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 2024-01-17.

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 3 3 2 3 3 4 6% 59%	74722
	Night	12% 5% 2 4 3 2 3 3 4 6% 55%	75114
Transparency	Day	27% 4 8% 21% 24% 16%	74441
	Night	30% 4 8% 20% 23% 16%	74917
Seeing	Day	13% 8% 22% 30% 20% 6%	14218
	Night	13% 5% 12% 32% 32% 7%	23584

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	23% 7% 3 6% 5% 3 3 3 5% 5% 38%	1611
	11th to 20th	Day	18% 6% 2 4 4 2 3 3 4 5% 47%	1675
	21st to end	Day	14% 7% 3 5% 5% 3 4 4 6% 6% 43%	1782
February	1st to 10th	Day	18% 5% 2 5% 4 2 4 4 3 5% 47%	1620
	11th to 20th	Day	14% 6% 2 6% 4 2 4 4 4 8% 46%	1607
	21st to end	Day	18% 6% 2 4 4 3 3 3 3 6% 48%	1480
March	1st to 10th	Day	20% 8% 4 6% 6% 3 3 4 5% 6% 35%	1966
	11th to 20th	Day	20% 7% 3 5% 4 3 4 5% 5% 7% 38%	1980
	21st to end	Day	17% 5% 2 4 4 2 5% 5% 5% 6% 44%	2187
April	1st to 10th	Day	17% 6% 3 4 4 3 4 4 5% 7% 41%	2160
	11th to 20th	Day	10% 5% 2 4 4 2 4 5% 5% 7% 53%	2129
	21st to end	Day	8% 3 2 3 4 2 3 4 5% 8% 57%	2160
May	1st to 10th	Day	7% 5% 2 3 3 2 3 3 4 6% 61%	2304
	11th to 20th	Day	7% 3 2 3 3 2 3 4 5% 6% 62%	2351
	21st to end	Day	6% 4 2 4 3 2 4 3 5% 7% 59%	2723
June	1st to 10th	Day	7% 5% 2 3 3 2 3 4 4 9% 59%	2520
	11th to 20th	Day	2 2 1 2 2 1 3 3 4 6% 75%	2520
	21st to end	Day	3 2 1 2 3 1 2 2 3 5% 77%	2520
July	1st to 10th	Day	2 2 1 2 2 1 2 2 2 5% 78%	2520
	11th to 20th	Day	1 2 1 2 2 1 3 3 4 6% 76%	2365
	21st to end	Day	1 1 1 3 2 1 3 2 4 5% 77%	2546
August	1st to 10th	Day	1 2 1 3 3 1 3 3 4 6% 73%	2328
	11th to 20th	Day	1 1 1 2 2 2 2 2 4 6% 77%	2236
	21st to end	Day	1 2 1 3 3 2 2 3 4 7% 72%	2376
September	1st to 10th	Day	1 1 1 1 2 1 2 3 3 5% 80%	2160
	11th to 20th	Day	4 3 1 4 2 2 2 4 5% 6% 67%	2156
	21st to end	Day	4 2 1 2 2 1 2 3 3 6% 75%	1895
October	1st to 10th	Day	7% 3 1 2 3 2 2 2 4 4 70%	1800
	11th to 20th	Day	8% 3 1 3 2 2 3 4 4 6% 65%	1800
	21st to end	Day	11% 3 1 3 3 2 3 3 4 6% 62%	1980
November	1st to 10th	Day	11% 3 1 4 5% 2 3 4 5% 7% 55%	1831
	11th to 20th	Day	13% 5% 2 5% 5% 2 3 3 5% 6% 51%	1672
	21st to end	Day	12% 4 2 3 4 3 4 4 5% 6% 54%	1520
December	1st to 10th	Day	19% 6% 2 3 4 2 4 3 4 7% 45%	1520
	11th to 20th	Day	34% 9% 3 4 3 2 3 3 4 4 31%	1928
	21st to end	Day	24% 9% 3 5% 4 3 3 3 4 8% 35%	2794
January	1st to 10th	Night	20% 8% 2 5% 4 3 4 4 5% 8% 37%	2551
	11th to 20th	Night	19% 6% 2 4 5% 2 4 4 5% 6% 43%	2429
	21st to end	Night	17% 6% 2 4 3 2 3 3 4 7% 49%	2574
February	1st to 10th	Night	18% 5% 2 4 4 1 4 4 4 6% 50%	2340
	11th to 20th	Night	13% 6% 2 6% 4 2 4 4 5% 7% 46%	2238
	21st to end	Night	16% 5% 1 3 3 2 3 3 3 7% 54%	1776
March	1st to 10th	Night	19% 9% 3 5% 5% 3 5% 4 4 5% 38%	1990
	11th to 20th	Night	17% 8% 2 5% 4 2 3 3 6% 6% 44%	1980
	21st to end	Night	17% 6% 2 5% 3 2 3 4 3 6% 50%	2167
