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 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	16% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	105261
	Night	18% 12% 4 9% 5% 5% 4 3 5% 6% 29%	104124
Transparency	Day	50% 6% 13% 22% 9% 1	108736
	Night	55% 5% 11% 19% 9% 1	108738
Seeing	Day	21% 13% 29% 23% 11% 3	14747
	Night	23% 12% 29% 26% 9% 1	23865

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	17% 17% 5% 11% 7% 5% 5% 3 4 5% 20%	2597
	11th to 20th	Day	13% 16% 6% 10% 8% 5% 6% 4 6% 5% 20%	2600
	21st to end	Day	15% 17% 6% 11% 5% 6% 6% 4 6% 7% 17%	2780
February	1st to 10th	Day	16% 15% 4 11% 6% 6% 5% 4 6% 6% 22%	1698
	11th to 20th	Day	13% 12% 5% 10% 7% 5% 5% 5% 6% 5% 27%	1748
	21st to end	Day	18% 14% 4 10% 7% 4 5% 3 5% 6% 25%	1570
March	1st to 10th	Day	20% 12% 4 9% 6% 5% 4 4 5% 6% 26%	3116
	11th to 20th	Day	12% 15% 5% 12% 7% 5% 5% 4 5% 5% 27%	3316
	21st to end	Day	15% 8% 3 8% 5% 4 4 3 5% 6% 38%	4134
April	1st to 10th	Day	21% 10% 3 6% 5% 3 4 4 4 6% 33%	2280
	11th to 20th	Day	19% 7% 3 6% 6% 3 4 4 6% 6% 36%	2254
	21st to end	Day	21% 9% 3 7% 5% 4 4 3 5% 6% 33%	2408
May	1st to 10th	Day	20% 9% 4 8% 5% 4 5% 4 6% 6% 30%	4389
	11th to 20th	Day	17% 9% 3 8% 5% 5% 4 4 6% 7% 34%	4398
	21st to end	Day	14% 7% 2 6% 4 5% 5% 5% 7% 9% 37%	4837
June	1st to 10th	Day	21% 8% 3 7% 5% 5% 4 4 5% 8% 31%	2660
	11th to 20th	Day	13% 6% 3 6% 5% 4 5% 4 7% 7% 39%	2660
	21st to end	Day	18% 7% 3 7% 5% 4 5% 4 6% 8% 32%	2660
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 4 6% 9% 38%	4440
	11th to 20th	Day	12% 6% 2 6% 4 5% 6% 5% 7% 8% 38%	4440
	21st to end	Day	11% 5% 2 6% 4 4 4 4 7% 9% 43%	4814
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 4 4 7% 9% 33%	4423
	11th to 20th	Day	13% 7% 3 7% 4 5% 4 4 6% 7% 40%	3958
	21st to end	Day	15% 6% 2 6% 3 4 5% 4 7% 8% 40%	4180
September	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 3 6% 7% 44%	2280
	11th to 20th	Day	13% 5% 2 6% 4 4 3 4 4 7% 49%	2214
	21st to end	Day	15% 6% 3 6% 4 4 5% 4 5% 7% 40%	2090
October	1st to 10th	Day	20% 7% 3 6% 4 5% 4 4 5% 7% 34%	1939
	11th to 20th	Day	17% 10% 4 9% 6% 6% 5% 4 5% 6% 30%	1881
	21st to end	Day	24% 11% 3 8% 4 4 4 3 5% 6% 27%	1881
November	1st to 10th	Day	17% 10% 3 7% 4 5% 4 4 6% 7% 32%	1761
	11th to 20th	Day	15% 12% 4 9% 5% 4 5% 4 6% 6% 28%	1709
	21st to end	Day	20% 15% 5% 8% 6% 5% 5% 4 7% 6% 20%	1600
December	1st to 10th	Day	20% 18% 7% 12% 6% 6% 5% 4 4 5% 14%	2600
	11th to 20th	Day	17% 13% 5% 11% 6% 6% 6% 4 5% 5% 22%	2986
	21st to end	Day	22% 15% 4 11% 6% 5% 6% 5% 5% 5% 17%	3960
January	1st to 10th	Night	17% 19% 7% 12% 6% 5% 5% 3 4 5% 19%	4569
	11th to 20th	Night	12% 16% 5% 15% 8% 7% 6% 4 6% 5% 16%	4580
	21st to end	Night	17% 20% 6% 11% 6% 5% 4 3 4 5% 20%	4899
February	1st to 10th	Night	15% 16% 6% 12% 8% 6% 5% 3 5% 5% 20%	2480
	11th to 20th	Night	14% 12% 5% 11% 6% 6% 6% 4 5% 6% 26%	2316
