Quetican Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Quetican Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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	13% 10% 4 10% 6% 5% 5% 4 5% 6% 33%	126650
	Night	14% 13% 5% 12% 7% 5% 5% 3 5% 6% 26%	123129
Transparency	Day	51% 6% 11% 20% 11% 1	130183
	Night	59% 5% 10% 16% 9% 1	127685
Seeing	Day	18% 13% 29% 25% 11% 3	16477
	Night	21% 13% 26% 26% 12% 2	25618

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	13% 17% 10% 20% 16% 6% 5% 3 3 2 5%	3158
	11th to 20th	Day	10% 18% 11% 29% 12% 8% 5% 2 2 2 3	3606
	21st to end	Day	13% 16% 7% 20% 10% 8% 5% 4 4 4 8%	4466
February	1st to 10th	Day	13% 18% 6% 17% 11% 6% 5% 3 4 4 13%	1800
	11th to 20th	Day	10% 15% 6% 15% 9% 8% 5% 5% 5% 5% 16%	1753
	21st to end	Day	12% 15% 5% 11% 8% 8% 6% 4 6% 5% 19%	1606
March	1st to 10th	Day	14% 11% 4 10% 6% 6% 4 4 5% 6% 29%	4770
	11th to 20th	Day	9% 13% 6% 13% 7% 6% 6% 4 6% 6% 26%	4980
	21st to end	Day	17% 11% 5% 11% 6% 4 5% 4 5% 6% 28%	5465
April	1st to 10th	Day	17% 11% 3 7% 5% 5% 4 4 5% 7% 31%	2316
	11th to 20th	Day	17% 9% 3 7% 4 4 4 3 4 6% 40%	2572
	21st to end	Day	18% 9% 3 6% 4 4 4 4 6% 7% 36%	2600
May	1st to 10th	Day	14% 8% 2 6% 4 4 5% 4 5% 7% 40%	5888
	11th to 20th	Day	11% 8% 3 7% 5% 4 5% 4 6% 7% 41%	6131
	21st to end	Day	16% 7% 3 7% 4 5% 4 3 5% 6% 40%	6949
June	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 5% 6% 8% 41%	2983
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 4 6% 8% 45%	3000
	21st to end	Day	12% 6% 2 5% 5% 3 4 4 6% 8% 44%	3000
July	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 4 6% 8% 43%	6819
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 5% 7% 54%	6731
	21st to end	Day	6% 5% 2 5% 4 3 4 3 5% 8% 55%	6475
August	1st to 10th	Day	10% 5% 2 5% 3 3 5% 4 7% 9% 46%	4234
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 6% 9% 42%	4174
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 47%	4655
September	1st to 10th	Day	12% 6% 2 7% 5% 4 5% 3 5% 8% 44%	2370
	11th to 20th	Day	12% 4 2 6% 4 3 4 4 7% 8% 47%	2200
	21st to end	Day	17% 7% 2 7% 5% 5% 4 3 5% 7% 38%	2200
October	1st to 10th	Day	17% 9% 3 6% 5% 4 5% 4 5% 7% 37%	2030
	11th to 20th	Day	21% 13% 4 9% 6% 5% 5% 4 5% 6% 24%	1980
	21st to end	Day	25% 14% 4 9% 6% 5% 5% 4 5% 6% 17%	2002
November	1st to 10th	Day	15% 16% 4 9% 7% 5% 5% 4 6% 5% 23%	1712
	11th to 20th	Day	17% 16% 4 10% 7% 7% 7% 4 5% 6% 17%	1600
	21st to end	Day	18% 24% 6% 14% 7% 6% 4 3 4 4 10%	1600
December	1st to 10th	Day	14% 28% 9% 16% 7% 6% 5% 3 3 3 5%	2600
	11th to 20th	Day	18% 22% 7% 18% 8% 5% 4 3 4 4 8%	2749
	21st to end	Day	25% 20% 6% 19% 6% 7% 4 2 3 3 5%	3476
January	1st to 10th	Night	14% 17% 8% 22% 12% 6% 4 3 3 3 7%	6791
	11th to 20th	Night	11% 18% 9% 26% 12% 7% 4 3 3 3 5%	6294
	21st to end	Night	11% 16% 9% 20% 11% 9% 6% 3 4 3 9%	6490
February	1st to 10th	Night	10% 18% 6% 17% 10% 6% 5% 4 4 5% 15%	2600
