Etna
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Etna clear sky chart from 2005-11-06 to 2026-07-16.

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	3 4 2 5% 4 4 4 4 5% 7% 58%	147171
	Night	3 5% 2 5% 4 4 5% 4 6% 7% 55%	142923
Transparency	Day	26% 7% 10% 23% 22% 12%	142015
	Night	28% 9% 13% 24% 19% 8%	139074
Seeing	Day	11% 17% 27% 27% 14% 4	17164
	Night	7% 12% 22% 34% 22% 3	26240

By Month

Percentage Cloud Cover SW (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	4 9% 3 9% 7% 7% 6% 6% 8% 9% 32%	4722
	11th to 20th	Day	2 7% 2 6% 4 4 4 3 5% 6% 58%	5178
	21st to end	Day	2 4 2 7% 5% 6% 6% 5% 8% 8% 47%	5843
February	1st to 10th	Day	3 8% 2 8% 5% 6% 7% 6% 8% 8% 38%	1890
	11th to 20th	Day	3 9% 3 8% 5% 7% 7% 4 8% 8% 38%	1845
	21st to end	Day	4 9% 3 7% 7% 5% 7% 6% 7% 7% 38%	1699
March	1st to 10th	Day	2 11% 4 9% 7% 8% 7% 5% 5% 6% 35%	4971
	11th to 20th	Day	5% 7% 2 9% 5% 5% 6% 5% 6% 7% 42%	5110
	21st to end	Day	3 8% 3 8% 7% 8% 8% 6% 8% 8% 31%	5651
April	1st to 10th	Day	4 8% 3 7% 8% 6% 6% 5% 6% 9% 37%	2520
	11th to 20th	Day	5% 10% 3 8% 5% 4 5% 4 6% 8% 43%	2489
	21st to end	Day	4 7% 2 6% 5% 5% 5% 3 5% 8% 48%	2606
May	1st to 10th	Day	4 5% 2 4 3 3 3 3 5% 6% 63%	7627
	11th to 20th	Day	2 2 1 3 3 3 3 3 4 6% 69%	8151
	21st to end	Day	5% 4 1 4 3 3 3 3 5% 8% 62%	8992
June	1st to 10th	Day	5% 6% 2 5% 4 3 4 4 5% 8% 54%	2940
	11th to 20th	Day	3 3 1 3 3 2 3 2 5% 6% 67%	2940
	21st to end	Day	3 2 1 3 2 2 2 3 4 4 75%	2940
July	1st to 10th	Day	1 1 1 2 1 1 2 2 3 4 82%	6459
	11th to 20th	Day	1 1 1 2 2 1 2 1 3 3 84%	6391
	21st to end	Day	1 1 1 2 1 2 3 3 5% 5% 77%	6428
August	1st to 10th	Day	2 1 1 2 2 2 3 2 4 5% 76%	5777
	11th to 20th	Day	2 1 2 1 1 2 2 3 4 81%	5796
	21st to end	Day	1 1 2 2 2 3 3 4 5% 77%	5994
September	1st to 10th	Day	1 1 2 1 2 2 2 4 6% 80%	2400
	11th to 20th	Day	3 2 1 4 3 3 3 3 5% 6% 65%	2385
	21st to end	Day	2 2 1 3 2 2 3 2 5% 7% 70%	2110
October	1st to 10th	Day	3 2 1 3 2 2 3 2 3 4 74%	3280
	11th to 20th	Day	2 3 1 4 4 4 5% 4 6% 7% 60%	3261
	21st to end	Day	5% 6% 2 7% 5% 5% 6% 5% 7% 8% 46%	3558
November	1st to 10th	Day	5% 7% 3 7% 6% 5% 5% 5% 7% 10% 41%	1932
	11th to 20th	Day	5% 6% 3 6% 7% 7% 7% 6% 8% 11% 35%	1706
