Melbourne
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Melbourne 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	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 39%	126249
	Night	7% 6% 2 7% 5% 5% 5% 4 7% 10% 41%	123810
Transparency	Day	20% 42% 15% 14% 7% 2	129917
	Night	23% 41% 13% 14% 8% 2	128211
Seeing	Day	7% 3 13% 26% 31% 20%	17161
	Night	9% 3 15% 28% 32% 14%	27234

By Month

Percentage Cloud Cover SE (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	7% 6% 2 6% 4 4 4 4 5% 8% 51%	4056
	11th to 20th	Day	16% 9% 4 8% 5% 5% 4 4 6% 8% 30%	4060
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 6% 8% 38%	4466
February	1st to 10th	Day	10% 6% 2 5% 5% 5% 4 4 6% 9% 44%	1980
	11th to 20th	Day	6% 4 2 5% 4 4 5% 4 6% 9% 51%	1991
	21st to end	Day	9% 5% 2 5% 4 3 4 3 6% 9% 50%	1815
March	1st to 10th	Day	6% 5% 2 8% 6% 5% 6% 4 7% 8% 43%	4935
	11th to 20th	Day	3 2 1 4 3 4 4 3 5% 9% 62%	4980
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	5465
April	1st to 10th	Day	5% 3 2 4 5% 4 5% 5% 8% 9% 51%	2200
	11th to 20th	Day	7% 5% 2 5% 5% 5% 5% 5% 8% 9% 43%	2284
	21st to end	Day	5% 4 2 5% 5% 4 5% 5% 7% 9% 50%	2400
May	1st to 10th	Day	2 2 1 4 4 4 6% 5% 8% 13% 52%	5405
	11th to 20th	Day	7% 4 2 7% 5% 5% 5% 5% 6% 9% 45%	5851
	21st to end	Day	4 4 2 5% 5% 5% 6% 6% 8% 12% 43%	6433
June	1st to 10th	Day	11% 9% 3 9% 7% 6% 8% 5% 9% 10% 25%	2600
	11th to 20th	Day	6% 5% 2 7% 7% 8% 7% 7% 11% 12% 29%	2600
	21st to end	Day	7% 6% 3 8% 7% 6% 7% 6% 9% 12% 29%	2600
July	1st to 10th	Day	5% 5% 2 9% 7% 6% 7% 7% 10% 13% 29%	5900
	11th to 20th	Day	4 5% 2 6% 5% 6% 6% 6% 10% 14% 36%	5900
	21st to end	Day	4 4 2 6% 6% 6% 7% 6% 9% 13% 37%	6424
August	1st to 10th	Day	3 4 2 8% 6% 8% 9% 7% 10% 16% 27%	4234
	11th to 20th	Day	4 3 2 6% 5% 6% 7% 7% 11% 15% 35%	3917
	21st to end	Day	6% 5% 2 8% 6% 7% 7% 7% 11% 15% 26%	4066
September	1st to 10th	Day	7% 6% 3 9% 7% 7% 8% 8% 11% 12% 23%	2200
	11th to 20th	Day	9% 6% 3 9% 6% 7% 8% 6% 9% 12% 25%	2200
	21st to end	Day	9% 6% 3 8% 7% 7% 9% 7% 9% 10% 25%	2200
October	1st to 10th	Day	12% 6% 3 8% 6% 5% 7% 6% 7% 12% 28%	2108
	11th to 20th	Day	7% 5% 2 6% 5% 6% 5% 5% 6% 10% 42%	2000
	21st to end	Day	8% 5% 2 6% 4 4 4 4 6% 10% 46%	2200
November	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 9% 40%	1977
	11th to 20th	Day	9% 7% 3 8% 4 6% 5% 4 7% 10% 38%	2000
	21st to end	Day	8% 6% 3 6% 5% 5% 6% 5% 7% 10% 40%	2000
December	1st to 10th	Day	6% 4 1 5% 4 4 5% 4 6% 8% 54%	2963
	11th to 20th	Day	9% 6% 3 7% 5% 7% 6% 6% 7% 11% 33%	3373
	21st to end	Day	9% 7% 2 8% 6% 6% 7% 6% 7% 8% 33%	4466
January	1st to 10th	Night	7% 5% 2 5% 4 4 4 4 7% 9% 50%	5889
	11th to 20th	Night	14% 11% 4 10% 5% 5% 4 4 6% 7% 30%	5900
	21st to end	Night	14% 7% 2 7% 4 4 4 3 6% 8% 40%	6490
February	1st to 10th	Night	10% 7% 2 6% 4 4 4 4 5% 8% 46%	2415
	11th to 20th	Night	9% 5% 2 5% 3 4 3 4 6% 8% 51%	2293
