Cobourg
Clear Sky Chart
History

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

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% 9% 3 8% 5% 4 4 4 5% 7% 36%	138079
	Night	16% 10% 3 8% 5% 4 4 4 5% 6% 34%	133925
Transparency	Day	46% 8% 13% 21% 11% 1	141648
	Night	47% 8% 12% 19% 12% 1	138431
Seeing	Day	18% 11% 28% 26% 13% 3	16460
	Night	19% 10% 29% 27% 12% 2	25803

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% 13% 5% 11% 5% 5% 4 3 5% 6% 27%	4661
	11th to 20th	Day	11% 23% 8% 16% 8% 6% 4 3 3 3 15%	4812
	21st to end	Day	13% 16% 7% 13% 6% 5% 4 3 4 5% 23%	5780
February	1st to 10th	Day	14% 16% 5% 11% 7% 4 6% 4 5% 4 24%	1890
	11th to 20th	Day	14% 12% 5% 13% 7% 5% 5% 4 4 5% 26%	1843
	21st to end	Day	19% 13% 5% 9% 6% 5% 4 4 4 5% 26%	1640
March	1st to 10th	Day	20% 11% 4 8% 5% 3 4 3 4 5% 33%	4946
	11th to 20th	Day	11% 13% 4 9% 5% 5% 5% 4 5% 7% 32%	5090
	21st to end	Day	20% 10% 3 6% 4 3 3 3 4 5% 39%	5646
April	1st to 10th	Day	18% 12% 3 8% 5% 4 4 4 5% 5% 31%	2520
	11th to 20th	Day	22% 8% 3 7% 4 5% 2 3 4 5% 37%	2494
	21st to end	Day	19% 9% 3 7% 5% 5% 5% 3 5% 5% 34%	2726
May	1st to 10th	Day	20% 8% 3 8% 4 4 4 4 5% 7% 33%	7875
	11th to 20th	Day	16% 9% 2 7% 5% 4 4 3 5% 8% 37%	8221
	21st to end	Day	19% 6% 2 5% 4 4 4 3 5% 7% 42%	9060
June	1st to 10th	Day	16% 7% 2 6% 5% 5% 5% 4 6% 9% 37%	2940
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 7% 9% 42%	2870
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 7% 8% 41%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	6360
	11th to 20th	Day	10% 4 2 4 4 4 4 4 6% 8% 49%	6360
	21st to end	Day	7% 3 2 6% 4 4 5% 5% 7% 9% 48%	6748
August	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 5% 7% 41%	4234
	11th to 20th	Day	13% 5% 2 5% 4 5% 4 4 7% 10% 40%	4174
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 7% 9% 44%	4393
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 4 6% 7% 46%	2400
	11th to 20th	Day	10% 5% 2 4 3 3 4 3 6% 8% 52%	2375
	21st to end	Day	15% 6% 2 6% 4 4 4 4 5% 7% 41%	2101
October	1st to 10th	Day	18% 6% 2 7% 4 4 4 4 5% 7% 38%	2000
	11th to 20th	Day	19% 7% 4 7% 5% 4 4 4 5% 7% 33%	2000
	21st to end	Day	24% 9% 3 8% 5% 4 5% 4 5% 6% 28%	2199
November	1st to 10th	Day	15% 9% 3 7% 5% 4 4 2 6% 7% 37%	1767
	11th to 20th	Day	15% 12% 3 7% 6% 5% 5% 4 6% 7% 30%	1680
	21st to end	Day	20% 14% 3 8% 6% 5% 4 3 5% 6% 25%	1680
December	1st to 10th	Day	19% 17% 5% 10% 6% 6% 4 4 4 5% 20%	2680
	11th to 20th	Day	19% 16% 5% 9% 4 4 4 3 5% 5% 26%	3066
	21st to end	Day	26% 14% 5% 11% 5% 4 3 3 4 5% 19%	4048
January	1st to 10th	Night	15% 14% 5% 11% 6% 5% 5% 4 5% 6% 25%	8234
	11th to 20th	Night	14% 17% 6% 14% 8% 5% 5% 3 5% 5% 18%	8057
	21st to end	Night	14% 13% 5% 11% 6% 5% 5% 4 5% 6% 27%	8401
February	1st to 10th	Night	14% 16% 4 10% 6% 5% 4 3 5% 6% 26%	2730
	11th to 20th	Night	14% 14% 5% 10% 6% 4 4 4 5% 6% 28%	2663
