Four Elements Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Four Elements Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
32%
15230
10%
46773
8%
15189
36%
15189
14%
35368

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
8%
899
1%
2616
0%
895
9%
895
4%
2408
January16th to endNight
16%
840
5%
2568
3%
840
18%
840
5%
2286
February1st to 15thNight
15%
702
5%
2287
2%
701
18%
701
6%
1956
February16th to endNight
23%
631
8%
1970
4%
631
28%
631
10%
1581
March1st to 15thNight
25%
720
12%
2033
7%
720
30%
720
16%
1533
March16th to endNight
38%
768
19%
2112
11%
768
44%
768
24%
1461
April1st to 15thNight
30%
647
15%
1794
6%
647
36%
647
22%
1247
April16th to endNight
39%
540
18%
1620
10%
540
45%
540
23%
1098
May1st to 15thNight
46%
537
14%
1617
12%
537
49%
537
22%
1101
May16th to endNight
50%
374
13%
1488
15%
374
56%
374
22%
882
June1st to 15thNight
50%
360
13%
1260
14%
360
55%
360
23%
792
June16th to endNight
60%
360
12%
1260
14%
360
62%
360
28%
767
July1st to 15thNight
68%
340
17%
1190
21%
340
70%
340
36%
633
July16th to endNight
63%
535
15%
1481
15%
502
63%
502
31%
918
August1st to 15thNight
62%
539
17%
1609
14%
536
65%
536
31%
962
August16th to endNight
59%
573
18%
1719
13%
573
62%
573
31%
1046
September1st to 15thNight
54%
705
14%
1869
9%
705
56%
705
30%
1250
September16th to endNight
49%
669
18%
1848
13%
669
51%
669
27%
1241
October1st to 15thNight
35%
660
12%
1958
9%
660
39%
660
16%
1456
October16th to endNight
21%
704
7%
2170
3%
704
26%
704
9%
1791
November1st to 15thNight
25%
700
11%
2357
11%
700
28%
700
10%
1834
November16th to endNight
18%
720
4%
2520
4%
720
19%
720
6%
2141
December1st to 15thNight
10%
747
1%
2547
0%
747
11%
747
2%
2343
December16th to endNight
7%
960
2%
2880
0%
960
9%
960
3%
2641

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%9%47%5%3445%7%33%
48026
Night
16%12%5%8%6%34446%27%
46941
Cloud CoverDay
15%9%37%5%3445%6%33%
48036
Night
17%12%5%8%6%34446%27%
46945
TransparencyDay
50%6%12%19%9%
47712
Night
57%6%11%15%8%
46773
SeeingDay
18%5%24%29%16%5%
5836
Night
22%10%25%26%13%2
15234

By Month

Percentage Cloud Cover NE (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
20%20%9%13%8%35%4228%
1319
16th to endDay
16%20%8%12%9%46%4439%
1654
February1st to 15thDay
13%17%8%12%9%45%335%15%
1575
16th to endDay
14%17%7%9%7%45%345%20%
1503
March1st to 15thDay
13%10%37%5%45%45%6%31%
1915
16th to endDay
13%7%37%5%45%45%6%35%
2112
April1st to 15thDay
20%9%35%433436%34%
2164
16th to endDay
18%8%2432235%6%41%
2340
May1st to 15thDay
17%7%24324447%39%
2334
16th to endDay
12%41443445%8%46%
2624
June1st to 15thDay
12%6%25%5%345%5%8%40%
2700
16th to endDay
11%5%25%4345%6%9%39%
2700
July1st to 15thDay
8%4245%2446%8%49%
2700
16th to endDay
8%42443446%9%47%
2583
August1st to 15thDay
10%42442435%7%48%
2340
16th to endDay
11%6%26%424449%42%
2483
September1st to 15thDay
13%5%26%4345%5%8%41%
2076
16th to endDay
16%5%25%4345%5%7%38%
1837
October1st to 15thDay
21%9%36%5%2445%6%30%
1672
16th to endDay
29%12%49%7%3434417%
1700
November1st to 15thDay
20%12%48%7%35%5%5%6%20%
1501
16th to endDay
23%18%6%10%7%4434411%
1440
December1st to 15thDay
21%24%6%12%9%45%3336%
1410
16th to endDay
21%22%10%13%7%333336%
1344
January1st to 15thNight
20%20%8%13%9%443237%
2616
16th to endNight
15%18%9%12%9%45%43411%
2568
February1st to 15thNight
12%19%8%13%8%34445%14%
2285
16th to endNight
14%14%7%9%7%45%44421%
1970
March1st to 15thNight
15%12%46%7%34345%30%
2021
16th to endNight
14%7%46%6%33445%39%
2112
April1st to 15thNight
21%9%24413446%35%
1794
16th to endNight
19%7%25%42445%7%37%
1620
May1st to 15thNight
16%7%445%35%45%6%35%
1617
16th to endNight
10%5%35%5%345%47%43%
1486
June1st to 15thNight
12%7%25%6%345%48%39%
1260
16th to endNight
9%5%25%5%45%6%5%9%41%
1260
July1st to 15thNight
7%314425%5%5%9%50%
1260
16th to endNight
7%414425%46%8%48%
1584
August1st to 15thNight
7%4244245%6%7%48%
1620
16th to endNight
9%5%15%5%3436%8%46%
1719
September1st to 15thNight
13%424425%5%6%8%41%
1869
16th to endNight
14%7%35%43345%7%41%
1848
October1st to 15thNight
21%9%38%5%24346%29%
1958
16th to endNight
26%11%38%6%34445%19%
2170
November1st to 15thNight
19%14%49%6%3445%6%21%
2357
16th to endNight
24%18%6%8%7%34435%13%
2520
December1st to 15thNight
22%21%8%12%8%343337%
2547
16th to endNight
23%23%8%12%7%333337%
2880

