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 2025-02-21.

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% 9% 3 7% 5% 4 4 4 5% 7% 35%	108772
	Night	16% 10% 3 8% 5% 4 4 4 5% 6% 34%	109785
Transparency	Day	45% 8% 14% 21% 11% 1	112388
	Night	47% 9% 12% 19% 11% 1	114320
Seeing	Day	18% 10% 28% 27% 14% 4	14732
	Night	19% 10% 29% 27% 13% 2	24186

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% 5% 10% 4 5% 4 3 5% 7% 30%	3597
	11th to 20th	Day	10% 21% 8% 15% 8% 5% 5% 3 4 4 18%	3690
	21st to end	Day	16% 18% 7% 12% 5% 5% 4 3 4 5% 21%	4466
February	1st to 10th	Day	14% 16% 5% 12% 7% 4 6% 4 5% 4 23%	1800
	11th to 20th	Day	13% 12% 5% 13% 7% 5% 5% 4 4 5% 27%	1753
	21st to end	Day	19% 13% 5% 9% 6% 5% 4 4 4 5% 28%	1488
March	1st to 10th	Day	21% 10% 3 7% 5% 3 5% 3 5% 6% 32%	3366
	11th to 20th	Day	10% 16% 5% 9% 5% 5% 4 3 5% 6% 32%	3480
	21st to end	Day	16% 8% 2 6% 4 3 3 3 4 6% 44%	3860
April	1st to 10th	Day	18% 12% 3 8% 5% 4 4 4 5% 5% 32%	2280
	11th to 20th	Day	21% 8% 3 6% 4 4 2 3 4 6% 38%	2254
	21st to end	Day	19% 9% 3 7% 5% 4 5% 3 5% 5% 34%	2466
May	1st to 10th	Day	18% 8% 3 8% 4 4 4 4 6% 7% 34%	4231
	11th to 20th	Day	16% 9% 2 7% 5% 4 4 4 6% 9% 34%	4398
	21st to end	Day	12% 5% 2 6% 4 4 4 4 5% 8% 47%	4837
June	1st to 10th	Day	16% 7% 2 6% 5% 5% 5% 4 6% 9% 36%	2660
	11th to 20th	Day	12% 6% 2 6% 4 4 4 5% 6% 9% 42%	2660
	21st to end	Day	14% 6% 2 6% 4 3 5% 4 7% 8% 41%	2660
July	1st to 10th	Day	10% 4 2 6% 4 5% 4 4 7% 10% 44%	4440
	11th to 20th	Day	11% 5% 1 4 4 4 4 5% 6% 8% 47%	4440
	21st to end	Day	7% 3 2 6% 5% 5% 5% 5% 7% 10% 45%	4692
August	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 5% 7% 40%	4104
	11th to 20th	Day	13% 5% 2 5% 4 5% 4 4 7% 10% 40%	4044
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 7% 9% 44%	4258
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 4 6% 7% 45%	2280
	11th to 20th	Day	11% 5% 2 4 3 4 4 3 6% 8% 51%	2256
	21st to end	Day	15% 6% 2 6% 4 4 4 4 5% 8% 41%	1996
October	1st to 10th	Day	18% 7% 2 7% 4 4 5% 4 6% 7% 36%	1900
	11th to 20th	Day	20% 7% 3 7% 5% 4 4 4 5% 7% 33%	1900
	21st to end	Day	24% 10% 3 8% 5% 4 5% 4 5% 6% 27%	2089
November	1st to 10th	Day	14% 9% 3 7% 6% 4 5% 2 6% 7% 36%	1681
	11th to 20th	Day	15% 11% 3 7% 6% 5% 5% 4 7% 7% 30%	1600
	21st to end	Day	20% 14% 3 7% 6% 5% 4 4 5% 6% 26%	1600
December	1st to 10th	Day	19% 17% 5% 10% 6% 6% 4 4 4 5% 20%	2600
	11th to 20th	Day	19% 16% 5% 9% 4 4 4 3 5% 5% 27%	2986
	21st to end	Day	26% 14% 5% 11% 5% 4 3 3 4 5% 19%	3960
January	1st to 10th	Night	15% 14% 5% 10% 6% 5% 5% 4 5% 5% 27%	6349
	11th to 20th	Night	14% 15% 5% 13% 8% 6% 5% 4 5% 6% 20%	6179
	21st to end	Night	17% 14% 6% 11% 5% 4 4 3 5% 6% 26%	6490
February	1st to 10th	Night	15% 16% 4 10% 6% 5% 5% 4 5% 6% 25%	2600
	11th to 20th	Night	14% 14% 5% 9% 6% 4 5% 4 5% 6% 28%	2533
	21st to end	Night	16% 11% 3 8% 6% 4 5% 4 6% 6% 31%	1966
