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 2024-12-09.

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	16% 11% 4 9% 6% 5% 5% 4 5% 6% 29%	102072
	Night	17% 14% 5% 11% 8% 6% 5% 3 5% 5% 22%	97806
Transparency	Day	58% 6% 13% 17% 6%	105509
	Night	64% 6% 10% 14% 5%	102446
Seeing	Day	28% 18% 28% 18% 7% 1	16363
	Night	28% 16% 24% 22% 9% 1	24076

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	13% 18% 9% 17% 16% 12% 5% 3 2 2 4	2207
	11th to 20th	Day	10% 17% 10% 18% 17% 5% 6% 3 4 4 7%	2210
	21st to end	Day	4 10% 6% 16% 12% 12% 8% 5% 5% 6% 15%	2771
February	1st to 10th	Day	8% 15% 6% 13% 10% 8% 6% 4 5% 6% 18%	1687
	11th to 20th	Day	11% 17% 7% 14% 8% 7% 6% 6% 4 5% 17%	1663
	21st to end	Day	7% 14% 5% 9% 8% 6% 8% 6% 7% 6% 24%	1469
March	1st to 10th	Day	11% 13% 4 11% 6% 6% 7% 4 5% 7% 25%	3238
	11th to 20th	Day	19% 21% 5% 11% 5% 5% 6% 4 4 4 17%	3480
	21st to end	Day	20% 18% 6% 8% 6% 4 3 2 4 4 25%	3816
April	1st to 10th	Day	16% 15% 5% 10% 6% 4 5% 4 5% 5% 25%	2307
	11th to 20th	Day	13% 13% 4 8% 6% 4 5% 4 5% 6% 33%	2442
	21st to end	Day	20% 12% 3 7% 4 4 4 4 5% 5% 32%	2470
May	1st to 10th	Day	18% 11% 3 8% 5% 4 4 4 5% 7% 30%	4252
	11th to 20th	Day	16% 9% 3 7% 4 4 5% 4 6% 8% 33%	4524
	21st to end	Day	23% 10% 3 7% 5% 4 5% 3 5% 7% 29%	5185
June	1st to 10th	Day	21% 8% 3 7% 5% 5% 4 4 6% 7% 30%	2850
	11th to 20th	Day	19% 7% 2 6% 4 4 4 4 6% 7% 36%	2850
	21st to end	Day	21% 8% 2 7% 4 4 5% 4 6% 8% 31%	2850
July	1st to 10th	Day	17% 7% 2 7% 5% 4 5% 4 6% 7% 37%	4760
	11th to 20th	Day	13% 5% 2 7% 4 5% 6% 4 6% 9% 38%	4760
	21st to end	Day	11% 6% 2 5% 3 4 5% 4 6% 8% 46%	5111
August	1st to 10th	Day	13% 5% 2 6% 4 4 5% 5% 6% 9% 40%	4142
	11th to 20th	Day	16% 6% 3 7% 5% 5% 5% 5% 7% 8% 32%	4045
	21st to end	Day	16% 5% 2 5% 4 4 4 4 6% 8% 42%	4532
September	1st to 10th	Day	21% 7% 2 6% 4 3 4 3 5% 8% 38%	2332
	11th to 20th	Day	24% 8% 2 5% 3 3 3 2 4 6% 41%	2095
	21st to end	Day	19% 9% 3 6% 4 3 5% 3 6% 7% 35%	2090
October	1st to 10th	Day	20% 9% 3 7% 5% 4 5% 3 5% 6% 35%	1918
	11th to 20th	Day	23% 13% 3 7% 5% 4 4 3 5% 6% 26%	1900
	21st to end	Day	25% 15% 4 8% 4 4 4 4 4 6% 21%	1892
November	1st to 10th	Day	22% 16% 6% 10% 5% 4 4 4 5% 5% 20%	1584
	11th to 20th	Day	21% 19% 7% 13% 5% 4 4 3 4 5% 16%	1600
	21st to end	Day	22% 19% 7% 17% 6% 4 4 3 4 4 10%	1555
December	1st to 10th	Day	15% 18% 9% 20% 9% 6% 4 2 4 4 7%	1386
	11th to 20th	Day	14% 16% 8% 21% 13% 8% 6% 3 3 3 6%	1668
	21st to end	Day	12% 18% 7% 19% 10% 7% 6% 4 4 4 9%	2431
January	1st to 10th	Night	10% 21% 8% 20% 17% 8% 4 2 3 2 4	4748
	11th to 20th	Night	11% 18% 7% 22% 14% 7% 5% 2 4 3 7%	4760
	21st to end	Night	5% 15% 6% 17% 10% 10% 8% 4 5% 5% 15%	4884
February	1st to 10th	Night	8% 15% 6% 12% 12% 8% 6% 4 5% 5% 19%	2491
