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 2005-11-05 to 2018-02-14.

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%
16773
38%
48820
32%
16731
82%
16731
61%
22139

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
64%
779
30%
2522
26%
776
72%
776
42%
1246
January16th to endNight
62%
832
39%
2514
30%
832
74%
832
47%
1256
February1st to 15thNight
66%
756
37%
2280
32%
756
75%
756
53%
1091
February16th to endNight
58%
632
33%
1895
30%
632
67%
632
46%
972
March1st to 15thNight
63%
720
35%
2097
31%
720
73%
720
53%
1007
March16th to endNight
70%
768
37%
2112
29%
768
79%
768
59%
1008
April1st to 15thNight
67%
719
40%
1844
22%
719
77%
719
68%
878
April16th to endNight
73%
720
44%
1800
26%
720
79%
720
79%
810
May1st to 15thNight
75%
545
41%
1625
27%
545
82%
545
73%
657
May16th to endNight
85%
561
45%
1684
35%
561
88%
561
82%
624
June1st to 15thNight
88%
540
38%
1620
31%
540
89%
540
80%
618
June16th to endNight
92%
540
40%
1620
34%
540
93%
540
82%
609
July1st to 15thNight
93%
510
31%
1530
26%
510
93%
510
69%
633
July16th to endNight
89%
594
33%
1621
25%
559
90%
559
61%
742
August1st to 15thNight
93%
717
35%
1790
24%
713
93%
713
71%
853
August16th to endNight
91%
764
43%
1910
31%
764
91%
764
71%
921
September1st to 15thNight
91%
720
38%
1941
33%
720
92%
720
70%
881
September16th to endNight
90%
716
48%
1980
43%
716
92%
716
80%
816
October1st to 15thNight
79%
720
43%
1980
34%
720
86%
720
72%
872
October16th to endNight
85%
768
46%
2217
43%
768
89%
768
69%
956
November1st to 15thNight
79%
760
36%
2464
35%
760
86%
760
59%
1044
November16th to endNight
73%
780
41%
2535
40%
780
80%
780
57%
1098
December1st to 15thNight
69%
780
36%
2535
34%
780
76%
780
45%
1225
December16th to endNight
64%
832
35%
2704
32%
832
73%
832
43%
1322

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
11222345%6%68%
49250
Night
112212346%73%
49019
TransparencyDay
15%46%11%26%36%
48948
Night
12%45%11%26%39%
48822
SeeingDay
412%30%34%13%5%
6373
Night
2214%28%37%14%
16781

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
12122235%5%7%64%
1746
16th to endDay
221332335%5%66%
2061
February1st to 15thDay
111233326%9%65%
1883
16th to endDay
11123345%8%10%57%
1579
March1st to 15thDay
111232346%6%67%
1862
16th to endDay
1221345%5%70%
2112
April1st to 15thDay
11122235%7%70%
2100
16th to endDay
111222482%
2160
May1st to 15thDay
11112347%74%
2324
16th to endDay
1122385%
2429
June1st to 15thDay
1113483%
2340
16th to endDay
11121222380%
2340
July1st to 15thDay
3213325%5%6%8%58%
2340
16th to endDay
43145%46%7%8%10%43%
2434
August1st to 15thDay
2113335%6%6%8%56%
2160
16th to endDay
22134246%7%8%55%
2292
September1st to 15thDay
42134335%5%8%57%
2019
16th to endDay
21111232377%
1980
October1st to 15thDay
111123481%
1980
16th to endDay
1212345%75%
2005
November1st to 15thDay
1312336%75%
1722
16th to endDay
2111213246%71%
1755
December1st to 15thDay
121232435%9%62%
1755
16th to endDay
11332346%8%62%
1872
January1st to 15thNight
1213425%5%5%8%60%
2522
16th to endNight
221332435%6%63%
2514
February1st to 15thNight
111331245%7%67%
2269
16th to endNight
12134235%6%8%58%
1895
March1st to 15thNight
1112223348%67%
2097
16th to endNight
11221335%8%69%
2112
April1st to 15thNight
12212246%76%
1844
16th to endNight
111125%84%
1800
May1st to 15thNight
11233481%
1625
16th to endNight
11289%
1684
June1st to 15thNight
11112386%
1620
16th to endNight
112486%
1620
July1st to 15thNight
1113337%74%
1620
16th to endNight
111222335%11%63%
1731
August1st to 15thNight
12112348%73%
1800
16th to endNight
11212135%78%
1910
September1st to 15thNight
21112335%78%
1941
16th to endNight
11121287%
1980
October1st to 15thNight
11112235%80%
1980
16th to endNight
1112235%78%
2217
November1st to 15thNight
1224346%73%
2464
16th to endNight
1212212246%72%
2535
December1st to 15thNight
12122245%5%9%62%
2535
16th to endNight
12123245%5%8%62%
2704

