Area 52 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Area 52 Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	4 3 1 4 3 3 3 3 5% 7% 64%	123157
	Night	5% 4 1 4 3 3 3 3 5% 7% 64%	124019
Transparency	Day	20% 4 10% 19% 26% 21%	122915
	Night	21% 4 9% 19% 27% 21%	123848
Seeing	Day	6% 7% 24% 37% 20% 6%	16393
	Night	6% 2 12% 33% 36% 11%	26209

By Month

Percentage Cloud Cover SW (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	4 2 1 2 2 2 2 2 3 5% 74%	3749
	11th to 20th	Day	6% 3 1 3 2 2 2 2 3 7% 67%	4100
	21st to end	Day	9% 4 2 4 2 3 4 3 6% 10% 54%	4664
February	1st to 10th	Day	9% 5% 1 4 2 2 2 3 5% 6% 61%	2000
	11th to 20th	Day	7% 3 1 4 3 2 3 3 6% 8% 60%	1950
	21st to end	Day	8% 2 1 4 3 3 3 3 4 6% 62%	1650
March	1st to 10th	Day	10% 4 2 5% 3 3 3 3 4 5% 58%	4518
	11th to 20th	Day	7% 4 1 4 3 3 3 3 5% 8% 60%	4867
	21st to end	Day	7% 6% 2 5% 4 4 4 4 6% 9% 51%	5895
April	1st to 10th	Day	5% 4 1 4 4 2 3 3 5% 7% 62%	2400
	11th to 20th	Day	4 4 1 3 3 2 3 3 5% 8% 65%	2369
	21st to end	Day	3 3 2 3 3 3 4 3 5% 7% 65%	2400
May	1st to 10th	Day	2 4 2 4 3 3 3 3 5% 6% 66%	5440
	11th to 20th	Day	2 5% 2 6% 4 3 4 3 5% 6% 59%	5770
	21st to end	Day	1 3 1 5% 3 4 4 3 5% 8% 63%	6423
June	1st to 10th	Day	4 6% 2 5% 4 3 4 4 5% 9% 54%	2780
	11th to 20th	Day	3 4 1 4 3 3 3 3 4 8% 64%	2660
	21st to end	Day	2 3 1 3 3 3 3 3 6% 7% 65%	2660
July	1st to 10th	Day	2 2 1 4 3 2 3 2 5% 6% 71%	4420
	11th to 20th	Day	2 2 1 4 3 3 3 3 6% 7% 68%	4270
	21st to end	Day	1 1 2 2 2 3 3 5% 7% 73%	4306
August	1st to 10th	Day	1 2 1 2 2 2 2 3 6% 7% 71%	3783
	11th to 20th	Day	1 1 1 2 1 1 2 2 4 6% 80%	3724
	21st to end	Day	1 1 1 2 2 2 3 2 4 7% 76%	4180
September	1st to 10th	Day	2 2 1 2 3 3 4 3 5% 9% 67%	2280
	11th to 20th	Day	2 2 1 3 3 2 3 3 5% 7% 69%	2200
	21st to end	Day	1 2 1 4 4 3 3 3 4 7% 69%	2090
October	1st to 10th	Day	1 2 1 2 1 1 2 2 4 6% 77%	3411
	11th to 20th	Day	2 6% 2 5% 3 2 4 3 5% 8% 60%	3161
	21st to end	Day	3 2 1 3 3 2 4 3 4 6% 69%	3448
November	1st to 10th	Day	2 2 1 3 3 2 3 3 5% 7% 69%	1804
	11th to 20th	Day	3 3 1 3 2 2 3 4 5% 6% 69%	1800
	21st to end	Day	4 2 1 4 3 3 3 3 5% 7% 64%	1800
December	1st to 10th	Day	4 2 1 3 4 4 5% 4 5% 7% 60%	2950
	11th to 20th	Day	11% 5% 1 4 3 3 5% 3 4 6% 55%	3231
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 11% 47%	4004
January	1st to 10th	Night	5% 2 1 4 2 2 2 2 4 5% 69%	6196
	11th to 20th	Night	6% 4 1 4 2 2 2 2 4 5% 67%	5880
	21st to end	Night	9% 4 1 4 3 3 4 3 5% 7% 57%	6318
February	1st to 10th	Night	9% 5% 1 4 3 2 3 3 3 6% 60%	2400
	11th to 20th	Night	8% 4 1 4 3 2 3 3 4 6% 62%	2338
	21st to end	Night	9% 4 1 4 4 3 3 2 4 4 62%	1980
March	1st to 10th	Night	6% 5% 2 5% 3 3 3 3 6% 8% 57%	5376
	11th to 20th	Night	6% 4 1 4 4 3 4 3 5% 5% 59%	5116
