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 2024-01-31.

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	19% 10% 4 7% 6% 3 5% 4 5% 7% 30%	74913
	Night	20% 12% 4 7% 6% 3 4 4 4 6% 30%	75211
Transparency	Day	54% 6% 12% 19% 8% 1	74618
	Night	56% 6% 10% 18% 9% 1	75040
Seeing	Day	26% 15% 29% 20% 8% 2	13553
	Night	26% 12% 28% 25% 8% 1	22617

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	21% 21% 6% 11% 6% 4 5% 3 2 4 16%	1517
	11th to 20th	Day	19% 17% 7% 10% 7% 4 5% 4 3 5% 19%	1520
	21st to end	Day	12% 15% 6% 10% 7% 4 7% 4 4 6% 24%	1664
February	1st to 10th	Day	17% 18% 6% 11% 6% 4 6% 4 4 4 21%	1526
	11th to 20th	Day	16% 16% 7% 10% 7% 3 5% 3 5% 6% 22%	1711
	21st to end	Day	16% 16% 7% 8% 7% 4 4 4 5% 6% 24%	1480
March	1st to 10th	Day	16% 13% 5% 10% 7% 5% 5% 4 4 5% 26%	1797
	11th to 20th	Day	19% 11% 5% 7% 6% 4 4 4 4 6% 31%	1841
	21st to end	Day	19% 11% 4 7% 5% 3 5% 4 5% 6% 32%	2376
April	1st to 10th	Day	23% 12% 4 9% 5% 3 4 4 4 5% 27%	2160
	11th to 20th	Day	22% 9% 2 6% 4 3 4 4 5% 5% 36%	2145
	21st to end	Day	25% 11% 3 5% 5% 3 4 4 4 5% 30%	2340
May	1st to 10th	Day	23% 8% 3 6% 5% 4 4 5% 4 6% 33%	2425
	11th to 20th	Day	18% 7% 3 6% 6% 3 5% 5% 6% 7% 36%	2478
	21st to end	Day	19% 6% 3 6% 5% 4 5% 6% 6% 8% 33%	2725
June	1st to 10th	Day	24% 7% 3 6% 5% 3 4 5% 5% 7% 30%	2520
	11th to 20th	Day	17% 6% 3 5% 5% 3 5% 5% 6% 8% 37%	2520
	21st to end	Day	22% 8% 3 7% 6% 3 5% 5% 5% 7% 29%	2520
July	1st to 10th	Day	14% 6% 2 5% 6% 4 5% 5% 6% 9% 37%	2520
	11th to 20th	Day	14% 6% 3 6% 5% 4 5% 6% 7% 9% 35%	2520
	21st to end	Day	16% 5% 3 5% 6% 3 5% 5% 7% 10% 34%	2744
August	1st to 10th	Day	16% 7% 2 7% 6% 4 5% 6% 6% 9% 33%	2506
	11th to 20th	Day	14% 5% 2 5% 5% 4 5% 6% 6% 9% 38%	2301
	21st to end	Day	16% 6% 2 5% 5% 3 5% 4 6% 7% 40%	2376
September	1st to 10th	Day	14% 6% 3 6% 4 3 5% 6% 5% 8% 40%	2160
	11th to 20th	Day	18% 5% 2 4 4 2 4 4 5% 7% 45%	2045
	21st to end	Day	19% 6% 2 5% 4 3 4 4 6% 8% 39%	1980
October	1st to 10th	Day	22% 8% 3 6% 6% 3 5% 5% 5% 7% 30%	1918
	11th to 20th	Day	22% 9% 3 7% 6% 3 5% 5% 6% 7% 26%	1716
	21st to end	Day	28% 12% 4 7% 4 3 4 3 4 5% 26%	1782
November	1st to 10th	Day	21% 12% 3 5% 5% 3 3 5% 5% 5% 32%	1671
	11th to 20th	Day	19% 13% 6% 8% 6% 3 5% 4 5% 5% 25%	1691
	21st to end	Day	23% 14% 5% 8% 5% 3 5% 4 5% 6% 22%	1520
December	1st to 10th	Day	26% 17% 6% 11% 7% 2 4 4 4 3 15%	1520
	11th to 20th	Day	23% 16% 6% 8% 5% 3 4 4 4 5% 23%	1906
	21st to end	Day	27% 16% 5% 10% 6% 3 3 3 3 4 18%	2772
January	1st to 10th	Night	21% 18% 7% 10% 6% 3 4 4 4 4 17%	2649
	11th to 20th	Night	17% 18% 7% 12% 8% 3 5% 3 3 4 21%	2660
	21st to end	Night	14% 15% 7% 9% 8% 4 4 4 5% 5% 25%	2919
February	1st to 10th	Night	16% 16% 7% 13% 8% 4 5% 4 4 5% 20%	2430
	11th to 20th	Night	15% 14% 6% 11% 8% 4 5% 3 4 5% 25%	2134
