Sainte-Julie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sainte-Julie clear sky chart from 2005-11-06 to 2024-08-15.

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% 7% 32%	95605
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 31%	93131
Transparency	Day	50% 6% 12% 21% 10% 1	95324
	Night	54% 5% 11% 19% 10% 1	92966
Seeing	Day	22% 11% 28% 24% 12% 3	14283
	Night	24% 9% 29% 28% 9% 1	23190

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	18% 16% 6% 13% 6% 5% 4 3 3 4 23%	2517
	11th to 20th	Day	15% 13% 5% 11% 6% 5% 4 3 5% 7% 26%	2520
	21st to end	Day	15% 16% 4 10% 6% 5% 5% 4 5% 6% 24%	2772
February	1st to 10th	Day	17% 17% 4 10% 5% 5% 4 4 5% 6% 25%	1647
	11th to 20th	Day	14% 13% 5% 12% 7% 5% 4 4 5% 5% 26%	1777
	21st to end	Day	18% 15% 4 9% 6% 4 3 4 4 5% 28%	1570
March	1st to 10th	Day	19% 12% 4 11% 7% 5% 5% 3 4 5% 26%	3116
	11th to 20th	Day	15% 16% 5% 11% 5% 5% 4 3 5% 5% 26%	3270
	21st to end	Day	15% 10% 4 9% 5% 4 4 3 4 5% 36%	4166
April	1st to 10th	Day	22% 12% 4 8% 5% 4 4 3 4 5% 30%	2280
	11th to 20th	Day	21% 9% 2 7% 4 4 4 3 5% 6% 36%	2254
	21st to end	Day	22% 9% 3 7% 5% 4 4 3 4 6% 32%	2451
May	1st to 10th	Day	20% 10% 3 8% 5% 4 4 4 6% 7% 30%	4327
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 8% 30%	4398
	21st to end	Day	15% 7% 2 7% 5% 4 6% 5% 7% 9% 35%	4837
June	1st to 10th	Day	21% 8% 3 7% 5% 5% 5% 4 6% 7% 30%	2660
	11th to 20th	Day	15% 6% 2 6% 4 5% 4 4 6% 9% 39%	2660
	21st to end	Day	21% 9% 2 6% 5% 4 5% 4 6% 7% 30%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 9% 36%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 6% 5% 7% 9% 36%	4440
	21st to end	Day	12% 6% 2 5% 5% 4 5% 4 6% 8% 44%	4814
August	1st to 10th	Day	12% 7% 3 8% 5% 5% 5% 4 6% 10% 36%	2646
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 7% 9% 41%	2349
	21st to end	Day	13% 5% 2 6% 5% 4 5% 4 6% 8% 42%	2376
September	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 6% 8% 41%	2160
	11th to 20th	Day	16% 6% 1 5% 3 3 3 3 5% 7% 48%	2070
	21st to end	Day	16% 6% 2 6% 4 5% 4 4 6% 7% 40%	1980
October	1st to 10th	Day	20% 7% 3 7% 5% 4 5% 3 5% 7% 33%	1880
	11th to 20th	Day	19% 9% 3 8% 6% 6% 6% 4 6% 6% 28%	1744
	21st to end	Day	26% 10% 3 7% 4 4 4 3 4 5% 29%	1782
November	1st to 10th	Day	17% 11% 4 7% 5% 4 3 4 6% 6% 32%	1671
	11th to 20th	Day	17% 13% 3 8% 5% 6% 4 4 4 7% 28%	1653
	21st to end	Day	23% 11% 5% 8% 5% 5% 4 4 5% 6% 25%	1520
December	1st to 10th	Day	24% 15% 5% 10% 6% 5% 4 3 5% 5% 19%	1520
	11th to 20th	Day	23% 14% 4 8% 5% 4 4 3 5% 5% 26%	1906
	21st to end	Day	27% 16% 5% 10% 5% 5% 4 3 3 3 19%	2772
January	1st to 10th	Night	17% 17% 6% 11% 6% 4 4 3 4 5% 23%	4429
	11th to 20th	Night	12% 14% 6% 13% 7% 6% 6% 4 5% 6% 21%	4440
	21st to end	Night	17% 18% 5% 10% 7% 4 4 3 4 4 24%	4884
February	1st to 10th	Night	15% 16% 6% 12% 8% 5% 4 3 4 6% 21%	2532
