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 2024-10-24.

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	14% 11% 4 9% 5% 4 4 4 5% 6% 33%	101386
	Night	15% 13% 5% 11% 6% 5% 4 3 5% 6% 28%	97413
Transparency	Day	27% 47% 6% 12% 6% 1	101143
	Night	31% 47% 5% 10% 5%	97276
Seeing	Day	19% 13% 29% 25% 12% 3	15183
	Night	21% 13% 26% 26% 12% 2	24373

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% 22% 15% 16% 9% 4 4 3 3 3 6%	2212
	11th to 20th	Day	11% 21% 10% 28% 11% 4 4 2 2 2 4	2532
	21st to end	Day	18% 20% 10% 15% 7% 6% 5% 3 4 4 8%	3124
February	1st to 10th	Day	13% 21% 6% 17% 10% 5% 4 2 4 5% 13%	1710
	11th to 20th	Day	11% 16% 8% 13% 10% 6% 5% 4 5% 5% 18%	1663
	21st to end	Day	13% 17% 5% 11% 7% 6% 6% 4 5% 5% 20%	1532
March	1st to 10th	Day	16% 14% 4 9% 5% 4 5% 3 5% 6% 30%	3309
	11th to 20th	Day	10% 16% 6% 13% 6% 5% 4 4 5% 5% 26%	3480
	21st to end	Day	14% 11% 5% 9% 5% 5% 5% 4 5% 6% 31%	3815
April	1st to 10th	Day	19% 12% 4 7% 4 5% 4 3 5% 7% 31%	2199
	11th to 20th	Day	18% 10% 2 7% 4 3 4 3 4 5% 38%	2442
	21st to end	Day	19% 9% 3 6% 4 4 4 3 6% 7% 36%	2470
May	1st to 10th	Day	15% 8% 3 6% 4 3 4 4 5% 7% 41%	4108
	11th to 20th	Day	12% 8% 2 6% 4 4 4 3 6% 8% 44%	4260
	21st to end	Day	14% 6% 2 5% 4 3 4 3 5% 7% 47%	4837
June	1st to 10th	Day	13% 6% 2 6% 4 5% 4 4 7% 7% 40%	2836
	11th to 20th	Day	10% 6% 2 6% 5% 4 5% 4 6% 8% 44%	2850
	21st to end	Day	14% 7% 3 6% 4 3 5% 4 6% 8% 41%	2850
July	1st to 10th	Day	13% 7% 3 7% 5% 4 5% 4 6% 7% 40%	4760
	11th to 20th	Day	10% 5% 2 5% 3 3 4 3 6% 8% 51%	4678
	21st to end	Day	8% 5% 2 5% 3 3 4 3 5% 8% 52%	4506
August	1st to 10th	Day	10% 6% 2 5% 3 4 4 4 7% 9% 45%	4104
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 6% 8% 42%	4044
	21st to end	Day	9% 6% 2 5% 4 4 5% 4 6% 8% 45%	4514
September	1st to 10th	Day	12% 7% 3 7% 5% 4 4 3 6% 7% 43%	2248
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 4 6% 7% 46%	2090
	21st to end	Day	16% 7% 3 8% 4 4 4 4 6% 6% 37%	2090
October	1st to 10th	Day	18% 10% 3 7% 5% 4 4 3 5% 7% 34%	1932
	11th to 20th	Day	23% 14% 4 9% 6% 5% 3 3 5% 6% 23%	1900
	21st to end	Day	27% 15% 4 9% 4 5% 4 3 4 5% 18%	1925
November	1st to 10th	Day	17% 16% 5% 10% 7% 5% 4 4 5% 6% 21%	1630
	11th to 20th	Day	18% 17% 5% 10% 7% 6% 5% 4 5% 6% 17%	1520
	21st to end	Day	20% 25% 6% 11% 6% 5% 4 4 4 5% 10%	1520
December	1st to 10th	Day	15% 29% 8% 17% 7% 4 4 3 3 3 7%	1520
	11th to 20th	Day	18% 25% 6% 16% 7% 4 4 3 3 5% 9%	1745
	21st to end	Day	27% 22% 7% 17% 6% 3 3 3 3 3 5%	2431
January	1st to 10th	Night	16% 23% 10% 19% 9% 4 4 3 3 3 7%	4739
