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 2005-11-05 to 2024-10-14.

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	17% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101373
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 32%	97189
Transparency	Day	49% 8% 13% 20% 9% 1	101132
	Night	52% 8% 12% 18% 9% 1	97055
Seeing	Day	21% 15% 30% 21% 10% 3	14404
	Night	22% 12% 30% 26% 9% 1	23451

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	17% 16% 6% 11% 6% 5% 5% 5% 4 4 21%	2517
	11th to 20th	Day	15% 12% 5% 13% 8% 7% 4 3 5% 5% 23%	2520
	21st to end	Day	14% 17% 6% 12% 6% 7% 5% 4 6% 5% 19%	2877
February	1st to 10th	Day	13% 14% 5% 12% 7% 6% 4 3 5% 5% 25%	1710
	11th to 20th	Day	13% 15% 5% 9% 6% 4 4 4 6% 5% 29%	1669
	21st to end	Day	19% 12% 4 9% 7% 5% 5% 5% 5% 4 26%	1570
March	1st to 10th	Day	22% 13% 3 8% 6% 5% 4 4 5% 5% 26%	3116
	11th to 20th	Day	12% 14% 5% 10% 6% 5% 6% 3 5% 5% 28%	3471
	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	23% 8% 3 8% 5% 5% 4 4 5% 7% 28%	1830
	21st to end	Day	26% 9% 2 7% 5% 5% 5% 3 5% 5% 28%	1831
November	1st to 10th	Day	16% 9% 3 7% 5% 5% 5% 4 6% 6% 34%	1671
	11th to 20th	Day	20% 12% 4 7% 5% 4 5% 4 6% 6% 27%	1530
	21st to end	Day	22% 14% 3 9% 6% 6% 5% 4 4 5% 21%	1520
December	1st to 10th	Day	22% 16% 5% 10% 5% 5% 4 4 5% 5% 17%	1520
	11th to 20th	Day	21% 15% 4 8% 6% 5% 5% 3 4 5% 25%	1906
	21st to end	Day	29% 18% 5% 10% 5% 3 3 2 3 4 19%	2772
January	1st to 10th	Night	17% 18% 7% 12% 5% 4 4 3 4 5% 21%	4429
	11th to 20th	Night	13% 14% 5% 13% 8% 6% 6% 3 5% 5% 23%	4440
	21st to end	Night	17% 21% 6% 10% 5% 5% 4 3 4 5% 21%	4777
February	1st to 10th	Night	15% 13% 5% 12% 7% 6% 5% 4 5% 5% 24%	2470
	11th to 20th	Night	13% 13% 5% 11% 6% 5% 4 3 4 6% 29%	2395
	21st to end	Night	17% 13% 4 8% 6% 4 5% 4 5% 6% 29%	1884
March	1st to 10th	Night	22% 11% 4 8% 5% 4 4 3 3 4 31%	3724
	11th to 20th	Night	17% 16% 5% 10% 6% 4 3 3 5% 5% 26%	3484
	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	22% 8% 2 7% 6% 5% 4 3 5% 7% 31%	2203
	21st to end	Night	24% 9% 4 7% 5% 5% 5% 4 5% 6% 28%	2524
November	1st to 10th	Night	20% 10% 2 5% 5% 5% 3 3 4 6% 35%	2407
	11th to 20th	Night	19% 11% 3 8% 5% 5% 5% 4 5% 6% 30%	2648
	21st to end	Night	22% 13% 4 9% 6% 5% 4 3 5% 6% 25%	2660
December	1st to 10th	Night	22% 17% 5% 9% 6% 5% 5% 4 4 5% 18%	2660
	11th to 20th	Night	23% 15% 4 9% 5% 3 3 3 4 4 27%	3288
	21st to end	Night	31% 17% 4 9% 4 3 4 2 3 4 18%	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	60% 14% 11% 9% 5% 1	2518
	11th to 20th	Day	62% 8% 12% 12% 6%	2520
	21st to end	Day	66% 9% 11% 9% 5%	2877
February	1st to 10th	Day	60% 6% 11% 17% 4 2	1710
	11th to 20th	Day	56% 7% 11% 16% 8% 1	1678
	21st to end	Day	58% 7% 11% 13% 9% 2	1570
March	1st to 10th	Day	58% 8% 10% 16% 8% 1	3119
	11th to 20th	Day	53% 10% 13% 14% 9% 1	3471
