Saint-Jérôme
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saint-Jérôme clear sky chart from 2005-11-06 to 2025-07-21.

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% 6% 32%	120320
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 33%	118811
Transparency	Day	51% 5% 12% 21% 10% 1	123810
	Night	53% 4 12% 20% 11% 1	123482
Seeing	Day	22% 15% 31% 21% 8% 2	15393
	Night	22% 11% 32% 27% 8% 1	24355

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% 19% 7% 13% 5% 3 3 3 5% 5% 23%	3597
	11th to 20th	Day	11% 14% 5% 13% 7% 5% 4 3 4 5% 27%	3570
	21st to end	Day	9% 16% 6% 11% 5% 5% 5% 4 6% 5% 28%	3960
February	1st to 10th	Day	13% 15% 4 11% 6% 6% 5% 4 4 6% 27%	1765
	11th to 20th	Day	13% 13% 5% 11% 6% 6% 5% 4 5% 6% 26%	1838
	21st to end	Day	16% 15% 4 10% 7% 4 5% 3 5% 4 27%	1650
March	1st to 10th	Day	18% 15% 5% 10% 6% 4 4 3 4 4 25%	4476
	11th to 20th	Day	10% 13% 4 9% 6% 4 4 4 5% 8% 34%	4739
	21st to end	Day	18% 10% 4 8% 5% 5% 4 3 4 5% 34%	5942
April	1st to 10th	Day	21% 11% 3 7% 4 4 4 3 4 5% 33%	2400
	11th to 20th	Day	21% 9% 3 5% 4 4 4 4 5% 6% 36%	2374
	21st to end	Day	21% 10% 3 7% 5% 5% 4 3 5% 5% 33%	2553
May	1st to 10th	Day	26% 10% 3 8% 5% 5% 5% 4 5% 6% 23%	6333
	11th to 20th	Day	21% 8% 3 8% 4 5% 5% 3 5% 8% 31%	6318
	21st to end	Day	22% 8% 2 6% 4 5% 5% 4 6% 7% 31%	6949
June	1st to 10th	Day	21% 7% 2 7% 6% 5% 5% 4 6% 7% 30%	2800
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 5% 6% 8% 36%	2800
	21st to end	Day	20% 8% 3 8% 5% 6% 6% 4 6% 6% 29%	2800
July	1st to 10th	Day	12% 6% 2 7% 6% 6% 6% 5% 7% 8% 35%	4580
	11th to 20th	Day	14% 5% 2 5% 5% 5% 6% 6% 7% 9% 36%	4580
	21st to end	Day	11% 5% 2 5% 4 5% 5% 4 6% 7% 47%	4814
August	1st to 10th	Day	14% 6% 2 7% 6% 6% 6% 5% 7% 9% 33%	4423
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 5% 6% 8% 37%	4004
	21st to end	Day	16% 5% 2 6% 5% 5% 5% 4 5% 8% 40%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 4 5% 4 5% 9% 42%	2280
	11th to 20th	Day	13% 4 2 6% 3 4 4 3 5% 6% 50%	2213
	21st to end	Day	17% 7% 2 6% 4 4 4 3 6% 7% 42%	2090
October	1st to 10th	Day	20% 7% 2 7% 4 4 4 3 5% 7% 37%	1943
	11th to 20th	Day	20% 8% 3 8% 6% 5% 4 3 6% 6% 30%	1867
	21st to end	Day	23% 9% 3 7% 5% 4 4 3 5% 6% 31%	1881
November	1st to 10th	Day	14% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	1761
	11th to 20th	Day	17% 11% 3 7% 5% 5% 4 4 6% 7% 31%	1694
	21st to end	Day	21% 11% 3 9% 5% 5% 5% 4 5% 7% 25%	1600
December	1st to 10th	Day	18% 17% 6% 12% 6% 5% 5% 3 4 4 20%	2600
	11th to 20th	Day	17% 16% 5% 8% 5% 4 4 3 4 4 30%	2986
	21st to end	Day	22% 14% 4 9% 4 4 4 4 4 4 26%	3960
January	1st to 10th	Night	12% 21% 7% 13% 6% 4 4 3 4 4 22%	6349
	11th to 20th	Night	8% 15% 7% 16% 7% 5% 5% 3 4 5% 24%	6315
	21st to end	Night	11% 14% 5% 12% 7% 6% 5% 4 4 6% 27%	6996
February	1st to 10th	Night	12% 13% 4 12% 6% 5% 5% 4 6% 6% 27%	2635
