Outback Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Outback Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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	13% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	78395
	Night	13% 10% 4 7% 6% 3 4 4 5% 7% 37%	81184
Transparency	Day	48% 4 12% 24% 11% 1	78095
	Night	48% 4 12% 24% 11% 1	81004
Seeing	Day	19% 14% 31% 22% 11% 3	14986
	Night	19% 12% 32% 27% 10% 1	25083

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	11% 14% 6% 11% 7% 4 5% 4 5% 5% 27%	2527
	11th to 20th	Day	10% 12% 5% 10% 9% 5% 9% 7% 6% 7% 20%	2530
	21st to end	Day	14% 17% 7% 12% 7% 3 4 4 5% 6% 22%	2783
February	1st to 10th	Day	9% 11% 5% 9% 6% 3 5% 6% 5% 6% 35%	1699
	11th to 20th	Day	10% 11% 4 8% 5% 3 6% 5% 4 7% 36%	1761
	21st to end	Day	12% 12% 5% 8% 6% 4 4 5% 4 7% 33%	1570
March	1st to 10th	Day	13% 10% 5% 9% 5% 3 5% 4 5% 6% 35%	1850
	11th to 20th	Day	12% 9% 5% 8% 7% 3 5% 4 5% 7% 37%	1880
	21st to end	Day	15% 10% 4 7% 7% 3 6% 5% 5% 7% 30%	2362
April	1st to 10th	Day	15% 11% 3 7% 7% 4 5% 5% 4 7% 32%	2160
	11th to 20th	Day	21% 10% 4 7% 5% 3 4 5% 4 6% 31%	2134
	21st to end	Day	17% 11% 3 6% 7% 4 5% 5% 5% 5% 31%	2283
May	1st to 10th	Day	17% 7% 3 7% 7% 3 5% 4 6% 8% 34%	2466
	11th to 20th	Day	15% 8% 4 7% 6% 3 4 4 5% 6% 39%	2479
	21st to end	Day	12% 6% 3 6% 6% 4 6% 5% 6% 7% 38%	2725
June	1st to 10th	Day	12% 5% 2 5% 6% 3 5% 4 5% 8% 43%	2520
	11th to 20th	Day	13% 6% 3 5% 6% 3 6% 4 6% 8% 39%	2520
	21st to end	Day	10% 6% 3 6% 5% 4 6% 5% 7% 10% 39%	2520
July	1st to 10th	Day	7% 3 1 4 5% 3 6% 6% 7% 10% 47%	2520
	11th to 20th	Day	9% 4 2 6% 5% 3 5% 6% 6% 9% 44%	2520
	21st to end	Day	8% 5% 2 4 6% 3 5% 5% 6% 8% 47%	2743
August	1st to 10th	Day	9% 4 2 6% 6% 4 6% 7% 7% 9% 41%	2507
	11th to 20th	Day	14% 5% 2 5% 5% 3 5% 5% 6% 7% 43%	2269
	21st to end	Day	14% 5% 3 5% 4 3 4 5% 6% 7% 45%	2376
September	1st to 10th	Day	13% 7% 3 5% 6% 3 4 4 5% 7% 44%	2160
	11th to 20th	Day	14% 5% 2 6% 4 3 4 5% 5% 8% 44%	2093
	21st to end	Day	13% 7% 3 6% 5% 4 6% 6% 7% 8% 35%	1980
October	1st to 10th	Day	16% 8% 2 5% 4 2 4 4 6% 9% 39%	1846
	11th to 20th	Day	20% 10% 3 7% 6% 3 5% 5% 4 6% 31%	1779
	21st to end	Day	20% 11% 4 6% 5% 3 4 4 4 5% 33%	1782
November	1st to 10th	Day	14% 9% 3 5% 5% 4 5% 5% 5% 8% 38%	1672
	11th to 20th	Day	14% 12% 7% 9% 7% 3 5% 5% 5% 6% 28%	1638
	21st to end	Day	14% 11% 5% 7% 5% 3 5% 5% 6% 6% 32%	1520
December	1st to 10th	Day	12% 12% 5% 9% 6% 3 6% 5% 6% 6% 30%	1520
	11th to 20th	Day	15% 14% 5% 8% 7% 4 6% 5% 7% 7% 22%	1918
	21st to end	Day	21% 23% 6% 8% 6% 2 3 3 4 4 20%	2783
January	1st to 10th	Night	13% 13% 7% 10% 6% 3 4 3 4 6% 31%	4428
	11th to 20th	Night	10% 13% 6% 10% 9% 5% 6% 5% 6% 7% 23%	4440
	21st to end	Night	12% 17% 9% 11% 6% 4 5% 4 4 5% 24%	4884
February	1st to 10th	Night	9% 13% 6% 8% 6% 4 5% 4 4 6% 35%	2480
