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 2024-01-14.

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	18% 9% 3 6% 6% 3 5% 5% 5% 7% 33%	74752
	Night	18% 10% 4 7% 6% 3 4 4 5% 6% 32%	75003
Transparency	Day	50% 6% 12% 20% 10% 1	74457
	Night	52% 6% 11% 19% 10% 1	74832
Seeing	Day	21% 9% 26% 25% 14% 5%	13392
	Night	22% 7% 26% 32% 11% 1	22565

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	18% 18% 6% 10% 7% 3 4 4 3 4 21%	1517
	11th to 20th	Day	20% 15% 6% 9% 6% 3 4 3 4 5% 24%	1464
	21st to end	Day	13% 13% 6% 9% 7% 4 5% 7% 4 7% 25%	1613
February	1st to 10th	Day	15% 14% 5% 11% 7% 3 6% 4 5% 5% 25%	1620
	11th to 20th	Day	15% 14% 6% 9% 7% 3 5% 4 4 6% 28%	1607
	21st to end	Day	20% 12% 5% 9% 7% 4 4 4 4 6% 24%	1480
March	1st to 10th	Day	16% 11% 4 9% 8% 4 5% 5% 4 5% 30%	1797
	11th to 20th	Day	17% 10% 4 7% 7% 4 5% 4 4 6% 32%	1938
	21st to end	Day	20% 8% 3 5% 6% 3 4 4 5% 5% 37%	2322
April	1st to 10th	Day	21% 11% 4 6% 5% 3 4 4 4 5% 33%	2160
	11th to 20th	Day	21% 7% 4 6% 5% 3 4 4 4 6% 36%	2134
	21st to end	Day	23% 9% 4 6% 6% 4 4 4 4 6% 30%	2283
May	1st to 10th	Day	20% 8% 3 6% 6% 3 4 5% 5% 6% 34%	2520
	11th to 20th	Day	18% 7% 3 5% 5% 3 4 4 4 7% 39%	2478
	21st to end	Day	17% 7% 3 5% 5% 4 5% 5% 6% 7% 37%	2725
June	1st to 10th	Day	22% 7% 3 6% 5% 4 5% 4 6% 7% 30%	2520
	11th to 20th	Day	14% 7% 2 5% 6% 3 6% 5% 6% 7% 38%	2520
	21st to end	Day	19% 6% 2 7% 5% 4 5% 6% 6% 8% 31%	2520
July	1st to 10th	Day	12% 6% 2 4 6% 4 5% 6% 6% 9% 40%	2520
	11th to 20th	Day	12% 5% 3 6% 6% 3 5% 6% 7% 9% 37%	2520
	21st to end	Day	12% 6% 3 5% 5% 4 5% 6% 7% 10% 38%	2744
August	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 6% 6% 8% 39%	2506
	11th to 20th	Day	12% 5% 2 5% 5% 4 5% 6% 6% 9% 40%	2259
	21st to end	Day	12% 6% 2 4 6% 3 5% 5% 6% 8% 43%	2376
September	1st to 10th	Day	14% 5% 2 4 5% 3 5% 6% 6% 7% 42%	2160
	11th to 20th	Day	14% 4 2 4 4 2 4 4 6% 7% 48%	2135
	21st to end	Day	17% 7% 2 4 5% 3 4 5% 5% 7% 41%	1962
October	1st to 10th	Day	20% 8% 3 5% 5% 3 4 4 5% 6% 36%	1800
	11th to 20th	Day	22% 9% 3 8% 6% 3 5% 5% 5% 6% 28%	1800
	21st to end	Day	26% 9% 4 6% 6% 4 4 4 4 6% 27%	1801
November	1st to 10th	Day	17% 9% 3 6% 5% 4 6% 5% 5% 7% 34%	1671
	11th to 20th	Day	19% 12% 5% 7% 7% 4 4 3 5% 6% 28%	1562
	21st to end	Day	22% 12% 4 8% 8% 4 5% 5% 4 7% 22%	1520
December	1st to 10th	Day	23% 14% 5% 9% 7% 4 5% 5% 5% 5% 18%	1520
	11th to 20th	Day	21% 15% 4 9% 6% 3 4 4 4 5% 25%	1906
	21st to end	Day	28% 18% 5% 9% 6% 2 3 3 3 4 20%	2772
January	1st to 10th	Night	19% 16% 7% 11% 7% 4 5% 4 4 4 20%	2649
	11th to 20th	Night	20% 16% 6% 9% 7% 3 4 4 4 4 23%	2569
	21st to end	Night	13% 14% 5% 9% 7% 4 5% 4 5% 6% 29%	2740
February	1st to 10th	Night	15% 12% 7% 10% 7% 4 7% 5% 5% 5% 23%	2340
	11th to 20th	Night	14% 12% 5% 10% 7% 3 5% 5% 4 5% 29%	2238
	21st to end	Night	17% 12% 5% 8% 6% 3 5% 5% 5% 6% 29%	1776
