Hume Cronyn Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hume Cronyn Observatory clear sky chart from 2005-11-06 to 2024-10-24.

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	15% 10% 4 8% 5% 5% 5% 4 6% 7% 31%	101675
	Night	15% 11% 4 8% 5% 4 4 4 5% 6% 32%	97006
Transparency	Day	50% 7% 12% 19% 10% 1	101441
	Night	51% 7% 12% 19% 11% 1	96860
Seeing	Day	18% 11% 28% 24% 13% 5%	14989
	Night	20% 10% 29% 29% 12% 1	24077

By Month

Percentage Cloud Cover NE (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% 21% 7% 13% 6% 5% 4 3 4 3 18%	2530
	11th to 20th	Day	13% 21% 10% 19% 6% 6% 5% 3 3 4 9%	2840
	21st to end	Day	23% 22% 9% 12% 6% 4 4 2 3 4 11%	3124
February	1st to 10th	Day	16% 18% 5% 12% 9% 6% 4 4 4 5% 17%	1710
	11th to 20th	Day	14% 14% 8% 14% 8% 6% 4 3 4 6% 18%	1663
	21st to end	Day	17% 16% 6% 12% 6% 5% 5% 3 4 4 22%	1570
March	1st to 10th	Day	19% 15% 6% 10% 5% 4 3 3 4 5% 26%	3341
	11th to 20th	Day	12% 15% 5% 10% 5% 4 4 4 5% 7% 28%	3480
	21st to end	Day	18% 12% 4 10% 5% 4 4 3 5% 5% 31%	3815
April	1st to 10th	Day	16% 15% 4 8% 5% 4 4 3 5% 8% 29%	2157
	11th to 20th	Day	18% 11% 2 6% 4 4 4 3 5% 8% 33%	2428
	21st to end	Day	20% 10% 3 8% 5% 4 3 3 5% 6% 33%	2470
May	1st to 10th	Day	18% 9% 3 7% 4 4 5% 4 6% 7% 33%	4108
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 7% 9% 31%	4081
	21st to end	Day	12% 5% 2 5% 4 4 4 5% 5% 7% 46%	4833
June	1st to 10th	Day	14% 6% 2 7% 6% 5% 5% 5% 6% 8% 38%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 8% 40%	2832
	21st to end	Day	13% 6% 2 5% 5% 4 5% 4 6% 9% 40%	2850
July	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 5% 7% 9% 40%	4760
	11th to 20th	Day	11% 5% 2 5% 4 5% 4 4 7% 10% 41%	4205
	21st to end	Day	8% 5% 2 7% 5% 6% 5% 5% 6% 9% 41%	4466
August	1st to 10th	Day	15% 6% 2 5% 4 5% 6% 5% 6% 10% 37%	4104
	11th to 20th	Day	11% 7% 3 7% 5% 5% 6% 6% 7% 10% 33%	4044
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 5% 6% 9% 41%	4475
September	1st to 10th	Day	10% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	2225
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 5% 8% 46%	2090
	21st to end	Day	18% 7% 2 6% 4 5% 4 4 7% 8% 35%	2090
October	1st to 10th	Day	17% 7% 2 7% 5% 4 4 3 7% 8% 36%	1941
	11th to 20th	Day	20% 10% 3 8% 5% 5% 5% 4 5% 6% 28%	1900
	21st to end	Day	25% 12% 3 9% 6% 5% 4 3 5% 6% 22%	1974
November	1st to 10th	Day	15% 12% 3 8% 5% 6% 4 4 6% 8% 31%	1672
	11th to 20th	Day	16% 15% 4 8% 5% 6% 5% 3 6% 7% 25%	1560