	11th to 20th	Night	14% 17% 10% 25% 10% 5% 4 3 3 3 6%	4436
	21st to end	Night	16% 20% 9% 16% 8% 6% 4 4 4 4 10%	4532
February	1st to 10th	Night	11% 20% 7% 17% 9% 5% 4 3 4 5% 14%	2470
	11th to 20th	Night	12% 17% 6% 14% 8% 6% 4 3 5% 5% 19%	2403
	21st to end	Night	14% 15% 6% 11% 7% 4 6% 3 5% 6% 22%	1918
March	1st to 10th	Night	12% 11% 3 9% 6% 5% 4 3 5% 6% 36%	3517
	11th to 20th	Night	10% 13% 4 10% 5% 4 4 3 6% 6% 35%	3479
	21st to end	Night	12% 9% 5% 10% 6% 5% 5% 3 5% 6% 33%	3817
April	1st to 10th	Night	20% 11% 4 7% 4 4 4 3 4 6% 32%	1997
	11th to 20th	Night	18% 9% 2 7% 3 4 4 4 6% 7% 36%	1687
	21st to end	Night	19% 10% 3 8% 5% 4 4 4 5% 6% 33%	1710
May	1st to 10th	Night	14% 7% 3 7% 5% 5% 5% 4 5% 7% 38%	2833
	11th to 20th	Night	12% 7% 3 7% 6% 4 4 4 6% 7% 41%	2631
	21st to end	Night	11% 5% 3 7% 4 4 4 4 6% 7% 44%	2738
June	1st to 10th	Night	12% 9% 2 7% 5% 5% 5% 3 5% 7% 39%	1340
	11th to 20th	Night	9% 6% 2 5% 5% 3 6% 5% 6% 10% 43%	1330
	21st to end	Night	11% 8% 2 7% 4 4 5% 4 6% 8% 40%	1330
July	1st to 10th	Night	10% 8% 3 6% 4 3 4 3 5% 7% 46%	2210
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 5% 7% 50%	2289
	21st to end	Night	7% 6% 2 5% 4 4 4 4 6% 8% 50%	3046
August	1st to 10th	Night	10% 8% 2 6% 4 4 4 4 6% 8% 44%	2825
	11th to 20th	Night	12% 7% 3 7% 5% 4 5% 4 5% 7% 41%	2785
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 8% 47%	3124
September	1st to 10th	Night	10% 6% 2 5% 5% 4 4 4 6% 8% 47%	1914
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 3 5% 7% 48%	2090
	21st to end	Night	16% 7% 3 8% 4 4 4 4 5% 6% 37%	2090
October	1st to 10th	Night	18% 8% 3 9% 5% 5% 5% 3 5% 6% 34%	2247
	11th to 20th	Night	23% 11% 4 10% 5% 5% 4 4 5% 6% 23%	2280
	21st to end	Night	25% 14% 4 9% 5% 5% 4 4 5% 4 19%	2495
November	1st to 10th	Night	18% 15% 4 9% 6% 5% 5% 4 5% 6% 24%	2446
	11th to 20th	Night	17% 18% 5% 12% 7% 4 5% 3 5% 6% 17%	2660
	21st to end	Night	22% 22% 5% 10% 6% 5% 4 3 4 5% 12%	2660
December	1st to 10th	Night	19% 27% 7% 15% 7% 4 4 3 4 4 7%	2660
	11th to 20th	Night	16% 24% 6% 16% 7% 5% 5% 3 4 4 10%	3449
	21st to end	Night	23% 22% 9% 17% 6% 4 3 2 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	58% 36% 3 4	2213
	11th to 20th	Day	60% 35% 1 2 1	2532
	21st to end	Day	52% 39% 5% 3 1	3124
February	1st to 10th	Day	27% 64% 2 6% 1	1710
	11th to 20th	Day	23% 63% 4 6% 4	1672
	21st to end	Day	23% 64% 3 7% 3	1532
March	1st to 10th	Day	36% 39% 9% 9% 6%	3312
	11th to 20th	Day	41% 39% 5% 12% 3	3480
	21st to end	Day	34% 39% 7% 11% 8% 1	3815
April	1st to 10th	Day	21% 64% 3 8% 4	2199
	11th to 20th	Day	19% 64% 2 10% 5% 1	2442
