Joliette
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joliette clear sky chart from 2005-11-06 to 2025-07-06.

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% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	120069
	Night	18% 11% 4 9% 5% 4 4 3 5% 6% 32%	118725
Transparency	Day	49% 7% 13% 20% 10% 1	123559
	Night	52% 6% 12% 18% 10% 1	123396
Seeing	Day	21% 10% 28% 25% 12% 3	15343
	Night	22% 7% 30% 31% 10% 1	24295

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	15% 19% 4 10% 5% 4 3 2 3 5% 29%	3597
	11th to 20th	Day	12% 15% 5% 10% 6% 5% 4 4 5% 5% 28%	3570
	21st to end	Day	10% 14% 6% 11% 6% 5% 4 4 5% 6% 30%	3960
February	1st to 10th	Day	14% 16% 4 10% 6% 4 5% 4 5% 5% 29%	1724
	11th to 20th	Day	13% 13% 5% 11% 6% 5% 4 3 4 6% 29%	1861
	21st to end	Day	16% 16% 4 8% 4 5% 5% 3 4 6% 28%	1650
March	1st to 10th	Day	20% 12% 4 8% 6% 5% 5% 3 4 5% 26%	4476
	11th to 20th	Day	12% 13% 3 9% 5% 4 4 3 5% 6% 34%	4685
	21st to end	Day	17% 11% 4 9% 5% 4 3 3 4 5% 34%	5970
April	1st to 10th	Day	21% 10% 4 7% 4 4 5% 3 4 6% 33%	2400
	11th to 20th	Day	22% 8% 2 6% 4 3 4 3 5% 6% 38%	2374
	21st to end	Day	21% 9% 3 7% 4 4 5% 3 5% 5% 33%	2586
May	1st to 10th	Day	27% 9% 3 8% 5% 5% 4 3 4 5% 27%	6253
	11th to 20th	Day	20% 8% 3 8% 4 4 4 4 5% 7% 33%	6318
	21st to end	Day	20% 8% 3 7% 5% 5% 5% 4 6% 7% 31%	6949
June	1st to 10th	Day	22% 6% 3 7% 5% 5% 5% 4 5% 7% 31%	2800
	11th to 20th	Day	15% 5% 2 6% 5% 4 5% 5% 6% 8% 38%	2800
	21st to end	Day	20% 8% 3 7% 6% 5% 5% 4 5% 7% 30%	2800
July	1st to 10th	Day	12% 6% 2 7% 6% 6% 6% 4 7% 8% 36%	4510
	11th to 20th	Day	13% 5% 2 6% 4 6% 6% 5% 7% 9% 36%	4440
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 45%	4814
August	1st to 10th	Day	13% 5% 2 7% 5% 6% 7% 6% 8% 9% 32%	4423
	11th to 20th	Day	16% 5% 2 6% 5% 5% 5% 4 6% 9% 36%	4051
	21st to end	Day	16% 6% 2 6% 4 5% 4 4 6% 7% 40%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 4 5% 5% 6% 8% 44%	2280
	11th to 20th	Day	14% 5% 2 5% 3 3 4 3 4 6% 50%	2190
	21st to end	Day	18% 6% 2 5% 4 4 4 3 4 6% 43%	2090
October	1st to 10th	Day	20% 7% 2 7% 4 4 4 4 5% 7% 37%	1976
	11th to 20th	Day	20% 7% 4 7% 5% 5% 4 5% 5% 6% 31%	1838
	21st to end	Day	23% 10% 3 8% 3 4 4 3 4 6% 33%	1881
November	1st to 10th	Day	15% 10% 3 6% 4 4 5% 4 5% 6% 37%	1761
	11th to 20th	Day	18% 9% 4 8% 4 4 4 3 6% 7% 33%	1716
	21st to end	Day	21% 12% 3 7% 5% 5% 5% 3 5% 5% 28%	1600
December	1st to 10th	Day	20% 17% 5% 11% 6% 4 4 2 4 5% 22%	2600
	11th to 20th	Day	20% 12% 4 9% 4 4 4 4 5% 5% 29%	2986
	21st to end	Day	24% 11% 4 9% 5% 4 4 4 5% 5% 25%	3960
January	1st to 10th	Night	14% 19% 6% 14% 5% 4 4 3 4 4 24%	6349
	11th to 20th	Night	10% 15% 7% 15% 7% 5% 4 3 5% 5% 24%	6315
	21st to end	Night	11% 13% 5% 12% 6% 6% 5% 4 5% 6% 27%	6996
February	1st to 10th	Night	13% 15% 5% 11% 6% 6% 4 3 5% 5% 28%	2675
	11th to 20th	Night	14% 11% 5% 10% 7% 5% 6% 3 4 4 31%	2425
