Gatineau Gliding Club
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gatineau Gliding Club clear sky chart from 2005-11-06 to 2026-01-02.

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 8% 5% 5% 5% 4 5% 7% 32%	127570
	Night	17% 12% 4 9% 5% 5% 4 3 5% 6% 30%	123788
Transparency	Day	50% 6% 12% 21% 10% 1	131022
	Night	53% 6% 11% 19% 10% 1	128423
Seeing	Day	21% 10% 27% 24% 13% 4	15895
	Night	22% 7% 26% 32% 11% 1	25000

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% 19% 7% 15% 6% 5% 4 3 4 4 19%	3605
	11th to 20th	Day	13% 15% 6% 14% 7% 5% 5% 3 5% 5% 23%	3570
	21st to end	Day	11% 19% 7% 11% 5% 6% 5% 4 5% 6% 22%	4031
February	1st to 10th	Day	14% 15% 4 12% 6% 5% 5% 3 5% 5% 26%	1800
	11th to 20th	Day	14% 14% 5% 11% 7% 4 5% 3 4 5% 26%	1791
	21st to end	Day	20% 13% 4 9% 6% 5% 4 4 5% 5% 24%	1650
March	1st to 10th	Day	19% 13% 5% 11% 6% 5% 4 4 4 5% 25%	4476
	11th to 20th	Day	12% 12% 4 9% 6% 5% 5% 4 6% 7% 30%	4882
	21st to end	Day	19% 10% 3 8% 6% 4 4 3 4 5% 36%	5832
April	1st to 10th	Day	21% 12% 4 7% 4 4 3 4 4 5% 33%	2400
	11th to 20th	Day	21% 10% 3 6% 4 4 4 3 4 6% 35%	2374
	21st to end	Day	22% 10% 3 8% 5% 5% 4 3 4 6% 31%	2538
May	1st to 10th	Day	24% 10% 4 9% 5% 5% 5% 3 6% 6% 24%	6346
	11th to 20th	Day	18% 10% 3 8% 5% 5% 4 4 5% 7% 31%	6318
	21st to end	Day	22% 8% 3 7% 4 4 4 4 5% 6% 32%	6949
June	1st to 10th	Day	21% 8% 3 7% 5% 5% 4 4 6% 6% 31%	2800
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 5% 7% 8% 38%	2800
	21st to end	Day	19% 7% 2 7% 4 5% 5% 5% 7% 7% 31%	2800
July	1st to 10th	Day	13% 7% 3 7% 6% 6% 6% 5% 7% 9% 33%	6360
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 4 6% 9% 40%	6360
	21st to end	Day	9% 6% 2 5% 4 4 5% 4 6% 10% 46%	6926
August	1st to 10th	Day	13% 7% 2 7% 5% 5% 5% 4 7% 8% 36%	4563
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 9% 38%	4085
	21st to end	Day	15% 5% 2 6% 4 4 5% 3 7% 9% 39%	4312
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 5% 6% 7% 43%	2400
	11th to 20th	Day	12% 4 1 5% 4 3 4 4 6% 7% 50%	2371
	21st to end	Day	18% 7% 2 5% 4 4 4 4 5% 7% 41%	2179
October	1st to 10th	Day	19% 8% 3 6% 4 3 4 3 5% 7% 38%	2000
	11th to 20th	Day	20% 10% 3 8% 5% 5% 5% 4 5% 6% 30%	2000
	21st to end	Day	25% 9% 3 7% 5% 4 4 3 4 6% 28%	2001
November	1st to 10th	Day	16% 10% 3 7% 5% 5% 5% 4 5% 7% 33%	1851
	11th to 20th	Day	17% 13% 4 9% 6% 5% 4 3 5% 6% 29%	1726
	21st to end	Day	23% 14% 5% 9% 6% 5% 4 4 4 6% 21%	1680
December	1st to 10th	Day	21% 21% 5% 10% 5% 5% 4 4 6% 5% 15%	2680
	11th to 20th	Day	18% 17% 4 11% 5% 4 4 3 4 4 25%	3066
	21st to end	Day	23% 16% 4 10% 5% 4 5% 3 4 4 22%	4048
January	1st to 10th	Night	15% 20% 8% 15% 5% 4 3 3 3 4 20%	6364
	11th to 20th	Night	11% 15% 7% 15% 8% 6% 4 4 5% 4 20%	6315
	21st to end	Night	14% 18% 6% 12% 5% 6% 5% 3 5% 5% 21%	6922
February	1st to 10th	Night	14% 14% 6% 11% 6% 6% 6% 4 5% 5% 24%	2600