	21st to end	Night	16% 15% 6% 9% 6% 3 5% 4 4 4 29%	1776
March	1st to 10th	Night	18% 15% 6% 8% 7% 3 4 3 4 4 27%	2150
	11th to 20th	Night	21% 13% 6% 7% 6% 3 4 2 4 5% 30%	2114
	21st to end	Night	20% 13% 4 6% 5% 3 4 4 4 5% 34%	1980
April	1st to 10th	Night	25% 12% 3 7% 6% 2 5% 4 4 5% 27%	1800
	11th to 20th	Night	23% 8% 3 6% 5% 3 3 4 5% 6% 34%	1763
	21st to end	Night	23% 11% 4 5% 4 3 4 4 4 6% 33%	1620
May	1st to 10th	Night	24% 9% 4 6% 5% 3 4 3 5% 6% 31%	1550
	11th to 20th	Night	20% 7% 2 7% 6% 3 4 4 5% 6% 36%	1415
	21st to end	Night	20% 6% 2 4 5% 2 5% 4 6% 8% 37%	1550
June	1st to 10th	Night	25% 7% 2 5% 5% 3 6% 4 5% 7% 30%	1440
	11th to 20th	Night	19% 6% 2 5% 5% 4 4 6% 6% 7% 38%	1440
	21st to end	Night	18% 6% 3 7% 5% 3 5% 6% 5% 8% 33%	1440
July	1st to 10th	Night	14% 6% 3 6% 6% 2 5% 5% 6% 9% 37%	1440
	11th to 20th	Night	12% 5% 2 6% 6% 3 5% 6% 6% 9% 39%	1440
	21st to end	Night	13% 7% 3 6% 6% 3 5% 5% 6% 8% 39%	1574
August	1st to 10th	Night	16% 6% 3 4 4 3 5% 5% 8% 8% 39%	1432
	11th to 20th	Night	14% 6% 3 6% 6% 4 5% 5% 6% 7% 39%	1577
	21st to end	Night	14% 7% 3 5% 5% 3 4 5% 5% 9% 40%	1980
September	1st to 10th	Night	16% 6% 3 6% 5% 3 4 4 5% 6% 42%	1800
	11th to 20th	Night	17% 5% 2 4 4 3 3 3 4 9% 47%	1914
	21st to end	Night	18% 6% 3 4 5% 3 4 4 4 8% 41%	1980
October	1st to 10th	Night	19% 6% 3 6% 5% 4 4 4 5% 6% 37%	2040
	11th to 20th	Night	23% 10% 3 7% 7% 3 5% 4 4 5% 31%	2242
	21st to end	Night	27% 10% 3 7% 5% 3 4 4 4 5% 27%	2574
November	1st to 10th	Night	21% 13% 3 7% 5% 3 4 4 4 6% 30%	2407
	11th to 20th	Night	21% 13% 4 7% 6% 3 4 4 4 5% 29%	2489
	21st to end	Night	23% 15% 6% 7% 5% 3 4 3 3 5% 26%	2660
December	1st to 10th	Night	24% 20% 6% 9% 5% 4 4 3 3 5% 16%	2660
	11th to 20th	Night	23% 16% 6% 9% 7% 3 4 4 3 4 22%	3288
	21st to end	Night	26% 18% 5% 9% 6% 3 4 3 3 4 20%	4884

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	74% 4 8% 11% 2	1518
	11th to 20th	Day	69% 5% 9% 12% 5%	1520
	21st to end	Day	62% 6% 11% 15% 6% 1	1664
February	1st to 10th	Day	68% 5% 8% 15% 4 1	1526
	11th to 20th	Day	65% 4 12% 12% 5% 1	1720
	21st to end	Day	63% 4 10% 14% 7% 1	1480
March	1st to 10th	Day	61% 5% 9% 16% 6% 2	1800
	11th to 20th	Day	56% 4 13% 14% 12% 1	1841
	21st to end	Day	55% 4 10% 20% 9% 2	2376
April	1st to 10th	Day	61% 5% 9% 17% 8% 1	2160
	11th to 20th	Day	51% 5% 9% 21% 13% 1	2145
	21st to end	Day	56% 5% 9% 17% 10% 2	2340
May	1st to 10th	Day	52% 4 9% 19% 13% 1	2425
	11th to 20th	Day	47% 7% 11% 21% 13% 2	2482
	21st to end	Day	49% 8% 11% 18% 12% 1	2725
June	1st to 10th	Day	53% 7% 11% 20% 9% 1	2520
	11th to 20th	Day	44% 7% 13% 23% 12% 2	2520
	21st to end	Day	54% 7% 11% 18% 9%	2520
July	1st to 10th	Day	41% 8% 15% 26% 9%	2450
	11th to 20th	Day	43% 9% 15% 27% 6%	2445
	21st to end	Day	45% 8% 17% 23% 7%	2591
August	1st to 10th	Day	47% 8% 16% 24% 5%	2492