	21st to end	Night	15% 12% 4 10% 6% 4 3 4 4 5% 32%	1980
March	1st to 10th	Night	23% 13% 4 8% 5% 4 4 3 3 4 29%	5364
	11th to 20th	Night	14% 13% 4 8% 5% 5% 5% 4 6% 6% 32%	5270
	21st to end	Night	17% 11% 5% 8% 6% 4 5% 3 4 5% 32%	4962
April	1st to 10th	Night	23% 9% 4 6% 5% 4 4 3 5% 6% 32%	2000
	11th to 20th	Night	22% 8% 3 6% 5% 4 4 3 4 5% 36%	1975
	21st to end	Night	23% 9% 3 5% 3 3 4 3 5% 5% 36%	1812
May	1st to 10th	Night	27% 9% 3 8% 5% 4 4 3 4 6% 25%	3717
	11th to 20th	Night	22% 8% 2 7% 4 5% 4 4 5% 6% 33%	3575
	21st to end	Night	20% 8% 3 8% 5% 5% 4 4 6% 8% 29%	3926
June	1st to 10th	Night	20% 8% 2 6% 4 4 5% 4 6% 7% 35%	1600
	11th to 20th	Night	18% 7% 2 6% 5% 4 5% 5% 5% 7% 37%	1600
	21st to end	Night	19% 7% 3 7% 6% 4 5% 3 6% 7% 34%	1600
July	1st to 10th	Night	12% 6% 3 8% 6% 6% 6% 4 7% 8% 34%	2560
	11th to 20th	Night	14% 6% 2 6% 4 5% 5% 4 6% 7% 42%	2520
	21st to end	Night	11% 5% 2 5% 5% 4 5% 4 6% 7% 47%	2739
August	1st to 10th	Night	13% 7% 2 9% 5% 5% 4 4 6% 6% 39%	2506
	11th to 20th	Night	16% 7% 3 6% 4 4 5% 4 5% 7% 39%	2741
	21st to end	Night	19% 6% 2 8% 4 4 4 3 5% 6% 40%	3476
September	1st to 10th	Night	12% 4 2 6% 4 5% 5% 4 5% 6% 47%	1900
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 5% 6% 51%	1990
	21st to end	Night	17% 5% 2 5% 4 4 4 3 4 7% 46%	2090
October	1st to 10th	Night	17% 6% 2 8% 4 3 4 3 4 5% 42%	2202
	11th to 20th	Night	19% 8% 2 7% 4 4 3 3 5% 6% 37%	2342
	21st to end	Night	23% 8% 3 7% 4 4 4 4 4 6% 33%	2717
November	1st to 10th	Night	18% 10% 4 8% 5% 4 4 3 5% 6% 34%	2537
	11th to 20th	Night	19% 10% 2 8% 5% 4 4 3 5% 5% 35%	2680
	21st to end	Night	23% 13% 4 7% 6% 3 4 3 4 5% 29%	2800
December	1st to 10th	Night	19% 14% 5% 11% 7% 6% 5% 4 5% 5% 21%	4580
	11th to 20th	Night	24% 12% 4 8% 5% 3 3 3 4 4 29%	5208
	21st to end	Night	24% 15% 4 8% 4 3 3 3 4 5% 26%	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	59% 6% 12% 19% 4 1	3598
	11th to 20th	Day	57% 6% 11% 17% 7% 2	3600
	21st to end	Day	53% 7% 11% 16% 12% 1	3960
February	1st to 10th	Day	57% 4 9% 19% 8% 2	1724
	11th to 20th	Day	55% 7% 11% 15% 11% 1	1870
	21st to end	Day	57% 5% 9% 17% 9% 3	1650
March	1st to 10th	Day	59% 6% 9% 13% 11% 3	4479
	11th to 20th	Day	49% 7% 18% 13% 11% 3	4685
	21st to end	Day	51% 5% 8% 16% 17% 2	5970
April	1st to 10th	Day	54% 5% 9% 18% 12% 2	2400
	11th to 20th	Day	48% 5% 10% 22% 13% 2	2374
	21st to end	Day	51% 7% 10% 16% 12% 3	2586
May	1st to 10th	Day	58% 7% 9% 18% 8% 1	6264
	11th to 20th	Day	49% 8% 15% 17% 8% 2	6322
	21st to end	Day	49% 8% 12% 18% 12% 2	6949
June	1st to 10th	Day	51% 7% 11% 19% 11% 2	2800
	11th to 20th	Day	41% 8% 14% 22% 12% 3	2800
	21st to end	Day	52% 8% 12% 18% 10% 1	2800
July	1st to 10th	Day	42% 9% 15% 24% 10%	4440
	11th to 20th	Day	39% 10% 18% 26% 7%	4365
	21st to end	Day	35% 9% 15% 31% 10%	4661
August	1st to 10th	Day	44% 10% 18% 21% 7%	4409
