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 2025-01-07.

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% 12% 4 10% 6% 5% 5% 4 5% 6% 27%	105112
	Night	16% 13% 5% 11% 6% 5% 4 3 5% 5% 26%	103941
Transparency	Day	56% 5% 11% 19% 8% 1	108598
	Night	59% 5% 10% 17% 8% 1	108544
Seeing	Day	26% 17% 28% 19% 8% 2	14834
	Night	25% 14% 27% 25% 9% 1	23803

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	14% 19% 9% 19% 7% 5% 4 2 3 3 14%	2565
	11th to 20th	Day	13% 15% 8% 19% 12% 5% 3 2 4 4 14%	2520
	21st to end	Day	12% 19% 8% 15% 6% 9% 4 3 4 4 16%	2772
February	1st to 10th	Day	12% 19% 6% 16% 8% 7% 5% 2 4 3 17%	1596
	11th to 20th	Day	12% 18% 7% 15% 9% 5% 5% 3 5% 3 17%	1844
	21st to end	Day	13% 19% 5% 12% 8% 6% 4 4 5% 5% 21%	1570
March	1st to 10th	Day	20% 17% 5% 11% 7% 5% 4 3 4 4 22%	3116
	11th to 20th	Day	13% 22% 7% 13% 5% 4 3 3 4 4 22%	3274
	21st to end	Day	16% 14% 5% 11% 5% 4 3 2 4 4 32%	4129
April	1st to 10th	Day	21% 17% 4 9% 5% 5% 4 3 4 5% 25%	2280
	11th to 20th	Day	19% 14% 4 7% 5% 4 3 3 4 4 33%	2282
	21st to end	Day	23% 12% 3 7% 5% 4 5% 3 5% 5% 27%	2470
May	1st to 10th	Day	23% 10% 3 8% 5% 4 4 4 5% 6% 27%	4188
	11th to 20th	Day	18% 8% 3 9% 6% 6% 5% 4 6% 7% 28%	4398
	21st to end	Day	14% 8% 2 8% 5% 5% 6% 4 8% 8% 33%	4837
June	1st to 10th	Day	25% 8% 3 6% 5% 4 5% 4 6% 7% 27%	2660
	11th to 20th	Day	17% 7% 2 7% 4 4 5% 5% 6% 8% 34%	2660
	21st to end	Day	22% 9% 2 7% 5% 5% 5% 5% 5% 6% 29%	2660
July	1st to 10th	Day	14% 6% 3 7% 6% 5% 6% 5% 7% 10% 32%	4440
	11th to 20th	Day	13% 6% 2 7% 6% 6% 6% 5% 8% 9% 32%	4440
	21st to end	Day	14% 8% 3 6% 4 5% 5% 4 6% 8% 39%	4814
August	1st to 10th	Day	17% 8% 3 8% 6% 6% 6% 5% 6% 8% 27%	4398
	11th to 20th	Day	17% 7% 3 9% 5% 5% 6% 5% 7% 9% 28%	4045
	21st to end	Day	16% 7% 3 7% 4 4 5% 4 6% 8% 36%	4181
September	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 4 6% 6% 40%	2280
	11th to 20th	Day	17% 7% 2 6% 4 3 4 3 5% 8% 42%	2138
	21st to end	Day	19% 9% 2 6% 4 4 4 4 5% 9% 35%	2090
October	1st to 10th	Day	22% 10% 2 7% 4 5% 5% 3 6% 6% 28%	2058
	11th to 20th	Day	19% 13% 3 8% 5% 5% 5% 4 5% 6% 28%	1794
	21st to end	Day	24% 18% 4 8% 4 4 3 3 3 4 25%	1881
November	1st to 10th	Day	17% 16% 5% 7% 5% 4 5% 3 4 5% 28%	1761
	11th to 20th	Day	16% 17% 6% 12% 5% 4 4 3 4 5% 23%	1800
	21st to end	Day	18% 18% 7% 11% 6% 5% 3 4 6% 5% 17%	1625
December	1st to 10th	Day	14% 22% 8% 20% 9% 4 4 2 3 3 11%	2600
	11th to 20th	Day	17% 18% 7% 14% 5% 4 4 3 4 4 20%	2986
	21st to end	Day	19% 16% 6% 15% 6% 4 5% 3 4 5% 18%	3960
January	1st to 10th	Night	14% 18% 8% 19% 8% 6% 4 3 4 4 14%	4514
	11th to 20th	Night	10% 16% 7% 17% 11% 7% 6% 3 4 4 14%	4440
	21st to end	Night	12% 20% 7% 16% 8% 6% 4 3 4 4 18%	4884
February	1st to 10th	Night	11% 17% 6% 16% 9% 6% 4 3 4 5% 18%	2584
	11th to 20th	Night	11% 16% 6% 15% 9% 6% 5% 3 5% 4 20%	2221
