C-Murrinsville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the C-Murrinsville clear sky chart from 2005-11-06 to 2026-07-16.

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	16% 11% 4 10% 5% 5% 4 4 5% 7% 29%	138012
	Night	16% 12% 5% 10% 5% 4 4 3 5% 6% 29%	134642
Transparency	Day	53% 5% 11% 19% 10% 1	141614
	Night	54% 5% 11% 18% 10% 1	139112
Seeing	Day	24% 16% 28% 19% 10% 3	16794
	Night	23% 14% 27% 24% 10% 1	26404

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	16% 20% 7% 23% 7% 4 3 2 3 4 10%	5063
	11th to 20th	Day	10% 20% 10% 22% 9% 7% 4 2 3 3 12%	5280
	21st to end	Day	17% 16% 7% 13% 10% 8% 4 3 4 4 15%	5780
February	1st to 10th	Day	16% 19% 5% 12% 7% 5% 3 3 3 4 21%	1890
	11th to 20th	Day	16% 14% 7% 15% 7% 5% 4 3 4 5% 19%	1843
	21st to end	Day	19% 16% 4 11% 5% 4 5% 3 4 6% 23%	1708
March	1st to 10th	Day	17% 11% 7% 11% 5% 3 3 3 4 5% 31%	5045
	11th to 20th	Day	12% 11% 5% 10% 6% 5% 4 3 5% 6% 33%	5090
	21st to end	Day	17% 13% 4 9% 6% 4 4 3 5% 6% 30%	5586
April	1st to 10th	Day	16% 16% 3 8% 5% 4 4 4 5% 7% 29%	2436
	11th to 20th	Day	18% 12% 3 8% 5% 4 4 3 5% 6% 32%	2533
	21st to end	Day	21% 11% 3 6% 4 4 3 3 5% 6% 33%	2730
May	1st to 10th	Day	21% 10% 3 9% 5% 5% 5% 4 5% 6% 26%	7616
	11th to 20th	Day	17% 10% 3 8% 5% 5% 5% 4 7% 8% 30%	7644
	21st to end	Day	20% 8% 3 7% 4 4 4 4 6% 6% 34%	9045
June	1st to 10th	Day	14% 7% 3 6% 6% 5% 5% 4 6% 8% 35%	2940
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 9% 33%	2940
	21st to end	Day	15% 5% 2 6% 5% 5% 5% 4 6% 9% 36%	2940
July	1st to 10th	Day	8% 6% 2 7% 5% 6% 6% 5% 7% 9% 39%	6500
	11th to 20th	Day	10% 7% 3 7% 5% 5% 5% 5% 7% 10% 35%	5965
	21st to end	Day	11% 6% 2 6% 5% 5% 5% 4 6% 9% 41%	6424
August	1st to 10th	Day	16% 9% 3 7% 5% 5% 5% 4 6% 8% 31%	4234
	11th to 20th	Day	13% 7% 3 8% 4 5% 6% 5% 7% 8% 33%	4174
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4453
September	1st to 10th	Day	15% 8% 3 5% 4 4 4 3 5% 7% 43%	2400
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 5% 8% 43%	2229
	21st to end	Day	20% 8% 3 6% 5% 4 5% 3 5% 7% 33%	2186
October	1st to 10th	Day	16% 7% 3 6% 5% 4 4 4 6% 8% 38%	2000
	11th to 20th	Day	19% 9% 2 8% 5% 6% 5% 3 5% 5% 33%	2000
	21st to end	Day	24% 10% 3 8% 4 4 4 3 5% 6% 29%	2200
November	1st to 10th	Day	11% 9% 3 8% 6% 5% 5% 4 5% 6% 39%	1962
	11th to 20th	Day	17% 15% 4 8% 5% 5% 4 4 5% 5% 28%	1698
	21st to end	Day	18% 19% 6% 11% 5% 4 4 3 4 5% 20%	1680
December	1st to 10th	Day	19% 19% 10% 21% 5% 3 4 2 3 3 12%	2680
	11th to 20th	Day	21% 20% 6% 11% 5% 3 3 2 4 6% 20%	3070
	21st to end	Day	22% 25% 6% 12% 5% 4 3 3 3 4 13%	4048
January	1st to 10th	Night	14% 20% 8% 24% 6% 4 4 3 3 4 10%	7813
	11th to 20th	Night	11% 17% 9% 21% 10% 7% 5% 3 3 4 10%	7680
	21st to end	Night	17% 16% 7% 13% 8% 7% 5% 3 3 4 18%	8401
February	1st to 10th	Night	17% 15% 5% 13% 8% 6% 4 3 4 4 22%	2730
