Highland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highland clear sky chart from 2005-11-06 to 2026-08-30.

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	5% 7% 2 6% 4 4 4 4 5% 7% 52%	152040
	Night	6% 7% 2 6% 4 4 4 4 5% 7% 52%	147712
Transparency	Day	30% 6% 11% 19% 21% 13%	146776
	Night	31% 6% 12% 20% 20% 11%	143983
Seeing	Day	12% 11% 25% 31% 18% 3	17216
	Night	12% 6% 22% 37% 21% 3	27775

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	10% 14% 5% 10% 6% 5% 5% 4 6% 6% 30%	5318
	11th to 20th	Day	6% 10% 3 12% 5% 4 4 3 4 4 45%	5340
	21st to end	Day	5% 10% 4 8% 4 4 4 3 4 6% 48%	5844
February	1st to 10th	Day	10% 13% 3 9% 5% 6% 5% 3 5% 6% 35%	1890
	11th to 20th	Day	9% 14% 4 10% 6% 5% 5% 5% 6% 6% 31%	1923
	21st to end	Day	8% 14% 4 9% 6% 4 4 4 6% 8% 34%	1730
March	1st to 10th	Day	5% 14% 4 7% 5% 5% 6% 4 5% 7% 37%	4947
	11th to 20th	Day	6% 10% 3 7% 5% 6% 6% 5% 6% 7% 38%	5110
	21st to end	Day	7% 16% 5% 12% 6% 5% 5% 4 4 6% 30%	5607
April	1st to 10th	Day	8% 9% 3 8% 4 4 5% 4 7% 8% 41%	2329
	11th to 20th	Day	8% 9% 2 7% 5% 4 5% 4 6% 7% 41%	2645
	21st to end	Day	8% 8% 3 7% 5% 4 4 3 5% 8% 45%	2730
May	1st to 10th	Day	6% 7% 2 5% 4 4 5% 4 5% 7% 51%	7626
	11th to 20th	Day	6% 5% 2 6% 4 5% 5% 4 6% 8% 50%	7596
	21st to end	Day	5% 4 2 6% 4 4 5% 4 5% 8% 54%	8370
June	1st to 10th	Day	4 4 2 5% 3 4 3 4 6% 9% 56%	2730
	11th to 20th	Day	5% 4 2 3 3 2 3 3 4 6% 64%	2793
	21st to end	Day	3 3 1 3 2 3 4 3 4 5% 70%	2730
July	1st to 10th	Day	1 2 1 3 3 3 3 3 4 6% 72%	7649
	11th to 20th	Day	2 2 1 4 3 4 5% 4 7% 9% 58%	7650
	21st to end	Day	2 2 1 3 3 3 4 4 5% 6% 67%	8304
August	1st to 10th	Day	2 2 1 3 2 3 4 3 5% 6% 69%	5909
	11th to 20th	Day	2 2 1 4 3 4 4 3 4 5% 70%	5928
	21st to end	Day	4 3 1 5% 4 4 5% 4 5% 7% 59%	6525
September	1st to 10th	Day	3 3 1 3 2 3 4 3 5% 6% 68%	2256
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 6% 63%	2200
	21st to end	Day	5% 3 1 3 3 3 2 3 4 5% 68%	2200
October	1st to 10th	Day	5% 3 1 3 3 2 3 3 3 4 68%	3438
	11th to 20th	Day	6% 5% 2 5% 3 3 3 3 5% 7% 59%	3250
	21st to end	Day	6% 6% 3 6% 3 3 3 3 4 6% 58%	3548
November	1st to 10th	Day	10% 6% 2 5% 5% 4 3 3 5% 6% 50%	1856
	11th to 20th	Day	11% 7% 3 6% 4 5% 4 3 6% 7% 44%	1890
	21st to end	Day	8% 9% 4 8% 5% 6% 5% 3 6% 6% 42%	1764
December	1st to 10th	Day	7% 6% 1 5% 3 3 4 4 4 10% 54%	2700
	11th to 20th	Day	9% 10% 3 8% 5% 5% 5% 4 6% 9% 36%	3106
	21st to end	Day	12% 11% 4 9% 5% 5% 5% 4 6% 7% 30%	4609
January	1st to 10th	Night	11% 12% 4 8% 5% 5% 6% 5% 6% 7% 33%	7605
	11th to 20th	Night	7% 10% 2 8% 4 4 4 3 4 5% 49%	7650
	21st to end	Night	4 9% 4 7% 4 3 3 3 5% 7% 51%	8370
February	1st to 10th	Night	8% 11% 3 7% 5% 5% 5% 5% 6% 7% 38%	2730
	11th to 20th	Night	8% 11% 3 8% 5% 4 5% 4 5% 6% 40%	2581
	21st to end	Night	7% 11% 3 9% 4 5% 4 4 6% 6% 40%	2076
March	1st to 10th	Night	6% 13% 5% 9% 5% 5% 5% 4 5% 6% 37%	5166
