Observatoire de Leclercville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Leclercville clear sky chart from 2005-11-06 to 2024-01-14.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 30%	74541
	Night	20% 11% 4 7% 6% 3 4 4 5% 6% 30%	75204
Transparency	Day	36% 38% 8% 12% 5% 1	74246
	Night	38% 38% 8% 11% 5% 1	75034
Seeing	Day	25% 15% 30% 20% 8% 2	13803
	Night	25% 12% 30% 25% 7% 1	22677

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	22% 15% 6% 11% 6% 3 5% 4 4 5% 19%	1517
	11th to 20th	Day	18% 17% 7% 9% 6% 4 5% 3 4 4 22%	1464
	21st to end	Day	11% 14% 6% 8% 8% 3 5% 6% 5% 6% 27%	1584
February	1st to 10th	Day	13% 16% 5% 12% 8% 4 5% 3 4 6% 23%	1467
	11th to 20th	Day	15% 17% 7% 8% 6% 4 6% 4 5% 5% 24%	1720
	21st to end	Day	15% 13% 5% 10% 7% 3 4 5% 4 6% 27%	1480
March	1st to 10th	Day	16% 12% 4 9% 7% 3 5% 4 5% 5% 31%	1797
	11th to 20th	Day	19% 11% 6% 7% 5% 2 5% 4 4 6% 30%	1862
	21st to end	Day	17% 11% 4 8% 6% 4 5% 4 5% 6% 31%	2347
April	1st to 10th	Day	23% 11% 5% 7% 6% 3 4 3 4 6% 28%	2160
	11th to 20th	Day	20% 9% 3 6% 5% 2 4 4 4 5% 38%	2188
	21st to end	Day	24% 9% 3 7% 5% 3 5% 3 5% 6% 30%	2340
May	1st to 10th	Day	22% 8% 3 5% 5% 3 4 4 5% 5% 34%	2420
	11th to 20th	Day	18% 6% 3 7% 5% 4 4 5% 6% 8% 35%	2478
	21st to end	Day	20% 7% 3 6% 6% 4 5% 5% 6% 6% 32%	2725
June	1st to 10th	Day	20% 7% 3 6% 7% 4 6% 5% 6% 8% 28%	2592
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 6% 6% 8% 35%	2700
	21st to end	Day	22% 8% 3 7% 6% 3 5% 5% 6% 6% 29%	2592
July	1st to 10th	Day	14% 6% 3 6% 6% 5% 5% 5% 7% 10% 33%	2520
	11th to 20th	Day	14% 6% 2 7% 6% 3 6% 6% 8% 10% 32%	2520
	21st to end	Day	15% 7% 3 5% 6% 4 6% 6% 7% 9% 32%	2744
August	1st to 10th	Day	17% 6% 3 6% 6% 3 6% 6% 7% 10% 29%	2506
	11th to 20th	Day	14% 6% 3 7% 6% 4 5% 5% 6% 8% 37%	2317
	21st to end	Day	16% 6% 3 5% 5% 3 4 6% 6% 7% 39%	2422
September	1st to 10th	Day	17% 6% 2 6% 6% 3 5% 5% 5% 7% 39%	2160
	11th to 20th	Day	19% 5% 2 4 5% 3 4 4 5% 8% 44%	2026
	21st to end	Day	22% 6% 2 4 5% 3 4 4 5% 6% 39%	1980
October	1st to 10th	Day	22% 8% 3 5% 5% 3 6% 4 5% 8% 31%	1944
	11th to 20th	Day	23% 10% 3 8% 6% 3 5% 5% 5% 6% 25%	1678
	21st to end	Day	29% 10% 4 5% 7% 3 4 4 4 5% 24%	1782
November	1st to 10th	Day	19% 10% 4 7% 6% 4 4 4 5% 5% 32%	1671
	11th to 20th	Day	22% 12% 6% 10% 6% 4 4 4 5% 4 24%	1687
	21st to end	Day	24% 15% 4 7% 6% 3 5% 4 4 5% 22%	1465
December	1st to 10th	Day	26% 15% 5% 10% 6% 3 3 3 3 5% 21%	1330
	11th to 20th	Day	23% 13% 5% 8% 7% 4 3 4 4 5% 25%	1668
	21st to end	Day	25% 17% 4 8% 6% 3 4 4 3 5% 21%	2688
January	1st to 10th	Night	20% 18% 7% 10% 6% 3 4 4 4 4 18%	2649
	11th to 20th	Night	19% 17% 5% 10% 7% 4 5% 3 5% 4 21%	2574
	21st to end	Night	12% 14% 5% 10% 8% 4 6% 4 5% 5% 28%	2772
February	1st to 10th	Night	13% 14% 7% 12% 8% 5% 5% 4 5% 4 24%	2488
