Canadian Ecology Centre Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Canadian Ecology Centre Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	17% 12% 4 9% 5% 4 4 3 5% 6% 30%	102103
	Night	17% 14% 5% 10% 5% 5% 4 3 4 5% 28%	97633
Transparency	Day	55% 5% 11% 20% 8% 1	105664
	Night	57% 5% 11% 18% 8% 1	102161
Seeing	Day	24% 16% 30% 20% 8% 2	15055
	Night	24% 13% 29% 24% 9% 1	24004

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% 22% 11% 16% 6% 4 3 3 4 4 13%	2208
	11th to 20th	Day	11% 14% 9% 20% 9% 4 4 3 4 6% 16%	2464
	21st to end	Day	16% 24% 9% 13% 6% 4 3 3 3 4 15%	3100
February	1st to 10th	Day	9% 20% 8% 15% 9% 6% 5% 3 4 4 17%	1710
	11th to 20th	Day	11% 20% 6% 12% 7% 5% 5% 4 4 5% 21%	1663
	21st to end	Day	17% 17% 5% 12% 8% 5% 3 4 4 4 20%	1426
March	1st to 10th	Day	20% 15% 5% 9% 4 5% 4 3 4 6% 25%	3388
	11th to 20th	Day	10% 18% 7% 15% 7% 5% 4 3 4 4 24%	3480
	21st to end	Day	13% 11% 5% 10% 7% 6% 4 3 4 5% 32%	3832
April	1st to 10th	Day	21% 16% 3 8% 4 4 4 3 4 6% 26%	2280
	11th to 20th	Day	22% 13% 4 7% 3 3 4 3 4 5% 33%	2349
	21st to end	Day	22% 13% 3 7% 4 3 3 3 4 5% 33%	2470
May	1st to 10th	Day	21% 10% 3 8% 5% 5% 5% 4 5% 6% 31%	4300
	11th to 20th	Day	15% 10% 3 8% 4 4 5% 3 5% 8% 35%	4398
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 7% 39%	4837
June	1st to 10th	Day	21% 10% 3 7% 5% 5% 5% 3 5% 6% 30%	2723
	11th to 20th	Day	16% 5% 2 7% 5% 5% 5% 4 6% 8% 37%	2850
	21st to end	Day	19% 8% 2 7% 5% 5% 5% 4 6% 8% 31%	2850
July	1st to 10th	Day	17% 8% 2 7% 5% 6% 5% 4 6% 9% 32%	4760
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	4608
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 8% 44%	4797
August	1st to 10th	Day	14% 7% 3 7% 6% 6% 6% 4 6% 9% 32%	4104
	11th to 20th	Day	18% 8% 2 6% 5% 5% 4 4 7% 8% 35%	4044
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 6% 9% 41%	4381
September	1st to 10th	Day	17% 8% 3 6% 4 4 5% 3 5% 8% 38%	2280
	11th to 20th	Day	17% 7% 2 5% 3 3 5% 3 4 7% 41%	2220
	21st to end	Day	23% 8% 3 7% 5% 4 5% 4 4 6% 32%	2020
October	1st to 10th	Day	18% 14% 3 7% 4 4 4 3 5% 5% 32%	1900
	11th to 20th	Day	25% 15% 3 8% 5% 4 4 3 5% 5% 22%	1900
	21st to end	Day	28% 17% 5% 9% 5% 4 4 3 4 4 18%	2062
November	1st to 10th	Day	20% 15% 5% 9% 4 4 3 4 4 6% 27%	1571
	11th to 20th	Day	18% 18% 6% 11% 6% 5% 4 3 4 6% 20%	1600
	21st to end	Day	24% 22% 6% 12% 6% 4 2 3 3 3 15%	1600
December	1st to 10th	Day	18% 24% 7% 14% 6% 5% 4 3 3 4 13%	1560
	11th to 20th	Day	18% 20% 5% 14% 8% 4 4 2 4 4 16%	1906
	21st to end	Day	20% 24% 9% 17% 4 3 2 1 2 3 15%	2462
January	1st to 10th	Night	16% 21% 9% 16% 7% 5% 4 3 4 3 11%	4748
	11th to 20th	Night	12% 15% 6% 17% 10% 8% 5% 4 5% 4 15%	4493
	21st to end	Night	12% 25% 9% 13% 6% 7% 4 3 4 3 14%	4555
February	1st to 10th	Night	11% 16% 6% 14% 11% 6% 4 4 6% 5% 18%	2470
	11th to 20th	Night	12% 16% 7% 13% 6% 6% 5% 4 4 4 23%	2403
