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 2025-01-07.

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%	105114
	Night	18% 12% 4 9% 5% 5% 4 3 5% 5% 29%	103939
Transparency	Day	51% 5% 12% 22% 9% 1	108601
	Night	55% 4 11% 19% 10% 1	108541
Seeing	Day	22% 14% 29% 22% 10% 3	14784
	Night	24% 12% 29% 26% 9% 1	23828

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%	2565
	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	15% 7% 3 8% 5% 5% 6% 5% 7% 9% 31%	4423
	11th to 20th	Day	14% 6% 2 7% 4 5% 5% 4 7% 8% 38%	3960
	21st to end	Day	14% 6% 2 6% 4 4 4 3 6% 9% 41%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 6% 7% 44%	2280
	11th to 20th	Day	15% 5% 2 5% 4 3 4 3 4 7% 47%	2180
	21st to end	Day	15% 5% 3 6% 5% 4 5% 4 5% 8% 40%	2090
October	1st to 10th	Day	21% 7% 3 7% 4 5% 5% 4 5% 7% 31%	1995
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 5% 7% 6% 31%	1844
	21st to end	Day	24% 12% 3 8% 5% 5% 4 2 4 5% 29%	1881
November	1st to 10th	Day	18% 12% 3 7% 4 5% 4 4 6% 5% 32%	1761
	11th to 20th	Day	18% 12% 3 8% 6% 5% 4 4 5% 7% 28%	1770
	21st to end	Day	21% 15% 4 8% 6% 5% 5% 4 6% 6% 21%	1600
December	1st to 10th	Day	18% 19% 6% 14% 6% 5% 4 3 4 4 16%	2600
	11th to 20th	Day	20% 13% 5% 10% 5% 5% 4 3 5% 6% 23%	2986
	21st to end	Day	22% 15% 5% 12% 6% 6% 4 5% 4 5% 17%	3960
January	1st to 10th	Night	17% 20% 7% 12% 5% 4 4 3 4 5% 20%	4514
	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	17% 8% 4 7% 5% 4 4 4 5% 7% 35%	2506
	11th to 20th	Night	15% 7% 3 7% 5% 5% 5% 3 6% 7% 37%	2832
	21st to end	Night	16% 6% 2 6% 4 4 4 4 5% 7% 42%	3476
September	1st to 10th	Night	13% 5% 2 7% 4 4 4 3 5% 8% 44%	1900
	11th to 20th	Night	14% 6% 2 5% 4 4 3 3 5% 6% 48%	2000
	21st to end	Night	18% 6% 2 5% 4 4 4 3 5% 5% 43%	2090
October	1st to 10th	Night	19% 7% 3 8% 4 4 4 4 5% 6% 36%	2182
	11th to 20th	Night	21% 9% 3 7% 5% 4 5% 3 5% 5% 32%	2335
	21st to end	Night	25% 9% 3 8% 5% 5% 4 3 5% 5% 28%	2717
November	1st to 10th	Night	20% 11% 3 7% 4 5% 4 3 5% 6% 31%	2537
	11th to 20th	Night	18% 11% 3 9% 5% 4 4 4 4 5% 32%	2629
	21st to end	Night	22% 14% 4 9% 5% 4 5% 4 5% 5% 24%	2800
December	1st to 10th	Night	18% 23% 6% 12% 6% 6% 5% 3 4 4 14%	4580
	11th to 20th	Night	23% 14% 5% 10% 6% 4 5% 3 5% 4 21%	5208
	21st to end	Night	23% 15% 5% 10% 5% 4 4 4 6% 4 18%	6996

