Three Pines Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Three Pines 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
34%
24836
18%
74680
9%
24777
42%
24777
25%
48734

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
23%
950
15%
2818
5%
946
33%
946
20%
1952
January11th to 20thNight
23%
925
12%
2488
4%
925
28%
925
17%
1894
January21st to endNight
19%
990
15%
2574
4%
990
27%
990
16%
1976
February1st to 10thNight
22%
900
13%
2340
3%
900
29%
900
20%
1699
February11th to 20thNight
23%
878
16%
2274
5%
874
30%
874
22%
1588
February21st to endNight
24%
650
16%
1834
3%
650
35%
650
20%
1308
March1st to 10thNight
28%
590
14%
2030
7%
590
37%
590
19%
1360
March11th to 20thNight
25%
540
18%
1980
8%
540
38%
540
18%
1305
March21st to endNight
32%
594
12%
2178
10%
594
38%
594
15%
1499
April1st to 10thNight
27%
540
15%
1887
10%
540
36%
540
20%
1216
April11th to 20thNight
29%
533
20%
1625
14%
533
39%
533
20%
1079
April21st to endNight
30%
540
18%
1620
12%
540
40%
540
22%
1091
May1st to 10thNight
32%
540
14%
1620
9%
540
38%
540
25%
1052
May11th to 20thNight
36%
531
18%
1499
8%
531
42%
531
28%
981
May21st to endNight
38%
584
13%
1552
4%
582
42%
582
28%
1039
June1st to 10thNight
54%
540
20%
1355
7%
540
57%
540
41%
821
June11th to 20thNight
43%
540
18%
1260
5%
540
48%
540
41%
822
June21st to endNight
57%
540
20%
1260
8%
540
60%
540
49%
747
July1st to 10thNight
62%
525
21%
1225
8%
525
65%
525
52%
719
July11th to 20thNight
60%
522
26%
1312
9%
522
65%
522
57%
691
July21st to endNight
64%
591
21%
1673
14%
558
67%
558
48%
852
August1st to 10thNight
61%
537
20%
1601
16%
534
65%
534
36%
924
August11th to 20thNight
58%
534
27%
1600
25%
534
66%
534
41%
881
August21st to endNight
59%
594
29%
1790
25%
594
69%
594
47%
914
September1st to 10thNight
53%
540
23%
1810
21%
540
62%
540
39%
934
September11th to 20thNight
48%
540
27%
1980
22%
540
61%
540
33%
1055
September21st to endNight
40%
540
27%
1980
17%
540
55%
540
30%
1065
October1st to 10thNight
34%
684
23%
2124
13%
684
43%
684
29%
1271
October11th to 20thNight
27%
720
23%
2160
9%
720
38%
720
27%
1331
October21st to endNight
30%
841
22%
2425
9%
841
40%
841
25%
1580
November1st to 10thNight
31%
925
23%
2446
9%
925
42%
925
28%
1580
November11th to 20thNight
26%
950
21%
2660
8%
950
36%
950
22%
1824
November21st to endNight
24%
950
18%
2660
7%
950
33%
950
25%
1769
December1st to 10thNight
22%
950
13%
2660
4%
950
30%
950
20%
1865
December11th to 20thNight
22%
949
12%
3229
3%
949
31%
949
15%
2218
December21st to endNight
16%
1039
9%
5151
4%
1026
26%
1026
8%
3832

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
12%7%37%5%35%5%5%7%40%
74813
Night
11%7%37%5%3445%7%42%
74987
TransparencyDay
43%7%14%23%12%1
74514
Night
42%6%14%24%13%2
74806
SeeingDay
16%11%32%27%12%3
14811
Night
14%10%36%30%9%1
24844

By Month

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 10thDay
8%10%5%9%8%6%6%5%5%6%33%
1344
11th to 20thDay
8%12%6%11%8%6%6%6%6%7%24%