	21st to end	Day	3 7% 2 6% 5% 5% 6% 5% 7% 9% 45%	1680
December	1st to 10th	Day	2 3 2 6% 4 5% 5% 5% 8% 9% 52%	2700
	11th to 20th	Day	4 8% 3 9% 7% 8% 8% 7% 10% 10% 26%	3108
	21st to end	Day	4 8% 3 11% 10% 10% 9% 7% 9% 9% 19%	4092
January	1st to 10th	Night	3 7% 3 9% 7% 7% 8% 7% 9% 9% 29%	8172
	11th to 20th	Night	2 5% 2 6% 5% 4 5% 3 5% 6% 56%	7786
	21st to end	Night	2 6% 3 8% 6% 7% 7% 5% 6% 7% 43%	8371
February	1st to 10th	Night	4 6% 2 6% 6% 6% 7% 5% 8% 10% 41%	2730
	11th to 20th	Night	3 8% 2 7% 6% 6% 6% 5% 8% 9% 39%	2662
	21st to end	Night	2 6% 3 7% 6% 6% 6% 6% 9% 10% 40%	2106
March	1st to 10th	Night	4 8% 3 8% 5% 6% 8% 6% 8% 8% 36%	5138
	11th to 20th	Night	2 6% 3 6% 6% 5% 6% 5% 7% 8% 48%	5110
	21st to end	Night	2 8% 3 9% 7% 7% 7% 6% 9% 10% 32%	5553
April	1st to 10th	Night	3 7% 3 7% 7% 5% 6% 5% 7% 9% 41%	2100
	11th to 20th	Night	3 7% 3 6% 5% 4 5% 5% 7% 7% 47%	2079
	21st to end	Night	5% 8% 2 6% 4 3 4 3 5% 8% 52%	2010
May	1st to 10th	Night	3 4 2 4 3 3 3 3 5% 6% 65%	5321
	11th to 20th	Night	3 3 1 4 3 3 3 3 4 6% 68%	4705
	21st to end	Night	5% 5% 2 4 2 2 2 3 4 6% 65%	5181
June	1st to 10th	Night	6% 5% 2 4 4 4 4 4 6% 7% 55%	1680
	11th to 20th	Night	5% 3 1 2 3 2 2 1 4 6% 71%	1680
	21st to end	Night	2 1 1 2 1 2 2 2 2 5% 79%	1680
July	1st to 10th	Night	1 2 2 2 2 1 3 4 84%	3720
	11th to 20th	Night	1 1 2 1 2 1 2 3 3 85%	3680
	21st to end	Night	1 1 2 2 3 2 4 4 81%	4440
August	1st to 10th	Night	1 2 1 2 2 2 2 2 3 5% 80%	4035
	11th to 20th	Night	2 2 1 2 1 2 1 2 2 3 83%	4052
	21st to end	Night	2 2 1 3 2 2 2 2 3 4 78%	5005
September	1st to 10th	Night	1 1 1 1 1 2 1 3 5% 84%	2000
	11th to 20th	Night	3 2 1 3 2 2 3 3 5% 7% 70%	2011
	21st to end	Night	3 3 1 3 3 2 3 2 4 6% 71%	2289
October	1st to 10th	Night	2 2 1 2 2 2 3 2 2 3 78%	3920
	11th to 20th	Night	3 3 1 4 3 3 4 3 5% 7% 64%	3897
	21st to end	Night	3 5% 2 5% 4 4 6% 5% 7% 9% 51%	4253
November	1st to 10th	Night	4 6% 2 7% 5% 5% 7% 5% 8% 9% 42%	2586
	11th to 20th	Night	5% 6% 2 6% 5% 7% 7% 6% 9% 11% 37%	2909
	21st to end	Night	3 6% 2 6% 5% 4 6% 5% 6% 9% 48%	2940
December	1st to 10th	Night	3 4 2 4 4 4 4 4 6% 9% 55%	4700
	11th to 20th	Night	4 7% 3 8% 7% 7% 9% 7% 9% 10% 28%	5316
	21st to end	Night	6% 8% 3 8% 7% 7% 7% 6% 7% 9% 32%	7106

