Observatoire de Gatineau
Clear Sky Chart
History

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

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	16% 9% 3 8% 5% 5% 5% 4 5% 6% 32%	108888
	Night	17% 11% 4 9% 5% 5% 4 3 5% 6% 30%	110113
Transparency	Day	49% 8% 13% 20% 9% 1	112401
	Night	53% 7% 12% 18% 9% 1	114764
Seeing	Day	21% 15% 30% 21% 10% 3	14802
	Night	22% 12% 30% 26% 9% 1	24047

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% 17% 7% 15% 6% 5% 5% 4 4 4 20%	3597
	11th to 20th	Day	13% 14% 6% 13% 8% 6% 4 4 4 5% 22%	3570
	21st to end	Day	10% 15% 6% 14% 6% 6% 5% 4 6% 6% 21%	4121
February	1st to 10th	Day	13% 14% 5% 12% 7% 6% 5% 3 5% 5% 25%	1800
	11th to 20th	Day	13% 15% 5% 10% 6% 4 4 4 6% 5% 28%	1760
	21st to end	Day	19% 12% 4 9% 7% 5% 5% 5% 5% 4 25%	1650
March	1st to 10th	Day	21% 13% 3 9% 6% 5% 4 4 4 5% 26%	3216
	11th to 20th	Day	12% 14% 5% 10% 6% 5% 6% 3 5% 5% 28%	3482
	21st to end	Day	14% 7% 3 7% 6% 4 4 4 5% 6% 41%	4031
April	1st to 10th	Day	22% 10% 3 7% 5% 4 3 3 5% 6% 32%	2280
	11th to 20th	Day	22% 9% 3 6% 5% 3 5% 3 4 5% 37%	2254
	21st to end	Day	23% 9% 2 8% 5% 5% 4 3 4 5% 31%	2417
May	1st to 10th	Day	21% 8% 2 7% 5% 4 5% 4 6% 7% 31%	4426
	11th to 20th	Day	18% 8% 3 8% 5% 4 5% 4 5% 6% 34%	4398
	21st to end	Day	16% 7% 2 6% 5% 5% 5% 4 6% 7% 38%	4837
June	1st to 10th	Day	21% 8% 3 7% 6% 5% 4 5% 5% 7% 30%	2660
	11th to 20th	Day	14% 5% 3 6% 5% 5% 5% 4 7% 8% 38%	2660
	21st to end	Day	19% 7% 2 6% 5% 4 6% 5% 7% 7% 31%	2660
July	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 7% 9% 36%	4440
	11th to 20th	Day	13% 5% 2 6% 4 5% 5% 4 7% 8% 41%	4440
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 7% 8% 45%	4814
August	1st to 10th	Day	14% 6% 3 8% 5% 5% 5% 5% 7% 8% 36%	4367
	11th to 20th	Day	16% 6% 2 6% 5% 4 4 4 7% 9% 38%	3990
	21st to end	Day	14% 5% 2 6% 4 5% 5% 4 6% 9% 41%	4180
September	1st to 10th	Day	13% 5% 2 6% 4 4 5% 4 5% 7% 43%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 3 5% 8% 47%	2278
	21st to end	Day	18% 5% 2 6% 4 4 4 3 5% 9% 39%	2031
October	1st to 10th	Day	20% 8% 3 6% 4 4 4 3 6% 6% 35%	1900
	11th to 20th	Day	22% 8% 3 7% 5% 5% 4 4 5% 7% 29%	1900
	21st to end	Day	25% 9% 2 7% 5% 5% 5% 3 5% 5% 29%	1932
November	1st to 10th	Day	15% 9% 3 7% 5% 5% 5% 4 6% 6% 35%	1761
	11th to 20th	Day	19% 11% 4 7% 5% 4 5% 4 6% 6% 28%	1610
	21st to end	Day	22% 14% 4 9% 6% 6% 5% 4 4 5% 21%	1600
December	1st to 10th	Day	21% 20% 6% 10% 5% 5% 5% 5% 6% 5% 14%	2600
	11th to 20th	Day	17% 16% 4 10% 6% 5% 5% 3 3 4 25%	2986
	21st to end	Day	24% 16% 5% 11% 6% 4 5% 3 4 4 20%	3960
January	1st to 10th	Night	14% 21% 8% 14% 5% 4 3 3 4 4 20%	6349
	11th to 20th	Night	11% 14% 6% 15% 8% 7% 6% 3 4 5% 21%	6315
	21st to end	Night	13% 18% 6% 12% 6% 6% 5% 4 4 6% 20%	6833
February	1st to 10th	Night	14% 14% 5% 12% 7% 6% 5% 4 5% 5% 25%	2600
	11th to 20th	Night	13% 13% 5% 11% 6% 6% 4 3 4 6% 29%	2524