	11th to 20th	Night	13% 18% 5% 13% 9% 9% 7% 4 5% 4 14%	2403
	21st to end	Night	9% 17% 6% 10% 9% 7% 5% 4 5% 5% 23%	1984
March	1st to 10th	Night	9% 12% 4 12% 7% 8% 7% 4 5% 5% 26%	3601
	11th to 20th	Night	20% 26% 6% 11% 6% 5% 3 2 3 3 14%	3479
	21st to end	Night	23% 21% 4 8% 7% 4 3 2 4 4 20%	3816
April	1st to 10th	Night	20% 15% 4 11% 7% 5% 4 3 4 5% 21%	1871
	11th to 20th	Night	17% 12% 3 7% 6% 4 5% 5% 5% 6% 32%	1688
	21st to end	Night	22% 12% 3 6% 5% 3 4 3 4 5% 33%	1710
May	1st to 10th	Night	21% 11% 4 10% 7% 4 4 4 6% 6% 23%	2693
	11th to 20th	Night	15% 9% 4 8% 6% 4 5% 4 8% 8% 28%	2396
	21st to end	Night	25% 10% 4 9% 6% 4 3 4 6% 6% 23%	2401
June	1st to 10th	Night	23% 9% 3 7% 5% 5% 4 3 6% 6% 27%	1330
	11th to 20th	Night	21% 9% 2 6% 4 4 5% 3 5% 7% 34%	1330
	21st to end	Night	21% 9% 3 9% 6% 4 5% 5% 5% 5% 29%	1330
July	1st to 10th	Night	19% 8% 3 8% 5% 4 5% 4 6% 6% 33%	2210
	11th to 20th	Night	14% 8% 3 8% 5% 6% 6% 5% 6% 9% 31%	2210
	21st to end	Night	15% 5% 2 5% 4 4 5% 4 7% 9% 40%	2448
August	1st to 10th	Night	17% 8% 3 9% 6% 5% 6% 5% 6% 9% 27%	2757
	11th to 20th	Night	14% 7% 3 9% 7% 7% 6% 5% 6% 7% 29%	2782
	21st to end	Night	19% 5% 2 5% 3 3 3 3 5% 6% 45%	3124
September	1st to 10th	Night	22% 6% 2 6% 5% 4 5% 4 5% 7% 35%	1848
	11th to 20th	Night	22% 8% 2 7% 4 4 4 3 4 5% 38%	2081
	21st to end	Night	21% 6% 3 7% 4 4 4 3 5% 5% 39%	2090
October	1st to 10th	Night	20% 9% 2 7% 5% 4 4 4 5% 6% 34%	2261
	11th to 20th	Night	29% 11% 3 8% 4 4 3 3 4 5% 26%	2280
	21st to end	Night	24% 15% 3 7% 4 5% 4 5% 4 6% 23%	2703
November	1st to 10th	Night	23% 19% 5% 9% 5% 4 5% 3 4 5% 18%	2713
	11th to 20th	Night	22% 21% 7% 11% 5% 4 4 3 3 5% 17%	2800
	21st to end	Night	19% 22% 7% 15% 6% 4 4 4 3 3 12%	2840
December	1st to 10th	Night	15% 21% 9% 20% 9% 6% 4 3 3 3 8%	2977
	11th to 20th	Night	14% 20% 7% 18% 12% 7% 5% 3 3 3 8%	3531
	21st to end	Night	13% 20% 8% 17% 10% 6% 5% 3 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	87% 5% 5% 2 1	2208
	11th to 20th	Day	81% 5% 5% 6% 2	2210
	21st to end	Day	65% 11% 5% 13% 6%	2771
February	1st to 10th	Day	67% 6% 8% 14% 5% 1	1687
	11th to 20th	Day	72% 5% 8% 11% 3	1671
	21st to end	Day	63% 5% 9% 17% 6%	1469
March	1st to 10th	Day	61% 6% 10% 18% 4	3242
	11th to 20th	Day	74% 5% 6% 10% 4 1	3480
	21st to end	Day	67% 3 6% 15% 7% 2	3816
April	1st to 10th	Day	65% 4 8% 14% 8% 1	2307
	11th to 20th	Day	56% 4 9% 19% 10% 1	2442
	21st to end	Day	56% 5% 11% 18% 9% 1	2470
May	1st to 10th	Day	57% 5% 12% 18% 7% 1	4266
	11th to 20th	Day	48% 7% 17% 19% 8%	4528
	21st to end	Day	57% 7% 11% 18% 8%	5185
June	1st to 10th	Day	55% 6% 11% 17% 9% 1	2850
	11th to 20th	Day	48% 7% 14% 19% 11% 1	2850
	21st to end	Day	54% 6% 14% 18% 8%	2850
July	1st to 10th	Day	47% 6% 15% 26% 6%	4685
	11th to 20th	Day	45% 8% 19% 22% 6%	4679