	11th to 20th	Night	14% 13% 5% 10% 6% 5% 6% 3 5% 4 29%	2288
	21st to end	Night	16% 15% 4 9% 5% 5% 3 4 5% 4 30%	1884
March	1st to 10th	Night	21% 10% 3 8% 5% 4 4 3 4 5% 33%	3724
	11th to 20th	Night	18% 19% 5% 8% 4 4 3 3 3 4 28%	3686
	21st to end	Night	14% 11% 4 10% 5% 5% 4 3 4 4 37%	3466
April	1st to 10th	Night	24% 10% 3 7% 4 4 4 3 4 6% 30%	1900
	11th to 20th	Night	22% 9% 3 7% 4 4 5% 3 4 6% 33%	1875
	21st to end	Night	21% 10% 3 6% 4 4 4 3 4 6% 34%	1727
May	1st to 10th	Night	21% 10% 3 7% 5% 5% 4 4 5% 7% 30%	2642
	11th to 20th	Night	22% 8% 3 7% 4 4 4 3 5% 6% 33%	2495
	21st to end	Night	15% 7% 3 7% 4 4 4 4 5% 8% 37%	2738
June	1st to 10th	Night	21% 8% 3 7% 5% 4 5% 4 6% 7% 32%	1520
	11th to 20th	Night	16% 6% 3 6% 5% 4 5% 4 6% 7% 38%	1520
	21st to end	Night	17% 8% 3 8% 5% 4 6% 3 5% 8% 32%	1520
July	1st to 10th	Night	14% 7% 3 8% 6% 5% 5% 4 7% 8% 34%	2520
	11th to 20th	Night	13% 7% 2 6% 5% 5% 5% 4 7% 8% 40%	2520
	21st to end	Night	11% 5% 3 7% 6% 4 5% 4 6% 7% 42%	2739
August	1st to 10th	Night	14% 5% 3 6% 5% 4 5% 4 6% 8% 39%	1512
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 4 7% 7% 41%	1630
	21st to end	Night	13% 6% 2 7% 5% 4 5% 4 6% 8% 41%	1980
September	1st to 10th	Night	13% 6% 3 7% 5% 4 4 4 5% 7% 43%	1800
	11th to 20th	Night	16% 6% 1 5% 3 3 3 3 5% 6% 48%	1890
	21st to end	Night	17% 7% 2 5% 4 4 3 3 5% 8% 42%	1980
October	1st to 10th	Night	18% 6% 3 6% 4 4 4 3 4 7% 39%	2078
	11th to 20th	Night	21% 9% 3 8% 5% 4 5% 3 5% 5% 32%	2215
	21st to end	Night	24% 9% 3 8% 5% 5% 5% 3 4 4 30%	2574
November	1st to 10th	Night	20% 10% 3 7% 5% 5% 4 4 5% 6% 32%	2407
	11th to 20th	Night	20% 11% 3 8% 5% 4 4 4 5% 5% 32%	2524
	21st to end	Night	24% 12% 4 8% 5% 4 4 3 4 5% 27%	2660
December	1st to 10th	Night	23% 17% 5% 10% 6% 3 4 3 4 5% 20%	2660
	11th to 20th	Night	23% 16% 4 9% 6% 4 4 3 3 5% 25%	3288
	21st to end	Night	26% 16% 5% 10% 4 3 4 2 4 4 22%	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	65% 6% 12% 14% 3	2518
	11th to 20th	Day	57% 5% 14% 16% 7%	2520
	21st to end	Day	60% 6% 13% 15% 5%	2772
February	1st to 10th	Day	62% 4 9% 18% 6% 2	1647
	11th to 20th	Day	59% 5% 11% 15% 9% 1	1786
	21st to end	Day	60% 3 10% 16% 10% 2	1570
March	1st to 10th	Day	59% 6% 8% 18% 7% 1	3119
	11th to 20th	Day	58% 6% 12% 11% 10% 3	3270
	21st to end	Day	48% 4 10% 20% 16% 2	4166
April	1st to 10th	Day	57% 4 8% 18% 11% 2	2280
	11th to 20th	Day	49% 5% 8% 22% 14% 2	2254
	21st to end	Day	53% 5% 9% 18% 12% 3	2451
May	1st to 10th	Day	51% 7% 10% 22% 9% 1	4341
	11th to 20th	Day	49% 8% 16% 17% 9% 1	4402
	21st to end	Day	43% 7% 12% 23% 13% 2	4837
June	1st to 10th	Day	51% 7% 10% 19% 11% 2	2660
	11th to 20th	Day	42% 6% 12% 24% 13% 2	2660
	21st to end	Day	51% 7% 11% 20% 10% 1	2660
July	1st to 10th	Day	42% 7% 13% 28% 9%	4370
	11th to 20th	Day	41% 7% 16% 29% 7%	4365
	21st to end	Day	37% 7% 14% 33% 9%	4661
