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 2026-04-17.

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	17% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	131588
	Night	17% 11% 4 9% 5% 5% 4 3 5% 6% 31%	130595
Transparency	Day	33% 38% 8% 14% 6%	135033
	Night	36% 37% 7% 12% 7% 1	135237
Seeing	Day	21% 12% 28% 24% 12% 3	16300
	Night	23% 9% 29% 29% 10% 1	25376

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	14% 17% 5% 11% 5% 4 4 3 4 5% 28%	4661
	11th to 20th	Day	11% 16% 6% 12% 7% 6% 4 3 5% 5% 24%	4650
	21st to end	Day	9% 12% 5% 12% 8% 6% 6% 4 5% 6% 27%	5124
February	1st to 10th	Day	15% 16% 3 8% 6% 5% 6% 3 4 5% 29%	1817
	11th to 20th	Day	13% 12% 4 11% 6% 5% 3 5% 6% 7% 28%	1961
	21st to end	Day	16% 15% 4 9% 5% 4 4 4 5% 6% 28%	1730
March	1st to 10th	Day	19% 12% 4 9% 6% 5% 5% 3 5% 5% 26%	4576
	11th to 20th	Day	12% 13% 4 9% 5% 4 4 3 5% 7% 33%	4790
	21st to end	Day	18% 10% 4 9% 5% 4 4 4 4 5% 33%	6102
April	1st to 10th	Day	21% 10% 3 8% 5% 5% 4 4 4 5% 31%	2520
	11th to 20th	Day	22% 9% 2 7% 5% 3 3 3 4 6% 36%	2446
	21st to end	Day	22% 8% 3 7% 5% 4 5% 4 5% 5% 33%	2581
May	1st to 10th	Day	26% 9% 3 8% 5% 4 4 3 5% 6% 26%	6246
	11th to 20th	Day	19% 8% 3 8% 5% 4 4 3 6% 8% 31%	6318
	21st to end	Day	21% 7% 3 7% 5% 5% 5% 4 6% 8% 31%	6949
June	1st to 10th	Day	21% 7% 2 7% 5% 4 5% 4 6% 8% 31%	2800
	11th to 20th	Day	14% 6% 2 7% 4 4 5% 4 6% 8% 38%	2800
	21st to end	Day	20% 7% 3 7% 5% 5% 5% 4 6% 7% 31%	2800
July	1st to 10th	Day	14% 6% 2 8% 6% 5% 6% 5% 7% 8% 33%	6360
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	6360
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 10% 47%	6926
August	1st to 10th	Day	13% 5% 2 7% 6% 5% 6% 5% 7% 9% 34%	4563
	11th to 20th	Day	14% 6% 3 7% 4 4 5% 4 6% 8% 38%	4157
	21st to end	Day	16% 6% 2 7% 4 4 4 4 6% 8% 40%	4312
September	1st to 10th	Day	11% 4 2 6% 4 5% 5% 5% 6% 9% 43%	2400
	11th to 20th	Day	13% 6% 2 4 3 3 4 3 5% 6% 50%	2305
	21st to end	Day	17% 6% 3 5% 3 4 5% 3 6% 6% 42%	2200
October	1st to 10th	Day	18% 6% 2 7% 5% 4 4 3 5% 7% 38%	2080
	11th to 20th	Day	19% 7% 3 8% 6% 6% 4 4 5% 7% 31%	1938
	21st to end	Day	24% 9% 3 7% 4 4 4 3 5% 6% 32%	1980
November	1st to 10th	Day	17% 10% 3 7% 4 4 4 4 5% 8% 34%	1851
	11th to 20th	Day	18% 11% 3 8% 4 5% 4 4 6% 6% 33%	1811
	21st to end	Day	23% 12% 3 7% 4 4 5% 4 5% 5% 27%	1680
December	1st to 10th	Day	20% 16% 5% 12% 6% 5% 3 3 4 5% 21%	2680
	11th to 20th	Day	19% 13% 4 9% 5% 4 4 4 5% 5% 28%	3066
	21st to end	Day	24% 13% 4 9% 5% 5% 5% 3 5% 5% 23%	4048
January	1st to 10th	Night	13% 17% 7% 14% 6% 5% 4 3 4 4 23%	8234
	11th to 20th	Night	12% 15% 7% 16% 8% 6% 5% 3 4 5% 20%	8235
	21st to end	Night	10% 12% 5% 13% 9% 6% 5% 4 5% 5% 26%	9057
February	1st to 10th	Night	13% 14% 6% 11% 7% 6% 4 4 5% 5% 26%	2799
	11th to 20th	Night	14% 12% 5% 9% 6% 5% 5% 4 4 5% 30%	2545
