École Gabriel-Le Courtoi
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the École Gabriel-Le Courtoi clear sky chart from 2005-11-06 to 2024-01-16.

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% 11% 4 8% 7% 4 5% 5% 5% 6% 28%	74661
	Night	17% 14% 5% 10% 8% 4 5% 5% 4 5% 22%	75154
Transparency	Day	41% 35% 8% 12% 4	74345
	Night	45% 35% 6% 10% 4	75005
Seeing	Day	29% 18% 27% 18% 7% 1	15105
	Night	28% 16% 24% 22% 9% 1	22961

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	15% 22% 8% 14% 13% 6% 7% 3 3 3 7%	1327
	11th to 20th	Day	15% 15% 8% 13% 14% 5% 8% 6% 3 4 10%	1295
	21st to end	Day	7% 13% 7% 11% 12% 7% 10% 7% 5% 5% 16%	1583
February	1st to 10th	Day	8% 13% 7% 12% 11% 7% 8% 6% 5% 6% 18%	1598
	11th to 20th	Day	11% 16% 6% 13% 8% 5% 7% 7% 4 5% 17%	1573
	21st to end	Day	8% 13% 7% 9% 8% 4 7% 8% 7% 6% 24%	1385
March	1st to 10th	Day	11% 15% 6% 9% 7% 4 6% 5% 5% 7% 26%	1863
	11th to 20th	Day	16% 15% 5% 10% 7% 3 6% 4 4 5% 23%	1980
	21st to end	Day	13% 18% 5% 7% 7% 4 4 4 5% 5% 30%	2178
April	1st to 10th	Day	17% 14% 6% 9% 7% 4 5% 4 5% 5% 23%	2184
	11th to 20th	Day	14% 12% 4 7% 6% 3 5% 4 5% 7% 33%	2312
	21st to end	Day	20% 10% 4 6% 5% 3 4 5% 4 6% 33%	2340
May	1st to 10th	Day	23% 9% 4 6% 6% 3 4 4 5% 5% 30%	2416
	11th to 20th	Day	21% 8% 2 5% 5% 3 5% 4 5% 7% 35%	2548
	21st to end	Day	22% 7% 3 5% 5% 3 4 5% 4 7% 34%	2919
June	1st to 10th	Day	21% 8% 3 6% 6% 4 5% 5% 5% 7% 30%	2700
	11th to 20th	Day	19% 7% 2 6% 5% 3 5% 5% 5% 8% 36%	2700
	21st to end	Day	21% 7% 3 6% 5% 3 5% 5% 6% 9% 31%	2700
July	1st to 10th	Day	17% 7% 3 6% 6% 3 5% 6% 6% 8% 33%	2700
	11th to 20th	Day	15% 5% 3 5% 5% 4 5% 6% 6% 9% 37%	2700
	21st to end	Day	13% 8% 3 6% 5% 4 6% 6% 6% 7% 36%	2916
August	1st to 10th	Day	14% 6% 3 6% 5% 3 6% 6% 6% 8% 36%	2350
	11th to 20th	Day	15% 6% 3 5% 5% 3 5% 5% 6% 9% 38%	2304
	21st to end	Day	19% 5% 3 5% 6% 3 5% 6% 6% 8% 34%	2574
September	1st to 10th	Day	21% 7% 2 5% 5% 3 4 4 4 8% 38%	2210
	11th to 20th	Day	25% 8% 2 4 3 2 3 3 4 6% 40%	1985
	21st to end	Day	20% 8% 3 5% 5% 2 5% 4 5% 7% 35%	1980
October	1st to 10th	Day	20% 9% 3 6% 6% 3 4 5% 5% 6% 35%	1818
	11th to 20th	Day	24% 12% 3 6% 6% 3 4 4 5% 6% 26%	1800
	21st to end	Day	25% 15% 4 7% 5% 3 4 5% 4 6% 21%	1793
November	1st to 10th	Day	21% 16% 6% 9% 6% 3 3 5% 5% 5% 20%	1503
	11th to 20th	Day	20% 17% 8% 13% 6% 3 4 4 4 5% 16%	1520
	21st to end	Day	22% 17% 9% 15% 7% 3 4 4 4 5% 10%	1478
December	1st to 10th	Day	17% 16% 9% 17% 13% 5% 5% 3 4 4 7%	1330
	11th to 20th	Day	14% 14% 9% 19% 15% 6% 8% 4 3 3 6%	1668
	21st to end	Day	12% 17% 7% 15% 14% 6% 6% 5% 4 4 9%	2431
January	1st to 10th	Night	15% 21% 8% 14% 14% 6% 6% 4 4 3 6%	2838
	11th to 20th	Night	14% 18% 6% 13% 13% 7% 7% 4 4 3 10%	2787
	21st to end	Night	8% 14% 7% 13% 10% 8% 10% 6% 5% 5% 14%	2772
February	1st to 10th	Night	8% 14% 6% 11% 13% 7% 7% 6% 5% 5% 17%	2360
