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 2025-07-06.

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	7% 7% 2 3 2 2 2 2 4 5% 63%	123823
	Night	8% 8% 2 4 3 3 3 3 4 5% 59%	123829
Transparency	Day	24% 4 8% 18% 26% 20%	123572
	Night	27% 4 8% 17% 24% 19%	123667
Seeing	Day	14% 16% 32% 24% 11% 3	15961
	Night	13% 7% 20% 34% 21% 5%	25321

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% 13% 3 4 2 2 3 3 5% 7% 48%	3639
	11th to 20th	Day	12% 9% 2 5% 3 3 2 2 3 4 56%	3870
	21st to end	Day	13% 10% 3 5% 4 3 4 3 4 5% 46%	4510
February	1st to 10th	Day	17% 11% 3 4 2 2 2 3 4 4 47%	1800
	11th to 20th	Day	11% 14% 3 5% 3 3 3 3 4 6% 44%	1931
	21st to end	Day	14% 15% 3 5% 3 2 3 3 4 4 44%	1650
March	1st to 10th	Day	10% 20% 7% 8% 4 3 3 3 5% 5% 31%	4535
	11th to 20th	Day	11% 15% 3 4 3 2 3 2 3 5% 49%	5000
	21st to end	Day	13% 21% 3 6% 4 3 3 3 4 5% 35%	5783
April	1st to 10th	Day	12% 13% 2 4 4 3 4 3 6% 7% 44%	2400
	11th to 20th	Day	9% 11% 2 5% 3 2 3 3 4 6% 51%	2369
	21st to end	Day	10% 8% 2 4 3 2 3 3 5% 7% 55%	2400
May	1st to 10th	Day	6% 4 2 4 2 2 2 2 3 5% 70%	5602
	11th to 20th	Day	4 4 1 3 3 2 2 2 3 5% 71%	6226
	21st to end	Day	4 3 1 2 2 2 2 2 3 4 75%	6902
June	1st to 10th	Day	6% 5% 1 4 3 3 3 3 5% 6% 62%	2800
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 77%	2800
	21st to end	Day	2 2 1 2 1 1 1 2 3 3 82%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 92%	4491
	11th to 20th	Day	1 1 1 2 2 2 2 2 4 4 80%	4420
	21st to end	Day	1 1 1 1 1 1 1 2 3 86%	4581
August	1st to 10th	Day	2 1 1 2 1 2 3 2 3 4 79%	4070
	11th to 20th	Day	1 1 1 1 1 1 1 3 3 88%	3724
	21st to end	Day	2 1 1 1 1 1 1 2 2 87%	4180
September	1st to 10th	Day	2 1 1 1 1 1 1 1 3 3 86%	2280
	11th to 20th	Day	4 2 1 3 2 3 3 2 3 4 73%	2271
	21st to end	Day	4 3 1 2 2 2 2 2 3 4 76%	2085
October	1st to 10th	Day	4 3 1 3 2 2 2 2 4 5% 71%	3180
	11th to 20th	Day	6% 2 1 2 2 2 2 1 3 5% 75%	3161
	21st to end	Day	5% 4 1 4 4 3 3 3 4 6% 64%	3427
November	1st to 10th	Day	10% 7% 2 4 3 4 3 3 4 7% 53%	1764
	11th to 20th	Day	11% 6% 1 4 3 3 4 3 5% 7% 53%	1800
	21st to end	Day	10% 9% 2 4 2 3 2 4 5% 6% 53%	1720
December	1st to 10th	Day	8% 4 1 3 3 3 3 4 5% 8% 58%	2620
	11th to 20th	Day	20% 13% 3 5% 3 3 4 3 5% 6% 35%	3028
	21st to end	Day	19% 10% 3 6% 3 4 3 4 6% 8% 34%	4004
January	1st to 10th	Night	8% 10% 3 5% 3 4 4 4 6% 8% 46%	6306
	11th to 20th	Night	13% 8% 2 4 3 3 4 2 4 5% 53%	6085
	21st to end	Night	10% 12% 3 5% 4 4 4 3 4 5% 47%	6468
February	1st to 10th	Night	15% 9% 2 5% 4 3 3 3 4 6% 47%	2600
	11th to 20th	Night	9% 14% 3 5% 3 3 4 3 6% 7% 44%	2355
	21st to end	Night	12% 12% 3 6% 3 3 3 3 4 4 48%	1980
March	1st to 10th	Night	10% 21% 5% 6% 3 3 3 3 4 6% 36%	5344
	11th to 20th	Night	12% 16% 3 4 2 2 2 2 3 5% 48%	5000
	21st to end	Night	13% 19% 3 5% 4 3 4 3 5% 6% 35%	5191