	21st to end	Day	20% 19% 6% 10% 5% 4 5% 4 5% 6% 16%	1520
December	1st to 10th	Day	16% 20% 7% 11% 6% 5% 4 4 6% 6% 16%	1520
	11th to 20th	Day	19% 18% 7% 13% 7% 5% 5% 3 5% 4 15%	1906
	21st to end	Day	28% 20% 8% 12% 5% 4 3 3 4 5% 8%	2731
January	1st to 10th	Night	17% 18% 8% 14% 6% 5% 4 3 4 5% 16%	4388
	11th to 20th	Night	14% 18% 8% 16% 7% 7% 7% 5% 4 4 10%	4120
	21st to end	Night	23% 18% 7% 15% 6% 4 4 3 4 4 13%	4532
February	1st to 10th	Night	16% 16% 5% 11% 9% 6% 5% 4 6% 5% 19%	2470
	11th to 20th	Night	15% 15% 5% 9% 6% 6% 5% 5% 6% 7% 21%	2401
	21st to end	Night	16% 13% 5% 12% 7% 5% 5% 4 6% 5% 23%	1884
March	1st to 10th	Night	16% 12% 5% 9% 5% 4 4 4 5% 5% 32%	3485
	11th to 20th	Night	11% 10% 4 9% 5% 5% 5% 4 6% 8% 34%	3479
	21st to end	Night	17% 11% 3 9% 4 4 4 3 4 5% 36%	3817
April	1st to 10th	Night	17% 11% 4 7% 5% 4 4 3 6% 6% 33%	2021
	11th to 20th	Night	17% 10% 2 6% 5% 4 4 3 5% 6% 36%	1717
	21st to end	Night	15% 9% 3 7% 5% 4 6% 4 6% 7% 33%	1710
May	1st to 10th	Night	19% 9% 2 6% 4 3 4 3 6% 7% 38%	2833
	11th to 20th	Night	10% 9% 3 8% 5% 5% 5% 5% 6% 7% 37%	2812
	21st to end	Night	11% 5% 2 4 3 3 4 3 6% 7% 51%	2738
June	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 6% 9% 43%	1520
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 5% 8% 10% 41%	1343
	21st to end	Night	10% 5% 2 6% 4 4 6% 3 5% 9% 46%	1330
July	1st to 10th	Night	6% 5% 1 5% 4 5% 3 4 6% 11% 50%	2210
	11th to 20th	Night	9% 5% 1 5% 3 3 3 3 5% 9% 52%	2736
	21st to end	Night	6% 5% 2 5% 4 4 6% 4 7% 9% 48%	3087
August	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 6% 8% 45%	2825
	11th to 20th	Night	11% 8% 3 5% 4 4 4 3 5% 7% 47%	2785
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 8% 48%	3147
September	1st to 10th	Night	9% 7% 3 6% 5% 4 4 2 6% 7% 47%	1952
	11th to 20th	Night	10% 5% 1 4 4 4 4 3 5% 6% 53%	2090
	21st to end	Night	17% 7% 2 6% 4 4 3 3 5% 7% 40%	2090
October	1st to 10th	Night	14% 8% 3 6% 5% 4 4 3 5% 7% 42%	2238
	11th to 20th	Night	19% 10% 3 8% 4 4 3 3 5% 7% 34%	2280
	21st to end	Night	24% 11% 3 8% 5% 4 5% 3 5% 6% 27%	2444
November	1st to 10th	Night	15% 9% 3 7% 4 4 5% 3 6% 8% 37%	2406
	11th to 20th	Night	17% 14% 4 8% 5% 5% 5% 4 6% 7% 26%	2617
	21st to end	Night	21% 14% 5% 9% 6% 5% 5% 4 5% 6% 21%	2660
December	1st to 10th	Night	20% 18% 5% 10% 6% 5% 4 4 6% 6% 17%	2660
	11th to 20th	Night	15% 20% 6% 11% 5% 4 5% 3 5% 6% 20%	3288
	21st to end	Night	26% 22% 8% 11% 6% 4 4 3 4 4 11%	4891

