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 2024-11-03.

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 7% 5% 5% 5% 4 5% 7% 34%	101539
	Night	18% 10% 3 8% 5% 4 4 3 5% 6% 34%	97456
Transparency	Day	48% 7% 14% 20% 10% 1	101300
	Night	51% 7% 12% 19% 10% 1	97315
Seeing	Day	20% 10% 28% 26% 13% 3	14547
	Night	22% 7% 29% 31% 10% 1	23455

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% 14% 4 8% 5% 5% 4 3 4 6% 31%	2517
	11th to 20th	Day	14% 14% 4 8% 5% 5% 4 4 5% 5% 32%	2520
	21st to end	Day	13% 15% 5% 10% 7% 5% 4 4 5% 6% 26%	2772
February	1st to 10th	Day	15% 17% 4 9% 6% 3 4 4 5% 5% 29%	1637
	11th to 20th	Day	13% 13% 5% 10% 6% 5% 4 3 5% 7% 30%	1765
	21st to end	Day	17% 16% 4 8% 4 5% 5% 3 4 6% 28%	1570
March	1st to 10th	Day	21% 10% 4 8% 6% 5% 5% 4 5% 5% 28%	3116
	11th to 20th	Day	13% 17% 4 10% 6% 4 4 3 5% 5% 29%	3269
	21st to end	Day	14% 9% 3 8% 4 4 4 3 5% 6% 39%	4166
April	1st to 10th	Day	21% 10% 4 8% 4 4 5% 3 4 6% 32%	2280
	11th to 20th	Day	22% 8% 2 6% 4 3 4 3 5% 6% 38%	2254
	21st to end	Day	22% 9% 3 7% 4 4 4 3 5% 4 33%	2456
May	1st to 10th	Day	22% 7% 3 7% 4 5% 4 4 4 6% 34%	4361
	11th to 20th	Day	17% 7% 3 8% 5% 5% 5% 4 6% 7% 34%	4398
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 5% 6% 8% 36%	4837
June	1st to 10th	Day	22% 6% 3 6% 5% 5% 5% 4 5% 8% 31%	2660
	11th to 20th	Day	15% 5% 2 6% 5% 4 5% 5% 6% 8% 37%	2660
	21st to end	Day	20% 8% 3 7% 6% 5% 5% 4 5% 7% 29%	2660
July	1st to 10th	Day	12% 6% 2 7% 6% 6% 6% 4 7% 8% 36%	4440
	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% 5% 4 5% 4 5% 6% 37%	1689
	11th to 20th	Day	19% 10% 4 8% 4 4 4 3 6% 6% 32%	1631
	21st to end	Day	21% 12% 3 7% 5% 5% 5% 3 5% 5% 29%	1520
December	1st to 10th	Day	24% 15% 3 8% 5% 4 4 3 4 4 26%	1520
	11th to 20th	Day	22% 14% 4 9% 4 3 3 3 4 5% 29%	1906
	21st to end	Day	28% 15% 5% 8% 4 4 3 2 3 4 23%	2772
January	1st to 10th	Night	16% 16% 5% 10% 5% 5% 4 3 5% 4 28%	4429
	11th to 20th	Night	11% 12% 4 11% 7% 6% 5% 4 5% 5% 28%	4440
	21st to end	Night	13% 15% 5% 10% 6% 5% 4 3 5% 5% 26%	4884
February	1st to 10th	Night	14% 14% 5% 11% 6% 6% 4 3 5% 5% 27%	2542
	11th to 20th	Night	14% 11% 5% 10% 7% 5% 6% 3 5% 4 31%	2301
	21st to end	Night	16% 12% 4 10% 6% 4 3 4 4 5% 32%	1884
March	1st to 10th	Night	23% 11% 3 7% 5% 3 4 3 4 5% 32%	3724
	11th to 20th	Night	17% 17% 4 9% 4 4 3 3 5% 3 29%	3686
	21st to end	Night	15% 10% 5% 8% 6% 4 4 3 4 5% 37%	3466
April	1st to 10th	Night	23% 9% 4 6% 5% 4 4 3 5% 6% 32%	1900
	11th to 20th	Night	22% 8% 2 5% 5% 4 4 3 4 6% 37%	1875
	21st to end	Night	23% 9% 3 5% 4 3 4 3 5% 5% 36%	1722
May	1st to 10th	Night	23% 9% 3 7% 5% 4 4 3 4 7% 31%	2595
	11th to 20th	Night	22% 7% 2 7% 4 5% 4 4 4 6% 36%	2495
	21st to end	Night	17% 6% 2 7% 5% 5% 4 4 6% 8% 35%	2738
June	1st to 10th	Night	20% 8% 2 6% 4 4 5% 4 6% 6% 35%	1520
	11th to 20th	Night	18% 8% 2 6% 4 4 4 5% 5% 7% 38%	1520
	21st to end	Night	19% 7% 3 7% 6% 5% 4 3 6% 7% 33%	1520
July	1st to 10th	Night	12% 6% 3 8% 6% 6% 6% 4 7% 8% 34%	2520
	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 4 5% 6% 34%	2434
	11th to 20th	Night	19% 10% 3 8% 5% 4 4 3 5% 5% 35%	2546
	21st to end	Night	22% 13% 4 7% 5% 3 3 3 4 5% 29%	2660
December	1st to 10th	Night	21% 13% 5% 9% 6% 4 4 4 5% 5% 24%	2660
	11th to 20th	Night	24% 13% 4 7% 5% 3 3 3 4 4 30%	3288
	21st to end	Night	27% 17% 4 8% 4 3 3 2 3 4 25%	4884

