Donnacona
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Donnacona clear sky chart from 2005-11-06 to 2026-03-18.

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	18% 10% 3 8% 5% 5% 5% 4 5% 7% 30%	130619
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 28%	130908
Transparency	Day	35% 38% 9% 12% 6% 1	134061
	Night	39% 36% 8% 11% 5%	135554
Seeing	Day	24% 15% 29% 21% 9% 2	16699
	Night	25% 11% 29% 27% 8%	25484

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% 17% 5% 12% 5% 4 4 3 4 5% 24%	4661
	11th to 20th	Day	12% 18% 7% 17% 7% 5% 4 3 4 4 20%	4650
	21st to end	Day	7% 13% 6% 10% 6% 5% 6% 6% 7% 8% 27%	5124
February	1st to 10th	Day	10% 16% 6% 11% 7% 5% 5% 4 4 6% 26%	1696
	11th to 20th	Day	14% 16% 5% 10% 6% 5% 5% 4 5% 6% 25%	2026
	21st to end	Day	12% 15% 5% 11% 6% 5% 4 4 5% 6% 28%	1730
March	1st to 10th	Day	22% 15% 4 9% 5% 4 4 3 4 4 26%	4576
	11th to 20th	Day	15% 14% 4 9% 5% 5% 4 4 5% 6% 29%	4775
	21st to end	Day	19% 13% 3 8% 4 4 4 3 4 4 33%	5872
April	1st to 10th	Day	22% 11% 4 8% 6% 5% 4 3 4 5% 29%	2400
	11th to 20th	Day	20% 7% 3 7% 5% 4 4 3 4 5% 37%	2447
	21st to end	Day	23% 9% 3 8% 5% 4 4 4 4 6% 31%	2600
May	1st to 10th	Day	27% 8% 3 7% 4 4 4 4 5% 6% 28%	6070
	11th to 20th	Day	20% 7% 2 7% 5% 4 5% 4 6% 8% 31%	6318
	21st to end	Day	20% 8% 3 7% 5% 5% 5% 4 5% 7% 30%	6949
June	1st to 10th	Day	19% 7% 2 8% 6% 6% 5% 5% 6% 8% 28%	2950
	11th to 20th	Day	18% 6% 3 6% 5% 4 5% 5% 6% 8% 35%	3000
	21st to end	Day	22% 9% 3 7% 5% 5% 5% 4 6% 7% 28%	2953
July	1st to 10th	Day	17% 7% 3 7% 6% 5% 6% 5% 7% 8% 29%	6360
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 5% 7% 9% 34%	6360
	21st to end	Day	12% 5% 2 5% 4 5% 5% 5% 7% 9% 42%	6926
August	1st to 10th	Day	16% 5% 2 7% 5% 5% 6% 5% 8% 10% 31%	4563
	11th to 20th	Day	21% 6% 2 7% 4 5% 5% 4 7% 8% 32%	4181
	21st to end	Day	21% 6% 2 6% 4 4 4 3 5% 6% 38%	4420
September	1st to 10th	Day	16% 6% 3 7% 4 4 4 4 5% 8% 38%	2400
	11th to 20th	Day	17% 5% 2 4 3 3 4 3 4 7% 47%	2240
	21st to end	Day	21% 7% 3 7% 3 3 4 3 4 7% 38%	2200
October	1st to 10th	Day	21% 7% 3 7% 4 5% 4 4 5% 7% 33%	2171
	11th to 20th	Day	23% 8% 3 9% 5% 5% 5% 4 6% 6% 26%	1850
	21st to end	Day	27% 11% 3 8% 5% 4 4 3 4 5% 25%	1980
November	1st to 10th	Day	20% 11% 3 8% 4 5% 4 3 5% 5% 30%	1851
	11th to 20th	Day	21% 15% 4 10% 6% 4 4 3 5% 5% 25%	1874
	21st to end	Day	22% 17% 4 8% 5% 4 4 5% 4 6% 20%	1570
December	1st to 10th	Day	19% 16% 6% 9% 6% 5% 5% 3 5% 5% 21%	2350
	11th to 20th	Day	21% 14% 5% 9% 6% 4 4 4 4 4 26%	2688
	21st to end	Day	21% 15% 4 9% 4 5% 5% 4 5% 5% 23%	3838
January	1st to 10th	Night	16% 17% 6% 14% 6% 5% 4 3 4 4 20%	8234
	11th to 20th	Night	13% 24% 8% 16% 6% 5% 4 3 3 4 15%	8235
	21st to end	Night	7% 12% 5% 13% 8% 6% 6% 5% 6% 6% 25%	9057
February	1st to 10th	Night	12% 14% 6% 12% 8% 5% 4 3 5% 4 28%	2922