March	1st to 10th	Night	16% 12% 5% 9% 7% 4 5% 4 4 4 29%	2150
	11th to 20th	Night	17% 13% 4 8% 6% 3 4 4 4 5% 33%	2019
	21st to end	Night	17% 11% 3 6% 5% 3 3 3 4 5% 39%	2034
April	1st to 10th	Night	23% 10% 3 6% 5% 3 4 4 4 6% 33%	1800
	11th to 20th	Night	20% 8% 3 5% 6% 3 4 4 4 6% 36%	1775
	21st to end	Night	21% 9% 3 7% 5% 2 5% 4 4 6% 35%	1690
May	1st to 10th	Night	21% 8% 2 6% 4 3 4 5% 5% 6% 37%	1440
	11th to 20th	Night	19% 7% 2 5% 5% 2 3 4 4 7% 41%	1415
	21st to end	Night	14% 6% 3 5% 5% 3 5% 4 6% 6% 42%	1550
June	1st to 10th	Night	17% 6% 3 6% 5% 4 4 5% 8% 10% 32%	1440
	11th to 20th	Night	15% 7% 3 6% 5% 2 4 5% 5% 8% 40%	1440
	21st to end	Night	17% 7% 2 4 6% 3 5% 5% 7% 7% 36%	1440
July	1st to 10th	Night	11% 5% 2 5% 5% 4 5% 5% 7% 7% 45%	1440
	11th to 20th	Night	11% 6% 3 6% 4 3 4 5% 7% 8% 43%	1440
	21st to end	Night	10% 5% 3 5% 5% 3 6% 6% 6% 8% 42%	1574
August	1st to 10th	Night	11% 5% 3 5% 6% 3 5% 6% 7% 8% 42%	1432
	11th to 20th	Night	12% 5% 2 5% 5% 3 4 5% 5% 9% 45%	1621
	21st to end	Night	12% 6% 3 5% 5% 3 5% 5% 7% 8% 43%	1980
September	1st to 10th	Night	11% 6% 2 6% 6% 4 5% 6% 5% 7% 43%	1800
	11th to 20th	Night	16% 4 2 4 5% 2 3 4 5% 7% 48%	1824
	21st to end	Night	16% 5% 2 5% 5% 4 4 4 4 7% 44%	1997
October	1st to 10th	Night	19% 8% 2 6% 4 3 4 5% 5% 7% 37%	2160
	11th to 20th	Night	21% 7% 3 6% 6% 4 4 4 5% 6% 32%	2160
	21st to end	Night	23% 9% 3 7% 7% 3 4 4 5% 6% 29%	2554
November	1st to 10th	Night	20% 9% 4 6% 6% 3 4 4 5% 6% 34%	2407
	11th to 20th	Night	19% 10% 4 7% 6% 3 6% 4 5% 5% 30%	2617
	21st to end	Night	22% 11% 4 8% 7% 4 4 4 5% 5% 24%	2660
December	1st to 10th	Night	21% 15% 7% 9% 6% 4 5% 5% 4 5% 19%	2660
	11th to 20th	Night	23% 14% 5% 7% 6% 3 4 4 4 4 26%	3288
	21st to end	Night	31% 17% 4 8% 5% 2 3 3 4 3 19%	4884

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	67% 6% 8% 14% 5%	1518
	11th to 20th	Day	64% 4 9% 12% 10% 1	1464
	21st to end	Day	58% 6% 12% 15% 8% 1	1613
February	1st to 10th	Day	60% 5% 9% 18% 5% 2	1620
	11th to 20th	Day	58% 4 13% 15% 8% 1	1616
	21st to end	Day	61% 5% 9% 14% 10% 1	1480
March	1st to 10th	Day	57% 5% 10% 16% 10% 1	1800
	11th to 20th	Day	54% 5% 12% 15% 12% 2	1938
	21st to end	Day	49% 6% 9% 17% 14% 5%	2322
April	1st to 10th	Day	54% 4 8% 19% 12% 3	2160
	11th to 20th	Day	49% 5% 7% 22% 15% 2	2134
	21st to end	Day	55% 5% 10% 14% 13% 4	2283
May	1st to 10th	Day	51% 5% 7% 19% 14% 3	2520
	11th to 20th	Day	45% 6% 9% 21% 16% 3	2482
	21st to end	Day	44% 8% 13% 19% 14% 2	2725
June	1st to 10th	Day	53% 6% 12% 18% 11% 1	2520
	11th to 20th	Day	42% 7% 12% 23% 13% 3	2520
	21st to end	Day	49% 9% 13% 18% 10% 1	2520
July	1st to 10th	Day	39% 8% 14% 25% 13% 1	2450
	11th to 20th	Day	39% 8% 16% 26% 10%	2445
	21st to end	Day	39% 9% 17% 24% 11%	2591
August	1st to 10th	Day	41% 9% 17% 24% 9%	2492
