Saint-Eustache
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saint-Eustache clear sky chart from 2005-11-06 to 2025-02-25.

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 6% 7% 33%	108666
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 31%	110016
Transparency	Day	49% 6% 12% 21% 10% 1	112159
	Night	53% 5% 11% 19% 10% 1	114687
Seeing	Day	20% 11% 28% 25% 12% 4	14833
	Night	22% 8% 29% 30% 10% 1	23965

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% 19% 5% 14% 5% 4 4 3 5% 5% 22%	3597
	11th to 20th	Day	12% 14% 7% 12% 6% 6% 5% 3 5% 5% 25%	3570
	21st to end	Day	11% 14% 5% 11% 5% 6% 6% 4 5% 5% 27%	3960
February	1st to 10th	Day	14% 15% 4 11% 5% 5% 5% 4 5% 6% 26%	1765
	11th to 20th	Day	14% 11% 4 11% 6% 5% 5% 5% 6% 5% 27%	1847
	21st to end	Day	18% 14% 4 10% 6% 4 4 3 5% 5% 27%	1610
March	1st to 10th	Day	20% 12% 4 10% 6% 5% 4 3 5% 5% 26%	3116
	11th to 20th	Day	12% 16% 5% 11% 6% 5% 5% 4 5% 5% 27%	3302
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 3 5% 6% 39%	4156
April	1st to 10th	Day	21% 11% 3 8% 5% 4 4 3 5% 5% 32%	2280
	11th to 20th	Day	20% 8% 3 7% 5% 4 4 3 4 5% 36%	2254
	21st to end	Day	21% 11% 3 7% 5% 3 4 3 4 5% 33%	2426
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 28%	4385
	11th to 20th	Day	17% 9% 3 8% 5% 4 5% 4 5% 7% 32%	4398
	21st to end	Day	15% 6% 2 7% 5% 4 5% 3 7% 8% 37%	4837
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 7% 31%	2660
	11th to 20th	Day	14% 6% 3 7% 5% 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	19% 8% 3 7% 6% 5% 5% 4 6% 7% 31%	2660
July	1st to 10th	Day	11% 6% 2 8% 6% 6% 6% 4 6% 9% 37%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 4 6% 5% 8% 9% 38%	4440
	21st to end	Day	11% 6% 2 5% 4 4 5% 4 7% 8% 45%	4814
August	1st to 10th	Day	13% 6% 3 8% 5% 5% 6% 4 7% 9% 33%	4423
	11th to 20th	Day	13% 6% 3 8% 5% 5% 4 3 6% 9% 39%	3993
	21st to end	Day	15% 4 2 6% 5% 4 5% 4 6% 9% 39%	4180
September	1st to 10th	Day	11% 6% 2 5% 5% 5% 5% 4 6% 10% 41%	2280
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 6% 6% 49%	2207
	21st to end	Day	16% 6% 3 6% 4 4 4 3 6% 7% 41%	2090
October	1st to 10th	Day	18% 8% 3 7% 4 5% 4 4 5% 6% 36%	1952
	11th to 20th	Day	18% 8% 3 7% 7% 6% 5% 4 6% 6% 30%	1866
	21st to end	Day	23% 10% 3 6% 4 4 4 3 5% 7% 30%	1881
November	1st to 10th	Day	16% 11% 3 6% 4 4 5% 4 6% 7% 34%	1761
	11th to 20th	Day	17% 10% 4 8% 4 5% 4 4 7% 6% 31%	1710
	21st to end	Day	22% 12% 3 7% 6% 5% 5% 4 6% 6% 24%	1600
December	1st to 10th	Day	21% 18% 6% 11% 5% 4 4 4 5% 5% 17%	2600
	11th to 20th	Day	17% 13% 4 10% 6% 5% 5% 4 5% 4 27%	2986
	21st to end	Day	24% 12% 4 10% 5% 4 6% 4 4 5% 22%	3960
January	1st to 10th	Night	14% 20% 8% 14% 5% 4 4 3 4 5% 20%	6349
	11th to 20th	Night	10% 15% 6% 16% 8% 6% 5% 3 5% 6% 20%	6315
	21st to end	Night	13% 15% 5% 11% 8% 5% 5% 4 5% 6% 25%	6996
February	1st to 10th	Night	14% 15% 5% 11% 7% 5% 5% 4 5% 6% 24%	2634
