Chambly
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chambly 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	17% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	105257
	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 30%	104128
Transparency	Day	50% 6% 13% 21% 9% 1	108719
	Night	54% 5% 11% 19% 10% 1	108755
Seeing	Day	21% 12% 28% 24% 11% 3	14775
	Night	23% 10% 29% 28% 9% 1	23843

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% 16% 6% 13% 6% 4 3 3 3 4 22%	2597
	11th to 20th	Day	15% 15% 5% 11% 6% 5% 4 4 5% 6% 24%	2600
	21st to end	Day	15% 17% 5% 10% 5% 5% 6% 4 5% 6% 23%	2780
February	1st to 10th	Day	17% 17% 4 10% 8% 5% 4 4 4 5% 23%	1648
	11th to 20th	Day	14% 13% 5% 12% 6% 5% 5% 4 5% 6% 26%	1782
	21st to end	Day	18% 15% 4 9% 6% 5% 3 3 5% 5% 27%	1570
March	1st to 10th	Day	19% 12% 4 10% 6% 5% 5% 4 5% 5% 26%	3116
	11th to 20th	Day	14% 16% 5% 10% 6% 4 4 3 5% 6% 26%	3269
	21st to end	Day	15% 9% 4 9% 5% 4 4 3 4 5% 37%	4166
April	1st to 10th	Day	23% 11% 3 8% 5% 4 4 3 5% 5% 29%	2280
	11th to 20th	Day	21% 9% 2 7% 5% 4 3 2 4 6% 37%	2254
	21st to end	Day	22% 9% 3 7% 5% 4 4 3 4 7% 31%	2451
May	1st to 10th	Day	21% 9% 3 8% 5% 4 4 4 5% 7% 29%	4318
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 5% 8% 31%	4398
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 7% 9% 35%	4837
June	1st to 10th	Day	21% 8% 2 6% 4 5% 5% 4 6% 8% 30%	2660
	11th to 20th	Day	15% 7% 3 6% 4 4 5% 4 6% 8% 39%	2660
	21st to end	Day	21% 8% 3 7% 5% 4 4 4 7% 6% 32%	2660
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 6% 4 7% 9% 36%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 38%	4440
	21st to end	Day	12% 6% 2 5% 4 4 5% 4 6% 8% 44%	4814
August	1st to 10th	Day	14% 6% 3 8% 5% 5% 5% 4 7% 10% 32%	4423
	11th to 20th	Day	14% 7% 2 6% 5% 4 5% 4 6% 9% 38%	3997
	21st to end	Day	16% 5% 2 6% 4 4 4 4 6% 8% 40%	4180
September	1st to 10th	Day	11% 6% 2 5% 4 4 5% 5% 6% 7% 43%	2280
	11th to 20th	Day	14% 6% 2 4 3 3 3 4 5% 7% 48%	2181
	21st to end	Day	15% 6% 2 7% 4 4 4 4 6% 8% 40%	2090
October	1st to 10th	Day	19% 7% 3 7% 5% 5% 5% 4 5% 7% 32%	1988
	11th to 20th	Day	18% 9% 3 7% 6% 5% 5% 4 5% 8% 29%	1840
	21st to end	Day	25% 11% 3 6% 4 5% 4 3 5% 5% 31%	1881
November	1st to 10th	Day	18% 11% 3 6% 6% 4 4 4 5% 7% 32%	1761
	11th to 20th	Day	17% 12% 3 9% 5% 5% 6% 4 4 7% 29%	1750
	21st to end	Day	23% 13% 4 9% 5% 5% 4 3 6% 5% 23%	1600
December	1st to 10th	Day	21% 20% 7% 11% 6% 4 4 3 3 4 17%	2600
	11th to 20th	Day	20% 14% 5% 9% 4 4 4 4 5% 6% 24%	2986
	21st to end	Day	23% 15% 4 11% 5% 5% 6% 4 6% 4 17%	3960
January	1st to 10th	Night	17% 18% 6% 11% 5% 4 4 4 4 5% 21%	4569
	11th to 20th	Night	12% 15% 5% 13% 7% 8% 6% 4 5% 6% 20%	4580
	21st to end	Night	18% 18% 6% 10% 7% 4 4 3 4 4 23%	4899
February	1st to 10th	Night	17% 16% 6% 11% 7% 6% 5% 3 5% 5% 20%	2528
