Keppel Henge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Keppel Henge clear sky chart from 2005-11-06 to 2025-10-19.

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	14% 11% 4 10% 6% 5% 4 3 5% 6% 32%	126731
	Night	14% 13% 5% 12% 6% 5% 5% 4 5% 6% 26%	123023
Transparency	Day	34% 37% 7% 14% 7% 1	130264
	Night	39% 37% 6% 12% 6% 1	127563
Seeing	Day	17% 7% 23% 29% 18% 5%	16414
	Night	20% 10% 26% 27% 14% 3	25531

By Month

Percentage Cloud Cover NE (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	11% 19% 10% 19% 14% 6% 5% 4 4 3 5%	3158
	11th to 20th	Day	9% 19% 11% 31% 11% 5% 4 2 2 2 3	3696
	21st to end	Day	13% 17% 9% 19% 9% 8% 5% 3 4 4 8%	4466
February	1st to 10th	Day	11% 20% 7% 19% 11% 7% 5% 3 4 4 10%	1800
	11th to 20th	Day	10% 15% 8% 16% 11% 7% 5% 3 5% 5% 14%	1753
	21st to end	Day	12% 17% 7% 13% 8% 8% 5% 3 5% 6% 17%	1595
March	1st to 10th	Day	15% 13% 4 11% 6% 6% 4 3 5% 5% 27%	4798
	11th to 20th	Day	10% 13% 7% 12% 7% 5% 6% 4 6% 5% 24%	4980
	21st to end	Day	17% 13% 6% 10% 5% 4 4 3 5% 5% 28%	5465
April	1st to 10th	Day	16% 13% 4 9% 5% 5% 4 3 5% 7% 29%	2305
	11th to 20th	Day	18% 10% 2 7% 4 3 4 2 5% 6% 38%	2570
	21st to end	Day	19% 9% 3 7% 4 3 4 3 6% 7% 35%	2600
May	1st to 10th	Day	14% 8% 3 7% 4 4 4 4 5% 7% 39%	5888
	11th to 20th	Day	13% 8% 3 7% 4 4 4 4 5% 7% 41%	6169
	21st to end	Day	18% 7% 3 6% 4 4 4 3 5% 7% 40%	6949
June	1st to 10th	Day	13% 7% 3 5% 4 5% 5% 5% 6% 8% 40%	2935
	11th to 20th	Day	10% 6% 3 5% 4 4 4 5% 6% 9% 43%	3000
	21st to end	Day	13% 7% 3 6% 4 4 4 4 6% 7% 42%	3000
July	1st to 10th	Day	12% 6% 3 6% 5% 4 4 4 6% 9% 42%	6819
	11th to 20th	Day	9% 5% 2 5% 3 3 3 3 5% 7% 54%	6699
	21st to end	Day	7% 5% 2 5% 4 3 4 3 5% 8% 54%	6424
August	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 7% 8% 44%	4234
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 4 6% 9% 41%	4174
	21st to end	Day	10% 4 2 6% 4 4 5% 4 6% 9% 46%	4625
September	1st to 10th	Day	13% 7% 3 6% 5% 4 4 4 6% 7% 41%	2390
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 9% 45%	2200
	21st to end	Day	17% 7% 3 8% 5% 5% 4 4 6% 6% 35%	2200
October	1st to 10th	Day	17% 8% 2 7% 5% 4 5% 3 5% 7% 35%	2019
	11th to 20th	Day	21% 12% 4 11% 6% 5% 5% 3 5% 6% 22%	1980
	21st to end	Day	27% 15% 4 10% 5% 4 5% 3 4 6% 17%	2024
November	1st to 10th	Day	14% 19% 3 11% 6% 5% 6% 4 5% 6% 21%	1701
	11th to 20th	Day	15% 17% 5% 11% 7% 6% 6% 5% 5% 6% 17%	1600