	11th to 20th	Night	10% 16% 7% 15% 9% 7% 6% 4 5% 5% 18%	2533
	21st to end	Night	14% 13% 5% 11% 8% 5% 6% 5% 5% 5% 22%	2020
March	1st to 10th	Night	12% 10% 4 10% 6% 7% 6% 4 5% 7% 29%	5069
	11th to 20th	Night	9% 11% 4 10% 6% 5% 5% 4 6% 7% 33%	4979
	21st to end	Night	17% 11% 4 10% 5% 6% 5% 3 5% 5% 29%	5467
April	1st to 10th	Night	19% 10% 4 7% 5% 4 4 3 4 6% 33%	2100
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 4 5% 6% 38%	1777
	21st to end	Night	19% 9% 3 8% 4 5% 4 5% 6% 6% 32%	1800
May	1st to 10th	Night	14% 8% 3 8% 5% 5% 5% 4 5% 7% 36%	4053
	11th to 20th	Night	11% 6% 2 9% 5% 5% 5% 4 6% 7% 40%	3759
	21st to end	Night	17% 7% 3 7% 5% 5% 4 3 5% 6% 38%	3926
June	1st to 10th	Night	12% 8% 2 7% 6% 6% 3 4 5% 8% 39%	1412
	11th to 20th	Night	10% 6% 2 5% 5% 4 5% 5% 7% 8% 44%	1400
	21st to end	Night	12% 6% 2 6% 5% 5% 6% 4 6% 8% 42%	1400
July	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 9% 44%	3160
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 5% 8% 48%	3245
	21st to end	Night	7% 6% 3 5% 4 4 4 3 6% 9% 50%	4376
August	1st to 10th	Night	10% 6% 3 5% 4 4 5% 4 7% 8% 45%	2915
	11th to 20th	Night	13% 6% 2 6% 4 5% 5% 4 6% 8% 40%	2875
	21st to end	Night	9% 7% 2 6% 4 4 5% 3 6% 8% 46%	3223
September	1st to 10th	Night	10% 5% 2 6% 4 4 5% 4 7% 8% 47%	2011
	11th to 20th	Night	11% 5% 2 6% 4 4 4 3 5% 7% 49%	2200
	21st to end	Night	17% 8% 3 7% 5% 5% 3 3 5% 7% 37%	2200
October	1st to 10th	Night	19% 7% 3 8% 5% 4 5% 3 6% 6% 35%	2370
	11th to 20th	Night	21% 11% 3 9% 5% 5% 5% 4 6% 7% 24%	2377
	21st to end	Night	24% 14% 4 9% 6% 6% 5% 4 5% 5% 18%	2593
November	1st to 10th	Night	17% 14% 3 9% 7% 6% 5% 4 5% 6% 24%	2584
	11th to 20th	Night	16% 18% 5% 11% 7% 7% 6% 4 4 6% 17%	2800
	21st to end	Night	21% 20% 5% 12% 7% 5% 5% 4 5% 5% 11%	2800
December	1st to 10th	Night	15% 23% 7% 18% 9% 6% 5% 3 4 4 6%	4580
	11th to 20th	Night	14% 22% 8% 20% 7% 5% 5% 3 4 4 7%	5448
	21st to end	Night	22% 22% 9% 18% 7% 5% 3 2 3 3 7%	7502

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	87% 4 4 4 1	3159
	11th to 20th	Day	92% 3 2 2 1	3637
	21st to end	Day	80% 6% 7% 6% 2	4466
February	1st to 10th	Day	74% 7% 8% 10% 2	1800
	11th to 20th	Day	69% 8% 9% 9% 5%	1762
	21st to end	Day	63% 8% 10% 15% 4	1606
March	1st to 10th	Day	56% 5% 13% 11% 12% 1	4773
	11th to 20th	Day	57% 7% 11% 18% 6% 1	4980
	21st to end	Day	54% 7% 12% 18% 8% 1	5465
April	1st to 10th	Day	51% 7% 11% 19% 11% 1	2316
	11th to 20th	Day	45% 6% 9% 23% 16% 2	2572
	21st to end	Day	46% 7% 12% 20% 12% 3	2600
May	1st to 10th	Day	41% 6% 13% 20% 16% 5%	5897
	11th to 20th	Day	40% 8% 12% 19% 20% 1	6135
	21st to end	Day	44% 5% 11% 19% 16% 4	6949
June	1st to 10th	Day	38% 8% 12% 25% 15% 1	2983
	11th to 20th	Day	36% 6% 12% 27% 17% 2	3000
	21st to end	Day	38% 7% 13% 26% 13% 2	3000
July	1st to 10th	Day	41% 3 15% 26% 13% 1	6746
	11th to 20th	Day	30% 4 11% 39% 14% 1	6650
