Angelus Oaks Heliport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Angelus Oaks Heliport clear sky chart from 2005-11-06 to 2025-08-05.

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	3 4 1 3 2 3 3 3 4 6% 68%	129937
	Night	3 5% 1 3 2 3 3 2 4 6% 69%	127131
Transparency	Day	18% 3 5% 14% 28% 33%	129662
	Night	17% 2 5% 14% 27% 35%	126921
Seeing	Day	8% 12% 30% 33% 12% 4	16691
	Night	6% 6% 20% 34% 27% 7%	26772

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	4 5% 2 3 2 2 2 2 3 5% 69%	4098
	11th to 20th	Day	5% 4 1 2 2 2 2 2 4 6% 69%	4220
	21st to end	Day	7% 9% 3 4 3 3 3 3 6% 8% 51%	5016
February	1st to 10th	Day	8% 8% 2 4 2 3 3 3 5% 5% 57%	2000
	11th to 20th	Day	6% 9% 1 5% 3 3 3 3 5% 6% 55%	1950
	21st to end	Day	8% 10% 3 5% 4 3 2 2 3 7% 53%	1650
March	1st to 10th	Day	6% 10% 2 4 4 4 3 3 4 7% 52%	4518
	11th to 20th	Day	5% 11% 2 5% 4 3 4 3 5% 8% 52%	4775
	21st to end	Day	4 8% 1 4 3 3 4 4 5% 7% 57%	5766
April	1st to 10th	Day	6% 7% 2 4 3 3 3 4 4 7% 58%	2400
	11th to 20th	Day	3 5% 1 3 3 3 3 3 5% 7% 65%	2369
	21st to end	Day	3 4 1 3 3 3 2 3 5% 8% 65%	2400
May	1st to 10th	Day	2 4 1 4 3 3 4 2 4 4 68%	5808
	11th to 20th	Day	2 2 1 2 2 2 3 3 4 6% 73%	5841
	21st to end	Day	1 1 2 1 2 2 2 4 6% 79%	6423
June	1st to 10th	Day	2 2 1 2 2 3 3 2 5% 6% 72%	2600
	11th to 20th	Day	1 1 1 2 2 2 3 4 84%	2600
	21st to end	Day	1 3 1 2 2 1 1 1 2 3 83%	2704
July	1st to 10th	Day	1 1 1 1 1 2 2 2 3 85%	6054
	11th to 20th	Day	1 1 2 2 2 3 2 5% 6% 75%	5880
	21st to end	Day	1 1 2 1 2 2 2 4 5% 80%	6279
August	1st to 10th	Day	1 1 1 2 2 2 5% 3 5% 7% 70%	3832
	11th to 20th	Day	1 1 1 1 2 2 2 3 4 82%	3724
	21st to end	Day	1 1 2 1 2 2 2 3 3 83%	4180
September	1st to 10th	Day	3 2 1 3 2 3 4 3 5% 6% 70%	2266
	11th to 20th	Day	1 1 2 2 2 2 2 2 4 83%	2090
	21st to end	Day	1 1 1 2 2 2 3 2 4 4 78%	2090
October	1st to 10th	Day	2 3 1 3 3 3 5% 2 4 5% 69%	3490
	11th to 20th	Day	1 1 1 1 1 2 2 4 5% 80%	3444
	21st to end	Day	4 3 1 3 2 2 3 3 4 5% 71%	3237
November	1st to 10th	Day	3 5% 1 4 3 2 2 2 4 5% 69%	1764
	11th to 20th	Day	4 4 1 4 3 3 2 3 5% 5% 67%	1800
	21st to end	Day	5% 5% 2 5% 3 4 4 3 4 8% 57%	1800
December	1st to 10th	Day	3 4 1 4 3 3 4 3 6% 7% 61%	2950
	11th to 20th	Day	7% 5% 2 4 3 5% 6% 5% 5% 7% 51%	3409
	21st to end	Day	5% 8% 3 7% 5% 5% 5% 4 7% 8% 45%	4510
January	1st to 10th	Night	3 5% 2 3 3 2 3 2 4 5% 67%	5867
	11th to 20th	Night	3 4 1 4 3 2 2 2 3 6% 69%	5750
	21st to end	Night	6% 9% 2 5% 3 3 4 3 5% 6% 54%	5984
February	1st to 10th	Night	7% 11% 2 4 3 2 2 3 4 6% 55%	2400
	11th to 20th	Night	5% 10% 1 4 4 2 3 4 5% 6% 57%	2338
	21st to end	Night	7% 10% 3 5% 4 4 3 3 5% 6% 51%	1980
March	1st to 10th	Night	4 10% 2 4 6% 6% 4 3 6% 8% 48%	5376
	11th to 20th	Night	3 10% 3 4 4 4 5% 4 5% 7% 52%	5224
