Hume Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hume Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	9% 4 1 4 2 2 3 3 4 6% 62%	140592
	Night	11% 5% 2 4 3 3 3 3 5% 6% 55%	139368
Transparency	Day	25% 4 7% 20% 24% 20%	135489
	Night	29% 5% 7% 18% 22% 19%	135461
Seeing	Day	13% 9% 23% 30% 19% 6%	17229
	Night	13% 5% 13% 32% 31% 6%	26601

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	17% 7% 2 6% 3 3 4 3 5% 6% 43%	5019
	11th to 20th	Day	13% 5% 2 4 3 2 3 2 4 5% 56%	5340
	21st to end	Day	15% 7% 3 6% 3 3 4 3 5% 7% 44%	5843
February	1st to 10th	Day	19% 6% 2 5% 4 3 4 3 3 5% 46%	1890
	11th to 20th	Day	16% 8% 3 7% 3 3 4 4 5% 8% 41%	1883
	21st to end	Day	18% 7% 2 5% 3 3 4 3 4 6% 45%	1730
March	1st to 10th	Day	18% 12% 3 7% 4 3 3 3 4 6% 36%	5034
	11th to 20th	Day	15% 7% 2 4 3 3 3 3 5% 7% 47%	5110
	21st to end	Day	18% 8% 3 6% 4 4 5% 4 5% 7% 35%	5642
April	1st to 10th	Day	16% 7% 2 5% 4 4 4 3 6% 7% 43%	2520
	11th to 20th	Day	10% 6% 2 5% 4 4 4 4 5% 7% 51%	2489
	21st to end	Day	7% 5% 1 4 3 3 3 4 5% 8% 56%	2520
May	1st to 10th	Day	4 2 1 2 2 2 2 2 3 5% 75%	5805
	11th to 20th	Day	3 2 1 3 2 2 2 2 4 5% 75%	5969
	21st to end	Day	2 2 1 2 1 2 2 2 3 5% 78%	6902
June	1st to 10th	Day	6% 5% 2 3 2 3 3 3 4 8% 60%	2800
	11th to 20th	Day	1 2 1 2 2 2 3 2 4 6% 75%	2800
	21st to end	Day	2 2 1 2 2 1 2 2 3 5% 78%	2800
July	1st to 10th	Day	1 1 1 2 1 1 2 1 3 4 83%	6319
	11th to 20th	Day	1 1 2 2 1 3 3 4 4 79%	5931
	21st to end	Day	2 1 3 1 2 2 2 3 5% 79%	6402
August	1st to 10th	Day	1 1 2 1 2 3 3 5% 6% 76%	5777
	11th to 20th	Day	1 2 1 2 1 2 3 4 83%	5630
	21st to end	Day	1 2 1 3 2 2 3 3 5% 6% 73%	5984
September	1st to 10th	Day	1 2 1 2 2 2 2 2 3 6% 78%	2400
	11th to 20th	Day	3 3 1 4 2 3 3 3 5% 6% 67%	2394
	21st to end	Day	4 2 1 2 2 2 2 2 3 6% 74%	2105
October	1st to 10th	Day	4 3 1 2 2 2 2 2 4 5% 72%	3280
	11th to 20th	Day	8% 3 1 3 2 2 3 3 3 5% 66%	3261
	21st to end	Day	8% 4 1 3 3 3 4 3 5% 7% 59%	3558
November	1st to 10th	Day	11% 3 1 4 4 3 3 3 5% 7% 56%	2027
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 5% 6% 48%	1848
	21st to end	Day	12% 4 2 4 3 3 4 3 5% 6% 55%	1680
December	1st to 10th	Day	11% 4 2 3 3 2 4 3 7% 9% 53%	2700
	11th to 20th	Day	30% 8% 2 5% 3 3 4 3 6% 7% 29%	3108
	21st to end	Day	27% 9% 3 7% 4 4 3 3 4 7% 28%	4092
January	1st to 10th	Night	20% 7% 2 4 3 3 4 3 5% 8% 41%	7887
	11th to 20th	Night	12% 5% 1 4 3 3 3 3 5% 6% 56%	7650
	21st to end	Night	17% 8% 3 6% 3 3 3 3 5% 7% 42%	8371
February	1st to 10th	Night	19% 5% 2 4 3 2 4 3 4 5% 48%	2730
	11th to 20th	Night	15% 8% 2 7% 3 3 4 3 5% 7% 43%	2622
	21st to end	Night	15% 7% 1 4 3 3 3 2 4 7% 52%	2076
March	1st to 10th	Night	17% 12% 3 6% 4 3 4 3 5% 6% 38%	5063
	11th to 20th	Night	17% 8% 2 4 3 2 3 2 4 5% 49%	5110
	21st to end	Night	19% 11% 3 6% 3 2 3 3 4 7% 39%	5573