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	70% 6% 10% 10% 4	2531
	11th to 20th	Day	76% 8% 8% 5% 2	2840
	21st to end	Day	77% 7% 7% 6% 3	3124
February	1st to 10th	Day	68% 6% 9% 12% 4 1	1710
	11th to 20th	Day	67% 5% 8% 13% 6%	1672
	21st to end	Day	65% 4 11% 13% 6% 1	1570
March	1st to 10th	Day	61% 5% 9% 20% 5%	3344
	11th to 20th	Day	55% 6% 15% 16% 7% 1	3480
	21st to end	Day	54% 5% 12% 17% 10% 1	3815
April	1st to 10th	Day	55% 5% 11% 19% 10%	2157
	11th to 20th	Day	49% 5% 13% 19% 13% 1	2428
	21st to end	Day	52% 5% 12% 18% 12% 2	2470
May	1st to 10th	Day	47% 5% 13% 20% 11% 3	4120
	11th to 20th	Day	46% 11% 14% 19% 8% 1	4085
	21st to end	Day	36% 7% 12% 20% 19% 5%	4833
June	1st to 10th	Day	42% 7% 13% 24% 13% 2	2660
	11th to 20th	Day	40% 7% 12% 22% 17% 2	2832
	21st to end	Day	39% 8% 12% 24% 16% 1	2850
July	1st to 10th	Day	38% 7% 14% 25% 14% 2	4686
	11th to 20th	Day	34% 8% 14% 31% 13% 1	4132
	21st to end	Day	37% 9% 13% 21% 19% 1	4324
August	1st to 10th	Day	40% 8% 14% 22% 14% 1	4091
	11th to 20th	Day	40% 10% 16% 24% 9% 1	4083
	21st to end	Day	36% 9% 14% 28% 12% 1	4475
September	1st to 10th	Day	39% 8% 14% 24% 13% 1	2225
	11th to 20th	Day	35% 6% 13% 29% 16%	2090
	21st to end	Day	45% 7% 13% 24% 10% 1	2090
October	1st to 10th	Day	45% 7% 13% 20% 13% 1	1941
	11th to 20th	Day	55% 7% 12% 16% 9%	1900
	21st to end	Day	62% 6% 12% 14% 6%	1974
November	1st to 10th	Day	51% 8% 11% 21% 8% 2	1672
	11th to 20th	Day	56% 8% 14% 13% 8% 1	1560
	21st to end	Day	68% 7% 11% 12% 3	1520
December	1st to 10th	Day	67% 8% 12% 11% 3	1520
	11th to 20th	Day	72% 6% 10% 9% 2	1906
	21st to end	Day	78% 6% 10% 6%	2731
January	1st to 10th	Night	69% 7% 11% 9% 4	4388
	11th to 20th	Night	74% 9% 8% 6% 3	4120
	21st to end	Night	74% 6% 8% 9% 3 1	4532
February	1st to 10th	Night	65% 6% 10% 13% 5%	2470
	11th to 20th	Night	60% 7% 12% 14% 7%	2403
	21st to end	Night	62% 5% 10% 16% 6%	1884
March	1st to 10th	Night	54% 4 13% 22% 6%	3495
	11th to 20th	Night	45% 6% 18% 19% 11% 1	3480
	21st to end	Night	50% 5% 11% 20% 13% 2	3817
April	1st to 10th	Night	51% 6% 10% 19% 13% 1	2021
	11th to 20th	Night	48% 4 10% 19% 17% 2	1717
	21st to end	Night	47% 7% 10% 18% 15% 3	1710
May	1st to 10th	Night	44% 6% 11% 18% 16% 4	2840
	11th to 20th	Night	43% 8% 13% 24% 10% 2	2813
	21st to end	Night	30% 8% 13% 22% 22% 4	2739
June	1st to 10th	Night	36% 7% 11% 27% 16% 3	1520
	11th to 20th	Night	34% 8% 14% 24% 18% 2	1343
	21st to end	Night	34% 7% 14% 24% 19% 1	1330
July	1st to 10th	Night	28% 6% 13% 28% 18% 7%	2175
	11th to 20th	Night	28% 7% 14% 30% 19% 2	2686
	21st to end	Night	30% 10% 16% 22% 19% 3	2988
August	1st to 10th	Night	36% 7% 13% 26% 17% 1	2814
	11th to 20th	Night	36% 7% 14% 30% 12% 1	2812
	21st to end	Night	32% 8% 12% 30% 17% 1	3147
September	1st to 10th	Night	35% 7% 13% 25% 17% 2	1952
	11th to 20th	Night	30% 6% 13% 31% 19% 2	2090
	21st to end	Night	43% 7% 12% 24% 14%	2090
October	1st to 10th	Night	43% 6% 11% 22% 18% 1	2238
	11th to 20th	Night	50% 6% 13% 21% 10% 1	2280
	21st to end	Night	57% 7% 9% 17% 10% 1	2444
November	1st to 10th	Night	43% 7% 13% 24% 12% 1	2406
	11th to 20th	Night	55% 8% 12% 18% 7% 1	2617
	21st to end	Night	62% 7% 15% 11% 3	2660
December	1st to 10th	Night	66% 8% 12% 10% 4	2660
	11th to 20th	Night	66% 6% 12% 12% 4	3288
	21st to end	Night	78% 5% 10% 6% 1	4891