	21st to end	Night	15% 12% 3 9% 6% 4 5% 4 6% 6% 30%	2165
March	1st to 10th	Night	19% 9% 3 8% 6% 5% 4 4 5% 5% 33%	5109
	11th to 20th	Night	12% 8% 3 7% 5% 5% 4 4 6% 7% 38%	5089
	21st to end	Night	22% 7% 2 6% 3 3 3 3 4 5% 42%	5527
April	1st to 10th	Night	20% 8% 3 6% 4 4 5% 4 5% 6% 34%	2100
	11th to 20th	Night	18% 9% 2 7% 5% 4 4 2 5% 6% 38%	2075
	21st to end	Night	19% 7% 2 7% 4 5% 4 4 6% 7% 36%	1911
May	1st to 10th	Night	26% 7% 2 7% 4 4 4 4 5% 6% 31%	5023
	11th to 20th	Night	16% 6% 2 7% 4 5% 5% 4 5% 7% 39%	4639
	21st to end	Night	19% 6% 2 6% 3 4 4 3 5% 6% 41%	5114
June	1st to 10th	Night	13% 7% 3 6% 5% 3 5% 4 6% 7% 40%	1680
	11th to 20th	Night	9% 6% 3 6% 4 5% 4 5% 7% 8% 43%	1640
	21st to end	Night	12% 7% 2 7% 5% 3 4 5% 6% 8% 42%	1600
July	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 6% 10% 44%	3600
	11th to 20th	Night	11% 4 2 5% 4 4 4 3 5% 9% 49%	3600
	21st to end	Night	10% 5% 2 4 3 3 4 3 5% 8% 52%	4100
August	1st to 10th	Night	11% 5% 2 5% 4 4 5% 4 5% 8% 48%	2915
	11th to 20th	Night	13% 5% 2 6% 3 4 3 3 5% 7% 49%	2875
	21st to end	Night	9% 4 2 5% 3 3 5% 3 6% 9% 50%	3472
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 8% 48%	2000
	11th to 20th	Night	12% 4 1 5% 3 3 3 4 6% 6% 54%	2022
	21st to end	Night	18% 6% 2 6% 4 3 4 3 3 6% 45%	2298
October	1st to 10th	Night	16% 7% 3 6% 4 4 3 3 5% 7% 41%	2400
	11th to 20th	Night	20% 7% 3 7% 4 4 5% 4 5% 6% 34%	2400
	21st to end	Night	20% 8% 3 7% 4 4 5% 4 6% 7% 32%	2640
November	1st to 10th	Night	18% 8% 2 6% 4 4 4 4 5% 7% 38%	2748
	11th to 20th	Night	16% 10% 3 7% 5% 5% 6% 4 6% 7% 31%	2940
	21st to end	Night	21% 11% 3 8% 4 5% 5% 4 6% 7% 26%	2940
December	1st to 10th	Night	18% 15% 4 8% 6% 5% 5% 4 6% 7% 24%	4720
	11th to 20th	Night	18% 16% 4 8% 5% 4 4 3 5% 6% 26%	5348
	21st to end	Night	26% 15% 5% 11% 5% 4 4 3 4 5% 19%	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	55% 10% 11% 15% 8% 1	4662
	11th to 20th	Day	72% 8% 8% 6% 5% 1	4842
	21st to end	Day	62% 7% 11% 12% 8% 1	5780
February	1st to 10th	Day	60% 9% 12% 14% 4 1	1890
	11th to 20th	Day	59% 8% 10% 14% 8% 1	1852
	21st to end	Day	59% 7% 11% 16% 7%	1640
March	1st to 10th	Day	52% 6% 12% 16% 13% 1	4949
	11th to 20th	Day	48% 7% 20% 15% 9% 2	5090
	21st to end	Day	47% 5% 8% 22% 17% 2	5646
April	1st to 10th	Day	52% 6% 11% 19% 11% 2	2520
	11th to 20th	Day	48% 5% 9% 21% 15% 1	2494
	21st to end	Day	50% 6% 11% 19% 12% 2	2726
May	1st to 10th	Day	48% 8% 12% 19% 11% 2	7884
	11th to 20th	Day	44% 10% 13% 19% 14% 1	8225
	21st to end	Day	40% 7% 12% 27% 13% 2	9061
June	1st to 10th	Day	43% 7% 13% 20% 15% 1	2940
	11th to 20th	Day	37% 7% 16% 26% 13% 1	2870
	21st to end	Day	39% 8% 16% 22% 14% 1	2800
July	1st to 10th	Day	34% 7% 15% 29% 15% 1	6290
	11th to 20th	Day	30% 7% 15% 32% 15% 1	6285
	21st to end	Day	29% 10% 15% 33% 13%	6553
August	1st to 10th	Day	41% 7% 15% 23% 13% 1	4221
