Observatoire Ébouliborg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Ébouliborg clear sky chart from 2005-11-06 to 2024-11-05.

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	15% 9% 3 7% 5% 5% 5% 4 6% 7% 34%	101568
	Night	16% 10% 3 8% 5% 4 4 3 5% 6% 35%	97518
Transparency	Day	46% 10% 16% 19% 9% 1	105034
	Night	49% 8% 15% 18% 9% 1	102142
Seeing	Day	21% 16% 30% 22% 9% 2	15529
	Night	21% 10% 30% 29% 9% 1	23757

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% 14% 4 8% 5% 5% 4 3 6% 8% 30%	2397
	11th to 20th	Day	11% 10% 4 10% 7% 5% 6% 4 6% 7% 31%	2520
	21st to end	Day	7% 8% 4 10% 5% 5% 6% 4 7% 9% 37%	2772
February	1st to 10th	Day	6% 12% 4 10% 8% 5% 5% 4 6% 7% 31%	1546
	11th to 20th	Day	9% 13% 4 12% 6% 5% 4 4 5% 5% 31%	1775
	21st to end	Day	11% 10% 3 9% 7% 6% 5% 4 6% 5% 34%	1570
March	1st to 10th	Day	16% 11% 4 8% 5% 4 5% 4 5% 5% 33%	3116
	11th to 20th	Day	13% 16% 4 9% 6% 4 5% 4 5% 6% 28%	3377
	21st to end	Day	12% 15% 5% 8% 5% 4 4 3 4 5% 36%	3970
April	1st to 10th	Day	20% 12% 4 8% 6% 4 4 4 4 6% 30%	2280
	11th to 20th	Day	16% 8% 2 7% 5% 5% 4 3 4 6% 38%	2394
	21st to end	Day	21% 10% 3 6% 5% 4 4 4 5% 6% 33%	2470
May	1st to 10th	Day	16% 8% 3 7% 4 5% 5% 5% 5% 6% 35%	4160
	11th to 20th	Day	18% 7% 2 7% 5% 5% 5% 4 5% 7% 34%	4398
	21st to end	Day	16% 6% 2 7% 5% 5% 5% 4 7% 8% 33%	5123
June	1st to 10th	Day	19% 7% 2 7% 5% 5% 6% 4 6% 7% 30%	2850
	11th to 20th	Day	17% 6% 2 6% 4 5% 5% 5% 6% 7% 37%	2850
	21st to end	Day	23% 6% 3 8% 5% 4 5% 5% 6% 8% 29%	2850
July	1st to 10th	Day	15% 6% 2 7% 6% 6% 6% 4 7% 9% 33%	4760
	11th to 20th	Day	12% 5% 3 8% 5% 6% 6% 5% 7% 8% 35%	4448
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 7% 8% 41%	4814
August	1st to 10th	Day	13% 5% 2 7% 5% 6% 7% 5% 8% 9% 33%	4361
	11th to 20th	Day	15% 6% 3 7% 6% 6% 6% 5% 8% 8% 31%	4045
	21st to end	Day	18% 4 2 6% 4 4 4 3 5% 7% 42%	4450
September	1st to 10th	Day	14% 6% 3 5% 4 4 5% 4 6% 7% 43%	2271
	11th to 20th	Day	14% 5% 2 5% 3 3 4 3 5% 6% 49%	2090
	21st to end	Day	18% 5% 2 6% 4 3 4 3 5% 8% 42%	2090
October	1st to 10th	Day	18% 6% 2 7% 5% 4 3 3 5% 7% 39%	2074
	11th to 20th	Day	21% 7% 2 7% 6% 4 5% 4 6% 7% 31%	1748
	21st to end	Day	23% 10% 3 6% 4 4 4 3 5% 6% 32%	1881
November	1st to 10th	Day	15% 10% 4 9% 4 4 4 4 5% 5% 36%	1708
	11th to 20th	Day	16% 11% 4 8% 4 6% 4 3 6% 6% 32%	1627
	21st to end	Day	16% 17% 4 7% 6% 4 4 3 5% 6% 27%	1354
December	1st to 10th	Day	16% 16% 4 9% 6% 4 5% 3 5% 5% 27%	1330
	11th to 20th	Day	18% 12% 4 9% 6% 3 6% 2 5% 4 31%	1668
	21st to end	Day	19% 13% 4 7% 5% 4 3 3 4 5% 35%	2431
January	1st to 10th	Night	11% 15% 5% 10% 6% 5% 5% 4 6% 6% 27%	4549
	11th to 20th	Night	9% 13% 5% 10% 7% 6% 5% 3 5% 6% 30%	4440
	21st to end	Night	7% 12% 6% 11% 6% 6% 6% 3 6% 7% 30%	4884
February	1st to 10th	Night	7% 11% 4 9% 6% 5% 5% 4 5% 7% 36%	2632
	11th to 20th	Night	9% 13% 5% 12% 6% 5% 4 3 5% 5% 32%	2287