April	1st to 10th	Night	11% 10% 2 5% 4 4 4 3 5% 6% 47%	2000
	11th to 20th	Night	9% 9% 3 5% 3 3 3 3 4 6% 52%	1979
	21st to end	Night	7% 8% 1 4 3 3 3 3 5% 7% 58%	2000
May	1st to 10th	Night	3 4 2 3 2 2 3 2 4 5% 71%	4386
	11th to 20th	Night	3 3 1 3 2 2 2 2 3 5% 75%	3665
	21st to end	Night	3 2 1 2 2 2 2 2 3 3 78%	3972
June	1st to 10th	Night	6% 4 1 3 2 3 3 3 5% 5% 65%	1600
	11th to 20th	Night	2 2 1 1 1 1 2 2 3 4 81%	1600
	21st to end	Night	2 2 1 2 2 2 2 2 3 2 81%	1600
July	1st to 10th	Night	1 1 1 1 2 1 92%	2580
	11th to 20th	Night	2 3 1 3 3 2 2 2 3 3 76%	2540
	21st to end	Night	1 1 1 1 2 2 2 2 4 83%	2974
August	1st to 10th	Night	2 2 1 2 2 2 2 3 4 5% 75%	2867
	11th to 20th	Night	1 1 1 1 1 1 2 1 2 3 87%	3126
	21st to end	Night	2 2 1 1 1 1 1 1 2 87%	3498
September	1st to 10th	Night	1 1 1 1 1 1 2 4 87%	1900
	11th to 20th	Night	3 2 2 1 1 2 2 3 5% 79%	1909
	21st to end	Night	3 2 1 2 2 2 2 2 3 5% 76%	2090
October	1st to 10th	Night	3 3 1 2 2 2 2 2 3 3 77%	3800
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 5% 78%	3777
	21st to end	Night	8% 3 1 2 2 3 4 3 4 5% 65%	4139
November	1st to 10th	Night	11% 8% 1 4 2 2 3 3 4 6% 56%	2535
	11th to 20th	Night	9% 5% 1 4 3 4 3 3 5% 7% 56%	2600
	21st to end	Night	10% 8% 2 4 3 3 3 3 4 6% 55%	2675
December	1st to 10th	Night	9% 5% 1 3 2 3 3 3 4 6% 62%	4560
	11th to 20th	Night	17% 14% 2 5% 3 3 5% 4 8% 9% 30%	5176
	21st to end	Night	17% 12% 3 7% 4 4 5% 3 5% 6% 33%	6952

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	37% 5% 14% 18% 18% 8%	3639
	11th to 20th	Day	33% 5% 7% 13% 26% 17%	3870
	21st to end	Day	39% 6% 7% 13% 18% 17%	4510
February	1st to 10th	Day	42% 4 10% 16% 18% 11%	1800
	11th to 20th	Day	40% 5% 10% 17% 21% 7%	1941
	21st to end	Day	43% 4 8% 20% 16% 8%	1650
March	1st to 10th	Day	51% 8% 8% 12% 16% 6%	4535
	11th to 20th	Day	39% 4 11% 28% 15% 3	5000
	21st to end	Day	47% 8% 13% 20% 10% 1	5783
April	1st to 10th	Day	39% 6% 14% 21% 17% 3	2400
	11th to 20th	Day	33% 7% 12% 24% 18% 6%	2372
	21st to end	Day	28% 6% 15% 28% 20% 3	2400
May	1st to 10th	Day	18% 4 9% 29% 28% 12%	5602
	11th to 20th	Day	17% 3 9% 33% 32% 6%	6229
	21st to end	Day	13% 5% 8% 32% 35% 7%	6904
June	1st to 10th	Day	22% 6% 10% 25% 28% 8%	2800
	11th to 20th	Day	11% 3 8% 23% 35% 20%	2800
	21st to end	Day	9% 2 4 16% 36% 33%	2800
July	1st to 10th	Day	3 1 2 6% 18% 70%	4422
	11th to 20th	Day	8% 2 3 9% 18% 60%	4345
	21st to end	Day	6% 2 3 7% 29% 54%	4436
August	1st to 10th	Day	10% 2 3 8% 26% 50%	4055
	11th to 20th	Day	4 1 3 7% 39% 45%	3760
	21st to end	Day	7% 1 3 10% 44% 35%	4179
September	1st to 10th	Day	6% 1 4 10% 36% 43%	2280
	11th to 20th	Day	15% 4 7% 20% 37% 18%	2271
	21st to end	Day	14% 3 5% 19% 36% 23%	2085
October	1st to 10th	Day	16% 3 5% 11% 33% 32%	3180