April	1st to 10th	Night	13% 7% 2 5% 4 2 3 3 4 6% 50%	1800
	11th to 20th	Night	10% 6% 2 4 4 2 3 3 4 7% 55%	1779
	21st to end	Night	7% 4 1 3 3 1 4 3 5% 6% 62%	1800
May	1st to 10th	Night	6% 4 2 5% 4 2 2 3 4 6% 61%	1652
	11th to 20th	Night	5% 3 2 4 4 2 3 4 5% 7% 61%	1540
	21st to end	Night	5% 4 2 4 2 2 4 3 4 7% 62%	1552
June	1st to 10th	Night	5% 5% 2 3 3 2 3 3 4 9% 61%	1440
	11th to 20th	Night	2 1 1 2 4 2 2 3 4 5% 75%	1440
	21st to end	Night	3 4 1 2 2 2 2 3 3 5% 72%	1440
July	1st to 10th	Night	1 2 1 2 2 2 2 3 3 5% 79%	1440
	11th to 20th	Night	2 2 1 2 3 1 2 2 3 6% 76%	1590
	21st to end	Night	1 2 1 4 3 2 4 3 5% 7% 68%	1773
August	1st to 10th	Night	2 3 1 4 4 2 3 3 4 6% 69%	1611
	11th to 20th	Night	2 1 2 3 3 4 3 5% 8% 69%	1662
	21st to end	Night	1 3 2 4 4 1 2 3 3 7% 69%	1980
September	1st to 10th	Night	1 1 1 3 1 2 3 3 7% 77%	1800
	11th to 20th	Night	5% 5% 1 3 3 1 3 3 3 7% 66%	1801
	21st to end	Night	3 3 2 3 2 1 2 2 3 6% 73%	2065
October	1st to 10th	Night	5% 5% 1 3 3 1 2 3 3 5% 69%	2160
	11th to 20th	Night	6% 3 2 3 4 2 4 4 4 6% 62%	2160
	21st to end	Night	10% 3 1 2 4 2 4 3 4 6% 61%	2376
November	1st to 10th	Night	12% 5% 1 4 4 2 2 4 4 9% 54%	2245
	11th to 20th	Night	13% 5% 2 4 3 2 3 4 6% 7% 51%	2505
	21st to end	Night	11% 4 2 4 4 2 3 4 3 6% 58%	2660
December	1st to 10th	Night	20% 6% 2 4 4 2 3 3 4 6% 45%	2660
	11th to 20th	Night	33% 7% 2 3 4 2 3 3 5% 6% 32%	3276
	21st to end	Night	24% 7% 2 5% 4 3 4 4 4 6% 37%	4862

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	49% 2 12% 22% 9% 6%	1611
	11th to 20th	Day	41% 3 9% 17% 16% 13%	1675
	21st to end	Day	42% 4 8% 16% 22% 9%	1782
February	1st to 10th	Day	42% 2 6% 20% 21% 9%	1620
	11th to 20th	Day	38% 5% 8% 21% 20% 8%	1616
	21st to end	Day	39% 4 9% 24% 16% 8%	1480
March	1st to 10th	Day	49% 4 10% 17% 16% 3	1966
	11th to 20th	Day	45% 5% 9% 22% 14% 5%	1980
	21st to end	Day	41% 5% 12% 21% 18% 4	2187
April	1st to 10th	Day	42% 5% 12% 21% 16% 4	2160
	11th to 20th	Day	32% 4 14% 23% 20% 6%	2132
	21st to end	Day	25% 4 14% 31% 22% 5%	2160
May	1st to 10th	Day	24% 4 7% 31% 26% 7%	2304
	11th to 20th	Day	23% 4 8% 34% 23% 8%	2354
	21st to end	Day	24% 4 16% 32% 19% 4	2724
June	1st to 10th	Day	23% 4 11% 29% 25% 7%	2520
	11th to 20th	Day	13% 3 10% 22% 37% 16%	2520
	21st to end	Day	11% 3 3 17% 37% 28%	2520
July	1st to 10th	Day	11% 4 2 12% 29% 42%	2451
	11th to 20th	Day	10% 5% 5% 11% 32% 37%	2294
	21st to end	Day	10% 4 2 11% 28% 44%	2405
August	1st to 10th	Day	13% 5% 3 18% 34% 28%	2312
	11th to 20th	Day	9% 4 3 13% 41% 31%	2236
	21st to end	Day	11% 6% 2 15% 37% 29%	2376
September	1st to 10th	Day	8% 4 2 11% 33% 42%	2160
	11th to 20th	Day	17% 4 5% 26% 36% 12%	2156
	21st to end	Day	13% 3 4 24% 31% 25%	1895
October	1st to 10th	Day	19% 3 5% 17% 31% 25%	1800