	21st to end	Day	19% 21% 7% 14% 6% 5% 6% 4 4 4 10%	1600
December	1st to 10th	Day	13% 27% 10% 15% 7% 4 5% 3 4 4 7%	2600
	11th to 20th	Day	20% 22% 7% 15% 7% 5% 5% 3 4 4 9%	2839
	21st to end	Day	25% 22% 6% 17% 8% 5% 3 2 3 3 6%	3476
January	1st to 10th	Night	13% 19% 9% 21% 8% 5% 5% 3 4 4 8%	6808
	11th to 20th	Night	10% 17% 9% 25% 11% 6% 5% 4 4 4 6%	6182
	21st to end	Night	12% 17% 10% 19% 9% 9% 6% 3 4 4 9%	6490
February	1st to 10th	Night	11% 17% 6% 18% 8% 6% 5% 4 5% 4 14%	2600
	11th to 20th	Night	11% 14% 7% 16% 10% 6% 4 3 5% 5% 18%	2533
	21st to end	Night	14% 13% 6% 12% 7% 6% 5% 4 5% 5% 22%	2035
March	1st to 10th	Night	13% 10% 4 11% 6% 6% 5% 4 5% 7% 29%	5041
	11th to 20th	Night	9% 11% 5% 9% 6% 5% 6% 4 5% 7% 32%	4979
	21st to end	Night	16% 12% 5% 9% 5% 4 4 3 4 4 32%	5467
April	1st to 10th	Night	19% 10% 3 7% 6% 5% 4 3 4 6% 32%	2094
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 4 5% 7% 36%	1796
	21st to end	Night	19% 9% 4 8% 5% 5% 4 3 5% 7% 32%	1800
May	1st to 10th	Night	15% 8% 4 8% 5% 4 4 4 5% 7% 36%	4053
	11th to 20th	Night	11% 6% 2 8% 6% 5% 4 4 6% 8% 41%	3723
	21st to end	Night	17% 7% 3 7% 4 4 4 3 5% 6% 39%	3926
June	1st to 10th	Night	13% 7% 2 7% 5% 5% 6% 3 6% 7% 39%	1460
	11th to 20th	Night	11% 6% 3 6% 5% 4 5% 5% 6% 9% 42%	1400
	21st to end	Night	13% 6% 2 7% 5% 4 5% 5% 5% 8% 41%	1400
July	1st to 10th	Night	12% 7% 2 7% 3 4 4 3 5% 8% 43%	3160
	11th to 20th	Night	11% 6% 3 5% 3 4 4 3 5% 7% 50%	3261
	21st to end	Night	8% 6% 2 6% 4 4 4 3 6% 7% 50%	4428
August	1st to 10th	Night	11% 6% 2 6% 4 4 5% 4 7% 8% 44%	2915
	11th to 20th	Night	14% 6% 3 7% 3 5% 5% 4 6% 8% 40%	2875
	21st to end	Night	11% 6% 3 6% 3 4 3 4 5% 9% 46%	3239
September	1st to 10th	Night	10% 5% 2 5% 3 3 5% 4 7% 8% 46%	2008
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 7% 49%	2200
	21st to end	Night	16% 8% 3 8% 6% 4 5% 3 5% 7% 36%	2200
October	1st to 10th	Night	17% 8% 2 8% 5% 4 4 3 6% 8% 35%	2380
	11th to 20th	Night	20% 14% 4 9% 6% 5% 4 3 5% 6% 24%	2377
	21st to end	Night	24% 15% 4 9% 5% 5% 6% 3 5% 5% 19%	2571
November	1st to 10th	Night	16% 14% 5% 10% 6% 5% 5% 4 5% 5% 25%	2596
	11th to 20th	Night	16% 17% 5% 11% 6% 6% 6% 4 5% 7% 17%	2800
	21st to end	Night	20% 21% 6% 11% 6% 5% 5% 4 5% 5% 12%	2800
December	1st to 10th	Night	14% 23% 8% 16% 7% 6% 6% 4 5% 5% 7%	4580
	11th to 20th	Night	13% 24% 8% 18% 7% 5% 4 3 4 4 10%	5344
	21st to end	Night	21% 22% 8% 18% 9% 4 3 2 2 3 8%	7502

