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 2026-07-16.

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% 7% 32%	138485
	Night	17% 11% 4 9% 5% 5% 5% 4 5% 6% 30%	134196
Transparency	Day	50% 7% 12% 21% 10% 1	141952
	Night	53% 7% 11% 18% 10% 1	138818
Seeing	Day	21% 15% 31% 21% 9% 3	16568
	Night	22% 12% 30% 27% 9% 1	25632

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% 16% 7% 14% 6% 5% 5% 4 5% 5% 20%	4661
	11th to 20th	Day	12% 17% 6% 15% 8% 6% 4 3 4 5% 20%	4650
	21st to end	Day	8% 14% 6% 14% 8% 8% 6% 4 6% 5% 20%	5341
February	1st to 10th	Day	13% 14% 5% 13% 6% 6% 4 3 5% 5% 25%	1890
	11th to 20th	Day	12% 15% 5% 10% 6% 5% 4 4 6% 5% 28%	1851
	21st to end	Day	18% 13% 5% 10% 7% 5% 5% 4 5% 4 24%	1730
March	1st to 10th	Day	19% 12% 4 10% 6% 5% 4 4 5% 5% 25%	4576
	11th to 20th	Day	13% 12% 4 9% 6% 5% 6% 4 6% 7% 30%	5081
	21st to end	Day	17% 10% 4 8% 6% 4 4 3 4 5% 36%	5907
April	1st to 10th	Day	22% 10% 3 7% 4 4 3 3 5% 6% 32%	2520
	11th to 20th	Day	22% 9% 3 6% 5% 3 5% 3 4 5% 36%	2494
	21st to end	Day	22% 9% 2 8% 6% 4 4 3 5% 5% 32%	2671
May	1st to 10th	Day	21% 9% 3 7% 5% 5% 5% 4 6% 7% 28%	8237
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 5% 7% 33%	8221
	21st to end	Day	20% 9% 2 6% 4 4 4 3 5% 6% 35%	9060
June	1st to 10th	Day	21% 7% 3 7% 6% 5% 4 5% 5% 7% 31%	2940
	11th to 20th	Day	14% 5% 3 7% 5% 5% 5% 4 6% 8% 38%	2940
	21st to end	Day	19% 7% 2 6% 5% 4 6% 5% 7% 7% 32%	2940
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 4 7% 9% 35%	6500
	11th to 20th	Day	11% 5% 2 7% 4 5% 5% 4 7% 8% 44%	6430
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 46%	6926
August	1st to 10th	Day	14% 5% 3 8% 4 5% 5% 5% 7% 8% 37%	4505
	11th to 20th	Day	16% 6% 2 6% 5% 4 4 4 7% 9% 38%	4118
	21st to end	Day	14% 5% 2 6% 4 5% 5% 4 6% 9% 41%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 5% 4 5% 8% 44%	2400
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 3 5% 7% 49%	2398
	21st to end	Day	18% 5% 2 6% 4 4 4 3 5% 9% 39%	2138
October	1st to 10th	Day	20% 8% 3 6% 4 4 4 3 6% 6% 37%	2000
	11th to 20th	Day	22% 8% 3 7% 5% 5% 5% 4 6% 7% 29%	2000
	21st to end	Day	25% 10% 2 6% 5% 5% 5% 3 5% 5% 29%	2033
November	1st to 10th	Day	16% 10% 3 7% 5% 5% 5% 4 6% 6% 34%	1851
	11th to 20th	Day	19% 12% 4 7% 5% 4 5% 4 6% 6% 27%	1690
	21st to end	Day	22% 14% 4 9% 6% 6% 5% 4 4 5% 21%	1680
December	1st to 10th	Day	20% 20% 6% 10% 5% 5% 5% 4 6% 5% 15%	2680
	11th to 20th	Day	17% 16% 5% 10% 6% 5% 5% 3 3 4 25%	3066
	21st to end	Day	23% 16% 4 11% 6% 5% 5% 3 4 4 19%	4048
January	1st to 10th	Night	14% 19% 8% 15% 6% 4 4 3 4 5% 20%	8234
	11th to 20th	Night	11% 18% 6% 15% 8% 6% 6% 3 4 5% 19%	8235
	21st to end	Night	11% 17% 5% 12% 7% 6% 6% 4 5% 6% 22%	8838
February	1st to 10th	Night	14% 13% 5% 12% 7% 6% 5% 4 5% 5% 25%	2730
	11th to 20th	Night	13% 13% 5% 11% 7% 6% 4 3 4 5% 29%	2653