	21st to end	Night	16% 13% 4 9% 6% 4 4 4 5% 6% 29%	1980
March	1st to 10th	Night	22% 11% 5% 8% 5% 4 4 3 3 4 31%	3844
	11th to 20th	Night	17% 15% 5% 10% 6% 4 3 3 5% 5% 26%	3502
	21st to end	Night	16% 8% 3 7% 4 3 4 3 5% 6% 40%	3600
April	1st to 10th	Night	20% 10% 4 7% 4 4 4 3 5% 5% 34%	1900
	11th to 20th	Night	20% 8% 3 6% 5% 4 5% 4 4 5% 36%	1875
	21st to end	Night	22% 9% 3 7% 4 4 5% 3 4 6% 34%	1781
May	1st to 10th	Night	21% 7% 3 8% 5% 4 5% 4 6% 7% 29%	2514
	11th to 20th	Night	21% 8% 3 6% 5% 4 4 3 5% 6% 35%	2495
	21st to end	Night	15% 7% 3 7% 4 4 5% 4 6% 7% 39%	2738
June	1st to 10th	Night	16% 6% 2 7% 6% 5% 5% 5% 6% 7% 34%	1520
	11th to 20th	Night	14% 6% 2 7% 4 3 4 5% 6% 8% 41%	1520
	21st to end	Night	19% 6% 2 6% 4 4 5% 5% 6% 7% 35%	1520
July	1st to 10th	Night	13% 6% 3 9% 6% 6% 6% 5% 6% 7% 35%	2520
	11th to 20th	Night	13% 6% 3 7% 4 4 5% 4 6% 7% 41%	2520
	21st to end	Night	10% 6% 2 7% 4 4 5% 4 6% 8% 44%	2739
August	1st to 10th	Night	12% 8% 3 7% 4 4 5% 4 6% 8% 39%	2559
	11th to 20th	Night	15% 6% 2 7% 4 4 5% 4 6% 7% 41%	2807
	21st to end	Night	13% 5% 3 7% 5% 5% 5% 4 6% 7% 41%	3476
September	1st to 10th	Night	13% 4 2 6% 4 5% 4 4 5% 6% 48%	1900
	11th to 20th	Night	15% 4 1 6% 4 3 4 3 5% 6% 50%	1901
	21st to end	Night	17% 6% 2 7% 5% 3 4 2 4 6% 44%	2147
October	1st to 10th	Night	19% 8% 2 6% 3 5% 4 3 5% 5% 39%	2280
	11th to 20th	Night	21% 8% 2 7% 6% 5% 4 3 5% 6% 32%	2280
	21st to end	Night	23% 9% 4 7% 5% 5% 5% 4 5% 6% 28%	2665
November	1st to 10th	Night	20% 10% 3 6% 5% 5% 3 3 4 6% 34%	2537
	11th to 20th	Night	19% 10% 3 9% 5% 5% 5% 4 5% 6% 30%	2788
	21st to end	Night	21% 13% 4 9% 6% 5% 4 3 5% 6% 24%	2800
December	1st to 10th	Night	19% 17% 5% 10% 7% 6% 5% 4 5% 6% 17%	4580
	11th to 20th	Night	23% 14% 4 9% 5% 4 4 2 4 5% 25%	5208
	21st to end	Night	27% 17% 4 9% 4 4 4 3 4 5% 20%	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	64% 10% 8% 13% 4 1	3598
	11th to 20th	Day	63% 6% 11% 12% 8%	3600
	21st to end	Day	62% 7% 11% 11% 7% 1	4121
February	1st to 10th	Day	60% 6% 11% 17% 5% 1	1800
	11th to 20th	Day	56% 7% 11% 16% 8% 1	1769
	21st to end	Day	59% 7% 11% 13% 9% 2	1650
March	1st to 10th	Day	58% 7% 10% 16% 9% 1	3219
	11th to 20th	Day	53% 10% 13% 14% 9% 1	3482
	21st to end	Day	40% 7% 10% 23% 16% 3	4031
April	1st to 10th	Day	52% 6% 8% 19% 11% 3	2280
	11th to 20th	Day	50% 5% 8% 22% 14% 2	2254
	21st to end	Day	54% 6% 9% 14% 14% 4	2417
May	1st to 10th	Day	48% 9% 11% 20% 10% 2	4440
	11th to 20th	Day	47% 11% 13% 18% 9% 2	4402
	21st to end	Day	42% 10% 12% 21% 14% 2	4837
June	1st to 10th	Day	52% 9% 10% 18% 11% 1	2660
	11th to 20th	Day	41% 10% 12% 23% 12% 2	2660
	21st to end	Day	48% 10% 13% 19% 10% 1	2660
July	1st to 10th	Day	41% 8% 15% 23% 12%	4370
	11th to 20th	Day	38% 8% 15% 30% 9%	4365
	21st to end	Day	35% 9% 14% 31% 11%	4661
August	1st to 10th	Day	44% 7% 16% 23% 9%	4353
