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 2024-03-23.

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	9% 7% 2 3 3 2 3 3 4 5% 59%	78808
	Night	10% 8% 2 3 3 2 3 3 4 6% 56%	81105
Transparency	Day	27% 5% 9% 18% 24% 17%	78519
	Night	30% 5% 9% 18% 23% 16%	80915
Seeing	Day	14% 16% 32% 24% 11% 3	14234
	Night	14% 7% 19% 33% 22% 5%	23725

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% 18% 3 4 3 2 3 3 4 6% 42%	2539
	11th to 20th	Day	17% 12% 3 6% 5% 4 4 4 4 6% 37%	2700
	21st to end	Day	16% 13% 4 6% 5% 2 4 4 4 6% 35%	3146
February	1st to 10th	Day	16% 10% 3 4 3 1 3 4 4 5% 47%	1710
	11th to 20th	Day	11% 13% 4 4 4 2 3 3 4 6% 45%	1831
	21st to end	Day	15% 14% 4 5% 3 2 3 3 4 4 43%	1570
March	1st to 10th	Day	13% 16% 5% 5% 5% 3 5% 3 5% 6% 33%	1905
	11th to 20th	Day	15% 13% 3 5% 3 2 3 4 4 6% 41%	2090
	21st to end	Day	14% 16% 3 4 4 2 3 4 4 7% 39%	2317
April	1st to 10th	Day	14% 11% 2 4 4 2 4 4 6% 7% 43%	2160
	11th to 20th	Day	10% 11% 3 5% 3 2 3 3 4 6% 50%	2129
	21st to end	Day	11% 6% 1 3 3 1 2 4 4 7% 56%	2160
May	1st to 10th	Day	8% 7% 2 3 2 2 3 3 5% 7% 58%	2218
	11th to 20th	Day	8% 7% 2 4 4 2 3 4 4 7% 57%	2452
	21st to end	Day	11% 7% 2 4 4 2 3 4 4 5% 54%	2723
June	1st to 10th	Day	7% 4 1 4 3 2 3 4 4 7% 61%	2520
	11th to 20th	Day	3 2 1 2 2 1 2 2 4 5% 76%	2520
	21st to end	Day	3 2 1 2 1 1 2 2 3 3 81%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 2 3 86%	2520
	11th to 20th	Day	2 1 1 1 1 1 2 2 3 4 83%	2520
	21st to end	Day	1 2 2 3 2 2 2 3 4 79%	2620
August	1st to 10th	Day	2 1 1 2 2 1 2 3 3 4 79%	2320
	11th to 20th	Day	1 1 1 1 1 1 2 4 4 82%	2122
	21st to end	Day	1 1 1 1 1 1 2 2 3 87%	2376
September	1st to 10th	Day	2 1 1 1 1 1 2 1 3 3 86%	2160
	11th to 20th	Day	4 2 1 3 3 2 3 3 3 4 73%	2152
	21st to end	Day	4 3 1 2 3 1 2 2 3 4 75%	1976
October	1st to 10th	Day	7% 4 1 3 2 2 3 3 4 5% 66%	1800
	11th to 20th	Day	6% 2 1 2 3 2 3 3 4 5% 68%	1800
	21st to end	Day	8% 3 3 3 2 3 3 4 5% 66%	1972
November	1st to 10th	Day	11% 7% 2 4 3 3 4 3 4 6% 53%	1674
	11th to 20th	Day	10% 5% 2 3 3 2 5% 4 5% 7% 54%	1710
	21st to end	Day	9% 7% 3 3 3 2 2 4 6% 6% 54%	1634
December	1st to 10th	Day	15% 6% 2 3 5% 3 4 5% 3 7% 48%	1520
	11th to 20th	Day	21% 12% 4 6% 4 3 4 3 4 5% 33%	1928
	21st to end	Day	11% 9% 4 5% 4 3 4 5% 6% 9% 40%	2794
January	1st to 10th	Night	10% 12% 4 5% 4 2 4 4 5% 6% 43%	4406
	11th to 20th	Night	19% 11% 3 4 5% 3 5% 5% 5% 6% 34%	4263
	21st to end	Night	15% 16% 3 5% 5% 3 5% 4 4 6% 33%	4521
February	1st to 10th	Night	14% 9% 2 4 5% 2 3 4 4 6% 48%	2470
	11th to 20th	Night	9% 13% 3 4 3 2 3 4 6% 7% 45%	2235
	21st to end	Night	13% 11% 4 5% 4 2 3 4 4 4 47%	1884
March	1st to 10th	Night	15% 15% 5% 5% 3 2 4 4 3 5% 38%	2273
	11th to 20th	Night	13% 13% 3 3 3 2 4 4 5% 6% 44%	2090
	21st to end	Night	13% 14% 2 3 4 3 3 4 5% 6% 43%	2083
April	1st to 10th	Night	12% 9% 3 5% 5% 2 5% 3 5% 6% 46%	1800
	11th to 20th	Night	10% 9% 3 4 3 2 4 4 4 6% 51%	1779
	21st to end	Night	8% 7% 1 3 3 2 3 4 4 7% 58%	1800
