Red Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red Hill Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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 5% 4 3 4 3 5% 7% 54%	105146
	Night	7% 7% 3 6% 4 4 4 4 5% 7% 50%	103296
Transparency	Day	28% 6% 10% 21% 20% 14%	104897
	Night	32% 7% 12% 21% 17% 11%	103135
Seeing	Day	9% 8% 24% 29% 22% 8%	14904
	Night	10% 6% 23% 40% 19% 2	24664

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% 17% 5% 11% 6% 5% 5% 3 5% 6% 26%	2539
	11th to 20th	Day	9% 15% 7% 9% 4 4 5% 3 5% 6% 33%	2540
	21st to end	Day	11% 15% 5% 8% 5% 4 4 4 5% 8% 30%	3057
February	1st to 10th	Day	8% 12% 4 8% 5% 4 5% 5% 6% 7% 36%	1710
	11th to 20th	Day	8% 11% 4 10% 4 4 4 5% 6% 8% 36%	1775
	21st to end	Day	6% 13% 3 10% 5% 4 4 4 5% 8% 36%	1570
March	1st to 10th	Day	8% 13% 4 10% 5% 5% 4 4 5% 7% 35%	3213
	11th to 20th	Day	6% 10% 2 6% 4 3 4 3 5% 6% 53%	3490
	21st to end	Day	9% 12% 4 8% 6% 6% 6% 4 7% 8% 30%	3825
April	1st to 10th	Day	9% 9% 2 7% 5% 5% 4 4 7% 7% 42%	2197
	11th to 20th	Day	7% 9% 2 5% 4 4 4 3 5% 7% 48%	2406
	21st to end	Day	7% 6% 2 6% 4 4 4 4 7% 8% 48%	2470
May	1st to 10th	Day	8% 8% 2 7% 4 5% 4 4 6% 6% 47%	4110
	11th to 20th	Day	5% 3 1 3 3 3 4 3 5% 6% 63%	4071
	21st to end	Day	7% 5% 2 5% 4 3 5% 4 6% 8% 53%	4501
June	1st to 10th	Day	6% 4 1 4 3 4 4 4 8% 9% 53%	2750
	11th to 20th	Day	5% 5% 1 4 3 3 3 2 5% 8% 61%	2850
	21st to end	Day	2 1 1 2 2 2 3 3 4 6% 73%	2713
July	1st to 10th	Day	1 1 1 2 2 2 2 2 4 5% 80%	4420
	11th to 20th	Day	2 2 3 3 3 4 4 6% 6% 68%	4420
	21st to end	Day	4 2 1 3 3 3 3 3 5% 6% 68%	4552
August	1st to 10th	Day	3 3 1 4 3 3 4 4 7% 7% 62%	4092
	11th to 20th	Day	2 1 1 3 2 2 3 2 4 5% 75%	4028
	21st to end	Day	2 2 1 3 2 2 3 2 3 5% 75%	4473
September	1st to 10th	Day	3 2 1 2 2 3 2 3 4 6% 72%	2170
	11th to 20th	Day	4 3 1 3 3 3 3 3 4 6% 68%	2090
	21st to end	Day	6% 3 1 3 2 3 2 3 4 6% 67%	2090
October	1st to 10th	Day	5% 3 1 4 3 2 3 2 4 5% 68%	3429
	11th to 20th	Day	5% 4 2 4 2 3 3 2 4 6% 64%	3150
	21st to end	Day	4 6% 2 5% 3 3 4 4 6% 8% 56%	3169
November	1st to 10th	Day	8% 9% 3 6% 5% 4 5% 3 5% 6% 46%	1764
	11th to 20th	Day	8% 6% 2 7% 4 4 5% 4 6% 9% 44%	1800
	21st to end	Day	8% 10% 3 8% 5% 4 5% 4 5% 8% 41%	1676
December	1st to 10th	Day	10% 10% 3 9% 5% 5% 5% 3 4 6% 40%	1584
	11th to 20th	Day	10% 12% 5% 10% 5% 6% 6% 5% 7% 8% 28%	1740
	21st to end	Day	9% 12% 5% 9% 6% 4 5% 4 5% 7% 36%	2712
January	1st to 10th	Night	9% 14% 5% 10% 5% 4 4 4 6% 8% 30%	4406
	11th to 20th	Night	9% 14% 5% 12% 5% 5% 4 4 5% 7% 29%	4420
	21st to end	Night	11% 14% 5% 10% 5% 5% 4 3 5% 6% 32%	4604
February	1st to 10th	Night	8% 11% 4 9% 6% 5% 5% 4 7% 7% 34%	2470
	11th to 20th	Night	8% 10% 3 6% 5% 4 4 3 6% 8% 41%	2290
	21st to end	Night	5% 9% 3 7% 6% 6% 6% 4 8% 8% 39%	1884
March	1st to 10th	Night	8% 10% 3 8% 5% 5% 5% 4 6% 8% 38%	3659