	21st to end	Night	15% 14% 4 10% 7% 5% 4 3 4 5% 30%	1884
March	1st to 10th	Night	20% 11% 3 8% 6% 4 4 3 5% 5% 32%	3724
	11th to 20th	Night	19% 18% 4 9% 5% 4 4 3 4 4 25%	3639
	21st to end	Night	14% 11% 4 8% 5% 4 4 3 4 6% 36%	3498
April	1st to 10th	Night	23% 9% 3 8% 6% 4 4 3 4 6% 29%	1900
	11th to 20th	Night	22% 10% 3 6% 4 4 4 4 5% 6% 32%	1875
	21st to end	Night	20% 11% 3 8% 4 3 5% 3 4 5% 34%	1772
May	1st to 10th	Night	22% 11% 3 7% 4 4 4 4 6% 7% 28%	2580
	11th to 20th	Night	20% 9% 3 6% 4 5% 4 3 4 6% 35%	2495
	21st to end	Night	14% 7% 3 7% 5% 4 4 4 6% 8% 37%	2738
June	1st to 10th	Night	19% 9% 2 7% 4 5% 5% 4 8% 9% 28%	1520
	11th to 20th	Night	16% 7% 3 6% 4 3 4 4 5% 6% 42%	1520
	21st to end	Night	18% 8% 3 8% 5% 3 4 4 5% 7% 34%	1520
July	1st to 10th	Night	13% 8% 3 8% 5% 5% 5% 4 7% 6% 35%	2520
	11th to 20th	Night	13% 6% 2 7% 4 5% 5% 4 7% 9% 40%	2520
	21st to end	Night	12% 8% 2 7% 5% 4 5% 4 5% 8% 42%	2739
August	1st to 10th	Night	15% 8% 3 8% 4 4 4 3 5% 7% 39%	2506
	11th to 20th	Night	16% 8% 2 7% 4 5% 5% 3 5% 6% 38%	2835
	21st to end	Night	14% 6% 2 6% 4 5% 4 3 6% 9% 40%	3476
September	1st to 10th	Night	12% 6% 2 7% 4 4 5% 4 5% 8% 42%	1900
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 7% 48%	1965
	21st to end	Night	17% 6% 3 5% 4 4 5% 3 5% 6% 41%	2090
October	1st to 10th	Night	19% 8% 2 6% 5% 5% 5% 4 5% 6% 35%	2237
	11th to 20th	Night	20% 9% 3 7% 6% 5% 5% 4 5% 6% 32%	2299
	21st to end	Night	23% 9% 3 9% 5% 5% 4 4 4 5% 28%	2717
November	1st to 10th	Night	19% 10% 3 8% 5% 5% 4 4 5% 6% 31%	2537
	11th to 20th	Night	19% 11% 4 8% 5% 4 4 4 5% 5% 31%	2690
	21st to end	Night	21% 13% 4 11% 6% 4 4 4 5% 5% 23%	2800
December	1st to 10th	Night	18% 21% 6% 12% 6% 5% 4 3 4 4 15%	4580
	11th to 20th	Night	23% 15% 5% 9% 5% 5% 4 4 5% 5% 21%	5208
	21st to end	Night	23% 16% 5% 11% 5% 3 4 3 5% 5% 19%	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% 6% 13% 12% 4	2598
	11th to 20th	Day	63% 7% 11% 12% 7%	2600
	21st to end	Day	65% 7% 13% 11% 4 1	2780
February	1st to 10th	Day	62% 5% 10% 17% 4 1	1698
	11th to 20th	Day	57% 6% 11% 17% 7% 1	1757
	21st to end	Day	60% 5% 11% 14% 9% 1	1570
March	1st to 10th	Day	59% 4 10% 19% 6% 1	3119
	11th to 20th	Day	57% 6% 11% 15% 9% 2	3316
	21st to end	Day	46% 5% 8% 22% 17% 2	4134
April	1st to 10th	Day	53% 5% 8% 21% 12% 2	2280
	11th to 20th	Day	48% 5% 8% 22% 16% 2	2254
	21st to end	Day	52% 5% 9% 18% 13% 4	2408
May	1st to 10th	Day	52% 6% 10% 21% 10% 1	4403
	11th to 20th	Day	49% 6% 14% 20% 9% 1	4402
	21st to end	Day	42% 6% 12% 25% 13% 2	4837
June	1st to 10th	Day	51% 6% 11% 19% 12% 1	2660
	11th to 20th	Day	43% 6% 12% 23% 13% 2	2660
	21st to end	Day	50% 6% 14% 20% 10% 1	2660
July	1st to 10th	Day	41% 5% 14% 29% 11%	4370
	11th to 20th	Day	39% 6% 16% 31% 7%	4365
	21st to end	Day	36% 7% 15% 33% 9%	4661
August	1st to 10th	Day	46% 6% 16% 23% 9%	4409
