Mont-Saint-Hilaire
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mont-Saint-Hilaire clear sky chart from 2005-11-06 to 2026-05-17.

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% 31%	131922
	Night	17% 12% 4 9% 6% 5% 4 3 5% 6% 29%	130906
Transparency	Day	51% 7% 12% 20% 9% 1	135366
	Night	55% 6% 11% 18% 9% 1	135536
Seeing	Day	22% 12% 29% 24% 11% 3	16457
	Night	23% 10% 29% 28% 9% 1	25489

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% 18% 6% 14% 6% 5% 3 2 3 4 22%	4661
	11th to 20th	Day	13% 17% 6% 15% 7% 6% 5% 3 4 6% 20%	4650
	21st to end	Day	10% 14% 5% 12% 9% 8% 6% 4 5% 5% 24%	5124
February	1st to 10th	Day	16% 16% 4 11% 7% 5% 4 4 4 5% 26%	1811
	11th to 20th	Day	14% 15% 5% 11% 7% 5% 4 3 5% 6% 25%	1979
	21st to end	Day	17% 15% 5% 8% 8% 4 4 3 4 6% 26%	1730
March	1st to 10th	Day	18% 13% 5% 11% 6% 5% 5% 4 4 5% 24%	4576
	11th to 20th	Day	13% 13% 4 9% 5% 5% 4 3 5% 7% 31%	4759
	21st to end	Day	18% 11% 4 9% 5% 4 4 3 4 5% 32%	6102
April	1st to 10th	Day	23% 11% 4 8% 5% 4 4 3 4 5% 29%	2520
	11th to 20th	Day	22% 9% 3 6% 4 4 4 3 4 6% 36%	2494
	21st to end	Day	22% 9% 3 7% 5% 5% 4 4 4 6% 32%	2718
May	1st to 10th	Day	27% 11% 3 9% 4 4 4 4 5% 6% 23%	6316
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 4 6% 8% 29%	6402
	21st to end	Day	21% 8% 3 7% 5% 4 5% 4 5% 8% 31%	6949
June	1st to 10th	Day	21% 8% 2 6% 4 5% 6% 3 5% 8% 30%	2800
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 4 6% 8% 39%	2800
	21st to end	Day	21% 8% 3 7% 5% 4 5% 4 6% 7% 31%	2800
July	1st to 10th	Day	13% 7% 3 8% 5% 6% 5% 5% 7% 9% 32%	6360
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 5% 7% 8% 40%	6360
	21st to end	Day	11% 6% 2 5% 4 4 4 4 6% 10% 45%	6926
August	1st to 10th	Day	14% 6% 3 8% 5% 6% 5% 4 7% 10% 33%	4563
	11th to 20th	Day	14% 6% 3 7% 5% 4 5% 4 6% 9% 37%	4146
	21st to end	Day	15% 6% 3 7% 4 5% 4 4 6% 8% 39%	4312
September	1st to 10th	Day	11% 5% 2 7% 4 4 4 5% 6% 7% 44%	2400
	11th to 20th	Day	15% 6% 1 4 4 3 4 3 5% 7% 49%	2293
	21st to end	Day	16% 7% 2 6% 4 4 5% 4 6% 7% 40%	2200
October	1st to 10th	Day	19% 7% 3 7% 5% 4 4 4 5% 7% 35%	2099
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 5% 7% 30%	1930
	21st to end	Day	25% 9% 4 7% 4 4 4 3 5% 6% 30%	1980
November	1st to 10th	Day	18% 12% 3 7% 5% 4 5% 3 5% 6% 32%	1851
	11th to 20th	Day	17% 13% 3 8% 5% 4 4 4 5% 7% 29%	1837
	21st to end	Day	24% 14% 3 8% 5% 5% 4 3 5% 6% 23%	1680
December	1st to 10th	Day	19% 20% 6% 12% 7% 4 4 2 4 5% 18%	2680
	11th to 20th	Day	20% 14% 4 10% 5% 4 4 3 5% 6% 25%	3066
	21st to end	Day	23% 13% 5% 11% 5% 5% 5% 5% 6% 4 17%	4048
January	1st to 10th	Night	14% 20% 7% 14% 6% 4 4 2 4 4 21%	8234
	11th to 20th	Night	12% 18% 7% 17% 8% 6% 5% 4 4 5% 16%	8235
	21st to end	Night	11% 14% 5% 13% 9% 6% 5% 4 5% 5% 24%	9057
February	1st to 10th	Night	14% 16% 6% 11% 8% 5% 4 3 5% 5% 22%	2805
