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 2024-08-15.

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 3 5% 6% 27%	95528
	Night	19% 14% 4 10% 5% 4 4 3 4 5% 26%	93192
Transparency	Day	57% 4 12% 19% 7% 1	95247
	Night	61% 3 11% 17% 7% 1	93027
Seeing	Day	28% 16% 28% 18% 8% 2	14390
	Night	27% 13% 26% 24% 9% 1	23220

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% 5% 4 3 3 3 13%	2517
	11th to 20th	Day	15% 16% 7% 19% 12% 4 3 2 4 3 15%	2520
	21st to end	Day	13% 19% 8% 15% 6% 8% 4 3 3 4 16%	2772
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% 7% 2 7% 5% 5% 5% 4 6% 9% 29%	2623
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 5% 6% 9% 32%	2359
	21st to end	Day	18% 7% 2 5% 5% 5% 5% 4 6% 9% 36%	2397
September	1st to 10th	Day	17% 7% 3 7% 4 5% 3 4 6% 7% 38%	2160
	11th to 20th	Day	21% 6% 2 6% 2 3 3 4 5% 6% 42%	2016
	21st to end	Day	20% 8% 3 5% 4 4 5% 4 5% 8% 35%	1980
October	1st to 10th	Day	25% 10% 3 6% 5% 4 4 4 5% 7% 28%	1962
	11th to 20th	Day	20% 12% 3 7% 5% 5% 4 4 6% 6% 27%	1688
	21st to end	Day	27% 18% 3 7% 4 4 4 3 4 4 22%	1782
November	1st to 10th	Day	20% 17% 5% 7% 4 5% 3 3 5% 4 28%	1671
	11th to 20th	Day	19% 18% 5% 10% 6% 3 3 4 5% 5% 22%	1710
	21st to end	Day	19% 19% 5% 11% 5% 4 4 4 4 6% 19%	1554
December	1st to 10th	Day	22% 24% 6% 12% 6% 4 4 2 3 3 14%	1520
	11th to 20th	Day	20% 20% 6% 11% 5% 4 4 3 4 4 20%	1906
	21st to end	Day	26% 18% 6% 14% 5% 4 4 2 3 3 16%	2772
January	1st to 10th	Night	16% 21% 8% 17% 7% 4 4 2 3 3 14%	4429
	11th to 20th	Night	13% 18% 7% 19% 9% 7% 5% 3 4 3 14%	4440
	21st to end	Night	15% 20% 7% 14% 7% 5% 4 3 3 4 18%	4884
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	18% 5% 2 6% 5% 4 5% 5% 7% 9% 35%	1517
	11th to 20th	Night	15% 8% 3 8% 4 5% 5% 3 5% 8% 37%	1641
	21st to end	Night	17% 7% 2 7% 4 4 4 3 6% 7% 40%	1956
September	1st to 10th	Night	17% 7% 3 8% 4 5% 4 4 5% 6% 38%	1800
	11th to 20th	Night	18% 6% 2 4 4 3 4 4 4 6% 46%	1944
	21st to end	Night	21% 6% 2 5% 3 3 3 3 4 9% 40%	1980
October	1st to 10th	Night	22% 8% 3 6% 4 5% 4 4 5% 6% 34%	1993
	11th to 20th	Night	23% 11% 3 9% 5% 5% 4 3 4 5% 28%	2272
	21st to end	Night	27% 13% 3 7% 4 4 3 3 4 5% 26%	2574
November	1st to 10th	Night	20% 16% 3 8% 4 5% 4 3 5% 6% 26%	2407
	11th to 20th	Night	19% 15% 6% 10% 5% 4 3 3 4 5% 27%	2470
	21st to end	Night	21% 17% 5% 11% 6% 4 3 2 3 4 23%	2622
December	1st to 10th	Night	23% 22% 6% 13% 6% 4 3 2 4 3 14%	2660
	11th to 20th	Night	21% 20% 6% 15% 7% 4 3 3 3 3 14%	3288
	21st to end	Night	24% 21% 5% 11% 5% 4 4 2 3 3 18%	4884

