Trois-Pistoles
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trois-Pistoles clear sky chart from 2005-11-06 to 2026-03-18.

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 9% 6% 5% 5% 4 5% 7% 29%	130987
	Night	16% 13% 5% 10% 6% 5% 5% 4 5% 6% 25%	130642
Transparency	Day	54% 7% 13% 18% 7% 1	134417
	Night	59% 7% 12% 16% 6%	135300
Seeing	Day	26% 17% 30% 18% 7% 1	17455
	Night	26% 16% 29% 21% 7% 1	25681

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% 7% 12% 8% 7% 7% 5% 4 4 9%	4093
	11th to 20th	Day	10% 17% 8% 18% 10% 6% 5% 5% 5% 5% 12%	4650
	21st to end	Day	4 8% 5% 14% 10% 9% 10% 8% 5% 6% 21%	5124
February	1st to 10th	Day	8% 13% 6% 11% 9% 9% 7% 5% 6% 7% 18%	1753
	11th to 20th	Day	14% 14% 6% 13% 6% 5% 5% 5% 5% 5% 21%	1890
	21st to end	Day	10% 12% 4 10% 7% 8% 7% 5% 5% 6% 25%	1730
March	1st to 10th	Day	17% 15% 3 9% 5% 6% 7% 5% 5% 6% 22%	4576
	11th to 20th	Day	17% 18% 4 8% 5% 6% 6% 5% 6% 6% 19%	5007
	21st to end	Day	18% 16% 5% 10% 5% 4 4 3 4 5% 26%	5551
April	1st to 10th	Day	21% 11% 3 8% 5% 4 5% 3 5% 6% 29%	2408
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 5% 6% 36%	2572
	21st to end	Day	22% 10% 3 6% 4 4 4 4 5% 5% 34%	2600
May	1st to 10th	Day	19% 9% 3 8% 5% 4 4 3 5% 5% 35%	5886
	11th to 20th	Day	24% 8% 3 6% 4 4 4 3 5% 6% 33%	6522
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 8% 33%	7451
June	1st to 10th	Day	19% 9% 3 7% 5% 4 5% 4 6% 7% 33%	3000
	11th to 20th	Day	18% 6% 2 6% 6% 4 5% 3 6% 7% 37%	3000
	21st to end	Day	20% 8% 3 8% 6% 4 5% 4 6% 7% 30%	3000
July	1st to 10th	Day	17% 8% 2 8% 5% 5% 5% 4 7% 9% 31%	6820
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	6696
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 5% 8% 44%	6926
August	1st to 10th	Day	13% 5% 2 6% 4 5% 6% 4 7% 10% 38%	4438
	11th to 20th	Day	17% 7% 3 9% 5% 5% 5% 4 6% 8% 32%	4175
	21st to end	Day	17% 6% 2 7% 4 5% 4 4 5% 9% 37%	4675
September	1st to 10th	Day	16% 5% 2 6% 4 3 4 3 6% 8% 43%	2386
	11th to 20th	Day	16% 6% 2 5% 4 3 3 2 5% 6% 48%	2200
	21st to end	Day	17% 6% 2 7% 4 4 3 3 5% 6% 42%	2200
October	1st to 10th	Day	17% 9% 2 6% 4 3 5% 4 6% 7% 37%	2130
	11th to 20th	Day	24% 8% 3 7% 5% 6% 4 3 5% 6% 29%	1893
	21st to end	Day	26% 11% 4 7% 4 3 5% 3 4 6% 27%	1980
November	1st to 10th	Day	20% 13% 3 9% 5% 4 4 4 6% 6% 27%	1851
	11th to 20th	Day	20% 14% 4 10% 5% 4 5% 4 6% 6% 22%	1680
	21st to end	Day	19% 19% 5% 9% 6% 4 4 2 5% 6% 21%	1533
December	1st to 10th	Day	15% 18% 5% 13% 10% 6% 4 3 3 6% 18%	2350
	11th to 20th	Day	16% 14% 5% 14% 9% 6% 5% 3 4 5% 19%	2688
	21st to end	Day	17% 15% 4 11% 10% 8% 6% 3 5% 6% 16%	3553
January	1st to 10th	Night	14% 22% 6% 14% 7% 7% 7% 4 3 4 11%	8813
	11th to 20th	Night	9% 20% 8% 17% 7% 6% 5% 3 5% 6% 15%	8235
	21st to end	Night	4 10% 6% 15% 9% 7% 9% 7% 7% 7% 20%	9057
February	1st to 10th	Night	9% 14% 5% 12% 9% 7% 6% 5% 5% 6% 21%	2866
