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 2024-11-03.

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% 10% 4 9% 6% 5% 5% 4 6% 7% 32%	101812
	Night	13% 11% 4 10% 6% 5% 5% 4 6% 7% 30%	97158
Transparency	Day	27% 49% 7% 11% 6%	101571
	Night	30% 49% 6% 9% 5%	97020
Seeing	Day	18% 10% 25% 26% 15% 5%	15002
	Night	21% 11% 25% 28% 13% 2	24013

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	14% 13% 8% 19% 10% 6% 6% 3 5% 4 12%	2220
	11th to 20th	Day	8% 15% 8% 22% 13% 8% 5% 3 4 4 10%	2776
	21st to end	Day	16% 19% 7% 15% 8% 7% 6% 3 4 4 11%	3124
February	1st to 10th	Day	11% 16% 6% 15% 9% 7% 6% 5% 5% 6% 15%	1710
	11th to 20th	Day	10% 12% 6% 16% 11% 7% 6% 4 5% 6% 16%	1663
	21st to end	Day	13% 16% 5% 13% 9% 7% 4 4 5% 6% 20%	1479
March	1st to 10th	Day	14% 13% 5% 11% 7% 5% 4 3 5% 6% 28%	3397
	11th to 20th	Day	9% 16% 8% 13% 7% 5% 6% 3 5% 4 25%	3480
	21st to end	Day	13% 12% 5% 9% 6% 5% 5% 4 5% 6% 32%	3815
April	1st to 10th	Day	15% 14% 4 10% 5% 5% 4 3 5% 6% 29%	2218
	11th to 20th	Day	17% 11% 3 7% 4 4 4 3 5% 6% 36%	2390
	21st to end	Day	18% 11% 3 7% 5% 3 3 4 5% 7% 34%	2470
May	1st to 10th	Day	14% 9% 3 7% 5% 4 4 3 5% 7% 39%	4108
	11th to 20th	Day	14% 8% 3 8% 5% 4 4 4 6% 7% 36%	4352
	21st to end	Day	11% 7% 2 6% 4 4 5% 4 5% 8% 45%	4837
June	1st to 10th	Day	15% 6% 2 6% 4 5% 4 5% 7% 7% 38%	2680
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 7% 9% 42%	2850
	21st to end	Day	13% 6% 2 6% 5% 4 5% 4 7% 7% 40%	2850
July	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 9% 37%	4760
	11th to 20th	Day	11% 5% 2 5% 4 5% 4 4 6% 9% 46%	4568
	21st to end	Day	8% 6% 2 7% 5% 4 4 4 5% 9% 46%	4479
August	1st to 10th	Day	12% 7% 2 6% 4 5% 5% 5% 7% 8% 40%	4104
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 5% 7% 9% 37%	4044
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 44%	4436
September	1st to 10th	Day	15% 7% 3 6% 5% 5% 5% 3 6% 8% 39%	2280
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 4 6% 9% 42%	2123
	21st to end	Day	15% 6% 3 8% 6% 5% 5% 4 6% 7% 35%	2080
October	1st to 10th	Day	17% 9% 3 7% 5% 4 4 4 6% 7% 34%	1900
	11th to 20th	Day	17% 11% 3 10% 6% 6% 6% 5% 5% 7% 24%	1900
	21st to end	Day	23% 17% 4 9% 5% 4 5% 4 5% 6% 18%	2072
November	1st to 10th	Day	14% 15% 4 9% 6% 6% 4 4 5% 7% 26%	1599
	11th to 20th	Day	12% 16% 6% 12% 7% 5% 7% 4 6% 6% 19%	1520
	21st to end	Day	16% 17% 6% 13% 6% 6% 6% 5% 6% 6% 13%	1520
December	1st to 10th	Day	12% 19% 9% 16% 8% 6% 4 4 7% 6% 9%	1520
	11th to 20th	Day	15% 16% 7% 16% 7% 6% 5% 5% 5% 6% 12%	1906
	21st to end	Day	20% 19% 6% 18% 6% 5% 5% 4 4 4 9%	2582
January	1st to 10th	Night	13% 17% 7% 16% 8% 6% 6% 4 5% 6% 12%	4715
	11th to 20th	Night	10% 12% 7% 21% 12% 8% 5% 4 5% 4 11%	4183
	21st to end	Night	15% 15% 8% 16% 10% 6% 6% 4 5% 5% 10%	4532
February	1st to 10th	Night	11% 16% 5% 12% 9% 7% 6% 5% 7% 5% 17%	2470
