OAGH
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the OAGH clear sky chart from 2005-11-05 to 2017-09-21.

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
73%
15560
34%
46938
29%
15518
78%
15518
49%
23220

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
71%
720
34%
2327
33%
716
77%
716
50%
1084
January16th to endNight
61%
768
34%
2496
29%
768
72%
768
40%
1286
February1st to 15thNight
69%
697
36%
2200
32%
696
79%
696
49%
1041
February16th to endNight
62%
632
39%
1796
31%
632
72%
632
50%
915
March1st to 15thNight
65%
720
40%
1980
30%
720
74%
720
56%
971
March16th to endNight
70%
768
39%
2112
28%
768
79%
768
60%
1012
April1st to 15thNight
67%
674
37%
1933
26%
674
77%
674
57%
910
April16th to endNight
66%
540
43%
1800
35%
540
80%
540
67%
683
May1st to 15thNight
72%
539
38%
1676
31%
539
81%
539
68%
661
May16th to endNight
77%
562
44%
1684
36%
561
83%
561
76%
653
June1st to 15thNight
79%
540
34%
1620
29%
540
82%
540
65%
691
June16th to endNight
84%
540
28%
1620
24%
540
85%
540
52%
789
July1st to 15thNight
77%
510
12%
1530
11%
510
77%
510
26%
980
July16th to endNight
74%
564
8%
1593
8%
531
74%
531
21%
1106
August1st to 15thNight
80%
539
18%
1611
17%
536
80%
536
28%
1008
August16th to endNight
80%
575
23%
1895
25%
575
80%
575
32%
1107
September1st to 15thNight
74%
720
23%
1980
20%
720
74%
720
35%
1237
September16th to endNight
86%
680
39%
1881
33%
680
88%
680
61%
910
October1st to 15thNight
80%
660
38%
1930
32%
660
83%
660
59%
903
October16th to endNight
83%
704
41%
2112
37%
704
86%
704
66%
913
November1st to 15thNight
79%
700
42%
2100
35%
700
84%
700
67%
890
November16th to endNight
69%
720
40%
2226
34%
720
75%
720
50%
1070
December1st to 15thNight
71%
720
37%
2340
37%
720
75%
720
48%
1118
December16th to endNight
63%
768
34%
2496
33%
768
68%
768
40%
1282

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
4313424446%60%
47913
Night
3213323346%64%
47143
TransparencyDay
23%46%10%26%27%
47608
Night
19%47%13%28%26%
46949
SeeingDay
6%10%22%29%22%8%
5407
Night
4313%34%36%7%
15569