	21st to end	Night	15% 13% 4 10% 6% 4 4 3 5% 4 32%	2076
March	1st to 10th	Night	23% 13% 3 8% 5% 4 4 3 3 4 30%	5484
	11th to 20th	Night	14% 13% 3 8% 5% 5% 4 3 6% 6% 31%	5387
	21st to end	Night	16% 11% 4 10% 6% 5% 4 3 4 5% 32%	5072
April	1st to 10th	Night	24% 9% 3 7% 4 4 4 4 5% 6% 31%	2100
	11th to 20th	Night	21% 8% 3 7% 5% 4 5% 4 4 5% 35%	2036
	21st to end	Night	24% 8% 3 6% 4 3 4 3 5% 5% 35%	1817
May	1st to 10th	Night	26% 9% 3 8% 5% 4 5% 3 5% 5% 25%	3737
	11th to 20th	Night	23% 9% 3 7% 5% 4 5% 3 5% 6% 31%	3575
	21st to end	Night	19% 8% 3 8% 5% 5% 5% 4 5% 8% 29%	3926
June	1st to 10th	Night	21% 8% 2 6% 4 5% 4 4 6% 7% 33%	1600
	11th to 20th	Night	16% 7% 3 6% 5% 4 4 4 6% 8% 38%	1600
	21st to end	Night	20% 6% 3 6% 6% 5% 4 5% 5% 7% 34%	1600
July	1st to 10th	Night	12% 6% 3 7% 6% 4 5% 5% 9% 9% 33%	3600
	11th to 20th	Night	15% 6% 2 6% 5% 5% 4 3 6% 7% 42%	3600
	21st to end	Night	10% 4 2 6% 5% 4 5% 4 7% 8% 45%	3926
August	1st to 10th	Night	14% 6% 3 9% 5% 5% 4 4 6% 6% 38%	2586
	11th to 20th	Night	15% 7% 3 7% 4 5% 4 4 5% 7% 39%	2854
	21st to end	Night	18% 6% 3 8% 5% 4 4 3 5% 6% 39%	3586
September	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 5% 6% 47%	2000
	11th to 20th	Night	14% 5% 2 6% 4 3 3 3 4 7% 50%	2095
	21st to end	Night	16% 6% 2 6% 4 4 4 3 5% 7% 44%	2200
October	1st to 10th	Night	18% 4 3 6% 5% 5% 4 3 5% 6% 42%	2316
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 5% 6% 36%	2461
	21st to end	Night	23% 8% 3 7% 4 4 5% 3 4 6% 33%	2860
November	1st to 10th	Night	20% 10% 3 7% 4 5% 4 3 5% 6% 34%	2667
	11th to 20th	Night	19% 10% 3 7% 4 4 4 4 5% 6% 34%	2806
	21st to end	Night	23% 13% 3 8% 5% 4 4 3 3 5% 28%	2940
December	1st to 10th	Night	17% 15% 6% 11% 7% 6% 5% 3 5% 5% 20%	4720
	11th to 20th	Night	23% 12% 4 9% 5% 4 4 3 5% 4 27%	5348
	21st to end	Night	24% 15% 5% 9% 4 3 5% 3 5% 4 24%	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	50% 24% 9% 14% 3	4662
	11th to 20th	Day	50% 23% 7% 11% 8%	4680
	21st to end	Day	48% 24% 8% 10% 9% 1	5124
February	1st to 10th	Day	24% 59% 4 8% 3 1	1817
	11th to 20th	Day	23% 59% 4 9% 5%	1970
	21st to end	Day	24% 59% 3 7% 5% 1	1730
March	1st to 10th	Day	44% 30% 6% 9% 8% 3	4579
	11th to 20th	Day	37% 31% 13% 9% 9% 2	4790
	21st to end	Day	40% 30% 5% 12% 12% 1	6102
April	1st to 10th	Day	23% 59% 4 7% 6% 1	2520
	11th to 20th	Day	22% 60% 3 9% 5% 1	2446
	21st to end	Day	21% 62% 4 7% 5%	2581
May	1st to 10th	Day	46% 32% 6% 14% 2	6257
	11th to 20th	Day	38% 33% 12% 12% 5% 1	6322
	21st to end	Day	38% 31% 9% 14% 7%	6949
June	1st to 10th	Day	19% 63% 4 8% 6% 1	2800
	11th to 20th	Day	16% 63% 5% 9% 6% 1	2800
	21st to end	Day	19% 60% 5% 9% 5% 1	2800
July	1st to 10th	Day	36% 28% 11% 19% 5%	6290
	11th to 20th	Day	28% 28% 12% 24% 8%	6285
	21st to end	Day	24% 27% 12% 31% 6%	6728
August	1st to 10th	Day	30% 38% 13% 14% 5%	4549
