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 2026-07-01.

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% 32%	138097
	Night	16% 11% 4 9% 5% 5% 5% 4 5% 6% 30%	134289
Transparency	Day	50% 6% 12% 21% 10% 1	141544
	Night	54% 5% 11% 19% 10% 1	138931
Seeing	Day	20% 11% 28% 25% 12% 3	16598
	Night	22% 9% 29% 30% 10% 1	25578

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	14% 17% 5% 14% 5% 4 4 3 5% 6% 23%	4661
	11th to 20th	Day	11% 15% 6% 13% 6% 6% 5% 3 5% 5% 23%	4650
	21st to end	Day	10% 12% 4 12% 9% 7% 6% 4 5% 5% 24%	5124
February	1st to 10th	Day	13% 15% 4 11% 6% 5% 5% 4 5% 6% 27%	1853
	11th to 20th	Day	13% 11% 5% 11% 6% 5% 5% 5% 6% 6% 27%	1942
	21st to end	Day	17% 15% 4 10% 6% 4 4 3 5% 5% 27%	1730
March	1st to 10th	Day	19% 12% 5% 11% 6% 5% 4 3 4 5% 25%	4576
	11th to 20th	Day	10% 12% 4 10% 6% 5% 5% 4 6% 6% 31%	4822
	21st to end	Day	18% 10% 3 8% 5% 5% 5% 3 4 5% 34%	6091
April	1st to 10th	Day	21% 11% 3 8% 4 4 4 3 4 5% 32%	2520
	11th to 20th	Day	20% 9% 3 7% 5% 4 4 3 4 5% 36%	2494
	21st to end	Day	20% 10% 3 7% 5% 4 4 3 5% 6% 33%	2682
May	1st to 10th	Day	21% 9% 3 9% 5% 5% 5% 4 6% 8% 24%	8168
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	8221
	21st to end	Day	21% 9% 2 7% 4 4 5% 3 6% 6% 33%	9060
June	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 4 6% 7% 31%	2940
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 8% 37%	2940
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 6% 8% 31%	2940
July	1st to 10th	Day	11% 6% 3 9% 6% 6% 6% 5% 7% 8% 34%	6360
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 4 7% 9% 41%	6360
	21st to end	Day	10% 6% 2 5% 3 4 5% 4 6% 9% 46%	6926
August	1st to 10th	Day	13% 6% 2 8% 5% 5% 6% 5% 7% 9% 34%	4563
	11th to 20th	Day	12% 6% 2 8% 5% 5% 4 3 6% 8% 39%	4121
	21st to end	Day	15% 4 2 6% 5% 4 5% 4 6% 9% 39%	4312
September	1st to 10th	Day	11% 6% 2 5% 5% 5% 5% 4 7% 10% 42%	2400
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 6% 7% 50%	2323
	21st to end	Day	16% 6% 3 6% 4 4 4 3 6% 7% 41%	2200
October	1st to 10th	Day	18% 8% 3 6% 4 5% 4 4 5% 6% 38%	2054
	11th to 20th	Day	17% 8% 3 7% 7% 6% 5% 4 6% 6% 31%	1964
	21st to end	Day	23% 10% 3 6% 4 4 4 3 5% 7% 30%	1980
November	1st to 10th	Day	16% 11% 3 7% 5% 4 5% 4 6% 7% 33%	1851
	11th to 20th	Day	17% 11% 4 9% 4 5% 5% 4 6% 6% 30%	1795
	21st to end	Day	22% 13% 3 7% 5% 5% 5% 4 6% 6% 24%	1680
December	1st to 10th	Day	20% 18% 6% 11% 5% 4 4 4 5% 5% 17%	2680
	11th to 20th	Day	17% 13% 4 10% 6% 5% 5% 3 5% 4 27%	3066
	21st to end	Day	23% 12% 4 10% 6% 4 6% 4 4 5% 22%	4048
January	1st to 10th	Night	13% 18% 7% 14% 5% 5% 4 3 4 5% 21%	8234
	11th to 20th	Night	11% 16% 6% 17% 7% 6% 6% 3 5% 5% 17%	8235
	21st to end	Night	11% 13% 5% 12% 9% 6% 5% 4 5% 6% 26%	9057
February	1st to 10th	Night	13% 14% 5% 11% 7% 5% 5% 4 5% 6% 24%	2765
	11th to 20th	Night	14% 11% 4 9% 6% 5% 6% 4 6% 7% 29%	2562
