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 2025-01-07.

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	10% 4 2 4 3 3 3 3 4 6% 60%	108796
	Night	12% 6% 2 4 3 3 3 3 4 6% 55%	108978
Transparency	Day	26% 4 7% 20% 23% 20%	108555
	Night	30% 4 7% 19% 21% 19%	108809
Seeing	Day	13% 9% 22% 30% 20% 6%	15502
	Night	13% 5% 12% 32% 31% 6%	24842

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	18% 8% 2 7% 4 4 3 2 5% 5% 41%	2746
	11th to 20th	Day	25% 10% 3 8% 4 3 4 2 4 5% 33%	2860
	21st to end	Day	23% 9% 3 7% 4 3 4 3 5% 6% 33%	3146
February	1st to 10th	Day	18% 6% 2 6% 4 3 4 3 3 5% 46%	1710
	11th to 20th	Day	15% 7% 2 7% 3 3 4 3 4 8% 43%	1699
	21st to end	Day	17% 7% 2 5% 3 3 3 2 4 6% 47%	1570
March	1st to 10th	Day	23% 14% 4 7% 5% 3 3 3 4 4 29%	3428
	11th to 20th	Day	12% 5% 2 4 3 3 3 3 5% 6% 54%	3490
	21st to end	Day	20% 8% 2 6% 4 4 5% 4 5% 7% 35%	3846
April	1st to 10th	Day	16% 7% 2 5% 4 4 4 3 6% 7% 42%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 6% 51%	2249
	21st to end	Day	7% 4 1 4 3 3 3 4 5% 8% 58%	2280
May	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 5% 71%	4048
	11th to 20th	Day	4 2 1 3 2 2 3 2 4 5% 73%	4160
	21st to end	Day	3 3 1 2 2 2 2 2 3 6% 73%	4813
June	1st to 10th	Day	7% 5% 2 3 2 3 3 3 4 8% 60%	2660
	11th to 20th	Day	2 2 1 2 2 2 3 2 4 7% 74%	2660
	21st to end	Day	3 2 1 2 2 1 2 2 3 5% 78%	2660
July	1st to 10th	Day	1 1 1 1 1 1 2 1 3 4 84%	4420
	11th to 20th	Day	1 2 1 2 2 2 3 3 4 5% 78%	4148
	21st to end	Day	1 1 3 2 2 2 1 3 5% 81%	4455
August	1st to 10th	Day	1 2 1 2 2 3 4 4 7% 8% 67%	4091
	11th to 20th	Day	1 2 1 2 1 2 3 5% 82%	3912
	21st to end	Day	1 3 1 3 2 2 3 2 4 5% 75%	4180
September	1st to 10th	Day	1 1 1 1 2 2 2 2 3 6% 80%	2280
	11th to 20th	Day	3 3 1 4 2 2 2 3 5% 6% 67%	2275
	21st to end	Day	4 2 1 2 2 2 2 2 3 6% 75%	2000
October	1st to 10th	Day	4 3 1 2 2 2 2 2 4 5% 73%	3180
	11th to 20th	Day	8% 3 1 3 2 2 3 3 3 5% 66%	3161
	21st to end	Day	8% 4 1 3 3 3 4 3 5% 7% 59%	3448
November	1st to 10th	Day	11% 3 1 4 4 3 3 3 5% 7% 56%	1929
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 5% 6% 50%	1760
	21st to end	Day	13% 5% 2 4 4 3 4 3 5% 6% 53%	1600
December	1st to 10th	Day	11% 4 2 3 3 2 4 3 6% 9% 53%	2620
	11th to 20th	Day	30% 8% 2 5% 3 3 4 3 7% 7% 29%	3028
	21st to end	Day	27% 9% 3 7% 4 4 3 3 5% 8% 28%	4004
January	1st to 10th	Night	17% 8% 2 5% 3 3 4 3 5% 8% 42%	4334
	11th to 20th	Night	23% 9% 2 6% 5% 4 4 4 5% 5% 32%	4110
	21st to end	Night	26% 10% 3 7% 4 3 4 3 4 6% 32%	4521
February	1st to 10th	Night	19% 5% 2 4 3 2 3 3 4 5% 49%	2470
	11th to 20th	Night	14% 8% 2 7% 3 3 4 3 5% 7% 44%	2366
	21st to end	Night	15% 6% 1 4 2 2 3 2 3 6% 54%	1884
March	1st to 10th	Night	22% 13% 3 6% 4 3 4 3 4 5% 34%	3442
	11th to 20th	Night	14% 5% 2 4 3 2 3 2 4 5% 56%	3490