	11th to 20th	Night	12% 18% 7% 12% 7% 5% 5% 4 5% 4 21%	2611
	21st to end	Night	12% 16% 5% 11% 7% 5% 4 3 5% 5% 27%	2076
March	1st to 10th	Night	19% 16% 5% 10% 6% 5% 6% 3 3 5% 22%	5484
	11th to 20th	Night	18% 21% 4 10% 6% 4 5% 3 5% 5% 19%	5105
	21st to end	Night	22% 18% 4 7% 4 3 3 2 3 5% 29%	5376
April	1st to 10th	Night	23% 16% 4 9% 5% 4 3 3 3 3 26%	1991
	11th to 20th	Night	21% 11% 2 6% 5% 5% 4 3 6% 6% 30%	1778
	21st to end	Night	25% 12% 4 7% 4 3 3 3 4 5% 31%	1800
May	1st to 10th	Night	21% 8% 3 6% 4 4 4 4 5% 6% 35%	4054
	11th to 20th	Night	26% 8% 3 7% 4 3 4 4 6% 6% 30%	3422
	21st to end	Night	19% 7% 3 7% 4 5% 5% 4 6% 7% 33%	3446
June	1st to 10th	Night	20% 9% 3 7% 7% 4 5% 4 6% 6% 30%	1400
	11th to 20th	Night	18% 8% 2 8% 5% 4 4 5% 6% 7% 33%	1400
	21st to end	Night	21% 9% 3 8% 5% 6% 4 4 6% 6% 28%	1400
July	1st to 10th	Night	15% 7% 3 8% 5% 6% 6% 4 7% 8% 29%	3160
	11th to 20th	Night	16% 7% 3 8% 5% 5% 5% 4 7% 8% 32%	3263
	21st to end	Night	12% 7% 2 7% 4 4 5% 4 5% 7% 42%	3926
August	1st to 10th	Night	16% 6% 3 6% 6% 5% 5% 4 6% 8% 34%	2680
	11th to 20th	Night	16% 8% 4 10% 6% 5% 6% 5% 6% 7% 27%	2872
	21st to end	Night	19% 7% 3 7% 3 4 4 3 4 6% 40%	3223
September	1st to 10th	Night	16% 7% 2 7% 4 4 5% 3 5% 7% 38%	2010
	11th to 20th	Night	19% 6% 3 7% 4 4 4 4 4 5% 40%	2200
	21st to end	Night	18% 6% 2 7% 4 5% 4 3 4 6% 42%	2200
October	1st to 10th	Night	19% 8% 2 6% 4 4 3 3 4 6% 41%	2270
	11th to 20th	Night	25% 10% 3 8% 4 4 5% 3 5% 5% 29%	2505
	21st to end	Night	23% 12% 4 8% 4 4 4 3 5% 6% 27%	2860
November	1st to 10th	Night	22% 13% 3 8% 5% 4 4 3 4 5% 28%	2667
	11th to 20th	Night	20% 15% 5% 8% 5% 5% 4 3 4 5% 25%	2938
	21st to end	Night	20% 19% 6% 11% 6% 4 4 3 5% 4 19%	3086
December	1st to 10th	Night	14% 18% 8% 14% 8% 5% 5% 3 4 5% 17%	5060
	11th to 20th	Night	19% 15% 5% 13% 9% 7% 5% 3 4 4 16%	5741
	21st to end	Night	14% 16% 6% 12% 8% 7% 5% 3 5% 6% 18%	7667

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	81% 6% 6% 4 2	4094
	11th to 20th	Day	72% 7% 10% 8% 3	4680
	21st to end	Day	59% 9% 12% 15% 5%	5124
February	1st to 10th	Day	64% 6% 12% 11% 5% 1	1753
	11th to 20th	Day	65% 7% 10% 13% 5%	1898
	21st to end	Day	59% 6% 8% 19% 8% 1	1730
March	1st to 10th	Day	61% 7% 12% 12% 7% 1	4579
	11th to 20th	Day	64% 7% 12% 11% 5%	5007
	21st to end	Day	61% 5% 8% 18% 7% 2	5551
April	1st to 10th	Day	56% 4 11% 18% 9% 2	2408
	11th to 20th	Day	50% 5% 11% 21% 11% 1	2572
	21st to end	Day	54% 5% 8% 19% 12% 1	2600
May	1st to 10th	Day	52% 7% 10% 21% 9% 1	5897
	11th to 20th	Day	53% 7% 13% 18% 7% 2	6526
	21st to end	Day	48% 7% 12% 23% 8% 1	7451
June	1st to 10th	Day	50% 6% 11% 21% 10% 1	3000
	11th to 20th	Day	46% 7% 14% 20% 11% 1	3000
	21st to end	Day	54% 6% 11% 19% 9%	3000
July	1st to 10th	Day	48% 7% 14% 23% 6%	6745
	11th to 20th	Day	45% 9% 22% 19% 4	6615
	21st to end	Day	38% 7% 19% 29% 7%	6728
