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 2025-01-22.

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% 4 4 5% 7% 32%	105259
	Night	18% 11% 4 9% 5% 4 4 3 5% 6% 30%	104123
Transparency	Day	50% 7% 13% 21% 8% 1	108721
	Night	54% 7% 11% 18% 9% 1	108737
Seeing	Day	22% 12% 28% 24% 11% 3	14772
	Night	23% 10% 29% 28% 9% 1	23826

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	19% 17% 7% 12% 6% 5% 3 2 3 4 23%	2597
	11th to 20th	Day	15% 15% 6% 11% 6% 5% 4 3 4 7% 25%	2600
	21st to end	Day	14% 16% 4 11% 6% 5% 5% 4 5% 6% 24%	2780
February	1st to 10th	Day	17% 17% 4 10% 7% 5% 4 4 4 5% 24%	1638
	11th to 20th	Day	14% 15% 5% 11% 7% 5% 4 3 5% 6% 25%	1785
	21st to end	Day	18% 15% 5% 7% 7% 4 4 3 4 6% 27%	1570
March	1st to 10th	Day	20% 12% 4 10% 6% 5% 4 4 4 5% 26%	3116
	11th to 20th	Day	15% 16% 5% 10% 5% 5% 4 3 5% 5% 26%	3254
	21st to end	Day	15% 10% 4 9% 5% 4 4 4 5% 5% 36%	4166
April	1st to 10th	Day	23% 11% 4 8% 5% 4 4 3 4 5% 29%	2280
	11th to 20th	Day	22% 8% 3 6% 4 4 4 3 4 6% 36%	2254
	21st to end	Day	22% 9% 3 7% 5% 5% 4 3 4 6% 32%	2459
May	1st to 10th	Day	22% 9% 3 8% 4 4 4 4 6% 7% 30%	4316
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 30%	4398
	21st to end	Day	15% 6% 2 6% 5% 5% 6% 5% 6% 9% 35%	4837
June	1st to 10th	Day	21% 8% 2 6% 4 5% 5% 4 5% 8% 30%	2660
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 7% 8% 38%	2660
	21st to end	Day	21% 8% 3 7% 5% 4 5% 4 6% 7% 30%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 6% 5% 4 7% 10% 36%	4440
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 5% 8% 9% 37%	4440
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 8% 44%	4814
August	1st to 10th	Day	14% 6% 3 9% 5% 6% 5% 4 7% 10% 32%	4423
	11th to 20th	Day	14% 6% 3 7% 5% 4 5% 4 6% 9% 37%	4017
	21st to end	Day	15% 6% 3 7% 4 5% 4 4 6% 7% 39%	4180
September	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 5% 7% 7% 42%	2280
	11th to 20th	Day	15% 6% 1 4 3 3 4 3 5% 7% 48%	2179
	21st to end	Day	16% 7% 2 6% 4 4 5% 4 6% 7% 40%	2090
October	1st to 10th	Day	19% 7% 3 7% 5% 5% 4 4 6% 7% 32%	1994
	11th to 20th	Day	18% 9% 3 8% 5% 6% 5% 4 5% 7% 30%	1834
	21st to end	Day	25% 9% 4 7% 4 4 4 3 5% 5% 30%	1881
November	1st to 10th	Day	17% 11% 3 7% 6% 4 5% 3 5% 7% 33%	1761
	11th to 20th	Day	17% 13% 3 9% 5% 4 4 4 5% 7% 30%	1750
	21st to end	Day	24% 13% 3 8% 6% 5% 4 4 5% 6% 23%	1600
December	1st to 10th	Day	20% 20% 6% 12% 7% 4 4 2 4 5% 18%	2600
	11th to 20th	Day	20% 14% 4 10% 5% 4 4 3 5% 6% 25%	2986
	21st to end	Day	23% 13% 5% 11% 5% 5% 5% 5% 6% 4 17%	3960
January	1st to 10th	Night	17% 18% 6% 11% 5% 4 4 3 4 5% 22%	4569
	11th to 20th	Night	12% 15% 5% 13% 8% 7% 5% 4 5% 5% 21%	4580
	21st to end	Night	17% 18% 5% 10% 7% 4 3 3 4 4 24%	4899
February	1st to 10th	Night	16% 17% 6% 11% 8% 5% 4 3 5% 5% 21%	2539
	11th to 20th	Night	15% 12% 6% 11% 7% 5% 5% 3 4 5% 28%	2280
