Ponte di Legno Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ponte di Legno Observatory clear sky chart from 2005-11-06 to 2024-02-25.

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% 11% 5% 8% 6% 3 4 4 5% 6% 31%	78182
	Night	16% 13% 6% 10% 7% 3 5% 4 5% 6% 25%	81129
Transparency	Day	54% 4 11% 21% 10% 1	77888
	Night	61% 3 10% 17% 8% 1	80958
Seeing	Day	19% 13% 29% 25% 12% 3	14173
	Night	22% 13% 26% 26% 12% 2	23615

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	17% 21% 15% 14% 11% 3 4 3 3 2 6%	2212
	11th to 20th	Day	11% 21% 10% 24% 15% 4 5% 3 2 2 4	2532
	21st to end	Day	19% 19% 11% 13% 9% 4 6% 4 3 4 8%	3124
February	1st to 10th	Day	13% 19% 8% 16% 11% 4 5% 3 4 5% 13%	1710
	11th to 20th	Day	11% 14% 9% 12% 11% 5% 5% 5% 4 5% 18%	1663
	21st to end	Day	14% 16% 6% 10% 8% 4 6% 5% 5% 6% 20%	1482
March	1st to 10th	Day	14% 9% 4 9% 7% 4 6% 4 5% 7% 32%	1905
	11th to 20th	Day	12% 11% 4 10% 6% 3 4 5% 5% 6% 32%	1980
	21st to end	Day	16% 9% 4 7% 7% 3 4 5% 5% 5% 36%	2178
April	1st to 10th	Day	19% 11% 5% 6% 5% 4 4 4 5% 7% 30%	2082
	11th to 20th	Day	18% 10% 2 6% 5% 2 4 4 4 6% 39%	2312
	21st to end	Day	19% 8% 4 6% 4 3 4 4 6% 7% 36%	2340
May	1st to 10th	Day	16% 7% 3 6% 5% 2 4 5% 5% 8% 38%	2340
	11th to 20th	Day	15% 7% 3 5% 5% 3 4 3 5% 6% 44%	2396
	21st to end	Day	11% 5% 2 5% 5% 3 4 4 5% 8% 48%	2725
June	1st to 10th	Day	13% 6% 2 5% 4 4 5% 5% 7% 8% 41%	2686
	11th to 20th	Day	10% 6% 3 5% 5% 3 5% 5% 6% 8% 44%	2700
	21st to end	Day	13% 6% 3 5% 4 2 4 5% 6% 9% 43%	2700
July	1st to 10th	Day	8% 4 2 5% 4 3 4 5% 6% 8% 51%	2700
	11th to 20th	Day	10% 5% 3 5% 5% 3 4 5% 6% 7% 47%	2660
	21st to end	Day	9% 5% 3 5% 4 3 4 6% 6% 9% 47%	2573
August	1st to 10th	Day	11% 6% 2 4 3 2 4 4 6% 9% 49%	2327
	11th to 20th	Day	10% 4 2 5% 5% 4 4 5% 7% 8% 46%	2303
	21st to end	Day	12% 7% 3 5% 5% 3 5% 5% 6% 8% 40%	2570
September	1st to 10th	Day	12% 6% 3 5% 6% 3 5% 4 6% 8% 42%	2130
	11th to 20th	Day	12% 6% 2 5% 6% 3 4 5% 6% 7% 44%	1980
	21st to end	Day	17% 6% 3 7% 5% 3 4 4 6% 6% 37%	1980
October	1st to 10th	Day	19% 10% 3 6% 6% 3 5% 4 5% 7% 33%	1831
	11th to 20th	Day	25% 14% 5% 8% 6% 3 3 4 5% 6% 22%	1800
	21st to end	Day	28% 15% 5% 8% 6% 3 5% 4 4 5% 18%	1895
November	1st to 10th	Day	17% 15% 6% 9% 7% 4 5% 4 5% 7% 21%	1630
	11th to 20th	Day	19% 15% 6% 9% 8% 5% 6% 5% 5% 6% 17%	1520
	21st to end	Day	20% 24% 7% 10% 7% 3 4 6% 4 5% 10%	1520
December	1st to 10th	Day	16% 26% 10% 15% 8% 3 4 4 3 3 7%	1520
	11th to 20th	Day	18% 24% 7% 14% 8% 3 4 4 3 6% 9%	1745
	21st to end	Day	27% 22% 8% 15% 8% 3 3 3 3 3 5%	2431
January	1st to 10th	Night	16% 22% 11% 16% 11% 3 4 4 3 3 7%	4739
	11th to 20th	Night	15% 16% 10% 21% 14% 4 4 4 3 3 6%	4436
	21st to end	Night	16% 19% 10% 14% 10% 4 5% 5% 4 4 10%	4532
February	1st to 10th	Night	11% 18% 8% 15% 11% 4 5% 4 4 5% 14%	2470
