Pigeon Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pigeon Lake Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	12% 8% 3 7% 4 4 5% 4 6% 7% 39%	127601
	Night	13% 9% 3 7% 4 4 4 3 5% 7% 40%	124662
Transparency	Day	43% 5% 12% 25% 13% 1	131088
	Night	43% 5% 12% 24% 15% 2	129249
Seeing	Day	16% 12% 31% 26% 12% 4	17600
	Night	17% 10% 31% 29% 12% 1	27575

By Month

Percentage Cloud Cover SE (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	8% 11% 4 11% 6% 4 6% 4 6% 7% 33%	3697
	11th to 20th	Day	10% 10% 4 10% 5% 5% 5% 5% 6% 7% 34%	3700
	21st to end	Day	13% 13% 6% 10% 4 4 4 3 5% 5% 33%	4070
February	1st to 10th	Day	10% 12% 5% 10% 5% 4 4 3 6% 7% 33%	1761
	11th to 20th	Day	12% 12% 4 7% 5% 3 5% 4 5% 6% 37%	1940
	21st to end	Day	12% 13% 4 8% 5% 5% 5% 4 5% 7% 33%	1650
March	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 5% 7% 44%	4480
	11th to 20th	Day	11% 8% 4 7% 4 4 4 4 6% 8% 41%	4653
	21st to end	Day	23% 12% 4 9% 5% 4 4 3 4 5% 28%	5967
April	1st to 10th	Day	14% 14% 4 8% 5% 5% 5% 4 5% 6% 30%	2400
	11th to 20th	Day	18% 9% 3 7% 5% 5% 5% 4 5% 6% 34%	2374
	21st to end	Day	17% 9% 4 8% 5% 4 5% 4 5% 6% 33%	2570
May	1st to 10th	Day	14% 8% 2 6% 4 3 4 4 5% 7% 43%	5907
	11th to 20th	Day	11% 7% 3 7% 4 4 4 4 6% 8% 43%	6319
	21st to end	Day	15% 7% 3 6% 4 5% 4 4 6% 8% 40%	6935
June	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 6% 9% 44%	2800
	11th to 20th	Day	12% 7% 2 5% 5% 5% 4 4 6% 8% 41%	2800
	21st to end	Day	10% 5% 3 6% 4 5% 4 4 6% 9% 44%	2800
July	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 7% 10% 40%	6360
	11th to 20th	Day	7% 5% 1 5% 4 4 5% 5% 7% 9% 49%	6360
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 6% 9% 46%	6924
August	1st to 10th	Day	9% 6% 2 6% 4 4 5% 4 6% 9% 44%	4563
	11th to 20th	Day	11% 4 2 6% 4 5% 4 4 6% 9% 46%	4021
	21st to end	Day	10% 6% 2 7% 5% 4 5% 4 6% 7% 43%	4312
September	1st to 10th	Day	10% 5% 3 7% 5% 4 5% 3 6% 8% 44%	2400
	11th to 20th	Day	11% 4 2 5% 5% 4 4 3 7% 8% 47%	2271
	21st to end	Day	12% 6% 3 7% 4 5% 5% 4 6% 7% 42%	2200
October	1st to 10th	Day	14% 6% 2 6% 4 4 4 3 4 7% 46%	2135
	11th to 20th	Day	21% 8% 3 7% 6% 6% 5% 4 5% 7% 29%	1940
	21st to end	Day	15% 9% 3 8% 5% 5% 5% 3 5% 6% 36%	1980
November	1st to 10th	Day	13% 8% 3 6% 4 4 5% 4 6% 8% 41%	1852
	11th to 20th	Day	11% 11% 4 10% 5% 5% 5% 5% 5% 7% 32%	1890
	21st to end	Day	16% 12% 3 8% 4 5% 4 3 5% 6% 35%	1722
December	1st to 10th	Day	10% 11% 4 7% 5% 5% 6% 4 6% 8% 34%	2690
	11th to 20th	Day	12% 16% 4 8% 5% 5% 5% 5% 5% 7% 29%	3088
	21st to end	Day	19% 20% 6% 12% 5% 4 3 3 4 5% 19%	4070
January	1st to 10th	Night	10% 10% 5% 10% 6% 4 4 3 4 6% 39%	6488
	11th to 20th	Night	10% 12% 4 11% 6% 5% 6% 5% 6% 7% 30%	6500
	21st to end	Night	10% 13% 5% 9% 4 4 4 4 5% 6% 35%	7150
February	1st to 10th	Night	11% 14% 4 9% 5% 5% 5% 3 4 5% 35%	2636
	11th to 20th	Night	10% 10% 3 9% 6% 4 3 4 5% 5% 39%	2344