	21st to end	Night	16% 14% 4 10% 6% 4 4 3 5% 5% 30%	1884
March	1st to 10th	Night	22% 10% 4 8% 5% 3 3 3 4 5% 33%	3724
	11th to 20th	Night	19% 19% 5% 8% 5% 4 3 3 3 4 27%	3703
	21st to end	Night	14% 12% 4 9% 5% 4 4 2 4 4 36%	3466
April	1st to 10th	Night	24% 10% 3 7% 4 4 4 4 4 6% 30%	1900
	11th to 20th	Night	22% 8% 3 7% 4 4 4 4 4 6% 33%	1875
	21st to end	Night	22% 10% 2 7% 4 4 3 3 4 6% 35%	1720
May	1st to 10th	Night	23% 9% 3 7% 4 4 5% 4 5% 7% 29%	2652
	11th to 20th	Night	23% 8% 3 6% 5% 3 4 4 5% 6% 33%	2495
	21st to end	Night	16% 7% 2 8% 4 5% 4 4 5% 8% 37%	2738
June	1st to 10th	Night	22% 9% 3 6% 4 4 5% 3 5% 7% 32%	1520
	11th to 20th	Night	17% 5% 3 7% 5% 4 4 5% 6% 8% 36%	1520
	21st to end	Night	18% 8% 3 8% 5% 4 5% 4 5% 7% 33%	1520
July	1st to 10th	Night	13% 8% 3 8% 6% 5% 5% 5% 6% 8% 33%	2520
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 4 7% 7% 40%	2520
	21st to end	Night	12% 5% 2 7% 5% 5% 5% 4 7% 7% 41%	2739
August	1st to 10th	Night	17% 8% 4 7% 5% 5% 4 4 6% 6% 34%	2506
	11th to 20th	Night	16% 7% 3 7% 5% 4 4 5% 6% 7% 36%	2775
	21st to end	Night	17% 6% 2 6% 4 5% 5% 4 5% 7% 38%	3476
September	1st to 10th	Night	14% 5% 2 7% 4 4 4 3 5% 8% 44%	1900
	11th to 20th	Night	15% 5% 3 5% 4 3 3 3 5% 6% 49%	2000
	21st to end	Night	17% 6% 3 6% 5% 4 3 2 5% 7% 42%	2090
October	1st to 10th	Night	18% 6% 2 7% 5% 4 3 4 5% 6% 39%	2184
	11th to 20th	Night	22% 7% 3 8% 5% 4 5% 3 4 5% 33%	2346
	21st to end	Night	24% 9% 3 9% 5% 5% 4 3 4 4 30%	2717
November	1st to 10th	Night	19% 12% 3 8% 5% 4 5% 3 5% 6% 31%	2537
	11th to 20th	Night	20% 11% 3 8% 5% 4 4 4 5% 4 32%	2645
	21st to end	Night	23% 13% 4 9% 5% 4 4 3 5% 5% 26%	2800
December	1st to 10th	Night	19% 18% 6% 13% 7% 5% 4 3 4 4 16%	4580
	11th to 20th	Night	23% 13% 5% 10% 5% 4 4 3 4 6% 24%	5208
	21st to end	Night	23% 16% 5% 9% 4 3 4 4 6% 6% 20%	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	65% 8% 12% 13% 2	2598
	11th to 20th	Day	58% 9% 12% 16% 5%	2600
	21st to end	Day	60% 9% 13% 13% 4	2780
February	1st to 10th	Day	62% 5% 10% 17% 5% 1	1638
	11th to 20th	Day	59% 6% 12% 15% 7% 1	1794
	21st to end	Day	60% 4 12% 15% 9% 1	1570
March	1st to 10th	Day	58% 8% 9% 18% 6% 1	3119
	11th to 20th	Day	57% 8% 12% 12% 9% 2	3254
	21st to end	Day	47% 6% 10% 21% 14% 1	4166
April	1st to 10th	Day	57% 5% 9% 18% 10% 1	2280
	11th to 20th	Day	48% 7% 9% 22% 13% 1	2254
	21st to end	Day	53% 6% 10% 18% 10% 3	2459
May	1st to 10th	Day	50% 8% 11% 21% 8% 1	4330
	11th to 20th	Day	48% 10% 17% 16% 8% 1	4402
	21st to end	Day	42% 9% 12% 23% 12% 1	4837
June	1st to 10th	Day	50% 8% 12% 18% 10% 1	2660
	11th to 20th	Day	41% 7% 13% 23% 13% 2	2660
	21st to end	Day	51% 8% 13% 19% 9% 1	2660
July	1st to 10th	Day	41% 7% 14% 28% 9%	4370
	11th to 20th	Day	41% 8% 17% 29% 6%	4365
	21st to end	Day	37% 7% 14% 33% 8%	4661
August	1st to 10th	Day	46% 8% 17% 22% 7%	4409