	11th to 20th	Night	14% 15% 6% 11% 8% 4 6% 5% 4 4 24%	2125
	21st to end	Night	17% 13% 5% 10% 6% 3 5% 5% 3 5% 30%	1776
March	1st to 10th	Night	17% 13% 5% 9% 7% 3 5% 4 4 5% 28%	2150
	11th to 20th	Night	17% 13% 5% 8% 6% 4 5% 4 5% 5% 28%	2097
	21st to end	Night	17% 12% 3 7% 5% 2 4 4 4 5% 36%	2008
April	1st to 10th	Night	25% 12% 4 7% 4 3 4 4 5% 5% 27%	1800
	11th to 20th	Night	23% 8% 3 6% 5% 3 4 4 4 7% 34%	1720
	21st to end	Night	24% 10% 3 6% 4 2 4 4 4 6% 33%	1620
May	1st to 10th	Night	24% 9% 3 6% 5% 3 4 3 5% 6% 32%	1553
	11th to 20th	Night	23% 7% 3 4 6% 3 4 4 5% 7% 34%	1415
	21st to end	Night	22% 7% 3 5% 4 3 4 4 5% 7% 36%	1550
June	1st to 10th	Night	22% 8% 4 5% 4 3 4 5% 7% 8% 31%	1364
	11th to 20th	Night	20% 7% 2 5% 5% 3 4 5% 6% 8% 36%	1260
	21st to end	Night	20% 7% 4 7% 5% 4 5% 6% 5% 7% 30%	1359
July	1st to 10th	Night	15% 5% 4 6% 6% 4 5% 6% 6% 9% 34%	1440
	11th to 20th	Night	15% 6% 3 6% 6% 4 5% 5% 5% 9% 37%	1440
	21st to end	Night	13% 5% 3 7% 6% 4 7% 6% 5% 9% 35%	1574
August	1st to 10th	Night	14% 5% 2 6% 5% 4 5% 6% 8% 10% 36%	1432
	11th to 20th	Night	15% 7% 2 7% 7% 4 5% 5% 7% 8% 33%	1566
	21st to end	Night	15% 6% 3 6% 5% 3 5% 5% 6% 8% 39%	1933
September	1st to 10th	Night	17% 6% 3 5% 6% 3 4 4 5% 7% 41%	1800
	11th to 20th	Night	17% 6% 2 4 4 2 4 3 4 8% 45%	1934
	21st to end	Night	19% 7% 2 5% 4 3 4 3 4 7% 42%	1980
October	1st to 10th	Night	18% 7% 3 5% 6% 3 5% 4 5% 6% 38%	2015
	11th to 20th	Night	24% 9% 3 6% 6% 4 4 5% 4 5% 30%	2281
	21st to end	Night	28% 10% 3 6% 5% 3 4 4 4 6% 27%	2574
November	1st to 10th	Night	20% 11% 4 7% 7% 3 4 3 5% 6% 31%	2407
	11th to 20th	Night	21% 12% 5% 8% 6% 3 4 4 4 6% 28%	2490
	21st to end	Night	23% 15% 4 8% 5% 3 4 4 4 5% 24%	2711
December	1st to 10th	Night	24% 15% 6% 9% 7% 3 4 4 4 4 20%	2850
	11th to 20th	Night	22% 15% 6% 10% 6% 3 4 4 4 4 22%	3531
	21st to end	Night	26% 19% 4 7% 5% 3 4 3 3 4 23%	4966

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	43% 41% 5% 9% 3	1518
	11th to 20th	Day	41% 42% 5% 9% 3 1	1464
	21st to end	Day	37% 38% 6% 10% 8% 1	1584
February	1st to 10th	Day	42% 37% 6% 10% 4 1	1467
	11th to 20th	Day	43% 39% 8% 5% 4 1	1729
	21st to end	Day	38% 37% 7% 13% 4	1480
March	1st to 10th	Day	37% 39% 7% 11% 5% 1	1800
	11th to 20th	Day	38% 38% 9% 11% 4	1862
	21st to end	Day	37% 38% 7% 11% 7% 1	2347
April	1st to 10th	Day	41% 37% 6% 9% 5% 2	2160
	11th to 20th	Day	31% 36% 8% 15% 9% 1	2188
	21st to end	Day	36% 37% 6% 12% 8% 2	2340
May	1st to 10th	Day	31% 38% 6% 12% 11% 2	2420
	11th to 20th	Day	30% 40% 8% 12% 9% 1	2482
	21st to end	Day	34% 38% 6% 12% 11% 1	2725
June	1st to 10th	Day	35% 40% 8% 12% 4 1	2592
	11th to 20th	Day	31% 39% 9% 14% 6% 1	2700
	21st to end	Day	40% 39% 7% 9% 5%	2592
July	1st to 10th	Day	29% 41% 12% 15% 4	2450
	11th to 20th	Day	31% 40% 10% 14% 5%	2445
	21st to end	Day	32% 42% 11% 11% 4	2591
