Athens
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Athens clear sky chart from 2005-11-06 to 2025-07-21.

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% 10% 3 8% 5% 4 5% 4 5% 7% 34%	120429
	Night	16% 10% 4 8% 5% 4 4 3 5% 6% 35%	118704
Transparency	Day	48% 5% 10% 22% 13% 2	124143
	Night	48% 5% 10% 22% 14% 2	123127
Seeing	Day	22% 13% 27% 21% 12% 5%	15868
	Night	21% 10% 25% 27% 15% 2	25952

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% 22% 7% 12% 7% 3 3 3 4 5% 19%	4056
	11th to 20th	Day	14% 20% 8% 12% 6% 5% 4 2 3 4 23%	4060
	21st to end	Day	20% 16% 6% 10% 7% 5% 4 3 3 4 22%	4466
February	1st to 10th	Day	22% 13% 5% 8% 5% 3 4 3 4 5% 28%	1800
	11th to 20th	Day	18% 14% 4 11% 5% 3 4 4 5% 5% 26%	1890
	21st to end	Day	19% 13% 4 9% 4 3 3 4 4 5% 31%	1650
March	1st to 10th	Day	18% 15% 4 8% 4 4 4 3 4 5% 32%	4797
	11th to 20th	Day	12% 7% 3 6% 4 4 5% 4 5% 7% 43%	4980
	21st to end	Day	18% 8% 3 8% 5% 4 5% 3 5% 7% 33%	5465
April	1st to 10th	Day	16% 11% 3 8% 5% 4 5% 4 6% 6% 33%	2200
	11th to 20th	Day	16% 9% 3 7% 4 4 5% 3 5% 6% 38%	2526
	21st to end	Day	18% 9% 3 6% 5% 5% 4 4 5% 7% 35%	2600
May	1st to 10th	Day	19% 10% 3 8% 5% 5% 5% 4 7% 8% 27%	5862
	11th to 20th	Day	19% 9% 3 8% 5% 5% 4 4 5% 8% 31%	5861
	21st to end	Day	15% 7% 2 7% 5% 5% 5% 5% 6% 9% 34%	6433
June	1st to 10th	Day	12% 6% 3 5% 5% 4 6% 4 8% 9% 39%	2600
	11th to 20th	Day	10% 6% 2 8% 6% 6% 5% 4 7% 9% 37%	2600
	21st to end	Day	11% 5% 2 6% 4 6% 5% 5% 7% 10% 37%	2600
July	1st to 10th	Day	9% 5% 3 7% 5% 6% 5% 4 6% 8% 41%	4250
	11th to 20th	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	4250
	21st to end	Day	13% 8% 3 8% 5% 6% 6% 5% 6% 8% 32%	4466
August	1st to 10th	Day	9% 6% 3 6% 6% 5% 6% 6% 8% 10% 36%	4104
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 10% 40%	4044
	21st to end	Day	6% 3 2 6% 4 5% 5% 4 6% 9% 50%	4450
September	1st to 10th	Day	14% 5% 2 5% 4 3 4 3 5% 8% 47%	2100
	11th to 20th	Day	10% 6% 1 6% 4 3 4 3 6% 7% 48%	2090
	21st to end	Day	19% 8% 3 5% 3 3 5% 3 5% 6% 41%	2090
October	1st to 10th	Day	13% 5% 2 6% 4 4 4 3 5% 8% 46%	2003
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 5% 6% 43%	1900
	21st to end	Day	20% 8% 3 6% 4 3 3 3 4 5% 40%	2090
November	1st to 10th	Day	12% 6% 2 5% 5% 3 3 3 5% 6% 50%	1777
	11th to 20th	Day	17% 14% 3 6% 4 3 4 3 5% 6% 35%	1800
	21st to end	Day	18% 13% 3 7% 5% 4 5% 4 4 5% 34%	1800
December	1st to 10th	Day	20% 12% 4 12% 5% 5% 4 3 3 5% 27%	2930
	11th to 20th	Day	24% 15% 5% 9% 4 4 4 2 4 6% 23%	3373
	21st to end	Day	20% 18% 5% 11% 6% 5% 5% 3 5% 6% 18%	4466
January	1st to 10th	Night	16% 16% 7% 17% 5% 4 3 3 4 4 19%	5889
	11th to 20th	Night	17% 17% 6% 13% 7% 5% 5% 3 4 4 21%	5900
	21st to end	Night	21% 12% 5% 10% 6% 3 4 3 3 4 29%	6490
February	1st to 10th	Night	20% 13% 5% 9% 5% 4 4 3 5% 5% 29%	2600
	11th to 20th	Night	21% 14% 4 8% 5% 5% 4 4 4 5% 27%	2392
