Salaberry-de-Valleyfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salaberry-de-Valleyfield 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	16% 10% 3 8% 5% 5% 5% 4 6% 7% 31%	131980
	Night	17% 12% 4 10% 6% 5% 4 4 5% 6% 28%	130866
Transparency	Day	51% 5% 12% 21% 9% 1	135437
	Night	56% 5% 11% 18% 9% 1	135496
Seeing	Day	21% 13% 29% 23% 11% 3	16436
	Night	23% 12% 29% 26% 9% 1	25530

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% 13% 6% 5% 5% 3 4 6% 18%	4661
	11th to 20th	Day	10% 15% 7% 14% 9% 6% 6% 4 5% 5% 19%	4650
	21st to end	Day	10% 13% 5% 12% 9% 8% 6% 4 6% 6% 19%	5124
February	1st to 10th	Day	15% 15% 4 11% 7% 6% 4 4 5% 6% 23%	1878
	11th to 20th	Day	13% 12% 5% 10% 7% 5% 5% 4 7% 5% 26%	1938
	21st to end	Day	18% 14% 4 11% 7% 4 5% 3 5% 6% 23%	1730
March	1st to 10th	Day	17% 12% 4 11% 6% 5% 4 4 6% 7% 25%	4576
	11th to 20th	Day	11% 12% 4 10% 6% 5% 5% 4 6% 7% 30%	4851
	21st to end	Day	18% 9% 3 10% 5% 4 4 3 5% 5% 34%	6055
April	1st to 10th	Day	20% 11% 3 7% 5% 3 5% 4 4 6% 32%	2520
	11th to 20th	Day	19% 8% 3 7% 6% 3 4 4 6% 5% 35%	2494
	21st to end	Day	21% 10% 3 7% 5% 4 4 3 5% 6% 33%	2662
May	1st to 10th	Day	24% 10% 4 9% 5% 4 5% 4 5% 5% 24%	6434
	11th to 20th	Day	19% 9% 3 8% 5% 5% 4 3 5% 7% 31%	6402
	21st to end	Day	20% 9% 3 7% 4 5% 4 4 6% 7% 32%	6949
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 4 4 5% 7% 32%	2800
	11th to 20th	Day	13% 6% 3 6% 5% 4 5% 4 6% 7% 39%	2800
	21st to end	Day	18% 7% 3 7% 5% 4 5% 4 6% 8% 33%	2800
July	1st to 10th	Day	11% 6% 3 8% 5% 6% 6% 5% 6% 9% 35%	6360
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 4 7% 8% 42%	6360
	21st to end	Day	11% 5% 2 5% 4 4 4 4 7% 10% 45%	6926
August	1st to 10th	Day	15% 7% 3 7% 5% 5% 4 4 7% 9% 34%	4563
	11th to 20th	Day	13% 7% 3 7% 4 5% 4 4 6% 7% 41%	4085
	21st to end	Day	15% 6% 2 6% 3 4 5% 5% 6% 8% 40%	4312
September	1st to 10th	Day	12% 6% 3 5% 4 4 4 3 6% 8% 45%	2400
	11th to 20th	Day	13% 5% 2 6% 4 4 3 4 4 6% 50%	2330
	21st to end	Day	16% 7% 3 6% 4 4 5% 4 5% 7% 40%	2200
October	1st to 10th	Day	19% 7% 3 6% 4 4 4 4 5% 7% 36%	2041
	11th to 20th	Day	17% 9% 3 9% 6% 5% 5% 4 5% 6% 31%	1980
	21st to end	Day	24% 11% 3 8% 4 5% 4 3 5% 6% 27%	1980
November	1st to 10th	Day	17% 11% 3 8% 5% 5% 4 4 6% 6% 31%	1851
	11th to 20th	Day	16% 13% 4 9% 5% 5% 5% 4 6% 6% 27%	1794
	21st to end	Day	20% 15% 5% 8% 6% 5% 5% 4 6% 6% 19%	1680
December	1st to 10th	Day	19% 18% 6% 12% 7% 6% 5% 4 4 5% 14%	2680
	11th to 20th	Day	17% 13% 5% 11% 7% 6% 6% 4 5% 5% 21%	3066
	21st to end	Day	22% 15% 4 11% 6% 5% 6% 5% 5% 5% 17%	4048
January	1st to 10th	Night	13% 21% 8% 15% 6% 4 4 3 4 5% 18%	8234
	11th to 20th	Night	11% 18% 7% 18% 8% 6% 5% 4 5% 4 14%	8235
	21st to end	Night	11% 16% 5% 13% 8% 6% 5% 4 5% 6% 21%	9057
February	1st to 10th	Night	14% 15% 6% 12% 8% 6% 5% 3 5% 5% 20%	2740
	11th to 20th	Night	14% 12% 5% 12% 6% 5% 6% 4 5% 5% 26%	2566