	11th to 20th	Day	15% 3 5% 18% 40% 19%	3161
	21st to end	Day	22% 4 6% 21% 34% 13%	3427
November	1st to 10th	Day	31% 4 10% 20% 22% 13%	1764
	11th to 20th	Day	31% 5% 11% 17% 25% 11%	1800
	21st to end	Day	31% 4 9% 18% 24% 13%	1720
December	1st to 10th	Day	25% 3 7% 22% 26% 17%	2620
	11th to 20th	Day	50% 4 8% 14% 15% 9%	3028
	21st to end	Day	45% 7% 13% 16% 15% 5%	4004
January	1st to 10th	Night	33% 6% 14% 23% 17% 7%	6306
	11th to 20th	Night	35% 5% 7% 10% 27% 16%	6085
	21st to end	Night	39% 5% 7% 11% 17% 21%	6468
February	1st to 10th	Night	41% 4 7% 16% 19% 14%	2600
	11th to 20th	Night	39% 6% 8% 19% 20% 9%	2356
	21st to end	Night	39% 5% 8% 20% 19% 9%	1980
March	1st to 10th	Night	48% 6% 8% 15% 16% 8%	5344
	11th to 20th	Night	40% 4 7% 25% 20% 3	5000
	21st to end	Night	47% 9% 12% 19% 10% 2	5191
April	1st to 10th	Night	38% 7% 13% 19% 17% 6%	2000
	11th to 20th	Night	34% 6% 13% 23% 17% 8%	1979
	21st to end	Night	27% 6% 11% 32% 19% 4	2000
May	1st to 10th	Night	15% 5% 10% 31% 28% 10%	4383
	11th to 20th	Night	14% 3 9% 31% 34% 10%	3665
	21st to end	Night	12% 4 10% 28% 37% 9%	3972
June	1st to 10th	Night	20% 7% 11% 25% 28% 10%	1600
	11th to 20th	Night	9% 3 7% 24% 35% 22%	1600
	21st to end	Night	10% 4 4 13% 36% 34%	1600
July	1st to 10th	Night	3 1 2 5% 18% 70%	2540
	11th to 20th	Night	13% 2 4 8% 15% 58%	2492
	21st to end	Night	7% 2 3 7% 24% 57%	2881
August	1st to 10th	Night	12% 2 4 7% 26% 48%	2858
	11th to 20th	Night	6% 2 3 7% 35% 47%	3156
	21st to end	Night	8% 1 2 12% 38% 39%	3498
September	1st to 10th	Night	5% 1 3 9% 35% 46%	1900
	11th to 20th	Night	10% 3 7% 20% 40% 20%	1909
	21st to end	Night	12% 3 6% 20% 33% 26%	2090
October	1st to 10th	Night	14% 2 5% 11% 28% 40%	3800
	11th to 20th	Night	12% 3 4 21% 42% 19%	3777
	21st to end	Night	21% 4 6% 21% 32% 17%	4139
November	1st to 10th	Night	29% 5% 9% 20% 21% 16%	2535
	11th to 20th	Night	28% 5% 9% 20% 27% 11%	2600
	21st to end	Night	32% 4 6% 20% 23% 15%	2675
December	1st to 10th	Night	25% 4 7% 19% 25% 21%	4560
	11th to 20th	Night	48% 5% 6% 13% 21% 7%	5176
	21st to end	Night	49% 7% 11% 13% 14% 6%	6952

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	37% 16% 21% 18% 9% 1	200
	11th to 20th	Day	25% 14% 23% 25% 11% 2	300
	21st to end	Day	26% 14% 24% 20% 13% 2	440
February	1st to 10th	Day	31% 17% 25% 17% 9% 2	400
	11th to 20th	Day	24% 22% 30% 17% 7%	486
	21st to end	Day	26% 17% 32% 20% 6%	414
March	1st to 10th	Day	32% 25% 22% 14% 6% 1	500
	11th to 20th	Day	29% 22% 22% 16% 9% 2	500
	21st to end	Day	27% 25% 25% 18% 5%	550
April	1st to 10th	Day	21% 22% 28% 22% 6% 1	500
	11th to 20th	Day	23% 22% 26% 21% 7% 2	492
	21st to end	Day	14% 20% 28% 24% 12% 2	500
May	1st to 10th	Day	15% 21% 33% 18% 10% 3	503
	11th to 20th	Day	17% 19% 27% 21% 12% 4	528