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	55% 7% 16% 17% 5% 1	2518
	11th to 20th	Day	53% 8% 13% 19% 8%	2520
	21st to end	Day	57% 8% 13% 15% 7% 1	2772
February	1st to 10th	Day	58% 4 9% 19% 7% 2	1637
	11th to 20th	Day	54% 7% 12% 15% 11% 1	1774
	21st to end	Day	57% 5% 10% 17% 9% 3	1570
March	1st to 10th	Day	57% 7% 10% 16% 9% 1	3119
	11th to 20th	Day	56% 6% 13% 12% 10% 4	3269
	21st to end	Day	44% 6% 10% 20% 17% 3	4166
April	1st to 10th	Day	54% 5% 9% 18% 11% 2	2280
	11th to 20th	Day	48% 5% 10% 22% 13% 2	2254
	21st to end	Day	52% 7% 10% 16% 12% 3	2456
May	1st to 10th	Day	49% 8% 11% 21% 10% 1	4375
	11th to 20th	Day	46% 9% 18% 17% 9% 2	4402
	21st to end	Day	42% 9% 12% 21% 14% 2	4837
June	1st to 10th	Day	51% 7% 12% 19% 10% 2	2660
	11th to 20th	Day	42% 8% 14% 21% 13% 3	2660
	21st to end	Day	53% 8% 12% 17% 10% 1	2660
July	1st to 10th	Day	42% 9% 15% 24% 10% 1	4370
	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	47% 6% 13% 23% 11% 1	1976
	11th to 20th	Day	52% 8% 14% 19% 6%	1838
	21st to end	Day	54% 4 15% 18% 9% 1	1881
November	1st to 10th	Day	46% 6% 14% 22% 10% 1	1689
	11th to 20th	Day	52% 6% 14% 18% 10% 1	1631
	21st to end	Day	56% 7% 14% 16% 6% 1	1520
December	1st to 10th	Day	63% 5% 11% 15% 6%	1520
	11th to 20th	Day	58% 5% 11% 18% 8%	1906
	21st to end	Day	66% 5% 11% 11% 7%	2772
January	1st to 10th	Night	58% 7% 16% 13% 5%	4429
	11th to 20th	Night	54% 9% 14% 17% 5% 1	4440
	21st to end	Night	58% 8% 13% 12% 7% 1	4884
February	1st to 10th	Night	59% 5% 11% 17% 8% 1	2542
	11th to 20th	Night	55% 5% 10% 18% 11% 1	2303
	21st to end	Night	54% 5% 10% 17% 13% 2	1884
March	1st to 10th	Night	54% 6% 10% 16% 9% 4	3734
	11th to 20th	Night	57% 6% 10% 12% 13% 2	3687
	21st to end	Night	48% 5% 8% 22% 14% 3	3466
April	1st to 10th	Night	53% 5% 10% 17% 14% 2	1900
	11th to 20th	Night	48% 6% 9% 20% 15% 2	1875
	21st to end	Night	49% 7% 7% 20% 14% 3	1722
May	1st to 10th	Night	51% 8% 12% 18% 8% 3	2601
	11th to 20th	Night	46% 11% 13% 18% 11% 2	2496
	21st to end	Night	46% 7% 11% 18% 16% 1	2739
June	1st to 10th	Night	47% 7% 11% 20% 14% 1	1520
	11th to 20th	Night	44% 7% 12% 20% 13% 4	1520
	21st to end	Night	49% 8% 11% 18% 14% 1	1520
July	1st to 10th	Night	44% 8% 17% 20% 11% 1	2480
	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	45% 6% 11% 24% 14% 1	2202
	11th to 20th	Night	48% 7% 14% 23% 8%	2342
	21st to end	Night	53% 5% 14% 17% 10% 1	2717
November	1st to 10th	Night	50% 7% 13% 20% 9% 1	2434
	11th to 20th	Night	51% 6% 13% 19% 11% 1	2546
	21st to end	Night	57% 5% 12% 17% 8%	2660
December	1st to 10th	Night	62% 6% 12% 16% 5%	2660
	11th to 20th	Night	59% 5% 9% 18% 8% 1	3288
	21st to end	Night	65% 5% 9% 16% 5% 1	4884

