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 2026-10-29.

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	16% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	150078
	Night	17% 10% 4 9% 5% 4 4 3 5% 6% 32%	142011
Transparency	Day	47% 7% 14% 21% 10% 1	153525
	Night	51% 6% 12% 19% 11% 1	146653
Seeing	Day	20% 10% 28% 26% 12% 3	17052
	Night	21% 7% 30% 31% 10% 1	25911

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	14% 17% 4 10% 4 4 3 3 4 6% 30%	4661
	11th to 20th	Day	12% 16% 6% 11% 7% 5% 5% 4 5% 5% 25%	4650
	21st to end	Day	8% 13% 5% 12% 7% 6% 5% 4 5% 6% 29%	5124
February	1st to 10th	Day	13% 16% 3 10% 6% 4 5% 4 5% 5% 30%	1810
	11th to 20th	Day	12% 13% 5% 11% 6% 5% 4 3 4 7% 30%	1957
	21st to end	Day	16% 16% 4 7% 5% 6% 5% 3 4 5% 29%	1730
March	1st to 10th	Day	20% 12% 4 8% 6% 5% 5% 3 4 5% 27%	4576
	11th to 20th	Day	12% 14% 4 9% 5% 4 4 3 5% 6% 34%	4788
	21st to end	Day	17% 11% 4 9% 5% 4 4 3 4 5% 34%	6102
April	1st to 10th	Day	21% 10% 4 7% 5% 4 5% 3 4 6% 32%	2520
	11th to 20th	Day	22% 8% 2 6% 4 3 4 3 5% 5% 37%	2494
	21st to end	Day	21% 10% 3 7% 4 4 5% 3 5% 5% 34%	2715
May	1st to 10th	Day	24% 9% 3 8% 6% 6% 5% 4 5% 6% 25%	8116
	11th to 20th	Day	19% 8% 3 8% 5% 4 5% 4 5% 7% 32%	8221
	21st to end	Day	20% 8% 3 6% 5% 5% 4 4 5% 7% 32%	9060
June	1st to 10th	Day	22% 6% 3 6% 5% 5% 5% 4 5% 8% 32%	2940
	11th to 20th	Day	16% 5% 2 6% 5% 4 5% 5% 6% 8% 37%	2940
	21st to end	Day	19% 8% 3 7% 6% 5% 5% 4 6% 8% 30%	2940
July	1st to 10th	Day	13% 5% 2 7% 5% 5% 5% 4 7% 9% 38%	8280
	11th to 20th	Day	10% 5% 2 5% 4 5% 5% 5% 7% 10% 42%	8280
	21st to end	Day	10% 5% 2 6% 4 5% 5% 4 7% 10% 41%	8993
August	1st to 10th	Day	14% 6% 3 8% 5% 6% 7% 5% 7% 8% 33%	6483
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 4 7% 9% 36%	5973
	21st to end	Day	14% 6% 2 6% 4 5% 5% 4 6% 9% 40%	6080
September	1st to 10th	Day	13% 5% 2 4 4 4 5% 4 6% 8% 44%	2520
	11th to 20th	Day	13% 5% 2 5% 3 3 4 4 4 6% 51%	2420
	21st to end	Day	18% 6% 2 5% 4 4 4 3 4 6% 43%	2310
October	1st to 10th	Day	19% 7% 2 6% 4 4 4 4 5% 7% 39%	2184
	11th to 20th	Day	20% 7% 4 7% 5% 5% 4 4 5% 6% 33%	2032
	21st to end	Day	22% 9% 3 8% 3 4 4 3 4 6% 34%	2052
November	1st to 10th	Day	15% 10% 4 7% 5% 4 5% 4 5% 6% 36%	1851
	11th to 20th	Day	18% 10% 4 7% 4 4 4 3 6% 7% 33%	1802
	21st to end	Day	21% 12% 3 8% 5% 5% 5% 3 5% 5% 28%	1680
December	1st to 10th	Day	20% 17% 5% 11% 6% 4 4 3 4 5% 23%	2680
	11th to 20th	Day	20% 12% 4 9% 5% 4 4 4 5% 6% 29%	3066
	21st to end	Day	24% 11% 4 9% 5% 4 4 4 5% 5% 25%	4048
January	1st to 10th	Night	13% 18% 6% 14% 5% 4 4 3 4 4 25%	8234
	11th to 20th	Night	11% 16% 7% 15% 7% 5% 4 3 5% 5% 22%	8235
	21st to end	Night	9% 12% 5% 13% 8% 6% 5% 4 5% 6% 27%	9057
February	1st to 10th	Night	13% 14% 5% 11% 6% 6% 4 3 5% 5% 28%	2809
	11th to 20th	Night	14% 11% 5% 10% 7% 5% 6% 3 4 5% 31%	2549