	11th to 20th	Day	39% 9% 16% 26% 9% 1	2259
	21st to end	Day	38% 8% 15% 26% 12% 1	2376
September	1st to 10th	Day	38% 7% 15% 26% 13%	2160
	11th to 20th	Day	35% 7% 14% 31% 13% 1	2135
	21st to end	Day	42% 7% 15% 28% 9%	1962
October	1st to 10th	Day	49% 6% 11% 23% 11% 1	1800
	11th to 20th	Day	56% 7% 14% 17% 6% 1	1800
	21st to end	Day	59% 5% 12% 17% 7% 1	1801
November	1st to 10th	Day	49% 6% 15% 22% 7% 1	1671
	11th to 20th	Day	56% 5% 14% 15% 9%	1562
	21st to end	Day	62% 7% 13% 13% 5%	1520
December	1st to 10th	Day	68% 6% 12% 11% 3	1520
	11th to 20th	Day	63% 6% 13% 14% 4	1906
	21st to end	Day	71% 4 8% 13% 4	2772
January	1st to 10th	Night	68% 5% 9% 12% 5%	2649
	11th to 20th	Night	66% 5% 9% 11% 8% 1	2569
	21st to end	Night	57% 5% 10% 16% 11% 1	2740
February	1st to 10th	Night	62% 5% 10% 16% 6% 1	2340
	11th to 20th	Night	57% 5% 10% 19% 8%	2240
	21st to end	Night	55% 5% 9% 18% 12%	1776
March	1st to 10th	Night	58% 5% 9% 16% 10% 2	2160
	11th to 20th	Night	54% 4 10% 17% 11% 3	2020
	21st to end	Night	48% 5% 7% 20% 15% 4	2034
April	1st to 10th	Night	53% 5% 9% 17% 14% 2	1800
	11th to 20th	Night	49% 5% 8% 21% 16% 2	1775
	21st to end	Night	51% 4 9% 17% 15% 4	1690
May	1st to 10th	Night	48% 4 8% 18% 16% 5%	1440
	11th to 20th	Night	43% 5% 9% 20% 19% 4	1416
	21st to end	Night	41% 6% 14% 19% 17% 3	1551
June	1st to 10th	Night	46% 8% 14% 21% 10% 1	1440
	11th to 20th	Night	43% 6% 11% 21% 17% 2	1440
	21st to end	Night	44% 9% 13% 19% 14%	1440
July	1st to 10th	Night	34% 9% 14% 26% 16% 2	1400
	11th to 20th	Night	36% 7% 14% 30% 13%	1392
	21st to end	Night	37% 9% 16% 24% 14%	1486
August	1st to 10th	Night	37% 9% 19% 24% 11% 1	1422
	11th to 20th	Night	36% 7% 17% 29% 10%	1621
	21st to end	Night	36% 8% 17% 28% 11%	1980
September	1st to 10th	Night	39% 7% 13% 26% 15% 1	1800
	11th to 20th	Night	36% 6% 13% 34% 11% 1	1824
	21st to end	Night	41% 5% 13% 30% 11%	1997
October	1st to 10th	Night	46% 6% 12% 23% 12% 1	2160
	11th to 20th	Night	52% 7% 12% 21% 9%	2160
	21st to end	Night	57% 6% 13% 16% 8% 1	2554
November	1st to 10th	Night	51% 5% 15% 20% 8%	2407
	11th to 20th	Night	54% 7% 12% 18% 9% 1	2617
	21st to end	Night	61% 7% 13% 15% 5%	2660
December	1st to 10th	Night	68% 5% 10% 13% 4	2660
	11th to 20th	Night	61% 5% 9% 16% 7% 1	3288
	21st to end	Night	70% 5% 8% 13% 4	4884

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	27% 12% 26% 29% 6% 2	180
	11th to 20th	Day	24% 10% 36% 23% 5% 2	166
	21st to end	Day	19% 8% 35% 28% 8% 1	190
February	1st to 10th	Day	31% 14% 40% 14% 2	240
	11th to 20th	Day	26% 12% 38% 22% 2	274
	21st to end	Day	28% 11% 31% 27% 3	346
March	1st to 10th	Day	22% 10% 31% 28% 9%	420
	11th to 20th	Day	20% 16% 31% 26% 6% 1	420
	21st to end	Day	27% 10% 28% 21% 11% 3	462
April	1st to 10th	Day	26% 15% 27% 20% 10% 2	420
	11th to 20th	Day	27% 13% 23% 19% 13% 4	412