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	66% 26% 4 4	3159
	11th to 20th	Day	70% 26% 2 2	3727
	21st to end	Day	58% 28% 8% 5% 1	4466
February	1st to 10th	Day	30% 62% 2 6% 1	1800
	11th to 20th	Day	27% 61% 3 6% 3	1762
	21st to end	Day	23% 61% 4 8% 3	1595
March	1st to 10th	Day	45% 28% 10% 8% 9% 1	4801
	11th to 20th	Day	44% 29% 8% 15% 4 1	4980
	21st to end	Day	45% 28% 7% 15% 5% 1	5465
April	1st to 10th	Day	22% 61% 3 9% 4	2305
	11th to 20th	Day	20% 61% 2 11% 6% 1	2570
	21st to end	Day	18% 61% 6% 9% 5% 1	2600
May	1st to 10th	Day	33% 29% 9% 14% 11% 4	5897
	11th to 20th	Day	33% 28% 8% 14% 16% 1	6173
	21st to end	Day	36% 27% 7% 14% 12% 3	6949
June	1st to 10th	Day	16% 61% 3 11% 7% 1	2935
	11th to 20th	Day	16% 62% 5% 10% 7% 1	3000
	21st to end	Day	17% 60% 3 11% 7% 1	3000
July	1st to 10th	Day	31% 27% 12% 19% 10% 1	6746
	11th to 20th	Day	23% 26% 8% 30% 12%	6618
	21st to end	Day	20% 26% 10% 29% 15% 1	6240
August	1st to 10th	Day	22% 36% 10% 20% 10% 1	4221
	11th to 20th	Day	29% 37% 11% 17% 6%	4213
	21st to end	Day	20% 37% 10% 26% 7%	4625
September	1st to 10th	Day	19% 57% 7% 12% 5%	2390
	11th to 20th	Day	13% 57% 4 18% 8%	2200
	21st to end	Day	19% 57% 6% 13% 5%	2200
October	1st to 10th	Day	25% 36% 8% 20% 9%	3279
	11th to 20th	Day	32% 36% 6% 18% 7%	3220
	21st to end	Day	37% 38% 10% 12% 3	3313
November	1st to 10th	Day	32% 55% 5% 6% 2	1701
	11th to 20th	Day	31% 57% 5% 6% 2	1600
	21st to end	Day	35% 57% 4 4	1600
December	1st to 10th	Day	56% 37% 4 3 1	2600
	11th to 20th	Day	56% 33% 4 6% 1	2838
	21st to end	Day	64% 26% 5% 4 1	3476
January	1st to 10th	Night	65% 25% 4 5% 1	6808
	11th to 20th	Night	66% 26% 4 2 1	6225
	21st to end	Night	60% 27% 6% 5% 1	6490
February	1st to 10th	Night	28% 62% 2 6% 3	2600
	11th to 20th	Night	25% 61% 3 8% 3	2535
	21st to end	Night	22% 61% 5% 7% 4	2035
March	1st to 10th	Night	41% 28% 10% 12% 7% 2	5051
	11th to 20th	Night	37% 28% 13% 16% 6% 1	4980
	21st to end	Night	46% 28% 4 14% 7% 1	5467
April	1st to 10th	Night	24% 61% 3 7% 5%	2094
	11th to 20th	Night	20% 61% 2 10% 6% 1	1796
	21st to end	Night	21% 61% 4 7% 6% 1	1800
May	1st to 10th	Night	36% 28% 6% 13% 12% 5%	4060
	11th to 20th	Night	32% 28% 6% 18% 14% 1	3724
	21st to end	Night	38% 27% 5% 19% 10% 1	3927
June	1st to 10th	Night	14% 61% 3 11% 10% 2	1460
	11th to 20th	Night	14% 62% 4 12% 7% 1	1400
	21st to end	Night	15% 60% 5% 12% 7% 1	1400
July	1st to 10th	Night	33% 26% 9% 19% 10% 3	3125
	11th to 20th	Night	27% 26% 7% 26% 14% 1	3219
	21st to end	Night	25% 26% 6% 27% 15% 1	4297
August	1st to 10th	Night	25% 35% 9% 19% 11% 1	2904
	11th to 20th	Night	31% 37% 11% 14% 7%	2902
	21st to end	Night	23% 37% 8% 24% 9%	3239
September	1st to 10th	Night	14% 57% 8% 15% 6%	2008
	11th to 20th	Night	13% 57% 5% 16% 10%	2200
	21st to end	Night	19% 56% 6% 12% 6% 1	2200
October	1st to 10th	Night	24% 36% 6% 20% 13%	3887
	11th to 20th	Night	30% 35% 10% 16% 9%	3876
	21st to end	Night	33% 38% 10% 17% 3	4232
November	1st to 10th	Night	30% 55% 5% 7% 2	2596
	11th to 20th	Night	30% 57% 6% 5% 2	2800
	21st to end	Night	35% 57% 3 4 1	2800
December	1st to 10th	Night	55% 36% 4 3 1	4580
	11th to 20th	Night	58% 31% 5% 5% 2	5344
	21st to end	Night	64% 26% 6% 3 1	7502