	11th to 20th	Night	14% 11% 4 9% 6% 5% 6% 4 6% 7% 29%	2437
	21st to end	Night	15% 15% 4 9% 5% 4 4 3 4 5% 31%	1939
March	1st to 10th	Night	20% 12% 3 8% 4 4 4 2 4 5% 33%	3724
	11th to 20th	Night	17% 18% 4 9% 5% 4 3 3 4 5% 27%	3653
	21st to end	Night	12% 10% 4 9% 5% 4 4 3 5% 5% 39%	3476
April	1st to 10th	Night	23% 9% 4 6% 4 4 4 3 6% 6% 31%	1900
	11th to 20th	Night	22% 9% 3 6% 5% 4 3 3 4 6% 35%	1875
	21st to end	Night	21% 9% 2 8% 4 4 4 3 5% 6% 34%	1753
May	1st to 10th	Night	21% 10% 3 8% 4 4 4 3 6% 7% 30%	2583
	11th to 20th	Night	23% 8% 2 6% 4 4 4 3 5% 6% 36%	2495
	21st to end	Night	15% 8% 3 7% 5% 4 4 4 5% 9% 36%	2738
June	1st to 10th	Night	20% 8% 3 7% 5% 4 4 4 6% 8% 31%	1520
	11th to 20th	Night	15% 7% 3 7% 4 3 4 3 6% 8% 40%	1520
	21st to end	Night	18% 7% 2 8% 5% 4 5% 4 6% 6% 34%	1520
July	1st to 10th	Night	13% 7% 3 8% 5% 5% 5% 5% 7% 8% 34%	2520
	11th to 20th	Night	13% 5% 2 7% 5% 4 4 3 6% 9% 41%	2520
	21st to end	Night	11% 6% 3 6% 4 4 4 4 7% 8% 43%	2739
August	1st to 10th	Night	14% 8% 3 8% 4 4 5% 3 5% 7% 38%	2506
	11th to 20th	Night	15% 7% 3 8% 4 4 4 3 6% 7% 39%	2800
	21st to end	Night	16% 6% 2 7% 5% 4 4 4 6% 7% 39%	3476
September	1st to 10th	Night	11% 4 3 7% 5% 5% 4 4 6% 8% 44%	1900
	11th to 20th	Night	14% 6% 3 6% 3 3 2 2 5% 7% 49%	1972
	21st to end	Night	17% 5% 2 6% 4 4 4 3 5% 7% 43%	2090
October	1st to 10th	Night	18% 7% 2 7% 4 5% 5% 3 5% 6% 38%	2227
	11th to 20th	Night	20% 8% 3 7% 4 5% 4 3 4 6% 36%	2313
	21st to end	Night	21% 9% 3 8% 5% 4 5% 3 5% 5% 31%	2717
November	1st to 10th	Night	19% 10% 3 6% 5% 4 4 4 6% 6% 32%	2537
	11th to 20th	Night	19% 9% 3 8% 4 4 4 4 6% 6% 33%	2688
	21st to end	Night	22% 13% 4 8% 6% 4 4 3 4 5% 27%	2800
December	1st to 10th	Night	17% 17% 5% 11% 7% 5% 6% 4 5% 5% 19%	4580
	11th to 20th	Night	23% 14% 4 9% 4 4 4 3 6% 5% 24%	5208
	21st to end	Night	25% 16% 4 9% 4 3 3 3 6% 5% 23%	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% 7% 9% 16% 3	3598
	11th to 20th	Day	59% 6% 11% 15% 7% 1	3600
	21st to end	Day	57% 6% 12% 15% 10% 1	3960
February	1st to 10th	Day	59% 4 9% 19% 6% 2	1765
	11th to 20th	Day	57% 7% 11% 15% 9% 1	1856
	21st to end	Day	59% 4 10% 16% 10% 2	1610
March	1st to 10th	Day	60% 6% 8% 18% 8% 1	3119
	11th to 20th	Day	57% 7% 10% 13% 11% 2	3302
	21st to end	Day	45% 6% 9% 20% 18% 2	4156
April	1st to 10th	Day	55% 5% 8% 18% 13% 2	2280
	11th to 20th	Day	49% 6% 7% 22% 15% 2	2254
	21st to end	Day	53% 5% 9% 17% 13% 3	2426
May	1st to 10th	Day	51% 7% 9% 22% 10% 1	4399
	11th to 20th	Day	48% 9% 14% 18% 9% 2	4402
	21st to end	Day	42% 7% 12% 24% 14% 2	4837
June	1st to 10th	Day	50% 7% 11% 19% 12% 2	2660
	11th to 20th	Day	43% 7% 11% 23% 14% 3	2660
	21st to end	Day	51% 7% 11% 20% 10% 1	2660
July	1st to 10th	Day	42% 7% 13% 27% 11% 1	4370
	11th to 20th	Day	39% 7% 15% 30% 8%	4365
	21st to end	Day	36% 6% 14% 34% 10%	4661