	21st to end	Night	15% 13% 4 9% 6% 5% 5% 3 5% 6% 28%	2076
March	1st to 10th	Night	22% 13% 4 9% 5% 4 4 3 3 4 28%	5484
	11th to 20th	Night	13% 12% 4 9% 6% 5% 4 4 6% 8% 29%	5094
	21st to end	Night	19% 9% 4 8% 5% 4 4 3 5% 6% 33%	5266
April	1st to 10th	Night	21% 10% 4 7% 4 4 4 3 5% 5% 33%	2100
	11th to 20th	Night	20% 9% 4 7% 5% 4 4 4 4 5% 36%	2075
	21st to end	Night	21% 9% 2 7% 4 4 4 3 4 6% 36%	1968
May	1st to 10th	Night	21% 8% 3 9% 5% 5% 6% 4 6% 7% 25%	4660
	11th to 20th	Night	16% 8% 3 7% 5% 4 5% 3 5% 7% 37%	4639
	21st to end	Night	20% 8% 3 7% 5% 5% 5% 3 6% 6% 34%	5114
June	1st to 10th	Night	16% 6% 2 7% 6% 5% 5% 5% 6% 7% 35%	1680
	11th to 20th	Night	15% 6% 2 7% 4 4 4 4 6% 8% 41%	1680
	21st to end	Night	19% 6% 2 7% 5% 4 5% 5% 6% 7% 35%	1680
July	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 5% 6% 8% 34%	3680
	11th to 20th	Night	12% 6% 2 7% 4 4 5% 4 6% 7% 43%	3640
	21st to end	Night	9% 5% 2 7% 4 4 5% 4 6% 7% 47%	3926
August	1st to 10th	Night	12% 7% 3 7% 4 4 5% 4 6% 8% 39%	2641
	11th to 20th	Night	14% 6% 2 7% 4 4 4 4 6% 7% 42%	2898
	21st to end	Night	13% 5% 2 7% 5% 5% 5% 4 6% 6% 41%	3586
September	1st to 10th	Night	12% 4 2 6% 4 5% 5% 4 5% 6% 48%	2000
	11th to 20th	Night	14% 4 1 5% 4 3 3 3 5% 6% 50%	2001
	21st to end	Night	17% 6% 2 7% 5% 3 4 2 4 6% 44%	2260
October	1st to 10th	Night	18% 8% 2 6% 3 5% 4 3 5% 5% 41%	2400
	11th to 20th	Night	21% 8% 2 7% 6% 5% 4 3 5% 6% 33%	2400
	21st to end	Night	23% 9% 3 7% 5% 4 5% 4 5% 6% 29%	2805
November	1st to 10th	Night	20% 10% 3 6% 5% 5% 3 3 4 6% 34%	2667
	11th to 20th	Night	19% 11% 3 9% 5% 5% 5% 4 5% 6% 30%	2928
	21st to end	Night	21% 13% 4 9% 6% 5% 4 3 5% 6% 24%	2940
December	1st to 10th	Night	19% 17% 5% 10% 7% 5% 5% 4 5% 6% 17%	4720
	11th to 20th	Night	23% 15% 4 9% 6% 4 4 3 4 5% 25%	5348
	21st to end	Night	27% 17% 4 9% 4 3 4 3 4 5% 20%	7150

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	62% 10% 10% 14% 4	4662
	11th to 20th	Day	66% 5% 9% 11% 9%	4680
	21st to end	Day	63% 7% 12% 10% 8% 1	5341
February	1st to 10th	Day	59% 6% 11% 17% 5% 1	1890
	11th to 20th	Day	56% 7% 11% 17% 8% 1	1860
	21st to end	Day	60% 6% 10% 13% 9% 1	1730
March	1st to 10th	Day	57% 6% 10% 12% 12% 3	4579
	11th to 20th	Day	50% 9% 17% 15% 9% 1	5081
	21st to end	Day	49% 5% 8% 19% 16% 2	5907
April	1st to 10th	Day	53% 6% 9% 19% 12% 3	2520
	11th to 20th	Day	51% 5% 7% 21% 14% 2	2494
	21st to end	Day	53% 6% 8% 15% 14% 4	2671
May	1st to 10th	Day	52% 6% 10% 20% 10% 2	8249
	11th to 20th	Day	48% 8% 12% 21% 10% 1	8225
	21st to end	Day	48% 7% 11% 22% 12% 1	9061
June	1st to 10th	Day	51% 8% 10% 18% 12% 1	2940
	11th to 20th	Day	41% 10% 11% 24% 12% 2	2940
	21st to end	Day	46% 10% 13% 20% 10% 1	2940
July	1st to 10th	Day	43% 7% 16% 25% 10%	6430
	11th to 20th	Day	36% 7% 13% 30% 13%	6355
	21st to end	Day	32% 8% 16% 35% 10%	6728
August	1st to 10th	Day	44% 7% 16% 23% 9%	4491
