Darling Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Darling Hill Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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	16% 12% 5% 10% 5% 5% 4 4 5% 6% 28%	127145
	Night	16% 13% 5% 12% 6% 4 4 3 4 5% 26%	122875
Transparency	Day	56% 6% 10% 19% 9% 1	130662
	Night	59% 6% 10% 16% 9% 1	127445
Seeing	Day	26% 19% 28% 17% 7% 2	15952
	Night	25% 18% 26% 22% 8% 1	25125

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	10% 19% 12% 24% 8% 3 4 2 4 3 12%	3597
	11th to 20th	Day	12% 21% 12% 19% 8% 6% 3 2 3 3 11%	3570
	21st to end	Day	13% 18% 8% 14% 10% 6% 5% 3 4 5% 15%	4438
February	1st to 10th	Day	14% 18% 7% 18% 10% 7% 5% 3 4 3 13%	1800
	11th to 20th	Day	13% 17% 8% 19% 10% 5% 4 3 3 4 14%	1788
	21st to end	Day	17% 17% 5% 16% 9% 4 4 3 3 4 18%	1650
March	1st to 10th	Day	17% 17% 7% 14% 7% 5% 3 3 3 4 20%	4583
	11th to 20th	Day	10% 18% 7% 9% 5% 3 4 3 4 6% 31%	4980
	21st to end	Day	15% 13% 7% 14% 5% 4 3 3 4 5% 27%	5712
April	1st to 10th	Day	16% 17% 5% 10% 5% 3 4 4 4 5% 27%	2400
	11th to 20th	Day	17% 14% 4 7% 4 4 3 3 5% 5% 33%	2374
	21st to end	Day	19% 15% 4 7% 4 3 3 2 5% 6% 31%	2422
May	1st to 10th	Day	29% 12% 3 7% 4 4 4 3 4 5% 25%	6249
	11th to 20th	Day	16% 9% 3 9% 6% 5% 5% 4 5% 7% 30%	6318
	21st to end	Day	21% 10% 3 7% 4 4 4 4 6% 7% 30%	6949
June	1st to 10th	Day	20% 8% 3 7% 4 4 5% 5% 6% 7% 32%	2800
	11th to 20th	Day	18% 6% 2 6% 5% 5% 5% 5% 7% 10% 33%	2800
	21st to end	Day	15% 7% 3 7% 5% 5% 4 4 7% 10% 33%	2800
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 5% 7% 11% 36%	6360
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 6% 8% 11% 32%	6360
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	6926
August	1st to 10th	Day	17% 6% 2 7% 5% 5% 5% 4 6% 9% 33%	4249
	11th to 20th	Day	15% 8% 4 8% 5% 5% 6% 5% 6% 8% 30%	4052
	21st to end	Day	15% 8% 3 8% 4 4 4 3 5% 7% 38%	4312
September	1st to 10th	Day	16% 6% 2 5% 5% 4 5% 4 6% 7% 39%	2400
	11th to 20th	Day	15% 7% 2 6% 4 4 3 3 4 7% 44%	2400
	21st to end	Day	17% 8% 3 7% 6% 4 5% 4 6% 6% 34%	2130
October	1st to 10th	Day	19% 8% 3 6% 5% 5% 5% 4 5% 7% 34%	2000
	11th to 20th	Day	20% 11% 3 6% 5% 4 5% 4 5% 7% 30%	2000
	21st to end	Day	24% 16% 3 8% 4 4 4 4 4 5% 24%	2116
November	1st to 10th	Day	13% 16% 3 9% 5% 5% 5% 4 4 6% 31%	1779
	11th to 20th	Day	16% 18% 5% 10% 5% 5% 4 3 5% 4 25%	1685
	21st to end	Day	17% 22% 6% 11% 5% 4 4 3 4 5% 19%	1600
December	1st to 10th	Day	14% 23% 12% 18% 6% 4 3 3 4 4 9%	2600
	11th to 20th	Day	17% 18% 8% 16% 5% 4 4 2 4 3 20%	2986
	21st to end	Day	17% 17% 8% 13% 6% 6% 5% 3 5% 6% 14%	3960
January	1st to 10th	Night	12% 17% 10% 30% 9% 4 3 2 3 2 8%	6349
	11th to 20th	Night	9% 19% 10% 22% 9% 5% 4 3 4 4 12%	6315
	21st to end	Night	13% 16% 6% 15% 10% 7% 6% 3 4 4 15%	6517
February	1st to 10th	Night	14% 18% 6% 16% 8% 5% 5% 3 4 4 16%	2600