May	1st to 10th	Night	7% 5% 2 4 3 2 4 3 5% 6% 59%	1738
	11th to 20th	Night	6% 5% 2 3 2 2 3 3 4 8% 61%	1437
	21st to end	Night	9% 5% 1 3 3 2 3 4 5% 6% 60%	1552
June	1st to 10th	Night	6% 4 1 3 3 2 3 3 4 5% 65%	1440
	11th to 20th	Night	2 2 1 1 1 1 2 2 3 5% 80%	1440
	21st to end	Night	3 2 1 2 2 1 3 2 3 3 80%	1440
July	1st to 10th	Night	1 1 1 2 2 3 3 86%	1440
	11th to 20th	Night	1 1 1 2 2 1 2 3 3 3 81%	1440
	21st to end	Night	2 2 1 2 2 2 3 3 3 4 76%	1694
August	1st to 10th	Night	3 2 1 2 2 2 2 3 3 4 75%	1616
	11th to 20th	Night	1 1 1 1 2 1 3 2 4 5% 78%	1780
	21st to end	Night	2 1 1 1 2 1 1 1 2 3 85%	1980
September	1st to 10th	Night	2 1 1 1 1 1 2 4 87%	1800
	11th to 20th	Night	3 1 2 1 1 1 2 3 5% 80%	1808
	21st to end	Night	3 2 1 2 3 1 2 3 3 6% 75%	1980
October	1st to 10th	Night	6% 4 1 2 2 2 2 3 3 4 71%	2160
	11th to 20th	Night	6% 3 1 2 2 2 3 3 3 6% 70%	2160
	21st to end	Night	7% 3 1 1 1 1 2 3 4 5% 70%	2382
November	1st to 10th	Night	11% 7% 2 3 2 1 3 3 4 7% 56%	2405
	11th to 20th	Night	9% 4 1 3 4 3 3 4 4 8% 57%	2470
	21st to end	Night	10% 7% 2 4 3 2 4 3 4 6% 55%	2541
December	1st to 10th	Night	16% 8% 2 3 3 2 3 4 4 6% 50%	2660
	11th to 20th	Night	22% 13% 3 5% 4 2 3 4 5% 7% 33%	3276
	21st to end	Night	14% 11% 3 6% 5% 3 5% 5% 5% 7% 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	52% 7% 9% 15% 14% 4	1905
	11th to 20th	Day	44% 5% 10% 19% 16% 5%	2090
	21st to end	Day	45% 8% 14% 18% 13% 3	2317
April	1st to 10th	Day	40% 6% 14% 20% 16% 4	2160
	11th to 20th	Day	34% 7% 12% 23% 18% 5%	2132
	21st to end	Day	28% 6% 15% 28% 19% 3	2160
May	1st to 10th	Day	25% 6% 12% 30% 22% 5%	2218
	11th to 20th	Day	27% 6% 12% 28% 22% 5%	2455
	21st to end	Day	30% 8% 13% 27% 17% 4	2724
June	1st to 10th	Day	24% 6% 11% 24% 27% 8%	2520
	11th to 20th	Day	12% 3 8% 24% 35% 18%	2520
	21st to end	Day	10% 3 4 17% 35% 30%	2520
July	1st to 10th	Day	6% 2 3 11% 30% 48%	2451
	11th to 20th	Day	8% 2 4 15% 28% 43%	2445
	21st to end	Day	10% 3 5% 11% 26% 45%	2474
August	1st to 10th	Day	11% 3 4 13% 30% 39%	2304
	11th to 20th	Day	6% 2 5% 12% 39% 36%	2122
	21st to end	Day	7% 1 2 12% 41% 37%	2376
September	1st to 10th	Day	7% 2 4 10% 35% 43%	2160
	11th to 20th	Day	14% 4 7% 20% 37% 18%	2152
	21st to end	Day	15% 3 6% 20% 36% 21%	1976
October	1st to 10th	Day	21% 5% 6% 18% 30% 20%	1800
	11th to 20th	Day	19% 4 7% 19% 29% 22%	1800
	21st to end	Day	22% 5% 7% 18% 28% 20%	1972
November	1st to 10th	Day	32% 4 11% 19% 21% 13%	1674
	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	48% 6% 9% 15% 16% 5%	2273
	11th to 20th	Night	40% 5% 9% 21% 19% 7%	2090
	21st to end	Night	41% 9% 11% 19% 15% 4	2083
April	1st to 10th	Night	40% 7% 13% 19% 16% 7%	1800
	11th to 20th	Night	35% 5% 13% 22% 17% 7%	1779
	21st to end	Night	27% 6% 12% 33% 19% 4	1800
May	1st to 10th	Night	25% 7% 11% 27% 25% 6%	1738
	11th to 20th	Night	22% 5% 12% 30% 25% 6%	1437
	21st to end	Night	24% 8% 16% 28% 21% 4	1552
June	1st to 10th	Night	21% 7% 11% 23% 28% 10%	1440