	11th to 20th	Day	41% 7% 16% 28% 8% 1	4157
	21st to end	Day	39% 7% 17% 26% 11% 1	4312
September	1st to 10th	Day	37% 9% 15% 28% 11%	2400
	11th to 20th	Day	33% 8% 14% 32% 13% 1	2398
	21st to end	Day	43% 7% 15% 25% 10%	2138
October	1st to 10th	Day	46% 6% 12% 29% 7%	3260
	11th to 20th	Day	45% 7% 16% 23% 8% 1	3240
	21st to end	Day	49% 6% 18% 20% 7%	3258
November	1st to 10th	Day	48% 9% 15% 21% 6% 1	1851
	11th to 20th	Day	56% 7% 13% 15% 8% 1	1690
	21st to end	Day	64% 8% 11% 10% 6%	1680
December	1st to 10th	Day	70% 7% 12% 9% 2	2680
	11th to 20th	Day	62% 6% 11% 14% 6%	3066
	21st to end	Day	68% 6% 8% 15% 4	4048
January	1st to 10th	Night	67% 6% 10% 12% 5%	8234
	11th to 20th	Night	66% 7% 10% 11% 6%	8280
	21st to end	Night	61% 6% 8% 12% 11% 1	8838
February	1st to 10th	Night	60% 6% 11% 16% 7% 1	2730
	11th to 20th	Night	57% 6% 10% 19% 7% 1	2655
	21st to end	Night	56% 6% 10% 18% 9%	2076
March	1st to 10th	Night	59% 5% 8% 14% 11% 3	5494
	11th to 20th	Night	50% 8% 16% 15% 7% 3	5095
	21st to end	Night	50% 5% 8% 21% 12% 2	5266
April	1st to 10th	Night	53% 6% 9% 18% 13% 2	2100
	11th to 20th	Night	50% 7% 8% 20% 15% 1	2075
	21st to end	Night	50% 5% 8% 18% 16% 3	1968
May	1st to 10th	Night	54% 9% 11% 17% 8% 2	4666
	11th to 20th	Night	45% 8% 12% 21% 13% 1	4640
	21st to end	Night	47% 8% 11% 18% 15% 1	5115
June	1st to 10th	Night	45% 9% 12% 22% 11% 2	1680
	11th to 20th	Night	39% 8% 11% 24% 16% 2	1680
	21st to end	Night	46% 8% 13% 19% 13% 1	1680
July	1st to 10th	Night	45% 7% 16% 19% 12% 1	3640
	11th to 20th	Night	37% 7% 13% 31% 11%	3592
	21st to end	Night	35% 7% 13% 30% 16%	3809
August	1st to 10th	Night	41% 8% 16% 24% 11% 1	2631
	11th to 20th	Night	41% 7% 15% 30% 8%	2925
	21st to end	Night	40% 7% 15% 24% 12% 2	3586
September	1st to 10th	Night	36% 7% 13% 30% 14% 1	2000
	11th to 20th	Night	33% 8% 14% 34% 10% 1	2001
	21st to end	Night	41% 6% 12% 28% 12%	2260
October	1st to 10th	Night	40% 6% 14% 27% 12% 1	3920
	11th to 20th	Night	45% 6% 15% 25% 9%	3899
	21st to end	Night	48% 7% 17% 20% 9%	4530
November	1st to 10th	Night	51% 6% 15% 20% 8%	2667
	11th to 20th	Night	56% 6% 12% 17% 9% 1	2928
	21st to end	Night	60% 8% 13% 15% 5%	2940
December	1st to 10th	Night	67% 6% 12% 12% 3	4720
	11th to 20th	Night	62% 5% 9% 13% 11% 1	5348
	21st to end	Night	68% 5% 7% 12% 8%	7150

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	21% 19% 34% 21% 4	220
	11th to 20th	Day	27% 15% 38% 15% 3 1	220
	21st to end	Day	20% 16% 35% 23% 6%	281
February	1st to 10th	Day	28% 19% 34% 16% 2	330
	11th to 20th	Day	25% 26% 36% 12% 1	338
	21st to end	Day	27% 19% 33% 19% 2	446
March	1st to 10th	Day	24% 17% 36% 18% 5%	540
	11th to 20th	Day	27% 17% 34% 18% 3 1	540
	21st to end	Day	28% 23% 26% 14% 7% 1	594
April	1st to 10th	Day	29% 22% 29% 15% 5% 1	540
	11th to 20th	Day	32% 19% 23% 16% 9% 2	532
	21st to end	Day	29% 19% 32% 12% 6% 1	540
