L'Assomption
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the L'Assomption clear sky chart from 2005-11-06 to 2024-01-17.

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	18% 8% 3 6% 6% 3 5% 5% 5% 7% 34%	74795
	Night	19% 10% 4 7% 6% 3 4 4 5% 6% 33%	75021
Transparency	Day	50% 7% 12% 20% 10% 1	74500
	Night	53% 6% 10% 19% 10% 1	74850
Seeing	Day	21% 11% 28% 25% 12% 3	13464
	Night	23% 8% 29% 29% 10% 1	22536

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% 16% 5% 8% 7% 3 5% 4 3 5% 26%	1517
	11th to 20th	Day	19% 15% 5% 8% 6% 4 4 4 3 5% 28%	1488
	21st to end	Day	11% 13% 4 8% 7% 3 6% 5% 6% 6% 30%	1584
February	1st to 10th	Day	17% 16% 5% 7% 6% 4 5% 4 4 5% 28%	1557
	11th to 20th	Day	15% 12% 5% 10% 6% 3 4 5% 5% 7% 28%	1674
	21st to end	Day	18% 14% 6% 9% 5% 3 4 5% 4 5% 28%	1480
March	1st to 10th	Day	16% 11% 4 7% 6% 5% 6% 5% 5% 5% 31%	1797
	11th to 20th	Day	16% 11% 4 5% 6% 3 5% 4 5% 6% 34%	1855
	21st to end	Day	18% 9% 4 6% 5% 3 4 4 5% 5% 36%	2376
April	1st to 10th	Day	22% 9% 4 6% 6% 4 4 5% 4 5% 32%	2160
	11th to 20th	Day	22% 7% 2 5% 5% 2 3 4 4 7% 38%	2134
	21st to end	Day	22% 8% 4 6% 5% 3 5% 5% 4 5% 32%	2322
May	1st to 10th	Day	20% 6% 3 7% 5% 3 4 4 5% 6% 36%	2476
	11th to 20th	Day	19% 6% 3 6% 5% 4 4 4 5% 7% 37%	2478
	21st to end	Day	18% 6% 3 5% 5% 4 6% 5% 5% 9% 35%	2725
June	1st to 10th	Day	22% 7% 3 6% 6% 3 5% 5% 6% 8% 31%	2520
	11th to 20th	Day	15% 6% 3 6% 5% 3 5% 5% 6% 8% 38%	2520
	21st to end	Day	20% 7% 3 7% 6% 3 6% 5% 6% 7% 31%	2520
July	1st to 10th	Day	13% 5% 2 5% 5% 3 5% 6% 7% 9% 39%	2520
	11th to 20th	Day	13% 5% 3 5% 6% 3 6% 6% 7% 9% 38%	2520
	21st to end	Day	12% 5% 3 6% 6% 4 5% 6% 7% 10% 38%	2744
August	1st to 10th	Day	13% 6% 2 5% 7% 4 6% 6% 6% 9% 37%	2506
	11th to 20th	Day	10% 4 3 6% 6% 4 5% 7% 7% 8% 41%	2304
	21st to end	Day	13% 5% 1 4 5% 3 5% 5% 6% 9% 44%	2376
September	1st to 10th	Day	12% 4 2 6% 5% 4 5% 6% 6% 9% 41%	2160
	11th to 20th	Day	14% 6% 2 4 3 2 4 4 4 6% 50%	2075
	21st to end	Day	16% 6% 3 5% 4 3 5% 4 6% 7% 42%	1980
October	1st to 10th	Day	20% 7% 3 6% 5% 3 4 4 6% 7% 36%	1872
	11th to 20th	Day	20% 7% 3 6% 8% 4 5% 5% 6% 7% 29%	1745
	21st to end	Day	25% 8% 4 6% 5% 3 4 4 5% 6% 31%	1782
November	1st to 10th	Day	17% 9% 3 6% 4 3 5% 5% 5% 8% 34%	1671
	11th to 20th	Day	19% 9% 4 7% 5% 3 4 5% 6% 6% 32%	1639
	21st to end	Day	23% 10% 3 5% 6% 4 5% 5% 4 6% 29%	1520
December	1st to 10th	Day	25% 12% 4 8% 7% 3 4 3 3 6% 24%	1520
	11th to 20th	Day	22% 13% 4 8% 6% 2 3 4 4 5% 30%	1906
	21st to end	Day	28% 16% 5% 8% 5% 3 3 3 3 4 23%	2772
January	1st to 10th	Night	18% 17% 5% 10% 6% 4 4 5% 4 5% 22%	2649
	11th to 20th	Night	17% 14% 6% 9% 7% 4 5% 4 4 4 25%	2611
	21st to end	Night	12% 12% 5% 8% 8% 3 6% 4 5% 6% 31%	2772
February	1st to 10th	Night	15% 14% 7% 11% 7% 5% 5% 4 4 5% 24%	2399
	11th to 20th	Night	15% 11% 6% 8% 7% 3 6% 5% 4 5% 30%	2172
