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 2005-11-05 to 2017-09-23.

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
35%
16128
18%
46791
9%
16081
43%
16081
26%
30583

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
25%
900
14%
2606
5%
895
34%
895
19%
1841
January16th to endNight
20%
960
14%
2496
4%
960
29%
960
17%
1895
February1st to 15thNight
25%
879
11%
2288
3%
875
30%
875
20%
1691
February16th to endNight
27%
729
16%
1991
5%
729
35%
729
22%
1401
March1st to 15thNight
30%
573
17%
2013
9%
573
40%
573
20%
1329
March16th to endNight
31%
576
13%
2112
11%
576
37%
576
15%
1452
April1st to 15thNight
30%
539
17%
1812
12%
539
41%
539
22%
1157
April16th to endNight
29%
540
17%
1620
11%
540
39%
540
20%
1135
May1st to 15thNight
32%
540
15%
1614
7%
540
39%
540
26%
1035
May16th to endNight
40%
563
14%
1498
4%
561
44%
561
28%
1003
June1st to 15thNight
46%
540
15%
1323
5%
540
50%
540
36%
863
June16th to endNight
54%
540
20%
1260
7%
540
58%
540
52%
738
July1st to 15thNight
60%
510
20%
1190
7%
510
63%
510
54%
682
July16th to endNight
65%
564
21%
1541
13%
531
67%
531
50%
774
August1st to 15thNight
64%
539
22%
1610
19%
536
69%
536
42%
873
August16th to endNight
59%
573
26%
1725
25%
573
66%
573
42%
931
September1st to 15thNight
57%
540
23%
1868
21%
540
67%
540
39%
949
September16th to endNight
41%
516
26%
1903
16%
516
57%
516
31%
1013
October1st to 15thNight
34%
638
26%
1958
15%
638
44%
638
30%
1140
October16th to endNight
33%
734
18%
2142
8%
734
40%
734
26%
1394
November1st to 15thNight
33%
875
23%
2361
10%
875
43%
875
29%
1530
November16th to endNight
28%
900
17%
2520
9%
900
35%
900
24%
1719
December1st to 15thNight
22%
900
11%
2520
3%
900
29%
900
17%
1861
December16th to endNight
20%
960
14%
2820
4%
960
30%
960
14%
2177

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%35%5%3445%7%39%
48115
Night
11%7%35%5%24446%43%
46960
Cloud CoverDay
12%7%35%5%3445%7%40%
48125
Night
11%7%35%5%2445%6%43%
46963
Cloud CoverDay
12%7%35%5%3445%7%39%
48126
Night
11%7%35%5%24446%43%
46964
Cloud CoverDay
12%7%36%5%3445%7%40%
48124
Night
11%7%35%5%34446%43%
46964
TransparencyDay
43%6%14%23%11%1
47802
Night
41%5%13%24%13%1
46791
SeeingDay
15%8%31%28%13%2
6130
Night
14%9%34%30%10%1
16129

