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 2025-03-12.

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 5% 2 5% 4 4 4 4 5% 6% 56%	112977
	Night	3 5% 2 5% 4 4 5% 4 6% 7% 54%	114817
Transparency	Day	28% 7% 10% 21% 21% 13%	112731
	Night	30% 10% 12% 22% 18% 9%	114652
Seeing	Day	12% 17% 28% 26% 14% 3	15372
	Night	7% 12% 23% 33% 22% 3	24613

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	3 9% 4 10% 7% 6% 7% 6% 8% 9% 30%	3639
	11th to 20th	Day	3 9% 3 8% 5% 4 4 3 5% 6% 51%	3980
	21st to end	Day	3 5% 2 8% 6% 6% 5% 4 6% 6% 49%	4510
February	1st to 10th	Day	4 8% 2 8% 5% 7% 7% 7% 8% 8% 37%	1800
	11th to 20th	Day	3 8% 3 8% 4 6% 6% 4 7% 9% 40%	1755
	21st to end	Day	3 9% 3 7% 6% 5% 7% 5% 7% 7% 39%	1620
March	1st to 10th	Day	3 12% 4 10% 9% 10% 9% 5% 6% 6% 27%	3487
	11th to 20th	Day	2 7% 2 7% 5% 5% 5% 4 5% 6% 52%	3503
	21st to end	Day	4 10% 4 9% 8% 8% 8% 6% 7% 8% 27%	3855
April	1st to 10th	Day	5% 9% 3 8% 8% 6% 5% 5% 6% 8% 36%	2280
	11th to 20th	Day	5% 10% 3 8% 5% 5% 5% 4 6% 8% 41%	2249
	21st to end	Day	4 8% 3 7% 5% 5% 5% 3 5% 8% 47%	2358
May	1st to 10th	Day	4 7% 2 6% 3 3 4 3 4 6% 57%	4110
	11th to 20th	Day	3 4 1 4 3 2 3 3 4 6% 67%	4368
	21st to end	Day	5% 5% 1 4 3 3 4 3 5% 8% 58%	4813
June	1st to 10th	Day	6% 6% 2 5% 4 4 4 4 6% 8% 52%	2660
	11th to 20th	Day	4 4 2 3 3 2 3 2 5% 6% 66%	2660
	21st to end	Day	3 2 1 3 2 2 2 3 4 4 75%	2660
July	1st to 10th	Day	1 1 2 1 1 2 1 2 3 86%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 1 3 3 80%	4420
	21st to end	Day	1 1 1 1 2 2 3 3 86%	4468
August	1st to 10th	Day	2 1 1 2 2 2 3 2 4 5% 75%	4091
	11th to 20th	Day	1 1 2 1 1 2 2 4 5% 81%	4026
	21st to end	Day	1 1 1 2 1 2 2 2 3 4 80%	4190
September	1st to 10th	Day	1 1 1 1 1 2 2 3 5% 82%	2280
	11th to 20th	Day	3 2 1 4 3 3 3 3 5% 7% 65%	2266
	21st to end	Day	2 2 1 3 2 2 3 2 5% 7% 69%	2005
October	1st to 10th	Day	3 2 1 2 2 2 3 2 3 4 75%	3180
	11th to 20th	Day	2 3 1 4 4 4 5% 4 6% 7% 60%	3161
	21st to end	Day	4 6% 2 7% 5% 5% 6% 5% 7% 8% 46%	3448
November	1st to 10th	Day	5% 8% 3 7% 6% 5% 5% 5% 7% 9% 41%	1838
	11th to 20th	Day	5% 6% 3 5% 7% 7% 7% 6% 8% 11% 35%	1625
	21st to end	Day	3 7% 2 6% 6% 5% 6% 6% 7% 9% 44%	1600
December	1st to 10th	Day	2 3 2 6% 4 5% 5% 5% 8% 9% 51%	2620
	11th to 20th	Day	4 8% 3 9% 7% 8% 9% 7% 10% 11% 25%	3028
	21st to end	Day	4 8% 3 12% 10% 10% 9% 7% 9% 9% 19%	4004
January	1st to 10th	Night	3 6% 3 9% 8% 8% 9% 7% 9% 9% 30%	6306
	11th to 20th	Night	2 7% 2 8% 6% 5% 6% 4 6% 7% 48%	5990
	21st to end	Night	3 7% 3 8% 6% 6% 7% 5% 5% 6% 44%	6468
February	1st to 10th	Night	4 6% 2 6% 6% 6% 7% 5% 8% 11% 40%	2600
	11th to 20th	Night	3 8% 3 7% 6% 6% 6% 5% 8% 10% 39%	2532
	21st to end	Night	1 6% 3 6% 6% 6% 6% 6% 9% 10% 41%	2009
March	1st to 10th	Night	3 8% 3 9% 6% 7% 10% 6% 9% 8% 31%	3602
	11th to 20th	Night	2 5% 3 5% 5% 4 5% 4 5% 7% 55%	3505
