Observatoire de Clarenceville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Clarenceville clear sky chart from 2005-11-06 to 2024-08-15.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 31%	95592
	Night	19% 12% 4 9% 5% 4 4 3 5% 5% 30%	93140
Transparency	Day	52% 5% 12% 21% 9% 1	95311
	Night	56% 4 11% 19% 9% 1	92975
Seeing	Day	22% 14% 29% 22% 10% 3	14335
	Night	24% 12% 29% 26% 9% 1	23252

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% 14% 6% 6% 4 4 4 5% 20%	2517
	11th to 20th	Day	15% 15% 7% 16% 7% 6% 4 3 4 5% 18%	2520
	21st to end	Day	16% 16% 5% 11% 6% 6% 6% 4 4 6% 19%	2772
February	1st to 10th	Day	16% 16% 5% 12% 8% 5% 5% 4 4 6% 20%	1657
	11th to 20th	Day	13% 17% 5% 11% 6% 4 4 4 4 6% 24%	1793
	21st to end	Day	16% 16% 4 8% 7% 6% 5% 4 4 7% 24%	1570
March	1st to 10th	Day	21% 13% 4 10% 5% 4 4 3 4 6% 25%	3116
	11th to 20th	Day	16% 18% 5% 10% 5% 5% 4 3 4 6% 25%	3268
	21st to end	Day	17% 10% 4 7% 5% 4 4 3 3 5% 38%	4166
April	1st to 10th	Day	22% 12% 3 7% 5% 4 4 4 4 5% 30%	2280
	11th to 20th	Day	21% 8% 3 8% 4 4 3 3 5% 5% 36%	2254
	21st to end	Day	22% 9% 3 7% 5% 5% 4 3 4 5% 32%	2446
May	1st to 10th	Day	23% 9% 3 7% 5% 4 5% 4 5% 7% 29%	4288
	11th to 20th	Day	17% 8% 3 8% 5% 6% 5% 3 6% 7% 32%	4398
	21st to end	Day	14% 7% 3 7% 5% 4 5% 5% 7% 8% 35%	4837
June	1st to 10th	Day	22% 8% 2 6% 5% 5% 5% 4 5% 7% 30%	2660
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 4 7% 8% 37%	2660
	21st to end	Day	21% 8% 3 7% 5% 4 4 4 6% 6% 32%	2660
July	1st to 10th	Day	12% 5% 3 7% 6% 5% 5% 4 8% 9% 36%	4440
	11th to 20th	Day	12% 6% 2 7% 5% 5% 6% 5% 8% 9% 37%	4440
	21st to end	Day	13% 6% 2 6% 4 5% 5% 4 7% 8% 41%	4814
August	1st to 10th	Day	13% 6% 3 7% 5% 5% 6% 5% 7% 9% 35%	2646
	11th to 20th	Day	12% 5% 2 6% 3 5% 5% 5% 8% 9% 40%	2318
	21st to end	Day	14% 6% 3 6% 5% 4 4 3 6% 8% 41%	2376
September	1st to 10th	Day	14% 6% 3 6% 4 4 5% 4 6% 7% 43%	2160
	11th to 20th	Day	16% 5% 2 5% 4 3 4 3 4 7% 47%	2066
	21st to end	Day	14% 5% 3 6% 5% 5% 5% 4 6% 8% 40%	1980
October	1st to 10th	Day	22% 7% 3 7% 4 5% 6% 4 5% 7% 30%	1890
	11th to 20th	Day	19% 8% 3 8% 5% 5% 5% 5% 7% 6% 30%	1747
	21st to end	Day	25% 12% 3 8% 5% 5% 3 2 4 5% 27%	1782
November	1st to 10th	Day	18% 12% 3 7% 4 5% 5% 4 6% 5% 32%	1671
	11th to 20th	Day	18% 12% 4 9% 6% 5% 5% 4 5% 6% 27%	1682
	21st to end	Day	21% 15% 4 8% 6% 5% 5% 4 6% 6% 21%	1520
December	1st to 10th	Day	23% 18% 5% 10% 5% 5% 4 3 3 4 19%	1520
	11th to 20th	Day	22% 14% 5% 9% 5% 5% 5% 3 4 6% 22%	1906
	21st to end	Day	26% 16% 5% 12% 6% 5% 3 3 3 3 17%	2772
January	1st to 10th	Night	17% 20% 7% 12% 6% 4 4 3 4 5% 20%	4429
	11th to 20th	Night	13% 16% 6% 14% 7% 6% 6% 4 5% 5% 17%	4440
	21st to end	Night	20% 17% 5% 11% 7% 5% 4 2 3 4 23%	4884
February	1st to 10th	Night	17% 16% 6% 13% 8% 5% 4 3 4 5% 19%	2519
	11th to 20th	Night	14% 14% 4 11% 7% 6% 5% 4 6% 5% 24%	2272