	11th to 20th	Night	18% 13% 5% 14% 6% 6% 5% 4 4 5% 20%	2663
	21st to end	Night	19% 13% 5% 12% 6% 4 3 4 4 5% 23%	2091
March	1st to 10th	Night	19% 14% 6% 8% 6% 4 3 2 4 5% 30%	5028
	11th to 20th	Night	13% 11% 6% 7% 4 4 4 3 4 6% 37%	5090
	21st to end	Night	17% 11% 5% 9% 5% 4 4 3 4 5% 33%	5588
April	1st to 10th	Night	18% 15% 3 7% 5% 4 3 3 5% 7% 29%	2182
	11th to 20th	Night	18% 10% 3 7% 4 5% 5% 3 6% 6% 34%	2054
	21st to end	Night	14% 11% 4 7% 5% 4 4 3 5% 7% 35%	1890
May	1st to 10th	Night	24% 10% 3 7% 4 4 4 3 5% 6% 29%	5237
	11th to 20th	Night	18% 10% 3 7% 4 4 4 4 5% 7% 35%	5198
	21st to end	Night	22% 8% 2 6% 3 3 3 3 5% 7% 37%	5108
June	1st to 10th	Night	10% 6% 2 5% 5% 5% 5% 4 6% 8% 44%	1680
	11th to 20th	Night	12% 6% 3 7% 4 4 5% 4 6% 7% 42%	1680
	21st to end	Night	11% 6% 3 6% 5% 3 5% 4 6% 9% 41%	1680
July	1st to 10th	Night	10% 8% 3 7% 4 4 4 4 5% 8% 42%	3678
	11th to 20th	Night	10% 6% 2 6% 4 5% 5% 5% 7% 10% 39%	4097
	21st to end	Night	9% 6% 2 6% 4 4 4 3 5% 8% 47%	4427
August	1st to 10th	Night	14% 9% 3 7% 5% 4 4 4 5% 7% 38%	2915
	11th to 20th	Night	14% 7% 3 6% 4 4 5% 3 5% 6% 42%	2875
	21st to end	Night	8% 6% 2 6% 4 4 5% 5% 7% 9% 45%	3411
September	1st to 10th	Night	13% 5% 2 5% 5% 3 4 3 6% 6% 49%	2000
	11th to 20th	Night	10% 4 2 5% 3 3 3 3 6% 8% 52%	2168
	21st to end	Night	18% 8% 3 7% 5% 4 5% 4 4 6% 37%	2213
October	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	2400
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 4 5% 7% 38%	2400
	21st to end	Night	22% 10% 3 6% 5% 4 4 3 5% 6% 33%	2640
November	1st to 10th	Night	12% 10% 3 6% 4 5% 4 3 5% 7% 41%	2551
	11th to 20th	Night	17% 15% 3 9% 6% 4 4 4 5% 7% 27%	2919
	21st to end	Night	19% 16% 5% 8% 5% 5% 4 3 4 6% 25%	2940
December	1st to 10th	Night	15% 18% 9% 17% 7% 4 4 3 5% 4 14%	4720
	11th to 20th	Night	20% 18% 7% 12% 5% 4 3 3 3 5% 20%	5345
	21st to end	Night	22% 20% 6% 12% 5% 4 4 3 5% 5% 14%	7150

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	79% 4 7% 6% 3	5064
	11th to 20th	Day	80% 3 6% 8% 3 1	5280
	21st to end	Day	74% 3 8% 11% 4	5780
February	1st to 10th	Day	68% 3 8% 14% 7%	1890
	11th to 20th	Day	67% 4 9% 13% 6%	1852
	21st to end	Day	63% 4 10% 15% 6% 1	1708
March	1st to 10th	Day	55% 4 11% 22% 8%	5045
	11th to 20th	Day	52% 5% 14% 20% 7% 2	5090
	21st to end	Day	56% 3 9% 19% 12% 1	5586
April	1st to 10th	Day	54% 4 12% 16% 12% 2	2436
	11th to 20th	Day	53% 4 10% 18% 13% 2	2533
	21st to end	Day	51% 5% 10% 20% 12% 2	2730
May	1st to 10th	Day	56% 6% 10% 18% 7% 3	7651
	11th to 20th	Day	51% 6% 11% 22% 10% 1	7648
	21st to end	Day	49% 5% 11% 18% 16% 2	9061
June	1st to 10th	Day	46% 6% 12% 22% 13% 1	2940
	11th to 20th	Day	47% 6% 14% 20% 13% 1	2940
	21st to end	Day	43% 6% 11% 26% 13% 1	2940
July	1st to 10th	Day	39% 8% 12% 26% 15% 1	6430
	11th to 20th	Day	41% 7% 14% 25% 13%	5896
	21st to end	Day	38% 7% 10% 24% 20% 1	6240