March	1st to 10th	Night	19% 10% 3 8% 5% 4 4 4 4 5% 33%	3469
	11th to 20th	Night	16% 10% 4 8% 5% 4 3 4 5% 7% 34%	3479
	21st to end	Night	17% 7% 2 5% 3 2 3 2 4 6% 48%	3771
April	1st to 10th	Night	20% 8% 3 6% 4 4 5% 4 5% 6% 35%	1900
	11th to 20th	Night	18% 9% 2 7% 6% 4 4 2 5% 6% 38%	1875
	21st to end	Night	19% 8% 2 7% 4 4 4 4 6% 7% 35%	1729
May	1st to 10th	Night	21% 7% 2 7% 4 4 4 4 5% 5% 36%	2709
	11th to 20th	Night	16% 6% 3 7% 5% 5% 5% 4 5% 7% 37%	2495
	21st to end	Night	11% 5% 3 5% 3 4 4 3 6% 8% 47%	2738
June	1st to 10th	Night	13% 7% 3 6% 5% 3 5% 4 6% 7% 39%	1520
	11th to 20th	Night	9% 6% 3 6% 4 5% 4 5% 7% 9% 43%	1520
	21st to end	Night	12% 7% 2 7% 5% 3 3 5% 6% 8% 42%	1520
July	1st to 10th	Night	8% 5% 2 6% 4 5% 4 4 7% 9% 46%	2520
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 9% 48%	2520
	21st to end	Night	9% 5% 2 4 3 3 4 3 5% 8% 52%	2857
August	1st to 10th	Night	11% 5% 2 5% 4 3 5% 4 5% 8% 48%	2825
	11th to 20th	Night	13% 5% 2 6% 3 4 3 3 5% 8% 49%	2785
	21st to end	Night	9% 4 2 5% 3 3 5% 3 6% 9% 50%	3366
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 6% 7% 47%	1900
	11th to 20th	Night	12% 4 2 5% 2 4 3 4 6% 6% 54%	1921
	21st to end	Night	17% 6% 2 6% 4 3 4 3 3 6% 45%	2183
October	1st to 10th	Night	16% 7% 3 7% 5% 4 3 3 5% 6% 40%	2280
	11th to 20th	Night	20% 8% 3 7% 4 4 5% 4 4 6% 34%	2280
	21st to end	Night	21% 9% 3 7% 4 4 5% 4 6% 7% 31%	2508
November	1st to 10th	Night	19% 8% 2 5% 4 4 4 4 5% 7% 38%	2614
	11th to 20th	Night	17% 10% 3 7% 5% 4 6% 4 6% 7% 32%	2800
	21st to end	Night	21% 11% 3 7% 4 5% 5% 4 6% 7% 27%	2800
December	1st to 10th	Night	19% 14% 4 8% 6% 5% 5% 4 6% 6% 23%	4580
	11th to 20th	Night	18% 16% 4 8% 5% 4 4 3 5% 6% 26%	5208
	21st to end	Night	27% 15% 5% 11% 5% 4 4 3 4 5% 19%	6996

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	51% 11% 11% 17% 9% 1	3598
	11th to 20th	Day	69% 9% 10% 6% 5%	3720
	21st to end	Day	65% 8% 10% 9% 7% 1	4466
February	1st to 10th	Day	61% 9% 12% 14% 4 1	1800
	11th to 20th	Day	58% 8% 10% 14% 9% 1	1762
	21st to end	Day	58% 7% 12% 16% 7% 1	1488
March	1st to 10th	Day	51% 7% 13% 19% 9% 1	3369
	11th to 20th	Day	48% 8% 17% 16% 9% 1	3480
	21st to end	Day	40% 6% 10% 25% 17% 2	3860
April	1st to 10th	Day	52% 6% 11% 19% 11% 2	2280
	11th to 20th	Day	47% 5% 10% 22% 15% 1	2254
	21st to end	Day	50% 6% 11% 18% 13% 2	2466
May	1st to 10th	Day	46% 9% 11% 19% 13% 2	4243
	11th to 20th	Day	45% 12% 15% 17% 10% 1	4402
	21st to end	Day	33% 9% 15% 25% 15% 3	4837
June	1st to 10th	Day	44% 7% 14% 20% 14% 1	2660
	11th to 20th	Day	36% 7% 16% 26% 14% 1	2660
	21st to end	Day	39% 8% 16% 22% 14% 1	2660
July	1st to 10th	Day	33% 7% 15% 29% 15% 1	4370
	11th to 20th	Day	31% 7% 16% 36% 9%	4365
	21st to end	Day	31% 11% 16% 27% 14% 1	4542
August	1st to 10th	Day	42% 7% 15% 23% 13% 1	4091
	11th to 20th	Day	36% 9% 17% 28% 10%	4083
