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 2017-09-10.

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 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
75%
15769
32%
46791
28%
15725
79%
15725
48%
23699

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
69%
716
29%
2416
30%
716
74%
716
43%
1182
January16th to endNight
61%
768
33%
2457
29%
768
70%
768
40%
1284
February1st to 15thNight
72%
699
36%
2101
34%
696
78%
696
44%
1109
February16th to endNight
62%
632
27%
1895
28%
632
65%
632
35%
1102
March1st to 15thNight
71%
720
28%
2133
26%
720
77%
720
49%
1073
March16th to endNight
72%
768
29%
2001
24%
768
75%
768
48%
1124
April1st to 15thNight
69%
719
31%
1799
20%
719
74%
719
51%
1000
April16th to endNight
72%
720
32%
1800
17%
720
76%
720
57%
954
May1st to 15thNight
75%
680
27%
1760
17%
680
77%
680
51%
961
May16th to endNight
77%
561
28%
1685
22%
561
79%
561
53%
826
June1st to 15thNight
76%
362
26%
1442
29%
362
78%
362
36%
696
June16th to endNight
89%
360
31%
1440
38%
360
89%
360
49%
581
July1st to 15thNight
87%
340
29%
1360
35%
340
87%
340
47%
566
July16th to endNight
81%
615
28%
1640
23%
578
82%
578
45%
865
August1st to 15thNight
86%
717
31%
1790
21%
713
86%
713
56%
954
August16th to endNight
87%
764
34%
1910
23%
764
87%
764
57%
1024
September1st to 15thNight
82%
700
32%
1750
26%
700
82%
700
52%
988
September16th to endNight
88%
656
38%
1805
36%
656
89%
656
59%
874
October1st to 15thNight
80%
660
35%
1892
36%
660
83%
660
57%
905
October16th to endNight
81%
704
40%
2112
43%
704
84%
704
54%
1004
November1st to 15thNight
81%
700
34%
2250
36%
700
85%
700
55%
1005
November16th to endNight
77%
720
36%
2340
37%
720
81%
720
51%
1076
December1st to 15thNight
69%
720
34%
2340
33%
720
76%
720
42%
1188
December16th to endNight
61%
768
31%
2673
29%
768
69%
768
37%
1358

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
4213313447%63%
47816
Night
4313323346%64%
46991
TransparencyDay
21%410%18%26%19%
47504
Night
22%38%17%26%22%
46803
SeeingDay
6%314%36%33%5%
5974
Night
6%19%27%37%16%
15781

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
7%313322336%62%
1519
16th to endDay
10%41312336%61%
1765
February1st to 15thDay
7%42321225%6%61%
1751
16th to endDay
9%313323347%55%
1579
March1st to 15thDay
41133245%5%7%61%
1824
16th to endDay
421232335%8%60%
2221
April1st to 15thDay
421341245%7%60%
2149
16th to endDay
3212212348%68%
2160
May1st to 15thDay
231332345%7%63%
2190
16th to endDay
222312349%67%
2429
June1st to 15thDay
5%413423348%57%
2514
16th to endDay
122322447%67%
2520
July1st to 15thDay
32442346%8%59%
2520
16th to endDay
32133135%5%8%60%
2412
August1st to 15thDay
12133225%7%10%58%
2160
16th to endDay
11131336%8%67%
2292
September1st to 15thDay
11231445%9%65%
2097
16th to endDay
112322337%71%
1823
October1st to 15thDay
432212346%67%
1735
16th to endDay
2112313437%68%
1760
November1st to 15thDay
2212312345%69%
1608
16th to endDay
3113322346%67%
1620
December1st to 15thDay
6%312324447%59%
1620
16th to endDay
8%323313337%60%
1548
January1st to 15thNight
6%223322346%62%
2416
16th to endNight
9%413322236%60%
2457
February1st to 15thNight
6%313212336%64%
2101
16th to endNight
11%41442334455%
1895
March1st to 15thNight
321321335%6%63%
2133
16th to endNight
431332335%7%60%
2001
April1st to 15thNight
6%312222246%65%
1799
16th to endNight
2322212347%67%
1800
May1st to 15thNight
3313323347%63%
1760
16th to endNight
2213312237%68%
1684
June1st to 15thNight
25%23423338%59%
1442
16th to endNight
13213349%68%
1440
July1st to 15thNight
221342336%9%61%
1440
16th to endNight
13135%235%6%12%52%
1751
August1st to 15thNight
121242446%10%58%
1800
16th to endNight
22414448%63%
1910
September1st to 15thNight
2313423349%62%
1750
16th to endNight
12323235%72%
1805
October1st to 15thNight
3112312345%70%
1892
16th to endNight
2313212335%70%
2112
November1st to 15thNight
221221223474%
2250
16th to endNight
3212212336%69%
2340
December1st to 15thNight
6%214323336%62%
2340
16th to endNight
10%313212235%61%
2673