May	1st to 10th	Day	25% 15% 33% 19% 7% 1	543
	11th to 20th	Day	17% 18% 35% 18% 10% 2	567
	21st to end	Day	20% 16% 30% 22% 10% 1	617
June	1st to 10th	Day	23% 12% 31% 23% 9% 2	570
	11th to 20th	Day	15% 15% 31% 26% 11% 2	570
	21st to end	Day	20% 13% 32% 23% 10% 2	570
July	1st to 10th	Day	12% 8% 29% 34% 13% 4	565
	11th to 20th	Day	11% 9% 34% 27% 16% 3	544
	21st to end	Day	11% 7% 33% 30% 14% 4	576
August	1st to 10th	Day	13% 6% 27% 33% 17% 4	526
	11th to 20th	Day	14% 8% 23% 28% 19% 8%	519
	21st to end	Day	13% 10% 30% 26% 14% 7%	583
September	1st to 10th	Day	15% 11% 30% 20% 15% 9%	530
	11th to 20th	Day	10% 8% 24% 24% 22% 12%	530
	21st to end	Day	18% 12% 29% 23% 13% 5%	530
October	1st to 10th	Day	22% 14% 25% 22% 12% 5%	530
	11th to 20th	Day	22% 20% 32% 18% 7% 1	530
	21st to end	Day	30% 12% 30% 22% 5%	490
November	1st to 10th	Day	25% 17% 30% 19% 8% 1	425
	11th to 20th	Day	24% 20% 36% 13% 7% 1	230
	21st to end	Day	30% 18% 34% 14% 3 1	220
December	1st to 10th	Day	29% 16% 32% 19% 4	220
	11th to 20th	Day	26% 23% 35% 14% 2	220
	21st to end	Day	31% 19% 32% 14% 3 1	242
January	1st to 10th	Night	25% 15% 36% 21% 3	840
	11th to 20th	Night	26% 18% 30% 21% 5% 1	840
	21st to end	Night	19% 12% 37% 27% 5%	924
February	1st to 10th	Night	23% 12% 35% 26% 4	840
	11th to 20th	Night	19% 17% 40% 20% 4	823
	21st to end	Night	24% 16% 30% 27% 3	692
March	1st to 10th	Night	23% 15% 36% 22% 4	840
	11th to 20th	Night	22% 19% 33% 21% 4	840
	21st to end	Night	24% 16% 29% 24% 7%	924
April	1st to 10th	Night	27% 14% 30% 24% 5%	840
	11th to 20th	Night	25% 14% 31% 23% 7%	831
	21st to end	Night	25% 14% 29% 24% 7% 1	708
May	1st to 10th	Night	22% 10% 31% 27% 9% 1	420
	11th to 20th	Night	21% 10% 29% 31% 9%	414
	21st to end	Night	15% 8% 39% 27% 10%	455
June	1st to 10th	Night	17% 4 30% 38% 10%	420
	11th to 20th	Night	15% 9% 31% 33% 11% 2	420
	21st to end	Night	20% 4 31% 31% 13%	420
July	1st to 10th	Night	10% 4 29% 43% 14%	410
	11th to 20th	Night	11% 6% 24% 44% 15% 1	398
	21st to end	Night	8% 4 28% 43% 16% 2	438
August	1st to 10th	Night	12% 4 22% 41% 21% 1	427
	11th to 20th	Night	13% 4 19% 37% 24% 2	604
	21st to end	Night	12% 7% 25% 36% 18% 2	880
September	1st to 10th	Night	13% 6% 29% 33% 19% 1	800
	11th to 20th	Night	15% 6% 20% 32% 23% 4	800
	21st to end	Night	19% 9% 25% 26% 20% 2	800
October	1st to 10th	Night	20% 9% 28% 26% 16% 1	800
	11th to 20th	Night	23% 12% 31% 26% 8% 1	800
	21st to end	Night	26% 13% 28% 27% 6%	880
November	1st to 10th	Night	25% 14% 27% 25% 8%	820
	11th to 20th	Night	24% 15% 34% 17% 9%	840
	21st to end	Night	28% 17% 27% 22% 6%	840
December	1st to 10th	Night	30% 14% 30% 23% 4	840
	11th to 20th	Night	27% 16% 31% 20% 5% 1	840
	21st to end	Night	33% 15% 29% 19% 3	924

Page generated at 2026-07-13 03:14:51. Version ac07

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