	11th to 20th	Day	22% 4 7% 20% 24% 24%	1800
	21st to end	Day	25% 3 7% 21% 26% 17%	1980
November	1st to 10th	Day	29% 4 7% 28% 20% 12%	1831
	11th to 20th	Day	35% 3 11% 24% 17% 9%	1672
	21st to end	Day	32% 3 10% 22% 19% 14%	1520
December	1st to 10th	Day	41% 4 8% 18% 20% 10%	1520
	11th to 20th	Day	58% 2 7% 12% 16% 5%	1928
	21st to end	Day	49% 4 12% 21% 10% 4	2794
January	1st to 10th	Night	46% 4 12% 21% 11% 6%	2551
	11th to 20th	Night	42% 4 10% 18% 14% 13%	2429
	21st to end	Night	38% 3 12% 14% 22% 11%	2574
February	1st to 10th	Night	38% 3 8% 19% 20% 12%	2340
	11th to 20th	Night	38% 4 9% 20% 21% 8%	2240
	21st to end	Night	33% 3 10% 27% 21% 6%	1776
March	1st to 10th	Night	48% 5% 11% 15% 17% 4	1990
	11th to 20th	Night	42% 3 8% 22% 19% 6%	1980
	21st to end	Night	38% 4 12% 24% 17% 6%	2167
April	1st to 10th	Night	36% 4 13% 21% 20% 5%	1800
	11th to 20th	Night	29% 4 12% 26% 19% 10%	1779
	21st to end	Night	23% 4 11% 32% 25% 6%	1800
May	1st to 10th	Night	25% 4 5% 24% 31% 11%	1652
	11th to 20th	Night	22% 5% 9% 28% 27% 9%	1541
	21st to end	Night	22% 5% 13% 32% 23% 6%	1552
June	1st to 10th	Night	22% 5% 9% 25% 29% 10%	1440
	11th to 20th	Night	12% 4 5% 24% 35% 20%	1440
	21st to end	Night	13% 6% 3 14% 33% 31%	1440
July	1st to 10th	Night	8% 6% 1 12% 30% 43%	1400
	11th to 20th	Night	10% 4 5% 12% 30% 40%	1538
	21st to end	Night	15% 6% 1 11% 24% 44%	1674
August	1st to 10th	Night	16% 5% 1 16% 30% 32%	1602
	11th to 20th	Night	12% 6% 2 11% 31% 37%	1662
	21st to end	Night	14% 6% 2 14% 32% 32%	1980
September	1st to 10th	Night	8% 5% 3 10% 32% 43%	1800
	11th to 20th	Night	20% 3 4 19% 38% 16%	1801
	21st to end	Night	14% 3 2 22% 28% 30%	2065
October	1st to 10th	Night	19% 4 5% 18% 28% 26%	2160
	11th to 20th	Night	21% 6% 6% 19% 23% 25%	2160
	21st to end	Night	24% 4 6% 20% 25% 20%	2376
November	1st to 10th	Night	29% 5% 9% 27% 19% 12%	2245
	11th to 20th	Night	32% 4 11% 26% 17% 10%	2505
	21st to end	Night	30% 3 8% 22% 22% 15%	2660
December	1st to 10th	Night	41% 4 8% 16% 20% 11%	2660
	11th to 20th	Night	54% 4 8% 14% 15% 4	3276
	21st to end	Night	50% 5% 11% 18% 13% 4	4862

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	37% 7% 24% 18% 12% 3	272
	11th to 20th	Day	25% 8% 22% 27% 14% 3	359
	21st to end	Day	18% 10% 21% 28% 19% 4	374
February	1st to 10th	Day	23% 9% 21% 24% 18% 5%	340
	11th to 20th	Day	21% 15% 27% 22% 14% 1	349
	21st to end	Day	21% 13% 24% 27% 15% 1	346
March	1st to 10th	Day	28% 14% 25% 22% 10% 2	420
	11th to 20th	Day	28% 11% 24% 22% 12% 3	420
	21st to end	Day	21% 15% 28% 25% 11%	462
April	1st to 10th	Day	22% 15% 24% 24% 12% 3	420
	11th to 20th	Day	18% 16% 29% 22% 11% 4	412
	21st to end	Day	11% 15% 28% 27% 13% 6%	420
May	1st to 10th	Day	13% 13% 29% 27% 14% 4	423
