Ice House Observation Plateau
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ice House Observation Plateau clear sky chart from 2005-11-06 to 2026-10-29.

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	6% 6% 2 3 2 2 2 2 4 5% 65%	157984
	Night	7% 7% 2 4 2 3 3 2 4 5% 61%	151596
Transparency	Day	23% 4 7% 18% 26% 23%	152953
	Night	26% 4 7% 18% 24% 21%	147611
Seeing	Day	14% 16% 32% 24% 11% 3	17727
	Night	13% 7% 21% 34% 20% 4	27018

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	12% 15% 2 4 2 2 3 3 5% 7% 45%	4722
	11th to 20th	Day	9% 7% 2 4 2 3 3 2 3 5% 60%	5040
	21st to end	Day	10% 8% 3 6% 4 3 4 4 5% 7% 46%	5843
February	1st to 10th	Day	16% 10% 3 5% 2 2 2 3 4 4 47%	1890
	11th to 20th	Day	11% 15% 3 5% 3 3 3 3 4 6% 43%	2030
	21st to end	Day	14% 15% 3 5% 3 2 3 3 4 5% 43%	1730
March	1st to 10th	Day	10% 20% 6% 8% 4 3 3 3 5% 5% 32%	4635
	11th to 20th	Day	11% 14% 3 4 3 2 3 2 3 5% 50%	5110
	21st to end	Day	13% 20% 3 6% 4 3 3 3 4 6% 35%	5911
April	1st to 10th	Day	12% 13% 2 4 4 3 4 3 5% 7% 44%	2520
	11th to 20th	Day	8% 11% 2 5% 3 2 3 3 4 6% 51%	2489
	21st to end	Day	10% 8% 2 4 3 2 3 3 5% 7% 54%	2520
May	1st to 10th	Day	6% 5% 2 4 3 2 2 2 3 5% 67%	7257
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 5% 75%	8097
	21st to end	Day	5% 4 1 3 2 2 2 2 3 4 72%	8992
June	1st to 10th	Day	6% 4 1 4 3 3 3 3 5% 6% 62%	2940
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 78%	2940
	21st to end	Day	2 2 1 2 1 1 1 2 3 3 82%	2940
July	1st to 10th	Day	1 1 1 1 1 1 2 2 91%	8219
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 3 79%	8220
	21st to end	Day	1 1 1 1 1 2 2 3 3 85%	8531
August	1st to 10th	Day	1 1 1 1 1 2 1 2 3 86%	7514
	11th to 20th	Day	1 1 1 1 2 2 3 4 84%	7001
	21st to end	Day	3 2 1 3 2 3 3 2 3 5% 75%	7750
September	1st to 10th	Day	2 1 1 2 1 1 1 1 3 3 83%	2520
	11th to 20th	Day	4 3 1 3 2 3 2 2 3 4 73%	2510
	21st to end	Day	4 3 1 3 2 2 2 2 3 4 76%	2305
October	1st to 10th	Day	5% 3 1 3 2 2 2 2 4 5% 71%	3380
	11th to 20th	Day	5% 2 1 2 2 2 2 1 3 4 74%	3361
	21st to end	Day	5% 4 1 4 4 3 3 3 4 6% 64%	3617
November	1st to 10th	Day	10% 7% 2 4 3 4 3 3 4 7% 54%	1854
	11th to 20th	Day	12% 6% 2 3 3 3 4 3 5% 7% 51%	1890
	21st to end	Day	10% 8% 2 4 2 3 2 4 5% 6% 54%	1806
December	1st to 10th	Day	8% 4 1 3 3 3 3 4 5% 8% 59%	2700
	11th to 20th	Day	20% 13% 3 5% 3 3 4 3 5% 6% 35%	3108
	21st to end	Day	19% 11% 3 6% 3 3 3 4 6% 8% 34%	4092
January	1st to 10th	Night	12% 12% 3 5% 3 3 4 3 5% 7% 41%	8172
	11th to 20th	Night	10% 6% 2 3 2 3 3 2 4 6% 59%	7920
	21st to end	Night	9% 11% 3 6% 4 4 4 3 4 6% 46%	8371
February	1st to 10th	Night	15% 9% 2 5% 4 3 3 3 4 6% 48%	2730
	11th to 20th	Night	8% 15% 3 5% 3 3 4 3 6% 7% 42%	2476
	21st to end	Night	13% 11% 3 6% 3 3 3 3 4 4 48%	2076
March	1st to 10th	Night	10% 21% 5% 6% 3 3 3 3 4 6% 37%	5464