	11th to 20th	Day	41% 8% 16% 27% 8%	4029
	21st to end	Day	39% 7% 17% 25% 11% 1	4180
September	1st to 10th	Day	38% 9% 15% 27% 11%	2280
	11th to 20th	Day	34% 8% 14% 30% 13% 1	2278
	21st to end	Day	43% 7% 15% 25% 10%	2031
October	1st to 10th	Day	47% 6% 12% 29% 6%	3160
	11th to 20th	Day	46% 7% 16% 24% 7%	3140
	21st to end	Day	49% 6% 18% 20% 7%	3157
November	1st to 10th	Day	47% 9% 16% 22% 6% 1	1761
	11th to 20th	Day	55% 7% 13% 15% 8% 1	1610
	21st to end	Day	64% 8% 11% 10% 6% 1	1600
December	1st to 10th	Day	70% 7% 13% 9% 2	2600
	11th to 20th	Day	62% 6% 11% 15% 6%	2986
	21st to end	Day	68% 6% 8% 15% 4	3960
January	1st to 10th	Night	68% 6% 11% 12% 4	6349
	11th to 20th	Night	63% 8% 12% 12% 5%	6360
	21st to end	Night	64% 7% 9% 9% 11% 1	6833
February	1st to 10th	Night	60% 6% 11% 15% 7% 1	2600
	11th to 20th	Night	57% 6% 10% 18% 7% 1	2526
	21st to end	Night	56% 6% 10% 18% 10% 1	1980
March	1st to 10th	Night	55% 7% 10% 17% 9% 2	3854
	11th to 20th	Night	57% 8% 13% 14% 7% 1	3503
	21st to end	Night	43% 7% 8% 23% 16% 3	3600
April	1st to 10th	Night	52% 7% 9% 17% 13% 2	1900
	11th to 20th	Night	49% 7% 8% 20% 15% 1	1875
	21st to end	Night	51% 5% 9% 17% 14% 4	1781
May	1st to 10th	Night	48% 12% 11% 17% 9% 3	2520
	11th to 20th	Night	45% 11% 12% 19% 11% 2	2496
	21st to end	Night	39% 11% 13% 18% 17% 1	2739
June	1st to 10th	Night	45% 9% 13% 22% 9% 1	1520
	11th to 20th	Night	39% 9% 11% 23% 16% 2	1520
	21st to end	Night	46% 9% 13% 18% 13% 1	1520
July	1st to 10th	Night	46% 8% 14% 18% 13% 1	2480
	11th to 20th	Night	39% 8% 14% 31% 8%	2472
	21st to end	Night	38% 8% 15% 25% 15%	2651
August	1st to 10th	Night	42% 8% 15% 23% 11%	2549
	11th to 20th	Night	41% 7% 15% 30% 7%	2834
	21st to end	Night	40% 8% 15% 24% 12% 2	3476
September	1st to 10th	Night	36% 7% 12% 29% 15% 1	1900
	11th to 20th	Night	34% 9% 14% 33% 10% 1	1901
	21st to end	Night	41% 6% 12% 29% 11%	2147
October	1st to 10th	Night	40% 6% 14% 27% 12%	3800
	11th to 20th	Night	46% 6% 15% 25% 9%	3779
	21st to end	Night	48% 7% 18% 19% 9%	4390
November	1st to 10th	Night	51% 6% 15% 20% 8% 1	2537
	11th to 20th	Night	55% 6% 12% 17% 9% 1	2788
	21st to end	Night	60% 8% 13% 15% 4	2800
December	1st to 10th	Night	67% 6% 13% 11% 2	4580
	11th to 20th	Night	62% 5% 9% 13% 10% 1	5208
	21st to end	Night	68% 5% 7% 12% 9%	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	22% 20% 34% 21% 4 1	200
	11th to 20th	Day	27% 14% 39% 17% 4 1	200
	21st to end	Day	21% 16% 35% 23% 5%	255
February	1st to 10th	Day	30% 21% 34% 14% 2	300
	11th to 20th	Day	26% 28% 35% 10% 1	307
	21st to end	Day	28% 20% 32% 18% 3	414
March	1st to 10th	Day	25% 17% 35% 19% 5%	500
	11th to 20th	Day	26% 18% 34% 18% 3 1	464
	21st to end	Day	28% 22% 26% 15% 8% 1	506
April	1st to 10th	Day	27% 21% 30% 16% 5% 1	460
	11th to 20th	Day	32% 19% 22% 16% 10% 1	452
	21st to end	Day	30% 20% 30% 12% 7% 2	460