	21st to end	Night	13% 12% 3 8% 5% 4 4 3 6% 7% 35%	1884
March	1st to 10th	Night	18% 13% 4 9% 5% 4 4 3 5% 6% 29%	3724
	11th to 20th	Night	12% 16% 5% 11% 6% 6% 6% 4 5% 5% 24%	3581
	21st to end	Night	17% 14% 4 7% 4 4 4 3 5% 5% 34%	3658
April	1st to 10th	Night	21% 14% 4 7% 4 3 4 3 4 5% 33%	1900
	11th to 20th	Night	20% 8% 3 7% 4 5% 5% 4 5% 6% 34%	1735
	21st to end	Night	23% 10% 2 6% 4 4 4 4 5% 4 35%	1710
May	1st to 10th	Night	19% 8% 3 6% 4 4 4 4 5% 7% 37%	2809
	11th to 20th	Night	20% 10% 2 6% 5% 4 4 4 6% 6% 33%	2495
	21st to end	Night	18% 6% 2 4 4 3 5% 4 6% 10% 37%	2461
June	1st to 10th	Night	19% 10% 3 7% 5% 4 4 4 6% 6% 33%	1330
	11th to 20th	Night	15% 6% 2 5% 5% 5% 4 4 6% 8% 42%	1330
	21st to end	Night	20% 9% 3 7% 5% 5% 4 3 6% 7% 32%	1330
July	1st to 10th	Night	15% 6% 3 6% 4 5% 4 4 6% 8% 38%	2210
	11th to 20th	Night	15% 6% 2 5% 5% 4 5% 4 7% 8% 39%	2509
	21st to end	Night	11% 4 1 4 4 5% 4 4 6% 9% 47%	2739
August	1st to 10th	Night	16% 6% 2 6% 4 5% 5% 4 6% 8% 38%	2536
	11th to 20th	Night	15% 5% 2 8% 7% 6% 6% 5% 6% 7% 33%	2782
	21st to end	Night	16% 6% 2 7% 3 3 4 3 4 7% 44%	3204
September	1st to 10th	Night	15% 5% 2 6% 4 4 4 3 6% 7% 45%	1909
	11th to 20th	Night	17% 6% 2 6% 3 4 5% 3 5% 6% 45%	2090
	21st to end	Night	18% 6% 2 5% 4 4 3 3 4 5% 45%	2090
October	1st to 10th	Night	16% 8% 3 7% 4 3 4 3 5% 5% 43%	2105
	11th to 20th	Night	23% 8% 3 5% 5% 3 4 3 4 6% 35%	2429
	21st to end	Night	22% 9% 2 5% 5% 4 4 3 5% 6% 36%	2717
November	1st to 10th	Night	16% 9% 3 7% 4 4 4 3 5% 7% 38%	2470
	11th to 20th	Night	18% 9% 3 7% 4 4 4 4 5% 6% 35%	2550
	21st to end	Night	16% 13% 4 8% 5% 5% 4 3 5% 6% 32%	2822
December	1st to 10th	Night	17% 15% 5% 9% 6% 5% 3 3 5% 4 29%	2850
	11th to 20th	Night	18% 12% 4 7% 5% 4 4 3 6% 6% 30%	3531
	21st to end	Night	18% 16% 5% 8% 4 3 3 2 5% 4 31%	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	52% 8% 18% 16% 5%	2398
	11th to 20th	Day	51% 8% 11% 21% 8% 1	2520
	21st to end	Day	43% 12% 14% 17% 14%	2772
February	1st to 10th	Day	51% 9% 13% 16% 10% 2	1546
	11th to 20th	Day	54% 8% 12% 15% 10% 2	1783
	21st to end	Day	48% 9% 10% 19% 11% 3	1570
March	1st to 10th	Day	51% 10% 14% 12% 9% 3	3119
	11th to 20th	Day	54% 10% 15% 13% 7% 1	3377
	21st to end	Day	50% 7% 9% 17% 12% 5%	3970
April	1st to 10th	Day	54% 8% 12% 13% 10% 3	2280
	11th to 20th	Day	45% 8% 12% 21% 11% 3	2394
	21st to end	Day	50% 7% 12% 16% 13% 2	2470
May	1st to 10th	Day	46% 10% 15% 16% 13% 1	4174
	11th to 20th	Day	45% 11% 18% 19% 6% 1	4402
	21st to end	Day	43% 12% 13% 19% 12% 1	5123
June	1st to 10th	Day	49% 11% 12% 20% 8% 1	2850
	11th to 20th	Day	44% 10% 14% 20% 10% 2	2850
	21st to end	Day	51% 11% 14% 16% 8% 1	2850
July	1st to 10th	Day	43% 11% 18% 21% 7%	4685
	11th to 20th	Day	41% 12% 21% 21% 4	4372
	21st to end	Day	39% 11% 19% 22% 9%	4661
August	1st to 10th	Day	41% 14% 20% 18% 7%	4347