	11th to 20th	Night	14% 16% 6% 11% 9% 7% 8% 5% 5% 5% 14%	2273
	21st to end	Night	10% 14% 8% 10% 9% 5% 6% 6% 5% 5% 22%	1870
March	1st to 10th	Night	11% 15% 6% 11% 7% 5% 7% 5% 5% 5% 24%	2083
	11th to 20th	Night	15% 18% 7% 11% 8% 4 4 3 4 4 23%	1979
	21st to end	Night	15% 18% 6% 8% 6% 4 4 4 4 4 27%	2178
April	1st to 10th	Night	21% 13% 5% 10% 8% 4 4 5% 4 5% 20%	1774
	11th to 20th	Night	17% 11% 3 7% 6% 3 5% 5% 5% 6% 32%	1598
	21st to end	Night	23% 11% 4 5% 6% 2 4 4 4 6% 33%	1620
May	1st to 10th	Night	27% 9% 3 7% 7% 2 4 3 4 6% 27%	1544
	11th to 20th	Night	19% 9% 4 6% 5% 4 4 4 6% 6% 31%	1362
	21st to end	Night	23% 7% 3 8% 7% 3 4 5% 6% 7% 28%	1356
June	1st to 10th	Night	24% 8% 4 7% 6% 3 5% 4 5% 7% 27%	1260
	11th to 20th	Night	22% 8% 2 5% 5% 3 6% 4 4 7% 35%	1260
	21st to end	Night	21% 9% 3 7% 7% 3 5% 5% 5% 5% 29%	1260
July	1st to 10th	Night	18% 8% 4 6% 7% 3 6% 5% 6% 7% 30%	1260
	11th to 20th	Night	12% 7% 3 6% 6% 4 7% 7% 6% 9% 33%	1260
	21st to end	Night	17% 6% 3 6% 5% 4 6% 6% 7% 8% 33%	1399
August	1st to 10th	Night	16% 7% 3 7% 6% 4 5% 6% 6% 9% 31%	1571
	11th to 20th	Night	15% 7% 3 7% 6% 5% 6% 5% 6% 8% 33%	1596
	21st to end	Night	18% 6% 3 6% 5% 3 4 5% 6% 8% 35%	1782
September	1st to 10th	Night	22% 5% 2 5% 6% 3 5% 5% 5% 7% 35%	1750
	11th to 20th	Night	23% 8% 2 6% 5% 3 4 4 4 5% 37%	1971
	21st to end	Night	21% 6% 3 6% 4 2 4 4 4 5% 40%	1980
October	1st to 10th	Night	21% 8% 2 6% 5% 3 5% 4 5% 7% 34%	2142
	11th to 20th	Night	29% 11% 4 7% 6% 3 4 4 4 5% 25%	2160
	21st to end	Night	25% 14% 3 6% 5% 4 4 6% 4 6% 23%	2560
November	1st to 10th	Night	23% 18% 5% 8% 6% 3 5% 5% 4 5% 18%	2574
	11th to 20th	Night	22% 20% 8% 10% 5% 3 3 4 3 5% 17%	2660
	21st to end	Night	19% 20% 9% 15% 7% 3 4 5% 3 4 12%	2698
December	1st to 10th	Night	16% 18% 10% 18% 11% 5% 5% 4 3 3 8%	2850
	11th to 20th	Night	15% 18% 7% 16% 15% 5% 6% 4 3 3 8%	3531
	21st to end	Night	13% 19% 8% 14% 13% 4 5% 4 4 4 10%	5236

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	56% 38% 4 1	1328
	11th to 20th	Day	50% 40% 3 5% 2	1295
	21st to end	Day	45% 38% 4 10% 4	1583
February	1st to 10th	Day	46% 35% 6% 9% 4	1598
	11th to 20th	Day	52% 36% 3 6% 2	1581
	21st to end	Day	44% 35% 5% 12% 4	1385
March	1st to 10th	Day	46% 34% 6% 11% 2	1867
	11th to 20th	Day	45% 35% 7% 9% 4	1980
	21st to end	Day	41% 34% 6% 11% 7% 1	2178
April	1st to 10th	Day	46% 35% 5% 10% 4	2184
	11th to 20th	Day	38% 34% 5% 15% 8%	2312
	21st to end	Day	36% 34% 8% 13% 8% 1	2340
May	1st to 10th	Day	41% 34% 5% 11% 8% 1	2416
	11th to 20th	Day	34% 35% 7% 15% 8% 1	2552
	21st to end	Day	36% 36% 7% 13% 8%	2919
June	1st to 10th	Day	37% 35% 8% 12% 7% 1	2700
	11th to 20th	Day	31% 36% 10% 13% 8% 1	2700
	21st to end	Day	38% 35% 10% 10% 6%	2700
July	1st to 10th	Day	33% 36% 12% 15% 4	2625
	11th to 20th	Day	33% 36% 9% 16% 6%	2619
	21st to end	Day	35% 36% 12% 13% 4	2753
