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 2024-07-08.

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	2 4 1 4 3 3 3 3 5% 7% 65%	89528
	Night	2 4 2 4 3 3 4 3 5% 7% 63%	89942
Transparency	Day	19% 4 8% 19% 27% 23%	89239
	Night	20% 5% 9% 22% 27% 18%	89752
Seeing	Day	5% 6% 19% 30% 26% 14%	14564
	Night	4 3 18% 42% 28% 5%	24207

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	2 4 2 4 3 4 4 4 5% 9% 59%	2539
	11th to 20th	Day	2 6% 2 6% 3 3 4 4 6% 8% 57%	2540
	21st to end	Day	4 7% 3 5% 4 4 4 5% 7% 9% 48%	3125
February	1st to 10th	Day	3 4 1 4 3 3 3 4 4 9% 61%	1900
	11th to 20th	Day	2 5% 1 5% 4 5% 3 4 5% 7% 58%	1850
	21st to end	Day	2 6% 2 4 4 4 4 3 4 6% 60%	1570
March	1st to 10th	Day	1 6% 2 6% 4 4 4 4 5% 9% 55%	3138
	11th to 20th	Day	1 5% 1 3 4 4 4 4 6% 8% 59%	3353
	21st to end	Day	2 9% 3 7% 5% 5% 5% 4 6% 8% 46%	4000
April	1st to 10th	Day	2 5% 2 5% 4 4 3 3 4 7% 60%	2280
	11th to 20th	Day	3 4 1 4 3 4 3 3 5% 6% 64%	2249
	21st to end	Day	3 4 2 4 3 3 3 3 5% 6% 65%	2381
May	1st to 10th	Day	1 3 1 4 3 3 3 3 4 5% 71%	4110
	11th to 20th	Day	2 3 1 3 3 3 3 3 4 6% 68%	4071
	21st to end	Day	3 3 1 5% 3 3 3 3 4 5% 68%	4477
June	1st to 10th	Day	2 2 1 5% 3 4 3 4 5% 6% 64%	2639
	11th to 20th	Day	1 2 1 3 2 3 3 2 3 5% 74%	2660
	21st to end	Day	1 2 1 3 2 2 2 2 3 5% 78%	2660
July	1st to 10th	Day	2 2 1 3 3 3 3 3 4 5% 71%	2621
	11th to 20th	Day	3 2 1 4 3 2 3 4 5% 7% 67%	2520
	21st to end	Day	3 4 2 5% 4 5% 4 5% 6% 7% 56%	2611
August	1st to 10th	Day	3 3 1 3 3 2 3 2 3 4 73%	2317
	11th to 20th	Day	2 2 1 3 2 3 3 2 5% 6% 73%	2122
	21st to end	Day	1 2 1 3 2 3 3 3 4 6% 74%	2376
September	1st to 10th	Day	1 2 1 3 3 2 3 3 4 6% 73%	2156
	11th to 20th	Day	1 2 1 2 2 3 4 2 3 4 76%	1980
	21st to end	Day	1 1 1 2 2 2 2 2 3 5% 79%	1980
October	1st to 10th	Day	2 2 1 3 3 3 3 3 3 5% 71%	1980
	11th to 20th	Day	1 2 1 3 3 2 3 2 3 5% 76%	1900
	21st to end	Day	1 2 1 2 2 2 2 3 4 5% 76%	1782
November	1st to 10th	Day	2 4 2 3 2 3 3 3 5% 8% 65%	1674
	11th to 20th	Day	1 2 1 3 2 2 2 2 4 7% 74%	1710
	21st to end	Day	2 3 1 3 3 3 3 3 5% 6% 66%	1710
December	1st to 10th	Day	3 3 1 4 4 3 3 4 5% 6% 63%	1710
	11th to 20th	Day	7% 10% 3 7% 5% 4 3 3 6% 9% 45%	2043
	21st to end	Day	2 4 2 5% 4 5% 5% 5% 7% 9% 52%	2794
January	1st to 10th	Night	2 4 2 7% 4 3 3 3 5% 7% 60%	4406
	11th to 20th	Night	2 4 2 5% 5% 4 5% 4 5% 8% 57%	4420
	21st to end	Night	5% 8% 2 5% 3 3 3 3 6% 8% 53%	4536
February	1st to 10th	Night	2 5% 2 5% 3 2 3 3 5% 7% 62%	2280
	11th to 20th	Night	3 5% 1 3 3 3 3 3 5% 8% 62%	2218
	21st to end	Night	1 6% 2 5% 3 4 4 3 5% 7% 59%	1884
March	1st to 10th	Night	1 4 2 6% 4 4 4 4 5% 6% 59%	3736
	11th to 20th	Night	1 4 1 6% 4 4 5% 4 6% 7% 57%	3625
	21st to end	Night	2 5% 2 6% 4 4 5% 5% 6% 8% 54%	3648