	11th to 20th	Night	12% 16% 3 4 2 2 2 2 3 5% 48%	5110
	21st to end	Night	13% 19% 3 5% 4 3 4 3 5% 6% 35%	5305
April	1st to 10th	Night	11% 10% 2 5% 4 3 4 2 5% 6% 47%	2100
	11th to 20th	Night	9% 10% 3 5% 3 3 3 3 4 6% 51%	2079
	21st to end	Night	7% 9% 1 4 3 3 3 3 4 7% 57%	2100
May	1st to 10th	Night	4 5% 2 4 2 3 3 2 4 5% 67%	5705
	11th to 20th	Night	2 3 1 2 2 2 2 2 2 5% 78%	4762
	21st to end	Night	3 3 1 3 2 2 3 2 3 4 73%	5181
June	1st to 10th	Night	6% 4 1 3 2 2 3 3 5% 5% 65%	1680
	11th to 20th	Night	2 2 1 1 1 1 2 2 3 4 82%	1680
	21st to end	Night	2 2 1 2 2 2 2 2 3 2 81%	1680
July	1st to 10th	Night	1 1 1 1 2 2 91%	4740
	11th to 20th	Night	3 4 1 3 2 2 2 2 3 3 75%	4740
	21st to end	Night	1 2 2 2 2 2 2 3 5% 79%	5562
August	1st to 10th	Night	1 1 1 1 1 1 1 2 3 3 84%	5307
	11th to 20th	Night	1 1 1 2 2 1 3 4 84%	5886
	21st to end	Night	3 3 1 3 2 2 2 2 3 4 74%	6499
September	1st to 10th	Night	2 1 1 1 1 1 2 4 85%	2100
	11th to 20th	Night	3 2 2 1 1 2 2 3 5% 78%	2110
	21st to end	Night	3 2 1 2 2 2 2 2 3 6% 75%	2310
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 3 76%	4040
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 5% 78%	4017
	21st to end	Night	8% 3 1 2 2 3 4 3 4 5% 65%	4368
November	1st to 10th	Night	11% 7% 1 3 2 2 3 3 4 7% 57%	2665
	11th to 20th	Night	10% 6% 1 4 3 4 3 3 5% 7% 54%	2730
	21st to end	Night	10% 8% 2 3 3 3 3 3 4 6% 56%	2809
December	1st to 10th	Night	9% 5% 1 3 2 3 3 3 4 6% 62%	4700
	11th to 20th	Night	17% 14% 2 5% 3 3 4 4 8% 9% 31%	5316
	21st to end	Night	17% 13% 3 7% 4 4 5% 3 5% 6% 33%	7106

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	39% 5% 13% 17% 19% 7%	4723
	11th to 20th	Day	27% 4 6% 11% 24% 29%	5040
	21st to end	Day	37% 5% 6% 17% 20% 15%	5843
February	1st to 10th	Day	41% 4 9% 17% 18% 12%	1890
	11th to 20th	Day	41% 5% 10% 18% 20% 7%	2040
	21st to end	Day	43% 4 9% 20% 16% 7%	1730
March	1st to 10th	Day	50% 8% 8% 12% 16% 6%	4635
	11th to 20th	Day	38% 4 11% 28% 16% 3	5110
	21st to end	Day	46% 8% 13% 20% 11% 1	5911
April	1st to 10th	Day	39% 6% 14% 21% 17% 4	2520
	11th to 20th	Day	33% 7% 12% 24% 17% 6%	2492
	21st to end	Day	28% 6% 15% 28% 20% 3	2520
May	1st to 10th	Day	21% 4 8% 27% 29% 11%	7257
	11th to 20th	Day	13% 3 7% 30% 36% 11%	8100
	21st to end	Day	16% 4 7% 33% 34% 7%	8994
June	1st to 10th	Day	22% 6% 10% 25% 29% 9%	2940
	11th to 20th	Day	11% 3 7% 22% 37% 20%	2940
	21st to end	Day	9% 2 4 16% 37% 32%	2940
July	1st to 10th	Day	4 1 1 6% 24% 63%	8151
	11th to 20th	Day	11% 1 2 7% 14% 64%	8145
	21st to end	Day	6% 2 3 13% 28% 48%	8341
August	1st to 10th	Day	8% 2 3 6% 29% 52%	5954
	11th to 20th	Day	7% 2 3 20% 36% 32%	5517
	21st to end	Day	12% 2 3 21% 38% 24%	6077
September	1st to 10th	Day	8% 2 4 13% 35% 39%	2520
	11th to 20th	Day	15% 4 7% 19% 39% 18%	2510
	21st to end	Day	14% 3 6% 19% 35% 23%	2305