	11th to 20th	Day	43% 8% 20% 24% 6%	4058
	21st to end	Day	42% 6% 16% 21% 14%	4180
September	1st to 10th	Day	37% 9% 16% 27% 11%	2280
	11th to 20th	Day	36% 6% 13% 32% 13%	2179
	21st to end	Day	42% 7% 15% 26% 10%	2090
October	1st to 10th	Day	45% 6% 14% 28% 7%	3306
	11th to 20th	Day	44% 7% 18% 25% 6%	3024
	21st to end	Day	46% 5% 19% 22% 8%	3081
November	1st to 10th	Day	51% 8% 13% 21% 7% 1	1761
	11th to 20th	Day	53% 7% 12% 18% 9%	1750
	21st to end	Day	61% 9% 13% 13% 5%	1600
December	1st to 10th	Day	71% 5% 8% 14% 2	2600
	11th to 20th	Day	60% 6% 10% 16% 8%	2986
	21st to end	Day	67% 6% 11% 10% 6%	3960
January	1st to 10th	Night	63% 8% 15% 11% 3	4569
	11th to 20th	Night	61% 10% 12% 12% 4	4580
	21st to end	Night	64% 6% 12% 12% 6%	4899
February	1st to 10th	Night	65% 6% 10% 14% 5% 1	2539
	11th to 20th	Night	58% 5% 11% 17% 8%	2282
	21st to end	Night	56% 6% 10% 16% 12% 1	1884
March	1st to 10th	Night	53% 7% 10% 19% 8% 3	3734
	11th to 20th	Night	60% 6% 8% 13% 12% 1	3704
	21st to end	Night	49% 6% 7% 23% 13% 2	3466
April	1st to 10th	Night	55% 5% 9% 18% 12% 1	1900
	11th to 20th	Night	52% 6% 8% 21% 12% 2	1875
	21st to end	Night	51% 6% 8% 20% 13% 3	1720
May	1st to 10th	Night	52% 10% 10% 19% 8% 3	2658
	11th to 20th	Night	48% 9% 11% 20% 10% 2	2496
	21st to end	Night	43% 8% 10% 20% 17% 2	2739
June	1st to 10th	Night	50% 7% 10% 22% 11% 1	1520
	11th to 20th	Night	43% 9% 12% 20% 13% 3	1520
	21st to end	Night	48% 9% 12% 18% 13% 1	1520
July	1st to 10th	Night	47% 7% 15% 20% 12%	2480
	11th to 20th	Night	40% 7% 17% 27% 9%	2472
	21st to end	Night	40% 7% 18% 23% 12%	2651
August	1st to 10th	Night	48% 7% 12% 25% 7%	2496
	11th to 20th	Night	46% 8% 18% 21% 7%	2800
	21st to end	Night	44% 7% 13% 22% 14% 1	3476
September	1st to 10th	Night	38% 8% 12% 25% 15% 1	1900
	11th to 20th	Night	36% 5% 15% 31% 12% 1	2000
	21st to end	Night	42% 7% 11% 26% 14% 1	2090
October	1st to 10th	Night	45% 6% 12% 27% 9%	3639
	11th to 20th	Night	46% 5% 11% 30% 8%	3895
	21st to end	Night	50% 4 14% 18% 11% 2	4467
November	1st to 10th	Night	52% 6% 12% 21% 7% 1	2537
	11th to 20th	Night	53% 6% 12% 17% 10% 1	2645
	21st to end	Night	60% 7% 12% 16% 5%	2800
December	1st to 10th	Night	72% 5% 10% 10% 2	4580
	11th to 20th	Night	63% 5% 8% 14% 9%	5208
	21st to end	Night	65% 5% 9% 14% 8%	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	30% 15% 30% 19% 8%	200
	11th to 20th	Day	28% 18% 34% 16% 5% 1	200
	21st to end	Day	21% 14% 32% 25% 8% 1	200
February	1st to 10th	Day	31% 19% 31% 17% 3	236
	11th to 20th	Day	22% 17% 37% 21% 3 1	393
	21st to end	Day	26% 15% 30% 25% 3	382
March	1st to 10th	Day	24% 13% 32% 24% 7%	460
	11th to 20th	Day	23% 16% 35% 19% 7% 1	460
	21st to end	Day	29% 11% 30% 21% 8% 1	506
April	1st to 10th	Day	29% 13% 30% 20% 7% 2	460
	11th to 20th	Day	29% 18% 24% 17% 9% 3	452
	21st to end	Day	26% 16% 30% 16% 10% 2	460