	11th to 20th	Night	5% 7% 2 5% 4 4 4 4 5% 6% 55%	3490
	21st to end	Night	8% 9% 3 7% 5% 5% 6% 4 6% 9% 37%	3828
April	1st to 10th	Night	6% 9% 3 7% 5% 4 5% 4 5% 6% 47%	1980
	11th to 20th	Night	8% 9% 3 5% 4 3 4 4 5% 6% 48%	1720
	21st to end	Night	7% 6% 2 5% 3 4 3 4 6% 7% 52%	1710
May	1st to 10th	Night	12% 7% 2 5% 4 4 4 4 5% 7% 47%	2860
	11th to 20th	Night	3 3 1 4 4 3 4 4 6% 6% 62%	2834
	21st to end	Night	7% 6% 2 5% 4 4 4 3 4 7% 54%	3080
June	1st to 10th	Night	5% 2 2 5% 4 4 4 5% 7% 9% 52%	1420
	11th to 20th	Night	5% 4 2 3 2 4 3 4 5% 5% 63%	1330
	21st to end	Night	3 2 4 2 3 3 2 5% 5% 71%	1456
July	1st to 10th	Night	2 1 1 2 2 2 3 2 4 5% 77%	2540
	11th to 20th	Night	1 2 1 2 2 2 3 3 5% 7% 72%	2540
	21st to end	Night	2 2 1 4 4 4 4 4 5% 6% 65%	3004
August	1st to 10th	Night	2 3 1 4 2 3 4 4 6% 9% 62%	2847
	11th to 20th	Night	3 2 1 3 3 3 4 3 5% 7% 67%	2811
	21st to end	Night	3 2 1 3 2 2 3 2 3 4 75%	3193
September	1st to 10th	Night	2 2 1 3 2 2 3 3 4 5% 72%	2009
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 5% 64%	2090
	21st to end	Night	6% 3 1 3 2 2 3 2 4 4 69%	2090
October	1st to 10th	Night	4 3 1 3 2 2 2 2 4 5% 71%	3547
	11th to 20th	Night	7% 5% 2 6% 4 4 3 3 4 5% 58%	3778
	21st to end	Night	4 6% 2 5% 4 5% 5% 4 6% 9% 50%	4386
November	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 7% 48%	2535
	11th to 20th	Night	9% 6% 3 7% 5% 4 4 4 6% 7% 46%	2600
	21st to end	Night	6% 8% 3 7% 5% 5% 5% 4 6% 7% 44%	2700
December	1st to 10th	Night	9% 11% 3 8% 5% 5% 4 4 6% 8% 38%	2779
	11th to 20th	Night	11% 11% 5% 10% 5% 5% 5% 5% 6% 8% 29%	3448
	21st to end	Night	9% 11% 6% 10% 5% 4 4 4 5% 7% 34%	4958

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	57% 9% 14% 17% 2 1	2539
	11th to 20th	Day	50% 12% 19% 15% 4 1	2540
	21st to end	Day	50% 12% 20% 14% 4 1	3057
February	1st to 10th	Day	45% 9% 19% 21% 5% 1	1710
	11th to 20th	Day	44% 10% 17% 21% 7% 1	1785
	21st to end	Day	44% 8% 16% 22% 7% 2	1570
March	1st to 10th	Day	44% 10% 15% 24% 7% 1	3213
	11th to 20th	Day	31% 6% 13% 34% 14% 1	3490
	21st to end	Day	45% 12% 17% 19% 7% 1	3825
April	1st to 10th	Day	39% 6% 16% 21% 15% 3	2197
	11th to 20th	Day	34% 5% 12% 27% 19% 3	2409
	21st to end	Day	31% 6% 13% 28% 21% 2	2470
May	1st to 10th	Day	31% 8% 8% 24% 24% 5%	4110
	11th to 20th	Day	20% 5% 8% 30% 29% 9%	4074
	21st to end	Day	27% 8% 11% 28% 24% 3	4501
June	1st to 10th	Day	25% 8% 13% 29% 22% 4	2750
	11th to 20th	Day	22% 4 9% 24% 27% 13%	2850
	21st to end	Day	12% 4 5% 20% 35% 24%	2713
July	1st to 10th	Day	8% 2 2 10% 23% 54%	4351
	11th to 20th	Day	14% 3 3 8% 23% 49%	4345
	21st to end	Day	17% 3 3 10% 26% 41%	4408
August	1st to 10th	Day	19% 4 4 15% 24% 34%	4078
	11th to 20th	Day	12% 3 3 15% 40% 27%	4067
	21st to end	Day	14% 3 3 17% 32% 32%	4472
September	1st to 10th	Day	15% 3 5% 17% 31% 29%	2170