	11th to 20th	Day	42% 6% 17% 28% 7%	4000
	21st to end	Day	39% 6% 18% 23% 12% 1	4180
September	1st to 10th	Day	38% 6% 13% 29% 14%	2280
	11th to 20th	Day	35% 5% 13% 31% 15% 1	2214
	21st to end	Day	42% 6% 14% 27% 11% 1	2090
October	1st to 10th	Day	47% 4 13% 28% 8%	3225
	11th to 20th	Day	45% 5% 17% 25% 7%	3109
	21st to end	Day	47% 5% 19% 23% 6%	3081
November	1st to 10th	Day	51% 5% 13% 22% 8% 1	1761
	11th to 20th	Day	54% 7% 11% 18% 10% 1	1709
	21st to end	Day	64% 8% 12% 13% 3	1600
December	1st to 10th	Day	72% 5% 11% 12% 1	2600
	11th to 20th	Day	62% 7% 10% 15% 6%	2986
	21st to end	Day	67% 5% 9% 15% 4	3960
January	1st to 10th	Night	69% 5% 13% 10% 4	4569
	11th to 20th	Night	66% 8% 10% 11% 5%	4580
	21st to end	Night	66% 6% 11% 11% 6%	4899
February	1st to 10th	Night	66% 5% 9% 14% 5% 1	2480
	11th to 20th	Night	58% 6% 10% 19% 8% 1	2318
	21st to end	Night	58% 5% 8% 17% 12% 1	1884
March	1st to 10th	Night	55% 4 9% 20% 9% 2	3734
	11th to 20th	Night	61% 6% 9% 14% 8% 2	3640
	21st to end	Night	49% 5% 5% 23% 16% 3	3498
April	1st to 10th	Night	56% 4 8% 18% 12% 1	1900
	11th to 20th	Night	53% 5% 8% 20% 13% 1	1875
	21st to end	Night	53% 4 7% 18% 14% 4	1772
May	1st to 10th	Night	54% 5% 11% 18% 9% 3	2586
	11th to 20th	Night	49% 5% 12% 20% 12% 2	2496
	21st to end	Night	43% 6% 11% 20% 18% 1	2739
June	1st to 10th	Night	50% 7% 12% 18% 12% 1	1520
	11th to 20th	Night	43% 5% 12% 21% 17% 2	1520
	21st to end	Night	48% 5% 13% 21% 12% 1	1520
July	1st to 10th	Night	46% 5% 14% 21% 13%	2480
	11th to 20th	Night	39% 6% 17% 30% 8%	2472
	21st to end	Night	40% 7% 16% 25% 13%	2651
August	1st to 10th	Night	45% 6% 14% 26% 9%	2496
	11th to 20th	Night	46% 5% 18% 22% 8%	2859
	21st to end	Night	41% 6% 17% 22% 14% 1	3476
September	1st to 10th	Night	40% 7% 10% 27% 15% 1	1900
	11th to 20th	Night	37% 4 14% 32% 13%	1965
	21st to end	Night	42% 7% 12% 26% 14% 1	2090
October	1st to 10th	Night	46% 6% 14% 26% 8%	3731
	11th to 20th	Night	47% 4 13% 27% 8%	3810
	21st to end	Night	50% 4 16% 20% 9% 1	4467
November	1st to 10th	Night	53% 5% 12% 20% 8% 1	2537
	11th to 20th	Night	55% 5% 11% 19% 9% 1	2690
	21st to end	Night	63% 7% 11% 15% 5%	2800
December	1st to 10th	Night	72% 5% 11% 10% 2	4580
	11th to 20th	Night	65% 5% 7% 14% 9%	5208
	21st to end	Night	66% 5% 7% 13% 9%	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	28% 14% 32% 21% 6%	200
	11th to 20th	Day	31% 19% 30% 15% 5% 1	200
	21st to end	Day	20% 13% 37% 23% 7%	200
February	1st to 10th	Day	28% 19% 35% 16% 3	265
	11th to 20th	Day	22% 16% 42% 18% 2	355
	21st to end	Day	29% 16% 29% 24% 2	382
March	1st to 10th	Day	24% 14% 33% 21% 7%	460
	11th to 20th	Day	20% 20% 36% 17% 6% 1	460
	21st to end	Day	27% 16% 28% 17% 11% 1	506
April	1st to 10th	Day	27% 14% 31% 20% 7% 1	460
	11th to 20th	Day	24% 21% 24% 20% 10% 1	452
	21st to end	Day	25% 15% 29% 20% 8% 2	460