	21st to end	Night	15% 15% 4 9% 5% 4 4 3 4 5% 32%	2076
March	1st to 10th	Night	21% 13% 3 9% 4 4 4 3 4 5% 30%	5484
	11th to 20th	Night	14% 14% 4 8% 5% 5% 4 4 6% 8% 29%	5353
	21st to end	Night	16% 10% 4 10% 5% 5% 5% 4 5% 5% 32%	5082
April	1st to 10th	Night	23% 9% 4 6% 4 4 4 4 5% 6% 31%	2100
	11th to 20th	Night	22% 9% 3 7% 5% 4 3 3 4 6% 34%	2075
	21st to end	Night	21% 9% 2 7% 4 4 4 3 5% 6% 35%	1937
May	1st to 10th	Night	21% 9% 3 9% 5% 5% 5% 4 6% 8% 25%	4785
	11th to 20th	Night	20% 9% 2 8% 4 4 4 4 6% 7% 31%	4639
	21st to end	Night	18% 9% 3 8% 5% 4 4 4 5% 8% 32%	5114
June	1st to 10th	Night	19% 7% 3 7% 5% 4 5% 4 6% 8% 32%	1680
	11th to 20th	Night	15% 7% 2 8% 4 3 4 3 6% 7% 39%	1680
	21st to end	Night	18% 7% 2 9% 5% 4 5% 5% 6% 6% 34%	1680
July	1st to 10th	Night	13% 6% 3 7% 5% 5% 6% 5% 8% 9% 33%	3600
	11th to 20th	Night	13% 5% 2 7% 5% 4 5% 4 6% 9% 41%	3600
	21st to end	Night	9% 5% 3 6% 4 5% 4 4 7% 8% 44%	3926
August	1st to 10th	Night	14% 7% 3 7% 4 4 5% 3 6% 8% 39%	2586
	11th to 20th	Night	14% 7% 3 7% 4 4 4 3 6% 7% 40%	2890
	21st to end	Night	16% 6% 2 7% 5% 4 4 4 6% 7% 39%	3586
September	1st to 10th	Night	11% 4 3 7% 4 5% 4 4 6% 8% 44%	2000
	11th to 20th	Night	13% 6% 3 5% 3 3 2 3 4 7% 50%	2076
	21st to end	Night	16% 5% 2 6% 4 4 4 3 5% 7% 43%	2200
October	1st to 10th	Night	18% 7% 2 6% 3 5% 5% 3 5% 7% 40%	2344
	11th to 20th	Night	19% 8% 3 7% 4 5% 4 3 4 6% 37%	2435
	21st to end	Night	21% 9% 3 7% 5% 4 5% 3 5% 6% 32%	2860
November	1st to 10th	Night	20% 10% 3 6% 5% 4 4 4 5% 6% 32%	2667
	11th to 20th	Night	18% 10% 3 9% 4 4 4 4 6% 6% 32%	2823
	21st to end	Night	21% 13% 4 9% 6% 5% 4 3 4 5% 26%	2940
December	1st to 10th	Night	17% 17% 5% 11% 6% 6% 6% 4 5% 5% 19%	4720
	11th to 20th	Night	22% 14% 4 10% 5% 4 4 3 6% 5% 24%	5348
	21st to end	Night	24% 16% 4 9% 4 3 3 3 6% 5% 23%	7150

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	63% 6% 10% 17% 4	4662
	11th to 20th	Day	61% 5% 10% 13% 10% 1	4680
	21st to end	Day	60% 6% 10% 13% 11% 1	5124
February	1st to 10th	Day	58% 4 9% 21% 6% 2	1853
	11th to 20th	Day	56% 7% 11% 16% 9% 1	1951
	21st to end	Day	60% 3 9% 16% 10% 2	1730
March	1st to 10th	Day	60% 5% 7% 14% 11% 3	4579
	11th to 20th	Day	51% 7% 16% 13% 11% 2	4822
	21st to end	Day	52% 5% 7% 16% 18% 2	6091
April	1st to 10th	Day	55% 4 8% 18% 13% 2	2520
	11th to 20th	Day	50% 5% 7% 21% 15% 2	2494
	21st to end	Day	52% 5% 9% 18% 13% 3	2682
May	1st to 10th	Day	56% 5% 8% 19% 10% 1	8180
	11th to 20th	Day	50% 7% 13% 21% 8% 1	8225
	21st to end	Day	50% 5% 10% 23% 11% 1	9061
June	1st to 10th	Day	50% 7% 10% 19% 13% 1	2940
	11th to 20th	Day	43% 7% 10% 23% 13% 3	2940
	21st to end	Day	50% 7% 11% 21% 10% 1	2940
July	1st to 10th	Day	45% 7% 13% 26% 9%	6290
	11th to 20th	Day	38% 6% 14% 30% 12%	6285
	21st to end	Day	34% 5% 14% 37% 9%	6728
August	1st to 10th	Day	44% 7% 17% 23% 8%	4549
