Observatoires de Cantley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoires de Cantley clear sky chart from 2005-11-06 to 2024-11-05.

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% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	101576
	Night	18% 11% 3 8% 5% 4 4 3 5% 6% 32%	97468
Transparency	Day	50% 7% 12% 21% 10% 1	105059
	Night	52% 6% 12% 20% 10% 1	102074
Seeing	Day	22% 15% 29% 22% 10% 3	14467
	Night	23% 11% 29% 27% 10% 1	23522

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% 16% 7% 12% 5% 5% 5% 3 5% 4 21%	2517
	11th to 20th	Day	15% 13% 5% 15% 6% 5% 5% 4 4 6% 22%	2520
	21st to end	Day	14% 18% 6% 12% 6% 6% 5% 4 5% 4 19%	2872
February	1st to 10th	Day	13% 16% 4 13% 7% 5% 4 4 5% 6% 24%	1710
	11th to 20th	Day	13% 15% 5% 10% 6% 5% 4 3 5% 5% 28%	1667
	21st to end	Day	18% 13% 4 11% 6% 5% 4 4 5% 5% 25%	1570
March	1st to 10th	Day	22% 14% 4 8% 6% 5% 4 3 5% 5% 26%	3116
	11th to 20th	Day	13% 15% 5% 10% 6% 5% 6% 3 5% 5% 28%	3471
	21st to end	Day	14% 7% 3 7% 6% 4 4 3 5% 5% 40%	4031
April	1st to 10th	Day	22% 11% 3 7% 5% 4 4 3 4 5% 32%	2280
	11th to 20th	Day	22% 9% 3 7% 4 4 3 3 4 5% 36%	2254
	21st to end	Day	23% 9% 4 7% 5% 5% 4 3 4 4 31%	2424
May	1st to 10th	Day	21% 9% 3 7% 5% 4 5% 4 6% 7% 30%	4426
	11th to 20th	Day	19% 8% 3 7% 6% 4 5% 3 5% 7% 34%	4398
	21st to end	Day	16% 7% 3 7% 5% 4 5% 4 6% 7% 37%	4837
June	1st to 10th	Day	22% 7% 2 7% 5% 5% 4 4 6% 6% 30%	2660
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 7% 8% 38%	2660
	21st to end	Day	21% 6% 2 6% 5% 5% 6% 5% 7% 6% 32%	2660
July	1st to 10th	Day	13% 6% 3 8% 5% 5% 5% 5% 7% 9% 35%	4440
	11th to 20th	Day	15% 5% 2 6% 4 5% 5% 4 6% 8% 41%	4440
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 6% 9% 46%	4814
August	1st to 10th	Day	14% 5% 3 8% 5% 5% 5% 4 6% 8% 37%	4371
	11th to 20th	Day	17% 5% 2 5% 4 4 5% 5% 7% 8% 39%	3993
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 6% 9% 41%	4180
September	1st to 10th	Day	15% 5% 2 6% 4 4 5% 3 5% 8% 43%	2280
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 5% 7% 48%	2280
	21st to end	Day	19% 5% 2 5% 4 4 4 3 5% 8% 40%	2028
October	1st to 10th	Day	22% 7% 3 7% 3 4 4 4 5% 6% 35%	1900
	11th to 20th	Day	24% 8% 2 7% 5% 5% 5% 4 5% 6% 29%	1900
	21st to end	Day	25% 10% 3 6% 5% 5% 5% 3 4 5% 29%	1929
November	1st to 10th	Day	15% 9% 3 7% 5% 5% 4 5% 5% 7% 35%	1708
	11th to 20th	Day	20% 12% 4 8% 4 5% 5% 4 5% 6% 27%	1522
	21st to end	Day	22% 15% 3 8% 6% 5% 5% 4 5% 6% 21%	1520
December	1st to 10th	Day	22% 17% 6% 10% 5% 4 5% 3 5% 5% 18%	1520
	11th to 20th	Day	21% 14% 3 10% 6% 5% 4 4 4 4 26%	1906
	21st to end	Day	28% 20% 5% 8% 4 3 4 3 3 3 19%	2772
January	1st to 10th	Night	17% 18% 6% 12% 5% 5% 3 3 4 5% 21%	4429
	11th to 20th	Night	13% 14% 5% 13% 7% 6% 5% 3 5% 5% 24%	4440
	21st to end	Night	17% 20% 6% 10% 6% 6% 4 3 4 4 21%	4781
February	1st to 10th	Night	14% 14% 5% 12% 6% 5% 5% 4 5% 5% 25%	2470
