St-Valérien-de-Milton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St-Valérien-de-Milton clear sky chart from 2005-11-06 to 2025-02-21.

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	18% 11% 4 9% 5% 5% 4 4 5% 6% 29%	108585
	Night	18% 14% 4 9% 5% 4 4 3 4 5% 28%	109986
Transparency	Day	54% 6% 12% 20% 8% 1	112089
	Night	57% 5% 10% 17% 9% 1	114646
Seeing	Day	26% 15% 29% 20% 8% 2	14883
	Night	26% 12% 28% 24% 8% 1	23943

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% 25% 6% 15% 5% 5% 3 2 3 3 15%	3597
	11th to 20th	Day	12% 17% 7% 18% 9% 5% 5% 3 3 5% 16%	3570
	21st to end	Day	11% 17% 7% 13% 6% 6% 5% 3 5% 5% 22%	3960
February	1st to 10th	Day	16% 18% 6% 11% 6% 5% 5% 4 4 4 22%	1696
	11th to 20th	Day	15% 17% 6% 13% 7% 5% 4 2 5% 5% 21%	1907
	21st to end	Day	16% 18% 5% 8% 6% 5% 4 3 5% 6% 24%	1570
March	1st to 10th	Day	20% 13% 5% 11% 6% 5% 4 3 4 5% 24%	3116
	11th to 20th	Day	16% 20% 5% 11% 5% 4 4 3 4 5% 25%	3257
	21st to end	Day	16% 12% 5% 9% 4 4 4 3 4 5% 35%	4166
April	1st to 10th	Day	23% 14% 3 9% 5% 4 4 3 4 5% 27%	2280
	11th to 20th	Day	22% 10% 2 7% 4 4 4 3 5% 5% 35%	2266
	21st to end	Day	24% 11% 3 6% 4 4 4 3 4 5% 30%	2470
May	1st to 10th	Day	24% 9% 3 7% 4 5% 4 4 5% 6% 29%	4261
	11th to 20th	Day	18% 8% 3 8% 6% 5% 5% 4 7% 7% 29%	4398
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	4837
June	1st to 10th	Day	23% 8% 3 7% 4 4 4 4 5% 7% 30%	2660
	11th to 20th	Day	16% 6% 3 6% 4 4 5% 4 6% 9% 37%	2660
	21st to end	Day	22% 9% 3 7% 5% 4 4 4 5% 7% 29%	2660
July	1st to 10th	Day	13% 6% 2 7% 6% 6% 5% 5% 7% 9% 34%	4440
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 5% 7% 8% 34%	4440
	21st to end	Day	14% 6% 2 5% 4 4 4 4 5% 9% 42%	4814
August	1st to 10th	Day	17% 7% 2 8% 5% 5% 5% 5% 7% 10% 29%	4423
	11th to 20th	Day	18% 6% 3 6% 5% 4 5% 4 6% 9% 34%	4027
	21st to end	Day	19% 6% 2 7% 4 4 4 3 6% 7% 39%	4180
September	1st to 10th	Day	13% 7% 2 6% 4 4 6% 4 6% 8% 41%	2280
	11th to 20th	Day	17% 6% 2 4 3 3 4 3 5% 7% 45%	2158
	21st to end	Day	19% 7% 2 6% 3 4 4 3 6% 8% 39%	2090
October	1st to 10th	Day	21% 8% 3 7% 5% 4 5% 4 5% 7% 31%	2024
	11th to 20th	Day	22% 9% 3 9% 5% 5% 4 4 6% 6% 28%	1811
	21st to end	Day	26% 12% 3 7% 4 4 4 3 4 6% 27%	1881
November	1st to 10th	Day	20% 13% 3 6% 5% 4 3 4 5% 5% 32%	1761
	11th to 20th	Day	18% 15% 5% 9% 5% 5% 4 2 5% 5% 26%	1779
	21st to end	Day	23% 15% 5% 8% 4 4 5% 3 5% 6% 21%	1600
December	1st to 10th	Day	21% 21% 6% 13% 7% 3 4 3 4 3 15%	2600
	11th to 20th	Day	21% 17% 5% 10% 5% 4 3 3 4 5% 23%	2986
	21st to end	Day	22% 16% 5% 11% 6% 4 4 3 6% 5% 17%	3960
January	1st to 10th	Night	16% 24% 9% 14% 5% 4 3 2 3 3 17%	6349
	11th to 20th	Night	11% 20% 7% 18% 8% 6% 5% 3 4 4 14%	6315
	21st to end	Night	12% 17% 7% 13% 7% 5% 4 3 4 4 23%	6996
February	1st to 10th	Night	15% 17% 6% 13% 8% 4 4 4 4 5% 20%	2700
