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 2024-11-04.

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 7% 5% 4 5% 4 6% 7% 35%	101211
	Night	16% 10% 3 7% 5% 4 4 3 5% 7% 36%	97760
Transparency	Day	46% 5% 11% 23% 14% 2	104927
	Night	46% 5% 10% 22% 14% 2	102183
Seeing	Day	21% 13% 27% 22% 13% 5%	14952
	Night	20% 10% 25% 28% 15% 2	25018

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	18% 20% 6% 8% 5% 3 4 3 5% 6% 22%	2836
	11th to 20th	Day	15% 20% 8% 12% 6% 5% 3 3 3 4 21%	2840
	21st to end	Day	25% 20% 7% 9% 5% 4 3 2 3 4 17%	3124
February	1st to 10th	Day	22% 13% 5% 8% 5% 3 4 3 4 5% 28%	1710
	11th to 20th	Day	18% 14% 4 11% 5% 3 4 4 5% 5% 26%	1792
	21st to end	Day	20% 14% 4 8% 4 3 3 4 4 5% 31%	1570
March	1st to 10th	Day	23% 16% 4 8% 4 3 3 3 4 5% 27%	3339
	11th to 20th	Day	14% 8% 3 7% 5% 4 5% 4 5% 6% 40%	3480
	21st to end	Day	19% 9% 3 7% 5% 4 4 3 6% 7% 33%	3815
April	1st to 10th	Day	14% 11% 3 8% 5% 4 5% 4 5% 6% 34%	2090
	11th to 20th	Day	16% 9% 3 7% 4 4 5% 3 5% 6% 38%	2398
	21st to end	Day	18% 9% 3 6% 5% 5% 4 4 5% 7% 35%	2470
May	1st to 10th	Day	20% 11% 3 8% 4 5% 4 4 6% 7% 27%	4082
	11th to 20th	Day	20% 9% 3 7% 5% 4 4 4 5% 7% 33%	4081
	21st to end	Day	10% 6% 2 7% 6% 5% 5% 5% 7% 10% 36%	4476
June	1st to 10th	Day	12% 6% 2 5% 5% 4 6% 4 8% 9% 39%	2470
	11th to 20th	Day	10% 6% 2 7% 6% 6% 6% 4 7% 10% 38%	2470
	21st to end	Day	11% 5% 2 6% 4 6% 5% 5% 7% 10% 36%	2470
July	1st to 10th	Day	9% 5% 3 7% 5% 6% 5% 5% 6% 8% 41%	4120
	11th to 20th	Day	8% 6% 2 6% 5% 5% 5% 5% 7% 9% 42%	4120
	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	11% 6% 2 5% 5% 3 3 3 5% 6% 51%	1714
	11th to 20th	Day	17% 13% 3 6% 4 3 4 3 4 7% 35%	1710
	21st to end	Day	18% 12% 3 7% 5% 4 5% 4 4 5% 35%	1710
December	1st to 10th	Day	23% 15% 5% 8% 5% 5% 4 3 3 5% 23%	1710
	11th to 20th	Day	18% 16% 6% 10% 4 4 3 2 5% 6% 25%	2153
	21st to end	Day	21% 20% 5% 10% 6% 5% 5% 3 5% 5% 15%	3124
January	1st to 10th	Night	16% 17% 6% 12% 5% 5% 4 4 5% 4 21%	4109
	11th to 20th	Night	18% 17% 6% 13% 5% 5% 4 3 4 4 21%	4120
	21st to end	Night	27% 15% 6% 10% 6% 3 3 3 3 4 20%	4532
February	1st to 10th	Night	20% 13% 4 9% 5% 4 4 3 5% 5% 29%	2470
	11th to 20th	Night	20% 13% 4 8% 5% 5% 4 4 4 5% 28%	2270
	21st to end	Night	21% 16% 5% 8% 4 3 3 3 4 4 29%	1884
March	1st to 10th	Night	21% 12% 3 6% 4 4 3 3 5% 6% 33%	3513
	11th to 20th	Night	14% 10% 3 6% 5% 4 4 3 5% 7% 40%	3480
	21st to end	Night	19% 9% 3 6% 4 3 4 3 4 6% 40%	3817
April	1st to 10th	Night	16% 10% 3 6% 5% 4 4 4 5% 6% 37%	2090
	11th to 20th	Night	15% 8% 2 5% 5% 4 4 4 6% 9% 39%	1746
	21st to end	Night	15% 8% 3 7% 4 4 4 3 5% 7% 39%	1710
May	1st to 10th	Night	24% 11% 3 7% 5% 4 4 4 4 6% 28%	2813
	11th to 20th	Night	19% 8% 3 6% 4 3 3 3 4 7% 40%	2812
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 10% 42%	3079
June	1st to 10th	Night	10% 5% 2 5% 5% 4 5% 5% 6% 9% 44%	1710
	11th to 20th	Night	8% 4 2 5% 5% 5% 4 5% 8% 11% 43%	1710
	21st to end	Night	10% 6% 2 4 4 5% 4 5% 7% 11% 44%	1710
July	1st to 10th	Night	10% 7% 3 6% 4 4 4 4 7% 8% 44%	2840
	11th to 20th	Night	8% 5% 2 7% 5% 5% 5% 4 6% 9% 44%	2840
	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 6% 4 3 4 3 4 5% 50%	2433
	11th to 20th	Night	17% 11% 3 6% 5% 4 4 3 5% 6% 37%	2470
	21st to end	Night	18% 12% 3 6% 5% 4 4 3 5% 5% 35%	2470
December	1st to 10th	Night	22% 14% 5% 8% 5% 4 4 3 4 5% 26%	2470
	11th to 20th	Night	17% 15% 6% 9% 5% 3 4 3 4 6% 28%	3042
	21st to end	Night	19% 18% 6% 10% 6% 5% 4 3 5% 6% 18%	4532