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	17% 19% 35% 21% 8% 2	200
	11th to 20th	Day	20% 14% 35% 23% 7% 1	295
	21st to end	Day	24% 9% 36% 24% 6% 1	330
February	1st to 10th	Day	18% 16% 41% 20% 6%	300
	11th to 20th	Day	16% 13% 42% 25% 3 1	300
	21st to end	Day	18% 20% 37% 22% 3	249
March	1st to 10th	Day	21% 10% 35% 25% 9% 1	439
	11th to 20th	Day	18% 13% 31% 29% 9% 1	500
	21st to end	Day	24% 8% 28% 30% 10% 1	550
April	1st to 10th	Day	19% 9% 32% 29% 10% 1	500
	11th to 20th	Day	24% 8% 28% 22% 14% 5%	492
	21st to end	Day	24% 6% 26% 30% 12% 2	500
May	1st to 10th	Day	19% 3 21% 37% 16% 3	503
	11th to 20th	Day	13% 4 20% 35% 21% 7%	527
	21st to end	Day	13% 4 17% 34% 24% 8%	573
June	1st to 10th	Day	14% 2 19% 39% 22% 4	665
	11th to 20th	Day	12% 3 18% 39% 25% 4	730
	21st to end	Day	15% 3 18% 35% 23% 5%	730
July	1st to 10th	Day	10% 2 12% 36% 32% 7%	721
	11th to 20th	Day	11% 3 17% 31% 27% 11%	702
	21st to end	Day	9% 3 12% 40% 27% 8%	576
August	1st to 10th	Day	11% 3 13% 30% 32% 11%	526
	11th to 20th	Day	12% 3 10% 31% 33% 11%	519
	21st to end	Day	14% 5% 16% 32% 25% 9%	583
September	1st to 10th	Day	16% 6% 17% 29% 24% 8%	530
	11th to 20th	Day	11% 4 17% 20% 30% 18%	530
	21st to end	Day	18% 7% 18% 26% 24% 7%	530
October	1st to 10th	Day	21% 6% 25% 23% 18% 8%	530
	11th to 20th	Day	22% 10% 28% 29% 9% 2	522
	21st to end	Day	33% 12% 26% 21% 8%	473
November	1st to 10th	Day	19% 19% 30% 20% 10% 2	269
	11th to 20th	Day	23% 12% 35% 23% 7% 2	200
	21st to end	Day	25% 12% 37% 24% 4	200
December	1st to 10th	Day	26% 17% 30% 22% 7%	200
	11th to 20th	Day	27% 21% 32% 15% 5%	200
	21st to end	Day	33% 16% 33% 12% 5%	220
January	1st to 10th	Night	24% 15% 34% 22% 6% 1	1000
	11th to 20th	Night	25% 17% 32% 20% 6% 1	938
	21st to end	Night	19% 10% 37% 24% 9% 1	880
February	1st to 10th	Night	20% 16% 38% 22% 4	800
	11th to 20th	Night	17% 14% 35% 25% 7% 1	783
	21st to end	Night	20% 11% 37% 25% 7%	660
March	1st to 10th	Night	17% 12% 36% 28% 7%	800
	11th to 20th	Night	16% 10% 36% 28% 8% 1	800
	21st to end	Night	19% 8% 28% 29% 13% 1	880
April	1st to 10th	Night	22% 9% 29% 31% 9% 1	800
	11th to 20th	Night	20% 7% 27% 30% 13% 3	612
	21st to end	Night	23% 6% 25% 30% 15% 2	600
May	1st to 10th	Night	17% 4 18% 39% 19% 4	600
	11th to 20th	Night	17% 4 15% 38% 23% 3	464
	21st to end	Night	13% 3 17% 39% 22% 5%	433
June	1st to 10th	Night	14% 3 18% 42% 19% 4	400
	11th to 20th	Night	12% 4 17% 38% 27% 3	400
	21st to end	Night	14% 3 18% 35% 27% 3	400
July	1st to 10th	Night	9% 2 9% 46% 27% 6%	390
	11th to 20th	Night	11% 3 16% 31% 34% 5%	411
	21st to end	Night	7% 4 14% 44% 27% 4	657
August	1st to 10th	Night	13% 2 14% 34% 31% 7%	597
	11th to 20th	Night	11% 4 13% 33% 31% 9%	594
	21st to end	Night	14% 4 18% 30% 29% 5%	663
September	1st to 10th	Night	13% 6% 18% 30% 25% 9%	800
	11th to 20th	Night	14% 4 17% 28% 26% 11%	800
	21st to end	Night	20% 6% 17% 27% 22% 8%	800
October	1st to 10th	Night	23% 6% 25% 26% 17% 3	800
	11th to 20th	Night	29% 11% 24% 25% 10% 2	793
	21st to end	Night	36% 10% 25% 22% 6%	836
November	1st to 10th	Night	25% 12% 28% 25% 8% 2	780
	11th to 20th	Night	25% 16% 33% 17% 9%	800
	21st to end	Night	32% 16% 30% 18% 5%	800
December	1st to 10th	Night	29% 19% 30% 17% 5%	800
	11th to 20th	Night	25% 18% 37% 16% 4 1	860
	21st to end	Night	33% 15% 32% 16% 5%	1100

Page generated at 2025-10-16 01:50:25. Version ac07

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