	21st to end	Night	15% 14% 3 7% 4 3 4 3 4 6% 38%	1980
March	1st to 10th	Night	14% 7% 2 6% 4 3 3 3 5% 7% 45%	5373
	11th to 20th	Night	10% 7% 3 6% 5% 4 5% 4 6% 8% 41%	5336
	21st to end	Night	18% 11% 4 9% 5% 5% 4 3 4 5% 32%	4962
April	1st to 10th	Night	17% 11% 3 6% 4 4 4 3 5% 7% 36%	2000
	11th to 20th	Night	19% 9% 3 7% 4 4 3 4 5% 6% 39%	1975
	21st to end	Night	17% 8% 4 6% 5% 4 4 3 5% 6% 39%	1830
May	1st to 10th	Night	14% 6% 2 6% 4 5% 4 3 5% 8% 43%	3975
	11th to 20th	Night	9% 6% 4 7% 5% 4 5% 4 6% 8% 42%	3596
	21st to end	Night	19% 7% 3 6% 4 4 4 4 5% 7% 39%	3942
June	1st to 10th	Night	10% 5% 2 6% 4 5% 5% 4 6% 7% 46%	1600
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 5% 9% 44%	1600
	21st to end	Night	8% 6% 2 6% 4 3 5% 4 6% 8% 47%	1600
July	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 46%	3618
	11th to 20th	Night	6% 5% 2 5% 3 3 4 3 6% 8% 55%	3617
	21st to end	Night	5% 4 2 6% 4 3 4 4 6% 8% 54%	3947
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 6% 8% 48%	2597
	11th to 20th	Night	10% 5% 2 6% 3 5% 4 4 5% 7% 50%	3024
	21st to end	Night	10% 5% 2 5% 3 4 5% 4 6% 7% 50%	3586
September	1st to 10th	Night	8% 5% 2 6% 4 3 4 3 5% 8% 53%	2000
	11th to 20th	Night	10% 4 2 4 4 4 3 3 5% 6% 54%	2107
	21st to end	Night	11% 7% 2 6% 4 4 4 3 6% 6% 47%	2200
October	1st to 10th	Night	12% 5% 2 6% 3 4 4 3 4 5% 51%	2261
	11th to 20th	Night	15% 8% 2 7% 4 4 5% 4 6% 6% 40%	2460
	21st to end	Night	16% 9% 2 6% 5% 4 4 3 6% 8% 37%	2860
November	1st to 10th	Night	13% 6% 2 5% 5% 4 4 3 5% 7% 47%	2666
	11th to 20th	Night	14% 8% 3 8% 5% 5% 4 4 6% 6% 35%	2730
	21st to end	Night	15% 10% 3 6% 4 5% 4 3 6% 5% 38%	2893
December	1st to 10th	Night	11% 9% 3 7% 4 4 4 4 6% 8% 42%	4720
	11th to 20th	Night	14% 15% 6% 9% 5% 5% 4 4 4 5% 29%	5339
	21st to end	Night	21% 16% 5% 9% 5% 4 4 3 4 5% 23%	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	49% 6% 15% 22% 8%	3698
	11th to 20th	Day	47% 6% 10% 21% 15% 2	3700
	21st to end	Day	53% 4 9% 21% 14%	4070
February	1st to 10th	Day	51% 4 11% 21% 12% 1	1761
	11th to 20th	Day	47% 5% 11% 22% 13% 2	1950
	21st to end	Day	51% 5% 11% 21% 11% 2	1650
March	1st to 10th	Day	41% 4 11% 22% 16% 6%	4480
	11th to 20th	Day	41% 3 15% 25% 14% 2	4653
	21st to end	Day	59% 4 10% 16% 11% 1	5969
April	1st to 10th	Day	52% 6% 13% 18% 10%	2400
	11th to 20th	Day	50% 5% 9% 21% 12% 2	2374
	21st to end	Day	50% 6% 12% 19% 11% 2	2570
May	1st to 10th	Day	40% 5% 12% 24% 16% 2	5942
	11th to 20th	Day	38% 7% 11% 28% 14% 1	6323
	21st to end	Day	42% 6% 9% 27% 14% 3	6949
June	1st to 10th	Day	36% 6% 12% 28% 16% 2	2800
	11th to 20th	Day	40% 6% 14% 25% 15% 1	2800
	21st to end	Day	35% 7% 15% 25% 15% 2	2800
July	1st to 10th	Day	39% 5% 13% 32% 10% 1	6291
	11th to 20th	Day	30% 6% 15% 34% 14% 1	6285
	21st to end	Day	33% 7% 14% 26% 18% 2	6728
August	1st to 10th	Day	36% 7% 14% 30% 12% 1	4548