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	64% 3 13% 14% 7%	2837
	11th to 20th	Day	68% 3 8% 14% 6%	2840
	21st to end	Day	72% 3 7% 13% 4 1	3124
February	1st to 10th	Day	58% 3 11% 19% 9% 1	1710
	11th to 20th	Day	59% 4 9% 18% 10%	1802
	21st to end	Day	56% 4 10% 20% 9% 2	1570
March	1st to 10th	Day	60% 3 8% 21% 7% 1	3339
	11th to 20th	Day	44% 4 10% 26% 15% 1	3480
	21st to end	Day	49% 4 9% 24% 13% 1	3815
April	1st to 10th	Day	49% 5% 10% 21% 12% 3	2090
	11th to 20th	Day	46% 4 10% 20% 16% 4	2398
	21st to end	Day	49% 5% 11% 21% 12% 2	2470
May	1st to 10th	Day	55% 5% 9% 21% 8% 1	4120
	11th to 20th	Day	51% 5% 11% 19% 13% 1	4085
	21st to end	Day	40% 8% 14% 20% 15% 4	4489
June	1st to 10th	Day	40% 6% 12% 24% 16% 2	2470
	11th to 20th	Day	40% 8% 14% 21% 15% 2	2470
	21st to end	Day	41% 7% 14% 22% 15% 2	2470
July	1st to 10th	Day	40% 7% 11% 24% 16% 3	4055
	11th to 20th	Day	35% 7% 11% 32% 14% 1	4051
	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% 4 10% 30% 19% 3	1714
	11th to 20th	Day	50% 3 7% 21% 16% 2	1710
	21st to end	Day	51% 4 9% 23% 13% 1	1710
December	1st to 10th	Day	65% 3 9% 18% 5% 1	1710
	11th to 20th	Day	60% 3 10% 19% 8%	2150
	21st to end	Day	71% 4 10% 10% 4	3124
January	1st to 10th	Night	66% 3 9% 15% 6%	4109
	11th to 20th	Night	67% 3 11% 14% 5% 1	4120
	21st to end	Night	70% 2 7% 16% 4 1	4532
February	1st to 10th	Night	58% 4 10% 19% 9% 1	2470
	11th to 20th	Night	58% 3 9% 18% 12% 1	2271
	21st to end	Night	59% 4 9% 18% 8% 3	1884
March	1st to 10th	Night	53% 4 7% 23% 12% 1	3513
	11th to 20th	Night	43% 4 10% 29% 13% 1	3480
	21st to end	Night	45% 4 7% 28% 14% 1	3817
April	1st to 10th	Night	47% 4 9% 21% 15% 3	2090
	11th to 20th	Night	41% 5% 11% 20% 17% 6%	1746
	21st to end	Night	45% 5% 10% 22% 16% 2	1710
May	1st to 10th	Night	57% 5% 10% 17% 10% 2	2840
	11th to 20th	Night	44% 7% 11% 24% 13% 2	2813
	21st to end	Night	35% 7% 14% 26% 14% 4	3087
June	1st to 10th	Night	35% 8% 10% 27% 18% 3	1710
	11th to 20th	Night	33% 8% 16% 22% 19% 2	1710
	21st to end	Night	33% 7% 14% 24% 19% 3	1710
July	1st to 10th	Night	37% 6% 10% 23% 19% 5%	2795
	11th to 20th	Night	35% 7% 12% 28% 16% 2	2786
	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% 24% 21% 4	2433
	11th to 20th	Night	49% 3 9% 21% 17% 3	2470
	21st to end	Night	51% 4 10% 22% 11% 1	2470
December	1st to 10th	Night	62% 3 10% 19% 6%	2470
	11th to 20th	Night	58% 4 11% 19% 7% 1	3044
	21st to end	Night	67% 3 9% 15% 5%	4532

