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 2026-10-14.

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% 65%	156789
	Night	4 4 1 4 3 3 3 3 5% 7% 64%	152593
Transparency	Day	19% 4 9% 19% 28% 20%	151871
	Night	21% 3 8% 20% 27% 20%	148486
Seeing	Day	6% 7% 24% 37% 20% 6%	18247
	Night	6% 2 12% 33% 36% 11%	27968

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	9% 3 1 3 2 2 3 2 3 5% 67%	4860
	11th to 20th	Day	5% 2 1 2 2 2 2 2 4 7% 71%	5340
	21st to end	Day	7% 4 2 4 3 3 4 4 6% 8% 55%	6039
February	1st to 10th	Day	9% 5% 1 3 2 2 2 3 5% 6% 61%	2100
	11th to 20th	Day	8% 3 1 4 3 2 3 3 6% 8% 59%	2050
	21st to end	Day	7% 2 1 4 3 3 3 3 4 7% 63%	1730
March	1st to 10th	Day	10% 4 2 5% 3 2 3 3 4 5% 59%	4618
	11th to 20th	Day	7% 4 1 4 3 3 3 3 5% 7% 61%	4974
	21st to end	Day	7% 6% 2 5% 4 4 4 4 6% 9% 50%	6025
April	1st to 10th	Day	5% 3 1 4 4 3 3 3 5% 8% 61%	2520
	11th to 20th	Day	3 4 1 3 3 2 3 3 5% 8% 65%	2489
	21st to end	Day	3 3 2 3 3 3 4 3 5% 7% 65%	2520
May	1st to 10th	Day	2 4 2 4 3 3 3 3 4 6% 67%	7058
	11th to 20th	Day	2 5% 2 6% 4 3 4 3 4 7% 61%	7500
	21st to end	Day	1 3 2 5% 3 4 3 3 5% 7% 63%	8370
June	1st to 10th	Day	4 5% 2 5% 4 4 4 4 5% 9% 54%	2931
	11th to 20th	Day	3 4 1 4 3 3 3 3 4 8% 63%	2940
	21st to end	Day	2 3 1 4 4 3 3 3 6% 7% 65%	2940
July	1st to 10th	Day	1 1 1 3 2 2 3 2 4 7% 73%	8219
	11th to 20th	Day	1 2 1 4 3 3 3 3 5% 7% 68%	7940
	21st to end	Day	1 2 1 3 2 2 2 3 4 7% 74%	8025
August	1st to 10th	Day	1 1 1 2 2 2 2 3 5% 8% 74%	6986
	11th to 20th	Day	1 1 1 2 2 3 3 3 4 7% 72%	7001
	21st to end	Day	1 2 1 2 2 2 3 2 4 7% 75%	7750
September	1st to 10th	Day	2 2 1 2 3 3 4 3 5% 8% 68%	2520
	11th to 20th	Day	2 2 1 3 3 3 3 3 5% 7% 68%	2432
	21st to end	Day	1 2 1 4 4 3 3 3 4 7% 68%	2310
October	1st to 10th	Day	1 2 1 2 1 1 2 2 4 6% 78%	3627
	11th to 20th	Day	2 5% 2 5% 3 2 4 3 5% 8% 61%	3292
	21st to end	Day	3 2 1 3 3 2 4 3 4 6% 69%	3558
November	1st to 10th	Day	2 2 1 3 3 2 3 3 5% 7% 69%	1896
	11th to 20th	Day	5% 3 1 3 2 2 3 3 5% 6% 66%	1890
	21st to end	Day	4 2 1 4 3 3 3 3 5% 7% 63%	1890
December	1st to 10th	Day	4 2 1 3 4 4 5% 4 5% 7% 61%	3040
	11th to 20th	Day	11% 4 1 4 3 3 5% 3 4 6% 55%	3317
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 10% 46%	4092
January	1st to 10th	Night	9% 4 2 4 3 3 3 2 3 5% 62%	8023
	11th to 20th	Night	5% 3 1 3 2 2 2 2 4 6% 70%	7650
	21st to end	Night	9% 5% 2 4 3 3 4 3 5% 6% 55%	8169
February	1st to 10th	Night	9% 5% 1 4 3 2 3 3 3 6% 61%	2520
	11th to 20th	Night	8% 5% 2 4 3 2 3 3 4 6% 60%	2458
	21st to end	Night	9% 4 1 3 3 3 3 3 5% 5% 62%	2076
March	1st to 10th	Night	6% 5% 2 5% 3 3 3 3 6% 8% 57%	5496
	11th to 20th	Night	6% 4 1 4 4 3 4 3 5% 5% 60%	5229
	21st to end	Night	10% 6% 2 4 3 3 3 2 4 6% 57%	5190