	11th to 20th	Night	12% 12% 4 10% 6% 5% 5% 4 5% 6% 31%	2448
	21st to end	Night	14% 13% 4 9% 5% 5% 4 3 5% 5% 32%	1980
March	1st to 10th	Night	21% 14% 4 9% 4 4 4 3 3 4 30%	5364
	11th to 20th	Night	12% 14% 3 7% 4 5% 5% 4 6% 7% 32%	5219
	21st to end	Night	15% 11% 4 9% 6% 5% 5% 3 5% 4 34%	4976
April	1st to 10th	Night	23% 9% 3 7% 5% 3 4 3 5% 6% 32%	2000
	11th to 20th	Night	19% 7% 3 7% 5% 4 4 3 5% 6% 37%	1975
	21st to end	Night	21% 8% 3 6% 3 4 5% 3 6% 5% 37%	1846
May	1st to 10th	Night	25% 10% 3 8% 5% 5% 4 3 5% 5% 26%	3650
	11th to 20th	Night	21% 8% 3 7% 4 4 4 3 5% 7% 34%	3575
	21st to end	Night	21% 8% 3 7% 5% 4 4 3 6% 6% 31%	3926
June	1st to 10th	Night	20% 7% 3 6% 4 4 4 4 6% 8% 33%	1600
	11th to 20th	Night	16% 8% 2 6% 4 4 4 4 5% 7% 40%	1600
	21st to end	Night	20% 6% 2 6% 5% 4 5% 4 5% 7% 37%	1600
July	1st to 10th	Night	12% 6% 2 8% 5% 5% 6% 5% 6% 7% 37%	2600
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	2600
	21st to end	Night	11% 5% 2 5% 4 4 5% 4 6% 7% 46%	2739
August	1st to 10th	Night	14% 6% 3 7% 5% 5% 5% 4 5% 7% 40%	2506
	11th to 20th	Night	15% 7% 2 7% 4 4 4 3 5% 6% 43%	2791
	21st to end	Night	18% 5% 2 6% 4 4 4 3 5% 6% 43%	3476
September	1st to 10th	Night	11% 5% 3 6% 4 4 5% 4 5% 7% 46%	1900
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 4 7% 51%	1966
	21st to end	Night	17% 4 2 4 4 3 4 3 5% 6% 46%	2090
October	1st to 10th	Night	18% 7% 3 6% 4 4 4 3 4 6% 40%	2234
	11th to 20th	Night	20% 7% 3 7% 4 3 4 4 5% 6% 37%	2312
	21st to end	Night	21% 8% 3 8% 5% 5% 4 3 5% 6% 32%	2717
November	1st to 10th	Night	18% 9% 3 8% 5% 5% 4 4 6% 7% 33%	2537
	11th to 20th	Night	17% 10% 3 8% 5% 4 4 3 5% 6% 35%	2705
	21st to end	Night	20% 13% 4 8% 5% 4 4 2 5% 6% 30%	2800
December	1st to 10th	Night	16% 14% 5% 10% 6% 6% 6% 4 6% 6% 22%	4580
	11th to 20th	Night	23% 13% 4 8% 5% 4 4 3 4 4 29%	5208
	21st to end	Night	24% 16% 5% 8% 4 3 3 2 4 4 27%	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	64% 4 8% 18% 4 1	3598
	11th to 20th	Day	59% 6% 9% 17% 7% 2	3600
	21st to end	Day	57% 5% 9% 16% 12% 1	3960
February	1st to 10th	Day	59% 4 8% 18% 8% 2	1765
	11th to 20th	Day	58% 5% 11% 16% 10% 1	1847
	21st to end	Day	60% 3 8% 16% 10% 3	1650
March	1st to 10th	Day	63% 4 6% 13% 11% 4	4479
	11th to 20th	Day	50% 5% 17% 14% 12% 2	4739
	21st to end	Day	53% 3 6% 17% 19% 2	5942
April	1st to 10th	Day	54% 5% 7% 18% 13% 3	2400
	11th to 20th	Day	49% 5% 7% 22% 15% 2	2374
	21st to end	Day	54% 4 8% 18% 13% 3	2553
May	1st to 10th	Day	62% 4 7% 18% 8% 1	6344
	11th to 20th	Day	52% 6% 15% 17% 9% 2	6322
	21st to end	Day	52% 5% 11% 19% 12% 1	6949
June	1st to 10th	Day	52% 6% 9% 19% 12% 2	2800
	11th to 20th	Day	44% 7% 11% 23% 13% 3	2800
	21st to end	Day	53% 7% 11% 19% 9% 1	2800
July	1st to 10th	Day	45% 5% 15% 26% 10%	4510
	11th to 20th	Day	42% 5% 16% 29% 8%	4505
	21st to end	Day	37% 6% 13% 33% 11%	4661
