Collingwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Collingwood clear sky chart from 2005-11-06 to 2026-10-14.

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	12% 10% 4 10% 6% 5% 5% 4 6% 7% 32%	150272
	Night	12% 10% 4 11% 6% 6% 5% 4 6% 7% 29%	141431
Transparency	Day	36% 33% 8% 15% 7% 1	153848
	Night	40% 34% 8% 12% 6% 1	145945
Seeing	Day	18% 10% 24% 27% 16% 5%	17535
	Night	21% 11% 25% 28% 13% 2	26466

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	11% 13% 7% 22% 14% 6% 5% 3 4 4 11%	4132
	11th to 20th	Day	7% 14% 8% 23% 13% 9% 6% 4 4 4 8%	5126
	21st to end	Day	9% 15% 6% 15% 11% 10% 9% 4 5% 5% 9%	5780
February	1st to 10th	Day	11% 16% 6% 15% 9% 7% 6% 5% 5% 6% 15%	1890
	11th to 20th	Day	11% 12% 7% 17% 11% 7% 6% 4 5% 5% 15%	1843
	21st to end	Day	12% 16% 5% 13% 8% 8% 4 4 5% 6% 19%	1631
March	1st to 10th	Day	14% 11% 5% 12% 7% 7% 5% 3 5% 6% 26%	4992
	11th to 20th	Day	8% 14% 6% 12% 6% 6% 5% 4 6% 7% 25%	5090
	21st to end	Day	13% 15% 6% 11% 6% 4 4 3 4 5% 28%	5586
April	1st to 10th	Day	14% 14% 4 10% 5% 5% 4 3 5% 6% 28%	2452
	11th to 20th	Day	16% 10% 4 7% 4 4 4 3 5% 6% 36%	2644
	21st to end	Day	18% 11% 3 7% 5% 3 4 4 6% 7% 34%	2730
May	1st to 10th	Day	12% 8% 3 7% 5% 4 5% 4 6% 8% 38%	7642
	11th to 20th	Day	12% 9% 3 8% 5% 5% 4 4 6% 7% 38%	8121
	21st to end	Day	15% 7% 2 6% 4 3 4 3 5% 7% 43%	9060
June	1st to 10th	Day	14% 6% 2 6% 4 5% 4 5% 6% 7% 39%	2962
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 7% 9% 41%	3150
	21st to end	Day	13% 6% 2 6% 5% 4 5% 4 7% 7% 40%	3150
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 4 6% 9% 39%	8879
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 6% 10% 50%	8520
	21st to end	Day	9% 5% 2 6% 5% 4 4 4 5% 8% 47%	8367
August	1st to 10th	Day	14% 7% 2 6% 4 4 5% 4 6% 7% 40%	6014
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 7% 10% 40%	5951
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 4 7% 9% 38%	6453
September	1st to 10th	Day	14% 6% 3 6% 5% 5% 5% 4 6% 8% 39%	2520
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 4 6% 9% 43%	2347
	21st to end	Day	15% 6% 3 8% 5% 5% 5% 4 6% 7% 37%	2298
October	1st to 10th	Day	16% 9% 3 7% 4 4 4 4 6% 8% 35%	2100
	11th to 20th	Day	17% 11% 3 10% 6% 6% 6% 5% 5% 7% 24%	2030
	21st to end	Day	22% 17% 4 9% 5% 4 5% 4 5% 6% 19%	2181
November	1st to 10th	Day	14% 15% 4 9% 6% 6% 5% 4 5% 6% 26%	1751
	11th to 20th	Day	12% 16% 6% 12% 8% 5% 7% 4 6% 6% 19%	1680
	21st to end	Day	15% 18% 6% 13% 6% 7% 7% 5% 6% 6% 12%	1680
December	1st to 10th	Day	16% 20% 11% 17% 8% 5% 4 4 5% 5% 6%	2680
	11th to 20th	Day	14% 17% 8% 17% 7% 6% 4 4 4 5% 15%	3066
	21st to end	Day	19% 16% 5% 17% 8% 5% 5% 4 5% 5% 11%	3774
January	1st to 10th	Night	11% 13% 6% 21% 12% 6% 6% 3 5% 6% 12%	8756
	11th to 20th	Night	7% 13% 7% 22% 12% 8% 5% 5% 5% 5% 11%	7744
	21st to end	Night	8% 11% 6% 13% 10% 10% 9% 5% 6% 6% 16%	8401