August	1st to 10th	Day	33% 40% 12% 12% 3	2492
	11th to 20th	Day	29% 39% 11% 15% 6%	2317
	21st to end	Day	29% 38% 9% 16% 7%	2422
September	1st to 10th	Day	29% 39% 10% 16% 6%	2160
	11th to 20th	Day	26% 38% 9% 18% 8%	2026
	21st to end	Day	32% 39% 10% 13% 6%	1980
October	1st to 10th	Day	34% 37% 9% 16% 4	1944
	11th to 20th	Day	40% 40% 10% 10% 1	1678
	21st to end	Day	40% 38% 5% 12% 4 1	1782
November	1st to 10th	Day	31% 42% 8% 13% 6%	1671
	11th to 20th	Day	40% 41% 6% 8% 5%	1687
	21st to end	Day	40% 42% 8% 9% 2	1465
December	1st to 10th	Day	44% 40% 6% 8% 2	1330
	11th to 20th	Day	44% 33% 5% 14% 3	1668
	21st to end	Day	52% 28% 7% 7% 5% 1	2688
January	1st to 10th	Night	44% 41% 6% 7% 2	2649
	11th to 20th	Night	41% 42% 6% 7% 3	2574
	21st to end	Night	39% 39% 7% 9% 6%	2772
February	1st to 10th	Night	41% 37% 6% 9% 6%	2488
	11th to 20th	Night	43% 39% 7% 6% 4 1	2127
	21st to end	Night	41% 37% 5% 11% 6%	1776
March	1st to 10th	Night	41% 36% 6% 12% 4	2160
	11th to 20th	Night	40% 38% 6% 9% 7%	2098
	21st to end	Night	34% 38% 7% 13% 7% 2	2008
April	1st to 10th	Night	39% 37% 8% 10% 5% 1	1800
	11th to 20th	Night	32% 37% 7% 14% 9% 1	1720
	21st to end	Night	36% 36% 5% 11% 10% 2	1620
May	1st to 10th	Night	34% 37% 7% 9% 10% 2	1553
	11th to 20th	Night	33% 37% 8% 9% 11% 2	1416
	21st to end	Night	32% 38% 6% 13% 11% 1	1551
June	1st to 10th	Night	34% 38% 8% 14% 5% 1	1364
	11th to 20th	Night	31% 38% 10% 12% 6% 2	1260
	21st to end	Night	37% 38% 8% 10% 6% 1	1359
July	1st to 10th	Night	29% 41% 13% 13% 5%	1400
	11th to 20th	Night	31% 41% 8% 14% 5% 1	1392
	21st to end	Night	32% 43% 9% 11% 5%	1486
August	1st to 10th	Night	28% 39% 12% 17% 4	1422
	11th to 20th	Night	29% 39% 13% 14% 5%	1566
	21st to end	Night	30% 38% 10% 16% 6%	1933
September	1st to 10th	Night	29% 38% 10% 16% 6% 1	1800
	11th to 20th	Night	28% 37% 11% 18% 7%	1934
	21st to end	Night	32% 38% 8% 15% 8%	1980
October	1st to 10th	Night	33% 37% 8% 15% 7%	2015
	11th to 20th	Night	38% 39% 9% 11% 3	2281
	21st to end	Night	38% 39% 8% 11% 5% 1	2574
November	1st to 10th	Night	33% 42% 8% 13% 3	2407
	11th to 20th	Night	36% 41% 9% 9% 5%	2490
	21st to end	Night	41% 40% 6% 10% 3	2711
December	1st to 10th	Night	45% 40% 6% 6% 2	2850
	11th to 20th	Night	45% 34% 6% 11% 4	3532
	21st to end	Night	52% 26% 6% 13% 3 1	4966

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	32% 19% 29% 17% 2 1	180
	11th to 20th	Day	28% 22% 34% 10% 5% 1	166
	21st to end	Day	26% 22% 32% 14% 6% 1	176
February	1st to 10th	Day	27% 28% 38% 6% 1 1	172
	11th to 20th	Day	25% 23% 38% 11% 3	388
	21st to end	Day	26% 24% 29% 18% 3	346
March	1st to 10th	Day	27% 20% 29% 19% 5%	420
	11th to 20th	Day	27% 21% 29% 17% 4 2	420
	21st to end	Day	25% 20% 26% 19% 8% 2	462
April	1st to 10th	Day	29% 19% 29% 17% 5% 1	420
	11th to 20th	Day	29% 18% 27% 20% 5% 1	412
