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 2018-03-11.

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%
16372
26%
49026
19%
16327
56%
16327
33%
28836

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%
973
27%
2522
11%
970
43%
970
31%
1592
January16th to endNight
33%
1040
30%
2704
12%
1040
44%
1040
34%
1690
February1st to 15thNight
29%
955
22%
2481
7%
951
37%
951
29%
1594
February16th to endNight
28%
596
26%
1962
11%
596
41%
596
25%
1187
March1st to 15thNight
33%
573
24%
2101
16%
573
44%
573
23%
1267
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
42%
540
25%
1800
20%
540
54%
540
29%
1034
May1st to 15thNight
43%
540
21%
1686
16%
540
53%
540
28%
1038
May16th to endNight
54%
563
23%
1685
22%
561
59%
561
31%
1043
June1st to 15thNight
74%
540
24%
1620
24%
540
77%
540
43%
880
June16th to endNight
76%
540
25%
1620
26%
540
77%
540
45%
847
July1st to 15thNight
78%
510
21%
1530
24%
510
78%
510
41%
853
July16th to endNight
82%
564
27%
1594
32%
531
83%
531
44%
848
August1st to 15thNight
81%
539
27%
1610
30%
536
83%
536
47%
830
August16th to endNight
73%
573
22%
1907
27%
573
74%
573
31%
1108
September1st to 15thNight
70%
540
24%
1841
27%
540
71%
540
33%
1032
September16th to endNight
72%
543
35%
1986
36%
543
76%
543
39%
999
October1st to 15thNight
61%
720
31%
2160
23%
720
66%
720
39%
1203
October16th to endNight
53%
768
37%
2304
24%
768
64%
768
44%
1199
November1st to 15thNight
48%
760
28%
2280
19%
760
57%
760
35%
1295
November16th to endNight
41%
865
33%
2425
18%
865
52%
865
33%
1472
December1st to 15thNight
38%
975
25%
2535
12%
975
46%
975
29%
1681
December16th to endNight
34%
1040
24%
2704
11%
1040
41%
1040
28%
1818

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%
49598
Night
13%423323347%51%
49223
TransparencyDay
39%5%10%21%18%5%
49298
Night
33%49%21%22%7%
49028
SeeingDay
14%5%20%25%25%8%
6189
Night
15%6%23%31%20%2
16374

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
19%6%2331323449%
1746
16th to endDay
20%6%2331233449%
1872
February1st to 15thDay
21%5%2442343443%
1710
16th to endDay
26%7%2431232440%
1805
March1st to 15thDay
22%6%23323345%43%
2095
16th to endDay
21%6%36%434335%38%
2110
April1st to 15thDay
16%5%24333346%45%
2091
16th to endDay
19%5%2432435%6%41%
2160
May1st to 15thDay
19%6%36%42445%6%38%
2262
16th to endDay
12%6%35%5%45%5%5%8%36%
2430
June1st to 15thDay
8%5%25%6%35%5%6%8%41%
2340
16th to endDay
6%435%5%36%5%7%9%42%
2340
July1st to 15thDay
9%426%6%37%6%7%10%34%
2340
16th to endDay
8%2245%36%6%7%10%41%
2466
August1st to 15thDay
6%3146%346%7%11%45%
2340
16th to endDay
10%425%7%36%6%6%7%38%
2294
September1st to 15thDay
14%5%15%4245%5%6%44%
2117
16th to endDay
8%413424446%53%
1962
October1st to 15thDay
15%425%423335%50%
1800
16th to endDay
14%31332235%59%
1920
November1st to 15thDay
17%424322346%49%
1908
16th to endDay
19%5%1432221452%
1863
December1st to 15thDay
19%6%24313245%45%
1755
16th to endDay
21%7%34323235%41%
1872
January1st to 15thNight
17%5%23312246%50%
2522
16th to endNight
17%5%1321222453%
2704
February1st to 15thNight
18%5%23313245%49%
2473
16th to endNight
18%5%3331334448%
1962
March1st to 15thNight
19%5%23313246%45%
2101
16th to endNight
16%6%34323336%46%
2112
April1st to 15thNight
11%5%24324347%50%
1857
16th to endNight
12%5%23423246%52%
1800
May1st to 15thNight
14%433423447%46%
1685
16th to endNight
9%5%2443346%9%45%
1683
June1st to 15thNight
5%31432345%8%58%
1620
16th to endNight
4323323348%59%
1620
July1st to 15thNight
5%31443346%14%48%
1620
16th to endNight
4213325%47%11%53%
1702
August1st to 15thNight
321321446%12%56%
1620
16th to endNight
7%4145%35%6%6%11%44%
1907
September1st to 15thNight
8%41442435%9%50%
1841
16th to endNight
7%32342345%6%57%
1986
October1st to 15thNight
10%413313346%56%
2160
16th to endNight
12%31211123464%
2304
November1st to 15thNight
11%413313345%56%
2280
16th to endNight
18%5%1321323453%
2425
December1st to 15thNight
18%6%2432424446%
2535
16th to endNight
21%6%24312336%42%
2704