	21st to end	Night	15% 12% 4 10% 6% 5% 4 4 4 5% 32%	2076
March	1st to 10th	Night	23% 13% 4 9% 5% 4 4 3 3 4 29%	5484
	11th to 20th	Night	14% 13% 4 8% 5% 5% 5% 4 6% 6% 32%	5386
	21st to end	Night	17% 11% 5% 8% 6% 4 5% 3 4 5% 32%	5072
April	1st to 10th	Night	23% 9% 4 6% 5% 4 4 3 5% 6% 32%	2100
	11th to 20th	Night	22% 8% 3 6% 5% 4 4 3 4 5% 36%	2075
	21st to end	Night	22% 9% 3 5% 4 3 4 3 5% 5% 37%	1903
May	1st to 10th	Night	23% 9% 3 8% 5% 5% 5% 4 5% 7% 27%	4825
	11th to 20th	Night	20% 8% 2 7% 4 5% 5% 4 5% 6% 33%	4639
	21st to end	Night	21% 8% 3 7% 4 5% 4 4 5% 8% 31%	5114
June	1st to 10th	Night	19% 8% 2 6% 4 5% 5% 3 6% 6% 36%	1680
	11th to 20th	Night	18% 7% 2 6% 5% 4 5% 5% 5% 7% 37%	1680
	21st to end	Night	18% 7% 3 7% 6% 5% 5% 3 6% 7% 34%	1680
July	1st to 10th	Night	12% 5% 3 7% 5% 5% 6% 4 8% 9% 37%	4680
	11th to 20th	Night	12% 6% 2 5% 3 5% 4 4 5% 8% 45%	4680
	21st to end	Night	12% 5% 2 6% 5% 5% 5% 4 6% 8% 42%	5084
August	1st to 10th	Night	15% 7% 3 9% 5% 5% 5% 4 6% 7% 35%	3666
	11th to 20th	Night	15% 6% 3 6% 4 4 5% 4 6% 7% 39%	4022
	21st to end	Night	16% 6% 2 7% 5% 5% 4 3 5% 6% 40%	5045
September	1st to 10th	Night	12% 4 2 5% 4 4 5% 4 5% 7% 47%	2100
	11th to 20th	Night	13% 5% 2 5% 3 3 3 4 5% 6% 52%	2200
	21st to end	Night	17% 5% 2 5% 4 4 4 3 4 7% 46%	2310
October	1st to 10th	Night	17% 6% 3 8% 4 3 4 3 4 5% 43%	2434
	11th to 20th	Night	18% 8% 3 7% 4 4 3 3 5% 6% 38%	2588
	21st to end	Night	22% 8% 3 7% 4 4 4 4 4 6% 35%	2965
November	1st to 10th	Night	19% 9% 4 8% 5% 4 4 3 5% 6% 34%	2667
	11th to 20th	Night	19% 10% 2 8% 5% 4 4 3 5% 5% 35%	2814
	21st to end	Night	22% 13% 4 8% 6% 3 4 3 4 5% 29%	2940
December	1st to 10th	Night	18% 14% 4 11% 7% 6% 5% 4 5% 5% 21%	4720
	11th to 20th	Night	23% 12% 4 8% 5% 3 4 3 4 4 29%	5348
	21st to end	Night	24% 15% 4 8% 4 3 3 3 4 5% 26%	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	56% 6% 13% 19% 5%	4662
	11th to 20th	Day	59% 6% 10% 15% 9% 1	4680
	21st to end	Day	54% 6% 11% 15% 13% 1	5124
February	1st to 10th	Day	57% 4 9% 20% 8% 2	1810
	11th to 20th	Day	54% 7% 11% 16% 11% 1	1966
	21st to end	Day	56% 5% 9% 17% 10% 2	1730
March	1st to 10th	Day	58% 6% 9% 13% 11% 3	4579
	11th to 20th	Day	50% 7% 18% 13% 11% 3	4788
	21st to end	Day	51% 5% 8% 16% 17% 2	6102
April	1st to 10th	Day	54% 5% 9% 18% 12% 2	2520
	11th to 20th	Day	49% 5% 10% 21% 13% 2	2494
	21st to end	Day	51% 7% 10% 17% 12% 3	2715
May	1st to 10th	Day	56% 8% 9% 18% 8% 1	8128
	11th to 20th	Day	49% 8% 15% 19% 8% 2	8225
	21st to end	Day	49% 8% 11% 20% 11% 1	9061
June	1st to 10th	Day	50% 6% 11% 20% 11% 2	2940
	11th to 20th	Day	42% 8% 14% 22% 12% 2	2940
	21st to end	Day	51% 8% 13% 18% 9% 1	2940
July	1st to 10th	Day	40% 8% 15% 25% 12%	8210
	11th to 20th	Day	33% 9% 17% 29% 12%	8205
	21st to end	Day	36% 9% 18% 29% 8%	8795
August	1st to 10th	Day	45% 9% 17% 19% 8% 2	6469
	11th to 20th	Day	40% 10% 21% 22% 8%	6015