April	1st to 10th	Night	6% 4 2 3 3 3 3 3 5% 7% 60%	2100
	11th to 20th	Night	4 5% 2 4 3 3 3 2 4 6% 64%	2079
	21st to end	Night	3 5% 2 3 3 3 3 3 4 7% 64%	2100
May	1st to 10th	Night	2 4 2 4 3 3 3 2 4 6% 67%	5919
	11th to 20th	Night	2 7% 2 4 3 2 2 3 3 5% 68%	5382
	21st to end	Night	1 2 1 3 2 2 2 2 3 6% 75%	5837
June	1st to 10th	Night	2 6% 2 5% 4 4 4 4 4 7% 58%	1683
	11th to 20th	Night	1 5% 2 5% 4 3 3 3 4 6% 66%	1680
	21st to end	Night	1 4 1 4 3 3 4 3 5% 8% 64%	1680
July	1st to 10th	Night	1 1 1 3 3 2 5% 4 6% 8% 68%	4740
	11th to 20th	Night	3 1 7% 4 3 4 5% 6% 7% 59%	5016
	21st to end	Night	2 1 3 3 2 3 3 6% 8% 69%	6098
August	1st to 10th	Night	1 1 1 2 2 2 4 4 5% 8% 72%	5866
	11th to 20th	Night	1 1 2 2 2 3 2 4 7% 74%	5886
	21st to end	Night	1 2 1 4 2 2 3 3 4 7% 71%	6499
September	1st to 10th	Night	3 4 1 3 3 3 3 2 4 8% 65%	2100
	11th to 20th	Night	3 3 1 3 3 3 4 3 4 7% 67%	2186
	21st to end	Night	2 2 1 5% 4 5% 4 2 4 5% 67%	2310
October	1st to 10th	Night	1 2 1 2 2 2 3 3 6% 7% 72%	3776
	11th to 20th	Night	3 6% 2 5% 3 3 3 3 4 7% 62%	3933
	21st to end	Night	2 3 1 3 2 2 2 2 3 5% 76%	4253
November	1st to 10th	Night	2 3 2 3 2 3 3 2 5% 6% 68%	2620
	11th to 20th	Night	5% 3 2 2 3 2 2 3 3 6% 69%	2730
	21st to end	Night	5% 3 1 3 3 3 4 3 4 7% 63%	2730
December	1st to 10th	Night	4 3 1 4 3 3 4 3 5% 6% 65%	4370
	11th to 20th	Night	12% 5% 2 3 3 3 3 3 6% 8% 53%	5103
	21st to end	Night	10% 4 2 5% 4 5% 5% 4 7% 10% 44%	7106

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	23% 2 7% 20% 28% 19%	4861
	11th to 20th	Day	16% 4 10% 11% 20% 39%	5340
	21st to end	Day	26% 4 8% 16% 24% 23%	6039
February	1st to 10th	Day	26% 4 6% 17% 25% 22%	2100
	11th to 20th	Day	24% 5% 8% 19% 25% 18%	2060
	21st to end	Day	22% 4 9% 22% 25% 18%	1730
March	1st to 10th	Day	27% 4 11% 20% 23% 16%	4618
	11th to 20th	Day	22% 6% 13% 26% 21% 12%	4974
	21st to end	Day	27% 7% 14% 27% 19% 5%	6025
April	1st to 10th	Day	22% 5% 14% 24% 24% 11%	2520
	11th to 20th	Day	19% 5% 9% 27% 28% 13%	2492
	21st to end	Day	18% 6% 12% 26% 30% 9%	2520
May	1st to 10th	Day	15% 6% 12% 22% 34% 10%	7058
	11th to 20th	Day	22% 6% 11% 23% 27% 11%	7503
	21st to end	Day	17% 6% 14% 32% 25% 5%	8371
June	1st to 10th	Day	27% 7% 13% 20% 26% 8%	2931
	11th to 20th	Day	20% 4 11% 16% 31% 18%	2940
	21st to end	Day	19% 3 10% 11% 31% 27%	2940
July	1st to 10th	Day	14% 2 7% 10% 25% 42%	8151
	11th to 20th	Day	18% 2 8% 14% 35% 23%	7865
	21st to end	Day	13% 3 8% 20% 34% 22%	7846
August	1st to 10th	Day	12% 2 7% 24% 40% 15%	5530
	11th to 20th	Day	12% 2 6% 22% 32% 26%	5517
	21st to end	Day	14% 1 8% 19% 34% 23%	6077
September	1st to 10th	Day	17% 3 9% 12% 31% 29%	2520
	11th to 20th	Day	18% 4 10% 16% 31% 22%	2432
	21st to end	Day	19% 3 8% 16% 29% 26%	2310
October	1st to 10th	Day	10% 2 7% 13% 21% 46%	3627