	21st to end	Night	11% 6% 2 4 3 3 3 2 4 6% 57%	5078
April	1st to 10th	Night	6% 4 1 3 3 3 3 3 6% 7% 61%	2000
	11th to 20th	Night	4 5% 2 4 3 3 3 2 4 6% 64%	1979
	21st to end	Night	3 5% 2 4 3 3 3 3 5% 7% 63%	2000
May	1st to 10th	Night	3 3 2 4 3 3 3 2 4 6% 69%	4560
	11th to 20th	Night	2 7% 2 5% 3 2 3 3 4 5% 65%	4134
	21st to end	Night	1 2 1 2 2 2 2 2 3 5% 78%	4474
June	1st to 10th	Night	2 7% 2 5% 4 4 4 4 4 8% 56%	1598
	11th to 20th	Night	1 5% 1 4 4 3 3 3 4 6% 67%	1520
	21st to end	Night	1 4 1 4 3 3 4 3 6% 9% 63%	1520
July	1st to 10th	Night	1 2 1 3 3 2 2 4 6% 6% 70%	2540
	11th to 20th	Night	2 1 4 3 3 5% 5% 8% 9% 61%	2690
	21st to end	Night	1 2 1 3 3 2 4 3 6% 9% 67%	3261
August	1st to 10th	Night	1 2 1 2 2 2 4 4 6% 8% 68%	3166
	11th to 20th	Night	1 2 1 3 3 2 2 2 4 4 76%	3126
	21st to end	Night	1 2 2 5% 3 2 3 3 5% 7% 68%	3498
September	1st to 10th	Night	3 4 1 3 3 3 3 3 4 9% 64%	1900
	11th to 20th	Night	2 3 1 3 3 3 3 3 4 7% 67%	1978
	21st to end	Night	2 1 1 5% 4 4 4 2 4 5% 68%	2090
October	1st to 10th	Night	2 2 1 2 2 2 3 3 6% 7% 72%	3552
	11th to 20th	Night	2 6% 2 5% 3 3 3 3 4 7% 61%	3777
	21st to end	Night	2 3 1 3 2 2 2 2 3 5% 76%	4121
November	1st to 10th	Night	2 3 2 3 2 3 3 2 5% 6% 69%	2492
	11th to 20th	Night	3 3 2 2 3 2 2 3 3 6% 71%	2600
	21st to end	Night	5% 3 1 4 3 3 4 3 4 7% 63%	2600
December	1st to 10th	Night	4 3 1 4 3 3 4 3 5% 6% 65%	4240
	11th to 20th	Night	12% 5% 2 3 3 3 3 3 6% 8% 52%	4969
	21st to end	Night	10% 4 2 5% 4 5% 5% 4 7% 10% 44%	6952

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	16% 2 5% 24% 32% 21%	3749
	11th to 20th	Day	20% 5% 12% 14% 18% 31%	4100
	21st to end	Day	25% 4 9% 17% 26% 19%	4664
February	1st to 10th	Day	26% 4 6% 18% 25% 22%	2000
	11th to 20th	Day	23% 5% 8% 19% 26% 19%	1960
	21st to end	Day	23% 4 10% 21% 25% 18%	1650
March	1st to 10th	Day	28% 4 11% 20% 23% 16%	4518
	11th to 20th	Day	23% 6% 13% 26% 20% 11%	4867
	21st to end	Day	27% 7% 15% 27% 19% 5%	5895
April	1st to 10th	Day	22% 5% 14% 24% 24% 11%	2400
	11th to 20th	Day	19% 5% 9% 26% 27% 13%	2372
	21st to end	Day	18% 6% 12% 25% 30% 9%	2400
May	1st to 10th	Day	16% 7% 13% 21% 31% 13%	5440
	11th to 20th	Day	23% 6% 13% 23% 29% 6%	5773
	21st to end	Day	16% 7% 15% 32% 25% 6%	6424
June	1st to 10th	Day	27% 7% 13% 20% 24% 8%	2780
	11th to 20th	Day	19% 5% 12% 16% 31% 18%	2660
	21st to end	Day	20% 3 9% 11% 30% 27%	2660
July	1st to 10th	Day	15% 2 7% 7% 14% 55%	4351
	11th to 20th	Day	17% 3 8% 12% 28% 32%	4195
	21st to end	Day	13% 4 8% 18% 28% 28%	4170
August	1st to 10th	Day	14% 2 9% 16% 38% 20%	3770
	11th to 20th	Day	10% 1 7% 12% 33% 37%	3760
	21st to end	Day	12% 2 9% 10% 36% 31%	4179
September	1st to 10th	Day	17% 3 10% 11% 30% 30%	2280
	11th to 20th	Day	18% 4 10% 16% 29% 23%	2200
	21st to end	Day	18% 3 8% 16% 29% 26%	2090
