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 2005-11-05 to 2017-04-25.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
49%
15188
26%
45535
19%
15143
56%
15143
33%
26796

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
33%
898
28%
2327
11%
895
44%
895
31%
1466
January16th to endNight
32%
960
29%
2496
11%
960
42%
960
33%
1576
February1st to 15thNight
30%
880
23%
2286
7%
876
38%
876
30%
1456
February16th to endNight
29%
550
28%
1812
12%
550
42%
550
27%
1062
March1st to 15thNight
33%
540
24%
1980
16%
540
44%
540
23%
1199
March16th to endNight
37%
576
21%
2112
15%
576
48%
576
24%
1278
April1st to 15thNight
34%
539
24%
1857
16%
539
48%
539
29%
1048
April16th to endNight
43%
525
25%
1750
20%
525
55%
525
30%
1002
May1st to 15thNight
42%
495
22%
1546
16%
495
51%
495
27%
974
May16th to endNight
55%
515
22%
1541
21%
513
60%
513
31%
960
June1st to 15thNight
73%
495
25%
1485
26%
495
76%
495
43%
804
June16th to endNight
76%
495
23%
1485
25%
495
77%
495
46%
771
July1st to 15thNight
77%
465
23%
1395
25%
465
78%
465
42%
773
July16th to endNight
83%
522
25%
1468
30%
489
83%
489
44%
789
August1st to 15thNight
82%
494
29%
1475
32%
491
84%
491
49%
749
August16th to endNight
74%
525
22%
1747
27%
525
74%
525
32%
1005
September1st to 15thNight
68%
495
24%
1687
28%
495
69%
495
31%
971
September16th to endNight
71%
497
33%
1820
33%
497
75%
497
39%
915
October1st to 15thNight
61%
660
31%
1980
24%
660
66%
660
39%
1108
October16th to endNight
53%
704
35%
2112
23%
704
63%
704
42%
1114
November1st to 15thNight
49%
700
30%
2100
20%
700
57%
700
36%
1178
November16th to endNight
39%
798
31%
2238
17%
798
50%
798
31%
1385
December1st to 15thNight
37%
900
24%
2340
12%
900
44%
900
28%
1560
December16th to endNight
35%
960
24%
2496
11%
960
43%
960
29%
1653

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 ForecastData
Points
Cloud CoverDay
15%5%2442445%6%44%
46098
Night
13%423323347%51%
45732
TransparencyDay
39%5%10%21%18%5%
45798
Night
33%49%21%22%7%
45537
SeeingDay
13%5%18%25%27%9%
5001
Night
15%6%23%31%20%2
15190

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
18%5%2331323449%
1611
16th to endDay
21%6%1331233447%
1728
February1st to 15thDay
20%5%24322435%44%
1575
16th to endDay
24%7%2431232442%
1668
March1st to 15thDay
22%6%23323335%42%
1980
16th to endDay
21%6%36%434335%38%
2110
April1st to 15thDay
16%5%24333346%45%
2091
16th to endDay
19%5%3432445%6%41%
2098
May1st to 15thDay
20%6%36%5%2445%6%35%
2073
16th to endDay
12%6%35%5%45%6%5%8%35%
2222
June1st to 15thDay
8%425%6%35%5%6%8%41%
2145
16th to endDay
6%4245%36%5%7%9%43%
2145
July1st to 15thDay
9%426%6%37%6%8%10%34%
2145
16th to endDay
8%2245%36%5%8%10%39%
2284
August1st to 15thDay
5%2135%346%7%11%47%
2145
16th to endDay
9%325%7%36%6%6%7%38%
2102
September1st to 15thDay
15%5%15%4245%6%7%42%
1941
16th to endDay
9%413434446%54%
1799
October1st to 15thDay
15%425%42333449%
1650
16th to endDay
14%31231335%59%
1760
November1st to 15thDay
15%424222347%51%
1758
16th to endDay
19%5%1442221451%
1720
December1st to 15thDay
21%6%2431324445%
1620
16th to endDay
22%7%2421323443%
1728
January1st to 15thNight
16%5%23312235%51%
2327
16th to endNight
17%5%1331332452%
2496
February1st to 15thNight
17%424313245%50%
2278
16th to endNight
17%5%3331234450%
1812
March1st to 15thNight
20%6%23313245%45%
1980
16th to endNight
16%6%34323336%46%
2112
April1st to 15thNight
11%5%24324347%50%
1857
16th to endNight
12%5%23423246%52%
1750
May1st to 15thNight
15%5%44423447%44%
1545
16th to endNight
9%5%2443345%9%46%
1539
June1st to 15thNight
5%324323348%58%
1485
16th to endNight
4223323348%59%
1485
July1st to 15thNight
5%31443346%14%48%
1485
16th to endNight
4213325%48%11%52%
1576
August1st to 15thNight
321221436%13%57%
1485
16th to endNight
7%3145%346%7%11%44%
1747
September1st to 15thNight
9%41442435%9%48%
1687
16th to endNight
7%32342345%7%57%
1820
October1st to 15thNight
10%42331335%6%56%
1980
16th to endNight
12%31211223462%
2112
November1st to 15thNight
11%413412345%57%
2100
16th to endNight
19%5%2321323452%
2238
December1st to 15thNight
19%6%2432424445%
2340
16th to endNight
20%6%23312336%44%
2496

