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 2024-03-18.

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 6% 5% 3 5% 5% 5% 7% 34%	78454
	Night	18% 10% 4 7% 6% 3 4 4 5% 6% 34%	81331
Transparency	Day	49% 7% 13% 20% 10% 1	78159
	Night	51% 7% 12% 19% 10% 1	81160
Seeing	Day	21% 10% 28% 25% 13% 3	13645
	Night	22% 7% 30% 31% 10% 1	22761

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% 13% 4 7% 5% 4 5% 4 4 6% 31%	2517
	11th to 20th	Day	14% 13% 5% 7% 6% 3 5% 5% 5% 5% 32%	2520
	21st to end	Day	13% 14% 6% 9% 8% 4 4 5% 5% 6% 26%	2772
February	1st to 10th	Day	15% 16% 4 8% 7% 3 5% 4 4 5% 29%	1637
	11th to 20th	Day	13% 13% 5% 10% 6% 3 5% 4 5% 7% 30%	1765
	21st to end	Day	17% 15% 5% 7% 5% 4 5% 4 4 6% 28%	1570
March	1st to 10th	Day	17% 9% 4 7% 6% 4 6% 5% 5% 6% 31%	1897
	11th to 20th	Day	15% 11% 4 6% 7% 3 4 4 5% 6% 35%	1924
	21st to end	Day	17% 10% 3 7% 5% 3 4 4 4 6% 37%	2376
April	1st to 10th	Day	21% 9% 4 7% 5% 3 5% 4 4 6% 32%	2160
	11th to 20th	Day	21% 7% 3 5% 5% 2 3 4 5% 6% 39%	2134
	21st to end	Day	22% 9% 3 6% 4 3 5% 4 5% 5% 33%	2326
May	1st to 10th	Day	21% 7% 3 6% 5% 3 4 4 4 6% 36%	2483
	11th to 20th	Day	19% 6% 3 6% 6% 3 4 4 6% 7% 37%	2478
	21st to end	Day	18% 6% 2 6% 6% 3 5% 5% 6% 7% 36%	2725
June	1st to 10th	Day	22% 6% 3 5% 6% 4 5% 5% 5% 8% 31%	2520
	11th to 20th	Day	16% 5% 2 5% 6% 3 5% 5% 6% 8% 38%	2520
	21st to end	Day	20% 7% 3 6% 6% 4 6% 6% 5% 8% 30%	2520
July	1st to 10th	Day	13% 5% 2 5% 6% 4 6% 6% 7% 8% 39%	2520
	11th to 20th	Day	13% 5% 2 5% 5% 4 6% 7% 7% 9% 37%	2520
	21st to end	Day	12% 5% 3 6% 5% 4 5% 7% 8% 9% 37%	2744
August	1st to 10th	Day	12% 5% 2 6% 6% 4 7% 6% 7% 8% 36%	2506
	11th to 20th	Day	11% 5% 2 5% 6% 4 5% 6% 7% 9% 40%	2313
	21st to end	Day	13% 5% 1 5% 5% 4 4 5% 6% 7% 45%	2376
September	1st to 10th	Day	14% 5% 2 4 4 3 5% 5% 6% 8% 44%	2160
	11th to 20th	Day	14% 5% 2 4 4 2 4 4 4 7% 50%	2075
	21st to end	Day	18% 6% 2 4 4 3 4 4 4 6% 43%	1980
October	1st to 10th	Day	21% 7% 3 5% 4 3 4 5% 5% 7% 37%	1872
	11th to 20th	Day	21% 7% 4 7% 6% 4 5% 6% 5% 6% 30%	1742
	21st to end	Day	25% 9% 4 7% 4 3 4 4 4 6% 31%	1782
November	1st to 10th	Day	15% 9% 4 5% 5% 3 4 5% 5% 6% 37%	1671
	11th to 20th	Day	20% 9% 4 7% 5% 2 5% 4 6% 7% 32%	1631
	21st to end	Day	21% 11% 3 6% 6% 4 5% 4 5% 5% 29%	1520
December	1st to 10th	Day	25% 14% 4 7% 6% 3 4 4 4 5% 26%	1520
	11th to 20th	Day	22% 13% 5% 8% 5% 2 3 4 4 6% 29%	1906
	21st to end	Day	28% 15% 5% 8% 5% 3 4 3 3 4 23%	2772
January	1st to 10th	Night	17% 15% 5% 9% 6% 4 4 4 5% 4 28%	4429
	11th to 20th	Night	11% 11% 5% 10% 8% 5% 5% 5% 5% 5% 29%	4440
	21st to end	Night	14% 14% 5% 9% 7% 4 5% 4 5% 6% 26%	4884
February	1st to 10th	Night	14% 13% 6% 10% 7% 4 5% 4 5% 5% 27%	2542
	11th to 20th	Night	14% 10% 5% 9% 8% 3 7% 4 4 5% 31%	2301
	21st to end	Night	16% 11% 4 9% 6% 3 4 4 4 5% 32%	1884
March	1st to 10th	Night	19% 11% 5% 6% 6% 3 4 5% 4 5% 32%	2270
	11th to 20th	Night	17% 13% 5% 8% 5% 4 4 4 5% 4 33%	2197
	21st to end	Night	18% 9% 4 6% 4 3 4 4 4 5% 38%	1980
April	1st to 10th	Night	24% 8% 5% 6% 5% 3 3 4 5% 6% 32%	1800
	11th to 20th	Night	21% 6% 3 4 5% 3 4 4 4 6% 38%	1775