By Month

Percentage Cloud Cover NE (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%10%6%9%8%45%5%5%8%29%
1326
16th to endDay
7%13%6%11%8%46%5%46%24%
1728
February1st to 15thDay
10%11%6%8%9%45%5%6%5%26%
1575
16th to endDay
9%10%5%8%6%5%5%6%45%29%
1491
March1st to 15thDay
15%10%5%8%5%24446%31%
1936
16th to endDay
15%11%5%7%6%3445%5%30%
2112
April1st to 15thDay
15%8%25%5%3335%8%37%
2134
16th to endDay
23%10%45%423345%32%
2340
May1st to 15thDay
21%6%26%5%34445%35%
2335
16th to endDay
17%5%245%345%5%9%36%
2617
June1st to 15thDay
16%5%25%5%35%5%5%7%38%
2634
16th to endDay
8%3145%245%6%8%48%
2700
July1st to 15thDay
5%31342446%10%53%
2700
16th to endDay
431333446%10%53%
2519
August1st to 15thDay
10%5%25%5%346%6%8%40%
2340
16th to endDay
10%31332445%7%52%
2477
September1st to 15thDay
10%5%2442445%6%50%
2091
16th to endDay
10%5%2432345%6%51%
1893
October1st to 15thDay
15%7%24423236%47%
1661
16th to endDay
16%7%245%24445%43%
1729
November1st to 15thDay
10%7%26%424445%47%
1496
16th to endDay
12%11%37%5%245%5%7%34%
1440
December1st to 15thDay
12%11%6%7%8%45%346%29%
1440
16th to endDay
15%11%6%8%7%35%348%25%
1401
January1st to 15thNight
7%7%5%7%8%46%6%5%6%33%
2606
16th to endNight
9%11%49%6%45%6%5%7%27%
2496
February1st to 15thNight
10%10%5%8%6%36%446%33%
2285
16th to endNight
7%8%37%7%35%5%5%7%36%
1991
March1st to 15thNight
11%10%36%5%24446%38%
2001
16th to endNight
16%9%5%6%6%2435%6%34%
2112
April1st to 15thNight
15%8%245%24445%42%
1812
16th to endNight
19%7%36%5%23346%36%
1620
May1st to 15thNight
17%6%3341235%6%45%
1614
16th to endNight
11%435%436%46%8%41%
1496
June1st to 15thNight
10%5%243245%48%47%
1323
16th to endNight
5%21232335%8%61%
1260
July1st to 15thNight
321231345%8%63%
1260
16th to endNight
32123135%6%9%61%
1647
August1st to 15thNight
5%31232446%9%56%
1620
16th to endNight
8%414222335%61%
1725
September1st to 15thNight
8%31231345%6%58%
1868
16th to endNight
9%423323346%55%
1903
October1st to 15thNight
14%5%14313336%51%
1958
16th to endNight
17%8%24412336%44%
2142
November1st to 15thNight
9%6%35%5%34336%47%
2361
16th to endNight
11%7%37%5%25%45%6%40%
2520
December1st to 15thNight
12%11%47%8%35%446%31%
2520
16th to endNight
15%11%6%8%6%445%45%26%
2820

Percentage Cloud Cover NW (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%9%6%9%8%45%45%8%30%
1327
16th to endDay
7%13%6%9%8%47%5%47%25%
1728
February1st to 15thDay
10%11%5%9%8%45%5%6%6%26%
1575
16th to endDay
9%10%5%8%7%45%6%6%5%29%
1491
March1st to 15thDay
15%10%5%9%5%24346%32%
1947
16th to endDay
15%11%5%7%6%3436%5%29%
2110
April1st to 15thDay
15%8%35%424448%37%
2134
16th to endDay
23%11%35%423335%32%
2340
May1st to 15thDay
20%6%25%6%34436%34%
2335
16th to endDay
17%6%25%5%35%45%8%36%
2617
June1st to 15thDay
17%5%245%3445%8%38%
2634
16th to endDay
8%31443446%8%49%
2700
July1st to 15thDay
5%31342445%10%54%
2700
16th to endDay
5%31333446%10%53%
2519
August1st to 15thDay
9%5%25%5%346%6%8%40%
2340
16th to endDay
10%32342345%7%52%
2477
September1st to 15thDay
11%5%245%23347%50%
2091
16th to endDay
11%42341345%6%51%
1893
October1st to 15thDay
15%7%25%323335%47%
1661
16th to endDay
16%8%24424345%43%
1729
November1st to 15thDay
9%8%35%423446%47%
1496
16th to endDay
12%10%47%5%2336%7%34%
1440
December1st to 15thDay
12%11%49%7%45%446%29%
1440
16th to endDay
15%9%7%9%6%35%347%26%
1401
January1st to 15thNight
7%6%5%7%8%46%5%5%6%33%
2606
16th to endNight
9%11%49%5%45%6%6%7%27%
2496
February1st to 15thNight
10%10%5%8%7%35%446%33%
2278
16th to endNight
7%8%46%7%45%5%5%7%36%
1991
March1st to 15thNight
12%9%47%6%3345%5%38%
2013
16th to endNight
15%10%46%5%24346%34%
2110
April1st to 15thNight
16%7%245%24445%42%
1812
16th to endNight
19%7%36%433445%36%
1620
May1st to 15thNight
17%6%24312346%45%
1613
16th to endNight
12%5%15%5%35%45%9%41%
1497
June1st to 15thNight
10%5%2431445%9%47%
1323
16th to endNight
5%21231235%8%62%
1260
July1st to 15thNight
321331335%8%63%
1260
16th to endNight
211231446%9%62%
1647
August1st to 15thNight
5%31332446%8%56%
1620
16th to endNight
8%313313237%60%
1725
September1st to 15thNight
8%31231345%6%58%
1868
16th to endNight
9%42332335%6%55%
1903
October1st to 15thNight
14%5%24223346%51%
1958
16th to endNight
17%8%24412246%44%
2142
November1st to 15thNight
9%6%36%434335%47%
2361
16th to endNight
11%8%36%5%3335%6%40%
2520
December1st to 15thNight
12%11%38%7%35%447%31%
2520
16th to endNight
16%10%6%8%7%345%5%5%27%
2820