August	1st to 10th	Day	47% 5% 17% 21% 9%	4409
	11th to 20th	Day	43% 5% 17% 28% 6%	4046
	21st to end	Day	42% 4 17% 22% 14% 1	4180
September	1st to 10th	Day	38% 7% 14% 29% 13%	2280
	11th to 20th	Day	35% 5% 14% 31% 13% 1	2213
	21st to end	Day	42% 5% 14% 27% 12% 1	2090
October	1st to 10th	Day	48% 3 12% 27% 9%	3229
	11th to 20th	Day	45% 4 16% 27% 8%	3083
	21st to end	Day	44% 4 21% 21% 10% 1	3081
November	1st to 10th	Day	47% 7% 14% 22% 10% 1	1761
	11th to 20th	Day	52% 6% 12% 18% 12% 1	1694
	21st to end	Day	59% 6% 14% 15% 6% 1	1600
December	1st to 10th	Day	69% 3 9% 15% 3	2600
	11th to 20th	Day	59% 3 9% 18% 11%	2986
	21st to end	Day	62% 3 9% 17% 8%	3960
January	1st to 10th	Night	66% 5% 11% 14% 4	6349
	11th to 20th	Night	62% 5% 11% 17% 5% 1	6360
	21st to end	Night	59% 5% 9% 11% 14% 1	6996
February	1st to 10th	Night	58% 4 10% 19% 9% 1	2635
	11th to 20th	Night	53% 5% 10% 21% 10% 1	2450
	21st to end	Night	55% 3 10% 18% 12% 2	1980
March	1st to 10th	Night	59% 4 7% 13% 12% 4	5374
	11th to 20th	Night	51% 5% 14% 16% 12% 3	5220
	21st to end	Night	53% 3 6% 22% 13% 3	4976
April	1st to 10th	Night	52% 4 7% 20% 15% 2	2000
	11th to 20th	Night	49% 4 8% 22% 15% 2	1975
	21st to end	Night	49% 4 8% 21% 14% 4	1846
May	1st to 10th	Night	60% 4 9% 18% 7% 2	3656
	11th to 20th	Night	50% 5% 13% 19% 11% 2	3576
	21st to end	Night	53% 5% 10% 17% 13% 1	3927
June	1st to 10th	Night	49% 6% 11% 21% 14% 1	1600
	11th to 20th	Night	43% 6% 11% 23% 15% 3	1600
	21st to end	Night	46% 7% 12% 20% 14% 1	1600
July	1st to 10th	Night	45% 5% 17% 21% 13% 1	2560
	11th to 20th	Night	40% 3 19% 31% 7%	2552
	21st to end	Night	37% 4 19% 26% 14%	2651
August	1st to 10th	Night	45% 5% 13% 28% 9%	2496
	11th to 20th	Night	43% 3 19% 27% 8%	2815
	21st to end	Night	43% 4 15% 23% 14% 1	3476
September	1st to 10th	Night	36% 6% 15% 26% 16% 1	1900
	11th to 20th	Night	34% 5% 14% 34% 12% 1	1966
	21st to end	Night	39% 5% 13% 29% 15%	2090
October	1st to 10th	Night	45% 2 14% 27% 11% 1	3728
	11th to 20th	Night	43% 3 13% 30% 11%	3835
	21st to end	Night	45% 3 19% 18% 13% 2	4467
November	1st to 10th	Night	50% 6% 12% 22% 9% 1	2537
	11th to 20th	Night	51% 4 12% 20% 11% 1	2705
	21st to end	Night	57% 5% 12% 18% 8% 1	2800
December	1st to 10th	Night	64% 3 13% 15% 4	4580
	11th to 20th	Night	60% 4 8% 16% 11% 1	5208
	21st to end	Night	63% 2 7% 15% 13%	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	21% 17% 39% 19% 5%	200
	11th to 20th	Day	26% 18% 37% 15% 4 1	200
	21st to end	Day	19% 22% 36% 19% 4	220
February	1st to 10th	Day	28% 25% 36% 10% 1	283
	11th to 20th	Day	23% 23% 41% 11% 2	385
	21st to end	Day	27% 19% 33% 18% 3	414
March	1st to 10th	Day	27% 18% 33% 18% 4	500
	11th to 20th	Day	21% 22% 35% 17% 4 1	500
	21st to end	Day	26% 21% 30% 14% 9% 1	550
April	1st to 10th	Day	28% 18% 31% 16% 6% 1	500
	11th to 20th	Day	32% 20% 23% 17% 8% 1	492
	21st to end	Day	29% 18% 30% 16% 6% 1	500
