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 2024-01-22.

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	20% 12% 4 8% 6% 3 5% 4 5% 6% 27%	74856
	Night	19% 13% 5% 8% 6% 3 4 4 4 5% 27%	75077
Transparency	Day	58% 4 11% 18% 8% 1	74561
	Night	60% 3 11% 18% 8% 1	74906
Seeing	Day	28% 16% 28% 18% 8% 2	13602
	Night	28% 13% 26% 24% 9% 1	22608

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	17% 20% 9% 13% 9% 4 5% 4 3 4 10%	1517
	11th to 20th	Day	19% 17% 6% 13% 10% 4 3 4 4 4 16%	1520
	21st to end	Day	11% 16% 7% 12% 8% 6% 7% 5% 4 5% 20%	1592
February	1st to 10th	Day	15% 19% 6% 13% 10% 5% 7% 3 3 3 15%	1499
	11th to 20th	Day	14% 18% 10% 13% 9% 3 5% 4 4 4 17%	1748
	21st to end	Day	13% 19% 7% 10% 8% 4 5% 4 4 5% 20%	1480
March	1st to 10th	Day	16% 16% 6% 11% 8% 4 4 3 3 5% 23%	1797
	11th to 20th	Day	18% 14% 6% 8% 7% 3 4 4 4 5% 27%	1867
	21st to end	Day	18% 15% 5% 9% 6% 3 4 3 4 4 29%	2339
April	1st to 10th	Day	24% 13% 4 8% 6% 3 4 4 4 5% 25%	2160
	11th to 20th	Day	21% 12% 3 5% 6% 3 4 4 4 4 35%	2173
	21st to end	Day	25% 12% 4 6% 5% 3 4 4 4 6% 27%	2340
May	1st to 10th	Day	24% 10% 3 5% 5% 3 4 4 4 6% 32%	2370
	11th to 20th	Day	20% 8% 3 5% 6% 4 4 4 6% 5% 34%	2478
	21st to end	Day	19% 8% 3 6% 6% 5% 6% 5% 6% 8% 30%	2725
June	1st to 10th	Day	28% 7% 3 6% 5% 3 5% 5% 6% 7% 26%	2520
	11th to 20th	Day	19% 7% 3 5% 5% 3 5% 5% 5% 8% 34%	2520
	21st to end	Day	21% 7% 3 7% 6% 4 5% 4 6% 7% 29%	2520
July	1st to 10th	Day	17% 6% 3 6% 6% 3 6% 5% 5% 8% 35%	2520
	11th to 20th	Day	16% 6% 3 6% 6% 4 6% 6% 6% 10% 31%	2520
	21st to end	Day	18% 6% 3 6% 6% 4 5% 5% 6% 9% 31%	2744
August	1st to 10th	Day	18% 7% 2 6% 6% 4 5% 5% 6% 9% 30%	2485
	11th to 20th	Day	17% 6% 3 5% 6% 3 5% 6% 6% 9% 32%	2304
	21st to end	Day	18% 6% 2 5% 5% 3 5% 5% 6% 9% 36%	2397
September	1st to 10th	Day	17% 6% 3 6% 5% 4 4 5% 6% 7% 38%	2160
	11th to 20th	Day	21% 6% 2 5% 3 2 3 5% 5% 6% 42%	2016
	21st to end	Day	21% 7% 3 5% 5% 3 4 5% 5% 8% 35%	1980
October	1st to 10th	Day	25% 9% 3 5% 5% 3 5% 4 5% 7% 28%	1962
	11th to 20th	Day	20% 12% 4 6% 7% 4 5% 5% 6% 6% 27%	1688
	21st to end	Day	28% 18% 3 7% 5% 3 4 3 4 4 22%	1782
November	1st to 10th	Day	20% 15% 5% 6% 5% 3 4 4 5% 4 28%	1671
	11th to 20th	Day	19% 17% 7% 9% 7% 2 3 4 5% 5% 22%	1710
	21st to end	Day	19% 18% 6% 9% 6% 3 5% 5% 4 6% 19%	1554
December	1st to 10th	Day	23% 21% 8% 12% 6% 3 4 3 3 3 14%	1520
	11th to 20th	Day	20% 19% 7% 10% 6% 3 4 4 3 4 20%	1906
	21st to end	Day	26% 17% 6% 13% 5% 2 4 3 3 3 16%	2772
January	1st to 10th	Night	18% 21% 8% 12% 8% 4 5% 4 3 4 14%	2649
	11th to 20th	Night	17% 18% 8% 14% 7% 4 6% 3 3 3 16%	2660
	21st to end	Night	12% 16% 7% 12% 9% 5% 5% 5% 4 5% 20%	2798
February	1st to 10th	Night	15% 17% 7% 13% 8% 5% 5% 4 4 4 18%	2457
	11th to 20th	Night	13% 17% 8% 13% 8% 5% 5% 3 3 4 20%	2098
	21st to end	Night	15% 18% 7% 8% 8% 4 6% 3 3 4 24%	1776
March	1st to 10th	Night	16% 17% 7% 9% 7% 3 5% 3 3 4 25%	2150
