OCA Go-To Group
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the OCA Go-To Group clear sky chart from 2005-11-05 to 2017-08-12.

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
77%
15779
32%
46339
29%
15734
79%
15734
49%
23618

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
72%
716
28%
2405
29%
716
76%
716
41%
1221
January16th to endNight
67%
768
33%
2304
29%
768
73%
768
40%
1264
February1st to 15thNight
73%
697
34%
2102
34%
697
76%
697
45%
1095
February16th to endNight
65%
632
27%
1895
29%
632
68%
632
34%
1118
March1st to 15thNight
74%
720
29%
2160
30%
720
77%
720
46%
1119
March16th to endNight
75%
768
28%
2013
24%
768
77%
768
47%
1129
April1st to 15thNight
68%
719
27%
1799
18%
719
71%
719
47%
1052
April16th to endNight
74%
720
30%
1800
18%
720
75%
720
53%
981
May1st to 15thNight
73%
608
28%
1688
19%
608
73%
608
47%
935
May16th to endNight
77%
561
27%
1685
22%
561
77%
561
49%
875
June1st to 15thNight
76%
519
25%
1599
23%
519
77%
519
47%
840
June16th to endNight
88%
360
35%
1440
43%
360
88%
360
55%
549
July1st to 15thNight
88%
340
31%
1360
38%
340
88%
340
52%
533
July16th to endNight
84%
662
28%
1683
22%
621
84%
621
53%
887
August1st to 15thNight
86%
701
34%
1750
23%
697
86%
697
65%
870
August16th to endNight
89%
700
39%
1750
27%
700
89%
700
69%
847
September1st to 15thNight
85%
660
39%
1686
31%
660
86%
660
64%
839
September16th to endNight
87%
656
43%
1815
42%
656
88%
656
70%
800
October1st to 15thNight
82%
660
36%
1815
35%
660
84%
660
57%
912
October16th to endNight
79%
704
37%
2139
40%
704
81%
704
52%
1039
November1st to 15thNight
82%
700
35%
2275
39%
700
86%
700
54%
1014
November16th to endNight
78%
720
35%
2340
38%
720
81%
720
47%
1136
December1st to 15thNight
70%
720
33%
2340
33%
720
75%
720
39%
1240
December16th to endNight
62%
768
32%
2496
29%
768
70%
768
38%
1323

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
4312212346%66%
47592
Night
5%413212346%64%
46543
TransparencyDay
19%37%17%26%25%
47285
Night
21%37%17%24%25%
46350
SeeingDay
6%6%25%39%17%4
5799
Night
6%18%34%39%10%
15793

