Rome
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rome clear sky chart from 2005-11-06 to 2025-12-18.

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% 4 5% 4 6% 7% 35%	127014
	Night	15% 10% 3 8% 5% 4 4 3 5% 7% 36%	124032
Transparency	Day	30% 37% 6% 16% 10% 1	130701
	Night	31% 37% 6% 15% 10% 1	128413
Seeing	Day	22% 13% 27% 21% 12% 5%	16288
	Night	20% 12% 25% 27% 15% 2	26361

By Month

Percentage Cloud Cover SE (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	16% 19% 6% 11% 5% 4 3 3 5% 5% 23%	4056
	11th to 20th	Day	14% 16% 8% 14% 5% 4 3 2 3 3 28%	4060
	21st to end	Day	21% 14% 5% 8% 6% 5% 4 3 4 5% 26%	4466
February	1st to 10th	Day	20% 13% 5% 10% 5% 3 4 3 4 4 29%	1850
	11th to 20th	Day	19% 12% 5% 10% 4 5% 4 4 4 5% 29%	1948
	21st to end	Day	20% 14% 4 7% 3 3 3 3 5% 6% 32%	1650
March	1st to 10th	Day	17% 15% 4 8% 4 4 4 3 4 5% 32%	4657
	11th to 20th	Day	13% 7% 3 6% 5% 4 4 4 5% 7% 41%	4980
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 6% 7% 34%	5465
April	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 5% 6% 37%	2261
	11th to 20th	Day	17% 8% 3 6% 4 4 4 4 4 7% 39%	2477
	21st to end	Day	17% 9% 3 7% 5% 5% 5% 3 5% 7% 35%	2600
May	1st to 10th	Day	19% 10% 3 8% 4 5% 5% 4 7% 7% 27%	5862
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 3 5% 7% 30%	5861
	21st to end	Day	15% 7% 3 7% 5% 5% 6% 5% 8% 9% 32%	6433
June	1st to 10th	Day	12% 5% 1 6% 5% 5% 6% 6% 6% 8% 40%	2600
	11th to 20th	Day	10% 5% 2 7% 5% 6% 7% 4 7% 8% 40%	2600
	21st to end	Day	10% 6% 2 6% 6% 5% 5% 5% 8% 9% 40%	2600
July	1st to 10th	Day	10% 6% 2 7% 4 5% 6% 4 6% 9% 41%	5900
	11th to 20th	Day	10% 7% 2 7% 5% 6% 7% 5% 8% 10% 33%	5900
	21st to end	Day	11% 9% 3 8% 6% 6% 6% 5% 8% 9% 29%	6424
August	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 11% 40%	4234
	11th to 20th	Day	9% 6% 3 6% 5% 5% 6% 4 7% 10% 38%	4174
	21st to end	Day	5% 4 1 5% 4 4 4 4 6% 8% 55%	4463
September	1st to 10th	Day	14% 5% 2 5% 3 4 4 4 4 6% 49%	2215
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 7% 50%	2200
	21st to end	Day	18% 6% 2 7% 4 3 4 3 4 6% 43%	2200
October	1st to 10th	Day	12% 5% 1 5% 3 4 4 3 6% 7% 51%	2180
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 4 6% 49%	2000
	21st to end	Day	20% 9% 2 6% 3 3 3 3 4 6% 41%	2144
November	1st to 10th	Day	13% 7% 2 5% 3 4 3 3 5% 6% 50%	1852
	11th to 20th	Day	15% 13% 3 6% 4 3 3 4 4 6% 38%	1890
