38% 21% 7%	415
	11th to 20th	Day	8% 9% 24% 38% 18% 2	455
	21st to end	Day	6% 7% 26% 38% 20% 3	382
March	1st to 10th	Day	11% 9% 24% 33% 20% 3	460
	11th to 20th	Day	6% 12% 27% 29% 21% 5%	460
	21st to end	Day	9% 13% 25% 34% 16% 3	506
April	1st to 10th	Day	9% 12% 25% 26% 21% 6%	460
	11th to 20th	Day	9% 13% 28% 28% 17% 6%	452
	21st to end	Day	9% 14% 22% 27% 22% 6%	460
May	1st to 10th	Day	6% 17% 29% 26% 16% 6%	463
	11th to 20th	Day	14% 9% 25% 26% 18% 8%	488
	21st to end	Day	11% 9% 19% 27% 24% 10%	529
June	1st to 10th	Day	4 11% 20% 32% 24% 10%	490
	11th to 20th	Day	6% 15% 25% 33% 16% 6%	490
	21st to end	Day	3 8% 23% 33% 25% 9%	490
July	1st to 10th	Day	1 3 22% 37% 28% 10%	486
	11th to 20th	Day	1 3 19% 37% 30% 10%	484
	21st to end	Day	2 2 17% 37% 27% 14%	531
August	1st to 10th	Day	5% 3 20% 32% 28% 13%	487
	11th to 20th	Day	3 5% 19% 31% 28% 15%	477
	21st to end	Day	2 5% 16% 37% 30% 10%	539
September	1st to 10th	Day	1 3 19% 32% 29% 16%	490
	11th to 20th	Day	6% 7% 17% 34% 24% 12%	490
	21st to end	Day	4 5% 25% 29% 28% 10%	490
October	1st to 10th	Day	5% 8% 22% 27% 26% 11%	490
	11th to 20th	Day	7% 8% 18% 28% 29% 10%	490
	21st to end	Day	6% 8% 23% 30% 24% 9%	344
November	1st to 10th	Day	8% 8% 25% 28% 24% 7%	276
	11th to 20th	Day	5% 4 20% 33% 29% 9%	270
	21st to end	Day	10% 7% 17% 34% 25% 7%	270
December	1st to 10th	Day	6% 6% 21% 34% 21% 12%	187
	11th to 20th	Day	10% 6% 22% 32% 21% 9%	180
	21st to end	Day	15% 6% 15% 36% 23% 6%	198
January	1st to 10th	Night	9% 5% 19% 37% 23% 8%	760
	11th to 20th	Night	7% 4 18% 41% 24% 6%	760
	21st to end	Night	13% 3 13% 40% 25% 7%	836
February	1st to 10th	Night	7% 4 18% 43% 24% 4	760
	11th to 20th	Night	7% 4 19% 43% 23% 4	744
	21st to end	Night	6% 5% 22% 44% 19% 3	628
March	1st to 10th	Night	10% 5% 21% 42% 19% 4	760
	11th to 20th	Night	7% 6% 17% 40% 27% 3	760
	21st to end	Night	10% 7% 21% 41% 17% 3	836
April	1st to 10th	Night	9% 6% 21% 40% 21% 3	760
	11th to 20th	Night	10% 8% 18% 39% 19% 6%	751
	21st to end	Night	11% 5% 18% 35% 25% 5%	672
May	1st to 10th	Night	7% 9% 23% 36% 21% 3	570
	11th to 20th	Night	7% 5% 19% 38% 26% 6%	510
	21st to end	Night	8% 6% 15% 33% 33% 6%	411
June	1st to 10th	Night	7% 3 18% 39% 27% 6%	380
	11th to 20th	Night	5% 4 19% 40% 30% 2	380
	21st to end	Night	2 3 14% 49% 30% 3	380
July	1st to 10th	Night	2 1 11% 49% 33% 3	370
	11th to 20th	Night	2 1 7% 50% 38% 2	368
	21st to end	Night	3 1 6% 42% 42% 6%	416
August	1st to 10th	Night	5% 2 10% 43% 38% 3	501
	11th to 20th	Night	3 2 9% 39% 40% 7%	752
	21st to end	Night	3 1 6% 41% 42% 7%	836
September	1st to 10th	Night	3 3 7% 38% 40% 9%	760
	11th to 20th	Night	5% 2 10% 34% 37% 12%	760
	21st to end	Night	4 3 9% 38% 33% 13%	760
October	1st to 10th	Night	7% 3 12% 38% 34% 7%	760
	11th to 20th	Night	6% 4 11% 39% 33% 7%	760
	21st to end	Night	6% 3 13% 41% 27% 10%	836
November	1st to 10th	Night	8% 4 17% 35% 29% 7%	748
	11th to 20th	Night	8% 3 14% 46% 24% 5%	760
	21st to end	Night	9% 3 18% 38% 28% 5%	760
December	1st to 10th	Night	9% 4 17% 44% 20% 6%	760
	11th to 20th	Night	15% 4 16% 38% 22% 5%	760
	21st to end	Night	14% 6% 20% 41% 16% 2	836

Page generated at 2024-10-31 00:39:27. Version ac07

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