February	1st to 10th	Night	10% 15% 5% 12% 9% 7% 6% 5% 6% 5% 19%	2730
	11th to 20th	Night	9% 13% 6% 15% 8% 7% 7% 5% 6% 6% 19%	2663
	21st to end	Night	11% 13% 4 13% 8% 6% 7% 4 6% 7% 23%	2170
March	1st to 10th	Night	13% 9% 5% 11% 6% 7% 5% 4 7% 7% 26%	5068
	11th to 20th	Night	8% 10% 4 9% 6% 6% 6% 5% 7% 8% 31%	5089
	21st to end	Night	14% 9% 5% 12% 7% 6% 5% 4 5% 5% 26%	5588
April	1st to 10th	Night	16% 11% 4 9% 5% 6% 5% 4 5% 6% 30%	2168
	11th to 20th	Night	16% 9% 3 8% 5% 5% 5% 3 4 6% 36%	1942
	21st to end	Night	15% 11% 4 8% 5% 5% 4 3 5% 7% 34%	1890
May	1st to 10th	Night	13% 7% 3 6% 5% 5% 5% 4 5% 7% 39%	5257
	11th to 20th	Night	13% 6% 3 6% 4 5% 4 3 6% 8% 43%	4725
	21st to end	Night	16% 6% 2 5% 4 4 3 3 5% 6% 46%	5114
June	1st to 10th	Night	13% 6% 3 6% 5% 5% 5% 4 5% 8% 40%	1652
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	1470
	21st to end	Night	12% 6% 2 6% 5% 4 4 4 7% 9% 43%	1470
July	1st to 10th	Night	9% 7% 2 6% 4 4 4 4 5% 9% 46%	4110
	11th to 20th	Night	9% 5% 2 6% 3 4 4 4 6% 7% 51%	4448
	21st to end	Night	10% 5% 2 6% 4 4 4 4 6% 9% 48%	5693
August	1st to 10th	Night	12% 6% 3 6% 5% 5% 4 3 6% 7% 44%	4135
	11th to 20th	Night	12% 5% 2 6% 4 3 4 3 5% 7% 51%	4095
	21st to end	Night	15% 8% 2 7% 4 4 4 4 5% 8% 38%	4626
September	1st to 10th	Night	12% 5% 2 5% 4 3 3 4 7% 10% 46%	2100
	11th to 20th	Night	11% 5% 2 5% 3 4 4 4 5% 8% 50%	2268
	21st to end	Night	16% 7% 3 6% 4 4 5% 3 5% 7% 40%	2320
October	1st to 10th	Night	18% 8% 2 6% 3 5% 4 3 4 8% 39%	2520
	11th to 20th	Night	19% 10% 3 7% 4 6% 6% 4 6% 7% 29%	2437
	21st to end	Night	21% 17% 3 7% 4 5% 5% 3 5% 7% 23%	2655
November	1st to 10th	Night	14% 14% 4 9% 5% 4 5% 4 5% 7% 29%	2766
	11th to 20th	Night	13% 17% 5% 11% 6% 5% 4 4 7% 7% 20%	2940
	21st to end	Night	16% 17% 5% 13% 6% 5% 5% 5% 6% 6% 17%	2940
December	1st to 10th	Night	13% 17% 8% 19% 7% 6% 6% 4 5% 5% 10%	4720
	11th to 20th	Night	10% 14% 6% 15% 8% 6% 6% 5% 7% 7% 16%	5348
	21st to end	Night	18% 17% 7% 17% 8% 6% 6% 3 4 4 9%	7413

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	65% 23% 7% 4 1	4133
	11th to 20th	Day	68% 21% 7% 3 2	5160
	21st to end	Day	59% 25% 10% 3 3	5780
February	1st to 10th	Day	30% 59% 3 6% 2	1890
	11th to 20th	Day	29% 59% 4 6% 2	1852
	21st to end	Day	25% 59% 5% 9% 1	1631
March	1st to 10th	Day	42% 28% 11% 8% 10% 1	4995
	11th to 20th	Day	42% 29% 10% 14% 4 1	5090
	21st to end	Day	43% 30% 6% 14% 6% 1	5586
April	1st to 10th	Day	25% 59% 3 9% 3	2452
	11th to 20th	Day	22% 59% 3 10% 6% 1	2644
	21st to end	Day	20% 59% 5% 9% 5% 1	2730
May	1st to 10th	Day	33% 24% 10% 20% 9% 4	7651
	11th to 20th	Day	36% 25% 10% 16% 13%	8125
	21st to end	Day	36% 23% 7% 21% 12% 1	9061
June	1st to 10th	Day	17% 59% 4 11% 8% 1	2962
	11th to 20th	Day	17% 61% 5% 10% 6% 1	3150
	21st to end	Day	18% 57% 5% 12% 7% 1	3150
July	1st to 10th	Day	35% 22% 14% 18% 11% 1	8806
	11th to 20th	Day	24% 21% 9% 33% 13%	8441