	21st to end	Night	16% 12% 5% 9% 7% 3 3 5% 5% 4 32%	1776
March	1st to 10th	Night	19% 12% 5% 7% 5% 3 4 5% 4 4 31%	2150
	11th to 20th	Night	17% 13% 5% 7% 6% 3 5% 3 5% 4 32%	2102
	21st to end	Night	18% 10% 4 6% 6% 3 4 4 3 4 39%	1980
April	1st to 10th	Night	25% 8% 4 6% 5% 3 4 5% 5% 7% 30%	1800
	11th to 20th	Night	22% 6% 3 6% 5% 3 5% 5% 4 6% 37%	1775
	21st to end	Night	24% 8% 3 5% 5% 3 3 4 5% 5% 35%	1636
May	1st to 10th	Night	22% 8% 3 6% 6% 3 3 4 4 6% 35%	1499
	11th to 20th	Night	20% 6% 3 6% 5% 3 4 4 6% 7% 36%	1415
	21st to end	Night	18% 6% 3 5% 5% 3 5% 5% 4 8% 38%	1550
June	1st to 10th	Night	22% 7% 2 5% 5% 3 5% 5% 6% 8% 33%	1440
	11th to 20th	Night	17% 6% 3 5% 5% 3 4 5% 5% 8% 38%	1440
	21st to end	Night	18% 6% 3 5% 7% 4 4 6% 6% 7% 34%	1440
July	1st to 10th	Night	10% 6% 3 5% 6% 3 5% 5% 8% 9% 41%	1440
	11th to 20th	Night	11% 6% 3 5% 5% 4 6% 5% 7% 8% 40%	1440
	21st to end	Night	13% 5% 2 5% 5% 3 5% 5% 7% 8% 41%	1574
August	1st to 10th	Night	13% 5% 3 6% 6% 3 5% 5% 7% 7% 42%	1432
	11th to 20th	Night	13% 6% 3 5% 5% 3 6% 5% 6% 7% 42%	1575
	21st to end	Night	14% 6% 2 6% 5% 3 4 4 6% 7% 43%	1980
September	1st to 10th	Night	13% 5% 2 6% 5% 3 5% 5% 5% 6% 45%	1800
	11th to 20th	Night	15% 5% 3 5% 4 2 3 3 4 7% 49%	1885
	21st to end	Night	16% 6% 2 4 5% 2 4 3 5% 7% 44%	1980
October	1st to 10th	Night	18% 5% 3 6% 6% 4 4 4 4 6% 40%	2084
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 4 4 6% 35%	2214
	21st to end	Night	24% 8% 4 6% 5% 3 4 4 4 6% 32%	2574
November	1st to 10th	Night	19% 9% 3 6% 6% 4 4 4 5% 6% 34%	2407
	11th to 20th	Night	20% 9% 4 6% 6% 2 5% 5% 5% 6% 34%	2538
	21st to end	Night	23% 13% 4 6% 6% 3 4 3 3 5% 29%	2660
December	1st to 10th	Night	21% 13% 6% 9% 6% 3 4 4 5% 6% 23%	2660
	11th to 20th	Night	24% 13% 5% 8% 5% 3 3 3 4 4 29%	3288
	21st to end	Night	28% 14% 5% 8% 5% 2 3 3 3 4 23%	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	66% 6% 8% 15% 5%	1518
	11th to 20th	Day	63% 5% 9% 13% 10%	1488
	21st to end	Day	55% 6% 11% 18% 10% 1	1584
February	1st to 10th	Day	61% 4 9% 18% 6% 2	1557
	11th to 20th	Day	58% 6% 11% 14% 9% 1	1683
	21st to end	Day	60% 4 10% 16% 9% 2	1480
March	1st to 10th	Day	56% 6% 8% 18% 10% 2	1800
	11th to 20th	Day	52% 6% 11% 16% 13% 2	1855
	21st to end	Day	51% 5% 10% 18% 13% 2	2376
April	1st to 10th	Day	56% 5% 8% 18% 11% 2	2160
	11th to 20th	Day	48% 4 9% 23% 14% 2	2134
	21st to end	Day	54% 6% 9% 17% 12% 3	2322
May	1st to 10th	Day	49% 5% 9% 21% 14% 2	2476
	11th to 20th	Day	46% 6% 11% 20% 15% 2	2482
	21st to end	Day	46% 7% 13% 18% 14% 2	2725
June	1st to 10th	Day	50% 7% 11% 19% 10% 2	2520
	11th to 20th	Day	41% 7% 12% 25% 12% 3	2520
	21st to end	Day	51% 7% 13% 19% 10% 1	2520
July	1st to 10th	Day	38% 9% 15% 26% 11% 1	2450
	11th to 20th	Day	39% 9% 16% 27% 9%	2445
	21st to end	Day	40% 9% 18% 25% 8%	2591
August	1st to 10th	Day	42% 9% 17% 24% 7%	2492
