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 2024-11-04.

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% 33%	101563
	Night	17% 10% 4 8% 5% 4 4 3 5% 6% 34%	97480
Transparency	Day	49% 5% 13% 21% 10% 1	105026
	Night	50% 5% 12% 21% 10% 1	102106
Seeing	Day	22% 15% 31% 22% 9% 2	14540
	Night	22% 11% 32% 27% 9% 1	23491

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% 15% 6% 13% 6% 4 4 3 5% 4 24%	2517
	11th to 20th	Day	13% 13% 5% 12% 6% 4 4 4 5% 6% 27%	2520
	21st to end	Day	12% 17% 5% 9% 6% 5% 6% 4 5% 5% 24%	2772
February	1st to 10th	Day	14% 15% 4 11% 6% 6% 5% 4 4 6% 27%	1676
	11th to 20th	Day	13% 13% 5% 11% 6% 6% 5% 4 6% 6% 27%	1743
	21st to end	Day	17% 15% 5% 10% 7% 4 5% 3 5% 4 27%	1570
March	1st to 10th	Day	19% 13% 4 9% 6% 5% 4 3 4 5% 27%	3116
	11th to 20th	Day	12% 17% 4 11% 6% 4 4 3 4 6% 29%	3309
	21st to end	Day	15% 8% 3 8% 5% 5% 5% 3 5% 6% 39%	4152
April	1st to 10th	Day	21% 12% 3 8% 4 5% 4 3 4 5% 32%	2280
	11th to 20th	Day	21% 8% 2 5% 4 4 4 4 5% 6% 36%	2254
	21st to end	Day	21% 10% 4 7% 5% 5% 4 3 5% 5% 33%	2425
May	1st to 10th	Day	20% 9% 3 8% 5% 5% 5% 3 5% 7% 30%	4413
	11th to 20th	Day	19% 7% 3 8% 5% 5% 5% 4 6% 8% 32%	4398
	21st to end	Day	16% 6% 2 7% 5% 5% 5% 4 6% 8% 37%	4837
June	1st to 10th	Day	21% 7% 2 7% 6% 5% 5% 4 6% 7% 30%	2660
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 5% 6% 7% 36%	2660
	21st to end	Day	20% 8% 3 8% 6% 6% 6% 4 6% 6% 28%	2660
July	1st to 10th	Day	12% 6% 2 7% 6% 6% 6% 5% 7% 9% 35%	4440
	11th to 20th	Day	14% 5% 2 5% 5% 5% 6% 6% 7% 9% 36%	4440
	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%	1698
	11th to 20th	Day	18% 11% 3 8% 5% 5% 4 4 6% 7% 30%	1610
	21st to end	Day	20% 11% 3 9% 5% 5% 5% 4 5% 7% 26%	1520
December	1st to 10th	Day	21% 15% 4 10% 6% 6% 5% 3 4 4 22%	1520
	11th to 20th	Day	20% 15% 4 8% 5% 4 3 3 5% 5% 28%	1906
	21st to end	Day	26% 17% 5% 10% 4 4 3 3 3 4 21%	2772
January	1st to 10th	Night	15% 15% 5% 11% 6% 5% 4 3 5% 5% 25%	4429
	11th to 20th	Night	11% 13% 5% 12% 6% 5% 5% 3 5% 6% 28%	4440
	21st to end	Night	13% 16% 6% 11% 6% 5% 5% 4 4 5% 25%	4884
February	1st to 10th	Night	13% 13% 4 12% 6% 5% 5% 4 6% 6% 27%	2504
	11th to 20th	Night	12% 11% 4 9% 6% 5% 5% 4 5% 6% 32%	2323
	21st to end	Night	14% 13% 4 9% 6% 5% 4 3 5% 5% 32%	1884
March	1st to 10th	Night	20% 12% 4 7% 4 4 4 3 4 5% 33%	3724
	11th to 20th	Night	15% 19% 4 8% 5% 5% 4 3 4 5% 29%	3649
	21st to end	Night	13% 9% 3 9% 6% 5% 4 3 4 4 40%	3480
April	1st to 10th	Night	22% 9% 3 7% 5% 3 4 4 5% 6% 32%	1900
	11th to 20th	Night	20% 7% 2 7% 6% 4 3 3 5% 6% 37%	1875
	21st to end	Night	21% 8% 3 6% 3 4 5% 3 6% 5% 36%	1754
May	1st to 10th	Night	21% 9% 3 8% 5% 4 4 3 5% 6% 32%	2556
	11th to 20th	Night	22% 7% 2 5% 4 3 4 3 5% 6% 38%	2495
	21st to end	Night	17% 7% 2 7% 5% 4 4 4 6% 7% 37%	2738