May	1st to 10th	Day	22% 13% 33% 22% 9% 2	463
	11th to 20th	Day	15% 13% 33% 21% 15% 2	487
	21st to end	Day	18% 14% 28% 26% 11% 3	529
June	1st to 10th	Day	23% 12% 24% 27% 11% 3	490
	11th to 20th	Day	14% 11% 29% 30% 12% 3	490
	21st to end	Day	23% 9% 30% 21% 13% 3	490
July	1st to 10th	Day	12% 8% 28% 30% 16% 5%	485
	11th to 20th	Day	15% 7% 29% 30% 15% 4	484
	21st to end	Day	14% 6% 27% 34% 16% 3	532
August	1st to 10th	Day	17% 5% 24% 30% 20% 4	486
	11th to 20th	Day	13% 7% 22% 35% 17% 7%	479
	21st to end	Day	16% 9% 27% 24% 18% 8%	539
September	1st to 10th	Day	14% 7% 29% 26% 16% 7%	490
	11th to 20th	Day	13% 9% 20% 26% 20% 13%	490
	21st to end	Day	15% 9% 28% 25% 17% 6%	490
October	1st to 10th	Day	23% 11% 26% 21% 13% 5%	490
	11th to 20th	Day	24% 16% 26% 21% 10% 2	480
	21st to end	Day	32% 15% 24% 21% 8%	429
November	1st to 10th	Day	29% 17% 25% 19% 10% 1	395
	11th to 20th	Day	27% 20% 27% 19% 6% 1	309
	21st to end	Day	28% 19% 29% 19% 6%	200
December	1st to 10th	Day	32% 14% 29% 18% 8%	200
	11th to 20th	Day	28% 20% 34% 16% 3 1	200
	21st to end	Day	32% 17% 29% 17% 5% 1	220
January	1st to 10th	Night	26% 16% 33% 22% 3	800
	11th to 20th	Night	27% 15% 31% 21% 5%	800
	21st to end	Night	20% 13% 36% 26% 5%	841
February	1st to 10th	Night	23% 15% 32% 25% 4	760
	11th to 20th	Night	20% 16% 37% 22% 5%	743
	21st to end	Night	22% 14% 34% 26% 4	628
March	1st to 10th	Night	25% 15% 31% 24% 5%	760
	11th to 20th	Night	24% 16% 32% 23% 5%	760
	21st to end	Night	25% 12% 28% 27% 7%	836
April	1st to 10th	Night	26% 15% 29% 25% 4	760
	11th to 20th	Night	26% 14% 31% 22% 7%	751
	21st to end	Night	27% 12% 28% 24% 9%	632
May	1st to 10th	Night	28% 8% 26% 28% 9%	420
	11th to 20th	Night	20% 7% 31% 31% 10% 1	374
	21st to end	Night	17% 7% 34% 32% 11%	411
June	1st to 10th	Night	21% 11% 28% 30% 9% 1	380
	11th to 20th	Night	19% 6% 28% 33% 13% 1	380
	21st to end	Night	19% 7% 29% 28% 17% 1	380
July	1st to 10th	Night	13% 4 28% 39% 15% 1	370
	11th to 20th	Night	12% 5% 25% 42% 15% 1	368
	21st to end	Night	14% 5% 27% 39% 13% 2	416
August	1st to 10th	Night	15% 4 19% 42% 19% 1	378
	11th to 20th	Night	15% 5% 21% 35% 23% 3	585
	21st to end	Night	15% 5% 27% 32% 19% 2	836
September	1st to 10th	Night	14% 7% 25% 36% 17% 1	760
	11th to 20th	Night	17% 7% 19% 34% 19% 4	760
	21st to end	Night	19% 8% 24% 27% 19% 2	760
October	1st to 10th	Night	23% 9% 26% 25% 16% 1	760
	11th to 20th	Night	24% 12% 27% 26% 10%	760
	21st to end	Night	28% 14% 28% 24% 5%	836
November	1st to 10th	Night	25% 17% 27% 24% 7%	780
	11th to 20th	Night	25% 17% 30% 19% 9% 1	800
	21st to end	Night	28% 18% 26% 21% 7%	800
December	1st to 10th	Night	30% 16% 30% 21% 4	800
	11th to 20th	Night	30% 17% 31% 18% 4 1	800
	21st to end	Night	34% 14% 30% 17% 4	880

Page generated at 2025-01-19 03:06:46. Version ac07

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