	21st to end	Night	17% 13% 3 7% 3 3 3 3 4 5% 38%	3805
April	1st to 10th	Night	12% 8% 2 6% 3 3 2 3 4 6% 51%	1900
	11th to 20th	Night	10% 6% 1 5% 4 3 3 3 4 7% 55%	1879
	21st to end	Night	6% 4 1 4 3 3 3 3 5% 6% 62%	1900
May	1st to 10th	Night	5% 3 2 3 2 2 2 2 3 4 71%	2906
	11th to 20th	Night	3 4 3 5% 4 2 3 3 4 6% 63%	2738
	21st to end	Night	3 3 1 2 1 2 2 2 3 4 77%	2762
June	1st to 10th	Night	5% 5% 2 3 3 3 3 3 4 8% 61%	1520
	11th to 20th	Night	2 1 1 3 3 2 2 2 4 5% 76%	1520
	21st to end	Night	3 4 1 2 2 2 2 2 3 5% 73%	1520
July	1st to 10th	Night	1 1 2 1 1 1 2 3 4 84%	2540
	11th to 20th	Night	1 2 1 3 3 3 3 3 3 4 74%	2816
	21st to end	Night	1 1 1 6% 3 3 3 3 6% 6% 68%	3109
August	1st to 10th	Night	2 2 1 3 2 3 4 3 12% 8% 59%	2848
	11th to 20th	Night	1 1 2 2 2 2 2 3 5% 79%	2928
	21st to end	Night	3 2 1 3 2 2 3 2 6% 5% 71%	3498
September	1st to 10th	Night	1 1 2 2 2 2 3 4 7% 77%	1900
	11th to 20th	Night	5% 4 1 3 2 2 4 2 4 7% 66%	1902
	21st to end	Night	3 3 1 3 2 2 2 2 3 6% 73%	2180
October	1st to 10th	Night	3 4 1 3 2 2 2 2 3 4 74%	3800
	11th to 20th	Night	5% 6% 1 5% 3 2 3 2 5% 5% 62%	3777
	21st to end	Night	10% 3 1 3 3 3 4 3 5% 6% 60%	4121
November	1st to 10th	Night	11% 5% 1 4 3 2 3 3 5% 9% 54%	2367
	11th to 20th	Night	13% 6% 2 5% 2 3 3 3 6% 7% 51%	2637
	21st to end	Night	12% 4 2 5% 3 3 3 3 4 6% 56%	2800
December	1st to 10th	Night	12% 4 1 4 2 3 3 3 5% 6% 55%	4560
	11th to 20th	Night	29% 8% 2 5% 4 3 4 4 6% 7% 29%	5176
	21st to end	Night	33% 8% 2 5% 3 3 3 3 4 5% 32%	6952

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	46% 3 13% 27% 8% 3	2746
	11th to 20th	Day	56% 3 10% 14% 10% 8%	2860
	21st to end	Day	53% 4 9% 18% 12% 5%	3146
February	1st to 10th	Day	42% 3 6% 20% 20% 9%	1710
	11th to 20th	Day	41% 5% 8% 21% 19% 7%	1708
	21st to end	Day	39% 4 9% 24% 16% 7%	1570
March	1st to 10th	Day	57% 5% 8% 16% 12% 2	3428
	11th to 20th	Day	31% 4 10% 30% 14% 11%	3490
	21st to end	Day	46% 6% 13% 21% 11% 2	3846
April	1st to 10th	Day	41% 5% 12% 22% 16% 4	2280
	11th to 20th	Day	33% 4 14% 23% 20% 6%	2252
	21st to end	Day	24% 4 14% 30% 23% 4	2280
May	1st to 10th	Day	17% 4 9% 31% 22% 17%	4048
	11th to 20th	Day	14% 5% 5% 31% 31% 14%	4163
	21st to end	Day	14% 3 12% 41% 25% 4	4814
June	1st to 10th	Day	23% 4 11% 29% 25% 7%	2660
	11th to 20th	Day	13% 3 9% 21% 38% 16%	2660
	21st to end	Day	11% 3 3 17% 36% 30%	2660
July	1st to 10th	Day	6% 2 2 7% 16% 67%	4351
	11th to 20th	Day	7% 4 3 6% 22% 58%	4077
	21st to end	Day	7% 3 1 8% 26% 55%	4315
August	1st to 10th	Day	12% 4 2 11% 27% 43%	4076
	11th to 20th	Day	6% 3 2 12% 45% 33%	3951
	21st to end	Day	10% 4 2 15% 38% 31%	4179
September	1st to 10th	Day	8% 3 2 11% 33% 44%	2280
	11th to 20th	Day	17% 4 5% 26% 36% 12%	2275
	21st to end	Day	13% 3 4 23% 32% 26%	2000
