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 2024-01-31.

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% 8% 3 6% 5% 3 5% 5% 5% 7% 36%	74842
	Night	17% 9% 3 6% 5% 3 5% 5% 5% 7% 35%	75279
Transparency	Day	46% 8% 14% 20% 11% 1	74551
	Night	49% 8% 12% 19% 11% 1	75104
Seeing	Day	18% 10% 28% 27% 14% 4	13395
	Night	20% 10% 29% 28% 13% 2	22846

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	16% 14% 4 9% 6% 3 5% 4 6% 8% 25%	1517
	11th to 20th	Day	16% 18% 6% 9% 7% 4 5% 5% 5% 5% 21%	1572
	21st to end	Day	14% 14% 6% 11% 7% 4 7% 4 5% 5% 22%	1872
February	1st to 10th	Day	14% 15% 6% 11% 9% 3 7% 5% 5% 5% 21%	1620
	11th to 20th	Day	14% 11% 6% 12% 8% 4 4 5% 4 5% 27%	1573
	21st to end	Day	20% 12% 6% 8% 6% 3 5% 4 3 5% 28%	1403
March	1st to 10th	Day	15% 11% 4 7% 7% 3 6% 5% 6% 6% 30%	1936
	11th to 20th	Day	14% 12% 5% 7% 5% 3 4 4 4 5% 36%	1980
	21st to end	Day	20% 10% 3 6% 6% 3 3 4 4 5% 37%	2196
April	1st to 10th	Day	17% 10% 4 8% 5% 3 4 5% 5% 6% 32%	2160
	11th to 20th	Day	20% 7% 3 5% 5% 3 3 4 4 6% 39%	2134
	21st to end	Day	19% 8% 3 7% 5% 3 5% 4 5% 5% 34%	2336
May	1st to 10th	Day	16% 8% 3 6% 5% 3 5% 5% 6% 7% 35%	2407
	11th to 20th	Day	14% 6% 2 5% 5% 3 4 5% 6% 9% 42%	2478
	21st to end	Day	12% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	2725
June	1st to 10th	Day	17% 5% 2 6% 5% 3 5% 5% 6% 10% 37%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 4 5% 6% 10% 43%	2520
	21st to end	Day	13% 6% 2 5% 5% 3 4 6% 6% 8% 42%	2520
July	1st to 10th	Day	8% 4 2 4 4 3 5% 5% 7% 10% 48%	2520
	11th to 20th	Day	11% 4 2 5% 5% 4 5% 6% 6% 9% 43%	2520
	21st to end	Day	9% 4 2 5% 6% 3 6% 7% 7% 10% 42%	2675
August	1st to 10th	Day	8% 6% 2 4 5% 3 6% 6% 7% 9% 44%	2327
	11th to 20th	Day	9% 5% 2 5% 5% 4 5% 6% 7% 10% 43%	2303
	21st to end	Day	11% 5% 3 4 5% 3 5% 5% 7% 10% 43%	2426
September	1st to 10th	Day	13% 5% 2 4 5% 3 5% 5% 6% 8% 45%	2160
	11th to 20th	Day	12% 4 2 4 4 2 4 4 6% 8% 50%	2138
	21st to end	Day	14% 5% 2 5% 5% 4 4 5% 5% 8% 42%	1891
October	1st to 10th	Day	19% 7% 2 7% 5% 4 4 5% 6% 6% 35%	1800
	11th to 20th	Day	20% 7% 4 7% 6% 4 4 5% 5% 8% 31%	1800
	21st to end	Day	25% 10% 3 7% 6% 3 4 5% 5% 6% 26%	1980
November	1st to 10th	Day	14% 8% 4 6% 7% 3 4 4 6% 7% 37%	1595
	11th to 20th	Day	15% 11% 3 7% 6% 3 6% 5% 7% 7% 30%	1520
	21st to end	Day	21% 12% 4 6% 7% 3 4 4 5% 6% 26%	1520
December	1st to 10th	Day	18% 16% 6% 8% 6% 4 5% 5% 4 6% 23%	1520
	11th to 20th	Day	19% 13% 5% 7% 5% 3 5% 5% 5% 6% 27%	1906
	21st to end	Day	29% 15% 5% 8% 5% 3 4 4 4 5% 18%	2772
January	1st to 10th	Night	19% 14% 5% 8% 7% 4 4 5% 4 4 26%	2649
	11th to 20th	Night	20% 15% 5% 9% 7% 4 5% 5% 4 5% 21%	2605
	21st to end	Night	14% 14% 6% 8% 7% 3 5% 5% 4 6% 27%	2711
February	1st to 10th	Night	16% 16% 5% 9% 7% 4 5% 5% 4 6% 23%	2340
	11th to 20th	Night	15% 12% 6% 8% 7% 3 5% 5% 5% 6% 29%	2273