	21st to end	Night	1 7% 3 9% 6% 8% 8% 6% 9% 11% 31%	3785
April	1st to 10th	Night	3 7% 3 8% 7% 5% 6% 5% 7% 9% 40%	1900
	11th to 20th	Night	3 7% 3 6% 5% 4 5% 5% 7% 8% 46%	1879
	21st to end	Night	5% 9% 2 6% 4 3 4 3 5% 8% 51%	1819
May	1st to 10th	Night	3 6% 2 6% 3 3 3 3 4 5% 62%	2860
	11th to 20th	Night	2 3 1 3 3 3 3 2 3 5% 70%	2521
	21st to end	Night	4 5% 1 4 3 3 3 4 4 6% 63%	2762
June	1st to 10th	Night	6% 5% 2 4 5% 4 4 4 6% 7% 53%	1520
	11th to 20th	Night	5% 3 1 3 3 2 2 1 4 6% 71%	1520
	21st to end	Night	2 1 1 2 1 1 2 1 3 5% 80%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 3 88%	2540
	11th to 20th	Night	2 1 1 2 2 2 2 2 3 3 81%	2540
	21st to end	Night	1 1 1 1 1 2 2 90%	3091
August	1st to 10th	Night	1 2 1 2 1 1 2 2 3 5% 81%	2848
	11th to 20th	Night	1 1 1 1 2 1 2 3 4 85%	2812
	21st to end	Night	2 2 1 3 1 2 2 2 3 3 79%	3488
September	1st to 10th	Night	1 1 1 1 1 2 1 2 5% 85%	1900
	11th to 20th	Night	2 2 1 3 2 2 3 3 5% 7% 70%	1910
	21st to end	Night	3 3 1 3 3 2 3 2 4 5% 71%	2174
October	1st to 10th	Night	2 2 1 2 2 2 3 2 2 3 79%	3800
	11th to 20th	Night	3 3 1 4 3 3 4 3 5% 7% 64%	3777
	21st to end	Night	3 5% 2 5% 4 4 6% 5% 7% 9% 50%	4121
November	1st to 10th	Night	3 6% 2 7% 5% 6% 7% 5% 8% 8% 42%	2460
	11th to 20th	Night	4 6% 2 6% 5% 7% 7% 6% 9% 10% 37%	2770
	21st to end	Night	3 6% 2 6% 5% 4 6% 5% 6% 9% 47%	2800
December	1st to 10th	Night	3 5% 2 4 4 4 4 4 6% 9% 55%	4560
	11th to 20th	Night	4 8% 3 8% 8% 7% 9% 7% 9% 10% 27%	5176
	21st to end	Night	5% 8% 3 8% 7% 7% 7% 6% 7% 8% 32%	6952

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	48% 14% 12% 21% 5% 1	3639
	11th to 20th	Day	36% 8% 7% 28% 16% 4	3980
	21st to end	Day	36% 9% 10% 14% 21% 11%	4510
February	1st to 10th	Day	43% 12% 13% 16% 12% 4	1800
	11th to 20th	Day	42% 11% 13% 19% 13% 2	1764
	21st to end	Day	45% 11% 11% 17% 13% 2	1620
March	1st to 10th	Day	53% 12% 11% 14% 10% 1	3487
	11th to 20th	Day	34% 9% 13% 18% 24% 2	3503
	21st to end	Day	53% 12% 13% 18% 4 1	3855
April	1st to 10th	Day	47% 11% 14% 16% 11% 2	2280
	11th to 20th	Day	42% 9% 15% 19% 11% 4	2252
	21st to end	Day	36% 8% 15% 24% 15% 1	2358
May	1st to 10th	Day	29% 7% 12% 26% 22% 3	4110
	11th to 20th	Day	20% 5% 9% 21% 36% 9%	4371
	21st to end	Day	24% 8% 15% 39% 13%	4814
June	1st to 10th	Day	31% 8% 14% 29% 17% 1	2660
	11th to 20th	Day	20% 7% 11% 30% 26% 7%	2660
	21st to end	Day	15% 4 7% 26% 33% 14%	2660
July	1st to 10th	Day	7% 2 5% 13% 19% 54%	4351
	11th to 20th	Day	11% 3 5% 11% 24% 46%	4345
	21st to end	Day	5% 2 4 17% 37% 36%	4327
August	1st to 10th	Day	12% 4 6% 14% 28% 38%	4076
	11th to 20th	Day	8% 3 6% 26% 38% 20%	4065
	21st to end	Day	9% 3 6% 25% 38% 18%	4189
September	1st to 10th	Day	7% 3 5% 16% 33% 35%	2280
	11th to 20th	Day	20% 6% 9% 21% 33% 12%	2266
	21st to end	Day	16% 6% 9% 24% 27% 17%	2005