	21st to end	Day	27% 10% 30% 20% 11% 2	420
May	1st to 10th	Day	24% 8% 30% 26% 9% 4	423
	11th to 20th	Day	19% 10% 29% 26% 12% 4	447
	21st to end	Day	18% 7% 32% 25% 13% 4	485
June	1st to 10th	Day	24% 7% 25% 28% 10% 5%	450
	11th to 20th	Day	14% 11% 24% 29% 16% 6%	450
	21st to end	Day	20% 8% 23% 28% 15% 5%	450
July	1st to 10th	Day	12% 6% 20% 34% 20% 8%	445
	11th to 20th	Day	12% 5% 26% 31% 21% 5%	444
	21st to end	Day	14% 4 24% 31% 22% 5%	488
August	1st to 10th	Day	14% 6% 17% 32% 25% 7%	446
	11th to 20th	Day	15% 5% 14% 29% 26% 10%	439
	21st to end	Day	15% 5% 21% 27% 21% 10%	495
September	1st to 10th	Day	16% 5% 23% 23% 18% 14%	450
	11th to 20th	Day	14% 6% 20% 22% 23% 14%	450
	21st to end	Day	19% 7% 26% 21% 18% 9%	450
October	1st to 10th	Day	25% 9% 23% 20% 18% 5%	450
	11th to 20th	Day	24% 14% 28% 22% 12% 1	450
	21st to end	Day	32% 8% 23% 26% 11%	405
November	1st to 10th	Day	23% 12% 24% 26% 13% 2	365
	11th to 20th	Day	25% 10% 33% 23% 7% 2	222
	21st to end	Day	26% 15% 25% 25% 8% 2	180
December	1st to 10th	Day	29% 8% 29% 23% 10%	180
	11th to 20th	Day	24% 15% 37% 21% 3 1	180
	21st to end	Day	33% 12% 34% 15% 6% 1	198
January	1st to 10th	Night	28% 9% 28% 29% 6%	760
	11th to 20th	Night	28% 9% 26% 30% 6% 1	735
	21st to end	Night	19% 7% 30% 36% 8% 1	792
February	1st to 10th	Night	22% 8% 35% 29% 6%	720
	11th to 20th	Night	21% 8% 35% 30% 6%	703
	21st to end	Night	24% 7% 31% 33% 5%	592
March	1st to 10th	Night	22% 9% 30% 32% 7%	720
	11th to 20th	Night	23% 9% 32% 29% 7% 1	720
	21st to end	Night	22% 7% 29% 31% 10%	792
April	1st to 10th	Night	27% 8% 27% 30% 7%	720
	11th to 20th	Night	24% 9% 30% 28% 9% 1	711
	21st to end	Night	26% 7% 27% 30% 9% 1	610
May	1st to 10th	Night	25% 5% 27% 32% 9% 2	360
	11th to 20th	Night	24% 4 28% 32% 12%	354
	21st to end	Night	16% 5% 30% 35% 14%	389
June	1st to 10th	Night	17% 4 25% 43% 10% 1	360
	11th to 20th	Night	16% 3 26% 40% 13% 1	360
	21st to end	Night	17% 3 25% 35% 18% 1	360
July	1st to 10th	Night	9% 4 21% 45% 19%	350
	11th to 20th	Night	11% 2 20% 45% 20% 1	348
	21st to end	Night	12% 3 17% 47% 19% 1	394
August	1st to 10th	Night	12% 4 13% 48% 22% 1	358
	11th to 20th	Night	14% 3 13% 38% 29% 3	557
	21st to end	Night	14% 3 20% 39% 21% 3	792
September	1st to 10th	Night	14% 4 20% 41% 21% 1	720
	11th to 20th	Night	18% 5% 16% 35% 24% 2	720
	21st to end	Night	18% 4 22% 32% 21% 2	720
October	1st to 10th	Night	23% 5% 24% 31% 17% 1	720
	11th to 20th	Night	25% 7% 25% 32% 10% 1	720
	21st to end	Night	26% 9% 25% 33% 7%	792
November	1st to 10th	Night	24% 9% 24% 31% 11% 1	740
	11th to 20th	Night	23% 9% 31% 25% 10%	760
	21st to end	Night	27% 9% 29% 26% 9%	760
December	1st to 10th	Night	29% 9% 29% 28% 6%	760
	11th to 20th	Night	28% 11% 29% 25% 6% 1	760
	21st to end	Night	35% 8% 29% 23% 4	836

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