	21st to end	Night	2 9% 2 4 3 4 4 4 6% 7% 56%	5192
April	1st to 10th	Night	3 8% 1 4 4 3 4 3 5% 6% 58%	2000
	11th to 20th	Night	2 6% 1 3 2 4 3 2 5% 6% 66%	1979
	21st to end	Night	2 4 2 3 3 3 3 3 4 7% 66%	2000
May	1st to 10th	Night	2 4 1 3 2 3 2 2 3 4 74%	4174
	11th to 20th	Night	1 2 1 1 2 2 2 2 4 5% 79%	4074
	21st to end	Night	1 1 1 1 1 2 2 4 6% 80%	4474
June	1st to 10th	Night	1 1 1 2 1 2 2 2 5% 5% 78%	1800
	11th to 20th	Night	1 1 1 1 1 1 2 1 2 4 86%	1800
	21st to end	Night	1 1 1 1 1 1 1 2 3 86%	1672
July	1st to 10th	Night	1 1 1 1 1 2 93%	3870
	11th to 20th	Night	1 1 1 1 2 2 2 3 3 84%	4100
	21st to end	Night	1 2 1 1 1 1 1 1 2 3 86%	4596
August	1st to 10th	Night	1 1 1 1 1 2 2 3 5% 84%	3206
	11th to 20th	Night	1 1 1 1 1 2 3 5% 86%	3126
	21st to end	Night	1 1 1 1 1 1 1 1 2 91%	3498
September	1st to 10th	Night	2 2 1 2 1 1 2 2 3 5% 79%	1912
	11th to 20th	Night	1 1 1 1 1 2 1 3 3 88%	2090
	21st to end	Night	1 1 1 1 1 2 2 2 4 85%	2090
October	1st to 10th	Night	2 2 2 1 1 2 2 2 3 82%	3490
	11th to 20th	Night	1 1 1 1 1 3 3 4 3 81%	3490
	21st to end	Night	2 4 1 3 2 2 2 2 2 5% 74%	4325
November	1st to 10th	Night	2 5% 2 3 3 2 2 2 3 6% 69%	2535
	11th to 20th	Night	2 4 2 4 3 3 3 3 4 6% 66%	2600
	21st to end	Night	3 7% 2 5% 4 4 4 3 5% 7% 56%	2600
December	1st to 10th	Night	4 4 2 4 3 3 3 3 5% 6% 65%	4240
	11th to 20th	Night	6% 6% 2 6% 4 4 5% 4 6% 8% 50%	4811
	21st to end	Night	3 5% 2 5% 4 5% 6% 5% 7% 11% 46%	6468

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	19% 2 4 17% 36% 23%	4099
	11th to 20th	Day	16% 3 7% 13% 20% 40%	4220
	21st to end	Day	29% 3 5% 11% 26% 27%	5016
February	1st to 10th	Day	27% 4 4 14% 23% 27%	2000
	11th to 20th	Day	27% 3 6% 15% 27% 22%	1960
	21st to end	Day	30% 3 7% 16% 23% 21%	1650
March	1st to 10th	Day	27% 3 8% 13% 23% 26%	4518
	11th to 20th	Day	28% 5% 5% 25% 24% 14%	4775
	21st to end	Day	22% 3 10% 26% 29% 10%	5766
April	1st to 10th	Day	26% 3 8% 20% 27% 16%	2400
	11th to 20th	Day	18% 2 7% 19% 31% 23%	2372
	21st to end	Day	16% 4 8% 21% 39% 14%	2400
May	1st to 10th	Day	18% 3 5% 18% 38% 19%	5808
	11th to 20th	Day	12% 2 5% 16% 38% 27%	5844
	21st to end	Day	10% 2 3 16% 34% 35%	6424
June	1st to 10th	Day	14% 2 4 15% 36% 28%	2600
	11th to 20th	Day	6% 2 4 9% 26% 53%	2600
	21st to end	Day	11% 1 3 6% 19% 60%	2704
July	1st to 10th	Day	8% 2 1 7% 12% 70%	5991
	11th to 20th	Day	15% 3 3 12% 31% 36%	5811
	21st to end	Day	10% 3 4 16% 16% 50%	6097
August	1st to 10th	Day	18% 3 6% 22% 22% 29%	3819
	11th to 20th	Day	8% 3 6% 12% 22% 51%	3760
	21st to end	Day	9% 2 2 6% 27% 54%	4179
September	1st to 10th	Day	16% 4 5% 6% 27% 41%	2266
	11th to 20th	Day	7% 2 2 7% 31% 50%	2090
	21st to end	Day	10% 2 4 13% 28% 43%	2090