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
3224324445%63%
1611
16th to endDay
5%3243235%46%57%
1728
February1st to 15thDay
332321234467%
1652
16th to endDay
342332234464%
1677
March1st to 15thDay
222214445%67%
1980
16th to endDay
2312212345%69%
2112
April1st to 15thDay
2112213346%70%
2015
16th to endDay
1112222380%
2160
May1st to 15thDay
12212326%76%
2271
16th to endDay
1111222381%
2429
June1st to 15thDay
2111112235%75%
2340
16th to endDay
32135%24445%61%
2340
July1st to 15thDay
7%326%8%5%9%8%8%9%29%
2340
16th to endDay
12%7%38%9%5%8%7%8%7%20%
2467
August1st to 15thDay
9%5%37%7%47%6%8%8%30%
2340
16th to endDay
6%426%8%47%8%7%8%34%
2303
September1st to 15thDay
8%5%26%6%36%6%6%7%39%
1980
16th to endDay
5%212323345%63%
1871
October1st to 15thDay
2212313445%68%
1699
16th to endDay
12231324474%
1760
November1st to 15thDay
112211346%74%
1759
16th to endDay
3213312345%67%
1731
December1st to 15thDay
3313324347%61%
1620
16th to endDay
432332335%7%60%
1728
January1st to 15thNight
3213323446%65%
2327
16th to endNight
6%314434346%58%
2496
February1st to 15thNight
2212323246%66%
2198
16th to endNight
1324324335%65%
1796
March1st to 15thNight
2212313246%69%
1980
16th to endNight
121221233472%
2112
April1st to 15thNight
1213213345%70%
1933
16th to endNight
11121223479%
1800
May1st to 15thNight
1111224478%
1676
16th to endNight
1122384%
1684
June1st to 15thNight
21221123476%
1620
16th to endNight
121322445%6%65%
1620
July1st to 15thNight
33146%46%9%9%12%36%
1620
16th to endNight
5%435%5%46%7%11%17%25%
1701
August1st to 15thNight
33245%46%6%7%13%42%
1620
16th to endNight
6%3234346%8%13%43%
1895
September1st to 15thNight
7%4245%35%48%9%44%
1980
16th to endNight
222213345%71%
1881
October1st to 15thNight
1112213335%72%
1930
16th to endNight
1123123478%
2112
November1st to 15thNight
112112235%77%
2100
16th to endNight
431332223466%
2226
December1st to 15thNight
4213223446%63%
2340
16th to endNight
3414424435%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
22%25%12%31%26%
1612
16th to endDay
26%3316%27%23%
1728
February1st to 15thDay
18%1312%29%33%
1652
16th to endDay
23%239%31%29%
1677
March1st to 15thDay
17%247%35%32%
1980
16th to endDay
17%137%35%34%
2112
April1st to 15thDay
14%138%36%34%
2015
16th to endDay
11%126%27%51%
2160
May1st to 15thDay
10%136%26%50%
2271
16th to endDay
9%125%33%47%
2432
June1st to 15thDay
12%23425%51%
2340
16th to endDay
22%5%6%7%23%34%
2340
July1st to 15thDay
44%13%15%11%9%6%
2201
16th to endDay
54%15%16%9%3
2312
August1st to 15thDay
45%12%13%15%11%1
2325
16th to endDay
39%12%14%14%11%7%
2303
September1st to 15thDay
40%7%9%15%21%6%
1980
16th to endDay
21%38%12%34%19%
1871
October1st to 15thDay
17%46%14%28%29%
1699
16th to endDay
13%2412%29%38%
1760
November1st to 15thDay
12%1412%34%34%
1759
16th to endDay
19%2313%30%31%
1731
December1st to 15thDay
22%15%17%32%20%
1620
16th to endDay
23%36%13%33%18%
1728
January1st to 15thNight
19%3413%30%28%
2327
16th to endNight
26%3415%30%19%
2496
February1st to 15thNight
19%3312%30%30%
2209
16th to endNight
21%2412%32%27%
1796
March1st to 15thNight
17%249%31%35%
1980
16th to endNight
15%249%36%32%
2112
April1st to 15thNight
16%2311%37%29%
1933
16th to endNight
10%39%29%46%
1800
May1st to 15thNight
8%237%34%43%
1677
16th to endNight
6%139%35%43%
1685
June1st to 15thNight
12%23430%47%
1620
16th to endNight
18%46%9%25%35%
1620
July1st to 15thNight
32%13%20%14%11%6%
1530
16th to endNight
38%16%30%11%21
1593
August1st to 15thNight
32%12%19%20%11%3
1611
16th to endNight
29%10%21%17%13%8%
1895
September1st to 15thNight
32%8%14%18%19%6%
1980
16th to endNight
15%27%19%39%15%
1881
October1st to 15thNight
14%37%18%30%25%
1930
16th to endNight
11%2413%29%38%
2112
November1st to 15thNight
10%2417%34%31%
2100
16th to endNight
20%2412%27%31%
2226
December1st to 15thNight
19%4417%33%20%
2340
16th to endNight
25%46%16%28%18%
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
8%11%24%42%13%
90
16th to endDay
5%13%19%33%18%9%
96
February1st to 15thDay
7%12%19%34%21%4
167
16th to endDay
8%28%28%21%10%2
238
March1st to 15thDay
6%18%30%23%17%4
270
16th to endDay
5%23%27%22%13%7%
288
April1st to 15thDay
5%19%34%24%13%2
269
16th to endDay
320%37%23%12%2
270
May1st to 15thDay
320%36%23%11%4
288
16th to endDay
111%40%36%7%2
330
June1st to 15thDay
4431%38%14%6%
315
16th to endDay
6%216%36%28%9%
315
July1st to 15thDay
10%11%32%35%9%
305
16th to endDay
13%17%29%29%18%
327
August1st to 15thDay
9%5%27%36%19%
315
16th to endDay
6%7%23%43%17%
332
September1st to 15thDay
14%110%32%32%9%
315
16th to endDay
6%5%18%30%28%10%
276
October1st to 15thDay
45%21%32%25%10%
139
16th to endDay
4216%21%31%23%
96
November1st to 15thDay
312%20%27%30%6%
90
16th to endDay
411%28%27%25%2
90
December1st to 15thDay
28%18%33%25%11%
90
16th to endDay
11%18%23%29%16%
96
January1st to 15thNight
4216%42%29%4
720
16th to endNight
8%418%38%27%2
768
February1st to 15thNight
26%14%42%29%3
704
16th to endNight
26%24%43%19%3
632
March1st to 15thNight
46%19%37%26%4
720
16th to endNight
35%16%40%28%4
768
April1st to 15thNight
25%19%48%22%1
674
16th to endNight
1425%43%22%2
540
May1st to 15thNight
5%18%45%26%3
540
16th to endNight
1217%40%35%2
563
June1st to 15thNight
2111%40%39%3
540
16th to endNight
215%35%51%3
540
July1st to 15thNight
5%417%61%10%
510
16th to endNight
8%313%55%18%
564
August1st to 15thNight
4213%56%22%
539
16th to endNight
8%311%53%22%
575
September1st to 15thNight
9%416%52%16%
720
16th to endNight
4331%51%8%
680
October1st to 15thNight
2111%38%37%9%
660
16th to endNight
118%35%42%10%
704
November1st to 15thNight
1213%37%38%6%
700
16th to endNight
5%415%36%30%7%
720
December1st to 15thNight
5%413%38%30%6%
720
16th to endNight
5%6%18%39%24%5%
768
Page generated at 2017-09-22 05:35:33. Version ac04

Copyright 2017 A. Danko


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