October	1st to 10th	Day	16% 3 5% 11% 33% 33%	3380
	11th to 20th	Day	15% 3 5% 18% 40% 20%	3361
	21st to end	Day	22% 4 6% 22% 34% 13%	3617
November	1st to 10th	Day	30% 4 11% 20% 22% 13%	1854
	11th to 20th	Day	33% 5% 11% 17% 24% 11%	1890
	21st to end	Day	30% 4 9% 19% 26% 13%	1806
December	1st to 10th	Day	24% 3 7% 22% 26% 16%	2700
	11th to 20th	Day	50% 4 8% 13% 15% 9%	3108
	21st to end	Day	45% 6% 13% 15% 15% 5%	4092
January	1st to 10th	Night	39% 6% 12% 19% 17% 6%	8172
	11th to 20th	Night	28% 4 5% 9% 24% 30%	7920
	21st to end	Night	39% 4 6% 13% 19% 19%	8371
February	1st to 10th	Night	40% 4 7% 17% 18% 15%	2730
	11th to 20th	Night	40% 6% 8% 18% 19% 8%	2477
	21st to end	Night	39% 5% 9% 20% 19% 8%	2076
March	1st to 10th	Night	48% 6% 8% 15% 16% 8%	5464
	11th to 20th	Night	39% 4 7% 25% 20% 3	5110
	21st to end	Night	46% 9% 12% 20% 11% 2	5305
April	1st to 10th	Night	38% 6% 13% 19% 17% 6%	2100
	11th to 20th	Night	34% 5% 13% 23% 16% 7%	2079
	21st to end	Night	27% 6% 11% 32% 19% 4	2100
May	1st to 10th	Night	20% 5% 9% 27% 27% 11%	5703
	11th to 20th	Night	12% 3 7% 28% 37% 14%	4762
	21st to end	Night	14% 4 9% 30% 35% 8%	5182
June	1st to 10th	Night	20% 7% 11% 24% 28% 11%	1680
	11th to 20th	Night	8% 3 7% 23% 36% 23%	1680
	21st to end	Night	10% 4 4 13% 36% 33%	1680
July	1st to 10th	Night	3 1 2 6% 26% 62%	4700
	11th to 20th	Night	16% 2 2 6% 15% 58%	4692
	21st to end	Night	9% 2 3 12% 23% 51%	5440
August	1st to 10th	Night	10% 1 3 6% 27% 53%	4189
	11th to 20th	Night	8% 2 4 18% 36% 33%	4636
	21st to end	Night	14% 1 2 23% 32% 28%	5092
September	1st to 10th	Night	6% 2 4 11% 35% 43%	2100
	11th to 20th	Night	10% 3 7% 20% 40% 21%	2110
	21st to end	Night	12% 3 6% 20% 33% 26%	2310
October	1st to 10th	Night	14% 2 5% 11% 28% 39%	4040
	11th to 20th	Night	12% 3 4 20% 41% 20%	4017
	21st to end	Night	21% 4 6% 21% 32% 17%	4368
November	1st to 10th	Night	28% 4 9% 21% 21% 16%	2665
	11th to 20th	Night	29% 6% 9% 19% 26% 10%	2730
	21st to end	Night	30% 4 6% 21% 24% 14%	2809
December	1st to 10th	Night	24% 3 7% 20% 25% 21%	4700
	11th to 20th	Night	47% 5% 7% 13% 20% 8%	5316
	21st to end	Night	49% 7% 10% 13% 14% 6%	7106

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	38% 15% 20% 17% 8% 1	220
	11th to 20th	Day	23% 13% 25% 26% 11% 2	325
	21st to end	Day	25% 14% 24% 22% 14% 2	473
February	1st to 10th	Day	30% 16% 25% 18% 10% 1	430
	11th to 20th	Day	26% 22% 28% 17% 7%	525
	21st to end	Day	25% 17% 32% 20% 5%	446
March	1st to 10th	Day	31% 24% 23% 15% 6% 1	540
	11th to 20th	Day	26% 21% 23% 18% 9% 2	540
	21st to end	Day	25% 25% 26% 19% 5%	594
April	1st to 10th	Day	21% 22% 28% 22% 7% 1	540
	11th to 20th	Day	22% 23% 26% 20% 7% 2	532
	21st to end	Day	15% 21% 27% 23% 12% 2	540
May	1st to 10th	Day	15% 20% 32% 19% 10% 3	543
	11th to 20th	Day	17% 19% 27% 21% 12% 4	568