	11th to 20th	Night	9% 4 8% 25% 34% 20%	1440
	21st to end	Night	11% 4 4 14% 34% 33%	1440
July	1st to 10th	Night	6% 2 3 10% 31% 48%	1400
	11th to 20th	Night	8% 3 5% 12% 25% 47%	1392
	21st to end	Night	12% 3 5% 10% 23% 47%	1600
August	1st to 10th	Night	13% 3 6% 12% 27% 40%	1607
	11th to 20th	Night	9% 3 6% 12% 30% 40%	1780
	21st to end	Night	8% 1 3 11% 34% 43%	1980
September	1st to 10th	Night	5% 2 4 9% 34% 47%	1800
	11th to 20th	Night	9% 3 7% 20% 40% 21%	1808
	21st to end	Night	12% 3 6% 21% 33% 24%	1980
October	1st to 10th	Night	18% 4 7% 18% 29% 23%	2160
	11th to 20th	Night	17% 4 6% 17% 34% 23%	2160
	21st to end	Night	17% 4 8% 19% 31% 21%	2382
November	1st to 10th	Night	29% 5% 9% 19% 22% 16%	2405
	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	26% 25% 25% 19% 5%	471
April	1st to 10th	Day	23% 22% 28% 21% 6% 1	420
	11th to 20th	Day	25% 22% 26% 19% 6% 1	412
	21st to end	Day	15% 19% 28% 23% 12% 3	420
May	1st to 10th	Day	16% 20% 32% 19% 10% 3	423
	11th to 20th	Day	18% 19% 28% 19% 12% 4	448
	21st to end	Day	15% 14% 29% 23% 13% 6%	485
June	1st to 10th	Day	9% 18% 30% 25% 10% 7%	450
	11th to 20th	Day	8% 21% 36% 20% 9% 6%	450
	21st to end	Day	3 15% 36% 29% 10% 7%	450
July	1st to 10th	Day	2 7% 53% 21% 11% 6%	446
	11th to 20th	Day	7% 46% 29% 11% 7%	444
	21st to end	Day	1 6% 45% 27% 14% 6%	487
August	1st to 10th	Day	3 13% 43% 25% 12% 5%	447
	11th to 20th	Day	1 9% 43% 28% 14% 5%	437
	21st to end	Day	3 6% 47% 28% 13% 3	495
September	1st to 10th	Day	3 7% 47% 27% 13% 2	450
	11th to 20th	Day	7% 15% 36% 29% 10% 2	450
	21st to end	Day	5% 17% 35% 35% 7% 1	450
October	1st to 10th	Day	8% 16% 30% 32% 12% 2	450
	11th to 20th	Day	10% 13% 29% 31% 14% 3	450
	21st to end	Day	11% 15% 29% 28% 13% 4	487
November	1st to 10th	Day	19% 15% 18% 24% 20% 4	270
	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% 23% 29% 13% 2	800
April	1st to 10th	Night	16% 8% 24% 33% 16% 2	720
	11th to 20th	Night	17% 9% 20% 33% 17% 3	711
	21st to end	Night	12% 7% 20% 36% 19% 6%	720
May	1st to 10th	Night	10% 8% 23% 31% 23% 4	658
	11th to 20th	Night	8% 6% 16% 41% 25% 5%	375
	21st to end	Night	11% 4 13% 34% 32% 5%	389
June	1st to 10th	Night	8% 3 15% 36% 31% 6%	360
	11th to 20th	Night	3 3 18% 39% 33% 4	360
	21st to end	Night	3 3 12% 41% 36% 5%	360
July	1st to 10th	Night	1 7% 44% 44% 4	350
	11th to 20th	Night	2 9% 43% 41% 5%	348
	21st to end	Night	2 1 8% 31% 46% 11%	512
August	1st to 10th	Night	3 1 10% 42% 39% 5%	542
	11th to 20th	Night	2 1 11% 45% 33% 9%	712
	21st to end	Night	2 1 10% 47% 37% 4	792
September	1st to 10th	Night	2 1 9% 45% 38% 5%	720
	11th to 20th	Night	3 2 14% 38% 33% 9%	720
	21st to end	Night	4 3 17% 41% 26% 9%	720
October	1st to 10th	Night	7% 5% 19% 39% 23% 7%	720
	11th to 20th	Night	8% 7% 15% 38% 26% 6%	720
	21st to end	Night	9% 9% 18% 30% 23% 10%	792
November	1st to 10th	Night	16% 6% 16% 33% 24% 6%	740
	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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