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	2566
	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	48% 6% 16% 22% 8%	4409
	11th to 20th	Day	41% 7% 18% 28% 6%	4000
	21st to end	Day	40% 5% 18% 22% 15%	4180
September	1st to 10th	Day	38% 5% 13% 29% 14% 1	2280
	11th to 20th	Day	37% 4 11% 34% 14%	2180
	21st to end	Day	42% 4 15% 27% 10% 1	2090
October	1st to 10th	Day	43% 5% 14% 30% 8%	3320
	11th to 20th	Day	43% 5% 19% 26% 7%	3047
	21st to end	Day	47% 3 18% 24% 7%	3081
November	1st to 10th	Day	52% 5% 13% 22% 8% 1	1761
	11th to 20th	Day	55% 6% 12% 17% 11% 1	1770
	21st to end	Day	62% 6% 13% 14% 5%	1600
December	1st to 10th	Day	70% 5% 10% 13% 2	2600
	11th to 20th	Day	61% 4 12% 16% 7% 1	2986
	21st to end	Day	69% 4 10% 12% 5%	3960
January	1st to 10th	Night	68% 3 14% 11% 4	4514
	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	48% 5% 13% 25% 9%	2496
	11th to 20th	Night	45% 6% 18% 21% 9%	2858
	21st to end	Night	41% 4 14% 24% 15% 1	3476
September	1st to 10th	Night	39% 5% 12% 29% 14% 1	1900
	11th to 20th	Night	37% 3 14% 32% 13% 1	2000
	21st to end	Night	42% 3 13% 26% 14% 1	2090
October	1st to 10th	Night	47% 4 12% 27% 10%	3637
	11th to 20th	Night	46% 4 10% 29% 11%	3871
	21st to end	Night	50% 3 14% 21% 11% 1	4467
November	1st to 10th	Night	53% 4 11% 22% 8% 1	2537
	11th to 20th	Night	54% 4 11% 20% 10% 1	2629
	21st to end	Night	62% 5% 12% 16% 6%	2800
December	1st to 10th	Night	74% 5% 10% 9% 2	4580
	11th to 20th	Night	64% 5% 9% 13% 9%	5208
	21st to end	Night	67% 3 9% 13% 8%	6996

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% 19% 29% 20% 6% 1	192
	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	14% 5% 28% 29% 18% 6%	479
	21st to end	Day	16% 10% 27% 25% 16% 7%	539
September	1st to 10th	Day	14% 9% 29% 27% 14% 7%	490
	11th to 20th	Day	15% 9% 20% 24% 19% 13%	490
	21st to end	Day	14% 12% 28% 23% 17% 7%	490
October	1st to 10th	Day	20% 13% 28% 20% 14% 5%	490
	11th to 20th	Day	24% 17% 29% 20% 8% 2	460
	21st to end	Day	32% 16% 27% 20% 5% 1	429
November	1st to 10th	Day	28% 17% 30% 20% 6% 1	395
	11th to 20th	Day	24% 22% 29% 16% 7% 2	370
	21st to end	Day	32% 21% 26% 17% 6% 1	200
December	1st to 10th	Day	33% 14% 28% 19% 8% 1	200
	11th to 20th	Day	24% 24% 36% 14% 3	200
	21st to end	Day	27% 24% 29% 14% 5% 2	220
January	1st to 10th	Night	26% 17% 33% 19% 4	785
	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 22% 35% 23% 2	584
	21st to end	Night	17% 5% 22% 35% 19% 2	836
September	1st to 10th	Night	15% 7% 26% 35% 16% 1	760
	11th to 20th	Night	17% 7% 19% 32% 23% 4	760
	21st to end	Night	19% 7% 28% 25% 18% 3	760
October	1st to 10th	Night	21% 10% 26% 26% 15% 2	760
	11th to 20th	Night	24% 12% 30% 26% 8% 1	760
	21st to end	Night	28% 10% 32% 23% 6%	836
November	1st to 10th	Night	25% 15% 32% 21% 6% 1	780
	11th to 20th	Night	24% 17% 30% 19% 9% 1	800
	21st to end	Night	29% 17% 30% 18% 6% 1	800
December	1st to 10th	Night	31% 16% 29% 20% 4	800
	11th to 20th	Night	31% 15% 30% 18% 5% 1	800
	21st to end	Night	32% 16% 31% 18% 4	880

Page generated at 2025-01-04 03:23:57. Version ac07

Copyright © 2025 Attilla Danko.