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 2024-09-29.

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%	101202
	Night	18% 11% 4 8% 5% 4 4 3 5% 6% 32%	97046
Transparency	Day	49% 7% 12% 21% 10% 1	100963
	Night	52% 6% 12% 19% 10% 1	96905
Seeing	Day	20% 10% 28% 26% 12% 4	14436
	Night	22% 8% 29% 30% 10% 1	23370

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	16% 14% 5% 14% 6% 5% 4 3 5% 5% 23%	2517
	11th to 20th	Day	15% 12% 6% 10% 6% 5% 4 4 6% 6% 26%	2520
	21st to end	Day	14% 16% 4 10% 5% 6% 6% 4 5% 6% 24%	2772
February	1st to 10th	Day	14% 15% 4 11% 5% 5% 5% 4 5% 6% 26%	1676
	11th to 20th	Day	14% 10% 4 11% 6% 5% 5% 5% 6% 6% 27%	1752
	21st to end	Day	18% 15% 4 10% 6% 4 4 3 5% 5% 28%	1570
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%	2070
October	1st to 10th	Day	19% 8% 3 6% 4 5% 4 4 5% 6% 36%	1850
	11th to 20th	Day	18% 8% 3 7% 7% 7% 5% 4 6% 6% 28%	1768
	21st to end	Day	24% 10% 4 6% 4 4 4 3 5% 6% 29%	1782
November	1st to 10th	Day	16% 10% 3 6% 4 4 5% 4 6% 7% 34%	1671
	11th to 20th	Day	18% 11% 4 9% 4 5% 4 4 7% 6% 29%	1625
	21st to end	Day	22% 11% 3 7% 6% 5% 6% 4 6% 6% 24%	1520
December	1st to 10th	Day	24% 14% 5% 9% 6% 4 4 3 6% 6% 19%	1520
	11th to 20th	Day	21% 14% 4 8% 5% 4 4 3 5% 5% 27%	1906
	21st to end	Day	28% 15% 5% 10% 5% 4 4 3 3 4 20%	2772
January	1st to 10th	Night	17% 15% 6% 10% 5% 5% 5% 3 5% 6% 22%	4429
	11th to 20th	Night	12% 13% 5% 12% 7% 6% 6% 4 5% 7% 23%	4440
	21st to end	Night	16% 16% 5% 10% 7% 5% 4 3 4 5% 24%	4884
February	1st to 10th	Night	14% 15% 5% 11% 7% 5% 5% 4 5% 6% 23%	2503
	11th to 20th	Night	14% 11% 4 9% 6% 5% 6% 4 6% 6% 29%	2312
	21st to end	Night	15% 15% 4 9% 5% 4 4 3 4 5% 32%	1884
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%	2078
October	1st to 10th	Night	18% 7% 2 7% 4 5% 5% 3 5% 7% 38%	2109
	11th to 20th	Night	20% 8% 3 8% 4 5% 4 3 4 6% 34%	2191
	21st to end	Night	22% 10% 3 8% 5% 4 5% 3 5% 5% 30%	2574
November	1st to 10th	Night	19% 10% 3 6% 5% 4 4 4 5% 6% 33%	2407
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 6% 6% 32%	2553
	21st to end	Night	22% 13% 4 8% 5% 5% 4 3 4 5% 27%	2660
December	1st to 10th	Night	21% 16% 5% 8% 6% 4 5% 3 5% 5% 21%	2660
	11th to 20th	Night	22% 16% 4 8% 4 4 4 3 4 5% 26%	3288
	21st to end	Night	29% 17% 4 9% 4 3 3 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	61% 10% 11% 13% 4 1	2518
	11th to 20th	Day	55% 7% 14% 15% 8%	2520
	21st to end	Day	59% 7% 13% 14% 5%	2772
February	1st to 10th	Day	59% 4 10% 20% 5% 2	1676
	11th to 20th	Day	55% 7% 11% 16% 9% 1	1761
	21st to end	Day	59% 4 10% 16% 10% 2	1570
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	42% 6% 14% 27% 11% 1	2070
October	1st to 10th	Day	49% 5% 12% 22% 11%	1850