	11th to 20th	Day	35% 6% 13% 34% 11% 1	4060
	21st to end	Day	39% 5% 15% 24% 16% 1	4311
September	1st to 10th	Day	37% 8% 12% 28% 14% 1	2400
	11th to 20th	Day	33% 7% 14% 32% 14% 1	2271
	21st to end	Day	40% 6% 12% 31% 11%	2200
October	1st to 10th	Day	25% 3 8% 38% 24% 2	3473
	11th to 20th	Day	45% 4 9% 24% 18%	3143
	21st to end	Day	42% 4 11% 28% 13% 1	3180
November	1st to 10th	Day	41% 7% 13% 24% 14% 2	1852
	11th to 20th	Day	50% 5% 14% 21% 9% 1	1890
	21st to end	Day	50% 5% 14% 22% 7% 1	1722
December	1st to 10th	Day	47% 6% 18% 24% 5%	2690
	11th to 20th	Day	53% 4 12% 18% 11% 2	3085
	21st to end	Day	69% 4 7% 13% 8%	4070
January	1st to 10th	Night	48% 4 9% 24% 15% 1	6488
	11th to 20th	Night	53% 7% 8% 13% 17% 2	6500
	21st to end	Night	50% 4 13% 20% 13%	7150
February	1st to 10th	Night	51% 4 10% 21% 12% 2	2636
	11th to 20th	Night	47% 4 10% 24% 13% 2	2345
	21st to end	Night	48% 4 13% 20% 13% 2	1980
March	1st to 10th	Night	39% 4 14% 27% 13% 3	5373
	11th to 20th	Night	39% 5% 16% 23% 14% 3	5336
	21st to end	Night	55% 4 9% 18% 12% 1	4962
April	1st to 10th	Night	47% 6% 9% 19% 18% 1	2000
	11th to 20th	Night	46% 5% 7% 22% 16% 3	1975
	21st to end	Night	45% 5% 12% 22% 15% 2	1830
May	1st to 10th	Night	40% 5% 12% 20% 20% 2	4002
	11th to 20th	Night	39% 7% 13% 23% 16% 2	3597
	21st to end	Night	46% 5% 8% 24% 12% 5%	3950
June	1st to 10th	Night	35% 7% 11% 30% 17% 1	1600
	11th to 20th	Night	38% 5% 11% 26% 18% 2	1600
	21st to end	Night	33% 8% 15% 24% 17% 3	1600
July	1st to 10th	Night	36% 5% 14% 31% 10% 4	3580
	11th to 20th	Night	28% 5% 15% 32% 18% 2	3572
	21st to end	Night	29% 5% 14% 27% 22% 3	3832
August	1st to 10th	Night	34% 6% 13% 27% 19% 2	2588
	11th to 20th	Night	33% 6% 12% 31% 18% 1	3051
	21st to end	Night	33% 5% 14% 24% 22% 3	3586
September	1st to 10th	Night	30% 7% 13% 27% 22% 2	2000
	11th to 20th	Night	30% 5% 10% 35% 18% 1	2107
	21st to end	Night	37% 5% 10% 30% 17% 2	2200
October	1st to 10th	Night	27% 3 7% 40% 21% 1	3703
	11th to 20th	Night	34% 4 13% 28% 18% 3	3996
	21st to end	Night	42% 4 11% 26% 18%	4610
November	1st to 10th	Night	38% 5% 11% 26% 18% 2	2666
	11th to 20th	Night	47% 5% 13% 21% 12% 2	2730
	21st to end	Night	48% 5% 15% 23% 9% 1	2893
December	1st to 10th	Night	41% 5% 19% 25% 6% 3	4720
	11th to 20th	Night	58% 5% 10% 13% 13% 2	5341
	21st to end	Night	64% 5% 8% 15% 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	18% 16% 35% 25% 5% 1	330
	11th to 20th	Day	17% 20% 38% 20% 4 1	330
	21st to end	Day	18% 17% 34% 25% 5% 1	363
February	1st to 10th	Day	16% 23% 41% 15% 4	300
	11th to 20th	Day	19% 26% 35% 15% 4	300
	21st to end	Day	23% 22% 40% 14% 2	249
March	1st to 10th	Day	21% 17% 46% 14% 1	300
	11th to 20th	Day	27% 15% 32% 18% 7% 1	335
	21st to end	Day	27% 13% 32% 22% 6% 1	550
April	1st to 10th	Day	25% 14% 34% 20% 7%	500
	11th to 20th	Day	24% 20% 28% 18% 8% 2	492
	21st to end	Day	22% 15% 31% 20% 10% 2	500