	21st to end	Night	16% 11% 3 7% 7% 4 4 5% 6% 6% 32%	1852
March	1st to 10th	Night	14% 10% 4 7% 7% 4 4 4 5% 5% 35%	2006
	11th to 20th	Night	18% 10% 4 7% 5% 3 4 3 4 6% 36%	1979
	21st to end	Night	16% 8% 3 7% 5% 3 4 4 5% 5% 42%	2159
April	1st to 10th	Night	20% 7% 4 5% 5% 3 5% 5% 5% 6% 35%	1800
	11th to 20th	Night	17% 8% 2 6% 6% 3 4 4 5% 6% 38%	1775
	21st to end	Night	20% 8% 2 6% 4 3 3 5% 6% 7% 35%	1638
May	1st to 10th	Night	18% 7% 2 6% 5% 3 6% 5% 6% 7% 36%	1552
	11th to 20th	Night	13% 4 2 5% 5% 4 5% 5% 5% 7% 44%	1415
	21st to end	Night	11% 5% 2 6% 3 3 4 4 6% 8% 48%	1550
June	1st to 10th	Night	13% 6% 3 5% 6% 3 5% 6% 5% 8% 40%	1440
	11th to 20th	Night	10% 5% 3 5% 5% 3 4 5% 6% 8% 44%	1440
	21st to end	Night	12% 6% 3 6% 6% 2 4 5% 6% 8% 43%	1440
July	1st to 10th	Night	5% 4 2 4 4 4 5% 4 5% 9% 54%	1440
	11th to 20th	Night	12% 4 2 5% 5% 3 5% 5% 5% 10% 46%	1440
	21st to end	Night	9% 5% 2 4 5% 3 4 5% 6% 8% 49%	1639
August	1st to 10th	Night	9% 4 3 4 5% 3 4 5% 6% 9% 48%	1611
	11th to 20th	Night	9% 5% 2 6% 4 3 5% 5% 6% 9% 49%	1598
	21st to end	Night	9% 5% 2 5% 4 2 5% 4 6% 8% 49%	1912
September	1st to 10th	Night	12% 4 2 5% 6% 3 4 5% 6% 8% 46%	1800
	11th to 20th	Night	13% 4 2 4 3 2 4 4 6% 6% 53%	1819
	21st to end	Night	17% 5% 2 5% 5% 2 4 4 3 6% 46%	2068
October	1st to 10th	Night	17% 8% 3 6% 5% 3 4 4 5% 7% 39%	2160
	11th to 20th	Night	21% 7% 3 7% 5% 3 5% 5% 4 6% 33%	2160
	21st to end	Night	22% 9% 3 7% 5% 3 5% 5% 6% 6% 30%	2376
November	1st to 10th	Night	19% 7% 2 5% 5% 3 4 5% 5% 7% 38%	2480
	11th to 20th	Night	18% 8% 3 6% 6% 3 5% 5% 5% 8% 32%	2660
	21st to end	Night	22% 10% 3 6% 5% 3 5% 5% 5% 8% 27%	2660
December	1st to 10th	Night	21% 13% 5% 7% 7% 4 5% 4 5% 6% 23%	2660
	11th to 20th	Night	18% 15% 5% 7% 6% 3 5% 4 5% 6% 27%	3288
	21st to end	Night	30% 15% 4 7% 5% 3 4 4 5% 5% 18%	4884

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	58% 9% 14% 13% 5%	1518
	11th to 20th	Day	65% 10% 9% 8% 7%	1572
	21st to end	Day	63% 10% 9% 11% 6% 1	1872
February	1st to 10th	Day	63% 9% 11% 12% 3 1	1620
	11th to 20th	Day	59% 7% 9% 14% 9% 2	1582
	21st to end	Day	59% 6% 11% 16% 7%	1403
March	1st to 10th	Day	51% 7% 16% 16% 9% 1	1939
	11th to 20th	Day	50% 6% 11% 19% 12% 2	1980
	21st to end	Day	50% 5% 8% 19% 15% 3	2196
April	1st to 10th	Day	51% 6% 11% 19% 11% 2	2160
	11th to 20th	Day	46% 5% 10% 22% 15% 2	2134
	21st to end	Day	50% 6% 11% 18% 13% 2	2336
May	1st to 10th	Day	46% 7% 11% 18% 14% 3	2407
	11th to 20th	Day	38% 8% 13% 24% 15% 2	2482
	21st to end	Day	37% 8% 17% 23% 13% 2	2725
June	1st to 10th	Day	43% 7% 14% 21% 14% 1	2520
	11th to 20th	Day	36% 6% 16% 26% 14% 1	2520
	21st to end	Day	38% 8% 17% 22% 14% 1	2520
July	1st to 10th	Day	28% 9% 14% 30% 17% 2	2450
	11th to 20th	Day	34% 8% 18% 30% 10%	2445
	21st to end	Day	34% 11% 17% 26% 11% 1	2525
August	1st to 10th	Day	34% 10% 18% 25% 12% 1	2314