	11th to 20th	Day	36% 9% 16% 29% 10%	4213
	21st to end	Day	32% 8% 15% 34% 9% 1	4393
September	1st to 10th	Day	35% 9% 14% 29% 11% 1	2400
	11th to 20th	Day	30% 8% 15% 32% 15% 1	2375
	21st to end	Day	40% 9% 15% 25% 10%	2101
October	1st to 10th	Day	36% 7% 14% 29% 13% 1	3260
	11th to 20th	Day	38% 8% 18% 22% 14% 1	3240
	21st to end	Day	46% 8% 16% 20% 9%	3525
November	1st to 10th	Day	46% 8% 15% 20% 11% 1	1767
	11th to 20th	Day	50% 10% 16% 15% 9% 1	1680
	21st to end	Day	59% 8% 13% 15% 5%	1680
December	1st to 10th	Day	63% 10% 15% 9% 3	2680
	11th to 20th	Day	58% 9% 11% 13% 8%	3066
	21st to end	Day	66% 9% 8% 11% 6%	4048
January	1st to 10th	Night	58% 10% 12% 13% 7%	8234
	11th to 20th	Night	64% 11% 9% 9% 7%	8102
	21st to end	Night	55% 10% 9% 12% 13% 1	8401
February	1st to 10th	Night	59% 8% 13% 15% 5% 1	2730
	11th to 20th	Night	56% 8% 11% 16% 8%	2665
	21st to end	Night	52% 8% 13% 18% 8% 1	2165
March	1st to 10th	Night	51% 6% 10% 17% 13% 4	5119
	11th to 20th	Night	42% 8% 17% 20% 10% 2	5090
	21st to end	Night	44% 4 9% 22% 18% 2	5527
April	1st to 10th	Night	49% 6% 11% 19% 13% 2	2100
	11th to 20th	Night	47% 6% 9% 19% 17% 2	2075
	21st to end	Night	45% 7% 11% 19% 15% 3	1911
May	1st to 10th	Night	52% 7% 9% 14% 15% 3	5030
	11th to 20th	Night	41% 9% 14% 20% 14% 2	4640
	21st to end	Night	42% 7% 10% 23% 15% 2	5115
June	1st to 10th	Night	41% 7% 11% 22% 15% 3	1680
	11th to 20th	Night	34% 8% 15% 20% 21% 3	1640
	21st to end	Night	39% 8% 12% 23% 15% 2	1600
July	1st to 10th	Night	33% 8% 15% 22% 20% 1	3560
	11th to 20th	Night	31% 7% 13% 31% 17% 1	3552
	21st to end	Night	30% 8% 13% 31% 18% 1	3980
August	1st to 10th	Night	34% 7% 13% 28% 16% 2	2904
	11th to 20th	Night	34% 6% 17% 28% 13% 2	2902
	21st to end	Night	29% 8% 13% 34% 14% 1	3472
September	1st to 10th	Night	33% 8% 15% 29% 13% 1	2000
	11th to 20th	Night	30% 7% 13% 32% 17% 1	2022
	21st to end	Night	42% 6% 11% 27% 14% 1	2298
October	1st to 10th	Night	34% 5% 10% 27% 23% 1	3920
	11th to 20th	Night	41% 8% 13% 29% 9%	3899
	21st to end	Night	40% 8% 15% 26% 10% 1	4252
November	1st to 10th	Night	44% 8% 13% 21% 13% 1	2748
	11th to 20th	Night	49% 9% 13% 17% 10% 1	2940
	21st to end	Night	55% 11% 16% 14% 4	2940
December	1st to 10th	Night	58% 10% 13% 15% 4	4720
	11th to 20th	Night	57% 10% 11% 11% 10% 1	5348
	21st to end	Night	66% 9% 10% 9% 6%	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	23% 18% 34% 16% 7% 2	220
	11th to 20th	Day	24% 25% 34% 14% 3 1	250
	21st to end	Day	23% 23% 31% 19% 4 1	363
February	1st to 10th	Day	22% 22% 37% 14% 4	330
	11th to 20th	Day	23% 19% 40% 16% 2	330
	21st to end	Day	28% 21% 35% 15% 1	356
March	1st to 10th	Day	22% 15% 37% 21% 5%	540
	11th to 20th	Day	24% 20% 29% 22% 4 1	540
	21st to end	Day	28% 12% 34% 18% 7%	594
April	1st to 10th	Day	24% 14% 34% 21% 7%	540
	11th to 20th	Day	25% 13% 31% 20% 8% 4	532
	21st to end	Day	23% 12% 32% 25% 7% 1	540