	11th to 20th	Night	12% 14% 8% 13% 10% 5% 5% 4 5% 5% 19%	2403
	21st to end	Night	15% 14% 7% 10% 8% 3 6% 5% 5% 5% 23%	1865
March	1st to 10th	Night	13% 11% 4 8% 7% 4 5% 4 5% 6% 32%	2042
	11th to 20th	Night	13% 13% 5% 8% 6% 3 4 4 5% 5% 34%	1979
	21st to end	Night	15% 9% 4 7% 6% 4 4 4 5% 5% 36%	2178
April	1st to 10th	Night	20% 10% 5% 5% 5% 2 5% 4 4 6% 33%	1893
	11th to 20th	Night	17% 8% 3 6% 4 2 4 5% 5% 7% 38%	1597
	21st to end	Night	19% 9% 4 7% 6% 3 4 4 5% 6% 33%	1620
May	1st to 10th	Night	14% 8% 3 5% 7% 3 5% 5% 5% 6% 38%	1620
	11th to 20th	Night	14% 6% 4 6% 6% 3 4 4 6% 6% 41%	1495
	21st to end	Night	10% 5% 2 6% 5% 4 5% 5% 7% 8% 45%	1550
June	1st to 10th	Night	12% 7% 2 6% 7% 4 5% 4 5% 8% 40%	1270
	11th to 20th	Night	10% 6% 2 5% 5% 2 5% 6% 6% 11% 43%	1260
	21st to end	Night	10% 8% 3 5% 6% 3 5% 6% 5% 9% 41%	1260
July	1st to 10th	Night	8% 4 2 4 4 3 4 4 5% 8% 54%	1260
	11th to 20th	Night	8% 5% 2 5% 6% 4 5% 5% 6% 9% 45%	1297
	21st to end	Night	8% 4 2 3 5% 3 6% 5% 6% 8% 48%	1743
August	1st to 10th	Night	9% 6% 2 4 5% 2 4 4 6% 8% 50%	1611
	11th to 20th	Night	8% 5% 2 4 6% 3 5% 6% 7% 8% 47%	1598
	21st to end	Night	11% 6% 3 6% 5% 3 4 5% 6% 8% 44%	1782
September	1st to 10th	Night	10% 5% 2 4 5% 3 4 4 6% 8% 46%	1812
	11th to 20th	Night	11% 5% 2 5% 5% 3 6% 4 5% 7% 46%	1980
	21st to end	Night	16% 7% 3 7% 6% 3 5% 5% 5% 6% 37%	1980
October	1st to 10th	Night	19% 8% 3 8% 6% 4 5% 4 4 7% 33%	2128
	11th to 20th	Night	24% 11% 5% 9% 6% 4 5% 5% 5% 6% 21%	2160
	21st to end	Night	26% 14% 5% 8% 6% 4 4 5% 5% 4 19%	2458
November	1st to 10th	Night	19% 13% 4 8% 7% 4 5% 5% 5% 6% 24%	2446
	11th to 20th	Night	18% 16% 6% 11% 8% 4 4 5% 5% 6% 18%	2660
	21st to end	Night	23% 21% 5% 9% 7% 4 4 4 4 6% 12%	2660
December	1st to 10th	Night	19% 24% 9% 13% 8% 3 5% 4 4 4 7%	2660
	11th to 20th	Night	16% 22% 8% 15% 8% 4 5% 5% 4 4 10%	3449
	21st to end	Night	24% 21% 10% 16% 7% 3 4 3 2 3 7%	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% 1 6% 5%	2213
	11th to 20th	Day	90% 2 3 4 1	2532
	21st to end	Day	82% 2 8% 7% 2	3124
February	1st to 10th	Day	75% 3 6% 13% 2	1710
	11th to 20th	Day	69% 3 9% 12% 7%	1672
	21st to end	Day	65% 4 8% 17% 5%	1482
March	1st to 10th	Day	53% 4 13% 19% 11% 2	1908
	11th to 20th	Day	54% 4 10% 21% 10% 2	1980
	21st to end	Day	51% 3 10% 20% 14% 2	2178
April	1st to 10th	Day	55% 4 11% 19% 12% 1	2082
	11th to 20th	Day	48% 3 8% 24% 16% 2	2312
	21st to end	Day	48% 4 12% 22% 12% 3	2340
May	1st to 10th	Day	44% 4 8% 26% 15% 3	2340
	11th to 20th	Day	43% 3 8% 26% 18% 2	2400
	21st to end	Day	35% 4 17% 25% 16% 2	2725
June	1st to 10th	Day	40% 3 12% 28% 15% 1	2686
	11th to 20th	Day	36% 4 11% 28% 19% 1	2700
	21st to end	Day	38% 4 14% 28% 14% 2	2700
July	1st to 10th	Day	30% 4 16% 30% 19% 2	2626
	11th to 20th	Day	35% 4 14% 33% 12% 2	2579
	21st to end	Day	35% 5% 14% 29% 16% 1	2430
August	1st to 10th	Day	33% 4 17% 30% 14% 1	2314