	21st to end	Night	7% 5% 2 4 3 4 4 4 7% 8% 52%	1815
March	1st to 10th	Night	7% 6% 3 7% 5% 5% 5% 4 6% 8% 46%	4918
	11th to 20th	Night	4 3 1 4 3 3 4 3 7% 10% 59%	4980
	21st to end	Night	7% 5% 2 7% 5% 4 5% 4 7% 9% 46%	5467
April	1st to 10th	Night	5% 3 1 5% 3 3 4 4 7% 9% 55%	2200
	11th to 20th	Night	5% 4 2 6% 5% 4 5% 4 7% 10% 48%	2065
	21st to end	Night	5% 4 1 5% 5% 4 5% 5% 6% 10% 51%	2000
May	1st to 10th	Night	3 3 1 5% 4 4 5% 4 7% 12% 53%	4490
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 4 7% 9% 46%	4083
	21st to end	Night	5% 4 2 6% 5% 6% 5% 5% 8% 11% 44%	4421
June	1st to 10th	Night	11% 7% 3 8% 5% 6% 7% 6% 8% 11% 29%	1800
	11th to 20th	Night	5% 7% 3 8% 6% 6% 7% 5% 9% 13% 32%	1800
	21st to end	Night	6% 6% 3 7% 6% 6% 7% 6% 9% 11% 34%	1800
July	1st to 10th	Night	8% 7% 3 9% 6% 6% 6% 5% 9% 12% 29%	4058
	11th to 20th	Night	4 4 2 6% 5% 5% 6% 6% 9% 13% 41%	4057
	21st to end	Night	3 5% 2 6% 6% 6% 6% 6% 8% 11% 42%	4427
August	1st to 10th	Night	3 5% 2 9% 6% 6% 6% 5% 9% 12% 35%	2915
	11th to 20th	Night	3 5% 3 7% 5% 6% 5% 5% 8% 13% 39%	3095
	21st to end	Night	6% 6% 3 7% 6% 6% 7% 7% 10% 14% 29%	3812
September	1st to 10th	Night	6% 7% 3 9% 7% 7% 8% 7% 8% 12% 26%	2200
	11th to 20th	Night	8% 8% 4 11% 6% 6% 6% 5% 9% 10% 27%	2200
	21st to end	Night	10% 7% 3 10% 6% 7% 5% 5% 9% 10% 28%	2200
October	1st to 10th	Night	12% 7% 3 8% 5% 6% 5% 5% 7% 11% 32%	2290
	11th to 20th	Night	6% 6% 3 8% 5% 5% 5% 5% 6% 9% 43%	2400
	21st to end	Night	9% 6% 2 5% 4 4 5% 4 6% 9% 45%	2640
November	1st to 10th	Night	7% 6% 3 7% 7% 6% 6% 5% 5% 8% 41%	2366
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 5% 7% 8% 42%	2400
	21st to end	Night	12% 6% 2 6% 4 5% 5% 5% 6% 9% 39%	2400
December	1st to 10th	Night	4 3 1 5% 4 4 4 4 6% 9% 54%	4212
	11th to 20th	Night	11% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	4822
	21st to end	Night	10% 7% 3 9% 6% 5% 6% 4 6% 8% 35%	6490

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	24% 28% 7% 16% 22% 3	4057
	11th to 20th	Day	44% 28% 7% 12% 8% 1	4060
	21st to end	Day	31% 32% 6% 19% 10% 2	4466
February	1st to 10th	Day	13% 63% 6% 8% 8% 2	1980
	11th to 20th	Day	8% 61% 5% 12% 11% 3	2001
	21st to end	Day	13% 62% 6% 8% 8% 3	1815
March	1st to 10th	Day	28% 33% 11% 12% 14% 2	4935
	11th to 20th	Day	11% 31% 8% 23% 15% 12%	4980
	21st to end	Day	26% 31% 9% 20% 11% 4	5465
April	1st to 10th	Day	8% 63% 7% 12% 7% 2	2200
	11th to 20th	Day	10% 64% 5% 8% 10% 3	2284
	21st to end	Day	8% 63% 5% 12% 11% 1	2400
May	1st to 10th	Day	14% 33% 21% 23% 7% 2	5437
	11th to 20th	Day	23% 32% 16% 21% 8%	5855
	21st to end	Day	16% 33% 17% 27% 8%	6447
June	1st to 10th	Day	16% 65% 11% 7% 1	2600
	11th to 20th	Day	14% 66% 11% 8% 1	2600
	21st to end	Day	11% 66% 16% 7% 1	2600
July	1st to 10th	Day	26% 33% 29% 10% 2	5835
	11th to 20th	Day	19% 33% 37% 10% 1	5831