	11th to 20th	Night	13% 14% 5% 11% 6% 5% 4 4 4 5% 29%	2399
	21st to end	Night	17% 13% 4 9% 5% 4 4 4 5% 5% 30%	1884
March	1st to 10th	Night	22% 12% 4 8% 5% 4 4 3 3 4 31%	3724
	11th to 20th	Night	16% 17% 5% 11% 5% 4 4 3 5% 5% 26%	3484
	21st to end	Night	16% 9% 3 8% 4 4 3 3 4 6% 40%	3600
April	1st to 10th	Night	21% 10% 3 7% 5% 3 4 3 5% 6% 33%	1900
	11th to 20th	Night	20% 8% 3 6% 5% 4 4 4 5% 5% 36%	1875
	21st to end	Night	22% 9% 3 6% 4 4 3 3 5% 6% 35%	1771
May	1st to 10th	Night	21% 8% 3 9% 5% 4 4 4 5% 7% 30%	2514
	11th to 20th	Night	22% 7% 3 7% 4 4 4 4 5% 6% 36%	2495
	21st to end	Night	16% 6% 3 7% 5% 4 5% 5% 5% 6% 39%	2738
June	1st to 10th	Night	17% 6% 2 6% 5% 5% 5% 5% 6% 8% 34%	1520
	11th to 20th	Night	15% 5% 3 6% 4 4 4 4 6% 7% 43%	1520
	21st to end	Night	19% 7% 2 5% 5% 6% 4 4 6% 7% 36%	1520
July	1st to 10th	Night	14% 6% 3 7% 5% 6% 5% 5% 6% 7% 36%	2520
	11th to 20th	Night	15% 7% 2 5% 4 4 5% 4 6% 6% 43%	2520
	21st to end	Night	11% 5% 2 6% 5% 4 5% 4 7% 7% 44%	2739
August	1st to 10th	Night	14% 6% 3 7% 4 4 6% 4 6% 8% 39%	2555
	11th to 20th	Night	16% 5% 2 6% 4 4 4 4 5% 7% 43%	2803
	21st to end	Night	15% 5% 2 7% 5% 5% 4 4 6% 7% 42%	3476
September	1st to 10th	Night	12% 5% 2 6% 5% 4 4 4 5% 7% 47%	1900
	11th to 20th	Night	15% 5% 1 4 4 3 3 3 5% 6% 50%	1900
	21st to end	Night	18% 6% 2 6% 5% 3 4 3 4 6% 45%	2147
October	1st to 10th	Night	19% 7% 2 5% 4 4 5% 4 4 6% 40%	2280
	11th to 20th	Night	22% 7% 2 7% 6% 5% 5% 3 5% 6% 33%	2280
	21st to end	Night	23% 10% 3 7% 5% 4 4 4 4 6% 30%	2667
November	1st to 10th	Night	20% 9% 3 6% 4 4 3 4 6% 6% 35%	2470
	11th to 20th	Night	19% 11% 3 9% 5% 4 5% 3 5% 6% 30%	2655
	21st to end	Night	22% 12% 4 9% 5% 5% 4 3 5% 6% 25%	2660
December	1st to 10th	Night	21% 17% 5% 9% 6% 5% 5% 4 5% 6% 19%	2660
	11th to 20th	Night	22% 14% 4 9% 5% 4 4 2 4 4 28%	3288
	21st to end	Night	30% 18% 4 9% 4 3 3 3 4 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	66% 8% 10% 10% 5% 1	2518
	11th to 20th	Day	63% 6% 12% 13% 6%	2520
	21st to end	Day	67% 8% 10% 10% 5%	2872
February	1st to 10th	Day	61% 5% 10% 18% 5% 2	1710
	11th to 20th	Day	58% 4 12% 15% 9% 1	1676
	21st to end	Day	59% 6% 11% 13% 10% 2	1570
March	1st to 10th	Day	60% 6% 9% 16% 9% 1	3119
	11th to 20th	Day	57% 6% 12% 14% 10% 2	3471
	21st to end	Day	45% 5% 7% 23% 17% 3	4031
April	1st to 10th	Day	55% 4 8% 18% 12% 3	2280
	11th to 20th	Day	51% 4 7% 21% 15% 2	2254
	21st to end	Day	56% 4 8% 15% 13% 4	2424
May	1st to 10th	Day	51% 7% 8% 22% 10% 2	4440
	11th to 20th	Day	48% 8% 14% 19% 9% 2	4402
	21st to end	Day	45% 7% 11% 21% 14% 2	4837
June	1st to 10th	Day	53% 6% 11% 18% 11% 1	2660
	11th to 20th	Day	42% 8% 12% 23% 12% 2	2660
	21st to end	Day	49% 9% 13% 20% 10% 1	2660
July	1st to 10th	Day	43% 7% 14% 24% 11%	4370
	11th to 20th	Day	40% 7% 15% 30% 8%	4365
	21st to end	Day	35% 8% 15% 31% 12%	4661
