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 2024-04-10.

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% 6% 3 5% 5% 5% 7% 33%	82934
	Night	17% 10% 4 7% 6% 3 4 4 5% 6% 34%	85850
Transparency	Day	51% 6% 11% 20% 11% 1	82639
	Night	51% 6% 12% 20% 10% 1	85679
Seeing	Day	22% 15% 31% 21% 8% 2	13725
	Night	22% 11% 32% 26% 8% 1	22880

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% 12% 7% 3 4 4 5% 5% 24%	2517
	11th to 20th	Day	14% 13% 5% 11% 8% 3 4 5% 4 6% 27%	2520
	21st to end	Day	12% 17% 5% 9% 6% 4 6% 5% 5% 5% 25%	2772
February	1st to 10th	Day	14% 14% 4 10% 7% 5% 5% 4 4 6% 27%	1676
	11th to 20th	Day	13% 12% 5% 9% 7% 5% 5% 4 6% 6% 28%	1743
	21st to end	Day	17% 14% 6% 9% 8% 3 5% 4 5% 4 27%	1570
March	1st to 10th	Day	19% 12% 4 8% 8% 4 5% 4 4 5% 27%	3116
	11th to 20th	Day	12% 17% 5% 9% 7% 3 5% 4 4 6% 29%	3309
	21st to end	Day	15% 8% 4 7% 5% 4 5% 4 5% 6% 39%	4152
April	1st to 10th	Day	21% 10% 4 6% 5% 3 4 4 4 5% 33%	2270
	11th to 20th	Day	21% 7% 3 4 5% 3 4 5% 5% 6% 37%	2134
	21st to end	Day	22% 9% 4 6% 6% 3 4 4 4 5% 32%	2297
May	1st to 10th	Day	20% 7% 3 7% 6% 3 5% 4 5% 6% 33%	2507
	11th to 20th	Day	20% 7% 3 5% 6% 3 5% 4 5% 8% 35%	2478
	21st to end	Day	17% 6% 3 6% 5% 4 5% 5% 6% 7% 35%	2725
June	1st to 10th	Day	22% 7% 3 5% 7% 3 5% 5% 6% 8% 30%	2520
	11th to 20th	Day	15% 6% 2 6% 6% 3 6% 6% 6% 7% 36%	2520
	21st to end	Day	20% 8% 3 7% 7% 4 7% 5% 6% 6% 28%	2520
July	1st to 10th	Day	11% 5% 2 5% 5% 4 7% 6% 6% 8% 40%	2520
	11th to 20th	Day	14% 5% 2 5% 6% 4 6% 7% 7% 10% 35%	2520
	21st to end	Day	12% 5% 3 5% 6% 4 6% 6% 7% 9% 37%	2744
August	1st to 10th	Day	12% 6% 2 6% 7% 4 6% 6% 6% 9% 36%	2506
	11th to 20th	Day	10% 6% 2 6% 6% 4 6% 7% 6% 8% 38%	2294
	21st to end	Day	14% 5% 2 5% 6% 4 5% 5% 5% 9% 43%	2376
September	1st to 10th	Day	14% 5% 2 4 5% 3 4 6% 5% 9% 41%	2160
	11th to 20th	Day	14% 4 2 5% 4 3 4 3 5% 6% 49%	2097
	21st to end	Day	17% 6% 2 5% 4 3 4 4 6% 7% 42%	1980
October	1st to 10th	Day	20% 7% 2 6% 5% 3 4 4 5% 7% 37%	1841
	11th to 20th	Day	20% 8% 3 7% 8% 4 5% 5% 5% 6% 28%	1769
	21st to end	Day	24% 9% 4 6% 6% 3 4 4 5% 5% 29%	1782
November	1st to 10th	Day	15% 8% 4 6% 6% 4 5% 5% 6% 7% 35%	1671
	11th to 20th	Day	18% 10% 4 7% 6% 4 4 5% 6% 7% 30%	1610
	21st to end	Day	21% 11% 3 8% 6% 4 5% 5% 5% 7% 26%	1520
December	1st to 10th	Day	22% 13% 5% 8% 7% 4 6% 4 4 4 22%	1520
	11th to 20th	Day	20% 14% 4 7% 5% 3 4 4 4 6% 28%	1906
	21st to end	Day	26% 16% 5% 9% 5% 2 3 4 3 4 22%	2772
January	1st to 10th	Night	15% 14% 6% 9% 7% 4 4 4 5% 5% 26%	4429
	11th to 20th	Night	11% 12% 6% 10% 8% 4 5% 4 5% 6% 28%	4440
	21st to end	Night	13% 15% 6% 10% 7% 4 5% 5% 4 5% 25%	4884
February	1st to 10th	Night	13% 12% 5% 10% 8% 4 6% 5% 5% 6% 27%	2504
	11th to 20th	Night	13% 11% 4 8% 6% 4 5% 6% 5% 6% 32%	2323
	21st to end	Night	15% 12% 4 8% 7% 3 5% 4 5% 5% 32%	1884
March	1st to 10th	Night	20% 11% 5% 7% 5% 3 4 4 4 5% 33%	3724
	11th to 20th	Night	15% 18% 5% 8% 5% 3 4 4 4 5% 29%	3649