	21st to end	Night	17% 14% 5% 10% 6% 4 4 3 4 4 30%	1884
March	1st to 10th	Night	22% 11% 4 8% 5% 4 3 3 4 5% 30%	3724
	11th to 20th	Night	20% 19% 4 9% 5% 4 3 3 3 4 27%	3686
	21st to end	Night	15% 11% 4 10% 6% 4 4 3 4 5% 35%	3466
April	1st to 10th	Night	23% 12% 3 8% 4 4 5% 3 4 5% 29%	1900
	11th to 20th	Night	24% 11% 3 7% 5% 4 4 3 4 5% 31%	1875
	21st to end	Night	20% 10% 3 7% 5% 5% 4 3 4 5% 34%	1734
May	1st to 10th	Night	22% 11% 3 8% 5% 4 4 4 5% 6% 28%	2681
	11th to 20th	Night	21% 10% 3 7% 4 4 3 3 4 6% 35%	2495
	21st to end	Night	15% 7% 2 7% 5% 5% 4 3 6% 9% 37%	2738
June	1st to 10th	Night	24% 8% 3 6% 4 5% 4 4 6% 8% 30%	1520
	11th to 20th	Night	18% 6% 2 7% 5% 4 4 4 7% 8% 36%	1520
	21st to end	Night	20% 7% 3 6% 5% 4 4 4 6% 7% 33%	1520
July	1st to 10th	Night	13% 7% 3 8% 5% 5% 6% 4 5% 8% 35%	2520
	11th to 20th	Night	13% 5% 3 6% 5% 5% 5% 4 6% 8% 41%	2520
	21st to end	Night	12% 7% 3 8% 5% 5% 5% 4 6% 6% 39%	2739
August	1st to 10th	Night	13% 6% 2 5% 4 5% 4 4 6% 9% 41%	1512
	11th to 20th	Night	14% 6% 3 6% 4 4 5% 3 6% 7% 41%	1659
	21st to end	Night	13% 8% 2 6% 4 4 4 4 5% 7% 43%	1980
September	1st to 10th	Night	13% 6% 2 7% 5% 4 4 3 5% 8% 43%	1800
	11th to 20th	Night	15% 6% 2 5% 3 4 3 3 5% 6% 47%	1894
	21st to end	Night	18% 6% 2 5% 4 4 4 3 5% 5% 43%	1980
October	1st to 10th	Night	19% 7% 3 8% 5% 4 4 4 5% 6% 36%	2067
	11th to 20th	Night	21% 9% 3 8% 5% 4 5% 4 5% 6% 31%	2212
	21st to end	Night	26% 9% 3 8% 5% 5% 3 3 5% 5% 27%	2574
November	1st to 10th	Night	20% 11% 3 7% 4 5% 4 3 5% 6% 31%	2407
	11th to 20th	Night	19% 11% 3 9% 5% 4 4 3 4 5% 31%	2497
	21st to end	Night	22% 14% 4 9% 5% 4 5% 4 4 5% 24%	2660
December	1st to 10th	Night	22% 18% 5% 10% 7% 5% 5% 3 4 4 16%	2660
	11th to 20th	Night	24% 16% 5% 10% 6% 4 5% 3 4 3 21%	3288
	21st to end	Night	27% 16% 5% 11% 6% 4 3 2 3 4 19%	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	67% 3 13% 14% 3	2518
	11th to 20th	Day	69% 4 12% 10% 5%	2520
	21st to end	Day	66% 5% 13% 11% 4	2772
February	1st to 10th	Day	66% 4 9% 16% 4 1	1657
	11th to 20th	Day	61% 4 11% 16% 7% 1	1802
	21st to end	Day	60% 5% 10% 15% 8% 1	1570
March	1st to 10th	Day	61% 3 9% 19% 6% 1	3119
	11th to 20th	Day	62% 4 10% 13% 10% 1	3268
	21st to end	Day	49% 3 7% 21% 18% 2	4166
April	1st to 10th	Day	56% 4 7% 20% 11% 2	2280
	11th to 20th	Day	51% 4 7% 21% 15% 2	2254
	21st to end	Day	54% 4 9% 19% 11% 3	2446
May	1st to 10th	Day	55% 4 9% 21% 11% 1	4302
	11th to 20th	Day	51% 3 14% 21% 9% 1	4402
	21st to end	Day	45% 4 12% 25% 12% 1	4837
June	1st to 10th	Day	53% 5% 10% 20% 11% 1	2660
	11th to 20th	Day	44% 5% 11% 24% 14% 2	2660
	21st to end	Day	52% 5% 12% 21% 9% 1	2660
July	1st to 10th	Day	41% 6% 14% 27% 10% 1	4370
	11th to 20th	Day	39% 7% 14% 33% 6%	4365
	21st to end	Day	39% 6% 12% 32% 10%	4661
August	1st to 10th	Day	44% 6% 17% 25% 9%	2632
