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 2025-02-21.

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% 4 4 4 5% 6% 30%	108586
	Night	18% 13% 4 9% 5% 4 4 3 4 6% 28%	109987
Transparency	Day	53% 6% 13% 20% 8% 1	112077
	Night	57% 5% 11% 18% 9% 1	114647
Seeing	Day	24% 13% 28% 22% 10% 3	14868
	Night	25% 10% 28% 27% 9% 1	23912

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	19% 23% 6% 13% 5% 4 3 3 3 4 18%	3597
	11th to 20th	Day	11% 17% 7% 19% 7% 5% 5% 3 4 4 19%	3570
	21st to end	Day	11% 16% 6% 13% 6% 6% 4 3 4 5% 25%	3960
February	1st to 10th	Day	15% 19% 4 11% 6% 6% 4 3 4 4 24%	1678
	11th to 20th	Day	15% 16% 5% 12% 7% 6% 4 3 5% 4 23%	1909
	21st to end	Day	15% 17% 5% 9% 6% 5% 4 4 4 6% 25%	1570
March	1st to 10th	Day	19% 13% 4 12% 6% 4 4 3 4 5% 26%	3116
	11th to 20th	Day	17% 18% 6% 11% 5% 4 3 3 4 5% 25%	3246
	21st to end	Day	16% 13% 4 8% 4 4 4 3 4 5% 35%	4161
April	1st to 10th	Day	23% 13% 4 7% 6% 4 5% 2 3 5% 28%	2280
	11th to 20th	Day	21% 9% 2 6% 5% 4 4 3 5% 5% 35%	2280
	21st to end	Day	24% 10% 3 7% 4 4 4 3 5% 5% 30%	2470
May	1st to 10th	Day	22% 9% 3 7% 5% 4 4 3 5% 7% 30%	4261
	11th to 20th	Day	17% 8% 3 7% 6% 4 6% 4 6% 8% 31%	4398
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 5% 6% 7% 34%	4837
June	1st to 10th	Day	23% 8% 3 7% 4 4 5% 5% 5% 8% 30%	2660
	11th to 20th	Day	17% 7% 2 6% 5% 5% 4 4 6% 8% 35%	2660
	21st to end	Day	21% 9% 3 8% 5% 5% 4 4 5% 6% 30%	2660
July	1st to 10th	Day	14% 6% 2 7% 6% 5% 6% 5% 6% 9% 34%	4440
	11th to 20th	Day	15% 6% 3 8% 5% 5% 5% 5% 7% 8% 34%	4440
	21st to end	Day	14% 6% 2 6% 4 4 4 3 5% 8% 43%	4814
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 5% 7% 9% 30%	4423
	11th to 20th	Day	17% 6% 2 7% 5% 4 5% 5% 6% 9% 33%	4060
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 7% 39%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 5% 6% 8% 41%	2280
	11th to 20th	Day	18% 5% 2 4 3 3 4 3 5% 8% 45%	2152
	21st to end	Day	19% 7% 3 5% 3 4 4 4 6% 8% 39%	2090
October	1st to 10th	Day	20% 7% 2 7% 5% 4 5% 3 6% 8% 32%	2030
	11th to 20th	Day	21% 10% 4 8% 5% 5% 4 3 5% 6% 28%	1800
	21st to end	Day	25% 12% 4 8% 5% 4 4 3 5% 6% 27%	1881
November	1st to 10th	Day	19% 12% 3 7% 5% 4 3 3 6% 5% 32%	1761
	11th to 20th	Day	17% 15% 5% 10% 5% 4 4 3 4 6% 27%	1776
	21st to end	Day	23% 17% 5% 8% 5% 4 4 3 5% 5% 22%	1600
December	1st to 10th	Day	20% 19% 6% 12% 6% 4 3 3 4 4 18%	2600
	11th to 20th	Day	21% 15% 6% 10% 5% 4 3 3 4 5% 25%	2986
	21st to end	Day	22% 17% 5% 11% 5% 4 4 4 5% 4 20%	3960
January	1st to 10th	Night	16% 23% 7% 13% 5% 4 4 2 3 4 18%	6349
	11th to 20th	Night	11% 19% 7% 18% 7% 6% 5% 3 4 4 15%	6315
	21st to end	Night	12% 16% 5% 14% 7% 5% 4 3 4 5% 24%	6996
February	1st to 10th	Night	14% 17% 5% 12% 8% 6% 4 3 5% 5% 21%	2720
	11th to 20th	Night	13% 16% 5% 13% 7% 5% 4 3 4 5% 25%	2376
