Mount Olson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Olson 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
28%
15298
13%
48828
8%
15268
34%
15268
16%
34799

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
14%
780
7%
2716
2%
776
20%
776
7%
2193
January16th to endNight
18%
832
10%
2847
5%
832
24%
832
10%
2190
February1st to 15thNight
13%
759
9%
2468
3%
757
20%
757
9%
1943
February16th to endNight
17%
631
13%
1940
5%
631
27%
631
12%
1491
March1st to 15thNight
19%
720
14%
2100
6%
720
28%
720
15%
1548
March16th to endNight
26%
768
19%
2034
8%
768
35%
768
21%
1425
April1st to 15thNight
21%
718
16%
1796
5%
718
26%
718
19%
1342
April16th to endNight
27%
669
17%
1749
6%
669
34%
669
22%
1227
May1st to 15thNight
34%
360
17%
1440
15%
360
45%
360
18%
932
May16th to endNight
32%
374
13%
1496
10%
374
43%
374
18%
937
June1st to 15thNight
35%
360
10%
1440
10%
360
44%
360
15%
969
June16th to endNight
37%
360
10%
1440
12%
360
43%
360
19%
891
July1st to 15thNight
50%
340
15%
1360
20%
340
57%
340
26%
755
July16th to endNight
50%
376
14%
1418
16%
354
56%
354
26%
812
August1st to 15thNight
48%
454
14%
1525
11%
452
53%
452
23%
968
August16th to endNight
49%
720
22%
1866
11%
720
54%
720
38%
1143
September1st to 15thNight
46%
720
17%
1800
8%
720
49%
720
32%
1202
September16th to endNight
47%
717
25%
1954
15%
717
52%
717
33%
1218
October1st to 15thNight
33%
720
17%
2160
11%
720
41%
720
20%
1476
October16th to endNight
23%
768
12%
2394
6%
768
32%
768
13%
1783
November1st to 15thNight
25%
760
16%
2513
11%
760
33%
760
16%
1748
November16th to endNight
20%
780
12%
2730
7%
780
28%
780
10%
2079
December1st to 15thNight
14%
780
6%
2730
2%
780
19%
780
7%
2182
December16th to endNight
14%
832
8%
2912
4%
832
20%
832
7%
2345

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
18%9%36%5%34446%32%
49256
Night
18%10%36%5%34446%32%
48998
Cloud CoverDay
18%9%36%5%34446%32%
49265
Night
18%10%46%5%34445%32%
49004
TransparencyDay
51%411%20%10%1
48943
Night
53%411%19%9%
48829
SeeingDay
24%13%28%20%9%3
5916
Night
24%12%28%24%9%
15300

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
21%15%49%6%45%33420%
1552
16th to endDay
15%14%6%9%7%45%345%22%
1726
February1st to 15thDay
15%14%6%11%7%35%44422%
1695
16th to endDay
20%14%5%8%6%3443424%
1533
March1st to 15thDay
18%13%5%9%7%4433326%
1848
16th to endDay
18%10%35%42323440%
2190
April1st to 15thDay
23%11%35%42434433%
2152
16th to endDay
19%8%26%5%24445%36%
2220
May1st to 15thDay
20%8%36%5%24447%33%
2511
16th to endDay
18%6%25%4245%5%8%35%
2618
June1st to 15thDay
23%6%35%5%3445%8%30%
2520
16th to endDay
18%6%25%5%35%45%7%33%
2520
July1st to 15thDay
13%5%25%5%35%5%6%8%39%
2520
16th to endDay
12%5%24446%6%8%8%35%
2654
August1st to 15thDay
12%7%38%5%35%45%7%35%
2424
16th to endDay
11%5%245%35%45%8%43%
2324
September1st to 15thDay
17%5%25%433447%41%
2160
16th to endDay
16%5%14433347%46%
2002
October1st to 15thDay
21%8%25%5%23346%35%
1800
16th to endDay
26%10%37%5%33346%25%
1829
November1st to 15thDay
15%8%26%7%45%445%34%
1674
16th to endDay
22%13%47%5%24345%25%
1560
December1st to 15thDay
23%15%5%8%8%2434419%
1560
16th to endDay
26%14%5%9%5%3443320%
1664
January1st to 15thNight
19%16%5%10%6%3443420%
2716
16th to endNight
14%15%5%9%7%35%445%23%
2847
February1st to 15thNight
16%13%6%11%7%3444421%
2466
16th to endNight
18%13%5%8%5%44335%26%
1940
March1st to 15thNight
20%12%46%5%23335%31%
2087
16th to endNight
18%8%46%423245%39%
2034
April1st to 15thNight
23%8%36%42434434%
1796
16th to endNight
20%7%24424346%38%
1749
May1st to 15thNight
20%7%25%414446%37%
1440
16th to endNight
15%6%27%42445%7%38%
1495
June1st to 15thNight
20%7%25%6%245%5%7%33%
1440
16th to endNight
15%6%245%246%6%7%37%
1440
July1st to 15thNight
10%425%43445%9%45%
1440
16th to endNight
8%415%4345%8%9%44%
1514
August1st to 15thNight
11%6%26%5%35%46%9%39%
1535
16th to endNight
11%41342445%8%49%
1866
September1st to 15thNight
15%5%25%5%23346%45%
1800
16th to endNight
14%424323446%48%
1954
October1st to 15thNight
19%7%35%433447%35%
2160
16th to endNight
26%9%36%5%24346%27%
2394
November1st to 15thNight
20%9%35%5%3344434%
2513
16th to endNight
22%11%47%6%35%345%26%
2730
December1st to 15thNight
21%17%5%8%6%3434420%
2730
16th to endNight
24%15%5%8%6%3433419%
2912