April	1st to 10th	Night	12% 8% 2 6% 3 3 3 3 4 6% 50%	2100
	11th to 20th	Night	10% 7% 2 5% 4 3 3 3 4 6% 54%	2079
	21st to end	Night	7% 5% 1 4 3 3 3 3 5% 6% 60%	2100
May	1st to 10th	Night	5% 3 2 3 2 2 1 2 3 5% 73%	4184
	11th to 20th	Night	4 4 3 5% 4 2 3 3 4 5% 65%	3936
	21st to end	Night	2 2 1 2 1 2 1 1 2 4 80%	3972
June	1st to 10th	Night	5% 5% 2 3 3 3 3 3 5% 8% 61%	1600
	11th to 20th	Night	2 1 1 3 3 2 2 2 4 5% 76%	1600
	21st to end	Night	3 4 1 2 2 2 2 2 3 5% 73%	1600
July	1st to 10th	Night	1 1 1 4 2 1 2 2 5% 4 79%	3640
	11th to 20th	Night	1 3 3 8% 4 3 4 4 5% 4 62%	4042
	21st to end	Night	1 6% 3 7% 3 2 3 2 5% 6% 62%	4472
August	1st to 10th	Night	2 2 1 2 2 2 3 2 9% 6% 69%	4035
	11th to 20th	Night	1 2 4 2 2 2 2 4 5% 76%	4224
	21st to end	Night	2 2 1 3 2 2 3 3 10% 6% 66%	5015
September	1st to 10th	Night	1 1 1 2 3 2 2 3 4 7% 76%	2000
	11th to 20th	Night	5% 4 1 3 2 2 4 2 4 7% 66%	2002
	21st to end	Night	4 3 1 3 2 2 2 2 3 5% 72%	2295
October	1st to 10th	Night	3 4 1 3 2 2 2 2 3 4 74%	3920
	11th to 20th	Night	5% 6% 1 5% 3 3 3 2 5% 5% 61%	3897
	21st to end	Night	10% 3 1 3 3 3 4 3 5% 6% 60%	4253
November	1st to 10th	Night	11% 5% 1 4 3 2 3 3 5% 8% 54%	2489
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 6% 7% 49%	2769
	21st to end	Night	12% 4 2 5% 3 3 3 3 4 6% 56%	2940
December	1st to 10th	Night	12% 4 1 4 2 3 3 3 5% 7% 55%	4700
	11th to 20th	Night	29% 8% 2 5% 4 3 4 4 6% 7% 29%	5316
	21st to end	Night	33% 8% 2 5% 3 3 3 3 4 5% 32%	7106

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	42% 6% 13% 23% 11% 7%	5020
	11th to 20th	Day	32% 2 5% 13% 23% 24%	5340
	21st to end	Day	40% 4 7% 19% 11% 19%	5843
February	1st to 10th	Day	42% 3 6% 20% 20% 9%	1890
	11th to 20th	Day	43% 5% 8% 20% 17% 7%	1892
	21st to end	Day	40% 4 9% 23% 16% 7%	1730
March	1st to 10th	Day	49% 4 7% 20% 18% 2	5034
	11th to 20th	Day	37% 4 13% 26% 11% 8%	5110
	21st to end	Day	46% 7% 13% 22% 11% 2	5642
April	1st to 10th	Day	40% 4 11% 23% 17% 4	2520
	11th to 20th	Day	33% 4 13% 23% 19% 7%	2492
	21st to end	Day	26% 4 13% 31% 22% 4	2520
May	1st to 10th	Day	13% 3 7% 27% 29% 20%	5805
	11th to 20th	Day	12% 4 6% 35% 33% 11%	5972
	21st to end	Day	11% 2 9% 36% 38% 5%	6904
June	1st to 10th	Day	22% 4 11% 29% 27% 7%	2800
	11th to 20th	Day	12% 3 9% 21% 38% 17%	2800
	21st to end	Day	10% 3 3 17% 36% 30%	2800
July	1st to 10th	Day	6% 3 1 6% 25% 59%	6251
	11th to 20th	Day	6% 4 2 5% 18% 66%	5860
	21st to end	Day	8% 3 3 17% 28% 41%	6217
August	1st to 10th	Day	11% 4 2 11% 29% 43%	4206
	11th to 20th	Day	6% 3 2 12% 45% 34%	4077
	21st to end	Day	10% 4 2 14% 38% 31%	4311
September	1st to 10th	Day	9% 3 2 12% 32% 42%	2400
	11th to 20th	Day	18% 4 5% 26% 36% 12%	2394
	21st to end	Day	14% 3 4 22% 32% 25%	2105
October	1st to 10th	Day	15% 2 4 12% 25% 41%	3280