	21st to end	Night	14% 14% 4 10% 7% 5% 4 3 4 5% 29%	2076
March	1st to 10th	Night	20% 13% 4 9% 6% 5% 4 3 4 5% 29%	5484
	11th to 20th	Night	16% 14% 4 8% 5% 5% 5% 4 6% 7% 28%	5324
	21st to end	Night	16% 12% 4 10% 6% 4 4 4 4 5% 30%	5119
April	1st to 10th	Night	23% 10% 3 9% 6% 4 4 3 4 6% 29%	2100
	11th to 20th	Night	23% 11% 3 7% 4 4 4 4 4 6% 31%	2075
	21st to end	Night	20% 11% 3 8% 4 3 4 3 4 5% 34%	1958
May	1st to 10th	Night	25% 11% 3 8% 5% 5% 4 3 5% 7% 23%	3770
	11th to 20th	Night	22% 9% 3 7% 5% 4 5% 3 5% 7% 31%	3623
	21st to end	Night	17% 9% 4 9% 5% 5% 5% 3 6% 7% 30%	3926
June	1st to 10th	Night	19% 9% 3 7% 5% 5% 5% 4 7% 9% 28%	1600
	11th to 20th	Night	16% 7% 3 6% 4 4 5% 4 5% 6% 41%	1600
	21st to end	Night	17% 8% 3 8% 5% 4 4 4 5% 7% 34%	1600
July	1st to 10th	Night	12% 7% 3 7% 5% 5% 5% 5% 8% 9% 33%	3600
	11th to 20th	Night	13% 6% 3 7% 4 4 4 4 6% 8% 41%	3600
	21st to end	Night	10% 7% 2 7% 5% 4 5% 4 6% 8% 42%	3926
August	1st to 10th	Night	15% 8% 3 8% 4 4 4 3 5% 8% 39%	2586
	11th to 20th	Night	16% 8% 3 7% 4 5% 5% 3 5% 6% 39%	2927
	21st to end	Night	14% 6% 2 7% 4 5% 4 3 6% 9% 40%	3586
September	1st to 10th	Night	12% 6% 2 7% 5% 4 5% 4 5% 8% 43%	2000
	11th to 20th	Night	14% 5% 2 6% 3 3 3 3 5% 7% 49%	2069
	21st to end	Night	17% 6% 3 6% 5% 4 5% 3 5% 6% 41%	2200
October	1st to 10th	Night	19% 7% 2 6% 5% 4 5% 4 5% 6% 37%	2355
	11th to 20th	Night	19% 9% 3 7% 6% 5% 5% 4 5% 6% 33%	2420
	21st to end	Night	23% 9% 3 9% 5% 5% 4 4 5% 5% 29%	2860
November	1st to 10th	Night	20% 10% 3 8% 5% 5% 4 4 5% 6% 31%	2667
	11th to 20th	Night	19% 12% 4 8% 5% 4 4 3 5% 5% 31%	2825
	21st to end	Night	21% 13% 4 11% 6% 4 4 4 5% 5% 22%	2940
December	1st to 10th	Night	17% 21% 6% 12% 7% 5% 4 3 4 4 15%	4720
	11th to 20th	Night	22% 15% 5% 9% 5% 5% 4 4 5% 5% 21%	5348
	21st to end	Night	23% 16% 5% 11% 5% 4 4 3 5% 5% 19%	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% 4 12% 14% 3	4662
	11th to 20th	Day	64% 5% 8% 13% 9% 1	4680
	21st to end	Day	64% 5% 11% 12% 9% 1	5124
February	1st to 10th	Day	61% 5% 10% 18% 5% 1	1878
	11th to 20th	Day	57% 5% 12% 18% 7% 1	1947
	21st to end	Day	61% 5% 10% 14% 9% 1	1730
March	1st to 10th	Day	58% 4 10% 17% 9% 3	4579
	11th to 20th	Day	52% 5% 16% 16% 9% 2	4851
	21st to end	Day	52% 5% 7% 19% 16% 2	6055
April	1st to 10th	Day	53% 5% 8% 20% 12% 2	2520
	11th to 20th	Day	49% 4 7% 22% 16% 1	2494
	21st to end	Day	52% 5% 9% 19% 13% 3	2662
May	1st to 10th	Day	60% 6% 8% 18% 7% 1	6445
	11th to 20th	Day	52% 6% 13% 19% 9% 1	6406
	21st to end	Day	50% 5% 12% 21% 11% 1	6949
June	1st to 10th	Day	50% 6% 11% 19% 13% 1	2800
	11th to 20th	Day	43% 6% 12% 24% 13% 2	2800
	21st to end	Day	49% 6% 14% 20% 10% 1	2800
July	1st to 10th	Day	45% 5% 13% 27% 9%	6290
	11th to 20th	Day	38% 6% 14% 29% 13%	6285
	21st to end	Day	34% 6% 14% 37% 9%	6728
August	1st to 10th	Day	45% 6% 16% 24% 9%	4549