October	1st to 10th	Day	10% 3 7% 13% 21% 46%	3411
	11th to 20th	Day	22% 4 9% 12% 32% 21%	3161
	21st to end	Day	17% 3 5% 10% 34% 30%	3448
November	1st to 10th	Day	18% 4 8% 17% 23% 31%	1804
	11th to 20th	Day	17% 4 8% 16% 22% 34%	1800
	21st to end	Day	21% 3 8% 16% 24% 28%	1800
December	1st to 10th	Day	21% 5% 6% 19% 21% 28%	2950
	11th to 20th	Day	30% 3 9% 17% 28% 13%	3230
	21st to end	Day	31% 10% 11% 25% 16% 7%	4004
January	1st to 10th	Night	19% 3 6% 19% 33% 20%	6196
	11th to 20th	Night	22% 3 8% 19% 20% 28%	5880
	21st to end	Night	26% 2 8% 18% 26% 20%	6318
February	1st to 10th	Night	27% 4 5% 15% 24% 24%	2400
	11th to 20th	Night	25% 4 6% 21% 22% 22%	2339
	21st to end	Night	27% 3 8% 17% 25% 21%	1980
March	1st to 10th	Night	23% 6% 10% 19% 30% 11%	5376
	11th to 20th	Night	25% 7% 11% 28% 16% 13%	5116
	21st to end	Night	28% 5% 12% 30% 19% 6%	5078
April	1st to 10th	Night	23% 4 12% 27% 23% 11%	2000
	11th to 20th	Night	21% 4 10% 24% 27% 14%	1979
	21st to end	Night	20% 5% 11% 23% 29% 11%	2000
May	1st to 10th	Night	17% 5% 13% 22% 31% 12%	4557
	11th to 20th	Night	18% 4 14% 25% 32% 8%	4135
	21st to end	Night	9% 2 9% 40% 34% 6%	4474
June	1st to 10th	Night	26% 6% 13% 21% 24% 9%	1598
	11th to 20th	Night	19% 4 8% 18% 35% 16%	1520
	21st to end	Night	20% 3 7% 13% 31% 27%	1520
July	1st to 10th	Night	13% 2 7% 7% 15% 58%	2500
	11th to 20th	Night	18% 2 11% 12% 26% 31%	2642
	21st to end	Night	14% 2 7% 23% 30% 24%	3159
August	1st to 10th	Night	14% 2 6% 21% 35% 22%	3156
	11th to 20th	Night	12% 2 4 11% 40% 32%	3156
	21st to end	Night	15% 2 7% 10% 38% 27%	3498
September	1st to 10th	Night	21% 2 7% 10% 28% 32%	1900
	11th to 20th	Night	21% 1 6% 13% 34% 25%	1978
	21st to end	Night	21% 2 4 14% 31% 29%	2090
October	1st to 10th	Night	15% 2 15% 10% 21% 37%	3552
	11th to 20th	Night	22% 4 9% 15% 28% 23%	3777
	21st to end	Night	14% 2 4 10% 36% 34%	4121
November	1st to 10th	Night	17% 4 7% 16% 25% 31%	2492
	11th to 20th	Night	18% 3 9% 12% 23% 35%	2600
	21st to end	Night	23% 4 6% 17% 20% 30%	2600
December	1st to 10th	Night	21% 3 5% 17% 24% 29%	4240
	11th to 20th	Night	31% 3 8% 16% 24% 18%	4969
	21st to end	Night	34% 7% 11% 27% 14% 7%	6952

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	14% 7% 29% 36% 13% 2	245
	11th to 20th	Day	12% 9% 29% 38% 12% 1	400
	21st to end	Day	9% 12% 32% 34% 10% 2	473
February	1st to 10th	Day	13% 9% 34% 32% 10% 3	500
	11th to 20th	Day	10% 11% 35% 32% 11% 1	495
	21st to end	Day	11% 12% 36% 30% 10% 1	414
March	1st to 10th	Day	14% 15% 37% 25% 10%	500
	11th to 20th	Day	11% 13% 35% 28% 13% 1	500
	21st to end	Day	10% 15% 33% 33% 8% 1	550
April	1st to 10th	Day	7% 10% 32% 31% 15% 4	500
	11th to 20th	Day	6% 13% 33% 33% 11% 4	492
	21st to end	Day	6% 9% 31% 32% 16% 6%	500
