San Pedro Martir Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Pedro Martir Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
70%
24873
39%
74421
29%
24814
79%
24814
60%
32856

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 10thNight
54%
760
31%
2457
23%
756
68%
756
42%
1170
January11th to 20thNight
57%
738
36%
2332
26%
738
73%
738
46%
1120
January21st to endNight
50%
792
43%
2376
26%
792
70%
792
47%
1145
February1st to 10thNight
56%
720
38%
2160
29%
720
70%
720
51%
1010
February11th to 20thNight
50%
700
36%
2099
24%
700
67%
700
45%
1036
February21st to endNight
48%
592
34%
1776
26%
592
62%
592
45%
867
March1st to 10thNight
48%
720
31%
2156
22%
720
63%
720
42%
1085
March11th to 20thNight
62%
720
37%
1980
27%
720
73%
720
55%
949
March21st to endNight
59%
792
37%
2178
23%
792
73%
792
52%
1058
April1st to 10thNight
58%
720
39%
1869
21%
720
70%
720
62%
899
April11th to 20thNight
59%
711
44%
1779
21%
711
71%
711
73%
817
April21st to endNight
66%
720
45%
1800
23%
720
76%
720
79%
786
May1st to 10thNight
67%
550
43%
1630
26%
550
78%
550
71%
652
May11th to 20thNight
76%
531
46%
1594
32%
531
82%
531
76%
618
May21st to endNight
75%
583
46%
1746
31%
582
82%
582
84%
634
June1st to 10thNight
78%
540
40%
1620
30%
540
81%
540
80%
618
June11th to 20thNight
84%
540
44%
1620
32%
540
89%
540
84%
588
June21st to endNight
85%
540
40%
1620
30%
540
88%
540
80%
615
July1st to 10thNight
90%
525
36%
1575
28%
525
91%
525
74%
627
July11th to 20thNight
95%
522
36%
1566
29%
522
95%
522
74%
623
July21st to endNight
88%
635
33%
1716
26%
600
90%
600
59%
818
August1st to 10thNight
90%
716
36%
1780
24%
712
91%
712
76%
818
August11th to 20thNight
93%
712
40%
1780
27%
712
94%
712
76%
823
August21st to endNight
91%
792
44%
1980
32%
792
92%
792
74%
931
September1st to 10thNight
89%
720
38%
1921
33%
720
89%
720
69%
892
September11th to 20thNight
90%
720
46%
1980
42%
720
93%
720
81%
814
September21st to endNight
83%
720
46%
1980
37%
720
89%
720
79%
819
October1st to 10thNight
76%
720
44%
1980
34%
720
84%
720
69%
879
October11th to 20thNight
77%
720
47%
1980
40%
720
84%
720
78%
827
October21st to endNight
77%
792
45%
2335
38%
792
86%
792
68%
982
November1st to 10thNight
73%
740
40%
2395
36%
740
84%
740
63%
958
November11th to 20thNight
72%
760
39%
2470
35%
760
82%
760
60%
1020
November21st to endNight
57%
760
39%
2470
31%
760
72%
760
50%
1107
December1st to 10thNight
59%
760
36%
2470
30%
760
71%
760
45%
1191
December11th to 20thNight
55%
759
33%
2930
27%
758
70%
758
34%
1464
December21st to endNight
51%
831
25%
4321
28%
817
65%
817
35%
1596

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
221232345%7%70%
74874
Night
1112223346%74%
74941
TransparencyDay
13%5%7%11%25%38%
74604
Night
11%5%6%11%25%41%
74733
SeeingDay
6%15%31%31%13%4
14476
Night
36%18%31%31%10%
24884