	11th to 20th	Day	54% 8% 12% 20% 7%	1768
	21st to end	Day	56% 5% 12% 18% 8% 1	1782
November	1st to 10th	Day	48% 6% 14% 22% 8% 1	1671
	11th to 20th	Day	53% 6% 12% 17% 11% 1	1625
	21st to end	Day	57% 9% 14% 15% 6%	1520
December	1st to 10th	Day	67% 5% 11% 13% 4	1520
	11th to 20th	Day	60% 5% 13% 17% 5%	1906
	21st to end	Day	69% 6% 10% 10% 5%	2772
January	1st to 10th	Night	61% 7% 14% 12% 4	4429
	11th to 20th	Night	58% 7% 14% 14% 5% 1	4440
	21st to end	Night	62% 6% 12% 13% 6% 1	4884
February	1st to 10th	Night	62% 5% 11% 16% 6% 1	2503
	11th to 20th	Night	53% 5% 11% 21% 9% 1	2314
	21st to end	Night	56% 5% 8% 17% 13% 1	1884
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% 14%	2078
October	1st to 10th	Night	46% 6% 10% 25% 12% 1	2109
	11th to 20th	Night	51% 5% 12% 24% 8%	2191
	21st to end	Night	56% 5% 13% 17% 9% 1	2574
November	1st to 10th	Night	51% 5% 12% 21% 9% 1	2407
	11th to 20th	Night	52% 5% 13% 19% 10% 1	2553
	21st to end	Night	59% 5% 12% 17% 6%	2660
December	1st to 10th	Night	65% 6% 11% 15% 4	2660
	11th to 20th	Night	62% 4 9% 18% 7%	3288
	21st to end	Night	67% 5% 9% 15% 5%	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	23% 11% 28% 27% 10%	180
	11th to 20th	Day	25% 15% 30% 23% 5% 2	180
	21st to end	Day	18% 15% 31% 26% 8% 2	198
February	1st to 10th	Day	29% 19% 34% 15% 3	254
	11th to 20th	Day	22% 14% 39% 21% 4	359
	21st to end	Day	26% 14% 31% 26% 3	382
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%	483
October	1st to 10th	Day	21% 10% 27% 22% 14% 5%	450
	11th to 20th	Day	21% 11% 31% 22% 13% 2	434
	21st to end	Day	33% 12% 25% 22% 8% 1	396
November	1st to 10th	Day	27% 12% 26% 23% 10% 1	365
	11th to 20th	Day	22% 15% 35% 19% 7% 1	285
	21st to end	Day	28% 14% 27% 24% 6% 1	180
December	1st to 10th	Day	32% 8% 24% 26% 8% 2	180
	11th to 20th	Day	25% 13% 38% 18% 4 1	180
	21st to end	Day	31% 16% 29% 17% 7% 1	198
January	1st to 10th	Night	24% 11% 31% 28% 5%	760
	11th to 20th	Night	25% 11% 32% 27% 5%	760
	21st to end	Night	18% 9% 36% 29% 8%	836
February	1st to 10th	Night	21% 9% 37% 28% 5% 1	760
	11th to 20th	Night	20% 11% 36% 28% 5%	743
	21st to end	Night	24% 8% 33% 31% 4	628
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% 33% 18% 2	756
October	1st to 10th	Night	22% 5% 27% 33% 12% 1	720
	11th to 20th	Night	23% 7% 29% 29% 11% 1	720
	21st to end	Night	28% 7% 31% 28% 6%	792
November	1st to 10th	Night	24% 10% 28% 28% 9%	740
	11th to 20th	Night	23% 10% 33% 24% 10% 1	760
	21st to end	Night	29% 12% 28% 23% 7% 1	760
December	1st to 10th	Night	30% 9% 31% 24% 6%	760
	11th to 20th	Night	27% 13% 32% 23% 5% 1	760
	21st to end	Night	33% 11% 31% 20% 5%	836

Page generated at 2024-09-26 09:52:24. Version ac07

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