May	1st to 10th	Day	11% 8% 26% 38% 13% 5%	503
	11th to 20th	Day	4 12% 24% 34% 22% 4	528
	21st to end	Day	5% 9% 26% 36% 19% 5%	573
June	1st to 10th	Day	6% 4 21% 36% 27% 5%	527
	11th to 20th	Day	3 3 21% 40% 25% 7%	490
	21st to end	Day	3 2 17% 43% 28% 8%	490
July	1st to 10th	Day	2 8% 45% 35% 10%	486
	11th to 20th	Day	2 1 7% 37% 39% 14%	484
	21st to end	Day	2 6% 43% 34% 14%	531
August	1st to 10th	Day	1 1 12% 41% 31% 13%	487
	11th to 20th	Day	2 8% 42% 32% 15%	477
	21st to end	Day	3 1 12% 42% 32% 11%	539
September	1st to 10th	Day	2 2 14% 44% 27% 11%	490
	11th to 20th	Day	3 5% 22% 47% 19% 5%	490
	21st to end	Day	1 5% 19% 42% 26% 7%	490
October	1st to 10th	Day	3 4 24% 42% 23% 4	490
	11th to 20th	Day	2 3 29% 43% 19% 3	490
	21st to end	Day	4 6% 24% 40% 23% 4	539
November	1st to 10th	Day	2 7% 23% 43% 22% 3	340
	11th to 20th	Day	3 5% 32% 38% 19% 3	300
	21st to end	Day	6% 9% 29% 37% 16% 3	300
December	1st to 10th	Day	9% 5% 26% 36% 21% 3	300
	11th to 20th	Day	6% 9% 27% 34% 20% 4	260
	21st to end	Day	14% 12% 33% 27% 11% 3	220
January	1st to 10th	Night	11% 3 19% 42% 19% 8%	800
	11th to 20th	Night	8% 2 22% 42% 23% 4	800
	21st to end	Night	11% 4 23% 41% 18% 4	880
February	1st to 10th	Night	11% 4 17% 41% 23% 6%	800
	11th to 20th	Night	10% 2 19% 40% 23% 6%	784
	21st to end	Night	10% 4 20% 40% 21% 4	660
March	1st to 10th	Night	11% 4 20% 40% 23% 3	800
	11th to 20th	Night	8% 4 17% 40% 26% 6%	800
	21st to end	Night	8% 2 16% 41% 29% 4	880
April	1st to 10th	Night	6% 3 16% 40% 31% 6%	800
	11th to 20th	Night	6% 3 16% 36% 33% 5%	791
	21st to end	Night	5% 4 12% 38% 31% 10%	800
May	1st to 10th	Night	5% 3 13% 38% 35% 7%	800
	11th to 20th	Night	4 3 12% 31% 40% 11%	625
	21st to end	Night	2 1 14% 35% 39% 8%	650
June	1st to 10th	Night	3 7% 28% 49% 13%	402
	11th to 20th	Night	1 1 6% 25% 54% 14%	380
	21st to end	Night	1 2 22% 56% 18%	380
July	1st to 10th	Night	2 1 6% 64% 27%	370
	11th to 20th	Night	2 1 5% 53% 39%	453
	21st to end	Night	2 2 9% 53% 35%	714
August	1st to 10th	Night	1 1 2 15% 55% 25%	756
	11th to 20th	Night	2 1 2 11% 57% 28%	752
	21st to end	Night	2 1 15% 55% 27%	836
September	1st to 10th	Night	3 1 3 17% 53% 23%	760
	11th to 20th	Night	3 2 4 25% 50% 16%	760
	21st to end	Night	2 1 5% 28% 47% 18%	760
October	1st to 10th	Night	3 1 6% 36% 47% 8%	760
	11th to 20th	Night	3 1 9% 36% 42% 9%	760
	21st to end	Night	4 2 11% 36% 36% 11%	836
November	1st to 10th	Night	4 2 13% 39% 33% 10%	780
	11th to 20th	Night	5% 1 12% 39% 35% 8%	800
	21st to end	Night	7% 2 19% 41% 25% 6%	800
December	1st to 10th	Night	9% 2 17% 40% 28% 5%	800
	11th to 20th	Night	13% 2 19% 42% 21% 4	800
	21st to end	Night	11% 4 20% 41% 18% 6%	880

Page generated at 2025-06-07 07:28:14. Version ac07

Copyright © 2025 Attilla Danko.