	21st to end	Day	39% 8% 19% 22% 12%	6080
September	1st to 10th	Day	35% 7% 17% 28% 12% 1	2520
	11th to 20th	Day	33% 7% 14% 32% 13% 1	2420
	21st to end	Day	42% 7% 13% 25% 13%	2310
October	1st to 10th	Day	42% 7% 16% 26% 9%	3496
	11th to 20th	Day	43% 7% 17% 25% 7% 1	3222
	21st to end	Day	41% 6% 21% 22% 10% 1	3252
November	1st to 10th	Day	47% 6% 13% 22% 10% 1	1851
	11th to 20th	Day	50% 6% 14% 19% 11% 1	1802
	21st to end	Day	57% 6% 13% 16% 6% 1	1680
December	1st to 10th	Day	65% 5% 9% 15% 5%	2680
	11th to 20th	Day	55% 7% 10% 17% 11%	3066
	21st to end	Day	60% 6% 11% 14% 8%	4048
January	1st to 10th	Night	62% 5% 11% 15% 6% 1	8234
	11th to 20th	Night	63% 7% 10% 14% 6% 1	8280
	21st to end	Night	56% 7% 9% 13% 14% 1	9057
February	1st to 10th	Night	58% 4 10% 17% 9% 1	2809
	11th to 20th	Night	55% 5% 9% 19% 11% 1	2551
	21st to end	Night	54% 5% 9% 18% 12% 2	2076
March	1st to 10th	Night	59% 5% 8% 13% 12% 4	5494
	11th to 20th	Night	50% 6% 15% 14% 13% 2	5387
	21st to end	Night	53% 5% 7% 21% 12% 2	5072
April	1st to 10th	Night	53% 5% 9% 18% 14% 2	2100
	11th to 20th	Night	49% 6% 9% 20% 14% 2	2075
	21st to end	Night	48% 6% 7% 20% 16% 3	1903
May	1st to 10th	Night	54% 7% 12% 17% 8% 1	4831
	11th to 20th	Night	49% 9% 11% 21% 9% 1	4640
	21st to end	Night	50% 6% 11% 17% 15% 1	5115
June	1st to 10th	Night	47% 6% 11% 20% 15% 1	1680
	11th to 20th	Night	45% 7% 12% 20% 13% 3	1680
	21st to end	Night	48% 8% 11% 19% 13% 1	1680
July	1st to 10th	Night	40% 8% 18% 22% 11% 1	4640
	11th to 20th	Night	34% 8% 17% 31% 10%	4632
	21st to end	Night	38% 8% 17% 28% 9%	4967
August	1st to 10th	Night	46% 8% 14% 21% 9% 1	3656
	11th to 20th	Night	41% 8% 18% 25% 8%	4046
	21st to end	Night	42% 8% 15% 22% 12% 1	5045
September	1st to 10th	Night	35% 8% 16% 26% 14% 1	2100
	11th to 20th	Night	33% 6% 14% 33% 13% 1	2200
	21st to end	Night	39% 6% 10% 28% 17%	2310
October	1st to 10th	Night	44% 6% 14% 24% 11%	3902
	11th to 20th	Night	41% 6% 13% 31% 9%	4137
	21st to end	Night	43% 5% 17% 19% 13% 2	4715
November	1st to 10th	Night	50% 6% 13% 21% 8% 1	2667
	11th to 20th	Night	50% 6% 13% 19% 11% 1	2814
	21st to end	Night	59% 5% 11% 17% 8%	2940
December	1st to 10th	Night	63% 7% 12% 14% 4	4720
	11th to 20th	Night	58% 6% 8% 15% 12% 1	5348
	21st to end	Night	61% 5% 8% 15% 10%	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	25% 11% 30% 26% 8%	220
	11th to 20th	Day	23% 15% 31% 27% 3 2	220
	21st to end	Day	15% 11% 31% 31% 9% 3	242
February	1st to 10th	Day	26% 15% 33% 21% 5%	289
	11th to 20th	Day	17% 14% 38% 24% 6%	445
	21st to end	Day	24% 11% 34% 26% 5%	446
March	1st to 10th	Day	23% 12% 32% 25% 7% 1	540
	11th to 20th	Day	21% 13% 34% 26% 6% 1	540
	21st to end	Day	25% 12% 34% 19% 9% 1	594
April	1st to 10th	Day	26% 16% 28% 21% 8% 1	540
	11th to 20th	Day	28% 18% 23% 20% 9% 2	532
	21st to end	Day	28% 11% 32% 19% 7% 2	540