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 10thDay
13122245%5%8%67%
1708
11th to 20thDay
322332445%5%68%
1719
21st to endDay
321332345%6%68%
1980
February1st to 10thDay
121333336%9%67%
1800
11th to 20thDay
132343337%8%64%
1750
21st to endDay
11133245%7%8%66%
1480
March1st to 10thDay
12134245%7%9%62%
1803
11th to 20thDay
221332336%7%69%
1980
21st to endDay
111112346%5%75%
2178
April1st to 10thDay
111232335%8%72%
2086
11th to 20thDay
111112346%79%
2129
21st to endDay
111112235%83%
2160
May1st to 10thDay
1112212346%77%
2327
11th to 20thDay
111112346%81%
2301
21st to endDay
111121488%
2530
June1st to 10thDay
11113245%82%
2340
11th to 20thDay
111222487%
2340
21st to endDay
2112212335%77%
2340
July1st to 10thDay
321232446%7%67%
2340
11th to 20thDay
33145%35%7%8%9%53%
2340
21st to endDay
43146%5%7%8%9%11%42%
2496
August1st to 10thDay
21134346%7%8%59%
2149
11th to 20thDay
2213446%7%8%9%52%
2122
21st to endDay
22134346%9%9%57%
2376
September1st to 10thDay
6%3244345%5%8%57%
2038
11th to 20thDay
2212323445%73%
1980
21st to endDay
111222333477%
1980
October1st to 10thDay
2111122345%79%
1980
11th to 20thDay
11121234481%
1980
21st to endDay
11212346%78%
2018
November1st to 10thDay
1212445%80%
1679
11th to 20thDay
1112313447%73%
1710
21st to endDay
3212324447%68%
1710
December1st to 10thDay
231442445%8%63%
1710
11th to 20thDay
3213335%5%6%9%61%
2169
21st to endDay
11123235%8%9%66%
3146
January1st to 10thNight
12134245%6%9%63%
2457
11th to 20thNight
2223335%45%6%65%
2332
21st to endNight
231432345%6%67%
2376
February1st to 10thNight
131342345%7%68%
2160
11th to 20thNight
22133245%5%8%65%
2098
21st to endNight
132343245%6%66%
1776
March1st to 10thNight
121333446%9%63%
2156
11th to 20thNight
111332346%8%69%
1980
21st to endNight
111222345%7%70%
2178
April1st to 10thNight
1112323345%75%
1869
11th to 20thNight
112112135%82%
1779
21st to endNight
111235%86%
1800
May1st to 10thNight
11121233483%
1630
11th to 20thNight
1111233386%
1594
21st to endNight
11112390%
1746
June1st to 10thNight
11112125%86%
1620
11th to 20thNight
11122291%
1620
21st to endNight
11121112486%
1620
July1st to 10thNight
111121333482%
1620
11th to 20thNight
11111133410%75%
1620
21st to endNight
211332446%11%63%
1817
August1st to 10thNight
1112212347%78%
1790
11th to 20thNight
1112111347%79%
1780
21st to endNight
212212235%80%
1980
September1st to 10thNight
211121234478%
1921
11th to 20thNight
21111221386%
1980
21st to endNight
11111122386%
1980
October1st to 10thNight
21121323481%
1980
11th to 20thNight
1112222485%
1980
21st to endNight
1111222346%79%
2335
November1st to 10thNight
11213346%77%
2395
11th to 20thNight
121222335%6%75%
2470
21st to endNight
131322345%7%69%
2470
December1st to 10thNight
23132245%5%8%64%
2470
11th to 20thNight
1213445%5%7%11%56%
3041
21st to endNight
12113345%7%8%65%
4521

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 10thDay
15%7%8%12%24%34%
1709
11th to 20thDay
18%6%6%12%28%30%
1719
21st to endDay
17%5%6%14%24%34%
1980
February1st to 10thDay
14%48%9%23%41%
1800
11th to 20thDay
19%6%7%12%26%30%
1760
21st to endDay
15%8%7%11%25%35%
1480
March1st to 10thDay
17%8%9%11%25%31%
1803
11th to 20thDay
15%6%7%9%27%35%
1980
21st to endDay
12%7%5%10%32%34%
2178
April1st to 10thDay
12%47%10%37%30%
2086
11th to 20thDay
8%35%9%29%47%
2132
21st to endDay
8%238%33%45%
2160
May1st to 10thDay
11%347%27%49%
2327
11th to 20thDay
5%36%7%26%52%
2304
21st to endDay
4136%35%51%
2530
June1st to 10thDay
7%235%24%59%
2340
11th to 20thDay
412319%70%
2340
21st to endDay
11%245%16%62%
2340
July1st to 10thDay
16%46%11%18%45%
2276
11th to 20thDay
23%8%11%25%18%15%
2271
21st to endDay
27%11%15%20%16%10%
2357
August1st to 10thDay
17%7%10%16%19%31%
2135
11th to 20thDay
20%8%12%18%22%21%
2122
21st to endDay
19%7%11%18%23%24%
2376
September1st to 10thDay
24%6%9%12%17%31%
2038
11th to 20thDay
13%348%28%44%
1980
21st to endDay
12%36%10%28%41%
1980
October1st to 10thDay
9%36%10%29%42%
1980
11th to 20thDay
8%446%26%52%
1980
21st to endDay
9%447%25%52%
2018
November1st to 10thDay
7%4413%28%43%
1679
11th to 20thDay
12%45%10%28%40%
1710
21st to endDay
17%6%6%9%22%39%
1710
December1st to 10thDay
18%7%8%11%23%33%
1710
11th to 20thDay
17%8%9%17%24%25%
2168
21st to endDay
11%10%9%16%31%24%
3146
January1st to 10thNight
17%7%9%9%26%32%
2457
11th to 20thNight
18%6%6%11%28%31%
2332
21st to endNight
18%47%12%24%34%
2376
February1st to 10thNight
15%5%8%10%21%41%
2160
11th to 20thNight
16%7%7%11%23%35%
2099
21st to endNight
18%5%9%9%20%40%
1776
March1st to 10thNight
17%8%8%8%20%39%
2156
11th to 20thNight
12%6%8%9%27%38%
1980
21st to endNight
14%6%7%11%31%33%
2178
April1st to 10thNight
12%35%9%31%39%
1869
11th to 20thNight
8%247%26%54%
1779
21st to endNight
4248%30%52%
1800
May1st to 10thNight
7%236%23%57%
1630
11th to 20thNight
5%335%25%58%
1595
21st to endNight
313428%60%
1746
June1st to 10thNight
6%125%21%65%
1620
11th to 20thNight
412316%75%
1620
21st to endNight
6%125%14%72%
1620
July1st to 10thNight
9%26%11%20%53%
1575
11th to 20thNight
7%312%35%23%20%
1566
21st to endNight
14%5%14%32%22%12%
1716
August1st to 10thNight
8%39%23%24%33%
1780
11th to 20thNight
8%39%24%30%26%
1780
21st to endNight
9%25%19%34%30%
1980
September1st to 10thNight
11%47%17%24%38%
1921
11th to 20thNight
6%238%32%50%
1980
21st to endNight
6%25%11%28%48%
1980
October1st to 10thNight
9%449%26%48%
1980
11th to 20thNight
6%249%24%55%
1980
21st to endNight
8%447%24%53%
2335
November1st to 10thNight
9%45%10%30%41%
2395
11th to 20thNight
11%5%6%10%24%46%
2470
21st to endNight
15%6%6%11%24%39%
2470
December1st to 10thNight
17%8%6%11%22%36%
2470
11th to 20thNight
19%10%8%13%23%27%
3041
21st to endNight
12%9%9%13%28%28%
4521