	21st to end	Day	29% 4 13% 36% 17% 1	6290
August	1st to 10th	Day	34% 4 15% 30% 15% 1	4221
	11th to 20th	Day	38% 5% 17% 28% 11%	4213
	21st to end	Day	33% 5% 15% 35% 11% 1	4655
September	1st to 10th	Day	38% 7% 15% 27% 12% 1	2370
	11th to 20th	Day	34% 8% 15% 31% 12%	2200
	21st to end	Day	46% 8% 14% 23% 9%	2200
October	1st to 10th	Day	42% 4 13% 26% 15%	3303
	11th to 20th	Day	54% 4 12% 22% 8%	3220
	21st to end	Day	61% 5% 12% 17% 5%	3278
November	1st to 10th	Day	62% 8% 10% 15% 5%	1712
	11th to 20th	Day	68% 8% 11% 9% 4	1600
	21st to end	Day	77% 7% 9% 6% 1	1600
December	1st to 10th	Day	87% 4 6% 3 1	2600
	11th to 20th	Day	81% 5% 7% 5% 2	2749
	21st to end	Day	87% 5% 4 4	3476
January	1st to 10th	Night	85% 4 5% 5% 1	6791
	11th to 20th	Night	87% 5% 4 2 1	6338
	21st to end	Night	79% 7% 5% 5% 3	6490
February	1st to 10th	Night	72% 6% 9% 10% 3	2600
	11th to 20th	Night	68% 6% 8% 13% 5%	2535
	21st to end	Night	61% 8% 11% 13% 6%	2020
March	1st to 10th	Night	55% 5% 13% 14% 10% 2	5079
	11th to 20th	Night	50% 5% 16% 19% 8% 1	4980
	21st to end	Night	55% 6% 8% 18% 11% 2	5467
April	1st to 10th	Night	52% 5% 10% 21% 11% 1	2100
	11th to 20th	Night	46% 5% 8% 22% 18% 1	1777
	21st to end	Night	51% 6% 10% 15% 16% 3	1800
May	1st to 10th	Night	47% 5% 9% 17% 16% 6%	4060
	11th to 20th	Night	41% 7% 10% 21% 20% 2	3760
	21st to end	Night	46% 5% 10% 23% 14% 3	3927
June	1st to 10th	Night	42% 7% 9% 20% 18% 3	1412
	11th to 20th	Night	36% 6% 13% 26% 19% 1	1400
	21st to end	Night	39% 7% 13% 26% 13% 2	1400
July	1st to 10th	Night	39% 2 13% 28% 15% 3	3125
	11th to 20th	Night	36% 4 8% 33% 18% 1	3203
	21st to end	Night	34% 4 9% 32% 20% 1	4247
August	1st to 10th	Night	37% 5% 14% 28% 16% 1	2904
	11th to 20th	Night	42% 5% 18% 22% 14% 1	2902
	21st to end	Night	36% 5% 12% 33% 13% 1	3223
September	1st to 10th	Night	34% 8% 14% 29% 14% 1	2011
	11th to 20th	Night	34% 8% 15% 30% 13%	2200
	21st to end	Night	47% 6% 14% 23% 10%	2200
October	1st to 10th	Night	41% 4 8% 30% 16%	3877
	11th to 20th	Night	53% 5% 13% 21% 8%	3876
	21st to end	Night	58% 5% 14% 18% 5%	4267
November	1st to 10th	Night	60% 7% 11% 17% 4	2584
	11th to 20th	Night	68% 8% 13% 7% 3 1	2800
	21st to end	Night	76% 8% 10% 6% 1	2800
December	1st to 10th	Night	85% 4 6% 3 1	4580
	11th to 20th	Night	83% 4 6% 4 3	5448
	21st to end	Night	85% 4 6% 3 1	7502

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	18% 25% 37% 15% 5% 2	200
	11th to 20th	Day	23% 21% 34% 16% 5%	300
	21st to end	Day	25% 16% 35% 18% 5%	330
February	1st to 10th	Day	24% 28% 31% 15% 2	300
	11th to 20th	Day	22% 28% 35% 15% 1	300
	21st to end	Day	25% 29% 34% 10% 1	249
March	1st to 10th	Day	21% 20% 35% 19% 5%	424
	11th to 20th	Day	21% 19% 34% 21% 5% 1	500
	21st to end	Day	27% 14% 31% 22% 5% 1	550
April	1st to 10th	Day	23% 14% 35% 19% 8% 1	500
	11th to 20th	Day	26% 17% 27% 15% 10% 5%	492
	21st to end	Day	26% 12% 35% 18% 7% 1	500