	11th to 20th	Day	44% 13% 21% 17% 5%	4084
	21st to end	Day	39% 10% 20% 18% 13%	4450
September	1st to 10th	Day	38% 10% 17% 23% 12%	2271
	11th to 20th	Day	35% 10% 17% 28% 11%	2090
	21st to end	Day	40% 11% 15% 24% 11%	2090
October	1st to 10th	Day	48% 11% 14% 21% 6%	3451
	11th to 20th	Day	45% 7% 19% 25% 4	2886
	21st to end	Day	44% 8% 21% 17% 10%	3081
November	1st to 10th	Day	50% 9% 13% 19% 8% 1	1708
	11th to 20th	Day	53% 8% 14% 18% 7% 1	1627
	21st to end	Day	58% 7% 16% 13% 5%	1354
December	1st to 10th	Day	62% 7% 12% 12% 7%	1330
	11th to 20th	Day	58% 6% 10% 16% 9% 1	1668
	21st to end	Day	54% 5% 15% 17% 6% 3	2431
January	1st to 10th	Night	57% 9% 15% 11% 8% 1	4549
	11th to 20th	Night	54% 8% 15% 15% 7% 1	4440
	21st to end	Night	49% 9% 13% 17% 11% 1	4884
February	1st to 10th	Night	49% 8% 13% 18% 11% 1	2632
	11th to 20th	Night	55% 6% 13% 14% 12% 1	2290
	21st to end	Night	49% 7% 13% 18% 12% 2	1884
March	1st to 10th	Night	55% 9% 11% 17% 7% 1	3734
	11th to 20th	Night	59% 11% 10% 13% 6% 1	3582
	21st to end	Night	53% 7% 10% 19% 10% 2	3658
April	1st to 10th	Night	55% 4 10% 15% 12% 3	1900
	11th to 20th	Night	49% 8% 11% 19% 12% 1	1735
	21st to end	Night	53% 6% 9% 19% 12% 2	1710
May	1st to 10th	Night	47% 8% 15% 18% 12% 1	2815
	11th to 20th	Night	47% 11% 16% 16% 10% 1	2496
	21st to end	Night	41% 8% 18% 19% 13% 1	2462
June	1st to 10th	Night	51% 7% 14% 20% 7% 1	1330
	11th to 20th	Night	40% 8% 15% 21% 13% 3	1330
	21st to end	Night	52% 10% 13% 16% 9%	1330
July	1st to 10th	Night	43% 9% 21% 23% 4	2175
	11th to 20th	Night	41% 10% 21% 23% 5%	2462
	21st to end	Night	34% 9% 25% 23% 9%	2651
August	1st to 10th	Night	43% 9% 19% 23% 6%	2526
	11th to 20th	Night	47% 14% 18% 13% 8%	2809
	21st to end	Night	42% 8% 14% 24% 12%	3204
September	1st to 10th	Night	39% 8% 16% 24% 12% 1	1909
	11th to 20th	Night	40% 9% 17% 24% 9% 1	2090
	21st to end	Night	42% 8% 13% 25% 12% 1	2090
October	1st to 10th	Night	45% 7% 13% 27% 7%	3508
	11th to 20th	Night	46% 6% 14% 28% 5%	4030
	21st to end	Night	43% 8% 20% 17% 11% 1	4467
November	1st to 10th	Night	48% 7% 17% 20% 8% 1	2470
	11th to 20th	Night	48% 9% 18% 16% 9% 1	2550
	21st to end	Night	56% 7% 15% 13% 8% 1	2822
December	1st to 10th	Night	61% 6% 14% 12% 6% 1	2850
	11th to 20th	Night	55% 9% 14% 13% 9% 1	3532
	21st to end	Night	57% 8% 13% 13% 8% 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	18% 17% 38% 22% 4 1	180
	11th to 20th	Day	23% 21% 36% 14% 7%	180
	21st to end	Day	14% 23% 37% 18% 6% 2	198
February	1st to 10th	Day	19% 23% 36% 17% 4	206
	11th to 20th	Day	17% 20% 39% 19% 4	420
	21st to end	Day	18% 21% 36% 19% 6% 1	382
March	1st to 10th	Day	23% 22% 29% 20% 5%	460
	11th to 20th	Day	21% 19% 32% 20% 8% 1	460
	21st to end	Day	22% 21% 29% 19% 7% 1	506
April	1st to 10th	Day	29% 20% 27% 18% 6% 1	460
	11th to 20th	Day	23% 20% 29% 19% 6% 2	452
	21st to end	Day	28% 18% 33% 16% 3 2	460