	21st to end	Night	15% 16% 4 9% 5% 5% 3 4 4 5% 30%	1885
March	1st to 10th	Night	22% 12% 4 8% 5% 4 3 3 4 4 31%	3724
	11th to 20th	Night	19% 19% 5% 10% 5% 5% 4 3 3 4 24%	3713
	21st to end	Night	14% 14% 6% 9% 5% 5% 4 3 4 4 33%	3466
April	1st to 10th	Night	24% 10% 4 8% 5% 3 4 4 5% 5% 28%	1900
	11th to 20th	Night	23% 9% 3 6% 4 4 4 3 4 6% 33%	1848
	21st to end	Night	23% 10% 3 7% 4 2 4 3 5% 5% 32%	1710
May	1st to 10th	Night	24% 9% 3 9% 4 4 4 3 5% 6% 28%	2709
	11th to 20th	Night	21% 7% 3 7% 4 4 4 4 5% 8% 33%	2495
	21st to end	Night	17% 7% 3 7% 5% 4 4 4 6% 8% 35%	2738
June	1st to 10th	Night	22% 7% 3 6% 5% 4 4 3 6% 9% 31%	1520
	11th to 20th	Night	18% 7% 2 6% 4 5% 5% 4 5% 9% 37%	1520
	21st to end	Night	20% 8% 3 6% 5% 5% 4 4 7% 7% 32%	1520
July	1st to 10th	Night	13% 8% 3 8% 5% 5% 5% 4 7% 8% 33%	2520
	11th to 20th	Night	16% 6% 2 7% 4 4 5% 5% 6% 8% 38%	2520
	21st to end	Night	14% 5% 2 6% 4 4 5% 3 7% 7% 41%	2739
August	1st to 10th	Night	20% 7% 3 8% 5% 4 5% 3 5% 7% 33%	2506
	11th to 20th	Night	17% 7% 2 7% 5% 5% 5% 4 5% 8% 34%	2721
	21st to end	Night	19% 6% 3 7% 4 4 5% 3 4 7% 39%	3475
September	1st to 10th	Night	15% 7% 2 6% 5% 4 4 3 5% 6% 43%	1900
	11th to 20th	Night	17% 5% 1 6% 4 3 3 3 4 6% 48%	2027
	21st to end	Night	17% 6% 2 7% 4 4 4 3 4 7% 41%	2090
October	1st to 10th	Night	19% 7% 3 7% 4 4 4 4 5% 6% 39%	2147
	11th to 20th	Night	22% 10% 3 7% 4 5% 5% 3 5% 6% 31%	2380
	21st to end	Night	25% 11% 3 7% 4 4 4 3 4 4 30%	2717
November	1st to 10th	Night	19% 12% 4 7% 6% 4 4 3 5% 6% 29%	2537
	11th to 20th	Night	19% 13% 4 8% 5% 5% 4 3 4 6% 29%	2620
	21st to end	Night	23% 17% 4 8% 6% 4 4 3 4 4 24%	2800
December	1st to 10th	Night	19% 20% 8% 13% 6% 5% 4 3 3 4 15%	4580
	11th to 20th	Night	22% 15% 5% 11% 6% 4 4 2 3 4 24%	5208
	21st to end	Night	22% 18% 5% 9% 4 3 3 3 4 6% 22%	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	72% 4 9% 14% 1	3598
	11th to 20th	Day	69% 5% 7% 14% 5%	3600
	21st to end	Day	61% 5% 8% 15% 10% 1	3960
February	1st to 10th	Day	64% 5% 8% 16% 6% 1	1678
	11th to 20th	Day	64% 5% 10% 12% 7% 1	1918
	21st to end	Day	60% 5% 9% 16% 7% 2	1570
March	1st to 10th	Day	60% 6% 8% 17% 7% 1	3119
	11th to 20th	Day	62% 5% 11% 10% 10% 1	3246
	21st to end	Day	51% 4 8% 21% 14% 2	4161
April	1st to 10th	Day	60% 4 8% 17% 9% 2	2280
	11th to 20th	Day	50% 6% 9% 20% 13% 2	2280
	21st to end	Day	56% 5% 8% 17% 11% 3	2470
May	1st to 10th	Day	52% 5% 11% 21% 9% 1	4275
	11th to 20th	Day	48% 9% 18% 16% 8% 1	4402
	21st to end	Day	45% 8% 11% 21% 13% 1	4837
June	1st to 10th	Day	51% 8% 11% 19% 9% 2	2660
	11th to 20th	Day	44% 7% 14% 22% 12% 1	2660
	21st to end	Day	55% 7% 10% 19% 9%	2660
July	1st to 10th	Day	45% 7% 15% 25% 8%	4370
	11th to 20th	Day	44% 7% 18% 26% 5%	4365
	21st to end	Day	40% 6% 15% 31% 8%	4661
August	1st to 10th	Day	48% 7% 18% 21% 6%	4409
	11th to 20th	Day	46% 7% 21% 21% 5%	4100