	21st to end	Day	18% 11% 4 6% 4 4 4 3 4 6% 36%	1890
December	1st to 10th	Day	20% 13% 4 8% 5% 3 3 3 3 4 34%	3020
	11th to 20th	Day	23% 14% 5% 7% 4 5% 4 3 4 5% 26%	3436
	21st to end	Day	20% 18% 5% 11% 5% 4 4 3 4 5% 21%	4466
January	1st to 10th	Night	15% 17% 7% 15% 7% 5% 4 3 4 4 18%	5889
	11th to 20th	Night	18% 16% 6% 12% 7% 4 4 2 4 4 24%	5900
	21st to end	Night	20% 11% 4 8% 5% 5% 4 2 4 4 32%	6490
February	1st to 10th	Night	21% 13% 4 9% 5% 4 3 3 5% 6% 28%	2547
	11th to 20th	Night	21% 13% 3 9% 4 5% 4 3 4 4 29%	2338
	21st to end	Night	22% 14% 4 7% 4 3 3 2 4 5% 29%	1980
March	1st to 10th	Night	18% 13% 2 6% 4 4 4 3 4 5% 37%	5194
	11th to 20th	Night	13% 8% 2 6% 3 3 4 4 6% 8% 43%	4980
	21st to end	Night	15% 10% 4 8% 6% 5% 5% 4 5% 6% 32%	5467
April	1st to 10th	Night	16% 10% 3 6% 5% 4 4 4 6% 7% 37%	2155
	11th to 20th	Night	14% 7% 3 6% 4 4 4 4 7% 6% 41%	1869
	21st to end	Night	16% 8% 3 7% 4 4 4 4 6% 7% 37%	1800
May	1st to 10th	Night	22% 10% 3 7% 4 4 4 4 5% 7% 29%	4033
	11th to 20th	Night	17% 7% 2 7% 5% 4 5% 4 7% 8% 33%	4032
	21st to end	Night	14% 7% 2 7% 4 5% 5% 4 7% 8% 36%	4421
June	1st to 10th	Night	8% 5% 2 5% 5% 5% 5% 5% 7% 8% 47%	1800
	11th to 20th	Night	7% 6% 1 6% 4 4 5% 4 7% 11% 45%	1800
	21st to end	Night	7% 5% 2 5% 4 4 6% 5% 7% 11% 45%	1800
July	1st to 10th	Night	8% 6% 3 7% 4 5% 4 4 6% 9% 44%	4058
	11th to 20th	Night	9% 7% 3 7% 6% 5% 6% 4 7% 10% 37%	4057
	21st to end	Night	9% 8% 3 7% 5% 5% 5% 5% 7% 9% 36%	4427
August	1st to 10th	Night	7% 6% 2 8% 4 5% 5% 4 7% 9% 43%	2915
	11th to 20th	Night	9% 7% 3 7% 4 5% 5% 4 5% 8% 43%	2875
	21st to end	Night	4 3 1 4 3 4 3 4 6% 9% 59%	3418
September	1st to 10th	Night	11% 5% 2 4 3 4 4 4 5% 8% 51%	2165
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 4 6% 54%	2200
	21st to end	Night	13% 6% 2 6% 4 3 4 4 5% 6% 46%	2200
October	1st to 10th	Night	10% 5% 2 5% 3 4 4 3 5% 7% 53%	2219
	11th to 20th	Night	14% 6% 2 5% 3 3 4 4 5% 8% 46%	2400
	21st to end	Night	20% 8% 2 5% 4 3 4 3 4 5% 42%	2693
November	1st to 10th	Night	13% 7% 2 5% 4 3 3 3 5% 6% 48%	2666
	11th to 20th	Night	16% 10% 3 7% 3 4 4 3 4 6% 40%	2730
	21st to end	Night	19% 13% 3 6% 5% 4 3 3 4 5% 35%	2730
December	1st to 10th	Night	18% 12% 4 8% 5% 3 3 2 4 5% 35%	4380
	11th to 20th	Night	19% 13% 7% 9% 4 3 3 2 4 6% 28%	4914
	21st to end	Night	20% 18% 6% 10% 6% 5% 4 3 4 5% 19%	6490

