Chisasibi
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chisasibi clear sky chart from 2005-11-06 to 2025-12-03.

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	14% 13% 5% 11% 7% 6% 6% 4 6% 6% 23%	127432
	Night	12% 15% 6% 14% 9% 7% 6% 5% 5% 5% 17%	123545
Transparency	Day	61% 5% 11% 17% 7%	130718
	Night	68% 5% 9% 13% 5%	128348
Seeing	Day	21% 7% 25% 28% 15% 5%	17537
	Night	20% 7% 23% 31% 16% 3	25923

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	7% 18% 7% 23% 10% 9% 8% 6% 5% 3 4	3136
	11th to 20th	Day	4 16% 9% 25% 17% 11% 7% 4 4 2 2	3133
	21st to end	Day	5% 10% 4 14% 10% 9% 13% 12% 12% 4 8%	3476
February	1st to 10th	Day	5% 11% 4 13% 10% 10% 13% 11% 11% 4 7%	1635
	11th to 20th	Day	5% 12% 5% 13% 9% 9% 11% 11% 12% 5% 7%	1753
	21st to end	Day	5% 11% 4 11% 7% 7% 11% 10% 10% 9% 15%	1485
March	1st to 10th	Day	6% 13% 5% 11% 8% 9% 9% 9% 10% 7% 13%	4512
	11th to 20th	Day	4 12% 7% 16% 14% 7% 8% 6% 6% 5% 14%	4980
	21st to end	Day	7% 11% 5% 12% 8% 8% 11% 6% 5% 5% 21%	5595
April	1st to 10th	Day	11% 15% 4 12% 8% 6% 7% 3 4 5% 25%	2453
	11th to 20th	Day	10% 13% 6% 11% 7% 6% 5% 4 4 5% 30%	2572
	21st to end	Day	13% 12% 4 11% 9% 5% 4 3 4 6% 29%	2740
May	1st to 10th	Day	11% 11% 6% 12% 7% 5% 5% 4 5% 6% 31%	6346
	11th to 20th	Day	14% 12% 6% 14% 6% 4 5% 3 5% 6% 26%	6717
	21st to end	Day	12% 10% 4 9% 5% 5% 5% 4 6% 8% 34%	7587
June	1st to 10th	Day	14% 8% 3 7% 4 4 5% 4 5% 7% 38%	3200
	11th to 20th	Day	14% 7% 3 7% 5% 4 4 4 5% 7% 40%	3200
	21st to end	Day	15% 9% 3 6% 4 4 4 3 6% 7% 39%	3200
July	1st to 10th	Day	14% 9% 3 7% 5% 4 5% 4 6% 8% 34%	7104
	11th to 20th	Day	21% 13% 4 8% 5% 4 4 3 5% 7% 25%	6820
	21st to end	Day	16% 11% 3 10% 6% 5% 5% 3 5% 7% 29%	7428
August	1st to 10th	Day	21% 15% 5% 10% 5% 5% 4 4 5% 7% 19%	4742
	11th to 20th	Day	15% 10% 3 7% 3 4 4 4 6% 9% 37%	4339
	21st to end	Day	19% 8% 2 7% 4 4 4 4 5% 8% 35%	4675
September	1st to 10th	Day	26% 12% 4 8% 5% 5% 4 4 5% 9% 21%	2420
	11th to 20th	Day	24% 14% 4 9% 6% 5% 4 4 4 5% 21%	2369
	21st to end	Day	26% 15% 3 9% 5% 4 4 3 4 5% 21%	2110
October	1st to 10th	Day	25% 16% 4 9% 5% 4 5% 3 5% 6% 19%	2000
	11th to 20th	Day	28% 22% 5% 10% 6% 4 3 3 3 4 13%	2000
	21st to end	Day	23% 22% 7% 12% 6% 6% 4 3 3 4 10%	1797
November	1st to 10th	Day	18% 28% 7% 15% 6% 5% 4 2 4 3 7%	1646
	11th to 20th	Day	21% 25% 8% 17% 7% 4 3 2 2 3 7%	1680
	21st to end	Day	14% 22% 8% 23% 9% 4 3 2 4 3 8%	1365
December	1st to 10th	Day	7% 18% 7% 19% 12% 7% 5% 3 3 3 14%	1972
	11th to 20th	Day	12% 19% 7% 19% 11% 10% 7% 2 2 2 9%	2253
	21st to end	Day	13% 25% 8% 18% 13% 6% 5% 3 3 2 4	2992
January	1st to 10th	Night	8% 20% 9% 21% 10% 8% 6% 5% 6% 2 5%	6828
	11th to 20th	Night	5% 18% 9% 24% 15% 10% 7% 4 4 2 3	6772
	21st to end	Night	5% 10% 4 13% 13% 11% 12% 11% 10% 3 9%	7502
February	1st to 10th	Night	4 11% 5% 13% 10% 11% 15% 11% 11% 4 5%	2761