	21st to end	Day	45% 5% 15% 20% 14%	4180
September	1st to 10th	Day	40% 7% 15% 27% 10% 1	2280
	11th to 20th	Day	38% 5% 14% 32% 12%	2152
	21st to end	Day	43% 6% 14% 26% 10%	2090
October	1st to 10th	Day	45% 5% 16% 28% 5%	3368
	11th to 20th	Day	49% 6% 18% 23% 4	2964
	21st to end	Day	48% 5% 19% 20% 7%	3081
November	1st to 10th	Day	54% 4 14% 20% 8%	1761
	11th to 20th	Day	58% 6% 11% 16% 9%	1776
	21st to end	Day	64% 7% 13% 13% 3	1600
December	1st to 10th	Day	70% 4 9% 13% 4	2600
	11th to 20th	Day	63% 3 7% 19% 8%	2986
	21st to end	Day	67% 5% 9% 12% 8%	3960
January	1st to 10th	Night	71% 5% 10% 10% 4	6349
	11th to 20th	Night	72% 5% 9% 11% 3	6360
	21st to end	Night	63% 4 9% 12% 12%	6996
February	1st to 10th	Night	65% 4 8% 15% 7% 1	2720
	11th to 20th	Night	63% 4 9% 15% 8%	2378
	21st to end	Night	57% 5% 9% 15% 12% 1	1885
March	1st to 10th	Night	56% 5% 10% 17% 8% 3	3734
	11th to 20th	Night	63% 5% 8% 12% 10% 2	3714
	21st to end	Night	54% 5% 7% 20% 11% 2	3466
April	1st to 10th	Night	57% 5% 9% 16% 12% 1	1900
	11th to 20th	Night	52% 5% 8% 20% 14% 2	1848
	21st to end	Night	52% 6% 9% 17% 14% 2	1710
May	1st to 10th	Night	56% 6% 11% 17% 9% 2	2715
	11th to 20th	Night	47% 8% 16% 18% 10% 2	2496
	21st to end	Night	45% 7% 11% 19% 17% 2	2739
June	1st to 10th	Night	50% 6% 12% 21% 11% 1	1520
	11th to 20th	Night	44% 7% 11% 23% 12% 3	1520
	21st to end	Night	50% 7% 11% 19% 12% 1	1520
July	1st to 10th	Night	47% 6% 16% 21% 10%	2480
	11th to 20th	Night	43% 6% 19% 24% 8%	2472
	21st to end	Night	39% 7% 19% 24% 11%	2651
August	1st to 10th	Night	51% 6% 13% 24% 6%	2496
	11th to 20th	Night	47% 7% 17% 22% 6%	2747
	21st to end	Night	45% 6% 11% 23% 14%	3475
September	1st to 10th	Night	41% 7% 14% 25% 14% 1	1900
	11th to 20th	Night	37% 5% 15% 32% 11% 1	2027
	21st to end	Night	44% 6% 10% 26% 13% 1	2090
October	1st to 10th	Night	50% 4 12% 25% 9%	3576
	11th to 20th	Night	49% 5% 12% 28% 6%	3955
	21st to end	Night	51% 4 14% 19% 10% 2	4467
November	1st to 10th	Night	56% 5% 12% 19% 7% 1	2537
	11th to 20th	Night	57% 5% 11% 17% 9% 1	2620
	21st to end	Night	63% 5% 11% 15% 5%	2800
December	1st to 10th	Night	73% 4 11% 9% 3	4580
	11th to 20th	Night	65% 5% 7% 16% 8%	5208
	21st to end	Night	64% 4 8% 15% 9%	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	32% 14% 34% 18% 3 1	200
	11th to 20th	Day	30% 17% 32% 17% 4	200
	21st to end	Day	20% 19% 33% 18% 9%	220
February	1st to 10th	Day	31% 20% 35% 11% 2 1	240
	11th to 20th	Day	26% 20% 33% 16% 4	457
	21st to end	Day	24% 20% 33% 20% 2	382
March	1st to 10th	Day	27% 17% 28% 23% 5%	460
	11th to 20th	Day	26% 19% 30% 19% 5% 1	460
	21st to end	Day	28% 15% 28% 19% 8% 1	506
April	1st to 10th	Day	29% 15% 28% 19% 8% 2	460
	11th to 20th	Day	30% 19% 25% 16% 9% 2	452
	21st to end	Day	27% 16% 34% 13% 8% 2	460
May	1st to 10th	Day	28% 14% 31% 16% 10% 1	463
