Sherbrooke
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sherbrooke clear sky chart from 2005-11-06 to 2025-01-22.

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	19% 12% 4 9% 5% 5% 4 4 5% 6% 27%	105203
	Night	19% 14% 5% 10% 5% 4 4 3 4 5% 26%	104167
Transparency	Day	57% 4 12% 19% 7% 1	108689
	Night	60% 3 11% 17% 7% 1	108770
Seeing	Day	28% 16% 28% 18% 8% 2	14868
	Night	27% 13% 26% 24% 9% 1	23851

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	16% 21% 8% 17% 7% 6% 4 2 3 3 13%	2597
	11th to 20th	Day	14% 16% 8% 20% 12% 4 3 2 4 3 15%	2600
	21st to end	Day	13% 19% 8% 15% 6% 8% 4 3 3 4 16%	2780
February	1st to 10th	Day	15% 20% 5% 15% 8% 7% 5% 3 3 4 16%	1582
	11th to 20th	Day	13% 19% 9% 15% 8% 4 5% 3 4 4 17%	1848
	21st to end	Day	13% 20% 5% 11% 7% 6% 5% 3 4 5% 21%	1570
March	1st to 10th	Day	23% 16% 4 10% 6% 4 4 3 3 5% 22%	3116
	11th to 20th	Day	17% 22% 6% 11% 6% 4 4 2 3 4 21%	3283
	21st to end	Day	17% 15% 6% 9% 5% 4 3 3 3 4 31%	4101
April	1st to 10th	Day	23% 16% 3 9% 5% 4 4 3 4 5% 26%	2280
	11th to 20th	Day	20% 13% 3 6% 5% 4 4 3 4 4 34%	2296
	21st to end	Day	24% 13% 4 7% 4 4 4 3 4 6% 27%	2470
May	1st to 10th	Day	25% 9% 3 7% 5% 5% 4 3 5% 6% 28%	4164
	11th to 20th	Day	20% 8% 3 7% 6% 5% 5% 4 6% 7% 30%	4398
	21st to end	Day	15% 8% 2 7% 5% 6% 5% 5% 7% 9% 32%	4837
June	1st to 10th	Day	26% 8% 3 6% 4 4 5% 4 6% 7% 26%	2660
	11th to 20th	Day	18% 7% 3 6% 5% 4 5% 4 6% 8% 34%	2660
	21st to end	Day	22% 9% 3 7% 6% 5% 5% 3 6% 6% 28%	2660
July	1st to 10th	Day	14% 7% 2 7% 5% 6% 6% 5% 8% 9% 32%	4440
	11th to 20th	Day	15% 6% 2 7% 5% 6% 6% 6% 7% 9% 31%	4440
	21st to end	Day	15% 7% 3 6% 4 4 4 4 6% 8% 39%	4814
August	1st to 10th	Day	18% 8% 3 8% 5% 6% 6% 5% 7% 9% 26%	4375
	11th to 20th	Day	19% 7% 3 7% 5% 5% 6% 5% 7% 10% 26%	4045
	21st to end	Day	19% 8% 2 5% 4 4 5% 4 6% 8% 36%	4215
September	1st to 10th	Day	16% 7% 2 6% 4 5% 3 4 6% 6% 40%	2280
	11th to 20th	Day	19% 6% 2 6% 2 3 4 4 5% 6% 42%	2127
	21st to end	Day	20% 8% 3 5% 4 4 5% 4 5% 8% 34%	2090
October	1st to 10th	Day	24% 10% 3 6% 5% 4 4 4 5% 7% 28%	2071
	11th to 20th	Day	19% 13% 3 7% 5% 5% 4 4 6% 6% 28%	1781
	21st to end	Day	26% 18% 3 7% 4 4 4 3 4 4 23%	1881
November	1st to 10th	Day	19% 17% 5% 7% 4 5% 3 3 5% 4 28%	1761
	11th to 20th	Day	18% 19% 5% 10% 6% 3 3 4 4 5% 23%	1800
	21st to end	Day	20% 19% 5% 11% 5% 4 4 4 4 5% 18%	1635
December	1st to 10th	Day	17% 22% 7% 19% 7% 5% 4 2 3 3 12%	2600
	11th to 20th	Day	19% 19% 6% 13% 5% 4 4 3 4 3 21%	2986
	21st to end	Day	20% 18% 5% 13% 4 6% 4 2 4 5% 18%	3960
January	1st to 10th	Night	16% 21% 8% 18% 7% 4 4 2 3 3 14%	4569
	11th to 20th	Night	12% 18% 7% 20% 9% 7% 5% 3 4 3 14%	4580
	21st to end	Night	15% 20% 7% 14% 7% 5% 4 3 3 4 18%	4899
February	1st to 10th	Night	14% 18% 7% 13% 7% 6% 4 3 4 4 19%	2594
	11th to 20th	Night	13% 19% 7% 15% 7% 6% 4 2 3 4 20%	2218