	21st to end	Day	17% 64% 5% 9% 5% 1	2470
May	1st to 10th	Day	27% 39% 6% 14% 13% 1	4120
	11th to 20th	Day	24% 38% 11% 20% 6% 1	4264
	21st to end	Day	25% 38% 7% 12% 14% 3	4837
June	1st to 10th	Day	15% 65% 3 10% 7% 1	2836
	11th to 20th	Day	16% 65% 4 9% 6% 1	2850
	21st to end	Day	15% 63% 4 10% 7% 1	2850
July	1st to 10th	Day	30% 38% 10% 14% 8% 1	4686
	11th to 20th	Day	18% 36% 10% 26% 9%	4597
	21st to end	Day	18% 36% 7% 25% 14% 1	4363
August	1st to 10th	Day	20% 38% 10% 20% 10% 1	4091
	11th to 20th	Day	28% 38% 11% 16% 6%	4083
	21st to end	Day	20% 39% 10% 24% 7%	4514
September	1st to 10th	Day	17% 60% 7% 11% 5%	2248
	11th to 20th	Day	13% 59% 4 16% 7%	2090
	21st to end	Day	17% 59% 7% 12% 4	2090
October	1st to 10th	Day	21% 59% 4 10% 5%	1932
	11th to 20th	Day	25% 59% 5% 9% 2	1900
	21st to end	Day	27% 61% 3 7% 2	1925
November	1st to 10th	Day	31% 57% 4 6% 2	1630
	11th to 20th	Day	28% 59% 5% 6% 1	1520
	21st to end	Day	30% 59% 5% 4 1	1520
December	1st to 10th	Day	34% 59% 3 3 1	1520
	11th to 20th	Day	43% 48% 2 7% 1	1745
	21st to end	Day	56% 36% 5% 3	2431
January	1st to 10th	Night	56% 35% 5% 4	4739
	11th to 20th	Night	58% 36% 3 3 1	4436
	21st to end	Night	50% 38% 5% 5% 1	4532
February	1st to 10th	Night	26% 64% 2 6% 2	2470
	11th to 20th	Night	20% 63% 3 10% 4	2405
	21st to end	Night	22% 64% 4 5% 5%	1918
March	1st to 10th	Night	30% 39% 10% 13% 8%	3527
	11th to 20th	Night	30% 38% 8% 16% 6% 1	3480
	21st to end	Night	34% 38% 4 17% 6% 1	3817
April	1st to 10th	Night	24% 64% 2 7% 4	1997
	11th to 20th	Night	18% 65% 2 8% 6% 1	1687
	21st to end	Night	20% 64% 4 6% 5% 1	1710
May	1st to 10th	Night	28% 39% 5% 14% 13% 1	2840
	11th to 20th	Night	28% 38% 6% 16% 11% 1	2632
	21st to end	Night	27% 38% 6% 16% 11% 2	2739
June	1st to 10th	Night	13% 64% 2 10% 9% 1	1340
	11th to 20th	Night	12% 64% 5% 12% 7% 1	1330
	21st to end	Night	14% 63% 3 12% 7% 1	1330
July	1st to 10th	Night	26% 37% 9% 14% 10% 4	2175
	11th to 20th	Night	22% 36% 6% 27% 9%	2247
	21st to end	Night	22% 35% 7% 15% 20% 1	2949
August	1st to 10th	Night	23% 37% 9% 19% 11% 1	2814
	11th to 20th	Night	30% 39% 11% 13% 7%	2812
	21st to end	Night	22% 38% 8% 24% 9%	3124
September	1st to 10th	Night	13% 60% 7% 14% 6%	1914
	11th to 20th	Night	14% 59% 4 13% 9%	2090
	21st to end	Night	19% 59% 6% 10% 6%	2090
October	1st to 10th	Night	22% 59% 4 10% 5%	2247
	11th to 20th	Night	24% 59% 5% 9% 3	2280
	21st to end	Night	27% 60% 4 7% 2	2495
November	1st to 10th	Night	29% 58% 3 7% 2	2446
	11th to 20th	Night	27% 59% 6% 6% 2	2660
	21st to end	Night	32% 59% 4 4 2	2660
December	1st to 10th	Night	32% 59% 4 5% 1	2660