	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	48% 7% 13% 22% 9% 1	1900
	11th to 20th	Day	54% 9% 16% 15% 6% 1	1831
	21st to end	Day	59% 7% 12% 14% 8%	1831
November	1st to 10th	Day	47% 9% 16% 21% 6% 1	1671
	11th to 20th	Day	56% 7% 14% 15% 8% 1	1530
	21st to end	Day	64% 8% 11% 10% 6% 1	1520
December	1st to 10th	Day	68% 7% 13% 9% 3 1	1520
	11th to 20th	Day	61% 8% 14% 13% 4	1906
	21st to end	Day	70% 6% 7% 14% 3	2772
January	1st to 10th	Night	64% 9% 14% 10% 3	4429
	11th to 20th	Night	59% 11% 14% 11% 5%	4440
	21st to end	Night	65% 8% 10% 10% 6% 1	4777
February	1st to 10th	Night	61% 7% 11% 15% 6% 1	2470
	11th to 20th	Night	57% 7% 10% 19% 7% 1	2397
	21st to end	Night	55% 6% 10% 18% 10% 1	1884
March	1st to 10th	Night	54% 7% 10% 18% 9% 2	3734
	11th to 20th	Night	57% 8% 13% 14% 7% 1	3485
	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	45% 7% 12% 22% 13% 1	2280
	11th to 20th	Night	53% 7% 12% 20% 8%	2207
	21st to end	Night	56% 7% 13% 15% 8%	2524
November	1st to 10th	Night	50% 6% 15% 20% 8%	2407
	11th to 20th	Night	55% 6% 12% 17% 8% 1	2648
	21st to end	Night	60% 8% 13% 15% 5%	2660
December	1st to 10th	Night	67% 7% 11% 11% 3	2660
	11th to 20th	Night	61% 6% 10% 15% 7% 1	3288
	21st to end	Night	71% 6% 7% 12% 3	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	23% 20% 29% 23% 4 1	180
	11th to 20th	Day	27% 15% 38% 15% 4 1	180
	21st to end	Day	23% 16% 34% 22% 6%	229
February	1st to 10th	Day	30% 20% 35% 13% 1	270
	11th to 20th	Day	26% 28% 36% 10% 1	276
	21st to end	Day	28% 21% 32% 16% 3	382
March	1st to 10th	Day	25% 16% 36% 18% 5%	460
	11th to 20th	Day	26% 17% 35% 18% 3 1	460
	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% 7% 1	462
	21st to end	Day	31% 13% 28% 22% 5%	420
November	1st to 10th	Day	23% 18% 29% 20% 9% 1	365
	11th to 20th	Day	26% 21% 34% 12% 5% 1	190
	21st to end	Day	28% 19% 32% 16% 4 1	180
December	1st to 10th	Day	29% 16% 34% 18% 2	180
	11th to 20th	Day	27% 24% 32% 15% 1 1	180
	21st to end	Day	32% 21% 33% 12% 2 1	198
January	1st to 10th	Night	25% 15% 35% 21% 3	760
	11th to 20th	Night	26% 17% 30% 21% 6%	760
	21st to end	Night	19% 11% 36% 28% 5%	836
February	1st to 10th	Night	24% 13% 36% 24% 3	760
	11th to 20th	Night	20% 17% 40% 19% 4	743
	21st to end	Night	25% 16% 30% 26% 3	628
March	1st to 10th	Night	23% 15% 36% 23% 4	760
	11th to 20th	Night	22% 19% 33% 20% 5%	760
	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% 30% 25% 8% 1	735
	21st to end	Night	27% 13% 28% 26% 5%	792
November	1st to 10th	Night	25% 13% 28% 24% 9% 1	740
	11th to 20th	Night	24% 16% 34% 16% 9% 1	760
	21st to end	Night	29% 16% 27% 22% 6%	760
December	1st to 10th	Night	31% 14% 30% 21% 3	760
	11th to 20th	Night	28% 16% 31% 20% 5% 1	760
	21st to end	Night	33% 15% 30% 19% 3	836

Page generated at 2024-10-11 10:49:59. Version ac07

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