	11th to 20th	Day	42% 6% 17% 28% 7%	4127
	21st to end	Day	40% 6% 18% 24% 12%	4312
September	1st to 10th	Day	37% 6% 13% 30% 13%	2400
	11th to 20th	Day	35% 5% 13% 32% 15% 1	2330
	21st to end	Day	42% 6% 14% 26% 11% 1	2200
October	1st to 10th	Day	46% 4 13% 28% 9%	3327
	11th to 20th	Day	45% 5% 17% 26% 7%	3208
	21st to end	Day	47% 5% 19% 23% 7%	3180
November	1st to 10th	Day	52% 5% 13% 21% 8% 1	1851
	11th to 20th	Day	55% 7% 11% 17% 9% 1	1794
	21st to end	Day	65% 8% 12% 12% 4	1680
December	1st to 10th	Day	71% 5% 11% 12% 1	2680
	11th to 20th	Day	62% 7% 10% 15% 6%	3066
	21st to end	Day	67% 5% 9% 15% 4	4048
January	1st to 10th	Night	70% 3 10% 12% 4	8234
	11th to 20th	Night	71% 6% 7% 10% 6%	8280
	21st to end	Night	63% 5% 8% 14% 10% 1	9057
February	1st to 10th	Night	65% 5% 8% 15% 6% 1	2740
	11th to 20th	Night	58% 5% 10% 19% 7%	2568
	21st to end	Night	58% 5% 8% 17% 11% 1	2076
March	1st to 10th	Night	59% 3 7% 16% 12% 3	5494
	11th to 20th	Night	54% 6% 14% 14% 9% 2	5325
	21st to end	Night	55% 5% 5% 22% 12% 2	5119
April	1st to 10th	Night	56% 4 7% 19% 12% 1	2100
	11th to 20th	Night	54% 5% 8% 20% 12% 1	2075
	21st to end	Night	52% 4 7% 18% 15% 4	1958
May	1st to 10th	Night	60% 5% 10% 16% 7% 2	3776
	11th to 20th	Night	52% 5% 10% 20% 11% 1	3624
	21st to end	Night	52% 5% 11% 18% 13% 1	3927
June	1st to 10th	Night	50% 7% 12% 18% 12% 1	1600
	11th to 20th	Night	44% 5% 12% 21% 16% 2	1600
	21st to end	Night	48% 5% 12% 21% 12% 1	1600
July	1st to 10th	Night	44% 6% 18% 22% 10%	3560
	11th to 20th	Night	40% 5% 15% 28% 11%	3552
	21st to end	Night	38% 7% 14% 29% 12%	3809
August	1st to 10th	Night	44% 5% 15% 27% 9%	2576
	11th to 20th	Night	46% 5% 18% 22% 9%	2951
	21st to end	Night	41% 6% 16% 23% 13% 1	3586
September	1st to 10th	Night	39% 7% 10% 29% 14% 1	2000
	11th to 20th	Night	36% 4 14% 33% 13%	2069
	21st to end	Night	42% 7% 11% 25% 15% 1	2200
October	1st to 10th	Night	45% 6% 14% 26% 9% 1	3849
	11th to 20th	Night	46% 4 13% 27% 9%	3931
	21st to end	Night	49% 4 16% 21% 9% 1	4610
November	1st to 10th	Night	54% 5% 12% 20% 8% 1	2667
	11th to 20th	Night	55% 5% 11% 19% 9% 1	2825
	21st to end	Night	63% 6% 11% 15% 5%	2940
December	1st to 10th	Night	72% 5% 11% 10% 2	4720
	11th to 20th	Night	65% 5% 7% 14% 8%	5348
	21st to end	Night	66% 5% 7% 13% 9%	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	27% 14% 33% 21% 6%	220
	11th to 20th	Day	29% 21% 30% 14% 5% 1	220
	21st to end	Day	19% 15% 38% 21% 7%	242
February	1st to 10th	Day	25% 18% 36% 17% 4	325
	11th to 20th	Day	22% 16% 43% 17% 2	425
	21st to end	Day	27% 16% 30% 24% 2	446
March	1st to 10th	Day	23% 15% 35% 21% 6%	540
	11th to 20th	Day	22% 18% 35% 18% 6% 1	540
	21st to end	Day	26% 17% 29% 17% 10% 1	594
April	1st to 10th	Day	26% 17% 31% 19% 6% 1	540
	11th to 20th	Day	24% 21% 25% 19% 10% 2	532
	21st to end	Day	25% 16% 29% 20% 8% 2	540