	11th to 20th	Night	5% 11% 5% 12% 9% 8% 11% 11% 13% 5% 10%	2533
	21st to end	Night	4 13% 5% 12% 7% 7% 8% 10% 10% 9% 13%	2145
March	1st to 10th	Night	5% 13% 4 12% 8% 8% 11% 10% 10% 6% 13%	5324
	11th to 20th	Night	6% 11% 5% 15% 14% 9% 9% 5% 6% 7% 13%	4979
	21st to end	Night	6% 9% 4 11% 8% 8% 13% 9% 6% 7% 19%	5336
April	1st to 10th	Night	13% 13% 4 11% 6% 7% 6% 3 5% 6% 26%	1965
	11th to 20th	Night	11% 11% 5% 9% 7% 6% 4 4 5% 7% 32%	1777
	21st to end	Night	12% 10% 4 9% 6% 6% 4 3 5% 7% 33%	1659
May	1st to 10th	Night	13% 11% 5% 15% 5% 3 4 3 4 6% 31%	3594
	11th to 20th	Night	18% 12% 5% 13% 5% 5% 4 3 4 7% 24%	3193
	21st to end	Night	12% 10% 4 10% 4 3 4 3 5% 6% 38%	3315
June	1st to 10th	Night	16% 8% 3 7% 4 4 5% 4 5% 6% 38%	1200
	11th to 20th	Night	14% 7% 2 6% 4 4 5% 3 6% 6% 42%	1200
	21st to end	Night	14% 8% 3 8% 5% 5% 4 4 4 7% 39%	1200
July	1st to 10th	Night	12% 9% 3 7% 3 4 5% 4 7% 10% 35%	2884
	11th to 20th	Night	21% 15% 4 9% 6% 4 3 3 4 4 27%	3160
	21st to end	Night	15% 15% 5% 10% 5% 4 4 4 5% 6% 26%	3446
August	1st to 10th	Night	20% 13% 3 9% 6% 5% 5% 3 6% 5% 25%	2412
	11th to 20th	Night	15% 10% 3 6% 4 4 4 4 5% 8% 37%	2708
	21st to end	Night	16% 9% 2 6% 4 4 4 2 4 7% 42%	3223
September	1st to 10th	Night	25% 12% 4 8% 5% 4 4 3 5% 5% 23%	1959
	11th to 20th	Night	21% 14% 4 9% 5% 5% 5% 4 5% 6% 22%	2030
	21st to end	Night	23% 13% 4 9% 5% 5% 4 3 4 6% 23%	2290
October	1st to 10th	Night	23% 16% 4 10% 6% 5% 5% 3 4 5% 19%	2400
	11th to 20th	Night	25% 22% 4 10% 5% 5% 3 3 4 5% 15%	2400
	21st to end	Night	23% 20% 6% 12% 5% 5% 4 3 4 5% 13%	3040
November	1st to 10th	Night	23% 27% 8% 15% 5% 4 3 2 2 3 8%	2872
	11th to 20th	Night	21% 26% 9% 16% 6% 5% 3 2 3 3 7%	2940
	21st to end	Night	14% 25% 10% 20% 7% 5% 4 2 3 3 8%	3248
December	1st to 10th	Night	7% 16% 8% 23% 12% 8% 5% 4 4 4 8%	5273
	11th to 20th	Night	11% 18% 8% 20% 14% 9% 5% 2 2 2 8%	5969
	21st to end	Night	13% 23% 6% 17% 14% 8% 6% 3 3 2 5%	8008

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	80% 7% 7% 5% 1	3137
	11th to 20th	Day	88% 3 3 4 1	3160
	21st to end	Day	67% 4 9% 14% 6%	3476
February	1st to 10th	Day	67% 9% 8% 11% 5%	1635
	11th to 20th	Day	66% 8% 9% 13% 5%	1762
	21st to end	Day	58% 6% 15% 16% 6%	1485
March	1st to 10th	Day	63% 5% 7% 16% 9%	4515
	11th to 20th	Day	69% 4 7% 12% 8%	4980
	21st to end	Day	64% 4 8% 18% 6%	5595
April	1st to 10th	Day	62% 3 6% 18% 9% 1	2453
	11th to 20th	Day	56% 4 8% 21% 11%	2572
	21st to end	Day	57% 3 10% 18% 11% 1	2740
May	1st to 10th	Day	53% 4 9% 23% 11%	6357
	11th to 20th	Day	57% 5% 9% 17% 11%	6721
	21st to end	Day	47% 5% 9% 20% 18% 1	7587
June	1st to 10th	Day	44% 6% 10% 27% 11% 1	3200
	11th to 20th	Day	44% 5% 9% 26% 15% 1	3200
	21st to end	Day	44% 5% 13% 26% 12% 1	3200
July	1st to 10th	Day	48% 5% 14% 25% 8%	7029
	11th to 20th	Day	58% 4 13% 20% 5%	6739