	21st to end	Night	14% 19% 5% 12% 7% 6% 5% 3 4 5% 20%	2027
March	1st to 10th	Night	15% 16% 5% 8% 4 4 5% 3 4 7% 29%	3448
	11th to 20th	Night	15% 20% 6% 10% 5% 4 4 3 4 4 25%	3479
	21st to end	Night	13% 13% 5% 11% 6% 5% 4 3 3 5% 33%	3799
April	1st to 10th	Night	20% 16% 3 8% 4 4 3 3 5% 5% 29%	1900
	11th to 20th	Night	20% 12% 3 7% 4 5% 4 3 4 4 35%	1796
	21st to end	Night	23% 12% 3 7% 4 4 4 4 4 5% 31%	1710
May	1st to 10th	Night	19% 10% 3 7% 4 4 5% 3 4 5% 36%	2641
	11th to 20th	Night	16% 9% 3 7% 4 4 4 3 5% 8% 36%	2495
	21st to end	Night	14% 8% 3 8% 5% 5% 3 3 5% 7% 39%	2738
June	1st to 10th	Night	16% 8% 4 8% 6% 5% 5% 3 5% 6% 34%	1453
	11th to 20th	Night	16% 7% 3 5% 4 4 4 3 5% 7% 42%	1330
	21st to end	Night	16% 8% 2 7% 5% 5% 5% 5% 5% 7% 35%	1330
July	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 5% 7% 38%	2210
	11th to 20th	Night	16% 8% 3 6% 5% 3 3 3 5% 7% 41%	2355
	21st to end	Night	12% 7% 2 4 3 4 4 3 5% 8% 48%	2754
August	1st to 10th	Night	13% 6% 2 6% 3 4 5% 4 7% 8% 42%	2825
	11th to 20th	Night	17% 7% 3 6% 4 4 6% 3 5% 6% 40%	2785
	21st to end	Night	16% 6% 2 5% 3 4 4 4 5% 7% 44%	3242
September	1st to 10th	Night	16% 5% 2 5% 4 3 4 2 4 7% 47%	1900
	11th to 20th	Night	16% 8% 2 6% 3 3 3 4 4 6% 46%	1957
	21st to end	Night	19% 8% 2 6% 4 4 3 3 4 7% 38%	2159
October	1st to 10th	Night	18% 10% 3 7% 5% 4 4 3 5% 6% 33%	2280
	11th to 20th	Night	25% 14% 3 7% 5% 4 4 3 4 4 27%	2280
	21st to end	Night	27% 15% 4 8% 5% 4 3 3 4 5% 22%	2535
November	1st to 10th	Night	20% 15% 4 8% 5% 4 4 3 4 5% 28%	2725
	11th to 20th	Night	18% 17% 4 11% 6% 5% 4 3 5% 5% 21%	2800
	21st to end	Night	23% 21% 5% 11% 5% 4 4 3 4 4 17%	2800
December	1st to 10th	Night	19% 24% 6% 14% 6% 4 3 3 4 4 12%	2737
	11th to 20th	Night	18% 20% 7% 14% 6% 5% 4 2 4 4 17%	3288
	21st to end	Night	21% 22% 7% 17% 5% 3 3 2 3 4 12%	5186

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	76% 3 8% 10% 3	2209
	11th to 20th	Day	71% 3 9% 10% 6%	2464
	21st to end	Day	74% 4 6% 11% 5% 1	3100
February	1st to 10th	Day	72% 3 6% 12% 6% 1	1710
	11th to 20th	Day	66% 5% 9% 12% 8% 1	1672
	21st to end	Day	68% 4 5% 15% 8% 1	1426
March	1st to 10th	Day	60% 5% 11% 15% 9% 1	3391
	11th to 20th	Day	63% 5% 9% 15% 8% 1	3480
	21st to end	Day	53% 5% 9% 20% 10% 2	3832
April	1st to 10th	Day	59% 4 8% 18% 9% 2	2280
	11th to 20th	Day	54% 5% 7% 22% 11% 1	2349
	21st to end	Day	55% 4 7% 18% 13% 3	2470
May	1st to 10th	Day	51% 9% 7% 22% 10% 2	4312
	11th to 20th	Day	46% 6% 11% 28% 8% 1	4402
	21st to end	Day	45% 5% 13% 18% 16% 2	4837
June	1st to 10th	Day	54% 6% 9% 20% 11% 1	2723
	11th to 20th	Day	45% 5% 11% 25% 12% 2	2850
	21st to end	Day	49% 7% 13% 19% 11% 1	2850
July	1st to 10th	Day	49% 5% 13% 25% 8%	4686
	11th to 20th	Day	42% 6% 16% 28% 7%	4527
	21st to end	Day	38% 4 13% 31% 13%	4644
August	1st to 10th	Day	47% 6% 12% 27% 7%	4091