	21st to end	Night	15% 19% 5% 9% 7% 6% 4 3 4 4 25%	1884
March	1st to 10th	Night	23% 17% 4 7% 5% 4 3 2 3 4 27%	3724
	11th to 20th	Night	18% 22% 6% 11% 5% 4 3 2 3 4 22%	3676
	21st to end	Night	17% 18% 5% 10% 6% 4 3 2 3 3 28%	3516
April	1st to 10th	Night	23% 13% 5% 7% 5% 4 4 3 5% 5% 27%	1900
	11th to 20th	Night	23% 11% 2 5% 5% 4 3 3 5% 5% 34%	1832
	21st to end	Night	23% 13% 3 7% 4 3 4 3 4 5% 31%	1710
May	1st to 10th	Night	27% 10% 3 6% 5% 5% 4 4 5% 5% 27%	2805
	11th to 20th	Night	22% 9% 3 8% 6% 4 5% 3 5% 6% 30%	2495
	21st to end	Night	17% 7% 2 7% 4 4 6% 4 5% 7% 37%	2738
June	1st to 10th	Night	26% 9% 2 6% 3 3 4 4 7% 8% 28%	1520
	11th to 20th	Night	20% 6% 3 5% 4 3 4 5% 7% 7% 35%	1520
	21st to end	Night	20% 9% 3 6% 5% 4 5% 4 6% 6% 31%	1520
July	1st to 10th	Night	14% 8% 3 9% 6% 5% 7% 4 7% 8% 31%	2520
	11th to 20th	Night	17% 8% 2 7% 5% 5% 6% 4 5% 7% 35%	2520
	21st to end	Night	16% 7% 3 7% 5% 4 5% 4 6% 7% 38%	2739
August	1st to 10th	Night	23% 8% 3 7% 5% 4 4 4 6% 7% 29%	2524
	11th to 20th	Night	16% 8% 3 8% 6% 5% 6% 4 6% 8% 30%	2782
	21st to end	Night	19% 7% 2 7% 4 4 4 3 6% 6% 39%	3438
September	1st to 10th	Night	17% 7% 3 7% 4 5% 3 4 5% 6% 39%	1900
	11th to 20th	Night	17% 6% 2 4 4 3 4 4 5% 6% 46%	2052
	21st to end	Night	21% 6% 2 5% 4 3 3 3 4 8% 40%	2090
October	1st to 10th	Night	21% 9% 3 7% 4 5% 4 4 5% 6% 33%	2104
	11th to 20th	Night	22% 11% 3 8% 5% 5% 4 3 4 5% 29%	2399
	21st to end	Night	26% 13% 3 7% 4 4 3 3 4 5% 27%	2717
November	1st to 10th	Night	20% 16% 3 8% 4 5% 4 3 5% 6% 26%	2537
	11th to 20th	Night	18% 16% 6% 10% 5% 4 3 3 4 5% 28%	2600
	21st to end	Night	21% 18% 5% 11% 6% 4 3 2 3 4 22%	2761
December	1st to 10th	Night	17% 25% 11% 18% 6% 4 3 2 3 2 9%	4580
	11th to 20th	Night	21% 20% 6% 15% 6% 4 3 2 3 5% 15%	5208
	21st to end	Night	20% 19% 5% 10% 6% 4 4 2 4 7% 18%	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	78% 2 11% 8% 1	2598
	11th to 20th	Day	75% 3 8% 11% 3	2600
	21st to end	Day	74% 2 9% 11% 3 1	2780
February	1st to 10th	Day	74% 2 6% 12% 5% 1	1582
	11th to 20th	Day	73% 2 9% 10% 5% 1	1857
	21st to end	Day	67% 2 9% 14% 6% 2	1570
March	1st to 10th	Day	66% 3 8% 13% 8% 2	3119
	11th to 20th	Day	67% 3 8% 11% 9% 1	3283
	21st to end	Day	58% 2 7% 18% 14% 1	4101
April	1st to 10th	Day	63% 3 7% 18% 8% 2	2280
	11th to 20th	Day	55% 3 7% 21% 13% 1	2296
	21st to end	Day	59% 3 9% 17% 9% 3	2470
May	1st to 10th	Day	58% 2 12% 18% 8% 1	4178
	11th to 20th	Day	54% 3 19% 17% 7% 1	4402
	21st to end	Day	47% 5% 14% 23% 11% 1	4837
June	1st to 10th	Day	56% 4 12% 19% 8% 1	2660
	11th to 20th	Day	47% 4 13% 23% 11% 1	2660
	21st to end	Day	55% 4 13% 20% 8%	2660
July	1st to 10th	Day	45% 7% 16% 25% 8%	4370
	11th to 20th	Day	44% 8% 16% 28% 4	4365
	21st to end	Day	43% 6% 14% 30% 6%	4661
August	1st to 10th	Day	52% 7% 16% 20% 5%	4361