	11th to 20th	Night	13% 16% 5% 11% 6% 5% 4 3 5% 5% 25%	2479
	21st to end	Night	15% 15% 4 9% 5% 4 4 3 5% 6% 29%	2076
March	1st to 10th	Night	23% 13% 4 10% 5% 3 5% 3 4 5% 24%	5484
	11th to 20th	Night	16% 13% 4 10% 6% 6% 5% 4 5% 6% 24%	5339
	21st to end	Night	19% 15% 4 8% 5% 3 4 3 4 5% 30%	5058
April	1st to 10th	Night	22% 14% 4 7% 4 3 4 3 5% 5% 28%	2000
	11th to 20th	Night	22% 9% 3 7% 5% 4 4 4 4 6% 32%	1901
	21st to end	Night	23% 10% 2 7% 4 3 3 3 5% 6% 34%	1800
May	1st to 10th	Night	27% 8% 3 7% 5% 4 5% 3 5% 6% 28%	3898
	11th to 20th	Night	26% 7% 2 7% 4 4 4 4 5% 6% 31%	3575
	21st to end	Night	19% 8% 2 7% 5% 5% 5% 4 5% 8% 32%	3926
June	1st to 10th	Night	22% 8% 2 5% 6% 4 5% 4 6% 9% 30%	1446
	11th to 20th	Night	20% 7% 2 6% 4 4 5% 4 7% 7% 35%	1400
	21st to end	Night	21% 10% 3 7% 4 4 4 3 6% 7% 30%	1439
July	1st to 10th	Night	15% 6% 3 8% 5% 5% 6% 5% 7% 9% 30%	3600
	11th to 20th	Night	22% 6% 2 6% 5% 4 4 3 6% 6% 37%	3600
	21st to end	Night	13% 6% 2 7% 4 5% 4 4 6% 8% 42%	3926
August	1st to 10th	Night	18% 7% 3 7% 5% 5% 4 4 6% 7% 34%	2586
	11th to 20th	Night	19% 6% 3 8% 5% 5% 5% 4 6% 7% 32%	2834
	21st to end	Night	20% 7% 3 8% 5% 4 4 4 4 6% 34%	3476
September	1st to 10th	Night	19% 5% 2 6% 4 3 4 3 5% 6% 42%	2000
	11th to 20th	Night	17% 4 2 6% 4 4 3 4 4 6% 45%	2160
	21st to end	Night	19% 6% 3 6% 5% 4 4 3 5% 6% 40%	2200
October	1st to 10th	Night	19% 7% 2 7% 5% 4 4 3 6% 5% 38%	2225
	11th to 20th	Night	23% 9% 3 8% 4 5% 4 3 5% 5% 31%	2550
	21st to end	Night	26% 10% 3 7% 4 4 4 3 5% 6% 28%	2860
November	1st to 10th	Night	21% 12% 3 7% 4 4 4 3 4 7% 30%	2667
	11th to 20th	Night	20% 13% 4 8% 5% 4 4 3 5% 5% 30%	2745
	21st to end	Night	23% 16% 4 9% 5% 4 4 3 4 4 23%	3045
December	1st to 10th	Night	18% 17% 6% 12% 8% 5% 4 3 4 4 18%	5060
	11th to 20th	Night	24% 15% 4 10% 6% 5% 4 3 4 5% 21%	5741
	21st to end	Night	22% 17% 4 9% 5% 4 4 3 5% 4 23%	7364

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% 21% 8% 13% 6%	4662
	11th to 20th	Day	56% 22% 5% 11% 5% 1	4680
	21st to end	Day	41% 23% 10% 17% 9%	5124
February	1st to 10th	Day	24% 59% 5% 7% 5% 1	1696
	11th to 20th	Day	25% 58% 4 9% 4	2035
	21st to end	Day	24% 59% 4 6% 5% 2	1730
March	1st to 10th	Day	47% 30% 5% 7% 7% 3	4579
	11th to 20th	Day	41% 29% 12% 9% 8%	4775
	21st to end	Day	41% 28% 5% 12% 11% 2	5872
April	1st to 10th	Day	22% 61% 4 7% 5% 2	2400
	11th to 20th	Day	21% 62% 3 9% 4 1	2447
	21st to end	Day	23% 62% 4 5% 5%	2600
May	1st to 10th	Day	43% 30% 7% 11% 8%	6081
	11th to 20th	Day	38% 31% 14% 11% 4 2	6322
	21st to end	Day	40% 32% 8% 10% 7% 2	6949
June	1st to 10th	Day	19% 63% 5% 9% 4 1	2950
	11th to 20th	Day	17% 63% 5% 8% 7%	3000
	21st to end	Day	19% 62% 5% 8% 5%	2953
July	1st to 10th	Day	39% 29% 10% 17% 5%	6290
	11th to 20th	Day	33% 29% 16% 19% 3	6285
	21st to end	Day	26% 28% 15% 24% 7%	6728
August	1st to 10th	Day	28% 40% 14% 13% 5%	4549