	11th to 20th	Day	30% 39% 13% 16% 3	4199
	21st to end	Day	29% 37% 10% 14% 10%	4312
September	1st to 10th	Day	13% 60% 8% 15% 4	2400
	11th to 20th	Day	13% 58% 7% 16% 5% 1	2305
	21st to end	Day	15% 58% 5% 14% 7%	2200
October	1st to 10th	Day	26% 37% 10% 21% 5%	3392
	11th to 20th	Day	25% 37% 14% 19% 5%	3128
	21st to end	Day	26% 38% 14% 16% 6%	3180
November	1st to 10th	Day	27% 55% 6% 8% 3	1851
	11th to 20th	Day	22% 55% 5% 11% 6%	1811
	21st to end	Day	29% 56% 5% 6% 4	1680
December	1st to 10th	Day	46% 35% 5% 12% 2	2680
	11th to 20th	Day	41% 32% 6% 11% 9%	3066
	21st to end	Day	48% 29% 9% 9% 5%	4048
January	1st to 10th	Night	53% 23% 10% 10% 4 1	8234
	11th to 20th	Night	55% 25% 6% 10% 4	8280
	21st to end	Night	49% 23% 7% 10% 11%	9057
February	1st to 10th	Night	25% 59% 4 8% 4	2799
	11th to 20th	Night	24% 58% 3 9% 6%	2547
	21st to end	Night	21% 59% 3 9% 7% 1	2076
March	1st to 10th	Night	43% 29% 5% 9% 9% 4	5494
	11th to 20th	Night	37% 30% 10% 11% 10% 1	5388
	21st to end	Night	42% 29% 4 15% 8% 1	5072
April	1st to 10th	Night	23% 59% 3 8% 7%	2100
	11th to 20th	Night	23% 61% 2 8% 5% 1	2036
	21st to end	Night	21% 62% 3 7% 6% 1	1817
May	1st to 10th	Night	45% 33% 7% 12% 3	3743
	11th to 20th	Night	40% 32% 8% 14% 6%	3576
	21st to end	Night	40% 30% 8% 12% 9%	3927
June	1st to 10th	Night	19% 62% 4 8% 7%	1600
	11th to 20th	Night	16% 62% 5% 9% 7% 1	1600
	21st to end	Night	19% 61% 4 8% 7% 1	1600
July	1st to 10th	Night	35% 28% 15% 15% 6%	3560
	11th to 20th	Night	31% 28% 13% 21% 7%	3552
	21st to end	Night	27% 28% 14% 23% 9%	3809
August	1st to 10th	Night	32% 38% 8% 18% 4	2576
	11th to 20th	Night	33% 38% 12% 14% 3	2878
	21st to end	Night	31% 37% 8% 13% 10% 1	3586
September	1st to 10th	Night	13% 59% 7% 13% 8% 1	2000
	11th to 20th	Night	15% 57% 7% 15% 6% 1	2095
	21st to end	Night	16% 58% 4 13% 9%	2200
October	1st to 10th	Night	28% 37% 10% 18% 7%	3784
	11th to 20th	Night	25% 37% 8% 24% 7%	4010
	21st to end	Night	30% 36% 11% 13% 9% 1	4610
November	1st to 10th	Night	27% 53% 6% 10% 3 1	2667
	11th to 20th	Night	25% 54% 5% 9% 5% 1	2806
	21st to end	Night	29% 55% 5% 7% 4	2940
December	1st to 10th	Night	47% 36% 7% 8% 2	4720
	11th to 20th	Night	44% 32% 6% 8% 10%	5348
	21st to end	Night	49% 26% 6% 11% 8%	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% 13% 32% 18% 10%	220
	11th to 20th	Day	25% 17% 34% 18% 5%	220
	21st to end	Day	18% 13% 35% 23% 10% 2	242
February	1st to 10th	Day	25% 15% 36% 19% 4	292
	11th to 20th	Day	21% 16% 32% 26% 4	449
	21st to end	Day	25% 13% 34% 24% 4	446
March	1st to 10th	Day	22% 15% 31% 24% 9%	540
	11th to 20th	Day	23% 14% 35% 21% 6% 1	540
	21st to end	Day	27% 13% 32% 21% 7% 1	594
April	1st to 10th	Day	28% 16% 28% 19% 7% 1	540
	11th to 20th	Day	29% 18% 24% 19% 7% 3	516
	21st to end	Day	28% 13% 31% 18% 9% 1	500
May	1st to 10th	Day	24% 11% 33% 21% 10% 2	503