	11th to 20th	Day	50% 8% 18% 19% 5%	4084
	21st to end	Day	44% 6% 15% 20% 12% 2	4215
September	1st to 10th	Day	43% 5% 14% 28% 9% 1	2280
	11th to 20th	Day	42% 4 12% 29% 13%	2127
	21st to end	Day	47% 5% 14% 24% 9% 1	2090
October	1st to 10th	Day	49% 6% 14% 24% 7%	3448
	11th to 20th	Day	53% 4 15% 24% 4	2932
	21st to end	Day	53% 3 15% 21% 7%	3081
November	1st to 10th	Day	59% 4 11% 18% 7% 1	1761
	11th to 20th	Day	64% 3 10% 13% 8% 1	1800
	21st to end	Day	68% 4 13% 12% 2	1635
December	1st to 10th	Day	79% 4 8% 7% 2	2600
	11th to 20th	Day	68% 3 8% 16% 5%	2986
	21st to end	Day	70% 3 8% 10% 8%	3960
January	1st to 10th	Night	77% 1 13% 7% 2	4569
	11th to 20th	Night	76% 2 11% 9% 2	4580
	21st to end	Night	73% 2 10% 11% 4 1	4899
February	1st to 10th	Night	70% 3 8% 13% 5%	2594
	11th to 20th	Night	70% 2 8% 14% 5%	2220
	21st to end	Night	64% 2 9% 15% 9% 1	1884
March	1st to 10th	Night	62% 3 10% 16% 7% 3	3734
	11th to 20th	Night	68% 2 8% 13% 8% 1	3677
	21st to end	Night	64% 1 6% 18% 10% 2	3516
April	1st to 10th	Night	61% 2 8% 17% 11% 1	1900
	11th to 20th	Night	53% 3 9% 22% 13% 1	1832
	21st to end	Night	57% 3 9% 18% 11% 2	1710
May	1st to 10th	Night	59% 2 12% 18% 8% 1	2811
	11th to 20th	Night	54% 4 15% 18% 8% 1	2496
	21st to end	Night	45% 4 15% 18% 17% 1	2739
June	1st to 10th	Night	53% 4 12% 23% 9%	1520
	11th to 20th	Night	45% 5% 13% 24% 10% 2	1520
	21st to end	Night	51% 5% 15% 20% 9% 1	1520
July	1st to 10th	Night	47% 7% 15% 21% 10%	2480
	11th to 20th	Night	46% 7% 15% 26% 6%	2472
	21st to end	Night	44% 7% 16% 25% 9%	2651
August	1st to 10th	Night	52% 5% 14% 24% 4	2514
	11th to 20th	Night	49% 8% 17% 18% 7%	2809
	21st to end	Night	43% 5% 13% 24% 14% 1	3438
September	1st to 10th	Night	46% 4 13% 25% 12% 1	1900
	11th to 20th	Night	38% 4 16% 29% 11% 1	2052
	21st to end	Night	43% 6% 13% 26% 11% 1	2090
October	1st to 10th	Night	52% 5% 11% 23% 9%	3507
	11th to 20th	Night	54% 4 12% 23% 6%	3987
	21st to end	Night	51% 3 14% 22% 8% 1	4467
November	1st to 10th	Night	59% 3 13% 18% 6% 1	2537
	11th to 20th	Night	61% 3 10% 16% 9% 2	2600
	21st to end	Night	68% 3 13% 13% 4	2761
December	1st to 10th	Night	82% 3 7% 6% 1	4580
	11th to 20th	Night	74% 2 6% 12% 6%	5208
	21st to end	Night	69% 2 9% 13% 6%	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	31% 20% 32% 15% 2 1	200
	11th to 20th	Day	33% 25% 28% 11% 3 1	200
	21st to end	Day	29% 21% 31% 14% 6% 1	200
February	1st to 10th	Day	39% 27% 21% 10% 2	212
	11th to 20th	Day	31% 25% 32% 9% 3	456
	21st to end	Day	31% 22% 27% 18% 2	382
March	1st to 10th	Day	33% 19% 28% 16% 4	460
	11th to 20th	Day	32% 23% 24% 15% 5% 1	460
	21st to end	Day	35% 19% 24% 14% 6% 2	506
April	1st to 10th	Day	38% 17% 24% 14% 5% 2	460
	11th to 20th	Day	35% 21% 23% 12% 7% 2	452
	21st to end	Day	35% 18% 30% 11% 5% 1	460
May	1st to 10th	Day	35% 14% 29% 14% 6% 1	463
