Magog
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Magog clear sky chart from 2005-11-06 to 2026-05-02.

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	16% 12% 4 10% 6% 5% 5% 4 5% 6% 26%	131625
	Night	15% 13% 5% 12% 7% 5% 5% 3 5% 5% 25%	130873
Transparency	Day	58% 5% 11% 18% 8% 1	135093
	Night	61% 4 10% 16% 8% 1	135492
Seeing	Day	26% 16% 29% 19% 8% 2	16492
	Night	25% 14% 27% 25% 9% 1	25492

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	11% 17% 9% 21% 8% 8% 4 3 3 3 13%	4661
	11th to 20th	Day	8% 18% 8% 20% 13% 8% 5% 3 4 4 10%	4650
	21st to end	Day	8% 14% 7% 15% 9% 13% 7% 4 5% 5% 14%	5124
February	1st to 10th	Day	11% 17% 6% 17% 9% 7% 6% 3 4 3 17%	1764
	11th to 20th	Day	12% 17% 7% 16% 9% 5% 5% 3 5% 4 17%	2044
	21st to end	Day	12% 18% 5% 12% 8% 6% 4 4 5% 5% 20%	1730
March	1st to 10th	Day	17% 15% 6% 15% 7% 5% 5% 3 3 3 19%	4576
	11th to 20th	Day	12% 17% 5% 11% 5% 5% 4 3 5% 5% 26%	4779
	21st to end	Day	19% 14% 6% 12% 5% 4 3 2 4 4 26%	6050
April	1st to 10th	Day	20% 17% 5% 9% 5% 5% 4 3 4 5% 25%	2520
	11th to 20th	Day	19% 14% 4 7% 5% 4 3 3 4 4 32%	2525
	21st to end	Day	22% 12% 4 8% 5% 4 5% 3 5% 6% 28%	2730
May	1st to 10th	Day	27% 13% 3 9% 5% 4 4 3 5% 5% 21%	6009
	11th to 20th	Day	18% 9% 3 9% 6% 6% 6% 4 6% 7% 28%	6318
	21st to end	Day	19% 9% 3 7% 5% 5% 5% 4 7% 7% 29%	6949
June	1st to 10th	Day	25% 8% 3 6% 5% 4 5% 4 6% 7% 27%	2800
	11th to 20th	Day	16% 7% 2 7% 5% 5% 5% 5% 6% 8% 34%	2800
	21st to end	Day	21% 9% 2 7% 5% 5% 5% 5% 5% 6% 29%	2800
July	1st to 10th	Day	14% 7% 3 8% 6% 6% 7% 5% 8% 10% 27%	6360
	11th to 20th	Day	12% 6% 2 7% 5% 5% 6% 5% 7% 9% 35%	6360
	21st to end	Day	13% 7% 2 6% 4 4 5% 4 6% 9% 40%	6926
August	1st to 10th	Day	16% 8% 3 8% 6% 6% 6% 5% 6% 8% 28%	4537
	11th to 20th	Day	17% 6% 3 9% 5% 5% 6% 5% 7% 9% 29%	4175
	21st to end	Day	16% 7% 3 7% 4 4 5% 4 6% 8% 36%	4313
September	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 4 6% 6% 41%	2400
	11th to 20th	Day	16% 7% 2 6% 3 3 4 3 5% 7% 43%	2250
	21st to end	Day	18% 8% 2 6% 4 4 4 4 5% 9% 35%	2200
October	1st to 10th	Day	21% 10% 2 7% 4 5% 5% 3 6% 7% 30%	2166
	11th to 20th	Day	18% 13% 3 8% 5% 5% 5% 3 5% 6% 28%	1888
	21st to end	Day	24% 18% 4 8% 4 3 3 3 4 4 24%	1980
November	1st to 10th	Day	17% 17% 5% 8% 5% 4 5% 3 4 5% 27%	1851
	11th to 20th	Day	15% 18% 7% 11% 5% 4 4 3 4 5% 23%	1890
	21st to end	Day	18% 19% 7% 12% 6% 5% 3 4 5% 5% 16%	1706
December	1st to 10th	Day	13% 22% 8% 20% 9% 4 4 2 3 3 11%	2680
	11th to 20th	Day	17% 17% 6% 15% 6% 4 4 3 4 4 20%	3066
	21st to end	Day	19% 16% 6% 15% 6% 5% 5% 3 4 5% 18%	4048
January	1st to 10th	Night	10% 18% 9% 20% 9% 7% 4 2 3 4 14%	8234
	11th to 20th	Night	9% 17% 8% 20% 12% 8% 6% 3 4 4 10%	8235
	21st to end	Night	7% 14% 5% 15% 10% 10% 7% 5% 5% 4 17%	9057
February	1st to 10th	Night	11% 17% 6% 17% 9% 6% 4 4 4 5% 19%	2855