October	1st to 10th	Day	15% 4 9% 16% 24% 32%	3180
	11th to 20th	Day	22% 6% 12% 35% 19% 6%	3161
	21st to end	Day	32% 8% 11% 23% 18% 7%	3448
November	1st to 10th	Day	39% 9% 14% 18% 15% 5%	1838
	11th to 20th	Day	43% 10% 16% 14% 12% 5%	1625
	21st to end	Day	38% 11% 11% 16% 17% 7%	1600
December	1st to 10th	Day	29% 8% 10% 26% 23% 4	2620
	11th to 20th	Day	49% 13% 18% 12% 7% 1	3028
	21st to end	Day	53% 15% 12% 14% 6% 1	4004
January	1st to 10th	Night	46% 16% 13% 19% 5% 1	6306
	11th to 20th	Night	35% 11% 10% 25% 15% 3	5990
	21st to end	Night	41% 9% 7% 15% 18% 10%	6468
February	1st to 10th	Night	41% 11% 13% 17% 14% 4	2600
	11th to 20th	Night	40% 11% 14% 20% 12% 2	2534
	21st to end	Night	37% 13% 18% 16% 13% 2	2009
March	1st to 10th	Night	47% 14% 16% 12% 10%	3602
	11th to 20th	Night	31% 10% 14% 20% 22% 3	3505
	21st to end	Night	44% 18% 19% 14% 5% 1	3785
April	1st to 10th	Night	42% 12% 18% 17% 9% 2	1900
	11th to 20th	Night	36% 12% 19% 19% 10% 4	1879
	21st to end	Night	33% 10% 20% 26% 9% 2	1819
May	1st to 10th	Night	26% 7% 17% 29% 17% 3	2860
	11th to 20th	Night	19% 7% 9% 34% 26% 4	2521
	21st to end	Night	20% 11% 23% 38% 8%	2762
June	1st to 10th	Night	32% 10% 15% 31% 11%	1520
	11th to 20th	Night	18% 6% 14% 37% 22% 4	1520
	21st to end	Night	10% 5% 9% 34% 34% 8%	1520
July	1st to 10th	Night	4 3 6% 14% 20% 53%	2500
	11th to 20th	Night	9% 3 4 14% 26% 44%	2492
	21st to end	Night	5% 1 4 18% 45% 27%	2994
August	1st to 10th	Night	9% 3 5% 21% 33% 29%	2839
	11th to 20th	Night	6% 3 6% 36% 34% 16%	2839
	21st to end	Night	11% 4 7% 31% 34% 12%	3488
September	1st to 10th	Night	5% 3 6% 17% 36% 32%	1900
	11th to 20th	Night	15% 5% 13% 25% 33% 10%	1910
	21st to end	Night	17% 6% 10% 24% 23% 19%	2174
October	1st to 10th	Night	13% 4 8% 16% 32% 27%	3800
	11th to 20th	Night	21% 7% 13% 37% 16% 6%	3777
	21st to end	Night	26% 10% 13% 25% 18% 7%	4121
November	1st to 10th	Night	38% 13% 14% 16% 14% 6%	2460
	11th to 20th	Night	40% 12% 16% 16% 12% 4	2770
	21st to end	Night	36% 10% 13% 16% 17% 8%	2800
December	1st to 10th	Night	27% 9% 9% 29% 23% 3	4560
	11th to 20th	Night	46% 15% 13% 17% 8% 1	5176
	21st to end	Night	45% 14% 16% 17% 7% 1	6952

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	27% 27% 22% 18% 5% 2	200
	11th to 20th	Day	18% 21% 27% 19% 12% 3	345
	21st to end	Day	15% 19% 30% 21% 14% 1	440
February	1st to 10th	Day	18% 23% 30% 21% 8% 1	400
	11th to 20th	Day	18% 28% 27% 20% 7% 1	395
	21st to end	Day	18% 26% 29% 21% 6% 2	399
March	1st to 10th	Day	22% 29% 28% 15% 6%	500
	11th to 20th	Day	21% 24% 26% 18% 10%	465
	21st to end	Day	22% 31% 25% 17% 5%	506
April	1st to 10th	Day	19% 25% 32% 18% 5% 1	460
	11th to 20th	Day	25% 22% 26% 18% 7% 2	452
	21st to end	Day	14% 27% 29% 20% 8% 3	460
May	1st to 10th	Day	19% 21% 29% 21% 9% 2	463