	11th to 20th	Day	22% 4 9% 12% 33% 21%	3292
	21st to end	Day	17% 3 5% 10% 34% 30%	3558
November	1st to 10th	Day	18% 4 8% 17% 23% 31%	1896
	11th to 20th	Day	20% 4 8% 15% 21% 33%	1890
	21st to end	Day	21% 3 8% 17% 24% 28%	1890
December	1st to 10th	Day	20% 4 6% 18% 22% 28%	3040
	11th to 20th	Day	30% 3 9% 17% 28% 13%	3316
	21st to end	Day	32% 9% 11% 24% 16% 8%	4092
January	1st to 10th	Night	26% 4 7% 17% 30% 18%	8023
	11th to 20th	Night	18% 2 6% 15% 19% 39%	7650
	21st to end	Night	29% 2 6% 15% 24% 24%	8169
February	1st to 10th	Night	27% 4 5% 15% 24% 24%	2520
	11th to 20th	Night	26% 4 6% 21% 22% 21%	2459
	21st to end	Night	26% 3 8% 19% 24% 20%	2076
March	1st to 10th	Night	23% 6% 10% 19% 31% 12%	5496
	11th to 20th	Night	25% 7% 11% 28% 16% 14%	5229
	21st to end	Night	28% 5% 12% 30% 19% 6%	5190
April	1st to 10th	Night	23% 4 11% 27% 23% 11%	2100
	11th to 20th	Night	21% 4 10% 25% 27% 14%	2079
	21st to end	Night	19% 5% 11% 24% 29% 11%	2100
May	1st to 10th	Night	18% 4 12% 23% 34% 9%	5917
	11th to 20th	Night	17% 3 12% 26% 32% 10%	5383
	21st to end	Night	11% 2 8% 41% 33% 5%	5838
June	1st to 10th	Night	25% 6% 13% 22% 25% 9%	1683
	11th to 20th	Night	19% 4 8% 18% 35% 16%	1680
	21st to end	Night	19% 3 7% 13% 32% 27%	1680
July	1st to 10th	Night	15% 1 7% 11% 23% 43%	4700
	11th to 20th	Night	23% 2 11% 13% 30% 21%	4968
	21st to end	Night	14% 2 8% 23% 34% 19%	5965
August	1st to 10th	Night	13% 2 7% 29% 34% 16%	4636
	11th to 20th	Night	14% 2 7% 20% 35% 22%	4636
	21st to end	Night	15% 2 7% 22% 33% 21%	5092
September	1st to 10th	Night	20% 2 7% 11% 30% 30%	2100
	11th to 20th	Night	21% 1 6% 13% 35% 23%	2186
	21st to end	Night	21% 2 5% 13% 30% 28%	2310
October	1st to 10th	Night	15% 2 14% 10% 21% 38%	3776
	11th to 20th	Night	22% 4 8% 15% 28% 23%	3933
	21st to end	Night	14% 2 4 11% 35% 34%	4253
November	1st to 10th	Night	18% 4 7% 16% 26% 30%	2620
	11th to 20th	Night	19% 3 9% 12% 23% 33%	2730
	21st to end	Night	23% 4 6% 18% 20% 30%	2730
December	1st to 10th	Night	21% 3 5% 18% 24% 29%	4370
	11th to 20th	Night	30% 3 8% 16% 24% 18%	5103
	21st to end	Night	35% 7% 11% 26% 14% 7%	7106

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	15% 6% 30% 34% 13% 1	267
	11th to 20th	Day	11% 8% 28% 38% 13% 2	430
	21st to end	Day	9% 11% 32% 34% 12% 3	509
February	1st to 10th	Day	12% 8% 33% 34% 10% 3	540
	11th to 20th	Day	11% 12% 35% 30% 10% 1	535
	21st to end	Day	11% 11% 36% 30% 11% 1	446
March	1st to 10th	Day	13% 15% 38% 25% 9%	540
	11th to 20th	Day	11% 12% 32% 29% 14% 2	540
	21st to end	Day	9% 14% 32% 34% 10% 2	594
April	1st to 10th	Day	7% 9% 33% 32% 15% 4	540
	11th to 20th	Day	5% 13% 32% 33% 11% 5%	532
	21st to end	Day	6% 10% 31% 32% 16% 5%	540
May	1st to 10th	Day	10% 9% 25% 38% 12% 5%	543