	11th to 20th	Day	33% 10% 17% 26% 13%	2303
	21st to end	Day	33% 9% 16% 29% 11% 1	2426
September	1st to 10th	Day	36% 9% 15% 28% 11% 1	2160
	11th to 20th	Day	31% 8% 15% 31% 15% 1	2138
	21st to end	Day	39% 10% 16% 26% 9%	1891
October	1st to 10th	Day	47% 8% 14% 19% 10% 1	1800
	11th to 20th	Day	50% 9% 16% 18% 6% 1	1800
	21st to end	Day	57% 8% 13% 13% 8% 1	1980
November	1st to 10th	Day	46% 8% 16% 18% 10% 1	1595
	11th to 20th	Day	51% 10% 16% 14% 8% 1	1520
	21st to end	Day	58% 8% 13% 15% 5%	1520
December	1st to 10th	Day	63% 10% 13% 11% 4	1520
	11th to 20th	Day	58% 11% 14% 11% 6%	1906
	21st to end	Day	69% 9% 9% 9% 3	2772
January	1st to 10th	Night	61% 8% 12% 13% 5%	2649
	11th to 20th	Night	65% 10% 9% 10% 5% 1	2605
	21st to end	Night	60% 8% 9% 14% 8% 1	2711
February	1st to 10th	Night	63% 8% 11% 13% 4 1	2340
	11th to 20th	Night	56% 8% 11% 16% 9%	2275
	21st to end	Night	53% 8% 12% 19% 8% 1	1852
March	1st to 10th	Night	50% 7% 12% 19% 11% 1	2016
	11th to 20th	Night	49% 6% 11% 21% 12% 1	1980
	21st to end	Night	45% 5% 9% 22% 16% 4	2159
April	1st to 10th	Night	49% 7% 10% 19% 14% 2	1800
	11th to 20th	Night	46% 7% 9% 18% 18% 2	1775
	21st to end	Night	46% 8% 11% 18% 15% 3	1638
May	1st to 10th	Night	45% 8% 10% 18% 16% 3	1552
	11th to 20th	Night	38% 6% 11% 25% 16% 4	1416
	21st to end	Night	35% 6% 14% 23% 18% 4	1551
June	1st to 10th	Night	41% 8% 12% 22% 15% 3	1440
	11th to 20th	Night	35% 6% 14% 20% 22% 3	1440
	21st to end	Night	39% 8% 13% 23% 16% 2	1440
July	1st to 10th	Night	28% 9% 11% 26% 24% 2	1400
	11th to 20th	Night	33% 8% 14% 27% 18% 1	1392
	21st to end	Night	32% 7% 14% 31% 14% 2	1548
August	1st to 10th	Night	32% 9% 16% 28% 14% 1	1600
	11th to 20th	Night	32% 8% 17% 27% 14% 1	1598
	21st to end	Night	32% 9% 14% 29% 15% 1	1912
September	1st to 10th	Night	35% 9% 15% 26% 13% 2	1800
	11th to 20th	Night	31% 7% 13% 30% 17% 1	1819
	21st to end	Night	41% 6% 11% 28% 13%	2068
October	1st to 10th	Night	46% 7% 12% 20% 15% 1	2160
	11th to 20th	Night	50% 10% 13% 20% 7%	2160
	21st to end	Night	53% 9% 13% 15% 10% 1	2376
November	1st to 10th	Night	44% 9% 13% 20% 13% 1	2480
	11th to 20th	Night	49% 9% 13% 17% 10% 1	2660
	21st to end	Night	54% 11% 16% 14% 4	2660
December	1st to 10th	Night	62% 11% 11% 12% 4	2660
	11th to 20th	Night	58% 10% 13% 13% 5% 1	3288
	21st to end	Night	68% 9% 12% 8% 3	4884

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	24% 17% 33% 16% 9% 2	180
	11th to 20th	Day	22% 24% 34% 16% 3 1	204
	21st to end	Day	23% 21% 30% 21% 5% 1	294
February	1st to 10th	Day	23% 25% 38% 12% 2	240
	11th to 20th	Day	21% 19% 43% 16% 2	240
	21st to end	Day	31% 21% 33% 15% 1	269
March	1st to 10th	Day	20% 13% 40% 21% 5%	420
	11th to 20th	Day	21% 19% 30% 24% 5% 1	420
	21st to end	Day	28% 8% 35% 20% 8%	462
April	1st to 10th	Day	20% 14% 34% 23% 9%	420
	11th to 20th	Day	24% 9% 32% 22% 9% 5%	412