	11th to 20th	Day	42% 9% 20% 24% 6%	4093
	21st to end	Day	40% 8% 16% 21% 14% 1	4180
September	1st to 10th	Day	36% 7% 17% 27% 12% 1	2280
	11th to 20th	Day	34% 7% 14% 31% 12% 1	2190
	21st to end	Day	42% 7% 14% 26% 11%	2090
October	1st to 10th	Day	43% 7% 16% 25% 8%	3288
	11th to 20th	Day	43% 7% 18% 25% 7%	3028
	21st to end	Day	41% 6% 22% 22% 9% 1	3081
November	1st to 10th	Day	46% 6% 14% 23% 10% 1	1761
	11th to 20th	Day	50% 6% 14% 19% 11% 1	1716
	21st to end	Day	57% 7% 14% 16% 6% 1	1600
December	1st to 10th	Day	66% 5% 9% 16% 4	2600
	11th to 20th	Day	55% 7% 10% 18% 11%	2986
	21st to end	Day	61% 6% 11% 14% 8%	3960
January	1st to 10th	Night	64% 5% 12% 13% 5%	6349
	11th to 20th	Night	61% 8% 11% 15% 4 1	6360
	21st to end	Night	56% 7% 11% 12% 13% 1	6996
February	1st to 10th	Night	59% 4 10% 17% 9% 1	2675
	11th to 20th	Night	56% 5% 10% 18% 10% 1	2427
	21st to end	Night	54% 5% 9% 17% 12% 2	1980
March	1st to 10th	Night	59% 5% 8% 13% 12% 4	5374
	11th to 20th	Night	50% 6% 15% 14% 13% 2	5271
	21st to end	Night	52% 5% 7% 21% 12% 2	4962
April	1st to 10th	Night	53% 5% 9% 17% 14% 2	2000
	11th to 20th	Night	49% 6% 8% 20% 15% 2	1975
	21st to end	Night	49% 7% 7% 20% 15% 3	1812
May	1st to 10th	Night	58% 7% 10% 16% 7% 2	3723
	11th to 20th	Night	50% 9% 11% 18% 10% 2	3576
	21st to end	Night	51% 7% 12% 16% 13% 1	3927
June	1st to 10th	Night	47% 7% 11% 19% 15% 1	1600
	11th to 20th	Night	44% 7% 12% 20% 13% 4	1600
	21st to end	Night	48% 8% 11% 19% 14% 1	1600
July	1st to 10th	Night	43% 8% 17% 20% 11% 1	2520
	11th to 20th	Night	38% 9% 19% 27% 7%	2472
	21st to end	Night	34% 8% 20% 26% 12%	2651
August	1st to 10th	Night	44% 8% 13% 25% 9%	2496
	11th to 20th	Night	42% 8% 17% 24% 8%	2765
	21st to end	Night	43% 7% 14% 21% 13% 1	3476
September	1st to 10th	Night	35% 9% 15% 25% 15% 1	1900
	11th to 20th	Night	34% 7% 15% 32% 12% 1	1990
	21st to end	Night	40% 6% 10% 29% 15%	2090
October	1st to 10th	Night	44% 6% 15% 24% 11%	3670
	11th to 20th	Night	41% 6% 13% 31% 9%	3891
	21st to end	Night	44% 5% 18% 18% 12% 2	4467
November	1st to 10th	Night	50% 7% 13% 21% 9% 1	2537
	11th to 20th	Night	50% 6% 13% 19% 11% 1	2680
	21st to end	Night	58% 5% 11% 17% 8%	2800
December	1st to 10th	Night	64% 7% 12% 13% 4	4580
	11th to 20th	Night	58% 6% 8% 15% 12% 1	5208
	21st to end	Night	61% 5% 8% 15% 10%	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	26% 12% 31% 24% 8%	200
	11th to 20th	Day	23% 12% 31% 29% 4 2	200
	21st to end	Day	16% 10% 32% 31% 9% 2	220
February	1st to 10th	Day	28% 16% 35% 19% 2	263
	11th to 20th	Day	18% 14% 39% 24% 5%	409
	21st to end	Day	25% 10% 33% 26% 5%	414
March	1st to 10th	Day	24% 11% 31% 25% 8% 1	500
	11th to 20th	Day	19% 14% 35% 26% 6% 1	500
	21st to end	Day	26% 12% 33% 19% 9% 1	550
April	1st to 10th	Day	25% 15% 27% 22% 9% 2	500
	11th to 20th	Day	26% 18% 25% 20% 9% 2	492
	21st to end	Day	28% 11% 32% 19% 8% 2	500