	11th to 20th	Night	9% 13% 6% 15% 8% 7% 7% 5% 6% 6% 19%	2403
	21st to end	Night	11% 12% 4 12% 7% 6% 7% 4 6% 7% 24%	1970
March	1st to 10th	Night	14% 11% 5% 9% 5% 4 4 4 6% 7% 30%	3443
	11th to 20th	Night	10% 13% 4 8% 6% 5% 5% 4 6% 7% 32%	3479
	21st to end	Night	12% 9% 5% 11% 7% 5% 5% 4 6% 6% 30%	3817
April	1st to 10th	Night	17% 12% 4 8% 5% 6% 5% 4 5% 5% 30%	1962
	11th to 20th	Night	17% 9% 2 7% 5% 5% 5% 3 4 6% 37%	1755
	21st to end	Night	16% 11% 4 8% 5% 5% 4 3 5% 6% 33%	1710
May	1st to 10th	Night	14% 7% 3 6% 5% 5% 4 4 5% 8% 39%	2833
	11th to 20th	Night	15% 6% 3 6% 4 5% 4 4 6% 8% 41%	2541
	21st to end	Night	9% 6% 2 6% 4 4 4 3 5% 7% 50%	2738
June	1st to 10th	Night	14% 6% 3 6% 5% 5% 4 4 5% 8% 39%	1495
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 5% 7% 10% 43%	1330
	21st to end	Night	12% 6% 2 6% 5% 3 4 4 7% 8% 43%	1330
July	1st to 10th	Night	8% 6% 2 6% 4 4 4 4 5% 8% 49%	2210
	11th to 20th	Night	10% 5% 1 5% 3 4 3 3 6% 6% 53%	2392
	21st to end	Night	7% 5% 2 6% 4 4 5% 4 6% 9% 49%	3071
August	1st to 10th	Night	8% 5% 3 6% 4 6% 4 4 6% 7% 47%	2825
	11th to 20th	Night	13% 5% 2 6% 4 3 4 4 5% 7% 47%	2785
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 9% 45%	3188
September	1st to 10th	Night	12% 4 1 5% 4 3 3 4 7% 10% 45%	1900
	11th to 20th	Night	11% 5% 2 5% 3 4 4 4 5% 7% 50%	2052
	21st to end	Night	17% 7% 3 6% 4 4 5% 3 5% 7% 39%	2099
October	1st to 10th	Night	19% 8% 2 6% 3 6% 4 3 4 7% 38%	2280
	11th to 20th	Night	19% 10% 3 7% 4 6% 6% 4 6% 7% 29%	2280
	21st to end	Night	22% 17% 3 7% 4 5% 5% 3 6% 7% 21%	2522
November	1st to 10th	Night	14% 14% 4 8% 5% 4 5% 4 5% 7% 30%	2523
	11th to 20th	Night	13% 17% 5% 10% 6% 5% 4 4 7% 7% 21%	2660
	21st to end	Night	16% 17% 5% 12% 6% 5% 5% 5% 6% 6% 18%	2660
December	1st to 10th	Night	16% 17% 7% 13% 6% 5% 6% 4 6% 6% 14%	2660
	11th to 20th	Night	12% 17% 6% 15% 7% 5% 5% 4 7% 7% 14%	3288
	21st to end	Night	21% 19% 8% 17% 7% 5% 5% 3 3 4 8%	5057

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	50% 39% 7% 3	2221
	11th to 20th	Day	52% 37% 8% 2 1	2776
	21st to end	Day	48% 41% 6% 4 1	3124
February	1st to 10th	Day	27% 65% 3 5% 1	1710
	11th to 20th	Day	23% 64% 4 6% 2	1672
	21st to end	Day	21% 65% 5% 8% 1	1479
March	1st to 10th	Day	35% 41% 8% 9% 6%	3400
	11th to 20th	Day	39% 40% 6% 11% 3 1	3480
	21st to end	Day	31% 43% 7% 11% 6% 1	3815
April	1st to 10th	Day	22% 65% 3 7% 3	2218
	11th to 20th	Day	18% 65% 2 8% 5% 1	2390
	21st to end	Day	17% 65% 5% 7% 4 1	2470
May	1st to 10th	Day	27% 41% 8% 15% 8% 1	4120
	11th to 20th	Day	27% 42% 12% 14% 4	4356
	21st to end	Day	23% 41% 7% 14% 13% 2	4837
June	1st to 10th	Day	15% 65% 4 9% 6% 1	2680
	11th to 20th	Day	14% 66% 4 8% 6% 1	2850
	21st to end	Day	15% 63% 4 10% 7% 1	2850
July	1st to 10th	Day	29% 37% 12% 12% 9% 1	4686
	11th to 20th	Day	21% 37% 8% 26% 8%	4489