June	1st to 10th	Night	20% 7% 3 6% 4 4 4 5% 6% 8% 33%	1520
	11th to 20th	Night	17% 8% 2 6% 4 4 4 4 5% 7% 40%	1520
	21st to end	Night	20% 6% 2 6% 6% 3 5% 4 5% 7% 36%	1520
July	1st to 10th	Night	12% 6% 3 8% 5% 5% 6% 5% 6% 7% 37%	2520
	11th to 20th	Night	13% 6% 2 5% 4 4 4 4 5% 7% 44%	2520
	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 7% 5% 4 4 4 6% 7% 34%	2453
	11th to 20th	Night	17% 10% 3 8% 5% 4 4 3 5% 6% 34%	2569
	21st to end	Night	20% 13% 4 7% 5% 4 3 2 5% 6% 30%	2660
December	1st to 10th	Night	18% 14% 5% 9% 5% 6% 5% 3 5% 6% 23%	2660
	11th to 20th	Night	22% 14% 4 7% 5% 4 4 3 4 5% 28%	3288
	21st to end	Night	27% 16% 5% 9% 4 3 3 2 4 4 23%	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	62% 6% 11% 15% 5% 1	2518
	11th to 20th	Day	55% 8% 11% 17% 8% 1	2520
	21st to end	Day	60% 7% 12% 14% 7% 1	2772
February	1st to 10th	Day	59% 4 8% 19% 7% 2	1676
	11th to 20th	Day	57% 5% 11% 16% 10% 1	1752
	21st to end	Day	60% 4 9% 15% 10% 3	1570
March	1st to 10th	Day	60% 5% 8% 17% 9% 1	3119
	11th to 20th	Day	56% 5% 11% 13% 12% 3	3309
	21st to end	Day	45% 5% 8% 20% 19% 3	4152
April	1st to 10th	Day	55% 5% 7% 19% 12% 3	2280
	11th to 20th	Day	48% 5% 8% 23% 14% 2	2254
	21st to end	Day	54% 4 8% 18% 12% 4	2425
May	1st to 10th	Day	53% 6% 8% 22% 10% 2	4427
	11th to 20th	Day	49% 8% 17% 16% 9% 2	4402
	21st to end	Day	43% 7% 11% 23% 15% 1	4837
June	1st to 10th	Day	52% 6% 10% 19% 12% 2	2660
	11th to 20th	Day	44% 7% 11% 22% 13% 3	2660
	21st to end	Day	54% 8% 11% 18% 9% 1	2660
July	1st to 10th	Day	44% 5% 15% 26% 10%	4370
	11th to 20th	Day	42% 5% 16% 28% 8%	4365
	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	46% 7% 14% 21% 10% 1	1698
	11th to 20th	Day	53% 6% 12% 17% 11% 1	1610
	21st to end	Day	57% 7% 14% 15% 6% 1	1520
December	1st to 10th	Day	65% 5% 11% 13% 5%	1520
	11th to 20th	Day	59% 5% 11% 18% 8%	1906
	21st to end	Day	67% 4 9% 13% 6%	2772
January	1st to 10th	Night	59% 7% 15% 14% 5%	4429
	11th to 20th	Night	56% 7% 14% 18% 5% 1	4440
	21st to end	Night	60% 8% 12% 12% 7% 1	4884
February	1st to 10th	Night	58% 4 10% 19% 8% 1	2504
	11th to 20th	Night	52% 6% 10% 21% 10% 1	2325
	21st to end	Night	55% 3 10% 17% 13% 2	1884
March	1st to 10th	Night	54% 6% 10% 17% 10% 4	3734
	11th to 20th	Night	57% 5% 9% 14% 13% 2	3650
	21st to end	Night	47% 5% 6% 22% 15% 4	3480
April	1st to 10th	Night	52% 4 8% 20% 15% 2	1900
	11th to 20th	Night	49% 4 7% 23% 15% 2	1875
	21st to end	Night	49% 5% 8% 20% 14% 4	1754
May	1st to 10th	Night	52% 6% 10% 20% 9% 3	2562
	11th to 20th	Night	46% 6% 15% 18% 12% 2	2496
	21st to end	Night	45% 7% 10% 20% 16% 2	2739
June	1st to 10th	Night	48% 6% 11% 21% 13% 1	1520
	11th to 20th	Night	43% 6% 11% 23% 15% 3	1520
	21st to end	Night	47% 7% 12% 20% 13% 1	1520
July	1st to 10th	Night	45% 5% 16% 20% 13% 1	2480
	11th to 20th	Night	40% 3 19% 31% 7%	2472