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	21% 22% 30% 19% 6% 1	238
	11th to 20th	Day	17% 21% 44% 13% 4 1	270
	21st to end	Day	28% 13% 35% 20% 4	297
February	1st to 10th	Day	25% 21% 37% 13% 4	270
	11th to 20th	Day	25% 23% 34% 17% 1	270
	21st to end	Day	27% 27% 35% 11% 1	225
March	1st to 10th	Day	25% 14% 38% 18% 5% 1	403
	11th to 20th	Day	22% 15% 34% 23% 4 2	460
	21st to end	Day	29% 13% 31% 20% 6% 1	506
April	1st to 10th	Day	19% 18% 33% 22% 8% 1	460
	11th to 20th	Day	26% 15% 27% 19% 9% 4	452
	21st to end	Day	24% 14% 29% 22% 9% 2	460
May	1st to 10th	Day	21% 12% 27% 26% 11% 3	463
	11th to 20th	Day	17% 9% 26% 23% 18% 6%	487
	21st to end	Day	13% 7% 25% 28% 19% 8%	529
June	1st to 10th	Day	14% 5% 32% 31% 14% 4	490
	11th to 20th	Day	11% 9% 28% 33% 15% 5%	662
	21st to end	Day	14% 9% 28% 31% 15% 4	680
July	1st to 10th	Day	10% 7% 21% 29% 24% 9%	671
	11th to 20th	Day	14% 6% 25% 27% 19% 9%	533
	21st to end	Day	9% 5% 20% 33% 24% 10%	532
August	1st to 10th	Day	11% 4 19% 28% 24% 14%	486
	11th to 20th	Day	14% 4 18% 26% 24% 14%	479
	21st to end	Day	10% 6% 22% 27% 24% 12%	539
September	1st to 10th	Day	11% 6% 24% 27% 20% 12%	490
	11th to 20th	Day	9% 3 21% 23% 29% 14%	490
	21st to end	Day	17% 12% 23% 26% 14% 8%	490
October	1st to 10th	Day	19% 10% 25% 24% 16% 6%	490
	11th to 20th	Day	21% 14% 33% 23% 8% 2	490
	21st to end	Day	27% 14% 34% 19% 5% 1	471
November	1st to 10th	Day	22% 16% 33% 17% 10% 3	270
	11th to 20th	Day	28% 15% 32% 16% 7% 3	198
	21st to end	Day	27% 17% 36% 17% 3	180
December	1st to 10th	Day	26% 21% 31% 16% 6% 1	180
	11th to 20th	Day	28% 20% 32% 17% 4	180
	21st to end	Day	30% 21% 32% 15% 2 1	198
January	1st to 10th	Night	23% 17% 38% 16% 5% 1	857
	11th to 20th	Night	29% 14% 32% 21% 4	760
	21st to end	Night	22% 11% 35% 25% 7%	836
February	1st to 10th	Night	24% 14% 36% 22% 3	760
	11th to 20th	Night	24% 14% 32% 26% 5%	743
	21st to end	Night	23% 15% 36% 22% 3	628
March	1st to 10th	Night	20% 11% 36% 26% 6%	760
	11th to 20th	Night	19% 14% 35% 24% 7% 1	760
	21st to end	Night	23% 12% 29% 26% 8% 1	836
April	1st to 10th	Night	23% 14% 31% 27% 5%	760
	11th to 20th	Night	22% 11% 33% 24% 9% 1	593
	21st to end	Night	18% 9% 34% 30% 8% 1	570
May	1st to 10th	Night	21% 6% 28% 31% 13% 1	570
	11th to 20th	Night	15% 4 27% 39% 12% 2	561
	21st to end	Night	13% 3 28% 39% 16% 1	411
June	1st to 10th	Night	15% 4 29% 40% 12% 1	380
	11th to 20th	Night	13% 3 26% 42% 15%	380
	21st to end	Night	11% 5% 23% 45% 16% 1	380
July	1st to 10th	Night	6% 2 20% 48% 22% 1	370
	11th to 20th	Night	10% 3 19% 41% 26% 2	542
	21st to end	Night	10% 2 16% 46% 24% 2	624
August	1st to 10th	Night	9% 2 14% 43% 29% 3	567
	11th to 20th	Night	9% 3 12% 40% 32% 4	564
	21st to end	Night	10% 3 19% 38% 27% 3	637
September	1st to 10th	Night	11% 5% 21% 35% 23% 5%	760
	11th to 20th	Night	11% 4 16% 36% 29% 4	760
	21st to end	Night	19% 6% 21% 33% 17% 4	760
October	1st to 10th	Night	17% 7% 26% 31% 18% 2	760
	11th to 20th	Night	22% 12% 27% 27% 11% 1	760
	21st to end	Night	29% 10% 31% 25% 5%	805
November	1st to 10th	Night	19% 12% 27% 30% 11% 1	740
	11th to 20th	Night	23% 12% 37% 21% 6% 1	760
	21st to end	Night	27% 12% 30% 24% 6%	760
December	1st to 10th	Night	29% 15% 32% 19% 5%	760
	11th to 20th	Night	25% 16% 38% 18% 3	760
	21st to end	Night	29% 12% 36% 20% 3	843

Page generated at 2024-10-21 02:20:00. Version ac07

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