August	1st to 10th	Day	45% 7% 17% 22% 9%	4409
	11th to 20th	Day	42% 6% 17% 28% 7%	4035
	21st to end	Day	40% 6% 17% 21% 15% 1	4180
September	1st to 10th	Day	37% 7% 15% 28% 13% 1	2280
	11th to 20th	Day	34% 6% 13% 31% 15% 1	2207
	21st to end	Day	41% 6% 14% 27% 11% 1	2090
October	1st to 10th	Day	45% 5% 13% 28% 9%	3238
	11th to 20th	Day	44% 5% 17% 27% 7%	3082
	21st to end	Day	44% 4 20% 23% 9% 1	3081
November	1st to 10th	Day	48% 5% 14% 23% 8% 1	1761
	11th to 20th	Day	52% 6% 12% 18% 12% 1	1710
	21st to end	Day	58% 8% 13% 15% 5%	1600
December	1st to 10th	Day	69% 4 9% 15% 3	2600
	11th to 20th	Day	59% 5% 10% 17% 9%	2986
	21st to end	Day	64% 5% 11% 13% 6%	3960
January	1st to 10th	Night	67% 5% 11% 13% 4	6349
	11th to 20th	Night	64% 6% 12% 14% 4	6360
	21st to end	Night	61% 5% 10% 12% 13% 1	6996
February	1st to 10th	Night	61% 5% 10% 16% 7% 1	2634
	11th to 20th	Night	54% 5% 12% 20% 9%	2439
	21st to end	Night	56% 5% 8% 17% 12% 1	1939
March	1st to 10th	Night	54% 4 10% 19% 9% 3	3734
	11th to 20th	Night	59% 5% 9% 14% 12% 2	3654
	21st to end	Night	47% 5% 6% 23% 15% 3	3476
April	1st to 10th	Night	53% 4 8% 19% 14% 2	1900
	11th to 20th	Night	52% 4 7% 21% 14% 2	1875
	21st to end	Night	50% 4 9% 18% 14% 4	1753
May	1st to 10th	Night	52% 7% 10% 20% 9% 3	2589
	11th to 20th	Night	48% 7% 12% 19% 11% 2	2496
	21st to end	Night	45% 6% 9% 20% 18% 1	2739
June	1st to 10th	Night	50% 7% 10% 21% 12% 1	1520
	11th to 20th	Night	42% 6% 12% 22% 15% 3	1520
	21st to end	Night	48% 8% 11% 19% 13% 1	1520
July	1st to 10th	Night	46% 6% 14% 20% 13%	2480
	11th to 20th	Night	39% 7% 18% 27% 9%	2472
	21st to end	Night	37% 7% 18% 25% 13%	2651
August	1st to 10th	Night	46% 6% 13% 26% 9%	2496
	11th to 20th	Night	44% 7% 18% 23% 8%	2824
	21st to end	Night	43% 7% 14% 21% 14% 1	3476
September	1st to 10th	Night	38% 6% 13% 26% 16% 1	1900
	11th to 20th	Night	36% 4 14% 32% 13% 1	1972
	21st to end	Night	41% 6% 12% 26% 15%	2090
October	1st to 10th	Night	44% 5% 14% 27% 10%	3721
	11th to 20th	Night	44% 4 13% 31% 9%	3836
	21st to end	Night	47% 4 17% 19% 12% 1	4467
November	1st to 10th	Night	52% 5% 12% 22% 8% 1	2537
	11th to 20th	Night	52% 5% 13% 19% 11% 1	2688
	21st to end	Night	60% 5% 12% 17% 6%	2800
December	1st to 10th	Night	68% 5% 12% 12% 4	4580
	11th to 20th	Night	62% 4 8% 16% 11%	5208
	21st to end	Night	63% 4 8% 14% 10%	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	24% 12% 31% 25% 9%	200
	11th to 20th	Day	25% 16% 30% 23% 5% 2	200
	21st to end	Day	19% 17% 31% 25% 7% 1	220
February	1st to 10th	Day	28% 19% 35% 15% 3	283
	11th to 20th	Day	22% 16% 38% 21% 3	394
	21st to end	Day	26% 13% 32% 26% 3	398
March	1st to 10th	Day	25% 12% 30% 25% 8%	460
	11th to 20th	Day	21% 13% 36% 23% 5% 1	460
	21st to end	Day	26% 12% 31% 19% 9% 2	506
April	1st to 10th	Day	26% 14% 28% 20% 9% 3	460
	11th to 20th	Day	27% 15% 24% 21% 10% 2	452
	21st to end	Day	27% 13% 29% 20% 8% 3	460