	21st to end	Day	32% 8% 15% 34% 10% 1	4258
September	1st to 10th	Day	36% 9% 15% 28% 11% 1	2280
	11th to 20th	Day	30% 8% 15% 31% 15% 1	2256
	21st to end	Day	39% 9% 15% 26% 10%	1996
October	1st to 10th	Day	36% 7% 14% 29% 12% 1	3160
	11th to 20th	Day	37% 8% 18% 22% 14%	3140
	21st to end	Day	46% 8% 17% 20% 9%	3415
November	1st to 10th	Day	46% 8% 16% 19% 10% 1	1681
	11th to 20th	Day	50% 9% 16% 15% 9% 1	1600
	21st to end	Day	59% 8% 13% 15% 5%	1600
December	1st to 10th	Day	63% 10% 16% 9% 2	2600
	11th to 20th	Day	58% 9% 12% 13% 8%	2986
	21st to end	Day	66% 9% 8% 10% 7%	3960
January	1st to 10th	Night	57% 10% 12% 13% 8%	6349
	11th to 20th	Night	62% 13% 10% 9% 5% 1	6224
	21st to end	Night	59% 11% 10% 10% 10% 1	6490
February	1st to 10th	Night	60% 8% 13% 14% 4	2600
	11th to 20th	Night	55% 8% 11% 17% 9%	2535
	21st to end	Night	52% 9% 13% 19% 7% 1	1966
March	1st to 10th	Night	52% 7% 10% 21% 9% 1	3479
	11th to 20th	Night	47% 9% 14% 18% 11% 1	3480
	21st to end	Night	37% 4 11% 25% 20% 3	3771
April	1st to 10th	Night	49% 6% 10% 19% 14% 2	1900
	11th to 20th	Night	47% 7% 9% 18% 18% 2	1875
	21st to end	Night	46% 8% 11% 18% 15% 3	1729
May	1st to 10th	Night	47% 9% 12% 15% 15% 2	2716
	11th to 20th	Night	44% 9% 16% 19% 9% 2	2496
	21st to end	Night	34% 7% 12% 24% 20% 2	2739
June	1st to 10th	Night	42% 8% 12% 22% 14% 3	1520
	11th to 20th	Night	35% 7% 14% 20% 21% 3	1520
	21st to end	Night	40% 8% 12% 23% 16% 2	1520
July	1st to 10th	Night	32% 8% 13% 24% 21% 1	2480
	11th to 20th	Night	33% 7% 13% 32% 15%	2472
	21st to end	Night	30% 8% 15% 32% 13% 1	2766
August	1st to 10th	Night	34% 7% 13% 28% 16% 2	2814
	11th to 20th	Night	34% 6% 17% 29% 12% 2	2812
	21st to end	Night	29% 8% 13% 34% 14% 1	3366
September	1st to 10th	Night	34% 8% 15% 27% 14% 1	1900
	11th to 20th	Night	30% 7% 13% 31% 18% 1	1921
	21st to end	Night	42% 6% 11% 27% 13%	2183
October	1st to 10th	Night	35% 5% 11% 26% 22% 1	3800
	11th to 20th	Night	41% 8% 14% 29% 9%	3779
	21st to end	Night	41% 8% 15% 26% 9% 1	4120
November	1st to 10th	Night	44% 8% 13% 21% 13% 1	2614
	11th to 20th	Night	49% 9% 13% 17% 10% 1	2800
	21st to end	Night	54% 11% 16% 15% 4	2800
December	1st to 10th	Night	59% 10% 13% 15% 4	4580
	11th to 20th	Night	58% 10% 11% 11% 10% 1	5208
	21st to end	Night	66% 9% 10% 9% 6%	6996

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% 8% 2	200
	11th to 20th	Day	22% 23% 36% 15% 3 1	227
	21st to end	Day	22% 23% 31% 20% 4 1	330
February	1st to 10th	Day	22% 24% 37% 13% 3	300
	11th to 20th	Day	23% 19% 40% 16% 2	300
	21st to end	Day	29% 20% 34% 16% 1	300
March	1st to 10th	Day	20% 13% 40% 21% 6%	460
	11th to 20th	Day	21% 20% 30% 23% 4 1	460
	21st to end	Day	27% 10% 35% 20% 8%	506
April	1st to 10th	Day	22% 12% 34% 23% 8%	460
	11th to 20th	Day	25% 11% 31% 21% 9% 4	452
	21st to end	Day	22% 12% 32% 26% 8% 1	460