	11th to 20th	Day	38% 7% 17% 27% 11%	2318
	21st to end	Day	40% 5% 15% 27% 13% 1	2376
September	1st to 10th	Day	39% 5% 13% 28% 14% 1	2160
	11th to 20th	Day	38% 4 10% 34% 14%	2066
	21st to end	Day	42% 4 15% 27% 10% 1	1980
October	1st to 10th	Day	52% 6% 11% 21% 10%	1890
	11th to 20th	Day	52% 5% 16% 19% 7%	1747
	21st to end	Day	61% 4 11% 17% 7% 1	1782
November	1st to 10th	Day	52% 5% 13% 21% 7% 1	1671
	11th to 20th	Day	56% 6% 12% 15% 10% 1	1682
	21st to end	Day	62% 6% 13% 15% 5%	1520
December	1st to 10th	Day	70% 4 11% 13% 3	1520
	11th to 20th	Day	64% 4 12% 15% 5%	1906
	21st to end	Day	73% 3 10% 11% 3	2772
January	1st to 10th	Night	68% 3 14% 11% 4	4429
	11th to 20th	Night	68% 5% 11% 12% 4	4440
	21st to end	Night	68% 2 11% 13% 6% 1	4884
February	1st to 10th	Night	67% 4 8% 14% 6% 1	2519
	11th to 20th	Night	59% 4 10% 19% 8%	2274
	21st to end	Night	58% 3 9% 17% 11% 1	1884
March	1st to 10th	Night	57% 3 9% 19% 9% 3	3734
	11th to 20th	Night	62% 3 8% 15% 10% 1	3687
	21st to end	Night	51% 4 5% 22% 15% 2	3466
April	1st to 10th	Night	57% 3 7% 19% 13% 1	1900
	11th to 20th	Night	56% 4 6% 20% 13% 1	1875
	21st to end	Night	53% 4 8% 18% 14% 4	1734
May	1st to 10th	Night	57% 3 10% 19% 9% 3	2687
	11th to 20th	Night	52% 3 10% 23% 11% 2	2496
	21st to end	Night	45% 4 10% 21% 18% 2	2739
June	1st to 10th	Night	52% 4 11% 21% 10% 1	1520
	11th to 20th	Night	44% 5% 12% 21% 15% 2	1520
	21st to end	Night	49% 5% 14% 20% 12% 1	1520
July	1st to 10th	Night	46% 6% 12% 22% 13% 1	2480
	11th to 20th	Night	38% 6% 15% 32% 9%	2472
	21st to end	Night	43% 6% 14% 24% 13%	2651
August	1st to 10th	Night	40% 5% 18% 26% 11%	1502
	11th to 20th	Night	40% 6% 16% 25% 13%	1659
	21st to end	Night	41% 4 15% 27% 13% 1	1980
September	1st to 10th	Night	40% 5% 12% 29% 13% 1	1800
	11th to 20th	Night	38% 3 14% 32% 12% 1	1894
	21st to end	Night	42% 3 13% 27% 13% 1	1980
October	1st to 10th	Night	48% 5% 12% 23% 12%	2067
	11th to 20th	Night	52% 5% 10% 24% 8%	2212
	21st to end	Night	59% 4 12% 16% 9% 1	2574
November	1st to 10th	Night	53% 4 11% 22% 9% 1	2407
	11th to 20th	Night	55% 4 11% 20% 9% 1	2497
	21st to end	Night	62% 5% 12% 16% 6%	2660
December	1st to 10th	Night	71% 4 10% 13% 2	2660
	11th to 20th	Night	67% 5% 9% 15% 5%	3288
	21st to end	Night	71% 3 10% 14% 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	26% 20% 25% 21% 7% 1	180
	11th to 20th	Day	30% 23% 27% 16% 3 1	180
	21st to end	Day	21% 19% 34% 19% 7% 1	198
February	1st to 10th	Day	32% 22% 37% 8% 1	245
	11th to 20th	Day	26% 21% 37% 13% 2	401
	21st to end	Day	28% 19% 30% 19% 3	382
March	1st to 10th	Day	28% 15% 31% 20% 5%	460
	11th to 20th	Day	25% 20% 32% 17% 5% 1	460
	21st to end	Day	33% 19% 25% 16% 7%	506
April	1st to 10th	Day	31% 18% 26% 18% 7%	460
	11th to 20th	Day	28% 21% 28% 13% 7% 4	452
	21st to end	Day	28% 16% 32% 14% 9% 1	460