	21st to end	Day	20% 37% 7% 20% 15% 1	4336
August	1st to 10th	Day	25% 39% 10% 17% 9%	4091
	11th to 20th	Day	29% 39% 12% 15% 6%	4083
	21st to end	Day	21% 38% 8% 25% 7%	4436
September	1st to 10th	Day	17% 61% 6% 11% 4	2280
	11th to 20th	Day	14% 60% 4 14% 7%	2123
	21st to end	Day	18% 61% 6% 12% 4	2080
October	1st to 10th	Day	19% 60% 6% 9% 5%	1900
	11th to 20th	Day	24% 60% 6% 7% 3	1900
	21st to end	Day	29% 60% 5% 4 2	2072
November	1st to 10th	Day	30% 58% 6% 4 2	1599
	11th to 20th	Day	27% 61% 4 6% 1	1520
	21st to end	Day	32% 60% 4 3	1520
December	1st to 10th	Day	33% 60% 4 3	1520
	11th to 20th	Day	42% 51% 3 4	1906
	21st to end	Day	51% 38% 6% 4	2582
January	1st to 10th	Night	51% 39% 7% 3	4715
	11th to 20th	Night	51% 38% 9% 2 1	4183
	21st to end	Night	49% 42% 6% 3 1	4532
February	1st to 10th	Night	27% 65% 3 4 1	2470
	11th to 20th	Night	22% 64% 2 9% 2	2405
	21st to end	Night	20% 65% 4 6% 4	1970
March	1st to 10th	Night	32% 42% 7% 14% 5%	3453
	11th to 20th	Night	32% 40% 11% 11% 5% 1	3480
	21st to end	Night	32% 46% 5% 11% 5% 1	3817
April	1st to 10th	Night	23% 65% 3 6% 3	1962
	11th to 20th	Night	17% 66% 2 8% 5% 1	1755
	21st to end	Night	18% 65% 6% 5% 6% 1	1710
May	1st to 10th	Night	25% 44% 8% 12% 10% 1	2840
	11th to 20th	Night	27% 41% 9% 14% 7% 1	2542
	21st to end	Night	22% 41% 7% 16% 13% 1	2739
June	1st to 10th	Night	13% 65% 3 9% 8% 1	1495
	11th to 20th	Night	12% 65% 4 11% 8%	1330
	21st to end	Night	15% 63% 3 11% 7% 1	1330
July	1st to 10th	Night	26% 37% 9% 14% 11% 3	2175
	11th to 20th	Night	22% 36% 7% 26% 9%	2349
	21st to end	Night	22% 37% 9% 20% 12% 1	2973
August	1st to 10th	Night	23% 37% 8% 19% 12% 1	2814
	11th to 20th	Night	28% 38% 11% 16% 6%	2812
	21st to end	Night	24% 38% 8% 20% 9%	3188
September	1st to 10th	Night	11% 62% 7% 14% 6%	1900
	11th to 20th	Night	13% 60% 5% 10% 11%	2052
	21st to end	Night	17% 60% 6% 12% 5%	2099
October	1st to 10th	Night	22% 59% 5% 7% 7%	2280
	11th to 20th	Night	23% 59% 7% 9% 3	2280
	21st to end	Night	27% 59% 4 7% 2	2522
November	1st to 10th	Night	29% 58% 6% 5% 2	2523
	11th to 20th	Night	28% 60% 5% 5% 2	2660
	21st to end	Night	30% 61% 5% 3 1	2660
December	1st to 10th	Night	32% 60% 4 3 1	2660
	11th to 20th	Night	38% 50% 6% 5%	3288
	21st to end	Night	55% 37% 4 4	5057

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	19% 17% 34% 19% 9% 2	180
	11th to 20th	Day	21% 15% 40% 15% 8% 1	252
	21st to end	Day	24% 10% 32% 26% 7% 1	297
February	1st to 10th	Day	20% 20% 37% 18% 4 1	270
	11th to 20th	Day	16% 20% 42% 19% 3	270
	21st to end	Day	22% 26% 31% 21%	225
March	1st to 10th	Day	19% 12% 38% 24% 7% 1	436
	11th to 20th	Day	17% 16% 32% 27% 7% 1	460
	21st to end	Day	27% 9% 30% 23% 9% 1	506
April	1st to 10th	Day	22% 13% 31% 25% 8% 1	460
	11th to 20th	Day	28% 14% 23% 19% 12% 5%	452
	21st to end	Day	24% 13% 25% 25% 11% 2	460