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	77% 2 12% 8% 1	2518
	11th to 20th	Day	75% 3 8% 11% 3	2520
	21st to end	Day	74% 2 9% 11% 3 1	2772
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	50% 6% 17% 22% 5%	2609
	11th to 20th	Day	47% 5% 19% 21% 8%	2359
	21st to end	Day	45% 5% 15% 24% 12%	2397
September	1st to 10th	Day	45% 5% 14% 26% 9% 1	2160
	11th to 20th	Day	43% 3 11% 28% 13%	2016
	21st to end	Day	47% 4 14% 24% 10% 1	1980
October	1st to 10th	Day	56% 4 12% 19% 8%	1962
	11th to 20th	Day	57% 4 15% 19% 5%	1688
	21st to end	Day	67% 3 9% 15% 6% 1	1782
November	1st to 10th	Day	59% 4 12% 18% 7% 1	1671
	11th to 20th	Day	65% 3 11% 13% 7% 1	1710
	21st to end	Day	67% 4 14% 12% 2	1554
December	1st to 10th	Day	76% 3 9% 9% 3	1520
	11th to 20th	Day	69% 3 8% 15% 5%	1906
	21st to end	Day	75% 3 9% 9% 5%	2772
January	1st to 10th	Night	77% 1 13% 7% 2	4429
	11th to 20th	Night	76% 2 11% 9% 2	4440
	21st to end	Night	73% 2 10% 11% 4 1	4884
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	43% 6% 18% 27% 6%	1507
	11th to 20th	Night	46% 4 17% 23% 10%	1641
	21st to end	Night	43% 4 15% 27% 10%	1956
September	1st to 10th	Night	46% 4 13% 25% 12% 1	1800
	11th to 20th	Night	40% 4 16% 29% 11% 1	1944
	21st to end	Night	43% 6% 14% 26% 11% 1	1980
October	1st to 10th	Night	52% 3 11% 23% 11% 1	1993
	11th to 20th	Night	58% 4 13% 20% 5%	2272
	21st to end	Night	62% 3 11% 16% 7% 1	2574
November	1st to 10th	Night	59% 3 12% 18% 7% 1	2407
	11th to 20th	Night	61% 3 11% 15% 8% 2	2470
	21st to end	Night	67% 3 13% 14% 4	2622
December	1st to 10th	Night	77% 2 9% 10% 2	2660
	11th to 20th	Night	76% 2 6% 11% 4	3288
	21st to end	Night	74% 2 9% 13% 2	4884

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	29% 19% 32% 17% 2 1	180
	11th to 20th	Day	36% 24% 27% 10% 3 1	180
	21st to end	Day	29% 21% 31% 13% 6% 1	198
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	20% 8% 27% 26% 15% 3	456
	21st to end	Day	23% 12% 24% 22% 12% 6%	495
September	1st to 10th	Day	19% 10% 31% 21% 12% 6%	450
	11th to 20th	Day	21% 12% 22% 19% 17% 8%	450
	21st to end	Day	20% 12% 26% 24% 13% 5%	450
October	1st to 10th	Day	26% 16% 24% 15% 14% 4	450
	11th to 20th	Day	30% 18% 24% 17% 10% 2	394
	21st to end	Day	43% 14% 22% 16% 6%	396
November	1st to 10th	Day	36% 16% 23% 21% 5%	365
	11th to 20th	Day	30% 21% 26% 15% 6% 1	370
	21st to end	Day	32% 21% 29% 14% 3	214
December	1st to 10th	Day	34% 19% 27% 16% 4 1	180
	11th to 20th	Day	36% 26% 27% 7% 5% 1	180
	21st to end	Day	43% 19% 25% 11% 2 1	198
January	1st to 10th	Night	32% 18% 28% 19% 3 1	760
	11th to 20th	Night	29% 19% 29% 18% 5%	760
	21st to end	Night	23% 17% 29% 25% 5%	836
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% 19% 1	547
	21st to end	Night	21% 4 22% 32% 19% 2	768
September	1st to 10th	Night	21% 6% 23% 34% 15% 1	720
	11th to 20th	Night	20% 7% 21% 29% 21% 2	720
	21st to end	Night	25% 9% 23% 26% 15% 2	720
October	1st to 10th	Night	28% 10% 22% 25% 15% 1	720
	11th to 20th	Night	30% 11% 23% 24% 9% 2	720
	21st to end	Night	35% 13% 24% 24% 4	792
November	1st to 10th	Night	32% 13% 28% 20% 8%	740
	11th to 20th	Night	28% 17% 26% 18% 9% 1	760
	21st to end	Night	33% 18% 24% 19% 5% 1	760
December	1st to 10th	Night	36% 17% 26% 16% 5%	760
	11th to 20th	Night	33% 18% 26% 18% 5% 1	760
	21st to end	Night	36% 18% 25% 17% 4	836

Page generated at 2024-08-12 09:52:48. Version ac07

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