August	1st to 10th	Day	40% 9% 21% 24% 6%	4424
	11th to 20th	Day	48% 9% 21% 19% 4	4214
	21st to end	Day	45% 7% 18% 18% 11%	4675
September	1st to 10th	Day	40% 6% 17% 27% 9%	2386
	11th to 20th	Day	38% 6% 17% 28% 10% 1	2200
	21st to end	Day	45% 6% 14% 26% 9%	2200
October	1st to 10th	Day	55% 6% 13% 20% 6%	3468
	11th to 20th	Day	54% 6% 16% 20% 3	3057
	21st to end	Day	54% 6% 17% 18% 6%	3180
November	1st to 10th	Day	59% 8% 12% 17% 4	1851
	11th to 20th	Day	64% 7% 11% 14% 4	1680
	21st to end	Day	68% 6% 11% 11% 3	1533
December	1st to 10th	Day	72% 7% 11% 9% 1	2350
	11th to 20th	Day	66% 8% 11% 10% 5%	2688
	21st to end	Day	69% 8% 11% 9% 3	3553
January	1st to 10th	Night	77% 7% 9% 6% 1	8813
	11th to 20th	Night	69% 7% 11% 9% 4	8280
	21st to end	Night	56% 8% 12% 18% 6%	9057
February	1st to 10th	Night	62% 5% 11% 14% 8% 1	2866
	11th to 20th	Night	66% 5% 10% 14% 5%	2614
	21st to end	Night	59% 5% 10% 18% 8%	2076
March	1st to 10th	Night	64% 6% 8% 14% 8%	5494
	11th to 20th	Night	66% 6% 11% 11% 6%	5106
	21st to end	Night	60% 4 7% 19% 9% 1	5376
April	1st to 10th	Night	64% 4 7% 13% 11% 2	1991
	11th to 20th	Night	53% 6% 9% 18% 13% 1	1778
	21st to end	Night	56% 5% 7% 19% 11% 2	1800
May	1st to 10th	Night	50% 7% 10% 19% 14% 1	4060
	11th to 20th	Night	53% 7% 10% 21% 9% 1	3423
	21st to end	Night	46% 8% 12% 22% 12% 1	3447
June	1st to 10th	Night	52% 8% 9% 19% 10% 1	1400
	11th to 20th	Night	48% 6% 11% 18% 14% 2	1400
	21st to end	Night	55% 7% 11% 17% 10%	1400
July	1st to 10th	Night	49% 9% 15% 23% 4	3125
	11th to 20th	Night	48% 8% 24% 18% 3	3221
	21st to end	Night	41% 8% 21% 23% 7%	3809
August	1st to 10th	Night	47% 8% 17% 22% 6%	2670
	11th to 20th	Night	52% 12% 18% 12% 5%	2899
	21st to end	Night	44% 6% 15% 23% 11%	3223
September	1st to 10th	Night	44% 7% 14% 25% 9% 1	2010
	11th to 20th	Night	46% 6% 17% 22% 9% 1	2200
	21st to end	Night	44% 6% 12% 25% 13% 1	2200
October	1st to 10th	Night	47% 6% 12% 26% 9% 1	3712
	11th to 20th	Night	55% 5% 13% 23% 3	4080
	21st to end	Night	56% 7% 15% 17% 4	4610
November	1st to 10th	Night	60% 7% 11% 16% 5%	2667
	11th to 20th	Night	64% 6% 11% 14% 5%	2938
	21st to end	Night	71% 6% 11% 9% 3	3086
December	1st to 10th	Night	72% 8% 11% 8% 1	5060
	11th to 20th	Night	71% 8% 9% 9% 2	5742
	21st to end	Night	68% 8% 10% 11% 3	7667

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% 27% 29% 11% 4	220
	11th to 20th	Day	28% 23% 32% 11% 6%	220
	21st to end	Day	19% 24% 34% 18% 5%	242
February	1st to 10th	Day	24% 22% 33% 14% 5% 1	293
	11th to 20th	Day	23% 26% 36% 13% 2	451
	21st to end	Day	24% 26% 30% 13% 4 1	446
March	1st to 10th	Day	28% 22% 30% 18% 2 1	540
	11th to 20th	Day	32% 21% 26% 13% 7% 1	528
	21st to end	Day	33% 20% 29% 13% 4 1	550
April	1st to 10th	Day	35% 20% 26% 14% 4 1	500
	11th to 20th	Day	31% 16% 31% 16% 6% 1	492
	21st to end	Day	30% 17% 35% 12% 4 2	500