	11th to 20th	Day	40% 9% 18% 22% 10%	2301
	21st to end	Day	42% 8% 15% 25% 11%	2376
September	1st to 10th	Day	41% 8% 15% 25% 10% 1	2160
	11th to 20th	Day	39% 6% 13% 30% 12%	2045
	21st to end	Day	44% 7% 14% 26% 9%	1980
October	1st to 10th	Day	53% 6% 12% 21% 7%	1918
	11th to 20th	Day	55% 8% 15% 18% 4	1716
	21st to end	Day	62% 5% 10% 16% 6% 1	1782
November	1st to 10th	Day	54% 6% 13% 20% 7%	1671
	11th to 20th	Day	61% 5% 11% 14% 8%	1691
	21st to end	Day	64% 7% 13% 13% 3	1520
December	1st to 10th	Day	73% 6% 9% 10% 2	1520
	11th to 20th	Day	65% 4 10% 16% 4	1906
	21st to end	Day	71% 5% 10% 9% 4	2772
January	1st to 10th	Night	71% 5% 9% 12% 3	2649
	11th to 20th	Night	70% 5% 8% 12% 5% 1	2660
	21st to end	Night	62% 5% 9% 14% 8% 1	2919
February	1st to 10th	Night	68% 5% 8% 14% 6% 1	2430
	11th to 20th	Night	63% 5% 9% 16% 7%	2136
	21st to end	Night	61% 4 9% 14% 11% 1	1776
March	1st to 10th	Night	61% 4 9% 17% 8% 1	2160
	11th to 20th	Night	59% 4 9% 14% 11% 2	2115
	21st to end	Night	54% 4 7% 20% 12% 3	1980
April	1st to 10th	Night	59% 4 9% 16% 11% 1	1800
	11th to 20th	Night	52% 4 8% 21% 13% 2	1763
	21st to end	Night	53% 5% 8% 18% 13% 2	1620
May	1st to 10th	Night	54% 4 7% 17% 14% 3	1550
	11th to 20th	Night	48% 6% 10% 18% 16% 3	1416
	21st to end	Night	45% 7% 11% 21% 14% 2	1551
June	1st to 10th	Night	52% 6% 11% 21% 9% 1	1440
	11th to 20th	Night	44% 7% 10% 23% 13% 3	1440
	21st to end	Night	48% 7% 14% 19% 11%	1440
July	1st to 10th	Night	40% 9% 14% 23% 14% 1	1400
	11th to 20th	Night	40% 9% 13% 27% 11%	1392
	21st to end	Night	41% 10% 15% 25% 8%	1486
August	1st to 10th	Night	40% 9% 17% 25% 9%	1422
	11th to 20th	Night	43% 8% 17% 23% 10%	1577
	21st to end	Night	41% 7% 15% 26% 11% 1	1980
September	1st to 10th	Night	42% 6% 13% 25% 13% 1	1800
	11th to 20th	Night	38% 5% 15% 32% 11% 1	1914
	21st to end	Night	42% 7% 10% 27% 13% 1	1980
October	1st to 10th	Night	47% 7% 11% 23% 12%	2040
	11th to 20th	Night	56% 6% 10% 22% 6%	2242
	21st to end	Night	61% 5% 11% 15% 8% 1	2574
November	1st to 10th	Night	56% 5% 11% 20% 6% 1	2407
	11th to 20th	Night	58% 6% 10% 16% 8% 2	2489
	21st to end	Night	62% 5% 12% 16% 5%	2660
December	1st to 10th	Night	73% 4 9% 11% 3	2660
	11th to 20th	Night	69% 4 8% 15% 5%	3288
	21st to end	Night	69% 5% 9% 13% 3	4884

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	37% 12% 31% 16% 4	180
	11th to 20th	Day	32% 21% 32% 11% 4	180
	21st to end	Day	25% 18% 31% 19% 5% 2	196
February	1st to 10th	Day	39% 23% 25% 12% 2	198
	11th to 20th	Day	30% 21% 36% 10% 3	379
	21st to end	Day	28% 21% 31% 18% 2	346
March	1st to 10th	Day	29% 18% 27% 22% 4	420
	11th to 20th	Day	28% 20% 30% 16% 4 1	420
	21st to end	Day	30% 19% 25% 19% 5% 2	462
April	1st to 10th	Day	34% 13% 31% 15% 7% 1	420
	11th to 20th	Day	35% 17% 24% 16% 6% 3	412
	21st to end	Day	32% 16% 33% 10% 6% 2	420