May	1st to 10th	Day	26% 15% 35% 18% 5% 1	503
	11th to 20th	Day	22% 15% 33% 21% 7% 2	527
	21st to end	Day	21% 18% 31% 22% 7% 1	573
June	1st to 10th	Day	23% 16% 33% 20% 7% 1	530
	11th to 20th	Day	18% 16% 31% 24% 9% 2	530
	21st to end	Day	24% 12% 31% 23% 8% 2	530
July	1st to 10th	Day	14% 10% 34% 28% 12% 3	525
	11th to 20th	Day	14% 8% 35% 30% 11% 2	524
	21st to end	Day	13% 8% 31% 32% 13% 2	532
August	1st to 10th	Day	14% 9% 26% 33% 15% 3	486
	11th to 20th	Day	13% 7% 25% 33% 15% 8%	479
	21st to end	Day	16% 11% 27% 25% 14% 7%	539
September	1st to 10th	Day	15% 8% 34% 24% 15% 5%	490
	11th to 20th	Day	12% 9% 26% 27% 18% 8%	490
	21st to end	Day	20% 11% 27% 24% 13% 4	490
October	1st to 10th	Day	24% 13% 27% 22% 12% 1	490
	11th to 20th	Day	21% 15% 33% 21% 9% 1	473
	21st to end	Day	30% 14% 31% 20% 5%	429
November	1st to 10th	Day	26% 16% 31% 19% 6% 1	395
	11th to 20th	Day	22% 19% 36% 18% 5%	294
	21st to end	Day	28% 21% 32% 15% 4 1	200
December	1st to 10th	Day	26% 15% 27% 26% 6% 2	200
	11th to 20th	Day	26% 23% 37% 14% 1 1	200
	21st to end	Day	30% 21% 26% 15% 6% 1	220
January	1st to 10th	Night	24% 13% 35% 24% 5%	800
	11th to 20th	Night	23% 14% 34% 22% 6%	800
	21st to end	Night	16% 12% 40% 26% 6%	880
February	1st to 10th	Night	18% 14% 41% 23% 3 1	800
	11th to 20th	Night	20% 15% 42% 19% 4	783
	21st to end	Night	22% 13% 34% 28% 2	660
March	1st to 10th	Night	24% 14% 33% 25% 4	800
	11th to 20th	Night	24% 14% 34% 23% 5%	800
	21st to end	Night	22% 13% 35% 24% 6%	880
April	1st to 10th	Night	27% 14% 30% 25% 5%	800
	11th to 20th	Night	25% 13% 33% 24% 5% 1	791
	21st to end	Night	27% 12% 35% 19% 7%	646
May	1st to 10th	Night	25% 9% 33% 24% 6% 2	430
	11th to 20th	Night	23% 9% 30% 29% 9%	394
	21st to end	Night	19% 8% 39% 27% 8%	433
June	1st to 10th	Night	25% 7% 32% 30% 8%	400
	11th to 20th	Night	21% 8% 28% 33% 10%	400
	21st to end	Night	22% 6% 27% 31% 14%	400
July	1st to 10th	Night	10% 6% 33% 37% 14% 1	390
	11th to 20th	Night	14% 4 23% 44% 15%	388
	21st to end	Night	13% 4 27% 40% 14% 2	416
August	1st to 10th	Night	15% 3 20% 44% 17% 1	378
	11th to 20th	Night	13% 4 23% 34% 23% 3	554
	21st to end	Night	15% 6% 26% 33% 18% 2	836
September	1st to 10th	Night	13% 5% 29% 39% 13% 1	760
	11th to 20th	Night	16% 6% 23% 32% 22% 2	760
	21st to end	Night	19% 7% 25% 30% 16% 3	760
October	1st to 10th	Night	21% 10% 27% 32% 11% 1	760
	11th to 20th	Night	23% 10% 30% 27% 8% 1	760
	21st to end	Night	26% 11% 32% 25% 6%	836
November	1st to 10th	Night	23% 14% 31% 25% 7% 1	780
	11th to 20th	Night	23% 12% 33% 22% 8% 1	800
	21st to end	Night	29% 14% 30% 20% 6%	800
December	1st to 10th	Night	27% 12% 34% 22% 5%	800
	11th to 20th	Night	27% 17% 31% 20% 5% 1	800
	21st to end	Night	33% 13% 30% 20% 4	880

Page generated at 2025-07-18 01:10:02. Version ac07

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