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	50% 25% 6% 13% 6%	4057
	11th to 20th	Day	46% 26% 3 13% 10% 2	4060
	21st to end	Day	46% 28% 4 16% 6% 1	4466
February	1st to 10th	Day	23% 61% 4 7% 5%	1850
	11th to 20th	Day	24% 60% 2 8% 6%	1958
	21st to end	Day	18% 61% 3 10% 7% 1	1650
March	1st to 10th	Day	42% 28% 3 13% 11% 4	4657
	11th to 20th	Day	27% 28% 6% 22% 15% 2	4980
	21st to end	Day	34% 29% 7% 18% 11% 1	5465
April	1st to 10th	Day	22% 61% 4 9% 4	2261
	11th to 20th	Day	18% 62% 4 11% 5% 1	2477
	21st to end	Day	18% 61% 5% 9% 5% 1	2600
May	1st to 10th	Day	41% 29% 8% 14% 8% 1	5897
	11th to 20th	Day	38% 29% 7% 19% 6%	5865
	21st to end	Day	36% 29% 9% 16% 9% 2	6447
June	1st to 10th	Day	16% 62% 5% 8% 9%	2600
	11th to 20th	Day	18% 62% 5% 8% 7%	2600
	21st to end	Day	16% 61% 6% 11% 6% 1	2600
July	1st to 10th	Day	30% 27% 9% 21% 13% 1	5835
	11th to 20th	Day	34% 27% 11% 21% 7%	5831
	21st to end	Day	40% 27% 9% 13% 10% 1	6240
August	1st to 10th	Day	24% 36% 10% 24% 5%	4221
	11th to 20th	Day	24% 36% 7% 22% 10%	4213
	21st to end	Day	15% 36% 11% 22% 16% 1	4462
September	1st to 10th	Day	14% 57% 6% 10% 10% 3	2215
	11th to 20th	Day	14% 56% 5% 13% 11% 1	2200
	21st to end	Day	18% 56% 4 13% 8% 1	2200
October	1st to 10th	Day	13% 35% 3 21% 27% 1	3557
	11th to 20th	Day	15% 35% 5% 21% 23% 2	3240
	21st to end	Day	18% 35% 7% 19% 18% 2	3446
November	1st to 10th	Day	22% 53% 5% 13% 7% 1	1852
	11th to 20th	Day	20% 54% 3 11% 11% 2	1890
	21st to end	Day	26% 53% 5% 12% 4	1890
December	1st to 10th	Day	35% 34% 3 17% 10%	3020
	11th to 20th	Day	45% 31% 4 14% 6% 1	3433
	21st to end	Day	51% 26% 6% 11% 4	4466
January	1st to 10th	Night	55% 26% 5% 10% 5%	5889
	11th to 20th	Night	49% 25% 3 14% 6% 3	5900
	21st to end	Night	41% 27% 4 18% 9% 1	6490
February	1st to 10th	Night	23% 61% 3 7% 5% 1	2547
	11th to 20th	Night	25% 60% 2 8% 5%	2339
	21st to end	Night	22% 61% 3 8% 6% 1	1980
March	1st to 10th	Night	38% 28% 3 21% 8% 2	5194
	11th to 20th	Night	25% 29% 5% 24% 18%	4980
	21st to end	Night	39% 28% 4 17% 11% 1	5467
April	1st to 10th	Night	21% 62% 4 7% 6%	2155
	11th to 20th	Night	17% 62% 3 11% 6% 1	1869
	21st to end	Night	19% 61% 4 9% 7% 1	1800
May	1st to 10th	Night	41% 29% 7% 15% 6% 1	4060
	11th to 20th	Night	35% 30% 11% 19% 5%	4033
	21st to end	Night	34% 29% 11% 16% 8% 2	4429
June	1st to 10th	Night	15% 62% 4 9% 9% 1	1800
	11th to 20th	Night	14% 62% 5% 8% 9% 1	1800
	21st to end	Night	13% 61% 7% 10% 8% 1	1800
July	1st to 10th	Night	27% 29% 9% 19% 15% 2	4015
	11th to 20th	Night	33% 28% 12% 19% 8%	4006
	21st to end	Night	36% 26% 8% 17% 11% 2	4297
August	1st to 10th	Night	26% 36% 10% 22% 5% 1	2904
	11th to 20th	Night	28% 37% 5% 18% 12%	2902
	21st to end	Night	12% 35% 12% 24% 16% 1	3418
September	1st to 10th	Night	12% 57% 6% 12% 10% 3	2165
	11th to 20th	Night	13% 56% 4 11% 13% 1	2200
	21st to end	Night	16% 56% 5% 12% 11%	2200
October	1st to 10th	Night	14% 35% 4 17% 29% 1	3622
	11th to 20th	Night	13% 35% 5% 18% 26% 3	3899
	21st to end	Night	18% 34% 5% 16% 21% 7%	4341
November	1st to 10th	Night	22% 53% 5% 12% 8% 1	2666
	11th to 20th	Night	21% 54% 2 11% 10% 2	2730
	21st to end	Night	27% 53% 4 12% 4	2730
December	1st to 10th	Night	35% 34% 7% 15% 9% 1	4380
	11th to 20th	Night	42% 31% 7% 14% 6%	4916
	21st to end	Night	52% 26% 6% 11% 5%	6490