	21st to end	Day	20% 35% 26% 20%	6240
August	1st to 10th	Day	23% 46% 24% 6% 1	4221
	11th to 20th	Day	14% 43% 23% 13% 7%	3955
	21st to end	Day	20% 46% 26% 7% 1	4066
September	1st to 10th	Day	20% 65% 10% 5% 1	2200
	11th to 20th	Day	18% 62% 12% 7% 1	2200
	21st to end	Day	16% 62% 11% 8% 3	2200
October	1st to 10th	Day	35% 42% 15% 6% 2	3433
	11th to 20th	Day	16% 39% 6% 18% 19% 2	3240
	21st to end	Day	14% 37% 8% 21% 17% 3	3538
November	1st to 10th	Day	14% 59% 9% 9% 7% 1	1977
	11th to 20th	Day	19% 59% 5% 8% 6% 3	2000
	21st to end	Day	17% 58% 5% 10% 6% 4	2000
December	1st to 10th	Day	14% 38% 15% 20% 10% 2	2963
	11th to 20th	Day	29% 35% 9% 12% 12% 3	3370
	21st to end	Day	36% 31% 9% 16% 6% 2	4466
January	1st to 10th	Night	24% 29% 7% 18% 17% 5%	5889
	11th to 20th	Night	44% 28% 10% 12% 6% 1	5900
	21st to end	Night	31% 30% 7% 18% 11% 3	6490
February	1st to 10th	Night	13% 63% 6% 9% 7% 2	2415
	11th to 20th	Night	10% 61% 5% 10% 11% 3	2294
	21st to end	Night	12% 62% 6% 9% 8% 3	1815
March	1st to 10th	Night	29% 33% 9% 14% 12% 3	4918
	11th to 20th	Night	12% 31% 15% 19% 14% 10%	4980
	21st to end	Night	25% 31% 9% 20% 13% 2	5467
April	1st to 10th	Night	9% 63% 7% 12% 6% 2	2200
	11th to 20th	Night	10% 64% 5% 9% 9% 3	2065
	21st to end	Night	9% 63% 6% 11% 10% 1	2000
May	1st to 10th	Night	17% 34% 19% 21% 7% 2	4520
	11th to 20th	Night	22% 32% 16% 24% 5%	4084
	21st to end	Night	20% 32% 17% 25% 6%	4429
June	1st to 10th	Night	17% 64% 12% 7% 1	1800
	11th to 20th	Night	17% 67% 9% 7% 1	1800
	21st to end	Night	14% 64% 14% 7% 1	1800
July	1st to 10th	Night	32% 33% 21% 12% 1	4015
	11th to 20th	Night	19% 33% 39% 9%	4006
	21st to end	Night	24% 33% 22% 20% 1	4297
August	1st to 10th	Night	27% 42% 23% 7% 2	2904
	11th to 20th	Night	20% 41% 22% 10% 7%	3123
	21st to end	Night	23% 44% 26% 6% 1	3812
September	1st to 10th	Night	21% 64% 9% 5% 1	2200
	11th to 20th	Night	19% 61% 12% 7% 1	2200
	21st to end	Night	18% 61% 8% 8% 4	2200
October	1st to 10th	Night	41% 40% 11% 5% 2	3745
	11th to 20th	Night	20% 39% 6% 17% 16% 2	3899
	21st to end	Night	19% 37% 6% 17% 17% 3	4252
November	1st to 10th	Night	18% 58% 8% 7% 7% 2	2366
	11th to 20th	Night	18% 59% 5% 8% 7% 2	2400
	21st to end	Night	18% 58% 4 9% 7% 3	2400
December	1st to 10th	Night	15% 38% 13% 23% 9% 3	4212
	11th to 20th	Night	27% 35% 13% 9% 11% 5%	4824
	21st to end	Night	35% 31% 12% 14% 5% 3	6490

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	11% 4 31% 37% 15% 2	300
	11th to 20th	Day	8% 7% 28% 37% 16% 4	300
	21st to end	Day	15% 10% 28% 37% 10%	330
February	1st to 10th	Day	11% 5% 21% 32% 25% 6%	300
	11th to 20th	Day	7% 4 23% 38% 23% 5%	343
	21st to end	Day	8% 2 23% 38% 24% 5%	414
March	1st to 10th	Day	5% 4 31% 41% 17% 2	500
	11th to 20th	Day	8% 4 24% 38% 23% 3	500
	21st to end	Day	5% 4 22% 37% 27% 5%	550
April	1st to 10th	Day	4 4 26% 38% 23% 5%	500