	11th to 20th	Night	15% 12% 5% 10% 7% 6% 5% 3 5% 5% 28%	2284
	21st to end	Night	17% 14% 3 9% 6% 5% 4 3 4 4 31%	1884
March	1st to 10th	Night	21% 11% 3 8% 5% 4 4 3 4 5% 33%	3724
	11th to 20th	Night	19% 19% 4 8% 5% 4 3 2 3 5% 28%	3687
	21st to end	Night	14% 11% 4 9% 5% 4 5% 3 4 4 37%	3466
April	1st to 10th	Night	24% 10% 3 7% 4 4 5% 3 5% 5% 30%	1900
	11th to 20th	Night	23% 9% 3 7% 4 4 4 3 4 5% 33%	1875
	21st to end	Night	21% 10% 3 6% 5% 3 4 3 4 6% 34%	1729
May	1st to 10th	Night	22% 9% 3 8% 4 5% 4 3 5% 7% 30%	2652
	11th to 20th	Night	22% 9% 3 7% 5% 4 3 3 4 6% 34%	2495
	21st to end	Night	15% 8% 2 7% 5% 5% 4 3 5% 7% 38%	2738
June	1st to 10th	Night	22% 8% 3 7% 4 3 4 4 6% 7% 32%	1520
	11th to 20th	Night	18% 5% 2 6% 5% 4 5% 4 6% 7% 38%	1520
	21st to end	Night	19% 8% 3 9% 4 4 4 4 5% 7% 34%	1520
July	1st to 10th	Night	15% 7% 3 8% 6% 4 5% 5% 6% 7% 34%	2520
	11th to 20th	Night	13% 6% 2 6% 5% 4 5% 4 6% 7% 42%	2520
	21st to end	Night	12% 6% 2 7% 5% 5% 5% 3 7% 7% 41%	2739
August	1st to 10th	Night	18% 8% 3 7% 4 4 4 3 6% 6% 36%	2506
	11th to 20th	Night	16% 7% 3 8% 5% 5% 5% 4 5% 6% 37%	2796
	21st to end	Night	17% 6% 2 7% 4 4 4 3 6% 7% 39%	3476
September	1st to 10th	Night	12% 6% 3 7% 4 3 4 4 7% 7% 43%	1900
	11th to 20th	Night	14% 6% 2 5% 4 3 3 2 5% 7% 49%	1997
	21st to end	Night	16% 6% 2 7% 5% 3 4 3 4 7% 42%	2090
October	1st to 10th	Night	18% 6% 3 7% 5% 3 4 3 6% 6% 39%	2190
	11th to 20th	Night	21% 9% 2 7% 5% 4 5% 4 4 5% 33%	2339
	21st to end	Night	24% 9% 3 8% 5% 4 4 3 5% 5% 30%	2717
November	1st to 10th	Night	20% 10% 4 8% 4 4 4 4 5% 6% 32%	2537
	11th to 20th	Night	20% 11% 3 8% 4 4 4 3 5% 5% 32%	2647
	21st to end	Night	23% 13% 4 8% 5% 5% 4 3 4 6% 26%	2800
December	1st to 10th	Night	18% 20% 6% 13% 6% 5% 4 3 4 5% 15%	4580
	11th to 20th	Night	23% 14% 5% 9% 4 4 4 3 4 5% 24%	5208
	21st to end	Night	24% 16% 5% 8% 4 3 4 4 6% 6% 20%	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	67% 5% 12% 13% 3	2598
	11th to 20th	Day	61% 5% 13% 15% 5%	2600
	21st to end	Day	61% 8% 13% 13% 4	2780
February	1st to 10th	Day	64% 3 10% 17% 4 1	1648
	11th to 20th	Day	58% 5% 12% 18% 7% 1	1791
	21st to end	Day	59% 4 12% 16% 9% 1	1570
March	1st to 10th	Day	59% 6% 9% 18% 7% 1	3119
	11th to 20th	Day	58% 6% 11% 13% 10% 2	3269
	21st to end	Day	49% 4 8% 22% 16% 1	4166
April	1st to 10th	Day	56% 4 8% 20% 10% 2	2280
	11th to 20th	Day	49% 4 9% 22% 14% 2	2254
	21st to end	Day	53% 4 10% 18% 11% 3	2451
May	1st to 10th	Day	53% 6% 10% 21% 9% 1	4332
	11th to 20th	Day	49% 8% 15% 18% 9% 1	4402
	21st to end	Day	42% 7% 12% 24% 12% 2	4837
June	1st to 10th	Day	51% 6% 11% 20% 11% 1	2660
	11th to 20th	Day	42% 6% 13% 24% 14% 2	2660
	21st to end	Day	51% 6% 12% 20% 10% 1	2660
July	1st to 10th	Day	41% 7% 14% 28% 10%	4370
	11th to 20th	Day	40% 7% 16% 30% 7%	4365
	21st to end	Day	38% 7% 14% 33% 9%	4661
August	1st to 10th	Day	45% 7% 17% 22% 8%	4409