May	1st to 10th	Day	24% 14% 33% 21% 8% 2	463
	11th to 20th	Day	17% 17% 33% 19% 11% 2	487
	21st to end	Day	18% 16% 31% 23% 12% 1	529
June	1st to 10th	Day	23% 12% 31% 23% 9% 1	490
	11th to 20th	Day	15% 14% 31% 26% 11% 3	490
	21st to end	Day	22% 13% 31% 22% 11% 2	490
July	1st to 10th	Day	12% 8% 27% 36% 13% 4	485
	11th to 20th	Day	11% 9% 33% 28% 16% 3	484
	21st to end	Day	12% 6% 31% 31% 14% 5%	532
August	1st to 10th	Day	14% 6% 27% 32% 17% 4	486
	11th to 20th	Day	13% 8% 23% 29% 19% 8%	479
	21st to end	Day	13% 10% 29% 26% 15% 7%	539
September	1st to 10th	Day	16% 10% 30% 20% 15% 9%	490
	11th to 20th	Day	11% 9% 25% 22% 21% 12%	490
	21st to end	Day	18% 12% 28% 23% 14% 5%	490
October	1st to 10th	Day	23% 14% 25% 21% 11% 5%	490
	11th to 20th	Day	23% 19% 31% 18% 8% 1	490
	21st to end	Day	31% 13% 29% 22% 5%	455
November	1st to 10th	Day	24% 17% 30% 19% 9% 1	395
	11th to 20th	Day	25% 20% 36% 13% 5% 1	210
	21st to end	Day	30% 19% 32% 15% 4 1	200
December	1st to 10th	Day	30% 17% 32% 18% 4	200
	11th to 20th	Day	28% 24% 32% 14% 2 1	200
	21st to end	Day	30% 19% 32% 14% 3 1	220
January	1st to 10th	Night	25% 15% 36% 20% 3	800
	11th to 20th	Night	25% 17% 31% 22% 5% 1	800
	21st to end	Night	19% 11% 37% 27% 5%	880
February	1st to 10th	Night	24% 13% 36% 25% 3	800
	11th to 20th	Night	20% 17% 39% 20% 4	783
	21st to end	Night	24% 16% 30% 27% 3	660
March	1st to 10th	Night	23% 15% 35% 22% 4	800
	11th to 20th	Night	22% 19% 34% 20% 5%	767
	21st to end	Night	23% 16% 29% 24% 8%	836
April	1st to 10th	Night	26% 14% 30% 24% 5%	760
	11th to 20th	Night	24% 15% 31% 22% 7%	751
	21st to end	Night	25% 14% 29% 24% 7% 1	641
May	1st to 10th	Night	22% 8% 32% 28% 9% 2	380
	11th to 20th	Night	22% 10% 28% 32% 9%	374
	21st to end	Night	14% 7% 40% 27% 11%	411
June	1st to 10th	Night	18% 4 31% 37% 10%	380
	11th to 20th	Night	14% 8% 30% 34% 12% 2	380
	21st to end	Night	21% 4 31% 30% 14% 1	380
July	1st to 10th	Night	11% 5% 28% 42% 15%	370
	11th to 20th	Night	11% 5% 25% 43% 15% 1	368
	21st to end	Night	9% 3 28% 42% 16% 2	416
August	1st to 10th	Night	13% 4 22% 40% 21% 1	405
	11th to 20th	Night	13% 4 19% 37% 24% 2	573
	21st to end	Night	12% 7% 25% 36% 18% 2	836
September	1st to 10th	Night	13% 6% 29% 33% 18% 1	760
	11th to 20th	Night	16% 6% 20% 31% 23% 3	760
	21st to end	Night	19% 10% 24% 26% 20% 2	760
October	1st to 10th	Night	21% 9% 28% 25% 16% 1	760
	11th to 20th	Night	24% 12% 29% 25% 8% 1	760
	21st to end	Night	26% 14% 28% 26% 6%	836
November	1st to 10th	Night	25% 14% 28% 24% 8% 1	780
	11th to 20th	Night	24% 15% 34% 17% 9% 1	800
	21st to end	Night	29% 17% 27% 22% 6%	800
December	1st to 10th	Night	30% 14% 30% 22% 4	800
	11th to 20th	Night	28% 16% 30% 20% 5% 1	800
	21st to end	Night	33% 15% 29% 20% 3	880

Page generated at 2025-03-09 08:08:45. Version ac07

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