	21st to end	Night	13% 17% 4 11% 7% 7% 4 3 4 4 26%	1884
March	1st to 10th	Night	20% 15% 4 8% 5% 5% 4 3 4 4 27%	3724
	11th to 20th	Night	15% 18% 5% 12% 6% 5% 4 3 4 3 24%	3685
	21st to end	Night	14% 16% 6% 13% 7% 4 3 3 3 3 28%	3500
April	1st to 10th	Night	20% 13% 4 8% 5% 5% 4 3 4 4 27%	1900
	11th to 20th	Night	20% 11% 4 7% 4 4 4 3 5% 5% 33%	1846
	21st to end	Night	21% 10% 3 8% 5% 4 5% 3 4 5% 31%	1710
May	1st to 10th	Night	22% 11% 4 8% 5% 5% 4 3 5% 6% 27%	2780
	11th to 20th	Night	19% 10% 3 8% 5% 5% 5% 4 5% 5% 32%	2495
	21st to end	Night	16% 7% 3 7% 4 5% 5% 4 5% 8% 38%	2738
June	1st to 10th	Night	25% 8% 3 5% 4 4 4 3 6% 8% 31%	1520
	11th to 20th	Night	18% 7% 3 6% 3 5% 3 5% 7% 9% 36%	1520
	21st to end	Night	19% 9% 2 6% 6% 3 5% 4 7% 8% 31%	1520
July	1st to 10th	Night	11% 8% 3 9% 6% 6% 6% 5% 6% 8% 32%	2520
	11th to 20th	Night	14% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	2520
	21st to end	Night	13% 8% 3 7% 5% 5% 4 4 6% 6% 38%	2739
August	1st to 10th	Night	20% 9% 4 7% 4 3 5% 3 5% 7% 33%	2506
	11th to 20th	Night	13% 7% 2 9% 5% 6% 6% 5% 7% 9% 32%	2777
	21st to end	Night	15% 7% 2 7% 5% 4 5% 4 5% 7% 39%	3471
September	1st to 10th	Night	16% 5% 2 6% 4 5% 5% 4 4 8% 41%	1900
	11th to 20th	Night	15% 5% 2 5% 3 3 4 4 5% 7% 46%	2042
	21st to end	Night	19% 7% 2 5% 3 4 4 3 4 7% 41%	2090
October	1st to 10th	Night	20% 8% 3 7% 4 4 4 4 5% 7% 33%	2118
	11th to 20th	Night	19% 10% 4 9% 5% 5% 5% 4 5% 5% 30%	2385
	21st to end	Night	23% 13% 3 8% 5% 4 4 3 5% 6% 26%	2717
November	1st to 10th	Night	17% 13% 4 8% 5% 6% 5% 4 5% 6% 27%	2537
	11th to 20th	Night	17% 13% 5% 10% 6% 4 4 3 4 6% 28%	2600
	21st to end	Night	16% 17% 7% 14% 6% 4 3 3 4 5% 22%	2770
December	1st to 10th	Night	15% 22% 9% 20% 9% 4 4 3 2 3 9%	4580
	11th to 20th	Night	19% 18% 6% 16% 7% 5% 4 2 5% 4 14%	5208
	21st to end	Night	18% 17% 5% 12% 7% 5% 5% 3 5% 7% 17%	6996

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	76% 4 10% 9% 1	2566
	11th to 20th	Day	74% 6% 7% 10% 3	2520
	21st to end	Day	72% 4 9% 10% 4 1	2772
February	1st to 10th	Day	73% 4 6% 12% 5% 1	1596
	11th to 20th	Day	71% 5% 8% 10% 5% 1	1853
	21st to end	Day	65% 5% 9% 13% 7% 2	1570
March	1st to 10th	Day	65% 6% 9% 11% 8% 1	3119
	11th to 20th	Day	66% 5% 9% 10% 9% 2	3274
	21st to end	Day	57% 3 7% 16% 15% 2	4129
April	1st to 10th	Day	62% 4 8% 16% 9% 1	2280
	11th to 20th	Day	54% 5% 7% 19% 13% 1	2282
	21st to end	Day	58% 5% 9% 16% 9% 2	2470
May	1st to 10th	Day	55% 7% 10% 19% 8% 1	4202
	11th to 20th	Day	52% 9% 15% 16% 7% 1	4402
	21st to end	Day	45% 9% 12% 23% 11% 1	4837
June	1st to 10th	Day	55% 6% 11% 18% 8% 1	2660
	11th to 20th	Day	46% 6% 12% 22% 12% 1	2660
	21st to end	Day	54% 8% 10% 19% 8%	2660
July	1st to 10th	Day	45% 5% 16% 25% 9%	4370
	11th to 20th	Day	46% 6% 15% 30% 4	4365
	21st to end	Day	43% 7% 12% 30% 7%	4661
August	1st to 10th	Day	54% 5% 15% 20% 6%	4384