	11th to 20th	Night	10% 15% 6% 16% 10% 7% 5% 3 5% 4 20%	2461
	21st to end	Night	12% 17% 5% 12% 7% 6% 4 3 4 4 26%	2076
March	1st to 10th	Night	18% 15% 5% 12% 6% 6% 4 3 4 4 23%	5484
	11th to 20th	Night	14% 15% 5% 12% 6% 5% 5% 4 5% 5% 24%	5400
	21st to end	Night	15% 14% 6% 13% 8% 5% 4 3 4 3 25%	5121
April	1st to 10th	Night	20% 14% 4 9% 5% 4 4 3 4 5% 27%	2100
	11th to 20th	Night	20% 12% 4 7% 4 4 4 3 5% 5% 32%	2042
	21st to end	Night	20% 10% 3 8% 5% 4 5% 3 4 5% 32%	1890
May	1st to 10th	Night	25% 13% 4 9% 5% 5% 4 3 4 5% 23%	3982
	11th to 20th	Night	21% 9% 2 8% 6% 5% 5% 4 5% 6% 30%	3575
	21st to end	Night	17% 10% 3 8% 5% 5% 4 4 5% 7% 33%	3926
June	1st to 10th	Night	25% 8% 3 5% 4 4 4 4 5% 7% 31%	1600
	11th to 20th	Night	18% 7% 3 6% 4 4 4 5% 7% 8% 35%	1600
	21st to end	Night	19% 9% 2 6% 6% 3 5% 4 7% 8% 31%	1600
July	1st to 10th	Night	11% 8% 3 9% 6% 6% 6% 5% 7% 8% 30%	3600
	11th to 20th	Night	15% 8% 3 7% 5% 4 5% 4 6% 8% 37%	3600
	21st to end	Night	10% 7% 2 7% 5% 5% 5% 5% 7% 8% 40%	3926
August	1st to 10th	Night	19% 8% 4 7% 4 3 5% 3 5% 7% 34%	2586
	11th to 20th	Night	13% 7% 2 9% 5% 5% 6% 5% 7% 9% 33%	2867
	21st to end	Night	15% 7% 2 7% 5% 4 5% 4 5% 7% 39%	3581
September	1st to 10th	Night	15% 5% 2 6% 4 5% 5% 4 4 8% 42%	2000
	11th to 20th	Night	15% 5% 2 5% 3 3 4 3 5% 7% 47%	2150
	21st to end	Night	19% 7% 2 5% 4 4 4 3 4 7% 41%	2200
October	1st to 10th	Night	20% 8% 2 7% 4 3 4 4 5% 7% 35%	2230
	11th to 20th	Night	19% 10% 4 9% 5% 5% 4 4 5% 5% 30%	2511
	21st to end	Night	23% 12% 4 8% 5% 4 4 3 5% 6% 26%	2860
November	1st to 10th	Night	17% 14% 4 8% 6% 5% 5% 3 4 6% 27%	2667
	11th to 20th	Night	16% 14% 6% 11% 6% 4 4 3 4 5% 27%	2730
	21st to end	Night	16% 17% 7% 14% 6% 4 4 3 4 5% 21%	2909
December	1st to 10th	Night	15% 22% 9% 19% 9% 5% 4 3 3 3 10%	4720
	11th to 20th	Night	19% 18% 6% 16% 8% 5% 4 2 5% 4 14%	5348
	21st to end	Night	18% 17% 5% 12% 7% 5% 5% 3 5% 7% 17%	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	79% 2 9% 9% 2	4662
	11th to 20th	Day	79% 3 5% 9% 4	4680
	21st to end	Day	72% 3 6% 11% 8% 1	5124
February	1st to 10th	Day	72% 3 5% 13% 5% 1	1764
	11th to 20th	Day	71% 5% 8% 11% 5% 1	2053
	21st to end	Day	65% 5% 8% 13% 7% 2	1730
March	1st to 10th	Day	70% 4 7% 9% 8% 3	4579
	11th to 20th	Day	59% 4 13% 13% 10% 1	4779
	21st to end	Day	62% 2 7% 14% 14% 1	6050
April	1st to 10th	Day	63% 4 8% 16% 9% 1	2520
	11th to 20th	Day	56% 4 7% 18% 13% 1	2525
	21st to end	Day	58% 5% 8% 17% 9% 2	2730
May	1st to 10th	Day	64% 5% 8% 16% 6% 1	6020
	11th to 20th	Day	54% 7% 14% 17% 7% 1	6322
	21st to end	Day	51% 6% 11% 21% 10% 1	6949
June	1st to 10th	Day	55% 6% 11% 18% 9% 1	2800
	11th to 20th	Day	46% 6% 12% 23% 12% 1	2800
	21st to end	Day	54% 7% 10% 20% 9% 1	2800
July	1st to 10th	Day	50% 4 16% 22% 8%	6290
	11th to 20th	Day	43% 6% 13% 30% 8%	6285
	21st to end	Day	40% 5% 13% 34% 8%	6728