April	1st to 10th	Night	2 4 1 4 3 3 4 3 6% 6% 62%	1900
	11th to 20th	Night	3 4 1 4 3 2 3 2 4 5% 68%	1879
	21st to end	Night	3 4 1 4 3 3 3 3 5% 7% 63%	1796
May	1st to 10th	Night	2 2 1 4 3 3 4 3 4 6% 67%	2860
	11th to 20th	Night	3 3 1 3 3 4 4 4 5% 6% 65%	2834
	21st to end	Night	3 4 1 5% 3 4 4 3 4 5% 64%	3110
June	1st to 10th	Night	2 1 1 3 3 3 3 4 5% 7% 67%	1535
	11th to 20th	Night	2 2 1 3 2 3 3 3 4 5% 71%	1520
	21st to end	Night	1 2 1 3 3 2 2 3 4 4 75%	1520
July	1st to 10th	Night	3 2 1 3 2 2 2 2 5% 6% 71%	1504
	11th to 20th	Night	3 3 2 5% 4 4 3 3 5% 7% 62%	1440
	21st to end	Night	2 4 2 5% 5% 4 5% 4 6% 7% 57%	1704
August	1st to 10th	Night	4 3 2 3 3 3 3 3 4 6% 66%	1619
	11th to 20th	Night	2 2 1 3 2 2 3 2 4 6% 73%	1780
	21st to end	Night	2 1 1 3 2 2 3 2 4 5% 76%	1980
September	1st to 10th	Night	1 1 3 3 2 3 3 3 4 77%	1804
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 4 76%	1980
	21st to end	Night	2 1 1 2 2 3 1 2 2 3 80%	1980
October	1st to 10th	Night	3 2 1 3 3 3 4 3 4 5% 71%	1980
	11th to 20th	Night	2 2 1 3 2 2 2 2 3 5% 76%	2054
	21st to end	Night	1 2 1 3 2 2 2 2 4 5% 77%	2574
November	1st to 10th	Night	2 4 1 3 2 2 3 2 4 7% 70%	2405
	11th to 20th	Night	2 2 1 3 2 3 3 3 5% 7% 70%	2470
	21st to end	Night	1 3 1 3 4 3 3 3 5% 7% 67%	2470
December	1st to 10th	Night	2 5% 2 6% 3 4 5% 3 4 7% 59%	2470
	11th to 20th	Night	6% 8% 2 5% 3 4 4 3 6% 9% 49%	3159
	21st to end	Night	2 5% 2 7% 5% 6% 6% 5% 7% 9% 46%	4862

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	20% 6% 19% 34% 19% 1	2539
	11th to 20th	Day	25% 5% 18% 31% 16% 6%	2540
	21st to end	Day	29% 6% 18% 26% 18% 3	3125
February	1st to 10th	Day	22% 5% 11% 29% 25% 8%	1900
	11th to 20th	Day	24% 4 9% 26% 29% 8%	1860
	21st to end	Day	24% 4 10% 29% 26% 6%	1570
March	1st to 10th	Day	25% 5% 8% 27% 26% 9%	3138
	11th to 20th	Day	19% 6% 10% 31% 27% 7%	3353
	21st to end	Day	30% 8% 12% 26% 21% 4	4000
April	1st to 10th	Day	24% 4 8% 25% 24% 16%	2280
	11th to 20th	Day	21% 4 7% 23% 29% 17%	2252
	21st to end	Day	19% 4 7% 25% 34% 11%	2381
May	1st to 10th	Day	16% 3 4 20% 39% 18%	4110
	11th to 20th	Day	16% 4 4 14% 37% 25%	4074
	21st to end	Day	17% 4 5% 15% 37% 21%	4477
June	1st to 10th	Day	18% 4 5% 14% 28% 30%	2639
	11th to 20th	Day	14% 2 3 8% 28% 45%	2660
	21st to end	Day	10% 3 2 5% 22% 57%	2660
July	1st to 10th	Day	16% 3 3 6% 15% 58%	2552
	11th to 20th	Day	16% 4 4 9% 20% 46%	2445
	21st to end	Day	24% 5% 6% 13% 18% 33%	2466
August	1st to 10th	Day	16% 3 3 7% 19% 53%	2302
	11th to 20th	Day	11% 4 4 9% 21% 50%	2122
	21st to end	Day	12% 3 2 9% 25% 48%	2376
September	1st to 10th	Day	13% 3 4 9% 21% 50%	2156
	11th to 20th	Day	12% 3 3 12% 27% 43%	1980
	21st to end	Day	11% 2 3 11% 36% 38%	1980
October	1st to 10th	Day	16% 3 6% 13% 33% 29%	1980