	11th to 20th	Night	6% 9% 3 8% 5% 4 5% 4 6% 8% 41%	5110
	21st to end	Night	9% 12% 4 8% 4 4 4 4 5% 6% 40%	5610
April	1st to 10th	Night	11% 10% 2 6% 3 3 3 3 5% 7% 47%	2289
	11th to 20th	Night	7% 7% 2 6% 5% 4 6% 5% 5% 7% 46%	1918
	21st to end	Night	9% 6% 3 6% 5% 4 5% 4 5% 6% 47%	1890
May	1st to 10th	Night	6% 6% 2 5% 4 4 5% 4 6% 7% 52%	5321
	11th to 20th	Night	5% 4 2 4 4 4 4 3 5% 7% 58%	5296
	21st to end	Night	6% 4 2 5% 3 3 4 3 5% 7% 57%	5837
June	1st to 10th	Night	6% 4 1 4 3 3 5% 4 5% 8% 57%	1888
	11th to 20th	Night	5% 4 1 4 2 3 2 2 4 6% 67%	1748
	21st to end	Night	3 3 1 4 2 2 3 3 4 7% 66%	1890
July	1st to 10th	Night	3 2 2 5% 4 4 3 3 4 5% 65%	5340
	11th to 20th	Night	2 3 2 5% 4 5% 5% 5% 8% 9% 51%	5340
	21st to end	Night	2 4 1 5% 3 4 5% 4 6% 7% 59%	5805
August	1st to 10th	Night	2 2 1 3 3 3 3 4 6% 7% 66%	4123
	11th to 20th	Night	2 3 1 5% 3 3 4 4 5% 6% 63%	4141
	21st to end	Night	5% 4 2 6% 4 5% 5% 4 4 5% 56%	4651
September	1st to 10th	Night	3 3 1 4 3 3 4 3 4 6% 66%	2140
	11th to 20th	Night	6% 3 1 4 3 3 4 3 5% 7% 62%	2200
	21st to end	Night	6% 3 2 4 3 2 2 2 3 5% 69%	2200
October	1st to 10th	Night	5% 3 1 3 3 2 3 2 3 5% 71%	3756
	11th to 20th	Night	9% 5% 2 4 3 2 3 3 4 5% 60%	3898
	21st to end	Night	5% 5% 2 5% 3 3 4 4 5% 7% 58%	4252
November	1st to 10th	Night	10% 7% 2 4 2 3 3 4 6% 7% 52%	2660
	11th to 20th	Night	9% 5% 1 5% 4 3 4 3 5% 8% 51%	2730
	21st to end	Night	8% 8% 3 6% 4 3 4 4 5% 7% 48%	2830
December	1st to 10th	Night	6% 6% 2 4 3 2 4 3 5% 6% 60%	4710
	11th to 20th	Night	10% 12% 3 5% 3 3 4 3 5% 6% 44%	5321
	21st to end	Night	9% 10% 4 9% 5% 6% 6% 4 6% 7% 33%	6640

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% 12% 18% 14% 6% 1	5321
	11th to 20th	Day	39% 7% 14% 22% 14% 4	5340
	21st to end	Day	35% 9% 16% 18% 19% 3	5844
February	1st to 10th	Day	50% 10% 14% 15% 10% 1	1890
	11th to 20th	Day	50% 6% 15% 18% 10% 1	1932
	21st to end	Day	46% 5% 15% 21% 11% 2	1730
March	1st to 10th	Day	40% 8% 14% 21% 12% 5%	4947
	11th to 20th	Day	36% 10% 13% 28% 11% 2	5110
	21st to end	Day	53% 5% 19% 16% 6% 1	5607
April	1st to 10th	Day	41% 6% 13% 20% 16% 5%	2329
	11th to 20th	Day	39% 4 13% 22% 17% 3	2648
	21st to end	Day	36% 5% 12% 25% 20% 2	2730
May	1st to 10th	Day	29% 6% 11% 24% 25% 6%	7626
	11th to 20th	Day	27% 9% 8% 22% 29% 6%	7599
	21st to end	Day	26% 6% 9% 26% 30% 4	8371
June	1st to 10th	Day	23% 4 9% 21% 32% 11%	2730
	11th to 20th	Day	21% 2 6% 16% 29% 25%	2793
	21st to end	Day	16% 2 3 12% 29% 37%	2730
July	1st to 10th	Day	13% 3 4 7% 19% 55%	7586
	11th to 20th	Day	18% 6% 12% 14% 22% 28%	7581
	21st to end	Day	16% 4 8% 14% 23% 35%	8120
August	1st to 10th	Day	19% 4 7% 21% 25% 25%	4338
	11th to 20th	Day	21% 4 6% 18% 27% 25%	4327
	21st to end	Day	18% 4 6% 16% 30% 28%	4732
September	1st to 10th	Day	16% 3 7% 17% 28% 29%	2256