	11th to 20th	Day	50% 6% 20% 19% 5%	4084
	21st to end	Day	46% 4 16% 20% 12% 2	4181
September	1st to 10th	Day	42% 7% 13% 27% 10% 1	2280
	11th to 20th	Day	41% 5% 13% 28% 13%	2138
	21st to end	Day	46% 7% 13% 23% 10% 1	2090
October	1st to 10th	Day	50% 4 13% 25% 8%	3422
	11th to 20th	Day	53% 4 13% 23% 6%	2958
	21st to end	Day	53% 3 14% 21% 8% 1	3081
November	1st to 10th	Day	57% 6% 12% 18% 7%	1761
	11th to 20th	Day	64% 5% 10% 13% 8% 1	1800
	21st to end	Day	68% 6% 13% 11% 2	1625
December	1st to 10th	Day	80% 3 8% 7% 2	2600
	11th to 20th	Day	67% 3 9% 16% 5%	2986
	21st to end	Day	69% 5% 7% 11% 9%	3960
January	1st to 10th	Night	74% 6% 10% 7% 2	4514
	11th to 20th	Night	74% 5% 9% 9% 3	4440
	21st to end	Night	71% 5% 8% 10% 5% 1	4884
February	1st to 10th	Night	69% 5% 8% 11% 5% 1	2584
	11th to 20th	Night	67% 5% 8% 13% 6%	2223
	21st to end	Night	63% 4 9% 14% 10% 1	1884
March	1st to 10th	Night	61% 4 9% 15% 7% 3	3734
	11th to 20th	Night	64% 5% 9% 12% 9% 1	3686
	21st to end	Night	63% 4 4 17% 11% 2	3500
April	1st to 10th	Night	59% 4 9% 16% 11% 1	1900
	11th to 20th	Night	52% 6% 8% 20% 13% 1	1846
	21st to end	Night	56% 5% 9% 17% 12% 2	1710
May	1st to 10th	Night	56% 8% 10% 17% 8% 1	2786
	11th to 20th	Night	52% 10% 13% 16% 8% 1	2496
	21st to end	Night	44% 8% 13% 19% 16% 1	2739
June	1st to 10th	Night	51% 7% 11% 22% 8% 1	1520
	11th to 20th	Night	45% 7% 12% 23% 11% 2	1520
	21st to end	Night	50% 7% 14% 19% 8% 1	1520
July	1st to 10th	Night	48% 6% 15% 21% 10%	2480
	11th to 20th	Night	45% 6% 14% 29% 7%	2472
	21st to end	Night	45% 6% 15% 24% 10%	2651
August	1st to 10th	Night	51% 6% 14% 25% 5%	2496
	11th to 20th	Night	47% 7% 19% 19% 7%	2804
	21st to end	Night	44% 5% 13% 23% 14% 1	3471
September	1st to 10th	Night	42% 8% 13% 25% 12%	1900
	11th to 20th	Night	37% 6% 16% 28% 12% 1	2042
	21st to end	Night	43% 7% 13% 25% 12% 1	2090
October	1st to 10th	Night	51% 4 11% 25% 8%	3534
	11th to 20th	Night	52% 4 11% 24% 9%	3960
	21st to end	Night	51% 4 14% 20% 9% 1	4467
November	1st to 10th	Night	57% 5% 12% 18% 7% 1	2537
	11th to 20th	Night	59% 5% 11% 15% 9% 2	2600
	21st to end	Night	66% 5% 10% 14% 4	2770
December	1st to 10th	Night	82% 3 7% 6% 2	4580
	11th to 20th	Night	74% 3 5% 11% 7%	5208
	21st to end	Night	68% 4 7% 13% 7%	6996

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	25% 22% 29% 19% 4	192
	11th to 20th	Day	28% 26% 30% 11% 5% 1	180
	21st to end	Day	27% 20% 29% 16% 8% 1	198
February	1st to 10th	Day	38% 25% 24% 10% 3	216
	11th to 20th	Day	28% 27% 31% 12% 2	452
	21st to end	Day	30% 23% 28% 18% 1	382
March	1st to 10th	Day	33% 18% 29% 17% 3	460
	11th to 20th	Day	31% 24% 26% 14% 4 1	460
	21st to end	Day	32% 22% 24% 14% 7% 1	506
April	1st to 10th	Day	35% 18% 25% 15% 5% 2	460
	11th to 20th	Day	36% 17% 27% 12% 6% 3	452
	21st to end	Day	33% 17% 31% 12% 6% 1	460