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	45% 13% 15% 23% 4 1	4723
	11th to 20th	Day	29% 7% 6% 23% 28% 8%	5178
	21st to end	Day	33% 8% 12% 19% 21% 8%	5843
February	1st to 10th	Day	42% 11% 13% 17% 12% 4	1890
	11th to 20th	Day	42% 11% 13% 19% 12% 2	1854
	21st to end	Day	45% 11% 13% 17% 12% 2	1699
March	1st to 10th	Day	45% 10% 10% 22% 10% 2	4971
	11th to 20th	Day	38% 10% 15% 16% 20% 2	5110
	21st to end	Day	45% 11% 15% 22% 6% 1	5651
April	1st to 10th	Day	44% 11% 14% 18% 10% 2	2520
	11th to 20th	Day	40% 8% 14% 20% 13% 4	2492
	21st to end	Day	35% 8% 15% 24% 16% 2	2606
May	1st to 10th	Day	22% 5% 9% 30% 27% 6%	7627
	11th to 20th	Day	15% 5% 11% 29% 34% 6%	8154
	21st to end	Day	20% 7% 12% 43% 17% 1	8994
June	1st to 10th	Day	29% 8% 13% 30% 19% 1	2940
	11th to 20th	Day	19% 6% 10% 29% 27% 8%	2940
	21st to end	Day	14% 4 7% 27% 33% 14%	2940
July	1st to 10th	Day	7% 3 5% 21% 24% 39%	6391
	11th to 20th	Day	8% 2 4 12% 29% 45%	6316
	21st to end	Day	8% 4 6% 27% 30% 25%	6242
August	1st to 10th	Day	12% 3 6% 15% 27% 36%	4206
	11th to 20th	Day	8% 3 6% 26% 38% 20%	4195
	21st to end	Day	9% 3 6% 25% 38% 18%	4321
September	1st to 10th	Day	8% 4 5% 17% 32% 34%	2400
	11th to 20th	Day	20% 6% 9% 22% 33% 11%	2385
	21st to end	Day	16% 6% 9% 24% 28% 17%	2110
October	1st to 10th	Day	16% 4 9% 16% 24% 31%	3280
	11th to 20th	Day	22% 6% 12% 36% 19% 5%	3261
	21st to end	Day	32% 8% 11% 24% 17% 7%	3558
November	1st to 10th	Day	38% 9% 15% 19% 15% 5%	1932
	11th to 20th	Day	42% 10% 17% 14% 12% 4	1706
	21st to end	Day	36% 11% 12% 18% 16% 7%	1680
December	1st to 10th	Day	28% 8% 11% 26% 22% 4	2700
	11th to 20th	Day	48% 13% 18% 12% 7% 1	3108
	21st to end	Day	52% 15% 12% 14% 6% 1	4092
January	1st to 10th	Night	45% 15% 16% 19% 4 1	8172
	11th to 20th	Night	29% 9% 8% 20% 30% 4	7786
	21st to end	Night	39% 8% 10% 19% 16% 8%	8371
February	1st to 10th	Night	40% 11% 13% 18% 15% 4	2730
	11th to 20th	Night	41% 12% 14% 20% 12% 2	2664
	21st to end	Night	38% 13% 18% 16% 13% 2	2106
March	1st to 10th	Night	41% 13% 16% 19% 11% 1	5138
	11th to 20th	Night	30% 11% 17% 20% 19% 3	5110
	21st to end	Night	41% 16% 18% 19% 5%	5553
April	1st to 10th	Night	40% 12% 19% 19% 9% 1	2100
	11th to 20th	Night	35% 12% 18% 20% 12% 4	2079
	21st to end	Night	32% 10% 19% 28% 10% 2	2010
May	1st to 10th	Night	20% 6% 14% 34% 24% 3	5319
	11th to 20th	Night	17% 7% 15% 37% 22% 2	4705
	21st to end	Night	20% 8% 16% 43% 11% 1	5182
June	1st to 10th	Night	29% 10% 14% 33% 13% 1	1680
	11th to 20th	Night	17% 6% 13% 36% 24% 5%	1680
	21st to end	Night	10% 5% 9% 35% 34% 8%	1680
July	1st to 10th	Night	7% 3 7% 25% 23% 36%	3680
	11th to 20th	Night	7% 3 4 12% 36% 38%	3632
	21st to end	Night	8% 3 10% 28% 32% 19%	4314
August	1st to 10th	Night	9% 3 5% 22% 32% 29%	2929
	11th to 20th	Night	6% 3 6% 35% 34% 16%	2929
	21st to end	Night	10% 4 7% 31% 34% 13%	3598
September	1st to 10th	Night	6% 3 7% 18% 35% 31%	2000
	11th to 20th	Night	15% 5% 13% 25% 33% 10%	2011
	21st to end	Night	17% 6% 10% 25% 24% 19%	2289
October	1st to 10th	Night	14% 4 9% 16% 32% 27%	3920
	11th to 20th	Night	20% 7% 13% 38% 16% 6%	3897
	21st to end	Night	26% 9% 14% 26% 18% 7%	4253
November	1st to 10th	Night	37% 13% 14% 17% 13% 6%	2586
	11th to 20th	Night	40% 12% 16% 16% 12% 4	2909
	21st to end	Night	35% 10% 13% 18% 17% 8%	2940
December	1st to 10th	Night	27% 8% 11% 29% 22% 3	4700
	11th to 20th	Night	46% 15% 13% 17% 8% 1	5316
	21st to end	Night	45% 14% 16% 17% 7% 1	7106