	11th to 20th	Day	20% 3 9% 19% 27% 22%	2200
	21st to end	Day	18% 4 6% 21% 32% 20%	2200
October	1st to 10th	Day	20% 3 5% 16% 38% 18%	3438
	11th to 20th	Day	26% 6% 8% 28% 27% 6%	3250
	21st to end	Day	28% 6% 12% 27% 23% 4	3548
November	1st to 10th	Day	35% 5% 14% 24% 19% 4	1856
	11th to 20th	Day	38% 6% 14% 27% 14% 1	1890
	21st to end	Day	40% 8% 16% 22% 13% 2	1764
December	1st to 10th	Day	26% 6% 15% 38% 13% 1	2700
	11th to 20th	Day	44% 10% 16% 19% 10% 1	3104
	21st to end	Day	48% 11% 15% 15% 11%	4609
January	1st to 10th	Night	46% 10% 20% 15% 8% 2	7605
	11th to 20th	Night	35% 7% 12% 26% 17% 3	7650
	21st to end	Night	31% 9% 17% 17% 23% 2	8370
February	1st to 10th	Night	44% 9% 17% 20% 8% 2	2730
	11th to 20th	Night	44% 6% 14% 21% 14% 2	2582
	21st to end	Night	41% 5% 14% 26% 11% 3	2076
March	1st to 10th	Night	44% 6% 11% 23% 12% 4	5166
	11th to 20th	Night	36% 8% 11% 27% 15% 2	5110
	21st to end	Night	43% 6% 17% 19% 14% 2	5610
April	1st to 10th	Night	37% 4 12% 22% 19% 6%	2289
	11th to 20th	Night	35% 4 13% 21% 22% 5%	1918
	21st to end	Night	35% 5% 14% 22% 22% 2	1890
May	1st to 10th	Night	27% 6% 10% 23% 29% 5%	5319
	11th to 20th	Night	22% 5% 8% 23% 31% 10%	5297
	21st to end	Night	25% 5% 7% 25% 35% 3	5838
June	1st to 10th	Night	24% 5% 8% 20% 31% 12%	1888
	11th to 20th	Night	19% 3 7% 16% 29% 26%	1748
	21st to end	Night	17% 3 5% 9% 29% 37%	1890
July	1st to 10th	Night	20% 3 4 7% 16% 49%	5295
	11th to 20th	Night	25% 6% 11% 10% 18% 31%	5286
	21st to end	Night	21% 5% 8% 13% 21% 32%	5677
August	1st to 10th	Night	20% 5% 8% 18% 22% 26%	3018
	11th to 20th	Night	24% 5% 8% 13% 26% 24%	3018
	21st to end	Night	20% 4 6% 12% 28% 31%	3375
September	1st to 10th	Night	20% 4 6% 14% 26% 31%	2140
	11th to 20th	Night	21% 4 7% 18% 27% 24%	2200
	21st to end	Night	20% 3 6% 16% 32% 24%	2200
October	1st to 10th	Night	18% 3 6% 16% 36% 22%	3756
	11th to 20th	Night	27% 3 6% 29% 26% 8%	3898
	21st to end	Night	25% 5% 10% 30% 26% 4	4252
November	1st to 10th	Night	30% 5% 11% 26% 21% 6%	2660
	11th to 20th	Night	32% 5% 16% 29% 15% 3	2730
	21st to end	Night	34% 7% 16% 27% 13% 3	2830
December	1st to 10th	Night	25% 5% 14% 36% 19% 1	4710
	11th to 20th	Night	40% 7% 21% 23% 10%	5322
	21st to end	Night	47% 9% 18% 17% 9%	6640

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	27% 13% 23% 20% 13% 4	330
	11th to 20th	Day	12% 13% 28% 29% 15% 2	330
	21st to end	Day	15% 8% 32% 29% 13% 3	363
February	1st to 10th	Day	25% 10% 30% 25% 9% 2	330
	11th to 20th	Day	21% 11% 30% 26% 10% 1	408
	21st to end	Day	15% 13% 35% 26% 10% 1	446
March	1st to 10th	Day	18% 15% 28% 25% 12% 2	540
	11th to 20th	Day	17% 14% 26% 28% 15% 1	540
	21st to end	Day	20% 17% 29% 24% 10%	594
April	1st to 10th	Day	16% 16% 24% 29% 14% 2	540
	11th to 20th	Day	17% 17% 30% 24% 9% 2	532
	21st to end	Day	16% 19% 26% 23% 13% 2	540
May	1st to 10th	Day	11% 15% 30% 30% 11% 2	543