	11th to 20th	Night	14% 16% 5% 13% 7% 5% 4 2 4 4 25%	2378
	21st to end	Night	15% 16% 5% 10% 5% 4 4 3 4 4 29%	1885
March	1st to 10th	Night	23% 12% 4 8% 4 3 4 3 4 4 32%	3724
	11th to 20th	Night	19% 20% 6% 9% 5% 4 3 2 3 3 25%	3698
	21st to end	Night	15% 15% 5% 9% 5% 4 3 3 3 4 33%	3466
April	1st to 10th	Night	24% 13% 2 8% 5% 3 4 3 5% 5% 28%	1900
	11th to 20th	Night	23% 10% 2 7% 5% 4 3 3 5% 6% 32%	1862
	21st to end	Night	23% 11% 3 6% 3 4 4 3 4 6% 33%	1710
May	1st to 10th	Night	25% 9% 4 7% 4 5% 4 3 5% 7% 27%	2708
	11th to 20th	Night	23% 8% 2 7% 4 4 4 3 5% 6% 34%	2495
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 5% 8% 36%	2738
June	1st to 10th	Night	24% 8% 2 5% 4 4 5% 4 6% 7% 30%	1520
	11th to 20th	Night	19% 6% 2 5% 5% 5% 4 4 6% 6% 38%	1520
	21st to end	Night	19% 8% 2 8% 4 5% 4 5% 5% 7% 32%	1520
July	1st to 10th	Night	14% 8% 2 9% 6% 5% 5% 4 6% 8% 32%	2520
	11th to 20th	Night	16% 6% 2 6% 5% 4 4 5% 6% 8% 39%	2520
	21st to end	Night	14% 7% 2 7% 4 4 5% 4 6% 8% 39%	2739
August	1st to 10th	Night	20% 9% 4 7% 4 4 4 4 6% 6% 33%	2506
	11th to 20th	Night	16% 7% 3 7% 6% 5% 5% 4 5% 6% 35%	2751
	21st to end	Night	18% 7% 3 6% 4 4 4 4 4 8% 40%	3476
September	1st to 10th	Night	16% 6% 2 7% 4 4 4 3 5% 6% 43%	1900
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 4 8% 48%	2021
	21st to end	Night	18% 6% 3 6% 4 4 4 3 4 8% 40%	2090
October	1st to 10th	Night	19% 7% 2 7% 4 5% 4 3 5% 6% 37%	2154
	11th to 20th	Night	22% 10% 3 7% 5% 4 4 3 4 5% 32%	2367
	21st to end	Night	26% 11% 3 8% 4 4 4 3 4 4 28%	2717
November	1st to 10th	Night	21% 13% 3 8% 4 4 5% 3 4 5% 29%	2537
	11th to 20th	Night	20% 14% 4 8% 5% 4 4 3 4 5% 29%	2620
	21st to end	Night	23% 16% 5% 8% 5% 4 3 2 3 5% 25%	2800
December	1st to 10th	Night	19% 24% 7% 13% 5% 5% 3 3 3 4 13%	4580
	11th to 20th	Night	23% 15% 5% 11% 6% 5% 3 3 3 3 22%	5208
	21st to end	Night	22% 18% 4 9% 4 4 4 3 5% 7% 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	76% 4 8% 11% 1	3598
	11th to 20th	Day	71% 7% 8% 11% 3	3600
	21st to end	Day	63% 6% 9% 13% 8%	3960
February	1st to 10th	Day	67% 5% 8% 14% 5% 1	1696
	11th to 20th	Day	66% 4 12% 12% 5% 1	1916
	21st to end	Day	62% 4 10% 15% 7% 1	1570
March	1st to 10th	Day	62% 6% 8% 18% 6% 1	3119
	11th to 20th	Day	62% 5% 11% 11% 9% 1	3257
	21st to end	Day	52% 4 10% 19% 14% 1	4166
April	1st to 10th	Day	60% 5% 8% 17% 8% 1	2280
	11th to 20th	Day	51% 5% 9% 21% 13% 1	2266
	21st to end	Day	56% 5% 10% 17% 11% 2	2470
May	1st to 10th	Day	53% 6% 11% 21% 8% 1	4275
	11th to 20th	Day	50% 9% 16% 16% 7% 1	4402
	21st to end	Day	46% 7% 11% 23% 12% 1	4837
June	1st to 10th	Day	52% 7% 10% 20% 9% 1	2660
	11th to 20th	Day	43% 7% 14% 22% 12% 2	2660
	21st to end	Day	54% 7% 11% 18% 9%	2660
July	1st to 10th	Day	44% 7% 14% 27% 7%	4370
	11th to 20th	Day	44% 8% 16% 28% 4	4365
	21st to end	Day	40% 7% 15% 31% 7%	4661