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
21%15%5%9%7%35%34320%
1552
16th to endDay
15%14%6%9%8%4444422%
1726
February1st to 15thDay
16%14%6%11%7%36%43421%
1695
16th to endDay
19%15%6%7%7%3443423%
1533
March1st to 15thDay
19%12%5%9%6%35%24325%
1858
16th to endDay
19%9%35%423235%40%
2189
April1st to 15thDay
23%11%35%42424433%
2152
16th to endDay
19%8%36%5%24345%37%
2220
May1st to 15thDay
20%7%35%5%24446%33%
2511
16th to endDay
17%5%35%4245%5%8%36%
2618
June1st to 15thDay
23%6%345%3445%8%30%
2520
16th to endDay
19%5%25%5%35%5%5%8%33%
2520
July1st to 15thDay
12%5%25%436%5%6%7%40%
2520
16th to endDay
12%5%15%5%45%5%7%9%36%
2654
August1st to 15thDay
12%6%37%6%35%5%5%7%36%
2424
16th to endDay
11%4145%35%46%8%42%
2324
September1st to 15thDay
17%5%24434347%41%
2160
16th to endDay
16%5%24323346%46%
2002
October1st to 15thDay
21%8%25%5%23346%34%
1800
16th to endDay
26%10%36%5%23445%26%
1829
November1st to 15thDay
16%7%36%7%46%45%6%32%
1674
16th to endDay
22%13%38%5%14345%25%
1560
December1st to 15thDay
23%16%5%8%8%23445%18%
1560
16th to endDay
26%15%6%7%6%3433320%
1664
January1st to 15thNight
20%16%6%9%6%25%34319%
2716
16th to endNight
14%16%6%9%7%34445%22%
2847
February1st to 15thNight
16%14%5%12%7%25%34321%
2459
16th to endNight
18%13%6%8%5%4443425%
1940
March1st to 15thNight
20%12%5%6%5%2334431%
2100
16th to endNight
19%9%36%423335%38%
2034
April1st to 15thNight
23%8%35%42334434%
1796
16th to endNight
20%7%244335%45%38%
1749
May1st to 15thNight
21%6%25%42435%7%36%
1440
16th to endNight
16%6%26%5%3445%7%37%
1495
June1st to 15thNight
20%6%36%5%2445%8%32%
1440
16th to endNight
15%6%25%5%35%5%6%7%37%
1440
July1st to 15thNight
11%424435%45%8%45%
1440
16th to endNight
8%5%235%246%7%10%43%
1514
August1st to 15thNight
12%5%25%5%245%6%8%39%
1535
16th to endNight
11%325%42345%7%50%
1866
September1st to 15thNight
15%5%25%5%23345%46%
1800
16th to endNight
14%5%23314447%47%
1954
October1st to 15thNight
19%7%35%43445%6%36%
2160
16th to endNight
25%9%36%5%24346%27%
2394
November1st to 15thNight
19%9%26%433445%34%
2513
16th to endNight
21%12%37%6%35%345%25%
2730
December1st to 15thNight
21%17%5%8%6%3343420%
2730
16th to endNight
24%15%6%8%6%3423419%
2912