October	1st to 10th	Day	15% 2 4 12% 25% 42%	3180
	11th to 20th	Day	20% 3 5% 21% 28% 22%	3161
	21st to end	Day	25% 3 8% 24% 27% 12%	3448
November	1st to 10th	Day	28% 4 7% 28% 21% 12%	1929
	11th to 20th	Day	36% 3 11% 24% 17% 8%	1760
	21st to end	Day	33% 3 10% 22% 19% 14%	1600
December	1st to 10th	Day	29% 3 6% 25% 27% 10%	2620
	11th to 20th	Day	55% 3 8% 16% 15% 3	3028
	21st to end	Day	56% 4 10% 18% 8% 3	4004
January	1st to 10th	Night	41% 4 20% 23% 8% 3	4334
	11th to 20th	Night	53% 5% 12% 13% 10% 8%	4110
	21st to end	Night	54% 4 10% 13% 13% 6%	4521
February	1st to 10th	Night	38% 3 9% 20% 19% 11%	2470
	11th to 20th	Night	39% 4 9% 20% 20% 8%	2368
	21st to end	Night	33% 4 10% 28% 20% 6%	1884
March	1st to 10th	Night	52% 5% 12% 14% 14% 3	3442
	11th to 20th	Night	32% 3 9% 22% 23% 11%	3490
	21st to end	Night	46% 6% 11% 23% 10% 3	3805
April	1st to 10th	Night	35% 4 13% 22% 20% 5%	1900
	11th to 20th	Night	29% 4 13% 27% 18% 9%	1879
	21st to end	Night	22% 4 11% 32% 25% 6%	1900
May	1st to 10th	Night	18% 3 5% 28% 28% 17%	2906
	11th to 20th	Night	16% 11% 5% 22% 27% 20%	2739
	21st to end	Night	12% 3 8% 42% 28% 6%	2762
June	1st to 10th	Night	21% 5% 9% 26% 29% 10%	1520
	11th to 20th	Night	12% 4 5% 23% 36% 20%	1520
	21st to end	Night	13% 6% 3 13% 33% 33%	1520
July	1st to 10th	Night	5% 4 1 6% 17% 67%	2500
	11th to 20th	Night	9% 5% 3 7% 19% 56%	2764
	21st to end	Night	10% 7% 1 7% 23% 53%	3011
August	1st to 10th	Night	14% 4 1 10% 24% 47%	2839
	11th to 20th	Night	8% 4 2 8% 39% 39%	2955
	21st to end	Night	12% 4 2 12% 36% 34%	3498
September	1st to 10th	Night	7% 5% 2 9% 31% 46%	1900
	11th to 20th	Night	19% 3 4 20% 38% 15%	1902
	21st to end	Night	14% 4 2 21% 29% 30%	2180
October	1st to 10th	Night	15% 3 3 11% 20% 48%	3800
	11th to 20th	Night	22% 5% 5% 22% 24% 22%	3777
	21st to end	Night	25% 3 5% 21% 27% 19%	4121
November	1st to 10th	Night	28% 5% 8% 27% 19% 12%	2367
	11th to 20th	Night	32% 4 12% 26% 17% 9%	2637
	21st to end	Night	31% 3 8% 21% 22% 15%	2800
December	1st to 10th	Night	30% 3 6% 20% 27% 14%	4560
	11th to 20th	Night	54% 4 8% 15% 15% 5%	5176
	21st to end	Night	56% 4 9% 17% 10% 3	6952

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	36% 7% 23% 19% 12% 3	286
	11th to 20th	Day	26% 8% 22% 26% 14% 3	370
	21st to end	Day	20% 9% 22% 28% 18% 3	407
February	1st to 10th	Day	24% 10% 21% 24% 17% 5%	370
	11th to 20th	Day	23% 15% 26% 22% 13% 1	381
	21st to end	Day	20% 12% 24% 29% 14% 1	382
March	1st to 10th	Day	28% 14% 24% 22% 10% 2	460
	11th to 20th	Day	27% 12% 24% 22% 12% 4	460
	21st to end	Day	22% 15% 28% 24% 11%	506
April	1st to 10th	Day	21% 15% 24% 24% 12% 4	460
	11th to 20th	Day	18% 15% 27% 23% 12% 4	452
	21st to end	Day	11% 14% 28% 27% 14% 6%	460
May	1st to 10th	Day	13% 13% 30% 26% 14% 4	463
