EAFB
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the EAFB clear sky chart from 2005-11-05 to 2017-09-16.

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
67%
15725
38%
46793
29%
15683
76%
15683
64%
20374

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
65%
716
30%
2506
29%
716
73%
716
47%
1139
January16th to endNight
63%
768
39%
2370
32%
768
73%
768
51%
1121
February1st to 15thNight
62%
697
36%
2105
31%
697
72%
697
54%
1004
February16th to endNight
56%
632
34%
1895
29%
632
67%
632
48%
944
March1st to 15thNight
61%
720
32%
2160
28%
720
71%
720
54%
1017
March16th to endNight
55%
768
37%
2012
21%
768
69%
768
63%
978
April1st to 15thNight
47%
719
36%
1799
13%
719
60%
719
62%
911
April16th to endNight
52%
720
39%
1800
15%
720
64%
720
72%
827
May1st to 15thNight
55%
588
38%
1667
22%
587
63%
587
75%
674
May16th to endNight
50%
561
37%
1685
21%
561
62%
561
72%
651
June1st to 15thNight
61%
439
38%
1519
29%
439
73%
439
81%
495
June16th to endNight
74%
360
42%
1440
42%
360
85%
360
86%
398
July1st to 15thNight
88%
340
37%
1360
41%
340
92%
340
69%
449
July16th to endNight
85%
564
38%
1589
31%
527
86%
527
69%
668
August1st to 15thNight
82%
717
39%
1790
23%
713
84%
713
85%
774
August16th to endNight
87%
764
46%
1910
29%
764
89%
764
83%
846
September1st to 15thNight
82%
720
44%
1833
29%
720
87%
720
81%
805
September16th to endNight
81%
660
48%
1826
39%
660
89%
660
84%
729
October1st to 15thNight
68%
660
42%
1826
32%
660
80%
660
68%
821
October16th to endNight
73%
704
45%
2157
40%
704
84%
704
69%
876
November1st to 15thNight
76%
700
39%
2275
38%
700
83%
700
64%
917
November16th to endNight
73%
720
40%
2340
39%
720
81%
720
60%
980
December1st to 15thNight
65%
720
35%
2340
31%
720
75%
720
48%
1095
December16th to endNight
58%
768
33%
2589
29%
768
69%
768
43%
1255

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
211212236%75%
47944
Night
211212235%75%
46989
TransparencyDay
12%25%16%27%36%
47633
Night
12%25%18%30%30%
46801
SeeingDay
39%25%29%20%11%
5861
Night
2323%41%26%2
15738

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
5%23234338%61%
1432
16th to endDay
6%424214337%59%
1847
February1st to 15thDay
211331335%8%64%
1751
16th to endDay
5%21332335%8%59%
1579
March1st to 15thDay
21121247%10%65%
1800
16th to endDay
11121225%5%8%67%
2208
April1st to 15thDay
2212212336%72%
2149
16th to endDay
1111237%79%
2160
May1st to 15thDay
11225%83%
2281
16th to endDay
11111225%81%
2429
June1st to 15thDay
11122483%
2436
16th to endDay
111289%
2520
July1st to 15thDay
1121222480%
2520
16th to endDay
212112225%76%
2462
August1st to 15thDay
11112385%
2160
16th to endDay
1122484%
2292
September1st to 15thDay
11213384%
2127
16th to endDay
1111387%
1823
October1st to 15thDay
121121223476%
1802
16th to endDay
11221235%77%
1713
November1st to 15thDay
112122246%74%
1584
16th to endDay
212323348%67%
1620
December1st to 15thDay
222442335%9%60%
1620
16th to endDay
5%323323447%58%
1629
January1st to 15thNight
4213313247%65%
2506
16th to endNight
4213212247%66%
2370
February1st to 15thNight
2213213246%67%
2101
16th to endNight
5%21232335%6%63%
1895
March1st to 15thNight
211222335%7%68%
2160
16th to endNight
1111212248%71%
2012
April1st to 15thNight
2112213236%73%
1799
16th to endNight
11112225%81%
1800
May1st to 15thNight
11235%82%
1667
16th to endNight
112135%83%
1684
June1st to 15thNight
122486%
1519
16th to endNight
1292%
1440
July1st to 15thNight
1111222481%
1440
16th to endNight
2111233478%
1700
August1st to 15thNight
1112388%
1800
16th to endNight
1112386%
1910
September1st to 15thNight
12111385%
1833
16th to endNight
1112388%
1826
October1st to 15thNight
1213335%77%
1826
16th to endNight
111124480%
2157
November1st to 15thNight
111112235%77%
2275
16th to endNight
31212347%72%
2340
December1st to 15thNight
3312223337%67%
2340
16th to endNight
5%212313447%63%
2589