May	1st to 10th	Day	32% 14% 29% 17% 6% 1	423
	11th to 20th	Day	22% 15% 29% 23% 9% 1	447
	21st to end	Day	21% 18% 32% 19% 8% 2	485
June	1st to 10th	Day	28% 13% 34% 18% 6% 2	450
	11th to 20th	Day	19% 15% 32% 22% 12%	450
	21st to end	Day	24% 12% 32% 21% 9% 2	450
July	1st to 10th	Day	18% 9% 30% 27% 14% 2	445
	11th to 20th	Day	17% 9% 34% 28% 9% 2	444
	21st to end	Day	19% 9% 31% 31% 9% 1	488
August	1st to 10th	Day	18% 10% 29% 26% 15% 3	446
	11th to 20th	Day	17% 7% 28% 28% 16% 4	439
	21st to end	Day	19% 12% 25% 22% 14% 7%	495
September	1st to 10th	Day	16% 13% 31% 24% 11% 6%	450
	11th to 20th	Day	19% 12% 23% 24% 15% 7%	450
	21st to end	Day	20% 12% 27% 22% 14% 5%	450
October	1st to 10th	Day	25% 14% 27% 20% 10% 4	450
	11th to 20th	Day	29% 16% 23% 21% 10% 1	408
	21st to end	Day	38% 14% 27% 16% 6%	396
November	1st to 10th	Day	32% 16% 27% 20% 5% 1	365
	11th to 20th	Day	31% 21% 23% 17% 8% 1	351
	21st to end	Day	30% 21% 31% 13% 5%	180
December	1st to 10th	Day	36% 16% 23% 18% 4 2	180
	11th to 20th	Day	34% 21% 31% 11% 2 1	180
	21st to end	Day	37% 21% 26% 11% 4 1	198
January	1st to 10th	Night	32% 13% 31% 19% 5%	760
	11th to 20th	Night	28% 18% 30% 20% 5%	760
	21st to end	Night	24% 13% 32% 26% 5%	835
February	1st to 10th	Night	26% 15% 36% 18% 4	720
	11th to 20th	Night	24% 18% 33% 21% 4 1	703
	21st to end	Night	25% 15% 33% 23% 4	592
March	1st to 10th	Night	27% 14% 31% 24% 4	720
	11th to 20th	Night	28% 15% 28% 23% 6%	720
	21st to end	Night	27% 12% 27% 26% 6% 1	792
April	1st to 10th	Night	32% 12% 27% 25% 5%	720
	11th to 20th	Night	27% 15% 26% 24% 7%	699
	21st to end	Night	30% 15% 27% 20% 8% 1	540
May	1st to 10th	Night	29% 9% 33% 21% 8% 1	470
	11th to 20th	Night	23% 11% 29% 28% 9% 1	354
	21st to end	Night	22% 7% 35% 29% 8%	389
June	1st to 10th	Night	29% 7% 30% 25% 8% 1	360
	11th to 20th	Night	21% 5% 32% 29% 13%	360
	21st to end	Night	18% 7% 29% 34% 12% 1	360
July	1st to 10th	Night	16% 6% 30% 35% 12% 1	350
	11th to 20th	Night	13% 6% 24% 39% 17% 1	348
	21st to end	Night	16% 5% 27% 40% 12% 1	394
August	1st to 10th	Night	19% 3 22% 37% 19% 1	358
	11th to 20th	Night	16% 4 25% 33% 21% 2	513
	21st to end	Night	19% 4 25% 34% 15% 3	792
September	1st to 10th	Night	18% 7% 26% 33% 14% 1	720
	11th to 20th	Night	21% 6% 22% 30% 19% 2	720
	21st to end	Night	22% 6% 30% 26% 14% 2	720
October	1st to 10th	Night	23% 11% 28% 26% 12% 1	720
	11th to 20th	Night	28% 11% 25% 26% 9% 1	720
	21st to end	Night	33% 13% 29% 21% 4	792
November	1st to 10th	Night	29% 15% 30% 19% 7% 1	740
	11th to 20th	Night	28% 18% 28% 17% 8% 1	760
	21st to end	Night	31% 19% 23% 20% 6% 1	760
December	1st to 10th	Night	37% 16% 25% 17% 4	760
	11th to 20th	Night	31% 17% 28% 18% 5% 1	760
	21st to end	Night	35% 17% 26% 18% 4	836

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