August	1st to 10th	Day	33% 35% 13% 15% 3	2336
	11th to 20th	Day	32% 35% 16% 16% 1	2304
	21st to end	Day	37% 35% 11% 14% 3	2574
September	1st to 10th	Day	35% 34% 10% 17% 4	2210
	11th to 20th	Day	31% 35% 11% 18% 5%	1985
	21st to end	Day	36% 35% 9% 16% 4	1980
October	1st to 10th	Day	39% 35% 11% 11% 3	1818
	11th to 20th	Day	42% 35% 8% 10% 4	1800
	21st to end	Day	47% 36% 3 10% 3 1	1793
November	1st to 10th	Day	42% 39% 8% 7% 3	1503
	11th to 20th	Day	46% 38% 8% 7% 1	1520
	21st to end	Day	52% 37% 6% 4 1	1478
December	1st to 10th	Day	54% 38% 4 4	1330
	11th to 20th	Day	60% 31% 3 5% 1	1668
	21st to end	Day	62% 23% 7% 7% 1	2431
January	1st to 10th	Night	56% 37% 4 2	2838
	11th to 20th	Night	50% 39% 2 5% 3	2787
	21st to end	Night	49% 37% 2 9% 3	2772
February	1st to 10th	Night	47% 35% 6% 8% 4	2360
	11th to 20th	Night	53% 36% 3 6% 3	2276
	21st to end	Night	45% 35% 5% 11% 3	1870
March	1st to 10th	Night	45% 34% 5% 13% 3	2092
	11th to 20th	Night	45% 34% 4 12% 4	1980
	21st to end	Night	43% 34% 6% 10% 7% 1	2178
April	1st to 10th	Night	47% 34% 6% 6% 6%	1774
	11th to 20th	Night	36% 34% 5% 15% 9% 1	1598
	21st to end	Night	34% 34% 6% 14% 10% 2	1620
May	1st to 10th	Night	40% 34% 6% 13% 6% 1	1544
	11th to 20th	Night	35% 35% 5% 17% 8%	1363
	21st to end	Night	38% 36% 7% 11% 7%	1357
June	1st to 10th	Night	39% 35% 6% 13% 6% 1	1260
	11th to 20th	Night	33% 35% 9% 13% 10% 1	1260
	21st to end	Night	40% 35% 8% 10% 6%	1260
July	1st to 10th	Night	35% 36% 10% 14% 5%	1225
	11th to 20th	Night	33% 38% 12% 13% 5%	1218
	21st to end	Night	32% 37% 12% 15% 4	1321
August	1st to 10th	Night	34% 36% 12% 15% 3	1561
	11th to 20th	Night	35% 35% 13% 14% 3	1596
	21st to end	Night	34% 35% 7% 20% 3	1782
September	1st to 10th	Night	34% 36% 9% 17% 5%	1750
	11th to 20th	Night	33% 34% 9% 17% 6%	1971
	21st to end	Night	34% 35% 8% 15% 7%	1980
October	1st to 10th	Night	37% 35% 11% 12% 4 1	2142
	11th to 20th	Night	43% 35% 9% 10% 4	2160
	21st to end	Night	43% 35% 8% 10% 3 1	2560
November	1st to 10th	Night	43% 39% 8% 7% 3	2574
	11th to 20th	Night	46% 38% 7% 7% 2	2660
	21st to end	Night	50% 39% 5% 5% 1	2698
December	1st to 10th	Night	56% 38% 3 3 1	2850
	11th to 20th	Night	60% 31% 2 6% 1	3532
	21st to end	Night	63% 23% 8% 5% 1	5236

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	25% 28% 24% 19% 3 1	180
	11th to 20th	Day	28% 26% 29% 10% 5% 1	170
	21st to end	Day	23% 30% 27% 15% 5% 1	176
February	1st to 10th	Day	23% 25% 31% 16% 4 1	318
	11th to 20th	Day	28% 27% 28% 12% 5%	336
	21st to end	Day	20% 27% 32% 13% 7% 2	304
March	1st to 10th	Day	23% 23% 32% 16% 6%	420
	11th to 20th	Day	32% 18% 27% 15% 7% 1	420
	21st to end	Day	29% 26% 26% 12% 5% 2	462
April	1st to 10th	Day	31% 23% 28% 12% 5% 1	420
	11th to 20th	Day	30% 20% 27% 15% 6% 2	412
	21st to end	Day	30% 18% 28% 15% 7% 3	420
May	1st to 10th	Day	34% 12% 30% 16% 6% 1	499