	11th to 20th	Night	13% 13% 4 11% 6% 5% 5% 4 4 5% 28%	2494
	21st to end	Night	16% 13% 5% 10% 6% 5% 4 3 5% 6% 28%	1980
March	1st to 10th	Night	22% 14% 5% 9% 5% 4 3 3 4 4 28%	5364
	11th to 20th	Night	13% 13% 3 8% 5% 5% 5% 4 6% 8% 31%	5075
	21st to end	Night	18% 11% 3 8% 5% 4 4 3 5% 5% 33%	5100
April	1st to 10th	Night	22% 11% 2 7% 5% 4 4 3 5% 6% 32%	2000
	11th to 20th	Night	19% 10% 3 7% 5% 5% 3 3 4 6% 35%	1975
	21st to end	Night	21% 9% 3 7% 4 3 4 3 4 6% 36%	1876
May	1st to 10th	Night	22% 9% 3 9% 4 6% 5% 4 6% 7% 24%	3594
	11th to 20th	Night	18% 9% 2 7% 5% 4 4 4 5% 7% 35%	3575
	21st to end	Night	18% 10% 4 8% 5% 5% 5% 3 5% 6% 30%	3926
June	1st to 10th	Night	16% 8% 3 8% 4 6% 5% 4 8% 9% 31%	1600
	11th to 20th	Night	14% 7% 2 7% 4 4 4 4 6% 8% 41%	1600
	21st to end	Night	18% 8% 2 6% 5% 4 5% 4 7% 7% 35%	1600
July	1st to 10th	Night	14% 7% 3 8% 5% 5% 6% 5% 7% 9% 32%	3600
	11th to 20th	Night	11% 7% 3 7% 4 4 5% 4 7% 8% 42%	3600
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 7% 46%	3926
August	1st to 10th	Night	12% 7% 3 8% 5% 4 4 5% 6% 7% 38%	2586
	11th to 20th	Night	15% 6% 2 7% 4 4 4 3 4 8% 42%	2927
	21st to end	Night	13% 7% 2 6% 5% 5% 5% 4 6% 7% 40%	3586
September	1st to 10th	Night	10% 6% 1 7% 5% 4 5% 4 5% 7% 45%	2000
	11th to 20th	Night	14% 4 1 5% 4 3 3 3 5% 7% 50%	2028
	21st to end	Night	16% 5% 2 6% 4 4 4 3 4 6% 44%	2219
October	1st to 10th	Night	18% 7% 2 6% 4 4 3 4 6% 6% 40%	2400
	11th to 20th	Night	20% 8% 3 7% 5% 6% 4 3 5% 6% 34%	2400
	21st to end	Night	22% 10% 3 8% 5% 4 4 3 5% 6% 30%	2838
November	1st to 10th	Night	21% 9% 3 7% 5% 4 4 3 5% 6% 32%	2667
	11th to 20th	Night	18% 11% 4 8% 5% 5% 5% 3 5% 5% 30%	2893
	21st to end	Night	21% 13% 4 10% 6% 5% 3 3 5% 5% 24%	2940
December	1st to 10th	Night	18% 17% 6% 12% 6% 5% 5% 4 4 5% 17%	4720
	11th to 20th	Night	24% 15% 5% 9% 5% 4 4 2 3 4 25%	5348
	21st to end	Night	27% 17% 4 9% 4 3 3 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	65% 7% 8% 15% 4 1	3606
	11th to 20th	Day	63% 5% 10% 14% 7% 1	3600
	21st to end	Day	63% 6% 11% 11% 8% 1	4031
February	1st to 10th	Day	59% 5% 9% 19% 6% 2	1800
	11th to 20th	Day	58% 5% 12% 15% 8% 1	1800
	21st to end	Day	60% 5% 10% 13% 11% 1	1650
March	1st to 10th	Day	60% 6% 8% 13% 11% 3	4479
	11th to 20th	Day	51% 7% 16% 15% 10% 1	4882
	21st to end	Day	51% 5% 6% 17% 18% 2	5832
April	1st to 10th	Day	54% 5% 7% 19% 13% 3	2400
	11th to 20th	Day	50% 5% 7% 22% 15% 2	2374
	21st to end	Day	55% 5% 9% 15% 13% 4	2538
May	1st to 10th	Day	58% 7% 7% 18% 8% 2	6357
	11th to 20th	Day	53% 7% 12% 17% 10% 1	6322
	21st to end	Day	50% 7% 12% 19% 12% 1	6949
June	1st to 10th	Day	52% 6% 11% 18% 12% 1	2800
	11th to 20th	Day	42% 7% 12% 24% 13% 2	2800
	21st to end	Day	48% 9% 13% 20% 10% 1	2800
July	1st to 10th	Day	45% 7% 14% 26% 9%	6290
	11th to 20th	Day	38% 6% 13% 30% 12%	6285
	21st to end	Day	33% 6% 16% 35% 10%	6728