	11th to 20th	Night	14% 12% 6% 11% 6% 5% 5% 3 4 5% 28%	2526
	21st to end	Night	15% 14% 4 10% 5% 5% 4 3 5% 5% 30%	2076
March	1st to 10th	Night	21% 12% 4 8% 5% 4 4 3 4 4 30%	5484
	11th to 20th	Night	15% 14% 4 7% 5% 5% 4 4 5% 6% 30%	5418
	21st to end	Night	16% 13% 4 11% 6% 4 4 3 4 4 30%	5072
April	1st to 10th	Night	24% 11% 3 7% 4 4 4 4 4 6% 30%	2100
	11th to 20th	Night	22% 9% 3 8% 4 4 3 4 4 5% 33%	2075
	21st to end	Night	21% 10% 3 7% 4 4 4 3 4 6% 35%	1901
May	1st to 10th	Night	26% 10% 4 9% 5% 4 5% 4 5% 6% 24%	3873
	11th to 20th	Night	24% 8% 3 8% 5% 4 4 4 5% 6% 30%	3623
	21st to end	Night	19% 9% 3 9% 5% 5% 4 4 5% 7% 31%	3926
June	1st to 10th	Night	22% 9% 3 6% 4 4 5% 3 5% 7% 32%	1600
	11th to 20th	Night	16% 5% 3 7% 5% 4 4 5% 6% 8% 36%	1600
	21st to end	Night	17% 8% 3 8% 4 4 5% 4 5% 7% 34%	1600
July	1st to 10th	Night	13% 7% 3 7% 6% 5% 5% 5% 7% 9% 32%	3600
	11th to 20th	Night	15% 6% 2 6% 5% 4 5% 4 6% 7% 40%	3600
	21st to end	Night	9% 5% 2 7% 5% 5% 5% 4 7% 8% 42%	3926
August	1st to 10th	Night	17% 8% 4 7% 5% 5% 4 4 6% 6% 35%	2586
	11th to 20th	Night	16% 7% 3 7% 5% 4 4 5% 6% 7% 37%	2865
	21st to end	Night	17% 6% 2 6% 4 5% 5% 4 5% 7% 38%	3586
September	1st to 10th	Night	13% 5% 2 7% 4 4 4 3 6% 7% 44%	2000
	11th to 20th	Night	14% 5% 3 5% 4 3 3 3 5% 7% 49%	2106
	21st to end	Night	17% 6% 3 6% 5% 4 3 3 5% 7% 42%	2200
October	1st to 10th	Night	18% 6% 2 6% 5% 3 3 4 5% 6% 41%	2299
	11th to 20th	Night	21% 7% 3 8% 5% 4 5% 3 4 6% 34%	2470
	21st to end	Night	23% 9% 3 9% 5% 5% 4 3 4 5% 30%	2860
November	1st to 10th	Night	20% 11% 3 8% 5% 4 5% 3 5% 6% 31%	2667
	11th to 20th	Night	20% 11% 3 8% 5% 4 4 4 5% 4 32%	2778
	21st to end	Night	23% 13% 4 9% 5% 4 4 3 4 4 26%	2940
December	1st to 10th	Night	19% 18% 6% 13% 7% 5% 4 3 4 4 16%	4720
	11th to 20th	Night	23% 13% 5% 10% 6% 4 4 3 4 6% 24%	5348
	21st to end	Night	23% 16% 5% 9% 4 3 4 4 6% 6% 20%	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	67% 5% 10% 15% 2	4662
	11th to 20th	Day	65% 6% 8% 13% 8%	4680
	21st to end	Day	61% 7% 9% 13% 10%	5124
February	1st to 10th	Day	61% 5% 9% 17% 6% 1	1811
	11th to 20th	Day	59% 6% 12% 17% 7% 1	1988
	21st to end	Day	60% 4 11% 15% 8% 1	1730
March	1st to 10th	Day	61% 6% 8% 14% 9% 3	4579
	11th to 20th	Day	51% 7% 16% 14% 10% 2	4759
	21st to end	Day	54% 5% 8% 18% 14% 1	6102
April	1st to 10th	Day	57% 5% 9% 18% 10% 1	2520
	11th to 20th	Day	49% 6% 9% 21% 13% 1	2494
	21st to end	Day	53% 6% 10% 19% 10% 2	2718
May	1st to 10th	Day	60% 7% 9% 18% 6% 1	6327
	11th to 20th	Day	50% 8% 15% 17% 8% 1	6406
	21st to end	Day	50% 7% 11% 20% 11% 1	6949
June	1st to 10th	Day	50% 8% 12% 18% 11% 1	2800
	11th to 20th	Day	41% 7% 13% 24% 13% 2	2800
	21st to end	Day	50% 8% 12% 20% 10% 1	2800
July	1st to 10th	Day	46% 7% 14% 25% 8%	6290
	11th to 20th	Day	38% 7% 15% 30% 10%	6285
	21st to end	Day	35% 7% 14% 36% 8%	6728
August	1st to 10th	Day	45% 8% 17% 23% 7%	4549