	21st to end	Day	23% 10% 32% 26% 8% 1	420
May	1st to 10th	Day	22% 7% 28% 27% 12% 4	423
	11th to 20th	Day	17% 5% 27% 34% 13% 4	447
	21st to end	Day	13% 3 24% 33% 21% 5%	485
June	1st to 10th	Day	17% 7% 24% 34% 17% 2	450
	11th to 20th	Day	11% 6% 27% 32% 20% 4	450
	21st to end	Day	17% 5% 20% 36% 17% 4	450
July	1st to 10th	Day	8% 2 17% 38% 29% 6%	445
	11th to 20th	Day	12% 3 19% 35% 23% 8%	444
	21st to end	Day	9% 3 24% 42% 16% 5%	488
August	1st to 10th	Day	8% 2 20% 35% 27% 8%	446
	11th to 20th	Day	11% 3 15% 34% 29% 7%	439
	21st to end	Day	11% 5% 21% 34% 22% 7%	495
September	1st to 10th	Day	12% 5% 23% 31% 22% 7%	450
	11th to 20th	Day	10% 4 20% 31% 22% 13%	450
	21st to end	Day	14% 6% 27% 28% 19% 6%	450
October	1st to 10th	Day	21% 11% 23% 21% 17% 6%	450
	11th to 20th	Day	20% 12% 33% 25% 9% 1	450
	21st to end	Day	28% 14% 29% 21% 8%	495
November	1st to 10th	Day	21% 16% 27% 24% 11% 1	289
	11th to 20th	Day	21% 18% 36% 20% 5% 1	180
	21st to end	Day	23% 16% 35% 20% 6%	180
December	1st to 10th	Day	23% 16% 35% 22% 4 1	180
	11th to 20th	Day	24% 26% 33% 14% 3 1	180
	21st to end	Day	33% 17% 35% 14% 1	198
January	1st to 10th	Night	25% 17% 35% 17% 6%	760
	11th to 20th	Night	27% 15% 31% 21% 6%	760
	21st to end	Night	21% 14% 33% 26% 5% 1	835
February	1st to 10th	Night	23% 16% 41% 19% 2	720
	11th to 20th	Night	21% 14% 38% 22% 4	703
	21st to end	Night	22% 17% 37% 20% 4	592
March	1st to 10th	Night	20% 12% 36% 26% 5% 1	720
	11th to 20th	Night	21% 14% 35% 24% 5% 1	720
	21st to end	Night	20% 6% 34% 28% 10% 1	792
April	1st to 10th	Night	23% 9% 32% 29% 7%	720
	11th to 20th	Night	20% 9% 32% 26% 12% 1	711
	21st to end	Night	21% 8% 28% 28% 14% 1	558
May	1st to 10th	Night	21% 4 22% 34% 17% 3	472
	11th to 20th	Night	14% 3 28% 38% 17%	354
	21st to end	Night	12% 2 23% 38% 23% 2	389
June	1st to 10th	Night	14% 1 28% 37% 18% 2	360
	11th to 20th	Night	12% 4 22% 37% 23% 2	360
	21st to end	Night	12% 3 21% 43% 21% 1	360
July	1st to 10th	Night	6% 2 18% 47% 24% 4	350
	11th to 20th	Night	10% 3 17% 40% 27% 3	348
	21st to end	Night	9% 3 17% 46% 23% 3	459
August	1st to 10th	Night	9% 2 12% 41% 31% 4	537
	11th to 20th	Night	10% 3 14% 35% 33% 5%	534
	21st to end	Night	11% 3 20% 35% 28% 3	724
September	1st to 10th	Night	13% 4 20% 33% 25% 4	720
	11th to 20th	Night	13% 3 18% 32% 27% 8%	720
	21st to end	Night	17% 6% 21% 28% 23% 5%	720
October	1st to 10th	Night	20% 7% 28% 24% 19% 3	720
	11th to 20th	Night	23% 10% 30% 27% 9% 1	720
	21st to end	Night	26% 11% 31% 27% 6%	792
November	1st to 10th	Night	22% 11% 25% 29% 12% 1	740
	11th to 20th	Night	22% 14% 32% 25% 6% 2	760
	21st to end	Night	25% 12% 33% 23% 7%	760
December	1st to 10th	Night	26% 18% 33% 19% 4	760
	11th to 20th	Night	24% 14% 37% 19% 5%	760
	21st to end	Night	31% 15% 35% 16% 3	836

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