	11th to 20th	Day	37% 9% 19% 25% 10%	2304
	21st to end	Day	37% 8% 16% 26% 13%	2376
September	1st to 10th	Day	37% 8% 14% 27% 12% 1	2160
	11th to 20th	Day	35% 6% 13% 32% 14% 1	2075
	21st to end	Day	41% 8% 14% 26% 11%	1980
October	1st to 10th	Day	48% 7% 14% 21% 10%	1872
	11th to 20th	Day	53% 8% 14% 19% 6%	1745
	21st to end	Day	56% 5% 12% 18% 8% 1	1782
November	1st to 10th	Day	49% 7% 14% 21% 9% 1	1671
	11th to 20th	Day	53% 7% 11% 17% 11%	1639
	21st to end	Day	57% 8% 14% 15% 6%	1520
December	1st to 10th	Day	66% 5% 11% 13% 5%	1520
	11th to 20th	Day	60% 5% 10% 19% 6%	1906
	21st to end	Day	68% 5% 12% 9% 5%	2772
January	1st to 10th	Night	65% 6% 9% 14% 5%	2649
	11th to 20th	Night	63% 7% 10% 12% 8% 1	2611
	21st to end	Night	56% 6% 9% 17% 11% 1	2772
February	1st to 10th	Night	64% 5% 8% 15% 6% 1	2399
	11th to 20th	Night	58% 5% 9% 18% 9% 1	2174
	21st to end	Night	56% 6% 8% 16% 13% 1	1776
March	1st to 10th	Night	57% 5% 9% 16% 11% 2	2160
	11th to 20th	Night	56% 5% 9% 15% 13% 3	2103
	21st to end	Night	52% 4 7% 19% 14% 4	1980
April	1st to 10th	Night	56% 4 7% 18% 14% 2	1800
	11th to 20th	Night	51% 4 8% 21% 15% 2	1775
	21st to end	Night	52% 4 8% 19% 13% 3	1636
May	1st to 10th	Night	51% 5% 7% 19% 14% 5%	1499
	11th to 20th	Night	48% 6% 9% 17% 16% 4	1416
	21st to end	Night	45% 6% 12% 20% 16% 3	1551
June	1st to 10th	Night	49% 6% 10% 22% 12% 1	1440
	11th to 20th	Night	44% 7% 10% 21% 14% 4	1440
	21st to end	Night	48% 8% 11% 19% 14%	1440
July	1st to 10th	Night	37% 9% 14% 25% 15% 1	1400
	11th to 20th	Night	38% 8% 14% 27% 13%	1392
	21st to end	Night	38% 10% 16% 25% 10%	1486
August	1st to 10th	Night	39% 9% 16% 25% 11%	1422
	11th to 20th	Night	39% 8% 16% 24% 11%	1575
	21st to end	Night	39% 7% 15% 26% 12% 1	1980
September	1st to 10th	Night	39% 8% 12% 26% 14% 1	1800
	11th to 20th	Night	37% 5% 13% 31% 13% 1	1885
	21st to end	Night	40% 8% 10% 27% 14%	1980
October	1st to 10th	Night	45% 6% 10% 26% 13% 1	2084
	11th to 20th	Night	52% 7% 10% 23% 7%	2214
	21st to end	Night	57% 6% 11% 17% 9% 1	2574
November	1st to 10th	Night	52% 5% 12% 21% 8% 1	2407
	11th to 20th	Night	52% 6% 12% 19% 10% 1	2538
	21st to end	Night	60% 5% 11% 17% 7%	2660
December	1st to 10th	Night	65% 6% 11% 13% 4	2660
	11th to 20th	Night	61% 5% 8% 17% 8%	3288
	21st to end	Night	66% 5% 9% 15% 5%	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	28% 13% 29% 18% 12%	180
	11th to 20th	Day	26% 15% 34% 19% 6% 1	172
	21st to end	Day	19% 11% 35% 23% 11% 1	176
February	1st to 10th	Day	32% 18% 34% 15% 1	212
	11th to 20th	Day	24% 13% 34% 25% 4 1	342
	21st to end	Day	29% 12% 31% 24% 5%	346
March	1st to 10th	Day	23% 11% 30% 26% 10%	420
	11th to 20th	Day	22% 13% 34% 22% 7% 1	420
	21st to end	Day	28% 9% 31% 22% 9% 2	462
April	1st to 10th	Day	29% 14% 27% 20% 9% 1	420
	11th to 20th	Day	27% 17% 23% 20% 9% 3	412