	11th to 20th	Day	17% 5% 9% 25% 28% 16%	2090
	21st to end	Day	20% 4 6% 25% 34% 11%	2090
October	1st to 10th	Day	21% 3 7% 18% 33% 18%	3429
	11th to 20th	Day	22% 4 7% 34% 27% 6%	3150
	21st to end	Day	25% 5% 12% 35% 19% 4	3169
November	1st to 10th	Day	38% 6% 13% 25% 16% 2	1764
	11th to 20th	Day	36% 9% 19% 27% 8% 1	1800
	21st to end	Day	41% 7% 19% 24% 10% 1	1676
December	1st to 10th	Day	44% 10% 18% 20% 6% 1	1584
	11th to 20th	Day	50% 10% 21% 17% 2	1739
	21st to end	Day	44% 10% 16% 20% 10%	2712
January	1st to 10th	Night	49% 9% 15% 22% 3 1	4406
	11th to 20th	Night	50% 12% 16% 17% 3 1	4420
	21st to end	Night	50% 10% 21% 15% 5% 1	4604
February	1st to 10th	Night	46% 9% 18% 21% 4 1	2470
	11th to 20th	Night	40% 8% 19% 23% 11%	2291
	21st to end	Night	39% 11% 17% 26% 7% 1	1884
March	1st to 10th	Night	40% 10% 14% 24% 11% 1	3659
	11th to 20th	Night	26% 8% 16% 31% 17% 1	3490
	21st to end	Night	39% 10% 15% 29% 7% 1	3828
April	1st to 10th	Night	37% 6% 13% 23% 16% 5%	1980
	11th to 20th	Night	35% 7% 10% 28% 18% 2	1720
	21st to end	Night	29% 5% 11% 25% 27% 2	1710
May	1st to 10th	Night	33% 8% 9% 21% 22% 7%	2860
	11th to 20th	Night	19% 6% 9% 24% 32% 10%	2835
	21st to end	Night	27% 7% 10% 24% 27% 4	3080
June	1st to 10th	Night	26% 7% 15% 23% 24% 4	1420
	11th to 20th	Night	22% 5% 6% 20% 32% 14%	1330
	21st to end	Night	14% 4 5% 13% 31% 32%	1456
July	1st to 10th	Night	11% 3 2 8% 19% 57%	2500
	11th to 20th	Night	12% 2 3 6% 20% 57%	2492
	21st to end	Night	18% 4 3 9% 29% 37%	2910
August	1st to 10th	Night	18% 4 4 12% 21% 40%	2838
	11th to 20th	Night	16% 4 4 14% 32% 30%	2838
	21st to end	Night	13% 3 3 14% 30% 36%	3193
September	1st to 10th	Night	14% 4 4 14% 29% 35%	2009
	11th to 20th	Night	20% 5% 5% 23% 26% 21%	2090
	21st to end	Night	20% 3 5% 20% 35% 16%	2090
October	1st to 10th	Night	17% 3 6% 16% 37% 22%	3547
	11th to 20th	Night	30% 4 5% 27% 27% 7%	3778
	21st to end	Night	28% 6% 13% 31% 19% 3	4386
November	1st to 10th	Night	34% 6% 14% 25% 18% 3	2535
	11th to 20th	Night	34% 7% 18% 27% 13% 1	2600
	21st to end	Night	36% 7% 18% 28% 10% 1	2700
December	1st to 10th	Night	42% 9% 22% 19% 7% 2	2779
	11th to 20th	Night	49% 9% 19% 20% 3	3449
	21st to end	Night	47% 9% 17% 18% 9%	4958

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	16% 10% 33% 26% 12% 2	180
	11th to 20th	Day	11% 10% 30% 31% 15% 3	180
	21st to end	Day	18% 7% 26% 30% 18% 2	274
February	1st to 10th	Day	19% 14% 30% 27% 8% 1	270
	11th to 20th	Day	14% 9% 36% 26% 13% 2	381
	21st to end	Day	13% 14% 29% 33% 10% 2	382
March	1st to 10th	Day	12% 12% 33% 30% 12% 2	460
	11th to 20th	Day	10% 9% 31% 32% 17% 2	460
	21st to end	Day	14% 15% 31% 24% 14% 2	506
April	1st to 10th	Day	13% 13% 30% 20% 17% 6%	460
	11th to 20th	Day	12% 16% 31% 25% 12% 4	452
	21st to end	Day	11% 13% 30% 24% 18% 4	460
May	1st to 10th	Day	7% 16% 25% 28% 17% 7%	463