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	32% 23% 32% 10% 3	300
	11th to 20th	Day	39% 26% 25% 9%	300
	21st to end	Day	34% 27% 28% 10% 1	330
February	1st to 10th	Day	33% 25% 28% 11% 2	300
	11th to 20th	Day	40% 26% 29% 4 2	300
	21st to end	Day	36% 21% 36% 6%	249
March	1st to 10th	Day	36% 22% 28% 12% 3	373
	11th to 20th	Day	29% 23% 31% 12% 5%	500
	21st to end	Day	36% 18% 29% 12% 4	550
April	1st to 10th	Day	31% 18% 27% 16% 7% 1	500
	11th to 20th	Day	26% 19% 30% 16% 6% 2	492
	21st to end	Day	26% 19% 33% 15% 6% 2	500
May	1st to 10th	Day	25% 20% 30% 15% 8% 2	503
	11th to 20th	Day	24% 12% 30% 21% 10% 4	527
	21st to end	Day	19% 10% 26% 25% 13% 7%	573
June	1st to 10th	Day	14% 9% 26% 29% 15% 6%	530
	11th to 20th	Day	12% 7% 28% 30% 16% 7%	530
	21st to end	Day	11% 9% 27% 27% 16% 9%	530
July	1st to 10th	Day	13% 6% 18% 23% 21% 18%	525
	11th to 20th	Day	10% 6% 23% 30% 21% 10%	524
	21st to end	Day	14% 5% 21% 29% 21% 11%	576
August	1st to 10th	Day	12% 5% 20% 30% 21% 12%	526
	11th to 20th	Day	13% 5% 20% 32% 22% 8%	519
	21st to end	Day	9% 5% 17% 32% 25% 11%	583
September	1st to 10th	Day	14% 6% 17% 27% 26% 9%	530
	11th to 20th	Day	11% 4 18% 29% 28% 12%	530
	21st to end	Day	24% 7% 22% 26% 19% 4	530
October	1st to 10th	Day	14% 5% 25% 31% 18% 7%	530
	11th to 20th	Day	18% 13% 33% 21% 12% 4	530
	21st to end	Day	25% 14% 33% 20% 8%	527
November	1st to 10th	Day	22% 14% 38% 19% 7% 2	330
	11th to 20th	Day	32% 17% 30% 15% 4 1	330
	21st to end	Day	31% 19% 33% 14% 2 1	330
December	1st to 10th	Day	31% 21% 33% 11% 5%	330
	11th to 20th	Day	28% 23% 33% 13% 2	321
	21st to end	Day	34% 22% 33% 9% 1	330
January	1st to 10th	Night	30% 19% 31% 16% 4	800
	11th to 20th	Night	34% 20% 29% 16% 2	800
	21st to end	Night	26% 21% 31% 20% 2	880
February	1st to 10th	Night	31% 17% 31% 20% 1	800
	11th to 20th	Night	32% 21% 29% 17% 1	783
	21st to end	Night	33% 20% 30% 16% 1	660
March	1st to 10th	Night	28% 16% 31% 21% 4	800
	11th to 20th	Night	27% 18% 30% 19% 6% 1	800
	21st to end	Night	23% 17% 32% 22% 6%	880
April	1st to 10th	Night	25% 15% 32% 21% 7%	755
	11th to 20th	Night	19% 12% 33% 25% 9% 1	593
	21st to end	Night	18% 12% 37% 25% 8% 1	600
May	1st to 10th	Night	21% 11% 29% 26% 11% 2	600
	11th to 20th	Night	20% 8% 24% 32% 16% 1	591
	21st to end	Night	11% 5% 22% 34% 24% 4	650
June	1st to 10th	Night	8% 5% 22% 42% 21% 2	600
	11th to 20th	Night	9% 3 21% 37% 27% 4	600
	21st to end	Night	8% 5% 22% 35% 27% 4	600
July	1st to 10th	Night	12% 2 15% 28% 33% 9%	585
	11th to 20th	Night	7% 3 14% 39% 33% 5%	582
	21st to end	Night	10% 4 13% 37% 32% 5%	657
August	1st to 10th	Night	8% 3 11% 40% 34% 5%	597
	11th to 20th	Night	9% 3 10% 39% 32% 7%	594
	21st to end	Night	8% 1 13% 35% 36% 7%	660
September	1st to 10th	Night	13% 3 12% 33% 34% 6%	765
	11th to 20th	Night	12% 3 15% 30% 33% 7%	800
	21st to end	Night	15% 7% 21% 34% 22% 2	800
October	1st to 10th	Night	13% 6% 20% 32% 26% 4	800
	11th to 20th	Night	17% 11% 26% 30% 15% 1	800
	21st to end	Night	23% 13% 25% 26% 11% 1	880
November	1st to 10th	Night	18% 12% 25% 28% 15% 1	820
	11th to 20th	Night	24% 15% 29% 23% 8% 1	840
	21st to end	Night	27% 14% 25% 25% 8% 1	840
December	1st to 10th	Night	30% 19% 25% 22% 5%	840
	11th to 20th	Night	26% 17% 30% 21% 5% 1	829
	21st to end	Night	30% 16% 30% 21% 3	880

Page generated at 2025-12-15 01:13:53. Version ac07

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