	11th to 20th	Day	20% 3 5% 22% 28% 21%	3261
	21st to end	Day	25% 3 8% 24% 27% 12%	3558
November	1st to 10th	Day	28% 4 7% 28% 21% 11%	2027
	11th to 20th	Day	38% 4 11% 24% 16% 8%	1848
	21st to end	Day	31% 3 9% 23% 20% 14%	1680
December	1st to 10th	Day	28% 3 6% 25% 27% 10%	2700
	11th to 20th	Day	55% 3 8% 16% 15% 4	3108
	21st to end	Day	56% 4 10% 18% 9% 3	4092
January	1st to 10th	Night	41% 6% 17% 19% 12% 4	7887
	11th to 20th	Night	31% 3 7% 13% 23% 23%	7650
	21st to end	Night	43% 3 6% 13% 17% 17%	8371
February	1st to 10th	Night	39% 3 8% 19% 19% 12%	2730
	11th to 20th	Night	41% 4 9% 20% 18% 7%	2624
	21st to end	Night	34% 3 10% 26% 19% 7%	2076
March	1st to 10th	Night	47% 4 9% 17% 19% 4	5063
	11th to 20th	Night	39% 4 9% 21% 20% 8%	5110
	21st to end	Night	44% 6% 11% 24% 12% 2	5573
April	1st to 10th	Night	35% 4 12% 23% 21% 5%	2100
	11th to 20th	Night	31% 4 12% 26% 17% 10%	2079
	21st to end	Night	24% 4 10% 32% 24% 5%	2100
May	1st to 10th	Night	16% 3 4 24% 32% 22%	4181
	11th to 20th	Night	17% 9% 4 28% 27% 14%	3937
	21st to end	Night	10% 2 6% 32% 39% 10%	3972
June	1st to 10th	Night	21% 6% 9% 26% 30% 9%	1600
	11th to 20th	Night	11% 4 5% 22% 37% 22%	1600
	21st to end	Night	12% 6% 3 13% 34% 32%	1600
July	1st to 10th	Night	5% 6% 1 6% 24% 58%	3600
	11th to 20th	Night	8% 13% 3 5% 15% 56%	3990
	21st to end	Night	18% 6% 1 10% 23% 41%	4345
August	1st to 10th	Night	14% 4 1 10% 25% 46%	2929
	11th to 20th	Night	8% 4 2 9% 38% 39%	3049
	21st to end	Night	12% 4 2 12% 35% 35%	3608
September	1st to 10th	Night	8% 4 3 10% 31% 44%	2000
	11th to 20th	Night	20% 4 4 20% 37% 15%	2002
	21st to end	Night	15% 4 2 21% 29% 30%	2295
October	1st to 10th	Night	16% 3 3 11% 20% 47%	3920
	11th to 20th	Night	23% 5% 5% 22% 24% 21%	3897
	21st to end	Night	25% 3 5% 21% 28% 18%	4253
November	1st to 10th	Night	29% 5% 8% 27% 20% 12%	2489
	11th to 20th	Night	34% 4 11% 25% 17% 9%	2769
	21st to end	Night	31% 3 8% 22% 22% 15%	2940
December	1st to 10th	Night	29% 3 6% 21% 27% 14%	4700
	11th to 20th	Night	54% 4 8% 14% 14% 6%	5316
	21st to end	Night	57% 4 9% 17% 10% 3	7106

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	35% 8% 24% 19% 11% 3	322
	11th to 20th	Day	23% 8% 22% 28% 16% 3	430
	21st to end	Day	18% 10% 23% 28% 18% 3	473
February	1st to 10th	Day	25% 9% 23% 23% 16% 4	430
	11th to 20th	Day	25% 16% 27% 20% 12% 1	445
	21st to end	Day	21% 11% 26% 28% 13% 1	446
March	1st to 10th	Day	27% 15% 24% 21% 10% 2	540
	11th to 20th	Day	27% 10% 24% 23% 13% 4	540
	21st to end	Day	23% 14% 28% 23% 12%	594
April	1st to 10th	Day	21% 14% 25% 25% 11% 4	540
	11th to 20th	Day	18% 15% 27% 23% 12% 4	532
	21st to end	Day	11% 14% 29% 26% 14% 6%	540
May	1st to 10th	Day	12% 13% 31% 26% 15% 4	508
	11th to 20th	Day	13% 12% 27% 26% 17% 6%	528