May	1st to 10th	Day	21% 10% 29% 27% 10% 3	543
	11th to 20th	Day	16% 8% 26% 32% 13% 4	567
	21st to end	Day	15% 6% 28% 29% 18% 4	617
June	1st to 10th	Day	16% 8% 25% 32% 17% 2	570
	11th to 20th	Day	10% 8% 29% 31% 19% 3	550
	21st to end	Day	18% 7% 23% 33% 15% 4	530
July	1st to 10th	Day	9% 3 21% 36% 26% 5%	525
	11th to 20th	Day	12% 4 21% 35% 21% 7%	524
	21st to end	Day	8% 4 26% 42% 16% 5%	576
August	1st to 10th	Day	10% 3 20% 35% 25% 7%	526
	11th to 20th	Day	12% 4 18% 33% 27% 6%	519
	21st to end	Day	10% 5% 23% 34% 21% 7%	583
September	1st to 10th	Day	12% 7% 23% 30% 21% 7%	530
	11th to 20th	Day	9% 4 18% 32% 24% 14%	530
	21st to end	Day	16% 5% 26% 30% 18% 5%	530
October	1st to 10th	Day	19% 11% 25% 22% 17% 6%	530
	11th to 20th	Day	19% 12% 34% 24% 9% 1	530
	21st to end	Day	27% 15% 29% 22% 7%	582
November	1st to 10th	Day	23% 16% 28% 22% 10% 1	341
	11th to 20th	Day	21% 19% 35% 19% 5% 1	220
	21st to end	Day	25% 19% 34% 18% 5%	220
December	1st to 10th	Day	23% 18% 35% 20% 4	220
	11th to 20th	Day	26% 25% 33% 13% 3	220
	21st to end	Day	33% 17% 35% 13% 2	242
January	1st to 10th	Night	23% 19% 36% 16% 6%	840
	11th to 20th	Night	28% 16% 32% 19% 5%	840
	21st to end	Night	21% 16% 33% 25% 5% 1	924
February	1st to 10th	Night	21% 16% 40% 20% 3	840
	11th to 20th	Night	21% 16% 37% 22% 4	823
	21st to end	Night	22% 18% 36% 21% 4	692
March	1st to 10th	Night	21% 13% 35% 25% 5%	840
	11th to 20th	Night	21% 15% 35% 24% 5% 1	840
	21st to end	Night	21% 9% 34% 26% 9% 1	924
April	1st to 10th	Night	23% 10% 32% 28% 7%	840
	11th to 20th	Night	20% 10% 33% 26% 10% 1	831
	21st to end	Night	20% 8% 29% 28% 13% 1	651
May	1st to 10th	Night	22% 5% 22% 33% 15% 2	550
	11th to 20th	Night	14% 4 28% 37% 16%	414
	21st to end	Night	14% 4 24% 36% 21% 2	455
June	1st to 10th	Night	13% 2 27% 38% 19% 2	420
	11th to 20th	Night	11% 5% 23% 38% 22% 2	410
	21st to end	Night	13% 5% 21% 41% 20% 1	400
July	1st to 10th	Night	5% 2 19% 47% 23% 3	390
	11th to 20th	Night	9% 4 17% 40% 27% 3	388
	21st to end	Night	9% 4 18% 44% 23% 2	511
August	1st to 10th	Night	9% 2 13% 40% 32% 3	597
	11th to 20th	Night	11% 3 14% 34% 33% 5%	594
	21st to end	Night	11% 3 21% 34% 28% 3	805
September	1st to 10th	Night	13% 4 21% 34% 25% 4	800
	11th to 20th	Night	12% 3 17% 32% 29% 8%	800
	21st to end	Night	18% 6% 21% 29% 22% 5%	800
October	1st to 10th	Night	19% 7% 27% 25% 20% 3	800
	11th to 20th	Night	23% 10% 30% 27% 9% 1	800
	21st to end	Night	24% 12% 32% 26% 6%	880
November	1st to 10th	Night	21% 13% 26% 28% 11% 1	820
	11th to 20th	Night	21% 15% 33% 25% 5% 1	840
	21st to end	Night	26% 13% 32% 22% 7%	840
December	1st to 10th	Night	26% 18% 33% 19% 4	840
	11th to 20th	Night	24% 16% 37% 18% 4	840
	21st to end	Night	31% 15% 35% 16% 3	924

Page generated at 2026-06-13 02:31:41. Version ac07

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