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
25%38%15%23%23%
1519
16th to endDay
26%47%17%19%24%
1765
February1st to 15thDay
23%5%6%17%26%20%
1751
16th to endDay
28%5%10%19%26%9%
1579
March1st to 15thDay
22%5%12%21%22%16%
1824
16th to endDay
22%5%14%23%20%13%
2221
April1st to 15thDay
22%5%13%25%23%9%
2149
16th to endDay
17%410%23%28%15%
2160
May1st to 15thDay
19%6%12%20%24%15%
2190
16th to endDay
17%6%14%27%26%8%
2432
June1st to 15thDay
27%5%10%17%28%10%
2514
16th to endDay
19%29%11%31%26%
2520
July1st to 15thDay
22%38%13%24%27%
2371
16th to endDay
22%5%11%18%26%15%
2260
August1st to 15thDay
23%210%13%30%18%
2146
16th to endDay
17%29%11%37%21%
2292
September1st to 15thDay
19%39%13%27%25%
2097
16th to endDay
17%27%15%30%26%
1823
October1st to 15thDay
18%39%21%23%23%
1735
16th to endDay
19%37%15%24%29%
1760
November1st to 15thDay
18%36%16%23%30%
1608
16th to endDay
17%38%19%21%29%
1620
December1st to 15thDay
24%5%9%17%24%18%
1620
16th to endDay
25%5%9%20%21%17%
1548
January1st to 15thNight
24%28%15%25%23%
2416
16th to endNight
28%27%15%16%29%
2457
February1st to 15thNight
23%45%16%24%24%
2112
16th to endNight
33%37%18%24%12%
1895
March1st to 15thNight
20%410%20%25%17%
2133
16th to endNight
23%5%12%22%22%15%
2001
April1st to 15thNight
23%39%28%24%10%
1799
16th to endNight
17%410%23%27%18%
1800
May1st to 15thNight
22%311%21%25%15%
1761
16th to endNight
18%310%25%31%10%
1685
June1st to 15thNight
25%5%9%17%31%10%
1442
16th to endNight
17%26%13%33%25%
1440
July1st to 15thNight
19%26%11%26%32%
1360
16th to endNight
25%38%22%22%17%
1640
August1st to 15thNight
21%16%14%31%24%
1790
16th to endNight
20%26%11%38%20%
1910
September1st to 15thNight
24%26%13%26%26%
1750
16th to endNight
18%1413%34%28%
1805
October1st to 15thNight
16%37%19%26%26%
1892
16th to endNight
18%26%14%25%32%
2112
November1st to 15thNight
17%27%15%24%32%
2250
16th to endNight
18%37%17%21%31%
2340
December1st to 15thNight
25%38%16%21%23%
2340
16th to endNight
26%48%18%22%19%
2673

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
14%421%46%11%1
147
16th to endDay
12%6%25%39%16%1
263
February1st to 15thDay
12%5%21%34%22%3
266
16th to endDay
12%7%24%35%18%1
238
March1st to 15thDay
48%21%38%25%1
270
16th to endDay
5%7%21%39%24%2
288
April1st to 15thDay
5%8%22%37%20%4
269
16th to endDay
27%25%39%20%3
270
May1st to 15thDay
4418%38%27%5%
288
16th to endDay
4419%39%28%3
330
June1st to 15thDay
8%214%37%30%6%
315
16th to endDay
25%34%46%10%
315
July1st to 15thDay
6%226%53%9%
305
16th to endDay
4223%55%12%
327
August1st to 15thDay
45%34%47%7%
315
16th to endDay
3326%57%9%
332
September1st to 15thDay
6%1441%41%5%
294
16th to endDay
18%40%43%4
255
October1st to 15thDay
5%316%43%28%2
255
16th to endDay
4213%43%33%3
272
November1st to 15thDay
35%12%35%28%15%
114
16th to endDay
4422%46%20%2
90
December1st to 15thDay
11%317%33%33%1
90
16th to endDay
6%10%28%40%12%1
66
January1st to 15thNight
8%111%43%26%8%
720
16th to endNight
11%317%32%29%5%
768
February1st to 15thNight
9%29%38%32%7%
704
16th to endNight
14%213%34%27%7%
632
March1st to 15thNight
5%314%34%34%8%
720
16th to endNight
6%214%31%37%8%
768
April1st to 15thNight
7%314%32%33%8%
719
16th to endNight
4314%29%37%10%
720
May1st to 15thNight
5%39%30%38%12%
681
16th to endNight
2112%26%42%13%
563
June1st to 15thNight
5%19%22%42%18%
362
16th to endNight
1213%57%24%
360
July1st to 15thNight
5%447%43%
340
16th to endNight
6%26%36%46%
615
August1st to 15thNight
3111%48%33%
717
16th to endNight
338%40%44%
764
September1st to 15thNight
6%1211%46%30%
700
16th to endNight
25%17%50%24%
656
October1st to 15thNight
48%27%47%11%
660
16th to endNight
6%6%29%41%15%
704
November1st to 15thNight
5%18%34%37%13%
700
16th to endNight
5%210%35%35%10%
720
December1st to 15thNight
7%212%37%32%7%
720
16th to endNight
11%218%36%24%5%
768
Page generated at 2017-09-11 16:35:24. Version ac04

Copyright 2017 A. Danko


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