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 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	7% 7% 2 3 2 2 2 2 4 5% 63%	101213
	Night	9% 8% 2 4 3 3 3 3 4 5% 59%	97980
Transparency	Day	24% 4 8% 18% 24% 21%	100961
	Night	28% 5% 8% 17% 23% 19%	97821
Seeing	Day	14% 16% 32% 24% 11% 3	15130
	Night	13% 7% 19% 34% 22% 5%	24456

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% 19% 3 5% 3 3 3 2 4 6% 42%	2539
	11th to 20th	Day	17% 12% 3 7% 4 5% 3 3 4 6% 37%	2700
	21st to end	Day	16% 14% 4 7% 4 3 4 3 4 6% 35%	3146
February	1st to 10th	Day	15% 10% 3 4 3 2 3 4 4 5% 47%	1710
	11th to 20th	Day	10% 14% 3 5% 3 3 3 3 4 6% 45%	1831
	21st to end	Day	14% 16% 3 6% 2 2 3 3 4 4 43%	1570
March	1st to 10th	Day	10% 22% 7% 8% 4 4 4 3 5% 6% 27%	3155
	11th to 20th	Day	10% 13% 2 4 2 2 2 2 3 4 56%	3490
	21st to end	Day	11% 23% 4 7% 4 3 3 3 5% 6% 32%	4031
April	1st to 10th	Day	12% 13% 2 4 4 3 4 3 6% 7% 43%	2280
	11th to 20th	Day	9% 12% 2 5% 2 2 3 3 4 6% 50%	2249
	21st to end	Day	10% 7% 1 3 3 2 3 3 5% 7% 55%	2280
May	1st to 10th	Day	8% 5% 2 3 2 1 2 2 3 4 68%	3910
	11th to 20th	Day	4 4 1 2 2 2 2 2 3 5% 74%	4339
	21st to end	Day	6% 4 1 3 2 2 2 2 4 4 68%	4813
June	1st to 10th	Day	7% 5% 1 4 3 3 3 3 5% 6% 61%	2660
	11th to 20th	Day	3 2 1 2 2 2 2 2 4 5% 76%	2660
	21st to end	Day	2 2 1 2 1 1 2 2 3 3 81%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 92%	4420
	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	7% 4 1 3 3 3 2 2 4 5% 67%	1900
	11th to 20th	Day	6% 2 1 2 3 2 2 2 4 5% 69%	1900
	21st to end	Day	7% 3 1 3 3 2 3 3 4 6% 65%	2081
November	1st to 10th	Day	11% 8% 2 4 3 4 3 3 4 7% 52%	1692
	11th to 20th	Day	10% 5% 1 3 3 3 4 3 5% 7% 54%	1710
	21st to end	Day	9% 8% 2 4 2 3 2 4 5% 6% 53%	1634
December	1st to 10th	Day	14% 6% 2 5% 4 3 4 4 3 8% 47%	1520
	11th to 20th	Day	21% 13% 4 6% 4 4 4 3 4 5% 33%	1928
	21st to end	Day	11% 9% 4 6% 3 4 4 4 6% 9% 40%	2794
January	1st to 10th	Night	10% 12% 4 6% 3 3 4 3 5% 6% 43%	4406
	11th to 20th	Night	18% 12% 3 5% 4 5% 5% 3 5% 6% 34%	4263
	21st to end	Night	15% 16% 3 6% 4 4 5% 3 5% 6% 33%	4521
February	1st to 10th	Night	14% 9% 2 5% 4 3 3 3 4 6% 47%	2470
	11th to 20th	Night	9% 14% 3 4 3 3 4 3 6% 7% 44%	2235
	21st to end	Night	13% 12% 3 6% 3 3 3 3 4 3 47%	1884
March	1st to 10th	Night	11% 24% 6% 5% 3 3 3 3 4 5% 33%	3717
	11th to 20th	Night	12% 11% 1 2 2 2 2 2 3 5% 56%	3490
	21st to end	Night	14% 20% 3 5% 4 4 4 3 5% 6% 32%	3621
April	1st to 10th	Night	11% 10% 3 5% 4 4 4 2 5% 6% 47%	1900
	11th to 20th	Night	9% 10% 3 5% 3 3 3 3 4 5% 52%	1879
	21st to end	Night	7% 8% 1 3 3 3 3 3 5% 7% 58%	1900
May	1st to 10th	Night	4 5% 3 3 2 2 3 2 4 5% 67%	3062
	11th to 20th	Night	3 3 1 2 1 2 2 2 3 6% 76%	2551
	21st to end	Night	5% 3 1 2 2 2 2 2 4 4 72%	2762
June	1st to 10th	Night	7% 5% 1 3 2 3 3 3 5% 5% 64%	1520
	11th to 20th	Night	2 2 1 1 1 1 2 2 3 4 81%	1520
	21st to end	Night	3 2 1 2 2 2 2 2 3 2 80%	1520