May	1st to 10th	Day	21% 7% 27% 29% 11% 4	463
	11th to 20th	Day	17% 5% 25% 34% 15% 4	487
	21st to end	Day	12% 4 26% 33% 21% 5%	529
June	1st to 10th	Day	17% 8% 23% 33% 18% 2	490
	11th to 20th	Day	10% 6% 28% 32% 21% 4	490
	21st to end	Day	18% 7% 22% 34% 16% 4	490
July	1st to 10th	Day	9% 3 18% 37% 28% 5%	485
	11th to 20th	Day	12% 3 21% 35% 22% 7%	484
	21st to end	Day	8% 4 23% 43% 17% 5%	532
August	1st to 10th	Day	11% 3 20% 33% 26% 7%	486
	11th to 20th	Day	11% 4 17% 34% 28% 6%	479
	21st to end	Day	10% 5% 22% 34% 22% 7%	539
September	1st to 10th	Day	12% 6% 24% 30% 21% 7%	490
	11th to 20th	Day	9% 4 19% 30% 24% 14%	490
	21st to end	Day	16% 6% 27% 28% 18% 5%	490
October	1st to 10th	Day	20% 12% 25% 22% 16% 6%	490
	11th to 20th	Day	19% 12% 33% 25% 10% 1	490
	21st to end	Day	27% 14% 29% 22% 8%	538
November	1st to 10th	Day	22% 16% 28% 23% 10% 1	315
	11th to 20th	Day	20% 19% 36% 19% 5% 1	200
	21st to end	Day	25% 18% 33% 19% 6%	200
December	1st to 10th	Day	24% 17% 34% 21% 5% 1	200
	11th to 20th	Day	27% 25% 32% 14% 3 1	200
	21st to end	Day	33% 16% 35% 14% 2	220
January	1st to 10th	Night	24% 18% 36% 16% 6%	800
	11th to 20th	Night	27% 15% 33% 20% 6%	800
	21st to end	Night	21% 15% 33% 25% 5% 1	880
February	1st to 10th	Night	22% 17% 40% 20% 2	800
	11th to 20th	Night	21% 15% 38% 22% 3	783
	21st to end	Night	22% 17% 36% 21% 4	629
March	1st to 10th	Night	20% 12% 36% 26% 5% 1	760
	11th to 20th	Night	21% 14% 35% 24% 5% 1	760
	21st to end	Night	20% 7% 34% 28% 10% 1	836
April	1st to 10th	Night	23% 10% 31% 29% 7%	760
	11th to 20th	Night	21% 9% 32% 26% 11% 1	751
	21st to end	Night	21% 8% 28% 28% 14% 1	589
May	1st to 10th	Night	21% 4 23% 34% 16% 3	498
	11th to 20th	Night	15% 3 27% 38% 17%	374
	21st to end	Night	12% 3 23% 37% 23% 2	411
June	1st to 10th	Night	13% 2 27% 37% 18% 2	380
	11th to 20th	Night	11% 4 22% 38% 23% 2	380
	21st to end	Night	13% 4 21% 41% 20% 1	380
July	1st to 10th	Night	6% 2 19% 46% 23% 4	370
	11th to 20th	Night	10% 3 17% 41% 27% 2	368
	21st to end	Night	9% 3 17% 45% 24% 2	485
August	1st to 10th	Night	10% 2 13% 40% 31% 4	567
	11th to 20th	Night	11% 3 15% 34% 32% 5%	564
	21st to end	Night	11% 3 20% 34% 28% 3	765
September	1st to 10th	Night	13% 4 21% 33% 25% 4	760
	11th to 20th	Night	12% 3 17% 31% 29% 8%	760
	21st to end	Night	18% 6% 21% 28% 22% 5%	760
October	1st to 10th	Night	19% 7% 27% 24% 19% 3	760
	11th to 20th	Night	23% 10% 29% 27% 9% 1	760
	21st to end	Night	24% 12% 31% 26% 6%	836
November	1st to 10th	Night	22% 12% 26% 28% 11% 1	780
	11th to 20th	Night	21% 14% 33% 25% 5% 2	800
	21st to end	Night	25% 13% 32% 23% 7%	800
December	1st to 10th	Night	26% 18% 33% 19% 4	800
	11th to 20th	Night	25% 15% 37% 18% 5%	800
	21st to end	Night	30% 15% 36% 16% 3	880

Page generated at 2025-02-18 03:26:30. Version ac07

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