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
68%39%11%6%1
1553
16th to endDay
64%411%11%6%
1726
February1st to 15thDay
65%47%17%3
1697
16th to endDay
63%49%11%9%1
1533
March1st to 15thDay
63%310%14%7%1
1858
16th to endDay
49%29%18%15%5%
2190
April1st to 15thDay
55%36%19%13%2
2152
16th to endDay
49%37%19%15%3
2220
May1st to 15thDay
50%49%20%14%1
2511
16th to endDay
45%6%12%21%11%1
2622
June1st to 15thDay
51%5%11%21%10%
2520
16th to endDay
48%6%11%20%11%
2520
July1st to 15thDay
38%6%12%29%12%
2371
16th to endDay
42%7%16%24%9%
2487
August1st to 15thDay
44%7%15%22%10%
2410
16th to endDay
36%416%29%11%
2324
September1st to 15thDay
42%5%11%27%12%
2160
16th to endDay
38%411%32%12%
2002
October1st to 15thDay
50%311%23%10%
1800
16th to endDay
60%413%15%6%
1829
November1st to 15thDay
51%5%13%20%8%
1674
16th to endDay
60%5%10%15%6%
1560
December1st to 15thDay
68%5%10%12%2
1560
16th to endDay
69%48%11%5%
1664
January1st to 15thNight
68%410%10%4
2716
16th to endNight
63%49%15%6%
2847
February1st to 15thNight
66%310%15%4
2468
16th to endNight
62%38%17%8%
1940
March1st to 15thNight
56%311%18%8%
2100
16th to endNight
49%38%19%16%3
2034
April1st to 15thNight
53%37%19%15%1
1796
16th to endNight
47%49%19%16%3
1749
May1st to 15thNight
47%5%8%20%14%4
1440
16th to endNight
44%5%13%19%14%2
1497
June1st to 15thNight
49%6%13%20%9%
1440
16th to endNight
44%5%13%21%14%
1440
July1st to 15thNight
34%5%13%31%15%
1360
16th to endNight
33%8%16%25%14%
1418
August1st to 15thNight
40%7%16%22%12%
1525
16th to endNight
32%414%33%14%
1866
September1st to 15thNight
40%412%29%12%
1800
16th to endNight
35%411%32%14%
1954
October1st to 15thNight
48%411%23%11%
2160
16th to endNight
58%314%17%5%
2394
November1st to 15thNight
52%413%18%10%1
2513
16th to endNight
61%5%11%16%4
2730
December1st to 15thNight
67%411%13%3
2730
16th to endNight
69%310%11%4
2912

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
26%22%31%12%7%
90
16th to endDay
30%19%33%12%3
110
February1st to 15thDay
33%30%31%3
130
16th to endDay
31%20%28%17%3
192
March1st to 15thDay
28%16%30%18%5%
270
16th to endDay
28%17%29%14%7%3
288
April1st to 15thDay
34%18%24%12%7%1
270
16th to endDay
25%17%29%15%6%5%
270
May1st to 15thDay
30%12%26%18%9%2
288
16th to endDay
22%16%31%16%10%2
331
June1st to 15thDay
26%12%29%20%9%1
315
16th to endDay
23%9%32%20%11%2
315
July1st to 15thDay
15%8%29%27%15%3
305
16th to endDay
14%6%30%31%12%4
326
August1st to 15thDay
16%5%25%31%14%5%
313
16th to endDay
12%7%27%25%14%12%
332
September1st to 15thDay
20%6%24%23%12%13%
315
16th to endDay
16%9%25%22%18%8%
314
October1st to 15thDay
26%11%26%18%11%5%
315
16th to endDay
34%14%27%18%4
313
November1st to 15thDay
23%11%31%23%7%2
238
16th to endDay
34%16%28%17%2
90
December1st to 15thDay
30%22%26%13%7%
90
16th to endDay
39%29%26%41
96
January1st to 15thNight
31%17%28%19%3
780
16th to endNight
24%17%31%21%4
832
February1st to 15thNight
25%19%34%18%2
760
16th to endNight
26%15%34%19%4
631
March1st to 15thNight
29%16%30%20%3
720
16th to endNight
24%15%27%23%8%
768
April1st to 15thNight
27%16%29%22%4
718
16th to endNight
27%13%28%22%8%
669
May1st to 15thNight
23%9%27%29%8%1
360
16th to endNight
17%9%35%26%10%
375
June1st to 15thNight
20%9%25%33%9%
360
16th to endNight
17%5%31%30%14%
360
July1st to 15thNight
11%6%25%43%13%
340
16th to endNight
8%429%40%15%1
376
August1st to 15thNight
14%325%35%19%1
454
16th to endNight
11%427%35%19%1
720
September1st to 15thNight
18%5%25%30%17%2
720
16th to endNight
16%8%24%24%23%2
717
October1st to 15thNight
23%10%27%22%14%1
720
16th to endNight
31%11%26%22%6%
768
November1st to 15thNight
26%12%28%21%10%
760
16th to endNight
30%17%25%17%9%
780
December1st to 15thNight
35%17%27%16%3
780
16th to endNight
34%15%27%18%2
832
Page generated at 2018-02-15 10:58:48. Version ac04

Copyright 2018 A. Danko


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