	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% 13% 22% 9% 1	2453
	11th to 20th	Night	51% 4 13% 20% 10% 1	2569
	21st to end	Night	56% 5% 12% 18% 8% 1	2660
December	1st to 10th	Night	63% 5% 12% 15% 5%	2660
	11th to 20th	Night	59% 5% 9% 19% 7% 1	3288
	21st to end	Night	66% 3 8% 17% 6%	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	18% 18% 37% 21% 5%	180
	11th to 20th	Day	26% 19% 36% 15% 4 1	180
	21st to end	Day	20% 21% 35% 19% 5% 1	198
February	1st to 10th	Day	29% 24% 35% 11% 1	254
	11th to 20th	Day	21% 23% 42% 12% 2	350
	21st to end	Day	27% 20% 32% 18% 3	382
March	1st to 10th	Day	26% 17% 33% 19% 5%	460
	11th to 20th	Day	22% 23% 33% 17% 4 1	460
	21st to end	Day	26% 21% 30% 14% 8% 1	506
April	1st to 10th	Day	28% 17% 32% 17% 6% 1	460
	11th to 20th	Day	31% 20% 23% 17% 8% 1	452
	21st to end	Day	29% 17% 30% 17% 6% 2	460
May	1st to 10th	Day	24% 16% 35% 18% 5% 1	463
	11th to 20th	Day	21% 15% 33% 23% 6% 2	487
	21st to end	Day	19% 19% 32% 22% 7% 1	529
June	1st to 10th	Day	23% 16% 31% 20% 8% 1	490
	11th to 20th	Day	18% 16% 30% 25% 10% 2	490
	21st to end	Day	25% 12% 28% 24% 9% 2	490
July	1st to 10th	Day	13% 10% 33% 28% 13% 3	485
	11th to 20th	Day	14% 9% 34% 30% 11% 2	484
	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% 17% 30% 20% 6% 1	374
	11th to 20th	Day	23% 19% 36% 17% 5%	270
	21st to end	Day	26% 22% 32% 16% 4 1	180
December	1st to 10th	Day	27% 16% 27% 24% 6% 1	180
	11th to 20th	Day	26% 22% 37% 13% 1 1	180
	21st to end	Day	32% 22% 27% 14% 5% 1	198
January	1st to 10th	Night	24% 13% 34% 24% 5%	760
	11th to 20th	Night	24% 14% 34% 22% 5%	760
	21st to end	Night	16% 12% 40% 25% 6%	836
February	1st to 10th	Night	18% 14% 40% 23% 4 1	760
	11th to 20th	Night	19% 15% 42% 20% 4	743
	21st to end	Night	22% 14% 34% 27% 2	628
March	1st to 10th	Night	24% 13% 34% 25% 4	760
	11th to 20th	Night	24% 15% 33% 22% 5%	760
	21st to end	Night	21% 12% 36% 24% 6%	836
April	1st to 10th	Night	26% 14% 30% 25% 5%	760
	11th to 20th	Night	24% 13% 33% 24% 5% 1	751
	21st to end	Night	26% 13% 35% 19% 7%	614
May	1st to 10th	Night	24% 9% 34% 24% 6% 2	409
	11th to 20th	Night	23% 9% 30% 30% 8%	374
	21st to end	Night	19% 8% 40% 26% 8%	411
June	1st to 10th	Night	24% 6% 31% 30% 8%	380
	11th to 20th	Night	21% 8% 28% 32% 11%	380
	21st to end	Night	22% 6% 27% 31% 14%	380
July	1st to 10th	Night	10% 6% 33% 36% 14% 1	370
	11th to 20th	Night	13% 4 24% 43% 15%	368
	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% 13% 31% 25% 7% 1	755
	11th to 20th	Night	24% 13% 33% 21% 8% 1	760
	21st to end	Night	29% 14% 30% 20% 6%	760
December	1st to 10th	Night	27% 12% 34% 21% 5%	760
	11th to 20th	Night	27% 17% 31% 19% 5% 1	760
	21st to end	Night	34% 13% 31% 18% 4	836

Page generated at 2024-11-01 22:47:35. Version ac07

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