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% 29% 24% 8%	180
	11th to 20th	Day	24% 11% 32% 28% 3 2	180
	21st to end	Day	17% 11% 31% 30% 10% 2	198
February	1st to 10th	Day	30% 17% 34% 18% 2	236
	11th to 20th	Day	18% 13% 40% 24% 5%	373
	21st to end	Day	26% 10% 33% 25% 5%	382
March	1st to 10th	Day	23% 10% 32% 26% 8% 1	460
	11th to 20th	Day	19% 14% 34% 26% 6% 1	460
	21st to end	Day	26% 11% 33% 20% 9% 2	506
April	1st to 10th	Day	26% 15% 26% 23% 9% 2	460
	11th to 20th	Day	27% 17% 25% 20% 9% 2	452
	21st to end	Day	29% 11% 32% 19% 8% 2	460
May	1st to 10th	Day	24% 11% 33% 22% 8% 2	463
	11th to 20th	Day	17% 9% 31% 26% 13% 3	487
	21st to end	Day	18% 12% 33% 24% 11% 2	529
June	1st to 10th	Day	23% 9% 29% 26% 12% 2	490
	11th to 20th	Day	15% 10% 28% 29% 16% 2	490
	21st to end	Day	22% 10% 24% 27% 13% 4	490
July	1st to 10th	Day	13% 5% 25% 33% 19% 5%	485
	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% 29% 26% 10% 1	371
	11th to 20th	Day	26% 11% 31% 21% 10% 1	291
	21st to end	Day	28% 9% 34% 18% 11%	180
December	1st to 10th	Day	28% 11% 25% 23% 11% 3	180
	11th to 20th	Day	22% 17% 33% 23% 4 1	180
	21st to end	Day	36% 13% 26% 18% 7% 1	198
January	1st to 10th	Night	25% 9% 31% 29% 6%	760
	11th to 20th	Night	24% 9% 33% 27% 7%	760
	21st to end	Night	16% 7% 33% 35% 7% 1	836
February	1st to 10th	Night	21% 7% 36% 29% 6% 1	760
	11th to 20th	Night	18% 9% 38% 28% 6% 1	743
	21st to end	Night	20% 9% 34% 32% 4	628
March	1st to 10th	Night	24% 7% 32% 31% 5%	760
	11th to 20th	Night	23% 9% 34% 27% 7%	760
	21st to end	Night	21% 7% 33% 30% 8%	836
April	1st to 10th	Night	28% 8% 29% 29% 6%	760
	11th to 20th	Night	25% 8% 34% 26% 6% 1	751
	21st to end	Night	27% 9% 32% 24% 7%	582
May	1st to 10th	Night	26% 7% 32% 28% 6% 1	435
	11th to 20th	Night	22% 6% 30% 33% 8%	374
	21st to end	Night	21% 6% 35% 31% 8%	411
June	1st to 10th	Night	22% 4 29% 36% 8% 1	380
	11th to 20th	Night	21% 3 28% 33% 14% 1	380
	21st to end	Night	20% 4 25% 36% 15%	380
July	1st to 10th	Night	11% 3 26% 44% 15% 1	370
	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% 9% 29% 28% 9% 1	749
	11th to 20th	Night	24% 9% 31% 24% 11% 1	760
	21st to end	Night	29% 8% 31% 24% 7% 1	760
December	1st to 10th	Night	28% 8% 30% 25% 8%	760
	11th to 20th	Night	26% 10% 30% 26% 6% 1	760
	21st to end	Night	31% 9% 31% 22% 6%	836

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