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 10thDay
11%18%37%24%9%2
270
11th to 20thDay
9%14%38%25%12%2
315
21st to endDay
7%27%37%22%5%1
462
February1st to 10thDay
5%21%39%23%10%2
420
11th to 20thDay
10%30%37%20%3
415
21st to endDay
12%32%35%14%7%1
346
March1st to 10thDay
10%30%39%15%5%1
420
11th to 20thDay
11%24%39%19%7%1
420
21st to endDay
10%33%37%15%5%1
462
April1st to 10thDay
5%28%34%22%8%4
420
11th to 20thDay
6%27%39%19%8%1
412
21st to endDay
6%20%37%24%9%4
420
May1st to 10thDay
5%24%32%27%8%4
423
11th to 20thDay
212%44%30%9%3
448
21st to endDay
217%44%27%8%2
485
June1st to 10thDay
215%40%30%11%3
450
11th to 20thDay
211%38%34%12%5%
450
21st to endDay
45%29%40%15%7%
450
July1st to 10thDay
2221%49%19%8%
446
11th to 20thDay
5%214%41%25%12%
444
21st to endDay
6%210%43%27%12%
487
August1st to 10thDay
4217%43%23%12%
447
11th to 20thDay
3210%45%30%11%
437
21st to endDay
3211%44%27%13%
495
September1st to 10thDay
10%123%40%19%7%
450
11th to 20thDay
45%25%45%16%4
450
21st to endDay
311%27%35%18%6%
450
October1st to 10thDay
314%37%33%12%2
450
11th to 20thDay
211%37%39%9%2
450
21st to endDay
49%32%33%19%3
335
November1st to 10thDay
312%31%37%15%2
270
11th to 20thDay
5%11%36%29%17%3
270
21st to endDay
6%22%36%21%12%3
270
December1st to 10thDay
8%18%35%25%13%2
270
11th to 20thDay
316%38%30%11%1
270
21st to endDay
11%23%34%19%9%4
297
January1st to 10thNight
6%11%24%32%21%5%
760
11th to 20thNight
5%9%25%32%22%7%
738
21st to endNight
7%13%26%33%19%3
792
February1st to 10thNight
311%25%32%22%7%
720
11th to 20thNight
6%12%29%33%17%3
704
21st to endNight
7%14%28%29%18%4
592
March1st to 10thNight
5%14%29%33%15%3
720
11th to 20thNight
414%18%31%24%9%
720
21st to endNight
6%10%22%37%21%5%
792
April1st to 10thNight
28%28%35%22%5%
720
11th to 20thNight
37%30%31%24%5%
711
21st to endNight
19%23%35%25%7%
720
May1st to 10thNight
16%24%39%24%6%
550
11th to 20thNight
1318%39%30%9%
531
21st to endNight
2319%39%32%5%
584
June1st to 10thNight
1118%36%37%7%
540
11th to 20thNight
1311%39%39%8%
540
21st to endNight
110%29%47%13%
540
July1st to 10thNight
116%21%55%17%
525
11th to 20thNight
2123%57%17%
522
21st to endNight
3217%55%23%
635
August1st to 10thNight
1420%53%22%
716
11th to 20thNight
11114%54%30%
712
21st to endNight
3217%52%26%
792
September1st to 10thNight
41424%47%20%
720
11th to 20thNight
35%31%50%11%
720
21st to endNight
1112%30%43%12%
720
October1st to 10thNight
2416%37%33%8%
720
11th to 20thNight
1217%38%32%11%
720
21st to endNight
3315%35%32%12%
792
November1st to 10thNight
27%17%35%29%11%
740
11th to 20thNight
45%18%34%27%12%
760
21st to endNight
6%7%26%31%22%8%
760
December1st to 10thNight
5%7%26%32%22%8%
760
11th to 20thNight
5%9%26%35%22%3
760
21st to endNight
6%13%28%32%16%7%
836
Page generated at 2024-01-12 04:31:47. Version ac07

Copyright 2024 Attilla Danko


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