	21st to end	Night	13% 9% 4 8% 7% 4 4 4 4 4 40%	3480
April	1st to 10th	Night	23% 7% 4 7% 5% 3 4 4 5% 6% 33%	1900
	11th to 20th	Night	20% 6% 3 6% 6% 3 3 4 5% 6% 38%	1775
	21st to end	Night	21% 8% 4 5% 3 3 4 4 5% 6% 36%	1662
May	1st to 10th	Night	21% 7% 3 6% 6% 3 4 5% 4 6% 36%	1468
	11th to 20th	Night	20% 7% 2 5% 4 3 4 4 5% 5% 40%	1415
	21st to end	Night	17% 5% 3 5% 6% 3 5% 4 5% 7% 42%	1550
June	1st to 10th	Night	21% 6% 3 6% 4 3 4 6% 6% 9% 33%	1440
	11th to 20th	Night	17% 8% 3 5% 4 3 4 5% 5% 7% 40%	1440
	21st to end	Night	18% 5% 3 5% 6% 2 5% 6% 5% 7% 37%	1440
July	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 6% 7% 8% 45%	1440
	11th to 20th	Night	11% 6% 3 4 6% 4 5% 5% 6% 9% 42%	1440
	21st to end	Night	12% 4 3 5% 5% 3 5% 5% 6% 9% 43%	1574
August	1st to 10th	Night	12% 4 3 6% 4 3 5% 5% 6% 9% 43%	1432
	11th to 20th	Night	11% 6% 2 5% 5% 3 4 5% 5% 6% 46%	1587
	21st to end	Night	14% 5% 2 4 5% 3 4 4 6% 7% 45%	1980
September	1st to 10th	Night	11% 5% 3 5% 5% 3 5% 6% 5% 7% 46%	1800
	11th to 20th	Night	14% 5% 2 4 3 2 3 4 4 7% 50%	1862
	21st to end	Night	17% 4 2 4 4 3 4 4 5% 6% 47%	1980
October	1st to 10th	Night	19% 7% 3 5% 4 4 4 4 4 6% 41%	2116
	11th to 20th	Night	21% 7% 3 6% 4 3 4 4 4 6% 36%	2190
	21st to end	Night	22% 8% 3 7% 6% 4 4 4 5% 5% 32%	2574
November	1st to 10th	Night	18% 8% 3 6% 6% 3 4 5% 5% 7% 33%	2407
	11th to 20th	Night	18% 9% 4 7% 6% 3 5% 4 5% 6% 34%	2569
	21st to end	Night	20% 12% 5% 6% 6% 3 4 3 5% 6% 30%	2660
December	1st to 10th	Night	19% 14% 6% 8% 6% 5% 5% 4 5% 6% 23%	2660
	11th to 20th	Night	22% 13% 5% 7% 6% 3 4 4 4 5% 28%	3288
	21st to end	Night	27% 16% 5% 8% 5% 2 3 3 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	54% 5% 7% 19% 12% 3	2270
	11th to 20th	Day	48% 5% 8% 23% 15% 2	2134
	21st to end	Day	55% 4 8% 17% 12% 4	2297
May	1st to 10th	Day	51% 5% 7% 20% 14% 3	2507
	11th to 20th	Day	47% 6% 10% 19% 16% 3	2482
	21st to end	Day	46% 6% 11% 20% 14% 2	2725
June	1st to 10th	Day	52% 6% 10% 19% 12% 2	2520
	11th to 20th	Day	44% 7% 10% 22% 13% 3	2520
	21st to end	Day	53% 8% 12% 17% 9% 1	2520
July	1st to 10th	Day	39% 8% 14% 27% 12% 1	2450
	11th to 20th	Day	40% 9% 15% 26% 11%	2445
	21st to end	Day	42% 9% 15% 25% 9%	2591
August	1st to 10th	Day	43% 8% 17% 23% 9%	2492
	11th to 20th	Day	40% 9% 17% 25% 10% 1	2294
	21st to end	Day	39% 6% 16% 24% 14% 1	2376
September	1st to 10th	Day	38% 7% 14% 27% 14%	2160
	11th to 20th	Day	36% 5% 14% 31% 14% 1	2097
	21st to end	Day	42% 5% 14% 27% 11% 1	1980
October	1st to 10th	Day	48% 5% 12% 23% 12% 1	1841
	11th to 20th	Day	55% 7% 12% 19% 7%	1769
	21st to end	Day	56% 5% 12% 17% 8% 1	1782
November	1st to 10th	Day	46% 7% 14% 21% 10% 1	1671
	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	48% 4 7% 23% 16% 2	1775
	21st to end	Night	50% 4 8% 20% 13% 4	1662
May	1st to 10th	Night	51% 4 7% 18% 15% 5%	1468
	11th to 20th	Night	46% 5% 8% 19% 18% 4	1416
	21st to end	Night	43% 6% 11% 20% 16% 3	1551