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%10%6%9%7%45%5%5%8%29%
1326
16th to endDay
7%12%6%10%8%5%6%6%46%24%
1728
February1st to 15thDay
10%11%6%8%9%45%5%6%5%26%
1575
16th to endDay
9%10%6%8%7%5%6%6%45%29%
1491
March1st to 15thDay
15%10%5%9%5%24446%32%
1947
16th to endDay
16%11%5%7%6%3445%5%30%
2112
April1st to 15thDay
15%8%35%43335%8%37%
2134
16th to endDay
23%10%45%423345%32%
2340
May1st to 15thDay
21%6%25%5%34445%35%
2335
16th to endDay
17%5%245%35%5%5%9%36%
2617
June1st to 15thDay
16%5%25%5%35%45%6%38%
2634
16th to endDay
8%3144245%6%8%49%
2700
July1st to 15thDay
5%21342446%10%53%
2700
16th to endDay
43234245%6%10%53%
2519
August1st to 15thDay
10%5%25%5%346%6%8%40%
2340
16th to endDay
10%31332445%7%52%
2477
September1st to 15thDay
10%5%24334446%50%
2091
16th to endDay
10%5%2433345%6%51%
1893
October1st to 15thDay
15%7%24422236%47%
1661
16th to endDay
16%7%245%24445%43%
1729
November1st to 15thDay
10%7%36%424435%47%
1496
16th to endDay
12%11%37%5%2445%7%34%
1440
December1st to 15thDay
12%11%6%7%8%45%346%29%
1440
16th to endDay
15%11%6%8%7%35%338%25%
1401
January1st to 15thNight
7%7%5%7%8%46%5%5%6%33%
2606
16th to endNight
9%12%49%6%45%6%5%7%27%
2496
February1st to 15thNight
10%10%48%7%36%446%33%
2278
16th to endNight
7%8%47%8%35%5%5%7%36%
1991
March1st to 15thNight
11%10%46%6%24446%38%
2013
16th to endNight
15%9%46%6%3435%6%34%
2112
April1st to 15thNight
15%8%245%24445%42%
1812
16th to endNight
19%7%36%423346%36%
1620
May1st to 15thNight
17%7%3341235%6%45%
1613
16th to endNight
11%435%436%46%8%41%
1496
June1st to 15thNight
10%5%243245%49%47%
1323
16th to endNight
5%21231335%8%61%
1260
July1st to 15thNight
321231345%8%63%
1260
16th to endNight
32123135%6%9%61%
1647
August1st to 15thNight
5%31232446%9%56%
1620
16th to endNight
8%414213335%61%
1725
September1st to 15thNight
8%31231345%6%58%
1868
16th to endNight
9%423323346%55%
1903
October1st to 15thNight
14%5%14213336%51%
1958
16th to endNight
17%8%24412336%44%
2142
November1st to 15thNight
9%6%35%5%34336%47%
2361
16th to endNight
11%7%37%5%25%45%6%40%
2520
December1st to 15thNight
12%11%47%8%35%446%31%
2520
16th to endNight
15%11%5%8%6%445%45%26%
2820