May	1st to 10th	Day	32% 17% 26% 18% 6% 1	463
	11th to 20th	Day	24% 16% 30% 20% 7% 2	487
	21st to end	Day	19% 21% 32% 21% 6% 1	529
June	1st to 10th	Day	30% 15% 30% 19% 6% 2	490
	11th to 20th	Day	22% 16% 29% 21% 11% 1	490
	21st to end	Day	25% 15% 35% 16% 8% 2	490
July	1st to 10th	Day	18% 11% 33% 26% 11% 2	485
	11th to 20th	Day	17% 10% 39% 24% 8% 2	484
	21st to end	Day	17% 10% 35% 27% 11% 1	532
August	1st to 10th	Day	17% 10% 29% 29% 14% 2	486
	11th to 20th	Day	18% 8% 26% 28% 15% 4	479
	21st to end	Day	19% 13% 25% 24% 14% 6%	539
September	1st to 10th	Day	17% 12% 31% 21% 13% 6%	490
	11th to 20th	Day	18% 11% 21% 21% 20% 8%	490
	21st to end	Day	19% 13% 25% 24% 14% 6%	490
October	1st to 10th	Day	25% 15% 25% 18% 13% 4	490
	11th to 20th	Day	29% 18% 23% 18% 12% 1	433
	21st to end	Day	37% 16% 24% 18% 6%	429
November	1st to 10th	Day	31% 18% 29% 17% 4 1	395
	11th to 20th	Day	29% 20% 28% 15% 7% 2	400
	21st to end	Day	32% 21% 30% 14% 2	225
December	1st to 10th	Day	33% 19% 26% 18% 4 2	200
	11th to 20th	Day	32% 26% 30% 10% 2 1	200
	21st to end	Day	36% 20% 25% 15% 3 1	220
January	1st to 10th	Night	28% 20% 30% 18% 4	785
	11th to 20th	Night	25% 19% 33% 18% 4	760
	21st to end	Night	21% 17% 32% 24% 5%	836
February	1st to 10th	Night	23% 20% 31% 22% 4	760
	11th to 20th	Night	21% 23% 31% 22% 3	743
	21st to end	Night	26% 16% 32% 23% 3	628
March	1st to 10th	Night	28% 18% 28% 22% 4	760
	11th to 20th	Night	28% 17% 27% 22% 6%	760
	21st to end	Night	28% 17% 27% 20% 7% 1	836
April	1st to 10th	Night	30% 15% 27% 22% 5%	760
	11th to 20th	Night	27% 17% 25% 23% 7%	722
	21st to end	Night	29% 15% 29% 20% 6%	570
May	1st to 10th	Night	25% 11% 31% 25% 8%	542
	11th to 20th	Night	21% 11% 29% 29% 9% 1	374
	21st to end	Night	19% 10% 31% 31% 9%	411
June	1st to 10th	Night	30% 6% 26% 30% 8% 1	380
	11th to 20th	Night	21% 6% 27% 32% 14%	380
	21st to end	Night	18% 7% 28% 36% 11%	380
July	1st to 10th	Night	14% 7% 25% 39% 15% 1	370
	11th to 20th	Night	13% 3 27% 39% 17% 1	368
	21st to end	Night	14% 4 25% 39% 18%	416
August	1st to 10th	Night	18% 4 15% 40% 21% 1	378
	11th to 20th	Night	16% 5% 22% 37% 19% 1	557
	21st to end	Night	17% 5% 22% 35% 19% 2	831
September	1st to 10th	Night	18% 7% 25% 35% 14% 1	760
	11th to 20th	Night	18% 8% 20% 30% 22% 3	760
	21st to end	Night	21% 9% 24% 26% 18% 2	760
October	1st to 10th	Night	25% 11% 23% 26% 13% 2	760
	11th to 20th	Night	28% 13% 24% 24% 10% 1	760
	21st to end	Night	30% 15% 28% 23% 4	836
November	1st to 10th	Night	28% 15% 30% 21% 6%	780
	11th to 20th	Night	26% 18% 28% 18% 9% 1	800
	21st to end	Night	30% 21% 26% 17% 5% 1	800
December	1st to 10th	Night	31% 21% 27% 17% 5%	800
	11th to 20th	Night	29% 19% 28% 19% 5% 1	800
	21st to end	Night	33% 20% 24% 19% 4	880

Page generated at 2025-01-04 03:23:59. Version ac07

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