July	1st to 10th	Night	1 1 1 1 2 1 92%	2540
	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	5% 4 1 2 2 3 2 3 3 4 72%	2280
	11th to 20th	Night	6% 3 1 2 2 2 3 3 3 6% 71%	2280
	21st to end	Night	7% 3 1 2 1 2 3 3 4 5% 70%	2515
November	1st to 10th	Night	11% 8% 1 4 2 2 3 3 4 6% 56%	2431
	11th to 20th	Night	9% 4 1 4 3 4 3 3 5% 7% 57%	2470
	21st to end	Night	9% 8% 2 4 3 3 3 3 4 6% 55%	2541
December	1st to 10th	Night	16% 8% 2 3 3 3 3 3 4 6% 49%	2660
	11th to 20th	Night	21% 14% 2 5% 3 3 3 3 5% 7% 33%	3276
	21st to end	Night	14% 11% 3 7% 4 4 5% 3 5% 6% 37%	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	44% 6% 9% 19% 18% 3	2539
	11th to 20th	Day	47% 7% 10% 15% 13% 8%	2700
	21st to end	Day	49% 7% 9% 17% 13% 5%	3146
February	1st to 10th	Day	41% 4 10% 16% 18% 10%	1710
	11th to 20th	Day	40% 5% 10% 17% 21% 7%	1841
	21st to end	Day	44% 4 8% 20% 17% 6%	1570
March	1st to 10th	Day	54% 10% 10% 11% 10% 5%	3155
	11th to 20th	Day	32% 5% 9% 30% 19% 4	3490
	21st to end	Day	48% 11% 13% 18% 9% 1	4031
April	1st to 10th	Day	40% 6% 14% 21% 16% 3	2280
	11th to 20th	Day	34% 7% 13% 24% 17% 5%	2252
	21st to end	Day	27% 6% 15% 29% 19% 3	2280
May	1st to 10th	Day	19% 5% 12% 29% 21% 12%	3910
	11th to 20th	Day	15% 3 8% 30% 35% 8%	4342
	21st to end	Day	18% 7% 10% 38% 24% 3	4814
June	1st to 10th	Day	23% 6% 11% 24% 27% 8%	2660
	11th to 20th	Day	12% 3 8% 24% 36% 18%	2660
	21st to end	Day	10% 3 4 16% 35% 33%	2660
July	1st to 10th	Day	3 1 2 6% 17% 71%	4351
	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	20% 4 6% 17% 30% 22%	1900
	11th to 20th	Day	18% 4 7% 19% 30% 22%	1900
	21st to end	Day	22% 4 7% 19% 29% 19%	2081
November	1st to 10th	Day	33% 4 10% 19% 21% 13%	1692
	11th to 20th	Day	30% 5% 11% 17% 26% 12%	1710
	21st to end	Day	30% 5% 10% 19% 26% 11%	1634
December	1st to 10th	Day	37% 5% 9% 19% 19% 12%	1520
	11th to 20th	Day	54% 5% 6% 14% 12% 9%	1928
	21st to end	Day	37% 8% 15% 18% 17% 6%	2794
January	1st to 10th	Night	39% 7% 11% 24% 15% 4	4406
	11th to 20th	Night	49% 7% 9% 12% 14% 9%	4263
	21st to end	Night	50% 6% 9% 14% 13% 7%	4521
February	1st to 10th	Night	40% 4 7% 17% 19% 13%	2470
	11th to 20th	Night	38% 6% 8% 19% 20% 9%	2236
	21st to end	Night	40% 5% 9% 21% 19% 7%	1884
March	1st to 10th	Night	52% 7% 10% 13% 13% 5%	3717
	11th to 20th	Night	32% 4 6% 27% 27% 4	3490
	21st to end	Night	48% 12% 9% 18% 10% 2	3621
April	1st to 10th	Night	39% 7% 13% 19% 16% 6%	1900
	11th to 20th	Night	34% 6% 13% 24% 17% 7%	1879
	21st to end	Night	26% 6% 12% 32% 19% 4	1900
May	1st to 10th	Night	19% 6% 12% 29% 25% 9%	3062
	11th to 20th	Night	12% 4 8% 24% 39% 14%	2551
	21st to end	Night	14% 6% 15% 35% 29% 2	2762
June	1st to 10th	Night	21% 7% 11% 23% 28% 10%	1520
	11th to 20th	Night	9% 3 7% 25% 36% 20%	1520
	21st to end	Night	10% 4 4 14% 34% 34%	1520
July	1st to 10th	Night	3 1 2 5% 18% 71%	2500