May	1st to 10th	Day	20% 11% 38% 21% 9% 2	522
	11th to 20th	Day	17% 13% 33% 24% 10% 3	725
	21st to end	Day	15% 10% 31% 26% 13% 5%	789
June	1st to 10th	Day	12% 10% 33% 32% 10% 3	730
	11th to 20th	Day	14% 8% 32% 31% 12% 3	730
	21st to end	Day	13% 7% 32% 32% 12% 4	730
July	1st to 10th	Day	9% 4 25% 36% 19% 7%	721
	11th to 20th	Day	9% 7% 28% 33% 17% 7%	718
	21st to end	Day	6% 4 31% 35% 17% 7%	794
August	1st to 10th	Day	8% 3 26% 38% 17% 9%	726
	11th to 20th	Day	11% 3 22% 31% 23% 9%	522
	21st to end	Day	13% 7% 21% 29% 23% 8%	583
September	1st to 10th	Day	13% 9% 23% 29% 17% 8%	530
	11th to 20th	Day	11% 3 22% 35% 21% 9%	530
	21st to end	Day	15% 12% 23% 26% 18% 5%	530
October	1st to 10th	Day	18% 9% 30% 27% 13% 3	465
	11th to 20th	Day	20% 18% 32% 22% 7%	330
	21st to end	Day	18% 17% 39% 19% 6% 1	363
November	1st to 10th	Day	17% 15% 37% 21% 7% 2	330
	11th to 20th	Day	18% 22% 34% 18% 7%	330
	21st to end	Day	22% 16% 40% 18% 4	330
December	1st to 10th	Day	20% 19% 38% 17% 5%	330
	11th to 20th	Day	23% 23% 35% 12% 5% 1	330
	21st to end	Day	28% 18% 36% 13% 4 1	363
January	1st to 10th	Night	19% 15% 39% 23% 4	1050
	11th to 20th	Night	19% 16% 36% 23% 5% 1	1050
	21st to end	Night	18% 12% 38% 25% 6%	1155
February	1st to 10th	Night	19% 16% 36% 23% 5% 1	1001
	11th to 20th	Night	17% 17% 36% 23% 6%	789
	21st to end	Night	22% 15% 39% 21% 3	660
March	1st to 10th	Night	19% 13% 34% 24% 9% 1	800
	11th to 20th	Night	16% 12% 38% 26% 6% 1	796
	21st to end	Night	20% 8% 29% 31% 10% 1	660
April	1st to 10th	Night	21% 9% 40% 24% 6%	600
	11th to 20th	Night	23% 10% 31% 25% 9% 1	593
	21st to end	Night	20% 8% 31% 30% 11% 1	600
May	1st to 10th	Night	19% 6% 32% 34% 9% 1	600
	11th to 20th	Night	18% 7% 30% 33% 12% 1	591
	21st to end	Night	15% 5% 22% 39% 17% 2	650
June	1st to 10th	Night	12% 6% 25% 41% 15% 1	600
	11th to 20th	Night	15% 4 27% 35% 18% 2	600
	21st to end	Night	9% 4 26% 41% 19% 1	600
July	1st to 10th	Night	10% 2 16% 43% 28% 2	585
	11th to 20th	Night	7% 3 21% 39% 28% 2	582
	21st to end	Night	5% 2 22% 46% 24% 2	657
August	1st to 10th	Night	9% 2 15% 43% 29% 3	597
	11th to 20th	Night	9% 2 17% 39% 28% 5%	594
	21st to end	Night	12% 3 18% 39% 25% 3	660
September	1st to 10th	Night	10% 4 25% 31% 26% 6%	600
	11th to 20th	Night	12% 4 20% 32% 26% 6%	707
	21st to end	Night	14% 8% 24% 30% 20% 4	800
October	1st to 10th	Night	15% 8% 29% 28% 19% 2	800
	11th to 20th	Night	20% 11% 32% 27% 10%	800
	21st to end	Night	21% 11% 30% 26% 11% 1	880
November	1st to 10th	Night	16% 11% 38% 25% 9% 1	820
	11th to 20th	Night	21% 15% 35% 22% 7%	840
	21st to end	Night	22% 15% 35% 21% 7%	1003
December	1st to 10th	Night	21% 15% 37% 22% 4	1050
	11th to 20th	Night	22% 15% 36% 20% 6% 1	1050
	21st to end	Night	27% 14% 35% 20% 4	1155

Page generated at 2026-01-29 00:21:40. Version ac07

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