	11th to 20th	Day	41% 6% 17% 28% 7%	4163
	21st to end	Day	40% 6% 17% 22% 15% 1	4312
September	1st to 10th	Day	36% 7% 15% 30% 12% 1	2400
	11th to 20th	Day	33% 6% 13% 32% 15% 1	2323
	21st to end	Day	41% 6% 14% 27% 12% 1	2200
October	1st to 10th	Day	44% 5% 13% 28% 10%	3340
	11th to 20th	Day	43% 5% 17% 27% 7%	3180
	21st to end	Day	44% 4 20% 23% 9% 1	3180
November	1st to 10th	Day	49% 5% 14% 22% 8% 1	1851
	11th to 20th	Day	53% 6% 12% 18% 11% 1	1795
	21st to end	Day	59% 8% 13% 14% 5%	1680
December	1st to 10th	Day	69% 4 9% 15% 3	2680
	11th to 20th	Day	60% 5% 11% 17% 8%	3066
	21st to end	Day	65% 5% 11% 13% 6%	4048
January	1st to 10th	Night	66% 5% 10% 14% 5% 1	8234
	11th to 20th	Night	67% 5% 9% 12% 6%	8280
	21st to end	Night	60% 4 9% 14% 13%	9057
February	1st to 10th	Night	61% 5% 10% 17% 7% 1	2765
	11th to 20th	Night	54% 5% 11% 21% 9%	2564
	21st to end	Night	55% 4 8% 18% 12% 1	2076
March	1st to 10th	Night	58% 4 7% 15% 12% 4	5494
	11th to 20th	Night	52% 5% 13% 16% 12% 2	5354
	21st to end	Night	54% 4 6% 21% 13% 2	5082
April	1st to 10th	Night	54% 4 8% 19% 14% 2	2100
	11th to 20th	Night	53% 3 7% 21% 14% 2	2075
	21st to end	Night	50% 4 9% 18% 15% 4	1937
May	1st to 10th	Night	57% 6% 11% 17% 8% 2	4791
	11th to 20th	Night	51% 6% 10% 23% 9% 1	4640
	21st to end	Night	51% 5% 9% 19% 16% 1	5115
June	1st to 10th	Night	49% 7% 9% 21% 13% 1	1680
	11th to 20th	Night	43% 6% 12% 22% 15% 2	1680
	21st to end	Night	48% 7% 11% 20% 13% 1	1680
July	1st to 10th	Night	44% 6% 17% 22% 10%	3560
	11th to 20th	Night	39% 6% 16% 28% 11%	3552
	21st to end	Night	37% 6% 16% 28% 13%	3809
August	1st to 10th	Night	45% 6% 13% 27% 9%	2576
	11th to 20th	Night	44% 6% 18% 23% 9%	2914
	21st to end	Night	43% 7% 14% 21% 13% 1	3586
September	1st to 10th	Night	37% 6% 13% 28% 16% 1	2000
	11th to 20th	Night	35% 4 14% 33% 13% 1	2076
	21st to end	Night	41% 6% 12% 26% 15%	2200
October	1st to 10th	Night	43% 5% 13% 27% 11% 1	3838
	11th to 20th	Night	43% 4 13% 31% 9%	3958
	21st to end	Night	47% 4 16% 19% 12% 1	4610
November	1st to 10th	Night	52% 4 12% 22% 8% 1	2667
	11th to 20th	Night	52% 5% 13% 19% 10% 1	2823
	21st to end	Night	60% 5% 12% 17% 6%	2940
December	1st to 10th	Night	68% 5% 11% 12% 4	4720
	11th to 20th	Night	62% 4 8% 15% 11%	5348
	21st to end	Night	64% 4 8% 15% 10%	7150

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% 32% 25% 9%	220
	11th to 20th	Day	25% 20% 28% 21% 4 2	220
	21st to end	Day	18% 18% 31% 25% 8% 1	242
February	1st to 10th	Day	26% 19% 34% 17% 4	311
	11th to 20th	Day	21% 17% 38% 21% 4	429
	21st to end	Day	25% 14% 33% 25% 3	446
March	1st to 10th	Day	25% 14% 32% 23% 7%	540
	11th to 20th	Day	23% 14% 36% 22% 5% 1	540
	21st to end	Day	26% 14% 31% 19% 8% 2	594
April	1st to 10th	Day	27% 16% 28% 18% 8% 2	540
	11th to 20th	Day	27% 17% 23% 21% 10% 2	532
	21st to end	Day	26% 14% 31% 19% 8% 2	540