	21st to end	Day	38% 8% 21% 25% 8%	4948
August	1st to 10th	Day	44% 7% 22% 24% 4	4128
	11th to 20th	Day	50% 9% 22% 15% 4	4084
	21st to end	Day	42% 7% 20% 24% 7%	4532
September	1st to 10th	Day	49% 5% 17% 22% 7%	2332
	11th to 20th	Day	48% 3 17% 25% 6%	2095
	21st to end	Day	53% 5% 14% 22% 6%	2090
October	1st to 10th	Day	52% 7% 14% 20% 6% 1	3178
	11th to 20th	Day	63% 6% 11% 19% 3	3140
	21st to end	Day	65% 5% 11% 14% 4	3092
November	1st to 10th	Day	71% 5% 11% 9% 3	1584
	11th to 20th	Day	75% 4 11% 9% 2	1600
	21st to end	Day	82% 3 8% 5% 1	1555
December	1st to 10th	Day	84% 3 8% 5%	1386
	11th to 20th	Day	83% 6% 4 6% 1	1668
	21st to end	Day	78% 6% 7% 7% 1	2431
January	1st to 10th	Night	87% 4 5% 3 1	4748
	11th to 20th	Night	79% 6% 4 7% 4	4760
	21st to end	Night	71% 7% 5% 10% 6% 2	4884
February	1st to 10th	Night	69% 6% 7% 12% 5% 1	2491
	11th to 20th	Night	74% 5% 7% 11% 3	2406
	21st to end	Night	65% 6% 8% 15% 6%	1984
March	1st to 10th	Night	58% 7% 9% 19% 7%	3610
	11th to 20th	Night	77% 4 4 9% 4 1	3480
	21st to end	Night	69% 3 8% 13% 6% 1	3816
April	1st to 10th	Night	68% 4 7% 11% 9% 1	1871
	11th to 20th	Night	53% 6% 8% 18% 13% 1	1688
	21st to end	Night	55% 5% 8% 19% 12% 2	1710
May	1st to 10th	Night	59% 8% 12% 14% 6% 1	2699
	11th to 20th	Night	48% 8% 15% 21% 8%	2397
	21st to end	Night	58% 9% 10% 15% 7%	2402
June	1st to 10th	Night	56% 5% 9% 20% 9% 1	1330
	11th to 20th	Night	49% 6% 12% 18% 13% 1	1330
	21st to end	Night	55% 6% 12% 17% 9%	1330
July	1st to 10th	Night	50% 6% 13% 25% 7%	2175
	11th to 20th	Night	48% 9% 19% 20% 4	2168
	21st to end	Night	39% 9% 21% 21% 11%	2370
August	1st to 10th	Night	51% 8% 19% 18% 4	2747
	11th to 20th	Night	50% 10% 21% 16% 3	2809
	21st to end	Night	40% 7% 15% 27% 10%	3124
September	1st to 10th	Night	49% 6% 11% 25% 8%	1848
	11th to 20th	Night	50% 5% 15% 22% 8%	2081
	21st to end	Night	48% 5% 13% 23% 10%	2090
October	1st to 10th	Night	50% 6% 14% 22% 8% 1	3768
	11th to 20th	Night	60% 5% 12% 19% 4	3779
	21st to end	Night	63% 6% 11% 15% 4	4453
November	1st to 10th	Night	71% 5% 11% 9% 4	2713
	11th to 20th	Night	74% 4 9% 9% 3	2800
	21st to end	Night	79% 5% 8% 6% 1	2840
December	1st to 10th	Night	84% 4 6% 4 1	2977
	11th to 20th	Night	83% 5% 5% 6% 1	3532
	21st to end	Night	78% 7% 7% 6% 2	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% 28% 29% 9% 5% 1	180
	21st to end	Day	23% 29% 26% 16% 5% 1	198
February	1st to 10th	Day	23% 24% 29% 17% 6% 1	347
	11th to 20th	Day	26% 28% 29% 12% 5%	366
	21st to end	Day	22% 27% 31% 12% 6% 1	334
March	1st to 10th	Day	22% 23% 34% 16% 5%	460
	11th to 20th	Day	32% 17% 27% 15% 7% 1	460
	21st to end	Day	32% 25% 25% 11% 5% 2	506
April	1st to 10th	Day	32% 22% 28% 12% 5% 1	460
	11th to 20th	Day	30% 19% 29% 14% 6% 2	452