	11th to 20th	Day	7% 4 21% 34% 30% 3	492
	21st to end	Day	5% 3 14% 35% 34% 9%	500
May	1st to 10th	Day	4 1 12% 39% 33% 10%	503
	11th to 20th	Day	9% 2 12% 27% 36% 14%	527
	21st to end	Day	7% 1 7% 21% 41% 23%	573
June	1st to 10th	Day	11% 1 6% 21% 40% 21%	530
	11th to 20th	Day	5% 1 4 16% 37% 38%	530
	21st to end	Day	5% 1 3 11% 29% 51%	530
July	1st to 10th	Day	5% 1 3 7% 29% 55%	525
	11th to 20th	Day	5% 1 2 9% 32% 52%	524
	21st to end	Day	6% 1 2 9% 35% 48%	576
August	1st to 10th	Day	4 1 5% 7% 35% 48%	526
	11th to 20th	Day	3 1 2 7% 33% 55%	519
	21st to end	Day	7% 1 5% 13% 33% 40%	583
September	1st to 10th	Day	7% 2 4 7% 40% 41%	530
	11th to 20th	Day	7% 2 6% 16% 39% 31%	530
	21st to end	Day	10% 1 6% 16% 36% 31%	530
October	1st to 10th	Day	17% 2 10% 25% 38% 9%	530
	11th to 20th	Day	5% 4 12% 33% 38% 9%	530
	21st to end	Day	7% 2 13% 37% 32% 8%	583
November	1st to 10th	Day	9% 7% 13% 33% 29% 10%	503
	11th to 20th	Day	12% 4 20% 30% 29% 4	500
	21st to end	Day	9% 3 20% 36% 28% 5%	500
December	1st to 10th	Day	6% 4 20% 38% 25% 7%	320
	11th to 20th	Day	8% 5% 22% 35% 24% 5%	300
	21st to end	Day	9% 6% 15% 40% 25% 4	330
January	1st to 10th	Night	13% 6% 25% 33% 20% 3	800
	11th to 20th	Night	11% 7% 27% 33% 20% 3	800
	21st to end	Night	11% 8% 28% 36% 16% 1	880
February	1st to 10th	Night	13% 7% 19% 36% 22% 3	800
	11th to 20th	Night	10% 6% 24% 37% 20% 3	783
	21st to end	Night	10% 2 21% 42% 23% 1	660
March	1st to 10th	Night	5% 5% 28% 43% 17% 2	800
	11th to 20th	Night	7% 5% 22% 37% 25% 4	800
	21st to end	Night	6% 4 23% 38% 27% 2	880
April	1st to 10th	Night	6% 3 21% 40% 26% 4	800
	11th to 20th	Night	6% 3 20% 38% 30% 3	791
	21st to end	Night	6% 2 15% 43% 31% 4	800
May	1st to 10th	Night	5% 2 11% 40% 39% 3	800
	11th to 20th	Night	9% 2 10% 32% 38% 10%	616
	21st to end	Night	8% 1 5% 22% 46% 17%	650
June	1st to 10th	Night	12% 1 5% 21% 46% 15%	600
	11th to 20th	Night	6% 1 5% 14% 42% 32%	600
	21st to end	Night	7% 1 4 10% 41% 39%	600
July	1st to 10th	Night	8% 1 4 8% 40% 40%	585
	11th to 20th	Night	6% 1 3 7% 37% 47%	582
	21st to end	Night	4 1 2 7% 44% 41%	657
August	1st to 10th	Night	5% 1 3 7% 42% 42%	597
	11th to 20th	Night	5% 3 5% 40% 46%	724
	21st to end	Night	10% 1 5% 11% 39% 34%	880
September	1st to 10th	Night	8% 2 5% 11% 41% 33%	800
	11th to 20th	Night	12% 2 6% 14% 41% 25%	800
	21st to end	Night	13% 2 5% 16% 41% 23%	800
October	1st to 10th	Night	15% 2 8% 28% 38% 9%	800
	11th to 20th	Night	8% 2 11% 26% 43% 10%	800
	21st to end	Night	11% 2 15% 30% 35% 8%	880
November	1st to 10th	Night	9% 3 18% 30% 31% 9%	789
	11th to 20th	Night	11% 4 17% 36% 26% 6%	800
	21st to end	Night	13% 3 20% 38% 24% 3	800
December	1st to 10th	Night	6% 4 21% 33% 30% 6%	800
	11th to 20th	Night	11% 5% 21% 31% 26% 6%	800
	21st to end	Night	9% 5% 22% 33% 27% 3	880

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