	11th to 20th	Day	28% 16% 27% 19% 8% 2	624
	21st to end	Day	34% 17% 26% 17% 4 1	680
June	1st to 10th	Day	28% 15% 27% 22% 8% 1	630
	11th to 20th	Day	27% 15% 25% 21% 11% 1	630
	21st to end	Day	26% 11% 28% 26% 7% 2	630
July	1st to 10th	Day	24% 14% 28% 24% 8% 2	620
	11th to 20th	Day	22% 12% 28% 26% 9% 1	618
	21st to end	Day	20% 9% 31% 27% 12% 1	660
August	1st to 10th	Day	24% 11% 31% 23% 8% 2	446
	11th to 20th	Day	20% 11% 32% 25% 11% 2	439
	21st to end	Day	23% 10% 32% 21% 11% 3	495
September	1st to 10th	Day	28% 17% 24% 22% 7% 2	450
	11th to 20th	Day	34% 13% 26% 18% 5% 3	450
	21st to end	Day	33% 17% 28% 14% 6% 2	450
October	1st to 10th	Day	30% 22% 24% 16% 7% 2	369
	11th to 20th	Day	40% 17% 20% 16% 6% 3	360
	21st to end	Day	43% 18% 18% 13% 7% 1	396
November	1st to 10th	Day	39% 22% 23% 14% 2 1	365
	11th to 20th	Day	34% 23% 25% 11% 6% 1	370
	21st to end	Day	34% 24% 25% 10% 5% 1	328
December	1st to 10th	Day	29% 23% 29% 12% 7% 1	180
	11th to 20th	Day	31% 24% 29% 13% 2	180
	21st to end	Day	31% 22% 31% 12% 3	198
January	1st to 10th	Night	27% 20% 29% 18% 5%	850
	11th to 20th	Night	25% 24% 28% 17% 5%	829
	21st to end	Night	19% 23% 28% 22% 7% 1	792
February	1st to 10th	Night	18% 25% 31% 18% 6% 1	720
	11th to 20th	Night	27% 20% 24% 21% 6% 1	703
	21st to end	Night	20% 18% 30% 21% 9% 2	592
March	1st to 10th	Night	20% 20% 28% 22% 10% 1	720
	11th to 20th	Night	29% 17% 23% 23% 7% 1	720
	21st to end	Night	26% 17% 23% 23% 9% 2	792
April	1st to 10th	Night	30% 16% 27% 18% 8% 1	608
	11th to 20th	Night	26% 17% 22% 22% 12% 1	534
	21st to end	Night	32% 11% 20% 25% 10% 2	540
May	1st to 10th	Night	34% 8% 21% 27% 9% 1	540
	11th to 20th	Night	26% 9% 25% 26% 12% 2	478
	21st to end	Night	29% 11% 29% 24% 8% 1	389
June	1st to 10th	Night	24% 8% 20% 36% 11%	360
	11th to 20th	Night	24% 8% 22% 29% 16% 1	360
	21st to end	Night	25% 8% 25% 30% 11% 1	360
July	1st to 10th	Night	22% 7% 25% 33% 11% 1	350
	11th to 20th	Night	14% 8% 27% 34% 16% 1	348
	21st to end	Night	19% 8% 19% 32% 19% 3	394
August	1st to 10th	Night	20% 7% 21% 33% 18% 1	497
	11th to 20th	Night	18% 7% 20% 34% 19% 2	532
	21st to end	Night	22% 8% 23% 29% 17% 2	594
September	1st to 10th	Night	26% 13% 19% 29% 12% 1	540
	11th to 20th	Night	30% 11% 21% 25% 11% 2	711
	21st to end	Night	28% 14% 25% 24% 8%	720
October	1st to 10th	Night	31% 16% 20% 24% 8% 1	720
	11th to 20th	Night	40% 14% 15% 20% 9% 1	720
	21st to end	Night	37% 16% 20% 17% 8% 1	792
November	1st to 10th	Night	38% 20% 22% 15% 3 1	821
	11th to 20th	Night	37% 18% 21% 15% 6% 1	850
	21st to end	Night	31% 23% 24% 14% 7%	850
December	1st to 10th	Night	29% 22% 27% 16% 5% 1	850
	11th to 20th	Night	34% 23% 24% 13% 6% 1	850
	21st to end	Night	30% 23% 22% 18% 4 2	935

Page generated at 2024-01-13 09:37:57. Version ac07

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