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	30% 21% 34% 12% 3 1	270
	11th to 20th	Day	37% 22% 33% 7% 1	270
	21st to end	Day	32% 25% 30% 10% 2	297
February	1st to 10th	Day	34% 22% 29% 13% 3	270
	11th to 20th	Day	38% 27% 30% 3 2 1	270
	21st to end	Day	35% 22% 35% 8%	225
March	1st to 10th	Day	29% 21% 29% 17% 4	398
	11th to 20th	Day	28% 21% 30% 15% 5% 1	460
	21st to end	Day	33% 17% 32% 14% 4	506
April	1st to 10th	Day	25% 20% 32% 14% 8% 1	460
	11th to 20th	Day	26% 16% 30% 19% 6% 3	452
	21st to end	Day	25% 18% 32% 17% 6% 1	460
May	1st to 10th	Day	27% 16% 30% 16% 8% 3	463
	11th to 20th	Day	22% 11% 29% 23% 11% 5%	487
	21st to end	Day	13% 8% 27% 29% 17% 6%	529
June	1st to 10th	Day	16% 10% 23% 27% 19% 5%	490
	11th to 20th	Day	13% 9% 25% 31% 14% 8%	490
	21st to end	Day	12% 9% 29% 27% 17% 6%	490
July	1st to 10th	Day	14% 5% 20% 23% 20% 17%	485
	11th to 20th	Day	9% 6% 22% 31% 22% 10%	484
	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	19% 15% 31% 25% 7% 2	294
	11th to 20th	Day	29% 17% 27% 20% 5% 1	270
	21st to end	Day	23% 19% 37% 16% 4 1	270
December	1st to 10th	Day	31% 17% 33% 14% 4 1	270
	11th to 20th	Day	27% 21% 36% 11% 4 1	270
	21st to end	Day	34% 21% 28% 13% 4	297
January	1st to 10th	Night	27% 18% 31% 19% 4	760
	11th to 20th	Night	33% 16% 28% 20% 3	760
	21st to end	Night	25% 18% 33% 20% 3	836
February	1st to 10th	Night	28% 14% 30% 26% 1	760
	11th to 20th	Night	31% 18% 31% 19% 1	743
	21st to end	Night	32% 16% 32% 19% 2	628
March	1st to 10th	Night	26% 16% 31% 23% 5%	760
	11th to 20th	Night	26% 16% 29% 20% 8% 1	760
	21st to end	Night	27% 15% 30% 21% 6%	836
April	1st to 10th	Night	24% 15% 32% 21% 7%	760
	11th to 20th	Night	19% 13% 33% 25% 9%	609
	21st to end	Night	21% 9% 35% 29% 6%	570
May	1st to 10th	Night	20% 9% 28% 29% 11% 2	570
	11th to 20th	Night	20% 6% 25% 30% 16% 2	561
	21st to end	Night	10% 5% 20% 33% 28% 3	617
June	1st to 10th	Night	12% 2 23% 40% 21% 1	570
	11th to 20th	Night	10% 4 21% 37% 26% 2	570
	21st to end	Night	12% 3 20% 35% 26% 2	570
July	1st to 10th	Night	12% 3 16% 33% 29% 7%	555
	11th to 20th	Night	7% 3 16% 34% 34% 5%	552
	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	17% 9% 27% 30% 16%	755
	11th to 20th	Night	24% 15% 26% 26% 9% 1	760
	21st to end	Night	25% 11% 28% 29% 7% 1	760
December	1st to 10th	Night	31% 13% 28% 21% 6%	760
	11th to 20th	Night	24% 17% 29% 24% 6%	760
	21st to end	Night	29% 16% 26% 26% 3	836

Page generated at 2024-11-01 22:47:37. Version ac07

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