	11th to 20th	Day	46% 6% 15% 25% 7% 1	4083
	21st to end	Day	38% 6% 13% 33% 10% 1	4381
September	1st to 10th	Day	45% 6% 14% 25% 11%	2280
	11th to 20th	Day	43% 5% 13% 30% 9%	2220
	21st to end	Day	54% 5% 12% 23% 7%	2020
October	1st to 10th	Day	54% 5% 11% 23% 7%	3160
	11th to 20th	Day	57% 4 13% 19% 6%	3140
	21st to end	Day	69% 4 13% 11% 3	3376
November	1st to 10th	Day	59% 4 14% 18% 5%	1571
	11th to 20th	Day	67% 4 12% 11% 7% 1	1600
	21st to end	Day	77% 4 8% 8% 3	1600
December	1st to 10th	Day	76% 4 8% 9% 3	1560
	11th to 20th	Day	74% 3 8% 10% 4	1906
	21st to end	Day	77% 2 5% 14% 2	2462
January	1st to 10th	Night	78% 5% 8% 6% 2	4748
	11th to 20th	Night	70% 6% 11% 9% 3	4493
	21st to end	Night	76% 4 6% 9% 5%	4555
February	1st to 10th	Night	68% 4 10% 12% 6%	2470
	11th to 20th	Night	64% 5% 9% 15% 5% 1	2405
	21st to end	Night	67% 4 8% 14% 6% 1	2027
March	1st to 10th	Night	54% 5% 14% 16% 10% 1	3458
	11th to 20th	Night	61% 6% 10% 15% 7% 1	3480
	21st to end	Night	54% 5% 8% 19% 13% 2	3799
April	1st to 10th	Night	57% 5% 7% 18% 11% 2	1900
	11th to 20th	Night	54% 4 7% 21% 14% 1	1796
	21st to end	Night	56% 4 8% 15% 14% 3	1710
May	1st to 10th	Night	48% 7% 11% 22% 11% 2	2648
	11th to 20th	Night	44% 8% 12% 25% 10% 1	2496
	21st to end	Night	43% 6% 12% 21% 15% 2	2739
June	1st to 10th	Night	51% 5% 9% 22% 11% 2	1453
	11th to 20th	Night	41% 6% 11% 25% 16% 1	1330
	21st to end	Night	46% 7% 13% 22% 11% 1	1330
July	1st to 10th	Night	44% 5% 13% 25% 12% 1	2175
	11th to 20th	Night	44% 4 17% 26% 7% 1	2313
	21st to end	Night	35% 5% 12% 32% 15%	2666
August	1st to 10th	Night	39% 5% 16% 29% 11% 1	2814
	11th to 20th	Night	43% 7% 17% 25% 8% 1	2812
	21st to end	Night	38% 4 16% 30% 10% 2	3242
September	1st to 10th	Night	38% 5% 16% 28% 12% 1	1900
	11th to 20th	Night	40% 5% 16% 29% 10%	1957
	21st to end	Night	46% 5% 14% 27% 8%	2159
October	1st to 10th	Night	48% 4 12% 28% 9%	3800
	11th to 20th	Night	55% 3 14% 21% 8%	3779
	21st to end	Night	60% 5% 17% 13% 5%	4171
November	1st to 10th	Night	58% 5% 13% 17% 6%	2725
	11th to 20th	Night	65% 5% 11% 13% 5% 1	2800
	21st to end	Night	73% 5% 10% 10% 3	2800
December	1st to 10th	Night	78% 4 7% 8% 3	2737
	11th to 20th	Night	72% 4 5% 13% 6%	3288
	21st to end	Night	79% 3 6% 10% 3	5186

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% 26% 32% 11% 7% 1	180
	11th to 20th	Day	24% 16% 38% 15% 7%	180
	21st to end	Day	24% 19% 32% 15% 9% 1	292
February	1st to 10th	Day	29% 25% 34% 9% 3	270
	11th to 20th	Day	24% 26% 39% 10% 1	270
	21st to end	Day	40% 19% 32% 9%	238
March	1st to 10th	Day	27% 20% 35% 15% 3 1	460
	11th to 20th	Day	24% 20% 34% 17% 4 1	460
	21st to end	Day	27% 19% 32% 16% 5%	506
April	1st to 10th	Day	29% 18% 30% 16% 5% 1	460
	11th to 20th	Day	36% 16% 22% 17% 6% 3	452
	21st to end	Day	31% 19% 28% 14% 6% 1	460