May	1st to 10th	Day	26% 14% 31% 20% 8% 1	463
	11th to 20th	Day	20% 21% 29% 21% 8% 2	487
	21st to end	Day	22% 19% 32% 20% 6% 1	698
June	1st to 10th	Day	24% 14% 30% 23% 8% 1	680
	11th to 20th	Day	21% 13% 27% 25% 13% 1	680
	21st to end	Day	24% 10% 29% 27% 10% 1	680
July	1st to 10th	Day	17% 10% 31% 30% 11% 1	670
	11th to 20th	Day	15% 12% 30% 30% 11% 2	491
	21st to end	Day	14% 10% 33% 29% 12% 2	532
August	1st to 10th	Day	14% 15% 27% 29% 13% 3	486
	11th to 20th	Day	15% 8% 29% 30% 15% 3	479
	21st to end	Day	16% 15% 30% 18% 17% 4	539
September	1st to 10th	Day	16% 14% 29% 26% 11% 3	490
	11th to 20th	Day	19% 11% 29% 25% 12% 4	490
	21st to end	Day	20% 14% 24% 24% 13% 5%	490
October	1st to 10th	Day	19% 16% 30% 22% 10% 3	481
	11th to 20th	Day	25% 14% 29% 22% 9% 2	390
	21st to end	Day	31% 11% 30% 21% 6%	429
November	1st to 10th	Day	27% 15% 31% 22% 3 1	378
	11th to 20th	Day	24% 16% 30% 21% 9% 1	370
	21st to end	Day	27% 25% 26% 19% 2	204
December	1st to 10th	Day	24% 14% 30% 18% 12% 2	180
	11th to 20th	Day	30% 18% 31% 15% 4 2	180
	21st to end	Day	28% 16% 29% 22% 4 1	198
January	1st to 10th	Night	22% 11% 37% 25% 5% 1	792
	11th to 20th	Night	19% 10% 38% 27% 5%	760
	21st to end	Night	13% 10% 33% 35% 8% 1	836
February	1st to 10th	Night	15% 10% 39% 28% 7% 1	760
	11th to 20th	Night	17% 14% 38% 24% 7% 1	743
	21st to end	Night	19% 11% 35% 28% 5% 1	628
March	1st to 10th	Night	19% 14% 34% 26% 6% 1	760
	11th to 20th	Night	20% 13% 35% 24% 7% 1	760
	21st to end	Night	22% 13% 33% 26% 6%	836
April	1st to 10th	Night	28% 11% 31% 24% 7%	760
	11th to 20th	Night	23% 13% 29% 26% 8%	611
	21st to end	Night	29% 11% 27% 26% 7%	570
May	1st to 10th	Night	26% 8% 31% 29% 5%	558
	11th to 20th	Night	23% 10% 24% 31% 11%	374
	21st to end	Night	27% 9% 28% 29% 7%	411
June	1st to 10th	Night	22% 5% 24% 38% 10% 1	380
	11th to 20th	Night	17% 5% 24% 36% 17% 1	380
	21st to end	Night	22% 6% 28% 32% 11% 1	380
July	1st to 10th	Night	18% 6% 30% 34% 12% 1	370
	11th to 20th	Night	14% 5% 23% 43% 14% 1	368
	21st to end	Night	15% 3 21% 46% 12% 2	416
August	1st to 10th	Night	13% 4 16% 47% 18% 1	395
	11th to 20th	Night	17% 3 22% 38% 19% 1	562
	21st to end	Night	16% 6% 24% 36% 16% 2	668
September	1st to 10th	Night	16% 7% 26% 37% 14% 1	760
	11th to 20th	Night	21% 8% 22% 32% 15% 3	760
	21st to end	Night	19% 6% 25% 34% 14% 1	760
October	1st to 10th	Night	21% 9% 29% 30% 9% 3	760
	11th to 20th	Night	26% 8% 27% 27% 12% 1	760
	21st to end	Night	26% 10% 31% 26% 8%	836
November	1st to 10th	Night	23% 14% 29% 27% 7%	760
	11th to 20th	Night	23% 14% 31% 23% 8% 1	798
	21st to end	Night	25% 14% 29% 25% 6% 1	850
December	1st to 10th	Night	25% 12% 32% 24% 7% 1	850
	11th to 20th	Night	22% 16% 32% 23% 6%	850
	21st to end	Night	26% 13% 32% 21% 8% 1	935

Page generated at 2024-11-03 02:11:29. Version ac07

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