	21st to end	Day	29% 19% 31% 14% 5% 1	420
May	1st to 10th	Day	28% 19% 31% 16% 5% 1	423
	11th to 20th	Day	21% 15% 32% 23% 8% 2	447
	21st to end	Day	21% 21% 34% 16% 7% 1	485
June	1st to 10th	Day	24% 14% 35% 19% 8% 1	522
	11th to 20th	Day	21% 12% 28% 26% 12% 1	630
	21st to end	Day	23% 10% 29% 27% 9% 2	522
July	1st to 10th	Day	16% 10% 31% 29% 11% 1	445
	11th to 20th	Day	16% 11% 35% 26% 10% 2	444
	21st to end	Day	18% 8% 32% 30% 10% 1	488
August	1st to 10th	Day	20% 9% 27% 27% 13% 4	446
	11th to 20th	Day	19% 7% 26% 29% 14% 5%	439
	21st to end	Day	21% 13% 27% 17% 14% 7%	495
September	1st to 10th	Day	19% 10% 29% 26% 11% 5%	450
	11th to 20th	Day	20% 11% 27% 22% 16% 4	450
	21st to end	Day	20% 14% 26% 23% 12% 5%	450
October	1st to 10th	Day	24% 12% 28% 24% 9% 3	450
	11th to 20th	Day	29% 14% 30% 17% 10% 1	389
	21st to end	Day	35% 16% 26% 18% 5%	396
November	1st to 10th	Day	32% 13% 30% 20% 5% 1	365
	11th to 20th	Day	29% 20% 26% 16% 8% 1	347
	21st to end	Day	33% 22% 28% 14% 2 1	180
December	1st to 10th	Day	36% 16% 24% 19% 4 2	180
	11th to 20th	Day	32% 22% 32% 9% 4 1	180
	21st to end	Day	35% 21% 26% 14% 5%	198
January	1st to 10th	Night	28% 14% 35% 18% 3	760
	11th to 20th	Night	29% 15% 32% 20% 4	736
	21st to end	Night	18% 12% 36% 28% 5%	792
February	1st to 10th	Night	21% 14% 36% 24% 4	720
	11th to 20th	Night	22% 18% 39% 16% 5%	703
	21st to end	Night	26% 15% 32% 22% 4	592
March	1st to 10th	Night	24% 13% 37% 22% 3	720
	11th to 20th	Night	26% 14% 35% 19% 5% 1	720
	21st to end	Night	22% 14% 31% 26% 6% 1	792
April	1st to 10th	Night	30% 14% 30% 21% 4	720
	11th to 20th	Night	27% 14% 33% 22% 5%	656
	21st to end	Night	29% 15% 28% 21% 6%	540
May	1st to 10th	Night	26% 12% 29% 27% 6%	473
	11th to 20th	Night	27% 8% 32% 27% 6%	354
	21st to end	Night	26% 10% 33% 25% 6%	389
June	1st to 10th	Night	26% 6% 30% 32% 6%	360
	11th to 20th	Night	23% 7% 27% 33% 11%	360
	21st to end	Night	20% 10% 26% 33% 12%	360
July	1st to 10th	Night	16% 6% 30% 37% 11%	350
	11th to 20th	Night	17% 5% 28% 36% 12% 1	348
	21st to end	Night	16% 6% 25% 44% 10%	394
August	1st to 10th	Night	16% 3 23% 39% 18% 1	358
	11th to 20th	Night	17% 6% 25% 37% 14% 1	502
	21st to end	Night	17% 8% 29% 28% 17% 1	745
September	1st to 10th	Night	19% 7% 28% 33% 11% 2	720
	11th to 20th	Night	20% 6% 27% 29% 16% 2	720
	21st to end	Night	20% 9% 30% 27% 14% 2	720
October	1st to 10th	Night	22% 10% 28% 31% 9% 1	720
	11th to 20th	Night	26% 13% 28% 25% 7% 1	720
	21st to end	Night	32% 11% 31% 20% 5%	792
November	1st to 10th	Night	28% 14% 29% 22% 7%	740
	11th to 20th	Night	28% 15% 29% 19% 9% 1	760
	21st to end	Night	31% 15% 26% 22% 5% 1	784
December	1st to 10th	Night	32% 15% 27% 20% 6%	850
	11th to 20th	Night	27% 20% 28% 19% 6%	850
	21st to end	Night	36% 14% 29% 17% 3 1	857

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