August	1st to 10th	Day	49% 8% 16% 22% 6%	4409
	11th to 20th	Day	45% 8% 20% 21% 6%	4067
	21st to end	Day	44% 6% 15% 20% 13% 1	4180
September	1st to 10th	Day	40% 8% 15% 27% 10% 1	2280
	11th to 20th	Day	38% 6% 13% 30% 12%	2158
	21st to end	Day	44% 6% 14% 26% 10%	2090
October	1st to 10th	Day	46% 5% 15% 28% 6%	3362
	11th to 20th	Day	48% 7% 16% 25% 4	2988
	21st to end	Day	50% 5% 18% 21% 7% 1	3081
November	1st to 10th	Day	53% 6% 12% 21% 7%	1761
	11th to 20th	Day	60% 5% 10% 15% 9%	1779
	21st to end	Day	65% 7% 12% 13% 3	1600
December	1st to 10th	Day	74% 6% 7% 11% 2	2600
	11th to 20th	Day	65% 4 8% 17% 6%	2986
	21st to end	Day	67% 5% 11% 11% 6%	3960
January	1st to 10th	Night	73% 5% 10% 9% 3	6349
	11th to 20th	Night	73% 6% 9% 9% 3	6360
	21st to end	Night	65% 4 9% 11% 11%	6996
February	1st to 10th	Night	67% 5% 8% 14% 6% 1	2700
	11th to 20th	Night	63% 4 9% 16% 7%	2380
	21st to end	Night	60% 5% 10% 14% 11% 1	1885
March	1st to 10th	Night	56% 4 10% 19% 8% 3	3734
	11th to 20th	Night	63% 5% 8% 12% 10% 1	3699
	21st to end	Night	55% 4 7% 21% 11% 2	3466
April	1st to 10th	Night	58% 4 9% 17% 11% 1	1900
	11th to 20th	Night	53% 5% 8% 20% 12% 2	1862
	21st to end	Night	52% 5% 9% 19% 13% 2	1710
May	1st to 10th	Night	55% 7% 10% 17% 8% 2	2714
	11th to 20th	Night	48% 8% 12% 20% 10% 2	2496
	21st to end	Night	45% 7% 10% 21% 16% 1	2739
June	1st to 10th	Night	51% 6% 10% 21% 10% 1	1520
	11th to 20th	Night	44% 7% 11% 23% 13% 3	1520
	21st to end	Night	50% 7% 13% 18% 11% 1	1520
July	1st to 10th	Night	47% 7% 15% 20% 11%	2480
	11th to 20th	Night	43% 7% 16% 26% 8%	2472
	21st to end	Night	42% 8% 17% 23% 11%	2651
August	1st to 10th	Night	50% 7% 13% 24% 6%	2496
	11th to 20th	Night	48% 7% 17% 21% 6%	2777
	21st to end	Night	43% 6% 12% 24% 15% 1	3476
September	1st to 10th	Night	42% 6% 13% 25% 14% 1	1900
	11th to 20th	Night	37% 5% 15% 32% 12% 1	2021
	21st to end	Night	43% 7% 10% 26% 13% 1	2090
October	1st to 10th	Night	50% 6% 11% 24% 9%	3596
	11th to 20th	Night	49% 5% 10% 28% 7%	3929
	21st to end	Night	52% 4 14% 18% 10% 2	4467
November	1st to 10th	Night	57% 5% 11% 20% 6% 1	2537
	11th to 20th	Night	57% 6% 10% 16% 9% 2	2620
	21st to end	Night	63% 5% 12% 16% 5%	2800
December	1st to 10th	Night	77% 4 9% 8% 2	4580
	11th to 20th	Night	68% 4 6% 14% 8%	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	39% 13% 30% 15% 4	200
	11th to 20th	Day	31% 22% 33% 12% 4	200
	21st to end	Day	27% 20% 32% 16% 5% 1	220
February	1st to 10th	Day	35% 25% 25% 13% 2	248
	11th to 20th	Day	30% 22% 34% 11% 2	455
	21st to end	Day	29% 21% 31% 18% 2	382
March	1st to 10th	Day	29% 18% 27% 22% 4	460
	11th to 20th	Day	28% 21% 31% 16% 3 1	460
	21st to end	Day	29% 21% 26% 18% 5% 1	506
April	1st to 10th	Day	33% 14% 30% 15% 7% 1	460
	11th to 20th	Day	35% 17% 25% 14% 6% 2	452
	21st to end	Day	32% 17% 33% 10% 6% 2	460