	11th to 20th	Day	18% 11% 28% 26% 14% 3	527
	21st to end	Day	21% 12% 29% 25% 10% 2	573
June	1st to 10th	Day	21% 12% 26% 30% 10% 2	530
	11th to 20th	Day	15% 11% 26% 31% 14% 2	530
	21st to end	Day	23% 11% 25% 26% 13% 3	530
July	1st to 10th	Day	13% 8% 25% 30% 18% 5%	525
	11th to 20th	Day	13% 8% 27% 33% 15% 4	524
	21st to end	Day	13% 7% 26% 33% 17% 3	576
August	1st to 10th	Day	13% 5% 23% 31% 21% 6%	526
	11th to 20th	Day	12% 6% 19% 31% 23% 9%	519
	21st to end	Day	15% 8% 23% 25% 18% 10%	583
September	1st to 10th	Day	12% 9% 27% 29% 16% 7%	530
	11th to 20th	Day	13% 7% 19% 28% 20% 13%	530
	21st to end	Day	18% 9% 26% 23% 18% 6%	530
October	1st to 10th	Day	19% 13% 26% 23% 15% 4	530
	11th to 20th	Day	22% 12% 30% 23% 11% 2	495
	21st to end	Day	30% 11% 26% 24% 8%	462
November	1st to 10th	Day	26% 15% 30% 19% 9%	425
	11th to 20th	Day	23% 15% 31% 21% 9% 1	351
	21st to end	Day	34% 13% 30% 15% 8%	220
December	1st to 10th	Day	29% 10% 28% 19% 11% 3	220
	11th to 20th	Day	25% 20% 34% 15% 4 1	220
	21st to end	Day	31% 17% 27% 19% 4 2	242
January	1st to 10th	Night	28% 10% 32% 26% 5%	840
	11th to 20th	Night	25% 11% 33% 24% 6%	840
	21st to end	Night	19% 10% 33% 30% 6% 1	924
February	1st to 10th	Night	21% 10% 35% 28% 5% 1	840
	11th to 20th	Night	20% 11% 38% 25% 5% 1	823
	21st to end	Night	21% 11% 33% 31% 4	692
March	1st to 10th	Night	25% 9% 32% 28% 5%	840
	11th to 20th	Night	25% 12% 31% 25% 7%	840
	21st to end	Night	23% 10% 31% 28% 7%	924
April	1st to 10th	Night	29% 12% 26% 27% 6%	840
	11th to 20th	Night	26% 13% 30% 25% 6%	816
	21st to end	Night	28% 11% 30% 24% 7%	617
May	1st to 10th	Night	26% 8% 31% 27% 7% 1	465
	11th to 20th	Night	23% 9% 28% 31% 9% 1	394
	21st to end	Night	18% 9% 35% 29% 9%	433
June	1st to 10th	Night	22% 6% 27% 35% 9% 1	400
	11th to 20th	Night	19% 4 29% 37% 12%	400
	21st to end	Night	19% 7% 27% 33% 14% 1	400
July	1st to 10th	Night	11% 6% 29% 38% 15% 1	390
	11th to 20th	Night	12% 3 24% 46% 14% 1	388
	21st to end	Night	13% 4 22% 45% 16%	438
August	1st to 10th	Night	13% 5% 17% 44% 19% 2	398
	11th to 20th	Night	14% 4 19% 38% 24% 2	570
	21st to end	Night	16% 5% 21% 37% 20% 2	880
September	1st to 10th	Night	15% 5% 24% 40% 16% 1	800
	11th to 20th	Night	16% 5% 20% 34% 23% 2	800
	21st to end	Night	18% 6% 26% 32% 15% 3	800
October	1st to 10th	Night	20% 7% 28% 31% 13% 1	800
	11th to 20th	Night	25% 8% 28% 29% 9% 1	800
	21st to end	Night	27% 10% 31% 26% 7%	880
November	1st to 10th	Night	25% 11% 31% 24% 8%	820
	11th to 20th	Night	25% 10% 33% 23% 9% 1	840
	21st to end	Night	29% 12% 31% 21% 7%	840
December	1st to 10th	Night	28% 11% 30% 25% 6%	840
	11th to 20th	Night	28% 13% 32% 21% 6% 1	840
	21st to end	Night	31% 11% 30% 20% 7%	924

Page generated at 2026-04-14 02:44:29. Version ac07

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