	21st to end	Night	20% 15% 4 8% 4 3 3 3 5% 4 30%	1980
March	1st to 10th	Night	19% 13% 3 6% 4 4 3 3 4 5% 36%	5055
	11th to 20th	Night	12% 9% 2 6% 4 3 4 3 5% 7% 44%	4980
	21st to end	Night	18% 10% 3 8% 5% 4 5% 4 4 5% 35%	5467
April	1st to 10th	Night	18% 11% 3 6% 5% 4 4 4 5% 6% 36%	2200
	11th to 20th	Night	15% 8% 2 5% 5% 4 4 4 6% 8% 39%	1838
	21st to end	Night	16% 8% 3 7% 4 4 4 3 5% 7% 39%	1800
May	1st to 10th	Night	23% 10% 3 7% 5% 5% 4 3 5% 7% 29%	4033
	11th to 20th	Night	16% 8% 3 6% 4 4 4 4 6% 9% 36%	4032
	21st to end	Night	15% 7% 3 7% 5% 4 4 4 6% 9% 36%	4421
June	1st to 10th	Night	10% 5% 2 5% 5% 4 5% 5% 6% 9% 45%	1800
	11th to 20th	Night	9% 5% 2 5% 5% 5% 4 4 7% 11% 43%	1800
	21st to end	Night	10% 5% 2 4 4 5% 4 5% 8% 11% 44%	1800
July	1st to 10th	Night	10% 7% 3 6% 4 4 4 4 7% 8% 44%	2930
	11th to 20th	Night	8% 5% 2 7% 5% 5% 5% 4 6% 9% 44%	2930
	21st to end	Night	10% 8% 3 8% 6% 5% 5% 4 7% 7% 39%	3087
August	1st to 10th	Night	7% 7% 3 8% 5% 5% 5% 4 6% 9% 40%	2825
	11th to 20th	Night	10% 7% 3 7% 5% 5% 4 3 5% 7% 44%	2785
	21st to end	Night	6% 3 2 5% 4 6% 4 4 6% 10% 50%	3172
September	1st to 10th	Night	12% 3 2 5% 3 4 4 4 4 6% 54%	2076
	11th to 20th	Night	9% 4 2 5% 4 4 4 3 4 6% 55%	2090
	21st to end	Night	16% 7% 3 6% 2 3 4 3 5% 6% 44%	2090
October	1st to 10th	Night	11% 5% 2 5% 4 3 3 4 5% 8% 50%	2175
	11th to 20th	Night	14% 7% 2 5% 4 3 4 3 5% 6% 46%	2280
	21st to end	Night	20% 7% 2 5% 4 3 4 3 4 6% 42%	2508
November	1st to 10th	Night	13% 7% 2 5% 4 3 4 3 4 5% 50%	2517
	11th to 20th	Night	18% 11% 3 6% 5% 4 4 3 5% 6% 36%	2600
	21st to end	Night	18% 13% 3 6% 5% 4 4 3 5% 5% 34%	2600
December	1st to 10th	Night	18% 12% 5% 11% 4 4 4 3 4 5% 29%	4250
	11th to 20th	Night	18% 16% 7% 10% 5% 4 4 3 3 5% 25%	4822
	21st to end	Night	20% 17% 5% 10% 6% 5% 4 3 5% 6% 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	68% 3 10% 14% 5%	4057
	11th to 20th	Day	67% 3 7% 12% 10% 1	4060
	21st to end	Day	67% 3 8% 15% 7% 1	4466
February	1st to 10th	Day	58% 3 11% 19% 8% 1	1800
	11th to 20th	Day	60% 4 9% 17% 10%	1900
	21st to end	Day	56% 3 11% 20% 9% 1	1650
March	1st to 10th	Day	55% 3 6% 23% 9% 3	4797
	11th to 20th	Day	40% 4 9% 29% 15% 3	4980
	21st to end	Day	50% 4 9% 22% 12% 3	5465
April	1st to 10th	Day	50% 5% 10% 21% 12% 3	2200
	11th to 20th	Day	46% 4 10% 20% 16% 4	2526
	21st to end	Day	48% 5% 11% 21% 13% 2	2600
May	1st to 10th	Day	53% 6% 11% 18% 10% 2	5897
	11th to 20th	Day	52% 5% 10% 21% 11% 1	5865
	21st to end	Day	44% 7% 12% 21% 14% 3	6447
June	1st to 10th	Day	40% 6% 13% 23% 16% 2	2600
	11th to 20th	Day	41% 8% 13% 21% 15% 2	2600
	21st to end	Day	40% 8% 14% 22% 15% 2	2600
July	1st to 10th	Day	40% 7% 11% 24% 16% 2	4185
	11th to 20th	Day	36% 7% 11% 31% 14% 1	4181
	21st to end	Day	47% 6% 11% 17% 16% 3	4324
August	1st to 10th	Day	38% 9% 13% 28% 11% 1	4091
	11th to 20th	Day	37% 7% 10% 31% 15% 1	4083