May	1st to 10th	Day	26% 13% 31% 22% 8% 1	543
	11th to 20th	Day	19% 10% 31% 25% 12% 2	567
	21st to end	Day	20% 11% 34% 23% 10% 2	617
June	1st to 10th	Day	23% 9% 28% 26% 12% 2	570
	11th to 20th	Day	16% 10% 28% 28% 15% 2	570
	21st to end	Day	20% 10% 25% 28% 13% 3	570
July	1st to 10th	Day	13% 6% 26% 32% 18% 5%	565
	11th to 20th	Day	13% 7% 28% 32% 18% 3	564
	21st to end	Day	13% 6% 24% 33% 20% 5%	620
August	1st to 10th	Day	14% 5% 22% 31% 24% 4	566
	11th to 20th	Day	11% 6% 20% 33% 21% 9%	559
	21st to end	Day	15% 7% 26% 23% 20% 9%	627
September	1st to 10th	Day	14% 8% 25% 30% 16% 8%	570
	11th to 20th	Day	12% 7% 19% 31% 20% 11%	570
	21st to end	Day	19% 7% 25% 22% 19% 7%	570
October	1st to 10th	Day	21% 9% 25% 26% 15% 4	570
	11th to 20th	Day	22% 10% 31% 24% 11% 2	531
	21st to end	Day	27% 11% 26% 24% 11% 1	486
November	1st to 10th	Day	23% 13% 30% 25% 8% 1	425
	11th to 20th	Day	24% 12% 30% 23% 10% 1	342
	21st to end	Day	30% 10% 35% 17% 9%	220
December	1st to 10th	Day	25% 10% 27% 23% 11% 3	220
	11th to 20th	Day	23% 15% 34% 24% 3 1	220
	21st to end	Day	31% 13% 26% 20% 8% 2	242
January	1st to 10th	Night	24% 9% 31% 31% 5%	840
	11th to 20th	Night	23% 10% 32% 27% 8%	840
	21st to end	Night	16% 7% 34% 34% 8% 1	924
February	1st to 10th	Night	19% 7% 36% 30% 7% 1	840
	11th to 20th	Night	18% 9% 38% 28% 6%	823
	21st to end	Night	20% 9% 34% 34% 4	692
March	1st to 10th	Night	25% 8% 33% 30% 5%	840
	11th to 20th	Night	23% 9% 35% 26% 6%	840
	21st to end	Night	22% 8% 33% 29% 8%	924
April	1st to 10th	Night	28% 9% 30% 28% 5%	840
	11th to 20th	Night	25% 9% 33% 26% 5%	831
	21st to end	Night	26% 10% 33% 24% 7%	643
May	1st to 10th	Night	25% 7% 32% 28% 6% 1	481
	11th to 20th	Night	22% 7% 29% 34% 8%	414
	21st to end	Night	22% 7% 34% 30% 8%	455
June	1st to 10th	Night	22% 4 28% 37% 8%	420
	11th to 20th	Night	21% 4 28% 34% 13%	420
	21st to end	Night	19% 4 25% 37% 15%	420
July	1st to 10th	Night	11% 3 27% 44% 14% 1	410
	11th to 20th	Night	12% 3 24% 46% 14% 1	408
	21st to end	Night	13% 3 20% 48% 15% 1	460
August	1st to 10th	Night	13% 3 14% 49% 20% 1	418
	11th to 20th	Night	13% 3 21% 39% 22% 2	587
	21st to end	Night	16% 4 22% 36% 21% 1	924
September	1st to 10th	Night	15% 4 24% 41% 16% 1	840
	11th to 20th	Night	14% 5% 19% 38% 22% 2	840
	21st to end	Night	18% 4 25% 35% 17% 2	840
October	1st to 10th	Night	20% 5% 28% 35% 11% 1	840
	11th to 20th	Night	23% 7% 30% 29% 11%	840
	21st to end	Night	26% 7% 31% 29% 7% 1	913
November	1st to 10th	Night	24% 10% 28% 28% 9% 1	820
	11th to 20th	Night	23% 8% 31% 25% 11% 1	840
	21st to end	Night	29% 8% 32% 24% 6% 1	840
December	1st to 10th	Night	27% 9% 30% 26% 8%	840
	11th to 20th	Night	26% 11% 31% 26% 6% 1	840
	21st to end	Night	30% 10% 31% 22% 7%	924

Page generated at 2026-10-26 04:37:45. Version ac07

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