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%313313335%62%
1507
16th to endDay
10%5%23322335%57%
1920
February1st to 15thDay
6%223213345%62%
1751
16th to endDay
11%424323347%52%
1579
March1st to 15thDay
43122235%5%8%59%
1800
16th to endDay
432332445%8%58%
2208
April1st to 15thDay
6%322313447%60%
2149
16th to endDay
4312212236%69%
2160
May1st to 15thDay
45%12212437%64%
2259
16th to endDay
45%23212246%64%
2429
June1st to 15thDay
5%7%13312226%63%
2357
16th to endDay
121221212479%
2520
July1st to 15thDay
2412212336%69%
2517
16th to endDay
2212212246%70%
2366
August1st to 15thDay
12111113479%
2114
16th to endDay
111112345%77%
2100
September1st to 15thDay
121212135%78%
1944
16th to endDay
11111235%78%
1815
October1st to 15thDay
5%212223345%66%
1815
16th to endDay
331221334469%
1730
November1st to 15thDay
22321234471%
1584
16th to endDay
5%213323336%64%
1620
December1st to 15thDay
6%31232436%9%56%
1620
16th to endDay
10%422212347%58%
1728
January1st to 15thNight
6%313323346%60%
2405
16th to endNight
10%423213335%59%
2304
February1st to 15thNight
6%323312325%63%
2101
16th to endNight
11%323424436%52%
1895
March1st to 15thNight
5%41222335%9%58%
2160
16th to endNight
442322345%9%58%
2013
April1st to 15thNight
7%5%23213346%59%
1799
16th to endNight
4422212335%66%
1800
May1st to 15thNight
5%6%23223148%60%
1688
16th to endNight
36%22212337%64%
1684
June1st to 15thNight
37%2321235%8%60%
1599
16th to endNight
1412213237%68%
1440
July1st to 15thNight
241222235%7%64%
1440
16th to endNight
3313314448%61%
1799
August1st to 15thNight
2312211336%71%
1760
16th to endNight
1212112236%74%
1750
September1st to 15thNight
2312212235%73%
1686
16th to endNight
12121113478%
1815
October1st to 15thNight
2212223345%69%
1815
16th to endNight
4313222236%68%
2139
November1st to 15thNight
2312212235%72%
2275
16th to endNight
4312222446%64%
2340
December1st to 15thNight
8%313423347%57%
2340
16th to endNight
11%413212235%60%
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
24%37%13%23%27%
1507
16th to endDay
29%37%13%17%27%
1920
February1st to 15thDay
23%35%15%25%25%
1751
16th to endDay
31%5%7%18%26%10%
1579
March1st to 15thDay
21%49%20%20%21%
1800
16th to endDay
23%412%24%19%14%
2208
April1st to 15thDay
24%410%25%22%12%
2149
16th to endDay
18%49%23%27%17%
2160
May1st to 15thDay
21%5%9%20%26%16%
2259
16th to endDay
21%39%28%27%9%
2432
June1st to 15thDay
23%27%16%32%17%
2357
16th to endDay
11%139%32%41%
2520
July1st to 15thDay
15%35%10%27%37%
2368
16th to endDay
15%38%21%30%19%
2219
August1st to 15thDay
10%1213%38%33%
2100
16th to endDay
10%3312%39%31%
2100
September1st to 15thDay
10%2410%34%36%
1944
16th to endDay
9%1315%33%35%
1815
October1st to 15thDay
20%26%19%25%25%
1815
16th to endDay
18%36%12%21%38%
1730
November1st to 15thDay
16%27%15%21%34%
1584
16th to endDay
21%46%12%22%32%
1620
December1st to 15thDay
24%5%10%16%18%24%
1620
16th to endDay
28%5%7%16%20%21%
1728
January1st to 15thNight
24%46%12%21%29%
2405
16th to endNight
28%38%14%14%30%
2304
February1st to 15thNight
24%36%16%21%27%
2112
16th to endNight
34%47%14%23%15%
1895
March1st to 15thNight
23%49%19%22%20%
2160
16th to endNight
23%5%12%21%22%14%
2013
April1st to 15thNight
26%310%25%20%13%
1799
16th to endNight
21%39%24%22%17%
1800
May1st to 15thNight
24%5%10%21%23%15%
1689
16th to endNight
20%5%11%28%23%10%
1685
June1st to 15thNight
23%410%17%29%14%
1599
16th to endNight
15%1412%31%33%
1440
July1st to 15thNight
17%15%13%30%32%
1360
16th to endNight
20%47%22%27%17%
1683
August1st to 15thNight
15%2313%40%25%
1750
16th to endNight
12%2314%38%29%
1750
September1st to 15thNight
15%25%10%32%33%
1686
16th to endNight
11%1214%34%35%
1815
October1st to 15thNight
18%35%19%29%24%
1815
16th to endNight
19%3411%21%38%
2139
November1st to 15thNight
17%35%16%21%36%
2275
16th to endNight
21%36%16%17%34%
2340
December1st to 15thNight
27%48%15%18%25%
2340
16th to endNight
28%39%14%23%20%
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
17%426%34%17%
92
16th to endDay
14%8%28%33%14%1
288
February1st to 15thDay
8%8%28%35%16%3
266
16th to endDay
14%13%28%29%11%
238
March1st to 15thDay
7%13%28%27%18%4
270
16th to endDay
6%10%36%32%12%1
288
April1st to 15thDay
7%14%37%27%9%4
269
16th to endDay
315%42%28%5%3
270
May1st to 15thDay
8%10%33%33%10%3
288
16th to endDay
7%7%37%32%12%2
330
June1st to 15thDay
7%5%26%40%17%2
315
16th to endDay
17%50%21%9%
315
July1st to 15thDay
413%47%26%7%
305
16th to endDay
39%49%26%10%
327
August1st to 15thDay
3112%57%20%6%
300
16th to endDay
211%54%21%8%
268
September1st to 15thDay
421%56%11%5%
255
16th to endDay
1226%46%14%7%
255
October1st to 15thDay
5%8%30%36%16%3
255
16th to endDay
5%5%24%38%21%4
239
November1st to 15thDay
2312%30%33%18%
90
16th to endDay
4431%33%22%4
90
December1st to 15thDay
2415%36%37%3
90
16th to endDay
13%417%40%21%2
96
January1st to 15thNight
7%212%40%28%9%
720
16th to endNight
12%210%36%30%7%
768
February1st to 15thNight
7%19%41%30%8%
704
16th to endNight
12%310%41%26%5%
632
March1st to 15thNight
5%111%42%29%8%
720
16th to endNight
5%28%41%34%6%
768
April1st to 15thNight
8%313%42%28%4
719
16th to endNight
5%210%40%32%7%
720
May1st to 15thNight
6%113%34%38%5%
609
16th to endNight
311%42%35%5%
563
June1st to 15thNight
311%38%41%4
519
16th to endNight
2126%64%5%
360
July1st to 15thNight
411%69%14%
340
16th to endNight
4218%57%17%
662
August1st to 15thNight
3119%59%14%
701
16th to endNight
2114%59%22%
700
September1st to 15thNight
3221%51%19%
660
16th to endNight
3328%50%14%
656
October1st to 15thNight
46%39%40%9%
660
16th to endNight
5%7%30%39%15%
704
November1st to 15thNight
37%36%38%14%
700
16th to endNight
5%8%36%35%12%
720
December1st to 15thNight
9%19%40%30%9%
720
16th to endNight
13%214%36%25%7%
768
Page generated at 2017-08-13 11:16:57. Version ac04

Copyright 2017 A. Danko


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