August	1st to 10th	Day	44% 7% 16% 23% 9%	4549
	11th to 20th	Day	41% 7% 15% 29% 7% 1	4124
	21st to end	Day	41% 7% 17% 23% 11% 1	4312
September	1st to 10th	Day	37% 7% 15% 28% 12%	2400
	11th to 20th	Day	33% 6% 14% 32% 14% 1	2371
	21st to end	Day	42% 6% 14% 26% 11%	2179
October	1st to 10th	Day	45% 5% 12% 29% 8%	3260
	11th to 20th	Day	46% 6% 15% 26% 7% 1	3240
	21st to end	Day	48% 5% 18% 22% 6%	3213
November	1st to 10th	Day	50% 6% 14% 21% 7% 1	1851
	11th to 20th	Day	56% 5% 13% 16% 10%	1726
	21st to end	Day	63% 7% 12% 12% 5%	1680
December	1st to 10th	Day	69% 6% 12% 11% 2	2680
	11th to 20th	Day	63% 5% 10% 15% 7%	3066
	21st to end	Day	66% 4 9% 16% 6%	4048
January	1st to 10th	Night	68% 5% 10% 12% 4	6364
	11th to 20th	Night	66% 7% 11% 12% 5%	6360
	21st to end	Night	65% 5% 9% 10% 11% 1	6922
February	1st to 10th	Night	60% 6% 10% 17% 7% 1	2600
	11th to 20th	Night	57% 5% 10% 19% 8%	2496
	21st to end	Night	55% 5% 9% 19% 11%	1980
March	1st to 10th	Night	59% 5% 6% 14% 13% 4	5374
	11th to 20th	Night	51% 6% 16% 16% 8% 3	5076
	21st to end	Night	51% 5% 7% 23% 12% 2	5100
April	1st to 10th	Night	54% 5% 8% 17% 14% 2	2000
	11th to 20th	Night	50% 6% 8% 20% 15% 1	1975
	21st to end	Night	50% 4 9% 18% 16% 3	1876
May	1st to 10th	Night	57% 7% 9% 17% 7% 3	3600
	11th to 20th	Night	47% 8% 12% 18% 13% 2	3576
	21st to end	Night	51% 8% 10% 16% 14% 1	3927
June	1st to 10th	Night	47% 8% 13% 20% 12% 1	1600
	11th to 20th	Night	42% 5% 12% 22% 17% 2	1600
	21st to end	Night	45% 9% 12% 19% 14% 1	1600
July	1st to 10th	Night	45% 7% 17% 20% 10% 1	3560
	11th to 20th	Night	38% 6% 14% 31% 10%	3552
	21st to end	Night	35% 6% 14% 30% 15%	3809
August	1st to 10th	Night	43% 7% 15% 26% 8%	2576
	11th to 20th	Night	40% 6% 16% 30% 8%	2954
	21st to end	Night	41% 7% 15% 23% 12% 2	3586
September	1st to 10th	Night	37% 7% 13% 28% 15% 1	2000
	11th to 20th	Night	34% 6% 14% 34% 12% 1	2028
	21st to end	Night	41% 5% 14% 28% 13%	2219
October	1st to 10th	Night	42% 6% 15% 26% 11% 1	3920
	11th to 20th	Night	45% 5% 14% 26% 9%	3899
	21st to end	Night	47% 6% 16% 20% 10%	4576
November	1st to 10th	Night	52% 5% 14% 20% 8% 1	2667
	11th to 20th	Night	54% 6% 11% 18% 9% 1	2893
	21st to end	Night	61% 6% 12% 15% 5%	2940
December	1st to 10th	Night	68% 5% 12% 12% 3	4720
	11th to 20th	Night	63% 4 7% 15% 10% 1	5348
	21st to end	Night	67% 4 6% 13% 9%	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	26% 12% 29% 27% 5% 1	202
	11th to 20th	Day	22% 12% 37% 23% 5% 2	200
	21st to end	Day	19% 10% 33% 30% 7% 1	237
February	1st to 10th	Day	28% 15% 37% 16% 4	300
	11th to 20th	Day	25% 16% 36% 22% 2	338
	21st to end	Day	27% 12% 31% 28% 3	414
March	1st to 10th	Day	24% 11% 30% 27% 8%	500
	11th to 20th	Day	19% 17% 33% 25% 5% 1	500
	21st to end	Day	27% 11% 31% 18% 10% 2	550
April	1st to 10th	Day	26% 18% 26% 18% 10% 1	500
	11th to 20th	Day	28% 14% 24% 18% 12% 3	492