	11th to 20th	Day	41% 7% 19% 26% 6%	4038
	21st to end	Day	40% 6% 18% 22% 14%	4180
September	1st to 10th	Day	37% 6% 16% 28% 12%	2280
	11th to 20th	Day	35% 5% 13% 33% 14% 1	2181
	21st to end	Day	41% 6% 15% 27% 11% 1	2090
October	1st to 10th	Day	44% 6% 15% 27% 8%	3300
	11th to 20th	Day	44% 7% 18% 25% 6%	3030
	21st to end	Day	46% 4 19% 23% 8% 1	3081
November	1st to 10th	Day	51% 5% 13% 21% 8% 1	1761
	11th to 20th	Day	54% 6% 11% 18% 10%	1750
	21st to end	Day	62% 7% 13% 13% 5%	1600
December	1st to 10th	Day	71% 5% 9% 13% 2	2600
	11th to 20th	Day	59% 6% 10% 16% 8%	2986
	21st to end	Day	66% 7% 12% 10% 5%	3960
January	1st to 10th	Night	64% 7% 14% 11% 3	4569
	11th to 20th	Night	64% 6% 12% 12% 5%	4580
	21st to end	Night	65% 5% 11% 12% 6%	4899
February	1st to 10th	Night	66% 4 9% 14% 6% 1	2528
	11th to 20th	Night	59% 3 11% 18% 8%	2286
	21st to end	Night	57% 4 9% 17% 12% 1	1884
March	1st to 10th	Night	54% 5% 10% 20% 9% 3	3734
	11th to 20th	Night	61% 5% 7% 14% 12% 1	3688
	21st to end	Night	50% 3 6% 24% 13% 3	3466
April	1st to 10th	Night	56% 3 8% 18% 13% 1	1900
	11th to 20th	Night	53% 4 7% 21% 13% 2	1875
	21st to end	Night	52% 4 8% 19% 13% 4	1729
May	1st to 10th	Night	53% 8% 8% 19% 8% 3	2658
	11th to 20th	Night	50% 6% 11% 20% 11% 2	2496
	21st to end	Night	45% 7% 9% 20% 18% 1	2739
June	1st to 10th	Night	52% 5% 9% 21% 12% 1	1520
	11th to 20th	Night	43% 6% 12% 22% 14% 3	1520
	21st to end	Night	49% 7% 11% 19% 13% 1	1520
July	1st to 10th	Night	46% 7% 13% 21% 13%	2480
	11th to 20th	Night	38% 8% 15% 29% 10%	2472
	21st to end	Night	40% 7% 16% 23% 13%	2651
August	1st to 10th	Night	48% 6% 13% 25% 8%	2496
	11th to 20th	Night	45% 8% 18% 21% 8%	2821
	21st to end	Night	42% 8% 12% 23% 14% 1	3476
September	1st to 10th	Night	39% 6% 13% 26% 15% 1	1900
	11th to 20th	Night	36% 5% 14% 30% 14% 1	1997
	21st to end	Night	42% 6% 11% 25% 15% 1	2090
October	1st to 10th	Night	44% 6% 14% 26% 9%	3658
	11th to 20th	Night	45% 5% 11% 30% 8%	3888
	21st to end	Night	49% 5% 14% 19% 12% 1	4467
November	1st to 10th	Night	52% 5% 11% 22% 8% 1	2537
	11th to 20th	Night	54% 4 12% 18% 10% 1	2647
	21st to end	Night	61% 5% 12% 16% 6%	2800
December	1st to 10th	Night	72% 5% 11% 10% 2	4580
	11th to 20th	Night	63% 4 9% 15% 10%	5208
	21st to end	Night	64% 4 10% 14% 8%	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% 15% 29% 17% 9% 1	200
	11th to 20th	Day	28% 18% 33% 18% 4 1	200
	21st to end	Day	20% 16% 32% 24% 9% 1	200
February	1st to 10th	Day	31% 19% 32% 17% 2	240
	11th to 20th	Day	22% 16% 38% 19% 4 1	390
	21st to end	Day	26% 16% 29% 26% 3	382
March	1st to 10th	Day	26% 12% 34% 22% 6%	460
	11th to 20th	Day	22% 17% 34% 19% 7% 1	460
	21st to end	Day	28% 16% 28% 19% 7% 2	506
April	1st to 10th	Day	30% 13% 29% 18% 8% 2	460
	11th to 20th	Day	28% 19% 25% 16% 9% 3	452
	21st to end	Day	27% 15% 29% 16% 10% 2	460