August	1st to 10th	Day	49% 7% 13% 22% 9%	4221
	11th to 20th	Day	43% 8% 13% 26% 9% 1	4213
	21st to end	Day	39% 7% 12% 28% 12% 1	4453
September	1st to 10th	Day	41% 6% 11% 23% 17% 3	2400
	11th to 20th	Day	38% 6% 14% 25% 16% 1	2229
	21st to end	Day	50% 5% 11% 21% 12%	2186
October	1st to 10th	Day	35% 5% 11% 29% 19% 1	3260
	11th to 20th	Day	45% 6% 11% 21% 13% 4	3240
	21st to end	Day	42% 4 12% 27% 13% 1	3538
November	1st to 10th	Day	46% 4 12% 20% 16% 2	1962
	11th to 20th	Day	56% 6% 11% 17% 8% 2	1698
	21st to end	Day	66% 5% 10% 14% 5% 1	1680
December	1st to 10th	Day	78% 3 9% 7% 3	2680
	11th to 20th	Day	68% 4 10% 15% 4	3066
	21st to end	Day	77% 3 8% 9% 3	4048
January	1st to 10th	Night	78% 4 8% 8% 2	7814
	11th to 20th	Night	78% 4 8% 7% 2	7680
	21st to end	Night	70% 3 9% 12% 5% 1	8401
February	1st to 10th	Night	67% 3 8% 16% 6%	2730
	11th to 20th	Night	66% 4 9% 15% 6%	2665
	21st to end	Night	63% 4 9% 14% 9% 1	2091
March	1st to 10th	Night	59% 3 11% 20% 7%	5028
	11th to 20th	Night	47% 5% 14% 23% 8% 3	5090
	21st to end	Night	53% 4 9% 18% 15% 1	5588
April	1st to 10th	Night	56% 5% 9% 17% 12% 1	2182
	11th to 20th	Night	50% 6% 10% 18% 14% 2	2054
	21st to end	Night	48% 6% 11% 23% 11% 2	1890
May	1st to 10th	Night	55% 6% 8% 16% 13% 3	5264
	11th to 20th	Night	48% 6% 10% 25% 10% 2	5199
	21st to end	Night	47% 5% 10% 22% 14% 2	5115
June	1st to 10th	Night	37% 6% 13% 25% 17% 2	1680
	11th to 20th	Night	40% 6% 14% 23% 15% 2	1680
	21st to end	Night	39% 7% 14% 23% 17%	1680
July	1st to 10th	Night	40% 6% 10% 25% 18% 1	3640
	11th to 20th	Night	37% 8% 18% 25% 11% 1	4047
	21st to end	Night	35% 6% 11% 21% 26% 1	4297
August	1st to 10th	Night	45% 7% 13% 22% 12% 1	2904
	11th to 20th	Night	40% 6% 12% 31% 11% 1	2902
	21st to end	Night	33% 9% 15% 29% 13% 2	3411
September	1st to 10th	Night	36% 5% 11% 25% 19% 4	2000
	11th to 20th	Night	29% 5% 13% 29% 22% 1	2168
	21st to end	Night	48% 4 11% 20% 16% 1	2213
October	1st to 10th	Night	36% 4 9% 27% 23% 1	3920
	11th to 20th	Night	40% 6% 11% 21% 15% 7%	3899
	21st to end	Night	38% 5% 12% 25% 18% 1	4252
November	1st to 10th	Night	42% 4 12% 24% 14% 3	2551
	11th to 20th	Night	55% 5% 12% 17% 9% 3	2919
	21st to end	Night	61% 4 11% 18% 5% 1	2940
December	1st to 10th	Night	72% 6% 11% 7% 3	4720
	11th to 20th	Night	68% 4 10% 14% 3	5348
	21st to end	Night	72% 5% 9% 12% 2	7150

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% 27% 26% 9% 3 1	294
	11th to 20th	Day	38% 28% 26% 6% 1 1	330
	21st to end	Day	33% 29% 29% 7% 2	363
February	1st to 10th	Day	32% 27% 33% 7% 2	330
	11th to 20th	Day	40% 26% 28% 5% 1	330
	21st to end	Day	37% 28% 28% 7%	308
March	1st to 10th	Day	31% 24% 31% 12% 3	540
	11th to 20th	Day	35% 20% 31% 10% 4 1	540
	21st to end	Day	32% 22% 29% 13% 4 1	594
April	1st to 10th	Day	34% 20% 27% 14% 5% 1	540
	11th to 20th	Day	28% 21% 29% 12% 7% 3	532
	21st to end	Day	29% 18% 33% 14% 5% 1	540