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
16%7%8%11%26%30%
1747
16th to endDay
18%46%13%26%30%
2061
February1st to 15thDay
16%47%10%26%35%
1883
16th to endDay
19%8%7%11%30%22%
1579
March1st to 15thDay
15%46%9%28%35%
1862
16th to endDay
14%46%10%31%31%
2112
April1st to 15thDay
12%47%9%35%29%
2100
16th to endDay
8%1210%32%44%
2160
May1st to 15thDay
8%347%27%47%
2324
16th to endDay
6%136%33%49%
2432
June1st to 15thDay
7%125%21%62%
2340
16th to endDay
10%12315%65%
2340
July1st to 15thDay
21%47%15%20%30%
2201
16th to endDay
30%7%12%21%19%8%
2281
August1st to 15thDay
20%5%8%18%20%25%
2146
16th to endDay
21%6%10%16%21%23%
2292
September1st to 15thDay
24%5%7%10%21%29%
2019
16th to endDay
13%238%26%46%
1980
October1st to 15thDay
8%248%30%44%
1980
16th to endDay
11%45%7%23%48%
2005
November1st to 15thDay
10%4414%31%34%
1722
16th to endDay
15%35%9%25%40%
1755
December1st to 15thDay
17%7%8%12%24%29%
1755
16th to endDay
18%6%7%15%27%23%
1872
January1st to 15thNight
20%6%7%10%27%27%
2522
16th to endNight
20%46%11%25%31%
2514
February1st to 15thNight
15%6%6%10%22%38%
2280
16th to endNight
19%6%9%10%25%27%
1895
March1st to 15thNight
15%5%6%8%24%39%
2097
16th to endNight
12%5%6%10%32%31%
2112
April1st to 15thNight
10%339%33%38%
1844
16th to endNight
5%239%29%49%
1800
May1st to 15thNight
7%237%25%53%
1626
16th to endNight
412330%57%
1685
June1st to 15thNight
6%11420%65%
1620
16th to endNight
5%25%14%71%
1620
July1st to 15thNight
10%28%16%24%37%
1530
16th to endNight
13%414%33%23%10%
1621
August1st to 15thNight
10%37%24%27%27%
1790
16th to endNight
11%2419%32%28%
1910
September1st to 15thNight
10%26%13%29%37%
1941
16th to endNight
6%129%28%50%
1980
October1st to 15thNight
8%249%25%48%
1980
16th to endNight
9%348%25%48%
2217
November1st to 15thNight
11%5%5%12%29%35%
2464
16th to endNight
14%449%25%42%
2535
December1st to 15thNight
16%8%6%12%24%31%
2535
16th to endNight
17%8%8%14%24%26%
2704

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
413%27%31%20%2
135
16th to endDay
221%36%27%10%1
333
February1st to 15thDay
312%44%23%12%3
320
16th to endDay
231%39%18%7%1
238
March1st to 15thDay
224%42%19%8%2
270
16th to endDay
326%39%20%6%3
288
April1st to 15thDay
5%25%41%17%7%2
269
16th to endDay
121%48%17%6%3
270
May1st to 15thDay
421%39%26%43
288
16th to endDay
214%40%30%9%1
330
June1st to 15thDay
110%43%32%8%3
315
16th to endDay
3225%49%12%7%
315
July1st to 15thDay
5%113%48%21%9%
305
16th to endDay
7%11%46%23%11%
327
August1st to 15thDay
5%12%50%19%13%
315
16th to endDay
6%9%49%22%12%
332
September1st to 15thDay
13%17%43%18%6%
315
16th to endDay
5%6%28%44%12%3
315
October1st to 15thDay
12%35%39%10%1
315
16th to endDay
47%24%38%20%4
229
November1st to 15thDay
18%22%37%25%3
135
16th to endDay
29%34%23%23%5%
135
December1st to 15thDay
114%22%31%26%2
135
16th to endDay
211%32%26%15%10%
144
January1st to 15thNight
35%22%33%27%7%
780
16th to endNight
45%22%33%25%7%
832
February1st to 15thNight
2322%35%27%8%
760
16th to endNight
46%27%34%21%5%
632
March1st to 15thNight
17%24%32%25%8%
720
16th to endNight
3417%34%28%10%
768
April1st to 15thNight
1325%36%27%5%
719
16th to endNight
420%36%27%10%
720
May1st to 15thNight
121%36%30%9%
546
16th to endNight
1110%37%38%9%
563
June1st to 15thNight
8%36%45%8%
540
16th to endNight
1223%57%14%
540
July1st to 15thNight
219%65%20%
510
16th to endNight
210%57%28%
594
August1st to 15thNight
26%58%32%
717
16th to endNight
317%50%37%
764
September1st to 15thNight
3215%53%25%
720
16th to endNight
25%24%48%18%
716
October1st to 15thNight
2115%28%39%12%
720
16th to endNight
10%29%39%19%
768
November1st to 15thNight
1214%34%33%13%
760
16th to endNight
3117%30%30%15%
780
December1st to 15thNight
3419%33%29%9%
780
16th to endNight
47%20%34%25%8%
832
Page generated at 2018-02-15 07:58:41. Version ac04

Copyright 2018 A. Danko


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