June	1st to 10th	Night	48% 6% 11% 22% 12% 1	1440
	11th to 20th	Night	44% 6% 10% 23% 14% 3	1440
	21st to end	Night	45% 8% 12% 21% 14%	1440
July	1st to 10th	Night	33% 9% 15% 25% 16% 1	1400
	11th to 20th	Night	38% 6% 16% 30% 11%	1392
	21st to end	Night	37% 7% 18% 25% 12%	1486
August	1st to 10th	Night	37% 8% 18% 26% 11%	1422
	11th to 20th	Night	37% 6% 18% 26% 12%	1587
	21st to end	Night	36% 7% 16% 28% 13%	1980
September	1st to 10th	Night	37% 7% 15% 26% 15% 1	1800
	11th to 20th	Night	35% 5% 14% 33% 12% 1	1862
	21st to end	Night	38% 5% 13% 30% 14%	1980
October	1st to 10th	Night	46% 4 10% 25% 14% 1	2116
	11th to 20th	Night	49% 5% 13% 24% 9%	2190
	21st to end	Night	54% 5% 13% 18% 9% 1	2574
November	1st to 10th	Night	50% 6% 12% 22% 9% 1	2407
	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% 16% 6% 1	457
	11th to 20th	Day	30% 19% 23% 18% 8% 1	412
	21st to end	Day	29% 16% 30% 16% 6% 1	420
May	1st to 10th	Day	25% 16% 35% 18% 5% 1	423
	11th to 20th	Day	23% 15% 34% 21% 6% 2	447
	21st to end	Day	18% 20% 33% 21% 6% 1	485
June	1st to 10th	Day	25% 16% 32% 18% 8% 1	450
	11th to 20th	Day	19% 16% 29% 24% 10% 2	450
	21st to end	Day	24% 12% 27% 26% 9% 2	450
July	1st to 10th	Day	13% 9% 32% 29% 14% 3	445
	11th to 20th	Day	14% 8% 33% 30% 12% 2	444
	21st to end	Day	14% 8% 31% 32% 13% 2	488
August	1st to 10th	Day	13% 9% 26% 33% 15% 3	446
	11th to 20th	Day	11% 7% 26% 34% 14% 8%	439
	21st to end	Day	16% 12% 27% 24% 14% 7%	495
September	1st to 10th	Day	15% 7% 34% 23% 15% 5%	450
	11th to 20th	Day	13% 9% 28% 27% 16% 6%	450
	21st to end	Day	20% 11% 27% 24% 13% 4	450
October	1st to 10th	Day	25% 13% 27% 21% 12% 1	450
	11th to 20th	Day	21% 16% 32% 21% 9% 1	435
	21st to end	Day	31% 14% 31% 20% 4	396
November	1st to 10th	Day	26% 17% 30% 20% 6% 1	365
	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% 25% 5% 1	711
	21st to end	Night	27% 12% 34% 19% 7% 1	582
May	1st to 10th	Night	23% 10% 34% 24% 7% 2	388
	11th to 20th	Night	23% 10% 31% 29% 8%	354
	21st to end	Night	19% 7% 40% 26% 8%	389
June	1st to 10th	Night	26% 6% 33% 28% 8%	360
	11th to 20th	Night	22% 7% 29% 31% 11%	360
	21st to end	Night	21% 6% 27% 30% 15%	360
July	1st to 10th	Night	9% 7% 34% 35% 15% 1	350
	11th to 20th	Night	13% 4 25% 43% 15%	348
	21st to end	Night	13% 4 27% 40% 14% 2	394
August	1st to 10th	Night	15% 3 20% 43% 17% 1	358
	11th to 20th	Night	12% 4 24% 34% 23% 3	523
	21st to end	Night	14% 6% 27% 32% 18% 2	792
September	1st to 10th	Night	13% 5% 29% 38% 13% 1	720
	11th to 20th	Night	17% 6% 24% 32% 19% 2	720
	21st to end	Night	19% 7% 26% 30% 16% 3	720
October	1st to 10th	Night	21% 10% 28% 31% 10% 1	720
	11th to 20th	Night	23% 10% 30% 27% 8% 1	720
	21st to end	Night	27% 11% 32% 24% 6%	792
November	1st to 10th	Night	23% 13% 31% 24% 7% 1	740
	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 2024-04-07 09:28:09. Version ac07

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