May	1st to 10th	Day	30% 20% 28% 15% 5% 2	543
	11th to 20th	Day	25% 14% 32% 18% 8% 3	567
	21st to end	Day	21% 12% 26% 23% 11% 6%	617
June	1st to 10th	Day	16% 16% 31% 24% 10% 3	570
	11th to 20th	Day	22% 16% 24% 25% 11% 2	570
	21st to end	Day	16% 13% 32% 24% 13% 2	570
July	1st to 10th	Day	11% 7% 24% 29% 22% 8%	565
	11th to 20th	Day	13% 7% 28% 27% 18% 7%	544
	21st to end	Day	12% 7% 28% 30% 15% 8%	576
August	1st to 10th	Day	13% 7% 24% 28% 21% 7%	526
	11th to 20th	Day	14% 6% 24% 30% 16% 9%	519
	21st to end	Day	12% 6% 26% 28% 18% 9%	583
September	1st to 10th	Day	20% 7% 21% 25% 19% 8%	530
	11th to 20th	Day	12% 5% 22% 29% 22% 11%	530
	21st to end	Day	25% 10% 25% 22% 15% 3	530
October	1st to 10th	Day	17% 10% 27% 24% 18% 4	530
	11th to 20th	Day	26% 17% 28% 19% 7% 2	530
	21st to end	Day	31% 16% 31% 17% 5%	583
November	1st to 10th	Day	22% 19% 34% 14% 9% 2	440
	11th to 20th	Day	31% 23% 29% 12% 4 2	228
	21st to end	Day	26% 30% 35% 8% 1	220
December	1st to 10th	Day	35% 26% 28% 6% 2 2	220
	11th to 20th	Day	37% 22% 31% 7% 3	220
	21st to end	Day	36% 25% 27% 10% 1	242
January	1st to 10th	Night	30% 23% 32% 12% 2	840
	11th to 20th	Night	32% 23% 30% 13% 2	840
	21st to end	Night	28% 23% 32% 15% 2	924
February	1st to 10th	Night	31% 19% 29% 20% 1	840
	11th to 20th	Night	31% 23% 32% 13% 1	823
	21st to end	Night	31% 20% 31% 15% 2	692
March	1st to 10th	Night	26% 20% 33% 18% 3	840
	11th to 20th	Night	31% 18% 26% 19% 6%	840
	21st to end	Night	26% 17% 36% 18% 3	924
April	1st to 10th	Night	28% 16% 31% 19% 5%	840
	11th to 20th	Night	24% 17% 31% 20% 8% 1	810
	21st to end	Night	22% 13% 33% 27% 5%	630
May	1st to 10th	Night	24% 11% 24% 30% 11% 1	630
	11th to 20th	Night	19% 11% 27% 32% 9%	611
	21st to end	Night	13% 6% 27% 31% 20% 3	455
June	1st to 10th	Night	9% 6% 31% 37% 16% 1	420
	11th to 20th	Night	13% 8% 27% 36% 15%	420
	21st to end	Night	10% 9% 27% 36% 18% 1	420
July	1st to 10th	Night	11% 3 17% 44% 20% 5%	410
	11th to 20th	Night	11% 4 19% 37% 26% 4	593
	21st to end	Night	13% 3 14% 42% 26% 2	657
August	1st to 10th	Night	13% 2 16% 42% 25% 3	597
	11th to 20th	Night	12% 5% 14% 37% 28% 4	594
	21st to end	Night	11% 4 21% 34% 25% 5%	770
September	1st to 10th	Night	15% 4 24% 30% 24% 3	800
	11th to 20th	Night	11% 5% 19% 33% 28% 4	800
	21st to end	Night	21% 10% 22% 26% 17% 4	800
October	1st to 10th	Night	19% 7% 24% 28% 21% 2	800
	11th to 20th	Night	20% 11% 35% 24% 8% 2	800
	21st to end	Night	28% 13% 29% 24% 6%	880
November	1st to 10th	Night	19% 13% 31% 26% 10%	820
	11th to 20th	Night	29% 18% 27% 19% 6% 1	840
	21st to end	Night	32% 17% 30% 18% 4	840
December	1st to 10th	Night	32% 23% 27% 16% 3	840
	11th to 20th	Night	30% 24% 26% 17% 3	840
	21st to end	Night	31% 19% 30% 17% 2	924

Page generated at 2026-07-13 03:14:48. Version ac07

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