May	1st to 10th	Day	33% 15% 29% 16% 7% 1	503
	11th to 20th	Day	27% 16% 28% 20% 7% 2	611
	21st to end	Day	28% 17% 31% 17% 6% 1	790
June	1st to 10th	Day	26% 14% 30% 22% 7% 1	730
	11th to 20th	Day	25% 15% 30% 20% 9% 1	730
	21st to end	Day	24% 13% 32% 23% 7% 1	730
July	1st to 10th	Day	22% 13% 32% 26% 8%	720
	11th to 20th	Day	15% 14% 35% 25% 9% 2	672
	21st to end	Day	18% 13% 35% 26% 7% 1	576
August	1st to 10th	Day	18% 12% 32% 26% 10% 2	526
	11th to 20th	Day	18% 8% 33% 30% 10% 1	519
	21st to end	Day	21% 14% 30% 21% 11% 2	583
September	1st to 10th	Day	23% 14% 31% 20% 10% 3	530
	11th to 20th	Day	23% 12% 32% 21% 11% 3	530
	21st to end	Day	25% 14% 29% 20% 8% 3	530
October	1st to 10th	Day	23% 17% 30% 18% 8% 3	491
	11th to 20th	Day	35% 18% 23% 14% 9% 2	420
	21st to end	Day	34% 21% 25% 11% 7% 1	462
November	1st to 10th	Day	37% 23% 24% 14% 2 1	425
	11th to 20th	Day	34% 19% 27% 15% 5% 1	430
	21st to end	Day	35% 25% 27% 10% 3	283
December	1st to 10th	Day	32% 23% 27% 14% 4 1	220
	11th to 20th	Day	31% 28% 31% 9% 1	220
	21st to end	Day	30% 29% 24% 13% 3	242
January	1st to 10th	Night	27% 22% 33% 15% 4	947
	11th to 20th	Night	27% 24% 27% 17% 4 1	840
	21st to end	Night	16% 19% 39% 21% 6%	924
February	1st to 10th	Night	17% 24% 34% 16% 7% 1	840
	11th to 20th	Night	24% 23% 31% 17% 4	823
	21st to end	Night	23% 17% 35% 18% 6% 1	692
March	1st to 10th	Night	26% 19% 33% 18% 5% 1	840
	11th to 20th	Night	28% 18% 31% 14% 8% 1	829
	21st to end	Night	28% 18% 28% 20% 5% 1	880
April	1st to 10th	Night	33% 14% 28% 17% 7% 1	791
	11th to 20th	Night	29% 12% 28% 23% 8%	594
	21st to end	Night	32% 12% 28% 21% 7% 1	600
May	1st to 10th	Night	30% 9% 28% 27% 7% 1	600
	11th to 20th	Night	27% 9% 29% 24% 11%	422
	21st to end	Night	27% 12% 27% 25% 7% 1	433
June	1st to 10th	Night	21% 7% 30% 34% 9% 1	400
	11th to 20th	Night	23% 9% 23% 32% 11% 2	400
	21st to end	Night	23% 8% 31% 27% 10% 1	400
July	1st to 10th	Night	18% 9% 32% 32% 8% 2	390
	11th to 20th	Night	14% 11% 30% 34% 10% 1	388
	21st to end	Night	18% 5% 30% 34% 12% 1	438
August	1st to 10th	Night	17% 6% 29% 32% 16%	453
	11th to 20th	Night	18% 7% 29% 33% 13% 1	592
	21st to end	Night	19% 10% 27% 30% 12% 2	660
September	1st to 10th	Night	20% 10% 29% 29% 10% 1	760
	11th to 20th	Night	24% 8% 30% 25% 11% 2	800
	21st to end	Night	22% 10% 30% 27% 10% 1	800
October	1st to 10th	Night	26% 13% 29% 24% 7% 1	800
	11th to 20th	Night	32% 14% 26% 20% 8% 1	800
	21st to end	Night	32% 16% 26% 20% 6% 1	880
November	1st to 10th	Night	34% 17% 28% 17% 4	820
	11th to 20th	Night	33% 20% 25% 16% 6% 1	950
	21st to end	Night	31% 18% 31% 14% 5%	950
December	1st to 10th	Night	29% 21% 29% 16% 5% 1	950
	11th to 20th	Night	31% 22% 28% 15% 4	950
	21st to end	Night	28% 22% 27% 16% 5% 1	1045

Page generated at 2026-03-15 02:23:51. Version ac07

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