	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	18% 4 7% 18% 29% 25%	2280
	11th to 20th	Night	16% 4 6% 17% 35% 22%	2280
	21st to end	Night	17% 4 8% 19% 31% 20%	2515
November	1st to 10th	Night	30% 5% 9% 19% 22% 16%	2431
	11th to 20th	Night	27% 6% 9% 19% 28% 11%	2470
	21st to end	Night	31% 4 7% 20% 24% 14%	2541
December	1st to 10th	Night	37% 4 8% 16% 20% 14%	2660
	11th to 20th	Night	51% 5% 6% 11% 19% 7%	3276
	21st to end	Night	43% 8% 12% 12% 18% 6%	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	38% 17% 19% 17% 9% 1	180
	11th to 20th	Day	26% 13% 22% 25% 11% 3	275
	21st to end	Day	26% 14% 24% 21% 14% 2	407
February	1st to 10th	Day	29% 17% 25% 18% 9% 2	370
	11th to 20th	Day	24% 21% 29% 18% 7%	446
	21st to end	Day	27% 17% 30% 20% 5% 1	382
March	1st to 10th	Day	33% 24% 22% 14% 6% 1	460
	11th to 20th	Day	27% 22% 22% 17% 10% 2	460
	21st to end	Day	25% 27% 25% 18% 5%	506
April	1st to 10th	Day	22% 23% 27% 21% 6% 1	460
	11th to 20th	Day	24% 22% 25% 21% 7% 2	452
	21st to end	Day	14% 19% 27% 25% 13% 3	460
May	1st to 10th	Day	16% 21% 33% 18% 10% 3	463
	11th to 20th	Day	16% 18% 27% 22% 13% 4	488
	21st to end	Day	14% 14% 30% 23% 13% 6%	529
June	1st to 10th	Day	9% 18% 31% 26% 11% 7%	490
	11th to 20th	Day	7% 21% 37% 20% 9% 6%	490
	21st to end	Day	3 16% 35% 29% 10% 7%	490
July	1st to 10th	Day	2 7% 52% 22% 11% 6%	486
	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	19% 15% 18% 24% 20% 4	276
	11th to 20th	Day	13% 12% 23% 32% 14% 6%	270
	21st to end	Day	14% 16% 25% 26% 17% 2	234
December	1st to 10th	Day	23% 13% 20% 23% 13% 7%	180
	11th to 20th	Day	18% 19% 26% 17% 15% 5%	180
	21st to end	Day	25% 13% 26% 21% 14% 2	198
January	1st to 10th	Night	24% 9% 23% 24% 15% 6%	760
	11th to 20th	Night	19% 11% 26% 31% 11% 3	760
	21st to end	Night	21% 12% 22% 24% 16% 4	836
February	1st to 10th	Night	19% 12% 24% 29% 14% 2	760
	11th to 20th	Night	20% 11% 22% 28% 15% 4	744
	21st to end	Night	22% 10% 25% 30% 10% 2	628
March	1st to 10th	Night	26% 11% 21% 25% 13% 3	760
	11th to 20th	Night	22% 9% 21% 24% 20% 4	760
	21st to end	Night	22% 11% 24% 28% 13% 2	836
April	1st to 10th	Night	16% 9% 25% 33% 16% 2	760
	11th to 20th	Night	16% 10% 20% 35% 16% 3	751
	21st to end	Night	12% 7% 20% 37% 18% 6%	760
May	1st to 10th	Night	11% 9% 24% 31% 22% 4	694
	11th to 20th	Night	7% 6% 17% 42% 24% 5%	396
	21st to end	Night	11% 4 14% 36% 30% 5%	411
June	1st to 10th	Night	8% 4 15% 38% 29% 6%	380
	11th to 20th	Night	2 3 19% 40% 32% 4	380
	21st to end	Night	3 2 13% 42% 34% 5%	380
July	1st to 10th	Night	1 9% 45% 42% 4	370
	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% 17% 32% 23% 6%	748
	11th to 20th	Night	12% 7% 24% 35% 16% 6%	760
	21st to end	Night	16% 9% 27% 28% 16% 4	760
December	1st to 10th	Night	22% 9% 21% 29% 14% 4	760
	11th to 20th	Night	26% 8% 21% 29% 14% 2	760
	21st to end	Night	26% 11% 23% 25% 12% 2	836

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