	21st to end	Day	28% 22% 10% 26% 14% 1	8182
August	1st to 10th	Day	32% 28% 12% 15% 12% 1	6001
	11th to 20th	Day	29% 28% 16% 21% 6%	5990
	21st to end	Day	32% 28% 11% 23% 5%	6453
September	1st to 10th	Day	19% 56% 7% 14% 4	2520
	11th to 20th	Day	15% 54% 5% 18% 8%	2347
	21st to end	Day	19% 55% 6% 13% 6%	2298
October	1st to 10th	Day	28% 36% 9% 19% 8%	3360
	11th to 20th	Day	31% 36% 8% 16% 8%	3270
	21st to end	Day	40% 38% 8% 10% 3	3507
November	1st to 10th	Day	34% 53% 5% 5% 2	1751
	11th to 20th	Day	31% 56% 5% 6% 1	1680
	21st to end	Day	37% 55% 4 3	1680
December	1st to 10th	Day	58% 36% 3 2	2680
	11th to 20th	Day	55% 33% 5% 5% 3	3066
	21st to end	Day	59% 28% 6% 5% 2	3774
January	1st to 10th	Night	67% 22% 6% 4 1	8756
	11th to 20th	Night	67% 22% 7% 2 2	7785
	21st to end	Night	57% 24% 8% 6% 4	8401
February	1st to 10th	Night	30% 59% 3 5% 2	2730
	11th to 20th	Night	28% 58% 3 8% 3	2665
	21st to end	Night	25% 60% 5% 7% 4	2170
March	1st to 10th	Night	42% 29% 9% 12% 7% 1	5078
	11th to 20th	Night	37% 29% 16% 12% 5% 1	5090
	21st to end	Night	45% 32% 6% 10% 7% 1	5588
April	1st to 10th	Night	27% 59% 5% 6% 4	2168
	11th to 20th	Night	21% 60% 3 9% 6% 1	1942
	21st to end	Night	20% 59% 6% 8% 6% 1	1890
May	1st to 10th	Night	35% 25% 7% 17% 12% 3	5264
	11th to 20th	Night	33% 25% 9% 19% 13% 1	4726
	21st to end	Night	34% 23% 6% 23% 12% 1	5115
June	1st to 10th	Night	15% 59% 3 11% 11% 1	1652
	11th to 20th	Night	15% 59% 5% 13% 8%	1470
	21st to end	Night	17% 58% 3 13% 8% 1	1470
July	1st to 10th	Night	33% 22% 13% 21% 10% 1	4075
	11th to 20th	Night	27% 21% 10% 28% 13%	4405
	21st to end	Night	28% 22% 8% 28% 13% 1	5563
August	1st to 10th	Night	31% 27% 9% 17% 15% 1	4124
	11th to 20th	Night	29% 26% 15% 24% 6%	4122
	21st to end	Night	37% 28% 10% 18% 7%	4626
September	1st to 10th	Night	13% 56% 8% 17% 6%	2100
	11th to 20th	Night	14% 54% 6% 13% 12%	2268
	21st to end	Night	19% 54% 6% 13% 6% 1	2320
October	1st to 10th	Night	27% 34% 8% 18% 13%	4040
	11th to 20th	Night	31% 36% 10% 14% 9%	3936
	21st to end	Night	31% 38% 11% 16% 4	4279
November	1st to 10th	Night	33% 53% 6% 6% 2	2766
	11th to 20th	Night	33% 55% 6% 5% 2	2940
	21st to end	Night	36% 55% 5% 3 1	2940
December	1st to 10th	Night	59% 35% 3 2 1	4720
	11th to 20th	Night	53% 32% 7% 5% 3	5348
	21st to end	Night	62% 26% 6% 5% 1	7413

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	17% 17% 38% 19% 7% 1	220
	11th to 20th	Day	20% 16% 39% 16% 7% 1	308
	21st to end	Day	21% 12% 34% 26% 7% 1	363
February	1st to 10th	Day	19% 20% 35% 19% 6% 1	330
	11th to 20th	Day	17% 19% 39% 21% 3	330
	21st to end	Day	21% 24% 27% 24% 4	273
March	1st to 10th	Day	18% 11% 38% 25% 7% 1	514
	11th to 20th	Day	19% 17% 31% 26% 7% 1	540
	21st to end	Day	27% 10% 29% 24% 8% 1	594
April	1st to 10th	Day	22% 14% 32% 24% 8% 1	540
	11th to 20th	Day	29% 13% 23% 19% 12% 5%	532
	21st to end	Day	23% 13% 24% 26% 12% 2	540