	21st to end	Day	28% 12% 30% 19% 10% 1	420
May	1st to 10th	Day	23% 9% 35% 20% 10% 2	423
	11th to 20th	Day	18% 11% 29% 26% 13% 4	447
	21st to end	Day	19% 12% 32% 25% 10% 2	485
June	1st to 10th	Day	23% 11% 26% 28% 10% 2	450
	11th to 20th	Day	16% 11% 25% 31% 15% 2	450
	21st to end	Day	22% 10% 23% 27% 15% 3	450
July	1st to 10th	Day	13% 7% 22% 31% 20% 5%	445
	11th to 20th	Day	14% 6% 26% 34% 16% 5%	444
	21st to end	Day	15% 7% 24% 33% 17% 4	488
August	1st to 10th	Day	14% 5% 24% 30% 21% 6%	446
	11th to 20th	Day	11% 5% 21% 32% 21% 10%	439
	21st to end	Day	15% 8% 23% 25% 18% 11%	495
September	1st to 10th	Day	12% 8% 27% 29% 16% 7%	450
	11th to 20th	Day	16% 8% 21% 28% 16% 11%	450
	21st to end	Day	18% 8% 27% 23% 17% 7%	450
October	1st to 10th	Day	22% 13% 24% 23% 14% 4	450
	11th to 20th	Day	23% 12% 28% 23% 12% 2	422
	21st to end	Day	31% 11% 27% 23% 8% 1	396
November	1st to 10th	Day	25% 13% 31% 21% 10%	365
	11th to 20th	Day	24% 15% 30% 20% 8% 2	299
	21st to end	Day	31% 12% 31% 17% 9% 1	180
December	1st to 10th	Day	30% 11% 23% 22% 12% 3	180
	11th to 20th	Day	24% 22% 33% 16% 4 1	180
	21st to end	Day	34% 17% 26% 18% 4 1	198
January	1st to 10th	Night	28% 10% 30% 27% 5%	760
	11th to 20th	Night	25% 10% 33% 25% 6%	747
	21st to end	Night	20% 9% 33% 31% 7% 1	792
February	1st to 10th	Night	23% 9% 36% 27% 5% 1	720
	11th to 20th	Night	20% 11% 37% 26% 5% 1	703
	21st to end	Night	22% 10% 32% 31% 5%	592
March	1st to 10th	Night	26% 8% 31% 30% 6%	720
	11th to 20th	Night	26% 9% 31% 26% 7%	720
	21st to end	Night	23% 8% 30% 30% 8%	792
April	1st to 10th	Night	28% 11% 26% 28% 7%	720
	11th to 20th	Night	25% 12% 29% 27% 6% 1	711
	21st to end	Night	28% 10% 30% 24% 7% 1	556
May	1st to 10th	Night	25% 7% 32% 27% 8% 1	419
	11th to 20th	Night	23% 9% 29% 31% 8% 1	354
	21st to end	Night	18% 8% 35% 30% 9%	389
June	1st to 10th	Night	23% 5% 28% 34% 9% 1	360
	11th to 20th	Night	19% 4 29% 35% 13%	360
	21st to end	Night	17% 6% 28% 34% 15% 1	360
July	1st to 10th	Night	12% 5% 29% 38% 16% 1	350
	11th to 20th	Night	11% 2 24% 46% 15% 1	348
	21st to end	Night	13% 4 22% 45% 16% 1	394
August	1st to 10th	Night	13% 5% 17% 43% 20% 2	358
	11th to 20th	Night	14% 3 19% 39% 23% 2	511
	21st to end	Night	16% 4 21% 36% 20% 2	792
September	1st to 10th	Night	15% 5% 23% 41% 15% 1	720
	11th to 20th	Night	18% 5% 22% 34% 20% 2	720
	21st to end	Night	18% 7% 26% 31% 15% 3	720
October	1st to 10th	Night	21% 7% 27% 31% 12% 1	720
	11th to 20th	Night	26% 8% 27% 29% 9% 1	720
	21st to end	Night	28% 9% 31% 25% 7%	792
November	1st to 10th	Night	24% 11% 31% 25% 8%	740
	11th to 20th	Night	25% 11% 32% 22% 9% 1	760
	21st to end	Night	30% 11% 30% 22% 8%	760
December	1st to 10th	Night	29% 11% 29% 24% 7%	760
	11th to 20th	Night	28% 12% 31% 22% 6% 1	760
	21st to end	Night	32% 11% 30% 21% 6%	836

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