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
40%27%22%20%6%
1612
16th to endDay
40%3422%23%5%
1728
February1st to 15thDay
42%37%20%20%5%
1576
16th to endDay
46%37%17%19%6%
1668
March1st to 15thDay
43%38%19%18%5%
1980
16th to endDay
49%47%19%16%2
2112
April1st to 15thDay
39%48%21%17%7%
2091
16th to endDay
42%5%9%20%18%4
2098
May1st to 15thDay
48%5%9%17%14%3
2073
16th to endDay
44%8%12%20%12%1
2226
June1st to 15thDay
37%7%13%25%14%1
2145
16th to endDay
34%8%12%24%18%1
2145
July1st to 15thDay
38%8%15%24%11%
2006
16th to endDay
34%8%18%26%11%
2129
August1st to 15thDay
27%7%16%29%18%1
2131
16th to endDay
38%7%18%19%11%3
2102
September1st to 15thDay
40%7%12%15%16%8%
1941
16th to endDay
29%49%25%22%8%
1799
October1st to 15thDay
38%46%15%21%12%
1650
16th to endDay
29%35%20%29%12%
1760
November1st to 15thDay
33%37%22%24%8%
1758
16th to endDay
40%2318%27%7%
1720
December1st to 15thDay
43%39%19%18%6%
1620
16th to endDay
45%27%20%19%4
1728
January1st to 15thNight
36%36%17%29%6%
2327
16th to endNight
37%26%19%26%8%
2496
February1st to 15thNight
37%37%22%21%7%
2288
16th to endNight
37%36%22%21%8%
1812
March1st to 15thNight
41%39%17%18%9%
1980
16th to endNight
40%49%20%21%4
2112
April1st to 15thNight
33%410%20%19%11%
1857
16th to endNight
34%47%22%24%6%
1750
May1st to 15thNight
39%5%9%21%15%8%
1546
16th to endNight
35%7%14%24%16%1
1541
June1st to 15thNight
24%5%10%32%22%3
1485
16th to endNight
23%414%27%25%4
1485
July1st to 15thNight
24%7%19%28%18%1
1395
16th to endNight
23%6%17%33%18%1
1468
August1st to 15thNight
18%7%17%31%22%3
1475
16th to endNight
30%8%14%23%18%4
1747
September1st to 15thNight
32%6%11%18%20%9%
1687
16th to endNight
26%48%23%24%12%
1820
October1st to 15thNight
29%48%18%22%15%
1980
16th to endNight
26%25%18%30%15%
2112
November1st to 15thNight
30%47%20%26%11%
2100
16th to endNight
37%3415%29%9%
2238
December1st to 15thNight
42%38%18%19%7%
2340
16th to endNight
41%38%21%18%6%
2496

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
18%15%36%23%5%
90
16th to endDay
18%21%34%16%8%
96
February1st to 15thDay
18%17%43%12%7%
90
16th to endDay
24%22%37%11%4
81
March1st to 15thDay
34%14%31%16%3
90
16th to endDay
15%22%28%28%5%
96
April1st to 15thDay
17%13%33%22%11%1
210
16th to endDay
23%6%27%22%16%3
250
May1st to 15thDay
19%6%31%29%10%1
330
16th to endDay
14%422%34%18%5%
437
June1st to 15thDay
10%113%26%38%9%
420
16th to endDay
5%215%31%31%13%
420
July1st to 15thDay
6%113%31%39%8%
400
16th to endDay
5%5%22%44%21%
445
August1st to 15thDay
6%5%25%43%18%
418
16th to endDay
14%5%20%40%19%
270
September1st to 15thDay
10%17%17%46%17%
216
16th to endDay
2114%26%45%10%
90
October1st to 15thDay
5%225%40%20%6%
90
16th to endDay
22%416%35%14%6%
96
November1st to 15thDay
15%8%25%30%16%3
90
16th to endDay
33%13%25%15%10%2
90
December1st to 15thDay
22%12%36%15%10%3
90
16th to endDay
29%17%33%15%22
96
January1st to 15thNight
21%11%30%28%7%
900
16th to endNight
20%10%34%28%5%
960
February1st to 15thNight
20%13%33%26%5%
880
16th to endNight
19%11%36%27%5%
550
March1st to 15thNight
22%9%31%30%6%
540
16th to endNight
17%10%32%31%7%
576
April1st to 15thNight
12%9%40%27%9%
539
16th to endNight
12%8%31%32%13%
525
May1st to 15thNight
15%331%35%12%
495
16th to endNight
11%223%34%25%2
515
June1st to 15thNight
5%10%44%36%2
495
16th to endNight
419%34%41%7%
495
July1st to 15thNight
5%5%34%48%5%
465
16th to endNight
3325%55%10%
522
August1st to 15thNight
47%28%46%12%
494
16th to endNight
8%5%31%46%7%
525
September1st to 15thNight
11%111%32%36%6%
495
16th to endNight
8%111%36%37%5%
497
October1st to 15thNight
13%218%34%27%4
660
16th to endNight
14%5%24%30%21%2
704
November1st to 15thNight
11%7%25%36%17%1
700
16th to endNight
21%8%27%25%15%
798
December1st to 15thNight
23%9%26%32%8%
900
16th to endNight
24%8%28%30%7%
960
Page generated at 2017-04-26 16:21:46. Version ac04

Copyright 2017 A. Danko


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