	11th to 20th	Night	10% 10% 4 8% 6% 3 6% 5% 5% 6% 38%	2305
	21st to end	Night	14% 12% 4 8% 7% 4 4 4 5% 5% 34%	1884
March	1st to 10th	Night	12% 8% 4 6% 6% 3 4 4 5% 6% 41%	2227
	11th to 20th	Night	12% 9% 4 5% 5% 3 4 5% 5% 6% 41%	2095
	21st to end	Night	16% 9% 3 7% 5% 3 4 3 4 7% 38%	1993
April	1st to 10th	Night	18% 11% 4 7% 5% 3 4 4 5% 7% 32%	1800
	11th to 20th	Night	21% 8% 3 4 5% 3 3 5% 5% 5% 37%	1775
	21st to end	Night	18% 8% 3 7% 5% 3 4 5% 5% 7% 34%	1675
May	1st to 10th	Night	18% 8% 3 6% 6% 3 4 5% 6% 8% 32%	1492
	11th to 20th	Night	18% 7% 3 6% 5% 3 3 5% 4 7% 38%	1416
	21st to end	Night	12% 6% 3 5% 5% 3 5% 5% 7% 9% 41%	1551
June	1st to 10th	Night	11% 5% 2 6% 5% 3 4 4 6% 7% 47%	1440
	11th to 20th	Night	11% 7% 2 7% 6% 3 5% 6% 7% 7% 40%	1440
	21st to end	Night	9% 4 2 5% 5% 3 5% 5% 6% 9% 47%	1440
July	1st to 10th	Night	7% 3 1 3 4 2 4 5% 5% 10% 55%	1440
	11th to 20th	Night	8% 4 2 4 5% 3 5% 5% 6% 9% 49%	1440
	21st to end	Night	5% 5% 2 3 5% 2 3 5% 6% 7% 56%	1575
August	1st to 10th	Night	7% 4 2 6% 6% 4 5% 5% 6% 8% 47%	1432
	11th to 20th	Night	10% 5% 3 4 5% 3 4 5% 5% 8% 48%	1630
	21st to end	Night	12% 5% 2 4 4 3 4 4 6% 6% 51%	1980
September	1st to 10th	Night	10% 5% 2 5% 4 2 4 4 5% 7% 51%	1800
	11th to 20th	Night	11% 5% 2 5% 3 2 4 3 5% 6% 52%	1849
	21st to end	Night	13% 7% 2 5% 5% 2 4 3 6% 8% 44%	1980
October	1st to 10th	Night	14% 6% 2 4 4 3 5% 5% 5% 8% 46%	2110
	11th to 20th	Night	15% 8% 4 6% 6% 3 4 5% 6% 7% 36%	2180
	21st to end	Night	19% 10% 3 6% 5% 3 5% 5% 5% 7% 32%	2574
November	1st to 10th	Night	14% 9% 3 5% 4 3 3 4 5% 8% 41%	2406
	11th to 20th	Night	13% 10% 5% 8% 6% 2 5% 4 4 7% 34%	2540
	21st to end	Night	14% 10% 4 8% 6% 3 5% 5% 5% 8% 33%	2660
December	1st to 10th	Night	13% 12% 4 8% 5% 3 6% 5% 5% 7% 32%	2660
	11th to 20th	Night	11% 15% 6% 9% 7% 4 5% 4 4 6% 30%	3279
	21st to end	Night	24% 18% 6% 8% 5% 2 3 3 3 4 23%	4884

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	60% 3 11% 20% 6% 1	2528
	11th to 20th	Day	63% 4 10% 15% 7% 1	2530
	21st to end	Day	65% 2 12% 16% 5%	2783
February	1st to 10th	Day	50% 5% 11% 20% 13% 1	1699
	11th to 20th	Day	48% 4 11% 25% 11% 2	1770
	21st to end	Day	51% 4 12% 21% 10% 2	1570
March	1st to 10th	Day	50% 4 12% 21% 11% 2	1850
	11th to 20th	Day	48% 4 13% 22% 12% 2	1880
	21st to end	Day	54% 4 12% 19% 10% 1	2362
April	1st to 10th	Day	53% 4 11% 19% 13% 1	2160
	11th to 20th	Day	54% 3 8% 21% 12% 1	2134
	21st to end	Day	54% 4 9% 19% 12% 2	2283
May	1st to 10th	Day	49% 4 13% 22% 11% 1	2466
	11th to 20th	Day	47% 3 10% 25% 14% 1	2483
	21st to end	Day	44% 5% 11% 26% 11% 2	2725
June	1st to 10th	Day	39% 4 14% 30% 12% 1	2520
	11th to 20th	Day	43% 4 14% 25% 13% 1	2520
	21st to end	Day	40% 5% 17% 26% 11% 1	2520
July	1st to 10th	Day	31% 4 15% 34% 14% 1	2451
	11th to 20th	Day	35% 4 15% 28% 15% 3	2445
	21st to end	Day	33% 5% 14% 29% 17% 2	2591