	21st to end	Day	29% 6% 14% 30% 18% 2	4450
September	1st to 10th	Day	36% 5% 10% 21% 22% 6%	2100
	11th to 20th	Day	34% 5% 11% 26% 22% 3	2090
	21st to end	Day	44% 4 8% 24% 19% 1	2090
October	1st to 10th	Day	25% 4 8% 31% 30% 2	3328
	11th to 20th	Day	32% 4 11% 28% 20% 4	3140
	21st to end	Day	34% 3 12% 29% 21% 2	3428
November	1st to 10th	Day	35% 3 10% 30% 19% 3	1777
	11th to 20th	Day	50% 3 7% 21% 16% 2	1800
	21st to end	Day	52% 4 9% 22% 13% 1	1800
December	1st to 10th	Day	61% 3 10% 21% 5%	2930
	11th to 20th	Day	64% 3 9% 18% 6%	3370
	21st to end	Day	68% 5% 10% 13% 5%	4466
January	1st to 10th	Night	69% 3 8% 15% 5%	5889
	11th to 20th	Night	67% 3 9% 13% 7% 2	5900
	21st to end	Night	60% 2 10% 19% 8% 2	6490
February	1st to 10th	Night	58% 4 10% 19% 9% 1	2600
	11th to 20th	Night	59% 3 9% 17% 11% 1	2393
	21st to end	Night	58% 4 9% 19% 8% 3	1980
March	1st to 10th	Night	50% 4 6% 26% 12% 2	5055
	11th to 20th	Night	39% 4 9% 30% 17% 1	4980
	21st to end	Night	51% 4 7% 23% 13% 2	5467
April	1st to 10th	Night	48% 4 9% 21% 15% 3	2200
	11th to 20th	Night	42% 5% 11% 20% 17% 6%	1838
	21st to end	Night	44% 5% 10% 23% 16% 2	1800
May	1st to 10th	Night	56% 6% 11% 15% 9% 4	4060
	11th to 20th	Night	44% 8% 12% 23% 13% 1	4033
	21st to end	Night	43% 7% 13% 24% 10% 3	4429
June	1st to 10th	Night	35% 7% 10% 26% 20% 3	1800
	11th to 20th	Night	34% 8% 15% 22% 19% 2	1800
	21st to end	Night	32% 8% 13% 24% 20% 2	1800
July	1st to 10th	Night	37% 6% 10% 24% 19% 4	2885
	11th to 20th	Night	36% 7% 13% 28% 15% 2	2876
	21st to end	Night	42% 8% 11% 21% 14% 5%	2988
August	1st to 10th	Night	39% 8% 14% 27% 11% 1	2814
	11th to 20th	Night	39% 6% 10% 23% 22% 1	2812
	21st to end	Night	29% 7% 12% 30% 20% 3	3172
September	1st to 10th	Night	32% 4 11% 24% 21% 7%	2076
	11th to 20th	Night	31% 4 10% 25% 27% 3	2090
	21st to end	Night	41% 4 9% 21% 23% 1	2090
October	1st to 10th	Night	28% 4 7% 28% 29% 4	3630
	11th to 20th	Night	30% 4 9% 26% 24% 7%	3779
	21st to end	Night	32% 3 7% 27% 26% 5%	4120
November	1st to 10th	Night	38% 3 10% 25% 20% 4	2517
	11th to 20th	Night	49% 3 8% 21% 16% 3	2600
	21st to end	Night	52% 4 10% 22% 11% 1	2600
December	1st to 10th	Night	58% 4 12% 21% 5%	4250
	11th to 20th	Night	62% 4 12% 17% 5%	4824
	21st to end	Night	66% 4 10% 15% 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	31% 22% 33% 11% 3 1	300
	11th to 20th	Day	38% 23% 32% 6% 1	300
	21st to end	Day	31% 27% 30% 10% 2	330
February	1st to 10th	Day	34% 23% 30% 11% 2	300
	11th to 20th	Day	41% 25% 28% 3 2 1	300
	21st to end	Day	32% 23% 37% 8%	249
March	1st to 10th	Day	29% 22% 28% 17% 4	435
	11th to 20th	Day	28% 21% 30% 15% 5% 1	500
	21st to end	Day	33% 17% 31% 14% 4	550
April	1st to 10th	Day	26% 21% 31% 14% 8% 1	500
	11th to 20th	Day	26% 16% 31% 18% 6% 3	492
	21st to end	Day	25% 17% 32% 18% 7% 1	500