August	1st to 10th	Day	52% 5% 15% 21% 6%	4523
	11th to 20th	Day	49% 6% 19% 20% 6%	4214
	21st to end	Day	46% 4 16% 21% 12% 2	4313
September	1st to 10th	Day	41% 7% 13% 29% 10% 1	2400
	11th to 20th	Day	41% 4 12% 29% 14%	2250
	21st to end	Day	45% 7% 13% 23% 11% 1	2200
October	1st to 10th	Day	49% 4 13% 25% 9%	3530
	11th to 20th	Day	52% 4 13% 24% 7%	3052
	21st to end	Day	53% 3 14% 21% 8% 1	3180
November	1st to 10th	Day	59% 6% 11% 17% 7%	1851
	11th to 20th	Day	64% 4 10% 12% 8% 1	1890
	21st to end	Day	69% 5% 12% 11% 2	1706
December	1st to 10th	Day	79% 3 8% 7% 2	2680
	11th to 20th	Day	68% 3 8% 16% 5%	3066
	21st to end	Day	69% 5% 7% 11% 8%	4048
January	1st to 10th	Night	76% 4 8% 9% 3	8234
	11th to 20th	Night	79% 3 6% 7% 4	8280
	21st to end	Night	69% 3 7% 11% 10%	9057
February	1st to 10th	Night	68% 5% 8% 13% 6%	2855
	11th to 20th	Night	68% 5% 8% 13% 6%	2463
	21st to end	Night	63% 4 8% 15% 9% 1	2076
March	1st to 10th	Night	66% 3 7% 12% 9% 3	5494
	11th to 20th	Night	61% 4 14% 13% 7% 1	5401
	21st to end	Night	65% 3 5% 16% 10% 1	5121
April	1st to 10th	Night	60% 4 8% 16% 11% 1	2100
	11th to 20th	Night	54% 5% 8% 19% 13% 1	2042
	21st to end	Night	55% 5% 8% 18% 13% 2	1890
May	1st to 10th	Night	63% 6% 9% 15% 6% 1	3988
	11th to 20th	Night	54% 8% 12% 18% 7% 1	3576
	21st to end	Night	51% 6% 12% 18% 12% 1	3927
June	1st to 10th	Night	51% 7% 11% 22% 9% 1	1600
	11th to 20th	Night	46% 6% 12% 22% 11% 3	1600
	21st to end	Night	49% 7% 14% 20% 9% 1	1600
July	1st to 10th	Night	49% 4 19% 21% 7%	3560
	11th to 20th	Night	46% 4 13% 29% 8%	3552
	21st to end	Night	42% 5% 16% 28% 9%	3809
August	1st to 10th	Night	49% 6% 14% 26% 5%	2576
	11th to 20th	Night	46% 7% 19% 20% 8%	2894
	21st to end	Night	44% 5% 13% 24% 13% 1	3581
September	1st to 10th	Night	41% 7% 13% 27% 12%	2000
	11th to 20th	Night	37% 6% 15% 29% 12% 1	2150
	21st to end	Night	43% 7% 12% 25% 12% 1	2200
October	1st to 10th	Night	50% 4 11% 25% 9%	3646
	11th to 20th	Night	51% 4 11% 25% 9%	4086
	21st to end	Night	51% 4 14% 20% 10% 1	4610
November	1st to 10th	Night	58% 5% 12% 18% 7% 1	2667
	11th to 20th	Night	60% 5% 11% 14% 8% 2	2730
	21st to end	Night	67% 5% 10% 13% 4	2909
December	1st to 10th	Night	81% 3 7% 7% 2	4720
	11th to 20th	Night	74% 3 5% 11% 7%	5348
	21st to end	Night	68% 4 7% 13% 7%	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	27% 21% 29% 19% 4	220
	11th to 20th	Day	25% 27% 32% 10% 4 1	220
	21st to end	Day	28% 20% 30% 15% 6%	242
February	1st to 10th	Day	33% 24% 28% 11% 3	264
	11th to 20th	Day	27% 25% 31% 14% 3	532
	21st to end	Day	29% 22% 30% 17% 1	446
March	1st to 10th	Day	32% 20% 30% 16% 3	540
	11th to 20th	Day	33% 23% 26% 14% 4 1	540
	21st to end	Day	33% 23% 24% 13% 6% 1	594
April	1st to 10th	Day	36% 17% 27% 14% 4 1	540
	11th to 20th	Day	37% 17% 26% 12% 5% 2	532
	21st to end	Day	32% 17% 31% 12% 6% 1	540