	11th to 20th	Day	13% 12% 28% 26% 15% 6%	448
	21st to end	Day	9% 12% 23% 32% 17% 7%	485
June	1st to 10th	Day	10% 11% 23% 33% 15% 8%	450
	11th to 20th	Day	6% 11% 28% 35% 18% 3	450
	21st to end	Day	2 5% 26% 37% 25% 6%	450
July	1st to 10th	Day	3 4 19% 44% 22% 6%	446
	11th to 20th	Day	1 2 17% 41% 29% 10%	444
	21st to end	Day	1 2 10% 48% 30% 9%	487
August	1st to 10th	Day	2 3 18% 41% 26% 10%	447
	11th to 20th	Day	2 2 21% 39% 27% 10%	437
	21st to end	Day	2 2 17% 38% 31% 11%	495
September	1st to 10th	Day	1 2 19% 38% 30% 10%	450
	11th to 20th	Day	7% 5% 21% 32% 26% 8%	450
	21st to end	Day	5% 7% 20% 36% 25% 7%	450
October	1st to 10th	Day	9% 6% 24% 26% 24% 11%	450
	11th to 20th	Day	8% 8% 18% 26% 28% 13%	450
	21st to end	Day	14% 7% 19% 29% 25% 7%	495
November	1st to 10th	Day	15% 7% 16% 26% 28% 8%	427
	11th to 20th	Day	13% 5% 15% 25% 30% 12%	252
	21st to end	Day	12% 9% 23% 30% 15% 11%	180
December	1st to 10th	Day	28% 6% 17% 21% 18% 9%	180
	11th to 20th	Day	27% 9% 21% 20% 14% 8%	180
	21st to end	Day	25% 8% 24% 24% 16% 4	198
January	1st to 10th	Night	24% 4 14% 32% 22% 4	760
	11th to 20th	Night	23% 5% 12% 37% 18% 5%	748
	21st to end	Night	19% 6% 14% 32% 25% 4	792
February	1st to 10th	Night	21% 5% 12% 36% 23% 3	720
	11th to 20th	Night	17% 7% 14% 36% 20% 5%	704
	21st to end	Night	20% 8% 15% 35% 19% 2	592
March	1st to 10th	Night	24% 7% 16% 29% 21% 4	720
	11th to 20th	Night	21% 6% 14% 32% 25% 3	720
	21st to end	Night	20% 6% 20% 31% 20% 2	792
April	1st to 10th	Night	17% 7% 18% 34% 20% 4	720
	11th to 20th	Night	14% 10% 18% 31% 22% 5%	711
	21st to end	Night	9% 10% 19% 28% 27% 6%	720
May	1st to 10th	Night	9% 5% 20% 28% 32% 6%	572
	11th to 20th	Night	7% 3 15% 32% 35% 7%	478
	21st to end	Night	7% 7% 17% 28% 36% 6%	389
June	1st to 10th	Night	8% 6% 15% 31% 36% 4	360
	11th to 20th	Night	3 5% 13% 44% 33% 2	360
	21st to end	Night	5% 3 9% 35% 42% 5%	360
July	1st to 10th	Night	1 1 6% 32% 52% 7%	350
	11th to 20th	Night	2 1 2 26% 54% 14%	494
	21st to end	Night	2 1 1 29% 55% 12%	591
August	1st to 10th	Night	2 2 3 31% 50% 12%	537
	11th to 20th	Night	1 1 5% 31% 51% 11%	594
	21st to end	Night	2 2 4 30% 51% 11%	792
September	1st to 10th	Night	1 1 7% 31% 50% 10%	720
	11th to 20th	Night	7% 3 6% 31% 44% 9%	720
	21st to end	Night	4 4 8% 35% 37% 12%	720
October	1st to 10th	Night	7% 6% 11% 30% 37% 10%	720
	11th to 20th	Night	8% 4 9% 32% 40% 8%	720
	21st to end	Night	12% 3 9% 31% 35% 11%	792
November	1st to 10th	Night	13% 4 12% 29% 33% 9%	740
	11th to 20th	Night	14% 3 11% 37% 30% 6%	760
	21st to end	Night	14% 5% 11% 38% 26% 6%	760
December	1st to 10th	Night	23% 6% 10% 31% 23% 6%	760
	11th to 20th	Night	28% 5% 13% 30% 20% 4	760
	21st to end	Night	24% 5% 18% 34% 17% 2	836

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