Drummondville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Drummondville clear sky chart from 2005-11-06 to 2026-06-16.

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	18% 11% 4 9% 5% 5% 4 4 5% 7% 30%	137732
	Night	18% 13% 4 10% 5% 5% 4 3 5% 6% 28%	134313
Transparency	Day	53% 5% 12% 20% 8% 1	141177
	Night	57% 5% 11% 18% 9% 1	138944
Seeing	Day	24% 13% 29% 22% 10% 3	16589
	Night	25% 10% 28% 27% 9% 1	25512

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% 6% 14% 5% 4 4 3 3 5% 20%	4661
	11th to 20th	Day	11% 17% 7% 18% 7% 5% 5% 3 4 4 18%	4650
	21st to end	Day	9% 14% 5% 14% 9% 8% 5% 4 4 5% 22%	5124
February	1st to 10th	Day	14% 18% 4 11% 6% 6% 5% 3 4 4 24%	1762
	11th to 20th	Day	15% 16% 6% 11% 7% 5% 4 3 5% 5% 23%	2007
	21st to end	Day	14% 17% 5% 9% 7% 5% 4 4 4 6% 25%	1730
March	1st to 10th	Day	19% 14% 6% 13% 7% 5% 4 3 4 4 23%	4576
	11th to 20th	Day	15% 15% 5% 9% 5% 4 4 3 4 6% 30%	4750
	21st to end	Day	20% 13% 5% 9% 4 4 4 3 4 5% 31%	6097
April	1st to 10th	Day	23% 13% 4 7% 6% 4 5% 2 3 5% 28%	2520
	11th to 20th	Day	22% 10% 2 7% 5% 4 4 3 5% 5% 34%	2523
	21st to end	Day	23% 10% 3 7% 5% 4 4 3 5% 5% 30%	2730
May	1st to 10th	Day	26% 10% 3 8% 5% 5% 5% 3 5% 7% 23%	7932
	11th to 20th	Day	19% 8% 3 7% 5% 5% 5% 4 6% 8% 30%	8221
	21st to end	Day	20% 9% 3 7% 4 4 5% 4 5% 6% 33%	9060
June	1st to 10th	Day	22% 8% 3 6% 4 4 5% 5% 5% 7% 31%	2940
	11th to 20th	Day	17% 7% 2 6% 5% 5% 4 4 6% 8% 35%	2870
	21st to end	Day	21% 9% 3 8% 5% 5% 4 4 5% 6% 30%	2800
July	1st to 10th	Day	16% 6% 3 8% 6% 6% 6% 5% 6% 9% 29%	6360
	11th to 20th	Day	13% 5% 3 7% 5% 5% 5% 5% 7% 9% 38%	6360
	21st to end	Day	12% 6% 2 5% 3 4 4 4 6% 9% 44%	6926
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 5% 7% 9% 31%	4563
	11th to 20th	Day	17% 6% 2 7% 5% 4 5% 5% 6% 9% 34%	4191
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 7% 39%	4312
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 4 6% 8% 42%	2400
	11th to 20th	Day	17% 5% 2 4 3 3 4 3 5% 8% 46%	2265
	21st to end	Day	19% 7% 3 5% 3 4 4 4 6% 8% 39%	2200
October	1st to 10th	Day	19% 7% 2 7% 5% 4 4 3 6% 8% 35%	2137
	11th to 20th	Day	21% 10% 4 8% 4 5% 4 3 5% 7% 29%	1895
	21st to end	Day	25% 12% 4 8% 4 3 4 3 5% 6% 26%	1980
November	1st to 10th	Day	19% 14% 3 8% 5% 4 3 2 5% 5% 31%	1851
	11th to 20th	Day	17% 16% 5% 10% 5% 4 4 3 4 6% 26%	1865
	21st to end	Day	23% 18% 5% 8% 5% 4 4 3 5% 4 21%	1680
December	1st to 10th	Day	20% 19% 6% 12% 6% 4 4 3 4 4 19%	2680
	11th to 20th	Day	21% 15% 6% 10% 5% 4 3 3 4 5% 25%	3066
	21st to end	Day	21% 16% 5% 11% 5% 4 4 4 5% 4 20%	4048
January	1st to 10th	Night	15% 21% 7% 13% 5% 4 5% 2 3 4 20%	8234
	11th to 20th	Night	14% 19% 8% 17% 7% 6% 5% 3 4 4 14%	8235
	21st to end	Night	9% 14% 5% 14% 10% 6% 4 4 5% 5% 23%	9057
February	1st to 10th	Night	13% 16% 5% 13% 8% 5% 4 3 5% 5% 22%	2856