May	1st to 10th	Day	24% 12% 31% 20% 11% 2	463
	11th to 20th	Day	17% 11% 30% 26% 13% 3	487
	21st to end	Day	18% 13% 33% 23% 10% 2	529
June	1st to 10th	Day	23% 11% 27% 28% 9% 2	490
	11th to 20th	Day	16% 9% 29% 31% 13% 2	490
	21st to end	Day	23% 11% 27% 24% 13% 2	490
July	1st to 10th	Day	13% 8% 27% 31% 17% 4	485
	11th to 20th	Day	14% 6% 31% 32% 13% 4	484
	21st to end	Day	15% 7% 27% 33% 16% 2	532
August	1st to 10th	Day	14% 6% 24% 32% 20% 4	486
	11th to 20th	Day	13% 6% 22% 33% 18% 8%	479
	21st to end	Day	15% 9% 24% 25% 18% 9%	539
September	1st to 10th	Day	13% 8% 29% 29% 13% 7%	490
	11th to 20th	Day	16% 7% 20% 27% 18% 12%	490
	21st to end	Day	18% 8% 26% 24% 18% 6%	490
October	1st to 10th	Day	21% 12% 28% 22% 13% 4	490
	11th to 20th	Day	23% 15% 29% 19% 13% 1	455
	21st to end	Day	31% 14% 26% 22% 7%	429
November	1st to 10th	Day	27% 15% 29% 22% 7% 1	395
	11th to 20th	Day	24% 17% 32% 19% 7% 1	350
	21st to end	Day	34% 14% 29% 18% 5% 1	200
December	1st to 10th	Day	34% 12% 21% 25% 6% 3	200
	11th to 20th	Day	25% 25% 33% 15% 3	200
	21st to end	Day	31% 19% 25% 18% 4 3	220
January	1st to 10th	Night	28% 12% 32% 24% 5%	800
	11th to 20th	Night	25% 12% 34% 23% 7%	800
	21st to end	Night	21% 10% 34% 27% 7% 1	841
February	1st to 10th	Night	23% 11% 36% 25% 5% 1	760
	11th to 20th	Night	20% 12% 39% 23% 5%	743
	21st to end	Night	24% 11% 32% 28% 4	628
March	1st to 10th	Night	24% 12% 31% 28% 5%	760
	11th to 20th	Night	26% 12% 31% 24% 7%	760
	21st to end	Night	23% 10% 31% 28% 7% 1	836
April	1st to 10th	Night	28% 12% 27% 27% 5%	760
	11th to 20th	Night	25% 15% 27% 26% 6% 1	751
	21st to end	Night	27% 12% 29% 25% 7% 1	580
May	1st to 10th	Night	26% 8% 32% 27% 6% 1	466
	11th to 20th	Night	22% 9% 31% 29% 8% 1	374
	21st to end	Night	18% 8% 35% 30% 9%	411
June	1st to 10th	Night	24% 7% 27% 32% 9% 1	380
	11th to 20th	Night	19% 5% 29% 35% 11%	380
	21st to end	Night	18% 6% 30% 33% 13% 1	380
July	1st to 10th	Night	12% 5% 29% 38% 15%	370
	11th to 20th	Night	11% 2 27% 45% 14% 1	368
	21st to end	Night	13% 4 23% 43% 16% 1	416
August	1st to 10th	Night	14% 6% 17% 44% 19% 1	378
	11th to 20th	Night	14% 3 22% 35% 24% 2	552
	21st to end	Night	16% 4 22% 36% 19% 2	836
September	1st to 10th	Night	16% 5% 24% 39% 15% 1	760
	11th to 20th	Night	17% 5% 20% 32% 22% 3	760
	21st to end	Night	19% 6% 27% 31% 15% 3	760
October	1st to 10th	Night	21% 7% 29% 30% 13% 1	760
	11th to 20th	Night	26% 9% 26% 29% 9% 1	760
	21st to end	Night	28% 11% 31% 25% 5%	836
November	1st to 10th	Night	25% 13% 30% 24% 7% 1	780
	11th to 20th	Night	25% 14% 30% 22% 9% 1	800
	21st to end	Night	29% 15% 30% 20% 6%	800
December	1st to 10th	Night	30% 13% 28% 24% 5%	800
	11th to 20th	Night	29% 14% 31% 20% 5% 1	800
	21st to end	Night	33% 13% 29% 19% 5%	880

Page generated at 2025-01-19 03:06:44. Version ac07

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