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%23%19%6%
1747
16th to endDay
39%2422%24%5%
1872
February1st to 15thDay
44%37%19%19%5%
1711
16th to endDay
48%46%16%18%6%
1805
March1st to 15thDay
43%38%19%18%6%
2095
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
2160
May1st to 15thDay
46%49%16%18%4
2262
16th to endDay
43%8%12%21%13%1
2434
June1st to 15thDay
37%7%12%25%15%1
2340
16th to endDay
35%8%12%23%18%1
2340
July1st to 15thDay
39%8%15%23%12%
2201
16th to endDay
32%7%18%27%12%
2311
August1st to 15thDay
30%7%16%27%16%1
2326
16th to endDay
40%7%17%20%11%3
2294
September1st to 15thDay
38%6%11%17%16%8%
2117
16th to endDay
29%5%10%25%21%7%
1962
October1st to 15thDay
37%48%17%20%12%
1800
16th to endDay
28%35%19%30%13%
1920
November1st to 15thDay
36%37%22%23%7%
1908
16th to endDay
39%2418%28%7%
1863
December1st to 15thDay
41%39%19%18%7%
1755
16th to endDay
45%37%20%18%4
1872
January1st to 15thNight
37%36%18%27%6%
2522
16th to endNight
36%25%18%27%8%
2704
February1st to 15thNight
38%38%21%20%6%
2483
16th to endNight
39%36%21%20%8%
1962
March1st to 15thNight
40%38%17%18%10%
2101
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%5%
1800
May1st to 15thNight
37%5%9%20%17%8%
1686
16th to endNight
34%7%15%24%16%1
1685
June1st to 15thNight
24%6%10%32%22%3
1620
16th to endNight
24%413%26%26%4
1620
July1st to 15thNight
25%7%18%29%17%1
1530
16th to endNight
22%6%16%33%18%1
1594
August1st to 15thNight
19%6%17%30%21%3
1610
16th to endNight
31%8%14%24%17%3
1907
September1st to 15thNight
30%6%11%19%22%9%
1841
16th to endNight
25%48%24%24%11%
1986
October1st to 15thNight
29%48%20%22%15%
2160
16th to endNight
24%25%18%31%16%
2304
November1st to 15thNight
30%5%8%20%25%10%
2280
16th to endNight
36%2416%30%9%
2425
December1st to 15thNight
41%38%18%19%8%
2535
16th to endNight
43%38%20%17%6%
2704

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
20%13%41%20%4
135
16th to endDay
16%20%37%15%8%
144
February1st to 15thDay
23%17%38%14%6%
135
16th to endDay
35%22%30%8%3
120
March1st to 15thDay
30%17%35%14%2
121
16th to endDay
15%22%28%28%5%
96
April1st to 15thDay
17%13%33%22%11%1
210
16th to endDay
25%7%27%21%15%3
270
May1st to 15thDay
17%7%31%28%12%2
399
16th to endDay
13%5%27%33%16%4
517
June1st to 15thDay
11%113%28%36%8%
495
16th to endDay
6%217%33%28%11%
495
July1st to 15thDay
6%112%29%40%9%
475
16th to endDay
5%5%22%45%20%
515
August1st to 15thDay
8%7%25%41%16%
493
16th to endDay
16%7%20%37%17%
334
September1st to 15thDay
9%17%19%45%16%
272
16th to endDay
2113%34%40%7%
135
October1st to 15thDay
5%227%33%22%7%
135
16th to endDay
20%6%22%29%13%6%
144
November1st to 15thDay
25%8%23%26%12%2
135
16th to endDay
28%10%29%18%9%3
135
December1st to 15thDay
18%15%36%17%8%3
135
16th to endDay
26%18%36%15%21
144
January1st to 15thNight
21%11%30%28%7%
975
16th to endNight
20%11%33%29%5%
1040
February1st to 15thNight
21%13%33%26%5%
955
16th to endNight
20%12%36%26%5%
596
March1st to 15thNight
22%9%31%30%5%
573
16th to endNight
17%10%32%31%7%
576
April1st to 15thNight
12%9%40%27%9%
539
16th to endNight
13%8%32%32%13%
540
May1st to 15thNight
15%430%34%13%1
540
16th to endNight
11%225%35%23%2
563
June1st to 15thNight
5%10%44%36%2
540
16th to endNight
5%19%36%40%6%
540
July1st to 15thNight
5%5%32%50%6%
510
16th to endNight
3425%54%10%
564
August1st to 15thNight
47%29%46%11%
539
16th to endNight
9%5%31%45%7%
573
September1st to 15thNight
10%110%32%38%6%
540
16th to endNight
7%111%35%38%5%
543
October1st to 15thNight
12%218%34%27%4
720
16th to endNight
13%5%25%31%21%2
768
November1st to 15thNight
12%7%25%36%16%1
760
16th to endNight
20%7%27%26%16%
865
December1st to 15thNight
22%9%26%32%8%
975
16th to endNight
25%8%28%29%7%
1040
Page generated at 2018-03-12 12:28:05. Version ac04

Copyright 2018 A. Danko


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