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	26% 25% 23% 18% 6% 2	220
	11th to 20th	Day	17% 19% 25% 18% 16% 5%	372
	21st to end	Day	14% 18% 28% 23% 15% 1	473
February	1st to 10th	Day	17% 21% 31% 21% 8% 2	430
	11th to 20th	Day	18% 27% 28% 20% 7%	425
	21st to end	Day	19% 25% 29% 21% 5% 2	430
March	1st to 10th	Day	21% 27% 28% 16% 6%	540
	11th to 20th	Day	21% 23% 26% 21% 9%	540
	21st to end	Day	21% 29% 25% 18% 6% 1	594
April	1st to 10th	Day	18% 23% 31% 18% 7% 3	540
	11th to 20th	Day	22% 20% 26% 20% 8% 3	532
	21st to end	Day	13% 25% 28% 22% 10% 4	540
May	1st to 10th	Day	17% 19% 29% 22% 11% 3	543
	11th to 20th	Day	17% 20% 28% 21% 11% 3	568
	21st to end	Day	13% 16% 27% 25% 14% 4	617
June	1st to 10th	Day	11% 18% 26% 26% 15% 4	570
	11th to 20th	Day	9% 20% 31% 25% 11% 4	570
	21st to end	Day	3 11% 31% 32% 18% 6%	570
July	1st to 10th	Day	2 8% 29% 35% 18% 8%	566
	11th to 20th	Day	1 7% 28% 37% 20% 7%	545
	21st to end	Day	1 5% 24% 41% 22% 8%	575
August	1st to 10th	Day	2 4 27% 36% 23% 8%	527
	11th to 20th	Day	2 10% 24% 32% 22% 10%	517
	21st to end	Day	3 7% 25% 36% 21% 8%	583
September	1st to 10th	Day	2 7% 27% 38% 19% 7%	530
	11th to 20th	Day	5% 12% 25% 35% 18% 5%	530
	21st to end	Day	6% 13% 29% 30% 19% 3	530
October	1st to 10th	Day	8% 16% 25% 27% 20% 3	530
	11th to 20th	Day	11% 13% 23% 29% 20% 4	530
	21st to end	Day	11% 17% 25% 28% 16% 3	583
November	1st to 10th	Day	13% 16% 25% 28% 14% 3	408
	11th to 20th	Day	14% 12% 29% 24% 19% 2	234
	21st to end	Day	10% 16% 26% 29% 15% 4	220
December	1st to 10th	Day	10% 18% 25% 25% 14% 9%	220
	11th to 20th	Day	17% 18% 25% 25% 11% 3	220
	21st to end	Day	17% 20% 26% 26% 9% 2	242
January	1st to 10th	Night	10% 18% 29% 28% 12% 3	840
	11th to 20th	Night	9% 18% 23% 27% 19% 4	840
	21st to end	Night	9% 16% 25% 31% 15% 4	924
February	1st to 10th	Night	10% 14% 27% 34% 14% 1	840
	11th to 20th	Night	9% 16% 30% 29% 14% 1	824
	21st to end	Night	9% 19% 27% 33% 11%	692
March	1st to 10th	Night	12% 22% 28% 27% 10% 3	840
	11th to 20th	Night	9% 19% 24% 32% 14% 2	840
	21st to end	Night	9% 22% 33% 25% 10% 1	924
April	1st to 10th	Night	10% 14% 32% 29% 14% 1	840
	11th to 20th	Night	9% 16% 30% 27% 16% 2	831
	21st to end	Night	9% 13% 23% 33% 20% 1	750
May	1st to 10th	Night	6% 10% 27% 33% 22% 1	630
	11th to 20th	Night	7% 7% 26% 34% 24% 2	419
	21st to end	Night	7% 8% 23% 34% 27% 1	455
June	1st to 10th	Night	8% 7% 19% 41% 25%	420
	11th to 20th	Night	5% 5% 24% 47% 19% 1	420
	21st to end	Night	1 4 14% 48% 33%	420
July	1st to 10th	Night	8% 51% 40% 1	410
	11th to 20th	Night	2 8% 55% 35% 1	398
	21st to end	Night	3 42% 50% 4	638
August	1st to 10th	Night	2 1 6% 40% 47% 5%	597
	11th to 20th	Night	2 1 6% 42% 44% 6%	594
	21st to end	Night	2 2 13% 41% 39% 3	870
September	1st to 10th	Night	1 3 13% 44% 36% 4	800
	11th to 20th	Night	3 4 15% 36% 36% 6%	800
	21st to end	Night	4 6% 16% 36% 32% 7%	800
October	1st to 10th	Night	4 6% 21% 37% 28% 4	800
	11th to 20th	Night	7% 7% 17% 36% 28% 5%	800
	21st to end	Night	8% 10% 19% 33% 23% 7%	880
November	1st to 10th	Night	9% 13% 27% 30% 17% 5%	820
	11th to 20th	Night	10% 14% 29% 30% 14% 3	840
	21st to end	Night	8% 13% 29% 29% 19% 2	840
December	1st to 10th	Night	9% 14% 25% 31% 17% 3	840
	11th to 20th	Night	11% 19% 26% 29% 13% 3	840
	21st to end	Night	13% 24% 28% 26% 8% 2	924

Page generated at 2026-07-13 00:14:50. Version ac07

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