	21st to end	Night	23% 9% 3 5% 4 2 4 4 5% 6% 35%	1632
May	1st to 10th	Night	23% 9% 3 6% 6% 2 4 3 4 5% 36%	1493
	11th to 20th	Night	20% 7% 2 6% 5% 3 5% 5% 4 6% 37%	1415
	21st to end	Night	19% 5% 2 5% 5% 3 5% 4 5% 7% 39%	1550
June	1st to 10th	Night	21% 7% 2 5% 5% 3 5% 5% 5% 6% 35%	1440
	11th to 20th	Night	19% 7% 3 6% 4 3 5% 5% 5% 7% 37%	1440
	21st to end	Night	18% 6% 3 6% 7% 3 5% 4 6% 8% 34%	1440
July	1st to 10th	Night	11% 5% 2 6% 6% 3 5% 5% 7% 9% 42%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 4 6% 6% 6% 7% 42%	1440
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 6% 9% 43%	1574
August	1st to 10th	Night	12% 5% 2 6% 6% 3 4 5% 6% 8% 43%	1432
	11th to 20th	Night	13% 5% 3 5% 4 4 4 6% 6% 7% 43%	1565
	21st to end	Night	15% 5% 2 6% 5% 3 4 4 4 7% 45%	1980
September	1st to 10th	Night	13% 4 2 5% 5% 3 5% 5% 5% 7% 47%	1800
	11th to 20th	Night	15% 4 2 4 4 2 3 4 4 6% 51%	1885
	21st to end	Night	18% 5% 2 4 4 3 4 4 4 7% 46%	1980
October	1st to 10th	Night	17% 6% 3 7% 6% 3 4 4 4 5% 42%	2086
	11th to 20th	Night	20% 8% 3 7% 5% 3 4 4 5% 6% 36%	2218
	21st to end	Night	24% 8% 3 6% 5% 4 4 5% 4 5% 32%	2574
November	1st to 10th	Night	18% 9% 4 6% 6% 3 4 5% 5% 6% 35%	2407
	11th to 20th	Night	20% 9% 3 7% 6% 3 4 4 5% 5% 35%	2546
	21st to end	Night	23% 12% 5% 6% 7% 3 4 3 4 5% 30%	2660
December	1st to 10th	Night	21% 13% 5% 8% 6% 3 4 4 5% 5% 24%	2660
	11th to 20th	Night	24% 12% 4 7% 6% 2 4 3 4 4 30%	3288
	21st to end	Night	27% 16% 5% 7% 5% 2 3 3 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	54% 6% 10% 17% 11% 2	1900
	11th to 20th	Day	51% 5% 13% 15% 13% 3	1924
	21st to end	Day	49% 5% 11% 18% 13% 4	2376
April	1st to 10th	Day	54% 5% 10% 17% 11% 2	2160
	11th to 20th	Day	48% 5% 10% 22% 13% 2	2134
	21st to end	Day	53% 6% 10% 16% 12% 3	2326
May	1st to 10th	Day	49% 6% 9% 20% 14% 2	2483
	11th to 20th	Day	47% 5% 11% 18% 16% 3	2482
	21st to end	Day	47% 7% 11% 18% 14% 2	2725
June	1st to 10th	Day	51% 7% 12% 19% 10% 2	2520
	11th to 20th	Day	42% 8% 13% 22% 13% 3	2520
	21st to end	Day	53% 8% 12% 17% 10% 1	2520
July	1st to 10th	Day	39% 9% 14% 24% 12% 1	2450
	11th to 20th	Day	40% 9% 18% 24% 10%	2445
	21st to end	Day	41% 11% 16% 23% 8%	2591
August	1st to 10th	Day	43% 10% 18% 23% 6%	2492
	11th to 20th	Day	38% 10% 18% 24% 10%	2313
	21st to end	Day	37% 7% 17% 25% 13%	2376
September	1st to 10th	Day	37% 7% 17% 26% 12% 1	2160
	11th to 20th	Day	35% 7% 14% 30% 13% 1	2075
	21st to end	Day	42% 7% 14% 25% 11%	1980
October	1st to 10th	Day	47% 5% 13% 23% 11% 1	1872
	11th to 20th	Day	54% 8% 13% 19% 6%	1742
	21st to end	Day	55% 4 14% 18% 8% 1	1782
November	1st to 10th	Day	46% 6% 14% 22% 10% 1	1671
	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	55% 6% 9% 17% 12% 2	2280
	11th to 20th	Night	54% 5% 10% 15% 13% 3	2198
	21st to end	Night	49% 5% 7% 20% 15% 4	1980
April	1st to 10th	Night	54% 5% 10% 17% 14% 2	1800
	11th to 20th	Night	47% 5% 9% 21% 16% 2	1775
	21st to end	Night	50% 7% 7% 19% 14% 3	1632
May	1st to 10th	Night	50% 4 9% 17% 14% 5%	1493
	11th to 20th	Night	47% 7% 8% 17% 16% 4	1416
	21st to end	Night	44% 7% 11% 20% 16% 2	1551