May	1st to 10th	Day	22% 12% 32% 24% 8% 2	543
	11th to 20th	Day	20% 9% 30% 26% 12% 3	567
	21st to end	Day	21% 11% 32% 23% 12% 2	617
June	1st to 10th	Day	22% 9% 26% 28% 12% 2	570
	11th to 20th	Day	16% 11% 26% 31% 13% 3	570
	21st to end	Day	19% 8% 28% 27% 15% 3	570
July	1st to 10th	Day	12% 7% 26% 32% 17% 6%	525
	11th to 20th	Day	13% 6% 28% 31% 18% 4	524
	21st to end	Day	12% 7% 23% 36% 18% 4	576
August	1st to 10th	Day	13% 5% 21% 33% 22% 6%	526
	11th to 20th	Day	11% 6% 20% 31% 21% 11%	519
	21st to end	Day	14% 9% 24% 24% 21% 8%	583
September	1st to 10th	Day	13% 5% 26% 27% 19% 9%	530
	11th to 20th	Day	12% 7% 19% 26% 23% 12%	530
	21st to end	Day	18% 8% 26% 25% 17% 6%	530
October	1st to 10th	Day	19% 11% 27% 23% 15% 5%	530
	11th to 20th	Day	20% 11% 32% 23% 12% 2	510
	21st to end	Day	31% 11% 26% 22% 10%	462
November	1st to 10th	Day	28% 14% 26% 21% 10% 1	425
	11th to 20th	Day	21% 16% 35% 20% 7% 1	335
	21st to end	Day	31% 15% 26% 20% 5% 1	220
December	1st to 10th	Day	29% 10% 26% 25% 8% 2	220
	11th to 20th	Day	25% 14% 40% 18% 3 1	220
	21st to end	Day	28% 16% 30% 19% 6% 1	242
January	1st to 10th	Night	23% 11% 33% 27% 5%	840
	11th to 20th	Night	24% 13% 31% 26% 6%	840
	21st to end	Night	18% 10% 35% 28% 8%	924
February	1st to 10th	Night	20% 9% 37% 28% 6%	840
	11th to 20th	Night	21% 10% 37% 27% 5%	823
	21st to end	Night	24% 8% 34% 31% 3	692
March	1st to 10th	Night	24% 13% 31% 28% 4	840
	11th to 20th	Night	25% 11% 31% 26% 7%	840
	21st to end	Night	22% 10% 31% 30% 6%	924
April	1st to 10th	Night	27% 10% 29% 29% 5%	840
	11th to 20th	Night	25% 10% 32% 26% 6%	831
	21st to end	Night	26% 10% 31% 25% 8%	677
May	1st to 10th	Night	25% 7% 31% 29% 6% 2	467
	11th to 20th	Night	22% 6% 27% 35% 9%	414
	21st to end	Night	18% 7% 36% 31% 8%	455
June	1st to 10th	Night	23% 6% 24% 35% 11%	420
	11th to 20th	Night	18% 6% 27% 35% 13%	420
	21st to end	Night	20% 5% 26% 34% 15% 1	420
July	1st to 10th	Night	11% 4 27% 43% 15% 1	390
	11th to 20th	Night	12% 3 21% 45% 18%	388
	21st to end	Night	12% 3 20% 46% 18% 1	438
August	1st to 10th	Night	14% 4 12% 45% 23% 1	398
	11th to 20th	Night	13% 4 19% 36% 26% 3	593
	21st to end	Night	15% 4 22% 37% 21% 2	880
September	1st to 10th	Night	13% 4 23% 42% 17% 1	800
	11th to 20th	Night	15% 4 18% 37% 23% 2	800
	21st to end	Night	17% 5% 25% 33% 18% 2	800
October	1st to 10th	Night	21% 6% 26% 34% 14% 1	800
	11th to 20th	Night	22% 8% 29% 30% 11% 1	800
	21st to end	Night	26% 8% 31% 29% 6%	880
November	1st to 10th	Night	24% 12% 28% 28% 8%	820
	11th to 20th	Night	23% 10% 32% 25% 9% 1	840
	21st to end	Night	28% 13% 29% 23% 6% 1	840
December	1st to 10th	Night	28% 10% 32% 24% 7%	840
	11th to 20th	Night	26% 14% 33% 22% 5% 1	840
	21st to end	Night	33% 11% 29% 21% 5% 1	924

Page generated at 2026-06-28 02:10:46. Version ac07

Copyright © 2026 Attilla Danko.