	21st to end	Day	26% 13% 31% 17% 10% 2	500
May	1st to 10th	Day	24% 8% 31% 26% 8% 3	503
	11th to 20th	Day	19% 10% 29% 24% 12% 5%	527
	21st to end	Day	20% 8% 30% 25% 14% 4	573
June	1st to 10th	Day	23% 9% 25% 27% 11% 5%	530
	11th to 20th	Day	13% 12% 26% 29% 15% 5%	530
	21st to end	Day	22% 10% 26% 25% 13% 4	530
July	1st to 10th	Day	13% 6% 23% 32% 18% 7%	525
	11th to 20th	Day	12% 5% 28% 30% 20% 5%	524
	21st to end	Day	13% 5% 26% 30% 21% 5%	576
August	1st to 10th	Day	13% 6% 17% 33% 25% 6%	526
	11th to 20th	Day	15% 6% 16% 29% 25% 10%	519
	21st to end	Day	16% 5% 22% 27% 20% 10%	583
September	1st to 10th	Day	17% 5% 25% 22% 18% 13%	530
	11th to 20th	Day	12% 5% 19% 22% 26% 16%	530
	21st to end	Day	19% 7% 27% 21% 18% 8%	530
October	1st to 10th	Day	23% 8% 24% 21% 18% 5%	530
	11th to 20th	Day	22% 14% 29% 22% 11% 1	530
	21st to end	Day	31% 8% 25% 25% 11%	473
November	1st to 10th	Day	25% 14% 24% 24% 12% 1	425
	11th to 20th	Day	25% 11% 33% 22% 7% 2	266
	21st to end	Day	31% 15% 25% 22% 6% 1	220
December	1st to 10th	Day	30% 9% 29% 23% 10%	220
	11th to 20th	Day	25% 15% 38% 18% 3	220
	21st to end	Day	31% 12% 36% 14% 6% 1	242
January	1st to 10th	Night	27% 9% 30% 28% 5%	805
	11th to 20th	Night	27% 9% 28% 29% 6% 1	800
	21st to end	Night	19% 7% 30% 36% 8% 1	880
February	1st to 10th	Night	21% 8% 35% 30% 6%	800
	11th to 20th	Night	20% 9% 36% 28% 6%	783
	21st to end	Night	24% 8% 30% 33% 5%	660
March	1st to 10th	Night	23% 9% 29% 32% 7%	800
	11th to 20th	Night	23% 9% 32% 29% 6% 1	800
	21st to end	Night	23% 8% 30% 30% 9%	880
April	1st to 10th	Night	28% 9% 28% 29% 6%	800
	11th to 20th	Night	24% 10% 30% 27% 8% 1	791
	21st to end	Night	26% 7% 28% 30% 8% 1	676
May	1st to 10th	Night	25% 6% 28% 31% 8% 2	400
	11th to 20th	Night	24% 5% 27% 32% 13%	394
	21st to end	Night	17% 6% 29% 34% 14%	433
June	1st to 10th	Night	16% 5% 26% 43% 11% 1	400
	11th to 20th	Night	18% 3 27% 40% 12% 1	400
	21st to end	Night	19% 4 25% 35% 17% 1	400
July	1st to 10th	Night	10% 4 21% 45% 19%	390
	11th to 20th	Night	11% 3 19% 46% 19% 1	388
	21st to end	Night	13% 3 17% 47% 18% 1	438
August	1st to 10th	Night	11% 4 14% 48% 23% 1	398
	11th to 20th	Night	14% 4 13% 37% 29% 3	620
	21st to end	Night	14% 3 20% 40% 20% 2	880
September	1st to 10th	Night	13% 4 20% 41% 21% 1	800
	11th to 20th	Night	16% 4 15% 34% 27% 3	800
	21st to end	Night	18% 5% 22% 32% 21% 2	800
October	1st to 10th	Night	22% 5% 24% 32% 18% 1	800
	11th to 20th	Night	24% 7% 26% 32% 10% 1	800
	21st to end	Night	25% 9% 25% 34% 7%	880
November	1st to 10th	Night	25% 9% 23% 31% 10% 1	820
	11th to 20th	Night	23% 10% 31% 26% 10%	840
	21st to end	Night	27% 10% 28% 25% 8%	840
December	1st to 10th	Night	28% 9% 29% 28% 6%	840
	11th to 20th	Night	29% 11% 29% 24% 6% 1	840
	21st to end	Night	35% 9% 28% 23% 5% 1	924

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