	11th to 20th	Night	19% 13% 6% 8% 6% 3 5% 3 4 5% 28%	2092
	21st to end	Night	19% 13% 6% 9% 5% 3 4 3 4 3 31%	2016
April	1st to 10th	Night	24% 12% 5% 7% 6% 3 4 3 5% 4 27%	1800
	11th to 20th	Night	23% 10% 2 5% 5% 3 4 4 5% 5% 35%	1735
	21st to end	Night	24% 12% 4 6% 4 3 4 4 4 5% 30%	1620
May	1st to 10th	Night	23% 11% 4 6% 4 3 4 4 5% 5% 30%	1605
	11th to 20th	Night	20% 8% 3 6% 6% 4 4 4 4 6% 35%	1415
	21st to end	Night	19% 7% 3 6% 5% 4 5% 5% 5% 7% 35%	1550
June	1st to 10th	Night	26% 8% 3 5% 4 3 4 4 7% 7% 29%	1440
	11th to 20th	Night	21% 5% 3 5% 5% 3 4 6% 7% 7% 36%	1440
	21st to end	Night	20% 7% 3 6% 5% 3 5% 6% 6% 7% 32%	1440
July	1st to 10th	Night	16% 6% 3 5% 5% 3 6% 5% 7% 9% 36%	1440
	11th to 20th	Night	13% 6% 2 5% 6% 4 6% 6% 6% 9% 36%	1440
	21st to end	Night	14% 6% 3 6% 6% 3 5% 5% 7% 7% 37%	1574
August	1st to 10th	Night	17% 4 2 4 6% 3 5% 6% 8% 9% 36%	1436
	11th to 20th	Night	15% 7% 3 7% 5% 3 5% 4 5% 8% 37%	1596
	21st to end	Night	17% 7% 2 6% 4 3 5% 4 6% 7% 40%	1956
September	1st to 10th	Night	17% 7% 3 7% 5% 4 4 5% 5% 7% 38%	1800
	11th to 20th	Night	18% 6% 2 4 4 2 3 5% 4 6% 46%	1944
	21st to end	Night	21% 6% 2 4 4 2 3 3 4 9% 40%	1980
October	1st to 10th	Night	22% 8% 3 5% 5% 4 4 5% 5% 6% 34%	1993
	11th to 20th	Night	23% 11% 3 7% 6% 3 5% 4 4 5% 28%	2272
	21st to end	Night	27% 13% 4 6% 5% 3 4 4 4 5% 26%	2574
November	1st to 10th	Night	20% 15% 4 7% 5% 4 4 3 4 6% 27%	2407
	11th to 20th	Night	19% 14% 6% 9% 6% 3 4 4 4 5% 27%	2470
	21st to end	Night	21% 17% 6% 10% 7% 3 4 3 3 4 23%	2622
December	1st to 10th	Night	24% 20% 7% 11% 7% 3 4 3 4 3 14%	2660
	11th to 20th	Night	21% 19% 7% 13% 8% 3 4 3 3 4 14%	3288
	21st to end	Night	25% 20% 5% 10% 6% 3 4 3 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	79% 2 8% 9% 2	1518
	11th to 20th	Day	73% 4 7% 11% 5% 1	1520
	21st to end	Day	68% 2 9% 14% 5% 1	1592
February	1st to 10th	Day	76% 2 6% 11% 4 1	1499
	11th to 20th	Day	73% 2 10% 10% 5% 1	1757
	21st to end	Day	68% 2 9% 14% 6% 2	1480
March	1st to 10th	Day	66% 3 8% 16% 6% 3	1800
	11th to 20th	Day	61% 3 10% 13% 11% 1	1867
	21st to end	Day	61% 2 7% 19% 9% 2	2339
April	1st to 10th	Day	63% 3 7% 17% 8% 2	2160
	11th to 20th	Day	54% 3 7% 21% 13% 1	2173
	21st to end	Day	60% 3 9% 17% 9% 3	2340
May	1st to 10th	Day	55% 2 8% 20% 14% 1	2370
	11th to 20th	Day	52% 3 11% 21% 12% 1	2482
	21st to end	Day	52% 5% 13% 19% 11% 1	2725
June	1st to 10th	Day	57% 4 12% 18% 7% 1	2520
	11th to 20th	Day	48% 4 12% 23% 11% 1	2520
	21st to end	Day	55% 4 13% 20% 8%	2520
July	1st to 10th	Day	46% 5% 15% 25% 9%	2450
	11th to 20th	Day	46% 5% 16% 26% 6%	2445
	21st to end	Day	50% 4 17% 23% 6% 1	2591
August	1st to 10th	Day	49% 6% 17% 23% 5%	2471
	11th to 20th	Day	47% 5% 19% 21% 9%	2304
	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% 2 8% 9% 3	2649
	11th to 20th	Night	75% 2 8% 11% 3	2660
	21st to end	Night	67% 3 8% 15% 5% 1	2798
February	1st to 10th	Night	72% 3 7% 13% 5%	2457
	11th to 20th	Night	70% 2 8% 14% 6%	2100