	21st to end	Day	13% 14% 32% 23% 13% 6%	573
June	1st to 10th	Day	8% 17% 32% 26% 11% 7%	530
	11th to 20th	Day	7% 22% 36% 20% 10% 5%	530
	21st to end	Day	3 16% 36% 28% 10% 7%	530
July	1st to 10th	Day	2 9% 51% 22% 11% 6%	507
	11th to 20th	Day	7% 46% 29% 11% 6%	484
	21st to end	Day	1 7% 45% 27% 14% 6%	531
August	1st to 10th	Day	3 13% 43% 25% 13% 5%	487
	11th to 20th	Day	2 12% 42% 28% 12% 5%	477
	21st to end	Day	4 7% 46% 27% 13% 3	539
September	1st to 10th	Day	3 9% 46% 27% 12% 2	490
	11th to 20th	Day	8% 15% 36% 29% 10% 2	490
	21st to end	Day	5% 16% 36% 35% 7% 1	490
October	1st to 10th	Day	8% 15% 30% 32% 13% 2	490
	11th to 20th	Day	10% 14% 29% 31% 14% 3	490
	21st to end	Day	11% 15% 30% 27% 12% 4	530
November	1st to 10th	Day	17% 16% 21% 23% 19% 4	300
	11th to 20th	Day	16% 13% 23% 31% 13% 5%	300
	21st to end	Day	18% 15% 24% 25% 16% 2	260
December	1st to 10th	Day	21% 13% 20% 24% 15% 8%	200
	11th to 20th	Day	20% 18% 24% 18% 16% 5%	200
	21st to end	Day	27% 13% 26% 20% 13% 1	220
January	1st to 10th	Night	23% 9% 25% 23% 14% 6%	800
	11th to 20th	Night	18% 11% 27% 31% 10% 3	800
	21st to end	Night	21% 12% 24% 24% 15% 4	880
February	1st to 10th	Night	21% 12% 25% 28% 14% 2	800
	11th to 20th	Night	20% 11% 23% 28% 14% 4	784
	21st to end	Night	21% 10% 27% 30% 10% 2	660
March	1st to 10th	Night	26% 11% 23% 26% 12% 3	800
	11th to 20th	Night	23% 9% 21% 24% 19% 4	800
	21st to end	Night	22% 12% 24% 28% 13% 2	880
April	1st to 10th	Night	16% 9% 26% 33% 15% 2	800
	11th to 20th	Night	15% 10% 22% 35% 16% 3	791
	21st to end	Night	12% 7% 21% 38% 18% 6%	800
May	1st to 10th	Night	10% 9% 24% 31% 22% 4	730
	11th to 20th	Night	7% 6% 19% 41% 23% 5%	417
	21st to end	Night	10% 3 15% 38% 29% 5%	433
June	1st to 10th	Night	7% 4 16% 39% 29% 6%	400
	11th to 20th	Night	2 3 20% 41% 31% 4	400
	21st to end	Night	3 2 14% 43% 33% 5%	400
July	1st to 10th	Night	1 9% 45% 41% 3	380
	11th to 20th	Night	2 1 10% 43% 39% 5%	368
	21st to end	Night	2 1 9% 33% 45% 11%	541
August	1st to 10th	Night	2 1 10% 44% 37% 5%	573
	11th to 20th	Night	1 1 13% 45% 31% 8%	752
	21st to end	Night	2 1 10% 48% 35% 3	836
September	1st to 10th	Night	2 1 11% 46% 36% 5%	760
	11th to 20th	Night	4 2 15% 38% 31% 9%	760
	21st to end	Night	4 3 18% 42% 25% 9%	760
October	1st to 10th	Night	7% 5% 19% 41% 22% 7%	760
	11th to 20th	Night	8% 6% 16% 38% 25% 6%	760
	21st to end	Night	10% 8% 20% 31% 22% 9%	836
November	1st to 10th	Night	16% 6% 18% 32% 23% 6%	780
	11th to 20th	Night	13% 8% 26% 34% 15% 5%	800
	21st to end	Night	17% 9% 27% 28% 15% 4	800
December	1st to 10th	Night	21% 9% 22% 30% 14% 4	800
	11th to 20th	Night	26% 8% 23% 29% 13% 2	800
	21st to end	Night	27% 12% 24% 24% 11% 2	880

Page generated at 2025-07-02 22:30:13. Version ac07

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