	11th to 20th	Day	13% 10% 22% 27% 19% 10%	488
	21st to end	Day	10% 8% 20% 26% 22% 14%	529
June	1st to 10th	Day	7% 7% 22% 26% 25% 12%	580
	11th to 20th	Day	8% 10% 26% 30% 21% 6%	680
	21st to end	Day	3 4 22% 36% 24% 11%	543
July	1st to 10th	Day	2 4 19% 31% 32% 12%	486
	11th to 20th	Day	2 3 20% 37% 32% 6%	484
	21st to end	Day	3 3 12% 32% 35% 15%	531
August	1st to 10th	Day	5% 4 18% 31% 31% 11%	487
	11th to 20th	Day	3 3 16% 27% 34% 17%	477
	21st to end	Day	3 4 17% 24% 33% 19%	539
September	1st to 10th	Day	3 5% 15% 26% 31% 19%	490
	11th to 20th	Day	5% 5% 19% 27% 30% 15%	490
	21st to end	Day	6% 5% 20% 27% 28% 13%	490
October	1st to 10th	Day	12% 3 19% 28% 25% 13%	455
	11th to 20th	Day	8% 11% 21% 22% 26% 12%	300
	21st to end	Day	12% 10% 23% 35% 17% 4	330
November	1st to 10th	Day	15% 7% 27% 31% 20% 1	300
	11th to 20th	Day	10% 8% 26% 37% 17% 2	300
	21st to end	Day	15% 5% 27% 33% 15% 4	300
December	1st to 10th	Day	18% 5% 24% 32% 14% 5%	294
	11th to 20th	Day	20% 9% 22% 31% 15% 2	205
	21st to end	Day	18% 11% 25% 29% 14% 4	198
January	1st to 10th	Night	14% 8% 26% 37% 13% 1	760
	11th to 20th	Night	15% 8% 22% 37% 16% 2	760
	21st to end	Night	14% 5% 21% 41% 18% 1	836
February	1st to 10th	Night	14% 8% 32% 34% 11% 1	760
	11th to 20th	Night	13% 6% 30% 38% 12% 1	744
	21st to end	Night	9% 8% 32% 38% 12% 1	628
March	1st to 10th	Night	12% 6% 28% 41% 11% 1	760
	11th to 20th	Night	9% 6% 26% 41% 16% 1	760
	21st to end	Night	13% 8% 28% 38% 11% 1	836
April	1st to 10th	Night	11% 10% 24% 38% 16% 2	760
	11th to 20th	Night	10% 9% 33% 35% 11% 1	592
	21st to end	Night	9% 7% 31% 36% 16% 1	570
May	1st to 10th	Night	8% 8% 30% 35% 18% 1	570
	11th to 20th	Night	8% 5% 22% 37% 27% 2	561
	21st to end	Night	12% 6% 19% 34% 25% 4	600
June	1st to 10th	Night	6% 5% 20% 40% 25% 3	380
	11th to 20th	Night	8% 7% 24% 45% 14% 2	380
	21st to end	Night	4 1 19% 48% 25% 3	380
July	1st to 10th	Night	3 2 11% 56% 27% 2	370
	11th to 20th	Night	1 1 14% 58% 25% 1	368
	21st to end	Night	2 1 9% 53% 32% 3	558
August	1st to 10th	Night	4 2 13% 51% 28% 2	567
	11th to 20th	Night	2 2 15% 49% 30% 2	564
	21st to end	Night	4 2 16% 48% 27% 3	648
September	1st to 10th	Night	4 2 14% 45% 31% 5%	760
	11th to 20th	Night	7% 2 14% 39% 32% 6%	760
	21st to end	Night	8% 4 16% 36% 30% 6%	760
October	1st to 10th	Night	9% 5% 19% 39% 28% 1	760
	11th to 20th	Night	9% 5% 17% 40% 25% 4	760
	21st to end	Night	8% 6% 24% 40% 19% 3	836
November	1st to 10th	Night	12% 4 25% 39% 18% 2	780
	11th to 20th	Night	11% 7% 26% 41% 14% 1	800
	21st to end	Night	9% 7% 25% 38% 19% 2	900
December	1st to 10th	Night	13% 7% 27% 39% 13% 1	993
	11th to 20th	Night	17% 7% 22% 40% 13% 1	950
	21st to end	Night	19% 8% 30% 32% 10% 1	893

Page generated at 2024-12-06 01:54:50. Version ac07

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