	21st to end	Day	55% 4 18% 20% 2	7216
August	1st to 10th	Day	64% 6% 17% 11% 2	4726
	11th to 20th	Day	44% 4 19% 27% 6%	4381
	21st to end	Day	47% 5% 14% 26% 7%	4674
September	1st to 10th	Day	62% 6% 14% 15% 2	2420
	11th to 20th	Day	65% 6% 13% 14% 2	2369
	21st to end	Day	66% 5% 12% 13% 3	2110
October	1st to 10th	Day	62% 4 15% 17% 2	3260
	11th to 20th	Day	76% 4 10% 9% 1	3240
	21st to end	Day	80% 4 7% 8% 1	2871
November	1st to 10th	Day	82% 5% 6% 5% 1	1646
	11th to 20th	Day	83% 4 7% 4 1	1680
	21st to end	Day	82% 5% 7% 6% 1	1365
December	1st to 10th	Day	76% 3 7% 13% 1	1972
	11th to 20th	Day	83% 4 7% 4 2	2253
	21st to end	Day	87% 4 4 4 2	2992
January	1st to 10th	Night	82% 4 5% 8% 1	6828
	11th to 20th	Night	87% 3 4 4 1	6820
	21st to end	Night	69% 5% 7% 12% 7%	7502
February	1st to 10th	Night	69% 9% 7% 11% 5%	2761
	11th to 20th	Night	62% 7% 11% 15% 6%	2535
	21st to end	Night	57% 7% 12% 16% 7%	2145
March	1st to 10th	Night	62% 6% 6% 15% 11%	5334
	11th to 20th	Night	68% 5% 7% 12% 7%	4980
	21st to end	Night	59% 5% 8% 18% 9%	5336
April	1st to 10th	Night	59% 4 7% 18% 10% 1	1965
	11th to 20th	Night	52% 4 9% 21% 12% 1	1777
	21st to end	Night	50% 4 9% 21% 15%	1659
May	1st to 10th	Night	54% 4 7% 21% 11% 3	3600
	11th to 20th	Night	60% 3 7% 18% 11% 1	3194
	21st to end	Night	46% 6% 8% 21% 18% 1	3316
June	1st to 10th	Night	45% 5% 8% 26% 14% 2	1200
	11th to 20th	Night	40% 4 10% 25% 19% 1	1200
	21st to end	Night	46% 5% 11% 24% 14% 1	1200
July	1st to 10th	Night	43% 6% 14% 30% 7%	2851
	11th to 20th	Night	61% 4 9% 19% 7%	3118
	21st to end	Night	58% 3 18% 18% 3	3344
August	1st to 10th	Night	59% 4 20% 15% 2	2404
	11th to 20th	Night	45% 5% 16% 30% 4	2732
	21st to end	Night	44% 4 13% 27% 11% 1	3223
September	1st to 10th	Night	63% 6% 15% 14% 2	1959
	11th to 20th	Night	61% 7% 15% 13% 3	2030
	21st to end	Night	62% 5% 13% 15% 4	2290
October	1st to 10th	Night	65% 4 13% 14% 2	3920
	11th to 20th	Night	75% 4 12% 8% 1	3899
	21st to end	Night	76% 5% 8% 9% 2	4916
November	1st to 10th	Night	83% 5% 6% 6% 1	2872
	11th to 20th	Night	84% 4 5% 5% 1	2940
	21st to end	Night	83% 5% 4 6% 1	3248
December	1st to 10th	Night	77% 3 8% 9% 3	5273
	11th to 20th	Night	84% 4 5% 5% 2	5969
	21st to end	Night	84% 5% 5% 5% 2	8008

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	13% 7% 25% 36% 15% 5%	200
	11th to 20th	Day	10% 7% 27% 29% 22% 6%	200
	21st to end	Day	12% 7% 20% 31% 22% 8%	220
February	1st to 10th	Day	10% 4 23% 35% 19% 8%	257
	11th to 20th	Day	9% 4 27% 30% 22% 8%	300
	21st to end	Day	10% 9% 30% 30% 15% 6%	249
March	1st to 10th	Day	12% 7% 25% 29% 16% 12%	428
	11th to 20th	Day	9% 7% 28% 30% 18% 8%	500
	21st to end	Day	14% 6% 27% 34% 15% 4	550
April	1st to 10th	Day	13% 5% 18% 36% 20% 7%	500
	11th to 20th	Day	15% 8% 25% 27% 18% 7%	492
	21st to end	Day	17% 7% 24% 26% 16% 10%	500