	21st to end	Day	8% 12% 26% 31% 17% 7%	573
June	1st to 10th	Day	9% 10% 25% 34% 15% 7%	530
	11th to 20th	Day	5% 12% 29% 34% 16% 4	530
	21st to end	Day	2 6% 26% 36% 23% 7%	530
July	1st to 10th	Day	3 5% 21% 43% 21% 7%	526
	11th to 20th	Day	1 1 19% 41% 29% 9%	524
	21st to end	Day	1 2 14% 45% 29% 9%	575
August	1st to 10th	Day	2 3 20% 39% 25% 11%	527
	11th to 20th	Day	2 3 24% 37% 25% 9%	517
	21st to end	Day	2 3 18% 38% 29% 11%	583
September	1st to 10th	Day	1 3 22% 37% 27% 9%	530
	11th to 20th	Day	7% 6% 22% 31% 26% 9%	530
	21st to end	Day	5% 7% 22% 35% 24% 7%	530
October	1st to 10th	Day	10% 7% 23% 26% 24% 10%	530
	11th to 20th	Day	9% 9% 20% 25% 26% 12%	530
	21st to end	Day	14% 8% 19% 28% 24% 6%	583
November	1st to 10th	Day	14% 9% 18% 26% 26% 8%	503
	11th to 20th	Day	18% 7% 18% 23% 25% 10%	308
	21st to end	Day	13% 9% 22% 29% 17% 10%	220
December	1st to 10th	Day	24% 6% 18% 22% 20% 9%	220
	11th to 20th	Day	27% 8% 22% 20% 15% 7%	220
	21st to end	Day	29% 10% 24% 21% 14% 3	242
January	1st to 10th	Night	25% 5% 14% 32% 20% 4	840
	11th to 20th	Night	21% 5% 13% 40% 17% 5%	840
	21st to end	Night	19% 6% 15% 32% 24% 4	924
February	1st to 10th	Night	22% 5% 14% 36% 20% 3	840
	11th to 20th	Night	20% 8% 15% 34% 19% 4	824
	21st to end	Night	20% 8% 16% 36% 18% 2	692
March	1st to 10th	Night	23% 8% 16% 29% 20% 3	840
	11th to 20th	Night	21% 6% 14% 32% 24% 3	840
	21st to end	Night	20% 6% 21% 31% 20% 2	924
April	1st to 10th	Night	16% 7% 19% 33% 21% 3	840
	11th to 20th	Night	14% 10% 18% 32% 22% 4	831
	21st to end	Night	9% 10% 19% 30% 26% 6%	840
May	1st to 10th	Night	9% 6% 20% 29% 31% 5%	639
	11th to 20th	Night	7% 4 15% 32% 35% 7%	532
	21st to end	Night	6% 7% 17% 28% 36% 6%	433
June	1st to 10th	Night	8% 6% 16% 33% 35% 4	400
	11th to 20th	Night	3 5% 13% 44% 33% 2	400
	21st to end	Night	5% 3 10% 35% 42% 6%	400
July	1st to 10th	Night	1 2 7% 33% 50% 7%	390
	11th to 20th	Night	2 1 3 28% 54% 13%	552
	21st to end	Night	2 1 2 29% 54% 12%	657
August	1st to 10th	Night	2 2 4 30% 50% 12%	597
	11th to 20th	Night	1 2 7% 32% 49% 10%	662
	21st to end	Night	2 3 5% 30% 50% 11%	880
September	1st to 10th	Night	2 1 8% 32% 48% 10%	800
	11th to 20th	Night	6% 3 8% 32% 43% 9%	800
	21st to end	Night	4 4 8% 34% 38% 11%	800
October	1st to 10th	Night	7% 5% 11% 31% 38% 9%	800
	11th to 20th	Night	8% 4 11% 31% 38% 8%	800
	21st to end	Night	12% 4 9% 32% 34% 10%	880
November	1st to 10th	Night	13% 5% 12% 29% 32% 9%	820
	11th to 20th	Night	16% 3 12% 36% 28% 5%	840
	21st to end	Night	14% 5% 12% 39% 25% 5%	840
December	1st to 10th	Night	21% 6% 12% 33% 24% 5%	840
	11th to 20th	Night	28% 5% 13% 30% 20% 4	840
	21st to end	Night	27% 5% 18% 33% 15% 2	924

Page generated at 2026-04-28 23:21:48. Version ac07

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