	11th to 20th	Day	34% 6% 16% 31% 13%	2303
	21st to end	Day	41% 5% 15% 25% 13% 1	2570
September	1st to 10th	Day	40% 5% 13% 28% 13% 1	2130
	11th to 20th	Day	39% 4 15% 32% 10%	1980
	21st to end	Day	47% 5% 15% 26% 7%	1980
October	1st to 10th	Day	51% 4 11% 22% 10% 1	1831
	11th to 20th	Day	64% 4 12% 15% 5% 1	1800
	21st to end	Day	69% 3 9% 14% 4	1895
November	1st to 10th	Day	62% 4 12% 17% 6%	1630
	11th to 20th	Day	68% 3 12% 11% 5%	1520
	21st to end	Day	78% 3 10% 8% 1	1520
December	1st to 10th	Day	84% 2 8% 5% 2	1520
	11th to 20th	Day	80% 2 7% 10%	1745
	21st to end	Day	87% 1 7% 4	2431
January	1st to 10th	Night	84% 2 7% 6% 1	4739
	11th to 20th	Night	86% 2 5% 5% 1	4436
	21st to end	Night	79% 2 7% 9% 2	4532
February	1st to 10th	Night	72% 4 8% 12% 4 1	2470
	11th to 20th	Night	68% 3 8% 16% 6%	2405
	21st to end	Night	64% 3 10% 16% 7%	1865
March	1st to 10th	Night	53% 3 11% 20% 12% 1	2052
	11th to 20th	Night	52% 2 11% 20% 13% 2	1980
	21st to end	Night	49% 3 9% 21% 15% 3	2178
April	1st to 10th	Night	52% 3 8% 23% 11% 2	1893
	11th to 20th	Night	46% 3 6% 24% 19% 2	1597
	21st to end	Night	52% 3 8% 18% 16% 2	1620
May	1st to 10th	Night	46% 4 9% 22% 16% 3	1620
	11th to 20th	Night	43% 2 7% 24% 20% 3	1496
	21st to end	Night	36% 4 14% 25% 16% 4	1551
June	1st to 10th	Night	43% 4 8% 23% 19% 3	1270
	11th to 20th	Night	36% 3 11% 30% 19% 2	1260
	21st to end	Night	41% 3 12% 27% 14% 2	1260
July	1st to 10th	Night	28% 3 12% 31% 22% 4	1225
	11th to 20th	Night	35% 5% 10% 31% 17% 2	1255
	21st to end	Night	34% 5% 14% 29% 18% 1	1646
August	1st to 10th	Night	32% 4 18% 28% 15% 2	1600
	11th to 20th	Night	34% 4 17% 28% 16% 1	1598
	21st to end	Night	38% 4 16% 27% 13% 2	1782
September	1st to 10th	Night	35% 4 14% 29% 16% 1	1812
	11th to 20th	Night	38% 4 15% 32% 12%	1980
	21st to end	Night	48% 3 14% 26% 8%	1980
October	1st to 10th	Night	53% 3 11% 23% 11%	2128
	11th to 20th	Night	63% 4 11% 17% 4	2160
	21st to end	Night	68% 3 10% 13% 5%	2458
November	1st to 10th	Night	61% 3 11% 20% 5%	2446
	11th to 20th	Night	67% 3 13% 12% 3 1	2660
	21st to end	Night	75% 3 12% 10% 1	2660
December	1st to 10th	Night	81% 3 8% 6% 1	2660
	11th to 20th	Night	79% 3 11% 7% 1	3448
	21st to end	Night	85% 2 8% 4 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	20% 26% 34% 14% 5% 2	182
	11th to 20th	Day	24% 20% 34% 17% 6%	270
	21st to end	Day	27% 14% 36% 18% 6%	297
February	1st to 10th	Day	25% 27% 30% 15% 2	270
	11th to 20th	Day	21% 26% 36% 16% 1	270
	21st to end	Day	27% 30% 35% 8%	210
March	1st to 10th	Day	22% 18% 36% 19% 5% 1	348
	11th to 20th	Day	21% 17% 35% 20% 5% 1	420
	21st to end	Day	26% 12% 31% 24% 5% 2	462
April	1st to 10th	Day	23% 13% 35% 20% 9% 1	420
	11th to 20th	Day	26% 14% 28% 16% 10% 5%	412
	21st to end	Day	26% 10% 35% 19% 8% 2	420
May	1st to 10th	Day	21% 9% 35% 22% 11% 2	423