May	1st to 10th	Day	34% 17% 25% 18% 6% 1	507
	11th to 20th	Day	24% 16% 30% 21% 7% 2	527
	21st to end	Day	20% 20% 32% 20% 6% 1	573
June	1st to 10th	Day	29% 14% 30% 20% 5% 2	530
	11th to 20th	Day	22% 15% 30% 21% 11% 1	530
	21st to end	Day	24% 14% 37% 16% 7% 2	530
July	1st to 10th	Day	18% 10% 34% 25% 10% 2	525
	11th to 20th	Day	16% 9% 40% 24% 8% 2	524
	21st to end	Day	16% 11% 35% 27% 10% 1	576
August	1st to 10th	Day	15% 10% 28% 29% 16% 2	526
	11th to 20th	Day	18% 8% 26% 28% 16% 5%	519
	21st to end	Day	19% 12% 26% 25% 13% 6%	583
September	1st to 10th	Day	16% 12% 31% 22% 14% 6%	530
	11th to 20th	Day	17% 11% 22% 22% 20% 9%	530
	21st to end	Day	19% 13% 24% 24% 14% 5%	530
October	1st to 10th	Day	23% 15% 25% 19% 14% 5%	530
	11th to 20th	Day	29% 17% 23% 18% 12% 1	467
	21st to end	Day	37% 15% 24% 19% 6%	462
November	1st to 10th	Day	32% 19% 29% 16% 4	425
	11th to 20th	Day	30% 19% 28% 15% 7% 2	430
	21st to end	Day	34% 21% 30% 13% 2	246
December	1st to 10th	Day	31% 20% 26% 18% 3 1	220
	11th to 20th	Day	30% 27% 31% 10% 2	220
	21st to end	Day	35% 21% 24% 16% 3 1	242
January	1st to 10th	Night	27% 20% 31% 19% 4	840
	11th to 20th	Night	25% 20% 32% 18% 5%	840
	21st to end	Night	20% 17% 33% 24% 6% 1	924
February	1st to 10th	Night	22% 20% 31% 23% 5%	840
	11th to 20th	Night	22% 21% 32% 22% 3	823
	21st to end	Night	26% 16% 32% 24% 3	692
March	1st to 10th	Night	28% 19% 29% 21% 3	840
	11th to 20th	Night	29% 18% 27% 21% 6%	840
	21st to end	Night	28% 17% 28% 20% 6% 1	924
April	1st to 10th	Night	31% 15% 27% 21% 5%	840
	11th to 20th	Night	28% 16% 26% 23% 6%	798
	21st to end	Night	29% 15% 30% 20% 6% 1	630
May	1st to 10th	Night	27% 10% 30% 25% 7%	574
	11th to 20th	Night	22% 11% 28% 29% 9% 1	394
	21st to end	Night	20% 10% 30% 31% 9%	433
June	1st to 10th	Night	30% 5% 26% 30% 8% 1	400
	11th to 20th	Night	22% 6% 27% 31% 14%	400
	21st to end	Night	18% 7% 28% 36% 11%	400
July	1st to 10th	Night	14% 6% 25% 39% 16% 1	390
	11th to 20th	Night	13% 3 26% 40% 16% 2	388
	21st to end	Night	13% 4 26% 40% 18%	438
August	1st to 10th	Night	17% 4 15% 41% 22% 1	398
	11th to 20th	Night	15% 5% 21% 37% 21% 1	587
	21st to end	Night	16% 5% 22% 36% 19% 2	875
September	1st to 10th	Night	17% 7% 25% 35% 15% 1	800
	11th to 20th	Night	17% 7% 20% 30% 23% 3	800
	21st to end	Night	21% 9% 25% 27% 17% 2	800
October	1st to 10th	Night	25% 10% 23% 27% 14% 2	800
	11th to 20th	Night	27% 12% 25% 25% 10% 1	800
	21st to end	Night	30% 15% 27% 24% 4	880
November	1st to 10th	Night	29% 15% 29% 21% 5%	820
	11th to 20th	Night	26% 18% 28% 18% 9% 1	840
	21st to end	Night	30% 21% 27% 17% 5% 1	840
December	1st to 10th	Night	30% 21% 27% 18% 4	840
	11th to 20th	Night	29% 19% 28% 18% 4	840
	21st to end	Night	33% 20% 23% 19% 4	924

Page generated at 2026-04-29 02:21:45. Version ac07

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