	21st to end	Day	31% 18% 28% 14% 7% 2	460
May	1st to 10th	Day	33% 12% 29% 17% 6% 1	544
	11th to 20th	Day	28% 16% 27% 19% 8% 2	674
	21st to end	Day	34% 18% 27% 16% 4 1	735
June	1st to 10th	Day	26% 15% 26% 22% 9% 2	680
	11th to 20th	Day	27% 16% 25% 21% 10% 1	680
	21st to end	Day	27% 12% 28% 25% 6% 2	680
July	1st to 10th	Day	24% 13% 30% 23% 8% 2	670
	11th to 20th	Day	21% 13% 30% 26% 9% 1	668
	21st to end	Day	20% 10% 32% 26% 11% 1	713
August	1st to 10th	Day	23% 12% 33% 22% 8% 2	486
	11th to 20th	Day	20% 11% 32% 25% 10% 2	479
	21st to end	Day	23% 10% 31% 23% 11% 3	539
September	1st to 10th	Day	27% 18% 26% 21% 7% 2	490
	11th to 20th	Day	31% 14% 28% 18% 6% 3	490
	21st to end	Day	31% 17% 28% 16% 6% 2	490
October	1st to 10th	Day	29% 22% 23% 17% 7% 3	399
	11th to 20th	Day	39% 17% 20% 16% 5% 2	390
	21st to end	Day	42% 19% 19% 13% 7%	429
November	1st to 10th	Day	40% 23% 22% 13% 2 1	395
	11th to 20th	Day	36% 23% 24% 11% 6% 1	400
	21st to end	Day	36% 25% 24% 9% 5% 1	355
December	1st to 10th	Day	28% 22% 30% 13% 6% 1	196
	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% 25% 28% 17% 5%	850
	21st to end	Night	19% 23% 28% 22% 7% 1	836
February	1st to 10th	Night	18% 25% 31% 19% 7% 1	760
	11th to 20th	Night	27% 21% 24% 22% 6% 1	743
	21st to end	Night	20% 19% 31% 20% 8% 2	628
March	1st to 10th	Night	19% 20% 29% 21% 9% 1	760
	11th to 20th	Night	29% 17% 23% 22% 8% 1	760
	21st to end	Night	27% 17% 24% 22% 8% 1	836
April	1st to 10th	Night	29% 16% 28% 19% 8% 1	641
	11th to 20th	Night	27% 16% 22% 22% 12% 1	564
	21st to end	Night	32% 12% 21% 24% 9% 2	570
May	1st to 10th	Night	33% 8% 21% 27% 9% 2	570
	11th to 20th	Night	24% 9% 25% 27% 13% 2	504
	21st to end	Night	29% 11% 29% 23% 7%	411
June	1st to 10th	Night	24% 7% 21% 36% 11% 1	380
	11th to 20th	Night	23% 9% 23% 27% 17% 1	380
	21st to end	Night	25% 9% 26% 29% 10% 1	380
July	1st to 10th	Night	22% 8% 25% 33% 11% 1	370
	11th to 20th	Night	15% 8% 27% 35% 15% 1	368
	21st to end	Night	19% 9% 20% 32% 18% 3	416
August	1st to 10th	Night	20% 8% 22% 32% 17% 1	525
	11th to 20th	Night	18% 7% 21% 34% 18% 2	562
	21st to end	Night	22% 8% 23% 29% 17% 2	627
September	1st to 10th	Night	26% 14% 19% 28% 11% 1	570
	11th to 20th	Night	29% 10% 21% 26% 12% 1	751
	21st to end	Night	28% 14% 24% 26% 9%	760
October	1st to 10th	Night	30% 16% 20% 24% 8% 1	760
	11th to 20th	Night	40% 14% 16% 20% 9% 1	760
	21st to end	Night	37% 16% 21% 17% 8% 1	836
November	1st to 10th	Night	38% 20% 23% 15% 3 1	870
	11th to 20th	Night	38% 18% 21% 15% 6% 1	900
	21st to end	Night	33% 22% 24% 13% 7%	900
December	1st to 10th	Night	28% 23% 28% 16% 5% 1	893
	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 2024-12-06 03:54:51. Version ac07

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