	11th to 20th	Night	42% 48% 5% 4 1	3448
	21st to end	Night	55% 35% 6% 3 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% 31% 33% 9%	225
March	1st to 10th	Day	22% 19% 35% 19% 5% 1	384
	11th to 20th	Day	21% 18% 34% 20% 5% 1	460
	21st to end	Day	25% 14% 32% 23% 5% 1	506
April	1st to 10th	Day	23% 14% 35% 19% 8% 1	460
	11th to 20th	Day	28% 16% 27% 15% 9% 5%	452
	21st to end	Day	27% 12% 34% 18% 8% 2	460
May	1st to 10th	Day	21% 10% 34% 23% 10% 2	463
	11th to 20th	Day	16% 10% 29% 29% 13% 4	487
	21st to end	Day	14% 7% 30% 30% 15% 5%	529
June	1st to 10th	Day	13% 7% 31% 33% 13% 2	666
	11th to 20th	Day	11% 8% 31% 34% 13% 3	680
	21st to end	Day	17% 6% 28% 33% 12% 3	680
July	1st to 10th	Day	9% 6% 27% 33% 22% 3	671
	11th to 20th	Day	12% 5% 26% 33% 17% 6%	668
	21st to end	Day	9% 6% 27% 34% 18% 5%	559
August	1st to 10th	Day	13% 5% 22% 32% 21% 6%	486
	11th to 20th	Day	12% 5% 18% 36% 19% 9%	479
	21st to end	Day	12% 9% 27% 27% 19% 5%	539
September	1st to 10th	Day	16% 10% 22% 27% 18% 6%	490
	11th to 20th	Day	11% 7% 25% 25% 24% 8%	490
	21st to end	Day	18% 12% 22% 27% 17% 4	490
October	1st to 10th	Day	22% 16% 24% 22% 12% 3	490
	11th to 20th	Day	22% 22% 30% 20% 6% 1	490
	21st to end	Day	30% 20% 28% 18% 3 1	422
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% 35% 21% 4	628
March	1st to 10th	Night	17% 15% 34% 25% 7% 1	760
	11th to 20th	Night	18% 18% 33% 22% 8% 1	760
	21st to end	Night	19% 12% 29% 29% 11%	836
April	1st to 10th	Night	25% 13% 29% 26% 6% 1	753
	11th to 20th	Night	22% 13% 27% 24% 12% 2	563
	21st to end	Night	25% 10% 24% 26% 14% 1	570
May	1st to 10th	Night	17% 5% 25% 34% 16% 2	570
	11th to 20th	Night	16% 6% 22% 35% 19% 2	458
	21st to end	Night	15% 3 24% 37% 18% 2	411
June	1st to 10th	Night	17% 6% 27% 35% 14% 2	380
	11th to 20th	Night	12% 6% 23% 40% 19% 1	380
	21st to end	Night	13% 5% 22% 36% 23% 1	380
July	1st to 10th	Night	9% 4 14% 50% 21% 2	370
	11th to 20th	Night	10% 3 22% 36% 25% 4	408
	21st to end	Night	9% 4 17% 42% 25% 3	624
August	1st to 10th	Night	11% 3 18% 38% 26% 3	567
	11th to 20th	Night	11% 6% 15% 31% 30% 7%	564
	21st to end	Night	14% 4 22% 30% 26% 4	627
September	1st to 10th	Night	12% 7% 21% 32% 21% 6%	746
	11th to 20th	Night	13% 6% 19% 31% 23% 7%	760
	21st to end	Night	19% 9% 20% 27% 19% 6%	760
October	1st to 10th	Night	23% 10% 25% 24% 17% 2	760
	11th to 20th	Night	28% 15% 23% 23% 9% 1	760
	21st to end	Night	34% 12% 27% 22% 4 1	805
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 2024-10-21 02:20:06. Version ac07

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