1573
21st to endDay
8%13%6%12%9%5%7%6%6%7%21%
1782
February1st to 10thDay
9%10%5%10%10%47%7%6%6%27%
1620
11th to 20thDay
9%10%6%10%6%5%6%7%5%6%29%
1574
21st to endDay
11%12%5%10%8%45%5%46%30%
1436
March1st to 10thDay
13%11%6%10%6%345%46%32%
1930
11th to 20thDay
14%10%48%7%35%35%7%34%
1980
21st to endDay
18%11%5%10%6%3445%5%28%
2178
April1st to 10thDay
17%9%26%5%345%5%8%36%
2072
11th to 20thDay
18%11%46%5%33346%35%
2284
21st to endDay
22%8%36%434446%36%
2340
May1st to 10thDay
19%7%35%6%45%5%5%6%35%
2340
11th to 20thDay
18%7%36%5%25%45%8%37%
2393
21st to endDay
16%6%25%5%446%5%8%39%
2725
June1st to 10thDay
12%5%245%35%5%6%7%46%
2600
11th to 20thDay
14%5%25%435%5%5%7%42%
2700
21st to endDay
8%425%5%35%5%7%9%47%
2700
July1st to 10thDay
8%3143345%7%10%52%
2700
11th to 20thDay
6%32442446%9%58%
2600
21st to endDay
6%314435%5%7%10%53%
2546
August1st to 10thDay
10%5%26%6%35%7%7%7%42%
2328
11th to 20thDay
12%4244445%6%8%47%
2301
21st to endDay
7%41433445%8%57%
2566
September1st to 10thDay
13%425%434346%52%
2147
11th to 20thDay
10%5%245%3347%7%51%
1980
21st to endDay
13%6%25%42445%6%50%
1980
October1st to 10thDay
16%8%25%5%3245%6%45%
1818
11th to 20thDay
14%9%244245%46%47%
1800
21st to endDay
16%9%36%5%23445%44%
1929
November1st to 10thDay
12%8%36%6%245%46%44%
1631
11th to 20thDay
10%10%411%7%45%446%36%
1520
21st to endDay
11%11%37%6%35%45%8%36%
1520
December1st to 10thDay
9%9%5%9%9%5%6%45%6%32%
1520
11th to 20thDay
9%11%6%9%7%45%46%8%31%
1914
21st to endDay
18%10%6%13%7%3445%6%24%
2442
January1st to 10thNight
7%8%5%8%8%46%6%6%6%36%
2818
11th to 20thNight
7%11%6%11%9%5%6%6%6%9%25%
2488
21st to endNight
11%13%5%10%7%45%6%6%6%27%
2574
February1st to 10thNight
8%9%5%9%8%5%7%5%5%6%33%
2340
11th to 20thNight
9%8%47%7%46%5%6%6%38%
2273
21st to endNight
10%9%5%8%7%445%6%7%35%
1834
March1st to 10thNight
10%10%48%7%345%6%7%37%
2030
11th to 20thNight
13%10%47%6%35%346%40%
1980
21st to endNight
17%10%5%6%6%3446%6%34%
2178
April1st to 10thNight
15%9%35%5%3445%6%41%
1887
11th to 20thNight
17%9%46%434446%39%
1625
21st to endNight
18%8%35%5%34446%40%
1620
May1st to 10thNight
16%8%25%33346%7%43%
1620
11th to 20thNight
15%5%25%4345%48%44%
1498
21st to endNight
13%436%5%445%5%7%43%
1551
June1st to 10thNight
8%4143245%6%8%53%
1355
11th to 20thNight
9%4244345%5%9%51%
1260
21st to endNight
7%32342445%8%59%
1260
July1st to 10thNight
5%32332445%10%60%
1260
11th to 20thNight
321322346%8%66%
1354
21st to endNight
43233245%6%10%59%
1772
August1st to 10thNight
7%424426%46%10%51%
1611
11th to 20thNight
9%32432335%7%60%
1600
21st to endNight
5%423323346%65%
1790
September1st to 10thNight
9%42332336%7%58%
1810
11th to 20thNight
9%42342445%7%56%
1980
21st to endNight
12%423424447%55%
1980
October1st to 10thNight
17%5%24323346%49%
2124
11th to 20thNight
14%7%35%423446%47%
2160
21st to endNight
16%8%36%423346%44%
2425
November1st to 10thNight
10%7%26%5%4445%6%47%
2446
11th to 20thNight
10%9%49%7%3445%5%41%