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%20%8%15%8%344328%
1319
16th to endDay
16%19%8%13%9%5%6%4338%
1654
February1st to 15thDay
13%18%8%12%9%46%335%15%
1575
16th to endDay
14%15%7%10%8%35%445%19%
1503
March1st to 15thDay
13%9%47%6%45%46%6%30%
1926
16th to endDay
13%7%36%6%36%45%6%35%
2111
April1st to 15thDay
21%9%345%23446%34%
2164
16th to endDay
18%7%2432335%7%41%
2340
May1st to 15thDay
17%7%2432445%6%39%
2334
16th to endDay
12%42442445%8%46%
2624
June1st to 15thDay
12%5%25%5%35%5%5%8%40%
2700
16th to endDay
11%5%35%5%35%5%6%8%40%
2700
July1st to 15thDay
8%4245%2445%8%49%
2700
16th to endDay
9%31433447%9%47%
2583
August1st to 15thDay
10%42342446%7%48%
2340
16th to endDay
11%6%25%425%45%9%41%
2483
September1st to 15thDay
12%5%26%425%45%7%42%
2076
16th to endDay
16%6%25%4236%48%38%
1837
October1st to 15thDay
21%8%46%5%335%45%31%
1672
16th to endDay
30%11%48%6%3444417%
1700
November1st to 15thDay
20%10%49%7%36%5%46%20%
1501
16th to endDay
24%19%5%10%8%3444412%
1440
December1st to 15thDay
20%24%7%13%9%35%3226%
1410
16th to endDay
21%24%8%13%6%342346%
1344
January1st to 15thNight
20%20%8%13%8%45%4347%
2616
16th to endNight
15%19%9%12%9%45%33411%
2568
February1st to 15thNight
13%18%10%12%9%3435%414%
2278
16th to endNight
14%14%7%11%6%35%5%35%21%
1970
March1st to 15thNight
16%11%5%6%6%35%35%5%30%
2033
16th to endNight
14%7%37%5%34436%39%
2112
April1st to 15thNight
21%9%25%414445%36%
1794
16th to endNight
18%7%3441446%7%37%
1620
May1st to 15thNight
16%8%36%435%45%6%35%
1616
16th to endNight
11%5%26%5%35%5%5%6%43%
1486
June1st to 15thNight
13%6%25%5%35%449%39%
1260
16th to endNight
9%5%15%5%35%6%5%8%41%
1260
July1st to 15thNight
7%313425%46%9%49%
1260
16th to endNight
8%414425%47%7%48%
1584
August1st to 15thNight
7%5%244246%6%7%48%
1620
16th to endNight
9%5%15%4345%5%8%47%
1719
September1st to 15thNight
14%325%4245%6%7%42%
1869
16th to endNight
14%7%24424347%41%
1848
October1st to 15thNight
23%7%46%5%34447%28%
1958
16th to endNight
27%11%47%5%35%445%19%
2170
November1st to 15thNight
20%13%49%6%24446%22%
2357
16th to endNight
25%17%6%9%6%34435%13%
2520
December1st to 15thNight
22%23%8%13%8%332337%
2547
16th to endNight
23%23%9%12%7%232337%
2880