	11th to 20th	Day	13% 3 3 16% 36% 29%	1900
	21st to end	Day	12% 2 3 21% 41% 20%	1782
November	1st to 10th	Day	18% 3 8% 25% 31% 14%	1674
	11th to 20th	Day	12% 3 8% 29% 36% 11%	1710
	21st to end	Day	19% 3 10% 26% 31% 12%	1710
December	1st to 10th	Day	20% 5% 13% 27% 26% 10%	1710
	11th to 20th	Day	34% 6% 10% 24% 21% 5%	2042
	21st to end	Day	24% 9% 17% 23% 21% 5%	2794
January	1st to 10th	Night	23% 5% 15% 33% 23% 2	4406
	11th to 20th	Night	24% 5% 16% 31% 18% 6%	4420
	21st to end	Night	28% 6% 17% 27% 17% 4	4536
February	1st to 10th	Night	23% 4 11% 28% 26% 8%	2280
	11th to 20th	Night	21% 5% 10% 23% 32% 10%	2219
	21st to end	Night	23% 5% 11% 29% 25% 7%	1884
March	1st to 10th	Night	21% 6% 9% 28% 26% 9%	3736
	11th to 20th	Night	22% 7% 12% 27% 24% 8%	3625
	21st to end	Night	24% 7% 12% 29% 23% 4	3648
April	1st to 10th	Night	20% 6% 10% 30% 23% 12%	1900
	11th to 20th	Night	19% 4 7% 27% 29% 14%	1879
	21st to end	Night	20% 4 6% 25% 36% 8%	1796
May	1st to 10th	Night	15% 5% 6% 18% 41% 15%	2860
	11th to 20th	Night	15% 6% 7% 15% 38% 19%	2835
	21st to end	Night	19% 6% 7% 15% 37% 16%	3110
June	1st to 10th	Night	14% 5% 7% 15% 32% 27%	1535
	11th to 20th	Night	14% 5% 3 9% 29% 40%	1520
	21st to end	Night	12% 2 3 5% 25% 51%	1520
July	1st to 10th	Night	15% 2 4 8% 14% 57%	1464
	11th to 20th	Night	21% 4 5% 11% 17% 43%	1392
	21st to end	Night	23% 5% 8% 17% 14% 33%	1609
August	1st to 10th	Night	17% 4 5% 9% 17% 48%	1610
	11th to 20th	Night	11% 4 6% 10% 21% 48%	1780
	21st to end	Night	11% 3 3 9% 25% 48%	1980
September	1st to 10th	Night	11% 3 4 8% 22% 51%	1804
	11th to 20th	Night	12% 3 4 12% 27% 42%	1980
	21st to end	Night	11% 2 3 12% 30% 42%	1980
October	1st to 10th	Night	16% 3 4 17% 30% 29%	1980
	11th to 20th	Night	13% 2 3 18% 34% 29%	2054
	21st to end	Night	11% 2 5% 20% 42% 20%	2574
November	1st to 10th	Night	15% 3 9% 27% 32% 16%	2405
	11th to 20th	Night	13% 4 8% 26% 38% 12%	2470
	21st to end	Night	18% 3 7% 24% 36% 12%	2470
December	1st to 10th	Night	24% 5% 11% 25% 25% 10%	2470
	11th to 20th	Night	32% 5% 12% 24% 22% 5%	3159
	21st to end	Night	32% 7% 13% 21% 21% 5%	4862

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	9% 6% 18% 40% 24% 3	180
	11th to 20th	Day	6% 4 24% 29% 28% 9%	180
	21st to end	Day	6% 4 17% 31% 30% 13%	330
February	1st to 10th	Day	7% 10% 28% 29% 19% 8%	460
	11th to 20th	Day	7% 9% 26% 33% 20% 5%	455
	21st to end	Day	5% 9% 30% 36% 13% 5%	382
March	1st to 10th	Day	9% 13% 26% 28% 20% 4	460
	11th to 20th	Day	6% 10% 27% 31% 19% 7%	460
	21st to end	Day	8% 10% 32% 30% 15% 5%	506
April	1st to 10th	Day	7% 13% 25% 26% 20% 10%	460
	11th to 20th	Day	6% 14% 25% 31% 17% 7%	452
	21st to end	Day	8% 9% 24% 29% 20% 11%	460
May	1st to 10th	Day	3 11% 27% 28% 21% 9%	463
