Observatoire de Val-Des-Bois
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Val-Des-Bois clear sky chart from 2005-11-06 to 2024-11-04.

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% 11% 4 9% 5% 5% 4 3 5% 7% 30%	101574
	Night	16% 13% 4 9% 5% 4 4 3 5% 5% 30%	97452
Transparency	Day	54% 3 11% 22% 9% 1	105044
	Night	55% 3 11% 20% 9% 1	102058
Seeing	Day	26% 16% 30% 19% 7% 2	14445
	Night	24% 13% 28% 25% 9% 1	23481

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	16% 18% 8% 15% 8% 5% 3 2 3 3 18%	2517
	11th to 20th	Day	13% 15% 7% 18% 7% 5% 4 3 4 5% 19%	2520
	21st to end	Day	12% 18% 8% 15% 7% 6% 5% 3 4 4 18%	2840
February	1st to 10th	Day	12% 18% 6% 14% 6% 5% 4 3 5% 5% 21%	1710
	11th to 20th	Day	11% 19% 6% 12% 6% 5% 3 3 3 5% 26%	1667
	21st to end	Day	17% 16% 6% 10% 7% 5% 4 3 4 5% 25%	1570
March	1st to 10th	Day	18% 16% 5% 10% 6% 5% 4 3 4 5% 25%	3116
	11th to 20th	Day	11% 19% 7% 11% 6% 5% 4 2 4 5% 25%	3464
	21st to end	Day	12% 9% 3 7% 7% 5% 4 3 5% 7% 37%	4038
April	1st to 10th	Day	22% 15% 3 7% 5% 4 3 3 4 6% 29%	2280
	11th to 20th	Day	22% 11% 4 8% 3 3 3 3 5% 5% 33%	2254
	21st to end	Day	21% 12% 4 8% 5% 3 4 4 3 5% 30%	2440
May	1st to 10th	Day	20% 11% 3 8% 5% 4 4 4 5% 7% 28%	4426
	11th to 20th	Day	17% 9% 3 8% 6% 4 5% 4 6% 7% 32%	4398
	21st to end	Day	17% 8% 3 8% 4 5% 4 4 5% 7% 35%	4837
June	1st to 10th	Day	22% 9% 3 8% 5% 5% 5% 3 5% 6% 29%	2660
	11th to 20th	Day	15% 6% 3 6% 5% 5% 5% 4 7% 8% 37%	2660
	21st to end	Day	20% 8% 2 7% 5% 4 5% 4 7% 8% 30%	2660
July	1st to 10th	Day	13% 7% 2 8% 5% 6% 6% 5% 7% 8% 33%	4440
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 4 7% 8% 36%	4440
	21st to end	Day	12% 7% 2 5% 4 4 4 4 5% 8% 45%	4814
August	1st to 10th	Day	15% 6% 3 8% 6% 5% 5% 4 6% 9% 32%	4404
	11th to 20th	Day	17% 7% 3 6% 4 4 4 4 6% 8% 36%	3994
	21st to end	Day	14% 6% 2 6% 4 4 5% 3 7% 9% 39%	4180
September	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 5% 8% 41%	2280
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 8% 43%	2275
	21st to end	Day	21% 7% 2 6% 4 3 4 4 5% 8% 38%	2037
October	1st to 10th	Day	20% 10% 3 7% 4 5% 5% 3 5% 6% 32%	1900
	11th to 20th	Day	25% 12% 3 8% 5% 5% 4 3 4 6% 25%	1900
	21st to end	Day	25% 14% 3 8% 4 4 4 4 5% 6% 24%	1918
November	1st to 10th	Day	15% 14% 4 7% 4 3 4 4 5% 7% 33%	1697
	11th to 20th	Day	19% 17% 5% 10% 5% 6% 5% 4 4 5% 21%	1520
	21st to end	Day	20% 18% 6% 12% 6% 4 5% 3 4 5% 18%	1520
December	1st to 10th	Day	21% 21% 6% 11% 7% 5% 4 3 3 5% 14%	1520
	11th to 20th	Day	18% 17% 7% 13% 6% 4 4 4 5% 5% 19%	1906
	21st to end	Day	23% 21% 6% 12% 6% 4 3 2 2 3 18%	2772
January	1st to 10th	Night	15% 19% 8% 12% 6% 5% 3 3 4 5% 20%	4429
	11th to 20th	Night	12% 15% 6% 15% 8% 6% 5% 3 4 5% 21%	4440
	21st to end	Night	13% 18% 9% 15% 6% 7% 4 3 4 4 19%	4812
February	1st to 10th	Night	12% 16% 6% 13% 8% 5% 5% 4 5% 5% 22%	2470