	11th to 20th	Day	17% 20% 27% 21% 12% 3	488
	21st to end	Day	15% 17% 27% 24% 14% 3	529
June	1st to 10th	Day	12% 19% 25% 27% 14% 4	490
	11th to 20th	Day	10% 21% 32% 24% 10% 2	490
	21st to end	Day	3 11% 32% 31% 18% 4	490
July	1st to 10th	Day	3 9% 30% 35% 17% 7%	486
	11th to 20th	Day	1 7% 30% 37% 19% 5%	484
	21st to end	Day	1 5% 25% 42% 21% 7%	531
August	1st to 10th	Day	2 5% 28% 37% 21% 7%	487
	11th to 20th	Day	1 11% 25% 33% 22% 9%	477
	21st to end	Day	3 7% 27% 36% 20% 7%	539
September	1st to 10th	Day	3 7% 28% 39% 19% 5%	490
	11th to 20th	Day	6% 13% 26% 35% 18% 3	490
	21st to end	Day	5% 14% 31% 30% 19% 2	490
October	1st to 10th	Day	8% 16% 26% 27% 21% 3	490
	11th to 20th	Day	11% 13% 24% 28% 20% 4	490
	21st to end	Day	11% 18% 26% 28% 14% 3	539
November	1st to 10th	Day	14% 16% 26% 28% 13% 3	374
	11th to 20th	Day	14% 13% 31% 23% 18% 2	213
	21st to end	Day	12% 18% 28% 26% 15% 3	200
December	1st to 10th	Day	12% 20% 25% 23% 12% 10%	200
	11th to 20th	Day	18% 19% 25% 26% 12% 1	200
	21st to end	Day	17% 19% 28% 26% 10%	220
January	1st to 10th	Night	10% 18% 29% 28% 12% 3	800
	11th to 20th	Night	10% 19% 25% 26% 17% 4	800
	21st to end	Night	9% 17% 25% 30% 15% 4	880
February	1st to 10th	Night	10% 15% 27% 33% 14% 1	800
	11th to 20th	Night	9% 16% 29% 29% 14% 2	784
	21st to end	Night	8% 19% 28% 33% 12%	660
March	1st to 10th	Night	12% 22% 28% 26% 10% 3	800
	11th to 20th	Night	9% 20% 23% 30% 15% 2	766
	21st to end	Night	10% 24% 32% 23% 10% 1	836
April	1st to 10th	Night	11% 15% 33% 28% 14% 1	760
	11th to 20th	Night	9% 17% 30% 25% 16% 2	751
	21st to end	Night	9% 13% 24% 32% 19% 1	679
May	1st to 10th	Night	7% 11% 29% 31% 21% 1	570
	11th to 20th	Night	7% 7% 26% 33% 25% 2	379
	21st to end	Night	7% 9% 24% 33% 27% 1	411
June	1st to 10th	Night	8% 7% 19% 39% 26% 1	380
	11th to 20th	Night	6% 5% 25% 45% 19% 1	380
	21st to end	Night	1 3 15% 46% 34% 1	380
July	1st to 10th	Night	1 1 8% 50% 39% 1	370
	11th to 20th	Night	2 7% 54% 35% 1	368
	21st to end	Night	3 43% 49% 4	606
August	1st to 10th	Night	2 1 6% 39% 47% 5%	567
	11th to 20th	Night	2 1 6% 42% 44% 6%	564
	21st to end	Night	2 2 14% 40% 39% 3	826
September	1st to 10th	Night	1 3 13% 44% 36% 4	760
	11th to 20th	Night	3 4 16% 36% 36% 6%	760
	21st to end	Night	5% 5% 17% 35% 31% 7%	760
October	1st to 10th	Night	3 6% 20% 37% 29% 4	760
	11th to 20th	Night	7% 8% 17% 34% 29% 5%	760
	21st to end	Night	8% 10% 19% 32% 22% 7%	836
November	1st to 10th	Night	9% 12% 28% 29% 17% 5%	780
	11th to 20th	Night	10% 15% 29% 30% 14% 3	800
	21st to end	Night	8% 14% 28% 29% 19% 2	800
December	1st to 10th	Night	9% 15% 25% 30% 17% 4	800
	11th to 20th	Night	11% 19% 27% 29% 12% 3	800
	21st to end	Night	13% 24% 29% 25% 8% 2	880

Page generated at 2025-03-09 05:08:46. Version ac07

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