	11th to 20th	Day	35% 40% 12% 11% 2	4220
	21st to end	Day	31% 38% 10% 10% 10%	4420
September	1st to 10th	Day	18% 59% 8% 12% 4	2400
	11th to 20th	Day	16% 59% 7% 13% 5%	2240
	21st to end	Day	17% 57% 5% 15% 6%	2200
October	1st to 10th	Day	34% 38% 8% 16% 3	3535
	11th to 20th	Day	33% 40% 12% 13% 1	2988
	21st to end	Day	34% 38% 14% 9% 5%	3180
November	1st to 10th	Day	30% 54% 6% 7% 3	1851
	11th to 20th	Day	27% 55% 4 10% 3 1	1874
	21st to end	Day	32% 55% 5% 5% 2	1570
December	1st to 10th	Day	43% 37% 6% 10% 4	2350
	11th to 20th	Day	43% 31% 7% 10% 9%	2688
	21st to end	Day	47% 27% 8% 10% 7% 1	3838
January	1st to 10th	Night	55% 22% 8% 9% 5%	8234
	11th to 20th	Night	63% 22% 5% 9% 2	8280
	21st to end	Night	46% 23% 9% 12% 9%	9057
February	1st to 10th	Night	24% 59% 3 10% 4 1	2922
	11th to 20th	Night	25% 58% 3 8% 5%	2481
	21st to end	Night	21% 59% 4 8% 7% 1	2076
March	1st to 10th	Night	47% 29% 7% 7% 8% 1	5494
	11th to 20th	Night	45% 30% 10% 9% 5% 1	5340
	21st to end	Night	45% 29% 3 16% 7% 1	5058
April	1st to 10th	Night	21% 61% 3 7% 7% 1	2000
	11th to 20th	Night	23% 62% 3 7% 4 1	1901
	21st to end	Night	19% 64% 3 8% 6%	1800
May	1st to 10th	Night	44% 30% 7% 12% 7%	3904
	11th to 20th	Night	40% 30% 10% 14% 5%	3576
	21st to end	Night	37% 31% 9% 11% 11% 2	3927
June	1st to 10th	Night	19% 62% 5% 8% 5%	1446
	11th to 20th	Night	17% 63% 4 8% 7% 1	1400
	21st to end	Night	21% 61% 5% 7% 6%	1439
July	1st to 10th	Night	37% 30% 15% 14% 4	3560
	11th to 20th	Night	35% 28% 16% 18% 2	3552
	21st to end	Night	28% 28% 14% 23% 7%	3809
August	1st to 10th	Night	34% 38% 10% 13% 5%	2576
	11th to 20th	Night	36% 40% 11% 10% 3	2861
	21st to end	Night	35% 38% 7% 12% 8%	3476
September	1st to 10th	Night	17% 58% 7% 12% 6% 1	2000
	11th to 20th	Night	16% 59% 8% 13% 3	2160
	21st to end	Night	17% 57% 5% 14% 8%	2200
October	1st to 10th	Night	34% 36% 10% 15% 4	3641
	11th to 20th	Night	31% 38% 10% 18% 2	4151
	21st to end	Night	32% 37% 13% 11% 7%	4610
November	1st to 10th	Night	29% 54% 6% 8% 4	2667
	11th to 20th	Night	27% 55% 4 10% 3	2745
	21st to end	Night	32% 55% 4 5% 3	3045
December	1st to 10th	Night	46% 36% 8% 8% 2	5060
	11th to 20th	Night	48% 32% 5% 12% 4	5742
	21st to end	Night	48% 26% 6% 13% 6% 1	7364

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	30% 19% 32% 15% 3	220
	11th to 20th	Day	30% 20% 31% 13% 5% 1	220
	21st to end	Day	18% 18% 40% 16% 7%	242
February	1st to 10th	Day	21% 27% 31% 15% 5% 1	228
	11th to 20th	Day	23% 21% 35% 17% 3	514
	21st to end	Day	25% 22% 33% 18% 3	446
March	1st to 10th	Day	26% 21% 29% 18% 5%	540
	11th to 20th	Day	27% 21% 31% 16% 5% 1	528
	21st to end	Day	27% 19% 28% 17% 8% 1	550
April	1st to 10th	Day	29% 19% 27% 20% 5%	500
	11th to 20th	Day	28% 18% 28% 19% 5% 1	492
	21st to end	Day	30% 19% 27% 16% 5% 2	500