	11th to 20th	Night	12% 16% 6% 12% 7% 6% 4 3 4 4 26%	2399
	21st to end	Night	13% 17% 5% 10% 5% 5% 4 4 4 6% 26%	1884
March	1st to 10th	Night	19% 14% 4 8% 5% 4 4 3 4 5% 31%	3724
	11th to 20th	Night	15% 19% 6% 10% 4 4 3 4 5% 5% 25%	3493
	21st to end	Night	13% 11% 4 9% 6% 4 4 3 4 5% 38%	3594
April	1st to 10th	Night	20% 14% 3 6% 5% 4 4 3 5% 6% 30%	1900
	11th to 20th	Night	19% 9% 3 7% 5% 4 4 4 5% 5% 36%	1875
	21st to end	Night	19% 12% 4 9% 3 3 4 3 4 5% 33%	1754
May	1st to 10th	Night	19% 10% 4 8% 6% 4 4 4 5% 6% 29%	2514
	11th to 20th	Night	18% 9% 2 7% 4 5% 5% 3 5% 6% 36%	2495
	21st to end	Night	17% 7% 3 8% 4 5% 5% 4 5% 6% 37%	2738
June	1st to 10th	Night	17% 9% 2 6% 4 4 5% 5% 6% 9% 32%	1520
	11th to 20th	Night	15% 7% 2 7% 5% 4 4 4 5% 7% 41%	1520
	21st to end	Night	19% 7% 2 6% 5% 5% 5% 4 6% 8% 34%	1520
July	1st to 10th	Night	13% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	2520
	11th to 20th	Night	14% 7% 2 7% 4 4 4 4 5% 7% 41%	2520
	21st to end	Night	10% 6% 1 5% 5% 4 5% 4 6% 8% 47%	2739
August	1st to 10th	Night	11% 7% 4 8% 5% 5% 5% 4 6% 7% 38%	2523
	11th to 20th	Night	15% 7% 3 7% 4 3 4 4 5% 6% 41%	2803
	21st to end	Night	17% 6% 3 6% 4 4 4 3 5% 7% 40%	3476
September	1st to 10th	Night	14% 6% 2 7% 5% 3 4 4 5% 5% 45%	1900
	11th to 20th	Night	15% 6% 2 5% 4 4 2 3 5% 7% 48%	1905
	21st to end	Night	17% 7% 2 7% 4 3 3 3 5% 5% 43%	2141
October	1st to 10th	Night	19% 9% 2 7% 4 4 4 3 4 7% 37%	2280
	11th to 20th	Night	20% 13% 3 7% 5% 5% 4 3 4 6% 30%	2280
	21st to end	Night	23% 13% 3 9% 5% 4 4 3 5% 5% 27%	2679
November	1st to 10th	Night	18% 13% 5% 7% 5% 3 4 4 5% 6% 30%	2453
	11th to 20th	Night	18% 14% 4 12% 5% 5% 4 3 4 5% 26%	2660
	21st to end	Night	21% 17% 5% 11% 5% 6% 4 3 4 4 20%	2660
December	1st to 10th	Night	19% 21% 6% 11% 6% 5% 3 3 4 5% 17%	2660
	11th to 20th	Night	21% 17% 6% 10% 5% 4 3 3 4 4 23%	3288
	21st to end	Night	24% 22% 5% 12% 5% 3 4 2 3 3 17%	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	72% 3 8% 12% 5%	2518
	11th to 20th	Day	69% 2 8% 14% 7%	2520
	21st to end	Day	71% 2 9% 12% 6% 1	2840
February	1st to 10th	Day	65% 2 7% 17% 7% 1	1710
	11th to 20th	Day	63% 2 10% 14% 10% 1	1676
	21st to end	Day	63% 3 9% 14% 11% 1	1570
March	1st to 10th	Day	64% 1 8% 15% 11% 1	3119
	11th to 20th	Day	63% 2 9% 14% 10% 2	3464
	21st to end	Day	48% 2 6% 24% 18% 2	4038
April	1st to 10th	Day	58% 2 6% 18% 12% 3	2280
	11th to 20th	Day	54% 2 6% 22% 14% 2	2254
	21st to end	Day	59% 2 6% 16% 13% 3	2440
May	1st to 10th	Day	57% 2 6% 24% 10% 2	4440
	11th to 20th	Day	53% 2 12% 22% 9% 2	4402
	21st to end	Day	49% 3 11% 22% 15% 1	4837
June	1st to 10th	Day	55% 4 9% 20% 11% 1	2660
	11th to 20th	Day	45% 3 12% 27% 12% 2	2660
	21st to end	Day	52% 4 13% 20% 10%	2660
July	1st to 10th	Day	45% 5% 13% 28% 8%	4370
	11th to 20th	Day	44% 5% 15% 28% 8%	4365
	21st to end	Day	38% 4 14% 34% 10%	4661