	11th to 20th	Day	42% 7% 19% 24% 6%	4187
	21st to end	Day	42% 6% 16% 22% 13%	4312
September	1st to 10th	Day	36% 8% 16% 29% 10%	2400
	11th to 20th	Day	35% 6% 13% 33% 13%	2293
	21st to end	Day	42% 7% 15% 25% 11%	2200
October	1st to 10th	Day	44% 6% 14% 29% 8%	3411
	11th to 20th	Day	44% 7% 17% 25% 6%	3120
	21st to end	Day	47% 5% 19% 22% 8%	3180
November	1st to 10th	Day	52% 7% 12% 20% 7% 1	1851
	11th to 20th	Day	54% 7% 12% 18% 9%	1837
	21st to end	Day	62% 8% 12% 13% 5%	1680
December	1st to 10th	Day	71% 5% 8% 15% 2	2680
	11th to 20th	Day	60% 6% 10% 16% 8%	3066
	21st to end	Day	67% 6% 11% 10% 6%	4048
January	1st to 10th	Night	67% 5% 11% 12% 4	8234
	11th to 20th	Night	70% 7% 8% 10% 5%	8280
	21st to end	Night	62% 5% 9% 13% 12%	9057
February	1st to 10th	Night	63% 5% 10% 15% 6% 1	2805
	11th to 20th	Night	59% 5% 11% 17% 8%	2528
	21st to end	Night	56% 6% 9% 17% 11% 1	2076
March	1st to 10th	Night	57% 5% 7% 15% 11% 4	5494
	11th to 20th	Night	54% 6% 12% 16% 11% 1	5419
	21st to end	Night	56% 5% 7% 21% 10% 2	5072
April	1st to 10th	Night	55% 5% 9% 18% 12% 1	2100
	11th to 20th	Night	53% 5% 7% 20% 12% 2	2075
	21st to end	Night	51% 6% 7% 20% 14% 3	1901
May	1st to 10th	Night	59% 8% 9% 16% 6% 2	3879
	11th to 20th	Night	53% 7% 10% 19% 9% 1	3624
	21st to end	Night	51% 7% 9% 18% 13% 1	3927
June	1st to 10th	Night	51% 6% 9% 21% 12% 1	1600
	11th to 20th	Night	43% 9% 11% 20% 14% 3	1600
	21st to end	Night	47% 8% 11% 19% 13% 1	1600
July	1st to 10th	Night	46% 7% 18% 20% 9%	3560
	11th to 20th	Night	41% 7% 15% 27% 10%	3552
	21st to end	Night	38% 7% 16% 28% 11%	3809
August	1st to 10th	Night	47% 7% 12% 26% 7%	2576
	11th to 20th	Night	45% 8% 17% 22% 8%	2890
	21st to end	Night	44% 7% 13% 22% 13% 1	3586
September	1st to 10th	Night	38% 8% 12% 27% 15% 1	2000
	11th to 20th	Night	35% 5% 15% 31% 12% 1	2106
	21st to end	Night	42% 7% 10% 25% 15% 1	2200
October	1st to 10th	Night	44% 6% 12% 27% 10%	3754
	11th to 20th	Night	46% 5% 11% 30% 8%	4019
	21st to end	Night	50% 5% 14% 18% 11% 2	4610
November	1st to 10th	Night	53% 6% 12% 22% 7% 1	2667
	11th to 20th	Night	54% 6% 12% 17% 10% 1	2778
	21st to end	Night	61% 7% 12% 16% 5%	2940
December	1st to 10th	Night	72% 5% 10% 10% 2	4720
	11th to 20th	Night	63% 5% 8% 14% 9%	5348
	21st to end	Night	65% 4 9% 14% 8%	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	29% 14% 30% 20% 8%	220
	11th to 20th	Day	29% 19% 33% 15% 4	220
	21st to end	Day	21% 16% 33% 22% 7% 1	242
February	1st to 10th	Day	26% 19% 32% 20% 3	289
	11th to 20th	Day	22% 16% 36% 22% 3	467
	21st to end	Day	24% 16% 33% 25% 3	446
March	1st to 10th	Day	23% 15% 34% 22% 6%	540
	11th to 20th	Day	26% 14% 34% 19% 6% 1	540
	21st to end	Day	30% 13% 29% 20% 7% 1	594
April	1st to 10th	Day	30% 15% 30% 17% 6% 1	540
	11th to 20th	Day	30% 18% 25% 17% 8% 2	532
	21st to end	Day	26% 17% 31% 14% 10% 2	540