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 15thDay
7%11%5%9%8%5%45%5%7%30%
1326
16th to endDay
7%13%5%11%8%46%6%46%25%
1728
February1st to 15thDay
11%11%5%10%8%35%6%5%5%26%
1575
16th to endDay
10%10%5%10%6%46%6%5%5%28%
1491
March1st to 15thDay
14%10%5%8%5%24446%31%
1947
16th to endDay
16%10%5%7%6%3435%5%30%
2110
April1st to 15thDay
15%8%25%5%3345%8%38%
2134
16th to endDay
23%9%46%333335%33%
2340
May1st to 15thDay
21%6%35%5%3445%5%34%
2335
16th to endDay
17%5%25%4345%5%8%37%
2617
June1st to 15thDay
16%5%25%435%45%6%38%
2634
16th to endDay
8%324425%5%6%8%48%
2700
July1st to 15thDay
6%21332446%10%54%
2700
16th to endDay
43143245%7%9%53%
2519
August1st to 15thDay
10%5%25%6%346%6%7%41%
2340
16th to endDay
10%41332445%7%52%
2477
September1st to 15thDay
11%5%14434346%50%
2091
16th to endDay
10%5%2431345%6%51%
1893
October1st to 15thDay
15%7%25%321335%47%
1661
16th to endDay
15%7%33424445%43%
1729
November1st to 15thDay
10%7%26%5%24445%47%
1496
16th to endDay
12%12%36%5%3445%7%34%
1440
December1st to 15thDay
12%12%5%8%7%45%346%28%
1440
16th to endDay
15%11%5%9%7%34347%25%
1401
January1st to 15thNight
7%8%5%8%7%45%6%6%6%33%
2606
16th to endNight
9%11%5%8%6%45%6%5%7%27%
2496
February1st to 15thNight
10%10%48%7%35%446%33%
2278
16th to endNight
7%7%5%8%6%45%46%7%36%
1991
March1st to 15thNight
11%10%46%5%34446%39%
2013
16th to endNight
16%9%46%5%24446%35%
2112
April1st to 15thNight
15%8%24424445%42%
1812
16th to endNight
20%8%35%5%23335%37%
1620
May1st to 15thNight
17%6%2432235%7%44%
1613
16th to endNight
11%425%445%5%5%8%41%
1496
June1st to 15thNight
10%5%244245%48%47%
1323
16th to endNight
5%21231335%8%61%
1260
July1st to 15thNight
321231435%8%63%
1260
16th to endNight
321221346%9%61%
1647
August1st to 15thNight
5%313325%35%8%57%
1620
16th to endNight
8%413222245%62%
1725
September1st to 15thNight
8%31332335%6%58%
1868
16th to endNight
10%323423347%55%
1903
October1st to 15thNight
14%424213336%52%
1958
16th to endNight
17%7%24423336%44%
2142
November1st to 15thNight
9%7%25%434345%47%
2361
16th to endNight
11%7%37%5%3445%6%40%
2520
December1st to 15thNight
12%11%47%8%35%346%32%
2520
16th to endNight
16%11%5%8%7%445%4427%
2820