August	1st to 10th	Day	48% 5% 16% 24% 7%	4390
	11th to 20th	Day	45% 4 15% 28% 7%	4033
	21st to end	Day	41% 4 17% 26% 12% 1	4180
September	1st to 10th	Day	42% 3 13% 29% 12%	2280
	11th to 20th	Day	40% 3 13% 32% 12% 1	2275
	21st to end	Day	45% 4 14% 27% 10%	2037
October	1st to 10th	Day	52% 3 10% 29% 6%	3160
	11th to 20th	Day	53% 5% 11% 22% 8%	3140
	21st to end	Day	54% 4 19% 17% 6%	3130
November	1st to 10th	Day	50% 4 14% 24% 7% 1	1697
	11th to 20th	Day	65% 4 11% 13% 7% 1	1520
	21st to end	Day	69% 3 12% 9% 6% 1	1520
December	1st to 10th	Day	73% 3 10% 10% 4	1520
	11th to 20th	Day	68% 3 10% 14% 6%	1906
	21st to end	Day	74% 2 5% 15% 5%	2772
January	1st to 10th	Night	68% 2 15% 12% 3	4429
	11th to 20th	Night	67% 2 12% 14% 5%	4440
	21st to end	Night	71% 2 9% 10% 7%	4812
February	1st to 10th	Night	63% 3 8% 17% 7% 1	2470
	11th to 20th	Night	61% 2 8% 19% 9% 1	2401
	21st to end	Night	59% 2 8% 18% 11% 1	1884
March	1st to 10th	Night	59% 2 9% 17% 11% 2	3734
	11th to 20th	Night	62% 2 10% 16% 8% 2	3494
	21st to end	Night	50% 3 6% 22% 17% 4	3594
April	1st to 10th	Night	56% 2 8% 18% 14% 2	1900
	11th to 20th	Night	51% 2 6% 24% 15% 1	1875
	21st to end	Night	53% 3 7% 19% 15% 3	1754
May	1st to 10th	Night	57% 1 8% 22% 9% 2	2520
	11th to 20th	Night	50% 2 10% 24% 11% 2	2496
	21st to end	Night	49% 2 10% 22% 15% 2	2739
June	1st to 10th	Night	47% 4 12% 25% 10% 1	1520
	11th to 20th	Night	43% 4 11% 28% 13% 2	1520
	21st to end	Night	47% 6% 12% 22% 12% 1	1520
July	1st to 10th	Night	46% 5% 17% 21% 11% 1	2480
	11th to 20th	Night	42% 5% 16% 30% 8%	2472
	21st to end	Night	35% 5% 16% 31% 13%	2651
August	1st to 10th	Night	44% 5% 16% 27% 9%	2513
	11th to 20th	Night	43% 4 16% 30% 7%	2830
	21st to end	Night	42% 4 15% 25% 12% 2	3476
September	1st to 10th	Night	40% 4 11% 30% 14% 1	1900
	11th to 20th	Night	37% 3 13% 36% 10% 1	1905
	21st to end	Night	43% 2 12% 31% 11%	2141
October	1st to 10th	Night	43% 4 13% 29% 12%	3800
	11th to 20th	Night	48% 6% 13% 24% 9%	3779
	21st to end	Night	52% 4 18% 16% 9%	4404
November	1st to 10th	Night	55% 2 14% 21% 8%	2453
	11th to 20th	Night	61% 4 10% 16% 8% 2	2660
	21st to end	Night	66% 4 11% 14% 4	2660
December	1st to 10th	Night	70% 3 8% 14% 5%	2660
	11th to 20th	Night	65% 2 7% 16% 8% 1	3288
	21st to end	Night	74% 2 5% 14% 5%	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	29% 15% 34% 19% 3	180
	11th to 20th	Day	29% 16% 37% 13% 4 1	180
	21st to end	Day	23% 20% 34% 19% 4	218
February	1st to 10th	Day	34% 25% 31% 8% 3	270
	11th to 20th	Day	31% 28% 33% 8%	274
	21st to end	Day	33% 21% 31% 12% 2	382
March	1st to 10th	Day	29% 19% 33% 14% 5%	460
	11th to 20th	Day	30% 20% 32% 13% 4 1	460
	21st to end	Day	33% 21% 25% 15% 5% 1	506
April	1st to 10th	Day	34% 18% 29% 14% 4 1	460
	11th to 20th	Day	36% 20% 23% 13% 8% 1	452
	21st to end	Day	33% 21% 27% 13% 5% 1	460