	21st to end	Night	65% 2 8% 14% 9% 1	1776
March	1st to 10th	Night	64% 3 8% 17% 7% 2	2160
	11th to 20th	Night	61% 2 9% 15% 10% 2	2093
	21st to end	Night	59% 2 7% 20% 9% 3	2016
April	1st to 10th	Night	62% 2 8% 17% 11% 1	1800
	11th to 20th	Night	52% 3 9% 22% 13% 1	1735
	21st to end	Night	58% 3 9% 18% 10% 2	1620
May	1st to 10th	Night	56% 3 6% 19% 14% 1	1605
	11th to 20th	Night	51% 4 11% 18% 14% 2	1416
	21st to end	Night	48% 6% 13% 20% 12% 1	1551
June	1st to 10th	Night	53% 4 12% 23% 8%	1440
	11th to 20th	Night	45% 5% 12% 25% 10% 3	1440
	21st to end	Night	50% 5% 15% 20% 9%	1440
July	1st to 10th	Night	44% 6% 16% 22% 12% 1	1400
	11th to 20th	Night	42% 6% 17% 27% 8%	1392
	21st to end	Night	43% 5% 19% 25% 9%	1486
August	1st to 10th	Night	41% 6% 19% 28% 6%	1426
	11th to 20th	Night	45% 4 18% 23% 10%	1596
	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	35% 24% 27% 9% 3 1	180
	21st to end	Day	29% 21% 31% 12% 6% 1	178
February	1st to 10th	Day	41% 28% 21% 9% 1	189
	11th to 20th	Day	31% 24% 32% 9% 3	416
	21st to end	Day	31% 22% 27% 18% 2	346
March	1st to 10th	Day	32% 20% 29% 15% 4	420
	11th to 20th	Day	31% 23% 25% 16% 5% 1	420
	21st to end	Day	34% 19% 24% 15% 7% 2	462
April	1st to 10th	Day	38% 16% 24% 14% 5% 2	420
	11th to 20th	Day	35% 19% 24% 12% 8% 2	412
	21st to end	Day	35% 17% 29% 12% 5% 1	420
May	1st to 10th	Day	36% 15% 30% 13% 6% 1	423
	11th to 20th	Day	26% 16% 31% 18% 7% 1	447
	21st to end	Day	22% 20% 30% 21% 6% 1	485
June	1st to 10th	Day	31% 16% 31% 17% 5% 1	450
	11th to 20th	Day	20% 20% 28% 23% 8% 1	450
	21st to end	Day	23% 16% 35% 16% 9% 1	450
July	1st to 10th	Day	20% 11% 31% 25% 11% 2	445
	11th to 20th	Day	18% 10% 40% 22% 8% 2	444
	21st to end	Day	19% 10% 35% 27% 8% 1	488
August	1st to 10th	Day	19% 10% 29% 26% 15% 1	446
	11th to 20th	Day	21% 8% 27% 26% 15% 3	439
	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%	800
February	1st to 10th	Night	26% 19% 32% 19% 4	720
	11th to 20th	Night	25% 20% 32% 20% 3 1	703
	21st to end	Night	29% 15% 31% 22% 3	592
March	1st to 10th	Night	29% 16% 30% 21% 4	720
	11th to 20th	Night	30% 15% 29% 20% 6%	720
	21st to end	Night	29% 14% 27% 21% 8% 1	792
April	1st to 10th	Night	34% 14% 25% 22% 6%	720
	11th to 20th	Night	30% 13% 26% 24% 8%	671
	21st to end	Night	31% 16% 26% 20% 6%	540
May	1st to 10th	Night	30% 9% 29% 23% 8%	525
	11th to 20th	Night	23% 12% 29% 29% 7% 1	354
	21st to end	Night	23% 7% 29% 32% 7% 1	389
June	1st to 10th	Night	32% 6% 23% 31% 8% 1	360
	11th to 20th	Night	22% 9% 24% 32% 13%	360
	21st to end	Night	19% 6% 29% 36% 10%	360
July	1st to 10th	Night	17% 3 29% 37% 14%	350
	11th to 20th	Night	14% 4 26% 39% 16% 1	348
	21st to end	Night	17% 4 21% 40% 17% 1	394
August	1st to 10th	Night	18% 4 15% 42% 20% 1	362
	11th to 20th	Night	17% 5% 20% 38% 18% 1	532
	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 2024-01-19 09:28:32. Version ac07

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