	11th to 20th	Night	13% 16% 5% 14% 6% 5% 4 3 4 5% 25%	2498
	21st to end	Night	15% 17% 4 8% 5% 5% 3 4 4 5% 30%	2076
March	1st to 10th	Night	20% 14% 4 10% 6% 4 3 3 4 4 27%	5484
	11th to 20th	Night	16% 15% 4 9% 5% 5% 5% 3 5% 7% 26%	5429
	21st to end	Night	16% 15% 5% 9% 5% 5% 4 3 4 4 28%	5072
April	1st to 10th	Night	24% 11% 4 8% 4 4 4 3 5% 5% 28%	2100
	11th to 20th	Night	23% 10% 3 6% 4 4 5% 3 4 6% 32%	2045
	21st to end	Night	22% 10% 3 7% 4 2 4 3 5% 5% 33%	1890
May	1st to 10th	Night	25% 9% 3 10% 5% 5% 5% 4 5% 6% 25%	5023
	11th to 20th	Night	22% 7% 3 7% 5% 5% 5% 4 5% 7% 30%	4639
	21st to end	Night	19% 9% 3 8% 4 4 4 4 6% 7% 31%	5114
June	1st to 10th	Night	22% 7% 3 6% 5% 4 4 3 6% 9% 32%	1680
	11th to 20th	Night	18% 7% 2 6% 4 5% 5% 4 6% 9% 35%	1640
	21st to end	Night	20% 8% 3 6% 5% 5% 4 4 6% 7% 33%	1600
July	1st to 10th	Night	15% 7% 3 8% 5% 6% 6% 5% 8% 9% 30%	3600
	11th to 20th	Night	17% 6% 2 7% 4 4 5% 4 6% 8% 37%	3600
	21st to end	Night	12% 5% 3 7% 5% 4 5% 4 7% 8% 41%	3926
August	1st to 10th	Night	19% 7% 3 8% 5% 4 5% 3 5% 7% 34%	2586
	11th to 20th	Night	17% 7% 2 7% 5% 5% 5% 4 5% 8% 35%	2809
	21st to end	Night	19% 6% 3 7% 4 4 5% 3 5% 7% 39%	3585
September	1st to 10th	Night	15% 7% 2 7% 4 4 4 3 5% 6% 44%	2000
	11th to 20th	Night	16% 5% 1 6% 4 3 3 3 4 6% 49%	2134
	21st to end	Night	17% 7% 2 7% 4 4 4 3 4 7% 41%	2200
October	1st to 10th	Night	18% 6% 3 7% 4 4 3 3 5% 6% 40%	2260
	11th to 20th	Night	21% 10% 3 7% 4 4 5% 3 5% 6% 32%	2505
	21st to end	Night	24% 11% 3 7% 5% 4 4 3 4 4 30%	2860
November	1st to 10th	Night	20% 12% 4 7% 6% 4 4 3 5% 6% 29%	2667
	11th to 20th	Night	20% 14% 4 8% 5% 5% 4 3 4 6% 29%	2751
	21st to end	Night	22% 17% 4 8% 6% 4 4 3 4 4 24%	2940
December	1st to 10th	Night	18% 20% 8% 13% 7% 5% 4 3 3 4 15%	4720
	11th to 20th	Night	21% 15% 5% 11% 6% 4 4 2 3 4 23%	5348
	21st to end	Night	22% 18% 5% 9% 4 3 3 3 4 6% 22%	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	68% 4 9% 15% 3	4662
	11th to 20th	Day	69% 4 6% 14% 7%	4680
	21st to end	Day	63% 4 7% 14% 10% 1	5124
February	1st to 10th	Day	63% 5% 8% 17% 6% 1	1762
	11th to 20th	Day	63% 5% 10% 14% 7% 1	2016
	21st to end	Day	61% 5% 9% 16% 8% 2	1730
March	1st to 10th	Day	66% 5% 6% 13% 8% 3	4579
	11th to 20th	Day	55% 5% 15% 13% 12% 1	4750
	21st to end	Day	56% 4 7% 18% 14% 2	6097
April	1st to 10th	Day	60% 4 8% 17% 9% 2	2520
	11th to 20th	Day	51% 6% 9% 20% 13% 2	2523
	21st to end	Day	55% 5% 8% 17% 12% 2	2730
May	1st to 10th	Day	60% 5% 9% 19% 7% 1	7944
	11th to 20th	Day	50% 7% 15% 20% 7% 1	8225
	21st to end	Day	50% 6% 11% 22% 11% 1	9061
June	1st to 10th	Day	51% 7% 11% 21% 9% 1	2940
	11th to 20th	Day	44% 7% 13% 23% 12% 1	2870
	21st to end	Day	54% 7% 10% 20% 9%	2800
July	1st to 10th	Day	49% 6% 15% 23% 6%	6290
	11th to 20th	Day	41% 7% 16% 29% 8%	6285
	21st to end	Day	37% 5% 16% 34% 8%	6728
August	1st to 10th	Day	46% 7% 18% 22% 6%	4549