May	1st to 10th	Day	32% 14% 29% 18% 6% 2	463
	11th to 20th	Day	21% 15% 28% 24% 10% 1	487
	21st to end	Day	21% 18% 32% 19% 8% 2	529
June	1st to 10th	Day	26% 13% 34% 19% 6% 2	490
	11th to 20th	Day	18% 16% 32% 23% 11%	490
	21st to end	Day	27% 12% 31% 20% 8% 2	490
July	1st to 10th	Day	17% 11% 31% 26% 13% 2	485
	11th to 20th	Day	18% 11% 34% 27% 9% 2	484
	21st to end	Day	19% 9% 31% 31% 9% 2	532
August	1st to 10th	Day	18% 9% 29% 27% 14% 3	486
	11th to 20th	Day	18% 8% 27% 27% 16% 4	479
	21st to end	Day	19% 12% 25% 24% 14% 7%	539
September	1st to 10th	Day	16% 13% 31% 24% 10% 5%	490
	11th to 20th	Day	18% 11% 21% 26% 17% 8%	490
	21st to end	Day	20% 12% 27% 22% 14% 5%	490
October	1st to 10th	Day	24% 14% 28% 20% 10% 3	490
	11th to 20th	Day	30% 16% 23% 21% 9% 1	443
	21st to end	Day	37% 14% 27% 16% 6%	429
November	1st to 10th	Day	33% 16% 27% 19% 5% 1	395
	11th to 20th	Day	30% 21% 23% 17% 7% 1	379
	21st to end	Day	33% 21% 31% 12% 5%	200
December	1st to 10th	Day	35% 17% 24% 18% 5% 2	200
	11th to 20th	Day	34% 22% 30% 11% 3 1	200
	21st to end	Day	35% 20% 26% 13% 5% 1	220
January	1st to 10th	Night	32% 14% 32% 18% 5%	800
	11th to 20th	Night	27% 18% 30% 20% 5%	800
	21st to end	Night	23% 13% 33% 24% 5%	880
February	1st to 10th	Night	26% 16% 36% 19% 4	800
	11th to 20th	Night	24% 19% 33% 19% 3 1	783
	21st to end	Night	25% 15% 34% 22% 3	629
March	1st to 10th	Night	27% 14% 31% 23% 4	760
	11th to 20th	Night	28% 16% 28% 22% 6%	760
	21st to end	Night	27% 13% 28% 25% 6% 1	836
April	1st to 10th	Night	31% 12% 28% 24% 4	760
	11th to 20th	Night	28% 15% 27% 23% 7%	738
	21st to end	Night	31% 15% 26% 19% 8% 1	570
May	1st to 10th	Night	29% 9% 33% 21% 7% 1	496
	11th to 20th	Night	23% 12% 28% 28% 9% 1	374
	21st to end	Night	21% 8% 36% 28% 7%	411
June	1st to 10th	Night	29% 8% 29% 26% 8% 1	380
	11th to 20th	Night	21% 5% 32% 30% 12%	380
	21st to end	Night	19% 7% 29% 33% 11% 1	380
July	1st to 10th	Night	15% 7% 29% 36% 12% 1	370
	11th to 20th	Night	14% 6% 23% 39% 16% 1	368
	21st to end	Night	16% 6% 26% 40% 12%	416
August	1st to 10th	Night	19% 3 21% 37% 19% 1	378
	11th to 20th	Night	16% 4 24% 32% 22% 1	542
	21st to end	Night	19% 4 25% 34% 15% 3	836
September	1st to 10th	Night	19% 7% 27% 33% 14% 1	760
	11th to 20th	Night	20% 6% 21% 30% 21% 2	760
	21st to end	Night	21% 6% 30% 26% 15% 2	760
October	1st to 10th	Night	23% 11% 28% 26% 12% 1	760
	11th to 20th	Night	28% 11% 25% 26% 8% 1	760
	21st to end	Night	32% 14% 29% 21% 4	836
November	1st to 10th	Night	30% 15% 30% 18% 6% 1	780
	11th to 20th	Night	28% 18% 28% 18% 8% 1	800
	21st to end	Night	32% 20% 23% 19% 6% 1	800
December	1st to 10th	Night	37% 16% 26% 17% 4	800
	11th to 20th	Night	31% 17% 28% 18% 5% 1	800
	21st to end	Night	34% 16% 26% 18% 5%	880

Page generated at 2025-02-18 03:26:28. Version ac07

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