August	1st to 10th	Day	43% 8% 16% 26% 8%	2632
	11th to 20th	Day	38% 7% 18% 26% 11%	2349
	21st to end	Day	38% 7% 15% 26% 13%	2376
September	1st to 10th	Day	38% 7% 14% 27% 13%	2160
	11th to 20th	Day	36% 5% 12% 33% 14% 1	2070
	21st to end	Day	42% 7% 14% 26% 11% 1	1980
October	1st to 10th	Day	50% 6% 13% 22% 10%	1880
	11th to 20th	Day	54% 7% 13% 19% 7%	1744
	21st to end	Day	58% 4 12% 18% 8% 1	1782
November	1st to 10th	Day	50% 7% 13% 20% 9% 1	1671
	11th to 20th	Day	55% 6% 12% 15% 11%	1653
	21st to end	Day	60% 7% 13% 14% 6%	1520
December	1st to 10th	Day	69% 5% 10% 12% 4	1520
	11th to 20th	Day	61% 5% 10% 18% 6%	1906
	21st to end	Day	69% 6% 12% 8% 5%	2772
January	1st to 10th	Night	63% 6% 14% 12% 5%	4429
	11th to 20th	Night	61% 7% 12% 14% 5% 1	4440
	21st to end	Night	64% 5% 10% 13% 6%	4884
February	1st to 10th	Night	65% 4 9% 15% 6% 1	2532
	11th to 20th	Night	58% 4 9% 18% 9% 1	2290
	21st to end	Night	56% 5% 9% 16% 13% 2	1884
March	1st to 10th	Night	54% 5% 10% 19% 9% 4	3734
	11th to 20th	Night	61% 4 9% 12% 13% 2	3687
	21st to end	Night	50% 4 7% 23% 14% 3	3466
April	1st to 10th	Night	55% 4 9% 17% 13% 2	1900
	11th to 20th	Night	52% 4 8% 20% 14% 2	1875
	21st to end	Night	52% 4 8% 19% 14% 3	1727
May	1st to 10th	Night	53% 8% 10% 19% 8% 3	2648
	11th to 20th	Night	49% 7% 11% 19% 11% 2	2496
	21st to end	Night	45% 6% 9% 20% 17% 2	2739
June	1st to 10th	Night	51% 6% 8% 22% 12% 1	1520
	11th to 20th	Night	44% 7% 11% 21% 14% 3	1520
	21st to end	Night	50% 7% 9% 19% 14% 1	1520
July	1st to 10th	Night	47% 6% 14% 20% 12% 1	2480
	11th to 20th	Night	40% 7% 16% 27% 9%	2472
	21st to end	Night	40% 7% 17% 24% 12%	2651
August	1st to 10th	Night	42% 7% 15% 25% 11%	1502
	11th to 20th	Night	40% 8% 16% 25% 12%	1630
	21st to end	Night	40% 7% 13% 27% 12% 1	1980
September	1st to 10th	Night	40% 7% 12% 25% 15% 1	1800
	11th to 20th	Night	37% 5% 14% 31% 13% 1	1890
	21st to end	Night	41% 7% 10% 26% 15% 1	1980
October	1st to 10th	Night	46% 5% 10% 25% 13% 1	2078
	11th to 20th	Night	54% 5% 10% 23% 7%	2215
	21st to end	Night	59% 5% 11% 16% 9% 1	2574
November	1st to 10th	Night	53% 4 12% 21% 8% 1	2407
	11th to 20th	Night	54% 5% 12% 18% 10% 2	2524
	21st to end	Night	60% 5% 11% 17% 6%	2660
December	1st to 10th	Night	67% 6% 11% 13% 4	2660
	11th to 20th	Night	63% 4 9% 17% 7%	3288
	21st to end	Night	67% 4 10% 15% 4	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	29% 13% 30% 18% 10%	180
	11th to 20th	Day	28% 15% 32% 19% 6%	180
	21st to end	Day	21% 12% 34% 21% 11% 1	198
February	1st to 10th	Day	32% 17% 33% 16% 3	240
	11th to 20th	Day	22% 15% 35% 24% 3 1	385
	21st to end	Day	28% 12% 30% 26% 4	382
March	1st to 10th	Day	23% 12% 31% 25% 8%	460
	11th to 20th	Day	22% 15% 34% 21% 8% 1	460
	21st to end	Day	26% 12% 32% 20% 9% 1	506
April	1st to 10th	Day	30% 13% 28% 20% 7% 2	460
	11th to 20th	Day	28% 19% 24% 18% 8% 3	452