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
83%5%6%4
1320
16th to endDay
80%5%6%5%1
1654
February1st to 15thDay
73%5%9%9%1
1577
16th to endDay
67%6%9%11%5%
1503
March1st to 15thDay
54%5%12%19%7%
1926
16th to endDay
47%6%13%18%13%2
2112
April1st to 15thDay
51%5%8%21%11%1
2164
16th to endDay
42%6%12%22%14%2
2340
May1st to 15thDay
43%6%8%23%14%2
2334
16th to endDay
35%5%15%25%16%1
2628
June1st to 15thDay
39%7%12%26%12%
2700
16th to endDay
39%7%15%25%12%
2700
July1st to 15thDay
30%6%15%29%16%1
2541
16th to endDay
31%9%15%28%14%1
2423
August1st to 15thDay
32%7%18%27%13%
2327
16th to endDay
39%7%15%26%11%1
2483
September1st to 15thDay
40%7%14%27%9%
2076
16th to endDay
42%7%15%25%8%
1837
October1st to 15thDay
55%5%11%18%9%
1672
16th to endDay
69%7%10%9%3
1700
November1st to 15thDay
63%7%12%11%5%
1501
16th to endDay
75%5%10%7%1
1440
December1st to 15thDay
84%5%6%21
1410
16th to endDay
84%47%3
1344
January1st to 15thNight
81%6%7%4
2616
16th to endNight
76%7%8%5%1
2568
February1st to 15thNight
72%6%8%9%2
2287
16th to endNight
64%6%11%11%5%
1970
March1st to 15thNight
55%5%12%18%6%
2033
16th to endNight
47%410%20%15%2
2112
April1st to 15thNight
49%310%22%12%1
1794
16th to endNight
45%5%9%18%18%2
1620
May1st to 15thNight
47%5%9%19%15%2
1617
16th to endNight
37%7%13%22%17%2
1488
June1st to 15thNight
41%6%10%23%16%1
1260
16th to endNight
38%5%15%25%14%
1260
July1st to 15thNight
28%5%14%29%19%2
1190
16th to endNight
33%8%13%26%17%
1481
August1st to 15thNight
33%7%16%26%15%1
1609
16th to endNight
35%6%17%26%13%1
1719
September1st to 15thNight
39%7%15%25%11%
1869
16th to endNight
43%5%14%26%10%
1848
October1st to 15thNight
55%5%11%17%9%
1958
16th to endNight
67%6%11%11%3
2170
November1st to 15thNight
61%7%12%13%4
2357
16th to endNight
73%5%13%6%
2520
December1st to 15thNight
83%5%6%21
2547
16th to endNight
83%47%4
2880

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
25%14%35%21%4
71
16th to endDay
37%428%23%6%
96
February1st to 15thDay
30%16%32%20%1
90
16th to endDay
30%14%30%22%1
81
March1st to 15thDay
20%12%29%31%5%
216
16th to endDay
22%5%29%28%11%3
288
April1st to 15thDay
27%5%29%25%9%1
270
16th to endDay
24%6%29%21%12%5%
270
May1st to 15thDay
21%227%27%15%5%
288
16th to endDay
16%5%21%32%17%6%
337
June1st to 15thDay
13%326%36%16%3
495
16th to endDay
14%224%36%18%3
495
July1st to 15thDay
11%220%38%20%6%
475
16th to endDay
10%222%32%24%6%
414
August1st to 15thDay
12%217%31%26%9%
313
16th to endDay
18%316%27%24%9%
332
September1st to 15thDay
14%319%25%25%12%
315
16th to endDay
17%6%19%27%20%8%
262
October1st to 15thDay
24%8%24%28%11%1
255
16th to endDay
32%12%28%20%5%1
212
November1st to 15thDay
12%11%35%32%6%1
77
16th to endDay
21%15%41%20%1
60
December1st to 15thDay
26%25%31%13%3
60
16th to endDay
34%35%25%4
64
January1st to 15thNight
28%18%31%15%4
900
16th to endNight
23%14%30%23%7%1
840
February1st to 15thNight
21%15%35%21%5%
704
16th to endNight
21%8%34%26%8%
631
March1st to 15thNight
20%13%32%25%7%1
720
16th to endNight
17%6%29%30%14%1
768
April1st to 15thNight
26%7%29%27%8%1
647
16th to endNight
22%8%24%26%15%1
540
May1st to 15thNight
19%219%35%20%2
537
16th to endNight
14%420%34%23%2
375
June1st to 15thNight
17%320%37%18%2
360
16th to endNight
11%219%37%28%1
360
July1st to 15thNight
10%213%44%25%3
340
16th to endNight
10%117%40%27%2
535
August1st to 15thNight
10%317%34%28%5%
539
16th to endNight
13%118%31%29%5%
573
September1st to 15thNight
15%5%18%29%20%10%
705
16th to endNight
17%5%20%26%22%7%
669
October1st to 15thNight
25%8%24%25%14%2
660
16th to endNight
33%12%27%21%41
704
November1st to 15thNight
24%15%27%22%9%1
700
16th to endNight
33%15%24%20%6%
720
December1st to 15thNight
32%21%29%13%3
747
16th to endNight
33%18%29%14%4
960
Page generated at 2017-09-19 07:32:30. Version ac04

Copyright 2017 A. Danko


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