	11th to 20th	Day	7% 5% 21% 29% 21% 16%	488
	21st to end	Day	8% 6% 15% 27% 27% 17%	529
June	1st to 10th	Day	3 7% 18% 26% 26% 20%	490
	11th to 20th	Day	3 8% 20% 29% 25% 16%	490
	21st to end	Day	3 3 14% 28% 36% 17%	490
July	1st to 10th	Day	3 1 12% 35% 33% 17%	475
	11th to 20th	Day	3 2 8% 34% 32% 22%	444
	21st to end	Day	5% 1 7% 30% 35% 22%	487
August	1st to 10th	Day	6% 1 12% 34% 27% 19%	447
	11th to 20th	Day	4 1 10% 27% 32% 26%	437
	21st to end	Day	2 2 12% 30% 36% 19%	495
September	1st to 10th	Day	3 3 12% 28% 29% 25%	450
	11th to 20th	Day	2 5% 17% 30% 28% 18%	450
	21st to end	Day	2 4 13% 30% 38% 13%	450
October	1st to 10th	Day	3 7% 20% 28% 28% 15%	450
	11th to 20th	Day	3 4 19% 24% 36% 14%	437
	21st to end	Day	3 3 18% 28% 32% 16%	297
November	1st to 10th	Day	5% 2 20% 30% 29% 14%	270
	11th to 20th	Day	1 4 13% 40% 26% 16%	270
	21st to end	Day	3 4 18% 29% 33% 13%	270
December	1st to 10th	Day	6% 3 18% 36% 29% 9%	270
	11th to 20th	Day	4 3 18% 39% 25% 11%	232
	21st to end	Day	6% 3 26% 33% 26% 7%	198
January	1st to 10th	Night	6% 3 21% 39% 24% 7%	760
	11th to 20th	Night	4 2 19% 46% 24% 5%	760
	21st to end	Night	7% 2 19% 45% 22% 6%	836
February	1st to 10th	Night	5% 3 23% 42% 23% 3	760
	11th to 20th	Night	5% 3 24% 42% 22% 4	744
	21st to end	Night	5% 4 25% 47% 17% 3	628
March	1st to 10th	Night	4 5% 23% 48% 17% 3	760
	11th to 20th	Night	4 4 24% 42% 22% 4	760
	21st to end	Night	6% 7% 28% 39% 18% 2	836
April	1st to 10th	Night	4 8% 23% 44% 20% 1	760
	11th to 20th	Night	5% 6% 28% 40% 18% 3	751
	21st to end	Night	5% 6% 24% 40% 22% 3	656
May	1st to 10th	Night	4 6% 31% 39% 17% 2	570
	11th to 20th	Night	6% 4 20% 41% 27% 2	561
	21st to end	Night	6% 6% 18% 37% 29% 3	617
June	1st to 10th	Night	2 3 14% 46% 33% 3	395
	11th to 20th	Night	2 3 19% 47% 27% 1	380
	21st to end	Night	1 1 11% 51% 34% 2	380
July	1st to 10th	Night	4 1 8% 47% 35% 5%	366
	11th to 20th	Night	4 5% 46% 41% 4	348
	21st to end	Night	3 1 5% 44% 43% 5%	522
August	1st to 10th	Night	4 1 13% 48% 31% 2	545
	11th to 20th	Night	2 7% 38% 46% 6%	712
	21st to end	Night	3 1 5% 41% 46% 5%	792
September	1st to 10th	Night	2 10% 32% 48% 8%	720
	11th to 20th	Night	3 2 11% 36% 42% 6%	720
	21st to end	Night	3 2 12% 37% 35% 11%	720
October	1st to 10th	Night	4 1 16% 42% 31% 6%	720
	11th to 20th	Night	3 2 13% 41% 36% 6%	720
	21st to end	Night	1 2 18% 38% 31% 10%	792
November	1st to 10th	Night	3 3 12% 41% 31% 9%	740
	11th to 20th	Night	3 1 16% 46% 28% 6%	760
	21st to end	Night	2 2 18% 42% 29% 6%	760
December	1st to 10th	Night	6% 2 18% 48% 19% 6%	760
	11th to 20th	Night	8% 2 18% 48% 20% 4	760
	21st to end	Night	5% 2 25% 48% 19% 3	836

Page generated at 2024-07-05 08:05:37. Version ac07

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