	11th to 20th	Day	45% 7% 20% 22% 5%	4231
	21st to end	Day	45% 5% 15% 21% 14%	4312
September	1st to 10th	Day	39% 7% 16% 29% 10% 1	2400
	11th to 20th	Day	37% 5% 14% 32% 12%	2265
	21st to end	Day	42% 6% 14% 26% 11%	2200
October	1st to 10th	Day	44% 5% 16% 28% 6%	3475
	11th to 20th	Day	48% 6% 18% 24% 4	3059
	21st to end	Day	49% 5% 19% 20% 7%	3180
November	1st to 10th	Day	56% 4 13% 19% 7%	1851
	11th to 20th	Day	59% 5% 11% 16% 9%	1865
	21st to end	Day	65% 6% 13% 13% 3	1680
December	1st to 10th	Day	70% 4 8% 13% 4	2680
	11th to 20th	Day	63% 3 7% 19% 8%	3066
	21st to end	Day	67% 5% 9% 12% 8%	4048
January	1st to 10th	Night	69% 4 10% 11% 5% 1	8234
	11th to 20th	Night	74% 5% 7% 10% 4	8280
	21st to end	Night	64% 3 8% 13% 12%	9057
February	1st to 10th	Night	64% 4 8% 16% 7% 1	2856
	11th to 20th	Night	62% 4 9% 15% 9%	2500
	21st to end	Night	58% 5% 9% 16% 12% 1	2076
March	1st to 10th	Night	61% 4 8% 14% 11% 3	5494
	11th to 20th	Night	58% 5% 13% 14% 10% 1	5430
	21st to end	Night	59% 4 6% 20% 10% 2	5072
April	1st to 10th	Night	57% 5% 8% 16% 12% 1	2100
	11th to 20th	Night	53% 5% 7% 19% 13% 2	2045
	21st to end	Night	51% 6% 8% 18% 14% 2	1890
May	1st to 10th	Night	59% 5% 11% 16% 8% 1	5029
	11th to 20th	Night	52% 6% 13% 20% 8% 1	4640
	21st to end	Night	51% 5% 10% 17% 16% 1	5115
June	1st to 10th	Night	49% 6% 11% 21% 12% 1	1680
	11th to 20th	Night	45% 6% 11% 22% 12% 3	1640
	21st to end	Night	50% 7% 11% 19% 13% 1	1600
July	1st to 10th	Night	48% 6% 18% 20% 7%	3560
	11th to 20th	Night	44% 5% 17% 25% 8%	3552
	21st to end	Night	39% 7% 18% 26% 10%	3809
August	1st to 10th	Night	49% 6% 13% 25% 7%	2576
	11th to 20th	Night	46% 7% 17% 23% 7%	2835
	21st to end	Night	45% 6% 11% 24% 14%	3585
September	1st to 10th	Night	40% 6% 14% 26% 13% 1	2000
	11th to 20th	Night	36% 5% 14% 32% 11% 1	2134
	21st to end	Night	44% 6% 10% 26% 14% 1	2200
October	1st to 10th	Night	48% 4 12% 25% 10%	3689
	11th to 20th	Night	49% 5% 12% 28% 6%	4080
	21st to end	Night	51% 4 14% 19% 10% 1	4610
November	1st to 10th	Night	56% 5% 12% 19% 7% 1	2667
	11th to 20th	Night	57% 5% 11% 17% 9% 1	2751
	21st to end	Night	63% 5% 11% 15% 6%	2940
December	1st to 10th	Night	73% 4 10% 10% 3	4720
	11th to 20th	Night	65% 5% 7% 15% 8%	5348
	21st to end	Night	64% 4 8% 15% 9%	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	30% 15% 33% 19% 4	220
	11th to 20th	Day	32% 16% 32% 16% 4	220
	21st to end	Day	20% 20% 32% 18% 9%	242
February	1st to 10th	Day	28% 19% 36% 13% 2 1	264
	11th to 20th	Day	26% 19% 34% 17% 4	495
	21st to end	Day	24% 19% 35% 20% 2	446
March	1st to 10th	Day	27% 19% 29% 21% 5%	540
	11th to 20th	Day	28% 17% 31% 19% 5% 1	540
	21st to end	Day	30% 17% 28% 18% 7% 1	594
April	1st to 10th	Day	30% 15% 29% 18% 7% 1	540
	11th to 20th	Day	30% 18% 24% 17% 8% 2	532
	21st to end	Day	26% 16% 34% 13% 8% 2	540