	11th to 20th	Day	17% 10% 28% 28% 13% 4	447
	21st to end	Day	14% 6% 30% 29% 16% 5%	485
June	1st to 10th	Day	12% 6% 32% 33% 14% 2	616
	11th to 20th	Day	12% 8% 31% 33% 13% 3	630
	21st to end	Day	16% 6% 28% 34% 13% 3	630
July	1st to 10th	Day	9% 5% 25% 34% 24% 3	621
	11th to 20th	Day	13% 5% 26% 32% 17% 6%	618
	21st to end	Day	10% 5% 28% 34% 18% 5%	514
August	1st to 10th	Day	15% 4 20% 32% 22% 7%	446
	11th to 20th	Day	11% 5% 17% 38% 19% 9%	439
	21st to end	Day	13% 10% 26% 26% 19% 5%	495
September	1st to 10th	Day	15% 10% 23% 26% 19% 7%	450
	11th to 20th	Day	12% 7% 27% 26% 22% 6%	450
	21st to end	Day	18% 13% 22% 26% 16% 4	450
October	1st to 10th	Day	24% 15% 23% 22% 13% 3	450
	11th to 20th	Day	24% 22% 30% 19% 5% 1	450
	21st to end	Day	30% 20% 28% 18% 3 1	410
November	1st to 10th	Day	26% 22% 32% 16% 4	250
	11th to 20th	Day	21% 27% 32% 16% 4 1	180
	21st to end	Day	27% 26% 32% 13% 2	180
December	1st to 10th	Day	27% 25% 31% 13% 4	180
	11th to 20th	Day	30% 24% 32% 12% 3	180
	21st to end	Day	31% 27% 34% 5% 2 1	198
January	1st to 10th	Night	24% 20% 32% 19% 5% 1	950
	11th to 20th	Night	27% 21% 27% 19% 6% 1	946
	21st to end	Night	21% 15% 30% 25% 8% 1	836
February	1st to 10th	Night	22% 21% 32% 20% 5%	760
	11th to 20th	Night	19% 17% 35% 21% 8%	743
	21st to end	Night	22% 18% 34% 23% 4	611
March	1st to 10th	Night	18% 16% 33% 25% 8% 1	720
	11th to 20th	Night	18% 18% 33% 22% 8% 1	720
	21st to end	Night	19% 12% 28% 29% 11% 1	792
April	1st to 10th	Night	25% 13% 29% 27% 6% 1	714
	11th to 20th	Night	21% 13% 27% 25% 13% 2	533
	21st to end	Night	25% 10% 24% 27% 14% 1	540
May	1st to 10th	Night	18% 5% 25% 34% 16% 2	540
	11th to 20th	Night	17% 6% 22% 34% 20% 2	434
	21st to end	Night	14% 3 24% 37% 19% 3	389
June	1st to 10th	Night	16% 4 28% 35% 14% 2	360
	11th to 20th	Night	13% 5% 23% 39% 19% 1	360
	21st to end	Night	12% 5% 22% 36% 24% 1	360
July	1st to 10th	Night	9% 4 14% 50% 21% 2	350
	11th to 20th	Night	10% 4 22% 35% 26% 4	385
	21st to end	Night	9% 4 18% 43% 24% 2	591
August	1st to 10th	Night	10% 3 19% 38% 26% 4	537
	11th to 20th	Night	10% 6% 14% 32% 30% 7%	534
	21st to end	Night	14% 5% 23% 30% 25% 4	594
September	1st to 10th	Night	12% 6% 21% 33% 22% 7%	706
	11th to 20th	Night	13% 7% 21% 33% 21% 5%	720
	21st to end	Night	19% 9% 21% 26% 19% 6%	720
October	1st to 10th	Night	24% 9% 25% 24% 17% 2	720
	11th to 20th	Night	29% 15% 24% 22% 9% 2	720
	21st to end	Night	34% 12% 27% 22% 4 1	792
November	1st to 10th	Night	28% 15% 25% 23% 8% 1	740
	11th to 20th	Night	26% 21% 26% 19% 8% 1	760
	21st to end	Night	32% 18% 27% 18% 4	760
December	1st to 10th	Night	32% 21% 28% 13% 6%	760
	11th to 20th	Night	28% 21% 32% 14% 4	873
	21st to end	Night	34% 17% 29% 16% 4	1045

Page generated at 2024-02-22 06:05:41. Version ac07

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