June	1st to 10th	Night	47% 6% 12% 20% 13% 1	1440
	11th to 20th	Night	44% 7% 12% 20% 13% 4	1440
	21st to end	Night	48% 8% 11% 19% 13%	1440
July	1st to 10th	Night	36% 8% 15% 25% 14% 1	1400
	11th to 20th	Night	38% 10% 14% 27% 11% 1	1392
	21st to end	Night	36% 8% 19% 24% 12%	1486
August	1st to 10th	Night	38% 10% 17% 25% 10%	1422
	11th to 20th	Night	38% 9% 16% 25% 12%	1565
	21st to end	Night	38% 7% 15% 26% 13%	1980
September	1st to 10th	Night	36% 9% 16% 25% 14% 1	1800
	11th to 20th	Night	35% 7% 14% 32% 11% 1	1885
	21st to end	Night	39% 6% 11% 29% 15%	1980
October	1st to 10th	Night	45% 6% 10% 24% 14% 1	2086
	11th to 20th	Night	49% 7% 14% 22% 8%	2218
	21st to end	Night	54% 5% 13% 17% 10%	2574
November	1st to 10th	Night	49% 7% 13% 20% 9% 1	2407
	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	449
	21st to end	Day	27% 10% 31% 21% 10% 2	462
April	1st to 10th	Day	26% 14% 26% 23% 10% 2	420
	11th to 20th	Day	25% 17% 24% 21% 10% 2	412
	21st to end	Day	29% 10% 31% 20% 9% 2	420
May	1st to 10th	Day	25% 11% 33% 22% 8% 2	423
	11th to 20th	Day	18% 10% 31% 26% 12% 3	447
	21st to end	Day	18% 11% 34% 24% 12% 2	485
June	1st to 10th	Day	23% 9% 29% 25% 11% 2	450
	11th to 20th	Day	16% 11% 27% 28% 16% 2	450
	21st to end	Day	21% 9% 24% 27% 14% 4	450
July	1st to 10th	Day	13% 5% 24% 33% 20% 5%	445
	11th to 20th	Day	15% 5% 25% 32% 20% 3	444
	21st to end	Day	13% 5% 24% 33% 22% 4	488
August	1st to 10th	Day	14% 5% 22% 30% 25% 4	446
	11th to 20th	Day	11% 6% 20% 32% 20% 11%	439
	21st to end	Day	15% 7% 26% 23% 20% 9%	495
September	1st to 10th	Day	14% 7% 25% 29% 16% 9%	450
	11th to 20th	Day	14% 8% 20% 31% 18% 9%	450
	21st to end	Day	19% 7% 27% 22% 19% 7%	450
October	1st to 10th	Day	24% 10% 24% 23% 16% 4	450
	11th to 20th	Day	23% 9% 30% 24% 11% 2	421
	21st to end	Day	30% 12% 26% 23% 10% 1	396
November	1st to 10th	Day	23% 12% 30% 25% 10% 1	365
	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% 10% 34% 27% 7%	752
	21st to end	Night	21% 7% 32% 31% 9% 1	792
April	1st to 10th	Night	28% 8% 29% 28% 6%	720
	11th to 20th	Night	24% 8% 33% 27% 6% 1	711
	21st to end	Night	28% 9% 32% 24% 7%	552
May	1st to 10th	Night	25% 7% 32% 28% 6% 1	413
	11th to 20th	Night	23% 6% 31% 32% 8%	354
	21st to end	Night	21% 5% 34% 31% 8%	389
June	1st to 10th	Night	23% 4 29% 34% 8% 1	360
	11th to 20th	Night	22% 3 28% 33% 14% 1	360
	21st to end	Night	19% 4 25% 36% 16%	360
July	1st to 10th	Night	11% 3 26% 43% 15% 1	350
	11th to 20th	Night	12% 3 23% 46% 15% 1	348
	21st to end	Night	13% 3 20% 49% 14% 1	394
August	1st to 10th	Night	13% 3 14% 48% 20% 1	358
	11th to 20th	Night	14% 2 22% 38% 22% 2	501
	21st to end	Night	16% 4 22% 35% 21% 2	792
September	1st to 10th	Night	15% 4 24% 41% 16% 1	720
	11th to 20th	Night	16% 5% 20% 37% 20% 2	720
	21st to end	Night	19% 5% 27% 32% 16% 2	720
October	1st to 10th	Night	20% 4 28% 36% 10% 1	720
	11th to 20th	Night	25% 7% 28% 29% 11% 1	720
	21st to end	Night	28% 7% 30% 28% 7%	792
November	1st to 10th	Night	24% 9% 28% 28% 9% 1	740
	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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