May	1st to 10th	Day	19% 9% 26% 27% 14% 4	463
	11th to 20th	Day	14% 9% 23% 28% 20% 7%	487
	21st to end	Day	15% 4 25% 27% 22% 8%	529
June	1st to 10th	Day	17% 8% 25% 27% 20% 3	510
	11th to 20th	Day	12% 7% 20% 35% 21% 5%	680
	21st to end	Day	16% 6% 22% 33% 18% 5%	680
July	1st to 10th	Day	10% 4 16% 38% 25% 8%	671
	11th to 20th	Day	13% 5% 19% 31% 22% 10%	556
	21st to end	Day	9% 4 17% 38% 23% 8%	532
August	1st to 10th	Day	12% 3 16% 30% 26% 13%	486
	11th to 20th	Day	11% 4 15% 31% 24% 15%	479
	21st to end	Day	14% 6% 19% 27% 24% 9%	539
September	1st to 10th	Day	15% 10% 18% 24% 22% 11%	490
	11th to 20th	Day	12% 5% 18% 24% 24% 17%	490
	21st to end	Day	15% 9% 22% 25% 22% 8%	490
October	1st to 10th	Day	24% 7% 22% 24% 17% 6%	490
	11th to 20th	Day	22% 13% 30% 25% 9% 2	490
	21st to end	Day	35% 14% 23% 18% 8% 1	521
November	1st to 10th	Day	23% 20% 22% 24% 9% 1	233
	11th to 20th	Day	21% 21% 34% 18% 5% 2	180
	21st to end	Day	31% 16% 37% 14% 2	180
December	1st to 10th	Day	24% 21% 32% 18% 5%	180
	11th to 20th	Day	22% 26% 29% 16% 6% 1	180
	21st to end	Day	27% 24% 33% 13% 3	198
January	1st to 10th	Night	23% 19% 32% 19% 7% 1	930
	11th to 20th	Night	25% 16% 29% 24% 6%	760
	21st to end	Night	19% 10% 33% 28% 9% 2	836
February	1st to 10th	Night	22% 16% 35% 23% 4	760
	11th to 20th	Night	18% 14% 33% 27% 7%	743
	21st to end	Night	22% 15% 32% 25% 5%	628
March	1st to 10th	Night	19% 13% 33% 28% 7%	760
	11th to 20th	Night	19% 14% 33% 24% 8% 1	760
	21st to end	Night	20% 10% 25% 31% 12% 1	836
April	1st to 10th	Night	24% 10% 28% 32% 6%	760
	11th to 20th	Night	23% 9% 25% 28% 13% 2	631
	21st to end	Night	24% 8% 23% 29% 16%	570
May	1st to 10th	Night	17% 5% 19% 38% 19% 2	570
	11th to 20th	Night	18% 4 20% 39% 17% 2	407
	21st to end	Night	12% 3 19% 40% 25% 1	411
June	1st to 10th	Night	17% 7% 19% 39% 16% 2	380
	11th to 20th	Night	12% 5% 15% 41% 26% 1	380
	21st to end	Night	15% 4 18% 37% 24% 2	380
July	1st to 10th	Night	8% 4 12% 45% 30% 1	370
	11th to 20th	Night	12% 2 18% 36% 29% 4	368
	21st to end	Night	8% 4 17% 40% 29% 2	608
August	1st to 10th	Night	12% 3 14% 37% 30% 4	567
	11th to 20th	Night	10% 3 12% 36% 32% 7%	564
	21st to end	Night	16% 4 16% 31% 30% 3	665
September	1st to 10th	Night	14% 5% 19% 32% 23% 7%	760
	11th to 20th	Night	17% 4 16% 31% 26% 7%	760
	21st to end	Night	19% 7% 19% 31% 19% 6%	760
October	1st to 10th	Night	26% 8% 22% 28% 14% 3	760
	11th to 20th	Night	27% 11% 25% 26% 9% 2	760
	21st to end	Night	36% 14% 23% 21% 5% 1	836
November	1st to 10th	Night	26% 14% 25% 25% 9% 1	749
	11th to 20th	Night	25% 20% 30% 17% 7% 1	760
	21st to end	Night	29% 18% 26% 22% 5%	760
December	1st to 10th	Night	30% 18% 32% 16% 4 1	760
	11th to 20th	Night	22% 20% 35% 18% 4 1	760
	21st to end	Night	30% 15% 32% 19% 3	944

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