May	1st to 10th	Day	26% 11% 32% 22% 8% 1	503
	11th to 20th	Day	19% 9% 31% 25% 13% 3	527
	21st to end	Day	19% 11% 33% 24% 11% 2	573
June	1st to 10th	Day	23% 9% 29% 26% 11% 2	530
	11th to 20th	Day	15% 11% 28% 28% 15% 2	530
	21st to end	Day	22% 10% 26% 27% 12% 3	530
July	1st to 10th	Day	13% 6% 25% 33% 18% 5%	505
	11th to 20th	Day	15% 6% 26% 32% 19% 3	484
	21st to end	Day	12% 5% 24% 33% 22% 4	532
August	1st to 10th	Day	14% 5% 22% 30% 24% 4	486
	11th to 20th	Day	12% 6% 20% 32% 20% 11%	479
	21st to end	Day	15% 7% 26% 23% 20% 9%	539
September	1st to 10th	Day	14% 7% 25% 30% 16% 8%	490
	11th to 20th	Day	13% 8% 18% 30% 20% 10%	490
	21st to end	Day	19% 7% 25% 23% 19% 7%	490
October	1st to 10th	Day	22% 10% 24% 24% 16% 4	490
	11th to 20th	Day	23% 10% 31% 24% 11% 2	457
	21st to end	Day	28% 11% 27% 23% 10%	429
November	1st to 10th	Day	23% 12% 30% 26% 9% 1	395
	11th to 20th	Day	24% 12% 31% 22% 10% 1	316
	21st to end	Day	30% 10% 35% 17% 10%	200
December	1st to 10th	Day	26% 11% 26% 23% 11% 4	200
	11th to 20th	Day	23% 17% 33% 24% 4 1	200
	21st to end	Day	34% 12% 25% 19% 8% 3	220
January	1st to 10th	Night	25% 9% 31% 30% 5%	800
	11th to 20th	Night	23% 9% 33% 28% 8%	800
	21st to end	Night	16% 7% 34% 36% 7% 1	880
February	1st to 10th	Night	20% 7% 37% 29% 6% 1	800
	11th to 20th	Night	18% 9% 38% 28% 6% 1	783
	21st to end	Night	20% 9% 34% 33% 4	660
March	1st to 10th	Night	25% 7% 32% 30% 5%	800
	11th to 20th	Night	22% 9% 35% 27% 7%	800
	21st to end	Night	22% 8% 33% 29% 8%	880
April	1st to 10th	Night	27% 9% 30% 28% 6%	800
	11th to 20th	Night	25% 9% 34% 26% 6% 1	791
	21st to end	Night	27% 10% 33% 24% 7%	612
May	1st to 10th	Night	26% 8% 32% 28% 6% 1	458
	11th to 20th	Night	22% 7% 29% 34% 8%	394
	21st to end	Night	21% 6% 33% 31% 8%	433
June	1st to 10th	Night	22% 4 29% 37% 8% 1	400
	11th to 20th	Night	21% 4 29% 34% 14% 1	400
	21st to end	Night	20% 4 26% 37% 14%	400
July	1st to 10th	Night	11% 3 26% 45% 14% 1	380
	11th to 20th	Night	13% 3 22% 46% 15% 1	368
	21st to end	Night	13% 3 19% 49% 15% 1	416
August	1st to 10th	Night	13% 3 14% 48% 20% 1	378
	11th to 20th	Night	14% 2 22% 38% 22% 2	530
	21st to end	Night	16% 4 22% 35% 21% 1	836
September	1st to 10th	Night	14% 4 24% 41% 16% 1	760
	11th to 20th	Night	15% 5% 19% 37% 22% 2	760
	21st to end	Night	19% 4 26% 33% 17% 2	760
October	1st to 10th	Night	20% 5% 28% 35% 11% 1	760
	11th to 20th	Night	24% 7% 28% 29% 11% 1	760
	21st to end	Night	27% 7% 31% 28% 7%	836
November	1st to 10th	Night	24% 10% 28% 28% 9% 1	780
	11th to 20th	Night	24% 9% 31% 25% 11% 1	800
	21st to end	Night	29% 8% 32% 24% 7% 1	800
December	1st to 10th	Night	28% 8% 30% 26% 8%	800
	11th to 20th	Night	27% 11% 30% 26% 6% 1	800
	21st to end	Night	31% 9% 30% 23% 7%	880

Page generated at 2025-07-03 01:30:14. Version ac07

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