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
22%47%24%27%13%
1432
16th to endDay
25%27%22%24%16%
1847
February1st to 15thDay
18%26%23%29%18%
1751
16th to endDay
22%28%24%30%11%
1579
March1st to 15thDay
13%29%26%27%20%
1800
16th to endDay
14%310%25%28%17%
2208
April1st to 15thDay
15%25%23%31%20%
2149
16th to endDay
7%16%24%32%26%
2160
May1st to 15thDay
7%1420%32%33%
2281
16th to endDay
9%1417%39%27%
2432
June1st to 15thDay
6%312%25%51%
2436
16th to endDay
42415%72%
2520
July1st to 15thDay
9%115%17%63%
2371
16th to endDay
12%1311%22%48%
2311
August1st to 15thDay
6%17%21%63%
2146
16th to endDay
7%11425%58%
2292
September1st to 15thDay
7%138%24%55%
2127
16th to endDay
5%17%32%52%
1823
October1st to 15thDay
12%2314%32%34%
1802
16th to endDay
10%2414%29%39%
1713
November1st to 15thDay
13%25%17%38%22%
1584
16th to endDay
16%36%20%29%22%
1620
December1st to 15thDay
21%49%23%27%14%
1620
16th to endDay
26%410%25%21%11%
1629
January1st to 15thNight
20%36%21%30%17%
2506
16th to endNight
19%37%22%25%21%
2370
February1st to 15thNight
18%28%20%27%22%
2112
16th to endNight
21%27%24%30%13%
1895
March1st to 15thNight
16%39%24%25%20%
2160
16th to endNight
12%310%29%28%15%
2012
April1st to 15thNight
14%27%31%28%15%
1799
16th to endNight
7%27%28%35%17%
1800
May1st to 15thNight
5%26%24%38%23%
1668
16th to endNight
6%17%21%43%19%
1685
June1st to 15thNight
45%17%31%41%
1519
16th to endNight
326%25%62%
1440
July1st to 15thNight
8%118%19%60%
1360
16th to endNight
11%1412%26%42%
1589
August1st to 15thNight
4118%26%56%
1790
16th to endNight
5%17%32%51%
1910
September1st to 15thNight
6%128%32%48%
1833
16th to endNight
418%38%45%
1826
October1st to 15thNight
11%1315%34%33%
1826
16th to endNight
9%2313%29%41%
2157
November1st to 15thNight
12%1417%35%28%
2275
16th to endNight
12%27%21%27%28%
2340
December1st to 15thNight
19%38%21%29%17%
2340
16th to endNight
22%410%24%24%13%
2589

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
16%8%21%31%18%3
60
16th to endDay
9%11%21%21%22%12%
271
February1st to 15thDay
5%12%24%23%21%13%
266
16th to endDay
8%20%23%22%14%10%
238
March1st to 15thDay
5%13%25%25%17%11%
270
16th to endDay
418%27%23%21%5%
288
April1st to 15thDay
7%19%32%18%14%7%
269
16th to endDay
5%17%37%21%11%6%
270
May1st to 15thDay
312%35%26%14%8%
288
16th to endDay
313%31%26%14%10%
330
June1st to 15thDay
19%34%28%15%9%
315
16th to endDay
334%28%19%12%
315
July1st to 15thDay
1121%39%23%12%
305
16th to endDay
2114%46%20%14%
327
August1st to 15thDay
126%37%18%15%
315
16th to endDay
1115%42%22%16%
332
September1st to 15thDay
323%32%25%14%
315
16th to endDay
16%17%29%29%15%
258
October1st to 15thDay
211%26%25%27%7%
255
16th to endDay
27%23%23%28%15%
225
November1st to 15thDay
3413%18%31%28%
90
16th to endDay
211%16%40%26%3
90
December1st to 15thDay
26%16%30%41%3
90
16th to endDay
7%13%15%30%29%3
79
January1st to 15thNight
5%320%40%27%2
720
16th to endNight
6%321%41%25%1
768
February1st to 15thNight
3324%40%25%2
704
16th to endNight
7%5%28%37%18%2
632
March1st to 15thNight
25%26%42%21%1
720
16th to endNight
26%34%36%18%1
768
April1st to 15thNight
28%39%30%18%1
719
16th to endNight
18%35%33%18%1
720
May1st to 15thNight
6%37%40%15%
588
16th to endNight
17%38%38%14%
563
June1st to 15thNight
5%32%51%10%
439
16th to endNight
23%57%17%
360
July1st to 15thNight
17%59%30%
340
16th to endNight
19%55%31%1
564
August1st to 15thNight
114%49%32%2
717
16th to endNight
19%41%42%4
764
September1st to 15thNight
111%40%39%6%
720
16th to endNight
115%36%40%5%
660
October1st to 15thNight
1224%38%30%2
660
16th to endNight
1119%33%36%5%
704
November1st to 15thNight
2117%41%32%4
700
16th to endNight
3216%40%31%5%
720
December1st to 15thNight
5%321%42%24%2
720
16th to endNight
6%426%39%21%2
768
Page generated at 2017-09-17 09:05:45. Version ac04

Copyright 2017 A. Danko


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