	11th to 20th	Day	4 12% 24% 34% 22% 4	568
	21st to end	Day	6% 9% 26% 36% 19% 5%	617
June	1st to 10th	Day	6% 4 21% 38% 26% 5%	570
	11th to 20th	Day	3 4 21% 40% 25% 7%	570
	21st to end	Day	3 3 18% 42% 26% 8%	570
July	1st to 10th	Day	2 1 11% 45% 32% 10%	566
	11th to 20th	Day	2 1 8% 38% 38% 13%	564
	21st to end	Day	2 7% 43% 33% 15%	619
August	1st to 10th	Day	1 1 12% 40% 31% 15%	567
	11th to 20th	Day	2 1 9% 43% 30% 15%	557
	21st to end	Day	3 1 12% 42% 31% 11%	627
September	1st to 10th	Day	2 3 15% 43% 26% 11%	570
	11th to 20th	Day	3 5% 23% 45% 18% 6%	570
	21st to end	Day	2 5% 22% 40% 23% 7%	570
October	1st to 10th	Day	3 4 24% 41% 22% 5%	570
	11th to 20th	Day	3 4 30% 42% 18% 3	543
	21st to end	Day	4 5% 24% 39% 23% 5%	583
November	1st to 10th	Day	2 6% 22% 43% 23% 3	372
	11th to 20th	Day	8% 5% 31% 36% 18% 3	330
	21st to end	Day	6% 8% 27% 37% 18% 3	330
December	1st to 10th	Day	8% 5% 25% 35% 23% 4	330
	11th to 20th	Day	6% 8% 26% 34% 22% 5%	286
	21st to end	Day	17% 12% 31% 27% 11% 3	242
January	1st to 10th	Night	12% 3 19% 41% 18% 7%	840
	11th to 20th	Night	7% 2 21% 43% 23% 4	840
	21st to end	Night	11% 4 22% 42% 18% 4	924
February	1st to 10th	Night	11% 4 17% 41% 22% 5%	840
	11th to 20th	Night	11% 2 19% 40% 22% 6%	824
	21st to end	Night	10% 4 20% 42% 21% 4	692
March	1st to 10th	Night	10% 3 21% 40% 22% 3	840
	11th to 20th	Night	8% 3 16% 40% 27% 6%	840
	21st to end	Night	8% 2 15% 41% 29% 4	924
April	1st to 10th	Night	6% 2 15% 40% 30% 5%	840
	11th to 20th	Night	6% 3 16% 37% 32% 5%	831
	21st to end	Night	5% 3 13% 40% 30% 9%	840
May	1st to 10th	Night	5% 3 12% 38% 34% 8%	840
	11th to 20th	Night	4 3 12% 31% 39% 11%	657
	21st to end	Night	2 1 14% 35% 40% 8%	683
June	1st to 10th	Night	3 6% 27% 50% 13%	423
	11th to 20th	Night	1 5% 25% 54% 15%	420
	21st to end	Night	1 3 23% 55% 19%	420
July	1st to 10th	Night	2 1 7% 66% 24%	410
	11th to 20th	Night	2 2 5% 52% 40%	502
	21st to end	Night	2 2 10% 53% 34%	790
August	1st to 10th	Night	1 1 2 15% 55% 26%	836
	11th to 20th	Night	2 2 11% 58% 27%	832
	21st to end	Night	2 1 16% 55% 26%	924
September	1st to 10th	Night	3 1 3 19% 53% 21%	840
	11th to 20th	Night	3 2 4 26% 50% 15%	840
	21st to end	Night	3 1 6% 29% 45% 17%	840
October	1st to 10th	Night	3 1 6% 37% 47% 7%	840
	11th to 20th	Night	4 1 11% 35% 40% 9%	812
	21st to end	Night	4 2 10% 37% 37% 10%	880
November	1st to 10th	Night	3 2 13% 39% 33% 10%	820
	11th to 20th	Night	7% 1 11% 40% 34% 8%	840
	21st to end	Night	7% 2 19% 41% 25% 6%	840
December	1st to 10th	Night	8% 2 17% 40% 28% 5%	840
	11th to 20th	Night	12% 2 18% 43% 22% 3	840
	21st to end	Night	11% 4 20% 41% 18% 6%	924

Page generated at 2026-10-11 02:06:32. Version ac07

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