May	1st to 10th	Day	16% 8% 24% 28% 19% 5%	503
	11th to 20th	Day	17% 10% 28% 28% 14% 3	692
	21st to end	Day	19% 9% 30% 30% 11% 3	847
June	1st to 10th	Day	17% 7% 27% 30% 15% 5%	930
	11th to 20th	Day	18% 7% 28% 28% 14% 5%	930
	21st to end	Day	19% 7% 24% 31% 14% 4	930
July	1st to 10th	Day	18% 7% 26% 30% 15% 4	848
	11th to 20th	Day	22% 5% 27% 29% 14% 3	718
	21st to end	Day	25% 4 21% 28% 15% 6%	794
August	1st to 10th	Day	31% 5% 17% 27% 15% 5%	641
	11th to 20th	Day	28% 7% 16% 26% 16% 7%	519
	21st to end	Day	23% 7% 20% 27% 15% 8%	583
September	1st to 10th	Day	32% 7% 26% 22% 9% 3	530
	11th to 20th	Day	27% 10% 26% 22% 13% 3	530
	21st to end	Day	35% 8% 25% 18% 11% 4	530
October	1st to 10th	Day	32% 11% 27% 20% 8% 3	530
	11th to 20th	Day	38% 5% 27% 17% 8% 4	530
	21st to end	Day	26% 12% 20% 23% 14% 5%	272
November	1st to 10th	Day	28% 14% 23% 22% 10% 4	220
	11th to 20th	Day	25% 12% 20% 24% 13% 6%	220
	21st to end	Day	23% 8% 21% 27% 15% 6%	220
December	1st to 10th	Day	15% 7% 23% 33% 20% 2	204
	11th to 20th	Day	16% 15% 24% 29% 14% 4	200
	21st to end	Day	18% 7% 26% 30% 17% 2	220
January	1st to 10th	Night	19% 6% 24% 32% 15% 4	1003
	11th to 20th	Night	14% 6% 21% 34% 21% 4	1000
	21st to end	Night	11% 4 17% 35% 26% 7%	1100
February	1st to 10th	Night	8% 5% 20% 39% 23% 5%	880
	11th to 20th	Night	10% 4 20% 36% 22% 7%	783
	21st to end	Night	9% 5% 23% 35% 22% 7%	660
March	1st to 10th	Night	11% 6% 22% 35% 23% 5%	800
	11th to 20th	Night	11% 6% 27% 35% 17% 4	800
	21st to end	Night	13% 7% 28% 32% 17% 3	880
April	1st to 10th	Night	17% 4 25% 35% 16% 3	765
	11th to 20th	Night	14% 5% 24% 34% 19% 4	593
	21st to end	Night	18% 5% 22% 35% 18% 1	459
May	1st to 10th	Night	21% 7% 25% 32% 13% 3	400
	11th to 20th	Night	21% 8% 26% 31% 11% 1	394
	21st to end	Night	19% 8% 27% 34% 12%	433
June	1st to 10th	Night	21% 4 25% 34% 16% 1	400
	11th to 20th	Night	18% 6% 26% 34% 14% 3	400
	21st to end	Night	17% 6% 26% 36% 14% 2	400
July	1st to 10th	Night	19% 4 21% 35% 19% 2	390
	11th to 20th	Night	21% 5% 24% 37% 13% 1	388
	21st to end	Night	23% 4 15% 33% 22% 3	438
August	1st to 10th	Night	26% 5% 16% 32% 20% 2	398
	11th to 20th	Night	28% 4 17% 31% 17% 3	489
	21st to end	Night	25% 3 20% 30% 19% 3	660
September	1st to 10th	Night	31% 7% 25% 25% 11% 1	759
	11th to 20th	Night	29% 8% 21% 30% 12%	800
	21st to end	Night	31% 8% 22% 25% 13% 1	800
October	1st to 10th	Night	34% 10% 23% 24% 9% 1	800
	11th to 20th	Night	35% 9% 24% 21% 8% 3	800
	21st to end	Night	32% 8% 22% 23% 14% 2	880
November	1st to 10th	Night	35% 12% 20% 23% 9% 1	820
	11th to 20th	Night	31% 12% 21% 23% 11% 1	840
	21st to end	Night	23% 10% 25% 26% 13% 3	1088
December	1st to 10th	Night	18% 8% 29% 29% 14% 2	1113
	11th to 20th	Night	16% 9% 24% 29% 18% 4	1100
	21st to end	Night	16% 8% 24% 32% 15% 5%	1210

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