	11th to 20th	Night	12% 16% 7% 17% 11% 5% 5% 4 3 5% 15%	2497
	21st to end	Night	17% 15% 6% 17% 7% 4 5% 2 4 5% 18%	1980
March	1st to 10th	Night	15% 12% 7% 15% 10% 4 4 3 4 5% 22%	5254
	11th to 20th	Night	13% 17% 6% 10% 4 3 3 3 4 7% 29%	4979
	21st to end	Night	19% 13% 6% 13% 5% 4 4 3 3 4 26%	5220
April	1st to 10th	Night	17% 16% 5% 10% 5% 5% 4 4 4 5% 26%	2000
	11th to 20th	Night	18% 14% 4 8% 5% 4 3 2 4 5% 33%	1975
	21st to end	Night	19% 12% 4 6% 4 4 4 3 5% 6% 34%	1995
May	1st to 10th	Night	31% 12% 3 8% 4 4 4 3 4 5% 23%	3690
	11th to 20th	Night	16% 9% 3 7% 4 5% 4 4 5% 7% 35%	3575
	21st to end	Night	23% 9% 3 7% 4 4 4 4 6% 6% 31%	3926
June	1st to 10th	Night	19% 6% 4 7% 4 4 4 3 6% 7% 36%	1600
	11th to 20th	Night	17% 7% 2 6% 5% 4 4 4 6% 9% 37%	1600
	21st to end	Night	14% 7% 3 6% 4 4 4 5% 5% 8% 41%	1600
July	1st to 10th	Night	9% 6% 2 8% 6% 5% 5% 4 7% 10% 37%	3600
	11th to 20th	Night	13% 6% 2 6% 5% 4 5% 4 6% 8% 42%	3600
	21st to end	Night	10% 7% 2 6% 4 4 4 3 6% 8% 46%	3926
August	1st to 10th	Night	19% 7% 2 6% 4 3 4 4 6% 7% 38%	2882
	11th to 20th	Night	13% 8% 3 9% 4 4 5% 3 5% 6% 40%	2963
	21st to end	Night	11% 8% 3 8% 4 4 5% 3 5% 7% 42%	3586
September	1st to 10th	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	2000
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 5% 6% 48%	2000
	21st to end	Night	17% 9% 2 5% 4 4 6% 4 6% 6% 36%	2265
October	1st to 10th	Night	20% 8% 3 7% 4 5% 4 4 5% 6% 34%	2400
	11th to 20th	Night	21% 10% 2 6% 5% 4 5% 3 4 6% 33%	2400
	21st to end	Night	25% 15% 3 7% 5% 3 3 3 4 5% 24%	2722
November	1st to 10th	Night	13% 16% 3 9% 5% 4 4 3 5% 6% 33%	2564
	11th to 20th	Night	17% 18% 5% 9% 4 4 4 3 4 6% 27%	2711
	21st to end	Night	15% 20% 7% 10% 6% 4 4 3 5% 5% 21%	2800
December	1st to 10th	Night	13% 21% 10% 17% 6% 5% 5% 4 4 4 11%	4580
	11th to 20th	Night	18% 19% 8% 12% 6% 4 3 2 3 4 19%	5208
	21st to end	Night	19% 19% 8% 12% 7% 4 4 3 3 4 16%	6996

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	79% 3 6% 10% 2	3598
	11th to 20th	Day	80% 4 6% 7% 4 1	3600
	21st to end	Day	72% 5% 8% 11% 4	4438
February	1st to 10th	Day	76% 4 7% 10% 3	1800
	11th to 20th	Day	76% 4 6% 11% 3	1797
	21st to end	Day	71% 4 8% 12% 5%	1650
March	1st to 10th	Day	69% 5% 9% 12% 6%	4586
	11th to 20th	Day	55% 4 17% 13% 8% 2	4980
	21st to end	Day	61% 5% 6% 16% 12% 1	5712
April	1st to 10th	Day	61% 4 8% 17% 9% 2	2400
	11th to 20th	Day	53% 4 11% 19% 12% 1	2374
	21st to end	Day	55% 4 9% 19% 11% 2	2422
May	1st to 10th	Day	62% 5% 8% 15% 9% 1	6260
	11th to 20th	Day	52% 7% 9% 21% 10% 1	6322
	21st to end	Day	52% 7% 11% 20% 11% 1	6949
June	1st to 10th	Day	49% 7% 11% 19% 13% 1	2800
	11th to 20th	Day	46% 7% 13% 22% 10% 1	2800
	21st to end	Day	46% 7% 15% 21% 11% 1	2800
July	1st to 10th	Day	41% 6% 14% 27% 12% 1	6290
	11th to 20th	Day	41% 9% 15% 24% 11% 1	6285
	21st to end	Day	40% 6% 12% 30% 12%	6728