2660
21st to endNight
10%8%47%6%3445%7%42%
2660
December1st to 10thNight
8%9%5%9%8%345%5%7%35%
2660
11th to 20thNight
12%9%5%9%7%35%5%5%8%32%
3279
21st to endNight
18%11%5%12%7%445%5%5%24%
5225

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
51%7%16%17%8%1
1345
11th to 20thDay
57%7%10%16%10%1
1573
21st to endDay
60%7%15%12%6%
1782
February1st to 10thDay
55%7%14%16%8%
1620
11th to 20thDay
54%6%12%17%9%2
1583
21st to endDay
55%6%11%15%11%2
1436
March1st to 10thDay
52%6%14%19%8%1
1930
11th to 20thDay
51%6%12%24%7%1
1980
21st to endDay
58%6%13%17%6%1
2178
April1st to 10thDay
46%7%13%22%10%1
2072
11th to 20thDay
51%412%20%12%1
2284
21st to endDay
50%6%12%23%8%
2340
May1st to 10thDay
50%7%10%21%11%
2340
11th to 20thDay
46%7%13%22%11%1
2397
21st to endDay
43%9%13%23%11%1
2725
June1st to 10thDay
36%7%16%28%12%1
2600
11th to 20thDay
41%7%13%23%14%2
2700
21st to endDay
32%8%17%26%14%2
2700
July1st to 10thDay
26%9%17%32%15%1
2626
11th to 20thDay
25%7%14%29%21%5%
2519
21st to endDay
26%7%18%28%18%3
2405
August1st to 10thDay
37%10%14%24%11%3
2314
11th to 20thDay
34%8%16%30%10%2
2301
21st to endDay
26%7%15%31%19%3
2566
September1st to 10thDay
34%6%11%31%17%1
2147
11th to 20thDay
33%7%16%30%13%1
1980
21st to endDay
35%6%10%30%17%1
1980
October1st to 10thDay
40%6%12%25%15%1
1818
11th to 20thDay
38%6%12%26%16%2
1800
21st to endDay
44%5%12%25%13%1
1929
November1st to 10thDay
41%5%12%23%15%3
1631
11th to 20thDay
50%6%13%21%11%1
1520
21st to endDay
46%6%16%20%11%2
1520
December1st to 10thDay
52%7%14%16%10%2
1520
11th to 20thDay
50%7%19%18%6%
1911
21st to endDay
60%5%11%17%6%1
2442
January1st to 10thNight
47%6%11%23%12%1
2818
11th to 20thNight
55%7%15%15%7%1
2488
21st to endNight
56%5%12%16%9%1
2574
February1st to 10thNight
50%6%12%20%11%2
2340
11th to 20thNight
45%6%13%21%12%3
2274
21st to endNight
48%7%11%18%13%4
1834
March1st to 10thNight
46%7%15%22%9%1
2030
11th to 20thNight
48%5%10%24%13%1
1980
21st to endNight
51%6%15%20%7%1
2178
April1st to 10thNight
44%6%13%24%11%1
1887
11th to 20thNight
47%411%22%14%2
1625
21st to endNight
45%6%11%25%11%2
1620
May1st to 10thNight
41%6%14%24%13%1
1620
11th to 20thNight
39%7%13%24%16%2
1499
21st to endNight
41%7%14%21%15%2
1552
June1st to 10thNight
27%8%16%29%17%3
1355
11th to 20thNight
31%7%16%23%20%3
1260
21st to endNight
23%6%18%31%20%2
1260
July1st to 10thNight
21%7%14%36%19%3
1225
11th to 20thNight
17%5%16%35%21%6%
1312
21st to endNight
20%7%17%33%21%4
1673
August1st to 10thNight
29%8%17%28%14%4
1601
11th to 20thNight
25%7%14%38%15%2
1600
21st to endNight
21%5%15%31%23%5%
1790
September1st to 10thNight
25%6%15%31%21%2
1810
11th to 20thNight
29%6%13%32%18%2
1980
21st to endNight
30%6%11%31%21%1
1980
October1st to 10thNight
36%5%11%28%19%2
2124
11th to 20thNight
38%5%11%25%18%3
2160
21st to endNight
42%414%23%15%1
2425
November1st to 10thNight
39%5%14%21%19%3
2446
11th to 20thNight
45%6%11%22%14%2
2660
21st to endNight
42%6%17%23%12%1
2660