	21st to end	Day	28% 13% 30% 17% 10% 2	460
May	1st to 10th	Day	24% 12% 31% 20% 11% 2	463
	11th to 20th	Day	17% 10% 29% 27% 14% 3	487
	21st to end	Day	19% 14% 30% 24% 10% 2	529
June	1st to 10th	Day	23% 10% 27% 28% 9% 2	490
	11th to 20th	Day	16% 10% 26% 31% 15% 2	490
	21st to end	Day	24% 9% 26% 24% 13% 3	490
July	1st to 10th	Day	13% 8% 25% 32% 18% 5%	485
	11th to 20th	Day	14% 7% 29% 32% 14% 4	484
	21st to end	Day	14% 6% 27% 32% 18% 2	532
August	1st to 10th	Day	14% 6% 23% 31% 21% 5%	486
	11th to 20th	Day	11% 5% 22% 33% 20% 9%	456
	21st to end	Day	15% 8% 25% 24% 18% 11%	495
September	1st to 10th	Day	12% 6% 29% 29% 15% 8%	450
	11th to 20th	Day	17% 7% 21% 27% 16% 11%	450
	21st to end	Day	17% 8% 28% 21% 19% 7%	450
October	1st to 10th	Day	23% 12% 26% 22% 14% 3	450
	11th to 20th	Day	23% 12% 30% 21% 12% 1	421
	21st to end	Day	32% 12% 26% 23% 6%	396
November	1st to 10th	Day	27% 13% 28% 22% 9%	365
	11th to 20th	Day	26% 14% 31% 20% 7% 2	313
	21st to end	Day	32% 10% 31% 20% 6% 1	180
December	1st to 10th	Day	36% 8% 22% 23% 8% 3	180
	11th to 20th	Day	26% 21% 36% 14% 4	180
	21st to end	Day	30% 21% 26% 18% 4 1	198
January	1st to 10th	Night	28% 11% 31% 25% 5%	760
	11th to 20th	Night	26% 11% 33% 24% 7%	760
	21st to end	Night	22% 10% 32% 29% 6% 1	836
February	1st to 10th	Night	23% 10% 36% 26% 4 1	760
	11th to 20th	Night	20% 11% 38% 25% 4 1	743
	21st to end	Night	24% 11% 32% 29% 4	628
March	1st to 10th	Night	25% 10% 31% 28% 6%	760
	11th to 20th	Night	28% 11% 30% 24% 7%	760
	21st to end	Night	23% 8% 32% 29% 7% 1	836
April	1st to 10th	Night	30% 11% 26% 27% 6%	760
	11th to 20th	Night	26% 14% 28% 24% 7% 1	751
	21st to end	Night	27% 11% 29% 25% 7% 1	587
May	1st to 10th	Night	26% 8% 31% 26% 7% 2	456
	11th to 20th	Night	23% 9% 29% 29% 9% 1	374
	21st to end	Night	18% 7% 36% 30% 8%	411
June	1st to 10th	Night	24% 5% 28% 32% 10% 1	380
	11th to 20th	Night	19% 3 30% 35% 12%	380
	21st to end	Night	20% 5% 27% 35% 13% 1	380
July	1st to 10th	Night	13% 5% 28% 39% 15% 1	370
	11th to 20th	Night	13% 1 25% 46% 14% 2	368
	21st to end	Night	14% 3 24% 43% 17%	416
August	1st to 10th	Night	14% 5% 17% 43% 19% 2	378
	11th to 20th	Night	13% 3 20% 38% 24% 2	536
	21st to end	Night	16% 5% 20% 37% 20% 2	792
September	1st to 10th	Night	16% 4 23% 40% 16% 1	720
	11th to 20th	Night	18% 5% 21% 35% 19% 3	720
	21st to end	Night	20% 5% 26% 31% 15% 3	720
October	1st to 10th	Night	22% 8% 28% 30% 12% 1	720
	11th to 20th	Night	27% 9% 26% 28% 9%	720
	21st to end	Night	29% 9% 31% 25% 6%	792
November	1st to 10th	Night	25% 11% 32% 23% 8% 1	740
	11th to 20th	Night	27% 11% 31% 21% 9% 1	760
	21st to end	Night	29% 12% 30% 20% 8%	760
December	1st to 10th	Night	31% 11% 29% 22% 6%	760
	11th to 20th	Night	29% 12% 33% 20% 6% 1	760
	21st to end	Night	34% 12% 30% 18% 6%	836

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