May	1st to 10th	Day	25% 17% 31% 16% 10% 1	463
	11th to 20th	Day	17% 16% 31% 25% 9% 1	487
	21st to end	Day	17% 14% 34% 26% 8% 2	529
June	1st to 10th	Day	24% 12% 30% 25% 8% 1	490
	11th to 20th	Day	17% 12% 30% 28% 11% 2	490
	21st to end	Day	23% 11% 32% 23% 8% 2	490
July	1st to 10th	Day	15% 5% 28% 35% 15% 3	485
	11th to 20th	Day	14% 6% 31% 31% 14% 4	484
	21st to end	Day	14% 5% 27% 36% 16% 2	532
August	1st to 10th	Day	15% 5% 28% 29% 18% 4	486
	11th to 20th	Day	13% 5% 27% 30% 18% 7%	456
	21st to end	Day	16% 11% 28% 24% 15% 7%	495
September	1st to 10th	Day	15% 8% 28% 27% 15% 7%	450
	11th to 20th	Day	16% 10% 22% 26% 16% 10%	450
	21st to end	Day	13% 13% 29% 22% 16% 7%	450
October	1st to 10th	Day	22% 13% 28% 18% 14% 5%	450
	11th to 20th	Day	24% 17% 29% 20% 8% 2	423
	21st to end	Day	35% 15% 27% 19% 4 1	396
November	1st to 10th	Day	27% 17% 29% 20% 6% 1	365
	11th to 20th	Day	24% 23% 29% 15% 7% 2	342
	21st to end	Day	29% 22% 25% 17% 6% 1	180
December	1st to 10th	Day	34% 13% 27% 19% 7% 1	180
	11th to 20th	Day	24% 24% 35% 14% 3	180
	21st to end	Day	29% 26% 28% 13% 4 1	198
January	1st to 10th	Night	26% 17% 33% 19% 4	760
	11th to 20th	Night	26% 16% 33% 21% 5%	760
	21st to end	Night	21% 14% 34% 25% 6% 1	836
February	1st to 10th	Night	25% 13% 34% 24% 4	760
	11th to 20th	Night	23% 16% 36% 22% 2	743
	21st to end	Night	26% 15% 31% 23% 4	628
March	1st to 10th	Night	27% 13% 30% 26% 4	760
	11th to 20th	Night	31% 14% 28% 21% 6%	760
	21st to end	Night	26% 16% 27% 24% 6%	836
April	1st to 10th	Night	29% 14% 26% 26% 5%	760
	11th to 20th	Night	30% 16% 25% 22% 7%	751
	21st to end	Night	26% 15% 29% 23% 7%	594
May	1st to 10th	Night	25% 10% 31% 24% 10% 1	482
	11th to 20th	Night	21% 10% 33% 26% 9% 1	374
	21st to end	Night	17% 9% 33% 32% 9%	411
June	1st to 10th	Night	27% 8% 23% 30% 11% 1	380
	11th to 20th	Night	19% 7% 28% 32% 14%	380
	21st to end	Night	21% 6% 26% 33% 14% 1	380
July	1st to 10th	Night	12% 4 31% 35% 18%	370
	11th to 20th	Night	10% 4 25% 45% 16% 1	368
	21st to end	Night	14% 3 19% 46% 17% 1	416
August	1st to 10th	Night	15% 4 16% 45% 19% 1	378
	11th to 20th	Night	15% 4 21% 35% 24% 2	565
	21st to end	Night	17% 5% 22% 36% 19% 2	792
September	1st to 10th	Night	15% 7% 25% 35% 16% 2	720
	11th to 20th	Night	18% 7% 19% 33% 20% 3	720
	21st to end	Night	19% 8% 28% 25% 17% 3	720
October	1st to 10th	Night	22% 11% 26% 26% 14% 1	720
	11th to 20th	Night	23% 12% 31% 25% 8% 1	720
	21st to end	Night	29% 10% 32% 22% 6%	792
November	1st to 10th	Night	25% 14% 32% 21% 7% 1	740
	11th to 20th	Night	24% 17% 31% 19% 8% 1	760
	21st to end	Night	29% 17% 30% 17% 6% 1	760
December	1st to 10th	Night	31% 16% 29% 19% 4	760
	11th to 20th	Night	31% 15% 30% 18% 5% 1	760
	21st to end	Night	32% 16% 32% 17% 3	836

Page generated at 2024-08-12 09:52:51. Version ac07

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