	11th to 20th	Day	18% 12% 31% 26% 10% 2	487
	21st to end	Day	22% 16% 30% 20% 10% 2	529
June	1st to 10th	Day	23% 13% 29% 24% 9% 3	490
	11th to 20th	Day	19% 11% 31% 24% 12% 2	490
	21st to end	Day	25% 11% 29% 21% 11% 3	490
July	1st to 10th	Day	16% 8% 28% 29% 16% 4	485
	11th to 20th	Day	15% 9% 30% 34% 10% 3	484
	21st to end	Day	17% 8% 27% 33% 14% 2	532
August	1st to 10th	Day	19% 8% 23% 28% 17% 4	486
	11th to 20th	Day	18% 5% 22% 30% 21% 4	479
	21st to end	Day	19% 11% 24% 23% 14% 9%	539
September	1st to 10th	Day	16% 9% 29% 27% 13% 6%	490
	11th to 20th	Day	18% 8% 21% 24% 20% 9%	490
	21st to end	Day	19% 10% 25% 24% 17% 5%	490
October	1st to 10th	Day	21% 10% 27% 26% 12% 5%	490
	11th to 20th	Day	25% 16% 27% 17% 12% 1	437
	21st to end	Day	34% 12% 27% 21% 7%	429
November	1st to 10th	Day	31% 12% 30% 20% 6% 1	395
	11th to 20th	Day	28% 18% 26% 20% 7% 2	376
	21st to end	Day	35% 18% 30% 11% 7% 1	200
December	1st to 10th	Day	34% 14% 24% 19% 7% 3	200
	11th to 20th	Day	31% 22% 27% 17% 3 1	200
	21st to end	Day	34% 20% 23% 15% 7% 1	220
January	1st to 10th	Night	30% 14% 30% 21% 5%	800
	11th to 20th	Night	27% 12% 32% 21% 7%	800
	21st to end	Night	19% 10% 35% 29% 6%	880
February	1st to 10th	Night	25% 12% 35% 23% 5%	800
	11th to 20th	Night	24% 16% 35% 21% 4 1	783
	21st to end	Night	25% 12% 32% 26% 5%	629
March	1st to 10th	Night	25% 12% 33% 26% 4	760
	11th to 20th	Night	29% 12% 30% 23% 6% 1	760
	21st to end	Night	23% 12% 31% 26% 7% 1	836
April	1st to 10th	Night	31% 13% 24% 26% 6%	760
	11th to 20th	Night	26% 14% 28% 24% 7%	724
	21st to end	Night	29% 12% 30% 21% 8%	570
May	1st to 10th	Night	27% 10% 29% 26% 8%	497
	11th to 20th	Night	23% 7% 30% 32% 7% 1	374
	21st to end	Night	22% 6% 35% 30% 8%	411
June	1st to 10th	Night	26% 6% 28% 32% 8%	380
	11th to 20th	Night	21% 5% 27% 33% 14%	380
	21st to end	Night	19% 7% 29% 34% 11% 1	380
July	1st to 10th	Night	14% 5% 28% 40% 13% 1	370
	11th to 20th	Night	11% 4 25% 45% 14% 1	368
	21st to end	Night	16% 5% 22% 45% 12%	416
August	1st to 10th	Night	17% 3 19% 40% 20% 1	378
	11th to 20th	Night	17% 4 22% 34% 22% 2	525
	21st to end	Night	18% 5% 23% 33% 18% 3	835
September	1st to 10th	Night	18% 4 25% 37% 14% 2	760
	11th to 20th	Night	19% 5% 21% 31% 22% 2	760
	21st to end	Night	20% 6% 27% 28% 16% 2	760
October	1st to 10th	Night	21% 9% 26% 31% 12% 1	760
	11th to 20th	Night	28% 9% 25% 27% 10% 1	760
	21st to end	Night	31% 11% 30% 23% 5%	836
November	1st to 10th	Night	28% 12% 29% 23% 7%	780
	11th to 20th	Night	26% 14% 30% 20% 10% 1	800
	21st to end	Night	33% 14% 27% 20% 6% 1	800
December	1st to 10th	Night	34% 13% 26% 22% 6%	800
	11th to 20th	Night	28% 15% 28% 21% 7% 1	800
	21st to end	Night	36% 13% 24% 21% 6%	880

Page generated at 2025-02-18 03:26:26. Version ac07

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