May	1st to 10th	Day	30% 16% 33% 13% 6% 2	463
	11th to 20th	Day	25% 16% 31% 18% 7% 3	487
	21st to end	Day	23% 17% 32% 19% 9%	529
June	1st to 10th	Day	28% 12% 34% 20% 6% 1	490
	11th to 20th	Day	20% 16% 31% 21% 9% 2	490
	21st to end	Day	25% 11% 33% 21% 8% 2	490
July	1st to 10th	Day	17% 8% 36% 28% 8% 4	485
	11th to 20th	Day	15% 13% 33% 27% 10% 2	484
	21st to end	Day	16% 8% 35% 29% 10% 3	532
August	1st to 10th	Day	19% 7% 28% 34% 10% 2	486
	11th to 20th	Day	21% 6% 25% 29% 12% 7%	479
	21st to end	Day	18% 12% 30% 23% 11% 6%	539
September	1st to 10th	Day	17% 12% 33% 20% 12% 6%	490
	11th to 20th	Day	15% 10% 25% 23% 17% 9%	490
	21st to end	Day	23% 14% 25% 22% 11% 6%	490
October	1st to 10th	Day	27% 15% 22% 23% 11% 2	490
	11th to 20th	Day	32% 20% 28% 12% 7% 1	490
	21st to end	Day	33% 13% 32% 17% 4	448
November	1st to 10th	Day	29% 17% 30% 18% 5% 1	373
	11th to 20th	Day	34% 21% 33% 8% 3 2	180
	21st to end	Day	32% 22% 31% 13% 2 1	180
December	1st to 10th	Day	33% 14% 34% 16% 3	180
	11th to 20th	Day	35% 26% 28% 10% 1 1	180
	21st to end	Day	35% 22% 28% 11% 3 1	198
January	1st to 10th	Night	30% 15% 33% 17% 4	760
	11th to 20th	Night	30% 16% 27% 21% 6%	760
	21st to end	Night	19% 13% 36% 24% 7% 1	836
February	1st to 10th	Night	22% 19% 32% 22% 4	760
	11th to 20th	Night	22% 20% 35% 18% 4 1	743
	21st to end	Night	26% 20% 26% 25% 3 1	628
March	1st to 10th	Night	26% 17% 31% 22% 5%	760
	11th to 20th	Night	25% 20% 30% 21% 4 1	760
	21st to end	Night	26% 16% 28% 22% 7%	836
April	1st to 10th	Night	28% 17% 24% 25% 5%	760
	11th to 20th	Night	27% 16% 29% 19% 7% 1	751
	21st to end	Night	28% 15% 27% 23% 7%	614
May	1st to 10th	Night	27% 11% 26% 27% 9% 2	380
	11th to 20th	Night	24% 9% 29% 28% 9%	374
	21st to end	Night	17% 11% 36% 25% 11%	411
June	1st to 10th	Night	21% 6% 30% 34% 8% 1	380
	11th to 20th	Night	18% 8% 27% 32% 14% 1	380
	21st to end	Night	22% 4 25% 36% 13% 1	380
July	1st to 10th	Night	11% 5% 29% 39% 15% 1	370
	11th to 20th	Night	16% 4 23% 40% 17%	368
	21st to end	Night	11% 4 26% 42% 15% 2	416
August	1st to 10th	Night	12% 4 23% 41% 20% 1	382
	11th to 20th	Night	14% 3 19% 37% 23% 4	569
	21st to end	Night	17% 6% 25% 31% 18% 2	836
September	1st to 10th	Night	18% 6% 29% 29% 18% 1	760
	11th to 20th	Night	19% 6% 24% 28% 21% 4	760
	21st to end	Night	21% 8% 25% 26% 18% 2	760
October	1st to 10th	Night	24% 11% 27% 23% 14% 1	760
	11th to 20th	Night	28% 13% 27% 25% 6% 1	760
	21st to end	Night	30% 14% 29% 22% 6%	836
November	1st to 10th	Night	29% 13% 26% 23% 8% 1	755
	11th to 20th	Night	28% 18% 29% 15% 10% 1	760
	21st to end	Night	31% 19% 23% 21% 5%	760
December	1st to 10th	Night	30% 17% 28% 21% 4	760
	11th to 20th	Night	29% 20% 26% 19% 5% 1	760
	21st to end	Night	36% 15% 27% 17% 4 1	836

Page generated at 2024-11-01 22:47:35. Version ac07

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