August	1st to 10th	Day	47% 7% 13% 20% 12% 1	4235
	11th to 20th	Day	49% 8% 14% 23% 6%	4091
	21st to end	Day	46% 5% 10% 31% 7% 1	4312
September	1st to 10th	Day	43% 6% 11% 28% 11% 1	2400
	11th to 20th	Day	42% 4 10% 26% 17% 1	2400
	21st to end	Day	49% 7% 10% 22% 10% 1	2130
October	1st to 10th	Day	45% 6% 10% 27% 12% 1	3260
	11th to 20th	Day	49% 4 14% 19% 14%	3240
	21st to end	Day	49% 6% 13% 23% 8% 1	3393
November	1st to 10th	Day	53% 6% 12% 17% 10% 2	1779
	11th to 20th	Day	61% 5% 11% 14% 7% 2	1685
	21st to end	Day	68% 6% 12% 12% 3	1600
December	1st to 10th	Day	80% 5% 7% 6% 2	2600
	11th to 20th	Day	70% 6% 9% 9% 6%	2986
	21st to end	Day	70% 7% 8% 10% 5%	3960
January	1st to 10th	Night	83% 4 6% 5% 2	6349
	11th to 20th	Night	75% 6% 6% 8% 5%	6360
	21st to end	Night	71% 5% 7% 8% 9% 1	6517
February	1st to 10th	Night	71% 5% 8% 11% 5%	2600
	11th to 20th	Night	73% 5% 8% 10% 4	2499
	21st to end	Night	69% 5% 9% 11% 6% 1	1980
March	1st to 10th	Night	65% 5% 11% 11% 7%	5264
	11th to 20th	Night	56% 5% 16% 14% 5% 3	4980
	21st to end	Night	62% 5% 5% 17% 10% 1	5220
April	1st to 10th	Night	60% 5% 10% 16% 7% 2	2000
	11th to 20th	Night	55% 4 10% 17% 14% 1	1975
	21st to end	Night	52% 5% 9% 19% 13% 3	1995
May	1st to 10th	Night	64% 6% 6% 12% 8% 4	3696
	11th to 20th	Night	48% 8% 13% 20% 10% 1	3576
	21st to end	Night	52% 7% 10% 18% 11% 1	3927
June	1st to 10th	Night	47% 6% 11% 22% 14% 1	1600
	11th to 20th	Night	45% 7% 13% 21% 13% 1	1600
	21st to end	Night	42% 8% 9% 28% 13% 1	1600
July	1st to 10th	Night	42% 7% 15% 22% 14% 1	3560
	11th to 20th	Night	39% 7% 14% 26% 13% 1	3552
	21st to end	Night	35% 6% 11% 29% 16% 1	3809
August	1st to 10th	Night	46% 6% 13% 24% 10% 1	2872
	11th to 20th	Night	44% 7% 13% 27% 9%	2990
	21st to end	Night	41% 6% 12% 31% 9% 1	3586
September	1st to 10th	Night	41% 6% 13% 25% 14% 2	2000
	11th to 20th	Night	36% 5% 11% 31% 16% 1	2000
	21st to end	Night	47% 7% 11% 22% 12% 1	2265
October	1st to 10th	Night	52% 6% 8% 22% 11%	3920
	11th to 20th	Night	49% 6% 12% 17% 13% 3	3899
	21st to end	Night	50% 6% 12% 25% 7% 1	4395
November	1st to 10th	Night	53% 7% 9% 18% 12% 2	2564
	11th to 20th	Night	60% 4 10% 17% 7% 3	2711
	21st to end	Night	65% 6% 12% 13% 4	2800
December	1st to 10th	Night	75% 6% 9% 8% 1	4580
	11th to 20th	Night	69% 5% 6% 11% 8%	5208
	21st to end	Night	72% 6% 6% 9% 6% 1	6996

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	32% 31% 26% 9% 3	200
	11th to 20th	Day	37% 30% 25% 7% 1 1	200
	21st to end	Day	29% 30% 32% 8% 1	323
February	1st to 10th	Day	42% 28% 25% 5% 1	300
	11th to 20th	Day	41% 30% 26% 3	335
	21st to end	Day	39% 24% 27% 8% 1	414
March	1st to 10th	Day	33% 24% 30% 10% 3	500
	11th to 20th	Day	34% 24% 27% 12% 3	500
	21st to end	Day	37% 23% 27% 10% 3 1	550
April	1st to 10th	Day	36% 25% 26% 10% 4	500
	11th to 20th	Day	31% 28% 22% 10% 7% 3	492
	21st to end	Day	33% 19% 28% 15% 5% 1	500