May	1st to 10th	Day	18% 9% 27% 30% 13% 4	543
	11th to 20th	Day	13% 8% 24% 29% 20% 6%	567
	21st to end	Day	17% 4 24% 28% 20% 7%	617
June	1st to 10th	Day	16% 7% 23% 30% 20% 4	592
	11th to 20th	Day	13% 6% 20% 36% 20% 4	780
	21st to end	Day	16% 6% 20% 34% 19% 5%	780
July	1st to 10th	Day	10% 3 15% 38% 26% 7%	771
	11th to 20th	Day	12% 4 18% 33% 23% 10%	644
	21st to end	Day	9% 4 17% 38% 24% 8%	620
August	1st to 10th	Day	12% 3 14% 30% 28% 13%	566
	11th to 20th	Day	11% 3 15% 32% 25% 14%	559
	21st to end	Day	14% 6% 18% 28% 25% 8%	627
September	1st to 10th	Day	14% 9% 18% 25% 24% 11%	570
	11th to 20th	Day	11% 5% 17% 25% 24% 18%	570
	21st to end	Day	14% 8% 20% 26% 24% 8%	570
October	1st to 10th	Day	22% 8% 21% 24% 19% 6%	570
	11th to 20th	Day	22% 12% 29% 26% 9% 2	542
	21st to end	Day	35% 13% 23% 20% 8% 1	564
November	1st to 10th	Day	25% 20% 23% 23% 8% 1	277
	11th to 20th	Day	20% 21% 33% 20% 5% 1	220
	21st to end	Day	31% 17% 35% 16% 2	220
December	1st to 10th	Day	25% 21% 30% 18% 6%	220
	11th to 20th	Day	22% 26% 29% 18% 5%	220
	21st to end	Day	27% 21% 33% 15% 4	242
January	1st to 10th	Night	22% 19% 34% 18% 6%	1027
	11th to 20th	Night	24% 17% 30% 23% 5%	840
	21st to end	Night	17% 12% 34% 27% 8% 1	924
February	1st to 10th	Night	20% 16% 35% 24% 5%	840
	11th to 20th	Night	18% 15% 33% 27% 7%	823
	21st to end	Night	22% 15% 31% 26% 5%	692
March	1st to 10th	Night	19% 13% 33% 28% 7%	840
	11th to 20th	Night	19% 14% 33% 24% 8% 1	840
	21st to end	Night	21% 11% 26% 30% 11% 1	924
April	1st to 10th	Night	24% 10% 28% 32% 6%	840
	11th to 20th	Night	22% 9% 25% 29% 13% 2	698
	21st to end	Night	23% 8% 23% 30% 16%	630
May	1st to 10th	Night	17% 5% 19% 38% 19% 2	630
	11th to 20th	Night	18% 4 20% 39% 17% 2	450
	21st to end	Night	13% 3 18% 41% 23% 1	455
June	1st to 10th	Night	16% 6% 19% 39% 17% 2	420
	11th to 20th	Night	13% 5% 16% 40% 26% 1	420
	21st to end	Night	14% 4 17% 38% 24% 2	420
July	1st to 10th	Night	8% 3 12% 44% 31% 1	410
	11th to 20th	Night	12% 2 17% 36% 29% 3	408
	21st to end	Night	8% 4 17% 41% 29% 2	672
August	1st to 10th	Night	12% 3 13% 36% 31% 4	627
	11th to 20th	Night	11% 3 12% 37% 31% 6%	624
	21st to end	Night	17% 4 15% 32% 29% 3	735
September	1st to 10th	Night	14% 5% 19% 32% 23% 7%	840
	11th to 20th	Night	16% 4 15% 31% 28% 7%	840
	21st to end	Night	18% 7% 18% 31% 21% 6%	840
October	1st to 10th	Night	25% 8% 22% 28% 15% 3	840
	11th to 20th	Night	27% 11% 26% 26% 9% 1	813
	21st to end	Night	36% 14% 23% 22% 6% 1	880
November	1st to 10th	Night	27% 14% 26% 24% 9% 1	820
	11th to 20th	Night	26% 20% 30% 17% 7% 1	840
	21st to end	Night	31% 17% 26% 21% 5%	840
December	1st to 10th	Night	29% 18% 32% 16% 4	840
	11th to 20th	Night	21% 20% 36% 18% 3 1	840
	21st to end	Night	30% 15% 32% 20% 3	1044

Page generated at 2026-10-11 05:06:32. Version ac07

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