May	1st to 10th	Day	26% 17% 33% 17% 5% 1	503
	11th to 20th	Day	20% 14% 31% 23% 10% 2	527
	21st to end	Day	24% 18% 32% 16% 9% 1	573
June	1st to 10th	Day	21% 11% 33% 24% 9% 1	680
	11th to 20th	Day	22% 10% 28% 27% 11% 1	730
	21st to end	Day	26% 9% 27% 24% 13% 1	683
July	1st to 10th	Day	17% 11% 31% 27% 13% 1	525
	11th to 20th	Day	16% 10% 35% 27% 11% 2	524
	21st to end	Day	16% 10% 31% 30% 11% 2	576
August	1st to 10th	Day	15% 9% 27% 32% 14% 3	526
	11th to 20th	Day	18% 6% 24% 28% 18% 5%	519
	21st to end	Day	22% 11% 25% 19% 16% 7%	583
September	1st to 10th	Day	17% 10% 30% 24% 14% 5%	530
	11th to 20th	Day	16% 11% 24% 25% 18% 6%	530
	21st to end	Day	21% 12% 27% 23% 13% 4	530
October	1st to 10th	Day	22% 12% 27% 26% 11% 2	530
	11th to 20th	Day	27% 13% 30% 20% 9% 1	447
	21st to end	Day	33% 15% 27% 19% 6%	462
November	1st to 10th	Day	33% 14% 26% 21% 5%	425
	11th to 20th	Day	30% 17% 28% 16% 7% 1	414
	21st to end	Day	32% 20% 30% 14% 3	220
December	1st to 10th	Day	31% 14% 29% 20% 5% 1	220
	11th to 20th	Day	29% 23% 28% 14% 5% 1	220
	21st to end	Day	34% 17% 32% 11% 5% 2	242
January	1st to 10th	Night	28% 13% 35% 21% 4	840
	11th to 20th	Night	27% 14% 33% 21% 5%	840
	21st to end	Night	17% 12% 34% 29% 7% 1	924
February	1st to 10th	Night	18% 11% 37% 26% 6%	840
	11th to 20th	Night	20% 17% 38% 20% 5%	823
	21st to end	Night	23% 12% 33% 28% 4	692
March	1st to 10th	Night	25% 13% 34% 23% 4	840
	11th to 20th	Night	26% 14% 35% 21% 5% 1	829
	21st to end	Night	24% 10% 32% 27% 6% 1	880
April	1st to 10th	Night	30% 13% 30% 22% 5%	800
	11th to 20th	Night	28% 11% 31% 25% 5%	717
	21st to end	Night	28% 14% 31% 22% 5%	600
May	1st to 10th	Night	27% 11% 32% 25% 4	535
	11th to 20th	Night	25% 7% 29% 32% 6% 1	394
	21st to end	Night	24% 9% 30% 29% 8%	433
June	1st to 10th	Night	26% 6% 28% 34% 7%	400
	11th to 20th	Night	21% 6% 26% 34% 13%	400
	21st to end	Night	23% 6% 26% 33% 12% 1	400
July	1st to 10th	Night	16% 5% 28% 39% 12%	390
	11th to 20th	Night	18% 4 23% 41% 13% 1	388
	21st to end	Night	15% 5% 23% 44% 14%	438
August	1st to 10th	Night	16% 5% 15% 43% 21% 1	398
	11th to 20th	Night	16% 5% 21% 38% 18% 1	566
	21st to end	Night	18% 5% 25% 33% 17% 1	809
September	1st to 10th	Night	21% 5% 25% 35% 13% 1	800
	11th to 20th	Night	19% 6% 21% 32% 21% 1	800
	21st to end	Night	21% 6% 28% 31% 13% 1	800
October	1st to 10th	Night	22% 9% 26% 34% 9%	800
	11th to 20th	Night	27% 10% 27% 27% 8% 1	800
	21st to end	Night	30% 11% 31% 24% 4	880
November	1st to 10th	Night	29% 12% 27% 25% 7% 1	820
	11th to 20th	Night	27% 14% 28% 22% 8% 1	840
	21st to end	Night	33% 14% 25% 21% 7%	895
December	1st to 10th	Night	31% 14% 27% 22% 7%	950
	11th to 20th	Night	28% 17% 28% 20% 6%	950
	21st to end	Night	34% 14% 28% 19% 4 1	973

Page generated at 2026-03-15 02:23:51. Version ac07

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