August	1st to 10th	Day	45% 7% 16% 23% 9%	4357
	11th to 20th	Day	41% 8% 15% 28% 8%	4032
	21st to end	Day	39% 6% 17% 25% 12% 1	4180
September	1st to 10th	Day	39% 7% 14% 28% 12%	2280
	11th to 20th	Day	36% 6% 14% 31% 12% 1	2280
	21st to end	Day	42% 7% 14% 26% 10%	2028
October	1st to 10th	Day	47% 7% 12% 28% 7%	3160
	11th to 20th	Day	46% 7% 15% 24% 7%	3140
	21st to end	Day	49% 5% 19% 20% 7%	3154
November	1st to 10th	Day	48% 7% 14% 23% 7% 1	1708
	11th to 20th	Day	57% 6% 13% 15% 8% 1	1522
	21st to end	Day	63% 8% 12% 10% 6% 1	1520
December	1st to 10th	Day	67% 7% 12% 11% 3	1520
	11th to 20th	Day	64% 5% 12% 14% 5%	1906
	21st to end	Day	71% 5% 7% 14% 3	2772
January	1st to 10th	Night	65% 6% 14% 11% 3	4429
	11th to 20th	Night	61% 8% 14% 13% 5%	4440
	21st to end	Night	67% 6% 10% 10% 6% 1	4781
February	1st to 10th	Night	61% 5% 10% 16% 7% 1	2470
	11th to 20th	Night	58% 5% 10% 19% 8% 1	2401
	21st to end	Night	56% 6% 9% 18% 11% 1	1884
March	1st to 10th	Night	57% 5% 9% 18% 9% 2	3734
	11th to 20th	Night	60% 6% 11% 14% 8% 2	3485
	21st to end	Night	46% 5% 7% 22% 17% 3	3600
April	1st to 10th	Night	53% 5% 10% 17% 14% 2	1900
	11th to 20th	Night	49% 6% 7% 20% 16% 1	1875
	21st to end	Night	51% 5% 8% 16% 16% 3	1771
May	1st to 10th	Night	52% 9% 8% 19% 9% 3	2520
	11th to 20th	Night	47% 9% 10% 20% 12% 2	2496
	21st to end	Night	43% 7% 12% 19% 17% 2	2739
June	1st to 10th	Night	46% 7% 12% 24% 10% 1	1520
	11th to 20th	Night	40% 8% 11% 24% 16% 2	1520
	21st to end	Night	46% 9% 12% 19% 14% 1	1520
July	1st to 10th	Night	45% 9% 14% 19% 13% 1	2480
	11th to 20th	Night	40% 7% 13% 32% 9%	2472
	21st to end	Night	37% 8% 15% 26% 14%	2651
August	1st to 10th	Night	41% 9% 15% 25% 10%	2545
	11th to 20th	Night	40% 7% 14% 31% 8%	2830
	21st to end	Night	41% 8% 15% 23% 13% 2	3476
September	1st to 10th	Night	36% 8% 11% 30% 15% 1	1900
	11th to 20th	Night	35% 8% 12% 34% 10% 1	1900
	21st to end	Night	42% 5% 12% 30% 11%	2147
October	1st to 10th	Night	39% 8% 13% 28% 11%	3800
	11th to 20th	Night	43% 7% 14% 27% 8%	3779
	21st to end	Night	46% 6% 18% 20% 9%	4392
November	1st to 10th	Night	50% 6% 15% 20% 9%	2470
	11th to 20th	Night	56% 6% 12% 16% 9% 1	2655
	21st to end	Night	61% 6% 13% 15% 5%	2660
December	1st to 10th	Night	67% 6% 10% 12% 4	2660
	11th to 20th	Night	61% 5% 9% 17% 8% 1	3288
	21st to end	Night	71% 5% 8% 13% 4	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% 16% 31% 24% 3 1	180
	11th to 20th	Day	25% 17% 38% 14% 6% 1	180
	21st to end	Day	22% 15% 37% 20% 5%	227
February	1st to 10th	Day	31% 22% 32% 12% 3	270
	11th to 20th	Day	26% 27% 33% 13% 1	274
	21st to end	Day	29% 20% 32% 17% 3	382
March	1st to 10th	Day	24% 17% 34% 19% 6%	460
	11th to 20th	Day	25% 19% 32% 20% 3 1	460
	21st to end	Day	28% 21% 28% 14% 7% 1	506
April	1st to 10th	Day	27% 22% 30% 15% 6%	460
	11th to 20th	Day	31% 20% 23% 16% 9% 1	452
	21st to end	Day	29% 20% 30% 13% 6% 2	460