May	1st to 10th	Day	27% 17% 30% 15% 8% 3	503
	11th to 20th	Day	22% 11% 29% 23% 11% 4	527
	21st to end	Day	16% 8% 28% 27% 16% 6%	573
June	1st to 10th	Day	15% 10% 24% 28% 18% 5%	530
	11th to 20th	Day	13% 9% 25% 32% 14% 8%	530
	21st to end	Day	12% 9% 27% 28% 18% 6%	530
July	1st to 10th	Day	14% 6% 19% 25% 21% 16%	525
	11th to 20th	Day	10% 6% 22% 31% 22% 10%	524
	21st to end	Day	14% 6% 21% 30% 19% 10%	532
August	1st to 10th	Day	12% 5% 20% 30% 23% 9%	486
	11th to 20th	Day	12% 5% 22% 33% 19% 10%	479
	21st to end	Day	10% 4 20% 31% 23% 12%	539
September	1st to 10th	Day	16% 5% 17% 27% 22% 12%	490
	11th to 20th	Day	10% 4 15% 29% 29% 12%	490
	21st to end	Day	24% 10% 21% 24% 17% 4	490
October	1st to 10th	Day	14% 8% 27% 27% 19% 6%	490
	11th to 20th	Day	18% 12% 30% 23% 14% 3	490
	21st to end	Day	25% 13% 31% 21% 10% 1	539
November	1st to 10th	Day	20% 15% 33% 23% 7% 2	315
	11th to 20th	Day	30% 16% 29% 19% 5% 1	300
	21st to end	Day	25% 21% 35% 15% 4 1	300
December	1st to 10th	Day	30% 18% 34% 13% 3 1	300
	11th to 20th	Day	29% 21% 36% 10% 4 1	300
	21st to end	Day	32% 22% 28% 12% 4	330
January	1st to 10th	Night	28% 18% 32% 18% 4	800
	11th to 20th	Night	33% 17% 29% 19% 3	800
	21st to end	Night	25% 18% 33% 21% 3	880
February	1st to 10th	Night	29% 15% 31% 25% 1	800
	11th to 20th	Night	32% 18% 30% 18% 1	783
	21st to end	Night	31% 16% 32% 20% 2	660
March	1st to 10th	Night	25% 16% 31% 23% 5%	800
	11th to 20th	Night	26% 16% 28% 20% 8% 1	800
	21st to end	Night	27% 16% 30% 21% 6%	880
April	1st to 10th	Night	25% 15% 32% 21% 7%	800
	11th to 20th	Night	19% 14% 33% 25% 9%	641
	21st to end	Night	21% 9% 35% 29% 6%	600
May	1st to 10th	Night	21% 10% 28% 30% 10% 2	600
	11th to 20th	Night	20% 7% 25% 29% 17% 2	591
	21st to end	Night	11% 5% 21% 33% 27% 3	650
June	1st to 10th	Night	13% 2 23% 40% 22% 1	600
	11th to 20th	Night	11% 5% 20% 37% 26% 2	600
	21st to end	Night	12% 3 20% 35% 28% 3	600
July	1st to 10th	Night	12% 3 16% 34% 29% 6%	585
	11th to 20th	Night	8% 4 16% 34% 34% 4	582
	21st to end	Night	12% 3 15% 33% 34% 4	624
August	1st to 10th	Night	8% 2 14% 35% 37% 4	567
	11th to 20th	Night	10% 2 14% 38% 31% 5%	564
	21st to end	Night	10% 2 16% 30% 35% 7%	649
September	1st to 10th	Night	14% 2 15% 34% 29% 6%	760
	11th to 20th	Night	11% 3 15% 34% 32% 6%	760
	21st to end	Night	18% 6% 20% 32% 20% 3	760
October	1st to 10th	Night	14% 4 22% 32% 26% 3	760
	11th to 20th	Night	19% 8% 28% 29% 16% 1	760
	21st to end	Night	24% 10% 25% 29% 11% 1	836
November	1st to 10th	Night	18% 9% 28% 29% 16%	780
	11th to 20th	Night	24% 15% 26% 25% 9% 1	800
	21st to end	Night	26% 11% 27% 29% 7% 1	800
December	1st to 10th	Night	31% 14% 28% 21% 6%	800
	11th to 20th	Night	25% 17% 29% 23% 6%	800
	21st to end	Night	29% 17% 26% 26% 3	880

Page generated at 2025-07-18 01:10:04. Version ac07

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