August	1st to 10th	Day	38% 5% 15% 30% 10% 2	2492
	11th to 20th	Day	39% 5% 14% 28% 13%	2269
	21st to end	Day	38% 5% 12% 27% 16% 1	2376
September	1st to 10th	Day	40% 4 12% 29% 14% 1	2160
	11th to 20th	Day	39% 3 18% 31% 8% 1	2093
	21st to end	Day	44% 5% 13% 28% 9%	1980
October	1st to 10th	Day	42% 3 15% 30% 8% 1	1846
	11th to 20th	Day	54% 5% 11% 21% 8% 1	1779
	21st to end	Day	54% 4 12% 21% 9%	1782
November	1st to 10th	Day	45% 4 12% 25% 13% 1	1672
	11th to 20th	Day	57% 3 12% 19% 8% 1	1638
	21st to end	Day	52% 4 15% 23% 4 1	1520
December	1st to 10th	Day	55% 4 10% 24% 6%	1520
	11th to 20th	Day	61% 3 14% 14% 7% 1	1915
	21st to end	Day	70% 2 7% 15% 7%	2783
January	1st to 10th	Night	56% 3 9% 23% 8% 1	4428
	11th to 20th	Night	61% 3 10% 20% 6%	4440
	21st to end	Night	64% 3 9% 18% 6%	4884
February	1st to 10th	Night	51% 3 9% 23% 12% 2	2480
	11th to 20th	Night	47% 5% 10% 24% 12% 2	2306
	21st to end	Night	53% 3 10% 22% 9% 2	1884
March	1st to 10th	Night	44% 4 13% 26% 12% 2	2227
	11th to 20th	Night	43% 4 12% 24% 15% 2	2095
	21st to end	Night	48% 3 10% 23% 14% 2	1993
April	1st to 10th	Night	52% 4 7% 18% 18% 1	1800
	11th to 20th	Night	49% 4 10% 21% 13% 3	1775
	21st to end	Night	48% 5% 10% 21% 15% 1	1675
May	1st to 10th	Night	51% 4 14% 18% 12% 1	1492
	11th to 20th	Night	47% 5% 9% 27% 11% 2	1417
	21st to end	Night	39% 5% 17% 23% 14% 1	1552
June	1st to 10th	Night	37% 4 15% 29% 14% 1	1440
	11th to 20th	Night	42% 4 14% 23% 16% 1	1440
	21st to end	Night	34% 4 16% 32% 11% 3	1440
July	1st to 10th	Night	26% 5% 13% 36% 19% 2	1400
	11th to 20th	Night	32% 6% 17% 28% 15% 3	1392
	21st to end	Night	26% 4 18% 31% 18% 3	1487
August	1st to 10th	Night	35% 4 15% 29% 15% 2	1423
	11th to 20th	Night	35% 5% 14% 28% 16% 2	1630
	21st to end	Night	34% 4 14% 27% 19% 2	1980
September	1st to 10th	Night	33% 5% 11% 34% 17% 1	1800
	11th to 20th	Night	34% 3 15% 36% 13%	1849
	21st to end	Night	38% 4 15% 32% 10% 1	1980
October	1st to 10th	Night	38% 3 13% 32% 12% 1	2110
	11th to 20th	Night	47% 4 14% 25% 10% 1	2180
	21st to end	Night	53% 4 13% 20% 11%	2574
November	1st to 10th	Night	43% 3 12% 27% 15% 1	2406
	11th to 20th	Night	51% 4 14% 18% 13% 1	2540
	21st to end	Night	50% 4 14% 24% 6% 1	2660
December	1st to 10th	Night	52% 4 14% 23% 6%	2660
	11th to 20th	Night	57% 3 12% 19% 8% 1	3281
	21st to end	Night	67% 2 7% 18% 6%	4884

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	20% 18% 33% 23% 6% 1	270
	11th to 20th	Day	24% 20% 34% 18% 3 1	270
	21st to end	Day	22% 17% 40% 17% 4	297
February	1st to 10th	Day	15% 26% 38% 15% 5% 1	270
	11th to 20th	Day	20% 32% 32% 11% 4	270
	21st to end	Day	22% 27% 42% 8% 1	225
March	1st to 10th	Day	22% 25% 36% 13% 4	255
	11th to 20th	Day	23% 20% 32% 17% 6% 2	240
	21st to end	Day	25% 18% 29% 19% 8% 2	448
April	1st to 10th	Day	23% 18% 33% 20% 5%	420
	11th to 20th	Day	32% 16% 26% 17% 8% 2	412