October	1st to 10th	Day	19% 3 3 8% 29% 38%	3490
	11th to 20th	Day	9% 2 3 7% 38% 41%	3444
	21st to end	Day	17% 2 2 7% 32% 38%	3237
November	1st to 10th	Day	17% 2 4 14% 33% 31%	1764
	11th to 20th	Day	20% 2 5% 13% 24% 38%	1800
	21st to end	Day	26% 3 6% 13% 27% 27%	1800
December	1st to 10th	Day	23% 2 4 14% 30% 27%	2950
	11th to 20th	Day	31% 3 6% 16% 28% 16%	3408
	21st to end	Day	34% 4 8% 17% 23% 15%	4510
January	1st to 10th	Night	19% 3 4 16% 28% 30%	5867
	11th to 20th	Night	16% 2 7% 15% 23% 37%	5750
	21st to end	Night	30% 3 6% 9% 24% 28%	5984
February	1st to 10th	Night	29% 4 5% 13% 21% 29%	2400
	11th to 20th	Night	28% 2 5% 13% 25% 26%	2339
	21st to end	Night	30% 3 7% 13% 21% 26%	1980
March	1st to 10th	Night	27% 2 12% 15% 20% 25%	5376
	11th to 20th	Night	27% 3 6% 21% 29% 14%	5224
	21st to end	Night	22% 3 9% 22% 32% 12%	5192
April	1st to 10th	Night	23% 4 9% 20% 27% 18%	2000
	11th to 20th	Night	17% 2 6% 19% 30% 26%	1979
	21st to end	Night	14% 3 7% 18% 39% 18%	2000
May	1st to 10th	Night	13% 3 5% 17% 34% 28%	4171
	11th to 20th	Night	9% 2 3 14% 43% 29%	4075
	21st to end	Night	8% 1 4 16% 34% 38%	4474
June	1st to 10th	Night	9% 1 5% 16% 33% 35%	1800
	11th to 20th	Night	6% 1 4 9% 25% 54%	1800
	21st to end	Night	7% 1 2 6% 20% 64%	1672
July	1st to 10th	Night	3 1 2 8% 9% 78%	3825
	11th to 20th	Night	9% 2 2 11% 27% 49%	4046
	21st to end	Night	7% 3 3 18% 17% 52%	4466
August	1st to 10th	Night	8% 2 4 25% 29% 32%	3196
	11th to 20th	Night	5% 2 5% 14% 25% 50%	3156
	21st to end	Night	5% 1 2 6% 24% 62%	3498
September	1st to 10th	Night	10% 2 4 8% 27% 48%	1912
	11th to 20th	Night	5% 1 3 9% 30% 53%	2090
	21st to end	Night	6% 1 3 14% 30% 45%	2090
October	1st to 10th	Night	10% 1 2 8% 32% 47%	3490
	11th to 20th	Night	9% 1 2 7% 32% 49%	3490
	21st to end	Night	15% 1 3 5% 27% 50%	4325
November	1st to 10th	Night	18% 1 3 11% 32% 34%	2535
	11th to 20th	Night	18% 2 4 11% 27% 38%	2600
	21st to end	Night	26% 4 7% 12% 23% 29%	2600
December	1st to 10th	Night	21% 2 3 12% 29% 33%	4240
	11th to 20th	Night	30% 2 8% 15% 27% 18%	4811
	21st to end	Night	29% 3 8% 21% 21% 19%	6468

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	21% 9% 33% 26% 10% 1	300
	11th to 20th	Day	16% 11% 28% 31% 11% 2	355
	21st to end	Day	14% 16% 33% 27% 10% 1	550
February	1st to 10th	Day	16% 18% 30% 23% 11% 2	500
	11th to 20th	Day	16% 17% 34% 26% 6% 1	495
	21st to end	Day	17% 21% 34% 24% 4	414
March	1st to 10th	Day	22% 19% 31% 22% 6%	500
	11th to 20th	Day	17% 18% 33% 25% 6% 1	500
	21st to end	Day	14% 23% 37% 21% 5% 1	550
April	1st to 10th	Day	13% 18% 30% 27% 10% 2	500
	11th to 20th	Day	10% 24% 34% 25% 7% 2	492
	21st to end	Day	8% 19% 32% 27% 10% 5%	500
May	1st to 10th	Day	8% 17% 35% 28% 8% 3	503