	11th to 20th	Day	12% 11% 26% 27% 17% 6%	488
	21st to end	Day	8% 11% 24% 32% 18% 7%	529
June	1st to 10th	Day	10% 11% 22% 34% 16% 7%	490
	11th to 20th	Day	5% 12% 28% 35% 17% 4	490
	21st to end	Day	2 5% 28% 36% 24% 6%	490
July	1st to 10th	Day	3 4 19% 45% 22% 7%	486
	11th to 20th	Day	1 1 19% 40% 29% 10%	484
	21st to end	Day	1 2 13% 47% 29% 9%	531
August	1st to 10th	Day	2 3 18% 41% 25% 10%	487
	11th to 20th	Day	2 4 23% 37% 25% 9%	477
	21st to end	Day	2 3 17% 37% 29% 11%	539
September	1st to 10th	Day	1 2 21% 37% 28% 10%	490
	11th to 20th	Day	7% 6% 22% 31% 25% 9%	490
	21st to end	Day	4 6% 21% 36% 25% 7%	490
October	1st to 10th	Day	9% 6% 24% 27% 24% 11%	490
	11th to 20th	Day	8% 9% 19% 25% 27% 12%	490
	21st to end	Day	14% 8% 19% 29% 24% 6%	539
November	1st to 10th	Day	14% 9% 18% 25% 27% 7%	465
	11th to 20th	Day	16% 6% 16% 24% 27% 11%	280
	21st to end	Day	15% 10% 22% 30% 14% 10%	200
December	1st to 10th	Day	26% 7% 18% 21% 19% 10%	200
	11th to 20th	Day	28% 9% 22% 20% 14% 8%	200
	21st to end	Day	27% 10% 23% 23% 15% 4	220
January	1st to 10th	Night	23% 4 14% 33% 22% 4	784
	11th to 20th	Night	23% 5% 12% 37% 18% 5%	760
	21st to end	Night	20% 6% 14% 32% 24% 4	836
February	1st to 10th	Night	21% 6% 13% 36% 22% 3	760
	11th to 20th	Night	18% 7% 15% 35% 20% 5%	744
	21st to end	Night	19% 8% 15% 36% 20% 3	628
March	1st to 10th	Night	24% 7% 16% 29% 20% 3	760
	11th to 20th	Night	21% 6% 14% 31% 25% 3	760
	21st to end	Night	20% 6% 21% 31% 19% 2	836
April	1st to 10th	Night	16% 7% 19% 34% 21% 4	760
	11th to 20th	Night	13% 10% 17% 32% 23% 5%	751
	21st to end	Night	9% 10% 20% 29% 27% 6%	760
May	1st to 10th	Night	9% 5% 21% 29% 31% 5%	603
	11th to 20th	Night	7% 3 15% 32% 36% 7%	505
	21st to end	Night	7% 7% 17% 28% 36% 6%	411
June	1st to 10th	Night	8% 6% 16% 31% 35% 4	380
	11th to 20th	Night	3 5% 12% 44% 33% 2	380
	21st to end	Night	5% 3 10% 34% 43% 5%	380
July	1st to 10th	Night	1 1 6% 32% 52% 7%	370
	11th to 20th	Night	2 2 3 27% 53% 13%	523
	21st to end	Night	2 1 1 29% 55% 12%	624
August	1st to 10th	Night	2 2 3 31% 50% 11%	567
	11th to 20th	Night	1 2 6% 31% 50% 10%	628
	21st to end	Night	2 3 5% 31% 49% 11%	836
September	1st to 10th	Night	1 1 7% 32% 49% 10%	760
	11th to 20th	Night	7% 3 7% 32% 43% 9%	760
	21st to end	Night	4 4 8% 35% 38% 12%	760
October	1st to 10th	Night	6% 6% 10% 30% 38% 10%	760
	11th to 20th	Night	8% 4 10% 31% 38% 9%	760
	21st to end	Night	12% 4 9% 32% 33% 11%	836
November	1st to 10th	Night	13% 5% 12% 29% 32% 9%	780
	11th to 20th	Night	14% 3 12% 37% 29% 6%	800
	21st to end	Night	15% 5% 12% 38% 25% 6%	800
December	1st to 10th	Night	22% 6% 11% 32% 24% 6%	800
	11th to 20th	Night	28% 6% 13% 30% 20% 4	800
	21st to end	Night	26% 5% 18% 33% 16% 2	880

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