May	1st to 10th	Day	24% 15% 30% 20% 8% 2	463
	11th to 20th	Day	20% 17% 30% 21% 11% 3	487
	21st to end	Day	19% 15% 30% 24% 10% 2	529
June	1st to 10th	Day	25% 11% 29% 25% 9% 2	490
	11th to 20th	Day	16% 15% 29% 26% 13% 2	490
	21st to end	Day	23% 13% 28% 22% 12% 2	490
July	1st to 10th	Day	12% 8% 27% 35% 13% 4	485
	11th to 20th	Day	13% 8% 32% 28% 16% 3	484
	21st to end	Day	12% 8% 29% 33% 15% 4	532
August	1st to 10th	Day	14% 8% 25% 32% 17% 4	486
	11th to 20th	Day	14% 9% 22% 29% 19% 8%	479
	21st to end	Day	14% 10% 27% 26% 16% 7%	539
September	1st to 10th	Day	16% 10% 28% 22% 15% 8%	490
	11th to 20th	Day	12% 9% 23% 22% 21% 13%	490
	21st to end	Day	20% 12% 26% 23% 14% 5%	490
October	1st to 10th	Day	24% 12% 26% 21% 12% 4	490
	11th to 20th	Day	27% 15% 30% 18% 8% 1	490
	21st to end	Day	29% 14% 27% 24% 5%	454
November	1st to 10th	Day	25% 17% 28% 20% 9% 1	378
	11th to 20th	Day	26% 20% 35% 13% 4 1	182
	21st to end	Day	29% 19% 29% 17% 4 2	180
December	1st to 10th	Day	28% 14% 36% 19% 3	180
	11th to 20th	Day	26% 24% 33% 16% 1 1	180
	21st to end	Day	32% 20% 32% 13% 2 1	198
January	1st to 10th	Night	28% 13% 34% 22% 4	760
	11th to 20th	Night	28% 15% 29% 22% 6%	760
	21st to end	Night	20% 10% 36% 28% 6% 1	836
February	1st to 10th	Night	22% 14% 34% 26% 3	760
	11th to 20th	Night	20% 17% 36% 22% 4	743
	21st to end	Night	24% 15% 30% 28% 3	628
March	1st to 10th	Night	25% 15% 33% 24% 4	760
	11th to 20th	Night	24% 17% 33% 22% 5%	760
	21st to end	Night	23% 15% 30% 24% 8%	836
April	1st to 10th	Night	28% 13% 30% 24% 5%	760
	11th to 20th	Night	23% 16% 31% 21% 8%	751
	21st to end	Night	27% 11% 28% 25% 8% 1	631
May	1st to 10th	Night	24% 7% 28% 29% 9% 2	380
	11th to 20th	Night	23% 10% 25% 33% 9% 1	374
	21st to end	Night	15% 7% 39% 27% 10%	411
June	1st to 10th	Night	19% 5% 29% 37% 11%	380
	11th to 20th	Night	16% 6% 27% 35% 14% 2	380
	21st to end	Night	20% 7% 26% 32% 15% 1	380
July	1st to 10th	Night	10% 4 28% 43% 16%	370
	11th to 20th	Night	12% 3 23% 44% 18% 1	368
	21st to end	Night	10% 3 26% 42% 18% 2	416
August	1st to 10th	Night	12% 4 21% 40% 23%	401
	11th to 20th	Night	14% 3 19% 36% 25% 3	569
	21st to end	Night	14% 7% 22% 36% 20% 2	836
September	1st to 10th	Night	14% 6% 27% 33% 19% 1	760
	11th to 20th	Night	17% 6% 19% 30% 24% 4	760
	21st to end	Night	21% 8% 23% 26% 20% 2	760
October	1st to 10th	Night	23% 8% 27% 24% 17% 2	760
	11th to 20th	Night	24% 11% 29% 25% 9% 1	760
	21st to end	Night	28% 12% 28% 27% 6%	836
November	1st to 10th	Night	26% 12% 25% 28% 8% 1	760
	11th to 20th	Night	25% 15% 33% 17% 9% 1	760
	21st to end	Night	29% 15% 28% 23% 6%	760
December	1st to 10th	Night	30% 14% 30% 22% 3	760
	11th to 20th	Night	28% 14% 31% 20% 5% 1	760
	21st to end	Night	34% 13% 30% 19% 4	836

Page generated at 2024-11-03 02:11:29. Version ac07

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