May	1st to 10th	Day	27% 17% 28% 19% 7% 2	463
	11th to 20th	Day	23% 16% 28% 21% 10% 2	487
	21st to end	Day	23% 15% 33% 19% 8% 2	529
June	1st to 10th	Day	25% 13% 32% 24% 6% 1	553
	11th to 20th	Day	18% 17% 31% 24% 8% 2	680
	21st to end	Day	22% 14% 32% 21% 8% 2	680
July	1st to 10th	Day	14% 12% 32% 32% 9% 1	671
	11th to 20th	Day	17% 14% 29% 27% 11% 2	581
	21st to end	Day	13% 12% 30% 30% 12% 3	532
August	1st to 10th	Day	17% 10% 28% 28% 13% 5%	486
	11th to 20th	Day	18% 6% 25% 27% 15% 8%	479
	21st to end	Day	17% 13% 30% 21% 14% 5%	539
September	1st to 10th	Day	22% 11% 30% 20% 12% 4	490
	11th to 20th	Day	18% 10% 26% 25% 13% 8%	490
	21st to end	Day	24% 14% 24% 21% 14% 3	490
October	1st to 10th	Day	27% 16% 24% 19% 12% 2	490
	11th to 20th	Day	29% 22% 29% 16% 4 1	490
	21st to end	Day	35% 17% 29% 16% 3	524
November	1st to 10th	Day	33% 23% 29% 13% 2	205
	11th to 20th	Day	29% 22% 31% 14% 5%	200
	21st to end	Day	33% 22% 32% 10% 3 1	200
December	1st to 10th	Day	29% 17% 33% 18% 2 1	190
	11th to 20th	Day	32% 21% 32% 12% 2 1	180
	21st to end	Day	31% 23% 30% 12% 3 1	198
January	1st to 10th	Night	28% 16% 33% 19% 4	950
	11th to 20th	Night	28% 14% 33% 20% 5% 1	787
	21st to end	Night	19% 12% 34% 24% 9% 1	836
February	1st to 10th	Night	18% 20% 38% 20% 4	760
	11th to 20th	Night	21% 17% 37% 20% 5%	743
	21st to end	Night	24% 19% 33% 21% 3	628
March	1st to 10th	Night	22% 19% 32% 22% 4	760
	11th to 20th	Night	23% 21% 32% 18% 5% 1	760
	21st to end	Night	22% 13% 33% 26% 6% 1	836
April	1st to 10th	Night	29% 15% 28% 23% 4	760
	11th to 20th	Night	27% 18% 25% 22% 8%	672
	21st to end	Night	27% 12% 28% 25% 8% 1	570
May	1st to 10th	Night	24% 10% 27% 30% 9%	456
	11th to 20th	Night	24% 9% 31% 26% 10%	374
	21st to end	Night	18% 10% 30% 32% 9%	411
June	1st to 10th	Night	18% 9% 33% 32% 8%	380
	11th to 20th	Night	21% 7% 28% 34% 11%	380
	21st to end	Night	18% 8% 29% 31% 14% 1	380
July	1st to 10th	Night	13% 4 32% 37% 12% 1	370
	11th to 20th	Night	14% 5% 28% 35% 17% 1	368
	21st to end	Night	13% 7% 28% 37% 15% 1	419
August	1st to 10th	Night	16% 6% 22% 37% 18% 1	567
	11th to 20th	Night	12% 6% 23% 35% 22% 2	564
	21st to end	Night	20% 8% 24% 31% 14% 3	693
September	1st to 10th	Night	20% 7% 25% 30% 17% 1	760
	11th to 20th	Night	19% 8% 25% 26% 20% 3	760
	21st to end	Night	22% 9% 23% 28% 16% 2	760
October	1st to 10th	Night	23% 12% 28% 25% 11% 1	760
	11th to 20th	Night	30% 14% 28% 21% 6% 1	760
	21st to end	Night	35% 13% 27% 21% 4	836
November	1st to 10th	Night	30% 14% 28% 21% 7% 1	780
	11th to 20th	Night	27% 19% 30% 17% 6%	800
	21st to end	Night	34% 15% 26% 19% 6%	800
December	1st to 10th	Night	33% 15% 30% 16% 5% 1	783
	11th to 20th	Night	28% 17% 32% 18% 4 2	760
	21st to end	Night	32% 16% 29% 18% 4	1021

Page generated at 2024-12-03 06:45:09. Version ac07

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