May	1st to 10th	Day	27% 13% 30% 19% 10% 1	543
	11th to 20th	Day	18% 12% 29% 27% 12% 2	551
	21st to end	Day	20% 13% 32% 23% 10% 2	573
June	1st to 10th	Day	23% 11% 28% 28% 8% 2	530
	11th to 20th	Day	17% 10% 30% 29% 12% 2	530
	21st to end	Day	23% 11% 28% 23% 12% 2	530
July	1st to 10th	Day	13% 9% 28% 30% 17% 4	525
	11th to 20th	Day	13% 7% 32% 32% 13% 4	524
	21st to end	Day	14% 8% 28% 32% 16% 2	576
August	1st to 10th	Day	13% 5% 25% 33% 19% 5%	526
	11th to 20th	Day	13% 6% 22% 33% 18% 7%	519
	21st to end	Day	15% 10% 24% 24% 19% 8%	583
September	1st to 10th	Day	13% 8% 29% 29% 13% 7%	530
	11th to 20th	Day	15% 7% 19% 27% 20% 12%	530
	21st to end	Day	18% 9% 26% 24% 17% 6%	530
October	1st to 10th	Day	20% 12% 28% 22% 14% 4	530
	11th to 20th	Day	22% 14% 30% 20% 12% 1	491
	21st to end	Day	32% 13% 25% 23% 6%	462
November	1st to 10th	Day	28% 15% 29% 20% 7%	425
	11th to 20th	Day	24% 16% 31% 20% 7% 1	377
	21st to end	Day	33% 14% 30% 17% 5% 1	220
December	1st to 10th	Day	31% 13% 23% 24% 6% 3	220
	11th to 20th	Day	25% 24% 35% 14% 3	220
	21st to end	Day	30% 19% 27% 18% 3 3	242
January	1st to 10th	Night	28% 12% 31% 24% 5%	840
	11th to 20th	Night	26% 12% 33% 22% 6%	840
	21st to end	Night	21% 11% 34% 27% 7% 1	924
February	1st to 10th	Night	22% 11% 34% 26% 5% 1	840
	11th to 20th	Night	21% 12% 39% 23% 5%	823
	21st to end	Night	24% 11% 33% 29% 4	692
March	1st to 10th	Night	24% 12% 32% 27% 5%	840
	11th to 20th	Night	25% 14% 31% 23% 6%	840
	21st to end	Night	24% 11% 30% 27% 7% 1	924
April	1st to 10th	Night	29% 13% 28% 26% 5%	840
	11th to 20th	Night	25% 15% 28% 25% 6%	831
	21st to end	Night	26% 12% 29% 25% 7% 1	641
May	1st to 10th	Night	27% 8% 32% 27% 6% 1	515
	11th to 20th	Night	22% 9% 31% 29% 8% 1	406
	21st to end	Night	18% 8% 34% 30% 9%	433
June	1st to 10th	Night	25% 7% 28% 33% 8% 1	400
	11th to 20th	Night	19% 6% 29% 35% 11%	400
	21st to end	Night	18% 6% 31% 34% 12% 1	400
July	1st to 10th	Night	12% 5% 30% 39% 15%	390
	11th to 20th	Night	12% 2 26% 45% 14% 1	388
	21st to end	Night	13% 4 24% 44% 15% 1	438
August	1st to 10th	Night	13% 5% 17% 45% 19% 2	398
	11th to 20th	Night	14% 3 21% 36% 24% 2	582
	21st to end	Night	16% 5% 21% 36% 19% 2	880
September	1st to 10th	Night	15% 5% 25% 39% 16% 1	800
	11th to 20th	Night	16% 5% 20% 33% 23% 3	800
	21st to end	Night	19% 6% 27% 31% 15% 3	800
October	1st to 10th	Night	21% 7% 29% 30% 13% 1	800
	11th to 20th	Night	25% 9% 27% 30% 9% 1	800
	21st to end	Night	28% 11% 31% 25% 5%	880
November	1st to 10th	Night	26% 13% 30% 24% 7%	820
	11th to 20th	Night	25% 13% 30% 22% 8% 1	840
	21st to end	Night	28% 15% 30% 20% 6%	840
December	1st to 10th	Night	30% 13% 28% 24% 5%	840
	11th to 20th	Night	29% 15% 32% 19% 5% 1	840
	21st to end	Night	33% 13% 29% 19% 5%	924

Page generated at 2026-05-14 01:58:54. Version ac07

Copyright © 2026 Attilla Danko.