May	1st to 10th	Day	23% 13% 31% 21% 10% 2	463
	11th to 20th	Day	16% 11% 31% 27% 12% 3	487
	21st to end	Day	19% 13% 32% 24% 11% 2	529
June	1st to 10th	Day	23% 12% 26% 28% 10% 2	490
	11th to 20th	Day	16% 10% 28% 30% 14% 2	490
	21st to end	Day	23% 10% 27% 23% 13% 2	490
July	1st to 10th	Day	13% 8% 25% 32% 18% 3	485
	11th to 20th	Day	14% 8% 30% 31% 13% 4	484
	21st to end	Day	15% 7% 26% 32% 18% 2	532
August	1st to 10th	Day	15% 5% 23% 32% 21% 4	486
	11th to 20th	Day	11% 7% 24% 31% 19% 7%	479
	21st to end	Day	15% 8% 25% 25% 18% 9%	539
September	1st to 10th	Day	12% 9% 28% 29% 14% 8%	490
	11th to 20th	Day	14% 8% 20% 27% 18% 12%	490
	21st to end	Day	17% 9% 28% 23% 18% 6%	490
October	1st to 10th	Day	20% 13% 28% 20% 14% 5%	490
	11th to 20th	Day	24% 15% 29% 19% 12% 2	457
	21st to end	Day	32% 14% 25% 21% 7%	429
November	1st to 10th	Day	27% 15% 28% 22% 7%	395
	11th to 20th	Day	23% 19% 31% 18% 7% 1	350
	21st to end	Day	33% 16% 30% 18% 4 1	200
December	1st to 10th	Day	34% 11% 24% 23% 7% 2	200
	11th to 20th	Day	25% 23% 37% 13% 4	200
	21st to end	Day	30% 20% 24% 19% 4 3	220
January	1st to 10th	Night	27% 13% 32% 23% 5%	800
	11th to 20th	Night	25% 12% 34% 22% 6%	800
	21st to end	Night	20% 11% 34% 27% 7% 1	841
February	1st to 10th	Night	25% 10% 36% 24% 4 1	760
	11th to 20th	Night	21% 11% 38% 24% 5%	743
	21st to end	Night	24% 12% 31% 28% 4	628
March	1st to 10th	Night	25% 11% 31% 27% 5%	760
	11th to 20th	Night	25% 12% 33% 23% 7%	760
	21st to end	Night	23% 10% 31% 27% 7% 1	836
April	1st to 10th	Night	27% 12% 29% 27% 5%	760
	11th to 20th	Night	25% 15% 29% 24% 7% 1	751
	21st to end	Night	27% 11% 30% 25% 7% 1	589
May	1st to 10th	Night	26% 7% 34% 24% 8% 1	466
	11th to 20th	Night	22% 9% 31% 29% 7% 1	374
	21st to end	Night	18% 7% 37% 31% 8%	411
June	1st to 10th	Night	24% 8% 27% 30% 11% 1	380
	11th to 20th	Night	19% 5% 29% 34% 12%	380
	21st to end	Night	19% 5% 32% 32% 12% 1	380
July	1st to 10th	Night	13% 5% 28% 39% 14% 1	370
	11th to 20th	Night	11% 3 26% 44% 14% 1	368
	21st to end	Night	13% 3 22% 46% 15% 1	416
August	1st to 10th	Night	14% 4 17% 47% 17% 2	378
	11th to 20th	Night	14% 4 21% 36% 23% 2	560
	21st to end	Night	15% 5% 19% 39% 20% 2	836
September	1st to 10th	Night	15% 4 25% 38% 16% 1	760
	11th to 20th	Night	17% 5% 19% 34% 22% 3	760
	21st to end	Night	19% 6% 27% 30% 14% 3	760
October	1st to 10th	Night	21% 7% 29% 29% 13% 1	760
	11th to 20th	Night	26% 8% 29% 28% 9%	760
	21st to end	Night	28% 13% 30% 24% 5%	836
November	1st to 10th	Night	24% 13% 31% 23% 7%	780
	11th to 20th	Night	25% 13% 31% 22% 9% 1	800
	21st to end	Night	29% 16% 30% 18% 7%	800
December	1st to 10th	Night	31% 13% 28% 23% 5%	800
	11th to 20th	Night	30% 15% 32% 18% 5% 1	800
	21st to end	Night	33% 13% 31% 18% 5%	880

Page generated at 2025-01-19 03:06:48. Version ac07

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