	21st to end	Day	25% 15% 30% 19% 10% 1	420
May	1st to 10th	Day	22% 17% 36% 17% 6% 2	549
	11th to 20th	Day	21% 14% 34% 20% 8% 3	625
	21st to end	Day	16% 13% 32% 23% 12% 4	679
June	1st to 10th	Day	11% 12% 34% 27% 13% 3	630
	11th to 20th	Day	17% 11% 31% 26% 11% 3	630
	21st to end	Day	14% 10% 30% 25% 17% 4	630
July	1st to 10th	Day	9% 6% 27% 33% 19% 7%	621
	11th to 20th	Day	11% 10% 30% 29% 13% 7%	618
	21st to end	Day	8% 7% 30% 32% 17% 6%	684
August	1st to 10th	Day	11% 5% 28% 32% 18% 6%	626
	11th to 20th	Day	18% 6% 20% 29% 20% 7%	522
	21st to end	Day	18% 8% 25% 24% 19% 6%	495
September	1st to 10th	Day	18% 9% 27% 24% 16% 6%	450
	11th to 20th	Day	16% 7% 28% 30% 15% 4	450
	21st to end	Day	19% 15% 27% 22% 14% 3	450
October	1st to 10th	Day	22% 14% 25% 23% 14% 2	316
	11th to 20th	Day	24% 24% 31% 17% 3	270
	21st to end	Day	30% 22% 35% 11% 2	297
November	1st to 10th	Day	19% 17% 40% 19% 4 1	270
	11th to 20th	Day	23% 21% 37% 16% 3 1	270
	21st to end	Day	21% 24% 37% 13% 4 1	270
December	1st to 10th	Day	21% 19% 43% 10% 6%	270
	11th to 20th	Day	27% 23% 33% 13% 4 1	270
	21st to end	Day	31% 19% 34% 14% 1	297
January	1st to 10th	Night	17% 16% 39% 24% 4	950
	11th to 20th	Night	21% 15% 37% 20% 6% 1	950
	21st to end	Night	18% 14% 37% 25% 6%	1045
February	1st to 10th	Night	14% 19% 36% 24% 6% 1	950
	11th to 20th	Night	16% 20% 35% 23% 6%	831
	21st to end	Night	24% 13% 37% 22% 4	628
March	1st to 10th	Night	19% 14% 34% 23% 9% 1	743
	11th to 20th	Night	18% 15% 39% 22% 6% 1	655
	21st to end	Night	22% 10% 31% 27% 9% 1	594
April	1st to 10th	Night	26% 12% 33% 22% 6% 1	540
	11th to 20th	Night	30% 9% 27% 28% 5% 1	533
	21st to end	Night	24% 10% 32% 26% 8% 1	540
May	1st to 10th	Night	22% 10% 34% 26% 7% 1	540
	11th to 20th	Night	22% 8% 31% 29% 8% 1	531
	21st to end	Night	14% 8% 31% 34% 13% 1	584
June	1st to 10th	Night	13% 8% 28% 39% 12%	540
	11th to 20th	Night	15% 6% 29% 39% 9% 1	540
	21st to end	Night	12% 4 27% 39% 16% 1	540
July	1st to 10th	Night	9% 3 24% 39% 22% 1	525
	11th to 20th	Night	10% 3 29% 37% 19% 1	522
	21st to end	Night	9% 3 29% 38% 18% 3	591
August	1st to 10th	Night	10% 2 26% 38% 23% 2	537
	11th to 20th	Night	13% 3 20% 34% 26% 4	534
	21st to end	Night	15% 5% 22% 36% 21% 2	594
September	1st to 10th	Night	13% 6% 25% 34% 19% 4	540
	11th to 20th	Night	13% 5% 30% 32% 16% 4	589
	21st to end	Night	18% 9% 28% 28% 16% 1	720
October	1st to 10th	Night	17% 11% 29% 25% 16% 1	720
	11th to 20th	Night	21% 16% 31% 26% 6%	720
	21st to end	Night	26% 11% 30% 23% 10% 1	792
November	1st to 10th	Night	21% 11% 38% 21% 7% 2	740
	11th to 20th	Night	20% 16% 38% 20% 6%	830
	21st to end	Night	20% 19% 32% 23% 5%	950
December	1st to 10th	Night	21% 18% 34% 20% 6%	950
	11th to 20th	Night	21% 17% 33% 23% 5% 1	950
	21st to end	Night	28% 15% 34% 20% 3	1045

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