May	1st to 10th	Day	31% 21% 28% 13% 6% 2	503
	11th to 20th	Day	24% 16% 31% 18% 8% 2	527
	21st to end	Day	21% 14% 32% 21% 10% 2	573
June	1st to 10th	Day	25% 16% 28% 22% 8% 1	530
	11th to 20th	Day	18% 16% 32% 23% 9% 2	530
	21st to end	Day	20% 18% 32% 22% 6% 2	530
July	1st to 10th	Day	15% 10% 32% 27% 13% 4	525
	11th to 20th	Day	13% 10% 33% 27% 15% 3	524
	21st to end	Day	14% 10% 38% 25% 10% 3	576
August	1st to 10th	Day	14% 10% 28% 28% 14% 6%	526
	11th to 20th	Day	18% 12% 27% 24% 12% 7%	519
	21st to end	Day	16% 13% 29% 23% 12% 7%	583
September	1st to 10th	Day	19% 12% 25% 23% 14% 7%	530
	11th to 20th	Day	15% 9% 26% 22% 18% 10%	530
	21st to end	Day	21% 15% 28% 21% 11% 4	530
October	1st to 10th	Day	24% 15% 25% 18% 13% 5%	530
	11th to 20th	Day	29% 22% 26% 15% 7% 1	530
	21st to end	Day	37% 18% 27% 15% 3	536
November	1st to 10th	Day	28% 25% 22% 19% 6%	401
	11th to 20th	Day	35% 25% 24% 13% 3 1	285
	21st to end	Day	40% 24% 30% 7%	200
December	1st to 10th	Day	39% 24% 29% 7% 2 1	200
	11th to 20th	Day	37% 29% 27% 8% 1	200
	21st to end	Day	33% 27% 31% 7% 1	220
January	1st to 10th	Night	29% 31% 28% 11% 2 1	800
	11th to 20th	Night	29% 25% 29% 14% 3	800
	21st to end	Night	24% 26% 31% 17% 2	880
February	1st to 10th	Night	31% 25% 28% 15% 1	800
	11th to 20th	Night	30% 26% 30% 12% 2	783
	21st to end	Night	32% 25% 28% 13% 3	660
March	1st to 10th	Night	28% 24% 30% 17% 2	800
	11th to 20th	Night	29% 24% 26% 18% 2	800
	21st to end	Night	31% 20% 27% 16% 6% 1	880
April	1st to 10th	Night	29% 21% 28% 19% 3	800
	11th to 20th	Night	29% 20% 25% 20% 6% 1	791
	21st to end	Night	29% 13% 28% 24% 6%	795
May	1st to 10th	Night	25% 15% 23% 27% 9% 1	444
	11th to 20th	Night	18% 13% 31% 29% 8% 1	394
	21st to end	Night	15% 9% 29% 33% 12%	433
June	1st to 10th	Night	21% 8% 26% 33% 12% 1	400
	11th to 20th	Night	18% 11% 25% 33% 14%	400
	21st to end	Night	16% 8% 27% 39% 10% 1	400
July	1st to 10th	Night	10% 4 25% 44% 15% 2	390
	11th to 20th	Night	12% 5% 22% 41% 19% 2	388
	21st to end	Night	14% 5% 24% 42% 14% 1	438
August	1st to 10th	Night	15% 5% 25% 34% 20% 1	577
	11th to 20th	Night	16% 6% 19% 33% 23% 3	643
	21st to end	Night	15% 7% 23% 34% 19% 1	880
September	1st to 10th	Night	17% 9% 25% 31% 15% 3	800
	11th to 20th	Night	17% 7% 16% 33% 23% 4	800
	21st to end	Night	20% 14% 23% 26% 16% 2	800
October	1st to 10th	Night	25% 13% 23% 21% 17% 1	800
	11th to 20th	Night	29% 16% 28% 20% 6% 1	800
	21st to end	Night	36% 16% 27% 18% 3	880
November	1st to 10th	Night	27% 19% 29% 19% 7%	789
	11th to 20th	Night	31% 23% 27% 14% 4 1	800
	21st to end	Night	28% 26% 25% 16% 4	800
December	1st to 10th	Night	34% 26% 24% 13% 3	800
	11th to 20th	Night	33% 24% 26% 15% 2	800
	21st to end	Night	32% 29% 26% 12% 2	880

Page generated at 2025-10-31 02:02:36. Version ac07

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