	21st to end	Day	14% 14% 31% 23% 13% 6%	617
June	1st to 10th	Day	8% 17% 33% 25% 11% 6%	570
	11th to 20th	Day	7% 21% 37% 20% 10% 5%	570
	21st to end	Day	4 16% 36% 27% 10% 6%	570
July	1st to 10th	Day	2 10% 50% 22% 10% 5%	566
	11th to 20th	Day	1 9% 47% 27% 12% 6%	564
	21st to end	Day	2 7% 45% 26% 13% 6%	619
August	1st to 10th	Day	3 12% 43% 25% 14% 4	567
	11th to 20th	Day	2 12% 41% 27% 13% 4	557
	21st to end	Day	4 8% 45% 26% 14% 3	627
September	1st to 10th	Day	4 13% 43% 26% 12% 2	570
	11th to 20th	Day	9% 15% 35% 29% 10% 2	570
	21st to end	Day	5% 16% 36% 34% 7% 2	570
October	1st to 10th	Day	9% 14% 31% 31% 13% 2	570
	11th to 20th	Day	12% 16% 28% 30% 12% 2	570
	21st to end	Day	12% 15% 30% 27% 13% 4	606
November	1st to 10th	Day	16% 15% 21% 25% 18% 5%	330
	11th to 20th	Day	19% 12% 23% 29% 12% 5%	330
	21st to end	Day	17% 14% 24% 27% 16% 2	286
December	1st to 10th	Day	19% 13% 20% 24% 17% 7%	220
	11th to 20th	Day	20% 17% 23% 20% 16% 5%	220
	21st to end	Day	30% 12% 26% 19% 12% 1	242
January	1st to 10th	Night	24% 10% 25% 22% 13% 5%	840
	11th to 20th	Night	17% 11% 29% 31% 10% 3	840
	21st to end	Night	20% 12% 24% 25% 15% 4	924
February	1st to 10th	Night	20% 12% 27% 27% 13% 2	840
	11th to 20th	Night	20% 12% 24% 27% 14% 4	824
	21st to end	Night	21% 10% 28% 29% 9% 2	692
March	1st to 10th	Night	25% 11% 25% 26% 12% 3	840
	11th to 20th	Night	22% 8% 22% 26% 18% 4	840
	21st to end	Night	21% 11% 25% 29% 12% 2	924
April	1st to 10th	Night	16% 9% 25% 34% 15% 2	840
	11th to 20th	Night	15% 10% 22% 35% 15% 3	831
	21st to end	Night	12% 7% 21% 37% 17% 5%	840
May	1st to 10th	Night	10% 9% 24% 32% 21% 4	767
	11th to 20th	Night	7% 7% 19% 41% 22% 4	438
	21st to end	Night	10% 4 15% 39% 28% 5%	455
June	1st to 10th	Night	7% 3 16% 40% 27% 5%	420
	11th to 20th	Night	2 3 19% 43% 29% 4	420
	21st to end	Night	2 2 15% 44% 32% 5%	420
July	1st to 10th	Night	1 12% 46% 38% 3	410
	11th to 20th	Night	3 1 11% 44% 36% 4	408
	21st to end	Night	2 1 11% 36% 41% 10%	599
August	1st to 10th	Night	2 1 12% 47% 34% 5%	634
	11th to 20th	Night	1 1 14% 47% 30% 7%	832
	21st to end	Night	2 1 11% 50% 33% 3	924
September	1st to 10th	Night	2 2 14% 46% 32% 4	840
	11th to 20th	Night	4 2 17% 40% 29% 8%	840
	21st to end	Night	4 3 19% 43% 23% 8%	840
October	1st to 10th	Night	7% 6% 20% 42% 20% 6%	840
	11th to 20th	Night	8% 7% 19% 38% 23% 5%	840
	21st to end	Night	10% 8% 22% 31% 21% 9%	912
November	1st to 10th	Night	15% 6% 18% 32% 23% 6%	820
	11th to 20th	Night	14% 8% 26% 33% 15% 5%	840
	21st to end	Night	16% 9% 29% 28% 14% 4	840
December	1st to 10th	Night	20% 9% 24% 30% 13% 3	840
	11th to 20th	Night	25% 8% 24% 28% 13% 2	840
	21st to end	Night	28% 12% 24% 24% 11% 2	924

Page generated at 2026-10-26 01:37:52. Version ac07

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