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
51%7%14%17%9%1
1327
16th to endDay
57%7%14%16%4
1728
February1st to 15thDay
55%7%13%17%5%
1576
16th to endDay
54%6%12%15%9%1
1491
March1st to 15thDay
52%6%13%21%6%
1947
16th to endDay
54%6%13%20%3
2112
April1st to 15thDay
45%5%15%23%8%1
2134
16th to endDay
54%6%11%19%8%
2340
May1st to 15thDay
50%6%10%22%9%
2335
16th to endDay
44%7%14%21%10%
2621
June1st to 15thDay
44%6%14%24%9%
2634
16th to endDay
31%7%16%27%14%2
2700
July1st to 15thDay
25%8%16%30%15%3
2541
16th to endDay
25%7%17%27%18%2
2362
August1st to 15thDay
37%8%14%25%10%2
2326
16th to endDay
30%6%16%28%14%3
2477
September1st to 15thDay
34%6%14%28%16%
2091
16th to endDay
33%5%13%30%15%
1893
October1st to 15thDay
39%5%13%23%16%1
1661
16th to endDay
42%6%14%24%12%
1729
November1st to 15thDay
38%5%12%23%17%1
1496
16th to endDay
47%7%16%18%9%
1440
December1st to 15thDay
56%6%10%15%8%1
1440
16th to endDay
58%5%12%15%6%1
1401
January1st to 15thNight
48%6%12%20%10%
2606
16th to endNight
53%6%14%18%6%
2496
February1st to 15thNight
51%6%12%19%9%
2288
16th to endNight
45%6%13%19%12%2
1991
March1st to 15thNight
45%5%12%25%9%1
2013
16th to endNight
50%6%14%21%6%
2112
April1st to 15thNight
42%5%12%25%12%
1812
16th to endNight
49%5%10%22%10%1
1620
May1st to 15thNight
40%5%14%24%13%1
1614
16th to endNight
39%7%14%22%14%1
1498
June1st to 15thNight
33%7%17%27%12%1
1323
16th to endNight
21%6%16%29%23%3
1260
July1st to 15thNight
18%6%16%34%19%4
1190
16th to endNight
16%7%18%32%19%4
1541
August1st to 15thNight
23%7%16%32%17%2
1610
16th to endNight
25%5%14%32%17%4
1725
September1st to 15thNight
25%415%32%20%1
1868
16th to endNight
29%6%11%34%18%1
1903
October1st to 15thNight
34%412%26%19%3
1958
16th to endNight
42%415%23%13%
2142
November1st to 15thNight
39%411%21%19%2
2361
16th to endNight
43%6%17%20%11%1
2520
December1st to 15thNight
54%415%17%8%
2520
16th to endNight
58%6%9%17%7%
2820

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
12%13%38%30%41
90
16th to endDay
17%13%39%27%2
96
February1st to 15thDay
21%16%43%15%3
90
16th to endDay
20%19%28%24%6%
81
March1st to 15thDay
17%15%34%31%1
90
16th to endDay
27%8%29%21%11%2
96
April1st to 15thDay
20%14%35%20%7%1
253
16th to endDay
27%17%26%19%8%1
450
May1st to 15thDay
22%10%33%24%8%1
468
16th to endDay
23%6%32%25%9%2
517
June1st to 15thDay
15%7%33%26%14%3
495
16th to endDay
7%8%35%31%14%2
495
July1st to 15thDay
7%5%26%37%18%4
475
16th to endDay
5%327%38%21%2
515
August1st to 15thDay
10%323%35%21%5%
493
16th to endDay
13%326%29%22%5%
517
September1st to 15thDay
10%5%30%32%17%4
246
16th to endDay
17%438%24%9%5%
111
October1st to 15thDay
11%16%34%24%10%3
90
16th to endDay
15%12%38%19%11%2
96
November1st to 15thDay
6%10%36%34%11%1
90
16th to endDay
34%8%31%21%31
90
December1st to 15thDay
23%14%38%16%6%
90
16th to endDay
29%25%29%14%2
96
January1st to 15thNight
11%14%42%24%6%1
900
16th to endNight
16%13%41%24%4
960
February1st to 15thNight
16%12%38%24%7%
880
16th to endNight
10%13%40%24%9%1
729
March1st to 15thNight
16%9%37%30%5%
573
16th to endNight
20%11%30%28%7%1
576
April1st to 15thNight
20%10%35%25%7%
539
16th to endNight
25%8%31%23%9%1
540
May1st to 15thNight
21%7%37%24%8%
540
16th to endNight
14%436%33%10%1
563
June1st to 15thNight
15%428%38%12%
540
16th to endNight
7%332%43%13%
540
July1st to 15thNight
4227%45%18%1
510
16th to endNight
5%124%47%18%1
564
August1st to 15thNight
6%122%43%23%1
539
16th to endNight
9%224%39%20%3
573
September1st to 15thNight
9%227%38%18%2
540
16th to endNight
11%8%35%29%13%1
516
October1st to 15thNight
16%12%33%27%8%1
638
16th to endNight
22%8%30%29%8%
734
November1st to 15thNight
14%12%36%28%9%
875
16th to endNight
14%13%40%24%7%
900
December1st to 15thNight
18%11%40%25%4
900
16th to endNight
22%11%35%23%5%
960
Page generated at 2017-09-24 08:15:55. Version ac04

Copyright 2017 A. Danko


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