May	1st to 10th	Day	23% 14% 31% 21% 8% 2	543
	11th to 20th	Day	17% 13% 32% 21% 15% 2	551
	21st to end	Day	20% 14% 27% 26% 10% 3	573
June	1st to 10th	Day	22% 13% 26% 27% 10% 3	530
	11th to 20th	Day	13% 12% 30% 30% 12% 3	530
	21st to end	Day	22% 9% 32% 21% 12% 3	530
July	1st to 10th	Day	12% 8% 29% 29% 17% 4	525
	11th to 20th	Day	14% 8% 29% 30% 16% 4	524
	21st to end	Day	14% 6% 28% 33% 16% 3	576
August	1st to 10th	Day	16% 5% 23% 32% 19% 5%	526
	11th to 20th	Day	13% 6% 22% 34% 16% 8%	519
	21st to end	Day	16% 8% 27% 23% 18% 8%	583
September	1st to 10th	Day	14% 8% 28% 25% 18% 8%	530
	11th to 20th	Day	12% 9% 19% 26% 21% 12%	530
	21st to end	Day	16% 8% 29% 25% 16% 6%	530
October	1st to 10th	Day	22% 11% 27% 22% 14% 5%	530
	11th to 20th	Day	23% 16% 28% 22% 10% 2	519
	21st to end	Day	32% 14% 24% 21% 8%	462
November	1st to 10th	Day	30% 18% 24% 18% 9%	425
	11th to 20th	Day	28% 19% 27% 19% 6% 1	334
	21st to end	Day	29% 20% 28% 18% 5%	220
December	1st to 10th	Day	31% 14% 29% 19% 7%	220
	11th to 20th	Day	27% 19% 35% 16% 3	220
	21st to end	Day	30% 17% 31% 17% 4 1	242
January	1st to 10th	Night	26% 16% 34% 22% 3	840
	11th to 20th	Night	28% 16% 30% 21% 4	840
	21st to end	Night	20% 13% 36% 25% 6%	924
February	1st to 10th	Night	22% 15% 33% 26% 5%	840
	11th to 20th	Night	20% 16% 38% 21% 4	823
	21st to end	Night	21% 14% 34% 27% 4	692
March	1st to 10th	Night	24% 16% 32% 23% 5%	840
	11th to 20th	Night	25% 16% 32% 23% 4	840
	21st to end	Night	25% 12% 29% 26% 7%	924
April	1st to 10th	Night	27% 15% 29% 24% 4	840
	11th to 20th	Night	27% 14% 30% 22% 7%	831
	21st to end	Night	27% 11% 29% 24% 9%	698
May	1st to 10th	Night	29% 9% 26% 28% 9%	464
	11th to 20th	Night	21% 7% 31% 31% 10% 1	406
	21st to end	Night	17% 8% 32% 32% 10%	433
June	1st to 10th	Night	21% 11% 29% 30% 8% 1	400
	11th to 20th	Night	19% 7% 28% 32% 13% 1	400
	21st to end	Night	19% 7% 30% 28% 16% 1	400
July	1st to 10th	Night	13% 4 28% 39% 16% 1	390
	11th to 20th	Night	12% 5% 24% 42% 15% 1	388
	21st to end	Night	14% 5% 27% 40% 13% 2	438
August	1st to 10th	Night	14% 4 19% 42% 19% 1	398
	11th to 20th	Night	14% 5% 21% 35% 23% 3	617
	21st to end	Night	15% 5% 27% 32% 19% 2	880
September	1st to 10th	Night	13% 7% 25% 36% 18% 1	800
	11th to 20th	Night	16% 7% 18% 35% 20% 5%	800
	21st to end	Night	19% 8% 24% 28% 19% 2	800
October	1st to 10th	Night	23% 9% 26% 26% 16% 1	800
	11th to 20th	Night	24% 12% 28% 27% 10%	800
	21st to end	Night	28% 14% 28% 25% 5%	880
November	1st to 10th	Night	26% 16% 27% 24% 7%	820
	11th to 20th	Night	25% 16% 30% 19% 9%	840
	21st to end	Night	27% 18% 27% 21% 7%	840
December	1st to 10th	Night	29% 16% 29% 22% 3	840
	11th to 20th	Night	30% 17% 31% 18% 4 1	840
	21st to end	Night	35% 14% 30% 17% 4	924

Page generated at 2026-05-14 01:58:56. Version ac07

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