December1st to 10thNight
49%5%17%20%9%1
2660
11th to 20thNight
49%7%19%19%6%
3281
21st to endNight
61%6%10%17%6%1
5225

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
17%10%36%27%8%2
270
11th to 20thDay
14%13%42%23%7%1
254
21st to endDay
15%13%42%23%5%1
264
February1st to 10thDay
16%17%47%19%1
240
11th to 20thDay
14%20%41%20%5%
240
21st to endDay
20%17%38%22%3
198
March1st to 10thDay
19%14%39%24%4
240
11th to 20thDay
23%7%39%24%6%1
240
21st to endDay
26%13%30%21%9%2
264
April1st to 10thDay
28%15%30%22%4
332
11th to 20thDay
28%14%28%23%7%1
562
21st to endDay
22%17%29%20%10%2
600
May1st to 10thDay
20%12%34%23%10%1
603
11th to 20thDay
22%10%32%22%12%3
625
21st to endDay
19%7%30%30%12%2
679
June1st to 10thDay
10%8%26%33%19%4
630
11th to 20thDay
15%9%34%29%10%3
630
21st to endDay
8%7%34%33%16%3
630
July1st to 10thDay
9%422%37%23%6%
621
11th to 20thDay
6%7%33%33%17%5%
618
21st to endDay
7%425%39%21%4
684
August1st to 10thDay
12%320%38%22%5%
626
11th to 20thDay
14%423%32%22%5%
615
21st to endDay
7%5%31%34%20%3
685
September1st to 10thDay
14%7%32%29%15%3
437
11th to 20thDay
11%5%33%31%16%4
270
21st to endDay
18%16%33%20%10%3
270
October1st to 10thDay
18%13%30%24%12%3
270
11th to 20thDay
15%23%34%19%9%1
270
21st to endDay
22%19%34%19%6%
297
November1st to 10thDay
21%17%32%20%7%1
270
11th to 20thDay
14%20%45%17%3
270
21st to endDay
20%17%36%21%5%1
270
December1st to 10thDay
11%16%40%25%7%
270
11th to 20thDay
16%17%44%18%6%
270
21st to endDay
25%19%35%19%21
297
January1st to 10thNight
12%13%44%23%6%1
950
11th to 20thNight
12%14%42%26%5%1
925
21st to endNight
18%14%39%24%5%
990
February1st to 10thNight
13%12%45%25%5%1
900
11th to 20thNight
14%16%41%23%7%
879
21st to endNight
14%14%39%25%8%1
650
March1st to 10thNight
13%13%39%28%6%1
590
11th to 20thNight
19%11%39%26%5%
540
21st to endNight
22%11%29%28%9%1
594
April1st to 10thNight
20%12%39%24%5%
540
11th to 20thNight
24%12%29%26%8%1
533
21st to endNight
21%10%35%24%9%1
540
May1st to 10thNight
19%9%36%27%8%
540
11th to 20thNight
17%6%37%29%10%1
531
21st to endNight
15%5%36%32%11%1
584
June1st to 10thNight
11%6%25%41%17%
540
11th to 20thNight
12%437%37%10%
540
21st to endNight
7%426%48%14%
540
July1st to 10thNight
5%424%45%21%2
525
11th to 20thNight
4330%46%17%1
522
21st to endNight
5%326%46%19%2
591
August1st to 10thNight
8%223%46%19%1
537
11th to 20thNight
10%423%40%20%3
534
21st to endNight
6%328%41%20%2
594
September1st to 10thNight
10%429%39%16%2
540
11th to 20thNight
9%6%33%36%14%2
540
21st to endNight
12%10%35%33%9%1
540
October1st to 10thNight
19%10%33%29%9%1
684
11th to 20thNight
17%14%37%24%7%1
720
21st to endNight
21%13%33%27%7%
841
November1st to 10thNight
14%12%38%28%8%
925
11th to 20thNight
15%15%40%23%7%1
950
21st to endNight
14%14%43%25%5%
950
December1st to 10thNight
14%13%43%25%5%
950
11th to 20thNight
19%10%39%25%6%
950
21st to endNight
22%14%38%21%4
1045
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