	11th to 20th	Day	14% 11% 26% 30% 16% 4	568
	21st to end	Day	10% 13% 23% 29% 20% 5%	617
June	1st to 10th	Day	6% 12% 23% 35% 21% 4	570
	11th to 20th	Day	9% 12% 30% 28% 19% 2	633
	21st to end	Day	5% 12% 27% 35% 17% 3	570
July	1st to 10th	Day	3 7% 25% 39% 22% 4	566
	11th to 20th	Day	5% 3 23% 45% 21% 3	564
	21st to end	Day	4 5% 18% 43% 24% 6%	619
August	1st to 10th	Day	7% 5% 23% 39% 23% 3	567
	11th to 20th	Day	5% 6% 25% 34% 25% 5%	557
	21st to end	Day	6% 6% 20% 38% 25% 5%	620
September	1st to 10th	Day	4 5% 20% 36% 28% 7%	530
	11th to 20th	Day	9% 8% 23% 31% 24% 5%	530
	21st to end	Day	8% 9% 19% 34% 25% 5%	530
October	1st to 10th	Day	11% 10% 24% 28% 22% 5%	433
	11th to 20th	Day	11% 14% 21% 26% 22% 7%	330
	21st to end	Day	12% 9% 28% 33% 16% 2	363
November	1st to 10th	Day	18% 12% 24% 25% 17% 4	330
	11th to 20th	Day	15% 12% 22% 33% 12% 6%	330
	21st to end	Day	15% 11% 21% 28% 22% 4	330
December	1st to 10th	Day	15% 10% 24% 30% 17% 5%	330
	11th to 20th	Day	16% 10% 25% 35% 12% 2	330
	21st to end	Day	27% 10% 20% 32% 10% 1	363
January	1st to 10th	Night	19% 6% 22% 32% 18% 4	840
	11th to 20th	Night	15% 5% 23% 34% 19% 3	840
	21st to end	Night	14% 5% 24% 37% 17% 3	924
February	1st to 10th	Night	18% 5% 24% 38% 12% 2	840
	11th to 20th	Night	14% 8% 28% 35% 14% 1	824
	21st to end	Night	12% 8% 29% 38% 12% 1	692
March	1st to 10th	Night	18% 8% 25% 35% 12% 2	840
	11th to 20th	Night	12% 6% 25% 37% 18% 2	840
	21st to end	Night	15% 10% 27% 35% 12% 2	924
April	1st to 10th	Night	18% 8% 23% 36% 14% 1	819
	11th to 20th	Night	11% 8% 30% 38% 12% 1	623
	21st to end	Night	13% 8% 25% 34% 18% 2	630
May	1st to 10th	Night	10% 7% 25% 41% 16% 1	630
	11th to 20th	Night	10% 5% 20% 35% 26% 2	621
	21st to end	Night	12% 6% 21% 35% 23% 3	683
June	1st to 10th	Night	8% 8% 19% 37% 26% 1	630
	11th to 20th	Night	8% 6% 27% 39% 19% 2	630
	21st to end	Night	6% 4 19% 40% 28% 2	630
July	1st to 10th	Night	6% 3 20% 32% 35% 4	615
	11th to 20th	Night	6% 1 13% 47% 29% 3	612
	21st to end	Night	6% 1 11% 35% 45% 2	690
August	1st to 10th	Night	5% 2 17% 44% 31% 1	627
	11th to 20th	Night	5% 3 14% 42% 33% 3	624
	21st to end	Night	6% 4 11% 43% 34% 2	687
September	1st to 10th	Night	5% 3 14% 41% 34% 4	740
	11th to 20th	Night	8% 3 18% 33% 32% 5%	800
	21st to end	Night	8% 3 17% 33% 32% 7%	800
October	1st to 10th	Night	11% 4 22% 36% 24% 4	800
	11th to 20th	Night	11% 5% 19% 36% 25% 4	800
	21st to end	Night	11% 5% 22% 38% 22% 3	880
November	1st to 10th	Night	13% 6% 22% 35% 21% 4	820
	11th to 20th	Night	14% 6% 21% 39% 16% 4	840
	21st to end	Night	13% 5% 23% 35% 19% 4	940
December	1st to 10th	Night	16% 5% 25% 36% 17% 2	1050
	11th to 20th	Night	19% 7% 22% 38% 12% 2	1050
	21st to end	Night	21% 7% 23% 37% 11% 1	940

Page generated at 2026-08-27 02:07:12. Version ac07

Copyright © 2026 Attilla Danko.