May	1st to 10th	Day	21% 10% 32% 25% 9% 2	463
	11th to 20th	Day	20% 8% 30% 27% 13% 3	487
	21st to end	Day	18% 11% 32% 24% 12% 3	529
June	1st to 10th	Day	23% 10% 25% 27% 12% 2	490
	11th to 20th	Day	17% 10% 24% 33% 14% 3	490
	21st to end	Day	21% 8% 26% 27% 15% 3	490
July	1st to 10th	Day	11% 7% 25% 34% 18% 6%	485
	11th to 20th	Day	13% 7% 27% 32% 17% 4	484
	21st to end	Day	12% 6% 22% 37% 19% 4	532
August	1st to 10th	Day	14% 6% 21% 33% 22% 5%	486
	11th to 20th	Day	11% 6% 20% 31% 20% 11%	479
	21st to end	Day	14% 8% 24% 26% 20% 8%	539
September	1st to 10th	Day	14% 5% 27% 27% 19% 9%	490
	11th to 20th	Day	13% 7% 21% 25% 21% 13%	490
	21st to end	Day	18% 8% 25% 26% 17% 6%	490
October	1st to 10th	Day	20% 11% 28% 22% 14% 5%	490
	11th to 20th	Day	21% 11% 32% 22% 13% 2	472
	21st to end	Day	31% 12% 25% 21% 9%	429
November	1st to 10th	Day	28% 12% 26% 23% 10% 1	395
	11th to 20th	Day	21% 16% 36% 20% 7% 1	310
	21st to end	Day	30% 15% 27% 22% 6% 1	200
December	1st to 10th	Day	30% 10% 25% 26% 8% 2	200
	11th to 20th	Day	25% 15% 38% 18% 4 1	200
	21st to end	Day	29% 16% 28% 19% 7% 1	220
January	1st to 10th	Night	24% 12% 33% 27% 5%	800
	11th to 20th	Night	24% 11% 32% 27% 6%	800
	21st to end	Night	18% 8% 36% 29% 8%	880
February	1st to 10th	Night	20% 9% 38% 28% 5% 1	800
	11th to 20th	Night	21% 11% 37% 27% 5%	783
	21st to end	Night	24% 8% 33% 31% 4	647
March	1st to 10th	Night	24% 11% 30% 30% 4	760
	11th to 20th	Night	26% 11% 30% 26% 7%	760
	21st to end	Night	21% 9% 31% 31% 7%	836
April	1st to 10th	Night	25% 10% 29% 30% 6%	760
	11th to 20th	Night	24% 10% 32% 27% 7% 1	751
	21st to end	Night	26% 9% 31% 25% 9%	613
May	1st to 10th	Night	24% 7% 31% 29% 7% 2	423
	11th to 20th	Night	23% 4 28% 36% 9% 1	374
	21st to end	Night	16% 7% 36% 32% 9%	411
June	1st to 10th	Night	24% 5% 24% 35% 11% 1	380
	11th to 20th	Night	18% 4 28% 36% 13% 1	380
	21st to end	Night	20% 4 26% 34% 16% 1	380
July	1st to 10th	Night	11% 4 26% 42% 15% 1	370
	11th to 20th	Night	12% 2 22% 46% 18%	368
	21st to end	Night	12% 3 19% 45% 19% 1	416
August	1st to 10th	Night	15% 4 12% 46% 23% 1	378
	11th to 20th	Night	13% 4 19% 36% 25% 3	563
	21st to end	Night	15% 3 22% 36% 22% 2	836
September	1st to 10th	Night	13% 4 23% 43% 16% 1	760
	11th to 20th	Night	16% 5% 19% 36% 23% 2	760
	21st to end	Night	17% 5% 25% 32% 18% 2	760
October	1st to 10th	Night	21% 6% 26% 33% 13% 1	760
	11th to 20th	Night	23% 7% 29% 30% 11% 1	760
	21st to end	Night	27% 8% 31% 29% 6%	836
November	1st to 10th	Night	24% 12% 28% 28% 8%	780
	11th to 20th	Night	23% 10% 32% 25% 10% 1	800
	21st to end	Night	28% 13% 28% 23% 7% 1	800
December	1st to 10th	Night	29% 9% 31% 24% 7%	800
	11th to 20th	Night	27% 13% 32% 22% 5% 1	800
	21st to end	Night	33% 11% 30% 21% 5% 1	880

Page generated at 2025-02-22 06:51:36. Version ac07

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