May	1st to 10th	Day	29% 14% 29% 17% 9% 1	543
	11th to 20th	Day	20% 14% 30% 25% 10% 2	567
	21st to end	Day	23% 16% 31% 19% 9% 1	617
June	1st to 10th	Day	23% 12% 28% 25% 10% 2	570
	11th to 20th	Day	19% 13% 31% 24% 12% 2	550
	21st to end	Day	25% 11% 30% 21% 10% 3	530
July	1st to 10th	Day	16% 8% 29% 28% 15% 3	525
	11th to 20th	Day	14% 9% 31% 34% 9% 3	524
	21st to end	Day	16% 8% 29% 32% 13% 2	576
August	1st to 10th	Day	18% 8% 23% 29% 17% 5%	526
	11th to 20th	Day	18% 5% 22% 29% 22% 5%	519
	21st to end	Day	18% 11% 25% 22% 15% 9%	583
September	1st to 10th	Day	15% 9% 29% 26% 14% 7%	530
	11th to 20th	Day	17% 8% 21% 25% 19% 10%	530
	21st to end	Day	19% 10% 25% 24% 17% 5%	530
October	1st to 10th	Day	20% 10% 27% 27% 12% 5%	530
	11th to 20th	Day	24% 16% 28% 18% 13% 1	472
	21st to end	Day	34% 11% 27% 21% 7%	462
November	1st to 10th	Day	32% 13% 31% 19% 6%	425
	11th to 20th	Day	29% 18% 26% 20% 7% 2	405
	21st to end	Day	35% 18% 30% 11% 6%	220
December	1st to 10th	Day	32% 14% 26% 19% 6% 3	220
	11th to 20th	Day	30% 20% 29% 17% 3 1	220
	21st to end	Day	33% 19% 24% 16% 7% 1	242
January	1st to 10th	Night	29% 13% 30% 22% 5%	840
	11th to 20th	Night	28% 12% 32% 20% 7%	840
	21st to end	Night	19% 11% 35% 28% 6% 1	924
February	1st to 10th	Night	24% 11% 34% 24% 7%	840
	11th to 20th	Night	23% 15% 35% 21% 5%	823
	21st to end	Night	25% 12% 32% 26% 5%	692
March	1st to 10th	Night	25% 13% 33% 25% 4	840
	11th to 20th	Night	29% 12% 31% 22% 6% 1	840
	21st to end	Night	24% 12% 31% 25% 7% 1	924
April	1st to 10th	Night	31% 14% 25% 24% 6%	840
	11th to 20th	Night	27% 13% 28% 24% 6%	801
	21st to end	Night	29% 11% 31% 21% 8%	630
May	1st to 10th	Night	28% 9% 29% 26% 7%	549
	11th to 20th	Night	23% 7% 30% 31% 7%	414
	21st to end	Night	22% 6% 34% 30% 8%	455
June	1st to 10th	Night	25% 5% 29% 33% 7%	420
	11th to 20th	Night	21% 5% 28% 33% 13%	410
	21st to end	Night	20% 7% 29% 34% 11% 1	400
July	1st to 10th	Night	14% 5% 28% 40% 13% 1	390
	11th to 20th	Night	11% 4 25% 45% 14% 1	388
	21st to end	Night	15% 5% 22% 46% 12%	438
August	1st to 10th	Night	16% 3 19% 41% 20% 1	398
	11th to 20th	Night	17% 4 22% 35% 22% 1	553
	21st to end	Night	18% 5% 23% 34% 18% 3	879
September	1st to 10th	Night	18% 5% 25% 37% 14% 2	800
	11th to 20th	Night	18% 5% 20% 32% 23% 2	800
	21st to end	Night	20% 6% 27% 29% 16% 2	800
October	1st to 10th	Night	21% 8% 26% 31% 13% 1	800
	11th to 20th	Night	27% 9% 25% 28% 10% 1	800
	21st to end	Night	30% 11% 30% 24% 5%	880
November	1st to 10th	Night	29% 12% 29% 22% 7%	820
	11th to 20th	Night	26% 14% 29% 20% 9% 1	840
	21st to end	Night	32% 14% 27% 20% 6% 1	840
December	1st to 10th	Night	33% 13% 27% 22% 5%	840
	11th to 20th	Night	28% 16% 29% 21% 6% 1	840
	21st to end	Night	36% 13% 25% 20% 5%	924

Page generated at 2026-06-13 02:31:45. Version ac07

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