May	1st to 10th	Day	20% 10% 36% 23% 9% 2	503
	11th to 20th	Day	15% 10% 30% 28% 13% 4	527
	21st to end	Day	16% 7% 28% 30% 15% 4	573
June	1st to 10th	Day	13% 8% 32% 33% 12% 2	713
	11th to 20th	Day	12% 8% 32% 34% 12% 3	730
	21st to end	Day	17% 7% 28% 33% 12% 3	730
July	1st to 10th	Day	9% 5% 28% 33% 22% 2	721
	11th to 20th	Day	12% 6% 27% 33% 17% 6%	718
	21st to end	Day	9% 6% 28% 35% 17% 5%	601
August	1st to 10th	Day	13% 5% 21% 33% 22% 6%	526
	11th to 20th	Day	13% 6% 18% 36% 19% 8%	519
	21st to end	Day	12% 9% 26% 28% 20% 5%	583
September	1st to 10th	Day	15% 11% 22% 27% 18% 6%	530
	11th to 20th	Day	10% 6% 23% 26% 25% 9%	530
	21st to end	Day	19% 12% 21% 28% 16% 4	530
October	1st to 10th	Day	21% 15% 24% 24% 13% 3	530
	11th to 20th	Day	21% 21% 31% 20% 5% 1	522
	21st to end	Day	29% 21% 28% 18% 2 1	451
November	1st to 10th	Day	27% 23% 31% 16% 4	275
	11th to 20th	Day	22% 26% 33% 15% 4 1	200
	21st to end	Day	27% 26% 32% 14% 2	200
December	1st to 10th	Day	28% 25% 30% 12% 6%	200
	11th to 20th	Day	30% 26% 30% 12% 3	200
	21st to end	Day	31% 26% 31% 8% 2	220
January	1st to 10th	Night	24% 20% 33% 19% 4 1	1000
	11th to 20th	Night	27% 21% 27% 19% 5% 1	991
	21st to end	Night	20% 16% 30% 24% 8% 1	880
February	1st to 10th	Night	21% 22% 33% 20% 5%	800
	11th to 20th	Night	20% 17% 35% 21% 8%	783
	21st to end	Night	21% 18% 35% 22% 4	660
March	1st to 10th	Night	17% 17% 34% 24% 7% 1	800
	11th to 20th	Night	18% 18% 34% 22% 8% 1	800
	21st to end	Night	20% 13% 28% 28% 10%	880
April	1st to 10th	Night	25% 14% 29% 26% 5% 1	795
	11th to 20th	Night	21% 13% 27% 24% 12% 2	593
	21st to end	Night	25% 12% 24% 26% 13% 1	600
May	1st to 10th	Night	17% 6% 26% 34% 15% 2	600
	11th to 20th	Night	16% 6% 23% 35% 19% 1	474
	21st to end	Night	16% 4 24% 36% 18% 2	433
June	1st to 10th	Night	17% 6% 28% 35% 13% 2	400
	11th to 20th	Night	12% 7% 22% 40% 18% 1	400
	21st to end	Night	13% 6% 23% 36% 22% 1	400
July	1st to 10th	Night	9% 4 15% 49% 20% 2	390
	11th to 20th	Night	10% 3 22% 36% 24% 4	421
	21st to end	Night	8% 4 19% 42% 24% 3	657
August	1st to 10th	Night	11% 3 18% 39% 26% 3	597
	11th to 20th	Night	12% 6% 15% 31% 29% 7%	594
	21st to end	Night	13% 5% 21% 31% 26% 3	660
September	1st to 10th	Night	12% 8% 20% 32% 21% 6%	786
	11th to 20th	Night	12% 6% 19% 31% 24% 7%	800
	21st to end	Night	19% 9% 20% 27% 20% 6%	800
October	1st to 10th	Night	22% 9% 25% 25% 17% 2	800
	11th to 20th	Night	27% 15% 24% 24% 9% 1	793
	21st to end	Night	32% 14% 28% 21% 4 1	836
November	1st to 10th	Night	28% 16% 25% 23% 7% 1	780
	11th to 20th	Night	25% 22% 25% 19% 8% 1	800
	21st to end	Night	32% 19% 27% 18% 4	800
December	1st to 10th	Night	32% 21% 28% 13% 6%	800
	11th to 20th	Night	28% 22% 32% 15% 4	915
	21st to end	Night	34% 17% 29% 15% 4	1100

Page generated at 2025-10-16 01:50:29. Version ac07

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