	11th to 20th	Day	26% 15% 30% 20% 8% 1	487
	21st to end	Day	23% 19% 30% 22% 5% 1	529
June	1st to 10th	Day	29% 15% 31% 18% 6% 1	490
	11th to 20th	Day	19% 20% 29% 23% 8% 1	490
	21st to end	Day	25% 17% 34% 15% 8% 1	490
July	1st to 10th	Day	20% 11% 32% 26% 10% 1	485
	11th to 20th	Day	18% 10% 40% 23% 8% 2	484
	21st to end	Day	19% 10% 35% 27% 8% 1	532
August	1st to 10th	Day	20% 10% 28% 27% 14% 1	486
	11th to 20th	Day	22% 8% 27% 26% 14% 4	479
	21st to end	Day	23% 12% 24% 23% 13% 6%	539
September	1st to 10th	Day	19% 10% 31% 22% 12% 6%	490
	11th to 20th	Day	20% 11% 21% 20% 19% 9%	490
	21st to end	Day	20% 12% 25% 24% 13% 5%	490
October	1st to 10th	Day	25% 16% 25% 16% 14% 4	490
	11th to 20th	Day	31% 17% 24% 17% 10% 2	427
	21st to end	Day	41% 14% 23% 16% 6%	429
November	1st to 10th	Day	36% 16% 23% 20% 4	395
	11th to 20th	Day	31% 20% 26% 17% 6% 1	400
	21st to end	Day	34% 22% 29% 13% 3	235
December	1st to 10th	Day	34% 18% 28% 15% 5% 1	200
	11th to 20th	Day	36% 25% 28% 7% 5% 1	200
	21st to end	Day	40% 18% 25% 13% 3 1	220
January	1st to 10th	Night	32% 18% 29% 18% 3 1	800
	11th to 20th	Night	29% 19% 29% 19% 5%	800
	21st to end	Night	23% 17% 29% 25% 5%	841
February	1st to 10th	Night	25% 18% 32% 21% 4	760
	11th to 20th	Night	24% 21% 32% 20% 3 1	743
	21st to end	Night	28% 15% 32% 21% 3	628
March	1st to 10th	Night	30% 15% 29% 21% 4	760
	11th to 20th	Night	30% 15% 28% 21% 5%	760
	21st to end	Night	29% 15% 27% 21% 7% 1	836
April	1st to 10th	Night	33% 14% 26% 22% 6%	760
	11th to 20th	Night	30% 14% 26% 23% 7%	708
	21st to end	Night	30% 17% 27% 20% 6%	570
May	1st to 10th	Night	30% 9% 29% 24% 8%	554
	11th to 20th	Night	22% 12% 29% 29% 7% 1	374
	21st to end	Night	23% 8% 30% 31% 7% 1	411
June	1st to 10th	Night	32% 6% 22% 31% 8% 1	380
	11th to 20th	Night	21% 9% 24% 32% 14%	380
	21st to end	Night	20% 6% 28% 36% 9%	380
July	1st to 10th	Night	16% 4 28% 38% 13%	370
	11th to 20th	Night	15% 5% 26% 38% 16% 1	368
	21st to end	Night	18% 4 20% 40% 17% 1	416
August	1st to 10th	Night	20% 5% 14% 41% 19% 1	383
	11th to 20th	Night	17% 5% 21% 38% 18% 1	562
	21st to end	Night	20% 4 22% 32% 19% 2	811
September	1st to 10th	Night	21% 6% 23% 34% 14% 1	760
	11th to 20th	Night	19% 6% 20% 29% 23% 2	760
	21st to end	Night	25% 8% 23% 26% 16% 2	760
October	1st to 10th	Night	27% 10% 21% 26% 15% 1	760
	11th to 20th	Night	31% 11% 23% 25% 9% 2	760
	21st to end	Night	34% 14% 25% 24% 4	836
November	1st to 10th	Night	32% 13% 27% 20% 7%	780
	11th to 20th	Night	29% 17% 26% 19% 9% 1	800
	21st to end	Night	34% 18% 24% 19% 5% 1	800
December	1st to 10th	Night	35% 17% 27% 16% 5%	800
	11th to 20th	Night	33% 17% 26% 18% 5% 1	800
	21st to end	Night	35% 18% 26% 17% 5%	880

Page generated at 2025-01-19 03:06:44. Version ac07

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