	11th to 20th	Day	8% 16% 34% 27% 11% 3	528
	21st to end	Day	6% 13% 36% 29% 12% 5%	573
June	1st to 10th	Day	3 11% 29% 34% 17% 7%	530
	11th to 20th	Day	3 12% 32% 36% 12% 6%	530
	21st to end	Day	3 9% 30% 38% 13% 6%	530
July	1st to 10th	Day	2 4 24% 48% 14% 9%	526
	11th to 20th	Day	2 1 21% 44% 20% 11%	524
	21st to end	Day	3 5% 19% 43% 17% 13%	575
August	1st to 10th	Day	2 3 28% 43% 14% 9%	504
	11th to 20th	Day	2 4 21% 45% 17% 11%	477
	21st to end	Day	2 2 24% 47% 16% 10%	539
September	1st to 10th	Day	4 4 31% 41% 15% 5%	490
	11th to 20th	Day	4 6% 33% 40% 16% 1	490
	21st to end	Day	3 12% 30% 36% 16% 3	490
October	1st to 10th	Day	4 13% 34% 34% 14% 1	490
	11th to 20th	Day	4 10% 34% 35% 15% 1	490
	21st to end	Day	5% 10% 30% 36% 17% 3	416
November	1st to 10th	Day	8% 11% 29% 38% 13% 1	300
	11th to 20th	Day	7% 11% 29% 36% 13% 4	300
	21st to end	Day	9% 14% 31% 32% 12% 2	300
December	1st to 10th	Day	11% 9% 33% 32% 12% 2	300
	11th to 20th	Day	8% 10% 31% 35% 13% 2	300
	21st to end	Day	15% 18% 34% 20% 9% 2	330
January	1st to 10th	Night	13% 8% 26% 29% 17% 7%	800
	11th to 20th	Night	10% 6% 27% 33% 19% 6%	800
	21st to end	Night	12% 8% 30% 32% 15% 4	880
February	1st to 10th	Night	14% 9% 26% 31% 14% 6%	800
	11th to 20th	Night	10% 10% 28% 30% 17% 5%	784
	21st to end	Night	14% 10% 31% 27% 14% 3	660
March	1st to 10th	Night	14% 10% 29% 30% 14% 3	800
	11th to 20th	Night	12% 10% 22% 31% 18% 7%	800
	21st to end	Night	9% 11% 28% 34% 15% 3	880
April	1st to 10th	Night	9% 9% 26% 36% 16% 4	800
	11th to 20th	Night	5% 9% 31% 32% 19% 4	791
	21st to end	Night	4 9% 25% 35% 19% 7%	800
May	1st to 10th	Night	6% 5% 23% 40% 21% 4	635
	11th to 20th	Night	3 6% 20% 37% 28% 6%	591
	21st to end	Night	4 5% 20% 39% 27% 4	650
June	1st to 10th	Night	1 4 13% 44% 33% 5%	600
	11th to 20th	Night	1 2 19% 42% 33% 3	600
	21st to end	Night	1 1 13% 41% 39% 5%	472
July	1st to 10th	Night	6% 35% 48% 11%	485
	11th to 20th	Night	3 3 39% 50% 6%	582
	21st to end	Night	2 1 6% 29% 53% 10%	706
August	1st to 10th	Night	1 1 7% 32% 47% 13%	772
	11th to 20th	Night	2 1 3 25% 54% 16%	752
	21st to end	Night	2 1 5% 26% 49% 17%	836
September	1st to 10th	Night	2 1 6% 31% 46% 14%	760
	11th to 20th	Night	1 2 10% 36% 38% 13%	760
	21st to end	Night	1 2 14% 36% 37% 11%	760
October	1st to 10th	Night	4 4 18% 42% 27% 5%	760
	11th to 20th	Night	3 3 19% 37% 28% 10%	760
	21st to end	Night	4 6% 23% 31% 25% 12%	836
November	1st to 10th	Night	7% 4 20% 37% 24% 8%	780
	11th to 20th	Night	5% 5% 22% 36% 23% 8%	800
	21st to end	Night	8% 7% 26% 31% 21% 7%	800
December	1st to 10th	Night	9% 6% 27% 33% 20% 5%	800
	11th to 20th	Night	13% 6% 27% 33% 17% 4	800
	21st to end	Night	11% 11% 30% 28% 15% 5%	880

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